JP5532617B2 - Piezoelectric actuator - Google Patents

Description

  The present invention relates to a piezoelectric actuator using a piezoelectric element, and more particularly to a piezoelectric actuator in which a member that is displaced by deformation of a piezoelectric element is connected to the piezoelectric element.

  Conventionally, piezoelectric actuators have been widely used for driving printer heads and hard disk drive heads. Piezoelectric actuators utilize displacement due to the piezoelectric effect of piezoelectric elements.

  As the above-described piezoelectric element, those utilizing the piezoelectric longitudinal effect and the lateral effect are widely known. However, it has been difficult to obtain a large displacement at a relatively low voltage. Therefore, the following Patent Document 1 discloses a piezoelectric actuator that uses a piezoelectric sliding strain effect instead of a piezoelectric longitudinal effect and a lateral effect.

  9A and 9B are a schematic plan view and a schematic front sectional view for explaining the piezoelectric actuator described in Patent Document 1. FIG.

  The piezoelectric actuator 101 has a piezoelectric plate 102. The piezoelectric plate 102 has a through hole 102a in the center. A plurality of annular piezoelectric bodies 103 to 108 are arranged concentrically with the through hole 102a and integrated.

  Each of the piezoelectric bodies 103 to 108 is polarized in the radial direction of the piezoelectric plate 102 as indicated by the arrows in the drawing. In the adjacent annular piezoelectric bodies, the polarization direction is opposite to the radial direction. For example, the polarization direction of the piezoelectric body 103 and the polarization direction of the piezoelectric body 104 positioned just outside the piezoelectric body 103 are opposite to each other.

  In the piezoelectric actuator 101, the first excitation electrode 109 is formed on the upper surface of the piezoelectric plate 102, and the second excitation electrode 110 is formed on the lower surface. A metal plate 111 is bonded to the lower surface of the piezoelectric plate 102. By applying a DC voltage between the first and second excitation electrodes 109 and 110, the piezoelectric plate 102 is displaced. For example, as shown in FIG. 9B, when a positive potential is applied to the first excitation electrode 109 and a negative potential is applied to the second excitation electrode 110, the piezoelectric plate 102 protrudes upward at the center portion. Displace to

  In Patent Document 1, it is said that a large displacement can be obtained by driving at a lower voltage by utilizing the piezoelectric slip strain effect in which the polarization direction and the voltage application direction are orthogonal to each other.

Japanese Patent Publication No. 2-57354

  Since the piezoelectric actuator 101 described in Patent Document 1 uses the piezoelectric slip strain effect, a large displacement can be obtained with a relatively low voltage. However, as indicated by an arrow A in FIG. 9, in the laminated body in which the piezoelectric plate 102 and the metal plate 111 are laminated, the central portion is displaced so as to protrude upward. There was a great stress applied. On the other hand, since the piezoelectric plate 102 is made of ceramics, it is weak against tensile stress. Therefore, when a large tensile stress is applied, a crack is generated on the upper surface of the piezoelectric plate 102 in FIG.

  Further, when the crack is generated, the first and second excitation electrodes 109 and 110 may eventually be short-circuited.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable piezoelectric actuator that utilizes the piezoelectric slip strain effect and can not only obtain a large amount of displacement but also hardly cause cracks or breakage in the piezoelectric element. .

  According to the present invention, the piezoelectric body polarized in the first direction and the first body formed on the outer surface of the piezoelectric body to apply an electric field in a direction orthogonal to the first direction of the piezoelectric body. There is provided a piezoelectric actuator comprising: a piezoelectric element having first and second excitation electrodes; and a driven member that is fixed to the piezoelectric element and is displaced by deformation of the piezoelectric element.

  In a specific aspect of the piezoelectric actuator according to the present invention, a portion of the driven member that has the largest displacement is made of a material that is less susceptible to brittle fracture than the piezoelectric body. A general piezoelectric element is ceramics, and is easily brittle fractured. When the strain increases, cracks occur and breakage occurs. For example, in the case of metal, since the strain that becomes the elastic limit is larger than that of ceramics, it is not easily broken mechanically, and the reliability is improved. Since the driven member is displaced in response to the sliding distortion deformation of the piezoelectric element, the displacement can be enlarged similarly to the lever principle. In this case, the entire driven member may be formed of the material that is easily elastically deformed. In that case, the structure of the driven member can be simplified.

  According to another specific aspect of the piezoelectric actuator according to the present invention, the piezoelectric body has a donut shape having an upper surface and a lower surface, an inner peripheral side surface formed of a cylindrical curved surface, and an outer peripheral side surface formed of a cylindrical curved surface. Have In this case, since the piezoelectric body is deformed so as to protrude from the upper surface or the lower surface of the piezoelectric body, a large amount of displacement can be obtained.

  When a donut-shaped piezoelectric body is used, in another specific aspect of the present invention, the polarization direction is a radial direction of the cylindrical curved surface, and the first and second excitation electrodes are the upper and lower surfaces of the piezoelectric body. Are formed respectively. In this case, after obtaining the piezoelectric body, the first and second excitation electrodes can be easily formed on the upper and lower surfaces of the piezoelectric body.

  In still another specific aspect of the piezoelectric actuator according to the present invention, the polarization direction is a direction connecting an upper surface and a lower surface of the doughnut-shaped piezoelectric body, and the first and second excitation electrodes are the piezoelectric body. Are respectively formed on the inner peripheral side surface and the outer peripheral side surface. Thus, the polarization direction may be a direction connecting the upper surface and the lower surface of the piezoelectric body. In that case, polarization becomes easy.

  According to still another specific aspect of the piezoelectric actuator according to the present invention, the driven member is made of a plate-like member that can be elastically deformed, and is fixed so as to cover the entire area of the upper surface or the lower surface of the doughnut-shaped piezoelectric body. Has been. Since the driven member is made of a plate-like member, the driven member can be easily fixed to the upper surface or the lower surface of the donut-shaped piezoelectric body, and the driven member made of the plate-like member is easily deformed by the deformation of the donut-shaped piezoelectric body. Due to the displacement, a large amount of displacement can be obtained.

  In still another specific aspect of the piezoelectric actuator according to the present invention, the driven member is supported by the piezoelectric element in a cantilever manner. Since it is supported in a cantilever manner, a larger amount of displacement can be extracted from the driven member.

  In still another specific aspect of the piezoelectric actuator according to the present invention, the driven member is supported by the piezoelectric body in both ends. In this case, the driven member can be stably supported by the piezoelectric body.

  In the piezoelectric actuator according to the present invention, the driven member is made of various materials, but preferably made of a metal plate. In the case of a metal plate, since it is easily elastically deformed, a large amount of displacement can be taken out.

  According to the piezoelectric actuator according to the present invention, the direction of the electric field applied from the first and second excitation electrodes is a direction orthogonal to the polarization direction, so that the piezoelectric element is deformed using the piezoelectric slip strain effect. Can do. The driven member is displaced using the deformation of the piezoelectric element. Since the deformation of the piezoelectric element may be relatively small, the piezoelectric element is unlikely to be cracked or broken. In particular, the conventional bimorph deforms more than the deformation of the piezoelectric body itself, so that a large stress is applied to the piezoelectric element and it is easy to break. On the other hand, in the present invention, since there is almost no deformation beyond the deformation of the piezoelectric element due to voltage application, no stress is applied to the piezoelectric element. Therefore, the reliability of strength is high. Therefore, the reliability of the piezoelectric actuator can be improved.

(A) is a disassembled perspective view of the piezoelectric actuator which concerns on the 1st Embodiment of this invention, (b) is front sectional drawing of this piezoelectric actuator. (A) is sectional drawing which shows typically the simultaneous displacement distribution of the piezoelectric actuator of 1st Embodiment, (b) is an enlarged view of the part shown by the line X in (a), (c) is a schematic diagram showing a scale appearing in the hatching shown in (a) and (b). (A) is typical sectional drawing which shows the displacement state and stress distribution of the piezoelectric actuator prepared for the comparison, (b) expands and shows the part shown by the line Y in (a). It is a schematic diagram. (A) is a typical front view for demonstrating the vertical effect and lateral effect of a piezoelectric material, (b) is a typical front view for demonstrating a piezoelectric slip distortion effect. (A) And (b) is each typical perspective view which shows the relationship between the polarization direction of a piezoelectric element using the piezoelectric slip distortion effect, and an electric field application direction. (A) is a typical perspective view of the piezoelectric actuator which concerns on the 2nd Embodiment of this invention, (b) is front sectional drawing of this piezoelectric actuator, (c) is the displacement state of this piezoelectric actuator. It is a typical perspective view for explaining. It is a perspective view which shows the piezoelectric actuator which concerns on the 3rd Embodiment of this invention. It is a perspective view which shows the piezoelectric actuator which concerns on the 4th Embodiment of this invention. (A) And (b) is a typical top view and a typical front sectional view for explaining the conventional piezoelectric actuator, respectively.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  FIGS. 1A and 1B are an exploded perspective view and a front sectional view of a piezoelectric actuator according to a first embodiment of the present invention.

  The piezoelectric actuator 1 includes a piezoelectric element 2 having a donut shape and a disk-like driven member 4 joined to the piezoelectric element 2 via an adhesive layer 3.

  The piezoelectric element 2 has a piezoelectric body 5. The piezoelectric body 5 has a donut shape. The piezoelectric body 5 has an inner peripheral side surface 5a made of a cylindrical curved surface, an outer peripheral side surface 5b made of a cylindrical curved surface, a planar upper surface 5c, and a planar lower surface 5d.

  The piezoelectric body 5 can be formed of an appropriate perovskite piezoelectric ceramic. Examples of such materials include PbNiNb-PbZrTi ceramics, PbZrNb-PbZrTi ceramics, or solid solution ceramics thereof.

  The piezoelectric body 5 is polarized in the direction indicated by the arrow P in the drawing. That is, the piezoelectric body 5 is polarized in the radial direction in the donut shape as the first direction. Such a polarization treatment can be easily performed by forming electrodes for polarization on the inner peripheral side surface 5a and the outer peripheral side surface 5b of the piezoelectric body 5 and applying a DC voltage therebetween. What is necessary is just to delete the electrode for polarization after polarization.

  On the other hand, a first excitation electrode 6 is formed on the upper surface 5c of the piezoelectric body 5, and a second excitation electrode 7 is formed on the lower surface 5d. The first and second excitation electrodes 6 and 7 have the same planar shape as the piezoelectric body 5. That is, the excitation electrodes 6 and 7 also have an annular shape. In driving, an excitation voltage is applied between the first and second excitation electrodes 6 and 7. Therefore, the excitation voltage application direction is a direction orthogonal to the polarization direction P.

  The excitation electrodes 6 and 7 are made of an appropriate metal or alloy such as Ag, Al, Cu, or Ag—Pd alloy.

  The adhesive layer 3 can be formed of an appropriate adhesive as long as the driven member 4 can be bonded to the upper surface of the piezoelectric body 5. In this embodiment, an epoxy adhesive is used as such an adhesive, but it is not particularly limited. For example, an adhesive mainly composed of another thermosetting resin such as a phenol resin adhesive may be used.

  The adhesive layer 3 is formed by applying an epoxy resin adhesive on the entire surface of the first excitation electrode 6, bonding the driven member 4, and then heating. Therefore, the adhesive layer 3 has the same planar shape as that of the first excitation electrode 6.

  In this embodiment, the driven member 4 is made of a disk-shaped metal plate. The metal which comprises a metal plate is not specifically limited, Phosphor bronze, stainless steel, etc. can be mentioned. The driven member 4 made of a metal plate is easily elastically deformed when an external force is applied. The driven member 4 made of a metal plate is a material that is less susceptible to brittle fracture than the piezoelectric body 5 made of piezoelectric ceramics and has a strain that becomes an elastic limit larger than that of the piezoelectric ceramics.

  Next, it will be described that when the piezoelectric actuator 1 is driven, a large displacement can be obtained, and cracks and breakage in the piezoelectric body 5 are difficult to occur.

  When the piezoelectric actuator 1 is driven, a DC voltage is applied between the first and second excitation electrodes 6 and 7. As a result, the piezoelectric body 5 is deformed so as to be inclined due to the piezoelectric slip strain effect. In response to the deformation of the piezoelectric body, the displacement of the driven member 4 bonded to the piezoelectric body 5 is enlarged.

  That is, since the piezoelectric body 5 has an annular shape, the driven member 4 made of a metal plate is not restrained in the space surrounded by the inner peripheral side surface 5a. Therefore, as shown in FIG. 2A, when the piezoelectric body 5 is deformed, the driven member 4 made of a metal plate bonded to the piezoelectric body 5 is greatly displaced so as to protrude downward. In particular, in the space surrounded by the inner peripheral side surface 5a of the piezoelectric body 5, since the driven member 4 is not restrained by the piezoelectric body 5, the central portion of the driven member 4 is displaced the most and protrudes downward. Become.

  The displacement and stress distribution in FIG. 2 (b), which is an enlarged view of the portion indicated by the line X in FIGS. 2 (a) and 2 (a), is analyzed by the finite element method using the piezoelectric actuator 1 as a model as follows. It is the result of having performed.

Piezoelectric body 5: inner diameter 20 mm, outer diameter 30 mm, dimension between inner peripheral side surface 5a and outer peripheral side surface 5b = 5 mm, thickness 1 mm. The material is lead zirconate titanate piezoelectric ceramics. Driven member 4: phosphor bronze plate, diameter 30 mm, thickness 0.5 mm

  Such a piezoelectric actuator can be manufactured by the following method. A conductive paste is applied to the upper and lower surfaces of the piezoelectric body 5 to form polarization electrodes. Next, after the polarization treatment, the polarization electrode was removed, and the first and second excitation electrodes were formed on the upper and lower surfaces of the piezoelectric body 5 by sputtering. The driven member 4 can be bonded to the piezoelectric body 5 using an epoxy adhesive to obtain the piezoelectric actuator 1.

An electric field is applied to the piezoelectric actuator 1 of the above embodiment in the thickness direction so that the voltage of the first excitation electrode is +20 V and the voltage of the second excitation electrode is −20 V as boundary conditions, and the stress distribution is obtained. It was. Each area | region which shows hatching in Fig.2 (a) and (b) shows that it is the stress amount of the scale shown in FIG.2 (c). Incidentally, 4.000000e + 004 in FIG. 2 (c) shows that the stress is + 4.0 × 10 ^4. Accordingly, among the four types of hatched areas on the scale in FIG. 2C, the cross hatched area 12a has the largest tensile stress, the hatched area 12b indicated by diagonal lines, and a large number of small dots. The hatched area 12c has a low stress. And it shows that compressive stress is large as it goes to the hatching area 12d indicated by a large number of large dots.

  As is clear from FIGS. 2A and 2B, the driven member 4 made of a metal plate is farthest from the piezoelectric body 5 in the central portion. Displaced and protrudes downward. On the other hand, since the piezoelectric body 5 is only deformed due to the original piezoelectric strain, no great stress is generated. That is, it can be seen that the displacement caused by the piezoelectric sliding strain effect in the piezoelectric body 5 is transmitted to the driven member 4, and the center of the driven member 4 is displaced the most and the displacement amount is increased.

  Therefore, according to the present embodiment, a large displacement can be obtained using the piezoelectric slip strain effect. Moreover, since the piezoelectric body 5 is not displaced so much, it is difficult for the piezoelectric body 5 to be subjected to a tensile stress that causes the piezoelectric body 5 to break. Therefore, cracks in the piezoelectric body 5 are unlikely to occur. Therefore, since short circuit or the like hardly occurs, the reliability can be effectively improved.

  3A and 3B are schematic front sectional views showing displacement and stress distribution of a piezoelectric actuator prepared for comparison, and the displacement and stress distribution in a portion surrounded by a line Y at the center. It is a schematic diagram.

  This comparative example is an analysis result of a finite element method using a bimorph structure piezoelectric actuator in which two layers of a piezoelectric body having a diameter of 30 mm and a thickness of 0.5 mm are bonded. The piezoelectric material used is the same as the piezoelectric material of the above embodiment. As boundary conditions, a voltage of +1.3 V was applied to the center electrode where the two piezoelectric elements were bonded together, and a voltage of -1.3 V was applied to the excitation electrodes on both sides. The boundary condition voltage was set so that the displacement amount of the comparative example was the same as the displacement amount of FIG. The polarization direction was the thickness direction, and the two-layer piezoelectric bodies were polarized in directions opposite to each other in the thickness direction.

  In the comparative example, a voltage is applied in the same direction as the polarization direction, and a bimorph piezoelectric actuator utilizing the piezoelectric lateral effect is formed. In addition, the meaning of the area | region which showed the hatching in FIG. 3 is the same as FIG.2 (c). As is clear from FIGS. 3A and 3B, in the piezoelectric actuator 111 of the comparative example, the central portion is displaced the most, but the piezoelectric body itself is greatly deformed in the portion where the displacement is the largest. That is, it can be seen that the lower surface side of the piezoelectric body on the lower surface side is greatly deformed in a state of being displaced so as to protrude downward. Therefore, in the piezoelectric actuator 111, it can be seen that a large tensile stress is applied to the piezoelectric body itself, and cracks are likely to occur.

  FIG. 4A is a diagram schematically showing the piezoelectric lateral effect in the piezoelectric actuator prepared as the comparative example. In the piezoelectric lateral effect, the piezoelectric body 121 is deformed between a state indicated by a solid line and a state indicated by a broken line. Will be.

  On the other hand, FIG. 4B is a schematic diagram showing the piezoelectric slip strain effect used in the above embodiment. In the piezoelectric slip strain effect, the piezoelectric element 31 in FIG. 4B is deformed from a state indicated by a solid line to a parallelogram shape indicated by a broken line. That is, it is deformed in an oblique direction. Therefore, when the one end 31a side of the piezoelectric element 31 is constrained, the piezoelectric deformation can be enlarged and displaced at a point on the extension line on the other end 31b side.

  FIGS. 5A to 5B are schematic perspective views for explaining the deformation amount of the piezoelectric element using such a piezoelectric sliding strain effect.

  In the piezoelectric element 32 shown in FIG. 5A, as in the case of the piezoelectric body 5, the polarization direction P is the horizontal direction, and the electric field application direction E is the direction E perpendicular to the horizontal direction.

  On the other hand, in the piezoelectric element 33 shown in FIG. 5B, the polarization direction P is a direction connecting the upper surface and the lower surface of the piezoelectric element 33, and the electric field application direction E is the horizontal direction. As described above, when the piezoelectric slip strain effect is used, as long as the polarization direction and the electric field application direction are orthogonal to each other, the polarization direction is not limited to the horizontal direction but can be various directions.

  Note that the thick lines Z1 and Z2 in FIGS. 5 (a) and 5 (b) are diagrams schematically showing the deformation state when deformed by the piezoelectric sliding strain effect, respectively, and are shown by the broken lines shown in FIG. 4 (b). It is an equivalent figure.

  When an electric field is applied as indicated by the dotted arrow in FIG. 5B, the piezoelectric element 33 is deformed as indicated by the dotted line. When the piezoelectric slip strain effect is utilized as described above, a relatively large deformation can be obtained in the piezoelectric element, and in the present invention, the deformation of the piezoelectric element due to the piezoelectric slip strain effect is driven in the present invention. Since the displacement is increased in the driven member by being transmitted to the member, a larger displacement amount can be obtained.

  6A to 6C are a perspective view, a front sectional view, and a schematic perspective view showing a displacement state of a piezoelectric actuator according to a second embodiment of the present invention.

  The piezoelectric actuator 41 includes a donut-shaped, ie, an annular piezoelectric element 42 as in the first embodiment. A disk-shaped driven member 44 made of a metal plate is bonded to the piezoelectric element 42 via an adhesive layer 43.

  The piezoelectric actuator 41 of this embodiment is different from the piezoelectric actuator 1 of the first embodiment in the polarization direction of the piezoelectric element 42 and the excitation electrode formation position. That is, as shown in FIG. 6 (b), the piezoelectric body 45 has an annular shape, like the piezoelectric body 5, and has an inner peripheral side surface 45a and an outer peripheral side surface 45b, an upper surface 45c, and a lower surface 45d made of a cylindrical curved surface. And have. Here, the direction connecting the upper surface 45c and the lower surface 45d, that is, the thickness direction is the polarization direction P. That is, the first direction of the present invention is the thickness direction of the piezoelectric body 45. The first and second excitation electrodes 46 and 47 are formed on the inner peripheral side surface 45a and the outer peripheral side surface 45b, respectively. Therefore, the electric field application direction E is the horizontal direction and the radial direction of the annular piezoelectric body 45. Therefore, the electric field application direction E is a direction orthogonal to the polarization direction P.

  Also in the present embodiment, when an excitation voltage is applied between the first and second excitation electrodes 46 and 47, as shown in FIG. 6C, the piezoelectric element 42 is deformed by the piezoelectric slip strain effect, and the alternate long and short dash line As shown in FIG. 2, the center of the driven member 44 is greatly displaced so as to protrude downward.

  Also in this embodiment, the piezoelectric slip strain effect is used, and the displacement amount is enlarged in the driven member 44, so that a large displacement amount can be taken out. Furthermore, since the piezoelectric body 45 is deformed similarly to the piezoelectric body 5 of the first embodiment, it is difficult to apply a large tensile stress to the piezoelectric body 45. Accordingly, also in the present embodiment, cracks are unlikely to occur in the piezoelectric body 45 and short-circuits in the piezoelectric element 42 are unlikely to occur.

  FIG. 7 is a schematic perspective view showing a piezoelectric actuator according to a third embodiment of the present invention. The piezoelectric actuator 51 of this embodiment has an elongated strip-shaped piezoelectric element 52. A driven member 54 is bonded to the piezoelectric element 52 via an adhesive layer 53.

  The piezoelectric element 52 has an elongated strip-shaped piezoelectric body 55 and first and second excitation electrodes 56 and 57. The piezoelectric body 55 has a pair of side surfaces 55a and 55b having an elongated rectangular shape, and an upper surface 55c and a lower surface 55d having an elongated rectangular shape. The piezoelectric body 55 is made of a piezoelectric ceramic such as a lead zirconate titanate-based ceramic and is polarized in the direction of arrow P. That is, the polarization direction P is a direction connecting the upper surface 55c and the lower surface 55d. In order to apply a voltage to the piezoelectric body 55, first and second excitation electrodes 56 and 57 are formed on the first and second side surfaces 55a and 55b, respectively. Therefore, the electric field application direction E is a direction orthogonal to the polarization direction P. Therefore, when an excitation voltage is applied between the first and second excitation electrodes 56 and 57, the piezoelectric element 52 is deformed by the piezoelectric slip strain effect as indicated by a thick line Z3 in FIG.

  On the other hand, the adhesive layer 53 is made of the same material as that of the adhesive layer 3 of the first embodiment.

  In this embodiment, the driven member 54 is made of a metal plate, and is made of a rectangular metal plate that is considerably larger than the planar shape of the piezoelectric element 52. In the lower surface 54 a of the driven member 54 made of this relatively large rectangular metal plate, the piezoelectric element 52 is joined to the lower surface of the driven member 54 by being brought closer to the one end 54 b side. Therefore, the other end 54c side of the lower surface of the driven member 54 is a free end. In other words, the driven member 54 is supported by the piezoelectric element 52 in a cantilever manner. Therefore, when the piezoelectric element 52 is driven, the driven member 54 is greatly displaced as indicated by the alternate long and short dash line due to the deformation of the piezoelectric element 52. In particular, the end 54 c opposite to the side supported by the piezoelectric element 52 is greatly displaced, and the displacement can be increased by the driven member 54.

  In the piezoelectric actuator 51 of the third embodiment, the portion where the driven member 54 is displaced most is the end 54c side.

  Also in the present embodiment, since the piezoelectric body 55 itself does not deform so much, a large tensile stress is not easily applied to the piezoelectric body 55. Accordingly, cracks in the piezoelectric body 55 hardly occur, and short-circuiting of the piezoelectric element 52 hardly occurs.

  FIG. 8 is a schematic perspective view showing a piezoelectric actuator according to the fourth embodiment of the present invention. The piezoelectric actuator 61 of the present embodiment corresponds to a modification of the piezoelectric actuator 51 shown in FIG. Here, the driven member 54 is made of a rectangular metal plate, but the driven member 54 is supported by a pair of piezoelectric elements 52 and 52 in both ends. In other respects, the piezoelectric actuator 61 is the same as the piezoelectric actuator 51. Since the driven member 54 is supported at both ends by the piezoelectric elements 52, 52, when the piezoelectric elements 52, 52 are driven, the side surfaces of the piezoelectric body 52 are fixed. The center part of 54 will be displaced so that it may protrude below.

  Also in the present embodiment, since the piezoelectric body 55 itself is not greatly deformed, cracks in the piezoelectric body 55 hardly occur, and short circuit of the piezoelectric element 52 hardly occurs.

  The portion of the driven member 54 that is displaced the most is the central portion of the driven member 54. The central portion is elastically deformed and protrudes downward. The amount of displacement is larger than the amount of deformation of the piezoelectric body 55 in the piezoelectric element 52. Therefore, also in the present embodiment, the displacement amount of the driven member 54 can be increased. However, in the structure in which the driven member 54 is supported by the cantilever shown in FIG. 7, the end portion 54c can obtain a larger amount of displacement, so the piezoelectric actuator 51 of the third embodiment is the fourth. It is more preferable than the piezoelectric actuator 61 of the embodiment. However, in the fourth embodiment, since the driven member 54 is supported by the piezoelectric elements 52 and 52 at both ends, the driven member 54 can be stably supported.

  In the first to fourth embodiments described above, a circular plate or a rectangular metal plate is used as the driven member, but other planar driven members may be used. Further, a driven member having various shapes such as a rod shape or an amorphous shape may be used instead of the plate shape. In addition, the driven member can be formed of an appropriate material that is less susceptible to brittle fracture than piezoelectric ceramics, not limited to metal materials. Examples of such a material include a hard synthetic resin such as an acrylic resin which is not easily brittlely broken.

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric actuator 2 ... Piezoelectric element 3 ... Adhesive layer 4 ... Driven member 5 ... Piezoelectric body 5a ... Inner peripheral side surface 5b ... Outer peripheral side surface 5c ... Upper surface 5d ... Lower surface 6,7 ... 1st, 2nd excitation electrode 31 ... Piezoelectric element 32, 33 ... Piezoelectric element 41 ... Piezoelectric actuator 42 ... Piezoelectric element 43 ... Adhesive layer 44 ... Driven member 45 ... Piezoelectric body 45a ... Inner peripheral side surface 45b ... Outer peripheral side surface 45c ... Upper surface 45d ... Lower surface 46, 47 ... Second Excitation electrode 51 ... Piezoelectric actuator 52 ... Piezoelectric element 52a, 52b ... Side surface 52c ... Upper surface 52d ... Lower surface 53 ... Adhesive layer 54 ... Driven member 55 ... Piezoelectric material 55a, 55b ... Side surface 55c ... Upper surface 55d ... Lower surface 56, 57 ... Second excitation electrode 61 ... piezoelectric actuator

Claims (7)

It has a donut shape having an upper surface and a lower surface, an inner peripheral side surface made of a cylindrical curved surface, and an outer peripheral side surface made of a cylindrical curved surface, and only in a first direction that does not include a reverse direction in the radial direction or the thickness direction Piezoelectric element having a polarized piezoelectric body and first and second excitation electrodes formed on the outer surface of the piezoelectric body to apply an electric field in a direction orthogonal to the first direction of the piezoelectric body Elements,
A piezoelectric actuator comprising: a driven member that is fixed to the piezoelectric element so as to have an unconstrained portion, and is displaced by deformation of the piezoelectric element.   2. The piezoelectric actuator according to claim 1, wherein a polarization direction is a radial direction of the cylindrical curved surface, and the first and second excitation electrodes are respectively formed on an upper surface and a lower surface of the piezoelectric body.   The polarization direction is a direction connecting an upper surface and a lower surface of the doughnut-shaped piezoelectric body, and the first and second excitation electrodes are respectively formed on an inner peripheral side surface and an outer peripheral side surface of the piezoelectric body. The piezoelectric actuator according to 1.   The said driven member consists of a plate-shaped member which can be elastically deformed, and is fixed so that the whole area | region of the upper surface or lower surface of the said donut-shaped piezoelectric material may be covered. Piezoelectric actuator. Wherein among the driven member, the displacement is made of a brittle fracture hardly material than most larger portion on the piezoelectric, the piezoelectric actuator according to any one of claims 1-4. The piezoelectric actuator according to claim 5 , wherein the entire driven member is made of a material that is not easily brittlely broken. The driven member is made of a metal plate, a piezoelectric actuator according to any one of claims 1-6.

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