Vibration actuator, optical device and electronic device

Abstract

To provide a vibration type actuator having excellent vibration characteristics, which suppresses deterioration of the vibration characteristics due to a penetrating portion.SOLUTION: A vibration type actuator that solves the above problems is characterized in that a rectangular piezoelectric material, an oscillator having a piezoelectric element having a penetrating portion penetrating the piezoelectric material, and a contact body in contact with the oscillator are included, and the penetrating portion is formed outside a region surrounded by connecting an intersection between a node of a primary out-of-plane bending vibration and a node of a secondary out-of-plane bending vibration mode.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a vibration type actuator including an ultrasonic motor. [Background technology]

[0002] Vibration type actuators are widely used, which are driven by two vibration modes excited by a vibrator consisting of an elastic diaphragm (elastic body) and a piezoelectric element bonded together. One example is a vibration type actuator that applies voltage to the piezoelectric element that makes up the vibrator to generate two vibrations, Mode A and Mode B, and cause elliptical vibration in the vibrator. In this type of vibration type actuator, the vibrator and the contact body move relative to each other due to the elliptical vibration generated in the vibrator by applying voltage and the friction force generated on the contact surface between the vibrator and the contact body.

[0003] Patent Document 1 discloses a vibration actuator that is driven by two vibration modes. It discloses that the piezoelectric element used in the vibration actuator is provided with through holes at the intersections of the nodal lines of vibration modes A and B so as not to impede the generated vibrations.

[0004] However, the piezoelectric material that makes up the piezoelectric element is partially damaged at the through-hole that penetrates the piezoelectric element, which causes a problem of degraded vibration characteristics of the vibration type actuator. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2017-158429 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides a vibration type actuator in which deterioration of vibration characteristics due to a through-hole is suppressed. [Means for solving the problem]

[0007] The vibration actuator that solves the above problems is: a rectangular piezoelectric material; and a pair of electrodes provided on the piezoelectric material; a piezoelectric element including a through hole that is electrically connected to one of the electrodes, penetrates the piezoelectric material, and has an inner wall made of a conductive material; and a vibrator including an elastic body; a contact body that comes into contact with the vibrator and moves relative to the vibrator; The through-hole is located outside a region surrounded by connecting the intersections of a nodal line of a primary out-of-plane bending vibration mode, in which two nodes of vibration occur along the long sides of the piezoelectric material, and a nodal line of a secondary out-of-plane bending vibration mode, in which three nodes of vibration occur along the short sides of the piezoelectric material. only It is formed in The piezoelectric material is characterized in that the amount of lead contained therein is less than 1000 ppm. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a vibration actuator having excellent vibration characteristics in which the deterioration of vibration characteristics due to the through-hole is suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] 1A and 1B are diagrams illustrating a schematic structure of a vibration type actuator according to the present invention. [Figure 2] 1A and 1B are diagrams illustrating the structure of a piezoelectric element that constitutes a vibration type actuator of the present invention. [Figure 3] 1A and 1B are diagrams illustrating two vibration modes generated by the vibrator of the present invention. [Figure 4] 1A and 1B are diagrams illustrating node and antinode positions of two vibration modes generated in a vibrator of the present invention. [Figure 5] 1A and 1B are diagrams illustrating the positions of nodes and antinodes of distortion in two vibration modes generated in a vibrator of the present invention. [Figure 6] 10A and 10B are diagrams illustrating the structure of a penetration portion according to an embodiment of the present invention. [Figure 7]10A and 10B are diagrams illustrating the arrangement of through-holes in a vibration actuator according to the present invention. [Figure 8] 10 is a diagram showing a piezoelectric ceramic 114P and a through portion 114E according to the present invention. FIG. [Figure 9] 1A and 1B are diagrams illustrating vibration-type actuators according to examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the vibration type actuator of the present invention will now be described with reference to the accompanying drawings.

[0011] That is, it consists of a rectangular piezoelectric material, a pair of electrodes provided on the piezoelectric material, a piezoelectric element that is electrically connected to one of the electrodes and has a through-hole that penetrates the piezoelectric material, a vibrator having an elastic body, and a contact body that is in contact with the vibrator and moves relative to the vibrator.

[0012] We focus on the nodal line of the primary out-of-plane bending vibration mode, where two vibration nodes occur along the long sides of the rectangular piezoelectric material, and the nodal line of the secondary out-of-plane bending vibration mode, where three vibration nodes occur along the short sides of the piezoelectric material. A through-hole is formed outside the area surrounded by the intersections of these nodal lines.

[0013] FIG. 1 is a perspective view illustrating the general structure of a vibration actuator 100. As shown in FIG.

[0014] The vibration actuator 100 includes a vibrator 115 and a contact body 111 that is in contact with the vibrator and is arranged so as to be movable relative to the vibrator. The vibrator 115 is composed of a plate-shaped elastic vibration plate 113 (elastic body), a substantially rectangular plate-shaped piezoelectric element 114 bonded to one surface of the vibration plate 113, and two protrusions 112 provided on the other surface of the vibration plate 113.

[0015] The contact body 111 and the vibrator 115 are configured to be in pressure contact with each other by a pressure section (not shown) that is configured by a spring member or a magnet or the like.

[0016] The term "contact body" refers to a member that comes into contact with the vibrator and moves relative to the vibrator due to vibrations generated in the vibrator. The contact between the contact body and the vibrator is not limited to direct contact where no other member is interposed between the contact body and the vibrator. The contact between the contact body and the vibrator may also be indirect contact where another member is interposed between the contact body and the vibrator, as long as the contact body moves relative to the vibrator due to vibrations generated in the vibrator. The "other member" is not limited to a member independent of the contact body and the vibrator (for example, a high-friction material made of a sintered body). The "other member" may also be a surface-treated portion formed on the contact body or the vibrator by plating, nitriding, or the like.

[0017] Therefore, the contact body 111 may be any member that is pressurized by the vibrator 115 and can move relative to the vibrator 115, and is not limited to being in direct contact with the vibrator 115, but may be in indirect contact with the vibrator 115 via another member.

[0018] In the vibration actuator 100, a voltage of a specific frequency is applied to the piezoelectric element 114, which excites the vibrator 115 in a predetermined vibration mode. By using a plurality of these vibration modes, elliptical vibrations are generated at the tips of the two protrusions. As a result, the contactor 111 can be driven in a predetermined driving direction by the frictional force generated at the contact point between the vibrator and the contactor. This elliptical vibration is generated, for example, by exciting the vibrator 115 in two vibration modes.

[0019] In the following description, "deterioration in the performance of the vibration actuator" may be explained as an increase in power consumption (rated power) at a certain movement speed, that is, a decrease in efficiency.

[0020] 2 is a diagram illustrating the structure of a piezoelectric element 114 that constitutes the vibration actuator 100 of the present invention. The piezoelectric element 114 is composed of a rectangular piezoelectric material and an electrode portion. The piezoelectric material may be any material that exhibits piezoelectricity, such as polycrystalline piezoelectric ceramics or piezoelectric single crystals, but the following description will be given taking polycrystalline piezoelectric ceramics as an example.

[0021] FIG. 2(a) shows the main surface of the piezoelectric element 114, and FIG. 2(b) shows the surface opposite to the main surface of the piezoelectric element 114. The rectangular piezoelectric ceramic 114P has a first region divided in half in the longitudinal direction and a second region adjacent to the first region. A first electrode 114A and a second electrode 114B are formed in the first and second regions, respectively. The piezoelectric ceramic 114P also has a third electrode 114D that sandwiches the piezoelectric ceramic 114P together with the first electrode 114A and the second electrode 114B. The piezoelectric ceramic 114P also has a through-hole 114E that penetrates the piezoelectric ceramic to pass electricity from the surface (main surface) on which the first electrode 114A and the second electrode 114B are provided to the third electrode.

[0022] The surface of the piezoelectric element 114 that faces the main surface is bonded to the surface of the vibration plate 113 on which the protrusions 112 are not provided.

[0023] The polarization direction of the piezoelectric ceramic 114P in the region where the first electrode 114A and the second electrode 114B are provided is the same direction, and the piezoelectric ceramic 114P may be previously subjected to polarization treatment by a known polarization treatment method.

[0024] In order to generate vibrations in Mode A and Mode B, the third electrode 114D of the piezoelectric element 114 is grounded, and an alternating voltage V is applied to the first electrode 114A. A is applied to the second electrode 114B, and an alternating voltage V B are applied independently.

[0025] Unless otherwise specified, the alternating voltage V A and V B The following description will be given assuming that the amplitudes of the signals are equal.

[0026] As a means for supplying power to the first electrode 114A and the second electrode 114B, for example, a flexible printed circuit board (not shown) is attached as a power supply member to the surface of the piezoelectric element 114. The flexible printed circuit board is provided with at least electrodes connected to the first electrode 114A and the second electrode 114B, respectively, for supplying an AC voltage, and an electrode at ground potential connected to the electrode 114E. In order to prevent electrical disconnection and improve the reliability of conduction, a fourth electrode 114F electrically connected to the through portion 114E may be formed on the main surface of the flexible printed circuit board as shown in FIG. 2(c).

[0027] As shown in FIG. 2(c), the through-hole 114E may be configured with a conductive material on the through-hole and its inner wall. In this case, filling the through-hole with a conductive material is preferable because it prevents the adhesive from diffusing and provides electrical conductivity with a sufficiently low resistance. Alternatively, as shown in FIG. 2(d), the through-hole 114E may be configured with a groove on the end surface of a piezoelectric ceramic (a rectangular piezoelectric material) connecting the main surface of the piezoelectric element 114 with the surface opposite the main surface, and the inner wall of the groove may be made of a conductive material. The conductive material may be the same conductive material as any of the first, second, and third electrodes, or may be a different conductive material as long as sufficient electrical conductivity is ensured.

[0028] The cross-sectional shape of the through-hole 114E is preferably circular, although it is not particularly limited. Circular shapes also include elliptical shapes with an ellipticity of 0.9 or more. When the through-hole is formed in the piezoelectric ceramic compact before firing the piezoelectric ceramic, if the cross-sectional shape of the through-hole is circular, isotropic shrinkage occurs during sintering, making it less likely to crack. The through-hole can be formed using a punch or drill while the piezoelectric ceramic is in the green sheet state before firing.

[0029] When electrode material is filled into through-holes in a compact containing the raw materials for piezoelectric ceramics and the electrode material and the compact are fired together, the higher the firing temperature, the higher the heat resistance required of the electrode material. In the case of silver-palladium electrodes, the proportion of expensive palladium must be increased, and if even higher heat resistance than that of silver-palladium electrodes is required, expensive platinum must be used.

[0030] On the other hand, in order to reduce production costs, it is advisable to employ a process in which a piezoelectric ceramic is obtained by firing a compact with pre-formed through-holes, and then filling the through-holes of the ceramic with an electrode material. By employing this process, an inexpensive electrode material such as silver paste can be used for the electrodes filled in the through-holes.

[0031] Furthermore, as shown in FIG. 2(d), when the through portion 114E is exposed on the side surface of the piezoelectric ceramic 114P, the cross-sectional shape may be a semicircular arc shape or another recessed groove shape.

[0032] To manufacture the through-hole 114E having such a shape, a pre-formed through-hole may be cut, or it may be manufactured by applying a rotating blade to the side surface to process it.

[0033] <Two out-of-plane bending vibration modes> FIG. 3 is a diagram illustrating two vibration modes generated by the vibrator used to drive the vibration actuator 100 of the present invention.

[0034] FIG. 3(a) is a perspective view illustrating a primary out-of-plane bending vibration mode (hereinafter referred to as "mode A") excited in the vibrator 115 constituting the vibration actuator 100. FIG. 3(b) is a perspective view illustrating a secondary out-of-plane bending vibration mode (hereinafter referred to as "mode B") excited in the vibrator 115 constituting the vibration actuator 100. The alternating voltage V A , V B The time phase difference between the two is 0°, and the alternating voltage V A , V BWhen the frequencies of the first and second regions are near the resonant frequency of mode A, the vibrator 115 generates vibration in mode A as shown in Fig. 3(a). In vibration in mode A, two vibration nodes are generated along the long sides of the rectangular piezoelectric material. Mode A is a vibration mode in which both the first region and the second region expand or contract.

[0035] On the other hand, the alternating voltage V A , V B is 180° and their frequency is near the resonant frequency of mode B, vibrator 115 generates mode B vibration shown in Fig. 3(b). In mode B vibration, three vibration nodes are generated along the short sides of the piezoelectric material. Mode B is a mode in which when the first region expands, the second region contracts, and conversely, when the first region contracts, the second region expands.

[0036] Protrusion 112 of the diaphragm is disposed at a position near the antinode (where the amplitude is maximum) of vibration in mode A and near the node (where the amplitude is minimum) of vibration in mode B. Vibration in mode A causes the tip surface of protrusion 112 of vibrator 115 to reciprocate in the Z direction. Vibration in mode B also causes the tip surface of protrusion 112 to reciprocate in the X direction.

[0037] In the vibration actuator 100, mode A and mode B are superimposed, and elliptical vibration is excited in the protrusions 112 of the diaphragm.

[0038] In Figure 3, the Z direction is the direction in which the vibrator is pressed against the contact body (the direction in which the protrusion moves up and down in vibration mode A). The X direction is the direction in which the vibrator and contact body move relative to each other (the direction in which the protrusion moves back and forth in vibration mode B). The Y direction is the direction perpendicular to the XZ plane.

[0039] AC voltage V A , V B When the phase difference is 0 to ±180°, modes A and B are superimposed, and an elliptical motion can be generated on the tip surface of the protrusion 112 within the XZ plane.

[0040] A frictional force due to pressure contact acts between the protrusion 112 and the contact body 111, and the elliptical motion of the protrusion 112 can generate a driving force (thrust) that drives the contact body 111 in the X direction.

[0041] The resonance frequencies of modes A and B can be adjusted by adjusting the dimensions of the long and short sides of the rectangular piezoelectric material. It is preferable that the long sides of the rectangular piezoelectric material are 1 mm or more and 20 mm or less, and the short sides are 0.5 mm or more and 10 mm or less. It is more preferable that the long sides are 6 mm or more and 20 mm or less, and the short sides are 3 mm or more and 10 mm or less, since variations in the resonance frequency due to processing accuracy are small.

[0042] A vibrating piezoelectric element has vibration antinodes, vibration nodes, strain antinodes, and strain nodes depending on the vibration mode.

[0043] <Vibration node / antinode> Fig. 4 shows the positions of the nodal lines and antinodes of vibrations corresponding to modes A and B generated in the vibrator of the present invention. Fig. 4 is a plan view of vibrator 115 as seen from the piezoelectric element 114 side.

[0044] In Figure 4(a), two nodal lines of vibration in mode A are shown by dashed lines 411, and three antinode lines of vibration are shown by dashed lines 412. The nodal lines and antinode lines of mode A can be obtained by connecting the node and antinode positions of vibration in any YZ plane in the X direction.

[0045] 4(b) also shows three nodal lines of vibration in mode B with dashed lines 421 and two antinode lines of vibration with dashed-dotted lines 422. The nodal lines and antinode lines of mode B can be obtained by connecting the node and antinode positions of vibration in any XZ plane in the Y direction.

[0046] When using the vibration actuator 100, both mode A and mode B of the vibrator 115 are used. FIG. 4(c) shows the nodal lines of mode A and mode B overlapping each other, illustrating a preferred position of the through-hole 114E (denoted as E in the figure). The intersection 423 of the nodal lines of mode A and mode B is indicated by a square. It can be seen that there are six intersections of the nodal lines generated by the vibrations of mode A and mode B. As will be explained later, the area 431 surrounded by these six intersections is indicated by a shaded area.

[0047] <Vibration nodal and antinode positions> The nodal positions and antinode positions of the vibration generated in the piezoelectric ceramic 114P by excitation of the vibrator 115 in modes A and B are measured as follows. That is, vibration in mode A or mode B is generated in the vibrator 115. When mode A is generated, an alternating voltage V A and V B The phase difference between the AC voltage V A and V B The phase difference between these is 180°. Then, for example, by using a laser Doppler vibrometer to measure the vibration velocity in the Z direction two-dimensionally on the XY plane and calculating the displacement in the Z direction at each point, the positions of the nodal lines and antinodes of Mode A and Mode B can be measured.

[0048] Note that a flexible printed circuit board may be attached to the piezoelectric element 114, making it difficult to directly measure the vibrations of the piezoelectric element 114 and the piezoelectric ceramic 114P. In such cases, the vibration state of the surface of the diaphragm 113 may be observed, and the positions of the observed nodal lines and antinode lines may be projected onto the piezoelectric element 114 and treated as the positions of the nodal lines and antinode lines of the vibration generated in the piezoelectric ceramic 114P. Furthermore, since the electrode material provided on the surface of the piezoelectric ceramic 114P is sufficiently smaller in thickness and rigidity than the piezoelectric ceramic 114P, the vibration generated on the piezoelectric element 114 may be considered as the vibration generated in the piezoelectric ceramic 114P. Alternatively, the positions of the nodes and antinodes of each vibration can also be determined by modal analysis using the finite element method.

[0049] The vibrator does not need to be pressed against the contact body during vibration measurement.

[0050] <Distortion Node / Belly> When the vibrator 115 vibrates, strain occurs inside the piezoelectric ceramic 114P. The strain nodes and antinodes in Mode A and Mode B can be obtained in the same manner as the vibration nodes and antinodes described above. The positions of the strain nodes and antinodes may differ from the vibration nodes and antinodes.

[0051] FIG. 5 shows the positions of the nodes and antinodes of the strain of the piezoelectric ceramic 114P in Mode A and Mode B that occur in the vibrator of the present invention.

[0052] 5(a) shows the strain nodes of the piezoelectric ceramic 114P in mode A with dashed lines 511 and the strain antinodes with dashed lines 512. FIG. 5(b) shows the strain node positions of the piezoelectric ceramic 114P in mode B with dashed lines 521 and the strain antinode positions with dashed lines 522.

[0053] The node of the strain of mode A exists near the end of the piezoelectric ceramic parallel to the long side.

[0054] The nodes of the strain of Mode B are located near the ends of the piezoelectric ceramic and at the center of the piezoelectric ceramic, parallel to the short sides. The antinodes are located between the nodes.

[0055] Figure 5(c) shows the nodal lines of strain in mode A and the nodal lines of strain in mode B superimposed on each other, and the nodal positions of the strain are mainly located on the outer periphery of the piezoelectric ceramic 114P and on the lines that intersect with and bisect the two long sides of the rectangular piezoelectric material.

[0056] 4 and 5, the areas near the two long sides of the piezoelectric ceramic 114P correspond to the antinodes of vibration in Mode A and also to the nodes of strain in Mode A. On the other hand, the areas near the two short sides of the rectangular piezoelectric ceramic 114P correspond to the antinodes of vibration in Mode B and also to the nodes of strain in Mode B. Unlike the nodes / antinodes of vibration, these are difficult to observe directly, so the positions of the nodes / antinodes of strain are determined by analysis using the finite element method.

[0057] <Suitable penetration position 1> The strain node position is the position where the work done by the piezoelectric ceramic 114P to generate vibration is minimal, and is an appropriate location for providing the through-hole 114E in the piezoelectric ceramic 114P.

[0058] On the other hand, the antinode position of the strain is the position where the work done by the piezoelectric ceramic 114P to generate vibration is greatest, and is not a preferable location for providing the through-hole 114E in the piezoelectric ceramic 114P.

[0059] FIG. 5(d) is a diagram illustrating region 431 and the antinodes of the strains of modes A and B. Region 431 includes the region where antinode 512 of the strains of mode A and antinode 522 of the strains of mode B intersect, and is a region where the strain of the piezoelectric ceramic due to vibration is large. If the strain amount at the intersection of antinode 512 of the strains of mode A and antinode 522 of the strains of mode B is 100%, the strain amount in region 431 is 30% or more. In other words, region 431 is a region where the work done by the piezoelectric ceramic 114P to generate vibration is large. Therefore, if a through hole is provided on or inside the outline of region 431 (the line connecting the intersections of the nodal lines of vibration), the vibration will decrease, and the efficiency of the vibration actuator will decrease.

[0060] Vibration node locations are ideal locations for bonding components such as flexible printed circuit boards while suppressing vibration blockage because the vibration magnitude is small. However, vibration node locations can generate large amounts of distortion in response to vibration, so vibration node locations are not necessarily the optimal locations for providing penetrations.

[0061] Therefore, the through portion 114E in the piezoelectric ceramic 114P is formed outside the area 431 surrounded by the intersection of the nodal line 411 of the vibration mode A and the nodal line 421 of the vibration mode B.

[0062] The phrase "through portion 114E is formed outside region 431" means that through portion 114E is not formed in the region inside region 431, but is formed in the region outside region 431.

[0063] At least one through-hole 114E should be provided in an area outside the outline of area 431 surrounded by the intersections of the vibration nodal lines shown in Figure 4(c). This makes it possible to suppress deterioration of vibration characteristics due to damage to the piezoelectric element, and to provide a vibration actuator with excellent vibration characteristics.

[0064] <Suitable position of penetration part 2> FIG. 7 is a diagram illustrating the arrangement of the through-holes in the vibration actuator of the present invention.

[0065] It is more preferable that the through-hole 114E (denoted as E in the drawings) be formed in a region extending from the nodal line 411 of Mode A toward the long edge side of the rectangular piezoelectric ceramic 114P (FIGS. 7(a), 7(b), and 7(c)). Such an arrangement of the through-hole 114E is more preferable in a region outside the region 431 surrounded by the intersections of the nodal lines of vibration. This is because in this region, there is no region where both the strain or amplitude of Mode A and Mode B become antinodes, and furthermore, this region is generally far from the antinode line 512 of the strain of Mode A (FIG. 5(a)), so that the vibration of Mode A is less inhibited by the through-hole 114E.

[0066] <Suitable position of penetration part 3> FIG. 8 is a diagram showing a piezoelectric ceramic 114P and a through portion 114E (denoted as E in the drawing) according to the present invention.

[0067] In the area outside of region 431 surrounded by the intersections of the vibration nodal lines (white squares in the figure), we focus on the lines that bisect the two long sides of rectangular piezoelectric ceramic 114P. It is preferable that at least one through-hole 114E is formed in an area within 300 microns (=0.3 mm) of this bisector. It is even better that the center of gravity of the XY plane cross section of through-hole 114E is located in this area.

[0068] This is because the region within 300 microns from the bisector includes both a node of the strain of mode B and a node of the vibration of mode B, and therefore the provision of the through portion 114E can further suppress a decrease in efficiency of the vibration actuator 100. Note that since the nodal line 521 of the strain of mode B and the nodal line 421 of the vibration of mode B overlap, for the sake of convenience they are depicted by a single dashed line in Figure 8, with some of the other nodal lines omitted.

[0069] <Diameter of through hole> The diameter of the through-hole is preferably greater than 140 microns and less than 400 microns. A diameter of 140 microns or less may increase the electrical resistance inside the through-hole, potentially reducing the efficiency of the vibration actuator 100. A diameter of 400 microns or more may result in significant loss of the piezoelectric material due to the through-hole 114E, potentially reducing the vibration characteristics. A diameter of 140 microns or more and 300 microns or less is more preferable because it maintains sufficient conductivity while also making it easier to fill and close the through-hole with a conductive material. If the diameter of the through-hole is not constant, the diameter of the through-hole in this specification is defined as the diameter of the largest through-hole.

[0070] FIG. 6 is a diagram showing an example of the cross-sectional shape of a through-hole 114E in which the through-hole and the inner wall of the through-hole are provided with a conductive material.

[0071] 6(a) is a schematic diagram showing a case where the through-hole is not filled (closed) with a conductive material, and FIG. 6(b) is a schematic diagram showing a case where the through-hole is filled with a conductive material. If the through-hole is closed with a conductive material, it is more preferable because it has the effect of preventing the adhesive used to bond the vibration plate 113 and the piezoelectric element 114 from diffusing through the through portion 114E and lowering the electrical resistance of the through-hole.

[0072] If the through-hole is not closed, light from a light source placed on the opposite surface of the piezoelectric element can be seen through the through-hole.

[0073] <Number of penetrations> Although there is no limit to the number of through-holes 114E, it is preferable that an even number of through-holes 114E are arranged symmetrically with respect to a line that bisects the short side of the rectangular piezoelectric ceramic 114P. By adopting such a configuration, the symmetry of Mode A is not lost, and a decrease in the efficiency of the vibration actuator 100 can be suppressed. Furthermore, this is preferable because it eliminates the need to align the orientation of the piezoelectric elements when attaching a flexible printed circuit board or the like.

[0074] On the other hand, having only one through-hole 114E is more preferable from the viewpoint of reducing production costs. In particular, if the diameter of the through-hole is greater than 140 microns and smaller than 300 microns, the symmetry of vibration is not disturbed even if there is only one through-hole, which is more preferable. In other words, it is preferable that the through-holes are arranged substantially symmetrically with respect to the bisector of the two short sides of the rectangular piezoelectric material.

[0075] <Amount of lead contained in piezoelectric material> Piezoelectric ceramic 114P included in piezoelectric element 114 can be made of lead zirconate titanate (PZT), which has excellent piezoelectric properties, but it is more preferable for the amount of lead contained in the piezoelectric material to be less than 1000 ppm, as this reduces the environmental impact. The amount of lead contained in the piezoelectric material can be evaluated by the amount of lead relative to the total weight of the piezoelectric material, which is determined by, for example, X-ray fluorescence analysis (XRF) or ICP atomic emission spectroscopy.

[0076] An example of a piezoelectric material with a low lead content is a piezoelectric material containing a perovskite-type oxide containing Ba, Ca, Ti, and Zr, and Mn. The molar ratio x of Ca to the sum of Ba and Ca is 0.02≦x≦0.30. The molar ratio y of Zr to the sum of Ti and Zr is 0.020≦y≦0.095 and y≦x. Additionally, the molar ratio a of Ba and Ca to the sum of Ti and Zr is 1.00≦a≦1.01. Furthermore, the content of Mn per 100 parts by weight of the oxide is preferably 0.02 to 0.40 parts by weight, calculated as metal. This composition will be referred to hereinafter as BCTZ.

[0077] As a second example of a piezoelectric material with a low lead content, a piezoelectric material containing an oxide containing Na, Ba, Nb, and Ti and at least one element selected from Mn and Ni can be used. The molar ratio x of Na to 1 mol of the oxide is 0.80≦x<0.92. The molar ratio y of Nb to the sum of Nb and Ti is 0.83≦y<0.92. Additionally, the molar ratio of Ba to the sum of Nb and Ti is greater than 0.08 and less than 0.20. The Ni content is 0.05 mol or less per mol of oxide (i.e., a molar ratio of 0.05 or less), and the Mn content is 0.005 mol or less per mol of oxide (i.e., a molar ratio of 0.005 or less). More preferably, the piezoelectric material is a perovskite-type piezoelectric material. This composition will hereinafter be referred to as NNBT.

[0078] <Thickness of piezoelectric ceramics> It is preferable that the piezoelectric ceramic 114P is a single layer having a thickness of 0.3 mm or more.

[0079] This is because a piezoelectric ceramic having a thickness of 0.3 mm or more increases the yield and is less likely to crack when pressure is applied when bonding components such as the diaphragm 113. Furthermore, single-layer piezoelectric elements are preferable because they are less expensive and more robust than multilayer piezoelectric elements with internal electrodes.

[0080] On the other hand, if the thickness of the piezoelectric ceramic is greater than 0.5 mm, it becomes difficult to form electrodes on the inner walls of the through-holes, and there is a risk that the electrodes may break inside the through-holes. Therefore, the thickness of the piezoelectric ceramic is preferably between 0.3 mm and 0.5 mm. [Example]

[0081] Next, the vibration actuator and vibrator of the present invention will be described with reference to examples, but the present invention is not limited to the following examples. Table 1 summarizes examples of the present invention and comparative examples.

[0082] Prior to describing the examples, a vibration type actuator of a comparative example will be described, which is to be compared with the examples. The shape of the electrodes formed on the main surface is changed as appropriate depending on the positions and number of the through-holes.

[0083] <Comparative Example 1> As shown in Figure 9(a), a piezoelectric element was fabricated with a total of two through-holes 114E inside an area 431 surrounded by the intersection of the nodal line of vibration in mode A and the nodal line of vibration in mode B. PZT with a thickness of 0.35 mm was used as the piezoelectric material. The two through-holes 114E were provided at the intersection of the antinode line of strain in mode A and the antinode line of strain in mode B, and the diameter of the through-holes was 600 microns. The rated power of the vibration actuator fabricated using this piezoelectric element was W. ref1 It was.

[0084] <Comparative Example 2> As shown in FIG. 9(b), a piezoelectric element was fabricated in which a through-hole was provided inside an area 431 surrounded by the intersection of the nodal line of vibration in mode A and the nodal line of vibration in mode B. That is, this piezoelectric element is the same as Comparative Example 1 except that a total of two through-holes 114E are provided at the intersection positions of the nodal line of vibration in mode A and the nodal line of vibration in mode B. The rated power of a vibration type actuator fabricated using this piezoelectric element is W ref2 and W ref2 The value of W is lower than that of Comparative Example 1. ref2 <W ref1 It was a relationship of ref2 and W ref1 The values ​​of were all large, and the efficiency of the vibration actuator was insufficient.

[0085] Example 1 9(c), a piezoelectric element was fabricated in which a through-hole was provided outside an area 431 surrounded by the intersection of the nodal line of vibration in mode A and the nodal line of vibration in mode B. In other words, this piezoelectric element was the same as Comparative Example 1, except that a total of two through-holes 114E were provided at the midpoint between the intersection of the nodal line of mode B and the line that bisects the two short sides of the piezoelectric ceramic, and the short sides of the piezoelectric ceramic.

[0086] The position where the through portion 114E is provided is outside the region 431 but is within the region sandwiched between the nodal lines of the vibration of mode A.

[0087] The rated power W of the vibration actuator made using this piezoelectric element ex1 Then, We x1 <W ref2 <W ref1 In other words, the efficiency of the vibration actuator was improved compared to the configurations of Comparative Example 1 and Comparative Example 2.

[0088] <Example 2> As shown in Figure 9(d), a piezoelectric element was fabricated in which a through-hole 114E having two through-holes with a diameter of 600 microns was provided outside an area 431 surrounded by the intersection of the nodal line of vibration in mode A and the nodal line of vibration in mode B. Specifically, the positions of the through-holes 114E are shifted by 400 microns symmetrically from the center of gravity of the piezoelectric element from the midpoint between the intersection of the line that bisects each of the two long sides of the piezoelectric ceramic and the nodal line of vibration in mode A and the long side of the piezoelectric ceramic. The rated power W of a vibration-type actuator fabricated using this piezoelectric element was ex2 Then, the measurement result is W ex2 <W ex1 <W ref2 <W ref1 That is, the efficiency of the vibration actuator was improved compared to the configurations of Comparative Examples 1 and 2. Furthermore, the efficiency of the vibration actuator was improved compared to the configuration of Example 1.

[0089] Example 3 As shown in Figure 9(e), a piezoelectric element was fabricated in which the positions of the two through holes 114E were outside the region 431, and the deviation in the X direction from the line that bisects the two long sides of the piezoelectric ceramic was within 300 microns. The rated power W of the vibration type actuator fabricated using this piezoelectric element was ex3 Then, the measurement result is W ex3 <W ex2 <W ex1 <W ref2 <W ref1 It was.

[0090] Example 4 The same piezoelectric element as in Example 3 was fabricated except that the diameter of the through-hole was 140 microns. ex4 is W ex4 <We x3 The efficiency of the vibration actuator was further improved.

[0091] <Example 5> The same piezoelectric element as in Example 3 was fabricated except that the diameter of the through-hole was 400 microns. The rated power W of the vibration type actuator using this element was ex5 is W ex4 It was almost the same.

[0092] <Comparative Example 3> The same piezoelectric element as in Example 3 was fabricated except that the diameter of the through-hole was 900 microns. The rated power W of the vibration type actuator using this element was ref3 is W ex3 <Wr ef3 The results of Examples 3-5 and Comparative Example 3 can be summarized as follows: W ex5 ≒W ex4 <W ex3 <W ref3 They were in a relationship.

[0093] From the above results, it is more preferable that the width of the through-hole is 140 microns or more and 400 microns or less.

[0094] Example 6 The same piezoelectric element as in Example 5 was fabricated except that the number of through-holes was one, and the rated power W of the vibration type actuator using the same element was measured. ex6 is W ex5 It was almost the same.

[0095] Example 7 A piezoelectric element was fabricated using BCTZ as the piezoelectric material. The piezoelectric element was fabricated in the same manner as in Example 6, except for the composition of the piezoelectric material. It was confirmed that the effects of the present invention could also be obtained with a vibration-type actuator using this element.

[0096] Example 8 A piezoelectric element was fabricated using NNBT as the piezoelectric material. The piezoelectric element was fabricated in the same manner as in Example 6, except that the composition of the piezoelectric material was different.

[0097] It was confirmed that the effects of the present invention could also be obtained with a vibration type actuator using this element.

[0098] Example 9 A piezoelectric element identical to that of Example 7 was fabricated, except that the diameter of the through-holes was 200 microns. The efficiency of a vibration actuator using this element was equivalent to that of the vibration actuator described in Example 7. The cross-section of the piezoelectric element including the through-holes was observed, and the average thicknesses of the electrodes formed on the element surface and the electrodes on the inner walls of the through-holes were determined. The average thickness was calculated by image processing the cross-sectional area of ​​the electrodes formed on the element surface or in the through-holes, and dividing the resulting cross-sectional area by the length of the electrode-forming portion. The average thickness of the electrodes inside the through-holes was obtained by dividing the cross-sectional area of ​​the electrodes inside the through-holes by twice the thickness of the piezoelectric material. As a result, the ratio of the average thickness of the surface electrodes to the electrodes inside the through-holes was 2.5 to 10 times, and the average thickness of the electrodes inside the through-holes was greater.

[0099] Example 10 A piezoelectric element was fabricated in the same manner as in Example 7, except that the diameter of the through-holes was 140 microns. It was confirmed that the effects of the present invention could also be obtained with a vibration-type actuator using this element.

[0100] <Comparative Example 4> Piezoelectric elements were fabricated in the same manner as in Example 9, except that the thickness of the piezoelectric ceramic was 0.25 mm. However, 10% of the piezoelectric elements were cracked when they were pressure-bonded to the diaphragm, indicating that the robustness of the piezoelectric elements was insufficient.

[0101] Example 11 A piezoelectric element similar to that of Example 9 was fabricated, except that the thickness of the piezoelectric ceramic was 0.3 mm, and a vibration actuator was fabricated using the same element. When the thickness of the piezoelectric ceramic was 0.3 mm, the frequency with which the piezoelectric element broke when bonding the vibration plate to the piezoelectric element was 1% or less. By increasing the thickness of the piezoelectric ceramic to 0.3 mm or more, the probability of the piezoelectric element breaking during the bonding process between the vibration plate and the piezoelectric element was reduced to 1% or less. In other words, a piezoelectric material thickness of 0.3 mm or more is robust and is more preferable.

[0102] Example 12 A vibration type actuator was fabricated in the same manner as in Example 9, except that the thickness of the piezoelectric ceramic was 0.5 mm. No cracks occurred in the piezoelectric element.

[0103] <Comparative Example 5> A vibration actuator was fabricated in the same manner as in Example 9, except that the thickness of the piezoelectric ceramic was 0.7 mm. No cracks occurred in the piezoelectric element, but the electrodes on the inner walls of the through-holes were disconnected, and the vibration actuator did not function. When the ratio of the average thickness of the surface electrodes to the electrodes inside the through-holes was measured using the same method as in Example 9, the ratio was found to be small, less than 2.5 times. Some of the inner walls were not covered with electrodes.

[0104] As described above, a vibration actuator of the present invention has been described, which uses a piezoelectric element having a through-hole provided outside the region 431 surrounded by the intersections of the nodal lines of the amplitude of Mode A and the nodal lines of the amplitude of Mode B. This vibration actuator can be driven more efficiently than a vibration actuator which uses a piezoelectric element having the through-hole provided inside the region 431.

[0105] [Table 1] [Industrial Applicability]

[0106] The vibration actuator of the present invention can be suitably used as a drive unit for optical devices, and can also be widely used as a drive unit for electronic devices.

[0107] Specifically, the vibration actuator of the present invention can be used for a variety of purposes, such as driving lenses and imaging elements in imaging devices (optical equipment), driving the rotation of photosensitive drums in copiers, driving stages, etc. Although a single vibration actuator has been described in this specification, it is also possible to arrange multiple vibration actuators in a circular ring shape and drive a ring-shaped contact body in rotation. [Explanation of symbols]

[0108] 100 Vibration Actuator 111 Contact body 112 Protrusion 113 Vibration plate 114 Piezoelectric element 114A First Electrode 114B Second electrode 114D Third electrode 114E Penetration 114F Fourth electrode 114P Piezoelectric ceramics 115 vibrator 411 Nodal lines of the first order out-of-plane bending vibration (mode A) 412 Line of first order out-of-plane bending vibration (mode A) 421 Nodal lines of second-order out-of-plane bending vibration (mode B) 422 Antinode of second-order out-of-plane bending vibration (mode B) 423 Intersection of Mode A nodal line and Mode B nodal line 431 The region enclosed by the intersection of the nodal line of vibration in mode A and the nodal line of vibration in mode B 511 Nodal Lines of Strain in Piezoelectric Ceramics in Mode A Vibration 512 Strain Antinodes of Piezoelectric Ceramics in Mode A Vibration 521 Nodal Lines of Strain in Piezoelectric Ceramics in Mode B Vibration 522 Strain Antinodes of Piezoelectric Ceramics in Mode B Vibration

Claims

1. a rectangular piezoelectric material; and a pair of electrodes provided on the piezoelectric material; a piezoelectric element including a through hole that is electrically connected to one of the electrodes, penetrates the piezoelectric material, and has an inner wall made of a conductive material; and a vibrator including an elastic body; a contact body that comes into contact with the vibrator and moves relative to the vibrator; the through holes are formed only outside a region surrounded by the intersections of a nodal line of a primary out-of-plane bending vibration mode, where two nodes of vibration occur along a long side of the piezoelectric material, and a nodal line of a secondary out-of-plane bending vibration mode, where three nodes of vibration occur along a short side of the piezoelectric material, A vibration actuator in which the piezoelectric material contains less than 1000 ppm of lead.

2. The vibration actuator of claim 1, wherein the electrodes are a first electrode provided in a first region of the piezoelectric material, a second electrode provided in a second region adjacent to the first region, and a third electrode that sandwiches the piezoelectric material between the first electrode and the second electrode, and the primary out-of-plane bending vibration mode is a vibration mode in which the first region and the second region both expand or contract, and the secondary out-of-plane bending vibration mode is a mode in which the second region contracts when the first region expands and the second region expands when the first region contracts.

3. 3. The vibration actuator according to claim 1, wherein the through-hole is formed in a region extending from a nodal line of the primary out-of-plane bending vibration mode toward a long edge side of the piezoelectric material.

4. 2. The vibration actuator according to claim 1, wherein the through-holes are filled with the conductive material.

5. 5. The vibration actuator according to claim 1, wherein the rectangular piezoelectric material has a long side of 1 mm or more and 20 mm or less, and a short side of 0.5 mm or more and 10 mm or less.

6. 6. The vibration actuator according to claim 1, wherein the thickness of the piezoelectric material is 0.3 mm or more.

7. 7. A vibration actuator according to claim 1, wherein the through-hole is formed within 300 microns of a line that intersects with two long sides of the rectangular piezoelectric material and bisects each of the two long sides.

8. 8. The vibration actuator according to claim 1, wherein the through-hole has a width of 140 microns or more and 400 microns or less.

9. 9. The vibration actuator according to claim 1, wherein the number of the through-holes is one.

10. 9. The vibration actuator according to claim 1, wherein the through holes are arranged symmetrically with respect to a line that intersects two short sides of the rectangular piezoelectric material and bisects the two short sides.

11. The piezoelectric material is Oxides having a perovskite structure containing Ba, Ca, Ti, and Zr; and a piezoelectric material containing Mn, 11. The vibration actuator according to claim 1, wherein the piezoelectric material is characterized in that x, which is the molar ratio of Ca to the sum of Ba and Ca, is 0.02≦x≦0.30, y, which is the molar ratio of Zr to the sum of Ti and Zr, is 0.020≦y≦0.095 and y≦x, and the content of Mn per 100 parts by weight of the oxide is 0.02 parts by weight or more and 0.40 parts by weight or less in terms of metal.

12. The piezoelectric material is an oxide containing Na, Ba, Nb, and Ti; Contains at least one element selected from Mn and Ni, 11. The vibration actuator according to claim 1, wherein the perovskite piezoelectric material is characterized in that x, which is the molar ratio of Na to the sum of Nb and Ti, is 0.80≦x<0.92, y, which is the molar ratio of Nb to the sum of Nb and Ti, is 0.80≦y<0.92, the molar ratio of Ba to the sum of Nb and Ti is greater than 0.08 and not more than 0.20, the molar ratio of Ni to the sum of Nb and Ti is 0.05 or less, and the molar ratio of Mn to the sum of Nb and Ti is 0.005 or less.

13. 13. The vibration actuator according to claim 1, wherein the electrode electrically connected to the through hole is an electrode provided between the piezoelectric material and the elastic body.

14. An optical device comprising the vibration actuator according to any one of claims 1 to 13 in a drive section.

15. 14. An electronic device comprising the vibration actuator according to claim 1 and a member attached to the vibration actuator.

16. An optical device comprising a lens and the vibration actuator according to claim 1 that drives the lens.

17. An imaging device comprising: an imaging element; and the vibration actuator according to claim 1 that drives the imaging element.

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