JP2009108715A - Piezoelectric pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric pump in which a crack hardly is generated in a piezoelectric-crystal layer of a piezoelectric vibrator, in the piezoelectric pump which has a pump chamber and an atmospheric chamber formed at both sides of a piezoelectric vibrator whose circumferential edge sealed liquid-tightly, and obtains a pumping action by causing the piezoelectric vibrator to vibrate. <P>SOLUTION: The piezoelectric pump includes a bias voltage application circuit for applying a bias voltage which causes the piezoelectric vibrator to convexedly deform toward the pump chamber side, separately from an alternating electric field, with respect to a piezoelectric vibrator having an alternate laminated structure with at least one sheet of shims formed of electrically conductive thin metal sheets and at least one layer of piezoelectric-crystal layers. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a piezoelectric pump that obtains a pump action by a vibrating piezoelectric vibrator.

A piezoelectric pump forms a pump chamber and an air chamber on the front and back sides of a piezoelectric vibrator whose periphery is held liquid-tight, and a pair of check valves (to the pump chamber) having different flow directions are formed in a pair of flow paths connected to the pump chamber. And a check valve that allows fluid flow from the pump chamber). When the piezoelectric vibrator is vibrated, the volume of the pump chamber changes, and as the volume changes, one of the pair of check valves closes and the other opens repeatedly, thereby obtaining a pump action. Since such a piezoelectric pump can be reduced in size, the present applicant is developing a piezoelectric pump used as a cooling water circulation pump of a water-cooled notebook type personal computer.
Japanese Patent Laid-Open No. 8-114408 JP-A-8-200216 Japanese Patent Laid-Open No. 9-74773 JP 2000-92876 JP 2006-294947 A WO96 / 14687 Publication

  The piezoelectric vibrator used in this piezoelectric pump is known as a unimorph type in which a piezoelectric layer is provided on one surface of a metal shim made of a conductive metal plate, and a bimorph type in which a piezoelectric layer is provided on both sides. The present applicant has proposed a multimorph type in which a plurality of piezoelectric layers are electrically connected in parallel or in series (Japanese Patent Application No. 2007-35879). This is common in that it has an alternately laminated structure of at least one shim made of a thin plate and at least one piezoelectric layer. Then, no matter what type of piezoelectric vibrator is used, a piezoelectric layer has conventionally been positioned on the atmosphere chamber side.

  However, it has been found that a piezoelectric vibrator provided with a piezoelectric layer on the atmosphere chamber side may cause cracks in the piezoelectric layer on the atmosphere chamber side when used for a long period of time.

  Accordingly, an object of the present invention is to obtain a piezoelectric pump in which cracks are unlikely to occur in a piezoelectric layer of a piezoelectric vibrator.

  As a result of research on the cause of cracks in the piezoelectric layer on the atmosphere chamber side, the present inventors have received a liquid pressure on the pump chamber side and applied a force in a direction that always protrudes to the atmosphere chamber side during operation. As a result, it was concluded that the application of tensile stress to the piezoelectric layer on the atmosphere chamber side caused the generation of cracks, and the present invention was made. That is, the piezoelectric layer made of ceramic is strong against compressive force but weak against tensile force.

  In addition to the alternating electric field that vibrates the piezoelectric vibrator, the present invention balances the deformation pressure caused by the liquid pressure and the deformation pressure caused by the bias voltage by applying a bias voltage that elastically deforms the piezoelectric vibrator toward the pump chamber. However, this is based on the viewpoint that the tensile stress applied to the piezoelectric layer can be relaxed.

  The present invention provides a piezoelectric pump in which a pump chamber and an air chamber are formed on the front and back sides of a piezoelectric vibrator having a liquid-tight peripheral edge, and an alternating electric field is applied to the piezoelectric vibrator to obtain a pump action. And having an alternating laminated structure of at least one shim made of a conductive metal thin plate and at least one piezoelectric layer, applying an alternating electric field to the piezoelectric vibrator, and In addition to the alternating electric field to be applied, a bias voltage applying circuit for applying a bias voltage for projecting the piezoelectric vibrator to the pump chamber side is provided.

  The present invention can be applied without questioning the type of piezoelectric vibrator. Specifically, for example, a unimorph type having a shim made of a conductive metal thin plate on the pump chamber side and a piezoelectric layer on the atmosphere chamber side; a piezoelectric layer on both sides of the shim made of a conductive metal thin plate Either a bimorph type having a shim made of a conductive metal thin plate on the pump chamber side and a multimorph type having a plurality of piezoelectric layers connected in series or in parallel on the atmosphere chamber side can be used. is there.

  The bias voltage application circuit may apply a constant voltage to the piezoelectric vibrator, monitor the deformation of the piezoelectric vibrator (temperature of the pump chamber), and change the applied voltage according to the amount of deformation.

  In the piezoelectric pump in which the pump chamber and the air chamber are formed on the front and back sides of the piezoelectric vibrator, the bias voltage for elastically deforming the piezoelectric vibrator to the pump chamber side separately from the alternating electric field that vibrates the piezoelectric vibrator. Therefore, it is possible to balance the deformation pressure due to the liquid pressure and the deformation pressure due to the bias voltage, relieve the tensile stress applied to the piezoelectric layer, and suppress the generation of cracks.

  1 and 2 show the basic structure of a piezoelectric pump targeted by the present invention. The piezoelectric pump 20 has a lower housing 21, a middle housing 22, and an upper housing 23 that are stacked in order from the bottom of the figure.

  A cooling water (liquid) suction port 24 and a discharge port 25 are opened in the lower housing 21. Between the middle housing 22 and the upper housing 23, an annular electrode terminal 29 disposed on the piezoelectric vibrator 10 and the back side (pump chamber P side) via a pair of annular narrowing members (O-ring 27, guide 28). Are supported tightly in a liquid-tight manner, and a pump chamber P is formed between the piezoelectric vibrator 10 and the middle housing 22. An atmospheric chamber A is formed between the piezoelectric vibrator 10 and the upper housing 23. The atmosphere chamber A may be opened or sealed.

  The lower housing 21 and the middle housing 22 are respectively formed with a suction flow path 30 for communicating the suction port 24 and the pump chamber P and a discharge path 31 for communicating the pump chamber P and the discharge port 25. Are provided with check valves (umbrellas) 32 and 33 in the suction flow path 30 and the discharge flow path 31, respectively. The check valve 32 is a suction-side check valve that allows a fluid flow from the suction port 24 to the pump chamber P and does not allow the reverse fluid flow. The check valve 33 transfers from the pump chamber P to the discharge port 25. This is a discharge-side check valve that allows the fluid flow of the fluid but does not permit the reverse fluid flow. The check valves 32 and 33 in the illustrated embodiment have the same configuration, and are provided with umbrellas 32b and 33b made of an elastic material on perforated substrates 32a and 33a that are bonded or welded and fixed to the flow path. .

  A rectangular housing recess 21 a is formed in the lower housing 21 at a position separated from the suction flow path 30 and the discharge path 31, and the piezoelectric vibrator 10 is interposed between the storage recess 21 a and the middle housing 22. A driver circuit board 26 for driving and controlling the liquid crystal is stored in a liquid-tight manner.

  When the piezoelectric vibrator 10 is elastically deformed (vibrated) in the forward and reverse directions, the piezoelectric pump 20 opens the suction side check valve 32 and closes the discharge side check valve 33 in the stroke in which the volume of the pump chamber P increases. The liquid flows into the pump chamber P from the suction port 24. On the other hand, in the stroke in which the volume of the pump chamber P decreases, the discharge side check valve 33 opens and the suction side check valve 32 closes, so that the liquid flows out from the pump chamber P to the discharge port 25. Accordingly, the pump action can be obtained by elastically deforming (vibrating) the piezoelectric vibrator 10 continuously in the forward and reverse directions.

  As described above, any of the unimorph type, the bimorph type, and the multimorph type can be used for the piezoelectric vibrator 10 having a planar circular shape. 1, 3, and 4 are basically configured by a bimorph type in which piezoelectric layers 12 f and 12 r are laminated and bonded to the front and back of the main shim 11, and further, on the piezoelectric layer 12 f facing the atmosphere chamber A side, A piezoelectric vibrator is formed by laminating and bonding a protective shim 13 and laminating and bonding a cover film 14 on the piezoelectric layer 12r facing the pump chamber P side. The front side (atmosphere chamber A side) piezoelectric layer 12 f is formed smaller than the diameter of the main shim 11, and the back side (pump chamber P side) piezoelectric layer 12 r is formed with the same diameter as the main shim 11. The guide 28 is positioned on the outer side of the outer portion of the piezoelectric layer 12f on the front side (atmosphere chamber A side) of the main shim 11 and supports the main shim 11 tightly. In FIG. 2, the piezoelectric layers 12f and 12r, the main shim 11, and the cover film 14 of the piezoelectric vibrator 10 are omitted. 1 to 4, film-like electrode layers are formed on both surfaces of the piezoelectric layers 12f and 12r, but the illustration is omitted.

  The main shim 11 is a conductive metal thin plate made of stainless steel or 42 alloy having a thickness of about 30 to 500 μm, and has rigidity for supporting the piezoelectric layers 12f and 12r.

The piezoelectric layers 12f and 12r on the front and back of the main shim 11 are made of a piezoelectric material such as PZT (Pb (Zr, Ti) O ₃ ) having a thickness of about 50 to 500 μm, for example, and are subjected to polarization treatment in the front and back directions. Has been. The polarization directions of the piezoelectric layers 12f and 12r on the front and back sides are the same direction. Such a piezoelectric vibrator is known as a bimorph type (parallel connection). When the same alternating electric field is applied to the front and back of each of the piezoelectric layers 12f and 12r, a cycle in which one of the front and back of the piezoelectric layers 12f and 12r extends and the other contracts is repeated, and the shim 11 (piezoelectric vibrator 10) is centered. It vibrates so that the amplitude of the part becomes the largest.

  Like the main shim 11, the protective shim 13 is a conductive metal thin plate made of stainless steel having a thickness of about 5 to 500 μm, 42 alloy, or the like. The protective shim 13 has a diameter that covers the entire piezoelectric layer 12f on the atmosphere chamber A side. By providing this protective shim 13, the tensile stress applied to the piezoelectric layer 12f on the atmosphere chamber A side is relieved and helps to prevent the occurrence of cracks. is not. In the piezoelectric vibrator 10, as described above, the front side (atmosphere chamber A side) piezoelectric layer 12f is formed to be smaller than the diameter of the main shim 11, and the guide 28 is a front side (atmosphere chamber A side) piezoelectric body of the main shim 11. The main shim 11 is supported tightly on the outer part of the outer shape of the layer 12f, but the front side (atmosphere chamber A side) piezoelectric layer 12f has the same diameter as the main shim 11, and the guide 28 is on the front side (atmosphere chamber A side). ) It may be a structure in contact with the piezoelectric layer 12f.

  The cover film 14 is laminated and bonded onto the piezoelectric layer 12r located on the pump chamber P side, and protects the piezoelectric layer 12r from the fluid entering and leaving the pump chamber P. The cover film 14 is made of a synthetic resin film having a thickness of about 10 to 100 μm, for example, PPS (polyphenylene sulfide).

  The annular electrode terminal 29 located on the back side of the piezoelectric vibrator 10 is in electrical contact with the exposed surface (electrode layer) of the piezoelectric layer 12r on the back side of the main shim 11 in an annular shape. Further, the protective shim 13 positioned on the front surface of the piezoelectric vibrator 10 is in electrical contact with the exposed surface electrode layer of the piezoelectric layer 12 on the front surface of the main shim 11 in a concentric manner. The main shim 11, the protection shim 13, and the annular electrode terminal 29 have wiring protrusions 11a, 13a, and 29a for connecting the wiring at their peripheral portions, respectively, and the middle housing 22 protrudes corresponding to the wiring protrusions 11a, 13a, and 29a. A recess 22 a is formed continuously with the pump chamber P. The diameter of the annular electrode terminal 29 is substantially the same as the diameter of the O-ring 27, and at least a portion thereof overlaps along the entire circumference, or the O-ring 27 extends over the entire circumference of the annular electrode terminal 29. It is formed so that it can be pressed. Therefore, when the annular electrode terminal 29 and the O-ring 27 are overlapped, the O-ring 27 is positioned in one plane and no minute unevenness is generated.

  In the present embodiment, for example, in the piezoelectric pump having the above configuration, as shown in FIG. 5, a bias voltage is constantly applied to the piezoelectric vibrator 10 so that the piezoelectric vibrator 10 protrudes toward the pump chamber P. A bias voltage application circuit 40 is provided. The bias voltage application circuit 40 is provided separately from the alternating electric field application circuit 41 that applies an alternating electric field to the piezoelectric vibrator 10. FIG. 5 shows only the main shim 11 and the piezoelectric layers 12 f and 12 r as the piezoelectric vibrator 10. When the polarization directions of the piezoelectric layers 12f and 12r are indicated by ▲ arrows, the bias voltage application circuit 40 applies a positive potential (+) to the main shim 11 (the surface of the piezoelectric layers 12f and 12r on the shim 11 side), By applying a negative potential (−) to the surfaces (exposed surfaces) of the layers 12f and 12r, the surface area of the back-side piezoelectric layer 12r is enlarged and the surface area of the front-side piezoelectric layer 12f is reduced, as exaggerated by a broken line. As a result, the piezoelectric vibrator 10 can be elastically deformed convexly toward the pump chamber P side. Therefore, by balancing the convex displacement due to the bias voltage with the concave displacement due to the liquid pressure, it is possible to prevent cracks from occurring in the piezoelectric layer 12f of the piezoelectric vibrator 10.

  FIG. 6 shows an embodiment when a unimorph type is used as the piezoelectric vibrator 10. The piezoelectric vibrator 10 is provided with a piezoelectric layer 12s on one surface of the main shim 11 and the surface on the atmosphere chamber A side. In this embodiment, when the polarization direction of the piezoelectric layer 12s is と し た, the bias voltage application circuit 40 applies a bias voltage in a direction in which the surface area of the piezoelectric layer 12s is reduced. By applying such a bias voltage, the piezoelectric vibrator 10 can be elastically deformed so as to protrude toward the pump chamber P, as exaggerated by a broken line. The bias voltage application circuit 40 is provided separately from the alternating electric field application circuit 41 that applies an alternating electric field to the piezoelectric vibrator 10.

  FIG. 7 shows an embodiment in which a bimorph series-connected multimorph type is used as the piezoelectric vibrator 10. In the piezoelectric vibrator 10, an electrode layer d, a large-diameter piezoelectric layer 12, an electrode layer d, an intermediate shim 40, an electrode layer d, a small-diameter piezoelectric layer 12 b, and an electrode layer d are stacked on a main shim 11. The periphery of the large-diameter piezoelectric layer 12a is tightly supported by an O-ring 27 and a guide 28. The small-diameter piezoelectric layer 12b is not restricted by the guide 28 and can be freely displaced. 5 and 6, illustration of the electrode layer is omitted.

  The large-diameter piezoelectric layer 12a and the small-diameter piezoelectric layer 12b have the same thickness, and the entire thickness of the piezoelectric body 12 is, for example, about 50 to 1000 μm. The intermediate shim 40 is a circular or annular metal elastic body (circular in the illustrated embodiment) having the same diameter as that of the large-diameter piezoelectric body layer 12 b, and is mechanically deformable as the laminated piezoelectric body 12 is displaced. Has resiliency. The intermediate shim 40 has a higher mechanical resilience than the main shim 11, and the intermediate shim 40 does not hinder the displacement of the laminated piezoelectric body 12 as much as possible. The intermediate shim 40 is formed of the same material as the main shim 11 and is thicker than the main shim 11, and a thin metal plate made of 42 alloy having a thickness of about 50 to 600 μm, for example, is used. By providing the intermediate shim 40, the mechanical strength of the laminated piezoelectric body 12 increases and the closing pressure can be increased. The intermediate shim 40 can be omitted.

  The intermediate electrode layer d positioned between the intermediate shim 40 and the large-diameter piezoelectric layer 12a and the small-diameter piezoelectric layer 12b functions as a neutral surface that electrically separates the large-diameter piezoelectric layer 12a and the small-diameter piezoelectric layer 12b. To do.

  In this laminated piezoelectric body 12, the large-diameter piezoelectric layer 12a on the main shim 11 side is electrically connected to the second feed line 15 via the shim-side electrode layer d and the main shim 11, and the small-diameter piezoelectric layer 12b on the atmosphere chamber A side is It is electrically connected to the first feed line 14 via the surface electrode layer d and the annular electrode terminal 29. That is, the large-diameter piezoelectric layer 12a and the small-diameter piezoelectric layer 12b are electrically connected in series (series connection). The polarization directions of the large-diameter piezoelectric layer 12a and the small-diameter piezoelectric layer 12b are reversed as shown by the arrows in FIG. 7, and an alternating electric field is applied via the first feed line 14 and the second feed line 15. When an alternating voltage is applied from the circuit 41, it is elastically deformed in a direction in which the surface area expands or contracts.

  In this embodiment, a bias voltage is applied to the piezoelectric vibrator 10 via the annular electrode terminal 29, the first feeding line 14 and the second feeding line 15 so that the piezoelectric vibrator 10 protrudes toward the pump chamber P side. Bias voltage application circuits 40A and 40B to be applied are provided. The bias voltage application circuits 40A and 40B apply a positive potential (+) to the main shim 11 (the surface on the main shim side of the large-diameter piezoelectric layer 12a) via the second power supply line 15, and the first power supply line 14 and the annular electrode terminal By applying a negative voltage (−) to the surface (exposed surface) of the small-diameter piezoelectric layer 12b via 29, the piezoelectric vibrator 10 is elastically deformed convex toward the pump chamber side, as exaggeratedly shown by a broken line. In FIG. 7, bias voltage application circuits 40A and 40B are provided on the first power supply line 14 side (upper piezoelectric layer 12a side) and the second power supply line 15 side (main shim 11 side), respectively, and applied from the bias voltage application circuit 40A. The magnitude relationship between the bias voltage Va applied and the bias voltage Vb applied from the bias voltage application circuit 40B is set to Va <Vb.

  When the piezoelectric vibrator 10 is vibrated, as in the previous embodiment, an alternating electric field is applied to the piezoelectric vibrator 10 by the alternating electric field application circuit 41 while the bias voltage is applied by the bias voltage application circuits 40A and 40B.

  Next, a calculation example of the bias voltage that should be actually applied to the piezoelectric vibrator 10 will be described. When the liquid temperature in the pump chamber P of the piezoelectric pump 20 increases, the internal pressure (kPa) of the pump chamber P increases. FIG. 8 shows an example of the relationship between the liquid temperature and the internal pressure. From such a liquid temperature-internal pressure curve, the internal pressure P at each liquid temperature can be obtained. Next, when the piezoelectric vibrator 10 is deformed to the pump chamber P side, the internal pressure of the pump chamber P increases. FIG. 9 shows an example of the relationship between the deformation amount (μm) of the piezoelectric vibrator 10 and the internal pressure. From such a deformation amount-internal pressure curve, the deformation amount to the pump chamber P side of the piezoelectric vibrator 10 to be applied as the liquid temperature rises can be obtained. Finally, FIG. 10 shows an example of the relationship between the bias voltage (Vop) applied to the piezoelectric vibrator 10 and the deformation amount (μm) of the vibrator caused by the bias voltage. Accordingly, the change in internal pressure is obtained from the pump chamber liquid temperature in FIG. 8, the amount of deformation of the piezoelectric vibrator 10 to cancel the change in internal pressure is obtained in FIG. 9, and the magnitude of the bias voltage that causes such deformation is obtained in FIG. be able to.

Table 1 calculated the internal pressure and offset voltage when the pump chamber liquid temperature was changed to 40, 50, 60, and 70 (° C.) using the piezoelectric vibrator 10 of the embodiment of FIG. It is a result.
"Table 1"
Liquid temperature (° C.) 40 50 60 70
Internal pressure (kPa) 8.4 12.2 20.0 36.0
Offset voltage (V) 34.0 57.6 94.5 145.5

  Of course, the calculation example in Table 1 is an example, and a specific magnitude of the bias voltage can be determined based on the method described with reference to FIGS. 8 to 10 according to the pump capacity and the properties of the piezoelectric vibrator. .

  In the above embodiment, the bias voltage applied to the piezoelectric vibrator 10 by the bias pressure application circuit 40 is constant. However, the displacement of the piezoelectric vibrator 10 or the liquid temperature in the pump chamber P is monitored, and the piezoelectric output is obtained by this monitor output. The bias pressure applied to the child 10 may be changed.

It is a disassembled perspective view which shows the basic structure of the piezoelectric pump which this invention makes object. It is sectional drawing of the same piezoelectric pump. It is a partial expanded sectional view which shows 1st Embodiment of the piezoelectric pump by this invention. It is a model exploded perspective view of the piezoelectric vibrator of the same piezoelectric pump. It is explanatory drawing which shows one Embodiment of the bias voltage application circuit with respect to the piezoelectric vibrator by this invention. It is explanatory drawing which shows one Embodiment of the bias voltage application circuit with respect to another piezoelectric vibrator. It is explanatory drawing which shows one Embodiment of the bias voltage application circuit with respect to the same another piezoelectric vibrator. It is a water vapor pressure diagram. It is a graph which shows an example of the deformation amount of a pump chamber internal pressure and a diaphragm. It is a graph which shows an example of the bias voltage which should be applied to the diaphragm in order to cancel the same displacement as the displacement of a diaphragm.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Piezoelectric vibrator 11 Main shim 11a Wiring protrusion 12 12f 12r 12s Piezoelectric layer 13 Protection shim 13a Wiring protrusion 14 Cover film 20 Piezoelectric pump 21 Lower housing 22 Middle housing 23 Upper housing 24 Suction port 25 Discharge port 29 Annular electrode terminal 29a Wiring protrusion 30 suction channel 31 discharge channel 32, 33 check valve 40 bias voltage application circuit 41 alternating electric field application circuit A atmosphere chamber P pump chamber

Claims (6)

In a piezoelectric pump that forms a pump chamber and an atmospheric chamber on the front and back of a piezoelectric vibrator having a liquid-tight peripheral edge, and obtains a pump action by applying an alternating electric field to the piezoelectric vibrator to obtain a pump action.
The piezoelectric vibrator has an alternately laminated structure of at least one shim made of a conductive metal thin plate and at least one piezoelectric layer, and an alternating electric field is applied to the piezoelectric layer. In addition to the alternating electric field to be applied to the piezoelectric vibrator, a bias voltage application circuit for applying a bias voltage for projecting the piezoelectric vibrator to the pump chamber side is provided.
A piezoelectric pump characterized by 2. The piezoelectric pump according to claim 1, wherein the piezoelectric vibrator is a unimorph type having a shim made of a conductive metal thin plate on the pump chamber side and a piezoelectric layer on the atmosphere chamber side. 2. The piezoelectric pump according to claim 1, wherein the piezoelectric vibrator is a bimorph type having piezoelectric layers on both sides of a shim made of a conductive metal thin plate. 2. The piezoelectric pump according to claim 1, wherein the piezoelectric vibrator has a shim made of a conductive metal thin plate on the pump chamber side and a plurality of piezoelectric layers connected in series or in parallel on the atmosphere chamber side. A morph type piezoelectric pump. 5. The piezoelectric pump according to claim 1, wherein the bias voltage application circuit applies a constant voltage. 6. 5. The piezoelectric pump according to claim 1, wherein the bias voltage application circuit is capable of varying the applied voltage. 6.

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