METHOD OF CONTROLLING A VOLUME WHICH CAN BE CONVEYED WITH A METERING PUMP

Abstract

The present invention concerns a method of controlling a liquid volume which can be conveyed with a metering pump in a given time, comprising the steps: a. providing an input signal for controlling the liquid volume which can be conveyed with the metering pump in the given time, and b.lLinking the input signal to an actuating signal which influences the liquid volume which can be conveyed with the metering pump in the given time so that a change in the input signal leads to a change in the actuating signal and thus a change in the liquid volume which can be conveyed. To react to individual process demands it is proposed according to the invention that linking in step b. is effected in such a way that a change in the input signal leads to a change in the liquid volume which can be conveyed with the metering pump in the given time, which change in the liquid volume is non-proportional to the change in the input signal.

Claims

1. A method of controlling a liquid volume which can be conveyed with a metering pump (10) in a given time, comprising the steps: a. providing an input signal (1) for controlling the liquid volume which can be conveyed with the metering pump (10) in the given time, and b. linking the input signal (1) to an actuating signal (2) which influences the liquid volume which can be conveyed with the metering pump (10) in the given time so that a change in the input signal (1) leads to a change in the actuating signal (2) and thus a change in the liquid volume which can be conveyed with the metering pump (10) in the given time, c. characterised in that linking in step b. is effected in such a way that a change in the input signal (1) leads to a change in the liquid volume which can be conveyed with the metering pump (10) in the given time, which change in the liquid volume is non-proportional to the change in the input signal (1).

2. A method according to claim 1 characterised in that linking in step b. is effected in such a way that a change in the input signal (1) leads to a change in the liquid volume which can be conveyed with the metering pump (10) in the given time, said change in the liquid volume being non-linear in relation to the change in the input signal (1).

3. A method according to claim 1 wherein linking of the input signal (1) to the actuating signal (2) is effected by way of a mathematical function, wherein the mathematical function is a non-proportional function.

4. A method according to claim 3 wherein the mathematical function is a strictly monotonically rising or a strictly monotonically falling function.

5. A method according to claim 1 wherein the mathematical function is a polynomial.

6. A method according to claim 1 wherein the input signal (1) is an analog signal wherein the analog input signal (1) in an additional step is converted into a digital intermediate signal (3), wherein the digital intermediate signal (3) is linked in step b. to the actuating signal (2).

7. A method according to claim 1 wherein in step b. linking is effected in such a way that a linearly increasing input signal firstly leads to an increase in the liquid volume which can be conveyed with the metering pump (10) in the given time and then a drop in the liquid volume which can be conveyed with the metering pump (10) in the given time.

8. A metering pump (10) for conveying a liquid volume of a liquid in a given time, comprising a metering chamber (11), a displacement element (12) moveable between a first and a second position, wherein the displacement element (12) is so connected to the metering chamber (11) that a metering chamber volume of the metering chamber (11) is varied with the movement of the displacement element (12) between the first and second positions, a drive (13) for moving the displacement element (12) between the first and the second position, and a control (14), wherein the control (14) is so connected to the drive (13) that during operation of the metering pump (10) the drive (13) is controlled by means of the actuating signal (2) by the control (14) so that the liquid volume of the liquid which is conveyed by the metering pump (10) in the given time is varied by a change in the actuating signal (2), wherein the control (14) further has an input for an input signal (1), wherein the input signal (1) at the input is linked in the control (14) to the actuating signal (2) so that a change in the input signal (1) leads to a change in the actuating signal (2), characterised in that the input signal (1) is linked to the actuating signal (2) in the control (14) in such a way that a change in the input signal (1) leads to change in the liquid volume conveyed by the metering pump (10) in the given time, said change in the liquid volume being non-proportional to the change in the input signal.

9. A metering pump (10) according to claim 8 wherein the actuating signal influences a stroke frequency, a stroke length and/or a stroke speed of the displacement element (12) of the metering pump (10).

10. A metering pump (10) according to claim 8 wherein the input signal (1) is a digital input signal (1) or is converted by means of an analog-digital converter (15) into a digital intermediate signal (3), wherein the actuating signal (2) is an analog signal, wherein the control (14) of the metering pump (10) further has a digital-analog converter (16), wherein the digital input signal (1) or the digital intermediate signal (3) is converted into the analog actuating signal (2) in the control (14) by means of the digital-analog converter (16), wherein the digital-analog converter (16) is a non-proportional digital-analog converter (16).

11. A method according to claim 3 wherein the mathematical function is a non-linear function.

12. A method according to claim 5 wherein the mathematical function is a polynomial of degree 2.

13. A method according to claim 5 wherein the mathematical function is a polynomial of degree 3.

14. A method according to claim 6 wherein the analog signal is a voltage.

Description

[0043] Further advantages, features and possible uses of the present invention will be apparent from the description hereinafter of an embodiment and the accompanying Figures. Identical components in that case are denoted by the same references.

[0044] FIG. 1 shows a diagrammatic view of an embodiment of the metering pump according to the invention,

[0045] FIG. 2a diagrammatically shows the digital intermediate signal in dependence on the input signal,

[0046] FIG. 2b diagrammatically shows the actuating signal in dependence on the digital intermediate signal in a first embodiment of the method according to the invention,

[0047] FIG. 2c diagrammatically shows the actuating signal in dependence on the digital intermediate signal in a second embodiment of the method according to the invention, and

[0048] FIG. 2d diagrammatically shows the actuating signal in dependence on the digital intermediate signal in a third embodiment of the method according to the invention.

[0049] FIG. 1 shows an embodiment of the metering pump 10 according to the invention having a metering chamber 11 and a displacement element 12 moveable between a first and a second position, wherein the displacement element 12 is reciprocated between the first and the second positions by a drive 13. In addition the metering pump 10 according to the invention has a control 14, the control 14 being so connected to the drive 13 that an actuating signal 2 is passed to the drive 13 by the control 14. The control 14 thus controls the drive 13 by means of the actuating signal 2.

[0050] Liquid is drawn into or pushed out of the stroke chamber 11 by the movement of the displacement element 12. In that situation the control 14 acts by means of the actuating signal 2 and the drive 13 on the stroke frequency of the displacement element 12 and the metering chamber volume of the metering pump 10. In that way the liquid volume which can be conveyed with the metering pump 10 in the given time can be varied.

[0051] The change in the liquid volume which can be conveyed with the metering pump 10 in a given time is implemented by means of an analog input signal 1, like for example a voltage signal which in a first step is converted into a digital intermediate signal 3 by an analog-digital converter 15. That digital intermediate signal can for example assume up to 25 discrete values. The ditial intermediate signal 3 is passed to the control 14 which in turn has a digital-analog converter 16 for converting the digital intermediate signal 3 into the analog actuating signal 2 in such a way that a change in the input signal 1 or the digital intermediate signal 3 leads to a non-proportional change in the actuating signal 2 and thus a non-proportional change in the liquid volume which can be conveyed with the metering pump 10 in a given time.

[0052] FIG. 2a shows the result of analog-digital conversion by means of the analog-digital converter 15. It can be seen that the analog-digital converter 15 converts the incoming input signal 1 proportionally into the digital intermediate signal 3, that is to say the values of the input signal 1 are linked to the values of the digital intermediate signal 3 by way of a proportionality factor.

[0053] FIG. 2b then shows the result of a first embodiment of the digital-analog converter 16 which links the digital intermediate signal 3 to the actuating signal 2 by way of a non-proportional mathematical function. As shown in FIG. 2 the mathematical function is a square function of the form y=x.sup.2. A change in the digital intermediate signal 3 or the input signal 1 at low values here results in a comparatively slight change in the actuating signal 3 and thus the liquid volume which can be conveyed with the metering pump 10 in a given time. A change in the ditial input signal 3 at higher values in contrast leads to a more marked change in the actuating signal 2. In this embodiment for example at the beginning of a process initially little liquid can be supplied in very targeted fashion and at a later time more liquid when a less accurate setting of the supply of liquid is adequate.

[0054] In FIG. 2c linking of the digital intermediate signal 3 to the actuating signal 2 is effected in the digital-analog converter 16 by way of a root-form function. While at low values of the digital intermediate signal a comparatively great change in the actuating signal 2 and thus also a great change in the liquid volume which can be conveyed with the metering pump 10 in a given time is achieved, a change in the digital intermediate signal 3 at higher values leads to a lesser change in the actuating signal. In this FIG. 2c embodiment therefore it is possible firstly to quickly achieve a desired liquid volume which can then be adjusted in fine steps.

[0055] FIG. 2d shows the output of a further embodiment of the digital-analog converter 16. It will be seen that here there is a first sub-interval 17 in the digital intermediate signal, in which a change in the digital intermediate signal 3 leads to no or almost no variation in the actuating signal 2. In a second sub-interval 18 of the digital intermediate signal 3 the actuating signal passes through a minimum.

[0056] In the case of such linking of the input signal 1 or the digital intermediate signal 3 to the actuating signal 2 therefore a local maximum is achieved in the first sub-interval 17 and a local minimum in the second sub-interval 18. Those local minima and maxima can be individually adapted to the process requirements.

[0057] In contrast to the known systems in the state of the art the conveyor speed can be very accurately set in the desired range with an analog input signal which is easy to generate. The user of the pump does not have to make any high-level demands on the reliability and accuracy of the input signal.

LIST OF REFERENCES

[0058] 1 input signal [0059] 2 actuating signal [0060] 3 intermediate signal [0061] 10 metering pump [0062] 11 metering chamber [0063] 12 displacement element [0064] 13 drive [0065] 14 control [0066] 15 analog-digital converter [0067] 16 digital-analog converter [0068] 17 first sub-interval [0069] 18 second sub-interval