EP0223643B1 - Process to define exactly the flow rate of a dosing pump, and such a pump - Google Patents

Abstract

A pump in accordance with the invention has moving equipment (32) driven by a reversible synchronous motor (42) whose windings (44, 45) are connected to a power source by means of optocoupled triacs (48, 49) which, under microprocessor control, are used to adjust the flow rate of the pump by acting on its admission period (by powering the windings in one direction) and on the pumping cycle time (by varying the period for which the pump is unpowered in each cycle).

Description

A pump is said to be "metering" when it is possible to vary its flow, by direct manual control or assisted by a servo-motor or in response to a suitable electric or pneumatic control signal.

The variation of the flow rate is generally obtained, in most of the known systems, by acting either on the rate of operation (more or less rapid succession of the pumping cycles), the flow rate per cycle being kept constant, or on the flow rate per cycle the cadence then being kept fixed. More rarely the adjustment of the flow rate is obtained by acting in a combined manner on the cadence and on the flow rate per cycle, as is the case in electromagnetic pumps where one acts by time delay on the frequency of the excitation times of l electromagnet and on the stroke of the electromagnet itself. Such systems require two inputs of information to the pump, i.e. two manual commands or two separate signals.

Among these known pumps, the invention is more mainly directed towards pumps in which the production of a flow rate results from the reciprocating movement of a piston or from a cyclic deformation of a mechanically actuated membrane.

In the case where the pumping member is a piston, the displacement of the pump is exactly proportional to the stroke of the piston and the flow generated is proportional to this stroke and to the pumping rate. In the case of a mechanically actuated diaphragm pump the relationship between the volume swept by the diaphragm and the displacement of the actuating member of the diaphragm coupled to the center thereof is a nonlinear, complex law which depends in particular the mode of connection between the actuating member and the membrane, the physical nature of the latter, the profile of its bearing surfaces and even the rate of actuation. This law is often determined experimentally.

In the type of pumps covered by the invention, the means allowing an adjustment of the displacement are generally located in the members for transmitting the movement of a motor to the piston or to the diaphragm actuator, means which greatly complicate this transmission. and disturb a correct transmission of forces. In addition, their operation, if it is automatic, requires the supply of a non negligible power which it is known that the implementation requires expensive equipment and limited flexibility of use compared to low current control devices including the components are cheap.

The search for means making it possible to construct a simple metering pump, with the greatest possible number of components of a current nature while offering an accuracy of less than a percent in the adjustment of the delivered flow rate, has led to the invention which is a process for establishing a determined flow rate by which the metering pump only needs a synchronous motor supplied by a current at fixed frequency, an extremely simple transmission mechanism from which any device with variable kinematics is eliminated, and an electronic control device associated with a microprocessor with great operating flexibility and low cost, all these factors being very advantageous as regards the economic aspect of the manufacture of such a pump. The invention also relates to the pump implementing the method.

More precisely, the first object of the invention is therefore a method for establishing precisely the value of the flow rate, expressed as a fraction of the maximum flow rate, of a variable-flow metering pump comprising a pumping member coupled to a transmission element animated by 'a rectilinear reciprocating movement creating a direct and positive connection between said pumping member and a reversible synchronous electric motor, supplied by an alternating current of fixed frequency.

• - établir une première phase d'alimentation correspondant à un sens de rotation du moteur et la maintenir pendant un premier espace de temps déterminé à partir d'une position d'origine déterminée et fixe de l'équipage mobile de la pompe.
• - commuter cette première alimentation à la fin dudit espace de temps pour inverser le sens de marche du moteur et maintenir cette alimentation inversée pendant un espace de temps égal à celui nécessaire à l'équipage mobile pour atteindre à nouveau sa position d'origine,
• - couper l'alimentation du moteur à la fin du second espace de temps susdit et maintenir coupée cette alimentation pendant un troisième espace de temps correspondant à la différence entre la somme des deux premiers espaces de temps et un temps de cycle de pompage au moins égal à ladite somme, ledit premier espace de temps et le temps de cycle étant sélectionnés par le microprocesseur en réponse à la fraction désirée du débit maximal affiché manuellement dans le microprocesseur, parmi une pluralité de valeurs de temps qu'il comporte en mémoire, toutes multiples d'une demi-période du courant d'alimentation.

According to one of the main characteristics of the invention, this method consists, for each pumping cycle, of controlling, by means of a microprocessor, the supply of the drive motor according to the following steps:

• - Establish a first supply phase corresponding to a direction of rotation of the motor and maintain it for a first space of time determined from a determined and fixed origin position of the movable assembly of the pump.
• switch this first supply at the end of said time space to reverse the direction of operation of the engine and maintain this reverse supply for a time space equal to that necessary for the moving assembly to reach its original position again,
• - cut the power supply to the motor at the end of the aforementioned second time space and keep this power supply cut for a third time space corresponding to the difference between the sum of the first two time spaces and a pumping cycle time at least equal at said sum, said first time space and the cycle time being selected by the microprocessor in response to the desired fraction of the maximum flow rate displayed manually in the microprocessor, from among a plurality of time values that it has in memory, all multiple half a period of the supply current.

If the pumping member is a piston with a sinusoidal movement, the values in memory of the first time space and of the cycle time are determined by calculation.

In the case, on the other hand, where the flow rate of the pump is a complex function of the movement of the motor because of the kinematic chain connecting the latter to the pumping member and the nature of the pumping if it is a membrane, the above-mentioned values in memory are determined experimentally.

Finally, it will be advantageous for the position of origin of the mobile assembly of the pump to be detected and controlled by at least one sensor whose signal is processed by the microprocessor.

A second object of the invention is a pump applying the above method which comprises a movable actuation device for a pumping member, driven in an alternating rectilinear movement by means of a transmission device coupled to a motor. and in which said motor is a reversible synchronous motor, each winding of which is connected to an alternating power source of fixed frequency by a triac optocoupled to an electroluminescent control diode, itself connected to the output of a microprocessor of management of the power supply and of the switching operations between the windings and the source, while a detector of the position of origin of the above-mentioned mobile assembly is connected at the input of said microprocessor.

The invention will be better understood during the description given below by way of purely indicative and nonlimiting example which will make it possible to identify the advantages and the secondary characteristics thereof.

• - à la figure 1 annexée représentant de manière schématique une pompe mettant en oeuvre le procédé selon l'invention, dans laquelle l'organe de pompage est un piston animé d'un mouvement rectiligne alternatif sinusoïdal ;
• -à la figure 2 annexée, illustrant schématiquement un dispositif de couplage d'une pompe à membrane avec un microprocesseur de commande de son fonctionnement selon l'invention.

During this description, reference will be made:

• - in attached FIG. 1 schematically representing a pump implementing the method according to the invention, in which the pumping member is a piston driven by a sinusoidal reciprocating rectilinear movement;
• in Figure 2 attached, schematically illustrating a device for coupling a membrane pump with a microprocessor for controlling its operation according to the invention.

• - une chambre de pompage 2 reliée à un conduit d'aspiration 3 par un clapet 4 et à un conduit de refoulement par un clapet 6,
• - un piston 7 constituant paroi mobile de la chambre 5 animé d'un mouvement rectiligne alternatif le long d'une glissière 8 du corps de pompe,
• - un dispositif de transmission attelé au piston 7 et comprenant un cadre 9 dans lequel un patin 10 peut coulisser transversalement au mouvement du piston 7, le patin étant attelé à un excentrique 11 de la roue 12 d'un système roue et vis sans fin 13,
• - un moteur synchrone 14 possédant deux sens de marche dont l'arbre de sortie est accouplé à la vie 13,
• - un dispositif de commande électronique 15 de la marche, de l'arrêt, de l'inversion du sens de marche du moteur 14,
• - un microprocesseur 16 de pilotage du dispositif 15 par lequel, au moyen d'un clavier 17 on peut afficher en 18 la valeur du débit à délivrer par la pompe (exprimé en fraction du débit maximal de celle-ci} et au moyen de touches 19 on peut mettre en ou hors service des sous-programmes de commande particuliers venant corriger un programme général de commande du fonctionnement de la pompe en fonction par exemple de la nature du fluide à doser,
• - et un capteur 20, relié en sortie audit microprocesseur, qui détecte la présence du piston 7 dans sa position de point-mort avant qui sera considérée et reconnue par le microprocesseur comme étant la position d'origine dans laquelle se trouve l'équipage mobile au début d'un cycle de pompage.

Referring to FIG. 1, there is seen a metering pump 1 with piston represented in an extremely schematic manner and which comprises the following essential organs:

• a pumping chamber 2 connected to a suction pipe 3 by a valve 4 and to a discharge pipe by a valve 6,
• a piston 7 constituting the movable wall of the chamber 5 driven by an alternating rectilinear movement along a slide 8 of the pump body,
• - A transmission device coupled to the piston 7 and comprising a frame 9 in which a shoe 10 can slide transversely to the movement of the piston 7, the shoe being coupled to an eccentric 11 of the wheel 12 of a wheel and worm system 13 ,
• a synchronous motor 14 having two directions of travel, the output shaft of which is coupled to life 13,
• an electronic control device 15 for running, stopping, reversing the direction of movement of the engine 14,
• - a microprocessor 16 for controlling the device 15 by which, by means of a keyboard 17, it is possible to display at 18 the value of the flow to be delivered by the pump (expressed as a fraction of the maximum flow thereof} and by means of keys 19 specific control subroutines can be turned on or off correcting a general program for controlling the operation of the pump as a function, for example, of the nature of the fluid to be metered,
• - And a sensor 20, connected at output to said microprocessor, which detects the presence of the piston 7 in its front dead center position which will be considered and recognized by the microprocessor as being the original position in which the mobile equipment is located at the start of a pumping cycle.

The maximum flow rate of the pump is obtained when the stroke of the piston is equal to twice the eccentricity and for the maximum rate of the pump. By way of example, it will be considered that the synchronous motor 14 has 16 poles and is supplied by an alternating current of fixed frequency equal to the network frequency of 50 Hz.

It will also be assumed that the transmission ratio between the screw 13 and the wheel 12 is 1/4. Thus in operation, the engine 14 rotating at 375 revolutions per minute, the wheel 12 will rotate at 93.75 revolutions per minute. The time taken to scan the maximum displacement is therefore 640 milliseconds.

One of the possible means for varying the flow rate of the pump is to act on the frequency of the supply current of the synchronous motor. This solution involves the implementation of a device for varying the frequency of an alternating power current which has not been selected for reasons of cost and reliability.

A second means lies in limiting the stroke of the piston for a given pumping cycle. To do this, the synchronous motor 14 with its control electronics 15, essentially ensuring switches and interruptions of the power circuit supplying it, is particularly suitable. Starting from the maximum flow rate for a cycle time of 640 milliseconds, we see that the suction stroke takes 320 milliseconds and the discharge stroke also 320 milliseconds. By supplying the motor 14 for a time of less than 320 milliseconds then by switching this supply at the end of this first space of time to reverse it and by maintaining this supply reversed until detection by the sensor 20 of the return of the piston to its original position, a pumping chamber volume swept below the volume swept by the piston during its maximum stroke. The motor is then kept unpowered until the entire cycle time, that is to say 640 milliseconds, has elapsed.

It is thus theoretically possible to obtain any fraction of the maximum flow rate of the pump by calculating, for the desired fraction, the time of the suction phase which corresponds to it and by feeding the motor as described above.

However, the control of the supply of the windings of the reversible synchronous motor being produced by means of triacs, as will be described with reference to FIG. 2, the operating characteristics of these components introduce an intrinsic imprecision in the time during which they are conductive, which can be equal to half a period of the current power supply, ie 10 milliseconds for a frequency of 50 Hz. Indeed, in principle a triac becomes conductive as soon as its control signal is present and does not cease to be so only on the double condition of disappearance of the control signal and the zero crossing of the supply voltage. To overcome this imprecision, it is advantageous to detect the zero crossing of this voltage to either warn the micropressor and form a means of synchronizing the emission of the triac control signal with the zero crossing of the voltage d 'power supply, or trigger the triac only at zero voltage passage of the supply current when the control signal is present. By then imposing on the time of presence of the control signal to be a multiple of the half-period of the supply current, it is certain that the time during which the triac will be conductive, will be strictly equal to the above-mentioned time of presence, with a slight delay when using the zero crossing detector on the triac.

It follows that the suction time can only be reduced, from the value of 320 milliseconds corresponding to the maximum suction stroke of the piston, in increments of 10 milliseconds for a frequency of 50 Hz.

The table below in which the values written opposite ti on all the possible values of the suction time between 320 and 160 milliseconds, indicates, opposite% Q, the fraction (in percentages) of corresponding theoretical flow to each of these values.

It will be recalled that the precision requested for a metering pump is ± 1% of the displayed flow rate. The table above shows that we cannot keep this precision as soon as we want to obtain a flow rate lower than 93% of the maximum flow rate. The theoretical relative imprecision is even of the order of 10% around 50% of the maximum flow. This procedure cannot therefore be entirely suitable, therefore the invention has recourse to a correction of these values by varying the duration of the pumping cycle (T), that is to say the sum suction time, delivery time and rest time of the pump moving assembly.

It is known in fact, as mentioned above, that to modify the flow rate of a pump, it is possible to modify the pumping rate. When a pumping cycle (T) includes a rest period for the moving part, as is the case when the stroke of the moving part has been limited as described above, it is possible to reduce or increase this rest time to shorten or increase the cycle time compared to the cycle time (640 milliseconds) corresponding to the maximum stroke of the piston, in increments of 10 milliseconds for the reasons already explained.

In this hypothesis, if the flow rate obtained for a cycle time of 640 milliseconds is Q, the flow rate Q obtained for a cycle time X milliseconds will be equal to Q = Qx x 640: X

It is undesirable to obtain, for example, a small fraction of the maximum flow rate of the pump, to exaggerate the cycle time excessively. In this case, in fact, the flow rate emitted by the dosing pump is so discontinuous that it is no longer suitable for continuous dosing applications without using additional means to "smooth" it (tanks, buffers, etc.). ) whose use is not always desired. Furthermore, it is not possible to reduce the cycle time corresponding to the maximum stroke of the moving assembly by a value greater than the rest time which this cycle time comprises when the piston stroke is reduced.

The choice of the cycle time ( ^T ) between these two extremes will essentially depend on the pace as a function of the time of the flow rate which one wishes to obtain, or which will be dictated by the application of the dosing pump.

By way of example, it is desired to obtain a flow rate equal to 75% of the maximum flow rate with an accuracy of ± 1%, that is to say a real theoretical flow rate between 75.7% and 74.3%. It can be seen from the table above that by simply adjusting the stroke of the piston, these values cannot be reached. Several solutions are possible.

• 1. We choose in the table above to reduce the suction time to 160 milliseconds. From the above table, a flow rate equal to 50% of the maximum flow rate is obtained for a cycle time ( ^T ) of 640 milliseconds which, the delivery time being assumed to be equal to the suction time, leaves a rest time of 320 milliseconds. You can therefore set the cycle time to 430 milliseconds. The theoretical flow obtained will therefore be 74.4% of the maximum flow. (The same technological constraint relating to the electronic control of the synchronous motor requires choosing a multiple cycle time of 10 milliseconds for a frequency of 50 Hz).
• 2. Choose the suction time closest to the desired flow rate from the table above (210 mil liseconds) and a cycle time slightly less than 640 milliseconds (630). A flow rate of 74.8% of the maximum flow rate is obtained.
• 3. We choose in the table above the longest possible suction time (320 milliseconds) which leads to a cycle time of 850 milliseconds to obtain 75.3% of the maximum flow rate (or 860 milliseconds to obtain 74.4%).
• 4. A plurality of intermediate solutions is still possible.

We can therefore draw up numerous tables combining cycle time and suction time for all the desired partial flow rates and we can choose one or the other of these tables according to the desired flow rate, the nature of the fluid dosed or other factors depending on the installation in which the metered fluid is delivered.

The implementation of the method described above will advantageously be carried out by an electronic device for controlling the synchronous motor controlled by a microprocessor comprising a program for managing various switching operations to be carried out by the electronic device, depending on the one hand, on the values cycle time and suction time spaces as determined experimentally or by calculation and which have been entered into the memory of the microprocessor, and, on the other hand, the desired flow rate which will be expressed at by means of a data input device of the microprocessor, operable manually, coupled with a device for displaying this flow rate.

FIG. 2 schematically illustrates an embodiment of a metering pump equipped with such a control device, in which the pump is a membrane and the electronic control device is shown in more detail.

As in the previous figure, the pumping chamber 30 is connected through unidirectional valves to a suction pipe and a delivery pipe not shown. The pumping member is constituted by a membrane 31 mechanically actuated by a movable assembly 32 driven in an alternating rectilinear movement by a linkage mechanism which includes a lever 33 articulated by one of its ends 33a around a fixed axis 34, articulated by the axis 35 at the end 32a of the movable assembly 32 opposite the membrane 31 and articulated at its other end 33b by the axis 36 at the end 37a of a drive rod 37.

The end 37b of the connecting rod 37 is in turn articulated by an axis 38 on a wheel 39 driven in rotation about a fixed axis 40. The distance separating the axes 38 and 40 constitutes the crank of the connecting rod system which thus constitutes l connecting rod 37 wheel 39. The wheel 39 is rotated by the output shaft 41 of a synchronous motor 42 by means of a reduction device not shown and simply shown diagrammatically by the difference in diameter of the wheel 39 and tree 41.

It will be noted, in this schematic representation, that the mobile assembly is represented in its front neutral position, that is to say at the end of its delivery phase or at the start of the suction phase. The connection between the moving element 32 and the crankshaft mechanism will be carried out so that, as shown in the drawing, the crank 38, 40 is in a position such that the force transmitted by the axis 38 to the connecting rod 37 is perpendicular to the latter. Thus, at start-up the resistive torque is zero to the nearest friction forces.

Furthermore, the suction stroke of the crew 32 takes place against the effect of a return spring 43 which is banded during this stroke, thus accumulating an energy of assistance to the effort of repression, the advantage of which will be explained below.

44 and 45 show the two windings of the reversible synchronous motor 42, a common point of which is connected to a terminal 46 of an alternative power source. Each of the windings is also connected to the other terminal 47 of this source via a triac 48, 49 optocoupled to a light-emitting diode 50, 51 which constitutes the control member. A capacitor 52 is disposed, in a known manner, between the two windings 44, 45. When the triac 48 is made conductive under the conditions described above, the windings are supplied, one 44 by the mains voltage and the other 45 by a phase-shifted voltage due to the capacitor causing rotation of the shaft 41 in a direction A and that of the wheel 39 in a direction B. The reversal of direction of rotation is obtained by switching the power supply , the triac 48 no longer passing while the triac 49 is made conductive.

The diodes 50 and 51 are connected to the microprocessor 60 which transmits to them the control signals corresponding to the different supply phases described above.

Finally, the wheel 39 can be formed into a disc provided with a slot 53 which cooperates with an optical detector 54 whose function is identical to that of the detector 20 of FIG. 1. This detector 54 is connected to the microprocessor 60 to supply it information relating to the presence or not of the moving element in its original position (dead center before represented), translated by the presence or not of the slit 53 on the light path from the light-emitting diode 55 to the receiver 56.

The front of the microprocessor 60 may include an on / off button 61, a first button 62 for selecting the flow adjustment mode known as "integrated adjustment", a second button 63 for selecting a "selective" adjustment mode for the flow by separate action on the pump cadence and its displacement, a third selection button 64, in the "selective" setting mode, of the cadence or displacement, a display device 65 of the selected value (s) and buttons 66 and 67 to determine and vary these values.

We have seen previously that one could memorize, in the microprocessor, at least one table of values determined by the manufacturer. These tables of values can be determined by calculation when the displacement is a simple function of the rotational movement of the synchronous motor.

Certain pumps, such as the mechanically actuated diaphragm pumps, illustrated in FIG. 2, have flow laws depending on the stroke of their drive mechanism and the rate which are much more complex and which cannot be note that through experience. It is quite certain that the combination tables mentioned above can be established for this type of pump, experimentally by measuring the flow rate actually delivered by the pump (or a prototype pump of the type considered) as a function of the suction and cycle times displayed.

In operating mode with integrated adjustment, the microprocessor has in memory a table of the optimal values of the first time space and of the cycle time corresponding per couple to each value of fraction of flow desired (variable for example from 2 to 100% every 1%).

In this case, by pressing button 62, the buttons 66 and 67 are displayed by displaying the fraction of maximum flow desired. From this data, the microprocessor determines the pumping cycle time and the first time space (duration of aspiration) corresponding to the desired flow rate. The pump being in its position in the figure, the excitation of the diode 50 during this first space of time causes a rotation of the wheel 39 over a certain amplitude. It will be noted in this regard, that the attachment of the motor to its synchronism speed will be very quickly because at start-up the resistive torque is zero, the motor being of low inertia, because small. This arrangement is important because it makes it possible to obtain satisfactory precision in the suction stroke which conditions the precision of the metering. Indeed, if there were hazards in the attachment of the synchronous motor due to an uncontrolled slip due to a non-zero resistive torque and of variable value, there would be disparities in the dose volume of a pumping cycle to another, despite a first perfectly constant space of time.

At the end of this space of time, the connection of the windings 44, 45 is reversed by excitation of the diode 51 and stop of excitation of the diode 50. In practice, this switching is not instantaneous and provision is made for a determined time between stopping the rotation of the motor and resuming its rotation in the opposite direction. This time, which can be 40 milliseconds, will be taken into account to determine the reduction ratio between the motor and the wheel of the connecting rod-crank system. Thus, in the numerical example given opposite FIG. 1, the cycle time for the maximum capacity of the pump remaining at 640 milliseconds, the suction stroke will be 280 milliseconds, as well as the discharge stroke, but the transmission ratio will be 0.285 to obtain a rotation speed of 107 revolutions per minute, and to maintain the same maximum speed.

When the motor starts its reverse rotation, the resistive torque is no longer zero. The attachment of the motor to its synchronism speed is therefore longer but this fact does not matter given the fact that the delivery time is not a priori fixed but determined by the return of the slot 53 opposite the optical sensor 54. However, it remains advantageous for this torque to be minimal and the spring 43, recalling the moving element to its front dead center, reduces this resistant torque.

When the optical detector 54 sends a signal to the microprocessor, the latter cuts off the excitation of the diodes 50, 51 and the motor is no longer supplied until the cycle time has elapsed completely. The same sequence of operations starts again for the following cycles.

To operate in selective adjustment mode, the microprocessor will have in memory a first table of values corresponding to the desired flow fraction which can vary from 5 to 5% the value of the first time space multiple of the half-period of the current. aforementioned supply closest to that which corresponds exactly to it, and a second table corresponding to the desired flow fraction varying in the same way, the value of the cycle time, multiple of the half-period, the closest. Thus, by pressing the button 63, the microprocessor is placed in a position to use one or the other of these tables. By pressing button 64, you decide to act on the flow rate only by the time of the suction stroke. The selection of 5 in% by buttons 66 and 67 assigns to the microprocessor the value of the corresponding time, in the first table and the installation works as described previously, the cycle time being kept constant equal to the value of the cycle time at maximum capacity. In the second case, the button 64 is not pressed and the flow rate is acted on by adjusting the cycle time (c-dence of the pump). The cycle time is then sought in the second table as a function of the flow fraction displayed.

These possibilities of selective adjustment, less fine than in the integrated adjustment mode, may be sufficient for certain applications.

The dosing pump thus equipped can be manufactured in a version with integrated adjustment only or in a version with selective adjustment only. The three possible versions will differ only by the electronics of the microprocessor, namely essentially the memories and the circuits allowing their selection. The design of this pump therefore allows very standardized manufacturing.

A fourth version, which is not shown, may consist of a pump in which the manual adjustment of the desired flow fraction is replaced by a signal controlling this flow to an external parameter (flow of the fluid in the stream of which the metered liquid is spilled for example). In this case also the basic components of this fourth version remain standard. Only an adapter to the servo signal is placed in the microprocessor.

Finally, the microprocessor program can also use one or more sub pro grams established to correct the values (experimental or calculated) stored in memory according to particular conditions of use of the pump (viscosity of the sucked fluid, pressure conditions at suction and discharge, inertias of the engine and the crew mobile, modification of the behavior of the membranes, change of the type of pumps if for example the microprocessor is designed to manage simultaneously or consecutively a battery of different pumps ...).

The front of the microprocessor 60 described with reference to FIG. 2 can be produced in various ways. It will be mentioned, by way of example not shown, that buttons 62, 63, 64 making it possible to select the adjustment mode can be grouped together in a single button which will cooperate with internal circuits to make the selection. Thus, for example, an action on the single button places the microprocessor in the "integrated adjustment" operating mode. The following action can place it in the "cycle time setting" operating mode. The following action will select the "stroke adjustment" operating mode. It will then be advantageous to provide, at the display device 65, a space for displaying an identification mark of the selected adjustment modes.

The invention finds an interesting application in the field of pumps and more particularly metering pumps.

Claims (11)

1. A method of accurately setting the flow rate of a variable-flow metering pump (1), said setting being expressed as a fraction of the pump's maximum flow rate, and said pump including a pumping member (7, 30) coupled to a transmission element (9, 10, 32) driven with a rectilinear reciprocating motion and creating a direct and positive link between said pumping member (7, 30) and a reversible synchronous electric motor (14, 42) which is powered by AC at fixed frequency, characterized by consisting in using a microprocessor (16, 60) to control the power supply to the drive motor (14, 42) for each pump cycle in accordance with the following steps:

- applying the power in a first step to the motor to rotate it in a first direction and maintaining said power applied for a first period of time (t1) determined from a fixed predetermined origin position of the moving equipment in the pump;

- switching the power applied to the motor at the end of said first period of time (t1) to reverse the direction in which the motor (14, 42) rotates, and maintaining said reverse power applied for a period of time equal to that required by the moving equipment of the pump to return to its origin position;

- turning off the power supply to the motor at the end of said second period of time and maintaining the power off for a third period of time corresponding to the difference between the sum of said first and second periods of time and a pumping cycle time (T) which is not less than said sum; said first period of time (t1) and said cycle time (T) being selected by the microprocessor as a function of the desired fraction of the maximum flow rate as indicated to the microprocessor, and being selected from a plurality of time values stored in the microprocessor memory and each equal to an integer multiple of one half of the period of the AC power supply.

2. A method according to claim 1, characterized in that only the said cycle time (T) is selected by the microprocessor as the desired flow rate fraction is manually selected, with said first (t1) period remaining constant.

3. A method according to claim 1, characterized in that only said first period (t1 ) is selected by the microprocessor as the desired flow rate fraction is manually selected, with the cycle time remaining constant.

4. A method according to claim 1, characterized in that the pumping member is a piston (7) driven in sinusoidal motion and the stored values for said first period (t1) and said cycle time (T) are determined by calculation.

5. A method according to any one of claims 1 to 3, characterized in that the flow rate of the pump being a complex function of the motion of the motor due to the nature of the drive chain connecting said motor to the pumping member and to the nature of the pumping member, if a membrane, the said stored values are determined experimentally.

6. A method according to anyone of the preceding claims characterized in that the origin position of the moving equipment of the pump is detected by a detector (20, 54) whose output signal is used by the microprocessor (16, 60).

7. A pump applying the method according to any one of the preceding claims, and comprising: moving equipment (7, 9, 32) for driving a pumping member (7, 30); said moving equipment being driven to perform reciprocating rectilinear motion by means of a transmission device (10, 11, 12, 13, 33, 37, 39, 41) coupled to a motor (14, 42) characterized in that said motor is a reversible synchronous motor (14, 42) with each of its winding (44, 45) connected to a source (46, 47) of AC power at fixed frequency via a triac (48,

49) which is optocoupled to a controlling light emitting diode (LED) (50, 51) which is itself connected to the output from a microprocessor (60, 16) for controlling the application of AC power to said windings and the switchings thereof, and in that a detector (20, 54) for detecting the origin position of said moving equipment is connected to an input of said microprocessor (60).

8. A pump according to claim 7, characterized in that transmission means for transmitting the motor drive to the moving equipment (32) is such that, ignoring friction, in the origin position of the moving equipment the torque opposing the transmission of said motion is nil.

9. A pump according to claim 7 or claim 8, characterized in that a resilient return member (43) is coupled to the moving equipment in order to return it towards its origin position.

10. A pump according to any one of claims 7 to 9, characterized in that microprocessor (60) includes a display device (65) for displaying the desired flow rate to which the pump is set.

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