WO2021056065A1

WO2021056065A1 - Methods and apparatus for control of an oxygen concentrator

Info

Publication number: WO2021056065A1
Application number: PCT/AU2020/051015
Authority: WO
Inventors: Rex Dael Navarro; Warwick John SAUNDERS
Original assignee: ResMed Asia Pte Ltd; ResMed Pty Ltd
Priority date: 2019-09-24
Filing date: 2020-09-24
Publication date: 2021-04-01

Abstract

Methods and apparatus provide controlled operations in an oxygen concentrator such as by adjusting compressor motor speed for regulating system pressure using one or more modes. A controller may implement switching between a plurality of such modes for operation of a portable oxygen concentrator (POC). The plurality of control modes may provide coarse pressure regulation and fine pressure regulation. One regulation mode (e.g., coarse pressure regulation) may be implemented for changing between the different flow rate settings of the POC and/or for initial starting/activation and may implemented with controlled speed ramping of the POC compressor using a monotonic control function. Another regulation mode (e.g., fine pressure regulation) may operate upon completion of an operation of the coarse pressure regulation mode and may maintain a target system pressure with closed loop pressure control. The controller may implement regression processing for computing parameter(s) that may be applied in the regulation process of the control mode(s).

Description

METHODS AND APPARATUS FOR CONTROL OF AN OXYGEN CONCENTRATOR

[0001] The present disclosure claims priority from U.S. Provisional Patent Application Serial No. 62/904,858, filed on September 24, 2019, the entire disclosure of which is hereby incorporated by reference.

FIELD OF THE TECHNOLOGY

[0002] The present technology relates generally to methods and apparatus for treating respiratory disorders, such as those involving gas adsorption or controlled pressure and/or vacuum swing adsorption. Such methodologies may be implemented in an oxygen concentrator using one or more sieve beds. In some examples, the technology more specifically concerns such methods and apparatus for a portable oxygen concentrator having multiple control modes such as to regulate system pressure based on accumulator pressure by means of compressor motor speed adjustment.

BACKGROUND

The human respiratory system and its disorders

[0003] The respiratory system of the body facilitates gas exchange. The nose and mouth form the entrance to the airways of a patient.

[0004] The airways include a series of branching tubes, which become narrower, shorter and more numerous as they penetrate deeper into the lung. The prime function of the lung is gas exchange, allowing oxygen to move from the inhaled air into the venous blood and carbon dioxide to move in the opposite direction. The trachea divides into right and left main bronchi, which further divide eventually into terminal bronchioles. The bronchi make up the conducting airways, and do not take part in gas exchange. Further divisions of the airways lead to the respiratory bronchioles, and eventually to the alveoli. The alveolated region of the lung is where the gas exchange takes place, and is referred to as the respiratory zone. See “Respiratory Physiology”, by John B. West, Lippincott Williams & Wilkins, 9th edition published 2012.

[0005] A range of respiratory disorders exist. Examples of respiratory disorders include respiratory failure, Obesity Hyperventilation Syndrome (OHS), Chronic Obstructive Pulmonary Disease (COPD), Neuromuscular Disease (NMD) and Chest wall disorders.

[0006] Respiratory failure is an umbrella term for respiratory disorders in which the lungs are unable to inspire sufficient oxygen or exhale sufficient CO₂ to meet the patient's needs. Respiratory failure may encompass some or all of the following disorders. [0007] A patient with respiratory insufficiency (a form of respiratory failure) may experience abnormal shortness of breath on exercise.

[0008] Obesity Hyperventilation Syndrome (OHS) is defined as the combination of severe obesity and awake chronic hypercapnia, in the absence of other known causes for hypoventilation. Symptoms include dyspnea, morning headache and excessive daytime sleepiness.

[0009] Chronic Obstructive Pulmonary Disease (COPD) encompasses any of a group of lower airway diseases that have certain characteristics in common. These include increased resistance to air movement, extended expiratory phase of respiration, and loss of the normal elasticity of the lung. Examples of COPD are emphysema and chronic bronchitis. COPD is caused by chronic tobacco smoking (primary risk factor), occupational exposures, air pollution and genetic factors. Symptoms include: dyspnea on exertion, chronic cough and sputum production.

[0010] Neuromuscular Disease (NMD) is a broad term that encompasses many diseases and ailments that impair the functioning of the muscles either directly via intrinsic muscle pathology, or indirectly via nerve pathology. Some NMD patients are characterised by progressive muscular impairment leading to loss of ambulation, being wheelchair-bound, swallowing difficulties, respiratory muscle weakness and, eventually, death from respiratory failure. Neuromuscular disorders can be divided into rapidly progressive and slowly progressive: (i) Rapidly progressive disorders: Characterised by muscle impairment that worsens over months and results in death within a few years (e.g. Amyotrophic lateral sclerosis (ALS) and Duchenne muscular dystrophy (DMD) in teenagers); (ii) Variable or slowly progressive disorders: Characterised by muscle impairment that worsens over years and only mildly reduces life expectancy (e.g. Limb girdle, Facioscapulohumeral and Myotonic muscular dystrophy). Symptoms of respiratory failure in NMD include: increasing generalised weakness, dysphagia, dyspnea on exertion and at rest, fatigue, sleepiness, morning headache, and difficulties with concentration and mood changes.

[0011] Chest wall disorders are a group of thoracic deformities that result in inefficient coupling between the respiratory muscles and the thoracic cage. The disorders are usually characterised by a restrictive defect and share the potential of long term hypercapnic respiratory failure. Scoliosis and/or kyphoscoliosis may cause severe respiratory failure. Symptoms of respiratory failure include: dyspnea on exertion, peripheral oedema, orthopnea, repeated chest infections, morning headaches, fatigue, poor sleep quality and loss of appetite. Therapies

[0012] Various respiratory therapies have been used to treat one or more of the above respiratory disorders.

Respiratory pressure therapies

[0013] Respiratory pressure therapy is the application of a supply of air to an entrance to the airways at a controlled target pressure that is nominally positive with respect to atmosphere throughout the patient's breathing cycle (in contrast to negative pressure therapies such as the tank ventilator or cuirass).

[0014] Non-invasive ventilation (NIV) provides ventilatory support to a patient through the upper airways to assist the patient breathing and/or maintain adequate oxygen levels in the body by doing some or all of the work of breathing. The ventilatory support is provided via a non-invasive patient interface. NIV has been used to treat respiratory failure, in forms such as OHS, COPD, NMD and Chest Wall disorders. In some forms, the comfort and effectiveness of these therapies may be improved.

[0015] Invasive ventilation (IV) provides ventilatory support to patients that are no longer able to effectively breathe themselves and may be provided using a tracheostomy tube. In some forms, the comfort and effectiveness of these therapies may be improved.

Flow therapies

[0016] Not all respiratory therapies aim to deliver a prescribed therapeutic pressure. Some respiratory therapies aim to deliver a prescribed respiratory volume, by delivering an inspiratory flow rate profile over a targeted duration, possibly superimposed on a positive baseline pressure. In other cases, the interface to the patient's airways is ‘open’ (unsealed) and the respiratory therapy may only supplement the patient's own spontaneous breathing with a flow of conditioned or enriched air. In one example, High Flow therapy (HFT) is the provision of a continuous, heated, humidified flow of air to an entrance to the airway through an unsealed or open patient interface at a “treatment flow rate” that is held approximately constant throughout the respiratory cycle. The treatment flow rate is nominally set to exceed the patient's peak inspiratory flow rate. HFT has been used to treat respiratory failure, COPD, and other respiratory disorders. One mechanism of action is that the high flow rate of air at the airway entrance improves ventilation efficiency by flushing, or washing out, expired CO₂ from the patient's anatomical deadspace. Hence, HFT is thus sometimes referred to as a deadspace therapy (DST). Other benefits may include the elevated warmth and humidification (possibly of benefit in secretion management) and the potential for modest elevation of airway pressures. As an alternative to constant flow rate, the treatment flow rate may follow a profile that varies over the respiratory cycle.

[0017] Another form of flow therapy is long-term oxygen therapy (LTOT) or supplemental oxygen therapy. Doctors may prescribe a continuous flow of oxygen enriched air at a specified oxygen concentration (from 21%, the oxygen fraction in ambient air, to 100%) at a specified flow rate (e.g., 1 litre per minute (LPM), 2 LPM, 3 LPM, etc.) to be delivered to the patient's airway.

Respiratory Therapy Systems

[0018] These respiratory therapies may be provided by a respiratory therapy system or device. Such systems and devices may also be used to screen, diagnose, or monitor a condition without treating it.

[0019] A respiratory therapy system may comprise an oxygen source, an air circuit, and a patient interface.

Oxygen source

[0020] Experts in this field have recognized that exercise for respiratory failure patients provides long term benefits that slow the progression of the disease, improve quality of life and extend patient longevity. Most stationary forms of exercise like tread mills and stationary bicycles, however, are too strenuous for these patients. As a result, the need for mobility has long been recognized. Until recently, this mobility has been facilitated by the use of small compressed oxygen tanks or cylinders mounted on a cart with dolly wheels. The disadvantage of these tanks is that they contain a finite amount of oxygen and are heavy, weighing about 50 pounds when mounted.

[0021] Oxygen concentrators have been in use for about 50 years to supply oxygen for respiratory therapy. Traditional oxygen concentrators have been bulky and heavy making ordinary ambulatory activities with them difficult and impractical. Recently, companies that manufacture large stationary oxygen concentrators began developing portable oxygen concentrators (POCs). The advantage of POCs is that they can produce a theoretically endless supply of oxygen. In order to make these devices small for mobility, the various systems necessary for the production of oxygen enriched air are condensed. POCs seek to utilize their produced oxygen as efficiently as possible, in order to minimise weight, size, and power consumption. This may be achieved by delivering the oxygen as series of pulses or “boluses”, each bolus timed to coincide with the start of inspiration. This therapy mode is known as pulsed or demand (oxygen) delivery (POD), in contrast with traditional continuous flow delivery more suited to stationary oxygen concentrators.

[0022] Oxygen concentrators may implement processes such as vacuum swing adsorption (VSA), pressure swing adsorption (PSA), or vacuum pressure swing adsorption (VPSA). For example, oxygen concentrators, e.g., POCs, may work based on depressurization (e.g., vacuum operation) and/or pressurization (e.g., compressor operation) in a swing adsorption process (e.g., Vacuum Swing Adsorption VSA, Pressure Swing Adsorption PSA or Vacuum Pressure Swing Adsorption VPSA, each of which are referred to herein as a “swing adsorption process”). For example, an oxygen concentrator may control a process of pressure swing adsorption (PSA). Pressure swing adsorption involves using a compressor to increase gas pressure inside a canister that contains particles of a gas separation adsorbent that attracts nitrogen more strongly than it does oxygen. Such a canister filled with adsorbent is referred to as a sieve bed. Ambient air usually includes approximately 78% nitrogen and 21% oxygen with the balance comprised of argon, carbon dioxide, water vapor and other trace gases. If a feed gas mixture such as air, for example, is passed under pressure through a sieve bed, part or all of the nitrogen will be adsorbed by the sieve bed, and the gas coming out of the vessel will be enriched in oxygen. When the sieve bed reaches the end of its capacity to adsorb nitrogen, it can be regenerated by reducing the pressure, thereby releasing the adsorbed nitrogen. It is then ready for another “PSA cycle” of producing oxygen enriched air. By alternating canisters in a two-canister system, one canister can be concentrating oxygen (the so-called “adsorption phase”) while the other canister is being purged (the “purge phase”). This alternation results in a continuous separation of the oxygen from the nitrogen. In this manner, oxygen can be continuously concentrated out of the air for a variety of uses include providing LTOT to users.

[0023] Vacuum swing adsorption (VSA) provides an alternative gas separation technique. VSA typically draws the gas through the separation process of the sieve beds using a vacuum such as a compressor configured to create a vacuum with the sieve beds. Vacuum Pressure Swing Adsorption (VPSA) may be understood to be a hybrid system using a combined vacuum and pressurization technique. For example, a VPSA system may pressurize the sieve beds for the separation process and also apply a vacuum for purging of the beds.

Air circuit

[0024] An air circuit is a conduit or a tube constructed and arranged to allow, in use, a flow of breathable gas to travel between two components of a respiratory therapy system such as the oxygen source and the patient interface. In some cases, there may be separate limbs of the air circuit for inhalation and exhalation. In other cases, a single limb air circuit is used for both inhalation and exhalation.

Patient Interface

[0025] A patient interface may be used to interface respiratory equipment to its wearer, for example by providing a flow of air to an entrance to the airways. The flow of air may be provided via a mask to the nose and/or mouth, a tube to the mouth or a tracheostomy tube to the trachea of a patient. Depending upon the therapy to be applied, the patient interface may form a seal, e.g., with a region of the patient's face, to facilitate the delivery of gas at a pressure at sufficient variance with ambient pressure to effect therapy, e.g., at a positive pressure of about 10 cmH₂O relative to ambient pressure. For other forms of therapy, such as the delivery of oxygen, the patient interface may not include a seal sufficient to facilitate delivery to the airways of a supply of gas at a positive pressure of about 10 cmH₂O. For flow therapies such as nasal LTOT, the patient interface is configured to insufflate the nares but specifically to avoid a complete seal. One example of such a patient interface is a nasal cannula.

SUMMARY OF THE TECHNOLOGY

[0026] Examples of the present technology may provide methods and apparatus for controlled operations of an oxygen concentrator, such as a portable oxygen concentrator. In particular, the technology provides methods and apparatus for a portable oxygen concentrator having multiple control modes such as to regulate system pressure based on accumulator pressure by means of compressor motor speed adjustment.

[0027] Some implementations of the present technology may include a method of operating an oxygen concentrator. The method may include, with a sensor configured to sense at a location associated with accumulation of oxygen enriched air produced by the oxygen concentrator, generating a signal representing a measure of pressure of the accumulated oxygen enriched air. The method may include, with a controller configured to receive the measured pressure signal, controlling operation of a compressor to achieve or maintain a target system pressure associated with a flow rate setting of the oxygen concentrator based on the measured pressure signal. The controlling with the controller may include a first control mode of operation for regulating pressure to achieve the target system pressure and a second control mode of operation to maintain the target system pressure.

[0028] In some implementations, the controller switches to the second control mode of operation when the controller detects a first condition in the first control mode of operation. The first condition may include a comparison of (a) the target system pressure, and (b) a system pressure estimate that may be based on the measured pressure signal. Detection of the first condition may include determining that the system pressure estimate equals or exceeds the target system pressure. The method may include, in the first control mode, generating the system pressure estimate. Generating the system pressure estimate may include determining parameters of a linear model of a plurality of accumulator pressure values from the measured pressure signal during a ramping of speed of a motor of the compressor. Generating the system pressure estimate may includes may include generating an estimate of a pressure-time profile of the system pressure as a function of the determined parameters, and a predetermined delay value. The predetermined delay value may be a time difference characteristic of a damped response of pneumatic components of the oxygen concentrator. The determining parameters of a linear model may include performing linear regression. The accumulator pressure values may include maximum pressure values, each corresponding to one of a plurality of adsorption phases. Each maximum pressure value may be obtained by regression on the accumulator pressure values from the measured pressure signal during a corresponding adsorption phase.

[0029] In some implementations, the function may be given by: m * (t + t) + b, such as where: m is a slope parameter of the linear model; b is an intercept parameter of the linear model; t is elapsed time since the start of the ramping, and t is the predetermined delay value.

[0030] In some implementations, the first condition may include a comparison of (a) a target speed, and (b) a current measured speed of a motor of the compressor. The current measured speed may be determined at least in part with a sensor associated with the motor of the compressor. The target speed may be determined with a speed function of an initial speed, a known speed ramp rate, a target system pressure value, determined parameters of a linear model, and/or a predetermined delay value. The speed function may be defined by: RPM_start + (SRR/m) * (P_target - m t - b), such as where m is a slope parameter of the linear model; b is an intercept parameter of the linear model; RPM_start is the initial speed; SRR is the known speed ramp rate; t is the predetermined delay value; and P_target is the target system pressure value.

[0031] In some implementations, the target system pressure value may be a target value for any one of (a) a starting pressure for entry to an adsorption phase of the oxygen concentrator, (b) an average pressure of an adsorption phase of the oxygen concentrator, and (c) a maximum pressure for an adsorption phase of the oxygen concentrator. The second control mode of operation may include generating a qualified pressure sample from the measured pressure signal, and controlling a speed of a motor of the compressor with the qualified pressure sample in a control loop. The qualified pressure sample may be generated with one or more parameters of a regression process. The second control mode of operation may include adjusting, in the control loop, a speed setting command to a motor driver, with an error signal generated based on a comparison of (a) the target system pressure and (b) the qualified pressure sample. The speed setting command may be adjusted by summing one or more modified error signals that are derived from a difference between the target system pressure and the qualified pressure sample. The modified error signals may include one or more of proportional, derivative and integral signals, wherein the method may include generating each of the one or more of proportional, derivative and integral signals with the difference between the target system pressure and the qualified pressure sample. The regression process may include computing linear parameters from a plurality of samples from the measured pressure signal. The linear parameters may include a slope and an intercept. The qualified pressure sample may be generated by determining one or more peak values with one or more of the linear parameters, such that each peak value may be a maximum value over an adsorption phase. The qualified pressure sample may be generated by determining a running average of the one or more peak values. The peak value may be the intercept if the slope may be negative. If the slope is positive, the peak value may be computed with the slope, the intercept and a time associated with an end of the adsorption phase.

[0032] Some implementations of the present technology may include an oxygen concentrator. The oxygen concentrator may include one or more sieve beds containing a gas separation adsorbent. The oxygen concentrator may include a compression system, including a motor-operated compressor, configured to feed a pressurised feed gas into the one or more sieve beds. The oxygen concentrator may include an accumulator configured to receive oxygen enriched air from the one or more sieve beds. The oxygen concentrator may include a pressure sensor configured to generate a signal representing a measure of pressure of the oxygen enriched air in the accumulator. The oxygen concentrator may include a speed sensor configured to generate a signal representing a measure of speed of the motor of the compressor. The oxygen concentrator may include a memory. The oxygen concentrator may include a controller may include one or more processors. The one or more processors may be configured by program instructions stored in the memory to execute any one or more features of any of the method of operating the oxygen concentrator described herein.

[0033] Some implementations of the present technology may include an oxygen concentrator. The oxygen concentrator may include one or more sieve beds containing a gas separation adsorbent. The oxygen concentrator may include a compressor configured to feed a pressurised feed gas into the one or more sieve beds. The oxygen concentrator may include an accumulator configured to receive oxygen enriched air from the one or more sieve beds. The oxygen concentrator may include a speed sensor configured to generate a signal representing a measure of speed of a motor of the compressor. The oxygen concentrator may include a pressure sensor configured to generate a signal representing a measure of pressure of the oxygen enriched air in the accumulator. The oxygen concentrator may include a controller coupled with the compressor, the pressure sensor, and the speed sensor. The controller may be configured to receive the measured pressure signal and the measured speed signal. The controller may be configured to control operation of the compressor to achieve or maintain a target system pressure associated with a flow rate setting of the oxygen concentrator based on the measured pressure signal. The controlling with the controller may include a first control mode of operation for regulating pressure to achieve the target system pressure and a second control mode of operation to maintain the target system pressure.

[0034] In some implementations, the controller may be configured to switch to the second control mode of operation when the controller detects a first condition in the first control mode of operation. The first condition may include a comparison of (a) the target system pressure, and (b) a system pressure estimate that may be based on the measured pressure signal. Detection of the first condition may include a determination that the system pressure estimate equals or exceeds the target system pressure. The controller may be configured to, in the first control mode, generate the system pressure estimate. To generate the system pressure estimate, the controller may be configured to determine parameters of a linear model of a plurality of accumulator pressure values from the measured pressure signal during a ramping of speed of a motor of the compressor. To generate the system pressure estimate, the controller may be configured to generate an estimate of a pressure-time profile of the system pressure as a function of the determined parameters, and a predetermined delay value. The predetermined delay value may be time difference characteristic of a damped response of pneumatic components of the oxygen concentrator. The controller may be configured to determine the parameters of the linear model by performing linear regression. The accumulator pressure values may include maximum pressure values, each from one of a plurality of adsorption phases. The controller may be configured to obtain each maximum pressure value by regression on the accumulator pressure values from the measured pressure signal of an adsorption phase of the plurality of adsorption phases. The function may be given by: m * (t + t) + b, such as where: m is a slope parameter of the linear model; b is an intercept parameter of the linear model; t is elapsed time since the start of the ramping; and t is the predetermined delay value.

[0035] In some implementations, the first condition may include a comparison of (a) a target speed, and (b) a current measured speed of a motor of the compressor. The controller may be configured to determine the current measured speed with the speed sensor. The controller may be configured to determine the target speed with a speed function of an initial speed, a known speed ramp rate, a target system pressure value, determined parameters of a linear model and a predetermined delay value. The speed function may be defined by: RPM_start + (SRR/m) * (P_{target -} m t - b), such as where m is a slope parameter of the linear model; b is an intercept parameter of the linear model; RPM_start is the initial speed; SRR is the known speed ramp rate; t is the predetermined delay value; and P_target is the target system pressure value.

[0036] In some implementations, the target system pressure value may be any of (a) a starting pressure for entry to an adsorption phase of the oxygen concentrator, (b) an average pressure of an adsorption phase of the oxygen concentrator, and (c) a maximum pressure for an adsorption phase of the oxygen concentrator.

[0037] In some implementations, the controller may be configured to, in the second control mode of operation, (a) generate a qualified pressure sample from the measured pressure signal, and (b) control speed of the motor of the compressor with the qualified pressure sample in a control loop. The controller may be configured to generate the qualified pressure sample with one or more parameters of a regression process. The controller may be configured to, in the control loop in the second control mode of operation, adjust an error signal to a motor driver, the error signal generated based on a comparison of (a) the target system pressure and (b) the qualified pressure sample. The error signal may be adjusted by summing one or more modified error signals that are derived from a difference between the target system pressure and the qualified pressure sample. The modified error signals may include one or more of proportional, derivative and integral signals, wherein the controller may be configured to generate each of the one or more of proportional, derivative and integral signals with the difference between the target system pressure and the qualified pressure sample. The controller may be configured, in the regression process, to compute linear parameters from a plurality of samples from the measured pressure signal. The linear parameters may include a slope and an intercept. The controller may be configured to generate the qualified pressure sample by determining one or more peak values from one or more of the linear parameters, such that each peak value may be a maximum over an adsorption phase. The controller may be configured to generate the qualified pressure sample by determining a running average of the one or more peak values. If the slope is negative, the peak value may be the intercept. If the slope is positive, the peak value may be computed with the slope, the intercept and a time associated with an end of the adsorption phase.

[0038] Some implementations of the present technology may include a method of operating an oxygen concentrator. The method may include, with a sensor configured to sense at a location associated with accumulation of oxygen enriched air produced by the oxygen concentrator, generating a signal representing a measure of pressure of the accumulated oxygen enriched air. The method may include, with a controller configured to receive the measured pressure signal, controlling operation of a motor of a compressor by changing, with a monotonic control function, motor speed over a period of time to achieve a target system pressure associated with a flow rate setting of the oxygen concentrator based on the measured pressure signal. The controlling with the controller may include, during the changing in motor speed over the period of time, computing an estimate of the system pressure based on the measured pressure. The controlling with the controller may include, comparing the estimate of the system pressure to the target system pressure. The controlling with the controller may include interrupting the changing in motor speed based on a result of the comparing.

[0039] In some implementations, the changing in motor speed may include ramping of speed of the motor and the period of time may include multiple adsorption cycles. The ramping of speed may include an increase in speed, and wherein the flow rate setting may be (a) a higher setting from a prior flow rate setting, or (b) an initial setting following power activation of the oxygen concentrator. The ramping of speed may include a decrease in speed, and wherein the flow rate setting may be a lower setting from a prior flow rate setting. The method may further include determining a target speed for the motor speed based on an estimate of a pressure-time profile for the system pressure. The estimate of the system pressure may be an estimate of sieve bed pressure. The computing the estimate of the system pressure may include applying a modeling function to data samples of the measured pressure. The modeling function may be further applied to determine a target speed for the motor speed. The modeling function may comprise a damped response modeling function. The modeling function may include a predetermined delay value. The predetermined delay value characterizes a damped response of the measured pressure relative to sieve bed pressure. The data samples may correspond with a plurality of adsorption phases controlled by the controller. The data samples may include a plurality of peak values. Each peak value may correspond with one adsorption phase of the plurality of adsorption phases. The modeling function may include one or more parameters derived by linear regression. The one or more parameters may include a slope value and an intercept value. The computing the estimate of the system pressure may be based on the slope value and intercept value.

[0040] Some implementations of the present technology may include an oxygen concentrator. The oxygen concentrator may include one or more sieve beds containing a gas separation adsorbent. The oxygen concentrator may include a compression system, including a motor-operated compressor, configured to feed a pressurised feed gas into the one or more sieve beds. The oxygen concentrator may include an accumulator configured to receive oxygen enriched air from the one or more sieve beds. The oxygen concentrator may include a pressure sensor configured to generate a signal representing a measure of pressure of the oxygen enriched air in the accumulator. The oxygen concentrator may include a speed sensor configured to generate a signal representing a measure of speed of the motor of the compressor. The oxygen concentrator may include a memory. The oxygen concentrator may include a controller may include one or more processors. The one or more processors may be configured by program instructions stored in the memory to execute any one or more of the features of the methods of operating the oxygen concentrator disclosed herein.

[0041] Some implementations of the present technology may include an oxygen concentrator. The oxygen concentrator may include one or more sieve beds containing a gas separation adsorbent. The oxygen concentrator may include a compression system, including a motor-operated compressor, configured to feed a pressurised feed gas into the one or more sieve beds. The oxygen concentrator may include an accumulator configured to receive oxygen enriched air from the one or more sieve beds. The oxygen concentrator may include a pressure sensor configured to generate a signal representing a measure of pressure of the oxygen enriched air in the accumulator. The oxygen concentrator may include a speed sensor configured to generate a signal representing a measure of speed of the motor of the compressor. The oxygen concentrator may include a controller coupled with the compression system, the pressure sensor, and the speed sensor. The controller may be configured to control the motor with a monotonic function that changes motor speed over a period of time to achieve a target system pressure associated with a flow rate setting of the oxygen concentrator based on the measured pressure signal. The controller may be configured to, during the changing of motor speed over the period of time, compute an estimate of the system pressure based on the measured pressure. The controller may be configured to compare the estimate of the system pressure to the target system pressure. The controller may be configured to interrupt the changing in motor speed based on a result of the comparing. [0042] In some implementations, the changes in motor speed may include ramping of speed of the motor and the period of time may include multiple adsorption cycles. The ramping of speed may include an increase in speed. The flow rate setting may be (a) a higher setting from a prior flow rate setting, or (b) an initial setting following power activation of the oxygen concentrator. The ramping of speed may include a decrease in speed. The flow rate setting may be a lower setting from a prior flow rate setting. The controller may be further configured to determine a target speed for the motor speed based on an estimate of a pressure-time profile of the system pressure. The estimate of the system pressure may be an estimate of sieve bed pressure. To compute the estimate of the system pressure, the controller may be configured to apply a modeling function to data samples of the measured pressure. The modeling function may be further applied to determine a target speed for the motor speed. The modeling function may include a damped response modeling function. The modeling function may include a predetermined delay value. The predetermined delay value may characterize a damped response of the measured pressure relative to sieve bed pressure. The data samples may correspond with a plurality of adsorption phases controlled by the controller. The data samples may include a plurality of peak values. Each peak value may correspond with one adsorption phase of the plurality of adsorption phases. The modeling function may include one or more parameters derived by linear regression. The one or more parameters may include a slope value and an intercept value. The computed estimate of the system pressure may be based on the slope value and intercept value.

[0043] Some implementations of the present technology may include a method of operating an oxygen concentrator. The method may include, with a speed sensor, generating a signal representing a measure of speed of a motor of a compressor. The method may include, with a controller, controlling operation of the motor of the compressor by changing, with a monotonic control function, motor speed over a period of time to achieve a target system pressure associated with a flow rate setting of the oxygen concentrator based on the measured motor speed signal. The controlling with the controller may include determining a target speed for the motor based on a current target motor speed, the target system pressure, a current target system pressure from a current flow rate setting, and a parameter representing a dynamic relationship between changes in system pressure and changes in motor speed The controlling with the controller may include comparing the measure of motor speed to the target speed. The controlling with the controller may include interrupting the changing in motor speed based on a result of the comparing. [0044] In some implementations, the method may include deriving the parameter with a regression process. The method may further include deriving the parameter with a known speed ramp rate. The method may further include deriving the parameter with a slope parameter. The parameter may include a normalised slope parameter. The changing of speed over the period of time may include an increase in speed. The flow rate setting may be a higher setting than the current flow rate setting. The changing of speed over the period of time may include a decrease in speed. The flow rate setting may be a lower setting than the current flow rate setting.

[0045] Some implementations of the present technology may include an oxygen concentrator. The oxygen concentrator may include one or more sieve beds containing a gas separation adsorbent. The oxygen concentrator may include a compression system, including a motor-operated compressor, configured to feed a pressurised feed gas into the one or more sieve beds. The oxygen concentrator may include an accumulator configured to receive oxygen enriched air from the one or more sieve beds. The oxygen concentrator may include a speed sensor configured to generate a signal representing a measure of speed of a motor of the motor-operated compressor. The oxygen concentrator may include a controller coupled with the compression system and the speed sensor. The controller may be configured to control an operation of the motor of the compressor by changing, with a monotonic control function, motor speed over a period of time to achieve a target system pressure associated with a flow rate setting of the oxygen concentrator based on the measure of speed. To control the operation by changing motor speed over the period of time, the controller may be configured to determine a target speed for the motor based on a current target motor speed, a target system pressure, a current target system pressure from a current flow rate setting, and a parameter representing a dynamic relationship between changes in system pressure and changes in motor speed. To control the operation by changing motor speed over the period of time, the controller may be configured to compare the measure of motor speed to the target speed. To control the operation by changing motor speed over the period of time, the controller may be configured to interrupt the changing in motor speed based on a result of the comparing.

[0046] In some implementations, the parameter may be derived with a regression process. The parameter may be derived with a known speed ramp rate. The parameter may be derived with a slope parameter. The parameter may include a normalised slope parameter. The changing of speed over the period of time may include an increase in speed. The flow rate setting may be a higher setting than the current flow rate setting. The changing of speed over the period of time may include a decrease in speed. The flow rate setting may be a lower setting than the current flow rate setting.

[0047] Of course, portions of the aspects may form sub-aspects of the present technology. Also, various ones of the sub-aspects and/or aspects may be combined in various manners and also constitute additional aspects or sub-aspects of the present technology.

[0048] Other features of the technology will be apparent from consideration of the information contained in the following detailed description, abstract, drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Advantages of the present technology will become apparent to those skilled in the art with the benefit of the following detailed description of implementations and upon reference to the accompanying drawings in which:

[0050] Fig. 1 depicts an oxygen concentrator in accordance with one form of the present technology.

[0051] Fig. 2 is a schematic diagram of the components of the oxygen concentrator of Fig. 1.

[0052] Fig. 3 is a side view of the main components of the oxygen concentrator of Fig. 1.

[0053] Fig. 4 is a perspective side view of a compression system of the oxygen concentrator of Fig. 1.

[0054] Fig. 5 is a side view of a compression system that includes a heat exchange conduit.

[0055] Fig. 6 is a schematic diagram of example outlet components of the oxygen concentrator of Fig. 1.

[0056] Fig. 7 depicts an outlet conduit for the oxygen concentrator of Fig. 1.

[0057] Fig. 8 depicts an alternate outlet conduit for the oxygen concentrator of Fig. 1.

[0058] Fig. 9 is a perspective view of a disassembled canister system for the oxygen concentrator of Fig. 1.

[0059] Fig. 10 is an end view of the canister system of Fig. 9.

[0060] Fig. 11 is an assembled view of the canister system end depicted in Fig. 10.

[0061] Fig. 12 a view of an opposing end of the canister system of Fig. 9 to that depicted in Figs. 10 and 11. [0062] Fig. 13 is an assembled view of the canister system end depicted in Fig. 12.

[0063] Fig. 14 depicts an example control panel for the oxygen concentrator of Fig. 1.

[0064] Fig. 15 is a flow chart of an example methodology for changing pressure control modes of a compression system of the oxygen concentrator of Fig. 1.

[0065] Fig. 16 is a flow chart of an example methodology for applying pressure control of the compression system in at least one mode such as for coarse pressure regulation.

[0066] Fig. 17 is a graph illustrating pressure control operations of the compression system in an example pressure regulation mode, such as a coarse pressure regulation mode.

[0067] Fig. 18 is a state diagram illustrating operations for pressure control of the compression system in an example pressure regulation mode, such as for the coarse pressure regulation mode.

[0068] Fig. 19 is a graph showing measured pressure and estimated pressure signals for control of operations of the compression system in a plurality of different regulation modes, such as a coarse pressure regulation mode and a fine pressure regulation mode.

[0069] Fig. 20 is a flow chart of an example methodology for applying pressure control of the compression system in at least one mode such as for fine pressure regulation.

[0070] Fig. 21 is a flow chart of an example methodology for determining regression related feedback control input in at least one mode such as for fine pressure regulation.

[0071] Fig. 22 is a system schematic of a control loop for applying pressure control of the compression system in at least one mode such as for fine pressure regulation.

[0072] Fig. 23 is a graph illustrating a pressure sampling process for the control loop for applying pressure control of the compression system in at least one mode such as for fine pressure regulation of Fig. 21.

[0073] Fig. 24 is a state diagram illustrating operations for pressure control of the compression system in an example pressure regulation mode, such as for the fine pressure regulation mode.

[0074] Fig. 25 is a graph illustrating pressure during operations through various flow rate settings of an oxygen concentrator employing the mode switching operations for pressure regulation as described herein. [0075] Fig. 26 is a graph illustrating compressor motor speed (e.g., RPM) during operations through various flow rate settings of an oxygen concentrator employing the mode switching operations for pressure regulation as described herein.

DETAILED DESCRIPTION OF THE IMPLEMENTATIONS

[0076] An example adsorption device of the present technology involving an oxygen concentrator may be considered in relation to the examples of the figures. The examples of the present technology may be implemented with any of the following structures and operations.

[0077] Oxygen concentrator 100 is configured as described in more detail below to deliver oxygen enriched air at one of multiple user-selectable flow rate settings, each of which corresponds to a flow rate of the delivered oxygen enriched air. In one implementation, there are six user-selectable flow rate settings. Table 1 contains example flow rates corresponding to each of the six flow rate settings, numbered 1 to 6. The flow rate values in Table 1 correspond to minute volumes (bolus volume in litres multiplied by breathing rate per minute) of delivered oxygen enriched air in litres per minute (LPM).

Table 1: Example flow rates corresponding to each of six flow rate settings in one implementation of the present technology.

Outer Housing

[0078] Fig. 1 depicts an implementation of an outer housing 170 of an oxygen concentrator 100. In some implementations, outer housing 170 may be comprised of a light-weight plastic. Outer housing includes compression system inlets 105, cooling system passive inlet 101 and outlet 173 at each end of outer housing 170, outlet port 174, and control panel 600. Inlet 101 and outlet 173 allow cooling air to enter the housing, flow through the housing, and exit the interior of housing 170 to aid in cooling of the oxygen concentrator 100. Compression system inlets 105 allow air to enter the compression system. Outlet port 174 is used to attach a conduit to provide oxygen enriched air produced by the oxygen concentrator 100 to a user.

Gas separation system

[0079] Fig. 2 illustrates a schematic diagram of gas separation system 110 of an oxygen concentrator such as the oxygen concentrator 100, according to an implementation. Gas separation system 110 may concentrate oxygen within an air stream to provide oxygen enriched air to a user.

[0080] Oxygen concentrator 100 may be a portable oxygen concentrator. For example, oxygen concentrator 100 may have a weight and size that allows the oxygen concentrator to be carried by hand and/or in a carrying case. In one implementation, oxygen concentrator 100 has a weight of less than about 20 pounds., less than about 15 pounds, less than about 10 pounds, or less than about 5 pounds. In an implementation, oxygen concentrator 100 has a volume of less than about 1000 cubic inches, less than about 750 cubic inches; less than about 500 cubic inches, less than about 250 cubic inches, or less than about 200 cubic inches.

[0081] Oxygen enriched air may be produced from ambient air by pressurising ambient air in canisters 302 and 304, which contain a gas separation adsorbent and are therefore referred to as sieve beds. Gas separation adsorbents useful in an oxygen concentrator are capable of separating at least nitrogen from an air stream to produce oxygen enriched air. Examples of gas separation adsorbents include molecular sieves that are capable of separating nitrogen from an air stream. Examples of adsorbents that may be used in an oxygen concentrator include, but are not limited to, zeolites (natural) or synthetic crystalline aluminosilicates that separate nitrogen from an air stream under elevated pressure. Examples of synthetic crystalline aluminosilicates that may be used include, but are not limited to: OXYSIV adsorbents available from UOP LLC, Des Plaines, IW; SYLOBEAD adsorbents available from W. R. Grace & Co, Columbia, MD; SILIPORITE adsorbents available from CECA S.A. of Paris, France; ZEOCHEM adsorbents available from Zeochem AG, Uetikon, Switzerland; and AgLiLSX adsorbent available from Air Products and Chemicals, Inc., Allentown, PA.

[0082] As shown in Fig. 2, air may enter the gas separation system 110 through air inlet 105. Air may be drawn into air inlet 105 by compression system 200. Compression system 200 may draw in air from the surroundings of the oxygen concentrator and compress the air, forcing the compressed air into one or both canisters 302 and 304. In an implementation, an inlet muffler 108 may be coupled to air inlet 105 to reduce sound produced by air being pulled into the oxygen concentrator by compression system 200. In an implementation, inlet muffler 108 may be a moisture and sound absorbing muffler. For example, a water absorbent material (such as a polymer water absorbent material or a zeolite material) may be used to both absorb water from the incoming air and to reduce the sound of the air passing into the air inlet 105.

[0083] Compression system 200 may include one or more compressors configured to compress air. Pressurized air, produced by compression system 200, may be forced into one or both of the canisters 302 and 304. In some implementations, the ambient air may be pressurized in the canisters to a pressure approximately in a range of 13-20 pounds per square inch gauge pressure (psig). Other pressures may also be used, depending on the type of gas separation adsorbent disposed in the canisters.

[0084] Coupled to each canister 302/304 are inlet valves 122/124 and outlet valves 132/134. As shown in Fig. 2, inlet valve 122 is coupled to canister 302 and inlet valve 124 is coupled to canister 304. Outlet valve 132 is coupled to canister 302 and outlet valve 134 is coupled to canister 304. Inlet valves 122/124 are used to control the passage of air from compression system 200 to the respective canisters. Outlet valves 132/134 are used to release gas from the respective canisters during a venting process. In some implementations, inlet valves 122/124 and outlet valves 132/134 may be silicon plunger solenoid valves. Other types of valves, however, may be used. Plunger valves offer advantages over other kinds of valves by being quiet and having low slippage.

[0085] In some implementations, a two-step valve actuation voltage may be used to control inlet valves 122/124 and outlet valves 132/134. For example, a high voltage (e.g., 24 V) may be applied to an inlet valve to open the inlet valve. The voltage may then be reduced (e.g., to 7 V) to keep the inlet valve open. Using less voltage to keep a valve open may use less power (Power = Voltage * Current). This reduction in voltage minimizes heat buildup and power consumption to extend run time from the battery. When the power is cut off to the valve, it closes by spring action. In some implementations, the voltage may be applied as a function of time that is not necessarily a stepped response (e.g., a curved downward voltage between an initial 24 V and a final 7 V).

[0086] In an implementation, pressurized air is sent into one of canisters 302 or 304 while the other canister is being vented. For example, during use, inlet valve 122 is opened while inlet valve 124 is closed. Pressurized air from compression system 200 is forced into canister 302, while being inhibited from entering canister 304 by inlet valve 124. In an implementation, a controller 400 is electrically coupled to valves 122, 124, 132, and 134. Controller 400 includes one or more processors 410 operable to execute program instructions stored in memory 420. The program instructions configure the controller to perform various predefined methods that are used to operate the oxygen concentrator, such as the methods described in more detail herein. The program instructions may include program instructions for operating inlet valves 122 and 124 out of phase with each other, i.e., when one of inlet valves 122 or 124 is opened, the other valve is closed. During pressurization of canister 302, outlet valve 132 is closed and outlet valve 134 is opened. Similar to the inlet valves, outlet valves 132 and 134 are operated out of phase with each other. In some implementations, the voltages and the durations of the voltages used to open the input and output valves may be controlled by controller 400.

[0087] The controller 400 may include a transceiver 430 that may communicate with external devices to transmit data collected by the processor 410 or receive instructions from an external computing device for the processor 410.

[0088] Check valves 142 and 144 are coupled to canisters 302 and 304, respectively. Check valves 142 and 144 may be one-way valves that are passively operated by the pressure differentials that occur as the canisters are pressurized and vented, or may be active valves. Check valves 142 and 144 are coupled to the canisters to allow oxygen enriched air produced during pressurization of each canister to flow out of the canister, and to inhibit back flow of oxygen enriched air or any other gases into the canister. In this manner, check valves 142 and 144 act as one-way valves allowing oxygen enriched air to exit the respective canisters during pressurization.

[0089] The term “check valve”, as used herein, refers to a valve that allows flow of a fluid (gas or liquid) in one direction and inhibits back flow of the fluid. Examples of check valves that are suitable for use include, but are not limited to: a ball check valve; a diaphragm check valve; a butterfly check valve; a swing check valve; a duckbill valve; an umbrella valve; and a lift check valve. Under pressure, nitrogen molecules in the pressurized ambient air are adsorbed by the gas separation adsorbent in the pressurized canister. As the pressure increases, more nitrogen is adsorbed until the gas in the canister is enriched in oxygen. The nonadsorbed gas molecules (mainly oxygen) flow out of the pressurized canister when the pressure reaches a point sufficient to overcome the resistance of the check valve coupled to the canister. In one implementation, the pressure drop of the check valve in the forward direction is less than 1 psig. The break pressure in the reverse direction is greater than 100 psig. It should be understood, however, that modification of one or more components would alter the operating parameters of these valves. If the forward flow pressure is increased, there is, generally, a reduction in oxygen enriched air production. If the break pressure for reverse flow is reduced or set too low, there is, generally, a reduction in oxygen enriched air pressure.

[0090] In an exemplary implementation, canister 302 is pressurized by compressed air produced in compression system 200 and passed into canister 302. During pressurization of canister 302 inlet valve 122 is open, outlet valve 132 is closed, inlet valve 124 is closed and outlet valve 134 is open. Outlet valve 134 is opened when outlet valve 132 is closed to allow substantially simultaneous venting of canister 304 to atmosphere while canister 302 is being pressurized. Canister 302 is pressurized until the pressure in canister is sufficient to open check valve 142. Oxygen enriched air produced in canister 302 exits through check valve and, in one implementation, is collected in accumulator 106.

[0091] After some time, the gas separation adsorbent will become saturated with nitrogen and will be unable to separate significant amounts of nitrogen from incoming air. This point is usually reached after a predetermined time of oxygen enriched air production. In the implementation described above, when the gas separation adsorbent in canister 302 reaches this saturation point, the inflow of compressed air is stopped and canister 302 is vented to remove nitrogen. During venting, inlet valve 122 is closed, and outlet valve 132 is opened. While canister 302 is being vented, canister 304 is pressurized to produce oxygen enriched air in the same manner described above. Pressurization of canister 304 is achieved by closing outlet valve 134 and opening inlet valve 124. The oxygen enriched air exits canister 304 through check valve 144.

[0092] During venting of canister 302, outlet valve 132 is opened allowing pressurized gas (mainly nitrogen) to exit the canister to atmosphere through concentrator outlet 130. In an implementation, the vented gases may be directed through muffler 133 to reduce the noise produced by releasing the pressurized gas from the canister. As gas is released from canister 302, the pressure in the canister 302 drops, allowing the nitrogen to become desorbed from the gas separation adsorbent. The released nitrogen exits the canister through outlet 130, resetting the canister to a state that allows renewed separation of nitrogen from an air stream. Muffler 133 may include open cell foam (or another material) to muffle the sound of the gas leaving the oxygen concentrator. In some implementations, the combined muffling components/techniques for the input of air and the output of oxygen enriched air may provide for oxygen concentrator operation at a sound level below 50 decibels. [0093] During venting of the canisters, it is advantageous that at least a majority of the nitrogen is removed. In an implementation, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, at least about 98%, or substantially all of the nitrogen in a canister is removed before the canister is re-used to separate nitrogen from air. In some implementations, a canister may be further purged of nitrogen using an oxygen enriched air stream that is introduced into the canister from the other canister.

[0094] In an exemplary implementation, a portion of the oxygen enriched air may be transferred from canister 302 to canister 304 when canister 304 is being vented of nitrogen. Transfer of oxygen enriched air from canister 302 to 304 during venting of canister 304, helps to further purge nitrogen (and other gases) from the canister. In an implementation, oxygen enriched air may travel through flow restrictors 151, 153, and 155 between the two canisters. Flow restrictor 151 may be a trickle flow restrictor. Flow restrictor 151, for example, may be a 0.009D flow restrictor (e.g., the flow restrictor has a radius 0.009” which is less than the diameter of the tube it is inside). Flow restrictors 153 and 155 may be 0.013D flow restrictors. Other flow restrictor types and sizes are also contemplated and may be used depending on the specific configuration and tubing used to couple the canisters. In some implementations, the flow restrictors may be press fit flow restrictors that restrict air flow by introducing a narrower diameter in their respective tube. In some implementations, the press fit flow restrictors may be made of sapphire, metal or plastic (other materials are also contemplated).

[0095] Flow of oxygen enriched air between the canisters is also controlled by use of valve 152 and valve 154. Valves 152 and 154 may be opened for a short duration during the venting process (and may be closed otherwise) to prevent excessive oxygen loss out of the purging canister. Other durations are also contemplated. In an exemplary implementation, canister 302 is being vented and it is desirable to purge canister 302 by passing a portion of the oxygen enriched air being produced in canister 304 into canister 302. A portion of oxygen enriched air, upon pressurization of canister 304, will pass through flow restrictor 151 into canister 302 during venting of canister 302. Additional oxygen enriched air is passed into canister 302, from canister 304, through valve 154 and flow restrictor 155. Valve 152 may remain closed during the transfer process, or may be opened if additional oxygen enriched air is needed. The selection of appropriate flow restrictors 151 and 155, coupled with controlled opening of valve 154 allows a controlled amount of oxygen enriched air to be sent from canister 304 to canister 302. In an implementation, the controlled amount of oxygen enriched air is an amount sufficient to purge canister 302 and minimize the loss of oxygen enriched air through venting valve 132 of canister 302. While this implementation describes venting of canister 302, it should be understood that the same process can be used to vent canister 304 using flow restrictor 151, valve 152 and flow restrictor 153.

[0096] The pair of equalization/vent valves 152/154 work with flow restrictors 153 and 155 to optimize the gas flow balance between the two canisters. This may allow for better flow control for venting one of the canisters with oxygen enriched air from the other of the canisters. It may also provide better flow direction between the two canisters. It has been found that, while flow valves 152/154 may be operated as bi-directional valves, the flow rate through such valves varies depending on the direction of fluid flowing through the valve. For example, oxygen enriched air flowing from canister 304 toward canister 302 has a flow rate faster through valve 152 than the flow rate of oxygen enriched air flowing from canister 302 toward canister 304 through valve 152. If a single valve was to be used, eventually either too much or too little oxygen enriched air would be sent between the canisters and the canisters would, over time, begin to produce different amounts of oxygen enriched air. Use of opposing valves and flow restrictors on parallel air pathways may equalize the flow pattern of the oxygen enriched air between the two canisters. Equalising the flow may allow for a steady amount of oxygen enriched air to be available to the user over multiple cycles and also may allow a predictable volume of oxygen enriched air to purge the other of the canisters. In some implementations, the air pathway may not have restrictors but may instead have a valve with a built-in resistance or the air pathway itself may have a narrow radius to provide resistance.

[0097] At times, oxygen concentrator may be shut down for a period of time. When an oxygen concentrator is shut down, the temperature inside the canisters may drop as a result of the loss of adiabatic heat from the compression system. As the temperature drops, the volume occupied by the gases inside the canisters will drop. Cooling of the canisters may lead to a negative pressure in the canisters. Valves (e.g., valves 122, 124, 132, and 134) leading to and from the canisters are dynamically sealed rather than hermetically sealed. Thus, outside air may enter the canisters after shutdown to accommodate the pressure differential. When outside air enters the canisters, moisture from the outside air may be adsorbed by the gas separation adsorbent. Adsorption of water inside the canisters may lead to gradual degradation of the gas separation adsorbents, steadily reducing ability of the gas separation adsorbents to produce oxygen enriched air.

[0098] In an implementation, outside air may be inhibited from entering canisters after the oxygen concentrator is shut down by pressurising both canisters prior to shutdown. By storing the canisters under a positive pressure, the valves may be forced into a hermetically closed position by the internal pressure of the air in the canisters. In an implementation, the pressure in the canisters, at shutdown, should be at least greater than ambient pressure. As used herein the term “ambient pressure” refers to the pressure of the surroundings in which the oxygen concentrator is located (e.g. the pressure inside a room, outside, in a plane, etc.). In an implementation, the pressure in the canisters, at shutdown, is at least greater than standard atmospheric pressure (i.e., greater than 760 mmHg (Torr), 1 atm, 101,325 Pa). In an implementation, the pressure in the canisters, at shutdown, is at least about 1.1 times greater than ambient pressure; is at least about 1.5 times greater than ambient pressure; or is at least about 2 times greater than ambient pressure.

[0099] In an implementation, pressurization of the canisters may be achieved by directing pressurized air into each canister from the compression system and closing all valves to trap the pressurized air in the canisters. In an exemplary implementation, when a shutdown sequence is initiated, inlet valves 122 and 124 are opened and outlet valves 132 and 134 are closed. Because inlet valves 122 and 124 are joined together by a common conduit, both canisters 302 and 304 may become pressurized as air and / or oxygen enriched air from one canister may be transferred to the other canister. This situation may occur when the pathway between the compression system and the two inlet valves allows such transfer. Because the oxygen concentrator operates in an alternating pressurize/venting mode, at least one of the canisters should be in a pressurized state at any given time. In an alternate implementation, the pressure may be increased in each canister by operation of compression system 200. When inlet valves 122 and 124 are opened, pressure between canisters 302 and 304 will equalize, however, the equalized pressure in either canister may not be sufficient to inhibit air from entering the canisters during shutdown. In order to ensure that air is inhibited from entering the canisters, compression system 200 may be operated for a time sufficient to increase the pressure inside both canisters to a level at least greater than ambient pressure. Regardless of the method of pressurization of the canisters, once the canisters are pressurized, inlet valves 122 and 124 are closed, trapping the pressurized air inside the canisters, which inhibits air from entering the canisters during the shutdown period.

[0100] Referring to Fig. 3, an implementation of an oxygen concentrator 100 is depicted. Oxygen concentrator 100 includes a compression system 200, a canister system 300, and a power supply 180 disposed within an outer housing 170. Inlets 101 are located in outer housing 170 to allow air from the environment to enter oxygen concentrator 100. Inlets 101 may allow air to flow into the compartment to assist with cooling of the components in the compartment. Power supply 180 provides a source of power for the oxygen concentrator 100. Compression system 200 draws air in through the inlet 105 and muffler 108. Muffler 108 may reduce noise of air being drawn in by the compression system and also may include a desiccant material to remove water from the incoming air. Oxygen concentrator 100 may further include fan 172 used to vent air and other gases from the oxygen concentrator via outlet 173.

Compression System

[0101] In some implementations, compression system 200 includes one or more compressors. In another implementation, compression system 200 includes a single compressor, coupled to all of the canisters of canister system 300. Turning to FIGS. 4 and 5, a compression system 200 is depicted that includes compressor 210 and motor 220. Motor 220 is coupled to compressor 210 and provides an operating force to the compressor to operate the compression mechanism. For example, motor 220 may be a motor providing a rotating component that causes cyclical motion of a component of the compressor that compresses air. When compressor 210 is a piston type compressor, motor 220 provides an operating force which causes the piston of compressor 210 to be reciprocated. Reciprocation of the piston causes compressed air to be produced by compressor 210. The pressure of the compressed air is, in part, estimated by the speed that the compressor is operated at, (e.g., how fast the piston is reciprocated). Motor 220, therefore, may be a variable speed motor that is operable at various speeds to dynamically control the pressure of air produced by compressor 210.

[0102] In one implementation, compressor 210 includes a single head wobble type compressor having a piston. Other types of compressors may be used such as diaphragm compressors and other types of piston compressors. Motor 220 may be a DC or AC motor and provides the operating power to the compressing component of compressor 210. Motor 220, in an implementation, may be a brushless DC motor. Motor 220 may be a variable speed motor configured to operate the compressing component of compressor 210 at variable speeds. Motor 220 may be coupled to controller 400, as depicted in Fig. 2, which sends operating signals to the motor to control the operation of the motor. For example, controller 400 may send signals to motor 220 to: turn the motor on, turn motor the off, and set the operating speed of the motor. Thus, as illustrated in Fig. 2, the compression system may include a speed sensor 201. The speed sensor may be a motor speed transducer used to determine a rotational velocity of the motor 220 and/or other reciprocating operation of the compression system 200. For example, a motor speed signal from the motor speed transducer may be provided to the controller 400. The speed sensor or motor speed transducer may, for example, be a Hall effect sensor. The controller 400 may operate the compression system via the motor 220 based on the speed signal and/or any other sensor signal of the oxygen concentrator, such as a pressure sensor (e.g., accumulator pressure sensor 107). Thus, as illustrated in Fig. 2, the controller 400 receives sensor signals, such as a speed signal from the speed sensor 201 and accumulator pressure signal from the accumulator pressure sensor 107. With such signal(s), the controller may implement one or more control loops (e.g., feedback control) for operation of the compression system based on sensor signals such as accumulator pressure and/or motor speed as described in more detail herein.

[0103] Compression system 200 inherently creates substantial heat. Heat is caused by the consumption of power by motor 220 and the conversion of power into mechanical motion. Compressor 210 generates heat due to the increased resistance to movement of the compressor components by the air being compressed. Heat is also inherently generated due to adiabatic compression of the air by compressor 210. Thus, the continual pressurization of air produces heat in the enclosure. Additionally, power supply 180 may produce heat as power is supplied to compression system 200. Furthermore, users of the oxygen concentrator may operate the device in unconditioned environments (e.g., outdoors) at potentially higher ambient temperatures than indoors, thus the incoming air will already be in a heated state.

[0104] Heat produced inside oxygen concentrator 100 can be problematic. Lithium ion batteries are generally employed as a power source for oxygen concentrators due to their long life and light weight. Lithium ion battery packs, however, are dangerous at elevated temperatures and safety controls are employed in oxygen concentrator 100 to shutdown the system if dangerously high power supply temperatures are detected. Additionally, as the internal temperature of oxygen concentrator 100 increases, the amount of oxygen generated by the concentrator may decrease. This is due, in part, to the decreasing amount of oxygen in a given volume of air at higher temperatures. If the amount of produced oxygen drops below a predetermined amount, the oxygen concentrator 100 may automatically shut down.

[0105] Because of the compact nature of oxygen concentrators, dissipation of heat can be difficult. Solutions typically involve the use of one or more fans to create a flow of cooling air through the enclosure. Such solutions, however, require additional power from the power supply and thus shorten the portable usage time of the oxygen concentrator. In an implementation, a passive cooling system may be used that takes advantage of the mechanical power produced by motor 220. Referring to Figs. 4 and 5, compression system 200 includes motor 220 having an external rotating armature 230. Specifically, armature 230 of motor 220 (e.g. a DC motor) is wrapped around the stationary field that is driving the armature. Since motor 220 is a large contributor of heat to the overall system it is helpful to pull heat off the motor and sweep it out of the enclosure. With the external high speed rotation, the relative velocity of the major component of the motor and the air in which it exists is very high. The surface area of the armature is larger if externally mounted than if it is internally mounted. Since the rate of heat exchange is proportional to the surface area and the square of the velocity, using a larger surface area armature mounted externally increases the ability of heat to be dissipated from motor 220. The gain in cooling efficiency by mounting the armature externally, allows the elimination of one or more cooling fans, thus reducing the weight and power consumption while maintaining the interior of the oxygen concentrator within the appropriate temperature range. Additionally, the rotation of the externally mounted armature creates movement of air proximate to the motor to create additional cooling.

[0106] Moreover, an external rotating armature may help the efficiency of the motor, allowing less heat to be generated. A motor having an external armature operates similar to the way a flywheel works in an internal combustion engine. When the motor is driving the compressor, the resistance to rotation is low at low pressures. When the pressure of the compressed air is higher, the resistance to rotation of the motor is higher. As a result, the motor does not maintain consistent ideal rotational stability, but instead surges and slows down depending on the pressure demands of the compressor. This tendency of the motor to surge and then slow down is inefficient and therefore generates heat. Use of an external armature adds greater angular momentum to the motor which helps to compensate for the variable resistance experienced by the motor. Since the motor does not have to work as hard, the heat produced by the motor may be reduced.

[0107] In an implementation, cooling efficiency may be further increased by coupling an air transfer device 240 to external rotating armature 230. In an implementation, air transfer device 240 is coupled to the external armature 230 such that rotation of the external armature causes the air transfer device to create an air flow that passes over at least a portion of the motor. In an implementation, air transfer device includes one or more fan blades coupled to the armature. In an implementation, a plurality of fan blades may be arranged in an annular ring such that the air transfer device acts as an impeller that is rotated by movement of the external rotating armature. As depicted in FIGS. 4 and 5, air transfer device 240 may be mounted to an outer surface of the external armature 230, in alignment with the motor. The mounting of the air transfer device to the armature allows air flow to be directed toward the main portion of the external rotating armature, providing a cooling effect during use. In an implementation, the air transfer device directs air flow such that a majority of the external rotating armature is in the air flow path.

[0108] Further, referring to FIGS. 4 and 5, air pressurized by compressor 210 exits compressor 210 at compressor outlet 212. A compressor outlet conduit 250 is coupled to compressor outlet 212 to transfer the compressed air to canister system 300. As noted previously, compression of air causes an increase in the temperature of the air. This increase in temperature can be detrimental to the efficiency of the oxygen concentrator. In order to reduce the temperature of the pressurized air, compressor outlet conduit 250 is placed in the air flow path produced by air transfer device 240. At least a portion of compressor outlet conduit 250 may be positioned proximate to motor 220. Thus, air flow, created by air transfer device, may contact both motor 220 and compressor outlet conduit 250. In one implementation, a majority of compressor outlet conduit 250 is positioned proximate to motor 220. In an implementation, the compressor outlet conduit 250 is coiled around motor 220, as depicted in Fig. 5.

[0109] In an implementation, the compressor outlet conduit 250 is composed of a heat exchange metal. Heat exchange metals include, but are not limited to, aluminum, carbon steel, stainless steel, titanium, copper, copper-nickel alloys or other alloys formed from combinations of these metals. Thus, compressor outlet conduit 250 can act as a heat exchanger to remove heat that is inherently caused by compression of the air. By removing heat from the compressed air, the number of molecules in a given volume at a given pressure is increased. As a result, the amount of oxygen that can be generated by each canister during each pressure swing cycle may be increased.

[0110] The heat dissipation mechanisms described herein are either passive or make use of elements required for the oxygen concentrator 100. Thus, for example, dissipation of heat may be increased without using systems that require additional power. By not requiring additional power, the run-time of the battery packs may be increased and the size and weight of the oxygen concentrator may be minimized. Likewise, use of an additional box fan or cooling unit may be eliminated. Eliminating such additional features reduces the weight and power consumption of the oxygen concentrator.

[0111] As discussed above, adiabatic compression of air causes the air temperature to increase. During venting of a canister in canister system 300, the pressure of the gas being released from the canisters decreases. The adiabatic decompression of the gas in the canister causes the temperature of the gas to drop as it is vented. In an implementation, the cooled vented gases 327 from canister system 300 are directed toward power supply 180 and toward compression system 200. In an implementation, base 315 of canister system 300 receives the vented gases from the canisters. The vented gases 327 are directed through base 315 toward outlet 325 of the base and toward power supply 180. The vented gases, as noted, are cooled due to decompression of the gases and therefore passively provide cooling to the power supply. When the compression system is operated, the air transfer device will gather the cooled vented gases and direct the gases toward the motor of compression system 200. Fan 172 may also assist in directing the vented gas across compression system 200 and out of the housing 170. In this manner, additional cooling may be obtained without requiring any further power requirements from the battery.

Canister System

[0112] Oxygen concentrator 100 may include at least two canisters, each canister including a gas separation adsorbent. The canisters of oxygen concentrator 100 may be disposed formed from a molded housing. In an implementation, canister system 300 includes two housing components 310 and 510, as depicted in Fig. 9. In various implementations, the housing components 310 and 510 of the oxygen concentrator 100 may form a two-part molded plastic frame that defines two canisters 302 and 304 and accumulator 106. The housing components 310 and 510 may be formed separately and then coupled together. In some implementations, housing components 310 and 510 may be injection molded or compression molded. Housing components 310 and 510 may be made from a thermoplastic polymer such as polycarbonate, methylene carbide, polystyrene, acrylonitrile butadiene styrene (ABS), polypropylene, polyethylene, or polyvinyl chloride. In another implementation, housing components 310 and 510 may be made of a thermoset plastic or metal (such as stainless steel or a lightweight aluminum alloy). Lightweight materials may be used to reduce the weight of the oxygen concentrator 100. In some implementations, the two housings 310 and 510 may be fastened together using screws or bolts. Alternatively, housing components 310 and 510 may be solvent welded together.

[0113] As shown, valve seats 322, 324, 332, and 334 and air pathways of conduit 330 and 346 may be integrated into the housing component 310 to reduce the number of sealed connections needed throughout the air flow of the oxygen concentrator 100.

[0114] Air pathways/tubing between different sections in housing components 310 and 510 may take the form of molded conduits. Conduits in the form of molded channels for air pathways may occupy multiple planes in housing components 310 and 510. For example, the molded air conduits may be formed at different depths and at different x,y,z positions in housing components 310 and 510. In some implementations, a majority or substantially all of the conduits may be integrated into the housing components 310 and 510 to reduce potential leak points. [0115] In some implementations, prior to coupling housing components 310 and 510 together, O-rings may be placed between various points of housing components 310 and 510 to ensure that the housing components are properly sealed. In some implementations, components may be integrated and/or coupled separately to housing components 310 and 510. For example, tubing, flow restrictors (e.g., press fit flow restrictors), oxygen sensors, gas separation adsorbents, check valves, plugs, processors, power supplies, etc. may be coupled to housing components 310 and 510 before and/or after the housing components are coupled together.

[0116] In some implementations, apertures 337 leading to the exterior of housing components 310 and 510 may be used to insert devices such as flow restrictors. Apertures may also be used for increased moldability. One or more of the apertures may be plugged after molding (e.g., with a plastic plug). In some implementations, flow restrictors may be inserted into passages prior to inserting plug to seal the passage. Press fit flow restrictors may have diameters that may allow a friction fit between the press fit flow restrictors and their respective apertures. In some implementations, an adhesive may be added to the exterior of the press fit flow restrictors to hold the press fit flow restrictors in place once inserted. In some implementations, the plugs may have a friction fit with their respective tubes (or may have an adhesive applied to their outer surface). The press fit flow restrictors and/or other components may be inserted and pressed into their respective apertures using a narrow tip tool or rod (e.g., with a diameter less than the diameter of the respective aperture). In some implementations, the press fit flow restrictors may be inserted into their respective tubes until they abut a feature in the tube to halt their insertion. For example, the feature may include a reduction in radius. Other features are also contemplated (e.g., a bump in the side of the tubing, threads, etc.). In some implementations, press fit flow restrictors may be molded into the housing components (e.g., as narrow tube segments).

[0117] In some implementations, spring baffle 139 may be placed into respective canister receiving portions of housing components 310 and 510 with the spring side of the baffle 139 facing the exit of the canister. Spring baffle 139 may apply force to gas separation adsorbent in the canister while also assisting in preventing gas separation adsorbent from entering the exit apertures. Use of a spring baffle 139 may keep the gas separation adsorbent compact while also allowing for expansion (e.g., thermal expansion). Keeping the gas separation adsorbent compact may prevent the gas separation adsorbent from breaking during movement of the oxygen concentrator 100. [0118] In some implementations, filter 129 may be placed into respective canister receiving portions of housing components 310 and 510 facing the inlet of the respective canisters. The filter 129 removes particles from the feed gas stream entering the canisters.

[0119] In some implementations, pressurized air from the compression system 200 may enter air inlet 306. Air inlet 306 is coupled to inlet conduit 330. Air enters housing component 310 through inlet 306 travels through conduit 330, and then to valve seats 322 and 324. Fig. 10 and Fig. 11 depict an end view of housing 310. Fig. 10 depicts an end view of housing 310 prior to fitting valves to housing 310. Fig. 11 depicts an end view of housing 310 with the valves fitted to the housing 310. Valve seats 322 and 324 are configured to receive inlet valves 122 and 124 respectively. Inlet valve 122 is coupled to canister 302 and inlet valve 124 is coupled to canister 304. Housing 310 also includes valve seats 332 and 334 configured to receive outlet valves 132 and 134 respectively. Outlet valve 132 is coupled to canister 302 and outlet valve 134 is coupled to canister 304. Inlet valves 122/124 are used to control the passage of air from conduit 330 to the respective canisters.

[0120] In an implementation, pressurized air is sent into one of canisters 302 or 304 while the other canister is being vented. For example, during use, inlet valve 122 is opened while inlet valve 124 is closed. Pressurized air from compression system 200 is forced into canister 302, while being inhibited from entering canister 304 by inlet valve 124. During pressurization of canister 302, outlet valve 132 is closed and outlet valve 134 is opened. Similar to the inlet valves, outlet valves 132 and 134 are operated out of phase with each other. Valve seat 322 includes an opening 323 that passes through housing 310 into canister 302. Similarly valve seat 324 includes an opening 375 that passes through housing 310 into canister 302. Air from conduit 330 passes through openings 323 or 375 if the respective valves 322 and 324 are open, and enters a canister.

[0121] Check valves 142 and 144 (See Fig. 9) are coupled to canisters 302 and 304, respectively. Check valves 142 and 144 are one way valves that may be passively operated by the pressure differentials that occur as the canisters are pressurized and vented. Oxygen enriched air produced in canisters 302 and 304 passes from the canisters into openings 542 and 544 of housing component 510. A passage (not shown) links openings 542 and 544 to conduits 342 and 344, respectively. Oxygen enriched air produced in canister 302 passes from the canister though opening 542 and into conduit 342 when the pressure in the canister is sufficient to open check valve 142. When check valve 142 is open, oxygen enriched air flows through conduit 342 toward the end of housing 310. Similarly, oxygen enriched air produced in canister 304 passes from the canister through opening 544 and into conduit 344 when the pressure in the canister is sufficient to open check valve 144. When check valve 144 is open, oxygen enriched air flows through conduit 344 toward the end of housing 310.

[0122] Oxygen enriched air from either canister travels through conduit 342 or 344 and enters conduit 346 formed in housing 310. Conduit 346 includes openings that couple the conduit to conduit 342, conduit 344 and accumulator 106. Thus, oxygen enriched air, produced in canister 302 or 304, travels to conduit 346 and passes into accumulator 106. As illustrated in Fig. 2, gas pressure within the accumulator 106 may be measured by a sensor, such as with an accumulator pressure sensor 107. (See also Fig. 6.) Thus, the accumulator pressure sensor provides a signal representing the pressure of the accumulated oxygen enriched air. An example of a suitable pressure transducer is a sensor from the HONEYWELL ASDX series. An alternative suitable pressure transducer is a sensor from the NPA Series from GENERAL ELECTRIC. In some versions, the pressure sensor may alternatively measure pressure of the gas outside of the accumulator 106, such as in an output path between the accumulator 106 and a valve (e.g., supply valve 160) that gates the release of the oxygen enriched air for delivery to a user in a bolus.

[0123] After some time, the gas separation adsorbent will become saturated with nitrogen and will be unable to separate significant amounts of nitrogen from incoming air. When the gas separation adsorbent in a canister reaches this saturation point, the inflow of compressed air is stopped and the canister is vented to remove nitrogen. Canister 302 is vented by closing inlet valve 122 and opening outlet valve 132. Outlet valve 132 releases the vented gas from canister 302 into the volume defined by the end of housing 310. Foam material may cover the end of housing 310 to reduce the sound made by release of gases from the canisters. Similarly, canister 304 is vented by closing inlet valve 124 and opening outlet valve 134. Outlet valve 134 releases the vented gas from canister 304 into the volume defined by the end of housing 310.

[0124] While canister 302 is being vented, canister 304 is pressurized to produce oxygen enriched air in the same manner described above. Pressurization of canister 304 is achieved by closing outlet valve 134 and opening inlet valve 124. The oxygen enriched air exits canister 304 through check valve 144.

[0125] In an exemplary implementation, a portion of the oxygen enriched air may be transferred from canister 302 to canister 304 when canister 304 is being vented of nitrogen. Transfer of oxygen enriched air from canister 302 to canister 304, during venting of canister 304, helps to further purge nitrogen (and other gases) from the canister. Flow of oxygen enriched air between the canisters is controlled using flow restrictors and valves, as depicted in Fig. 2. Three conduits are formed in housing component 510 for use in transferring oxygen enriched air between canisters. As shown in Fig. 12, conduit 530 couples canister 302 to canister 304. Flow restrictor 151 (not shown) is disposed in conduit 530, between canister 302 and canister 304 to restrict flow of oxygen enriched air during use. Conduit 532 also couples canister 302 to 304. Conduit 532 is coupled to valve seat 552 which receives valve 152, as shown in Fig. 13. Flow restrictor 153 (not shown) is disposed in conduit 532, between canister 302 and 304. Conduit 534 also couples canister 302 to 304. Conduit 534 is coupled to valve seat 554 which receives valve 154, as shown in Fig. 13. Flow restrictor 155 (not shown) is disposed in conduit 534, between canister 302 and 304. The pair of equalization/vent valves 152/154 work with flow restrictors 153 and 155 to optimize the air flow balance between the two canisters.

[0126] Oxygen enriched air in accumulator 106 passes through supply valve 160 into expansion chamber 162 which is formed in housing component 510. An opening (not shown) in housing component 510 couples accumulator 106 to supply valve 160. In an implementation, expansion chamber 162 may include one or more devices configured to estimate an oxygen concentration of gas passing through the chamber.

Outlet System

[0127] An outlet system, coupled to one or more of the canisters, includes one or more conduits for providing oxygen enriched air to a user. In an implementation, oxygen enriched air produced in either of canisters 302 and 304 is collected in accumulator 106 through check valves 142 and 144, respectively, as depicted schematically in Fig. 6. The oxygen enriched air leaving the canisters may be collected in an oxygen accumulator 106 prior to being provided to a user. In some implementations, a tube may be coupled to the accumulator 106 to provide the oxygen enriched air to the user. Oxygen enriched air may be provided to the user through an airway delivery device that transfers the oxygen enriched air to the user's mouth and/or nose. In an implementation, an outlet may include a tube that directs the oxygen toward a user's nose and/or mouth that may not be directly coupled to the user's nose.

[0128] Turning to Fig. 6, a schematic diagram of an implementation of an outlet system for an oxygen concentrator is shown. A supply valve 160 may be coupled to an outlet tube to control the release of the oxygen enriched air from accumulator 106 to the user. In an implementation, supply valve 160 is an electromagnetically actuated plunger valve. Supply valve 160 is actuated by controller 400 to control the delivery of oxygen enriched air to a user. Actuation of supply valve 160 is not timed or synchronized to the pressure swing adsorption process. Instead, actuation is synchronized to the user's breathing as described below. In some implementations, supply valve 160 may have continuously-valued actuation to establish a clinically effective amplitude profile for providing oxygen enriched air.

[0129] Oxygen enriched air in accumulator 106 passes through supply valve 160 into expansion chamber 162 as depicted in Fig. 6. In an implementation, expansion chamber 162 may include one or more devices configured to estimate an oxygen concentration of gas passing through the expansion chamber 162. Oxygen enriched air in expansion chamber 162 builds briefly, through release of gas from accumulator 106 by supply valve 160, and then is bled through a small orifice flow restrictor 175 to a flow rate sensor 185 and then to particulate filter 187. Flow restrictor 175 may be a 0.025 D flow restrictor. Other flow restrictor types and sizes may be used. In some implementations, the diameter of the air pathway in the housing may be restricted to create restricted gas flow. Flow rate sensor 185 may be any sensor configured to generate a signal representing the rate of gas flowing through the conduit. Particulate filter 187 may be used to filter bacteria, dust, granule particles, etc., prior to delivery of the oxygen enriched air to the user. The oxygen enriched air passes through filter 187 to connector 190 which sends the oxygen enriched air to the user via delivery conduit 192 and to pressure sensor 194.

[0130] The fluid dynamics of the outlet pathway, coupled with the programmed actuations of supply valve 160, may result in a bolus of oxygen being provided at the correct time and with an amplitude profile that assures rapid delivery into the user's lungs without excessive waste. If the bolus can be delivered in this manner, there may be a linear relationship between the prescribed continuous flow rate and the therapeutically equivalent bolus volume required in pulsed delivery mode for a user at rest with a given breathing pattern. For example, the total volume of the bolus required to emulate continuous-flow prescriptions may be equal to 11 mL for each LPM of prescribed continuous flow rate, i.e., 11 mL for a prescription of 1 LPM; 22 mL for a prescription of 2 LPM; 33 mL for a prescription of 3 LPM; 44 mL for a prescription of 4 LPM; 55 mL for a prescription of 5 LPM; etc. This amount is generally referred to as the LPM equivalent bolus volume. It should be understood that the LPM equivalent may vary between oxygen concentrators due to differences in construction design, tubing size, chamber size, etc. The LPM equivalent will also vary depending on the user's breathing pattern (e.g. breathing rate).

[0131] Expansion chamber 162 may include one or more oxygen sensors adapted to determine an oxygen concentration of gas passing through the chamber. In an implementation, the oxygen concentration of gas passing through expansion chamber 162 is estimated using an oxygen sensor 165. An oxygen sensor is a device configured to measure oxygen concentration in a gas. Examples of oxygen sensors include, but are not limited to, ultrasonic oxygen sensors, electrical oxygen sensors, chemical oxygen sensors, and optical oxygen sensors. In one implementation, oxygen sensor 165 is an ultrasonic oxygen sensor that includes an ultrasonic emitter 166 and an ultrasonic receiver 168. In some implementations, ultrasonic emitter 166 may include multiple ultrasonic emitters and ultrasonic receiver 168 may include multiple ultrasonic receivers. In implementations having multiple emitters/receivers, the multiple ultrasonic emitters and multiple ultrasonic receivers may be axially aligned (e.g., across the gas flow path which may be perpendicular to the axial alignment).

[0132] In use, an ultrasonic sound wave from emitter 166 may be directed through oxygen enriched air disposed in chamber 162 to receiver 168. The ultrasonic oxygen sensor 165 may be configured to detect the speed of sound through the oxygen enriched air to determine the composition of the oxygen enriched air. The speed of sound is different in nitrogen and oxygen, and in a mixture of the two gases, the speed of sound through the mixture may be an intermediate value proportional to the relative amounts of each gas in the mixture. In use, the sound at the receiver 168 is slightly out of phase with the sound sent from emitter 166. This phase shift is due to the relatively slow velocity of sound through a gas medium as compared with the relatively fast speed of the electronic pulse through wire. The phase shift, then, is proportional to the distance between the emitter and the receiver and inversely proportional to the speed of sound through the expansion chamber 162. The density of the gas in the chamber affects the speed of sound through the expansion chamber and the density is proportional to the ratio of oxygen to nitrogen in the expansion chamber. Therefore, the phase shift can be used to measure the concentration of oxygen in the expansion chamber. In this manner the relative concentration of oxygen in the accumulator may be estimated as a function of one or more properties of a detected sound wave traveling through the accumulator.

[0133] In some implementations, multiple emitters 166 and receivers 168 may be used. The readings from the emitters 166 and receivers 168 may be averaged to reduce errors that may be inherent in turbulent flow systems. In some implementations, the presence of other gases may also be detected by measuring the transit time and comparing the measured transit time to predetermined transit times for other gases and/or mixtures of gases.

[0134] The sensitivity of the ultrasonic sensor system may be increased by increasing the distance between the emitter 166 and receiver 168, for example to allow several sound wave cycles to occur between emitter 166 and the receiver 168. In some implementations, if at least two sound cycles are present, the influence of structural changes of the transducer may be reduced by measuring the phase shift relative to a fixed reference at two points in time. If the earlier phase shift is subtracted from the later phase shift, the shift caused by thermal expansion of expansion chamber 162 may be reduced or cancelled. The shift caused by a change of the distance between the emitter 166 and receiver 168 may be approximately the same at the measuring intervals, whereas a change owing to a change in oxygen concentration may be cumulative. In some implementations, the shift measured at a later time may be multiplied by the number of intervening cycles and compared to the shift between two adjacent cycles. Further details regarding sensing of oxygen in the expansion chamber may be found, for example, in U.S. Published Patent Application No. 2009-0065007, published March 12, 2009, and entitled “Oxygen Concentrator Apparatus and Method”, which is incorporated herein by reference.

[0135] Flow rate sensor 185 may be used to determine the flow rate of gas flowing through the outlet system. Flow rate sensors that may be used include, but are not limited to: diaphragm/bellows flow meters; rotary flow meters (e.g. Hall effect flow meters); turbine flow meters; orifice flow meters; and ultrasonic flow meters. Flow rate sensor 185 may be coupled to controller 400. The rate of gas flowing through the outlet system may be an indication of the breathing volume of the user. Changes in the flow rate of gas flowing through the outlet system may also be used to determine a breathing rate of the user. Controller 400 may generate a control signal or trigger signal to control actuation of supply valve 160. Such control of actuation of the supply valve may be based on the breathing rate and/or breathing volume of the user, as estimated by flow rate sensor 185.

[0136] In some implementations, ultrasonic sensor 165 and, for example, flow rate sensor 185 may provide a measurement of an actual amount of oxygen being provided. For example, flow rate sensor 185 may measure a volume of gas (based on flow rate) provided and ultrasonic sensor 165 may provide the concentration of oxygen of the gas provided. These two measurements together may be used by controller 400 to determine an approximation of the actual amount of oxygen provided to the user.

[0137] Oxygen enriched air passes through flow rate sensor 185 to filter 187. Filter 187 removes bacteria, dust, granule particles, etc prior to providing the oxygen enriched air to the user. The filtered oxygen enriched air passes through filter 187 to connector 190. Connector 190 may be a “Y” connector coupling the outlet of filter 187 to pressure sensor 194 and delivery conduit 192. Pressure sensor 194 may be used to monitor the pressure of the gas passing through conduit 192 to the user. In some implementations, pressure sensor 194 is configured to generate a signal that is proportional to the amount of positive or negative pressure applied to a sensing surface. Changes in pressure, sensed by pressure sensor 194, may be used to determine a breathing rate of a user, as well as the onset of inhalation (also referred to as the trigger instant) as described below. Controller 400 may control actuation of supply valve 160 based on the breathing rate and/or onset of inhalation of the user. In an implementation, controller 400 may control actuation of supply valve 160 based on information provided by either or both of the flow rate sensor 185 and the pressure sensor 194.

[0138] Oxygen enriched air may be provided to a user through conduit 192. In an implementation, conduit 192 may be a silicone tube. Conduit 192 may be coupled to a user using an airway delivery device 196, as depicted in FIGS. 7 and 8. Airway delivery device 196 may be any device capable of providing the oxygen enriched air to nasal cavities or oral cavities. Examples of airway delivery devices include, but are not limited to: nasal masks, nasal pillows, nasal prongs, nasal cannulas, and mouthpieces. A nasal cannula airway delivery device 196 is depicted in Fig. 7. Airway delivery device 196 is positioned proximate to a user's airway (e.g., proximate to the user's mouth and or nose) to allow delivery of the oxygen enriched air to the user while allowing the user to breathe air from the surroundings.

[0139] In an alternate implementation, a mouthpiece may be used to provide oxygen enriched air to the user. As shown in Fig. 8, a mouthpiece 198 may be coupled to oxygen concentrator 100. Mouthpiece 198 may be the only device used to provide oxygen enriched air to the user, or a mouthpiece may be used in combination with a nasal airway delivery device 196 (e.g., a nasal cannula). As depicted in Fig. 8, oxygen enriched air may be provided to a user through both a nasal airway delivery device 196 and a mouthpiece 198.

[0140] Mouthpiece 198 is removably positionable in a user's mouth. In one implementation, mouthpiece 198 is removably couplable to one or more teeth in a user's mouth. During use, oxygen enriched air is directed into the user's mouth via the mouthpiece. Mouthpiece 198 may be a night guard mouthpiece which is molded to conform to the user's teeth. Alternatively, mouthpiece may be a mandibular repositioning device. In an implementation, at least a majority of the mouthpiece is positioned in a user's mouth during use.

[0141] During use, oxygen enriched air may be directed to mouthpiece 198 when a change in pressure is detected proximate to the mouthpiece. In one implementation, mouthpiece 198 may be coupled to a pressure sensor 194. When a user inhales air through the user's mouth, pressure sensor 194 may detect a drop in pressure proximate to the mouthpiece. Controller user at the onset of inhalation.

[0142] During typical breathing of an individual, inhalation may occur through the nose, through the mouth or through both the nose and the mouth. Furthermore, breathing may change from one passageway to another depending on a variety of factors. For example, during more active activities, a user may switch from breathing through their nose to breathing through their mouth, or breathing through their mouth and nose. A system that relies on a single mode of delivery (either nasal or oral), may not function properly if breathing through the monitored pathway is stopped. For example, if a nasal cannula is used to provide oxygen enriched air to the user, an inhalation sensor (e.g., a pressure sensor or flow rate sensor) is coupled to the nasal cannula to determine the onset of inhalation. If the user stops breathing through their nose, and switches to breathing through their mouth, the oxygen concentrator 100 may not know when to provide the oxygen enriched air since there is no feedback from the nasal cannula. Under such circumstances, oxygen concentrator 100 may increase the flow rate and/or increase the frequency of providing oxygen enriched air until the inhalation sensor detects an inhalation by the user. If the user switches between breathing modes often, the default mode of providing oxygen enriched air may cause the oxygen concentrator 100 to work harder, limiting the portable usage time of the system.

[0143] In an implementation, a mouthpiece 198 is used in combination with a nasal airway delivery device 196 (e.g., a nasal cannula) to provide oxygen enriched air to a user, as depicted in Fig. 8. Both mouthpiece 198 and nasal airway delivery device 196 are coupled to an inhalation sensor. In one implementation, mouthpiece 198 and nasal airway delivery device 196 are coupled to the same inhalation sensor. In an alternate implementation, mouthpiece 198 and nasal airway delivery device 196 are coupled to different inhalation sensors. In either implementation, the inhalation sensor(s) may detect the onset of inhalation from either the mouth or the nose. Oxygen concentrator 100 may be configured to provide oxygen enriched air to the delivery device (i.e. mouthpiece 198 or nasal airway delivery device 196) proximate to which the onset of inhalation was detected. Alternatively, oxygen enriched air may be provided to both mouthpiece 198 and nasal airway delivery device 196 if onset of inhalation is detected proximate either delivery device. The use of a dual delivery system, such as depicted in Fig. 8 may be particularly useful for users when they are sleeping and may switch between nose breathing and mouth breathing without conscious effort. Controller System

[0144] Operation of oxygen concentrator 100 may be performed automatically using an internal controller 400 coupled to various components of the oxygen concentrator 100, as described herein. Controller 400 includes one or more processors 410 and internal memory 420, as depicted in Fig. 2. Methods used to operate and monitor oxygen concentrator 100 may be implemented by program instructions stored in internal memory 420 or an external memory medium coupled to controller 400, and executed by one or more processors 410. A memory medium may include any of various types of memory devices or storage devices. The term “memory medium” is intended to include an installation medium, e.g., a Compact Disc Read Only Memory (CD-ROM), floppy disks, or tape device; a computer system memory or random access memory such as Dynamic Random Access Memory (DRAM), Double Data Rate Random Access Memory (DDR RAM), Static Random Access Memory (SRAM), Extended Data Out Random Access Memory (EDO RAM), Random Access Memory (RAM), etc.; or a non-volatile memory such as a magnetic medium, e.g., a hard drive, or optical storage. The memory medium may comprise other types of memory as well, or combinations thereof. In addition, the memory medium may be located proximate to the controller 400 by which the programs are executed, or may be located in an external computing device that connects to the controller 400 over a network, such as the Internet. In the latter instance, the external computing device may provide program instructions to the controller 400 for execution. The term “memory medium” may include two or more memory media that may reside in different locations, e.g., in different computing devices that are connected over a network.

[0145] In some implementations, controller 400 includes processor 410 that includes, for example, one or more field programmable gate arrays (FPGAs), microcontrollers, etc. included on a circuit board disposed in oxygen concentrator 100. Processor 410 is configured to execute programming instructions stored in memory 420. In some implementations, programming instructions may be built into processor 410 such that a memory external to the processor 410 may not be separately accessed (i.e., the memory 420 may be internal to the processor 410).

[0146] Processor 410 may be coupled to various components of oxygen concentrator 100, including, but not limited to compression system 200, one or more of the valves used to control fluid flow through the system (e.g., valves 122, 124, 132, 134, 152, 154, 160), oxygen sensor 165, pressure sensor 194, flow rate sensor 185, temperature sensors (not shown), fan 172, and any other component that may be electrically controlled. In some implementations, a separate processor (and/or memory) may be coupled to one or more of the components. [0147] Controller 400 is configured (e.g. programmed by program instructions) to operate oxygen concentrator 100 and is further configured to monitor the oxygen concentrator 100 such as for malfunction states or other process information. For example, in one implementation, controller 400 is programmed to trigger an alarm if the system is operating and no breathing is detected by the user for a predetermined amount of time. For example, if controller 400 does not detect a breath for a period of 75 seconds, an alarm LED may be lit and/or an audible alarm may be sounded. If the user has truly stopped breathing, for example, during a sleep apnea episode, the alarm may be sufficient to awaken the user, causing the user to resume breathing. The action of breathing may be sufficient for controller 400 to reset this alarm function. Alternatively, if the system is accidentally left on when delivery conduit 192 is removed from the user, the alarm may serve as a reminder for the user to turn oxygen concentrator 100 off.

[0148] Controller 400 is further coupled to oxygen sensor 165, and may be programmed for continuous or periodic monitoring of the oxygen concentration of the oxygen enriched air passing through expansion chamber 162. A minimum oxygen concentration threshold may be programmed into controller 400, such that the controller lights an LED visual alarm and/or an audible alarm to warn the user of the low concentration of oxygen.

[0149] Controller 400 is also coupled to internal power supply 180 and may be configured to monitor the level of charge of the internal power supply. A minimum voltage and/or current threshold may be programmed into controller 400, such that the controller lights an LED visual alarm and/or an audible alarm to warn the user of low power condition. The alarms may be activated intermittently and at an increasing frequency as the battery approaches zero usable charge.

[0150] Further functions that may be implemented with or by the controller 400 are described in detail in other sections of this disclosure.

[0151] For example, and as discussed in more detail herein including the detailed sections below, the controller of the POC may implement compressor control to regulate pressure in the system. Thus, the POC may be equipped with a pressure sensor such as in the accumulator downstream of the sieve beds. The controller 400 in the POC can control adjusting of the speed of the compressor using signals from the pressure sensor as well as a motor speed sensor such as in one or more modes. In this regard, the controller may implement dual control modes, designated herein a coarse pressure regulation mode and a fine pressure regulation mode. The coarse pressure regulation mode may be implemented for changing between the different flow rate settings of the POC and for initial starting/activation. The fine pressure regulation mode may then take over upon completion of each operation of the coarse pressure regulation mode.

[0152] In the coarse pressure regulation mode, the motor speed is set/controlled to ramp up or down depending the prior state of operations. During the ramping, the controller uses the samples of the signal from the pressure sensor to generate an estimated pressure upstream of the pressure sensor, in the sieve beds. In some implementations, the estimated pressure is used in a test to terminate the ramp, e.g. when the estimated pressure reaches a predetermined target pressure value, created at manufacturing time, that is associated with the selected flow rate setting of the POC.

[0153] Table 2 contains example target pressure values associated with each of six flow rate settings and flow rates listed in Table 1 according to one implementation of the present technology.

Table 2: Example target pressure values at each of the six flow rate settings in Table 1.

[0154] The pressure estimate may be calculated by performing a regression (e.g., linear) using samples of the signal from the pressure sensor whereby the controller determines regression parameters (e.g., slope and intercept parameters of a line) from the pressure sensor signal samples. The pressure estimate may be calculated with the regression parameters and a known system response delay.

[0155] In the fine pressure regulation mode, the motor is set/controlled to maintain the pressure of the system using the signal from pressure sensor. Upon completion of the coarse pressure regulation mode, the motor speed ramping is terminated, at which time the motor speed has reached a base motor speed, and any further changes to the base motor speed resulting from the coarse mode may be instead implemented with a plurality of controllers (e.g., two controllers) such as PID (proportional, integral, derivative) controllers. During the fine pressure regulation mode, the target pressure is compared with a qualified pressure estimate to generate a first error signal that is applied to the first controller (e.g. a PID controller) to produce a correction to a motor speed setting command for control of the motor speed using a second controller (e.g. a PID controller). The qualified pressure estimate for the first PID controller is computed using regression on samples of the pressure signal. In this regard, samples from the pressure signal may be applied to a best fit algorithm (e.g., linear regression) to determine regression parameters (e.g., slope and intercept of a line) of the data from the pressure signal during an adsorption cycle. If the slope is positive, these parameters (slope and intercept rather than pressure samples from the pressure sensor) may then be applied with the particular time of the given adsorption phase of the pressure swing adsorption cycle to determine a peak value of the regression line from the linear regression. If the slope is negative, the intercept parameter may be taken as the peak value. The peak values from the regression information may be then applied to a running average buffer that maintains an average of the most recent peak values (e.g., six or more). The average peak value may then serve as the qualified pressure estimate for the controller. Versions of such processes are discussed in more detail herein.

Control Panel

[0156] Control panel 600 serves as an interface between a user and controller 400 to allow the user to initiate predetermined operation modes of the oxygen concentrator 100 and to monitor the status of the system. Fig. 14 depicts an implementation of control panel 600. Charging input port 605, for charging the internal power supply 180, may be disposed in control panel 600.

[0157] In some implementations, control panel 600 may include buttons to activate various operation modes for the oxygen concentrator 100. For example, control panel may include power button 610, flow rate setting buttons 620 to 626, active mode button 630, sleep mode button 635, altitude button 640, and a battery check button 650. In some implementations, one or more of the buttons may have a respective LED that may illuminate when the respective button is pressed, and may power off when the respective button is pressed again. Power button 610 may power the system on or off. If the power button is activated to turn the system off, controller 400 may initiate a shutdown sequence to place the system in a shutdown state (e.g., a state in which both canisters are pressurized). Flow rate setting buttons 620, 622, 624, and 626 allow a flow rate of oxygen enriched air to be selected (e.g., 0.2 LPM by button 620, 0.4 LPM by button 622, 0.6 LPM by button 624, and 0.8 LPM by button 626). Altitude button 640 may be activated when a user is going to be in a location at a higher elevation than the oxygen concentrator 100 is regularly used by the user.

[0158] Battery check button 650 initiates a battery check routine in the oxygen concentrator 100 which results in a relative battery power remaining LED 655 being illuminated on control panel 600.

[0159] A user may have a low breathing rate or depth if relatively inactive (e.g., asleep, sitting, etc.) as estimated by comparing the detected breathing rate or depth to a threshold. The user may have a high breathing rate or depth if relatively active (e.g., walking, exercising, etc.). An active/sleep mode may be estimated automatically and/or the user may manually indicate active mode or sleep mode by pressing button 630 for active mode or button 635 for sleep mode.

Methods of operating the POC

[0160] The methods of operating and monitoring the POC 100 described below may be executed by the one or more processors, such as the one or more processors 410 of the controller 400, configured by program instructions, such as including, as previously described, the one or more functions and/or associated data corresponding thereto, stored in a memory such as the memory 420 of the POC 100. Alternatively, some or all of the steps of the described methods may be similarly executed by one or more processors of an external computing device to which the controller is connected via the transceiver 430. In this latter implementation, the processors 410 may be configured by program instructions stored in the memory 420 of the POC 100 to transmit to the external computing device the measurements and parameters necessary for the performance of those steps that are to be carried out at the external computing device.

[0161] The main use of an oxygen concentrator 100 is to provide supplemental oxygen to a user. Generally, the continuous flow rate of supplemental oxygen to be provided is prescribed by a physician. Typical prescribed continuous flow rates of supplemental oxygen may range from about 1 LPM to up to about 10 LPM. The most commonly prescribed continuous flow rates are 1 LPM, 2 LPM, 3 LPM, and 4 LPM. Such example flow rate settings may be selected on a user interface of the oxygen concentrator 100, which then will control operations to achieve production of the oxygen enriched air according to the selected flow rate setting. [0162] In order to minimize the amount of oxygen enriched air that is needed to be produced to emulate the prescribed continuous flow rate, controller 400 may be programmed to synchronise release of the oxygen enriched air with the user's inhalations, according to a therapy mode known as pulsed oxygen delivery (POD) or demand oxygen delivery. Releasing a bolus of oxygen enriched air to the user as the user inhales may prevent unnecessary oxygen generation (further reducing power requirements) by not releasing oxygen, for example, when the user is exhaling. Reducing the amount of oxygen required may effectively reduce the amount of air compression needed by oxygen concentrator 100 and consequently may reduce the power demand from the compressors. For concentrators that operate in POD mode, the flow rate settings on the user interface may correspond to actual flow rates (bolus volume multiplied by breathing rate) of delivered oxygen, e.g. 0.2 LPM, 0.4 LPM, 0.6 LPM, 0.8 LPM, 1.1 LPM.

[0163] Oxygen enriched air produced by oxygen concentrator 100 is stored in an oxygen accumulator 106 and, in POD mode, released to the user as the user inhales. The amount of oxygen enriched air provided by the oxygen concentrator 100 is controlled, in part, by supply valve 160. In an implementation, supply valve 160 is opened for a sufficient amount of time to provide the appropriate amount of oxygen enriched air, as estimated by controller 400, to the user. In order to minimize the amount of oxygen required to emulate the prescribed continuous flow rate of a user, the oxygen enriched air may be provided as a bolus soon after the onset of a user's inhalation is detected. For example, the bolus of oxygen enriched air may be provided in the first few milliseconds of a user's inhalation.

[0164] In an implementation, pressure sensor 194 may be used to determine the onset of inhalation by the user. For example, the user's inhalation may be detected by using pressure sensor 194. In use, conduit 192 for providing oxygen enriched air is coupled to a user's nose and/or mouth through the nasal airway delivery device 196 and/or mouthpiece 198. The pressure in conduit 192 is therefore representative of the user's airway pressure. At the onset of an inhalation, the user begins to draw air into their body through the nose and/or mouth. As the air is drawn in, a negative pressure is generated at the end of the conduit 192, due, in part, to the venturi action of the air being drawn across the end of the conduit. Controller 400 analyses the pressure signal from the pressure sensor 194 to detect a drop in pressure indicating the onset of inhalation. Upon detection of the onset of inhalation, supply valve 160 is opened to release a bolus of oxygen enriched air from the accumulator 106. A positive change or rise in the pressure indicates an exhalation by the user, upon which the release of oxygen enriched air is discontinued. In one implementation, when a positive pressure change is sensed, supply valve 160 is closed until the next onset of inhalation is detected. Alternatively, supply valve 160 may be closed after a predetermined interval known as the bolus duration. By measuring the intervals between adjacent onsets of inhalation, the user's breathing rate may be estimated. By measuring the intervals between onsets of inhalation and the subsequent onsets of exhalation, the user's inspiratory time may be estimated.

[0165] In other implementations, the pressure sensor 194 may be located in a sensing conduit that is in pneumatic communication with the user's airway, but separate from the delivery conduit 192. In such implementations the pressure signal from the pressure sensor 194 is therefore also representative of the user's airway pressure.

[0166] In some implementations, the sensitivity of the pressure sensor 194 may be affected by the physical distance of the pressure sensor 194 from the user, especially if the pressure sensor 194 is located in oxygen concentrator 100 and the pressure difference is detected through the conduit 192 coupling the oxygen concentrator 100 to the user. In some implementations, the pressure sensor 194 may be placed in the airway delivery device 196 used to provide the oxygen enriched air to the user. A signal from the pressure sensor 194 may be provided to controller 400 in the oxygen concentrator 100 electronically via a wire or through telemetry such as through Bluetooth™ or other wireless technology.

[0167] In some implementations, if the user's current activity level, such as that estimated using the detected user's breathing rate, exceeds a predetermined threshold, controller 400 may implement an alarm (e.g., visual and/or audio) to warn the user that the current breathing rate is exceeding the delivery capacity of the oxygen concentrator 100. For example, the threshold may be set at 40 breaths per minute (BPM).

Compression System Control

[0168] As previously described, an oxygen concentrator may employ a compression system to pressurize the sieve beds for the adsorption process. A typical control scheme of such a compression system and concentrator may simply involve providing a fixed amount of power to the compression system (e.g., a motor of a compressor) while the oxygen concentrator is operating in a continuous fashion. Such powering can be less energy efficient such as if the operations exceed the oxygen enriched air use/demands of the user. It may be desirable to provide greater control over the compression system such as to regulate pressure of such a system, such as to achieve a desired pressure in each sieve bed for the PSA process. Such regulation may improve, for example, power consumption of such oxygen concentrator such as to increase battery life during mobility. Thus, in some versions of the present technology a controller 400 of the oxygen concentrator 100 may be implemented to provide a more dynamic control over the operations of the compression system.

[0169] However, compressor variability can make pressure control difficult in such systems. As a compressor is typically controlled by speed (e.g., via RPM sensing with a speed sensor), compressors can vary significantly with respect to their characteristics such that predicting a relationship between speed and pressure/flow can be difficult. The compressor is not typically a calibrated component and as such it can be difficult to ensure a particular RPM- to-pressure relationship. Additionally, sieve bed effective volumetric capacity could be different depending on its state of degradation. Minor leaks within the system could additionally alter the RPM-to-pressure response of the POC. Moreover, other system characteristics can also add to the difficulty such as (a) variability in the nature of the pneumatic path of the system (e.g., component tolerances such as check valves and constraints of the pneumatic path such a flow resistors); (b) variations in ambient temperature which can, for example, change inlet air density, (c) system leak, which can vary between different units of the same model oxygen concentrator. Some systems attempt to achieve improved control through pump calibration by establishing a speed (RPM)-to-pressure/flow mapping where only speed is controlled. However, such systems may be vulnerable to drift since no real pressure sensor is provided for correction of the assumptions of the mapping. Accordingly, in some versions of the present technology as described in more detail herein, improved control over the compression system may be achieved by implementing pressure regulation with a measure of pressure from a pressure sensor. Such control may then also involve a target pressure for the regulation scheme in a control loop of the controller. The measure of pressure may be provided by a pressure sensor such as the pressure sensor 107 that may generate a measure of accumulated gas pressure in the accumulator 106 of the oxygen concentrator 100.

[0170] However, such pressure control can still present difficulties. For example, accumulator pressure may sometimes be in a holding state if it does not always follow the sieve bed pressure. This may be a limitation of the pneumatic architecture of the apparatus. Accumulator pressure can be lower than actual sieve bed pressure which is a more suitable system pressure for the PSA process. Accumulator pressure may also be somewhat dependent on the check valve(s) (e.g., umbrella valve) crack pressure which is typically located between the accumulator and the sieve bed(s). (See, e.g., Fig. 5.) Additionally, timing of sampling of the pressure in the accumulator can also present difficulties. For example, the pressure of the accumulator can be affected (perturbed) by operation of the supply valve (f-valve) opening time, which can result in drops in pressure of the accumulator. Moreover, such regulation should be able to change according to the different settings selectable by the user so that different flow rates may be achieved according to user selection (e.g., 0.2 LPM, 0.4 LPM, 0.6 LPM, and 0.8 LPM etc. as listed in Table 1).

[0171] In some versions of the present technology, pressure regulation may be achieved by providing a plurality of pressure regulation modes, where each mode utilizes a different pressure control methodology. In general, for each flow rate setting of the oxygen concentrator 100, a target system pressure, e.g. a target sieve bed pressure, may be defined, e.g. as listed in Table 2. This target system pressure may be a target value for the starting pressure upon entry to the adsorption phase, an average pressure of the adsorption phase, or a maximum pressure during the adsorption phase. The processes may implement a dynamically determined RPM- to-pressure relationship, which may be estimated during startup such as in an initial pressure regulation mode. One such example mode is described herein as a “coarse” or “dynamic” pressure regulation mode. Such a mode, when compared to other modes, may enable more significant changes to the motor speed, such as by employing controlled ramping of motor speed to adapt the system pressure of the oxygen concentrator 100 to a new flow rate setting. Subsequently, a different control mode may then be operated, such as after achievement of a particular state of the prior pressure regulation mode. One example of such a subsequent mode is described herein as a “fine” or “static” pressure regulation mode. Such a subsequent mode may, for example, implement a proportional-integral-derivative (PID) type of control loop, which may provide a finer control adjustment of the RPM to maintain the system pressure at a predetermined target pressure value.

[0172] Thus, to achieve the different modes, the controller of the oxygen concentrator may implement a control mode switching process as illustrated as the process 1500 in Fig. 15. The process 1500 may initiate such control mode switching with activation (e.g., turning on power to the POC or changing of a flow rate setting) of the oxygen concentrator at step 1502. At step 1504, the controller 400 may then regulate operations (e.g., pressure control) of the oxygen concentrator in a first mode. Such a mode may be the control process illustrated in Fig. 16. Upon completion of the mode of step 1504 such as upon detection of a condition evaluated in the first mode, the controller 400 may then regulate operations (e.g., pressure control) of the oxygen concentrator in a second mode at step 1506. Upon termination of the second mode of step 1506 such as upon detection of a condition, the controller 400 may then return to step 1504 to regulate operations (e.g., pressure control) of the oxygen concentrator in the first mode. In some versions, each mode may be implemented by a different state machine, such as the state machines illustrated in FIGS. 18 and 24. Such modes may implement pressure regulation using a measure of pressure such as from an accumulator pressure sensor 107.

Coarse Pressure Regulation Mode

[0173] As illustrated in Figs. 16 to 19, the controller 400 may implement a pressure regulation control mode that may be initially applied or may be additionally applied upon selection of a different flow rate setting of the oxygen concentrator or at other times as desired. In general, such a mode may establish or determine an estimate of the dynamic relationship between changes in motor speed (e.g., RPM) and changes in system pressure such as when PSA is started, the compressor is started, a new flow rate setting is selected, etc. In some versions, the pneumatic system of the oxygen concentrator may be approximated or modeled to be similar to a resistor/capacitor (RC) circuit (e.g., low-pass filter) as discussed in more detail herein. As previously mentioned, the controller may then transition to a different pressure regulation mode (e.g., a fine pressure regulation mode) after an estimate (e.g., a prediction) of system pressure (e.g., a sieve bed pressure estimate) based on a pressure measurement in the accumulator reaches a target pressure (e.g., a desired pressure for the sieve bed such as to achieve a flow rate setting of the oxygen concentrator). Thus, in some versions, a pressure regulation scheme of the first mode may be implemented to enable the system pressure to achieve or approach a target pressure associated with a newly selected flow rate setting of the oxygen concentrator. Moreover, a different pressure regulation scheme of the second mode may be implemented to maintain the system pressure at the target pressure associated with the newly selected flow rate setting for continued operations at that setting.

[0174] For example, as illustrated in Fig. 16, a method 1600 of the first pressure regulation control mode may involve ramping the speed of the motor (e.g., a linear increase in RPM) of the compressor at a known rate during a ramping interval in step 1602 such as with the controller 400. Parameters of the ramping may include the rate of change of the motor speed used during the ramping interval and a speed value of the ramping interval such as an initial speed. At 1604, the controller may determine parameters (e.g., coefficients such as slope and/or intercept) of a model (e.g., a linear model) of accumulator pressure using a plurality of representative accumulator pressure values from a signal from an accumulator pressure sensor during the ramping. The parameters may be determined by regression (e.g., linear regression). Such representative accumulator pressure values may be representative of particular intervals, such as the adsorption phases of the PSA cycle, which may be determined according to the schedule/timing of the actuation of the valves of the oxygen concentrator. Such representative accumulator pressure values may optionally be maximum pressure values during the intervals. For example, during the ramping interval, a set of maximum pressure values may be determined from a plurality of measured pressure values over a plurality of respective adsorption phases of the PSA cycle, where each maximum pressure value is a maximum over one adsorption phase. At step 1606, the controller may then generate a system pressure-time profile as a function of the determined parameters of the model (e.g. the linear model), and a predetermined delay value. The predetermined delay may be a time value (t) that characterizes the delay of the pneumatic system components (e.g., the damped response of the measured pressure of the accumulator relative to the pressure of the sieve bed). Such a delay value (t) may be determined from a pre-calibration process. In some implementations, a default value of 4 seconds may be used for the delay value t.

[0175] In this regard, the pneumatic system including PSA components may be approximated/modeled to be similar to an RC (low-pass) filter. As such, the following relationship may be derived modelling a step response between the response pressure P(t) and the control pressure P_in

where t is time and t is the time constant of the RC (low-pass) filter model.

[0176] The damped response may be derived by integrating the step response:

[0177] where the delay t between the control and response pressures is equal to the time constant of the low-pass filter model. The damped response may be considered with respect to Fig. 17 which presents a graphic representation of the damped control relationship between the control pressure (e.g. actual sieve bed pressure, where no measurement is taken) (trace 1700) and the response pressure (i.e. measured accumulator pressure) (trace 1720). (Trace 1705 represents motor speed.) With such a pneumatic system, step control and damped control may be considered in terms of speed control (e.g., RPM) rather than in the direct form of pressure. Assuming a linear response from RPM to control pressure, a linear ramped control of the RPM can provide approximate equivalent damped control as in Fig. 17. Unfortunately, the approximate linear mapping between RPM and control pressure is not always the same between compressors across different units and also for the same compressor at various conditions (e.g., temperature, sieve bed state). Thus, while a target pressure (e.g. for the sieve bed) may be specified for each flow rate setting of the oxygen concentrator, the equivalent RPM for achievement of that pressure is not known. With instantaneous RPM adjustment, response pressure would be harder to control and may result to pressure overshoots that are not desirable.

[0178] Thus, a damped control scheme (e.g. via ramped RPM as previously described) may allow prediction of the system pressure-time profile for a given RPM ramp. At a given constant RPM ramp rate and after some multiple of the predetermined delay (e.g., 4 × t), the response pressure-time profile is within 2% of a delayed replica of the (invisible or unknown - i.e., not measured) control pressure-time profile. The slope of the (invisible or unknown - i.e., not measured) control pressure-time profile will be very close to the slope of the response pressure-time profile (which may be measured). At any time during the ramping interval, the (invisible or unknown - i.e., not measured) control pressure may be estimated from the current (measured) response pressure and the slope of the response pressure-time profile multiplied by the delay t. With the aim of making the control pressure (i.e., sieve bed pressure) achieve the target pressure, the control system can terminate the speed ramp (e.g., transition to a sustained RPM or some other pressure regulation mode) when the estimated control pressure achieves the target pressure.

[0179] Thus, the system pressure-time profile, which for example may be a sieve bed pressure-time profile, may then be applied by the controller to switch between modes as previously described, such as by comparing the current system pressure estimate to the target pressure value (step 1608). Such a comparison may then serve as logic to terminate the ramping operation of the coarse pressure regulation mode such that the speed of the motor may then be controlled for system pressure regulation according to a different control methodology of the subsequent pressure regulation mode.

[0180] In general, the parameters derived from the regression process during a previous ramp may be re-utilized when the coarse mode is re-activated, such as when the controller ramps the motor speed (up or down) between different flow rate settings of the POC (e.g., when a different flow rate setting is selected via the buttons 620 on the user interface for operation of the POC). In this regard, the controller, in the coarse mode, may change the motor speed, such as in a monotonic fashion or with a monotonic control function that gradually changes the motor control speed set point (RPM set point), to ramp (by an increase or, alternatively a decrease) the motor speed until the system pressure estimate (which may be computed using the previously derived regression parameters) reaches the predetermined target pressure that is associated with the newly selected flow rate setting. Additionally, or alternatively, the speed control may be implemented to achieve the target pressure as discussed in more detail herein by computing a target speed from the target pressure and the previously derived regression parameters and issuing a command to the motor to achieve the target speed.

[0181] Example operations of such a coarse mode for regulation of system pressure may be further considered in relation to the following points:

[0182] (1) The compressor motor speed (e.g., RPM) may be controlled (e.g., by ramping the speed of the motor over a period of time) to increase (or decrease) at a known speed ramp rate (SRR), i.e. with a fixed or pre-determined rate of change, such as during a ramping interval from its initial speed (RPMstart) to a current speed RPM_current, which it will reach at time t according to the following speed-time profile:

RPM_current = RPM_start + SRR * t (1) where t is the elapsed time since the start of the ramping interval. Such a linear function may be understood to be an example of a monotonic control function or of a monotonic motor speed control function, and the rate of change of such a control function may encompass a period of time having multiple adsorption cycles (e.g., two or more, three or more, four or more, etc.).

[0183] (2) Accumulator (tank) pressure-time profile P_tank(t) may be modeled from measured pressure values during the ramping interval (e.g. an initial ramp, or when subsequently ramping from setting to setting) as follows: P_tank(t) = mt + b

[0184] where t is the elapsed time since the start of the ramp, and parameters m (slope) and parameter b (intercept) may be estimated by linear regression such as by using a number of representative accumulator pressure values P_rep(i), i = 0 to N (where N may be 4 or other plurality of values as desired). In one implementation, the representative pressure values P_rep(i) may be peak or maximum pressure values. The representative pressure values may be obtained from pressure samples measured by the accumulator pressure sensor during each adsorption phase. For example, as illustrated in Fig. 17, each representative pressure value P_rep(i) is a maximum pressure value P_max(i), e.g. 1710-i, that may be determined from the accumulator pressure values of trace 1720 during a corresponding adsorption phase 1730-i during the ramping interval. Such maximum values may be taken, for example from successive adsorption phases. Each maximum pressure value P_max(i) may itself be derived by regression on the actual accumulator pressure values over the corresponding adsorption phase 1730-i. Optionally, an initial adsorption phase 1740 of the ramping interval may be disregarded such that pressure measurements 1760 from the initial adsorption phase are disregarded or ignored. The line 1750 represents the regression line computed from the representative pressure values P_rep(i)·

[0185] In some versions, the regression process may be conditioned on a number of available measurements and/or an amount of a target pressure. For example, if the target pressure achieved by the ramp is less than a particular threshold (e.g., 100 kPa or other suitable amount as desired by the system configuration), the regression may be aborted or the determined parameters ignored. Similarly, if the number of representative pressure values used for the regression is below a threshold (e.g., three or other suitable number), the regression may be aborted or the determined parameters ignored.

[0186] (3) Sieve bed pressure-time profile P_bed(t) may be modeled during ramping using the parameters of the regression process as follows: P_bed(t) = P_tank(t + t) = mt + m t + b (2) where t is the predetermined delay value known from pre-calibration as previously described. Such a pressure-time profile model may then be used in a test to terminate the ramp, such as when P_bed(t) reaches the target pressure Aarget.

[0187] (4) At some times, a target motor speed as a function of the target pressure such as for the ramp speed control may be determined based on the aforementioned models (e.g., the determined parameters from the regression, the predetermined delay value, and ramp parameters) as follows:

[0188] At t = t₀, the sieve bed pressure P_bed(t) will reach the target pressure Aarget for the new flow rate setting (a predetermined value that is associated with the flow rate setting as previously described with reference to Table 2, which may be accessed from a memory of the POC), where to is computable from Equation (2) as follows: to = (P_target - m t - b) / m (3) where:

• m is the slope as determined from the regression process previously described;

• b is the intercept as determined from the regression process previously described;

• t is the predetermined delay value known from pre-calibration as previously described.

[0189] A target speed RPM_target may be determined for the motor controller using the time to taken for P_bed(t) to reach the target pressure Aarget by combining Equation (1) with Equation (3) to obtain the following speed function:

RPM_target = RPM_start + (SRR/m) * (P_target - m t - b) (4) [0190] The compressor may be controlled to ramp to speed RPM_target during the ramping interval, such that the ramp is terminated when the current speed reaches RPM_target.

[0191] (5) At any time, the pressure of the sieve bed may be estimated as a function of the determined parameters from the regression, the current motor speed RPM_current, parameters of the ramping (RPM_start and SRR), and the predetermined delay value (t) as follows:

P_bed( RPM_current) = m * (l + (RPM_current - RPM_start)/SRR) + b (5)

[0192] Such a pressure estimate may then be used in a test to terminate the ramp, such as when P_bed reaches the target pressure P_target.

[0193] In general, the parameters derived from the regression process during the initial ramp may be applied to compute the sieve bed pressure estimate in the initial ramp for ensuring that the target pressure is achieved by comparing the pressure estimate to the target pressure value, or the current speed to the target speed value. However, as previously mentioned, such parameters derived in the initial ramp may be saved and re-utilized such as when the coarse mode is activated again when the controller ramps the motor (e.g., speed increase or speed decrease) between different flow rate settings of the POC (i.e., when a new flow rate setting is selected for operation of the POC). In this regard, the controller may compute a new target speed RPM_target(new) using the regression parameters and the current and new target pressure.

[0194] In one such example of re-utilization, the slope parameter m may be divided by the ramp rate SRR of the initial ramping interval before saving as a normalised slope parameter M. In a subsequent ramp from a current flow rate setting to a new flow rate setting, the normalised slope parameter M (in units of pressure per RPM) may be used to compute a new target speed RPM_target(new) from the new target pressure P_target(new) using the following formula: RPM_target(new) = RPM_target + (P target_(new) — P_target) / M (6) which is independent of the rate at which the motor speed is ramped during the subsequent ramp. The normalised slope parameter M represents the dynamic relationship between changes in system pressure and changes in motor speed (e.g., RPM).

[0195] Optionally, the regression parameters from the initial ramp may be used in other modes (e.g., fine pressure control mode).

[0196] New regression parameters may be saved each time an initial ramp (from an off state to a particular flow rate setting) is utilized, to adapt the coarse pressure regulation mode to changes over time in the PSA system. [0197] In some implementations, the target speed RPM_target corresponding to the target pressure P_target may be saved to memory and re-utilized at subsequent iterations of the coarse pressure regulation mode to obtain the new target speed RPM_target(new) from the new target pressure P_target(new), rather than using Equation (6) to compute the new target speed RPM_target(new). A method of expiration of the validity of the saved speed values for each target pressure may be by elapsed time since last usage (e.g., of the order of days/weeks) as well as hard power cycles (e.g. where boards, compressor, sieve beds may have been changed). Under expired conditions of the saved target speed values, the controller 400 shall revert to re- determining/re-leaming of compressor/system behaviors via coarse pressure regulation.

[0198] Such a control methodology may be implemented, such as by a state machine, for operation of the oxygen concentrator to achieve pressure regulation. An example methodology of a state machine of a controller 400 implementing an example of the coarse pressure regulation mode using the controlled ramping and a sieve bed pressure estimate may be considered in relation to state machine diagram of Fig. 18. As illustrated in the example, the state machine 1800 may have any of an idle state 1832, a ramp up state 1834, a ramp down state 1836, a sustain state 1838, a completion state 1840. Optionally, it may also have a fault state (not shown) and a stopping state 1844.

[0199] The idle state 1832 may be entered upon initial activation of the POC or if the coarse mode is inactive. Upon operational activation, such as by selection of a particular flow rate setting for the POC, the POC enters the ramp up state 1834 from the idle state 1832. In the ramp up state 1834, the controller ramps up the compressor motor speed (e.g., a linear increase in RPM using a known ramp rate (SRR) from a start speed (RPM_start) in accordance of Equation (1)) while performing the regression with the model previously described so as to compute regression parameters as previously described. The controller 400, in order to control ramping of the motor speed, may set a series of intermediate target speed values with appropriate timings and control the motor with the motor speed sensor to achieve the series of intermediate target speed values at the respective timings. In the absence of previously determined regression parameters, during the ramping the intermediate target speed values may be derived simply from the start speed and the known ramp rate (SRR) to achieve a linear ramp. However, if regression parameters from a previous ramping interval are available, the controller may determine the target speed of the ramping interval using the regression parameters such as by applying Equation (6) to determine the target speed of the motor such that the target speed is set to RPM_target during the ramping interval. Once the regression parameters have been computed, the controller may determine the target speed of the ramping interval using the computed regression parameters such as by applying Equation (4). The regression parameters may be updated during the ramping interval as more representative pressure samples become available, so each time the regression parameters are updated, the target speed is also updated by re-applying Equation (4).

[0200] During the ramping of the ramp up state 1834, accumulator pressure is measured/monitored and estimated sieve bed pressure is repeatedly calculated using the regression parameters as previously described. In this regard, during the RPM controlled ramping of the ramp up state 1834, the sieve bed pressure estimate may be repeatedly computed with the regression parameters when they are available (e.g., by applying Equation (2)). Otherwise, the sieve bed pressure estimate may be computed simply from default values of the regression parameters if the computed regression parameters are not yet available, such as if a certain number of representative accumulator pressure values are not yet measured. In one example, default values for the regression parameters are 3.0 units of pressure per second for the slope m and 0 for the intercept b.

[0201] The ramping up may continue until the computed pressure estimate satisfies the target pressure that is associated with the flow rate setting. For example, when the pressure estimate exceeds or is equal to the target pressure, the controller may interrupt the ramping by transitioning into the sustain state 1838. In some implementations, if the pressure estimate equals or exceeds the target pressure and the speed of the compressor (measured) is less than a minimum value, the controller may transition into the fault state from the ramp up state 1834. In some implementations, if the speed of the compressor (measured) is greater than a maximum value, the controller may transition into the fault state from the ramp up state 1834. In an alternative implementation, the controller may refrain from transitioning to the fault state under either condition, but may instead limit the compressor motor speed to the maximum value or the minimum value, and transition to the completion state 1840.

[0202] Optionally, if in the ramp up state 1834 the target pressure changes to a new target pressure (such as if user selects a new flow rate setting) and the new target pressure is less than the pressure estimate, then the controller transitions to the ramp down state 1836. If, in the ramp up state 1834, the POC is deactivated (e.g., turned off), the controller transitions to the stopping state 1844.

[0203] When in the sustain state 1838, ramping is terminated such that the last speed of the compressor motor is maintained (i.e., speed is effectively neither increased nor decreased). A timer may be initiated upon entry in the sustain state 1838 to permit pressure to settle in the tystem. For example, after a certain amount of time (e.g., some multiple of the predetermined delay t), the controller may transition into a completion state 1840. Alternatively, when in the sustain state 1838, if the POC is deactivated (e.g., turned off), the controller transitions to the stopping state 1844.

[0204] When in the completion state 1840, the controller 400 may activate a different pressure control mode (e.g., a fine pressure regulation mode as described in more detail herein), which corresponds with a deactivation of the coarse pressure regulation mode. In some implementations, the measured pressure at the moment of transition from the coarse pressure regulation mode to the fine pressure regulation mode may be compared with the target pressure and the difference used to adjust the value of the delay t. This adjustment of the delay value t could be particularly useful when system “capacitance” changes over time as a result of sieve bed degradation and/or system leak increase.

[0205] Optionally, from the completion state 1840, the now activated fine pressure regulation mode may be interrupted/deactivated, such as if a change to the flow rate setting of the POC is selected by user. Thus, from the completion state 1840, the controller may transition back to the coarse pressure regulation mode by transitioning into either the ramp up state 1834 or the ramp down state 1836 depending on whether the change to the flow rate setting represents an increase or a decrease respectively from the prior flow rate setting. Alternatively, in the completion state 1840, if the POC is deactivated (e.g., turned off), the controller transitions to the stopping state 1844.

[0206] When in the ramp down state 1836, the controller 400 may employ the previously determined regression parameters (e.g., from an initial ramping interval) and use them in a ramp down process of the compressor. In the ramp down process, the controller may reduce the speed (RPM) of the compressor using the known ramp rate (SRR) such as by computing a target motor speed according to Equation (6), since previously computed regression parameters are available. The ramp down process may continue by assessment of a target pressure with respect to the estimated sieve bed pressure that is calculated using the previously determined regression parameters (e.g., applying Equation (2)). For example, if during the ramp down process, the pressure estimate is less than or equal to the target pressure (i.e., from the selected flow rate setting), the controller may transition to the sustain state 1838, where the ramping down of the compressor is terminated. Alternatively, if in the ramp down state 1836, the pressure estimate is less than or equal to the target pressure and the compressor motor speed (e.g., measured RPM) is greater than some maximum speed (e.g., a maximum RPM value), the controller may transition to the fault state. Similarly, if in the ramp down state 1836, the compressor motor speed (e.g., measured RPM) is less than some minimum speed (e.g., a minimum RPM value), the controller may transition to the fault state. In an alternative implementation, the controller may refrain from transitioning to the fault state under either condition, but may instead limit the compressor motor speed to the maximum speed or the minimum speed, and transition to the completion state 1840.

[0207] Optionally, if in the ramp down state 1836 the target pressure changes to a new target pressure (such as if user selects a new flow rate setting) and the new target pressure is greater than the pressure estimate, then the controller transitions to the ramp up state 1834. If in the ramp down state 1836 the POC is deactivated (e.g., turned off), the controller transitions to the stopping state 1844.

[0208] In the fault state, the controller 400 may record and/or display the conditions associated with the failure to achieve the target pressure. Moreover, from the fault state, the controller may then transition to stopping state 1844. Thus, the compressor may be deactivated as a result of entering the fault state.

[0209] As illustrated in the example pressure-time graph 1900 of Fig. 19, the coarse pressure regulation mode (during the interval 1950) of the controller can ramp the motor speed of the compressor, and using accumulator pressure values from a pressure sensor of the accumulator, regulate an estimated system pressure to achieve a target pressure associated with a selected flow rate setting of the POC, and then transition the control into a different control mode (e.g. a fine pressure regulation mode). The trace 1910 in Fig. 19 represents the target pressure, which is constant throughout both control modes. The trace 1920 in Fig. 19 represents the estimated system pressure during an initial ramp, which as the motor speed is ramped during the coarse pressure regulation mode generally increases according to successive straight line segments with slightly different slope and intercept parameters, as the regression parameters are refined during the initial ramp. The trace 1930 represents the measured accumulator pressure, which during the adsorption phases generally follows the linear rise of the estimated system pressure, apart from dips due to bolus releases every few seconds. When the estimated system pressure (trace 1920) reaches the target pressure (trace 1910), after an interval corresponding to the sustain state 1838, the controller transitions to the fine pressure regulation mode for the interval 1960 at the instant 1940.

Fine Pressure Regulation Mode

[0210] As previously described, the controller of the oxygen concentrator may implement another different pressure regulation scheme in a subsequent or second mode that is dynamically activated for operation, such as when the previously described coarse pressure regulation mode is deactivated. Optionally, such a mode may be implemented in a POC controller without the coarse regulation mode and vice versa. Control of such an additional regulation mode may be considered in relation to Figs. 20 to 24. For example, Fig. 20 contains a flow chart illustrating a process methodology 2000 of such a control mode, which may be implemented in the second mode. At step 2002 pressure regulation by a controller of an oxygen concentrator apparatus may involve generating a signal representing a measure of the pressure of the accumulated oxygen enriched air such as with a pressure sensor (e.g., the accumulator pressure sensor). At step 2004, the controller may then generate a qualified pressure sample by a regression process using the measured pressure signal. Such a qualified pressure sample may be computed from one or more parameters of the regression process such as where the regression process determines parameters (e.g., linear parameters) by a best fit process using a regression algorithm (e.g., linear regression). For example, the qualified pressure sample may be determined or computed using one or more linear parameters (e.g., slope and intercept) from a linear regression process. At step 2006, the controller may then control the compressor (e.g., setting the motor speed) with the qualified pressure sample, such as to achieve a desired target pressure, in a control loop such as a feedback control loop.

[0211] In some versions, the qualified pressure may comprise an average. However, rather than an average of measured pressure values, the qualified pressure sample may be an average of a plurality of peak values computed from different adsorption phases where each peak value of an adsorption phase is produced using the regression parameters corresponding to that phase. For example, as previously mentioned and illustrated in Fig. 21, the peak of a given adsorption phase may be determined from the regression parameters. In one example, during a time period of an adsorption phase, regression (e.g., linear regression) may be performed using pressure samples from the accumulator pressure sensor in the adsorption phase time period. Thus, at step 2108 pressure may be repeatedly sampled during an adsorption phase. At step 2110, regression parameters may be computed from the pressure samples. In the case of linear regression, a slope parameter and an intercept parameter may be determined. One or more of these parameters may then be used to determine a peak pressure value of the adsorption phase at step 2112. For example, if the slope (m) is negative or zero, the peak value of the adsorption phase may be taken as the intercept ( b ) parameter of the regression (e.g., Peak_adsorption = b). In this regard, such a peak value may be determined with an initial time (/i_nitial) of the adsorption phase being zero, the slope and the intercept with a linear function of the parameters (e.g., Peak_adsorption = m(t_initial)+b). Otherwise, if the slope (m) is positive, the slope and intercept parameters as well as a time (t_end) associated with the adsorption phase (e.g., at or near the end of the period) may be used to compute the peak value with the linear function of the parameters (e.g., Peak_adsorption = m(t_end)+b). In this way, the computed peak value may correspond with an end of the adsorption phase. With a set of such peak values, such as a plurality of peak values stored in a buffer, an average may be computed at step 2114. This average (a qualified estimate) may then serve as an input to a pressure feedback control loop for setting/adjusting the speed of the motor as discussed in more detail herein to maintain system pressure at a target pressure value.

[0212] Although in the aforementioned implementations estimated peak values derived from regression are used in motor control, in an alternative version to using regression, the control loop input may be based on determining an average of actual pressure samples (measured pressure values) from the pressure sensor. Such an average of pressure samples may be more susceptible to variation, such as random noise or in relation to transient system changes downstream of the accumulator (e.g., triggering of the bolus), when compared to an average of estimated peak values of the regression process, such that average values of pressure samples are less likely to correspond with actual sieve bed pressures upstream of the accumulator.

[0213] A control process 2200 in an example of the fine pressure control mode may be further considered in relation to the schematic representation of Fig. 22. The process 2200 may be implemented with any of hardware and/or software. As illustrated, in the mode, the controller may receive a pressure signal 2202, such as from the accumulator pressure sensor 107, that provides a measure of the accumulator pressure over time, including during the phases or intervals of the PSA cycles as previous described. The controller may then implement a regression process 2204 by processing of the pressure signal 2202. The regression process 2204 produces a pressure estimate 2206 that is a qualified version of the accumulator pressure such as according to the method described in relation to Fig. 21 and/or otherwise previously discussed. The regression process 2204 produces the qualified pressure sample (pressure estimate 2206) which may represent the average of a series of peak values from a series of adsorption phases. The average may be a running average that is repeatedly updated by averaging a first-in-first-out buffer of peak values, with each new average being computed on entry of each new peak value from the regression process 2204.

[0214] As illustrated in Fig. 22, the qualified pressure sample (pressure estimate 2206) (e.g., the average regression peak value) may be compared with a target pressure value 2210, such as at a comparator or summer 2208, that may be implemented to determine a difference such as by subtraction. The target pressure value 2210 may be a predetermined target pressure value, which may correspond with a desired sieve bed pressure, and is associated with a particular flow rate setting of the POC as previously described. The output signal from the summer 2208 may be an error signal 2209 that is applied to a first controller such as any of a P, PI, or PID control process 2211 (e.g., where P is proportional, I is integral and D is derivative). The integrated error, proportional error and/or derivative error signals may be scaled and applied to a summer 2212 to adjust a speed setting command 2216. The speed setting command 2216 may be initialised to a motor speed at the end of the coarse pressure regulation mode that preceded the initiation of the control process 2200. In some implementations, the speed setting command 2216 may be initialised to the target speed RPM_target corresponding to the target pressure P_target. The speed setting command 2216 may then be applied to a second controller such as any of a P, PI, or PID control process or driver 2217 that is applied to adjust the operating current or voltage of the motor of the compressor to control the speed of the motor according to the speed setting command 2216. The second controller using driver 2217 may make use of a motor speed signal 2214 from a speed sensor 201 that is associated with the compressor motor as described above. With these feedback control processes, the motor of the compressor may be operated with speed regulation to maintain the desired target pressure by monitoring changes in the pressure condition of the accumulator 106 and responding with appropriate output changes in the pressurized air 2220 to the gas separation system 2230.

[0215] Such operations may be considered in relation to the signal graph 2300 of Fig. 23. The graph 2300 contains a pressure signal 2302 from accumulator pressure sensor, which represents one example of the pressure signal 2202 in Fig. 22. The graph 2300 also contains dots 2306 representing samples of the pressure signal 2302 during successive adsorption phases. The graph 2300 also contains, plotted on a common time scale, a signal 2304 representing the adsorption regression peak values which are averaged to generate the qualified pressure estimate 2206 generated by the regression process 2204 previously described. The graph 2300 illustrates how for each adsorption phase, the samples (dots 2306) are employed to generate the qualified pressure estimate.

[0216] Such a control methodology may be implemented, such as by a state machine, for operation of the oxygen concentrator to achieve fine pressure regulation. An example methodology of a state machine of a controller 400 implementing an example of the fine pressure regulation mode using the control process of Fig. 22 may be considered in relation to state machine diagram of Fig. 24. As illustrated, the state machine 2400 of the fine pressure regulation mode may have any of an idle state 2440, an initialization state 2442, a regression/sampling state 2444, a fine control adjustment state 2446, and a fault state 2448.

[0217] The idle state 2440 may be set by the controller 400 when control of the motor for pressure regulation is not actively implemented by the fine pressure regulation mode. The controller may be in this state when the controller 400 is implementing pressure regulation according to another pressure regulation mode such as the coarse pressure regulation mode previously described. The controller 400 may be in this state when the controller has previously detected a fault such as in relation to the fault state 2448 and has been reset. The controller 400 may switch to the initialization state 2442 when the fine pressure regulation mode becomes active, such as if a fine pressure regulation flag is set to true or the fine pressure regulation mode is activated by a prior regulation mode (e.g., the coarse pressure regulation mode). With such a transition, the speed setting command of the motor may be initialized to the speed of the motor from the prior mode (e.g., a speed at the completion of the prior ramping interval as previously described). In the initialization state 2442, variables and buffers for the fine pressure regulation mode may be reset. For example, the peak value buffer previously described may be reset or otherwise initialized. If from the initialization state 2442, the fine pressure regulation flag is set to false or the fine pressure regulation mode is otherwise deactivated (such as by the detection of a change in a flow rate setting of the POC), the controller transitions the fine pressure regulation mode to the idle state 2440. If from the initialization state, the controller 400 enters an adsorption phase (such as in relation to the controller setting of the absorption phase by timing of the operation of control signals for the sieve bed related valves (e.g., valves 122, 124, 132, 134, 152, 154) as previously described), the controller 400 transitions to the regression/sampling state 2444.

[0218] In the regression/sampling state 2444, the controller implements sampling, during the adsorption phase, of the pressure values used by the regression process 2204 previously described. Thus, when the controller 400 determines that the adsorption phase has concluded, the controller implements a regression algorithm (e.g., using steps of a simple linear regression method) and determines a peak with the regression parameters as previously described. The controller 400 then stores the peak value into the peak buffer. Optionally such as process may repeat for each subsequent adsorption phase until a suitable number of peaks are within the buffer for determining an average of such peak values. When such a new peak value is added to the peak buffer, in the regression/sampling state 2224, the controller may determine the average of the peak buffer to generate a value for the qualified pressure sample (e.g., the average adsorption peak regression pressure). Upon completing the average determination, the controller then transitions to the fine control adjustment state 2446 from the regression/sampling state 2444. If from the regression / sampling state 2444, the fine pressure regulation flag is set to false or the fine pressure regulation mode is otherwise deactivated (such as by the detection of a change in a flow rate setting of the POC), the controller transitions the fine pressure regulation mode to the idle state 2440.

[0219] In the fine control adjustment state 2446, the controller 400 determines or otherwise computes signals for motor control as described in relation to the first and second controller of Fig. 22. Thus, the controller 400 may generate proportional, integral and/or derivative error adjustments from the comparison of the target pressure and the qualified pressure sample (e.g., the average adsorption peak regression pressure). These error signals may then be summed to determine an adjustment to the speed setting command. The controller 400 may then apply the speed setting command to the second controller for adjusting the speed of the motor of the compressor. Upon completion of the application of the speed setting command to the second controller, the controller 400 may then transition back to the regression/sampling state 2444 for the next adsorption cycle. When in the fine control adjustment state 2446, if the controller 400 detects, using the speed signal from the speed sensor 201, that the motor speed exceeds a maximum speed or falls below a minimum speed, the controller transitions to the fault state 2448. In an alternative implementation, the controller may refrain from transitioning to the fault state 2448 under either condition, but may instead limit the compressor motor speed to the maximum speed or the minimum speed and remain in the fine control adjustment state 2446.

[0220] When in the fine control adjustment state 2446, the controller may also transition to the idle state 2440 such as if the controller detects that the flow rate setting of the POC has been changed by a user.

[0221] In the fault state 2448, the controller 400 may log the error and/or otherwise set a fault state flag to true. The controller may optionally discontinue operation or adjustment of the compressor, such as by stopping the compressor or ceasing to change the compressor motor speed. The controller 400 may then transition to the idle state 2440 if the controller receives a reset signal.

[0222] A pressure signal 2502 and a speed signal 2602 of an oxygen concentrator implementing an example of such a dual pressure regulation scheme are depicted in the graphs 2500 and 2600 of Figs. 25 and 26 respectively. The graphs 2500 (Fig. 25) and 2600 (Fig. 26) illustrate how the pressure changes and how the speed of the compressor changes as the controller is switched between the various flow rate settings of the POC. In the graphs 2500 and 2600, the example POC is operated by the controller 400 through five flow rate settings starting with the highest and progressing to the lowest setting and then progressing again to the highest flow rate setting. The controller 400 of the POC applies the coarse pressure regulation mode for each transition between each of the flow rate settings as previously described in relation to the initial selection of each flow rate setting. The controller 400 of the POC then applies the fine pressure regulation mode when the target pressure associated with each selected flow rate setting is achieved. In the graph 2500 of Fig. 25, a target signal 2506 represents the target pressure as it changes for each flow rate setting. In the expanded section 2520, the signal 2502 shows the changes in the accumulator pressure. The signal 2508 shows the changes of the determined regression peaks as each is successively determined in each adsorption phase of the various flow rate settings. Finally, the average signal 2510 depicts the changes of the qualified pressure sample (e.g., the average adsorption peak regression pressure) as it computed during the operation of each flow rate setting.

GLOSSARY

[0223] For the purposes of the present technology disclosure, in certain forms of the present technology, one or more of the following definitions may apply. In other forms of the present technology, alternative definitions may apply.

[0224] Air: In certain forms of the present technology, air may be taken to mean atmospheric air, consisting of 78% nitrogen (N₂), 21% oxygen (O₂), and 1% water vapour, carbon dioxide (CO₂), argon (Ar), and other trace gases.

[0225] Oxygen enriched air: Air with a concentration of oxygen greater than that of atmospheric air (21%), for example at least about 50% oxygen, at least about 60% oxygen, at least about 70% oxygen, at least about 80% oxygen, at least about 90% oxygen, at least about 95% oxygen, at least about 98% oxygen, or at least about 99% oxygen. “Oxygen enriched air” is sometimes shortened to “oxygen” and may be so understood in light of its context.

[0226] Medical Oxygen: Medical oxygen is defined as oxygen enriched air with an oxygen concentration of 80% or greater.

[0227] Ambient: In certain forms of the present technology, the term ambient will be taken to mean (i) external of the treatment system or user, and (ii) immediately surrounding the treatment system or user.

[0228] Flow rate: The volume (or mass) of air delivered per unit time. Flow rate may refer to an instantaneous quantity. In some cases, a reference to flow rate will be a reference to a scalar quantity, namely a quantity having magnitude only. In other cases, a reference to flow rate will be a reference to a vector quantity, namely a quantity having both magnitude and direction. Flow rate may be given the symbol Q. ‘Flow rate’ is sometimes shortened to simply ‘flow’ or ‘airflow’.

[0229] Patient: A person, whether or not they are suffering from a respiratory disorder.

[0230] Pressure: Force per unit area. Pressure may be expressed in a range of units, including cmH₂O, g-f/cm2 and hectopascal. 1 cmH₂O is equal to 1 g-f/cm2 and is approximately 0.98 hectopascal (1 hectopascal = 100 Pa = 100 N/m² = 1 millibar ~ 0.001 atm). In this specification, unless otherwise stated, pressure is given in units of cmH₂O.

General remarks

[0231] The term “coupled” as used herein means either a direct connection or an indirect connection (e.g., one or more intervening connections) between one or more objects or components. The phrase “connected” means a direct connection between objects or components such that the objects or components are connected directly to each other. As used herein the phrase “obtaining” a device means that the device is either purchased or constructed.

[0232] In the present disclosure, certain U.S. patents, U.S. patent applications, and other materials (e.g., articles) have been incorporated by reference. The text of such U.S. patents, U.S. patent applications, and other materials is, however, only incorporated by reference to the extent that no conflict exists between such text and the other statements and drawings set forth herein. In the event of such conflict, then any such conflicting text in such incorporated by reference U.S. patents, U.S. patent applications, and other materials is specifically not incorporated by reference in this patent.

[0233] Further modifications and alternative implementations of various aspects of the present technology may be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the technology. It is to be understood that the forms of the technology shown and described herein are to be taken as implementations. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the technology may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the technology. Changes may be made in the elements described herein without departing from the spirit and scope of the technology as described in the appended claims. Label List oxygen concentrator 100 inlet 101 inlet 105 accumulator 106 accumulator pressure sensor 107 muffler 108 gas separation system 110 valves 122 valves 124 filter 129 outlet 130 valve 132 muffler 133 outlet valve 134 spring baffle 139 check valve 142 check valve 144 flow restrictor 151 valve 152 flow restrictor 153 valve 154 flow restrictor 155 supply valve 160 chamber 162 oxygen sensor 165 emitter 166 receiver 168 housing 170 fan 172 outlet 173 outlet port 174 flow restrictor 175 power supply 180 flow rate sensor 185 filter 187 connector 190 delivery conduit 192 pressure sensor 194 airway delivery device 196 mouthpiece 198 compression system 200 speed sensor 201 compressor 210 compressor outlet 212 motor 220 armature 230 air transfer device 240 compressor outlet conduit 250 canister system 300 canister 302 canister 304 inlet 306 housing 310 base 315 valve seat 322 opening 323 valve seat 324 outlet 325 gases 327 conduit 330 valve seats 332 apertures 337 conduit 342 conduit 344 conduit 346 opening 375 controller 400 processor 410 memory 420 transceiver 430 housing component 510 conduit 530 conduit 532 conduit 534 opening 542 opening 544 valve seat 552 control panel 600 input port 605 power button 610 flow rate setting buttons 620 buttons 620 flow rate setting buttons 622 button 624 button 626 button 630 button 635 altitude button 640 battery check button 650 relative battery power remaining LED 655 process 1500 step 1502 step 1504 step 1506 method 1600 step 1602 step 1606 step 1608 trace 1700 trace 1705 maximum pressure value 1710-i trace 1720 adsorption phase 1730-i initial adsorption phase 1740 line 1750 pressure measurements 1760 state machine 1800 idle state 1832 state 1834 state 1836 state 1838 completion state 1840 stopping state 1844 example pressure - time graph 1900 trace 1910 trace 1920 trace 1930 instant 1940 interval 1950 interval 1960 process methodology 2000 step 2002 step 2004 step 2006 step 2108 step 2110 step 2112 step 2114 control process 2200 pressure signal 2202 regression process 2204 pressure estimate 2206 summer 2208 error signal 2209 target pressure value 2210

PID control process 2211 summer 2212 motor speed signal 2214 speed setting command 2216 driver 2217 air 2220 regression / sampling state 2224 gas separation system 2230 graph 2300 pressure signal 2302 signal 2304 dots 2306 state machine 2400 idle state 2440 initialization state 2442 regression / sampling state 2444 fine control adjustment state 2446 fault state 2448 graph 2500 pressure signal 2502 target signal 2506 signal 2508 average signal 2510 section 2520 speed signal 2602

Claims

1. A method of operating an oxygen concentrator, the method comprising: with a sensor configured to sense at a location associated with accumulation of oxygen enriched air produced by the oxygen concentrator, generating a signal representing a measure of pressure of the accumulated oxygen enriched air; and with a controller configured to receive the measured pressure signal, controlling operation of a compressor to achieve or maintain a target system pressure associated with a flow rate setting of the oxygen concentrator based on the measured pressure signal, wherein the controlling with the controller comprises a first control mode of operation for regulating pressure to achieve the target system pressure and a second control mode of operation to maintain the target system pressure.

2. The method of claim 1 wherein the controller switches to the second control mode of operation when the controller detects a first condition in the first control mode of operation.

3. The method of claim 2 wherein the first condition comprises a comparison of (a) the target system pressure, and (b) a system pressure estimate that is based on the measured pressure signal.

4. The method of claim 3 wherein detection of the first condition comprises determining that the system pressure estimate equals or exceeds the target system pressure.

5. The method of any one of claims 3 to 4 further comprising, in the first control mode, generating the system pressure estimate, wherein generating the system pressure estimate comprises: determining parameters of a linear model of a plurality of accumulator pressure values from the measured pressure signal during a ramping of speed of a motor of the compressor; and generating an estimate of a pressure-time profile of the system pressure as a function of the determined parameters, and a predetermined delay value.

6. The method of claim 5 wherein the predetermined delay value is a time difference characteristic of a damped response of pneumatic components of the oxygen concentrator.

7. The method of any one of claims 5 to 6 wherein the determining parameters of a linear model comprises performing linear regression.

8. The method of any one of claims 5 to 7 wherein the accumulator pressure values comprise maximum pressure values, each corresponding to one of a plurality of adsorption phases.

9. The method of claim 8, wherein each maximum pressure value is obtained by regression on the accumulator pressure values from the measured pressure signal during a corresponding adsorption phase.

10. The method of any one of claims 5 to 9 wherein the function is given by: m x (t + t) + b where: m is a slope parameter of the linear model; b is an intercept parameter of the linear model; t is elapsed time since the start of the ramping, and t is the predetermined delay value.

11. The method of any one of claims 2 to 10 wherein the first condition comprises a comparison of (a) a target speed, and (b) a current measured speed of a motor of the compressor.

12. The method of claim 11, wherein the current measured speed is determined at least in part with a sensor associated with the motor of the compressor.

13. The method of any one of claims 11 to 12, wherein the target speed is determined with a speed function of an initial speed, a known speed ramp rate, a target system pressure value, determined parameters of a linear model, and a predetermined delay value.

14. The method of claim 13 wherein the speed function is defined by:

RPM_start + (SRR/m) * (P_target - m t - b) where m is a slope parameter of the linear model; b is an intercept parameter of the linear model;

RPM_start is the initial speed; and SRR is the known speed ramp rate; t is the predetermined delay value; and Ptarget is the target system pressure value.

15. The method of any one of claims 1 to 14 wherein the target system pressure value is a target value for any one of (a) a starting pressure for entry to an adsorption phase of the oxygen concentrator, (b) an average pressure of an adsorption phase of the oxygen concentrator, and (c) a maximum pressure for an adsorption phase of the oxygen concentrator.

16. The method of any one of claims 1 to 15 wherein the second control mode of operation comprises generating a qualified pressure sample from the measured pressure signal, and controlling a speed of a motor of the compressor with the qualified pressure sample in a control loop.

17. The method of claim 16 wherein the qualified pressure sample is generated with one or more parameters of a regression process.

18. The method of any one of claims 16 to 17 wherein the second control mode of operation comprises adjusting, in the control loop, a speed setting command to a motor driver, with an error signal generated based on a comparison of (a) the target system pressure and (b) the qualified pressure sample.

19. The method of claim 18 wherein the speed setting command is adjusted by summing one or more modified error signals that are derived from a difference between the target system pressure and the qualified pressure sample.

20. The method of claim 19 wherein the modified error signals comprise one or more of proportional, derivative and integral signals, wherein the method comprises generating each of the one or more of proportional, derivative and integral signals with the difference between the target system pressure and the qualified pressure sample.

21. The method of claim 17 wherein the regression process comprises computing linear parameters from a plurality of samples from the measured pressure signal.

22. The method of claim 21 wherein the linear parameters comprise a slope and an intercept.

23. The method of claim 22 wherein the qualified pressure sample is generated by determining one or more peak values with one or more of the linear parameters, such that each peak value is a maximum value over an adsorption phase.

24. The method of claim 23 wherein the qualified pressure sample is generated by determining a running average of the one or more peak values.

25. The method of any one of claims 23 to 24 wherein the peak value is the intercept if the slope is negative.

26. The method of any one of claims 23 to 25 wherein, if the slope is positive, the peak value is computed with the slope, the intercept and a time associated with an end of the adsorption phase.

27. An oxygen concentrator comprising: one or more sieve beds containing a gas separation adsorbent; a compression system, including a motor-operated compressor, configured to feed a pressurised feed gas into the one or more sieve beds; an accumulator configured to receive oxygen enriched air from the one or more sieve beds; a pressure sensor configured to generate a signal representing a measure of pressure of the oxygen enriched air in the accumulator; a speed sensor configured to generate a signal representing a measure of speed of the motor of the compressor; a memory; and a controller comprising one or more processors, the one or more processors configured by program instructions stored in the memory to execute the method of operating the oxygen concentrator according to the method of any one of claims 1 to 26.

28. An oxygen concentrator comprising: one or more sieve beds containing a gas separation adsorbent; a compressor configured to feed a pressurised feed gas into the one or more sieve beds; an accumulator configured to receive oxygen enriched air from the one or more sieve beds; a speed sensor configured to generate a signal representing a measure of speed of a motor of the compressor; a pressure sensor configured to generate a signal representing a measure of pressure of the oxygen enriched air in the accumulator; and a controller coupled with the compressor, the pressure sensor, and the speed sensor, the controller configured to: receive the measured pressure signal and the measured speed signal; and control operation of the compressor to achieve or maintain a target system pressure associated with a flow rate setting of the oxygen concentrator based on the measured pressure signal, wherein the controlling with the controller comprises a first control mode of operation for regulating pressure to achieve the target system pressure and a second control mode of operation to maintain the target system pressure.

29. The oxygen concentrator of claim 28 wherein the controller is configured to switch to the second control mode of operation when the controller detects a first condition in the first control mode of operation.

30. The oxygen concentrator of claim 29 wherein the first condition comprises a comparison of (a) the target system pressure, and (b) a system pressure estimate that is based on the measured pressure signal.

31. The oxygen concentrator of claim 30 wherein detection of the first condition comprises a determination that the system pressure estimate equals or exceeds the target system pressure.

32. The oxygen concentrator of any one of claims 30 to 31 wherein the controller is configured to, in the first control mode, generate the system pressure estimate, wherein to generate the system pressure estimate, the controller is configured to: determine parameters of a linear model of a plurality of accumulator pressure values from the measured pressure signal during a ramping of speed of a motor of the compressor; and generate an estimate of a pressure-time profile of the system pressure as a function of the determined parameters, and a predetermined delay value.

33. The oxygen concentrator of claim 32, wherein the predetermined delay value is time difference characteristic of a damped response of pneumatic components of the oxygen concentrator.

34. The oxygen concentrator of any one of claims 32 to 33 wherein the controller is configured to determine the parameters of the linear model by performing linear regression.

35. The oxygen concentrator of any one of claims 32 to 34 wherein the accumulator pressure values comprise maximum pressure values, each from one of a plurality of adsorption phases.

36. The oxygen concentrator of claim 35 wherein the controller is configured to obtain each maximum pressure value by regression on the accumulator pressure values from the measured pressure signal of an adsorption phase of the plurality of adsorption phases.

37. The oxygen concentrator of any one of claims 32 to 36 wherein the function is given by: m x (t + t) + b where: m is a slope parameter of the linear model; b is an intercept parameter of the linear model; t is elapsed time since the start of the ramping; and t is the predetermined delay value.

38. The oxygen concentrator of any one of claims 29 to 37 wherein the first condition comprises a comparison of (a) a target speed, and (b) a current measured speed of a motor of the compressor.

39. The oxygen concentrator of claim 38 wherein the controller is configured to determine the current measured speed with the speed sensor.

40. The oxygen concentrator of any one of claims 38 to 39 wherein the controller is configured to determine the target speed with a speed function of an initial speed, a known speed ramp rate, a target system pressure value, determined parameters of a linear model and a predetermined delay value.

41. The oxygen concentrator of claim 40 wherein the speed function is defined by:

RPM_start + (SRR /m) * (P_target - m t - b) where m is a slope parameter of the linear model; b is an intercept parameter of the linear model;

RPM_start is the initial speed;

SRR is the known speed ramp rate; t is the predetermined delay value; and P_target is the target system pressure value.

42. The oxygen concentrator of any one of claims 28 to 41 wherein the target system pressure value is any of (a) a starting pressure for entry to an adsorption phase of the oxygen concentrator, (b) an average pressure of an adsorption phase of the oxygen concentrator, and (c) a maximum pressure for an adsorption phase of the oxygen concentrator.

43. The oxygen concentrator of any one of claims 28 to 42 wherein the controller is configured to, in the second control mode of operation, (a) generate a qualified pressure sample from the measured pressure signal, and (b) control speed of the motor of the compressor with the qualified pressure sample in a control loop.

44. The oxygen concentrator of claim 43 wherein the controller is configured to generate the qualified pressure sample with one or more parameters of a regression process.

45. The oxygen concentrator of any one of claims 43 to 44 wherein the controller is configured to, in the control loop in the second control mode of operation, adjust an error signal to a motor driver, the error signal generated based on a comparison of (a) the target system pressure and (b) the qualified pressure sample.

46. The oxygen concentrator of claim 45 wherein the error signal is adjusted by summing one or more modified error signals that are derived from a difference between the target system pressure and the qualified pressure sample.

47. The oxygen concentrator of claim 46 wherein the modified error signals comprise one or more of proportional, derivative and integral signals, wherein the controller is configured to generate each of the one or more of proportional, derivative and integral signals with the difference between the target system pressure and the qualified pressure sample.

48. The oxygen concentrator of claim 44 wherein the controller is configured, in the regression process, to compute linear parameters from a plurality of samples from the measured pressure signal.

49. The oxygen concentrator of claim 48 wherein the linear parameters comprise a slope and an intercept.

50. The oxygen concentrator of claim 49 wherein the controller is configured to generate the qualified pressure sample by determining one or more peak values from one or more of the linear parameters, such that each peak value is a maximum over an adsorption phase.

51. The oxygen concentrator of claim 50 wherein the controller is configured to generate the qualified pressure sample by determining a running average of the one or more peak values.

52. The oxygen concentrator of any one of claims 50 to 51 wherein, if the slope is negative, the peak value is the intercept.

53. The oxygen concentrator of any one of claims 50 to 52 wherein, if the slope is positive, the peak value is computed with the slope, the intercept and a time associated with an end of the adsorption phase.

54. A method of operating an oxygen concentrator, the method comprising: with a sensor configured to sense at a location associated with accumulation of oxygen enriched air produced by the oxygen concentrator, generating a signal representing a measure of pressure of the accumulated oxygen enriched air; and with a controller configured to receive the measured pressure signal, controlling operation of a motor of a compressor by changing, with a monotonic control function, motor speed over a period of time to achieve a target system pressure associated with a flow rate setting of the oxygen concentrator based on the measured pressure signal, wherein the controlling with the controller comprises: during the changing in motor speed over the period of time, computing an estimate of the system pressure based on the measured pressure; comparing the estimate of the system pressure to the target system pressure; and interrupting the changing in motor speed based on a result of the comparing.

55. The method of claim 54 wherein the changing in motor speed comprises ramping of speed of the motor and the period of time comprises multiple adsorption cycles.

56. The method of claim 55 wherein the ramping of speed comprises an increase in speed, and wherein the flow rate setting is (a) a higher setting from a prior flow rate setting, or (b) an initial setting following power activation of the oxygen concentrator.

57. The method of claim 55 wherein the ramping of speed comprises a decrease in speed, and wherein the flow rate setting is a lower setting from a prior flow rate setting.

58. The method of any one of claims 54 to 57 further comprising determining a target speed for the motor speed based on an estimate of a pressure-time profile for the system pressure.

59. The method of any one of claims 54 to 58 wherein the estimate of the system pressure is an estimate of sieve bed pressure.

60. The method of any one of claims 54 to 59 wherein the computing the estimate of the system pressure comprises applying a modeling function to data samples of the measured pressure.

61. The method of claim 60 wherein the modeling function is further applied to determine a target speed for the motor speed.

62. The method of any one of claims 60 to 61 wherein the modeling function comprises a damped response modeling function.

63. The method of any one of claims 60 to 62 wherein the modeling function comprises a predetermined delay value.

64. The method of claim 63 wherein the predetermined delay value characterizes a damped response of the measured pressure relative to sieve bed pressure.

65. The method of any one of claims 60 to 64 wherein the data samples correspond with a plurality of adsorption phases controlled by the controller.

66. The method of any one of claims 60 to 65 wherein the data samples comprise a plurality of peak values, wherein each peak value corresponds with one adsorption phase of the plurality of adsorption phases.

67. The method of any one of claims 60 to 66 wherein the modeling function comprises one or more parameters derived by linear regression.

68. The method of claim 67 wherein the one or more parameters comprise a slope value and an intercept value, and wherein the computing the estimate of the system pressure is based on the slope value and intercept value.

69. An oxygen concentrator comprising: one or more sieve beds containing a gas separation adsorbent; a compression system, including a motor-operated compressor, configured to feed a pressurised feed gas into the one or more sieve beds; an accumulator configured to receive oxygen enriched air from the one or more sieve beds; a pressure sensor configured to generate a signal representing a measure of pressure of the oxygen enriched air in the accumulator; a speed sensor configured to generate a signal representing a measure of speed of the motor of the compressor; a memory; and a controller comprising one or more processors, the one or more processors configured by program instructions stored in the memory to execute the method of operating the oxygen concentrator according to the method of any one of claims 54 to 68.

70. An oxygen concentrator comprising: one or more sieve beds containing a gas separation adsorbent; a compression system, including a motor-operated compressor, configured to feed a pressurised feed gas into the one or more sieve beds; an accumulator configured to receive oxygen enriched air from the one or more sieve beds; a pressure sensor configured to generate a signal representing a measure of pressure of the oxygen enriched air in the accumulator; a speed sensor configured to generate a signal representing a measure of speed of the motor of the compressor; and a controller coupled with the compression system, the pressure sensor, and the speed sensor, the controller configured to: control the motor with a monotonic function that changes motor speed over a period of time to achieve a target system pressure associated with a flow rate setting of the oxygen concentrator based on the measured pressure signal, during the changing of motor speed over the period of time, compute an estimate of the system pressure based on the measured pressure; compare the estimate of the system pressure to the target system pressure; and interrupt the changing in motor speed based on a result of the comparing.

71. The oxygen concentrator of claim 70 wherein the changes in motor speed comprise ramping of speed of the motor and the period of time comprises multiple adsorption cycles.

72. The oxygen concentrator of claim 71 wherein the ramping of speed comprises an increase in speed, and wherein the flow rate setting is (a) a higher setting from a prior flow rate setting, or (b) an initial setting following power activation of the oxygen concentrator.

73. The oxygen concentrator of claim 71 wherein the ramping of speed comprises a decrease in speed, and wherein the flow rate setting is a lower setting from a prior flow rate setting.

74. The oxygen concentrator of any one of claims 70 to 73 wherein the controller is further configured to determine a target speed for the motor speed based on an estimate of a pressure time profile of the system pressure.

75. The oxygen concentrator of any one of claims 70 to 74 wherein the estimate of the system pressure is an estimate of sieve bed pressure.

76. The oxygen concentrator of any one of claims 70 to 75 wherein to compute the estimate of the system pressure, the controller is configured to apply a modeling function to data samples of the measured pressure.

77. The oxygen concentrator of claim 76 wherein the modeling function is further applied to determine a target speed for the motor speed.

78. The oxygen concentrator of any one of claims 76 to 77 wherein the modeling function comprises a damped response modeling function.

79. The oxygen concentrator of any one of claims 76 to 78 wherein the modeling function comprises a predetermined delay value.

80. The oxygen concentrator of claim 79 wherein the predetermined delay value characterizes a damped response of the measured pressure relative to sieve bed pressure.

81. The oxygen concentrator of any one of claims 76 to 80 wherein the data samples correspond with a plurality of adsorption phases controlled by the controller.

82. The oxygen concentrator of any one of claims 76 to 81 wherein the data samples comprise a plurality of peak values, wherein each peak value corresponds with one adsorption phase of the plurality of adsorption phases.

83. The oxygen concentrator of any one of claims 76 to 82 wherein the modeling function comprises one or more parameters derived by linear regression.

84. The oxygen concentrator of claim 83 wherein the one or more parameters comprise a slope value and an intercept value, and wherein the computed estimate of the system pressure is based on the slope value and intercept value.

85. A method of operating an oxygen concentrator, the method comprising: with a speed sensor, generating a signal representing a measure of speed of a motor of a compressor; and with a controller, controlling operation of the motor of the compressor by changing, with a monotonic control function, motor speed over a period of time to achieve a target system pressure associated with a flow rate setting of the oxygen concentrator based on the measured motor speed signal, wherein the controlling with the controller comprises: determining a target speed for the motor based on a current target motor speed, the target system pressure, a current target system pressure from a current flow rate setting, and a parameter representing a dynamic relationship between changes in system pressure and changes in motor speed; comparing the measure of motor speed to the target speed; and interrupting the changing in motor speed based on a result of the comparing.

86. The method of claim 85 further comprising deriving the parameter with a regression process.

87. The method of any one of claims 85 to 86 further comprising deriving the parameter with a known speed ramp rate.

88. The method of any one of claims 85 to 87 further comprising deriving the parameter with a slope parameter.

89. The method of any one of claims 85 to 88 wherein the parameter comprises a normalised slope parameter.

90. The method of any one of claims 85 to 89 wherein the changing of speed over the period of time comprises an increase in speed, and wherein the flow rate setting is a higher setting than the current flow rate setting.

91. The method of any one of claims 85 to 89 wherein the changing of speed over the period of time comprises a decrease in speed, and wherein the flow rate setting is a lower setting than the current flow rate setting.

92. An oxygen concentrator comprising: one or more sieve beds containing a gas separation adsorbent; a compression system, including a motor-operated compressor, configured to feed a pressurised feed gas into the one or more sieve beds; an accumulator configured to receive oxygen enriched air from the one or more sieve beds; a pressure sensor configured to generate a signal representing a measure of pressure of the oxygen enriched air in the accumulator; a speed sensor configured to generate a signal representing a measure of speed of the motor of the compressor; a memory; and a controller comprising one or more processors, the one or more processors configured by program instructions stored in the memory to execute the method of operating the oxygen concentrator according to the method of any one of claims 85 to 91.

93. An oxygen concentrator comprising: one or more sieve beds containing a gas separation adsorbent; a compression system, including a motor-operated compressor, configured to feed a pressurised feed gas into the one or more sieve beds; an accumulator configured to receive oxygen enriched air from the one or more sieve beds; a speed sensor configured to generate a signal representing a measure of speed of a motor of the motor-operated compressor; and a controller coupled with the compression system and the speed sensor, the controller configured to: control an operation of the motor of the compressor by changing, with a monotonic control function, motor speed over a period of time to achieve a target system pressure associated with a flow rate setting of the oxygen concentrator based on the measure of speed, wherein to control the operation by changing motor speed over the period of time the controller is configured to: determine a target speed for the motor based on a current target motor speed, a target system pressure, a current target system pressure from a current flow rate setting, and a parameter representing a dynamic relationship between changes in system pressure and changes in motor speed; compare the measure of motor speed to the target speed; and interrupt the changing in motor speed based on a result of the comparing.

94. The oxygen concentrator of claim 93 wherein the parameter is derived with a regression process.

95. The oxygen concentrator of any one of claims 93 to 94 wherein the parameter is derived with a known speed ramp rate.

96. The oxygen concentrator of any one of claims 93 to 95 wherein the parameter is derived with a slope parameter.

97. The oxygen concentrator of any one of claims 93 to 96 wherein the parameter comprises a normalised slope parameter.

98. The oxygen concentrator of any one of claims 93 to 97 wherein the changing of speed over the period of time comprises an increase in speed, and wherein the flow rate setting is a higher setting than the current flow rate setting.

99. The oxygen concentrator of any one of claims 93 to 98 wherein the changing of speed over the period of time comprises a decrease in speed, and wherein the flow rate setting is a lower setting than the current flow rate setting.