GB2085091A

GB2085091A - Peristaltic Fluid-machines

Info

Publication number: GB2085091A
Application number: GB8129221A
Authority: GB
Original assignee: Terumo Corp
Current assignee: Terumo Corp
Priority date: 1980-09-27
Filing date: 1981-09-28
Publication date: 1982-04-21
Also published as: JPH0157584B2; FR2490958A1; FR2490958B1; IT1138642B; GB2085091B; DE3138478C2; JPS5759539A; IT8124172A0; DE3138478A1

Abstract

In a method of dispensing a medical liquid intermittently with the aid of a peristaltic pump, which may be a conventional one of the roller type, Fig. 1 (not shown), the pump is operated such that irrespective of the pumping rhythm the total quantity of liquid displaced per period of intermittent pumping is constant. The pump may be driven by an electric motor, which may be either a conventional DC one or a stepping one. Controlling means for each kind of motor are described with reference to Figs. 3 and 4 (not shown).

Description

SPECIFICATION Method and Apparatus for Intermittently Dispensing Medical Solution in Minute Doses This invention relates to a method and apparatus for intermittently dispensing a medical solution in minute doses over a long period of time by means of a peristaltic pump.

Apparatus for administering medical solutions such as hormone agents and chemotherapeutic agents in minute doses over a long period of time is well known. Such apparatus is now portable using a battery cell as a power source in order that treatment can be effectively continued without disturbing the daily living of a patient. In general, the apparatus dispenses medical solutions intermittently and not continuously, primarily because it is necessary for prolonged use to minimize current consumption of battery cells and to operate the drive section under optimum conditions. Another reason is that continuous feeding results in an overcharge of medical solutions which would adversely affect the patient. Also an extremely complicated mechanism is required to continuously feed medical solutions in minute doses.For example, in the case of insulin administration, a daily dose of 10 ml of insulin solution is adminstered little by little at intervals of 1 5 minutes. It is substantially impossible to feed this minute volume continuously. Most administration apparatus thus uses a peristaltic pump which is intermittently actuated to dispense a medical solution in minute doses over a long period of time.

Peristaltic pumps feed liquid through a tube by locally applying pressure to the tube to clamp the tube and progressively moving the clamping point toward the discharge end. The clamping of the tube is released when the clamping point reaches the discharge end. This operation is cyclically repeated. Inconveniently, since the clamped tube returns to cylindrical shape immediately after the release of clamping, liquid supply is temporarily interrupted at this point. Counter flow occurs at the discharge end. Differently stated, pulsation occurs in liquid supply. A variety of methods have heretofore been proposed to prevent such pulsation. All the prior methods tried to minimize the influence of pulsation by approximating the flow of liquid to be dispensed to a steady flow.

Since pulsation inherently occurs in peristaltic pumps, apparatus for dispensing medical solutions in minute doses over a long period of time using such peristaltic pumps has the disadvantage that a substantial error occurs in the dose per single dispensing if the pulsation cycle is improperly selected. Such an error in the dose will have an undesired influence on the patient. This error is not significant in relation to the intended dose if the time of single dispensing is sufficiently longer than the period of pulsation. However, an errror in the dispensing dose will widely deviate from the desired accuracy if the time of single dispensing is shorter or a few times longer than the period of pulsation. If pump operation is continuous, error in the dispensing dose due to pulsation is soon compensated for.On the contrary, since a long time interval is set between one dispensing and the subsequent dispensing in the case of intermittent operation, an error in the dispensing dose is not compensated for until subsequent dispensing begins. In intermittent operation, variation in a single dispensing dose due to pulsation cannot be avoided.

Pulsation occurs upon release of clamping of the tube immediately after the point of clamping has reached the discharge end. The amount of a solution discharged by the movement of a clamping point from the suction end to the discharge end is always constant. Since the movement of a clamping point from the suction end to the discharge end is accurately repeated, the amount of a solution fed between the start of movement of a clamping point from a certain position and the end of movement at the initial position is also constant. That is, the amount of a solution discharged during one period of pulsation is constant. According to the invention the dose per single intermittent dispensing is set to an integral multiple of one period of pulsation, successive doses are then equal irrespective of pulsation occurring in a peristaltic pump.In the prior art, the dispensing dose was not precisely set and it was difficult to adjust the dose to a value desired for a particular user. Recently, input devices having a digital electronic control circuit built therein were developed in which a numerical value representative of a desired dose can be input by the user. In such devices, an input value in the form of an integer can be set. With a dispensing apparatus combined with a digital control device, the dispensing dose is changed in proportion to the set value. Accordingly, the user can easily set a desired value. Another advantage is an increased accuracy due to digital control. In such controlled dispensing apparatus, all the settable dispensing doses are multiples of the minimum unit. The dose per single intermittent dispensing can be constant by using the minimum unit corresponding to one period of pulsation.

According to a first aspect of the present invention, there is provided a method for intermittently dispensing a medical solution in minute doses by means of a peristaltic dispensing unit, wherein the dose per single intermittent dispensing is set to be equal to a dose corresponding to a period which is an integral multiple of the pulsation period of the peristaltic dispensing unit whereby the single dose is constant independent of the pulsation. Preferably, an accumulative dose per unit time is variable in accordance with the therapy for and the symptom of a patient. The accumulative dose may be varied by changing the integral multiple of the pulsation period and/or the time interval of intermittent dispensing.

According to a second aspect of the present invention, there is provided an apparatus for intermittently dispensing a medical solution in minute doses over a long period of time by the intermittent operation of a peristaltic pump, the apparatus including a motor for driving the peristaltic pump, and control means for intermittently actuating the motor for a time corresponding to an integral multiple of the pulsation period of the peristaltic pump. The apparatus may also have means for selectively setting the integral multiple of the pulsation period of the peristaltic pump and/or means for selectively setting the time interval of actuating the motor, whereby an accumulative dose per unit time is selectively varied so as to meet particular therapy and symptom.

The peristaltic pump which can be used in the present invention may be any of roller, finger or other type. When a roller-type peristaltic pump is used, a rotor is fixedly secured on a rotatable drive shaft and a plurality of equally spaced-apart rollers are rotatably mounted on the rotor in a mutually symmetric relationship with respect to the drive shaft. The rotatable drive shaft may preferably be associated with a revolution detector for detecting the revolution of the shaft to develop.detection pulses in proportion to the detected number of revolutions. The preferred motor for driving the peristaltic pump is a stepping motor.

In the accompanying drawings: Fig. 1 is a schematic illustration of a roller-type peristaltic pump; Fig. 2 is a diagram showing the waveform of pulsation of the peristaltic pump; Fig. 3 is a block diagram of one embodiment of the present invention using a DC motor; and Fig. 4 is a block diagram of another embodiment of the present invention using a stepping motor.

Referring to.Fig. 1, a typical roller-type peristaltic pump is shown as comprising a rotable drive shaft 3, a rotor 1 fixedly secured on the shaft, and a plurality of, four in this embodiment, equally spaced-apart rollers 2 rotatably mounted on the rotor 1 in a mutual symmetric relationship with respect to the shaft 3. A stator 4 has a semicircular recess which is disposed concentric with the rotor. A tube 5 having an inlet connected to a source of medical solution and an outlet connected to a needle (not shown) extends between the rotor 1 and the stator 4. The tube 5 is tighly clamped at two or three points by rollers 2 abutting against the stator recess via the tube.

As the rotor 1 rotates, in the direction shown by an arrow, medical solution is fed in a dose defined in the tube 5 between the two adjacent points clamped by the rollers. A pulsating flow or peristaltic feed develops when the leading roller 2 is brought out of engagement with the stator 4 at the discharge end. Since four rollers are on the rotor 1 in this embodiment, pulsation occurs four times per revolution of the rotor 1. The symmetric arrangement of the rollers results in pulsating flows of the same waveform. The waveform of pulsating flow is shown in Fig. 2. When intermittent dispensing is carried out in equal.

sections of the pulsation period represented at t and t' according to the prior method, the amount or dose of solution dispensed varies each time under the influence of pulsation as understood from Fig. 2. According to the present invention, intermittent dispensing is carried out in a dose corresponding to one period of pulsation represented at TorT' or an integral multiple of one period. Then each dose is always kept to a predetermined dose over a long period of time.

A preferred embodiment of the present invention is illustrated in the block diagram of Fig.

3. The construction of the block diagram will be described in conjunction with its operation.

Numeral 8 is a roller-type peristaitic pump as shown in Fig. 1. The rotatable drive shaft of the pump rotor is connected to the final output shaft of a reduction gear 7 which has a primary input shaft connected to a DC motor 6. Rotation of the motor 6 causes the shaft to drive the pump 8.

Associated with the drive shaft of the pump 8 is a revolution detector 9 for detecting the revolution of the pump shaft to develop detection pulses in proportion to the number of revolutions. The revolution detector 9 may be a pulse encoder, for example.

Numeral 12 is a dose setting unit where the dose is set by means of a thumb wheel digital switch, for example, and the set value is developed as a BCD (binary-coded decimal) digital signal at the output. The dose setting unit 12 is electrically connected to a control circuit 11 in the form of a presettable down counter, for example. The control circuit 11 is electrically connected to a timer 13 for transmitting a preset signal to the control circuit 11 each time when intermittent dispensing is to be conducted.

Receiving the preset signal from the timer 13, the control circuit 11 fetches the BCD digital signal from the dose setting unit 12 into the counter to preset the content of the counter to the set value.

The counter is designed such that its "0" output delivers a drive signal to a motor drive circuit 10 to actuate the motor when the content of the counter has a value other than "0". Since the preset content of the counter is at the dose setting value, the "0" output of the counter delivers a motor drive signal with which the motor 6 starts rotating. In accordance with rotation of the motor, the revolution detector 9 generates detection pulses. A divider 14 having a frequency dividing ratio of 1/n is interconnected between the detector 9 and the control circuit 11 when the ratio of the pulsating number to the detection pulses is 1 :n. The divider 14 may be omitted when this ratio is 1:1.

The detection pulses from the divider 14 or directly from the revolution detector 9 are supplied to the count input of the presettable down counter 11. The counter 11 subtracts "1" from its content each time it receives one detection pulse. When the content of the counter 11 is eventually reduced to "0", the "0" output ceases to deliver a motor drive signal, thereby stopping the motor 6. The revolution detector 9 also ceases to generate a detection pulse so that the content of the counter is held at "O". As a result, the motor and hence, the peristaltic pump is kept stopped until the subsequent dispensing time. At the subsequent dispensing time, the timer 1 3 develops a preset signal at its output, and then the above-mentioned operation is repeated.

With the above arrangement, the count input of the presettable down counter 11 receives detection pulses at the points corresponding to the same positions on the waveforms of pulsation generated by the pump 8. Accordingly, the rollertype peristaltic pump 8 always starts and stops dispensing at the same positions on pulsation waveforms independent of the set value in the dose setting unit. The dose of the solution dispensed between the start and the stop of the pump 8 is always an integral multiple of the quantity of solution dispensed during one pulsation cycle, thereby eliminating any error due to pulsation. In the above-described embodiment, the minimum dose unit on the basis of which any desired dose is set is equal to the quantity of solution dispensed during one pulsation cycle.If the minimum dose unit is m times larger than the quantity of solution dispensed during one pulsation cycle, the divider 14 must have a dividing ratio of 1/nm wherein m is an integer of 2 or more.

Another embodiment of the present invention is shown in the block diagram of Fig. 4. The arrangement of Fig. 4 is similar to that of Fig. 3 except that the revolution detector 9 is omitted from the arrangement of Fig. 3 by replacing the conventional DC motor 6 by a stepping motor 6', and that a drive pulse generator 1 5 is additionally inserted. Unlike the conventional DC motor, the stepping motor requires a special driving circuit 10' because simply applying voltage is not effective to energize the stepping motor. Since the stepping motor rotates one step in response to one pulse received at its input the number of revolutions can be controlled on the basis of the number of input pulses.The driving pulse generator 1 5 generates pulses at a constant frequency when the content of the presettable down counter 11 is not "0", but stops pulse generation when the counter content is "O". The divider 14 divides the number of driving pulses and supplies the divided value to the count input of the counter 11.

Provided that the number of steps required for the stepping motor 6' to accomplish one revolution is P, the reduction ratio of the reduction gear 7 is Q, and the number of pulses developed per revolution of the peristaltic pump 8, is R, the divider 14 has a dividing ratio of R/PQ. Then, the minimum dose unit on the basis of which any desired dose is set in the dose setting unit 12 becomes equal to the quantity of solution dispensed during one pulsation cycle, thereby eliminating any variation or error in the dose due to pulsation as done in the first embodiment shown in Fig. 3.

Although the roller-type peristaltic pump is used in the above-described embodiments, the present invention is not limited thereto. Fingertype peristaltic pumps or other peristaltic pumps may also be equally used in the present invention as long as they can create pulsating flow in a cyclic manner.

As apparent from the foregoing, the dose of a medical solution per single intermittent dispensing can be kept at a desired fixed value over a long period of time according to the present invention. The dose can be selectively varied depending on the therapy for and the symptom of a patient. The control system is simple and reliable.

Claims

1. A method for intermittently dispensing a medical solution in minute doses by means of a peristaltic dispensing unit, wherein the dose per single intermittent dispensing is set to be equal to a dose corresponding to a period which is an integral multiple of the pulsation period of the peristaltic dispensing unit whereby the single dose is constant independent of the pulsation.

2. A method according to claim 1 wherein the accumulative dose per unit time is variable by changing the integral multiple of the pulsation period and/or the time interval of intermittent dispensing.

3. Apparatus for intermittently dispensing a medical solution in minute doses over a long period of time by the intermittent operation of a peristaltic pump, the apparatus including a motor for driving said peristaltic pump, and control means for intermittently actuating said motor for a time corresponding to an integral multiple of the pulsation period of said peristaltic pump.

4. Apparatus according to claim 3 having means for selectively setting the integral multiple of the pulsation period of said peristaltic pump and/or means for selectively setting the time interval of actuating said motor to drive said peristaltic pump whereby the accumulative dose per unit time is selectively variable.

5. Apparatus according to claim 4 wherein the peristaltic pump is a roller-type peristaltic pump which comprises a rotor fixedly secured on a rotatable drive shaft and a plurality of equally spaced-apart rollers mounted on the rotor in a mutually symmetric relationship with respect to the drive shaft.

6. Apparatus according to claim 3 or 4 wherein the peristaltic pump is a finger-type peristaltic pump.

7. Apparatus according to any one of claims 3 to 6 including a revolution detector associated with the rotatable drive shaft of said peristaltic pump for detecting the number of revolutions of the shaft to develop detection pulses in proportion to the detected number of revolutions.

8. Apparatus according to any one of claims 3 to 7, the motor for the peristaltic pump is a stepping motor.

9. A method for intermittently dispensing a medical solution in minute doses, the method being substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawings.

10. A method for intermittently dispensing a medical solution in minute doses, the method being substantially as hereinbefore described with reference to Fig. 4 of the accompanying drawings.

11. Apparatus for intermittently dispensing a medical solution in minute doses, the apparatus being substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawings.

12. Apparatus for intermittently dispensing a medical solution in minute doses, the apparatus being substantially as hereinbefore described with reference to Fig. 4 of the accomanying drawings.