JP2625533B2 - Infusion pump and its drive system - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to improvements in pumps that deliver metered amounts of drugs or other fluids.

BACKGROUND OF THE INVENTION In our co-pending patent application AU-A42019 / 85 (U.S. Pat. No. 4,741,732 to Crankshaw et al.), The contents of which are hereby disclosed by cross-reference, the drive engaged by a toothed drive belt We have described a drug infusion pump with a drive system that biases a drive wheel on the output shaft of a DC gear motor to engage an elastic drive ring on a drive wheel that transmits drive power to the head.
The drive system described can be used in an experimental pump designed to implement the operation of the drug infusion control system described in the above application, but after considering the drive system, it will not be commercially available. It has been found that there are certain drawbacks that make it unsuitable.

In particular, it has been found that this drive system has a tendency to reverse the drive motor due to recoil caused by deformation of the injector, bending of the support structure, elasticity of the drive belt, slackness of the drive system, and the like. . Even if such recoil could be successfully monitored by the controller to adjust the actual position of the injector plunger, it would still be best to directly calculate the pump speed and plunger position. Furthermore, it has been found that achieving lower drive speeds and wider speed ranges without recoil is virtually impossible using the drive systems described above.

A positive drive system has been proposed for delivering medication from an injector, but for example, taking U.S. Pat.No. 4,407,659 as an example, this system allows for quick and accurate positioning of the injector actuator. This has several disadvantages, such as the inability to separate the drive means conveniently or to achieve a low feed rate in combination with a high feed rate. As explained in the above-referenced co-pending patent applications, drug infusion control systems often require very fast delivery rates early in controlled delivery as well as very slow rates late in infusion. These prior art drive systems are unlikely to achieve such a supply scheme.

A wide range of infusion pumps that are controlled in delivering medication from an infusion device are currently available and are widely used in the medical field for several purposes. Some of these pumps have one or more standard injector dimensions (Atom 235 or
It has only a limited ability to "accept" Terufusion STC-521). Other pumps include a range of different standard injectors (Medfusion Systems-Type 100).
1, Vial Medical Program 3, Sky Electronics-ps 200
Some are highly programmable that accept 0). However, a non-standard injector can be attached to the pump or the operator can enter data about the injector so that the fluid supply from the non-standard injector is accurately controlled accordingly. Nor can any of the currently available programmable infusion pumps accept them. Failure to do so risks the inaccurate delivery when non-standard injectors are used. Assuming that one of the standard injectors programmed is actually inserted, at least some of the above pumps will work once a non-standard injector is inserted. The dangers associated with this type of operation are obvious.

SUMMARY OF THE INVENTION It is a first object of the present invention to provide an improved drive system for a drug infusion pump that at least partially overcomes the above disadvantages.

It is a second object of the present invention to provide a pump whose supply is controlled and which is used to supply fluid from the injector which reduces the difficulties associated with the use of non-standard injectors.

In connection with a first object, the present invention provides a drive motor, a worm gear mounted on an output shaft of the motor, and a worm wheel configured to mesh with the worm gear and drive the output reduction gear. And a clutch means associated with the output gear for separating driving force to a drive member associated with the output gear, wherein the drive member operates an infusion pump. To provide.

In a preferred embodiment, the worm wheel includes:
A spline hub or pinion with which the output reduction gear meshes is preferably provided, the clutch means is interposed between the output gear and the drive member, and a clutch operating means is provided with the frame and the clutch means. And when the clutch is disengaged, the output gear is configured to move downward along the spline hub.

The clutch means is preferably a spring-loaded sprag clutch adapted to automatically disengage when the force applied to the output gear exceeds a predetermined value.

In a particularly preferred form of the invention, the drive motor and the worm wheel are supported by another frame member which is easily removed from the frame as a unit for easy adjustment, repair and replacement. .

It is easier than described above that a drive scheme with deceleration and with a drive separation clutch is achieved in a particularly compact configuration with the ability to provide a wide range of drive speeds while still maintaining acceptable dimensions. Will be perceived.

In connection with a second object, the present invention comprises means for receiving and positioning an injector body, injector actuator means for engaging a plunger of an injector held by the receiving and positioning means, and the injector actuator Means for generating an electrical signal indicative of the position of the means, and the electric means associated with the actuator means for moving the plunger into the injector to supply fluid and relating the position of the drive means and the actuator means. A drive means having a connection means permanently maintained between said means for generating a signal, a movable arm which contacts the injector body when held by said housing arrangement means, Means for generating an electrical signal during the movement of the injector body and the arm to engage to provide a representative signal; and one or more injectors. Programmable means for holding the diameter data, and logic means for determining whether the value of the electrical signal relating to the diameter is a programmed value and producing a signal corresponding to the determination; and Prior to engaging the plunger with the actuator means, the actuator means is moved to engage the plunger of the required volume of fully consumed injector to permit the pump control means to input data. In use by means responsive to said signal representing a negative decision, and from that information and the known volume of the desired injector, control means for controlling the supply of fluid contained in the injector at a predetermined supply rate. Means for calculating the discharge supply rate stored in the storage means for supplying a controlled amount of fluid from an injector having a main body and a plunger. It is intended to provide that pump.

It will be more readily appreciated that the operator can quickly calibrate the pump to control fluid delivery to any injector, even while operation is in progress. This means that some drugs are very short
This is important in the case of anesthetic injections, for example, to allow the patient to regain consciousness in two minutes.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a perspective view of a pump embodying the present invention; FIG. 2 is a schematic block diagram of a control system of the pump; FIG. 1
FIG. 4 is a cutaway longitudinal sectional view taken along line 4-4 in FIG. 3; FIG. 5 is a longitudinal sectional view taken along line 5-5 in FIG. is there.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1 of the drawings, an infusion pump embodying the present invention comprises a casing 1 in which a drive system embodying the present invention is disposed. You will see that. The casing 1 comprises an injector cradle 2 having a groove 3 in the center of the main body of the injector S (FIG. 3) and a notch 4 for receiving and arranging the flange of the injector. . The injector S is held in place in the groove 3 by a spring-loaded injector clamp arm 5 pivotally provided in a housing 6 extending upwardly from the cradle 2. The actuator 7 of the injector is mounted so as to slide along a pair of guide rods 8 supported by the casing 1 and is driven by a driving mechanism disposed in the casing 1. I have. This drive mechanism will be described in more detail with respect to the engagement of the injector S with the plunger, which allows the fluid in the injector to be dispensed while being driven by the central control system of the pump (FIG. 2). It is described below. The actuator 7 carries a proximity microswitch 9 and a clutch release button 10. The proximity switch 9 detects the first engagement of the actuator 7 with the plunger of the injector in order to make the controller of the pump sense that contact with the plunger has been made. The clutch release button 10 serves to decouple the drive motor from the drive system to allow the actuator to be freely moved between its operational limit positions for the purposes further described below.

The infusion pump casing 1 includes a keypad 11 including a normal arrangement of numeric keys, a registration key, a clear key, and a stop key. Several other keys 12 are also provided on the front panel. That is: Battery test-to check the state of charge of the battery, associated LED (emitting diode)
If it is charging, it will be displayed.

Alarm—Allows the alarm to be canceled, with the associated LED flashing when the alarm is tripped.

Operation-The operation of the pump is started,
The associated LED lights up when the drive button is pressed.

The full dose-injection is to perform a full dose injection while overriding the control program and at approximately the same rate as a manual injection, with the LED illuminating again when the full dose key is pressed.

 Stop-stop the pump.

 Assist-Activate the interaction assist program.

 Yes-Make a positive response to the input.

 Gives a negative response to no-input.

Liquid crystal diode (LCD) that can display information to the operator in alphabetical and numeric messages in the following conditions
A display panel 13 is also provided.

Referring to FIG. 2 of the drawings, there is shown a block diagram of a pump controller circuit. As the central microprocessor 20, a Z80 type is typically used, and an EPROM 21 (EPROM), a RAM (RAM) 22, an EPROM (EPROM) 23, a keypad 11, and a clamp arm potential difference It is controlled by a meter 24 and an injector actuator potentiometer 25 via a multi-channel 26 and an analog-to-digital converter 27. The control microprocessor 20 then controls the operation of the drive step motor 28 via the step drive circuit 29, controls the liquid crystal diode display 13 and the alarm buzzer 30, and then connects the printer (not shown) to UART) 31 for control. The step driving circuit 29
Power supply 32 providing 5V rail and 8V rail regulated from rechargeable battery to step driver
Supplies electricity.

EPROM 21 contains variable programmed information on which the pump controller operates, that is, information including a series of drug injection forms relating to various drugs to be injected. In this context, reference is made to the co-pending patent application referenced above, which fully describes the mode of infusion of the drug and its derivation methods. Further, the present application is primarily concerned with the drive system and the basic control system of the infusion pump, and will not be described in its form. The ram 22 forms the working memory of the control microprocessor 20 while the EPROM 23 has the fixed program data, and the clamp arm 5 when a predetermined volume of the injector S is loaded on the cradle 2. Can be stored.

The control microprocessor 20 also includes various microswitches that detect manual disconnection of the clutch or unexpected disconnection of the clutch caused by the occurrence of a blockage that impedes contact and injection between the microswitch 9 and the injector S plunger. , For receiving electrical signals.

Referring now to FIGS. 3-5 of the accompanying drawings, the injector clamp arm 5 is turned on / off when the clamp arm 5 is moved from its rest or bottom position to activate the pump control system. Off type micro switch
Support carried by a rotatably mounted shaft 40 supporting a notched cam 41 arranged to actuate 42
Extends from 39. This support takes the form of a cam which rests on a spring-loaded lever (not shown) which engages with the injector carried by the cradle 2 and provides a biasing force which holds the clamping arm 5. doing. The cam supports 39 are arranged so as to be shifted to the center when the clamp arm 5 is raised to the highest position. This allows the operator to position the clamp arm 5 at its highest point so that the injector can be loaded onto the cradle 2.

The shaft 40 further carries a gear wheel 43 meshed with a pinion 44 carried by a shaft 45 of the potentiometer 24. Thus, the total angular movement of the clamp arm 5 up to about 35 degrees is amplified by the gear ratio of the gear 43 and the pinion 44, usually about 4: 1 or 5: 1. Thus, very small fluctuations in the position of the clamp arm 5 cause an easily discernable change in the resistance of the potentiometer 24 which causes a change in the voltage signal sent to the multiple channels 26.

The shaft 45 further includes a hair spring or a clock spring 46 having one end fixed to the casing 6 and the other end fixed to the shaft 45.
Is carried. The spring biases the pinion 44 in a desired direction to prevent the effect of backlash between the gears 43, 44 transmitted to the potentiometer 24.

The shape of the clamp arm 5 is 10 to
For most injectors in the range of 50 ml, it has been selected that there is an approximately linear relationship between injector diameter and potentiometer 24 resistance. Thus, the position of the clamp arm 5 controls the display about the diameter of the injector.
20 to be able to generate a voltage signal to be provided.

In this embodiment, the voltage or "diameter" information of the clamp arm potentiometer corresponding to the four selected injector dimensions, such as 10, 20, 30, and 50 ml, is provided before, during or after sale. In any case, the information is stored in the EPROM 23. Thus, when the selected injector is loaded into the cradle 2 and the clamp arm 5 is lowered to engage the injector body, a diametric potential signal is generated by the potentiometer 24 and the multi-channel 26 and analog-to-digital The signal is transmitted to the central control microprocessor 20 via the converter 27. This diameter signal is compared to the programmed diameter information contained in the EPROM 23, typically in the form of a lookup. If this diameter signal corresponds to one of the standard diameters within a reasonable tolerance, such as ± 2.5%, the controller 20 will determine if the indicated volume is the correct volume of the inserted syringe. The corresponding volume of the injector is displayed on the liquid crystal diode display 13 so that the operator can confirm by pressing the yes button. Once confirmation has been registered by the operator, the pump is ready to operate in accordance with the selected infusion rate configuration in the general state described in the co-pending application referenced above.

If an injector whose pump has not been previously calibrated (hereinafter "non-standard") is inserted into the injector cradle 2, the diameter signal generated by the potentiometer 24 will be the diameter programmed into the program. And the controller must be manually programmed or calibrated to allow operation using this non-standard injector. Before describing the manner in which the controller is programmed to accept a non-standard injector, it is appropriate to further describe a drive system embodying the present invention with reference to FIGS. 3-5 in the drawings. There will be.

The drive system comprises a step motor 28 mounted horizontally on a vertical support plate 50 having a horizontal portion 51 mounted on a frame 52 supporting the cover 1. In this embodiment, the step motor 28 is an ESCAP step motor P31 which is particularly suitable for this purpose and which is said to be superior in operation to other step motors.
It is 0. The use of a stepper motor, especially the stepper motor described above, is particularly preferred because the drive system can be positioned quickly with high precision, and thus with high precision and fast operation of the infusion pump. It will be readily appreciated that motors of the form are also used.

The worm gear 53 is supported by a bearing plate 54 fixed to the output shaft of the step motor 28 and attached to the plate portion 51. The worm gear 53 meshes with a worm wheel 55 having a spline hub or pinion 56, and the worm wheel 55 and the pinion 56
It is supported by a bearing 57 mounted on 52 and a bearing 58 mounted on a support 59 mounted on and overlying the plate 50.

Support plate 50 and frame portion 52 are, in the preferred embodiment, motor 50, worm gear 53 and worm wheel 55.
Are detachable as a unit so that they can be easily adjusted, repaired, or replaced.

The output reduction gear 60 meshes with the spline hub 56 and is mounted so as to be driven by the drive head 61 via the wheel stopper clutch 62. The wheel stopper clutch 62 has a known structure, and includes members 63 and 64 with engagement teeth which are held in a mutually engaged state by a compression spring 65 in a normal state. The biasing force exerted by the compression spring 65 is adjustable by a packing washer 66 so as to change the load at which the clutch 62 automatically disengages when an undesired overpressure occurs in the injector S injection line. ing.

The drive head 61 is also moved by the frame 52
Saddle frame carrying bearing 68 supporting the top end of 61
Supported by 67.

The wheel stopper clutch 62 includes a frame 52 and a clutch member 63,
The lowermost toothed member 64 can be released by hand by moving the lowermost toothed member 64 against the action of the spring 65 by a lever arm 65 disposed between the drive sleeve 70 and the drive sleeve 70 surrounding the same. The lever 69 is linked to a pivoted rod 72 which is pivoted by actuation of the clutch release button 10 carried by the injector actuator 7
Connected via 71. The mechanism for disengaging the clutch is as basically described in the co-pending application referenced above, although only one tube is used to convey the clutch disengaging motion. .

The button 10 is connected to one of the tubes 89 surrounding the guide rod 8.
It is arranged to engage a radial arm 90 connected to the two. As described in more detail in that co-pending application, tube 89 is connected to actuator 7
(And inside the slider 8) and engages the rod 70 pivoted as the tube 89 rotates in response to the movement of the arm 90 caused by pushing the button 10 by hand. It carries a drive release cam 90 arranged to fit.

The microswitch 73 is located between the frame 52 and the top surface of the output gear 60 so as to generate an electrical signal whenever the sprocket clutch 62 is partially or completely disengaged. Although the micro switch 73 is mounted on the output gear 60 in the present embodiment, it is
It can be more conveniently located inside 62. Further, the actuation of the clutch release mechanism prior to clutch release occurs to distinguish between clutch disengagement caused by actuation of clutch release button 10 and clutch disengagement caused by possible clutch overload in the event of blockage. A further microswitch 73a is located adjacent to the rod 72 pivoted to detect. These different inputs to microprocessor 20 are labeled "manual override" and "occlusion sensor". The input labeled "Head Engage"
Input the signal generated by 49.

The drive head 61 has a central toothed portion 82 rotatably mounted at the opposite end of the frame 52 and drive-engaged by a toothed drive belt 83 engaged with yet another drive head 84 similar to the drive head 61. have. The axis of the drive head 84 is connected to a potentiometer 85 that constantly monitors the position of the drive belt 83 accurately. The drive belt 83 is permanently connected to the injector actuator 7 by a belt clamp 86 having a connecting plate 87 which is sequentially attached to a slider 88 which is connected to the injector actuator 7 by a pair of tubes 89. These assemblies are slidably mounted on guide rods 8 carried by casing 1 and injector cradle 2. In this way, a permanent drive connection is made between the drive belt 83 and the injector actuator 7. This drive connection is maintained independently of the release of the wheel stopper clutch 62 by the clutch release button 10. Thus, the position of the injector actuator 7 is always known by the central control computer 20 since the voltage signal generated by the potentiometer 25 is sent to the microprocessor 20 via the multi-channel 26 and the analog-to-digital converter 27. . This allows the injector actuator 7
Is determined by microprocessor 20 and the distance it has traveled during a particular time.

Since a permanent drive connection is maintained between drive belt 83 and injector actuator 7, the drive clutch
62 is disengaged by pressing the button 10 and the injector actuator 7 is free to move along its guide rod 89 to perform manual injection or to program the controller to work with a non-standard injector. The potentiometer 25 can always accurately detect the position of the injector actuator 7 even when it is given.

As mentioned above, the controller detects the presence of a non-standard injector in the injector cradle 2 and via a liquid crystal diode indicator 13 indicates that a program is required before injection can take place. To the operator. An empty injector of the required volume to program against a non-standard injector is first loaded into the injector cradle 2 and the clamp arm 5 is lowered. Injector actuator 7
Is the guide rod after the clutch is released by button 10.
Slide along 89. The controller moves the injector actuator 7 until closing of the microswitch 9 indicating that contact with the injector plunger has occurred. The position of the injector actuator 7 thus required to empty the desired injector is determined by the potentiometer
Indicated by 25, controller 20 then receives this data via multi-channel 26 and analog-to-digital converter 27. The empty injector is then removed and injector actuator 7 is returned to its rest position. Next, a full injector is loaded on the cradle 2 and the clamp arm 5 is lowered. The injector actuator 7 is then advanced manually or under the action of a controller until the microswitch 9 contacts the injector plunger. The starting position of the injector actuator before the injection takes place is input from the potentiometer 25 to the controller 20. After this procedure is completed, the controller
Requests the operator to enter the volume of the non-standard injector. The required feed rate is then calculated by dividing this volume by the distance measurement derived from the data for each position of the injector actuator 7 described above. The controller is then ready to perform the desired form of infusion using the non-standard injector just programmed. In this embodiment, only four calibrations are stored in a look-up table, but if a more non-standard injector would be used, the data associated with the Y injector would be Substitute one of the previously entered "diameters". Of course, the ability to store the "diameter" of the injector can be extended if necessary, even if four are currently considered sufficient.

A representative series of operator advice displayed on the liquid crystal diode display 13 for a range of operating modes will now be described to assist in a more complete understanding of the above embodiment.

When the injector clamp arm 5 is first lifted from its rest position, the microswitch 42 allows the controller to be powered and a liquid crystal diode indicator
13 displays the message: "Load filled injector and unload clamp".

If the injector is a "standard" injector, i.e. one that has been pre-calibrated and has a "diameter" value that is in a look-up table housed in EPROM 23, and contains 50 ml of fluid Assuming a 60ml injector, the indicator will display the message: "Estimated volume ml50.00 Is this correct? Yes / No ”is displayed.

If the operator is satisfied with the estimated volume and presses the yes button, the display 13 will register: "Volume ml50.00" and "Is this a new injector? Yes / No ”is displayed.

If a new infusion is needed, the operator presses the YES button and the display 13 shows: "Is it confirmed or programmed? ] Is shown.

If the operator selects confirm, the display 13 requests that the required speed be entered using the keypad 11. If the operator selects a program, the display 13 requests the operator to enter the desired medication or patient data in the same manner as described in the co-pending application referenced above.

If the estimated volume value referenced above is incorrect, the following display appears: "Estimated volume ml50.00 Register correct volume? Or press "clear" to recalibrate the injector. '

If the operator registers the correct volume and it is within ± 2.5% of 50 ml, the system will proceed with the infusion. If the registered volume is outside ± 2.5% and the “Clear” button is pressed, the following display appears: “Calibration:-Load empty injector-Drive head Call-press register-"clear" for restart. The controller moves injector actuator 7 toward the plunger until microswitch 9 closes. The potential value from the potentiometer 24 is registered in the EEPROM 23 of the look-up table with the closest diameter value. The voltage from potentiometer 25 is registered in a look-up table, and display 13 then reads: "Calibration: volume ml00.00-Load filled syringe-Register volume of fluid in injector “Clear” to get started ”.

The controller moves the injector actuator 7 into engagement with the full injector plunger until the switch 9 closes when the voltage from the potentiometer 25 is registered in the EPROM 23. From the data of the volume and position referred to above, a “supply rate” that can produce a result is calculated, and the display 13
Is: "Volume ml50.00 Is this a new injector? Yes / No.

 The operator then proceeds as described above.

It will also be appreciated that an infusion pump embodying the present invention, in addition to the functions described above, may also perform each of the functions described in more detail in the co-pending patent applications referenced above. Thus, for a full understanding of the infusion pumps embodying the present invention, reference should be had to the description and drawings in the specification that accompany those applications.

The preferred embodiment of the drive system is designed to obtain an overall reduction ratio of 1000: 1 in a particularly compact and simple manner from an engineering point of view. With the described arrangement, the infusion pump is capable of supplying fluid in the range of 0.1 ml / hr to 1500 ml / hr without any recoil or drive reliability issues. In comparison, commercially available infusion pumps have a delivery rate range on the order of 0.1 ml / hr to 150 ml / hr which is insufficient for the drug infusion control system described in more detail in the co-pending application. Thus, for a given injector size, the present drive system provides the speed attainable with conventional devices.
The injector can be operated at up to 10 times the speed. The particularly preferred stepper motor selected for use in this embodiment is such that a suitable torque is maintained over a speed range of up to 3000 rpm, so that the high feed rates referenced above are easily obtained. Can be.

Further, it is recognized that the worm drive system described in more detail above provides certain advantages, such as:

1. Prevent the drive motor from reversing under load (as described in more detail above) and allow the system to effectively self-lock.

2. Allow the stepping motor to power down between steps, eliminating the need to hold the motor between steps, thereby reducing power loss.

3. High speed reduction ratio with minimum components, especially in compact form.

4. Silent operation is performed by the continuous engagement of the toothed gears.

5. Enable the use of a stepper motor at low speed without having to encode on the axis.

In a preferred form of the invention, a buckle clutch is desirable as the clutch means because the load is distributed over a number of teeth to minimize wear. Adjustment of the separating force can be adapted to various requirements by biasing the spring of the wheel stopper clutch. Similarly, the use of a spline hub or pinion ensures that the buckle clutch is properly positioned and that the clutch can be disengaged under load.

Although the preferred embodiment has been described in the context of a drug infusion pump, the infusion pump and the drive system work equally well in either direction, so that the pump draws in and discharges fluid. It will be easily perceived to be used for. For example, in certain types of blood analysis, a certain amount of blood to be analyzed needs to be rapidly inhaled, and the drive system according to the above embodiment is such that such a rapid inhalation is realized. . Further, the pump is used for pumping other fluids other than the drug.

Claims (5)

(57) [Claims] 1. A pump for supplying a controlled volume of fluid from an injector having a body and a plunger, comprising: housing and arranging means for housing and arranging the body of the injector; and supported by the housing and arranging means. Injector actuator means for engaging the plunger of the injector; actuator position signal generating means for generating an electrical signal indicating the position of the injector actuator means; connected to the injector actuator means; A drive unit that supplies the fluid by moving the plunger; a drive control unit that controls the drive unit; a movable arm that contacts a main body of the injector supported by the housing arrangement unit; Arm position signal generating means for generating a signal corresponding to the position of the arm in contact with the main body; Storage means for storing predetermined data associated with the position occupied by the arm in contact with one or more injectors together with rate information; and the value of the signal associated with the arm position is a programmed value. Logic circuit means for determining whether or not the output signal of the logic circuit means indicates a negative decision, and in response to an output signal of the logic circuit means indicating a negative determination, engaging the plunger of the injector when empty. Means for storing calibration injector data into the drive control means by storing the position of the injector actuator means and storing the position of the injector actuator means which engages the plunger of the injector when full; Means for inputting the volume of the injector to a storage location of the injector actuator means, and the injector input by a user Means for calculating from the volume the supply rate used by the drive control means to control the supply of fluid contained in the injector at a predetermined supply rate; and an output signal of a logic circuit means indicating a positive decision. Means for retrieving a stored supply rate corresponding to the stored data in response to the stored data. 2. The pump according to claim 1, wherein said drive means has a permanently maintained connection between said drive means and said actuator position signal generating means. 3. The movement of the movable arm causes a corresponding movement of the input shaft with respect to the potentiometer to generate the signal indicative of the position of the arm and to be disposed between the arm and the potentiometer. 3. The pump according to claim 1, wherein the gear means increases the rotation speed of the input shaft. 4. The pump according to claim 3, further comprising means for biasing said gear means in a direction to reduce movement of said input shaft caused by gear backlash. 5. The storage means includes a look-up table of pre-programmed data, wherein the calibration data entry is replaced by pre-programmed data having a volume value closest to the data currently being entered. The pump according to any one of claims 1 to 4, wherein: