CN115813397A - Active magnetic compensation closed-loop control system in magnetic shielding cylinder and design method - Google Patents
Active magnetic compensation closed-loop control system in magnetic shielding cylinder and design method Download PDFInfo
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Abstract
The invention discloses an active magnetic compensation closed-loop control system in a magnetic shielding cylinder and a design method, firstly, a magnetic field compensation range is determined by combining a magnetic field expression and background magnetic field distribution in the magnetic shielding cylinder, a two-stage active magnetic compensation algorithm is designed, and magnetic field compensation is realized through open-loop coarse compensation and closed-loop fine compensation; secondly, designing a functional unit for realizing a magnetic compensation closed-loop control system, designing a high-precision signal acquisition unit, a compensation control unit and a drive output unit, and realizing a closed-loop feedback loop; and finally, designing a compensation control upper computer system to realize man-machine interaction, real-time adjustment and real-time compensation. On the basis of the existing passive magnetic shielding scheme, the invention adds an active magnetic compensation closed-loop control scheme, thereby effectively realizing a long-term uniform and stable extremely weak magnetic environment; a two-stage active magnetic compensation scheme is designed, so that the static residual magnetic field and the dynamic disturbance magnetic field are simultaneously compensated, external interference is eliminated, and the accuracy of measuring the heart pole weak magnetic signal is improved.
Description
Technical Field
The invention belongs to the technical field of magnetic shielding, and particularly relates to an active magnetic compensation closed-loop control system in a magnetic shielding cylinder and a design method.
Background
The SERF atomic magnetometer is a magnetometer with the highest low-frequency sensitivity at present, and the measurement of magnetocardiogram signals can be realized through the SERF atomic magnetometer. The magnetocardiogram measurement is a non-invasive, non-destructive and non-contact detection technology, and has the accuracy and sensitivity which are incomparable with the traditional detection methods such as electrocardiogram and the like for diagnosing coronary heart disease, myocardial infarction and the like, and the detection time can be reduced from several hours to about 20 minutes.
To realize an ultra-high sensitivity SERF atomic magnetometer, three conditions for realizing the SERF state, namely pumping light, high temperature and weak magnetic environment, need to form a large uniform region and high stability weak magnetic environment, wherein the research on magnetic shielding and magnetic compensation technology is a key problem. The magnetic shielding cylinder has extremely high shielding capability on high-frequency and radio-frequency magnetic disturbance, but has limited shielding capability on low-frequency magnetic fields, and the characteristics of remanence and easy magnetization of materials limit the performance of passive magnetic shielding. Meanwhile, factors such as the influence of an environmental geomagnetic field, personnel walking, other electromagnetic equipment in the environment and the like can also generate a dynamic disturbance magnetic field, so that the magnetic field in the magnetocardiogram measuring device fluctuates to influence the accuracy of magnetocardiogram measuring signals.
The combination of active and passive is the application trend of a new generation magnetic shielding device technology, on the basis of using a magnetic shielding cylinder, the residual magnetic field can be further reduced by adopting active magnetic compensation, the applied current acts on a compensation coil to generate a compensation magnetic field, and a magnetic compensation closed-loop control system is built at the same time, so that the fluctuation of the magnetic field can be effectively inhibited, the value of the compensation magnetic field is adjusted in real time according to the value of the detected magnetic field, the magnetic field can be stabilized near zero magnetism for a long time, the stability of a magnetocardiogram measuring device is improved, and the accuracy of magnetocardiogram measuring data can also be improved.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides an active magnetic compensation closed-loop control system in a magnetic shielding cylinder and a design method thereof, the method solves the problem of weak magnetic environment required by a SERF atomic magnetometer in measuring magnetocardiogram signals, and combines passive magnetic shielding and active magnetic compensation to stabilize a magnetic field near a zero point for a long time, thereby being beneficial to improving the stability of a magnetocardiogram measuring device and improving the accuracy of magnetocardiogram measuring data.
In order to achieve the purpose, the invention adopts the technical scheme that:
an active magnetic compensation closed-loop control system in a magnetic shielding cylinder, comprising: the high-precision signal acquisition unit, the compensation control unit, the drive output unit and the compensation control upper computer system are arranged on the high-precision signal acquisition unit; the high-precision signal acquisition unit comprises an atomic magnetometer, a signal amplification module, a level adjustment module and an AD acquisition module, the compensation control unit comprises a filtering module, a data conversion module and a PID (proportion integration differentiation) control module, and the driving output unit comprises a DA conversion module, a voltage-controlled current source module and a compensation coil; the upper computer system realizes real-time display of the collected magnetic field, adjustment of parameters of a closed-loop control system and control of two-stage compensation on-off, realizes man-machine interaction, real-time adjustment and real-time compensation, and enables the magnetic field in the magnetic shielding cylinder to be uniformly stabilized near zero for a long time; determining a magnetic field compensation range and a reference channel position by combining a magnetic field expression and background magnetic field distribution in the magnetic shielding cylinder, designing a two-stage active magnetic compensation algorithm, and respectively realizing compensation of a static direct current component magnetic field and a dynamic disturbance component magnetic field through open-loop coarse compensation and closed-loop fine compensation; a high-precision signal acquisition unit, a compensation control unit and a drive output unit are designed to realize magnetic field compensation of a closed-loop feedback loop; and the upper computer system is designed, compensated and controlled through the RS232 communication unit.
The invention also provides a design method of the active magnetic compensation closed-loop control system in the magnetic shielding cylinder, which comprises the following steps:
determining a magnetic field compensation range and a reference channel position, designing a two-stage active magnetic compensation algorithm, and realizing magnetic field compensation through open-loop coarse compensation and closed-loop fine compensation;
designing a functional unit for realizing a magnetic compensation closed-loop control system, wherein the functional unit for realizing the magnetic compensation closed-loop control system comprises a high-precision signal acquisition unit, a compensation control unit and a drive output unit, and is used for realizing a closed-loop feedback loop;
and (3) designing a compensation control upper computer system, realizing real-time display of a collected magnetic field, adjustment of closed-loop control system parameters and control of two-stage compensation on-off by the upper computer system, and realizing man-machine interaction, real-time adjustment and real-time compensation, so that the magnetic field in the magnetic shielding cylinder is uniformly stabilized near zero magnetism for a long time.
Further, in step (1), determining the magnetic field compensation range and the reference channel position includes:
step (11): calculating the accurate magnetic field value of the magnetic field in the magnetic shielding cylinder, and obtaining a linear matrix equation for magnetic field calculation according to the magnetic field function expression:
B mat α＝b
where α is the column vector containing 8 coefficients, B is the target magnetic field column vector, B mat Is a matrix that characterizes the field produced by the eight unit-weighted field components on the N zero-field magnetometer arrays, based on the sensor position and orientation measured at each T time point; wherein, B mat There are 8 columns, T x N rows, each column corresponding to a field component, each sensor having a row at each time point representing the magnetic field measured by the corresponding sensor at that time point and the position and orientation of the sensor; the target magnetic field column vector B contains the magnetic fields measured by the N zero-field magnetometers at the T time point, corresponding to B mat A zero field magnetometer of the same position and orientation; the coefficient α best fit to b is obtained by identifying a pseudo-inverse matrix or similar process;
for an array of N zero field magnetometers measuring their motion at T points in time, B mat Has rows of T x N; the column vector b of the target field also has lines T × N, the column vector of the coefficient α is unchanged, and the value of α is obtained by the following formula, thereby obtaining the magnetic field value in the device:
step (12): the magnetic field distribution of the array box for measuring the cardiac magnetic field in the magnetic shielding cylinder is measured, the size of a magnetic field value at each row of channels in the cylinder axis direction and the heaven-earth direction is obtained, so that the magnetic field distribution is obtained, the magnetic field value is averaged for each row of channels, the larger the distance from the cylinder bottom is, the larger the magnetic field value is, the more parallel and level the cylinder axis direction and the center position of the array box are selected, the reference channel is placed at the position with the same height as the array box in the heaven-earth direction, and the magnetic field detection and compensation are carried out on the area where the array box for measuring the cardiac magnetic field is located.
Further, in the step (1), the two-stage active magnetic compensation algorithm is as follows: the method comprises the steps of dividing a background magnetic field in a magnetic shielding cylinder into a static direct-current component and a dynamic disturbance component, simultaneously compensating by adopting a two-stage active magnetic compensation algorithm, compensating the static background magnetic field in the magnetic shielding cylinder by open-loop coarse compensation to eliminate the static direct-current component, compensating the magnetic field near a zero point, and compensating the dynamic disturbance magnetic field by closed-loop fine compensation to eliminate the dynamic disturbance component, so that the magnetic field is stabilized near the zero point for a long time. And by a two-stage active magnetic compensation algorithm, a compensation output value drive coil generates a compensation magnetic field, and finally a large uniform area high-stability near-zero magnetic environment is formed.
Further, in the step (2), the process of designing and implementing the magnetic compensation closed-loop control system functional unit is divided into the following 3 steps:
the high-precision signal acquisition unit detects a background magnetic field in the magnetic shielding cylinder through an SERF atomic magnetometer, a bipolar weak analog voltage signal of an output signal of the atomic magnetometer amplifies the signal to a voltage level through a signal amplification module, and the signal amplification module consists of an AD623 chip and a peripheral circuit; then the level adjustment module is used for carrying out level lifting on the generated bipolar signal, positive voltage is superposed to enable the collected signal to become a complete positive voltage signal, the level adjustment module is composed of an OP07 chip and a corresponding peripheral circuit, and the level adjustment reference voltage is +1.5V; the signals are collected by an AD collection module and enter a main control chip, the AD7606 chip is determined to be used for collection based on factors such as collection voltage range, collection precision and sampling rate, the AD7606 chip is an 8-channel 16-bit ADC chip, the sampling rate is 2KHz, and the signals are transmitted to a control chip in a high-speed parallel transmission mode to be subjected to the next operation;
in the step (22), the compensation control unit uses TMS320F28335DSP as a control chip to realize functions of data transmission, processing, control and the like, firstly, filter processing and data conversion processing are carried out on AD acquisition signals, a filter module comprises moving average filtering and amplitude limiting filtering, a fixed size is used as a queue window through the moving average filtering, moving average of data is realized through continuous forward sliding window of acquisition of each new data, periodic interference is effectively inhibited, meanwhile, accidental pulse interference is filtered through the amplitude limiting filtering, upper and lower limits of the data are set, if the upper and lower limits are exceeded, a numerical value acquired last time is used as a data acquisition value of this time, and interference influence caused by accidental variation factors is eliminated; after filtering processing, voltage magnetic field relation conversion and precision digit conversion are carried out on the signals, data conversion processing is realized, PID control is realized, an ideal background magnetic field value is set to be zero, namely a set value of a PID controller is zero, closed-loop feedback control is carried out by adopting a position type digital PID formula, kp, ki and Kd parameters are determined by combining an upper computer system, current errors and control quantity are calculated according to a signal acquisition value, a compensation control output value is obtained, a compensation magnetic field is generated by applying the compensation magnetic field on a compensation coil, and a magnetometer carries out real-time detection to form a closed-loop feedback loop;
and (23) the driving output unit outputs PID control output quantity through a DA conversion module, a TLV5620 digital-to-analog conversion chip is used for realizing an external DAC conversion circuit, the chip has 4-channel 8-bit DAC output, the analog voltage output range is 0 to +3.8V, the resolution is 12.9mV, SPI communication is adopted, the DA output is then converted into output current through a voltage control current source module, a compensation magnetic field is generated by applying the output current to a coil, a nested saddle-shaped Helmholtz coil is used as the compensation coil, the saddle-shaped Helmholtz coil comprises 4 sections of circular arcs and 4 sections of straight lines, and the length of the central side of the coil in a cube with a radius of one fourth of the radius reaches 10 -3 ～10 -4 The theoretical uniformity of magnitude, adopt the saddle type coil of constituteing by inner circle and outer lane, turn ratio is outer/interior =20/10, radial uniformity is less than 0.01@ +/-100 mm, and the coil constant is 20nT/mA, adopts the height 400mm, diameter 800mm, and the number of turns is Helmholtz coil of 10, and the uniformity is less than 0.01@ +/-100 mm, and the coil constant is 22nT/mA.
Further, in the step (3), the designing of the compensation control upper computer system includes:
step (31) communication between a control system lower computer and a PC end upper computer system is realized through an SCI serial communication protocol, connection is established through an RS232 interface, transmission is carried out in a byte mode, the baud rate is set to be 9600, data bits are 8 bits, no check bit N exists, and serial asynchronous full-duplex data transmission is realized;
step (32) transmitting the magnetic field data acquired by the control chip DSP to an upper computer for displaying, converting the acquired magnetic field value into a character string by using a sending interface of an external resource SCIA, sending the character string to a computer, receiving and processing the character string by using the upper computer interface, and realizing real-time numerical value and waveform display of the magnetic field signal through a waveform chart and a character string control, so that a user can visually check the real-time magnetic field signal;
step (33), PID control parameters regulated by an upper computer system are transmitted to a control chip DSP, a receiving port of a peripheral resource SCIA is used, after PID control parameters Kp, ki and Kd are regulated by the upper computer, the control parameters are transmitted by 6 bits, and are converted into floating point numbers with symbols in a program, and PID control is carried out by utilizing the received control parameters;
and (34) feeding back the on and off response of the compensation set by the upper computer to the control chip DSP, setting whether the compensation is on or not by using a receiving port of a peripheral resource SCIA (peripheral interface architecture), and transmitting a setting instruction to the control chip DSP, wherein the method comprises the following conditions:
when the open-loop coarse compensation is not started, the control is not carried out, and the output is 0;
when the open-loop coarse compensation is started and the closed-loop fine compensation is not started, outputting open-loop control quantity for compensation by using an open-loop control algorithm, and reducing the background magnetic field in the magnetic shielding cylinder to be near zero magnetism;
when the open-loop coarse compensation and the closed-loop fine compensation are both started, PID closed-loop control is achieved through a two-stage active compensation algorithm, PID parameter adjustment is achieved by a user on an upper computer, parameters are transmitted to a control chip DSP through RS232 communication to be controlled, and after a control quantity u is obtained, the control quantity u is output through a DA, so that a background magnetic field in the magnetic shielding cylinder is uniformly stabilized near zero magnetism for a long time.
Compared with the prior art, the invention has the advantages that:
(1) The invention designs an active magnetic compensation closed-loop control system, adds an active magnetic compensation technology on the basis of a passive magnetic shielding cylinder, designs a closed-loop control system to compensate in real time, and realizes a long-term uniform and stable near-zero magnetic environment;
(2) The invention designs a two-stage active magnetic compensation algorithm scheme, which respectively compensates a static direct-current magnetic field and a dynamic disturbance magnetic field by an open-loop coarse compensation algorithm and a closed-loop fine compensation algorithm, eliminates a direct-current component and a disturbance component, and enables the magnetic field compensation to be faster and more accurate;
(3) The invention adopts the design of functional units, divides three units of the high-precision signal acquisition unit, the compensation control unit and the drive output unit, continues subdividing each unit module, completes the design of each unit module and carries out integration verification, and improves the overall performance of the system.
Drawings
FIG. 1 is a schematic diagram of the structure of an active magnetic compensation closed-loop control system in a magnetic shielding cylinder according to the present invention;
FIG. 2 is a flow chart of a design method of an active magnetic compensation closed-loop control system in a magnetic shielding cylinder according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, the active magnetic compensation closed-loop control system in the magnetic shielding cylinder of the present invention includes a high-precision signal acquisition unit, a compensation control unit and a drive output unit, wherein the high-precision signal acquisition unit includes an atomic magnetometer, a signal amplification module, a level adjustment module and an AD acquisition module; the compensation control unit comprises a filtering module, a data conversion module and a PID control module; the drive output unit comprises a DA conversion module, a voltage-controlled current source module and a compensation coil.
As shown in fig. 2, the design method of the active magnetic compensation closed-loop control system in the magnetic shielding cylinder of the present invention includes: the system carries out AD acquisition, filtering processing and data conversion on signals after initialization, transmits the converted data to an upper computer through a serial port for real-time display, and simultaneously carries out instruction setting on the upper computer by a user, wherein the instruction setting comprises the setting of whether open-loop coarse compensation is started or not and whether closed-loop fine compensation is started or not, if the compensation is started, the execution of a control algorithm is carried out in an F28335 control chip, and a control quantity u is output, if the compensation is not started, 0 is output, and an output value is output to a subsequent module through a DAC chip, so that the stable control on a magnetic field is realized.
As can be seen from fig. 1 and 2, in the active magnetic compensation closed-loop control system in the magnetic shielding cylinder of the present invention, firstly, a magnetic field compensation range and a reference channel position are determined by combining a magnetic field expression and a background magnetic field distribution in the magnetic shielding cylinder, a two-stage active magnetic compensation algorithm is designed, and compensation of a static direct current component magnetic field and a dynamic disturbance component magnetic field is respectively realized by open-loop coarse compensation and closed-loop fine compensation; secondly, designing a functional unit for realizing a magnetic compensation closed-loop control system, designing a high-precision signal acquisition unit, a compensation control unit and a drive output unit, realizing magnetic field compensation of a closed-loop feedback loop, wherein the high-precision signal acquisition unit comprises an atomic magnetometer, a signal amplification module, a level adjustment module and an AD acquisition module, the compensation control unit comprises a filtering module, a data conversion module and a PID control module, and the drive output unit comprises a DA conversion module, a voltage-controlled current source module and a compensation coil; and finally, designing a compensation control upper computer system through an RS232 communication unit, realizing real-time display of a collected magnetic field, adjustment of closed-loop control system parameters and control of two-stage compensation on-off in the upper computer system, and realizing man-machine interaction, real-time adjustment and real-time compensation, so that the magnetic field in a uniform area in the magnetic shielding cylinder is stabilized near zero for a long time.
The specific design method comprises the following steps:
determining a magnetic field compensation range and a reference channel position, designing a two-stage active magnetic compensation algorithm, and realizing magnetic field compensation through open-loop coarse compensation and closed-loop fine compensation, wherein the method comprises the following steps:
step (11): the magnetic field in the magnetic shielding cylinder is subjected to accurate magnetic field value calculation, and a linear matrix equation of the magnetic field calculation can be obtained according to a magnetic field function expression:
B mat α＝b
where α is the column vector containing 8 coefficients, B is the target magnetic field column vector, B mat Is a matrix that characterizes the field produced by the eight unit-weighted field components over the N OPM arrays, based on the sensor position and orientation measured at each T time point; wherein, B mat There are 8 columns, T x N rows, each column corresponding to a field component, each sensor having a row at each time point representing the magnetic field measured by the corresponding sensor at that time point and the position and orientation of the sensor; the target field column vector B contains the magnetic field measured by the N OPMs at the T time point, corresponding to B mat The same position and orientation of the OPM; the coefficients α that best fit b are obtained by identifying a pseudo-inverse matrix or similar process;
for an array of N zero field magnetometers measuring their motion at T points in time, B mat Has rows of T x N; the column vector b of the target field also has T × N rows, the column vector of the coefficient alpha is unchanged, and the value of alpha is obtained by the formula as follows, so that the magnetic field value in the device is obtained;
step (12): measuring the magnetic field distribution of the array box for measuring the cardiac magnetic field in the magnetic shielding cylinder to obtain the magnetic field value of each row channel in the cylinder axis direction and the heaven-earth direction so as to obtain the magnetic field distribution, carrying out average treatment on the magnetic field value of each row channel to obtain that the farther the distance from the cylinder bottom, the larger the magnetic field value, selecting a position which is parallel to the center position of the array box in the cylinder axis direction, placing a reference channel in the position with the same height as the array box in the heaven-earth direction, and carrying out magnetic field detection and compensation on the area where the array box for measuring the cardiac magnetic field is located;
step (13) based on the fact that a background magnetic field in a magnetic shielding cylinder is divided into a static direct current component and a dynamic disturbance component, two-stage active magnetic compensation algorithm is adopted for simultaneous compensation, in the first step, the static background magnetic field in the magnetic shielding cylinder is compensated through open-loop coarse compensation, the static direct current component is eliminated, before the magnetocardiogram measurement work, the static background magnetic field in the magnetic shielding cylinder is collected, the control quantity is output through open-loop control for coarse compensation, and the large background magnetic field is compensated to be close to a zero point; and secondly, compensating the dynamic disturbance magnetic field in real time through closed-loop fine compensation to eliminate dynamic disturbance components, acquiring the disturbance magnetic field on the basis of coarse compensation to form a closed-loop feedback loop, outputting feedback control quantity to be applied to a compensation coil, stabilizing the magnetic field near a zero point for a long time, inhibiting magnetic field fluctuation and reducing external interference. And by a two-stage active magnetic compensation algorithm, a two-stage compensation output value drive coil generates a compensation magnetic field, and finally a large uniform area high-stability near-zero magnetic environment is formed.
Step (2) designs and realizes the magnetic compensation closed-loop control system function unit, designs the high-precision signal acquisition unit, the compensation control unit and the drive output unit, realizes the closed-loop feedback loop, and comprises the following steps:
the magnetic compensation closed-loop control system functional unit comprises a high-precision signal acquisition unit, a compensation control unit and a drive output unit, wherein the high-precision signal acquisition unit comprises an atomic magnetometer, a signal amplification module, a level adjustment module and an AD acquisition module; the compensation control unit comprises a filtering module, a data conversion module and a PID control module; the drive output unit comprises a DA conversion module, a voltage-controlled current source module and a compensation coil;
step (21), a high-precision signal acquisition unit detects a background magnetic field in a magnetic shielding cylinder through an SERF atomic magnetometer, the output signal of the atomic magnetometer is a bipolar weak analog voltage signal, the signal is amplified to a voltage level through a signal amplification module, and the signal amplification module is composed of an AD623 chip and a peripheral circuit; then the level adjustment module is used for carrying out level lifting on the generated bipolar signal, positive voltage is superposed to enable the collected signal to become a complete positive voltage signal, the level adjustment module is composed of an OP07 chip and a corresponding peripheral circuit, and the level adjustment reference voltage is +1.5V; the signals are collected by an AD collection module and enter a main control chip, the AD7606 chip is determined to be used for collection based on factors such as collection voltage range, collection precision and sampling rate, the AD7606 chip is an 8-channel 16-bit ADC chip, the sampling rate is 2KHz, and the signals are transmitted to a control chip in a high-speed parallel transmission mode to be subjected to the next operation;
in the step (22), a TMS320F28335DSP is used as a control chip in a compensation control unit to realize functions of data transmission, processing, control and the like, AD acquisition signals are subjected to filtering processing and data conversion processing, a filtering module comprises moving average filtering and amplitude limiting filtering, a fixed size is used as a queue window through the moving average filtering, a moving average of data is realized through the continuous forward sliding window of acquisition of each new data, periodic interference is effectively inhibited, meanwhile, accidental pulse interference is filtered through the amplitude limiting filtering, upper and lower limits of the data are set, if the upper and lower limits are exceeded, a numerical value acquired last time is used as a data acquisition value of this time, and interference influence caused by accidental variation factors is eliminated; after filtering processing, carrying out voltage magnetic field relation conversion and precision digit conversion on the signals to realize data conversion processing, then realizing PID control, setting an ideal background magnetic field value to be zero, namely setting a PID controller value to be zero, adopting a position type digital PID formula to carry out closed loop feedback control, determining Kp, ki and Kd parameters by combining an upper computer system, calculating current error and control quantity according to a signal acquisition value to obtain a compensation control output value, applying the compensation control output value on a compensation coil to generate a compensation magnetic field, and detecting a magnetometer in real time to form a closed loop feedback loop;
and (23) driving an output unit to output the PID control output quantity through a DA conversion module, and realizing external use by using a TLV5620 digital-to-analog conversion chipThe DAC conversion circuit comprises a DAC conversion circuit, wherein the chip is provided with 4 channels and 8-bit DAC output, the analog voltage output range is 0 to +3.8V, the resolution ratio is 12.9mV, SPI communication is adopted, the output voltage is converted into output current through a voltage control current source module after the DA output, a compensation magnetic field is generated by applying the output current on a coil, a nested saddle-shaped Helmholtz coil is adopted as a compensation coil, the saddle-shaped Helmholtz coil comprises 4 sections of circular arcs and 4 sections of straight lines, and the length of the center line of the coil is one fourth of the radius of a cube to reach 10 -3 ～10 -4 The theoretical homogeneity of magnitude adopts the saddle coil of compriseing inner circle and outer lane, and the turn ratio is outer/interior =20/10, and radial homogeneity is less than 0.01@ +/-100 mm, and the coil constant is 20nT/mA, adopts the height 400mm, and diameter 800mm, the number of turns is the Helmholtz coil of 10, and the homogeneity is less than 0.01@ +/-100 mm, and the coil constant is 22nT/mA.
And (3) designing a compensation control upper computer system, realizing real-time display of a collected magnetic field, adjustment of parameters of a closed-loop control system and control of two-stage compensation on-off in the upper computer system, realizing man-machine interaction, real-time adjustment and real-time compensation, and enabling the magnetic field in the magnetic shielding cylinder to be uniformly stabilized near zero magnetism for a long time, wherein the compensation control upper computer system comprises the following steps:
step (31) communication between a lower computer of a control system and an upper computer system at a PC end is realized through an SCI serial communication protocol, connection is established through an RS232 interface, transmission is carried out in a byte mode, the Baud rate is set to be 9600, the data bit is 8 bits, no check bit N exists, and serial asynchronous full-duplex data transmission is realized;
step (32) transmitting the magnetic field data acquired by the control chip DSP to an upper computer for display, converting the acquired magnetic field value into a character string by using a sending interface of an external resource SCIA, sending the character string to a computer, receiving and processing the character string by the upper computer interface, and realizing real-time numerical value and waveform display of the magnetic field signal through a waveform chart and a character string control, so that a user can visually check the real-time magnetic field signal;
step (33), PID control parameters regulated by an upper computer system are transmitted to a control chip DSP, the receiving port of the peripheral resource SCIA is used, after the PID control parameters kp, ki and kd are regulated by the upper computer, the control parameters are transmitted by 6 bits and are converted into floating point numbers with symbols in a program, and the received control parameters are utilized for PID control;
and (34) feeding back the on and off response of the compensation set by the upper computer to the control chip DSP, setting whether the compensation is on or not by using a receiving port of a peripheral resource SCIA (peripheral interface architecture), and transmitting a setting instruction to the control chip DSP, wherein the method comprises the following conditions:
when the open-loop coarse compensation is not started, no control is performed, and the output is 0;
when the open-loop coarse compensation is started and the closed-loop fine compensation is not started, outputting open-loop control quantity for compensation by using an open-loop control algorithm, and reducing the background magnetic field in the magnetic shielding cylinder to be near zero magnetism;
when the open-loop coarse compensation and the closed-loop fine compensation are both started, PID closed-loop control is realized through a two-stage active compensation algorithm, PID parameter adjustment is realized by a user on an upper computer, parameters are transmitted to a control chip DSP through RS232 communication to be controlled, and the control quantity u is obtained and then output through DA, so that the background magnetic field in the magnetic shielding cylinder is uniformly stabilized near zero magnetism for a long time.
Those skilled in the art will appreciate that the invention may be practiced without these specific details. It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (6)
1. An active magnetic compensation closed-loop control system in a magnetic shielding cylinder, comprising: the high-precision signal acquisition unit, the compensation control unit, the drive output unit and the compensation control upper computer system are arranged in the high-precision signal acquisition unit; the high-precision signal acquisition unit comprises an atomic magnetometer, a signal amplification module, a level adjustment module and an AD acquisition module, the compensation control unit comprises a filtering module, a data conversion module and a PID (proportion integration differentiation) control module, and the driving output unit comprises a DA conversion module, a voltage-controlled current source module and a compensation coil; the upper computer system realizes real-time display of the collected magnetic field, adjustment of parameters of a closed-loop control system and control of two-stage compensation on-off, realizes man-machine interaction, real-time adjustment and real-time compensation, and enables the magnetic field in the magnetic shielding cylinder to be uniformly stabilized near zero for a long time; determining a magnetic field compensation range and a reference channel position by combining a magnetic field expression and background magnetic field distribution in the magnetic shielding cylinder, designing a two-stage active magnetic compensation algorithm, and respectively realizing compensation of a static direct current component magnetic field and a dynamic disturbance component magnetic field through open-loop coarse compensation and closed-loop fine compensation; designing a high-precision signal acquisition unit, a compensation control unit and a drive output unit to realize magnetic field compensation of a closed-loop feedback loop; and designing the upper computer system through an RS232 communication unit.
2. A design method of an active magnetic compensation closed-loop control system in a magnetic shielding cylinder according to claim 1, characterized by comprising the following steps:
determining a magnetic field compensation range and a reference channel position, designing a two-stage active magnetic compensation algorithm, and realizing magnetic field compensation through open-loop coarse compensation and closed-loop fine compensation;
designing a functional unit for realizing a magnetic compensation closed-loop control system, wherein the functional unit for realizing the magnetic compensation closed-loop control system comprises a high-precision signal acquisition unit, a compensation control unit and a drive output unit, and is used for realizing a closed-loop feedback loop;
and (3) designing a compensation control upper computer system to realize man-machine interaction, real-time adjustment and real-time compensation, so that the magnetic field in the magnetic shielding cylinder is uniformly stabilized near zero magnetism for a long time.
3. The design method of the active magnetic compensation closed-loop control system in the magnetic shielding cylinder according to claim 2, characterized in that: in the step (1), determining the magnetic field compensation range and the reference channel position includes:
step (11): and (3) carrying out accurate magnetic field value calculation on the magnetic field in the magnetic shielding cylinder, and obtaining a linear matrix equation for magnetic field calculation according to a magnetic field function expression:
B mat α＝b
wherein α is a group consisting of 8Column vector of coefficients, B is the target magnetic field column vector, B mat Is a matrix that characterizes the field produced by the eight unit-weighted field components on the N zero-field magnetometer arrays, based on the sensor position and orientation measured at each T time point; wherein, B mat There are 8 columns, T x N rows, each column corresponding to a field component, each sensor having a row at each time point representing the magnetic field measured by the corresponding sensor at that time point and the position and orientation of the sensor; the target magnetic field column vector B contains the magnetic fields measured by the N zero-field magnetometers at the T time point, corresponding to B mat A zero field magnetometer of the same position and orientation; the coefficient alpha best fit to the target magnetic field column vector b is obtained by identifying a pseudo-inverse matrix or similar process;
for an array of N zero field magnetometers measuring their motion at T points in time, B mat Has rows of T x N; the column vector b of the target field also has lines T × N, the column vector of the coefficient α is unchanged, and the value of α is obtained by the following formula, thereby obtaining the magnetic field value in the device:
step (12): measuring the magnetic field distribution of the array box for measuring the cardiac magnetic field in the magnetic shielding cylinder to obtain the magnetic field value of each row channel in the cylinder axis direction and the heaven-earth direction so as to obtain the magnetic field distribution, placing a reference channel at the position which is parallel to the center position of the array box in the cylinder axis direction and has the same height with the array box in the heaven-earth direction, and detecting and compensating the magnetic field in the region where the array box for measuring the cardiac magnetic field is located.
4. The design method of the active magnetic compensation closed-loop control system in the magnetic shielding cylinder according to claim 3, characterized in that: in the step (1), the two-stage active magnetic compensation algorithm is as follows: based on the fact that a background magnetic field in a magnetic shielding cylinder is divided into a static direct current component and a dynamic disturbance component, a two-stage active magnetic compensation algorithm is adopted for simultaneous compensation, in the first step, the static background magnetic field in the magnetic shielding cylinder is compensated through open-loop coarse compensation, the static direct current component is eliminated, and the magnetic field is compensated near a zero point; and secondly, compensating the dynamic disturbance magnetic field in real time through closed-loop fine compensation, and eliminating a dynamic disturbance component to enable the magnetic field to be stabilized near a zero point for a long time. And a large uniform area high-stability near-zero magnetic environment is formed by a two-stage active magnetic compensation algorithm.
5. The design method of active magnetic compensation closed-loop control system in magnetic shielding cylinder according to claim 4, characterized in that: in the step (2), the process of designing and realizing the magnetic compensation closed-loop control system functional unit is divided into the following 3 steps:
the high-precision signal acquisition unit detects a background magnetic field in the magnetic shielding cylinder through an SERF atomic magnetometer, and a bipolar weak analog voltage signal of an output signal of the atomic magnetometer amplifies the signal to a voltage level through a signal amplification module; then, the level adjustment module is used for carrying out level lifting on the generated bipolar signal, and positive voltage is superposed to enable the collected signal to be changed into a complete positive voltage signal; the signals are acquired by an AD acquisition module and enter a main control chip, and the signals are transmitted to a control chip in a high-speed parallel transmission mode for the next operation;
in the step (22), the compensation control unit uses a TMS320F28335DSP as a control chip to realize functions of data transmission, processing, control and the like, firstly, the AD acquisition signal is subjected to filtering processing and data conversion processing, a filtering module comprises moving average filtering and amplitude limiting filtering, periodic interference is effectively inhibited through the moving average filtering, and meanwhile, interference influence caused by accidental variation factors is eliminated through the amplitude limiting filtering; carrying out data conversion processing on the signals after filtering processing, then realizing PID control, setting an ideal background magnetic field value to be zero, carrying out closed-loop feedback control by adopting a position type digital PID formula, determining Kp, ki and Kd parameters by combining an upper computer system, calculating current error and control quantity according to the signal acquisition value to obtain compensation control output, and carrying out real-time detection by a magnetometer to form a closed-loop feedback loop;
the drive output unit outputs the PID control output quantity through the DA conversion module and then through the voltage control current sourceThe module converts output voltage into output current, applies the output current to a coil to generate a compensation magnetic field, adopts a nested saddle-shaped Helmholtz coil as the compensation coil, wherein the saddle-shaped Helmholtz coil comprises 4 sections of circular arcs and 4 sections of straight lines, and the length of the center side of the coil is one fourth of the radius of a cube, and reaches 10 -3 ～10 -4 Theoretical uniformity of magnitude.
6. The design method of active magnetic compensation closed-loop control system in magnetic shielding cylinder according to claim 5, characterized in that: in the step (3), the designing, compensating and controlling upper computer system includes:
step (31) communication between a lower computer of the control system and an upper computer system of a PC end is realized through an SCI serial communication protocol, connection is established through an RS232 interface, and serial asynchronous full-duplex data transmission is realized;
step (32), transmitting the magnetic field data acquired by the control chip DSP to an upper computer for display, transmitting the acquired magnetic field value to a computer by using a transmitting interface of an external resource SCIA, and receiving and processing the magnetic field value by the upper computer interface to realize real-time numerical value and waveform display of the magnetic field signal, so that a user can visually check the real-time magnetic field signal;
step (33), PID control parameters regulated by the upper computer system are transmitted to a control chip DSP, transmission is completed after the PID control parameters Kp, ki and Kd are regulated by the upper computer by using a receiving port of the peripheral resource SCIA, and PID control is carried out by using the received control parameters;
and (34) feeding back the on and off response of the compensation set by the upper computer to the control chip DSP, setting whether the compensation is on or not by using a receiving port of a peripheral resource SCIA (peripheral component interface application), and transmitting a setting instruction to the control chip DSP, wherein the method comprises the following conditions:
when the open-loop coarse compensation is not started, the control is not carried out, and the output is 0;
when the open-loop coarse compensation is started and the closed-loop fine compensation is not started, outputting open-loop control quantity for compensation by using an open-loop control algorithm, and reducing the background magnetic field in the magnetic shielding cylinder to be near zero magnetism;
when the open-loop coarse compensation and the closed-loop fine compensation are both started, PID closed-loop control is achieved through a two-stage active compensation algorithm, PID parameter adjustment is achieved by a user on an upper computer and is transmitted to a control chip DSP for control, and after a control quantity u is obtained, the control quantity u is output through a DA (digital-to-analog) so that a background magnetic field in the magnetic shielding cylinder is uniformly stabilized near zero magnetism for a long time.
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