US20140322054A1

US20140322054A1 - System and Method for Holding Tubing for a Peristaltic Pump

Info

Publication number: US20140322054A1
Application number: US14/204,841
Authority: US
Inventors: David T. Bach; James J. Bach
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-05-24
Filing date: 2014-03-11
Publication date: 2014-10-30

Abstract

A system and method for holding tubing for a peristaltic pump the prevents tubing stretch or deformation. The present invention compensates for tube stretching and minimizes tube deformation due to peristaltic roller tube expansions.

Description

This is a continuation-in-part of application Ser. No. 14/033,183 filed Sep. 20, 2013 which was a continuation in part of application Ser. No. 13/114,266 filed May 24, 2011 which claimed priority from U.S. Provisional Patent Application No. 61/396,049 filed May 24, 2010. Applications Ser. Nos. 14/033,183, 13/114,266 and 61/396,049 are hereby incorporated by reference in their entireties.

BACKGROUND

1. Field of the Invention
The present invention relates generally to peristaltic pumps used in the bio-sciences and more particular to a system and method for holding tubing for a peristaltic pump the prevents tubing stretch or deformation. The present invention compensates for tube stretching and minimizes tube deformation due to peristaltic roller tube expansions.
2. Description of the Prior Art
Fluid dispensing in the pharmaceutical and other markets such as biotechnology are moving away from positive piston pumps and moving to peristaltic pump systems. The main driving force is that peristaltic pump systems do not create shear in the fluid being pumped, and the cleaning validation is simplified as compared to positive piston displacement systems. In sealless positive displacement pumps, it has been demonstrated that the fluid experiences shear forces that have an adverse effect on delicate cell structures.
Peristaltic pumps use a series of rollers to compress tubing that passes through the pump to move a fluid. There are many companies that make peristaltic pumps such as Watson-Marlow, Flexicon and Masterfiex, and they all use the same principle of compressing tubing to advance fluid. It has been demonstrated in numerous studies that the use of a peristaltic pump allows for the effective handling of protein and cell structures without the shear forces of piston pumps. Peristaltic pumps have a fluid path only consisting of the tubing that can easily be sterilized, and in many cases discarded after use. This makes the cleaning validation much simpler and reliable.
As peristaltic pumps are being used more for various products, there is a need to carefully support and control the tubing that is being used in the pump Peristaltic pump tubing needs to be held at the input to the peristaltic pump so that when the tubing is compressed it does not advance into the pump. Some manufacturers such as Watson-Marlow and others use tubing clamps and a Y-structure that is must be carefully inserted around two fixed posts, one post being at the input and the other at the output. When such tubing clamps are used, they can have a negative effect of restricting the flow due to sizing or if tightened too much. There are a number of attachment devices known in the art designed to secure and hold tubing, but none of the systems provides for tubing elongation when the peristaltic pump is exercised. Action of the pump can force the tubing to elongate in the direction of rotation. This can be seen in the field where the Y is stretched around the two fixed posts at before running, but after running, the tubing is loose at the output post. If individual tubes holders are used, the output clamp will exhibit a loose-tube condition present as the tube stretches during use. In some units such as the Colanar peristaltic pump FSP-1001, the rollers are geared so that the forward stretching is less than in non-geared systems; nevertheless, elongation still takes place. Tubing stretch occurs in all peristaltic pump systems, and none of the systems currently known in the art have a way of compensating for this stretch. Many of the systems offer a drip retention or suck-back feature where the rollers in the pump are reversed at the end of a pump run in order to move the fluid back into the output tubing. In these cases, drip retention is part of the relaxing of the tube elongation and movement of fluid back into the tube. Tube stretching and relaxing leads to a loss of accuracy since it has the effect of causing variability in each fill.
It would be advantageous to have a system and method of holding the tubing in a peristaltic pump where the input side is held fixed, but there is no restriction introduced into the fluid passage. Also, the output part of the system needs to compensate for tube elongation.
The Watson Marlow 505 type peristaltic pump uses a “Double-Y” set of peristaltic tubing that is secured in the pump by stretching the tubing set over a set of retention pegs. The distance is predetermined and if single tubes are used in the 505L the nominal distance between tubing clamps is 145 mm for bore sizes up to 8.0 and 150 mm for 9.6 mm bore tubes. In most cases each peristaltic tube is held firmly at the input to the peristaltic pump and slightly stretched and secured with output clamps. Shown in FIG. 4 are Double-Y tubing sets from Watson Marlow that are inserted into the peristaltic pump.
These tubing sets are stretched over the retention pegs as shown in FIG. 5. When using Marprene tubing the 505Di pump the tubing must be readjusted: “after the first 30 minutes of running, re-tension the tube in the pump head by releasing the tube clamp on the delivery side a little and pulling the tube tight. This is to counteract the normal stretching that occurs with Marprene which can go unnoticed and result in poor tube life.”
The Watson-Marlow 505L type pump uses peristaltic pressure shoes that the cantilever and positioned in opposite directions as shown in FIG. 7. FIG. 8 indicates the uneven wear that exhibited by using offset shoes.
All manufacturers use some form of mechanical clamp to secure the input and output tube at fixed positions. In FIG. 6 is the Watson Marlow 314D pump head with adjustable clamps on both sides of the pump for the input and output tubes.
The Masterflex series of pumps also uses mechanical locks for their tube sets but in each case they are fixed in place so they do not compensate for tube elongation.
Gibson and Bannistar use a method of tube races to secure the tubing and assure that it stays aligned. U.S. Pat. No. 7,513,757 describes a different method of tube holding.
Shown in FIG. 9 is are the Flexicon type pump shoes that are hinged from the tube input side with both shoes going in the same direction. The Flexicon type pump uses offset rollers to phase the pumping of fluid and minimize fluid pulsations. The peristaltic rollers utilize two cantilever shoes that are oriented so the cantilever end of the shoes are both pointing to the output of the pump. The tube wear looks even and not as drastic as the 505L type of pump. The tube input is held by the spacer shown in the photograph and the pressure shoe cover force. This approach securely holds the input tubing but new holding blocks are need for each tube diameter as shown by the 4.8 mm tubes.
FIG. 10 is the shoe that exists with the 313 Watson-Marlow pump which is with a fixed curvature. The Watson-Marlow 313 pump series of molded pump heads uses a holders for securing the input and output section of tube. The picture below shows the molded pump head tube holding devices in the closed head positions. The top of the pressure shoe assembly is fixed while the bottom input tube holder is spring loaded. This model of pump also has a fixed curvature pressure shoe and different heads can support either the 1.6 or 2.4 wall thickness tubes.
The shoes used in the Flexicon and Watson-Marlow 505L type of pumps use two shoes that are cantilevered. The Watson-Marlow in opposite directions while the Flexicon has its two shoes aligned in one direction. Our design will be using one fixed shoes that are either designed for the 1.6 or 2.4 wall tubes.
It would be advantageous to have a smart peristaltic pump which allows users to monitor pump motion as well as peristaltic tube health.

SUMMARY OF THE INVENTION

Input Tube Holding

The present invention relates to two ways to hold the input tubing to the peristaltic pump. The first method uses a set of “V” holders with the pressure between the “V” holders defined as the force exhibited by a spring or motor. The second method uses a motor to hold an input roller impeding the tubing from entering the pump.

Pressure Shoe Design:

The present invention uses offset rollers to reducing the pulsations in a peristaltic pump. The design uses a fixed curvature that imparts peristaltic tube motion where at least two of the offset rollers are in contact with the pressure shoe at all times. For a four roller system the offset is 45 degrees and 30 degrees for a six roller system. The pressure shoe is positioned at manufacturing using two pin locations and 4 adjustable buttons in each corner of the pressure shoe. By inserting pin locators between the pressure shoe and the primary outer two roller disks the gap for a 2.4 mm wall tubing can be set minimizing any tolerance that can be developed. If a 1.6 mm tube wall is used the pressure shoe would need to be exchanges and the pins would also be different. The pressure shoe provides for one of the two input “V” holders and springs or a motor that work to provide pressure to hold the output tube. The pressure shoe is removable from its fixed position manually but could easily be released by a solenoid from the main body of the pump.

Peristaltic Tube Monitoring and Control:

The peristaltic pumping action creates a tube compression resulting in an elongation in peristaltic tubes as they pump fluid material. The elongation in the peristaltic tube is measured by a motor encoder and the motor provides programmable motor torque to the exiting tube. The tube compression and elongation provides the pump system with a tube pumping signature. Stepper, servo or negator motors can be used interchangeably in the design. The use of Lexium motors works well. A thin film sensor can be use to monitor the pressure used on the peristaltic tubing by the rollers. The thin film would be installed on the fixed part of the pressure shoe between the tubing and surface of the pressure shoe to monitor pressure and wear characteristics.

DESCRIPTION OF THE FIGURES

Illustrations are now presented to aid in understanding features of the present invention:

FIG. 1 shows a prior art peristaltic pump.

FIG. 2 shows an embodiment of the present invention attached to the pump of FIG. 1

FIG. 3 shows the embodiment of FIG. 2 with tubing installed.

FIG. 4 shows “Y” type of prior art peristaltic sets offered by Watson Marlow.

FIG. 5 shows prior art stretched “Y” tubing set over fixed posts.

FIG. 6 shows prior art adjustable inlet and outlet tube clamps.

FIG. 7 shows a prior art Watson-Marlow 505L type pump uses peristaltic pressure shoes.

FIG. 8 indicates the uneven wear that exhibited by using prior art offset shoes.

FIG. 9 shows prior art Flexicon type pump shoes that are hinged from the tube input side with both shoes going in the same direction.

FIG. 10 is a prior art shoe that exists with the 313 Watson-Marlow pump which is with a fixed curvature.

FIG. 11 is a perspective top view of an embodiment of the present invention.

FIG. 12 shows an embodiment of a tube holding mechanism.

FIG. 13 shows the set of six offset rollers where one set is offset by 30 degrees.

FIG. 14 shows a Watson-Marlow 313 pump head with the input lower holder pushed down manually with a screwdriver.

FIG. 15 shows a holding roller mechanism.

FIG. 16 shows a holding roller.

FIG. 17 shows a thin-film sensor on a pressure shoe.

FIG. 18 shows a tubing holder output motor and shaft encoder.

Several drawings and illustrations have been presented. The scope of the present invention is not limited to what is shown in the figures.

DESCRIPTION OF THE INVENTION

The present invention relates to a smart peristaltic pump which allows users to monitor pump motion as well as peristaltic tube health.
Turning to FIG. 1, a prior art peristaltic pump can be seen in a top-down perspective view. The pump body 100 supports a series of rollers 200 through which tubing is threaded. Successive compression of the tubing between the rollers 2 and a shoe cause fluid to be pumped through the device.
FIG. 2 shows a possible embodiment of the present invention in the pump of FIG. 1 without any tubing. A spring steel tube holder 500 can be installed on part 300 of the frame at both the input and output sides of the pump. FIG. 2 shows installation with a screw 600; however, any fastening means is within the scope of the present invention. The tube holder 500 can have a elongated slot 400 on each side for, in this case, two tubes. The tube-holder 500 can be concave upward in a preferred configuration; however, any other configuration is within the scope of the present invention. Embodiments of the present invention can have one, or any number of slots or other holding means for any number of tubes.
FIG. 3 shows the embodiment of FIG. 2 with two tubes 800 installed. In this particular example, a larger tube 800 has been inserted 1000 over a smaller tube 900 at the slot 400 in the holder 500. This is completely optional and for convenience. Single tubes of constant OD, or any number of tube size changes are within the scope of the present invention. In any case, the input and output tube holders 500 function as previously described to cause an tremendous increase in the performance and accuracy of the peristaltic pump.
A tube holder has been designed that easily holds peristaltic tubing without reducing the tube ID and can use a small or longer section of a second tube that can be bonded to the outside diameter of the pump tube. These tubes allow the peristaltic tube to be easily loaded into the pump and can be used with the tension devices. The present invention provides a spring loaded input and output tube holder for peristaltic pump tubing that will provide a tension while holding the tubing in an elongated position. The tube holder provides for a constant tension on the tubing without allowing a backward slipping.
A particular embodiment of the present invention is a tube holding device for a peristaltic pump that allows for elongation of peristaltic pump tubing without letting the tubing move backward that includes a frame holding a peristaltic pump, a pair of substantially cylindrical roller gears mounted on the frame, the roller gears having longitudinal teeth or being knurled, and positioned to cooperate with the peristaltic pump by clamping a peristaltic pump tube between them. At least one of said roller gears can be attached to a negator spring located in a string pot where the negator spring assists in providing force between said roller gears for small tubing. The device can have a tube-holding member attached to the frame where the tube-holding member is concave to cause the tubing to center on the roller gears.
In this embodiment, located on two ⅛ 316 inch shoulder screws, can be two roller clutches, stock drive parts S99NH3-URCo204. Delrin spacers to Dremmel standard sanding discs to complete the assembly. The distance between the two rollers allow the tubing to elongate, but not move backward toward the peristaltic rollers. Laboratory tests show that it takes approximately three cycles to elongate the silicon tubing. The tubing is held in this position until the operator opens the pump. This is shown in FIG. 7. The configuration can be in the vertical direction or can be in the horizontal direction as shown in FIG. 8.
The configuration shown in FIG. 8 has been tested in the laboratory, and the settling time for peristaltic tubing can be directly seen in the graph, FIG. 9. The extension of the peristaltic tube requires approximately three pump cycles. Data was taken for 50 pump cycles after the “y” configuration, and holding system for each system was primed. The corresponding fluid weights were recorded using a Sartoris BP 121 S 4 place scale for each volume of water dispensed. The data using the “load & go” breadboard hardware has a faster settling time compensating for tubing elongation.
The “held” data represents the gear rollers compensating for each cycle of tube extrusion. The “free” data represents the “y” tubing mounted on posts. Peristaltic pumps can take advantage of using the holding device defined in the patent application. The drawing below is a prototype design with the holding gear elements. There are two separate holding mechanisms at the input and exit of the peristaltic pump due to the fact that the 505L peristaltic pump has offset pressure shoes that minimizes pulsating fluid flow.

Input Tube Holding

There are two methods of holding the input peristaltic tubing. The first method uses a set of “V” holders with the pressure between the “V” holders defined as the force exhibited by a spring or motor. The second method uses a motor to hold an input roller impeding the tubing from entering the pump.
For V-holders, the lower “V” is moved upward by programmable motor torque against the input tubing which is pushed against a fixed upper “V” holder to secure the tubing entering the pump. A rack mechanism coupled to a gear is used to provide programmable motor torque to the lower “V.” The upper “V” is fixed to the top shoe and is positioned with the shoe. The “V” position can be moved to the lower position by using the motor to move to the position. The motor is programmed from a torque mode of operation to a down direction position value which is in the opposite direction. The open position is used to load tubing or for an index of tubing into the pump. The opening of the holders is the mechanism that allows indexing of a tube to compensate for peristaltic wear.
FIG. 12 shows a tube holding mechanism. The tubes enter the pump through the open sections and then are securely held using the upper and lower “v” holders. The rack gear can be seen in the open hole and the pinion and gears are not shown. The motor can be replaced with springs where the indexing of tubing would be completed using a manual mechanism. The spring holding force could be removed with either a manual or solenoid operation.
The input tubing can also be held by input rollers similar in nature to the output rollers secured in position by a motor or brake type system. The roller bearings are not of the clutch one-direction type, but conventional bearings. The motor can hold the tube and then be put into motion from the stopped position to feeding the tubing into the pump in a controlled fashion for indexing. A motor can be used to hold the tubing and meter the tubing into the pump. A Lexium 17 motor has been used to hold the tubing rollers with less than 50% holding current for a Watson-Marlow Marprene 3.2 ID bore 2.4 mm set of tubes. The motor direction can also be rotated so that the motor encoder meters the tubing into the peristaltic pump. The motor in this experiment can be replaced with an electrical break that would release its holding. A signal indicating an index is needed is based on wear conditions, a fluid dispense weight scale determination or a thin film pressure sensor

Peristaltic Pump Rollers and Pressure Shoe

The “smart peristaltic pump” of the present invention has a fixed curvature shoe that has been designed to work with a four or six roller offset roller design such as seen in the six roller design pictured in FIG. 13. FIG. 13 shows the set of six offset rollers where one set is offset by approximately 30 degrees.
Different pressure shoes are used for 2.4 mm or 1.6 mm wall peristaltic tubes as the radius of the curvature for the pressure shoe is different for each peristaltic tube wall size. The shoe design has been developed for a minimum of four rollers as the fixed shoe must always have two of the offset rollers in the compression region of the pressure shoe. A six roller system has rollers that are approximately 60 degrees apart in order to phase these rollers to a second set of rollers either 45 or 30 degrees out of phase with the front rollers.
Two peristaltic tubes are used in the front and back portion of the fixed shoe and have been combined in the downstream fluid path using a “Y” tube combiner. This phasing of front and back rollers provide minimal pulsations to the output when the tube outputs are combined. The tubes can be independent and not combined. The fixed shoe angular position where a primary roller is providing a tube compression needs to be at least 90 degrees for a four roller system. A preferred embodiment uses an approximately 100 degree fixed compression angle which compensates for tolerance and assures the roller requirement is met. The upper surface of the curvature needs to be machined so that it does not impede the tube indexing through the pump as the tube is compression by the peristaltic rollers. This force provides the motion to move the pump tubing during an index. Output roller torque and tube displacement can be monitored using the motor encoder associated with the output holding rollers.
The primary peristaltic pump rollers are controlled and move the tube through the fixed pressure shoe without opening the shoe during the index. Peristaltic tubes that have adequate stiffness will easily move through the output holding rollers but other tubes need to have a forward moving torque applied. Any indexing design with motors can be electronically geared. The minimum case is where a peristaltic pump releases its input tube holding and allows the primary rollers to index the tube through the system without the use of output rollers. Shown in FIG. 14 is a Watson-Marlow 313 pump head with the input lower holder pushed down manually with a screwdriver.
Peristaltic tube compression can be measured by using a thin film sensor such as the devices made by Measuring Systems, located in Hampton, Va. The use of a piezoelectric film or similar sensor allows the tube compression to be measured continually as the rollers impact the tube and then to the sensor on the opposite side of the tube between the tube and pressure shoe. This sensor can also be used to trigger an index based on tube wear and provides a means to assure the system is working properly.

Tube Output Holding

The tube exits the peristaltic pump into two rollers that have bearings that move only in one direction and secure the pump tubing from moving back into the pump after elongation. The output lower roller has torque applied using a Lexium series 17 motor to provide a pulling action for tubes and control the tubing during elongation and indexing. The motor has an encoder which provides an elongation signature for each tube and chemistry being pumped along with metering the index. It is necessary to make sure that the smaller peristaltic tubes, after elongation or having been indexed, have moved into the rollers assuring that the tubes are secured and monitored. The motor has programmable torque applied to the lower roller so that all of the tubes can be controlled. The torque can be modified dynamically by software for any torque between 0-100%.
Motor electronic gearing can also motors to be put into position mode and meter the indexed tubing. The holding rollers can minimize the downward holding force from the user roller using springs or another mechanism. A motor and shaft encoder is shown in FIG. 18. Experimentation with numerous roller designs including a sharp knurled surface has found that the staircase design works best with the system. FIG. 15 shows the cuts of the output rollers. One-direction bearings which are pressed into a brass gear and then pressed into a hard coated sleeve that has a staircase cut on the outside surface. This type of roller sleeve can be machined or can be an aluminum extrusion. Both can be hard-coated for wear characteristics. There is one roller on the bottom and a second one above that have the roller cuts and directional bearings incorporated. Springs are used to provide the holding force between the two rollers to the output roller tubes. An embodiment uses one continuous roller for both tubes. FIG. 16 shows a roller with a staircase design.

Tube Indexing

Peristaltic tube wear or spallation takes place as the tubing is compressed by the primary rollers and is based on the tubing being used. The Gore Sta-Pure peristaltic tubing exhibits minimal elongation and wear resistance. This tubing is very expensive and with the advancement of automatic indexing the overall dispensing costs can be lowered using conventional peristaltic tubes. The amount of wear is also based on the chemistry being pumped and the makeup of particles in the fluid stream. Where fluid stream particles are measured, the indexing of the peristaltic tube minimizes the amount of particles impacted into the tubing walls during the tube compressions.
The minimum indexing configuration is where a peristaltic pump can release the input tube holding and the primary rollers move the tubing through the pump. It should be noted that the index can be moved upstream by using a reverse of the primary rollers. The use of output rollers to hold the peristaltic tubing has been shown to be equivalent or improve accuracy especially where a drip retention is used to move the fluid back into the tube or nozzle. Drip retention is beneficial when the tubing needs to be moved in a robotic motion where the fluid is retained in the tubing. In tubing that requires re-stretching after use as stated by Watson-Marlow, the tube holding rollers take into consideration elongation as it results. The use of a motor assures that the tubing advances into the rollers and the motor encoders monitor the tube elongation and provide for metering the tubing during an index. The Watson-Marlow literature states that their tubing lasts longer avoiding tubing changes. The use of “y” connectors and fixed tube holders does not anticipate the use of tube indexing by releasing the tube input holding power with the primary rollers and pressure shoe locked in position providing a forward driving force to the peristaltic tubing.
Watson-Marlow states that: “Bioprene lasts at least ten times as long as other tubing materials thereby reducing stoppages for tube changes.” This technology reduces the overall production costs as the tube indexing is part of the overall dispensing process and can be done on demand without opening the tubing system.
The Flexicon peristaltic pump does not need indexing as the pump uses either a “y” holder or fixed tube holders that are secured with the top pressure shoe. The Masterflex pump has the tube holders built in the lifting pressure shoe mechanism and again does not need indexing.
The use of motor encoders for monitoring the elongation does not provide a good mechanism for the determining the tubing wear, but the use of a thin film sensor incorporated into the pressure shoe provides for automated tubing wear monitoring and triggering of an index. FIG. 17 shows such a sensor in a shoe.
Several descriptions an illustrations have been provided to aid in understanding the present invention. One of skill in the art will realize that numerous changes and variations are possible without departing from the spirit of the invention. Each of these changes and variations is within the scope of the present invention.

Claims

We claim:

1. A peristaltic pump system comprising:

a peristaltic pump body having a set of six main rollers that are approximately 60 degrees apart phased with a second set of rollers approximately 30 degrees out of phase with the main rollers;

a peristaltic pump input tubing holder including a lower and upper V-shaped member, the lower V-shaped member being movable upward by programmable motor torque against the input tubing which is pushed against the fixed upper V-shaped member to secure the tubing entering the pump;

a pair of peristaltic pump pressure shoes using an approximately 100 degree fixed compression angle, each having an upper surface of curvature machined so that it does not impede peristaltic pump tubing indexing through the pump as the peristaltic pump tube is compressed;

a peristaltic pump output tubing holder having two output rollers with bearings adapted to move only in one direction whereby, the peristaltic pump tubing is prevented from moving back into the pump after elongation, said output rollers each having a stair-stepped surface.

2. The peristaltic pump system of claim 1 wherein at least one of said pressure shoes is equipped with a thin-film sensor to measure pressure on the peristaltic pump tubing and wear.

3. The peristaltic pump system of claim 1 further comprising a motor positioned to assure that the peristaltic pump tubing advances into the rollers, said motor having an encoder that monitors the tube elongation and allows metering the tubing during indexing.

4. A peristaltic pump system comprising:

a peristaltic pump body having a set of four main rollers that are approximately 690 degrees apart phased with a second set of rollers approximately 45 degrees out of phase with the main rollers;

5. The peristaltic pump system of claim 4 wherein at least one of said pressure shoes is equipped with a thin-film sensor to measure pressure on the peristaltic pump tubing and wear.

6. The peristaltic pump system of claim 4 further comprising a motor positioned to assure that the peristaltic pump tubing advances into the rollers, said motor having an encoder that monitors the tube elongation and allows metering the tubing during indexing.

7. A peristaltic pump system comprising:

a peristaltic pump body having a set of four or six main rollers that are approximately 60 or 90 degrees apart phased with a second set of rollers approximately 30 or 45 degrees out of phase with the main rollers;

a pair of peristaltic pump pressure shoes using an approximately 100 degree fixed compression angle, each having an upper surface of curvature machined so that it does not impede peristaltic pump tubing indexing through the pump as the peristaltic pump tube is compressed, at least one of these shoes having a thin-film pressure sensor.

8. The peristaltic pump system of claim 7 further comprising a peristaltic pump output tubing holder having two output rollers with bearings adapted to move only in one direction whereby, the peristaltic pump tubing is prevented from moving back into the pump after elongation, said output rollers each having a stair-stepped surface.

9. The peristaltic pump system of claim 8 further comprising a motor positioned to assure that the peristaltic pump tubing advances into the rollers, said motor having an encoder that monitors the tube elongation and allows metering the tubing during indexing.