Drive circuit, actuator, and pump

Abstract

Provided is a drive circuit 66 for an electromagnet 61 used in a pump 1 in which movable plates 62, 63 vibrate by means of a magnetic field generated by the electromagnet 61, thereby suctioning or discharging a fluid. The drive circuit 66 alternates between: an energization period in which the movable plates 62, 63 are deformed in a direction approaching the electromagnet 61 by supplying a current to the electromagnet 61; and a non-energization period in which the movable plates 62, 63 are returned from the deformed state by cutting off the supply of the current to the electromagnet 61. During the non-energization period, the current flowing through the electromagnet 61 is suppressed by a counter-electromotive force.

Description

Drive Circuit, Actuator, and Pump

[0001] The present disclosure relates to a drive circuit, an actuator, and a pump.

[0002] Patent Document 1 below discloses a pump that supplies current to a solenoid, moves a plunger by the magnetic force generated by the solenoid, and operates a diaphragm by the plunger to discharge fluid.

[0003] Japanese Patent Application Laid-Open No. 2012-092772

[0004] The pump of Patent Document 1 is configured to use the biasing force of a return spring to retract the plunger by stopping the supply of current to the solenoid and eliminating the magnetic force generated by the solenoid.

[0005] However, the pump of Patent Document 1 may have a problem that even though the supply of current to the solenoid is stopped, a current due to the back electromotive force flows through the solenoid, generating a magnetic force in the solenoid. In this case, the magnetic force generated by the solenoid will reduce the retraction force of the plunger.

[0006] An object of the present disclosure is to provide a drive circuit, an actuator, and a pump that can suppress a decrease in amplitude due to the back electromotive force of a vibrating body that vibrates due to the magnetic field generated by a solenoid.

[0007] A drive circuit according to an aspect of an embodiment of the present invention is a drive circuit for a solenoid used in an actuator that vibrates an elastic spring by the magnetic field generated by the solenoid. The drive circuit alternately switches between a conduction period in which the elastic spring is deformed in a direction approaching the solenoid by supplying current to the solenoid and a non-conduction period in which the elastic spring is restored from deformation by stopping the supply of current to the solenoid. In the non-conduction period, the current flowing through the solenoid due to the back electromotive force is suppressed.

[0008] According to the present disclosure, it is possible to provide a drive circuit, an actuator, and a pump that can suppress a decrease in amplitude due to the back electromotive force of a vibrating body that vibrates due to the magnetic field generated by a solenoid.

[0009] Figure 1 shows an example of the external appearance of the pump according to the embodiment. Figure 2 shows a schematic diagram of the general configuration inside the pump housing. Figure 3 shows a schematic diagram of the general configuration of the resonant actuator. Figure 3 shows an exploded perspective view of the resonant actuator. Figure 4 shows a schematic diagram of the cross-sectional shape along the axis of symmetry CA of the pump according to the embodiment. Figure 5 shows a schematic diagram of the cross-sectional shape along the axial direction of the fourth flow path of the pump according to the embodiment. Figure 6 shows a schematic diagram showing the operation of the pump when the coil is energized. Figure 7 shows a schematic diagram showing the area around the first pump chamber in the state shown. Figure 7 shows a schematic diagram showing the operation of the pump when the coil is not energized. Figure 9 shows a schematic diagram showing the area around the first pump chamber in the state shown. Figure 6 shows a schematic diagram of the magnetic field generated in an electromagnet using a flat core as a comparative example. Figure 7 shows a plan view of the internal structure of the pump housing from the Z-positive direction. Figure 8 shows a schematic diagram of the pump chamber in an enlarged view. Figure 9 shows a state in which the piston moves in a direction that reduces the volume of the pump chamber. Figure 1 shows a schematic diagram illustrating a state of movement in the direction of increasing volume. Figure 1 shows an application example of the pump according to the embodiment. Figure 1 shows a circuit diagram of the drive circuit of the pump according to the embodiment. Figure 1 shows a relationship between the input signal and the current amount of the electromagnet in the drive circuit according to the embodiment. Figure 1 shows various measurement results in the drive circuit according to the embodiment. Figure 1 shows various measurement results in the drive circuit according to the embodiment. Figure 1 shows a relationship between the duty cycle of the input pulse signal, the cancellation period of the back electromotive force and the current flowing through the electromagnet in the drive circuit according to the embodiment. Figure 1 shows a schematic diagram illustrating a state of movement in the direction of increasing volume. Figure 1 shows a circuit diagram of the drive circuit of the pump according to the embodiment. Figure 1 shows a circuit diagram of the drive circuit of the pump according to the embodiment. Figure 1 shows various measurement results in the drive circuit according to the embodiment.

[0010] The embodiments will be described below with reference to the attached drawings. To facilitate understanding of the explanation, the same reference numerals are used for identical components in each drawing whenever possible, and redundant explanations are omitted.

[0011] In the following explanation, the X, Y, and Z directions are perpendicular to each other. The X and Y directions are horizontal, and the Z direction is vertical. The X direction is the longitudinal direction of the housing 2 and the resonant actuator 6. The Y direction is the short direction of the housing 2 and the resonant actuator 6. Also, for the sake of clarity in the following explanation, the positive Z direction may be referred to as the upper side, and the negative Z direction as the lower side.

[0012] [Basic configuration of the pump] The basic configuration of the pump 1 according to the embodiment will be described with reference to Figures 1 to 6.

[0013] Figure 1 is a perspective view showing an example of the external appearance of the pump 1 according to the embodiment. As shown in Figure 1, the pump 1 comprises a housing 2, an inlet 3, and an outlet 4.

[0014] The housing 2 incorporates elements related to the pump function, such as the flow path 5 and the resonant actuator 6, which will be described later. In the example shown in Figure 1, the housing 2 has a pair of rectangular main surfaces 21 and 22, and the dimensions between each main surface 21 and 22 form a rectangular parallelepiped shape that is relatively thin with respect to each side of the main surface.

[0015] The pair of main surfaces 21 and 22 are formed to be the same shape and are arranged opposite each other in the Z direction. The pair of main surfaces 21 and 22 are arranged so that the long sides of the rectangle face each other in the Y direction and the short sides face each other in the X direction. That is, the pair of main surfaces 21 and 22 are formed to be line-symmetric in the Y direction with respect to a symmetry axis CA (see Figure 2) that passes through the center of the short side in the Y direction and extends in the X direction, and also to be line-symmetric in the X direction with respect to a symmetry axis CB (see Figure 2) that passes through the center of the long side in the X direction and extends in the Y direction. Figure 1 shows the center line CO of the pump 1 that passes through the intersection of these two symmetry axes CA and CB (i.e., the centers of the pair of main surfaces 21 and 22) and extends in the Z direction.

[0016] Between the pair of main surfaces 21 and 22, there are four side surfaces 23 to 26 that connect the sides of each of the four sides of each main surface. One pair of side surfaces 23 and 24 of the four side surfaces are formed in the same rectangular shape and are arranged opposite each other in the X direction, with their respective long sides connected to the short sides of the pair of main surfaces 21 and 22. The other pair of side surfaces 25 and 26 of the four side surfaces are formed in the same rectangular shape and are arranged opposite each other in the Y direction, with their respective long sides connected to the long sides of the pair of main surfaces 21 and 22.

[0017] The intake port 3 draws fluid into the housing 2. The outlet port 4 discharges the fluid pressurized by the pump function inside the housing 2. In the example shown in Figure 1, the intake port 3 is located on the negative Y-direction side of the side 23 of the housing 2, and the outlet port 4 is located on the positive Y-direction side of the side 24. Both the intake port 3 and the outlet port 4 are in communication in the X-direction, and are positioned so that the direction of fluid intake from the intake port 3 into the housing 2 and the direction of fluid discharge from the housing 2 to the outlet port 4 are the same. Furthermore, the intake port 3 and the outlet port 4 are positioned so as to be point-symmetric when viewed from the Z-direction with respect to the center line CO of the pump 1.

[0018] Figure 2 is a schematic diagram showing the general internal configuration of the housing 2 of the pump 1 shown in Figure 1. Figure 2 is a plan view of the pump 1 as seen from the positive Z direction. In Figure 2, the internal structure of the housing 2 is schematically illustrated, and the external shape of the housing 2 (i.e., the four sides 23-26) is shown by dashed lines. In Figure 2, the axis of symmetry CA, which passes through the center in the Y direction of the main surfaces 21 and 22 of the housing 2 and extends in the X direction, and the axis of symmetry CB, which passes through the center in the X direction and extends in the Y direction, are shown by dashed lines. In Figure 2, the intersection of the axis of symmetry CA and the axis of symmetry CB is shown as the center line CO.

[0019] As shown in Figure 2, the pump 1 has a flow path 5 inside the housing 2 that connects the intake port 3 and the discharge port 4. The flow path 5 has a first flow path 51, a second flow path 52, a third flow path 53, a fourth flow path 54, a fifth flow path 55, a sixth flow path 56, a seventh flow path 57, and an eighth flow path 58.

[0020] The first channel 51 is arranged so as to extend in the positive X direction, with its upstream end connected to the downstream end of the intake port 3. The second channel 52 and the third channel 53 branch off, with their upstream ends both connected to the downstream end of the first channel 51, and are arranged so as to extend in the negative X direction and the positive X direction, respectively. The fourth channel 54 is arranged so as to extend in the positive Y direction, with its upstream end connected to the downstream end of the second channel 52. The fifth channel 55 is arranged so as to extend in the positive Y direction, with its upstream end connected to the downstream end of the third channel 53. The sixth channel 56 extends in the positive X direction, with its upstream end connected to the downstream end of the fourth channel 54, and the seventh channel 57 extends in the negative X direction, with its upstream end connected to the downstream end of the fifth channel 55, and the sixth channel 56 and the seventh channel 57 merging at their downstream ends. The eighth flow path 58 is positioned such that its upstream end is connected to the confluence of the sixth flow path 56 and the seventh flow path 57, extends in the positive X direction, and its downstream end is connected to the upstream end of the discharge port 4. In Figure 2, the flow direction of the fluid flowing inside the intake port 3, flow path 5, and discharge port 4 is illustrated with arrows.

[0021] As explained with reference to Figure 1, the arrangement of the inlet 3 and outlet 4 is such that they are point-symmetrical when viewed from the Z direction with respect to the center line CO of the pump 1. Therefore, it is preferable that the overall shape of the flow path 5 is also arranged in a similar way, so that it is point-symmetrical when viewed from the Z direction with respect to the center line CO of the pump 1. This makes it easier for fluid to flow from the inlet 3 to the outlet 4 through the flow path 5.

[0022] Furthermore, a resonant actuator 6 is installed inside the housing 2 as a drive source for the pump 1. The resonant actuator 6 has an electromagnet 61 and is a device that generates vibration motion by switching the electromagnet 61 on and off. The resonant actuator 6 also causes the movable parts to resonate by setting the frequency of the control signal that switches between on and off (i.e., the switching frequency) to be the same as, or near, the resonant frequency of, the movable parts (a group of components including movable plates 62, 63 and leaf springs 64, 65, etc., which will be described later), which are the vibration elements. As a result, when the electromagnet 61 is on, the resonant actuator 6 can efficiently vibrate the movable parts by utilizing the resonance of the movable parts in addition to the attraction of the movable parts by the electromagnet 61.

[0023] In the example shown in Figure 2, the resonant actuator 6 is positioned such that its longitudinal direction is in the X direction and its short direction is in the Y direction, and is located at the center when viewed in the Z direction. Furthermore, like the housing 2, the resonant actuator 6 is formed to be symmetrical in the Y direction with respect to the symmetry axis CA, and symmetrical in the X direction with respect to the symmetry axis CB. The electromagnet 61 is located in the center of the resonant actuator 6.

[0024] Furthermore, the fourth channel 54 of channel 5 is positioned adjacent to the electromagnet 61 on the X-negative side and is arranged to penetrate the resonant actuator 6 in the Y direction. Similarly, the fifth channel 55 of channel 5 is positioned adjacent to the electromagnet 61 on the X-positive side and is arranged to penetrate the resonant actuator 6 in the Y direction.

[0025] Furthermore, a first pump chamber 7 and a second pump chamber 8 are provided in the portions of the fourth flow path 54 and the fifth flow path 55 that overlap with the resonant actuator 6 in a view in the Z direction. The first pump chamber 7 and the second pump chamber 8 are elements that pressurize and send fluid from the upstream side to the downstream side of the flow path 5 in conjunction with the vibrational motion of the resonant actuator 6. The fluid in the flow path 5 can flow from the inlet 3 to the outlet 4 by the operation of the first pump chamber 7 and the second pump chamber 8. In the example of Figure 2, both the first pump chamber 7 and the second pump chamber 8 are arranged on the axis of symmetry CA of the housing 2 and the resonant actuator 6. Also, as described above, in the example of Figure 2, the shape of the flow path 5 is arranged to be point-symmetric in a view in the Z direction with respect to the central axis CO passing through the centers of the pair of main surfaces 21 and 22 of the housing 2. As a result, the first pump chamber 7 and the second pump chamber 8 are positioned approximately midway along the flow path 5, making it possible to make the energy required for drawing fluid into the first pump chamber 7 and the second pump chamber 8 and for discharging fluid from the first pump chamber 7 and the second pump chamber 8 approximately the same.

[0026] The configuration of the resonant actuator 6 of the pump 1 according to this embodiment will be described with reference to Figures 3 and 4. Figure 3 is a perspective view showing the schematic configuration of the resonant actuator 6. Figure 4 is an exploded perspective view of the resonant actuator 6 shown in Figure 3. The perspective views in Figures 3 and 4 are the same as in Figure 1.

[0027] As shown in Figures 3 and 4, the resonant actuator 6 includes an electromagnet 61, a pair of movable plates 62 and 63, and a pair of leaf springs 64 and 65.

[0028] The electromagnet 61 is positioned in the center of the resonant actuator 6 in the Z direction. As shown in Figure 4, the electromagnet 61 has a core 611 and a coil 612. The core 611 has a winding portion 611A and a pair of widening portions 611B. The winding portion 611A is the central part of the core 611 in the X direction and extends in the X direction. The winding portion 611A has a rectangular cross-sectional shape along the YZ plane, and its outer circumferential surface is formed on four surfaces with the positive Y direction, negative Y direction, positive Z direction, and negative Z direction as normal directions. The coil 612 is wound around the outer circumferential surface of the winding portion 611A. The pair of widening portions 611B are formed at both ends of the winding portion 611A along the X direction, protruding on both sides in the Z direction relative to the winding portion. The widened portion 611B also has a rectangular cross-sectional shape along the YZ plane and has four surfaces with the positive Y direction, negative Y direction, positive Z direction, and negative Z direction as normal directions. In other words, the widened portion 611B has an upper end surface and a lower end surface that protrude by the same amount from the winding portion 611A along the Y direction.

[0029] The electromagnet 61 generates a magnetic field passing through the center of the coil 612 when an electric current flows through the wires constituting the coil 612, thereby energizing the coil 612. The magnetic field generated by the coil 612 is further strengthened by the core 611.

[0030] The pair of movable plates 62 and 63 are plate-shaped members formed from a magnetic material, and consist of a first movable plate 62 and a second movable plate 63. The first movable plate 62 is positioned on the positive Z side of the electromagnet 61, and the second movable plate 63 is positioned on the negative Z side of the electromagnet 61. The first movable plate 62 and the second movable plate 63 are formed to be the same shape and are positioned opposite each other in the Z direction.

[0031] Since the first movable plate 62 and the second movable plate 63 are magnetic materials, they are attracted to the electromagnet 61 by the magnetic field generated when the electromagnet 61 is energized. Furthermore, when the electromagnet 61 is switched from energized to de-energized, the first movable plate 62 and the second movable plate 63 move in the opposite direction to the attractive motion due to the biasing force added by the leaf springs 64 and 65 to which they are attached. In other words, the first movable plate 62 and the second movable plate 63 can perform vibrational motion in the Z direction by switching the energization of the electromagnet 61 between energization and de-energization.

[0032] As shown in Figure 4, the first movable plate 62 has a central portion 621 and a pair of ends 622 and 623. The central portion 621 is the central part of the first movable plate 62 in the X direction, and is formed in a rectangular shape with its long sides facing each other in the Y direction and its short sides facing each other in the X direction when viewed in the Z direction. The shape of the central portion 621 is formed to cover the entire outer shape of the electromagnet 61 when viewed from the positive Z direction. The pair of ends 622 and 623 are provided connected to both ends of the central portion 621 along the X direction, i.e., the short sides of the rectangular shape described above. In the example in Figure 4, one end 622 is positioned on the negative X direction side of the central portion 621, and the other end 623 is positioned on the positive X direction side of the central portion 621. The dimensions of the pair of ends 622 and 623 in the Y direction are the same as those of the central portion 621. The dimensions of the pair of ends 622 and 623 in the X direction are approximately the same for both. Furthermore, it is preferable that the thickness dimension of the pair of end portions 622 and 623 in the Z direction be formed to be thinner than the central portion 621, as illustrated in Figures 3 and 4.

[0033] At the pair of ends 622 and 623 of the first movable plate 62, pistons 71 and 81 are installed on the Z-negative direction side of their respective surfaces, extending in the Z-negative direction. The pistons 71 and 81 will be described later.

[0034] The second movable plate 63 has a central portion 631 and a pair of ends 632 and 633. The central portion 631 is the central part of the second movable plate 63 in the X direction and is formed in a rectangular shape with its long sides facing each other in the Y direction and its short sides facing each other in the X direction when viewed in the Z direction. The shape of the central portion 631 is formed to cover the entire outer shape of the electromagnet 61 when viewed from the negative Z direction side. The pair of ends 632 and 633 are provided connected to both ends of the central portion 631 along the X direction, i.e., the short sides of the rectangular shape described above. In the example of Figure 4, one end 632 is positioned on the negative X direction side of the central portion 621, and the other end 633 is positioned on the positive X direction side of the central portion 631. The dimensions of the pair of ends 632 and 633 in the Y direction are the same as those of the central portion 631. The dimensions of the pair of ends 632 and 633 in the X direction are approximately the same for both. Furthermore, it is preferable that the thickness dimension of the pair of end portions 632 and 633 in the Z direction be formed to be thinner than the central portion 631, as illustrated in Figures 3 and 4.

[0035] A pair of pistons 72 and 82 are installed on the Z-positive side of the respective Z-positive surfaces of the second movable plate 63, at the ends 632 and 633, respectively, so as to extend in the Z-positive direction. The pistons 72 and 82 will be described later.

[0036] The pair of leaf springs 64 and 65 are elastic members that bias in the Z direction, and consist of a first leaf spring 64 and a second leaf spring 65. The first leaf spring 64 is positioned on the positive Z side of the first movable plate 62, and the first movable plate 62 is attached to it. The second leaf spring 65 is positioned on the negative Z side of the second movable plate 63, and the second movable plate 63 is attached to it. The first leaf spring 64 and the second leaf spring 65 are formed in the same shape and are positioned opposite each other in the Z direction. In other words, as shown in Figure 3, the first leaf spring 64 and the second leaf spring 65 form the outermost part of the resonant actuator 6 in the Z direction. The first leaf spring 64 biases the first movable plate 62 in the opposite direction (positive Z side) to the attraction movement of the first movable plate 62 to the electromagnet 61. Similarly, the second leaf spring 65 biases the second movable plate 63 in the opposite direction (negative Z direction) to the attraction movement of the second movable plate 63 to the electromagnet 61.

[0037] As shown in Figure 4, the first leaf spring 64 has a central portion 641, a pair of fixed ends 642, and a pair of flexible portions 643. The central portion 641 is the central part of the first leaf spring 64 in the X direction, and is a flat plate-shaped portion formed such that its width dimension in the Y direction is constant and its outer edges on both sides in the Y direction extend along the X direction. The first leaf spring 64 is installed so that it can move integrally with the first movable plate 62 by attaching the first movable plate 62 to the central portion 641.

[0038] The pair of fixed ends 642 are positioned at both ends of the first leaf spring 64 along the X direction, and are flat plate-shaped portions formed such that their outer edges in the X direction both extend along the Y direction. The pair of fixed ends 642 of the first leaf spring 64 are fixed to a support 9 (see Figure 5, etc.), which is an example of a fixed object installed inside the housing 2, thereby fixing both ends in the X direction.

[0039] The pair of flexible portions 643 are located between the central portion 641 and the pair of fixed ends 642 of the first leaf spring 64, along the X direction. The pair of flexible portions 643 elastically deform and bend so that the relative positional relationship in the Z direction between the central portion 641 to which the first movable plate 62 is attached and the pair of fixed ends 642 fixed to the support 9 changes. The first leaf spring 64 can bias the first movable plate 62 attached to the central portion 641 by the elastic deformation of this pair of flexible portions 643.

[0040] Furthermore, as shown in Figure 4 and other figures, the pair of flexible portions 643 are formed with a relatively small width dimension perpendicular to the direction connecting the central portion 641 and the pair of fixed ends 642, in order to facilitate elastic deformation, and are also formed to curve in an S-shape when viewed in the Z direction. In addition, in order to make the amount of deflection in the Y direction more uniform, the S-shaped curved portions are arranged on both sides in the Y direction with respect to the axis of symmetry CA, and are formed to be symmetric with respect to the axis of symmetry CA. Note that the curved portions may have shapes other than S-shape.

[0041] As shown in Figure 4, the second leaf spring 65 has a central portion 651, a pair of fixed ends 652, and a pair of flexible portions 653. The central portion 651 is the central part of the second leaf spring 65 in the X direction, and is a flat plate-shaped portion formed such that its width dimension in the Y direction is constant and its outer edges on both sides in the Y direction extend along the X direction. The second leaf spring 65 is installed so that it can move integrally with the second movable plate 63 by attaching the second movable plate 63 to the central portion 651.

[0042] The pair of fixed ends 652 are positioned at both ends of the second leaf spring 65 along the X direction, and are flat plate-shaped portions formed such that their outer edges in the X direction both extend along the Y direction. The pair of fixed ends 652 of the second leaf spring 65 are fixed to a support 9 (see Figure 5, etc.), which is an example of a fixed object installed inside the housing 2, thereby fixing both ends in the X direction.

[0043] The pair of flexure portions 653 are portions disposed between the central portion 651 along the X direction of the second leaf spring 65 and the pair of fixed end portions 652. The pair of flexure portions 653 elastically deform and flex so that the relative positional relationship in the Z direction between the central portion 651 to which the second movable plate 63 is attached and the pair of fixed end portions 652 fixed to the support 9 varies. The second leaf spring 65 can bias the second movable plate 63 attached to the central portion 651 by the elastic deformation of such a pair of flexure portions 653.

[0044] Also, as shown in FIG. 4 and the like, the pair of flexure portions 653 are formed such that the width dimension orthogonal to the direction connecting the central portion 651 and the pair of fixed end portions 652 is relatively small so as to be easily elastically deformed, and are formed to be curved in an S shape when viewed in the Z direction. Further, in order to make the amount of flexure in the Y direction more uniform, the S-shaped curved portions are arranged on both sides in the Y direction with the symmetry axis CA interposed therebetween, and are formed to be line-symmetric with respect to the symmetry axis CA. Note that the curved portion may have a shape other than an S shape.

[0045] Also, as shown in FIG. 4, each element of the resonance actuator 6 is arranged such that the center position of each outer shape in the Z direction view coincides with the center line CO of the pump 1. Thereby, the center of gravity position of the resonance actuator 6 can be made near the center line CO of the pump 1, and the resonance actuator 6 can be operated in a balanced manner.

[0046] In the present embodiment, the first leaf spring 64 and the second leaf spring 65 are illustrated with a configuration in which the first movable plate 62 and the second movable plate 63 are attached to the central portions 641 and 651, respectively. However, a configuration in which the first movable plate 62 and the second movable plate 63 are attached to arbitrary positions other than the central portions in the X direction of the first leaf spring 64 and the second leaf spring 65 may also be used. Also, the first leaf spring 64 and the second leaf spring 65 are illustrated with a configuration in which they are fixed to the support 9 at the pair of fixed end portions 642 and 652, respectively. However, a configuration in which they are fixed to the support 9 at an arbitrary position other than both ends in the X direction may also be used.

[0047] Also, in the present embodiment, as described above, the first movable plate 62 and the second movable plate 63 are formed in the same shape, and the first leaf spring 64 and the second leaf spring 65 are formed in the same shape. The attachment positions of the first movable plate 62 to the first leaf spring 64 and the second movable plate 63 to the second leaf spring 65 are also the same. Therefore, the resonance frequencies of the first movable part (the first movable plate 62 and the first leaf spring 64) and the second movable part (the second movable plate 63 and the second leaf spring 65) are the same. Thus, if the switching frequency for switching the energized state and the non-energized state of the single electromagnet 61 disposed between the first movable part and the second movable part is set to the same frequency or a frequency close to the resonance frequency common to the first movable part and the second movable part, both the first movable part and the second movable part can be put into a resonance state together. Thereby, the resonance actuator 6 of the present embodiment can vibrate the movable part more efficiently.

[0048] Referring to FIGS. 5 and 6, the configurations of the first pump chamber 7 and the second pump chamber 8 of the pump 1 according to the embodiment will be described. FIG. 5 is a schematic diagram of a cross-sectional shape along the symmetry axis CA of the pump 1 according to the embodiment. In FIG. 5, among the components of the pump 1, the illustration of the components outside the resonance actuator 6 including the housing 2 is omitted.

[0049] As shown in FIG. 5, the fourth flow path 54 and the fifth flow path 55 are holes provided in the support 9 as an example of a fixture installed inside the housing 2. The support 9 includes, for example, a block-shaped component fixed to the inner wall surface of the housing 2 or the like. The other flow paths in the flow path 5 other than the fourth flow path 54 and the fifth flow path 55 are also holes provided in the support 9. In the example of FIG. 5, the support 9 in which the flow path 5 is provided and the support 9 to which the pair of fixed ends 642 of the first leaf spring 64 and the pair of fixed ends 652 of the second leaf spring 65 of the resonance actuator 6 are fixed are shown as an integral component, but a configuration in which separate components are integrally connected may also be used. Similarly, a configuration in which the first to eighth flow paths 51 to 58 constituting the flow path 5 are provided in separate supports and these supports are connected to form the flow path 5 may also be used.

[0050] The cross-section in Figure 5 is a cross-section along the axis of symmetry CA of the pump 1, and as is clear from Figure 2, it is a cross-section of the portion of the fourth flow path 54 in which the first pump chamber 7 is located, and the portion of the fifth flow path 55 in which the second pump chamber 8 is located. As shown in Figure 5, the first pump chamber 7 and the second pump chamber 8 are provided with cylinders 73 and 83, respectively, that communicate along the Z direction.

[0051] The cylinder 73 of the first pump chamber 7 is formed with openings on the positive Z-direction and negative Z-direction sides of the support 9. Furthermore, in this embodiment, the first piston 71 provided on the first movable plate 62 and the second piston 72 provided on the second movable plate 63 are positioned so that their axial directions coincide with those of the first pump chamber 7, i.e., coincide with the axial direction of the cylinder 73. Therefore, as shown in Figure 5, the first piston 71 is slidably inserted into the cylinder 73 from the opening on the positive Z-direction side, and the second piston 72 is slidably inserted into the cylinder 73 from the opening on the negative Z-direction side.

[0052] The cylinder 83 of the second pump chamber 8 is formed with openings on the Z-positive and Z-negative sides of the support 9. Furthermore, in this embodiment, the first piston 81 provided on the first movable plate 62 and the second piston 82 provided on the second movable plate 63 are positioned so that their axial directions coincide with those of the second pump chamber 8, i.e., coincide with the axial direction of the cylinder 83. Therefore, as shown in Figure 5, the first piston 81 is slidably inserted into the cylinder 83 from the opening on the Z-positive side, and the second piston 82 is slidably inserted into the cylinder 83 from the opening on the Z-negative side.

[0053] These first pistons 71, 81 and second pistons 72, 82 are installed in the first movable plate 62 and the second movable plate 63, respectively. Therefore, in conjunction with the vibrational motion of the first movable plate 62 and the second movable plate 63 in the Z direction, controlled by the energization of the electromagnet 61, the first pistons 71, 81 and the second pistons 72, 82 slide within the respective cylinders 73, 83, repeatedly moving closer to and further apart from each other. This allows the volume of the first pump chamber 7 and the second pump chamber 8 to be increased or decreased.

[0054] Figure 6 is a schematic diagram of the axial cross-sectional shape of the fourth passage 54 of the pump 1 according to the embodiment. As shown in Figure 6, an intake valve 74 and a discharge valve 75 are provided on the upstream and downstream sides of the first pump chamber 7 within the fourth passage 54, respectively. When the first piston 71 and the second piston 72 move closer together in the cylinder 73 and the volume of the first pump chamber 7 decreases, the intake valve 74 is configured to close to stop the inflow of fluid from the upstream side of the fourth passage 54 into the first pump chamber 7, and the discharge valve 75 is configured to open to discharge fluid from the first pump chamber 7 to the downstream side of the fourth passage 54. On the other hand, when the first piston 71 and the second piston 72 move further apart in the cylinder 73 and the volume of the first pump chamber 7 increases, the intake valve 74 is configured to open to allow fluid to flow from the upstream side of the fourth passage 54 into the first pump chamber 7, and the discharge valve 75 is configured to close to stop the discharge of fluid from the first pump chamber 7 to the downstream side of the fourth passage 54.

[0055] Figure 6 illustrates a configuration for achieving this effect in which both the intake valve 74 and the discharge valve 75 have a sphere positioned upstream of the fourth flow path 54 to seal the flow path, and a spring on the downstream side that biases the sphere upstream. However, the intake valve 74 and the discharge valve 75 may have structures other than those shown in Figure 6.

[0056] In this embodiment, the area between the lower end surface of the first piston 71 and the upper end surface of the second piston 72 within the cylinder 73 constitutes the volume of the first pump chamber 7. This volume increases or decreases in accordance with the vertical movement of the first piston 71 and the second piston 72 within the cylinder 73.

[0057] Although Figure 6 illustrates the cross-section of the fourth flow path 54 and explains the configuration of the first pump chamber 7, the configuration of the second pump chamber 8 in the fifth flow path 55 is similar. That is, the area between the lower end surface of the first piston 81 and the upper end surface of the second piston 82 within the cylinder 83 becomes the volume of the second pump chamber 8. This volume increases or decreases in accordance with the vertical movement of the first piston 81 and the second piston 82 within the cylinder 83.

[0058] [Pump Operation] The operation of the pump 1 according to this embodiment will be described with reference to Figures 7 to 10.

[0059] Figure 7 is a schematic diagram showing the operation of pump 1 when the coil is energized. Figure 8 is a schematic diagram showing the area around the first pump chamber 7 in the state shown in Figure 7. The outlines of Figures 7 and 8 are the same as those of Figures 5 and 6.

[0060] As shown in Figure 7, when the coil 612 of the electromagnet 61 is energized, a magnetic field M1 is generated passing through the center of the coil 612. The magnetic field M1 generated by the coil 612 is further strengthened by the winding portion 611A of the core 611, which is installed penetrating the center of the coil 612. In the example in Figure 7, a magnetic field M1 directed towards the positive X direction is generated inside the winding portion 611A.

[0061] The magnetic field M1 generated in this way branches in the positive Z and negative Z directions along the protruding direction of one of the widening sections 611B, which is located on the X-positive side of the winding section 611A of the core 611. Next, it flows through the interior of the first movable plate 62 and the second movable plate 63, which are located opposite each other on the upper and lower end surfaces of the widening section 611B, towards the X-negative side. Then, from the upper and lower end surfaces of the other widening section 611B, which is located on the X-negative side of the winding section 611A, it flows through the interior of this widening section 611B toward the central part in the Z direction, merges, and then flows back into the winding section 611A. In other words, when viewed from the Y-negative side, the magnetic field M1 illustrated in Figure 7 flows clockwise on the first movable plate 62 side and counterclockwise on the second movable plate 63 side.

[0062] As a result of the generation of this magnetic field M1, the first movable plate 62 is attracted to the electromagnet 61 and moves toward the negative Z direction, as shown by arrow A in Figure 7. Similarly, the second movable plate 63 is attracted to the electromagnet 61 and moves toward the positive Z direction, as shown by arrow B.

[0063] As the first movable plate 62 and the second movable plate 63 move toward the side attracted to the electromagnet 61, the first piston 71 slides within the cylinder 73 in the negative Z direction, as indicated by arrow C, and the second piston 72 slides within the cylinder 73 in the positive Z direction, as indicated by arrow D. As a result, the lower end surface of the first piston 71 and the upper end surface of the second piston 72 move closer to each other, reducing the volume of the first pump chamber 7.

[0064] Similarly, in the second pump chamber 8, the first piston 81 slides within the cylinder 83 in the negative Z direction, as indicated by arrow E. Also, the second piston 82 slides within the cylinder 83 in the positive Z direction, as indicated by arrow F. As a result, the lower end surface of the first piston 81 and the upper end surface of the second piston 82 move closer to each other, reducing the volume of the second pump chamber 8.

[0065] Ideally, the first movable plate 62 and the second movable plate 63 are both moved in the Z direction by the magnetic field M1. Therefore, the amount of sliding movement of the two first pistons 71 and 81 installed on the first movable plate 62 is the same as the amount of sliding movement of the two second pistons 72 and 82 installed on the second movable plate 63. Consequently, the amount of reduction in volume of the first pump chamber 7 and the second pump chamber 8 is also the same.

[0066] Furthermore, as the first movable plate 62 moves toward the side attracted to the electromagnet 61, the central portion 641 of the first leaf spring 64 to which the first movable plate 62 is attached also moves integrally with the first movable plate 62 in the direction of arrow A. At this time, since the fixed end 642 of the first leaf spring 64 is fixedly installed on the support 9, the central portion 641 is displaced toward the negative Z direction relative to the fixed end 642. Figure 7 shows the position of the first leaf spring 64 in the steady state in the Z direction as shown in Figure 5, indicated by the dotted line S1. As a result of this displacement, the deflection portion 643 located between the central portion 641 and the fixed end 642 elastically deforms toward the negative Z direction, and as a result, a biasing force f1 is generated in the deflection portion 643 to elastically return toward the positive Z direction, as shown by the dotted arrow f1 in Figure 7.

[0067] Similarly, as the second movable plate 63 moves toward the side attracted to the electromagnet 61, the central portion 651 of the second leaf spring 65 to which the second movable plate 63 is attached also moves integrally with the second movable plate 63 in the direction of arrow B. At this time, since the fixed end 652 of the second leaf spring 65 is fixedly installed on the support 9, the central portion 651 is displaced toward the positive Z direction relative to the fixed end 652. Figure 7 shows the position of the second leaf spring 65 in the Z direction in the steady state as shown in Figure 5, indicated by the dotted line S2. As a result of this displacement, the deflection portion 653 located between the central portion 651 and the fixed end 652 is elastically deformed toward the positive Z direction, and as a result, a biasing force f2 is generated in the deflection portion 653 to elastically return toward the negative Z direction, as shown by the dotted arrow f2 in Figure 7.

[0068] As shown in Figure 7, when the first pistons 71 and 81 and the second pistons 72 and 82 move closer together, the volumes of the first pump chamber 7 and the second pump chamber 8 decrease. As a result, as shown in Figure 8, in the first pump chamber 7, the spheres of the intake valve 74 and the discharge valve 75 are pressed upstream and downstream of the fourth passage 54, respectively, by the fluid in the first pump chamber 7. At this time, the sphere of the intake valve 74 blocks the upstream side of the fourth passage 54, so the intake valve 74 is closed. On the other hand, the sphere of the discharge valve 75 is movable downstream as indicated by arrow G, so the discharge valve 75 is opened. As a result, the fluid in the first pump chamber 7 is pressurized and discharged to the downstream side of the fourth passage 54.

[0069] As mentioned above, the reduction in volume between the first pump chamber 7 and the second pump chamber 8 is the same. Therefore, in the second pump chamber 8, the fluid is pressurized and discharged to the downstream side of the fifth flow path 55, similar to the operation of the first pump chamber 7 shown in Figure 7.

[0070] Figure 9 is a schematic diagram showing the operation of pump 1 when the coil is switched from energized to de-energized after being energized in Figure 7. Figure 10 is a schematic diagram showing the area around the first pump chamber 7 in the state shown in Figure 9. The outlines of Figures 9 and 10 are the same as those of Figures 5 and 6.

[0071] As shown in Figure 9, when the coil 612 of the electromagnet 61 is switched from the energized state shown in Figure 7 to the de-energized state, the magnetic field M1 that was generated around the electromagnet 61 disappears.

[0072] As the magnetic field M1 disappears, the attractive force that the first movable plate 62 and the second movable plate 63 were receiving from the electromagnet 61 also disappears. Therefore, the biasing force f1 generated in the deflected portion 643 of the first leaf spring 64, as shown by the dotted arrow in Figure 7, causes the first leaf spring 64 to elastically return to its original position, and in response to this movement, the first movable plate 62 also moves toward the positive Z direction. However, since the attractive force that was balanced by the biasing force f1 has disappeared, neither the first movable plate 62 nor the first leaf spring 64 remain stationary at the steady position S1, but move further toward the positive Z direction. Finally, as shown by the arrow H in Figure 9, they move toward the positive Z direction from the steady position S1 by an amount equal to the amount of movement due to the attraction of the electromagnet 61. Similarly, as indicated by arrow I, the second movable plate 63 and the second leaf spring 65 also move from the steady position S2 toward the negative Z direction due to the biasing force f2 in the negative Z direction that was generated in the deflected portion 653.

[0073] As the first movable plate 62 and the second movable plate 63 move away from the electromagnet 61, the first piston 71 slides in the positive Z direction within the cylinder 73, as indicated by arrow J, and the second piston 72 slides in the negative Z direction within the cylinder 73, as indicated by arrow K. As a result, the lower end surface of the first piston 71 and the upper end surface of the second piston 72 move apart from each other, increasing the volume of the first pump chamber 7.

[0074] Similarly, in the second pump chamber 8, the first piston 81 slides within the cylinder 83 in the positive Z direction, as indicated by arrow L. Also, the second piston 82 slides within the cylinder 83 in the negative Z direction, as indicated by arrow M. As a result, the lower end surface of the first piston 81 and the upper end surface of the second piston 82 are separated from each other, increasing the volume of the second pump chamber 8.

[0075] Ideally, the first movable plate 62 and the second movable plate 63 move parallel to each other in the Z direction due to the biasing forces f1 and f2 of the flexible portions 643 and 653. Therefore, the amount of sliding movement of the two first pistons 71 and 81 installed on the first movable plate 62 is the same as the amount of sliding movement of the two second pistons 72 and 82 installed on the second movable plate 63. Consequently, the amount of increase in volume of the first pump chamber 7 and the second pump chamber 8 is also the same.

[0076] As shown in Figure 9, when the first pistons 71, 81 and the second pistons 72, 82 move apart, the volumes of the first pump chamber 7 and the second pump chamber 8 increase. As a result, as shown in Figure 10, in the first pump chamber 7, the spheres of the intake valve 74 and the discharge valve 75 are each drawn towards the cylinder 73 by the fluid in the first pump chamber 7. At this time, the sphere of the discharge valve 75 moves to block the upstream side of the fourth passage 54 as indicated by arrow N, so the discharge valve 75 is closed. On the other hand, the sphere of the intake valve 74 can move downstream as indicated by arrow O, so the intake valve 74 is opened. As a result, the fluid on the upstream side of the fourth passage 54 is drawn into the first pump chamber 7.

[0077] As mentioned above, the volume increases of the first pump chamber 7 and the second pump chamber 8 are the same. Therefore, in the second pump chamber 8, the fluid upstream of the fifth flow path 55 is drawn into the second pump chamber 8, similar to the operation of the first pump chamber 7 shown in Figure 10.

[0078] In this embodiment, the pump 1 can be driven by controlling the energization of the electromagnet 61 to the coil 612 so as to repeatedly cycle between the state when the coil is energized (first state) shown in Figures 7 and 8, and the state when the coil is not energized (second state) shown in Figures 9 and 10.

[0079] In this control system, the pressure of the fluid discharged from the pump 1 can be adjusted according to the amount and speed of movement of the first pistons 71, 81 and the second pistons 72, 82. To adjust the pressure, it is necessary to adjust the amount and speed of movement of the first movable plate 62 and the second movable plate 63 on which the first pistons 71, 81 and the second pistons 72, 82 are mounted. To adjust the movement of the movable plates 62, 63, it is necessary to adjust the strength (magnetic flux density, etc.) of the magnetic field M1 generated by the electromagnet 61. To adjust the magnetic field M1, it is necessary to control the magnitude of the current flowing through the coil 612 of the electromagnet 61. In other words, in the pump 1 of this embodiment, the discharge of fluid at a desired pressure can be controlled by controlling the current value flowing through the coil 612 of the resonant actuator 6.

[0080] Alternatively, in the pump 1 of this embodiment, the discharge of fluid at a desired pressure can also be controlled by adjusting various structural elements, such as the number of turns of the wire in the coil 612 of the electromagnet 61, the dimensions of the winding portion 611A of the core 611 in the X and Y directions, the amount of protrusion in the Z direction and the dimensions in the X and Y directions of the widening portion 611B of the core 611, the area and shape of the first movable plate 62 and the second movable plate 63 in the Z direction, and the spring constants of the first leaf spring 64 and the second leaf spring 65.

[0081] The pump 1 of this embodiment includes an electromagnet 61, a first movable plate 62 and a second movable plate 63 which are attracted to the electromagnet 61 by the magnetic field M1 generated when the electromagnet 61 is energized, and a first leaf spring 64 which is attached to the first movable plate 62 and the second movable plate 63 respectively, and biases the first movable plate 62 and the second movable plate 63 in the opposite direction to the attraction movement of the first movable plate 62 and the second movable plate 63 to the electromagnet 61. The system includes a second leaf spring 65, a fluid passage 5, a first pump chamber 7 and a second pump chamber 8 provided on the passage 5, and an electromagnet 61 that operates to reduce the volume of the first pump chamber 7 and the second pump chamber 8 in response to the attraction operation of the first movable plate 62 and the second movable plate 63, and when the electromagnet 61 is switched off after the attraction operation, the biasing force of the first leaf spring 64 and the second leaf spring 65 causes the electromagnetic forces of the first movable plate 62 and the second movable plate 63 to act. The pumps include, as an example of volume-changing members that operate to increase the volume of the first pump chamber 7 and the second pump chamber 8 in response to a separation operation that moves away from the stone 61, first pistons 71, 81 and second pistons 72, 82, first pistons 71, 81 and second pistons 72, 82, which open when the first pistons 71, 81 and second pistons 72, 82 move in the direction of increasing the volume of the first pump chamber 7 and the second pump chamber 8, drawing fluid into the first pump chamber 7 and the second pump chamber 8 from the upstream side of the flow path 5, and discharge valves 75 that are provided on the downstream side of the flow path 5 in the first pump chamber 7 and the second pump chamber 8, which open when the first pistons 71, 81 and second pistons 72, 82 move in the direction of decreasing the volume of the first pump chamber 7 and the second pump chamber 8, and discharge fluid from the first pump chamber 7 and the second pump chamber 8 to the downstream side of the flow path 5.

[0082] Here, the electromagnet 61 among the above components can also be described as the "fixed part." Furthermore, the first movable plate 62 and the second movable plate 63, and the first leaf spring 64 and the second leaf spring 65 can also be described as "movable parts that are attracted to the fixed part by the magnetic field generated when the electromagnet 61 is energized, and that perform a vibrating motion that separates them from the fixed part by the biasing force generated when the electromagnet 61 is not energized."

[0083] With this configuration, the vibration generated in the movable parts (first movable plate 62 and second movable plate 63, first leaf spring 64 and second leaf spring 65) by the fixed part (electromagnet 61) allows the first piston 71 and the second piston 72 installed in the first pump chamber 7 to slide synchronously within the common cylinder 73. In other words, the resonant actuator 6 can be used as the drive source for the pump 1. As a result, the amount of piston movement required to increase or decrease the volume of the first pump chamber 7 and the second pump chamber 8 can be reduced compared to a conventional solenoid-driven metering pump, thereby reducing vibration during pump 1 operation. Furthermore, by setting the switching frequency for switching between the energized and de-energized states of the electromagnet 61 to the same frequency as, or near, the resonant frequency of, the resonant frequency of the movable part, which is the vibration element, the movable part can be made to resonate. As a result, the resonant actuator 6 can efficiently vibrate the movable part by utilizing the resonance of the movable part in addition to the attraction of the movable part by the electromagnet 61 when the electromagnet 61 is energized. As a result, the pump 1 of this embodiment can be made highly efficient.

[0084] Furthermore, in the pump 1 of this embodiment, the first movable plate 62 and the second movable plate 63 are arranged opposite each other with the electromagnet 61 in between. The first movable plate 62 and the second movable plate 63 are attached to the first leaf spring 64 and the second leaf spring 65, respectively. In other words, the first leaf spring 64 and the second leaf spring 65 are also arranged opposite each other with the electromagnet 61 in between. The first pistons 71 and 81 are installed on the first movable plate 62 and move in conjunction with the operation of the first movable plate 62. The second pistons 72 and 82 are installed on the second movable plate 63 and move in conjunction with the operation of the second movable plate 63.

[0085] This configuration allows a single electromagnet 61 to synchronize the vibration of a pair of opposing movable parts (the first movable plate 62 and the first leaf spring 64, and the second movable plate 63 and the second leaf spring 65). Since the pair of movable parts are positioned opposite each other with the electromagnet 61 in between, they are attracted to the electromagnet 61 in opposite directions. Therefore, the vibration directions of the pair of movable parts are in opposite phase. This allows the vibrations generated in the pump 1 by the operation of each movable part to cancel each other out.

[0086] Furthermore, in the pump 1 of this embodiment, the first movable part (first movable plate 62 and first leaf spring 64) and the second movable part (second movable plate 63 and second leaf spring 65) are arranged opposite each other with a fixed part (electromagnet 61) in between. The first pistons 71 and 81 are linked to the operation of the first movable part, and the second pistons 72 and 82 are linked to the operation of the second movable part. The first piston 71 and the second piston 72 are installed in the same first pump chamber 7. Similarly, the first piston 81 and the second piston 82 are installed in the same second pump chamber 8.

[0087] This configuration allows for the common pump chamber in which a pair of pistons are installed, so only one flow path (fourth flow path 54) and one valve (suction valve 74, discharge valve 75) are needed for the pair of first piston 71 and second piston 72. Similarly, only one flow path (fifth flow path 55) and one valve (suction valve 74, discharge valve 75) are needed for the pair of first piston 81 and second piston 82. This reduces the number of parts and simplifies the structure of pump 1. Furthermore, because the pump chamber is common, the reaction force on the pair of pistons installed in this pump chamber is the same, and the misalignment of the operation of the pair of movable parts that are positioned opposite each other is reduced. As a result, the number of parts is reduced while increasing the number of pump chambers and improving pump efficiency.

[0088] Here, with reference to Figure 7 and Figure 11, the effects of the core 611 of the electromagnet 61 according to this embodiment will be explained. Figure 11 is a schematic diagram showing the magnetic field M2 generated in an electromagnet 61A using a flat plate-shaped core 611C as a comparative example.

[0089] In the comparative example shown in Figure 11, the electromagnet 61A has a flat core 611C. The core 611C of the comparative example differs from the core 611 of the embodiment in that it does not have the widened portion 611B shown in Figure 7, etc. The core 611C is formed so that the dimensions in the Z direction are uniform throughout the entire X direction. In other words, the core 611C has a shape in which the winding portion 611A of the core 611 of the embodiment extends to the range on both sides in the X direction where the widened portion 611B is located.

[0090] If the core 611C has the shape shown in Figure 11, when the coil 612 is energized, a magnetic field M2 is generated inside the core 611C in the positive X direction. This magnetic field M2 initially enters the space of the resonant actuator 6 in the positive X direction from the X-positive end of the core 611C. After that, it branches into the positive Z direction and the negative Z direction, curves, reverses direction, and enters the interior from the X-positive ends of the first movable plate 62 and the second movable plate 63, heading towards the negative X direction. Then, from the X-negative ends of the first movable plate 62 and the second movable plate 63, it again enters the space of the resonant actuator 6 in the negative X direction, curves into the negative Z direction and the positive Z direction, reverses direction to the positive X direction, merges, and flows into the X-negative end of the core 611C.

[0091] In other words, the magnetic field M2 of the comparative example illustrated in Figure 11 is similar to the magnetic field M1 of the embodiment shown in Figure 7 in that, when viewed from the negative Y direction side, the flow is clockwise on the first movable plate 62 side and counterclockwise on the second movable plate 63 side. However, the magnetic field M2 of the comparative example tends to increase in magnetic resistance because, compared to the magnetic field M1 of the embodiment, a larger proportion of the magnetic field M2 flows within the space of the resonant actuator 6, meaning the air gap is larger.

[0092] In contrast, in the electromagnet 61 of this embodiment, by providing a widened portion 611B on the core 611, as shown in Figure 7, the air gap in the magnetic field M1 can be limited to the gap between the upper end surface of the widened portion 611B and the first movable plate 62, and the gap between the lower end surface of the widened portion 611B and the second movable plate 63. This reduces the air gap in the magnetic field M1 and decreases magnetic resistance, so that magnetic force can be generated more efficiently than in the comparative example.

[0093] Furthermore, in this embodiment, the core 611 of the electromagnet 61 is formed by stacking multiple electromagnetic steel sheets in the Y direction, as shown in Figures 3 and 4. Since adjacent electromagnetic steel sheets are bonded together with adhesive, this adhesive portion becomes an air gap, which acts as magnetic resistance, making it difficult for magnetic flux to flow. The magnetic flux generated by the coil 612 flows through the core 611 toward the movable plates 62 and 63. Therefore, if the stacking direction is the Y direction as in this embodiment, the air gap is positioned parallel to the flow of magnetic flux, which reduces the obstruction to the flow of magnetic flux and improves the energy transfer efficiency.

[0094] On the other hand, in a configuration where the stacking direction is 90 degrees different from that of this embodiment, that is, the X direction is the stacking direction, the air gap is placed in a position that obstructs the flow of magnetic flux, resulting in a decrease in efficiency.

[0095] Next, with reference to Figure 12, the effects of the shapes of the movable plates 62, 63 and the leaf springs 64, 65 in this embodiment will be explained. Figure 12 is a plan view of the internal structure of the housing 2 of the pump 1 as seen from the positive Z direction. Figure 12 shows the inside of the housing 2 as seen from the first leaf spring 64 side, with the main surface portion on the positive Z direction side of the housing 2 removed from the pump 1 shown in Figure 1.

[0096] When the direction perpendicular to the direction (X direction) of the magnetic field M1 generated by the electromagnet 61 (Y direction) is defined as the width direction, as shown in Figure 12, the widthwise dimension W1 of at least the flex portion 643 of the first leaf spring 64 is formed to be larger than the widthwise dimension W2 of the first movable plate 62. Similarly, in Figure 12, the relationship between the second movable plate 63 and the second leaf spring 65, which are hidden in the background of the figure, is also such that the widthwise dimension W1 of at least the flex portion 653 of the second leaf spring 65 is formed to be larger than the widthwise dimension W2 of the second movable plate 63.

[0097] As explained with reference to Figure 7, when the electromagnet 61 is energized during the operation of the resonant actuator 6, the first movable plate 62 and the second movable plate 63 ideally move in parallel in the direction approaching the electromagnet 61 (Z direction) due to the magnetic field M1 generated by the electromagnet 61. However, if a magnetic field M1 with uneven magnetic flux density is generated across the width direction of the movable plates 62 and 63, twisting may occur during operation, such as the first movable plate 62 or the second movable plate 63 tilting in the X or Y direction. Therefore, as in this embodiment, by making the width dimension W1 of the leaf springs 64 and 65 larger than that of the movable plates 62 and 63, the twisting of the movable plates 62 and 63 during operation can be more easily absorbed by the leaf springs 64 and 65, making it possible to move the first movable plate 62 and the second movable plate 63 in parallel more stably. As a result, the pump 1 of this embodiment can reduce noise and vibration in a configuration in which the resonant actuator 6 is used as the drive source.

[0098] Furthermore, the first pump chamber 7 and the second pump chamber 8 are positioned opposite each other at the locations where a pair of first pistons 71 and 81 are provided at both ends of the first movable plate 62 along the direction of the magnetic field M1 (X direction). Similarly, the second movable plate 63 is positioned opposite each other at the locations where a pair of second pistons 72 and 82 are provided at both ends along the direction of the magnetic field M1 (X direction). In this configuration with two pump chambers, since two pistons are installed on a single movable plate, the relationship between the widthwise dimension W1 of the leaf springs 64 and 65 and the widthwise dimension W2 of the movable plates 62 and 63 allows for stabilization of the sliding of the two pistons on a single movable plate relative to each pump chamber 7 and 8, thus particularly demonstrating the effect of suppressing twisting of the movable plates 62 and 63.

[0099] Next, the effects of the arrangement of the first pump chamber 7 and the second pump chamber 8 will be explained. As shown in Figures 2 and 7, the fourth flow path 54 of the flow path 5 of the pump 1, which includes the first pump chamber 7, is positioned adjacent to the winding portion 611A of the core 611 of the electromagnet 61, on the opposite side (negative X direction side), with the widened portion 611B on the negative X direction side of the core 611, and the flow direction is aligned with the width direction (Y direction). Similarly, the fifth flow path 55 of the flow path 5 of the pump 1, which includes the second pump chamber 8, is positioned adjacent to the winding portion 611A of the core 611 of the electromagnet 61, on the opposite side (positive X direction side), with the widened portion 611B on the positive X direction side of the core 611, and the flow direction is aligned with the width direction (Y direction).

[0100] Therefore, the first piston 71, which is inserted into the first pump chamber 7, is positioned adjacent to the winding portion 611A on the opposite side (negative X direction side) of the widened portion 611B on the X-negative X direction side of the electromagnet 61 of the first movable plate 62. Similarly, the second piston 72, which is inserted into the first pump chamber 7, is positioned adjacent to the winding portion 611A on the opposite side (negative X direction side) of the widened portion 611B on the X-negative X direction side of the second movable plate 63. Likewise, the first piston 81, which is inserted into the second pump chamber 8, is positioned adjacent to the winding portion 611A on the opposite side (positive X direction side) of the widened portion 611B on the X-positive X direction side of the first movable plate 62. Similarly, the second piston 82, which is inserted into the second pump chamber 8, is positioned adjacent to the winding portion 611A of the second movable plate 63, on the opposite side (the X-positive side) from the widened portion 611B on the X-positive side of the electromagnet 61.

[0101] By providing widened portions 611B at both ends in the X direction of the core 611 of the electromagnet 61, a magnetic field M1 is generated such that the magnetic flux concentrates and passes through the upper and lower end surfaces of the widened portions 611B, as shown in Figure 7. In other words, when the electromagnet 61 is energized, the portion of the first movable plate 62 facing the upper end surface of the widened portion 611B receives the strongest attractive force, and the portion of the second movable plate 63 facing the lower end surface of the widened portion 611B receives the strongest attractive force. Therefore, by arranging the first pistons 71, 81 and the second pistons 72, 82 adjacent to the widened portion 611B, each piston can be positioned near the portion of the first movable plate 62 and the second movable plate 63 that receives the strongest attractive force from the electromagnet 61. This makes it possible to efficiently apply sliding external force from the first movable plate 62 and the second movable plate 63 to the first pistons 71 and 81 and the second pistons 72 and 82, thereby improving the operating efficiency of both the first pump chamber 7 and the second pump chamber 8.

[0102] Furthermore, by positioning the first pistons 71, 81 and the second pistons 72, 82 near the point where the first movable plate 62 and the second movable plate 63 receive the strongest attractive force from the electromagnet 61, the attractive force generated when the electromagnet 61 is energized can further suppress the twisting of the direction of movement of the first pistons 71, 81 and the second pistons 72, 82 during the attraction operation. As a result, the direction of movement of the first pistons 71, 81 and the second pistons 72, 82 can be aligned with the axial direction (Z direction) of the cylinders 73, 83 of each pump chamber 7, 8, thereby further improving the operating efficiency of the first pump chamber 7 and the second pump chamber 8. As a result, the pump 1 of this embodiment can achieve improved performance and higher efficiency in a configuration that uses the resonant actuator 6 as a drive source.

[0103] Furthermore, the first pump chamber 7 is positioned adjacent to the core 611 of the electromagnet 61 on the opposite side (negative X direction) from the winding portion 611A, with one of the pair of widened portions 611B of the core 611 in between. The second pump chamber 8 is positioned adjacent to the winding portion 611A on the opposite side (positive X direction) from the pair of widened portions 611B, with the other of the pair of widened portions 611B in between. In this configuration with two pump chambers, since two pistons are installed on a single movable plate, by positioning each pump chamber 7 and 8 adjacent to the widened portion 611B, it becomes easier to equalize the external force applied to the two pistons provided on the single movable plate, and it becomes easier to synchronize the sliding of the pistons in each pump chamber 7 and 8. This particularly enhances the effect of improving the operating efficiency of the pump chambers.

[0104] Furthermore, as shown in Figure 2 and other figures, it is preferable that both the first pump chamber 7 and the second pump chamber 8 are positioned on the axis of symmetry CA of the housing 2. As shown in Figure 7 and other figures, the coil 612 of the electromagnet 61 is positioned so that its central axis is the axis of symmetry CA, so the magnetic flux tends to be most concentrated on the axis of symmetry CA on the center side of the coil 612. Therefore, the first movable plate 62 and the second movable plate 63 are most likely to receive the strongest attractive force from the electromagnet 61 on the axis of symmetry CA. For this reason, if the first pump chamber 7 and the second pump chamber 8 are positioned on the axis of symmetry CA, the first pistons 71, 81 and the second pistons 72, 82 are also positioned on the axis of symmetry CA, so it becomes possible to efficiently apply sliding external force to the first pistons 71, 81 and the second pistons 72, 82 from the first movable plate 62 and the second movable plate 63, and the operating efficiency of the first pump chamber 7 and the second pump chamber 8 can be further improved.

[0105] [Detailed Configuration of Pump Rooms 7 and 8] Next, with reference to Figures 13 to 15, the detailed configuration of pump rooms 7 and 8 according to this embodiment will be further described.

[0106] Figure 13 is a schematic diagram showing an enlarged view of the pump chambers 7 and 8 according to this embodiment. The outline of Figure 13 corresponds to Figure 6. Figure 13 shows an enlarged view of the portion of the first pump chamber 7 in a steady state that is on the positive Z side from the axis of symmetry CB. In Figure 13, the upper end (positive Z side) of the first piston 71 is omitted from the illustration, as are the lower side (negative Z side) of the fourth flow path 54, cylinder 73, intake valve 74, and discharge valve 75. In addition, in Figure 13, and in Figures 14 and 15 described later, the fluid as the object to be transferred flowing in the flow path 5 is illustrated with a dot pattern.

[0107] As shown in Figure 13, the first pump chamber 7 is equipped with an O-ring 76. The O-ring 76 is provided on the outer circumferential surface of the first piston 71 and is an example of a first sealing member that closes the gap between the outer circumferential surface of the first piston 71 and the inner circumferential surface of the cylinder 73. The O-ring 76 is positioned in the Z direction on the outer circumferential surface of the first piston 71 such that its outer circumferential portion is always in contact with the inner circumferential surface of the cylinder 73 during the sliding range of the first piston 71 within the cylinder 73. For example, as shown in Figure 13, it is preferable that the O-ring 76 be positioned in the Z direction near the tip of the first piston 71 on the fourth flow path 54 side of the outer circumferential surface of the first piston.

[0108] The O-ring 76 is, for example, an annular member made of rubber, and is installed on the outer surface of the first piston 71 along the circumferential direction of the outer surface. If the cross-sectional shape of the first piston 71 when viewed in the Z direction is circular, the O-ring 76 will also be annular. By providing the O-ring 76 on the first piston 71 in this way, when the first piston 71 slides inside the cylinder 73, it is possible to suppress the leakage of fluid in the first pump chamber 7 from the gap between the first piston 71 and the cylinder 73 to the positive Z direction.

[0109] The first pump chamber 7 is further equipped with a diaphragm seal 77. The diaphragm seal 77 is located outside the first pump chamber 7, beyond the O-ring 76 (first sealing member), and is an example of a second sealing member that prevents further leakage of fluid that has leaked out from the O-ring 76. The diaphragm seal 77 is an annular elastic membrane, with its central end 77A connected to the outer circumferential surface of the first piston 71 and its centrifugal end 77B connected to the support 9.

[0110] In the example shown in Figure 13, a recess 91 is formed around the opening of the cylinder 73 on the Z-positive side of the support 9, so as to be evenly recessed on the Z-negative side. The recess 91 has a bottom surface 91A and an inner surface 91B. The inner surface 91B is a circumferential surface that rises from the bottom surface 91A in the Z-positive direction along the outer shape of the bottom surface 91A and is formed facing the central axis CO of the cylinder 73. The central end 77A of the diaphragm seal 77 is connected and fixed to a predetermined position in the Z direction on the outer surface of the first piston 71, and is movable in the Z direction as the first piston 71 slides. The centrifugal end 77B of the diaphragm seal 77 is connected and fixed to the inner surface 91B of the recess 91, and its position in the Z direction is maintained at the same position regardless of the sliding of the first piston 71.

[0111] The diaphragm seal 77 is attached to two parts (in this embodiment, the first piston 71 and the support 9) that perform relative motion, and can also be described as a membrane-like seal that deforms to accommodate the relative motion. The diaphragm seal 77 is made of a flexible and pliable material such as rubber.

[0112] When the cross-sectional shape of the first piston 71 and cylinder 73 in the Z direction is circular, the outer shape of the bottom surface 91A of the recess 91 is also circular, and is formed concentrically with the first piston 71 and cylinder 73 so that the axis CO of the first piston 71 and cylinder 73 is at the center. For this reason, the inner surface 91B of the recess 91 also has a circular hole shape when viewed from the Z direction. In this case, the shape of the diaphragm seal 77 in the Z direction is formed to be donut-shaped. The inner diameter of the circular hole provided in the center of the donut shape is formed to be smaller than the diameter of the first piston 71. The outer diameter of the donut shape is formed to be larger than the inner diameter of the inner surface 91B of the recess 91 of the support 9.

[0113] With the above configuration, the opening on the Z-positive side of the recess 91 of the support 9 is completely sealed by the diaphragm seal 77 and the first piston 71 connected to its center. This prevents further leakage of fluid that has flowed through the fourth passage 54 and leaked out from the O-ring 76 to the outside. In other words, in this embodiment, the O-ring 76 (first sealing member) and the diaphragm seal 77 (second sealing member) provide a double layer of protection against fluid leakage from the first pump chamber 7.

[0114] The first pump chamber 7 is further equipped with a return passage 78. The return passage 78 returns the fluid leaked from the O-ring 76 to the upstream side of the first pump chamber 7 (more specifically, the suction valve 74) in the passage 5 (fourth passage 54).

[0115] In the example shown in Figure 13, the return channel 78 has a horizontal channel 78A and a vertical channel 78B. The horizontal channel 78A is formed extending centrifugally from the central edge of the bottom surface 91A of the depression 91. Preferably, the direction of extension of the horizontal channel 78A is the same direction as the fourth channel 54 and is toward the upstream side of the fourth channel 54 from the position of the cylinder 73. Also, in the example shown in Figure 13, the horizontal channel 78A is a groove provided on the bottom surface 91A of the depression 91.

[0116] The vertical channel 78B is a through-hole that penetrates between the recess 91 of the support 9 and the fourth channel 54. The vertical channel 78B extends, for example, in the Z direction, with one end on the positive Z side connected to the centrifugal end of the horizontal channel 78A, and the other end on the negative Z side opening into the fourth channel 54. The opening of the vertical channel 78B into the fourth channel 54 is located upstream of the suction valve 74 of the first pump chamber 7 (on the negative Y side in the example of Figure 13).

[0117] One end of the horizontal flow path 78A of the return flow path 78, on the central side, is provided to open toward the first pump chamber 7 side (fourth flow path 54 side) than the diaphragm seal 77 (second sealing member) in the sliding direction of the first piston 71.

[0118] With these configurations, the return channel 78 can collect the fluid leaking from the O-ring 76 into the horizontal channel 78A of the return channel 78, flow it to the vertical channel 78B, and then flow it further into the vertical channel 78B of the return channel 78 to flow into the fourth channel 54, thereby allowing it to be returned to the upstream side of the first pump chamber 7.

[0119] Next, with reference to Figures 14 and 15, the recirculation process of the fluid leaking from the O-ring 76 will be explained.

[0120] Figure 14 is a schematic diagram showing the state in which the first piston 71 is moving in a direction that reduces the volume of the first pump chamber 7. The outline of Figure 14 is the same as that of Figure 8. In other words, Figure 14 illustrates the state in which the coil 612 of the electromagnet 61 of the resonant actuator of the pump 1 is energized, and the first piston 71 slides inside the cylinder 73 in the negative Z direction (downward in the figure), as indicated by arrow C.

[0121] As the first piston 71 slides downward, the O-ring 76 moves downward within the cylinder 73 together with the first piston 71, while maintaining its position on the outer circumferential surface of the first piston 71 and maintaining contact with the inner circumferential surface of the cylinder 73.

[0122] Furthermore, since the central end 77A of the diaphragm seal 77 is connected and fixed to the outer circumferential surface of the first piston 71, it moves downward together with the first piston 71. On the other hand, since the centrifugal end 77B of the diaphragm seal 77 is connected and fixed to the support 9 (the inner surface 91B of the recess 91), its position in the Z direction is maintained. As a result of this connection state at both ends of the diaphragm seal 77, when the first piston 71 slides downward, the central end 77A of the diaphragm seal 77 moves downward relative to the centrifugal end 77B, as shown in Figure 14, and the central portion of the diaphragm seal 77 becomes recessed toward the bottom surface 91A of the recess 91.

[0123] In the state shown in Figure 14, as the volume of the first pump chamber 7 decreases, the spheres of the intake valve 74 and the discharge valve 75 are pressed upstream and downstream of the fourth flow path 54, respectively, by the fluid in the first pump chamber 7. At this time, the sphere of the intake valve 74 blocks the upstream side of the fourth flow path 54, so the intake valve 74 is closed. On the other hand, the sphere of the discharge valve 75 is movable downstream as indicated by arrow G, so the discharge valve 75 is opened. As a result, the fluid in the first pump chamber 7 is pressurized and discharged to the downstream side of the fourth flow path 54.

[0124] As shown in Figure 14, when the fluid in the first pump chamber 7 is pressurized, the pressurized fluid may leak out upward (towards the positive Z direction) from the O-ring 76, passing through the contact area between the O-ring 76 and the cylinder 73, as indicated by the dotted arrow in the figure. In this embodiment, a diaphragm seal 77 is provided on the outside of the O-ring 76 as another sealing member, so that the fluid leaking from the O-ring 76 is prevented from leaking further to the outside by the diaphragm seal 77.

[0125] Figure 15 is a schematic diagram showing the state in which the first piston 71 is moving in a direction that increases the volume of the first pump chamber 7. The outline of Figure 15 is the same as that of Figure 10. In other words, Figure 15 illustrates the state in which the coil 612 of the electromagnet 61 of the resonant actuator of the pump 1 is switched from the energized state shown in Figure 14 to the de-energized state, and the first piston 71 slides inside the cylinder 73 in the positive Z direction (upwards in the figure) as indicated by the arrow J.

[0126] As the first piston 71 slides upward, the O-ring 76 moves upward within the cylinder 73 together with the first piston 71, while maintaining its position on the outer circumferential surface of the first piston 71 and maintaining contact with the inner circumferential surface of the cylinder 73. This upward movement of the O-ring 76 causes the fluid leaking from the O-ring 76, as illustrated in Figure 14, to be pushed upward by the O-ring 76 and flow out onto the bottom surface 91A of the recess 91, where it is collected in the horizontal flow path 78A of the return channel 78 provided on the bottom surface 91A.

[0127] Furthermore, since the central end 77A of the diaphragm seal 77 is connected and fixed to the outer circumferential surface of the first piston 71, it moves upward together with the first piston 71. On the other hand, since the centrifugal end 77B of the diaphragm seal 77 is connected and fixed to the support 9 (the inner surface 91B of the recess 91), its position in the Z direction is maintained. As a result of this connection state at both ends of the diaphragm seal 77, when the first piston 71 slides upward, the central end 77A of the diaphragm seal 77 rises relative to the centrifugal end 77B, as shown in Figure 15, and the central portion of the diaphragm seal 77 becomes a convex shape that bulges upward.

[0128] In the state shown in Figure 15, as the volume of the first pump chamber 7 increases, the spheres of the intake valve 74 and the discharge valve 75 are each drawn toward the cylinder 73 by the fluid in the first pump chamber 7. At this time, the sphere of the discharge valve 75 moves to block the upstream side of the fourth passage 54 as indicated by arrow N, so the discharge valve 75 is closed. On the other hand, the sphere of the intake valve 74 can move toward the downstream side as indicated by arrow O, so the intake valve 74 is opened. As a result, the fluid on the upstream side of the fourth passage 54 is drawn into the first pump chamber 7.

[0129] Furthermore, when the fluid upstream of the fourth flow path 54 is drawn into the first pump chamber 7, the fluid accumulated in the return flow path 78 is similarly drawn in. As a result, as shown by the dotted arrow in Figure 15, the fluid collected in the horizontal flow path 78A of the return flow path 78 flows centrifugally, then flows downward through the vertical flow path 78B, flows from the vertical flow path 78B into the fourth flow path 54, and is drawn into the first pump chamber 7 again.

[0130] In Figures 13 to 15, the configuration and operation of the first piston 71 and its surroundings are illustrated and explained by magnifying the portion of the first pump chamber 7 on the positive Z side of the axis of symmetry CB. The configuration and operation of the second piston 72 on the negative Z side of the axis of symmetry CB in the first pump chamber 7 are similar. In the example shown in Figures 13 to 15, the second piston 72 is positioned below the support 9, so if a recess 91 is provided, the opening of the recess 91 will face downwards. In this case, in order to allow fluid to flow through the horizontal passage 78A of the return passage 78, it is preferable that the horizontal passage 78A be a through-hole provided inside the support 9, similar to the vertical passage 78B, instead of a groove on the bottom surface 91A. Also, in Figures 13 to 15, the configuration of the first pump chamber 7 is explained by illustrating the cross-section of the fourth passage 54, but the configuration of the second pump chamber 8 in the fifth passage 55 is similar.

[0131] The pump 1 according to this embodiment includes a flow path 5 through which a fluid to be transferred flows, pump chambers 7 and 8 provided on the flow path 5, pistons 71, 72, 81, and 82 that slide inside cylinders 73 and 83 to reduce and increase the volume of the pump chambers 7 and 8, O-rings 76 provided on the outer circumferential surface of the pistons 71, 72, 81, and 82 to seal the gap with the inner circumferential surface of the cylinders 73 and 83, diaphragm seals 77 provided outside the pump chambers 7 and 8 beyond the O-rings 76 to prevent further leakage of fluid that has leaked out from the O-rings 76 to the outside, and a return flow path 78 that returns the fluid that has leaked out from the O-rings 76 to the upstream side of the pump chambers 7 and 8 in the flow path 5. One end of the return flow path 78 facing the cylinders 73 and 83 is provided to open towards the pump chambers 7 and 8 side than the diaphragm seal 77 in the sliding direction of the pistons.

[0132] Here, if the O-rings 76, which are provided on the outer surfaces of pistons 71, 72, 81, and 82, are made larger (the diameter of the circumferential cross-sectional shape is increased) relative to the gap with the inner surfaces of cylinders 73, 83, the performance of preventing fluid leakage from the pump chambers 7, 8 to the outside via cylinders 73, 83 by the O-rings 76 (sealing performance) is improved. However, in this case, although sealing performance can be improved, the sliding resistance of the pistons increases by the amount the O-rings 76 are enlarged, and the vibration efficiency of the pump 1 decreases. On the other hand, if the O-rings 76 are made smaller, sliding resistance decreases and vibration efficiency increases, but fluid leakage from the O-rings 76 becomes more likely, and sealing performance decreases.

[0133] Therefore, in this embodiment, by providing a double structure with a diaphragm seal 77 in addition to the O-ring 76, the O-ring 76 can prioritize suppressing the increase in piston sliding resistance and the reduction in the vibration efficiency of the pump 1 caused by the installation of the O-ring 76, rather than improving sealing performance. At the same time, the diaphragm seal 77 can also ensure the sealing performance of the entire pump 1. As a result, the pump 1 according to this embodiment can suppress the increase in piston sliding resistance, suppress the reduction in the vibration efficiency of the pump 1, and also improve sealing performance. It should be noted that fluid leakage occurs from the O-ring 76, so it can be said that the flow efficiency of the pump 1 is reduced somewhat by the amount of leakage. However, the amount of leakage from the O-ring 76 is very small compared to the flow rate of the fluid discharged from the pump chambers 7 and 8 (main flow rate), so the overall efficiency of the pump 1 in this embodiment is increased as a result. As a result, the pump 1 according to this embodiment can suppress a decrease in pump efficiency even when fluid leakage occurs from the pump chambers 7 and 8 as the material to be transferred.

[0134] Furthermore, in this embodiment, by providing a return channel 78 that opens towards the pump chambers 7 and 8 side of the diaphragm seal 77 in the piston's sliding direction, it is possible to return the fluid leaked from the O-ring 76 back to the pump chambers 7 and 8. This prevents the fluid leaked outside the pump chambers 7 and 8 from exceeding the volume of the space between the O-ring 76 and the diaphragm seal 77, thereby preventing damage to the diaphragm seal 77 and ensuring a more reliable sealing performance.

[0135] Even with the configuration that includes an O-ring 76 to prevent fluid leakage, leakage may still occur in situations such as when the piston slides at high speed. Such situations may arise, for example, when the pump 1 is applied to an espresso machine 100 (see Figure 16), where a configuration that increases the fluid pressure within the pump 1 and discharges high-pressure fluid (high-pressure pump) is required. Therefore, the above-mentioned effects of the pump 1 of this embodiment are particularly pronounced when the pump 1 is a high-pressure pump.

[0136] [Examples of applications for pump 1] Figure 16 shows examples of applications for pump 1 according to this embodiment. As shown in Figure 16, pump 1 according to this embodiment can be applied to beverage supply devices such as espresso machines 100.

[0137] The espresso machine 100 comprises a tank 101, a heater 102, a damper 103, and an extraction unit 104.

[0138] Tank 101 stores the water used for espresso. The tank 101 and pump 1, the pump 1 and heater 102, and the heater 102 and extraction unit 104 are connected by a water channel 107 that transports the water supplied from tank 101.

[0139] Pump 1 pressurizes the water transported from tank 101 and sends it to heater 102. In the case of an espresso machine 100, it is preferable for pump 1 to pressurize the water to, for example, 9 atmospheres.

[0140] The heater 102 heats the pressurized water transported from the tank 101 and sends it to the extraction unit 104.

[0141] The extraction unit 104 has powdered coffee beans 105 packed into the lower part of its interior and is pressed downwards by a damper 103. Hot water heated and pressurized by a heater 102 is supplied to the pressed coffee bean powder 105, and coffee is extracted from the extraction hole 106 at the lower end of the extraction unit 104.

[0142] Espresso machines require a high-pressure pump to extract coffee under high pressure. Therefore, conventional espresso machines often utilize solenoid-driven metering pumps. However, solenoid-driven metering pumps have drawbacks such as high vibration and poor efficiency.

[0143] In contrast, the pump 1 of this embodiment uses a resonant actuator 6 as a drive source, thus solving the problems of the conventional solenoid-driven metering pump described above and providing a more convenient espresso machine 100.

[0144] Furthermore, the pump 1 can be applied to any beverage supply device that requires pressure boosting, not just the espresso machine 100. Such a beverage supply device only needs to include at least a tank for storing beverages, a pump 1 according to the embodiment that sucks the beverage from the tank and discharges it at a predetermined pressure, and a discharge unit (corresponding to the extraction unit 104 in the example of Figure 13) that discharges the beverage discharged from the pump 1.

[0145] Furthermore, pump 1 can be applied to any device other than beverage supply equipment that requires pressure boosting. Examples of such devices include industrial manufacturing equipment (such as semiconductor manufacturing equipment), medical equipment, household equipment (such as toilets, washbasins, and bathtubs), and agricultural equipment.

[0146] (Configuration of the drive circuit 66) Figures 17 to 19 are circuit diagrams of the drive circuit 66 provided in the pump 1 according to one embodiment. Figure 17 shows the state of the drive circuit 66 during the period when the electromagnet 61 is not energized. Figure 18 shows the state of the drive circuit 66 during the period when the electromagnet 61 is energized. Figure 19 shows the state of the drive circuit 66 when the back electromotive force is canceled.

[0147] As shown in Figures 17 to 19, the drive circuit 66 is a so-called full-bridge circuit comprising a DC power supply 66A, an electromagnet 61 (an example of a "solenoid"), and four switches SW1, SW2, SW3, and SW4.

[0148] In the drive circuit 66, switches SW1 and SW2 are connected in series. Switches SW3 and SW4 are also connected in series. Switches SW1 and SW2 are connected in parallel with switches SW3 and SW4. Switches SW1, SW2, SW3, and SW4 are, for example, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). Switches SW1, SW2, SW3, and SW4 can be switched on and off by a control IC (not shown in the figure).

[0149] Furthermore, the positive terminal of the electromagnet 61 is connected between switch SW1 and switch SW2. Also, the negative terminal of the electromagnet 61 is connected between switch SW3 and switch SW4.

[0150] Furthermore, the positive terminal of the DC power supply 66A is connected to switches SW1 and SW3. The negative terminal of the DC power supply 66A is connected to switches SW2 and SW4. A diode 66B is provided between the positive terminal of the DC power supply 66A and switches SW1 and SW3 to prevent reverse current flow to the DC power supply 66A.

[0151] (Operation of the drive circuit 66) During the energizing period of the electromagnet 61, switches SW1 and SW4 of the drive circuit 66 are switched on, as shown in Figure 18. As a result, the current supplied from the DC power supply 66A flows from the positive terminal to the negative terminal of the electromagnet 61 (see arrow A in Figure 18), and the electromagnet 61 generates a magnetic field. Consequently, the first movable plate 62 and the second movable plate 63 (an example of an "elastic spring") are attracted towards the electromagnet 61 by the magnetic field generated by the electromagnet 61 and undergo elastic deformation.

[0152] Furthermore, during periods when the electromagnet 61 is not energized, as shown in Figure 17, all switches SW1, SW2, SW3, and SW4 of the drive circuit 66 are turned off. As a result, no current flows to the electromagnet 61, and the electromagnet 61 stops generating a magnetic field. Consequently, the first movable plate 62 and the second movable plate 63 are no longer attracted to the electromagnet 61, and recover from elastic deformation due to the reaction forces of the first movable plate 62 and the second movable plate 63.

[0153] The drive circuit 66 repeatedly switches between energized and de-energized periods for the electromagnet 61, thereby causing the first movable plate 62 and the second movable plate 63 to vibrate reciprocatingly by elastically deforming and recovering from this deformation in a direction toward the electromagnet 61.

[0154] In particular, the drive circuit 66 of this embodiment switches between energized and de-energized periods of the electromagnet 61 at the same frequency as the resonant frequencies of the first movable plate 62 and the second movable plate 63, thereby causing the first movable plate 62 and the second movable plate 63 to resonate and maximizing the amplitude of the first movable plate 62 and the second movable plate 63.

[0155] (Method for adjusting the amplitude of movable plates 62 and 63) Figure 20 is a diagram showing the relationship between the input signal and the current of the electromagnet 61 in a drive circuit 66 according to one embodiment. As shown in Figure 20, when an input pulse signal is input from the control IC during the period T, the solenoid current rises.

[0156] The drive circuit 66 of this embodiment can adjust the amount of current flowing through the electromagnet 61 during the energized period by controlling the duty cycle of the energized period of the electromagnet 61 in the input pulse signal input from the control IC, thereby adjusting the amplitude of the first movable plate 62 and the second movable plate 63.

[0157] For example, as shown in Figure 20(a), the drive circuit 66 of this embodiment reduces the amount of current flowing through the electromagnet 61 during the energized period (the period during which a Hi signal is supplied from the control IC) in the input pulse signal input from the control IC, thereby reducing the amplitude of the first movable plate 62 and the second movable plate 63.

[0158] Furthermore, as shown in Figure 20(b), the drive circuit 66 of this embodiment can increase the amount of current flowing through the electromagnet 61 during the energized period (the period during which a Hi signal is supplied from the control IC) in the input pulse signal input from the control IC, thereby increasing the amplitude of the first movable plate 62 and the second movable plate 63.

[0159] (Method for canceling back electromotive force) In the drive circuit 66, when the electromagnet 61 switches from an energized period to an unenergized period, the power stored in the electromagnet 51 becomes a back electromotive force, and there is a risk that the current generated by this back electromotive force will flow from the positive terminal to the negative terminal of the electromagnet 61. In this case, there is a risk that the force recovering from the elastic deformation of the first movable plate 62 and the second movable plate 63 will be canceled out by the magnetic force generated by the electromagnet 61, making it impossible to maximize the amplitude of the first movable plate 62 and the second movable plate 63.

[0160] Therefore, in this embodiment, the drive circuit 66 cancels out the current generated by the back electromotive force by flowing a reverse current from the negative terminal to the positive terminal of the electromagnet 61 after switching from the energized period to the de-energized period of the electromagnet 61.

[0161] Specifically, when the back electromotive force is canceled, the drive circuit 66 switches switches SW2 and SW3 to ON, as shown in Figure 19. As a result, the current supplied from the DC power supply 66A flows in the reverse direction through the electromagnet 61 from the negative terminal to the positive terminal (see arrow B in Figure 19), canceling out the current generated by the back electromotive force. Consequently, the current flowing through the electromagnet 61 becomes zero, and the electromagnet 61 no longer generates a magnetic force that would attenuate the amplitude of the first movable plate 62 and the second movable plate 63.

[0162] Therefore, according to the drive circuit 66 of one embodiment, it is possible to suppress the reduction in amplitude due to the back electromotive force of the first movable plate 62 and the second movable plate 63 (vibrating body) which are elastically deformed by the magnetic field generated by the electromagnet 61 (solenoid).

[0163] In particular, the drive circuit 66 shortens the length of the back electromotive force cancellation period (the period during which a reverse current flows through the electromagnet 61) to a length of the energized period of the electromagnet 61. This allows the drive circuit 66 to suppress the excessive flow of reverse current through the electromagnet 61 beyond the point of canceling the back electromotive force, and therefore, to suppress the electromagnet 61 from generating a magnetic field greater than necessary.

[0164] Furthermore, the drive circuit 66 can pre-determine the optimal length of the period during which a reverse current flows through the electromagnet 61 (back electromotive force cancellation period) through simulation or the like, thereby canceling the current generated by the back electromotive force while suppressing the generation of excessive magnetic force in the electromagnet 61.

[0165] (Comparative Examples of Back EMF Cancellation Period Length) Figures 21 and 22 show various measurement results in a drive circuit 66 according to one embodiment. Figures 21 and 22 show various measurement results, including power supply voltage (thick line in the figure), differential voltage of electromagnet 61 (dotted line in the figure), current flowing through electromagnet 61 (dashed line in the figure), and amplitude of movable plates 62 and 63 (solid line in the figure). Figure 21 shows an example where the length of the back EMF cancellation period is equal to the length of the energizing period of the electromagnet 61. Figure 22 shows an example where the length of the back EMF cancellation period is shorter than the length of the energizing period of the electromagnet 61.

[0166] As shown in Figure 21, when the length of the back electromotive force cancellation period is made equal to the length of the energized period of the electromagnet 61 by controlling the drive circuit 66, the current flowing through the electromagnet 61 does not become 0 [A] but becomes a negative current. This negative current causes the electromagnet 61 to generate more magnetic force than necessary, making it impossible to maximize the amplitude of the movable plates 62 and 63.

[0167] On the other hand, as shown in Figure 22, by controlling the drive circuit 66, the length of the back electromotive force cancellation period can be appropriately adjusted to reduce the current flowing through the electromagnet 61 to 0 [A]. Specifically, if the length of the back electromotive force cancellation period is shorter than the length of the energized period of the electromagnet 61, the current flowing through the electromagnet 61 becomes 0 [A], and the electromagnet 61 does not generate more magnetic force than necessary, thus maximizing the amplitude of the movable plates 62 and 63.

[0168] Furthermore, as described above, the drive circuit 66 according to one embodiment can reduce the current flowing through the electromagnet 61 to 0 [A] by appropriately adjusting the length of the back electromotive force cancellation period. In other words, the drive circuit 66 according to one embodiment can adjust the amplitude of the first movable plate 62 and the second movable plate 63 by adjusting the length of the back electromotive force cancellation period. For this reason, for example, the drive circuit 66 according to one embodiment can reduce the amplitude of the first movable plate 62 and the second movable plate 63 to less than the maximum by adjusting the length of the back electromotive force cancellation period and making the current flowing through the electromagnet 61 other than 0 [A].

[0169] (Relationship between the duty cycle of the input pulse signal and the back electromotive force cancellation period) Figure 23 is a diagram showing the relationship between the duty cycle of the input pulse signal, the back electromotive force cancellation period, and the current flowing through the electromagnet 61 in a drive circuit 66 according to one embodiment.

[0170] As shown in Figure 23, in one embodiment of the drive circuit 66, the length of the back electromotive force cancellation period can be linearly increased as the duty cycle of the input pulse signal (i.e., the length of the energizing period of the electromagnet 61) increases. However, in this case, the current flowing through the electromagnet 61 cannot be kept constant at 0 [A].

[0171] Therefore, in order to keep the current flowing through the electromagnet 61 constant at 0 [A], the drive circuit 66 according to one embodiment requires that the length of the back electromotive force cancellation period be determined in advance for each duty cycle of the input pulse signal and stored in memory as table data.

[0172] (Modified configuration of the drive circuit 66) Figures 24 to 26 are circuit diagrams of the drive circuit 66-2 provided in the pump 1 according to one embodiment. Figure 24 shows the state of the drive circuit 66 during the period when the electromagnet 61 is not energized. Figure 25 shows the state of the drive circuit 66 during the period when the electromagnet 61 is energized. Figure 26 shows the state of the drive circuit 66 during the back electromotive force cancellation period.

[0173] The drive circuit 66-2 shown in Figures 24 to 26 is a modified example of the drive circuit 66 shown in Figures 17 to 19. The drive circuit 66-2 differs from the drive circuit 66 in that it further includes a diode 66C and a capacitor 66D.

[0174] Diode 66C is provided between the connection point of switch SW1 and switch SW2 and the electromagnet 61. Diode 66C is an example of a "rectifier means" and prevents reverse current (i.e., current flowing from the negative terminal to the positive terminal of the electromagnet 61) from flowing through the electromagnet 61.

[0175] Capacitor 66D is connected in parallel with switches SW3 and SW4. Capacitor 66D is an example of an "energy storage means" and stores the power generated by the back electromotive force during periods when the electromagnet 61 is not energized.

[0176] (Operation of drive circuit 66-2) During the energizing period of the electromagnet 61, switches SW1 and SW4 of the drive circuit 66-2 are switched ON, as shown in Figure 25. As a result, the current supplied from the DC power supply 66A flows from the positive terminal to the negative terminal of the electromagnet 61 (see arrow A in Figure 25), and the electromagnet 61 generates a magnetic field. Consequently, the first movable plate 62 and the second movable plate 63 are attracted towards the electromagnet 61 by the magnetic field generated by the electromagnet 61 and undergo elastic deformation.

[0177] Furthermore, during periods when the electromagnet 61 is not energized, the drive circuit 66-2 switches SW1, SW2, SW3, and SW4 are all turned off, as shown in Figure 24. As a result, no current flows to the electromagnet 61, and the electromagnet 61 stops generating a magnetic field. Consequently, the first movable plate 62 and the second movable plate 63 are no longer attracted to the electromagnet 61, and recover from elastic deformation due to the reaction forces of the first movable plate 62 and the second movable plate 63.

[0178] The drive circuit 66-2 repeatedly switches between energized and de-energized periods for the electromagnet 61, thereby causing the first movable plate 62 and the second movable plate 63 to vibrate reciprocatingly by elastically deforming and recovering from this deformation in a direction toward the electromagnet 61.

[0179] In particular, the drive circuit 66-2 of this embodiment switches between energized and de-energized periods of the electromagnet 61 at the same frequency as the resonant frequencies of the first movable plate 62 and the second movable plate 63, thereby causing the first movable plate 62 and the second movable plate 63 to resonate and maximizing the amplitude of the first movable plate 62 and the second movable plate 63.

[0180] Furthermore, in this embodiment, during the back electromotive force cancellation period after the electromagnet 61 switches from energized to de-energized, the drive circuit 66-2 switches switches SW2 and SW3 to ON, as shown in Figure 26. As a result, the current supplied from the DC power supply 66A flows in the reverse direction through the electromagnet 61 from the negative terminal to the positive terminal, canceling the current generated by the back electromotive force.

[0181] As a result, the current flowing through the electromagnet 61 becomes zero, and the electromagnet 61 no longer generates a magnetic force that would attenuate the amplitude of the first movable plate 62 and the second movable plate 63. Therefore, according to the drive circuit 66-2 of one embodiment, it is possible to suppress the reduction in amplitude due to the back electromotive force of the first movable plate 62 and the second movable plate 63 (vibrating body) that vibrate due to the magnetic field generated by the electromagnet 61 (solenoid).

[0182] (Effects of diode 66C and capacitor 66D) Here, the drive circuit 66-2 can prevent reverse current (i.e., current flowing from the negative terminal to the positive terminal of the electromagnet 61) from flowing through the electromagnet 61 by diode 66C during the back electromotive force cancellation period shown in Figure 26 (see arrow B in Figure 26). For this reason, the drive circuit 66-2 can set the current flowing through the electromagnet 61 to 0 [A] regardless of the length of the back electromotive force cancellation period. Therefore, even if the length of the back electromotive force cancellation period is equal to the length of the energizing period of the electromagnet 61, the current flowing through the electromagnet 61 will not be a negative current but will be 0 [A], the electromagnet 61 will not generate more magnetic force than necessary, and the amplitude of the movable plates 62 and 63 can be maximized.

[0183] Furthermore, the drive circuit 66-2 can store power generated by the back electromotive force during the period when the electromagnet 61 shown in Figure 24 is not energized in the capacitor 66D (see arrow C in Figure 24). For example, if SW1 to SW4 are MOSFETs, the current generated by the back electromotive force during the period when the electromagnet is not energized passes through the parasitic diodes of SW2 and SW3, and can be stored in the capacitor 66D. The energy of the electromagnet 61 is dissipated as heat as it passes through the parasitic diodes. Therefore, by controlling SW2 and SW3 to be ON during the period when the electromagnet is not energized, the drive circuit 66-2 can store more power in the capacitor 66D.

[0184] Furthermore, the drive circuit 66-2 can effectively utilize the power stored in the capacitor 66D during the preceding non-energized period to drive the electromagnet 61 during the energized period of the electromagnet 61 shown in Figure 25 (see arrow D in Figure 25).

[0185] In addition, the drive circuit 66-2 may be equipped with a means for consuming the power generated by the back electromotive force (for example, a resistor) instead of a means for storing the power generated by the back electromotive force. In this case as well, the drive circuit 66-2 can reduce the current flowing through the electromagnet 61 to 0 [A] by consuming the power generated by the back electromotive force using the means for consuming the power.

[0186] (Effect of keeping the current flowing through the electromagnet 61 constant at 0 [A]) Figure 27 is a diagram showing various measurement results in the drive circuit 66-2 according to one embodiment. Figure 27 shows the various measurement results, including the switch control signals IN1 and IN2 (dotted lines in the figure), the amplitude AMP of the movable plates 62 and 63 (solid lines in the figure), and the current IOUT flowing through the electromagnet 61 (dashed line in the figure). The switch control signals IN1 and IN2 are represented by square waves. A square wave is represented by two values, "Hi" or "Lo". The voltage value of "Hi" is higher than the voltage value of "Lo". Figure 27 shows an example where the duty cycle of the input pulse signal is "15%".

[0187] Here, when both control signals IN1 and IN2 are "Lo", switches SW1 to SW4 are all controlled to "Off".

[0188] Furthermore, when control signal IN1 is "Lo" and control signal IN2 is "Hi", switches SW2 and SW3 are controlled to "On", and switches SW1 and SW4 are controlled to "Off".

[0189] Furthermore, when control signal IN1 is "Hi" and control signal IN2 is "Lo", switches SW2 and SW3 are controlled to "Off", and switches SW1 and SW4 are controlled to "On".

[0190] Furthermore, when both control signals IN1 and IN2 are set to "Hi", switches SW2 and SW4 are controlled to "On", and switches SW1 and SW3 are controlled to "Off".

[0191] By providing diode 66C, the drive circuit 66-2 can keep the current flowing through the electromagnet 61 constant at 0 [A] regardless of the duty cycle of the input pulse signal.

[0192] For example, as shown in the measurement results in Figure 27, the drive circuit 66-2 can keep the current flowing through the electromagnet 61 constant at 0 [A] even when the duty cycle is set to "15%".

[0193] Therefore, the drive circuit 66-2 does not need to change the length of the back electromotive force cancellation period according to the duty cycle of the input pulse signal. Consequently, it is not necessary to pre-determine the length of the back electromotive force cancellation period for each duty cycle of the input pulse signal, nor is it necessary to store such data as table data in memory.

[0194] The embodiments have been described above with reference to specific examples. However, this disclosure is not limited to these specific examples. Modifications made to these specific examples by those skilled in the art are also included within the scope of this disclosure, as long as they retain the features of this disclosure. The elements, their arrangement, conditions, shapes, etc., of each of the aforementioned specific examples are not limited to those illustrated and can be modified as appropriate. The elements of each of the aforementioned specific examples can be combined in different ways as appropriate, as long as no technical inconsistencies arise.

[0195] For example, in this embodiment, the diode 66C may be provided between the connection point of switch SW3 and switch SW4 and the electromagnet 61. Even in this case, the diode 66C prevents reverse current (i.e., current flowing from the negative terminal to the positive terminal of the electromagnet 61) from flowing through the electromagnet 61.

[0196] The pump 1 according to this embodiment only needs to be capable of dispensing fluid from the flow path 5, and the structure of the pump 1 may be other than the configuration described above. For example, in the above embodiment, a configuration in which the intake port 3 is located on the side surface 23 of the housing 2 and the discharge port 4 is located on the side surface 24 was illustrated, but the arrangement of the intake port 3 and the discharge port 4 may be changed as desired.

[0197] Furthermore, although the above embodiment illustrates a configuration in which both the first pump chamber 7 and the second pump chamber 8 are arranged on the axis of symmetry CA, the arrangement of the first pump chamber 7 and the second pump chamber 8 is not limited to the axis of symmetry CA, but is limited to at least the fourth flow path 54 and the fifth flow path 55.

[0198] Furthermore, although the above embodiment illustrates a configuration in which two pistons, first pistons 71, 81 and second pistons 72, 82, are arranged in each pump chamber 7, 8, a configuration in which only a single piston is installed in one pump chamber is also acceptable.

[0199] Furthermore, although the above embodiment illustrates a configuration in which two pump chambers 7 and 8 are provided within the flow path 5, a configuration in which only a single pump chamber is provided within the flow path 5 is also acceptable.

[0200] Furthermore, in the above embodiment, a configuration was illustrated in which two movable parts, a first movable part (a first movable plate 62 and a first leaf spring 64) and a second movable part (a second movable plate 63 and a second leaf spring 65), are provided flanking a single fixed part including an electromagnet 61. However, a configuration in which only one of the pair of movable parts is provided is also acceptable.

[0201] In the above embodiment, a configuration was shown in which a fluid (liquid) is used as the object to be transferred through the flow path 5 of the pump 1, but the object to be transferred may also be a gas.

[0202] In the above embodiment, a double structure using an O-ring 76 and a diaphragm seal 77 was exemplified as a leakage prevention structure for the material being transferred from the pump chambers 7 and 8, but other elements may be applied. The O-ring 76, which is an annular rubber member as an example of the "first sealing member," may be replaced with other elements that can perform the function of "being provided on the outer circumferential surface of the pistons 71, 72, 81, and 82 and sealing the gap between the outer circumferential surface of the pistons 71, 72, 81, and 82 and the inner circumferential surface of the cylinders 73, and 83." Examples of such elements include metal piston rings and annular resin members other than rubber. The diaphragm seal 77, which is an annular elastic membrane as an example of the "second sealing member," may be replaced with other elements that can perform the function of "being provided outside the pump chambers 7 and 8 more than the first sealing member and preventing further leakage of fluid that has leaked from the first sealing member to the outside." Examples of such elements include bellows. Furthermore, the material of the diaphragm seal 77 may be a combination of rubber and a base fabric instead of rubber alone.

[0203] In the above embodiment, a configuration in which the return passage 78 has a horizontal passage 78A and a vertical passage 78B is illustrated, but it is sufficient that the fluid leaking from the O-ring 76 (first sealing member) can be returned to the upstream side of the first pump chamber 7 in the passage 5, and the configuration is not limited to this. For example, if the inner diameter of the fourth passage 54 upstream of the first pump chamber 7 (suction valve 74) is enlarged compared to the configuration shown in Figure 13, etc., and the upper end of the inner circumferential surface of the passage is above the position of the horizontal passage 78A in the Z direction, then the return passage 78 may have only a horizontal passage 78A, and the end of the horizontal passage 78A on the Y-negative direction side (upstream side) opens into the fourth passage 54.

[0204] This international application claims priority based on Japanese Patent Application No. 2025-024916, filed on 19 February 2025, and the entire contents of said application are incorporated herein by reference.

[0205] 1 Pump 5 Flow path 6 Resonant actuator (actuator) 61 Electromagnet (fixed part, solenoid) 62 First movable plate (movable part, elastic spring) 63 Second movable plate (movable part, elastic spring) 64 First leaf spring (movable part) 65 Second leaf spring (movable part) 66, 66-2 Drive circuit 66A DC power supply 66B Diode 66C Diode (rectifier means) 66D Capacitor (energy storage means) SW1, SW2, SW3, SW4 Switch 7 First pump chamber 71 First piston 72 Second piston 73 Cylinder 8 Second pump chamber 81 First piston 82 Second piston 83 Cylinder 9 Support (fixed object) 100 Espresso machine (beverage supply device) 101 Tank 104 Extraction unit (discharge part) 76 O-ring (first sealing member) 77 Diaphragm seal (second sealing member) 78 Recirculation channel

Claims

1. A drive circuit for a solenoid used in an actuator that vibrates an elastic spring by a magnetic field generated by the solenoid, the drive circuit alternately switches between an energizing period in which the elastic spring is deformed toward the solenoid by supplying current to the solenoid, and a non-energizing period in which the elastic spring recovers from the deformation by stopping the supply of current to the solenoid, and the current flowing through the solenoid is suppressed by back electromotive force during the non-energizing period.

2. The drive circuit according to claim 1, characterized in that, during the non-energized period, a current in the opposite direction to the current flowing through the solenoid due to the back electromotive force is supplied to the solenoid, thereby suppressing the current flowing through the solenoid due to the back electromotive force.

3. The drive circuit according to claim 2, characterized in that the time for supplying the reverse current to the solenoid is shorter than the energizing period.

4. The drive circuit according to claim 1, further comprising rectifier means for suppressing the flow of current due to the back electromotive force through the solenoid during the non-energized period.

5. The drive circuit according to claim 4, characterized in that the rectifier means is a diode.

6. The drive circuit according to claim 5, further comprising a power storage means for storing power generated by the back electromotive force during the non-energized period.

7. The drive circuit according to claim 6, characterized in that the power stored in the power storage means during the non-energized period is supplied to the solenoid during the energized period.

8. An actuator comprising the solenoid, the elastic spring, and the drive circuit described in any one of claims 1 to 7.

9. A pump comprising the actuator described in claim 8, characterized in that the elastic spring vibrates due to the magnetic field generated by the solenoid, thereby drawing in and discharging fluid.

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