WO1993018807A1

WO1993018807A1 - Liquid drug infusion pump control device

Info

Publication number: WO1993018807A1
Application number: PCT/FR1993/000297
Authority: WO
Inventors: Michael V. Wiernicki; Mark G. Scattergood
Original assignee: Laboratoire Aguettant
Priority date: 1992-03-24
Filing date: 1993-03-24
Publication date: 1993-09-30
Also published as: FR2689015B1; FR2689015A1; AU3758093A

Abstract

A device including a d.c. motor driving a screw (15) in a rotationally locked but freely translatable nut (16) secured to a plunger (7) and provided with an electrically conductive element (20) having, along its path on either side thereof, two hard contacts (22, 23) mounted on the motor power supply circuit for stopping the motion of the motor when one of them is contacted by the conductive element. Resilient members (10, 13, 14) are provided to allow further motion of the motor during its stopping phase after the conductive element (20) has contacted a hard contact and prevents further motion of the plunger (7). The device is useful for out-patient infusion therapy.

Description

DEVICE FOR CONTROLLING A LIQUID PERFUSION PUMP

MEDICAL

The present invention relates to a device for controlling a pump for infusion of medical liquids. The treatment of serious pathologies, such as cancer, very often involves intravenous infusions. If certain basic treatments are carried out in a hospital environment, continuity of care is more and more often carried out in the patient's home.

The effectiveness of the treatments being linked to the prescribed doses, to the number of drugs dispensed during the same treatment, and to the patient's receptivity according to his biological rhythm, it is necessary to have injection equipment which is reliable but also effective, that is to say, to dose, very precisely, determined quantities of liquids with flow rates varying over a very wide range.

Since the treatment is ambulatory, it is also desirable that the material be as compact and as light as possible so as not to disturb the patient.

Currently, the most common perfusion device uses a peristaltic pump which crushes a polymer or silicone tube to transport the liquid.

This system has the disadvantage of combining technical solutions of bulk and significant weight since:

- the crushing of the tube requires a large force which is exerted by a bulky and heavy roller system,

- the motor must be sized according to the crushing forces and is therefore of significant weight,

- the engine being largely dimensioned, its consumption is important, and its supply must be carried out by large cells or batteries.

All this is in contradiction with the ambulatory destination of a pump.

The object of the invention is to provide a device for controlling an infusion pump making it possible to meet the requirements of miniaturization, combining a low weight and size, while providing high precision. To set in motion the liquid to be perfused, it is advantageous to use a piston pump which makes it possible to obtain a very wide working range in terms of flow rate: from 1 to 12,000, to have high precision, optimize the size and weight of the pump, and offer maximum safety for the patient.

The device according to the invention comprises a direct current motor driving a screw engaged in a nut locked in rotation but free in translation, integral with the piston and on which is fixed an electrically conductive element on the path of which are arranged, on the and on the other side of the conductive element, two hard contacts mounted on the motor supply circuit and intended to stop the movement of the motor when the conductive element comes into contact with one of them, elastic means being designed to allow the movement of the engine to continue during its stopping phase, after the conductive element has arrived against a hard contact and prevents further movement of the piston.

The piston stroke is provided by the distance between the two hard contacts minus the thickness of the conductive element. The implementation of the hard contacts provides a high reproducibility of each movement of the piston, which results in high precision of the pump.

It should be noted that, when the conducting element reaches a hard contact, the movement of the piston is clearly stopped, without any risk of deterioration because the elastic means allow the movement of the motor to continue during its stopping phase. without driving the screw and therefore without driving the piston. The time corresponding to the engine stopping, from the moment when one of the hard contacts has received information, can be of the order of a quarter of a turn, while the stroke of the piston can correspond to several turns of the screw.

To this end, the drive screw is wedged on a disc on which is pressed, elastically and with the possibility of axial play, a pinion meshing with a pinion wedged on the output shaft of the motor.

The screw is therefore frictionally driven by the pinion meshing with the pinion wedged on the output shaft of the motor, so that when the movement of the piston is blocked by element support conductor against hard contact, the disc-pinion assembly subjected to an axial elastic pressure acts like a torque limiter.

According to another characteristic of the invention, Técrou is placed inside a jacket integral with the piston, open at its end opposite to that fitted with the piston and in which Técrou is maintained in elastic pressure, under the action of a spring pushing it towards the end of the jacket fitted with the piston.

This second spring also participates, during the period of return of the piston, to achieve a damping when the engine stops in order to avoid damaging jolts for all the constituent parts of the device.

According to one characteristic, in this case, the conductive element consists of a ring mounted around the jacket and fixed on the latter.

In accordance with another characteristic of the invention, on the screw shaft is fixed a coding disc making it possible to detect fractions of the turn of the screw.

According to a first possibility, the coding disc comprises openings or slots arranged in a regular angular distribution, while a diode and a phototransistor are arranged on either side of the disc, so that the beam emitted by the diode can be received by the phototransistor when an opening or slot in the disc is between these two elements.

This solution is interesting, because without mechanical wear. However, it has the drawback that the emitting diode consumes a non-negligible amount of current.

According to another possibility, the coding disc comprises two concentric series of conductive elements angularly offset from one series to another, each series alternately comprising floating elements and elements connected to ground, two brushes resting on the two series of elements, which are connected to the inputs of an RS door (anti-rebound device).

For example, if the stroke of the piston is 2 millimeters, corresponding to a volume of liquid transported of 100 μj, this stroke is carried out in 5.7 turns of the screw, and the coding disc can appreciate angular values d 'a tenth of a turn. The piston stroke can thus be broken down into 57 parts which can be, thanks to a control device, managed independently of each other.

In any case, the invention will be clearly understood with the aid of the description which follows, with reference to the appended schematic drawing representing, by way of nonlimiting examples, two embodiments of this device:

Figure 1 is a very summary perspective view of a complete infusion pump;

Figures 2 and 3 are two views in longitudinal section and on an enlarged scale of the piston control device, in two positions thereof;

Figure 4 is a schematic view showing a variant of the coding device.

FIG. 1 represents a medical liquid infusion pump comprising a housing 2 and a removable cassette 3. The housing 2 contains the control and programming elements, as well as the power source for several piston pumps, while the cassette 3 includes the liquid suction device, and transfer thereof to a catheter connected to the patient. Figures 2 and 3 show a liquid transfer system comprising a metering cylinder 4 connected to an inlet pipe 5 and an outlet pipe 6. However, this representation is purely schematic and does not, in any case, part of the invention, nor should be considered as limiting the invention. A piston 7 reciprocating inside the cylinder 4 is capable of creating a vacuum inside of it to suck the liquid from the inlet pipe 5, and to discharge this liquid into the outlet pipe 6.

The device according to the invention comprises a direct current motor, the housing 8 of which is shown in the drawing and on the output shaft of which a pinion 9 is wedged. This pinion 9 meshes with a pinion 10 which is mounted centered on a shaft 12, with the possibility of rotation around this shaft, and of sliding along this shaft, the pinion 10 being subjected to the action of a spring 13 which pushes it axially with respect to shaft 12. On this shaft 12 is wedged a disc 14 against which the spring 13 keeps pressed the piston 10. This shaft 12 is finished, at one of its ends, by a screw 15 which is engaged in a nut 16 mounted locked in rotation, but capable of translation.

This nut 16 is surrounded by a jacket 17, one end of which is open to allow engagement of the nut, and the other closed end of which serves to fix the piston 7. The jacket 17 is made integral with the nut 16 by means of a spring 18 pushing the nut 16 against the bottom of the jacket 17 located on the side of the piston, this spring 18 bearing against a removable stop 19, such as a circlip, located on the side of the open end of the shirt. On this jacket is fixed a ring 20 made of an electrically conductive material. This ring 20 is capable of moving during the advancement and retreat of Técrou 16 on the screw and, consequently, of the che¬ setting 17, between two positions in which it abuts against two hard contacts 22 and 23 constituted for example by printed circuits, mounted on the electrical supply circuit of the motor 8, and capable, when the ring 20 comes to bear against such a stop, to stop the motor and reverse the direction of rotation of this one.

The stroke of the piston is therefore determined by the spacing between the two printed circuits 22, 23, reduced by the thickness of the ring 20. The end of the shaft 12, which is not equipped with the screw 15, serves mounting a coding disc 24.

In the embodiment, shown in Figures 2 and 3, this disc has a number of openings or lights arranged in a regular angular distribution, these openings and lights being capable of letting pass or not the beam emitted by a diode 25, and intended to be received by a phototransistor 26.

In the embodiment shown in Figure 4, the coding disc 25 comprises two concentric series of conductive elements angularly offset from one series to another. Each series comprises floating elements 26, extending over a certain angular range, and elements 27 connected to ground extending over a lower angular range.

The two series of elements 26 and 27 are angularly offset. Two brushes 28, 29 bear on the two series of elements and are connected to the inputs of an RS door. It is thus possible, thanks to the coding disc, to have information corresponding to a fraction of a turn of the disc, for example a tenth of a turn of this disc which corresponds to a linear advance of the piston which can easily be determined and, consequently, at a known volume of liquid sucked in or discharged according to the direction of displacement of the piston.

As an example, it is possible to determine ten angular positions of the disc, knowing that the stroke of the piston corresponds to 5.7 revolutions of the disc, and the stroke of the piston has 2 millimeters. It is thus possible to detect 57 positions over 2 millimeters of travel. Starting from the position shown in FIG. 2, when the screw is driven in a direction of screwing inside the nut 16, the piston 7 moves back until the panel 20 comes to bear against the hard contact 23. moment, the nut-liner-piston assembly is blocked in translation, and the motor receives a stop command, the motor shaft being capable of continuing, during this stop phase, its pivoting thanks to the torque limiter constituted by the disc 14, the pinion 10 and the spring 13 associated therewith. The spring 18 also plays a damper function in this sense.

On the contrary, when the piston 7 leaves, it is the contact 22 which forms a stop for the panel 20 and, consequently, for the piston, and which controls the stop of the advance of the piston, then the return of this one.

As is apparent from the above, the invention brings a great improvement to the existing technique by providing an infusion pump of extremely compact structure, the flow rate of which can be controlled very precisely over very wide flow rate ranges, by the implementation of the hard contacts, as well as by the implementation of the coding which makes it possible to divide each race in a large number of elementary movements thus obtaining a good resolution.

It goes without saying that the invention is not limited to the sole embodiments of this device, described above by way of examples; on the contrary, it embraces all its variants.

Thus, in particular, the device for supplying and removing liquid from the metering chamber could be different, the piston could be produced in several parts, one of which remains permanently in the metering chamber, and the other of which remains integral with Técrou, this coupling being able to be made by magnetization, that the removing the cassette 3 from the housing 2 could result in a control of the movement of the piston in a direction of retraction inside the housing, or that the hard contact could be formed not by circuits printed, but by other types of hard contacts, such as rings surrounding the shirt, forming stops for the conductive element fixed on the shirt, without thereby departing from the scope of the invention.

Claims

1. - Device for controlling the piston of a medical liquid infusion pump, characterized in that it comprises a direct current motor driving a screw (15) engaged in a nut (10) locked in rotation but free in translation , integral with the piston (7) and on which is fixed an electrically conductive element (20) on the path of which are arranged, on either side of the conductive element, two hard contacts (22, 23) mounted on the circuit motor supply and intended to stop the movement of the motor when the conductive element comes into contact with one of them, elastic means (10, 13, 14) being provided to allow the movement of the motor to continue during its stop phase, after the conductive element (20) has arrived against a hard contact and prevents further movement of the piston (7).

2. Device according to claim 1, characterized in that each hard contact (22, 23) further controls the change of the direction of rotation of the motor.

3. Device according to any one of claims 1 and 2, characterized in that the hard contacts (22, 23) are constituted by printed circuits.

4. Device according to any one of claims 1 to 3, characterized in that the drive screw (15) is wedged on a disc (14) on which is pressed, elastically and with the possibility of axial play, a pinion ( 10) meshing with a pinion (9) wedged on the motor output shaft.

5. Device according to any one of claims 1 to 4, characterized in that the nut (16) is disposed inside a jacket (17) integral with the piston (7), open at its end opposite to that equipped with the piston and in which the nut (16) is maintained in elastic pressure, under the action of a spring (18) pushing it towards the end of the jacket fitted with the piston.

6. Device according to claim 5, characterized in that conductive element (20) consists of a ring mounted around the jacket and fixed thereon.

7. Device according to any one of claims 1 to 6, characterized in that on the shaft (12) of the screw (15) is wedged a coding disc for detecting fractions of the turn of the screw.

8. Device according to claim 7, characterized in that the coding disc (24) comprises openings or slots arranged in a regular angular distribution, while a diode (25) and a phototransistor (26) are arranged on the side and on the other side of the disc, so that the beam emitted by the diode can be received by the phototransistor when an opening or slot in the disc is located between these two elements.

9. Device according to claim 7, characterized in that the coding disc (24) comprises two concentric series of conductive elements (26, 27) angularly offset from one series to another, each series alternately comprising floating elements (26) and elements (27) connected to ground, two brushes (28, 29) bearing on the two series of elements, which are connected to the inputs of an RS door.