JP2019009309A - Piezoelectric generator - Google Patents

Abstract

To provide a power generator that has little secular change of a structure under a use environment and is capable of stable power generation for a long time.SOLUTION: A piezoelectric generator 1 includes a piezoelectric element 2, a support plate 3, and a pressing member 4. The support plate 3 has a first surface 3a and a second surface 3b opposite to each other, and a pair of fixing portions F1 and F2 arranged so as to be separated from and opposed to each other across a central portion of the support plate 3 in a first direction (x direction) of the first surface 3a. The piezoelectric element 2 is bonded to the first surface 3a of the support plate 3, and the pressing member 4 is an elastic body having a pressing surface 4a arranged along the second surface 3b of the support plate 3 and pressing the second surface 3b when a force is applied from the outside.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a piezoelectric power generation device.

  The piezoelectric body is distorted when stress is applied, and charges are generated by the piezoelectric effect. The electric charges generated by the distortion of the piezoelectric body can be directly used for driving electric products and electronic products (electric products, etc.). Moreover, the generated electric charge can be stored in a storage battery or a capacitor (capacitor), and these capacitors can be used as a drive power source for electric products or as a backup power source in the event of a power failure or emergency.

  For example, Patent Document 1 discloses a power generation member that generates electricity by pressing a piezoelectric element supported by a support member with a pressing member.

JP 2010-153777 A

  The piezoelectric power generation device of the present disclosure includes a piezoelectric element, a support plate, and a pressing member, and the support plate has a first surface and a second surface that face each other, and a first surface of the first surface. A pair of fixing portions separated in a direction, the pair of fixing portions are arranged so as to face each other with a central portion of the support plate in the first direction sandwiched therebetween, and the piezoelectric element is arranged on the support plate. Joined to the first surface, the pressing member is an elastic body that is disposed along the second surface of the support plate and has a pressing surface that presses the second surface when a force is applied from the outside. .

It is sectional drawing which shows typically 1st Embodiment of a piezoelectric type electric power generating apparatus. In 1st Embodiment, it is sectional drawing which shows another form of the fixing method of a support plate. It is a top view which shows a 1st embodiment typically. It is sectional drawing which shows an example of a monomorph type piezoelectric element. It is sectional drawing which shows an example of a bimorph type piezoelectric element. In 1st Embodiment, it is sectional drawing of the state by which the support plate is pressed by the press member. It is a schematic block diagram which shows an example of the piezoelectric type electric power generating apparatus provided with the electrical energy storage means. It is sectional drawing which shows typically 2nd Embodiment of a piezoelectric type electric power generating apparatus. It is sectional drawing which shows typically 3rd Embodiment of a piezoelectric power generation device.

  FIG. 1 is a cross-sectional view schematically illustrating a first embodiment of a piezoelectric power generation device 1 (sometimes simply referred to as a power generation device 1). The piezoelectric power generation device 1 of this embodiment includes a piezoelectric element 2, a support plate 3, and a pressing member 4. The support plate 3 has a first surface 3a and a second surface 3b facing each other. Here, as shown in FIG. 1, the longitudinal direction of the opposing first surface 3a and second surface 3b of the support plate 3 is the x direction, the direction perpendicular to the longitudinal direction is the y direction, and the thickness direction of the support plate 3 is the thickness direction. It is called the z direction. The positive direction in the z direction in FIG. 1 may be simply referred to as “up”, and the negative direction in the z direction may be simply referred to as “down”.

  The support plate 3 is fixed by a fixing member 6 with a pair of fixing portions F1 and F2 located at both ends in the x direction. The support plate 3 and the fixing member 6 may be joined by a joining material 5. The joint between the support plate 3 and the fixing member 6 may be any of a dot shape, a linear shape extending in the y direction, and a planar shape.

  The support plate 3 and the fixing member 6 may not be joined. For example, as shown in FIG. 2, the structure which pinches | interposes the fixing | fixed part F1, F2 of the 1st surface 3a and the site | part corresponded to the fixing | fixed part F1, F2 of the 2nd surface 3b from the upper and lower sides may be sufficient.

  The material of the fixing member 6 is preferably an elastic body such as silicon rubber. By fixing the support plate 3 with an elastic body, the support plate 3 can be held in a state of being easily deformed. In particular, when the pressing member 4 is pressed against the support plate 3, the repulsive force by the fixing member 6 is reduced by using the fixing member 6 as an elastic body. As a result, it is possible to suppress the deformation amount of the support plate 3 from being reduced due to the repulsive force of the fixing member 6 and to obtain a large electric energy.

  The piezoelectric element 2 is disposed on the first surface 3 a of the support plate 3 and is bonded to the first surface 3 a of the support plate 3 via the bonding material 5. The pressing member 4 is disposed above the second surface 3b of the support plate 3 and has a pressing surface 4a that presses the second surface 3b when a force is applied from the outside.

  FIG. 3 is a plan view of the piezoelectric power generator 1. As shown in FIG. 3, the piezoelectric element 2 and the pressing member 4 are arranged between the fixing portions F1 and F2 in the first direction (x direction). When a line that passes through the center of each member in the x direction (position that bisects the length in the x direction) and is perpendicular to the x direction is a center line C in the x direction (sometimes simply referred to as the center line C), The center line C of the piezoelectric element 2, the center line C of the pressing member, and the center line C between F1 and F2 of the support plate 3 are preferably matched. Hereinafter, the center line C may be referred to as a center portion C including the vicinity thereof.

  The piezoelectric element 2 includes a rectangular piezoelectric plate 7 and an electrode 8 polarized in the thickness direction. For example, as shown in FIG. 4, the piezoelectric element 2 may be one in which electrodes 8 a and 8 b are formed on both surfaces of a piezoelectric plate 7 (so-called monomorph element). The monomorph element becomes a unimorph element by being bonded to the support plate 3.

  As shown in FIG. 5, the piezoelectric element 2 has piezoelectric layers 7a, 7b, 7c and 7d polarized in the thickness direction (z direction) and electrode layers 8c, 8d and 8e alternately stacked. A laminated body may be sufficient. You may have surface electrode 8a, 8b and side electrode 8f, 8g further on the surface of the laminated body. The side electrode 8f electrically connects the surface electrode 8a and the electrode layer 8d, and the side electrode 8g electrically connects the surface electrode 8b and the electrode layers 8c and 8e. The surface electrode layers 8a and 8b are connected to, for example, lead terminals (not shown).

The piezoelectric element 2 shown in FIG. 5 is a bimorph element, and as indicated by the white arrows in FIG. 5, the piezoelectric layers 7a and 7d are polarized in the same direction in the z direction, and the piezoelectric layers 7b and 7c are in the z direction. Are polarized in the same direction. The piezoelectric layers 7a and 7d and the piezoelectric layers 7b and 7c are polarized in opposite directions. Although FIG. 5 shows the piezoelectric element 2 including four piezoelectric layers 7, the number of the piezoelectric layers 7 may be three or less, or five or more.

  In such a piezoelectric power generation device 1, when a force is applied from the outside, the second surface 3b of the support plate 3 is pressed by the pressing surface 4a of the pressing member 4 as shown in FIG. 3 is bent and deformed. When the support plate 3 is bent and deformed, the piezoelectric element 2 disposed on the first surface 3a of the support plate 3 and bonded to the first surface 3a is bent and deformed. In FIG. 6, the description of the bonding material 5 and the electrode 8 is omitted.

When the piezoelectric element 2 is a monomorph element as shown in FIG. 4, the piezoelectric element 2 is bent and deformed as shown in FIG. 6, and tensile stress or compressive stress is applied to the piezoelectric plate 7, and polarization charges are applied to the surface of the piezoelectric plate 7. Will occur. As a result, a potential difference is generated between the electrodes 8a and 8b, and electric energy is generated.

  When the piezoelectric element 2 is a bimorph element as shown in FIG. 5, for example, when the piezoelectric element 2 is bent and deformed as shown in FIG. 6, compressive stress is applied to the piezoelectric layers 7a and 7b in FIG. A tensile stress is applied to the layers 7c and 7d. At this time, compressive stress is applied to the piezoelectric layers 7a and 7b, so that the crystal structure of the piezoelectric material constituting the piezoelectric layers 7a and 7b extends in the thickness direction (z direction) and contracts in the x direction. As a result, negative charges are generated in the surface electrode 8a and the electrode layer 8d, and positive charges are generated in the electrode layer 8c. On the other hand, when a tensile stress is applied to the piezoelectric layers 7c and 7d, the crystal structure of the piezoelectric material constituting the piezoelectric layers 7c and 7d contracts in the thickness direction (z direction) and extends in the x direction. As a result, negative charges are generated in the electrode layer 8d and the surface electrode 8a, and positive charges are generated in the electrode layer 8e. Therefore, negative charges are generated on the surface electrode 8a and positive charges are generated on the surface electrode 8b. As a result, a potential difference is generated between the surface electrode 8a and the surface electrode 8b, and electric energy is generated.

  In addition, when the piezoelectric element 2 that has been bent and deformed returns to its original shape, a charge having a sign opposite to that when the piezoelectric element 2 has been bent and deformed is generated in the electrodes 8a and 8b. The electric energy generated when the piezoelectric element 2 repeats bending deformation in this way is alternating current. Therefore, in order to take out and store the generated electric energy, the piezoelectric power generation device 1 may include a rectifier circuit 12 and a capacitor 13 as shown in FIG. The rectifier circuit 12 includes a diode bridge circuit, and full-wave rectifies the AC electrical signal (electric energy) output from the piezoelectric element 2. The electric energy subjected to full-wave rectification is charged in the battery 13.

  As the battery 13, for example, a secondary battery or a capacitor (capacitor) can be used. Electricity obtained through the rectifier circuit 12 may be directly used for driving various electronic devices.

  In the present embodiment, it is the support plate 3 to which an external force is applied by the pressing member 4. When the support plate 3 is bent and deformed, the piezoelectric element 2 bonded to the support plate 3 is bent and deformed to generate electric energy. Thus, by not applying an external force directly to the piezoelectric element 2, it is possible to suppress damage to the piezoelectric element 2 due to the application of the external force.

  An elastic body (elastomer) is used for the pressing member 4. In particular, it is preferable to use a material having an elastic modulus of 0.1 MPa to 1.0 GPa, for example, hard rubber. The hard rubber is obtained by vulcanizing sulfur by vulcanizing natural rubber or synthetic rubber, and may contain carbon powder.

  When the second surface 3b of the support plate 3 is pressed by the pressing member 4 that is an elastic body, the support plate 3 is not only bent and deformed, but the pressing member 4 is also deformed. When the pressing member 4 is deformed, the contact area between the support plate 3 and the pressing member 4 is increased. As a result, a region where the support plate 3 and the piezoelectric element 2 are deformed is widened compared to the case where a hard material that is difficult to deform is used as the pressing member 4, so that a large electric energy can be obtained.

  The material of the support plate 3 is preferably a metal material having a spring property. Examples of the metal material having a spring property include phosphor bronze (for example, C5210, C5240, etc.), stainless steel (SUS304CSP, SUS301CSP, etc.), and white (C7521, C7701, etc.).

By making the support plate 3 a leaf spring made of a metal material having such a spring property, the support plate 3 having a high restoring force can be obtained. Even if such a support plate 3 is pressed and pressed and deformed by the pressing member 4, it can be easily returned to the state before the deformation by removing the pressing by the pressing member 4. Moreover, even if such a support plate 3 is repeatedly bent and deformed, the restoring force is unlikely to decrease, and thus the durability against bending deformation is high. Therefore, it is possible to configure the piezoelectric power generation device 1 with little decrease in the amount of power generation even when power generation by bending deformation is repeated. In particular, phosphor bronze is a material having excellent mechanical properties such as springiness, strength, and wear resistance, and is characterized by being strong against chemical corrosion and good in heat conduction. By using phosphor bronze as the material of the support plate 3, it is possible to provide the power generation apparatus 1 that is capable of stable power generation over a long period of time with little change over time in the structure under the usage environment.

  The support plate 3 may be one in which the surface of a metal plate (plate spring) having spring properties is covered with a plating layer. Ni or Cr is preferably used as the plating material. By plating the surface of the leaf spring made of the spring material with Ni or Cr having a high hardness, it is possible to suppress an excessive stress from being applied to the piezoelectric element 2 and to improve the durability of the power generation device 1.

  The support plate 3 may have a structure in which two leaf springs are bonded together with a material having a low elastic modulus. By disposing an intervening layer made of a material having a low elastic modulus between two leaf springs having spring properties, the stress when the support plate 3 is deformed can be relaxed by the intervening layer. Thereby, it can suppress that an excessive stress is added to the piezoelectric element 2, and the durability of the electric power generating apparatus 1 can be improved. For the intervening layer, for example, an epoxy resin-based or silicon resin-based adhesive, or a material composed of a viscoelastic body such as a double-sided tape may be used.

  As the bonding material 5 for bonding the piezoelectric element 2 and the support plate 3, it is preferable to use a viscoelastic body such as an adhesive or a double-sided tape. By using a viscoelastic body as the bonding material 5, the piezoelectric element 2 and the support plate 3 can be easily deformed. In addition, even when an excessive external force is applied and the support plate 3 is deformed, the stress applied to the piezoelectric element due to the deformation of the support plate 3 is relaxed by the bonding material 5. As a result, it becomes difficult to apply excessive stress to the piezoelectric element 2, and damage to the piezoelectric element 2 can be suppressed.

  The pressing surface 4a of the pressing member 4 may be a flat surface or a shape having a recess 4b that is recessed with respect to the second surface 3b of the support plate 3 as in the second embodiment shown in FIG. Also good. When the pressing surface 4a has the recess 4b, the recess 4b is preferably arranged in a region including the center line C in the x direction. In this case, the pressing member 4 presses the second surface 3b of the support plate 3 with the pressing surface 4a around the recess 4b.

  Here, as shown in FIGS. 1 to 3, the distance in the first direction (x direction) between the pair of fixing portions F1 and F2 is L1, and the length of the pressing member 4 in the x direction is L2. As described above, when the pressing surface 4a is a flat surface or has a recess, the ratio L2 / L1 of L2 to L1 is preferably 0.5 or more and 0.9 or less.

  L1 is the shortest distance in the x direction between the fixing portions F1 and F2, as shown in FIGS. In other words, the fixing portions F1 and F2 are fulcrums when the support plate 3 is bent and deformed. When force is applied to the pressing member 4 from the outside, the pressing member 4 presses the second surface 3b of the support plate 3, and as shown in FIG. 6, the support plate 3 is negative in the z direction with F1 and F2 as fulcrums. It bends and deforms so as to protrude toward the lower side (lower side in FIG. 5). By setting L2 / L1 to 0.5 or more, the concentration of stress on the central portion C of the support plate 3 is relaxed, and the entire support plate 3 can be bent and deformed relatively uniformly between F1 and F2. Further, by setting L2 / L1 to 0.9 or less, it is possible to give the piezoelectric element 2 bending deformation enough to generate sufficient electric energy.

In a state where no force is applied from the outside, the pressing member 4 may be disposed so that the pressing surface 4a and the second surface 3b of the support plate 3 are spaced apart by a distance D1, for example, or supported by the pressing surface 4a. The 2nd surface 3b of the board 3 may be joined. The pressing member 4 is preferably arranged so that the pressing surface 4a and the second surface 3b of the support plate 3 are in contact with each other from the viewpoint of obtaining large power generation energy and downsizing the power generation device 1.

  The pressing surface 4a of the pressing member 4 may have a curved shape protruding toward the second surface 3b of the support plate 3 as shown in the third embodiment of FIG. In particular, in the cross section of the zx plane of the pressing member 4, the pressing surface 4a has an arc shape as shown in FIG. 9, so that the support plate 3 and the piezoelectric element 2 can be bent and deformed evenly in the x direction. When the pressing surface 4a has a curved shape protruding toward the second surface 3b of the support plate 3, the ratio L2 / L1 of L2 to L1 may be 1.0 or more.

  Here, let R be the radius of curvature of the arc formed by the pressing surface 4a in the cross section of the zx plane. The length of the piezoelectric element 2 in the x direction is L3. At this time, the ratio of R to L3 (R / L3) is preferably 0.5 or more and 10.0 or less. By setting R / L3 to 0.5 or more, particularly 0.7 or more, and further 0.9 or more, the support plate 3 and the piezoelectric element 2 can be bent and deformed along the shape of the pressing surface 4a. The plate 3 and the piezoelectric element 2 can be bent and deformed more evenly. Further, by setting R / L3 to 10 or less, particularly 5 or less, and even 2 or less, the bending deformation of the support plate 3 and the piezoelectric element 2 can be further increased.

  In the first direction (x direction), the ratio (L3 / L1) of the length L3 of the piezoelectric element 2 to the distance L1 between the fixed portions F1 and F2 is, for example, 0.3 or more and 1.0 or less. Good.

  At this time, depending on the fixing method of the fixing portions F1 and F2, the deformed state of the support plate 3 may be bent and deformed to the opposite side to the deformed state of the entire support plate 3, for example, in the vicinity of F1 and F2. For example, the support plate 3 as a whole is deformed into a convex state in the negative direction (downward) in the z direction, but the positive direction in the z direction in the vicinity of F1 and F2 because F1 and F2 are fixed. There is a case of being deformed so as to be convex (upward) (deformed in a wave shape). Since the piezoelectric element 2 is deformed in accordance with the deformation of the support plate 3, the deformation state of the piezoelectric element 2 (direction of bending deformation) is reversed between the center between F1 and F2 and the vicinity of F1 and F2. For example, in the case of the surface electrode 8a, a negative charge is generated near the center between F1 and F2, whereas a positive charge is generated near F1 and F2. In the case of the surface electrode 8b, a positive charge is generated near the center between F1 and F2, whereas a negative charge is generated near F1 and F2. As a result, the generated electrical energy is partially offset.

  At this time, by setting L3 / L1 to 1.0 or less, the canceled electric energy can be reduced. L3 / L1 is particularly preferably 0.9 or less, and more preferably 0.8 or less. Further, by setting L3 / L1 to 0.3 or more, even if the support plate 3 is deformed in a wave shape, the bending deformation of the piezoelectric element 2 is maintained to be convex only downward, and the generated electric energy is reduced. Electric power can be generated efficiently without being offset. In order to obtain larger electric energy, L3 / L1 is particularly preferably 0.4 or more, and more preferably 0.5 or more.

  As mentioned above, although embodiment of this indication was described, this indication is not restricted to such a form. For example, the power generation apparatus 1 of the present disclosure is not applied only to power generation applications. When an external force acts on the power generation apparatus 1 and the piezoelectric element 2 bends, a voltage corresponding to the amount of displacement is generated in the piezoelectric element 2, so that the power generation apparatus 1 can be detected by detecting the voltage generated in the piezoelectric element 2. A sensor that measures the magnitude of the applied force or a sensor that detects the amount of displacement of the power generation apparatus 1 can be configured.

When an external force that freely vibrates the power generation device 1 acts on the power generation element 1, for example,
If a force for operating a push-on / push-off type switch or a force for opening and closing various doors acts on the power generation device 1, these on-off operations can be performed by detecting an alternating voltage generated in the piezoelectric element 2. Opening and closing operations can be detected.

  A multilayer piezoelectric element having a bimorph structure was prepared using a lead zirconate titanate piezoelectric material. The piezoelectric element was a laminate having 12 piezoelectric layers by alternately laminating piezoelectric layers of 25 mm × 15 mm and a thickness of 24 μm and internal electrode layers of a thickness of 1 μm. For the internal electrode, an Ag / Pd material was used. Ag paste was baked on the surface and side surfaces of the laminate to form a pair of surface electrodes and a pair of side electrodes, respectively. The total thickness of the piezoelectric element was 300 μm. Lead wires were attached to the surface electrodes of the piezoelectric element.

  A phosphor bronze leaf spring was prepared as a material for the support plate. Two sheets of phosphor bronze (material: C5210) having a size of 40 mm × 20 mm and a thickness of 100 μm were bonded together with a double-sided tape (manufactured by Nitto Denko, No. 5601, thickness 10 μm) to form a support plate. A piezoelectric element was attached to the center of the first surface of the support plate using a double-sided tape.

  A silicon rubber having a thickness of 2 mm was used as a fixing member, and both ends of the support plate to which the piezoelectric element was attached were sandwiched from above and below by silicon rubber as shown in FIG. 2 and fixed to a fixing jig. The distance between the fixed parts was 38 mm.

  A lead wire attached to the piezoelectric element was connected to a rectifier circuit, and a capacitor having a capacity of 10 μF was connected as a capacitor to obtain a power generator.

  A hard rubber having a size of 10 mm × 10 mm and a thickness of 10 mm was used as the pressing member. The support plate and the piezoelectric element were bent and deformed by hitting the central portion of the surface (second surface) of the fixed support plate on which the piezoelectric element was not pasted with the pressing surface (10 mm × 10 mm) of the pressing member.

The power generation amount W of the piezoelectric element was confirmed using an oscilloscope. The capacitance of the capacitor C, and the voltage charged in the capacitor and V, and the power generation amount W, formula: was calculated using the ^{W = C · V 2/2} . In the above power generator, a power generation amount of 220 μJ was obtained by bending and deforming the second surface of the support plate once by hitting it with a pressing member.

DESCRIPTION OF SYMBOLS 1: Piezoelectric power generation device 2: Piezoelectric element 3: Support plate 3a: 1st surface of a support plate 3b: 2nd surface of a support plate 4: Pressing member 5: Bonding material 6: Fixing member 7: Piezoelectric plate, piezoelectric body layer 8: Electrode 12: Rectifier circuit 13: Capacitors F1, F2: fixed part

Claims (6)

A piezoelectric element, a support plate, and a pressing member;
The support plate has a first surface and a second surface facing each other, and has a pair of fixing portions separated in a first direction of the first surface, and the pair of fixing portions are in the first direction. It is arranged so as to face each other across the center part of the support plate,
The piezoelectric element is bonded to the first surface of the support plate,
The piezoelectric power generator is an elastic body that is disposed along the second surface of the support plate and has a pressing surface that presses the second surface when a force is applied from the outside.   The piezoelectric power generation device according to claim 1, wherein a material of the support plate is a metal material having a spring property. The pressing surface is planar;
In the first direction, when the distance between the pair of fixed portions is L1 and the length of the pressing member is L2, the ratio of L2 to L1 (L2 / L1) is 0.5 or more and 0.0. The piezoelectric power generator according to claim 1 or 2, wherein the number is 9 or less.   The piezoelectric power generation device according to claim 1 or 2, wherein the pressing surface has a curved shape protruding toward the second surface.   In the first direction, when the distance between the pair of fixed portions is L1, and the length of the pressing member is L2, the ratio of L2 to L1 (L2 / L1) is 1.0 or more. The piezoelectric power generation device according to claim 4. In a cross section parallel to the first direction, the pressing surface has a radius of curvature R;
6. The ratio according to claim 4, wherein a ratio of R to R3 (R / L3) is 0.5 or more and 10.0 or less, where L3 is a length of the piezoelectric element in the first direction. Piezoelectric generator.

Images