WO2011089803A1 - Piezoelectric electricity generating element, piezoelectric electricity generating device and production method for piezoelectric electricity generating element - Google Patents

Abstract

Disclosed are a small-sized and highly durably piezoelectric electricity generating element which is capable of generating electricity at a high electricity generation rate even by means of low frequency vibrations, a piezoelectric electricity generating device which is provided with the piezoelectric electricity generating element, and a production method for the piezoelectric electricity generating element. A piezoelectric electricity generating element (2) comprises a spiral shaped piezoelectric body (20), and first and second electrodes (21, 22). The spiral shaped piezoelectric body (20) comprises a first end section (20A) which is fixed to a first member (3), and a second end section (20B) which is fixed to a second member (4). The first and the second electrodes (21, 22) are formed along the direction in which the spiral shaped piezoelectric body (20) extends.

Description

Piezoelectric power generation element, piezoelectric power generation apparatus, and method for manufacturing piezoelectric power generation element

The present invention relates to a piezoelectric power generation element, a piezoelectric power generation apparatus including the same, and a method for manufacturing the piezoelectric power generation element. In particular, the present invention is disposed between first and second members that are relatively displaceable along a first direction, and the second member is first with respect to the first member. The present invention relates to a piezoelectric power generation element that generates electric power by vibrating along the direction of the above, a piezoelectric power generation apparatus including the same, and a method for manufacturing the piezoelectric power generation element.

2. Description of the Related Art Conventionally, a piezoelectric power generation device that vibrates due to acceleration, strain, or the like and generates power by a piezoelectric effect is known. Unlike a battery, a piezoelectric power generator is a power source that can be used semipermanently. For this reason, the piezoelectric power generation device is useful as a power source for a wireless communication device, for example.

An example of such a piezoelectric power generator is disclosed in Patent Document 1 below. FIG. 17 is a schematic perspective view of the piezoelectric power generation device described in Patent Document 1. A piezoelectric power generation device 100 shown in FIG. 17 is a unimorph type piezoelectric power generation device in a cantilever manner. The piezoelectric power generation apparatus 100 includes a piezoelectric power generation element 102. A metal plate 103 is bonded to the piezoelectric power generation element 102. One end of the piezoelectric power generation element 102 and the metal plate 103 is fixed to the case 101. A weight 104 is attached to the other end of the piezoelectric power generation element 102 and the metal plate 103.

In this piezoelectric power generation device 100, when acceleration is applied to the piezoelectric power generation device 100, the weight 104 vibrates. Thereby, tensile stress and compressive stress are alternately applied to the piezoelectric power generation element 102. As a result, electric power is generated in the piezoelectric power generation element 102.

Japanese Patent No. 3170965

Incidentally, in the piezoelectric power generation apparatus 100, the resonance frequency of the piezoelectric power generation element 102 correlates with the length of the piezoelectric power generation element 102 and the weight of the weight 104. Specifically, the resonance frequency of the piezoelectric power generation element 102 decreases as the length from the fixed end to the free end of the piezoelectric power generation element 102 increases. Further, as the weight 104 is heavier, the resonance frequency of the piezoelectric power generation element 102 is lower.

For this reason, in order to generate power by vibration at a low frequency, the length between the fixed end and the free end of the piezoelectric power generation element 102 is increased, and the weight 104 is increased in weight to increase the weight of the piezoelectric power generation element. The resonance frequency of 102 needs to be lowered. Therefore, there has been a problem that the piezoelectric power generation apparatus 100 is increased in size when power generation is performed by vibration at a low frequency.

Further, in the piezoelectric power generation apparatus 100, when vibration is applied to the piezoelectric power generation apparatus 100, stress concentrates on the fixed end side portion of the piezoelectric power generation element 102, and the piezoelectric power generation element 102 has a free end side portion. Stress is not so much. For this reason, there is a problem that the power generation efficiency is low and the portion on the fixed end side of the piezoelectric power generation element 102 to which a large stress is applied is easily damaged.

The present invention has been made in view of such points, and an object of the present invention is to provide a small piezoelectric power generating element that can generate power with high power generation efficiency even with low-frequency vibration and has high durability, and the piezoelectric power generating element. Another object of the present invention is to provide a method for manufacturing a piezoelectric power generation device and a piezoelectric power generation element.

The piezoelectric power generating element according to the present invention is disposed between first and second members that are relatively displaceable along a first direction, and the second member is relative to the first member. The present invention relates to a piezoelectric power generation element that generates power by oscillating along a first direction. The piezoelectric power generating element according to the present invention includes a spiral piezoelectric body and first and second electrodes. The spiral piezoelectric body is formed in a spiral shape centering on a central axis extending in the first direction. The spiral piezoelectric body has a first end and a second end. The first end is fixed to the first member. The second end is fixed to the second member. Each of the first and second electrodes is formed on the spiral piezoelectric body along the extending direction of the spiral piezoelectric body.

In the present invention, the spiral piezoelectric body means a spiral piezoelectric body. More specifically, the term “spiral piezoelectric body” refers to a piezoelectric body in which the center line connecting the centers of the cross sections of the spiral piezoelectric body has a spiral shape. The spiral shape means a shape represented by r = constant or f (z), z = aθ in a cylindrical coordinate system (r, θ, z). Note that f (z) is a function of z. The radius of the spiral piezoelectric body is r. The pitch of the spiral piezoelectric body is 2πa.

In a specific aspect of the piezoelectric power generation element according to the present invention, the spiral piezoelectric body has a surface whose normal direction is directed outward. Both the first and second electrodes are provided on a surface whose normal direction faces outward. In this configuration, it is easy to form the first and second electrodes. In particular, compared to a so-called laminated piezoelectric power generation element in which an electrode is also provided inside the piezoelectric body, the formation of the electrode is very easy. Therefore, the piezoelectric power generation element can be easily manufactured. The surface whose normal direction faces outward is not limited to the surface whose normal direction faces radially outward. The surface in which the normal line direction faces outward means the entire surface in which the normal line faces outward when viewed from the direction in which the central axis of the spiral piezoelectric body extends.

In another specific aspect of the piezoelectric power generating element according to the present invention, two second electrodes are provided. The two second electrodes are disposed on both sides of the first electrode on the surface having the normal direction facing outward. In this configuration, the potential difference between the first and second electrodes can be increased while keeping the capacitance between the first and second electrodes large. Therefore, the obtained current value can be increased.

In another specific aspect of the piezoelectric power generating element according to the present invention, the shape of the cross section of the spiral piezoelectric body is rectangular. With this configuration, it is easy to produce a helical piezoelectric body. Therefore, the piezoelectric power generation element can be easily manufactured.

In yet another specific aspect of the piezoelectric power generating element according to the present invention, the shape of the cross section of the spiral piezoelectric body is a rectangular shape whose longitudinal direction is along the first direction. In this configuration, higher power generation efficiency can be obtained when the first and second electrodes are formed on the surface facing the outside of the spiral piezoelectric body.

In yet another specific aspect of the piezoelectric power generating element according to the present invention, the helical piezoelectric body is polarized along the first direction. In this configuration, the vibration mode is the d33 mode. For this reason, the conversion efficiency from kinetic energy to electrical energy can be further increased.

In another specific aspect of the piezoelectric power generating element according to the present invention, the spiral piezoelectric body is polarized along a radial direction perpendicular to the first direction. In this configuration, the polarization of the helical piezoelectric body is easy. Therefore, the piezoelectric power generation element can be easily manufactured.

In another specific aspect of the piezoelectric power generating element according to the present invention, the first electrode and the second electrode are formed when the second member of the helical piezoelectric body vibrates with respect to the first member. At least one of the direction and magnitude of the applied stress is formed on different portions.

In yet another specific aspect of the piezoelectric power generating element according to the present invention, the helical piezoelectric body is made of piezoelectric ceramics. In this configuration, the rigidity of the helical piezoelectric body can be increased. Therefore, a piezoelectric power generating element having high durability can be obtained.

In yet another specific aspect of the piezoelectric power generating element according to the present invention, the spiral piezoelectric body is formed so that the radius is constant in the first direction. That is, r = constant in the cylindrical coordinate system (r, θ, z).

In still another specific aspect of the piezoelectric power generating element according to the present invention, the spiral piezoelectric body is formed so that the radius decreases from the first member side toward the second member side in the first direction. Has been. That is, r = f (z) in the cylindrical coordinate system (r, θ, z), and r = f (z) is a monotone decreasing function.

The piezoelectric power generation apparatus according to the present invention includes the piezoelectric power generation element according to the present invention. Specifically, the piezoelectric power generation device according to the present invention includes first and second members and a piezoelectric power generation element. The first and second members are provided so as to be relatively displaceable along the first direction. The piezoelectric power generation element is formed in a spiral shape centering on a central axis extending in the first direction. The piezoelectric power generation element includes a spiral piezoelectric body and first and second electrodes. The spiral piezoelectric body has a first end and a second end. The first end is fixed to the first member. The second end is fixed to the second member. The first and second electrodes are each formed along the direction in which the spiral piezoelectric body extends.

In a specific aspect of the piezoelectric power generation device according to the present invention, a plurality of piezoelectric power generation elements having different radial dimensions are provided. A plurality of piezoelectric power generation elements having different radial dimensions have different resonance frequencies. Specifically, a piezoelectric power generation element having a small radial dimension has a low resonance frequency, and a piezoelectric power generation element having a large radial dimension has a high resonance frequency. For this reason, in the several piezoelectric power generation element from which the dimension of radial direction differs, the frequency with high electric power generation efficiency mutually differs. Therefore, by providing a plurality of piezoelectric power generation elements having different radial dimensions, it is possible to expand a frequency band with high power generation efficiency.

In another specific aspect of the piezoelectric power generation device according to the present invention, the plurality of piezoelectric power generation elements are provided so as to have the same central axis. In this configuration, the first and second members are likely to vibrate along the first direction. Therefore, power generation efficiency can be increased.

The method for manufacturing a piezoelectric power generation element according to the present invention relates to the method for manufacturing a piezoelectric power generation element according to the present invention. The method of manufacturing a piezoelectric power generating element according to the present invention includes a step of preparing a cylindrical piezoelectric body made of piezoelectric ceramic, a step of forming a conductive film on the outer peripheral surface of the cylindrical piezoelectric body, and a conductive film is formed. Forming a spiral piezoelectric body by cutting the cylindrical piezoelectric body into a spiral, and forming first and second electrodes by dividing the conductive film along a first direction; It has. According to this method, a helical piezoelectric body can be easily created. Therefore, the piezoelectric power generation element can be manufactured easily and inexpensively.

In the present invention, the spiral piezoelectric body is formed in a spiral shape centering on the central axis extending in the first direction. For this reason, the resonance frequency can be lowered without increasing the size. Therefore, it is possible to provide a piezoelectric power generation element that is small in size and capable of generating power with high power generation efficiency even with low-frequency vibration. Further, when a spiral piezoelectric body is used, when the first and second members vibrate along the first direction, stress is applied to the entire spiral piezoelectric body with high uniformity. Therefore, high durability can be realized. Moreover, since power generation is performed by the entire piezoelectric power generation element, high power generation efficiency can be obtained.

FIG. 1 is a schematic side view of the piezoelectric power generation device according to the first embodiment. FIG. 2 is a view taken along line II-II in FIG. FIG. 3 is a schematic perspective view of the piezoelectric power generating element according to the first embodiment. 4 is a schematic cross-sectional view taken along line IV-IV in FIG. FIG. 5 is a schematic diagram showing a process of creating a helical piezoelectric body. FIG. 6 is a schematic diagram illustrating a process of creating a helical piezoelectric body. FIG. 7 is a schematic diagram illustrating a process of creating a helical piezoelectric body. FIG. 8 is a schematic cross-sectional view of the piezoelectric power generating element in the first modification. FIG. 9 is a schematic cross-sectional view of the piezoelectric power generating element in the second modification. FIG. 10 is a schematic cross-sectional view of a piezoelectric power generator according to a third modification. FIG. 11 is a schematic cross-sectional view of a piezoelectric power generator according to a fourth modification. FIG. 12 is a schematic cross-sectional view of a piezoelectric power generator according to a fifth modification. FIG. 13 is a schematic side view of a piezoelectric power generating device according to a sixth modification. FIG. 14 is a schematic cross-sectional view of the piezoelectric power generation device according to the second embodiment. FIG. 15 is a schematic perspective view of the piezoelectric power generation element according to the second embodiment. FIG. 16 is a graph showing the relationship between the frequency of vibration applied to the piezoelectric power generation element and the power generation voltage in the second embodiment. The graph 2a is a graph showing the power generation voltage of the piezoelectric power generation element 2a. A graph 2b is a graph showing the power generation efficiency of the piezoelectric power generation element 2b. A graph 2c is a graph showing the power generation efficiency of the piezoelectric power generation element 2c. FIG. 17 is a schematic perspective view of the piezoelectric power generation device described in Patent Document 1.

(First embodiment)
Hereinafter, a preferred embodiment in which the present invention is implemented will be described by taking a piezoelectric power generation apparatus 1 including the piezoelectric power generation element 2 shown in FIG. 1 as an example. However, the piezoelectric power generation device 1 is merely an example. The piezoelectric power generation device and the piezoelectric power generation element according to the present invention are not limited to the piezoelectric power generation device 1 and the piezoelectric power generation element 2.

The piezoelectric power generation device 1 is a device used for applications where low-frequency vibration is applied. The piezoelectric power generation device 1 is used by being attached to a device to which vibration of a specific low frequency of about 1 to 100 Hz is applied, such as a car, a human body, a boiler, and a motor. The piezoelectric power generation device 1 is used as a power source for a wireless sensor network, for example.

FIG. 1 is a schematic side view of a piezoelectric power generator according to a first embodiment. FIG. 2 is a view taken along line II-II in FIG. FIG. 3 is a schematic perspective view of the piezoelectric power generating element according to the first embodiment. 4 is a schematic cross-sectional view taken along line IV-IV in FIG.

As shown in FIG. 1, the piezoelectric power generation apparatus 1 includes first and second members 3 and 4 and a piezoelectric power generation element 2. The first and second members 3 and 4 are arranged along the first direction z. The first and second members 3 and 4 are relatively displaceable along the first direction z. In the piezoelectric power generation apparatus 1, the first and second members 3 and 4 relatively vibrate along the first direction, so that the piezoelectric power generation element 2 expands and contracts along the first direction z, thereby generating power. Is called.

Each of the first and second members 3 and 4 may constitute a fixed end, or may constitute a free end. When the 1st and 2nd members 3 and 4 comprise the free end, the 1st and 2nd members 3 and 4 function as a weight. In addition, the material of the 1st and 2nd members 3 and 4 is not specifically limited. The first and second members 3 and 4 may be made of, for example, a metal, an alloy, a resin, or wood.

The piezoelectric power generation element 2 is disposed between the first member 3 and the second member 4. The piezoelectric power generation element 2 includes a spiral piezoelectric body 20. One end portion 20 </ b> A of the spiral piezoelectric body 20 is fixed to the first member 3. The other end 20 </ b> B of the spiral piezoelectric body 20 is fixed to the second member 4.

The spiral piezoelectric body 20 can be formed of an appropriate piezoelectric material. The spiral piezoelectric body 20 can be formed of, for example, piezoelectric ceramics, a piezoelectric resin, or a piezoelectric composite material. Specific examples of piezoelectric ceramics include lead zirconate titanate ceramics. Specific examples of the piezoelectric resin include polyvinylidene fluoride (PVDF). The piezoelectric composite material is a material including at least one of piezoelectric ceramics and piezoelectric resin and a resin not having piezoelectricity. Examples of the non-piezoelectric resin used for the composite material include silicone resin, PPS (polyphenylene sulfide) resin, PBT (polybutylene terephthalate) resin, PTFE (polytetrafluoroethylene) resin, PET (polyethylene terephthalate) resin, and PE ( Polyethylene) resin and the like.

When the piezoelectric resin and the composite material are used as the material for forming the helical piezoelectric body 20, the helical piezoelectric body 20 can be relatively easily formed for any reason that the high-temperature firing step can be omitted as compared with the case of using only piezoelectric ceramics. Can be molded. Furthermore, when a composite material is used, the local piezoelectric amount of the piezoelectric power generation device and the piezoelectric body can be adjusted by controlling the ratio of the contained piezoelectric ceramics or piezoelectric resin.

On the other hand, when the helical piezoelectric body 20 is formed of piezoelectric ceramics, the rigidity of the helical piezoelectric body 20 can be increased.

As shown in FIGS. 1 to 3, the spiral piezoelectric body 20 is formed in a spiral shape centering on a central axis C extending along the first direction z. That is, the central axis C is located on the z axis of the cylindrical coordinate system (r, θ, z). In this embodiment. The spiral piezoelectric body 20 is formed so that the radius is constant in the first direction z. That is, r is constant in the cylindrical coordinate system (r, θ, z).

As shown in FIGS. 2 and 4, the spiral piezoelectric body 20 is formed in a shape having a surface in which the normal direction is directed outward. Specifically, the spiral piezoelectric body 20 is formed so that the cross-sectional shape of the spiral piezoelectric body 20 is a rectangular shape whose longitudinal direction is along the first direction z. Specifically, the spiral piezoelectric body 20 includes an inner peripheral surface 20a facing the center side, an outer peripheral surface 20b facing the outer side, and a first side surface 20c facing the first member 3 in the first direction z. And a second side face 20d facing the second member 4 side in the first direction z.

The polarization direction P (see FIG. 4) of the spiral piezoelectric body 20 is not particularly limited. The polarization direction P of the spiral piezoelectric body 20 may be parallel to the first direction z or may be a radial direction x parallel to the first direction z. In the present embodiment, as shown in FIG. 4, an example in which the spiral piezoelectric body 20 is polarized along the radial direction x will be described.

As shown in FIGS. 1 to 4, first and second electrodes 21 and 22 are formed on the surface of the spiral piezoelectric body 20. In the present embodiment, no electrode is formed inside the spiral piezoelectric body 20.

The first and second electrodes 21 and 22 can be formed of an appropriate conductive material. Specifically, the first and second electrodes 21 and 22 are made of, for example, a metal such as Al, Ag, Cu, Pt, Au, Cr, or Ni, or an alloy containing one or more of these metals. Can do.

The first and second electrodes 21 and 22 have at least one of the direction and the magnitude of the stress applied when the second member 4 vibrates with respect to the first member 3 of the helical piezoelectric body 20. It is formed on different parts. For this reason, when the second member 4 vibrates with respect to the first member 3, a voltage is generated between the first and second electrodes 21 and 22 due to the piezoelectric effect.

Specifically, as shown in FIGS. 2 and 4, each of the first and second electrodes 21 and 22 extends in the direction in which the spiral piezoelectric body 20 extends (that is, the spiral direction) on the outer peripheral surface 20 b. It is spirally formed along. For this reason, the vibration mode of the piezoelectric power generation element 2 is d31.

As described above, in the present embodiment, the spiral piezoelectric body 20 is formed in a spiral shape centering on the central axis C extending in the first direction z. For this reason, compared with the piezoelectric power generation device 100 shown in FIG. 17, for example, in the piezoelectric power generation device 1 of this embodiment, the resonance frequency can be lowered without increasing the size. That is, the piezoelectric power generation apparatus 1 is small in size, and can generate power with high power generation efficiency even by low-frequency vibration.

Further, for example, in the piezoelectric power generation device 100 shown in FIG. 17, when vibration is applied to the piezoelectric power generation device 100, stress is concentrated on the portion of the piezoelectric power generation element 102 on the fixed end side, and the piezoelectric power generation element 102 is free. There is not much stress on the end part. For this reason, the power generation efficiency is low, and the portion on the fixed end side of the piezoelectric power generation element 102 to which a large stress is applied is likely to be damaged.

On the other hand, in this embodiment, when vibration is applied to the piezoelectric power generation device 1, stress is uniformly applied to the entire piezoelectric power generation element 2. For this reason, since electric power generation is performed by the whole piezoelectric power generation element 2, the power generation efficiency is high. Furthermore, compared with the case where stress concentrates on a part of the piezoelectric power generation element, the piezoelectric power generation element is not easily damaged and has high durability.

Incidentally, for example, a so-called laminated piezoelectric power generation element in which an electrode is formed inside a piezoelectric body is difficult to manufacture. This is because the electrode provided inside diffuses or evaporates in the firing process of the piezoelectric body. On the other hand, in this embodiment, the piezoelectric power generating element 2 is not a laminated type, and the first and second electrodes 21 and 22 are formed on the surface of the spiral piezoelectric body 20. For this reason, an electrode can be formed after baking of a piezoelectric material. In addition, the first and second electrodes 21 and 22 can be easily formed. In particular, in this embodiment, since both the first and second electrodes 21 and 22 are formed on the outer peripheral surface 20b, the first and second electrodes 21 and 22 can be easily formed. . Therefore, the piezoelectric power generation element 2 of the present embodiment is easy to manufacture. Further, it is not necessary to use an Ag—Pd alloy or Pt having a high melting point for forming the electrode. Therefore, the manufacturing cost can be kept low.

In this embodiment, the spiral piezoelectric body 20 is polarized along the radial direction x. For this reason, the spiral piezoelectric body 20 can be easily polarized.

In this embodiment, the spiral piezoelectric body 20 is formed so that the radius is constant in the first direction z. That is, r = constant in the cylindrical coordinate system (r, θ, z). For this reason, the helical piezoelectric body 20 can be easily manufactured. Accordingly, the piezoelectric power generation element 2 can be easily manufactured.

In addition, the manufacturing method of the piezoelectric power generation element 2 is not particularly limited. Hereinafter, an example of a method for manufacturing the piezoelectric power generation element 2 will be described with reference to FIGS.

First, as shown in FIG. 5, a cylindrical piezoelectric body 30 is prepared. The cylindrical piezoelectric body 30 is obtained, for example, by forming a material containing piezoelectric ceramic powder into a cylindrical shape and then firing it. Next, as shown in FIG. 6, conductive films 31 and 32 are formed on the inner and outer peripheral surfaces of the cylindrical piezoelectric body 30. The formation method of the electrically conductive films 31 and 32 is not specifically limited. The conductive films 31 and 32 can be formed by a thin film forming method such as a sputtering method or a vapor deposition method, a metal foil laminate, or the like.

Next, the piezoelectric body 30 is polarized along the radial direction x by applying a voltage between the conductive films 31 and 32. After the polarization, the conductive film 31 is removed. Note that the conductive film 31 is not necessarily removed and may be left.

Thereafter, the piezoelectric body 30 and the conductive film 32 are cut along the spiral cutting line L1 shown in FIG. Finally, the piezoelectric power generating element 2 can be completed by forming the first and second electrodes 21 and 22 by dividing the conductive film 32 along the cutting line L2 shown in FIG. According to the manufacturing method, the spiral piezoelectric power generating element 2 can be easily manufactured.

The polarization of the piezoelectric body 30 may be performed before the piezoelectric body 30 is cut.

Hereinafter, modifications of the first embodiment and other embodiments will be described. In the following description, members having substantially the same functions as those of the first embodiment are referred to by the same reference numerals, and description thereof is omitted.

(First and second modifications)
FIG. 8 is a schematic cross-sectional view of the piezoelectric power generating element in the first modification. FIG. 9 is a schematic cross-sectional view of the piezoelectric power generating element in the second modification.

In the above embodiment, an example in which the pair of electrodes 21 and 22 are provided on the outer peripheral surface 20b of the spiral piezoelectric body 20 and the spiral piezoelectric body 20 is polarized along the radial direction x has been described. However, in the present invention, the configuration and position of the electrodes and the polarization direction P of the helical piezoelectric body are not particularly limited.

For example, as shown in FIG. 8, the spiral piezoelectric body 20 may be polarized along the first direction z. In this case, the vibration mode of the piezoelectric power generation element 2 is d33. Therefore, for example, compared with the case where the vibration mode of the piezoelectric power generation element 2 is d31, the conversion efficiency from kinetic energy to electrical energy can be increased. As a result, high power generation efficiency can be realized.

Alternatively, two second electrodes 22 may be provided, and these two second electrodes 22 may be provided on both sides of the first electrode 21 in the first direction z on the outer peripheral surface 20b. As described above, by providing a plurality of second electrodes 22, the potential difference between the first and second electrodes 21 and 22 is increased while maintaining a large capacitance between the first and second electrodes 21 and 22. Can do. Therefore, the obtained current value can be increased.

Further, as shown in FIG. 9, the spiral piezoelectric body 20 has the polarization directions P reversed in the z1 side portion and the z2 side portion in the first direction z of the spiral piezoelectric body 20. Also good. Specifically, in the example illustrated in FIG. 9, the portion on the z1 side in the first direction z of the spiral piezoelectric body 20 is polarized toward the z1 side in the first direction z. A portion on the z2 side in the first direction z of the spiral piezoelectric body 20 is polarized toward the z2 side in the first direction z.

(Third to fifth modifications)
FIG. 10 is a schematic cross-sectional view of a piezoelectric power generator according to a third modification. FIG. 11 is a schematic cross-sectional view of a piezoelectric power generator according to a fourth modification. FIG. 12 is a schematic cross-sectional view of a piezoelectric power generator according to a fifth modification.

In the first embodiment, the example in which the cross-sectional shape of the helical piezoelectric body 20 is a rectangular shape whose longitudinal direction is along the first direction z has been described. However, the present invention is not limited to this configuration.

For example, as shown in FIG. 10, the shape of the cross section of the spiral piezoelectric body 20 may be a rectangular shape whose longitudinal direction is along the radial direction x.

The shape of the cross section of the spiral piezoelectric body 20 may be a shape other than a rectangular shape. The shape of the cross section of the spiral piezoelectric body 20 may be, for example, a square.

Further, as shown in FIG. 11, the shape of the cross section of the spiral piezoelectric body 20 may be a polygon such as a regular polygon. Specifically, in the example shown in FIG. 11, the shape of the cross section of the spiral piezoelectric body 20 is a regular hexagon. The first and second electrodes 21 and 22 are formed on the surfaces 20 e to 20 g facing the outside of the spiral piezoelectric body 20. Specifically, the first electrode 21 is formed on the surface 20e, and the second electrode 22 is formed on the surface 20g.

Further, as shown in FIG. 12, the shape of the cross section of the spiral piezoelectric body 20 may be circular, elliptical or oval.

(Sixth Modification)
FIG. 13 is a schematic side view of a piezoelectric power generating device according to a sixth modification.

In the first embodiment, the example in which the spiral piezoelectric body 20 is formed so as to have a constant radius in the first direction z has been described. However, the present invention is not limited to this configuration. For example, as shown in FIG. 13, the spiral piezoelectric body 20 may be formed so that the radius decreases from the first member 3 side toward the second member 4 side in the first direction z. Good.

In the present modification example in which the first member 3 is a fixed end and the second member 4 is a movable end, the spiral piezoelectric body 20 is formed so as to become thinner toward the second member 4 side. ing. Specifically, in this modification, the spiral piezoelectric body 20 is formed so that the width W becomes narrower toward the second member 4 side. By doing in this way, stress can be uniformly given to the whole spiral piezoelectric body 20. Therefore, higher power generation efficiency can be obtained.

(Second Embodiment)
FIG. 14 is a schematic cross-sectional view of the piezoelectric power generation device according to the second embodiment. FIG. 15 is a schematic perspective view of the piezoelectric power generation element according to the second embodiment.

In the first embodiment, the piezoelectric power generation apparatus 1 having only one piezoelectric power generation element 2 has been described. However, the present invention is not limited to this configuration. For example, the piezoelectric power generation apparatus may have a plurality of piezoelectric power generation elements 2. The piezoelectric power generation apparatus 1a shown in FIG. 14 includes three piezoelectric power generation elements 2a to 2c. The piezoelectric power generation elements 2a to 2c have substantially the same configuration as that of the piezoelectric power generation element 2 of the first embodiment. However, the piezoelectric power generating elements 2a to 2c differ in the dimension (radius) in the radial direction x.

The piezoelectric power generation elements 2a to 2c may be provided so as to have different central axes, but in the present embodiment, they are provided so as to have the same central axis. That is, the piezoelectric power generation elements 2a to 2c are provided on the same axis. For this reason, the piezoelectric power generating element 2a having the largest radius is located on the outermost side, the piezoelectric power generating element 2b having the next largest radius is located inside the piezoelectric power generating element 2a, and the piezoelectric power generating element 2b is located most inside. The piezoelectric power generation element 2c having a small radius is located.

The resonance frequency of the piezoelectric power generation elements 2a to 2c, that is, the frequency of vibration when the power generation efficiency is highest, varies depending on the radius of the piezoelectric power generation elements 2a to 2c. Therefore, the piezoelectric power generation elements 2a to 2c having different radii have different resonance frequencies. Specifically, as shown in FIG. 16, the piezoelectric power generating element 2a having the largest radius has the lowest resonance frequency, and the piezoelectric power generating element 2c having the smallest radius has the highest resonance frequency.

For example, in the case where only the piezoelectric power generation element 2c is provided, when vibration in a frequency band near the resonance frequency of the piezoelectric power generation element 2c is applied, high power generation efficiency is obtained, but vibration in other frequency bands is obtained. When is added, high power generation efficiency cannot be obtained.

On the other hand, in the present embodiment, since a plurality of piezoelectric power generating elements 2a to 2c having different radii are provided, not only the case where vibration in a frequency band near the resonance frequency of the piezoelectric power generating element 2c is applied, but also the piezoelectric power generating element 2c. High power generation efficiency can be obtained even when vibrations in a frequency band near the resonance frequency of the power generation elements 2b and 2c are applied. Therefore, the frequency band with high power generation efficiency can be expanded. Therefore, the piezoelectric power generation device of this embodiment is particularly useful when it is attached to a device that can vibrate the frequency of applied vibration, such as a human body.

In this embodiment, as described above, the piezoelectric power generation elements 2a to 2c are arranged on the same axis. For this reason, since it becomes easy for the 1st and 2nd members 3 and 4 to vibrate along the 1st direction z, higher power generation efficiency is obtained.

Also, for example, when electrodes are formed on the inner peripheral surfaces of the piezoelectric power generation elements 2a to 2c, the electrodes may come into contact with each other and short-circuit between the piezoelectric power generation elements adjacent in the radial direction. On the other hand, in the present embodiment, the first and second electrodes 21 and 22 are formed on the surface where the normal direction of the spiral piezoelectric body 20 faces outward. For this reason, even if the piezoelectric power generating elements adjacent in the radial direction come into contact with each other, it is difficult to short-circuit.

In this embodiment, the example in which the separate second members 4a to 4c are connected to the piezoelectric power generation elements 2a to 2c has been described. However, a common second member is connected to the piezoelectric power generation elements 2a to 2c. May be.

L1, L2 ... Cutting line 1, 1a ... Piezoelectric generators 2, 2a-2c ... Piezoelectric generator 3 ... First member 4, 4a-4c ... Second member 20 ... Spiral piezoelectric bodies 20A, 20B ... Spiral End 20a of the piezoelectric body ... Inner peripheral surface 20b of the spiral piezoelectric body ... Outer peripheral surface 20c of the spiral piezoelectric body ... First side surface 20d of the spiral piezoelectric body ... Second side surfaces 20e-20g of the spiral piezoelectric body ... The surface 21 of the spiral piezoelectric body ... the first electrode 22 ... the second electrode 30 ... the piezoelectric bodies 31, 32 ... the conductive film

Claims (15)

It arrange | positions between the 1st and 2nd member provided relatively displaceably along the 1st direction, and the said 2nd member follows the said 1st direction with respect to the said 1st member. A piezoelectric power generation element that generates power by vibrating
A first end fixed to the first member and a second end fixed to the second member are formed in a spiral shape centering on a central axis extending in the first direction. A helical piezoelectric body having a portion;
A piezoelectric power generating element, comprising: first and second electrodes formed on the spiral piezoelectric body along a direction in which the spiral piezoelectric body extends. The spiral piezoelectric body has a surface in which a normal direction faces outward, and both the first and second electrodes are provided on the surface in which the normal direction faces outward. The piezoelectric power generating element according to claim 1. Two of the second electrodes are provided, and the two second electrodes are disposed on both sides of the first electrode on the surface in which the normal direction faces outward. Item 3. The piezoelectric power generation element according to Item 2. The piezoelectric power generating element according to any one of claims 1 to 3, wherein a shape of a cross section of the spiral piezoelectric body is a rectangular shape. The piezoelectric power generating element according to claim 4, wherein a shape of a cross section of the spiral piezoelectric body is a rectangular shape whose longitudinal direction is along the first direction. The piezoelectric power generating element according to any one of claims 1 to 5, wherein the spiral piezoelectric body is polarized along the first direction. 6. The piezoelectric power generating element according to claim 1, wherein the spiral piezoelectric body is polarized along a radial direction perpendicular to the first direction. The first electrode and the second electrode are at least one of a direction and a magnitude of stress applied to the helical piezoelectric body when the second member vibrates with respect to the first member. The piezoelectric power generating element according to any one of claims 1 to 7, wherein one is formed on different portions. The piezoelectric power generating element according to any one of claims 1 to 8, wherein the helical piezoelectric body is made of piezoelectric ceramics. The piezoelectric power generating element according to any one of claims 1 to 9, wherein the spiral piezoelectric body is formed to have a constant radius in the first direction. 10. The spiral piezoelectric body according to claim 1, wherein the spiral piezoelectric body has a radius that decreases from the first member side toward the second member side in the first direction. The piezoelectric power generation element according to item. First and second members that are relatively displaceable along the first direction;
A first end fixed to the first member and a second end fixed to the second member are formed in a spiral shape centering on a central axis extending in the first direction. And a piezoelectric power generation device having first and second electrodes each formed along a direction in which the spiral piezoelectric body extends. The piezoelectric power generation device according to claim 12, wherein a plurality of the piezoelectric power generation elements having different radial dimensions are provided. The piezoelectric power generation device according to claim 13, wherein the plurality of piezoelectric power generation elements are provided so as to have the same central axis. A method for manufacturing a piezoelectric power generating element according to any one of claims 1 to 11,
Preparing a cylindrical piezoelectric body made of piezoelectric ceramic;
Forming a conductive film on the outer peripheral surface of the cylindrical piezoelectric body;
Forming the spiral piezoelectric body by spirally cutting the cylindrical piezoelectric body on which the conductive film is formed;
Forming the first and second electrodes by dividing the conductive film along the first direction.

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