GB2102503A - Peristaltic fluid-machines - Google Patents

Abstract

In a pump for a liquid compensation and correction is provided for the varying liquid flow in a pumping tube 7 over an angle of rotation of a rotor (1) between two mutually adjacent tube- compressing rollers (2) thereof. Indicating means are provided to indicate to control means the rotation position of the rotor at initiation of operation and adjustment means are provided in the control means to adjust the extent of rotation of the rotor for a desired quantity of pickup and/or dispensing of the liquid to take account of the initial position of the rotor. The indicating means may comprise means (13) to project a light beam (12) onto the rotor and a sensor incorporated in the beam- projecting means to detect markings (1b) on the rotor impinged on by the beam. <IMAGE>

Description

SPECIFICATION Peristaltic liquid pickup and/or dispensing means The invention relates to peristaltic pumps and particularly though not exclusively to peristaltic pumps of the kind described in the specifications of our Applications 8015274 and 8114119.

In a peristaltic pump, spaced apart rollers are caused to pass in succession over a length of flexible tube, each roller occluding the bore of the tube in turn thereby to cause a flow of liquid in the tube in the direction in which the rollers pass over the tube. Each roller causes movement along the tube of a small aliquot of liquid and the flexibility of the wall of the tube causes the tube to revert to its original shape after the roller has passed thereover, thereby to suck liquid forward to fill the tube behind the roller. Usually the rollers are provided at the periphery of a rotor with their axes extending parallel to the axis of rotation of the rotor, the tube preferably being mounted on a shoe which is located with respect to a stator of the pump.

Peristaltic pumps exhibit variations in pumped volumes in the lower volume ranges for the same amount of rotation of the rotor due to the push-pull effect of the rollers on the liquid in the tube. Thus, when the roller first occludes the bore of the tube by compressing the tube against the stator, the action of the roller is to push fluid already in the tube in a forward direction. This is the period of maximum pumping. As the roller moves along the tube, the portion of the tube immediately behind the roller returns to its original shape and by so doing pulls more fluid along the tube from a reservoir from which the pump is pumping. The efficiency of this period of peristaltic action is dependent mainly on the recovery rate of the tube but is less efficient than the pushing action referred to above.As the roller continues to move over the tube, the volume of pushed fluid is continuously decreasing while the volume of pulled fluid is continuously increasing and the overall efficiency of fluid flow is therefore continuously decreasing during this further stage. When the roller ceases to act upon the tube, no fluid is being pushed by the roller and the action of the pump is therefore purely a pulling action and this is the period of least efficiency. The next following roller of the rotor must occlude the tube bore before the preceding roller ceases to act upon the tube otherwise peristalsis is lost completely. Once said next following roller has occluded the bore of the tube, the peristaltic efficiency returns to a maximum since a new cycle of operations has then started.

Thus if fluid flow is plotted against rotor rotation, a generally saw-tooth characteristic would be produced with maximum flow at the start of a roller's operation and minimum flow at the end of its operation.

However, the change from minimum to maximum efficiency is not abrupt in practice since the pushed flow at the start of a roller's operation offsets the low pulled flow at the end of the preceding roller's operation since the angle of the arc between a roller and the next following roller is smaller than the angle of the arc over which each roller acts upon the tube and the characteristic obtained by plotting flow against rotor rotation is therefore an undulating rather than a jagged characteristic.

According to the invention, in peristaltic liquid pickup and/or dispensing means, means are provided to indicate to control means the position of rotation of a rotor of the pump and said control means includes means to adjust the extent of rotation of the rotor for a desired pickup and/or dispensing of liquid by the pump to take account of said position of rotation at initiation of operation of the pump.

Said means may be a physical sensor such as a beam projected onto the rotor and a sensor to detect markings on the rotor impinged on by the beam or may be electronic, such as a counter counting stepping pulses supplied to the motor.

The invention proceeds from the realisation that all the changes from maximum to minimum flow rate are contained within and act upon a segment of fluid contained in the tube between a roller and a next following roller. The changes occur during the period taken for the next following roller to reach the position of the preceding roller. The varying but reproducable flow pattern of peristalsis is dependent upon the design of the pump. Thus if the dispensed or picked up volume comprises one complete fluid segment precision will be excellent in peristalsis terms since a mean volume will be delivered which takes account of both the pull and push effects. Likewise, precision will be excellent if the dispensed or picked up volume is a whole number multiple of complete segment volumes.

Providing a large number of rollers, that is to say positioning the rollers close together improves the precision of dispensed or picked up volumes but the flow rate will be reduced since the tube will only partially recover its normal shape before it is again compressed by the next following roller. In the limiting case, if a rotor with a smooth circumference was used, such a rotor can be considered to have an infinite number of rollers, a zero flow rate would result since the tube would never recover its shape and thus no fluid would be dispensed or picked up.

If the dispensed or picked up volume is less than that corresponding to one segment then, due to the saw-tooth characteristic, a volume otherthan that required will be dispensed or picked up.

Obviously it is an undesirable limitation that a pump can only dispense volumes which correspond to the volume of a segment of the tube between two rollers or whole number multiples of such a segment volume although the larger the volume dispensed or picked up the smaller will be the percentage error since error will only occur in the initial part segment and/or the final part segment dispensed.

The further the rollers are spaced apart, this is to say the lower the number of rollers provided on the rotor, the greater the saw-tooth effect particularly for smaller tube sizes and the greater the minimum volume which can be pumped with precision.

The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which: Figure 1 is a plan view of peristaltic liquid pickup and/or dispensing means; Figure 2 is a fragmentary view taken in the direction of arrow II of Figure 1; Figure 3 shows a plot of volume dispensed against rotor rotation in peristaltic liquid pickup and/or dispensing means; Figure 4 shows graphically the correlation between motor steps, segments of tube and keyboard volumes; and Figure 5 shows graphically the variation in volume pumped by a peristaltic liquid pickup and/or dispensing means over one segment of operation.

Referring to the drawings, a peristaltic pump has a rotor 1 with rollers 2, in the example shown six rollers 2, a stator 3 pivotally mounted about a pivot 4 and supporting a shoe 5 having an arcuate face 6 with a tube 7 secured by adhesive in a groove in the arcuate face 6. The shoe 5 is located by its face 8 against a face 9 of the stator 3. Rotation of the rotor 1 will cause the rollers 2 sequentially to occlude the bore of the tube 7 and to cause liquid to be dispensed from the end of the tube towards which the rollers move while in engagement with the tube. A cover 10 through which extends a shaft connecting the rotor 1 to an electric stepping motor (notshown) has an aperture 11, Figure 2, through which a beam indicatedati2 passesfrom asource 13to intersect the bottom flange la of the rotor 1.The bottom flange la has cut-outs 16 or other markings thereon which modulate the beam 12, the modulated beam being sensed by a sensor built into the source 13 such that an indication in the form of a strobe pulse will be given by the sensor each time one of the cut-outs or markings lb passes through the beam 12. By suitably iocating the source and sensor 13 at an angle oto a line 14 joining the pivot 4 to the axis of the rotor 10 and with the knowledge of the number of rotors on the roller, an indication can be caused to be given by the sensor 13 when one of the rollers, as shown the roller 2a, is in a centre position of engagement with the tube 7 located on the arcuate face 6 of the shoe 5. The angle swill of course vary according to the number of rollers 2 provided on the rotor.

With the sensor picking up a roller marker it when another roller is approximately perpendicular to the stator 3, the programme will operate on either side of the marker pulse, that is to say push, marker, pull, push, marker, pull etc. Figure 3 shows, in the upper part, the varying characteristic V of volume pumped plotted against rotor rotation and having a mean value M and in the lower part pulses 15 received from the sensor 13 for the rollers 2a and 2ffor one rotation of the rotor 1. It will be seen that the pulses 15 approximate to the positions at which the mean volume M crosses the characteristic V. An advantage of this is that the change from low delivery to high delivery as a roller starts its operation is easier to programme between pulses than if this change was aligned with the marker pulse 15.A microprocessor unit in the control means can make corrections caused by alignment errors but these will occur in the mean volume section rather than the peak volume section thereby reducing potential errors.

In one example, using a six roller rotor and a one by one millimeter tube, an uncalibrated figure of 42 u litres was dispensed per revolution of the rotor. For each arc of operation between adjacent rollers therefor, hereinafter referred to as one segment, 7 a litres would be dispensed. If the stepping motor driving the rotor 1 had 200 steps per revolution, there would be 200 divided by 6, that is to say 33.33 steps per segment. 1 11 Litre therefore corresponds to 33.33 divided by 7, that is to say 4.8 steps or 5 steps equals 42 times 5 divided by 200 = 1.051l litres. This is plotted in Figure 4 where a first segment is indicated at X and a second segment is indicated at Y.

The actual delivered volumes would be different because the system is not calibrated but this is not relevant to the programming procedure.

One segment S of operation is indicated in Figure 5 plotted against volume, the result being a characteristic in the form of a modified saw-tooth which will be repeated for each of the other five segments and further repeated after the rotor has passed back through a zero position to commence a further rotation.

If the volume dispensed during the segment S of operation is, as suggested above 7 R litres, the area under the graph can be divided into seven approximately equal volumes I - Vll. It will be seen however that the number of motor steps necessary to dispense these 1 u litre volumes is not equal, that is to say the first volume I requires 7 steps, the second volume II approximately 11 steps, the third volume Ill approximately 3 steps, the fourth volume IV approximately 2 steps, the fifth volume V 3 steps, the sixth volume VI 3 steps and the seventh volume VII 4 steps.Once the pattern of variation over the segment S is known, the microprocessor unit can be programmed to control the motor to rotate the rotor 1 by the required number of motor steps for a desired volume to be dispensed so long as the programmer is advised of the position which the rotor 1, within the segment S, was in at the time that the delivery is commenced.

For example, if the requirement is to deliver 12 litres, the microprocessor unit, starting from a position at which a strobe pulse was received from the sensor 13 would effect movement of the rotor 1 through twelve segments, the twelve segments having the number of steps each as follows: 7+11+3+2+3+3+4+7+11+3+2+3 In this example the strobe pulse must be received at the beginning of dispensing, that is to say one of the rollers must be stationary in the mid-position with respect to the stator, that is to say the position at which roller 2a is shown in Figure 1 when the dispense control is operated. The microprocessor unit will know this condition because of the logic output from the strobe sensor 13.Thus the microprocessor unit must remember its stopped position in order to operate under conditions where a roller is not aligned with the stator at the end of the previous dispensing operation since this will be the start of the subsequent dispensing operation.

In a second example, if the microprocessor unit knows that the last function which it performed comprised 7 steps then from the sequence 7 + 11 + 3 + 2 + 3 + 3 + 4 of volumes I - VII, it knows that its next volume will be 11 steps and thus if required to deliver S 51l litres, it will step the motor by 11 + 3 + 2 + 3 + 3 steps giving five volumes and thus the required 5 R litres.

In a further example, if it is required to deliver 7 ij litres and the microprocessor unit knows that the last two operations which it performed were for 3 steps and 2 steps, it will cause the rotor 1 to rotate by 3 + 3 + 4 steps, it will then receive a strobe pulse and continue to cause the rotor to rotate by 7 + 11 + 3 + 2 steps to give the required 7 F litres. The strobe pulse signal occurring intermediate the ends of the operation confirms that the start position was correct.

Manually moving the rotor will upset the dispensing sequence up to receipt of a strobe pulse signal but operations after such receipt will be correct. Timing or making a small delivery before the required test or operational delivery will reset the microprocessor unit so that it knows where the rotor is and thus after any manual handling of a pump, a priming step sufficiently long to include a strobe pulse should be effected.

Preferably the microprocessor unit would be provided with an alarm which would be operated if there had been manual adjustments and thus the actual rotor position and the rotor position recorded in the microprocessor unit were not in agreement.

As set out in our earlier specifications 8015274 and 8114119, the peristaltic pump is precise rather than accurate and requires calibration before use. Since the compensation for the variation within one segment relies on the fact that the variation pattern within each segment is constant for a particular tube type, it is independent of calibration changes. Thus, when the system is calibrated, the pattern remains the same and each F litre segment will still deliver more or less than 1 Il litre according to the calibration. The effect of calibration is to increase or decrease the total number of F litre segments in order to deliver the correct amount of fluid.

The examples given above concern a six roller rotor 1 but it is suggested that a five roller rotor 1 would be more advantageous particularly with a 200 steps per revolution motor since one segment then comprises 40 steps and, for a given tube, the volume output per revolution of the rotor will also be higher since the number of rotor rollers has been reduced by one.

Claims (7)

1. Peristaltic liquid pickup and/or dispensing means including a pump having a rotor with a plurality of rollers thereon which sequentially engage a tube in operation to cause liquid to move through the tube and including compensation means to take account of variation in flow of liquid during rotation of the rotor through an arc of rotation subtended by the angle between one of the rollers and a next following rotor.

2. Peristaltic liquid pickup and/or dispensing means according to claim 1, in which said compensation means comprises indicating means to indicate to control means the position of rotation of the rotor at initiation of operation and adjustment means in the control means to adjust the extent of rotation of the rotor effected for a desired quantity of pickup and/or dispensing of liquid to take account of said position of the rotor at initiation of operation.

3. Peristaltic liquid pickup and/or dispensing means according to claim 2, in which said indicating means is a physical sensor.

4. Peristaltic liquid pickup and/or dispensing means according to claim 3, in which said physical sensor is a beam projected onto the rotor and a sensor to detect markings on the rotor impinged on by the beam.

5. Peristaltic liquid pickup and/or dispensing means according to claim 2, in which the said indicating means is an electronic sensor.

6. Peristaltic liquid pickup and/or dispensing means according to claim 5, in which said electronic sensor is a counter counting stepping pulses supplied to a motor which drives the rotor.

7. Peristaltic liquid pickup and/or dispensing means substantially as hereinbefore described and illustrated with reference to the accompanying drawings.