EP2515970A1

EP2515970A1 - Alternating positive-displacement pump having a membrane for medical use

Info

Publication number: EP2515970A1
Application number: EP10807428A
Authority: EP
Inventors: Jean-Denis Rochat
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-12-23
Filing date: 2010-12-20
Publication date: 2012-10-31
Also published as: WO2011075859A1; US9050408B2; CH702437A1; US20120315157A1

Abstract

The invention relates to an alternating positive-displacement pump (1) having a membrane that is intended for fluids and for medical use, and including a driving portion (10) in which an electromagnetic actuator (11) is arranged, said actuator including at least one coil (12) and actuating a piston (14) of a mobile member (15) capable of linear cyclic movement. The pump includes a pump body (20) in which a pre-stressed membrane (22) is provided, said membrane being capable of translation by means of elastic deformation from a normal rest position to an adjacent position by means of the transmission of the piston (14) operation. Said pump also includes means (30) for detecting tolerance-exceeding variations in the intensity of the supply current using measurements (33), means (40) for continuously measuring the position of the mobile member (15), and means (30, 45) for analyzing and processing said measurements for generating at least one alarm signal (35) indicating the detection of at least one malfunction of the pump.

Description

ALTERNATE MEMBRANE VOLUMETRIC PUMP FOR MEDICAL USE

The present invention relates to an alternative volumetric diaphragm pump for pumping liquids in the context of medical use. Such a pump may be an enteral or parenteral pump, typically a portable infusion pump, in particular a single-use metering pump whose flow rate is determined in advance.

The miniaturized diaphragm and single-use medical pumps are essentially made up of two separate parts that mate removably. Denominated driving part, the first of these parts consists of a reusable module provided with a drive system, for example piston. This piston allows to actuate an elastic membrane which is truly a flexible portion of the wall of a chamber of a pump body. The latter forms the second so-called removable portion of the pump. This part is in the form of a cassette through which the liquid to be pumped passes and therefore comprises at the inlet a feed pipe located upstream of the membrane and at the outlet a discharge pipe disposed downstream of the membrane . Each of these conduits is connected to a tubing which is connected upstream to a bag containing a liquid and downstream to a catheter. The cassette can be easily associated or removed from the driving part, generally by sliding. Once assembled, these two parts form a particularly light pump whose overall dimensions are typically of the order of 50 x 50 x 25 mm only.

As described and illustrated in EP1967223, the drive system of the so-called alternative displacement pumps is typically obtained by the reciprocating movement of a piston actuator. The driving force may be that of, for example, an electromagnet traversed by a current. In order to be able to take full advantage of the generated force, the magnetic field is preferably channeled by a magnetic circuit. The latter is often formed by a pot surrounding the coil and by a pole piece which closes the upper part of this pot. Solidarity of the piston and by the same movement, the pole piece defines with the upper part of the pot a gap whose thickness varies depending on the position of the piston along its stroke. In the rest position, the piston exerts only a slight pressure against the diaphragm of the pump body and the gap is maximum. This position defines the starting point of a pumping cycle where the membrane is also in its rest position and releases a maximum volume in the chamber of the pump body. Thanks to the magnetic field that can generate the solenoid, the pole piece is then attracted by the pot until coming to lean against the upper part of the latter. The displacement of the membrane then reduces the volume of the chamber of the pump body and generates an overpressure on this membrane. The pressure exerted by the latter on the liquid makes it possible to empty the chamber by expelling the liquid out of the pump body via the discharge pipe. When the membrane initiates its return to its initial position by elastic relaxation, the volume of the chamber increases again gradually until returning to its maximum initial value. During this return phase, a depression settles in the chamber which generates the influx of a new volume of liquid through the upstream duct. Non-return valves prevent the flow of liquid in the wrong direction during the compression and intake phases.

In the phase of approaching the pole piece until it is placed against the pot, the feed stream follows a characteristic curve which makes it possible to determine the precise moment when the pole piece came to rest against the pot. From this moment, the useful supply current of the coil is interrupted to allow the raising of the piston to its initial rest position thus completing a complete cycle of pumping. The return of the piston and the pole piece in its rest position is typically effected by means of a leaf spring whose return force is sufficient to overcome the friction forces and the weight of the moving assembly.

One of the drawbacks of this drive device lies in the fact that the movement of the piston is not controlled in its stroke between its two distal positions. As its movement directly influences that of the membrane, the volume of liquid that it is able to pump can not be guaranteed with great precision. It follows that the flow of the pump is likely to fluctuate uncontrollably.

Furthermore, becoming free in its movement as soon as the supply current is established in the coil, the pole piece acquires an increasing acceleration to be stopped in its race by the stop that constitutes the upper face of the pot. Despite the relatively short length of this race, typically between 0.2 to 2 mm, preferably of the order of 0.5 mm, the impact of the pole piece generates undesirable nuisances, particularly at frequencies of pumping up to 8 to 50 cycles per second. Although it has been thought to dampen the impact of the moving part against the pot by the arrangement of a highly compressible damping member, made for example of a resilient material such as foam, this means does not, however, give satisfaction because of its significant wear observed over a long period of operation of the pump and the loss of precision in volume that it would generate. Another drawback arising from the pumps described above lies in the lack of safety for the patient. Their use may present a number of dangers for the latter because of several malfunctions, the main ones being the following:

- appearance of air in the infusion line,

- upstream occlusion occurring for example when the tubing is bent or the infusion bag is empty,

downstream occlusion occurring, for example, when a valve is kept in the closed position or when the access path to the patient is obstructed,

- upstream disconnection of the tubing,

- disconnection of the tubing downstream of the pump body,

- absence or incorrect arrangement of the cassette in the driving part.

In the first and fourth cases, namely when air appears or an upstream disconnection (generating a suction of air), the effort that must provide the pump becomes less because the pumping of the Air requires less force than pumping an infusion fluid. Thus, the current absorbed by the coil also decreases (about -20%) for a supply voltage that remains constant.

In the case of an upstream occlusion, the intrinsic force of the elastic membrane is no longer sufficient for it to return to its initial rest position. As a result, the initial starting position of the next cycle will be changed. This will have the main effect of reducing the value of the gap. Thus, the current absorbed by the coil at the beginning of the next cycle will be well below the normal value (about -75%).

In the presence of a downstream occlusion, the reverse phenomenon occurs. Due to the downstream pressure, the diaphragm is braked or stopped in its forward movement even to reach his working position furthest from his rest position. This renewed effort is manifested by a significant increase (about + 25%) of the feed current of the coil.

In the penultimate case, namely that of the downstream disconnection located in particular near the pump body, a sudden decrease in pressure occurs downstream of the membrane. This pressure drop implies a reduction of the effort that must provide the membrane which results in a decrease in the current absorbed by the coil.

In the devices known to date, the detection of a variation of the supply current outside a predefined tolerance range (typically ± 5% of the value of the normal current at a given moment) generates the emission of an alarm signal immediately informing the patient or clinician of the sudden onset of an abnormality. In such a situation, adequate measures must be taken immediately to ensure the often essential therapy of the patient, or even the survival of the latter.

By using only the detection of a non-standard variation of the supply current without other means of additional detection, the pumps of this type do not allow to be qualified as sufficiently reliable. This is particularly understandable when the life of the patient depends on it. The reliability of any device can be effective only by a superabundance of controls or means of detecting the various possible anomalies.

For this purpose, it is known to propose the arrangement of additional devices arranged on the tubing of the supply or discharge circuit of the pump. Such devices may be for example a drop detection system which makes it possible to detect the moment when the infusion bag is empty thanks to an optical control system which fits on the drip chamber. Another apparatus could be that for detecting the appearance of air by means of an ultrasonic detection member disposed around the tubing. There is also a pressure sensing system consisting of a pressure sensor (strain gauge, inductive sensor) which is the subject of an integrated device within the tubing and which prevents an occlusion.

The disadvantage common to all these additional systems lies in the fact that they increase singularly the number of devices that it becomes necessary to set up to be able to ensure a reliable operation of the pump and to obtain superabundant control means on the possible malfunctions of the latter.

The object of the present invention aims to overcome at least in part the aforementioned problems and disadvantages by integrating within the pump additional continuous measurement means which allow, at each pumping cycle, to obtain additional measurements from another type that are characteristic of the instantaneous state of the pump. By this means, these data can be exploited on the one hand as superabundant control measures to increase and attest the reliability of the pump, and on the other hand as measures that can be exploited by means of servocontrol of the position of the pump. movable member of the pump, between the two ends of its race, to control its movement.

To this end, the subject of the present invention is an alternative volumetric diaphragm pump for medical use according to claim 1.

Advantageously, the addition of such embedded means in the pump gives the latter a simple, unique and compact set which avoids the use of the use of several additional devices to ensure patient safety. In addition, the processing of additional data independent of the measurements made on the current or the supply voltage of the coil, makes it possible to control the movement of all the movable members of the pump (membrane, piston, polar part), outside their two most distant opposite positions. Advantageously, the object of the present invention makes it possible to increase the autonomy of the pumps operating with battery or battery and to reduce the wear and nuisances generated mainly by the repeated movements of the pole piece. Such nuisances can be not only sound type but also be formed of a shock wave propagated in the tubes by the movement of the piston. This phenomenon causes jolts in the pipes connected to the pump body.

In addition the small size and high autonomy of the pumps according to the subject of the present invention make them perfectly suitable for ambulatory application while ensuring easy and reliable use and installation.

Other advantages and specific features will become apparent in the light of the description which follows and which refers to a preferred embodiment of the subject of the invention, taken as a non-limitative and illustrated schematically and by way of example by the appended figures in which:

Figure 1 is an elevational view in vertical section of the pump according to the invention.

FIG. 2 is a diagram illustrating the means implemented to process and exploit the signals characteristic of the instantaneous state of the pump.

FIG. 3 is a graph showing, on a full pumping cycle and in a normal situation, a first characteristic curve of the position of the movable member of FIG. the pump and a second characteristic curve of the supply current absorbed by the driving part of the pump.

With reference to FIG. 1, this illustrates an alternative volumetric diaphragm pump 1, in particular a single-use pump, used in the medical field for drawing liquids from a reservoir and injecting it into a living body (human or animal) by means of tubing and a catheter. These liquids may typically be blood solutions or medicated solutes.

As can be seen, this disposable pump is formed of two distinct parts, namely a reusable driving part 10 and a disposable pump body 20 removably attached to the driving part, for example to the using a sliding system (not shown).

The driving part 10 essentially comprises an electromagnetic actuator 11. The latter is formed of at least one coil 12 arranged in a magnetic circuit preferably constituted by a pot 13. According to the preferred embodiment, the pot 13 is made in three parts. , 13a, 13b, 13c from one or more ferromagnetic materials to be able to better channel the magnetic flux generated by the coil. The source of electrical energy, not shown in this figure, can be embedded in the pump 1, for example in the form of a battery or a battery, or be kept outside the pump 1. In the latter case, connecting means will be provided to be able to connect the pump to its source of energy.

At the center of the coil is a piston 14 forming the central element of a movable member 15 in linear cyclic displacement. The guide of the movable member, in particular of the piston 14, is obtained by two bearings 16a, 16b preferably made of a non-magnetic material, self-lubricating. In order to reduce as much as possible the friction in the bearings and to avoid undesirable effects during its displacement (disturbing forces, eddy current), it will be noted that the bearings and the piston are preferably made of low-temperature materials. coefficient of friction, such as ceramic and hard metal. According to the preferred embodiment of the invention, the upper part of the movable member consists of a pole piece 17 made integral with the piston 14 and which determines with said pot 13 a gap δ whose thickness varies according to the position of the movable member on its axis of displacement 15 '.

To ensure the proper functioning of the pump in any position, a compensation member 19 is arranged in the driving part bearing against the pole piece 17. This member forces, at all times, the movable part 15 to be in contact With the elastic membrane 22. According to the preferred embodiment of the invention, this compensation member 19 consists of a compression spring sized to deliver a very light force, just enough to perform its function. This force is slightly greater than the weight of the movable member 15 plus the friction forces in the bearings 16a, 16b.

The second main part of the pump 1 is constituted by a pump body 20 in the form of a removable cassette comprising a chamber within which there is a membrane 22. Of elastic nature, this prestressed membrane is intended to be in contact with a liquid that may be contained in the chamber. The peripheral portion 22a of the membrane is connected to the pump body so that the membrane 22 can, by itself, constitute an expandable portion of the wall of the chamber pump body. According to the preferred embodiment, the central portion dedicated to 1 ¹ actuation of the membrane comprises a boss 22b establishing a reinforcement useful for transmitting, to a thinned portion 22c of the membrane, the force exerted by the piston 14 on the latter. Thus, the membrane can be translated, by elastic deformation, from a normal rest position to an adjacent position by the transmission of work carried by the piston. For this purpose, the lower end portion of the piston 14 will preferably be in direct abutment against the outer surface of the membrane, at the right of the boss 22b.

A first check valve 23, of the non-return type, is arranged at the inlet of the chamber, upstream of the diaphragm 22. This valve aims to close the internal end of an intake duct 24 and thus prevent any liquid discharge on the inlet side of the pump body. A second valve 25 of the same type, without necessarily being identical, is disposed downstream of the membrane in order to prevent any gravity flow through a discharge pipe 26 situated at the outlet of the pump body, when the pump is not operated. Note however that the function to prevent gravity flow could be attributed to the first valve 23 rather than the second valve 25.

According to the invention, the prestressing applied to the membrane 22 is dimensioned so that it is sufficient to be able on its own to bring the movable member back into the rest position. In other words, the elastic force inherent in the membrane, which manifests itself when it is deformed, is calculated in order to be able to suck up a new volume of liquid to be pumped, to overcome the weight of the movable member 15 added with the forces of friction and the force exerted by the compensating organ 19. It will then be even to be able to push the movable member 15 to its initial position without resorting to a complementary means.

With reference to FIG. 2, this illustrates means 30 making it possible, on the one hand, to detect variations outside the tolerances of the current I of the supply current of the coil, and on the other hand to generate at least one signal alarm 35 and, if necessary, immediately interrupt this current. Detection and treatment of these possible out-of-tolerance current variations occurs during each piston cycle, typically by means of an analog / digital converter 31 and a processing and control unit such as a microprocessor 32. The converter 31 having in this case the task of transforming the incoming signal 33 characteristic of the measurement of the current I of the coil.

In addition to these first means, the object of the present invention also incorporates means 40 for continuously measuring the position of the movable member 15 on its axis of displacement 15 '. As illustrated mainly in FIG. 1, these means 40 consist of electro-optical elements comprising a transmitter 41 generating an energy flux, for example a luminous flux, a receiver 42 providing a response signal 43 whose intensity is characteristic of the position of the movable member 15 along its stroke. They are supplemented by means 45 for processing and analyzing the signal 43, as illustrated in FIG.

According to the preferred embodiment, the transmitter 41 and the receiver 42 are located on either side of the movable member 15 and vis-à-vis one another so that at least a part the energy flow emitted by the transmitter 41 can be picked up by the receiver 42. The position of the movable member 15 is determined by the variation of the intensity of the response signal 43 which is generated by the displacement of a shutter 18. Solidarity of the movable member 15, the shutter 18 is intended to partially interpose between the transmitter and the receiver by penetrating through the energy flow in order to influence the amount of energy received by the receiver 42. When the membrane 22, and hence the movable member 15, are in the initial rest position, as shown in Figure 1, the shutter 18 obstructs the energy flow more importantly than when the membrane and the movable member 15 are in their opposite adjacent position, namely that where the gap δ is reduced to its minimum value. Note that the obstruction caused by the compensation member 19 is considered negligible or invariable. Typically, the width of the emission zone emanating from the transmitter 41 will be slightly greater than the length of the travel of the mobile member 15. By continuously measuring the response signal 43 and knowing the corresponding values of this signal at the two distal positions of the movable member 15, it then becomes possible to determine in real time the position of this member or in other words the position of the piston 14 and thereby the position of the membrane 22. The signal 43 can therefore be qualified as a position signal of the movable member of the pump.

According to the preferred version of the invention, the transmitter consists of a light emitting diode (LED) and the receiver of a phototransistor sensitive to the wavelength range of the transmitter. More preferably, the emission and reception spectrum of these electro-optical means will be located in the infrared range. However, it will be understood that other wavelengths, in particular those in the visible range, could be used. Also, although means 40 were presented as means of analog nature and electro-optical type, it will be agreed that means of another kind could also be used (for example laser or ultrasound, or even digital by means of an optical encoder).

Returning to FIG. 2, it will be seen that the means 30 making it possible to detect out-of-tolerance variations of the intensity I of the current before generating an alarm signal 35 as well as the means 45 for processing and analyzing the signal 43 can be physically constituted by the same organs or be integrated into common organs. In this case, the members 31 and 32 are simultaneously dedicated to the tasks of the means 30 and 45 and can be considered as constituting both of these means simultaneously. It would indeed be unnecessary to provide the arrangement of two microprocessors 32, one for processing the signals 33 characteristic of the intensity of the current I and the other for processing the signals 43 of position of the movable member, while a single microprocessor is perfectly capable of simultaneously performing these two tasks. However, it will be mentioned that separate means 30 and 45 could nevertheless be envisaged.

Other means 50 for controlling the position of the movable member 15 along its axis of displacement 15 'can still be associated with the pump 1, as shown in FIG. 2. These means 50 are essentially intended to exploit the signals 33, 43 so as to control the movement of the electromagnetic actuator 11, in particular the movement of the movable member 15, that of the membrane 22, during its movement on its axis 15 '.

With reference to FIG. 3, this represents a graph illustrating a first characteristic curve of the position of the movable member 15 and a second curve characteristic of the feed stream I absorbed by the driving part 10 of the pump. On the abscissa, the curves extend over a complete pumping cycle. The situations illustrated in these figures are representative of normal operating conditions of the pump. The beginning of the cycle is represented by the instant to which the supply current I of the coil 12 is zero and the air gap δ is at its maximum value 5 _ma ' _x . This situation corresponds to that shown in Figure 1 where the movable member 15 is in its highest position. Between the instant to and the instant ti, the member 15 remained stationary despite the energization of the coil. This is mainly due to the time required for the coil to create a magnetic field sufficient from its power up and results in a current peak temporarily reaching a maximum value I _max . This value is also due to the maximum thickness of the gap at this moment. Between times t ₁ and t ₂ , the speed of the movable member, drawn towards the pot 13 by the magnetic flux, is made relatively constant by progressively reducing the current in the same interval until reaching the value Ιχ in t ₂ . At this moment, the value δι of the air gap is sufficiently small so that the kinetic energy stored by the movable member, by its inertia, can compensate for a more sudden reduction of the current reaching a minimum value I ₂ . It follows a progressive deceleration of the movable member between instants t ₂ and t ₃ during which the current is progressively raised to a value I ₃ . The time interval t ₃ -t ₄ corresponds to the situation where the movable member 15 has reached the end of its travel. The air gap δ is then reduced to its minimum value δ _m i _n - However, a current of an intensity I ₃ is still necessary to be able to retain the movable member in this position by opposing the force useful return, generated by the intrinsic elasticity of the membrane 22. From time t ₄ , the mobile then begins its recovery towards its initial position. The current can then be completely interrupted until the end of the cycle. By resuming its initial shape, the membrane will generate a relaxing effect which, between times t and ts will result in a short acceleration due to the return of the energy released by the membrane, followed by a deceleration between ts and At this last moment, the movable member 15 is immobilized and has reached its initial rest position.

Alternatively, it would also be possible to influence the movement of the movable member during its return phase in its initial position, for example by introducing a peak current (shown in broken lines in Figure 3) in the vicinity of the instants t ₅ and t ₆ - Many parameters directly influence the current values at the various times mentioned, during the same operating cycle. For the most part, these parameters correspond to the value of the gap, the permeability of the materials of the movable member and its magnetic circuit, the induction of the coil, the mass of the movable member and the friction in the bearings. Also, it will be specified that, according to different cases, the value I ₂ could be zero, the values Ι χ and i ₃ could be equal, and the minimum air gap δmi _n could be reduced to zero.

Advantageously, it is found mainly that the movement of the movable member 15 can be controlled in its stroke between its two distal positions. In anticipation, it can be seen that the intensity of the supply current of the coil is varied in order to modify the behavior of the movable member throughout its travel. In particular, the effect of this variation will be to dampen the end-of-travel arrival of the movable member and thus to prevent the nuisance that it could cause. Control of the movement of this member, and hence of the flow rate of the pump, is advantageously rendered minute thanks to means 45 for processing and rapidly analyzing the position signal 43.

As illustrated in FIG. 2, the microprocessor 32 of the means 45 is able to control the means 50 dedicated to the servocontrol of the electromagnetic actuator 11 to control the movable member 15. Thanks to measurements that can be made continuously on the duration of each cycle, it is found that the means 30, 40 are not limited in any way to deliver an all-or-nothing type of information but allow to obtain a real continuous measurement of the state in which the electromagnetic actuator is located. the pump.

Thanks to the measurements 43 characteristic of the position of the movable member 15, the processing and analysis means of the pump have additional measures which, with the measurements 33 of the supply current of the actuator 11, make it possible to diversify the checks carried out during the operation of the pump and thereby increase its reliability as much as the safety of the patient.

For this purpose, the microprocessor 32 will generate alarm signals 35 when the characteristic values of the current and / or the position of the movable member are outside acceptable ranges defined in advance. Note that the range of the tolerance ranges associated with measurements 33, 43 need not be constant but may instead vary, for example depending on the importance of certain selected measurement times.

The alarm signals indicate the presence of at least one malfunction detected by the pump. Such malfunctions will typically be the appearance of air in the infusion lines, an upstream occlusion, a downstream occlusion, an upstream disconnection of the tubing, a disconnection downstream or the lack or incorrect arrangement of the cassette in the driving part. In the case of an upstream occlusion, the initial starting position of the next cycle will be modified, which will generate a position signal 43 different from that which should normally be generated in the initial position. In case of downstream occlusion, the maximum amplitude of the position signal 43 can not be reached or will be equaled only tardily because the membrane will be braked or stopped in its movement. If the cassette is absent from the rest of the pump or is not properly introduced, the force generated by the elasticity of the membrane can not produce its effect to push the movable member to its initial position of rest. As a result, the position signal 43 will adopt a specific value characteristic of a minimum thickness of the gap.

Advantageously, it can be seen that the signals 33, 43 can not only be used as control data for the operation of the pump, but can also be used to control the movable member 15 between the two distal positions which define its travel.

It is also noted that in order to control the slaving of the movable member and / or to generate the alarms, the signals 33 and 43 can either be chosen independently of one another, or can be combined by the microprocessor 32 or else be used in a complementary way by the latter.

The alarm signal 35 may thus result from one or other of these possibilities. To be able to benefit from a high degree of reliability resulting from the processing of a superabundance of measurements, the microprocessor 32 will preferentially use the exploitation of the two signals 33 and 43.

In general, it can be seen that the means 30, 45 and 50 make it possible to process and exploit the signals 33, 43 characteristics of the instantaneous state of the pump to ensure its proper functioning and increase patient safety.

In a variant, it will also be mentioned that the electromagnetic actuator 11 could consist of a rotary motor, for example a direct current motor, incorporating means for transforming a rotary movement into a cyclic linear movement applied to the piston 14. Such means transformations typically obtainable by a cam or connecting rod system. The means 40 for determining the instantaneous position of the movable member 15 could then include an optical sensor or a Hall effect encoder on the engine.

In another variant, this motor could consist of a step-by-step actuator making it possible to transform an electrical signal (pulse or train of driving pulses) into a displacement (angular or linear). In this case, the means 40 useful for measuring the instantaneous position of the movable member 15 could advantageously consist of counting means steps or half-steps of the engine, namely electronic calculation means for counting the control pulses to determine the instantaneous position of the piston.

The electromagnetic actuator 11 could be constituted by other types of actuators, among which we will mention the linear electrodynamic actuator of the "voice-coil" type.

Claims

1. Pump (1) volumetric alternative membrane for pumping liquids in a medical use, comprising on the one hand a driving part (10) in which are found:

an electromagnetic actuator (11) formed of a magnetic circuit integrating at least one coil (12) and activating a piston (14) of a member (15) movable in linear cyclic displacement,

and on the other hand a removable pump body (20) within which are:

a diaphragm (22) prestressed which can be translated by elastic deformation from a normal rest position to an adjacent position by transmission of work from the piston (14), a first non-return valve (23) arranged upstream of said membrane ( 22) for closing the inner end of an intake duct (24) at the inlet of the pump casing (20) and preventing any backflow of liquid, a second non-return valve (25) arranged downstream of the membrane (22), one of said valves (23, 25) being also intended to prevent gravity flow through a discharge pipe (26) at the outlet of said pump body (20),

said pump (1) further comprises means (30) for detecting, at each cycle, variations outside the tolerances of the intensity of the supply current of the actuator (11) from measurements (33) of this current,

characterized in that it further comprises means (40) for continuously measuring (43) the instantaneous position of the movable member (15) along its axis of movement (15 ') and the processing means and analyzing (30; 45) said measurements (33, 43) that can generate at least one alarm signal (35) attesting the detection of at least one malfunction of the pump.

2. Pump according to claim 1, characterized in that it further comprises means (50), controlled by at least one of said processing and analysis means (30; 45), for controlling the position of the organ mobile (15) along its axis of movement (15 ').

3. Pump according to claim 1, characterized in that it comprises a compensation member (19) which delivers, in the direction of the membrane (22), a force of intensity slightly greater than the sum of the weight of the moving part.

(15) and frictional forces associated with the movable member

(15).

4. Pump according to claim 1 or 3, characterized in that the preload applied to the membrane (22) is sufficient to suck a new volume of liquid to pump and return the movable member (15) in the rest position.

5. Pump according to claim 1, characterized in that said means (40) useful for measuring the instantaneous position of the movable member (15) consist of electro-optical means comprising a transmitter (41) generating an energy flow. and a receiver (42) providing a response signal (43) whose intensity varies as a function of the position of the movable member (15) along its path.

6. Pump according to claim 5, characterized in that the variation of the intensity of said response signal (43) is obtained by the displacement of a shutter (18) associated with the movable member (15), which can interposing between the transmitter (41) and the receiver (42) to influence the amount of energy received by the receiver (42).

7. Pump according to claim 1, characterized in that the pump body (20) consists of a disposable removable cassette.

8. Pump according to claim 1, characterized in that the magnetic circuit comprises a pot (13) of ferromagnetic material surrounding said coil (12) to channel the magnetic flux and a pole piece (17) integral with the piston (14). ) which determines with said pot (13) a gap (δ) whose thickness varies depending on the position of the movable member (15) on its axis of movement (15 ').

9. Pump according to claim 1, characterized in that the piston (14) is guided in displacement by non-magnetic bearings (16a, 16b) and in that this piston (14) and these bearings (16a, 16b) are made in materials with a low coefficient of friction, such as ceramic and hard metal.

10. Pump according to claim 1, characterized in that the electromagnetic actuator (11) consists of a rotary motor incorporating means for transforming a rotary movement into a cyclic linear movement applied to the piston (14).

11. Pump according to claim 1, characterized in that the electromagnetic actuator (11) consists of a linear or rotary stepper motor and in that said means (40) useful for measuring the instantaneous position. of the movable member (15) consist of means for counting the steps of said motor.