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Electromagnetic pump driving methodRelated Patent Categories: Pumps, Condition Responsive Control Of Pump Drive Motor, By Control Of Electric Or Magnetic Drive MotorElectromagnetic pump driving method description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070025861, Electromagnetic pump driving method. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to a method of driving an electromagnetic pump, and in more detail to a method of driving an electromagnetic pump used to convey a fluid such as a gas or a liquid. BACKGROUND ART [0002] The present applicant has previously proposed a smaller and slimmer electromagnetic pump where a plunger composed of a magnetic material is housed inside a cylinder of a stator so as to be capable of reciprocal movement and a current is passed through a single-phase electromagnetic coil fitted around the cylinder so that in one pump chamber out of the pump chambers formed between both end surfaces of the cylinder and both side surfaces in the direction of movement of the plunger, fluid is introduced from outside via a first valve and fluid is expelled to the outside via a second valve, with the same pumping action being realized in the other pump chamber. By passing a current through the electromagnetic coil, the plunger is caused to move in the axial direction of the cylinder in reaction to the electromagnetic force received by the electromagnetic coil from the magnetic field (see Patent Document 1). Patent Document 1 [0003] Japanese Patent Application No. 2002-286188 [0004] As a method of driving the electromagnetic pump described above, there is a method that applies a square wave voltage as shown in FIG. 14 to both ends of the electromagnetic coil to switch the direction of the current flowing in the electromagnetic coil and drive the plunger. FIG. 14 shows the relationship between the driving voltage and the opening/closing operations of a first intake valve and a first outflow valve and a second intake valve and a second outflow valve provided on the pump chambers. For example, when the square-wave driving voltage on the positive side is applied to the electromagnetic coil, the first intake valve of the pump chamber is opened and then the first outflow valve is closed to introduce fluid into the pump chamber. Also, the second outflow valve is opened and then the second intake valve is closed to expel fluid from the pump chamber. On the other hand, when the square wave voltage on the negative side is applied to the electromagnetic coil, the first outflow valve of the pump chamber is opened and then the first intake valve is closed to expel fluid from the pump chamber. Also, the second intake valve is opened and then the second outflow valve is closed to introduce fluid into the pump chamber. DISCLOSURE OF THE INVENTION [0005] In the method of driving the electromagnetic pump described above, a current with an approximately square waveform flows in the electromagnetic coil so that the thrust produced for the plunger also has an approximately square waveform. Accordingly, when the polarity of the driving voltage is inverted between positive and negative, the pressure in the pump chamber fluctuates abruptly and the abrupt fluctuation in the forces that act on the inner surfaces of the pump chamber causes the cylinder side surfaces to vibrate. Due to the abrupt fluctuation in the electromagnetic force that acts on the electromagnetic coil on the stator, the stator also vibrates. In addition, when the first intake valve and the second outflow valve or the first outflow valve and the second intake valve are opened, noise and vibration are produced when the valves strongly collide with and come to rest upon engaging surfaces of the frames that form the pump chambers. [0006] In addition, although the first intake/outflow valves and the second intake/outflow valves are opened and closed due to changes in pressure inside the pump chamber that accompany movement of the plunger, for any of the valves, compared to when the valve is opened from a closed state, the timing at which the valve is closed from an opened state is slightly delayed due to the fluid temporarily flowing in the opposite direction to the preceding direction of flow. At this time, a phenomenon called a "water hammer" occurs where the fluid flowing in the opposite direction collides with the valve to momentarily produce a high-pressure part in the fluid in a narrow flow channel. This water hammer also produces vibration and noise. As one example, a noise level of 33 db was detected for the driving method that applies the square wave driving voltage shown in FIG. 14. [0007] The present invention was conceived to solve the problems described above and it is an object of the present invention to provide a method of driving an electromagnetic pump that reduces noise and vibration that accompany abrupt fluctuations in pressure inside a pump chamber when the electromagnetic pump is driven. [0008] To achieve the stated object, a method of driving an electromagnetic pump according to the present invention conveys a fluid from a pump chamber formed inside a cylinder by housing a plunger including a permanent magnet inside the cylinder and passing a current through an aircore electromagnetic coil fitted around the cylinder to reciprocally move the plunger in the axial direction inside the cylinder, wherein a pulse voltage is applied alternately on a positive side and a negative side to drive the electromagnetic coil such that a change in voltage that occurs when the polarity of the pulse voltage is inverted has a continuous slope at least between the positive side and the negative side. [0009] According to another method, the current flowing through the electromagnetic coil is detected and a pulse current flows where a change in current that occurs when the polarity of the current is inverted has a continuous slope at least between the positive side and the negative side. [0010] According to yet another method, a pulse voltage is applied or a pulse current flows including a period where a voltage or current value is zero when the polarity of a driving voltage or a supplied current of the electromagnetic coil is inverted. [0011] According to yet another method, a pulse voltage is applied or a pulse current flows so that an offset voltage of no greater than 30% of a maximum voltage is applied or an offset current of no greater than 30% of a maximum current flows when the polarity of a driving voltage or a supplied current of the electromagnetic coil is inverted. EFFECT OF THE INVENTION [0012] By using the method of driving an electromagnetic pump described above, a pulse voltage is applied alternately on a positive side and a negative side to drive the electromagnetic coil such that a change in voltage that occurs when the polarity of the pulse voltage is inverted has a continuous slope at least between the positive side and the negative side, or the current flowing through the electromagnetic coil is detected and a supplying of current is controlled so that a pulse current flows where a change in current when the polarity of the current is inverted has a continuous slope at least between a positive side and a negative side, and therefore the excitation direction of the electromagnetic coil is not abruptly inverted. Accordingly, the movement speed of the plunger is eased and abrupt fluctuations in the pressure of the pump chamber are reduced, making it possible to reduce vibration in the cylinder side walls due to abrupt fluctuations in the force that acts on the inner surfaces of the pump chamber. It is also possible to reduce vibration in the stator due to abrupt fluctuations in the electromagnetic force that acts on the electromagnetic coil on the stator. In addition, reverse flow of the fluid when an intake valve or an outflow valve is closed is reduced, thereby easing the water hammer phenomenon and reducing the production of noise and vibration. [0013] Also, by having a pulse voltage applied or a pulse current flow with a period where a value of the voltage or current is zero when the polarity of a driving voltage or a supplied current of the electromagnetic coil is inverted, it is possible to reduce the closing speed of the intake valve or outflow valve for fluid in the pump chamber, reducing reverse flow and easing the water hammer phenomenon, thereby reducing the production of noise and vibration. [0014] Also, by having a pulse voltage applied or a pulse current flow so that an offset voltage of no greater than 30% of a maximum voltage is applied or an offset current of no greater than 30% of a maximum current flows in advance when the polarity of a driving voltage or a supplied current of the electromagnetic coil is inverted, it is possible to reduce the closing speed of the intake valve or outflow valve for fluid on the pump chamber before the maximum voltage is applied or the maximum current flows with the inverted polarity, reducing reverse flow and easing the water hammer phenomenon and thereby reducing the production of noise and vibration. Biasing of the thrust that acts on the plunger in the non-excitation state can be eased by adjusting the offset voltage or offset current so that weak excitation is produced in the opposite direction to the direction of the thrust that acts on the plunger. [0015] Also, by having a minute voltage pulse of at least 30% of a maximum voltage applied or a minute current pulse of at least 30% of a maximum current flow before the period where the value of the voltage or current is zero or the period where the offset voltage is applied or the offset current flows, it is possible to shorten the excitation period for weakening the previous excitation state of the electromagnetic coil, thereby reducing the drop in pump efficiency. BRIEF DESCRIPTION OF THE DRAWINGS [0016] FIG. 1 is a driving voltage waveform diagram for an electromagnetic pump according to a first embodiment. [0017] FIG. 2 is a driving voltage waveform diagram for an electromagnetic pump according to the first embodiment. [0018] FIG. 3 is a driving voltage waveform diagram for an electromagnetic pump according to the first embodiment. Continue reading about Electromagnetic pump driving method... Full patent description for Electromagnetic pump driving method Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Electromagnetic pump driving method patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Electromagnetic pump driving method or other areas of interest. ### Previous Patent Application: Sewage lift mechanism with remote alarm Next Patent Application: Compressible gas ejector with unexpanded motive gas-load gas interface Industry Class: Pumps ### FreshPatents.com Support Thank you for viewing the Electromagnetic pump driving method patent info. 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