Solenoid Pump Driver

Abstract

A method of driving a solenoid pump of the type comprising a metal shuttle urged by a solenoid against a spring with the spring providing the force for the pumping stroke of the shuttle is disclosed. The method comprises applying a periodic driving voltage to the solenoid. Each period of the driving voltage comprises a first portion during which the driving voltage increases from a minimum voltage to a maximum voltage to compress the spring, a second portion during which the driving voltage decreases from the maximum voltage to the minimum voltage to release the spring, and a third portion during which the driving voltage is maintained at the minimum voltage. The duration of the second portion is substantially less than the duration of the first portion and may be substantially instantaneous. The driving voltage increases from the minimum voltage to the maximum voltage substantially linearly during the first portion, such that the driving voltage has a sawtooth waveform.

Claims

1. A method of driving a solenoid pump of the type comprising a metal shuttle urged by a solenoid against a spring with the spring providing the force for a pumping stroke of the shuttle, the method comprising applying a periodic driving voltage to the solenoid, wherein each period of the driving voltage comprises a first portion during which the driving voltage increases from a minimum voltage to a maximum voltage to compress the spring, a second portion during which the driving voltage decreases from the maximum voltage to the minimum voltage to release the spring, and a third portion during which the driving voltage is maintained at the minimum voltage, wherein the duration of the second portion is substantially less than the duration of the first portion.

2. A method as claimed in claim 1, wherein the driving voltage decreases from the maximum voltage to the minimum voltage substantially instantaneously during the second portion.

3. A method as claimed in claim 1, wherein the driving voltage increases from the minimum voltage to the maximum voltage substantially linearly during the first portion.

4. A method as claimed in claim 1, wherein the driving voltage has a sawtooth waveform.

5. A method as claimed in claim 1 further comprising controlling the duration of the third portion to provide a required flow rate through the pump.

6. A method as claimed in claim further comprising controlling the maximum voltage to provide a required flow rate through the pump.

7. A method as claimed in claim 1, wherein the frequency of the driving voltage is different to the frequency of a supply voltage providing electrical power for the driving voltage.

8. A method as claimed in claim 1 further comprising controlling the frequency of the driving voltage to provide a required flow rate through the pump.

9. A method as claimed in claim 1, wherein the minimum voltage is zero volts.

10. A driver circuit for a solenoid pump, the driver circuit configured to generate a driving voltage in accordance with the method of claim 1.

11. A solenoid pump in combination with the driver circuit of claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

[0016] FIG. 1 is a sectional view of an electromagnetic pump;

[0017] FIG. 2 is a graph showing a comparison between a known driving method for the electromagnetic pump of FIG. 1 and a driving method according to an embodiment of the present invention;

[0018] FIG. 3 is a graph illustrating a driving method according to a further embodiment of the present invention;

[0019] FIG. 4 is a graph illustrating a driving method according to a yet further embodiment of the present invention; and

[0020] FIG. 5 is a schematic of a driving circuit according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0021] FIG. 2 shows, in the upper graph, a comparison of a sawtooth driving voltage for a solenoid pump according to an embodiment of the invention (dashed line) to a half-wave rectified driving voltage of the prior art (solid line). The solenoid pump may be of the type described in relation to FIG. 1. The lower graph in FIG. 2 shows the corresponding spring force of the power spring 3. As shown in FIG. 2, to achieve the same spring force from the power spring 3, the sawtooth driving voltage requires only 60% of the maximum voltage of the rectified driving voltage. Furthermore, the rapid decrease of the sawtooth driving voltage from the (60%) maximum voltage to zero volts, also saves energy. The amount of energy saved by using the sawtooth driving voltage is shaded in FIG. 2.

[0022] FIG. 3 shows a variation of the sawtooth driving voltage of an embodiment of the invention in a representation corresponding to FIG. 2. In this case, the first portion of the sawtooth waveform has a duration of 10 ms, as in the waveform of FIG. 2. The second portion of the sawtooth waveform, in which the driving voltage drops from a maximum value to zero volts is substantially instantaneous. In FIG. 3, the duration of the third portion of the sawtooth waveform in which the driving voltage is maintained at zero volts is reduced relative to the waveform shown in FIG. 2 from 10 ms to 8 ms. In this way, the frequency of the driving voltage is increased from 50 Hz to 56 Hz. The shorter duration of each period of the sawtooth waveform increases the flow rate through the pump.

[0023] FIG. 4 shows a variation of the sawtooth driving voltage of an embodiment of the invention in a representation corresponding to FIGS. 2 and 3. In this case, the first portion of the sawtooth waveform has a duration of 8 ms, which is shorter than in the waveform of FIGS. 2 and 3. The rate of change (gradient) of the driving voltage remains the same, however, such that the maximum voltage achieved during the first portion of the waveform is reduced, compared to FIGS. 2 and 3. Again, the second portion of the sawtooth waveform, in which the driving voltage drops from a maximum value to zero volts is substantially instantaneous. In FIG. 4, the duration of the third portion of the sawtooth waveform in which the driving voltage is maintained at zero volts is longer than in the waveforms of FIGS. 2 and 3 at 12 ms. In this way, the frequency of the driving voltage is maintained at 50 Hz, as in FIG. 3, but the flow rate through the pump is reduced as the power spring 3 only reaches 80% of its maximum compression.

[0024] The sawtooth driving voltage has the advantage that it uses less energy to achieve the same spring force than a conventional driving voltage. This means that a smaller power supply can be used and less heat is generated during operation of the pump, which increases the pump duty cycle. Furthermore, the operating frequency of the pump can be tuned to achieve the minimum mechanical noise from the pump components. For example, we have found that known pumps can operate at their quietest at a driving frequency of 47 Hz, rather than the conventional 50 Hz. Any suitable driver circuit may be used to generate the required sawtooth waveform.

[0025] FIG. 5 is a schematic of a driving circuit according to an embodiment of the present invention. The driving circuit 20 comprises a power supply 22 connecter to a microcontroller 24. The microcontroller is connected to a pump solenoid 28 via a switching circuit 26. The pump solenoid is typically the solenoid 5 as described in FIG. 1. The microcontroller 24 comprises a memory and at least one processor. The memory of the microcontroller 24 includes instructions which, when executed, cause the at least one processor to control the switching circuit 26 and the pump solenoid 28 to operate in accordance with methods as described previously. The switching circuit 26 provides inputs for the microcontroller 24 to control the operation of the pump solenoid 28.

[0026] In summary, a method of driving a solenoid pump of the type comprising a metal shuttle urged by a solenoid against a spring with the spring providing the force for the pumping stroke of the shuttle is disclosed. The method comprises applying a periodic driving voltage to the solenoid. Each period of the driving voltage comprises a first portion during which the driving voltage increases from a minimum voltage to a maximum voltage to compress the spring, a second portion during which the driving voltage decreases from the maximum voltage to the minimum voltage to release the spring, and a third portion during which the driving voltage is maintained at the minimum voltage. The duration of the second portion is substantially less than the duration of the first portion and may be substantially instantaneous. The driving voltage increases from the minimum voltage to the maximum voltage substantially linearly during the first portion, such that the driving voltage has a sawtooth waveform.

[0027] Throughout the description and claims of this specification, the words comprise and contain and variations of them mean including but not limited to, and they are not intended to (and do not) exclude other components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0028] Features, integers, characteristics or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.