Vibration actuator and electronic apparatus

Abstract

To provide a vibration wave motor with high output and high adhesion reliability, and an electronic apparatus comprising the same.SOLUTION: A vibration actuator comprises: a vibrator having an electric-mechanical energy conversion element and an elastic body adhered to each other via adhesive; and a contactor in contact with the elastic body, where vibration of the vibrator causes the vibrator and the contactor to be relatively moved. The elastic body includes: a flat plate part adhered to the electric-mechanical energy conversion element via the adhesive; and a projection part that is continuous to the flat plate part and projects from the flat plate part. In a part of the adhesive, a first adhesive layer, and a second adhesive layer which is adjacent to the first adhesion layer and has a thickness larger than the first adhesion layer and increasing toward the projection part are provided between the electric-mechanical energy conversion element and the flat plate part.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a vibration actuator and an electronic device equipped with the same. [Background technology]

[0002] An example of a vibration wave motor that uses an electromechanical energy conversion element such as a piezoelectric element as a vibration generating source is described in Patent Document 1. Patent Document 1 describes a vibration wave motor that has two protrusions provided on the surface of a flat elastic body, a vibrator in which a piezoelectric element is fixed to the back surface of the elastic body, and a contact body that is in pressure contact with the protrusions.

[0003] In this vibration wave motor, a predetermined AC voltage is applied to the electromechanical energy conversion element. This excites two bending vibrations (standing waves), and an elliptical or circular motion occurs at the tip of the protrusion (including the contact surface that comes into pressure contact with the contact body) within a plane that includes the direction connecting the two protrusions and the protruding direction of the protrusions. The contact body that comes into pressure contact with the protrusions receives a frictional driving force (thrust force) from the two protrusions, and the oscillator and the contact body can be moved relatively in the direction connecting the two protrusions.

[0004] Now, in order to miniaturize electronic devices, actuators including such oscillatory wave motors are being required to drive larger objects with smaller sizes, which means that the output density of actuators needs to be increased. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5930595 Summary of the Invention [Problem to be solved by the invention]

[0006] By the way, adhesive is usually used to bond the piezoelectric element and the elastic body. As mentioned above, if the output density of the vibration wave motor is increased, the stress on the vibrator increases, and there is a concern that the adhesive may come off.

[0007] The present invention has been made in view of the above problems, and has an object to provide a vibration wave motor that has high output and high adhesion reliability, and an electronic device equipped with the same. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a vibration actuator including a vibrator having an electromechanical energy conversion element and an elastic body bonded via an adhesive, and a contact body in contact with the elastic body, in which the vibrator and the contact body move relatively due to vibration of the vibrator, the elastic body has a flat plate portion bonded to the electromechanical energy conversion element via the adhesive, and a protrusion portion connected to the flat plate portion and protruding from the flat plate portion, A part of the adhesive is provided between the electromechanical energy conversion element and the flat plate portion. A first adhesive layer; The present invention provides a vibration actuator, characterized in having a second adhesive layer adjacent to the first adhesive layer, the second adhesive layer being thicker than the first adhesive layer and increasing in thickness toward the protrusion. Effect of the Invention

[0009] It is possible to provide a vibration wave motor that has high output and high adhesive reliability, and an electronic device equipped with the same. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is an exploded perspective view of a vibration wave motor according to a first embodiment of the present invention. [Diagram 2] FIG. 1 is an assembled perspective view of a vibration wave motor according to a first embodiment of the present invention. [Diagram 3] FIG. 2 is a perspective view illustrating a vibration mode in the first embodiment of the present invention. [Figure 4] 1A is a top view of a vibrator according to a first embodiment of the present invention, FIG. 1B is a cross-sectional view, FIG. 1C is an enlarged cross-sectional view of the vicinity of a rising portion of a protrusion, and FIG. [Diagram 5] 3 is a diagram showing the regions of the adhesive layers of the vibrator according to the first embodiment of the present invention. FIG. [Figure 6] FIG. 4 is a diagram showing the shear stress of the adhesive surface of the elastic body in each vibration mode in the first embodiment of the present invention. [Figure 7] 11A and 11B are a top view and a block diagram showing a schematic configuration of an imaging device (electronic device) using a vibration wave motor in Example 2 of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Example 1] This embodiment is an example in which the present invention is applied to a linear type vibration wave motor, and its details will be described with reference to Figs. 1 to 6. Fig. 1 is an exploded perspective view of a vibration wave motor 1 in the first embodiment of the present invention. Fig. 2 is an assembled perspective view. Here, the driving direction of the slider 9, which is a contact body (the direction in which the vibrator 2 described below and the slider 9 are moved relatively) is defined as the "X direction" (or simply "X"). Also, the direction in which the slider 9 comes into pressure contact with the vibrator 2 (pressure direction) is defined as the "Z direction" (or simply "Y"). Also, the direction perpendicular to the X direction and the Z direction is defined as the "Y direction" (or simply "Y").

[0012] A piezoelectric element 4, which is an electro-mechanical energy conversion element, is fixed to the elastic body 3 via an adhesive, and a flexible printed circuit board 5 is electrically connected to the piezoelectric element 4 on the side opposite the elastic body 3, forming the vibrator 2. The flexible printed circuit board 5 is fixed to the piezoelectric element 3 with an anisotropic conductive paste or anisotropic conductive film that allows electricity to flow only in the Z direction. The elastic body 3 is formed of two protrusions 3a and a plate-shaped flat portion 3b that protrude from the side opposite the piezoelectric element 4.

[0013] Lead zirconate titanate is used for the piezoelectric element 4. Alternatively, it may be made mainly of a piezoelectric material that does not contain lead, such as barium titanate or bismuth sodium titanate, i.e., the lead content is 1000 ppm or less. Electrode patterns 4a are formed on both sides of the piezoelectric element 4, and power is supplied from a flexible printed circuit board 5.

[0014] A pressure member 6 is provided below the vibrator 2 to apply pressure to and support the vibrator 2. A pressure spring 7 applies pressure to the pressure member in the Z direction, and the reaction force is received by a base 8, which is a pressure receiving member. A conical coil spring is used as the pressure spring 7 in order to reduce the size of the vibration wave motor 1 in the Z direction. Note that the coil shape is illustrated in a simplified form.

[0015] A slider 9 is provided above the vibrator 2 and is in pressure contact with the elastic body 3. The slider 9 is fixed to a slider holder 10 and is driven in the X direction as a unit. Rubber for vibration damping may be provided between the slider 9 and the slider holder 10. The slider 9 is made of highly wear-resistant metal, ceramic, resin, or a composite material thereof. In particular, a material made by nitriding stainless steel such as SUS420J2 is preferable from the viewpoints of wear resistance and mass production.

[0016] Three balls 11 are sandwiched between three pairs of upper and lower rails provided on the slider holder 10 and ball rail 12, and the ball rail 12 is fixed to the base 8, allowing the slider 9 and slider holder 10 to move in the X direction relative to the other components. An output transmission part of a desired shape is attached to the slider holder 10 to transmit output to the outside. This embodiment shows an example in which the vibrator 2 is fixed and the slider 9 moves, but it is also possible to fix the slider 9 and move the vibrator 2.

[0017] Next, the vibration mode excited in the vibrator 2 will be described with reference to Fig. 3. In this embodiment, two AC voltages with different phases are applied to the piezoelectric element 4 through the flexible printed circuit board 5, exciting two different out-of-plane bending vibrations in the vibrator 2, and generating a vibration that is a combination of these vibrations.

[0018] Mode A, which is the first vibration mode, is a primary out-of-plane bending vibration mode in which two nodes appear parallel to the X direction, which is the longitudinal direction of the vibrator 2. Since the protrusion 3a is arranged at a position where the vibration amplitude in the Z direction of mode A is maximum, i.e., at the antinode position, the vibration in mode A displaces the two protrusions 3a in the Z direction, which is the pressure direction. Mode B, which is the second vibration mode, is a secondary out-of-plane bending vibration mode in which three nodes appear approximately parallel to the Y direction, which is the short side direction of the vibrator 2. Since the protrusion 3a is arranged at a position where the vibration amplitude in the Z direction of mode B is minimum, i.e., at the node position, the vibration in mode B displaces the two protrusions 3a in the X direction.

[0019] By combining the vibrations of these modes A and B, the two protrusions 3a generate elliptical or circular motion in the ZX plane. By pressing the slider 9 against the two protrusions 3a, frictional force is generated in the X direction, generating a driving force (thrust) that moves the vibrator 2 and the slider 9 relatively. In this embodiment, the vibrator 2 is held by a method described later, so the slider 9 is driven in the X direction.

[0020] In order to efficiently drive the vibration wave motor 1, it is necessary to apply pressure to the vibrator 2 without impeding the vibration (displacement) of the two vibration modes excited in the vibrator 2, and for this purpose, it is desirable to support the vicinity of the nodes of these two vibration modes. For this reason, two protrusions 6a are provided on the pressure member 6, and pressure is applied to and held at the common node of the two vibration modes, thereby more efficiently applying pressure to the vibrator 2.

[0021] Furthermore, the protrusion 6a also plays a role in holding the vibrator 2 in the X and Y directions. In this embodiment, the flexible printed circuit board 5 and the protrusion 6a are in contact with each other in the vibrator 2, and the pressure and friction coefficient are adjusted so that the maximum static friction force is always greater than the thrust force generated in the slider 9. In other words, the vibrator 2 does not move relative to the pressure member 6 while the vibration wave motor 1 is being driven.

[0022] On the other hand, the pressure member 6 is provided with four loose-fitting portions 6b, which are supported (loosely fitted) with some play against the outer circumferential surface of the vibrator 2. These loose-fitting portions 6b serve to position the vibrator 2 when it is assembled, and also to function as a stopper when some external force acts on the slider 9.

[0023] Also, the loose fit portion 6b may be in contact with the outer circumferential surface of the vibrator 2 at two points other than the vibration nodes. However, as described above, the maximum frictional force between the flexible printed circuit board 5 and the protruding portion 6a is greater than the thrust force generated in the slider 9. Therefore, no forces in the X and Y directions act on the contact portion between the loose fit portion 6b and the vibrator 2. Therefore, the loss here is negligible, and no problems with driving occur.

[0024] In this way, the protrusions 6a of the pressure member 6 come into direct contact with the vicinity of the nodes of the vibrator 2, and the loose-fitting parts 6b come into direct contact with the outer peripheral surface of the vibrator 2. Therefore, it is desirable that the material of the pressure member 6 is a resin with high vibration insulation properties to prevent the generation of abnormal noise. For the protrusions 6a, a high friction coefficient is preferable to increase the holding force of the vibrator 2 for the reasons mentioned above, while a low friction coefficient is preferable for the loose-fitting parts 6b in order to further reduce friction loss with the vibrator 2. For these reasons, it is possible to separately apply a coating to the protrusions 6a to increase the friction coefficient, and a coating to the loose-fitting parts 6b to decrease the friction coefficient. It is also possible to configure separate parts with friction coefficients suitable for each by bonding or press-fitting.

[0025] Next, the vibrator 2 will be described in detail with reference to Fig. 4. Fig. 4(a) is a top view of the vibrator 2, and Fig. 4(b) is a cross-sectional view taken along line AA in Fig. 4(a). The protrusion 3a formed on the elastic body 3 is hollow and has a spring property (flexibility) in the pressure direction. This spring property allows the vibrator 2 and slider 9 to come into smooth contact with each other, suppressing the generation of abnormal noise.

[0026] Fig. 4(c) is an enlarged view of part B in Fig. 4(b), and Fig. 4(d) is an enlarged view of part C in Fig. 4(b). There is an adhesive 13 between the flat plate portion 3b of the elastic body 3 and the piezoelectric element 4. If this adhesive layer is too thick, it will attenuate the vibration of the vibrator 2, and if it is too thin, the adhesive strength may decrease. Therefore, it is preferable that the thickness of the first adhesive layer 13a, which accounts for most of the adhesive layer, is 0 μm or more and 3 μm or less. Here, 0 μm means that the elastic body and the piezoelectric element 4 are in contact. There is a certain degree of thickness distribution due to the presence of minute irregularities, undulations, and warping on the surface.

[0027] Figure 6 shows the results of a simulation in which the shear stress on the adhesive surface of the elastic body 2 was calculated in Mode A and Mode B. Each part was divided into a mesh for the calculation, and the mesh areas where the shear stress was relatively high are shown filled in black. Naturally, the calculation also included the piezoelectric element 4, but for ease of understanding, this is not shown in Figure 6. From this figure, we can see that the shear stress is high near the base of the protrusion 3a and near the edge of the rectangular part.

[0028] In order to relieve the shear stress near the protrusion 3a, a second adhesive layer 13b is provided adjacent to the first adhesive layer 13a, and the thickness of the second adhesive layer 13b gradually increases toward the protrusion 3a. The thickness of the second adhesive layer 13b is 3 μm or more and 10 μm or less. By making the second adhesive layer 13b thicker than the first adhesive layer 13a, the stress acting on the adhesive layer is relieved. Furthermore, by gradually increasing the thickness, localized stress concentration is suppressed. The radial length (L2) of the second adhesive layer 13b is preferably 100 μm or more and 400 μm or less, since if it is too short, the effect of stress relief decreases, and if it is too long, vibration may be dampened.

[0029] By appropriately determining the radial length of the protrusion portion of the second adhesive layer, which is the section from the end of the first adhesive layer to the inflection point of the R portion, in this manner, a greater effect can be expected.

[0030] Although the second adhesive layer 13b is adjacent to the R portion at the base of the protrusion 3a, the two are distinguished from each other by the inflection point.

[0031] The second adhesive layer 13b shown as an example in Fig. 4(c) has a maximum thickness of t2. At the inflection point of the R portion shown in Fig. 4(c), a line indicating the upper end of the maximum thickness t2 and a line indicating the right end of the length (L2) intersect.

[0032] The cross section of the adhesive surface of the elastic body 3 in the area of ​​the second adhesive layer 13b is distinguished from the R portion at the base of the protrusion 3a in that it has a different curvature or is straight.

[0033] 4(c), in addition to the first adhesive layer and the second adhesive layer, an adhesive pool may be arranged adjacent to the second adhesive layer and formed from the inflection point of the R portion toward the protrusion. By providing an adhesive pool in an adjacent portion of the second adhesive layer that is not on the first adhesive layer side, a strong vibrating body can be constructed, and the stress relaxation effect of the second adhesive layer can be expected more reliably.

[0034] On the other hand, as shown in FIG. 4(d), in order to relieve the stress near the edge of the piezoelectric element 4, a third adhesive layer 13c is provided adjacent to the first adhesive layer 13a and gradually increases in thickness toward the edge of the flat plate portion 3b. The thickness of the third adhesive layer 13c is 3 μm or more and 10 μm or less. By increasing the thickness from the first adhesive layer 13a, the stress acting on the adhesive layer is relieved. Also, by gradually increasing the thickness, localized stress concentration is prevented. The radial length (L3) of the third adhesive layer 13c is preferably 100 μm or more and 400 μm or less, because if it is too short, the effect of stress relief decreases, and if it is too long, vibration is attenuated. FIG. 5 shows the distribution of each adhesive layer, and when compared with FIG. 6, it can be seen that the second adhesive layer 13b and the third adhesive layer 13c cover the relatively high stress areas.

[0035] To provide such second adhesive layer 13b and third adhesive layer 13c, it is sufficient to process either the elastic body 3 or the piezoelectric element 4 into a non-planar shape as described above. However, since the piezoelectric element 4 is made of ceramics and is difficult to process, it is more advantageous to process the elastic body 3 into a non-planar shape. The elastic body 3 can be manufactured by pressing, forging, sintering, cutting, etc., but the pressing method is most desirable from the standpoint of cost and dimensional accuracy.

[0036] In order to obtain the height of the protrusion a, it may be necessary to perform a crushing process and to flow the resulting volume into the protrusion 3a. In this case, a shock line is formed around the protrusion 3a on the bonding surface, which deteriorates the flatness, and cutting such as lapping is required after pressing. In this embodiment, since the non-flat shape is removed if lapping is performed, the protrusion 3a is formed without crushing by adjusting the height of the protrusion 3a. In other words, the volume inside the rising part of the protrusion 3a is equal before and after the formation of the protrusion 3a. Since there is no crushing process, it is possible to maintain the flatness of the bonding surface and to eliminate the need for processing such as lapping.

[0037] Another effect of not performing processing such as lapping is that the thickness of the flat portion 3b is stable and the thickness difference, i.e., the difference between the maximum and minimum thicknesses of the flat portion, is within 10 μm, thereby stabilizing the resonant frequencies of modes A and B of the vibrator 2.

[0038] The elastic body 3 is preferably made of a material with low vibration damping, such as metal. Particularly preferred is martensitic stainless steel, which has particularly low vibration damping and can be hardened after processing to increase hardness and wear resistance. As described above, in this embodiment, no processing such as lapping is performed, so the adhesive surface of the elastic body 3 is formed only by the surface that is hardened after rolling, that is, the plastically processed surface. There are various types of finishing for rolling, but sufficient adhesive strength can be achieved by selecting an appropriate surface roughness. The surface roughness Ra is preferably 0.025 μm or more and 0.2 μm or less. This is because a certain degree of surface roughness increases adhesive strength due to the anchor effect and increased surface area.

[0039] [Example 2] The oscillatory wave motor can be used, for example, for driving lenses in an imaging device (optical equipment), etc. As an example, an imaging device that uses an oscillatory wave motor to drive a lens arranged in a lens barrel will be described.

[0040] 7(a) is a top view showing a schematic configuration of an imaging device 700. The imaging device 700 includes a camera body 730 equipped with an imaging element 710 and a power button 720. The imaging device 700 also includes a lens barrel 740 having a first lens group (not shown), a second lens group 320, a third lens group (not shown), a fourth lens group 340, and vibration type driving devices 620 and 640. The lens barrel 740 is replaceable as an interchangeable lens, and a lens barrel 740 suitable for a subject to be photographed can be attached to the camera body 730. In the imaging device 700, the second lens group 320 and the fourth lens group 340 are driven by the two vibration type driving devices 620 and 640, respectively.

[0041] Although the detailed configuration of the vibration type driving device 620 is not shown, the vibration type driving device 620 has a vibration wave motor and a driving circuit for the vibration wave motor. The vibration type driving device 620 moves the second lens group 320 in the optical axis direction. The vibration type driving device 640 has a similar configuration to the vibration type driving device 620, and moves the fourth lens group 340 in the optical axis direction.

[0042] 7(b) is a block diagram showing a schematic configuration of the imaging device 700. The first lens group 3a0, the second lens group 320, the third lens group 330, the fourth lens group 340, and the light amount adjustment unit 350 are disposed at predetermined positions on the optical axis inside the lens barrel 740. Light passing through the first lens group 3a0 to the fourth lens group 340 and the light amount adjustment unit 350 forms an image on the imaging element 710. The imaging element 710 converts the optical image into an electrical signal and outputs it, and the output is sent to the camera processing circuit 750.

[0043] The camera processing circuit 750 performs amplification, gamma correction, and the like on the output signal from the image sensor 710. The camera processing circuit 750 is connected to the CPU 790 via an AE gate 755, and is also connected to the CPU 790 via an AF gate 760 and an AF signal processing circuit 765. The video signal that has been subjected to a predetermined process in the camera processing circuit 750 is sent to the CPU 790 via the AE gate 755, the AF gate 760, and the AF signal processing circuit 765. The AF signal processing circuit 765 extracts high frequency components from the video signal to generate an evaluation value signal for autofocus (AF), and supplies the generated evaluation value to the CPU 790.

[0044] The CPU 790 is a control circuit that controls the overall operation of the imaging device 700, and generates control signals for determining exposure and adjusting focus from the acquired video signal. The CPU 790 adjusts the optical axis positions of the second lens group 320, the fourth lens group 340, and the light amount adjustment unit 350 by controlling the driving of the vibration type driving devices 620, 640 and the meter 630 so as to obtain the determined exposure and an appropriate focus state. Under the control of the CPU 790, the vibration type driving device 620 moves the second lens group 320 in the optical axis direction, the vibration type driving device 640 moves the fourth lens group 340 in the optical axis direction, and the light amount adjustment unit 350 is driven and controlled by the meter 630.

[0045] The optical axis direction position of the second lens group 320 driven by the vibration type driving device 620 is detected by a first linear encoder 770, and the detection result is notified to the CPU 790, thereby being fed back to the driving of the vibration type driving device 620. Similarly, the optical axis direction position of the fourth lens group 340 driven by the vibration type driving device 640 is detected by a second linear encoder 775, and the detection result is notified to the CPU 790, thereby being fed back to the driving of the vibration type driving device 640. The optical axis direction position of the light amount adjustment unit 350 is detected by an aperture encoder 780, and the detection result is notified to the CPU 790, thereby being fed back to the driving of the meter 630.

[0046] In the above, the optical device has been described in which the vibration actuator drives an optical element such as a lens, but it may also be configured to drive an image sensor, or to drive both. It is possible to provide an optical device in which at least one of an optical element and an imaging element is driven by the vibration type actuator described above.

[0047] This vibration actuator can be used in other electronic devices without any restrictions, and it is possible to provide electronic devices in which the target member is driven by the vibration actuator. [Explanation of symbols]

[0048] 1. Vibration motor 2. Vibration body 3 Elastic body 3a Protrusion 3b Flat plate part 4. Piezoelectric element (electromechanical energy conversion element) 4a electrode 13. Glue 13a First adhesive layer 13b Second adhesive layer 13c Third adhesive layer

Claims

1. A vibrating body having an electromechanical energy conversion element bonded via an adhesive, and an elastic body, The elastic body is provided with a contact body that is in contact with the elastic body, A vibratory actuator in which the vibrator and the contact body move relative to each other due to the vibration of the vibrator, The elastic body has a flat plate portion bonded to the electromechanical energy conversion element via the adhesive, and a projection portion connected to the flat plate portion and protruding from the flat plate portion. Between the electromechanical energy conversion element and the flat plate portion, the adhesive is The first adhesive layer, A second adhesive layer adjacent to the first adhesive layer, which is thicker than the first adhesive layer and increases in thickness toward the protrusion, A vibrating actuator characterized by having the following features.

2. The vibration-type actuator according to claim 1, characterized in that the thickness of the first adhesive layer is 3 μm or less, and the thickness of the second adhesive layer is 3 μm or more and 10 μm or less.

3. The vibration-type actuator according to claim 1, characterized in that the first adhesive layer has a constant thickness.

4. At the base of the projection, an R-shaped portion is formed which has a different curvature from the flat portion that is in contact with the second adhesive layer. The vibration actuator according to claim 1 or 2, wherein the radial length of the projection of the second adhesive layer, which is the section from the end of the adjacent first adhesive layer to the inflection point of the R portion, is 100 μm or more and 400 μm or less.

5. The vibration actuator according to claim 1 or 2, wherein the second adhesive layer has an adhesive reservoir in an adjacent portion that is not on the side of the first adhesive layer.

6. The vibration-type actuator according to claim 1 or 2, characterized in that the elastic body is made of martensitic stainless steel, and the surface of the elastic body on the side of the electromechanical energy conversion element is a surface that has been hardened after rolling.

7. The vibration-type actuator according to claim 6, characterized in that the surface roughness Ra of the aforementioned surface is 0.025 μm or more and 0.2 μm or less.

8. The device comprises an electromechanical energy conversion element bonded via an adhesive, an elastic body, a vibrator having an elastic body, and a contact body in contact with the elastic body, A vibratory actuator in which the vibrator and the contact body move relative to each other due to the vibration of the vibrator, The elastic body has a flat plate portion bonded to the electromechanical energy conversion element via the adhesive, and a projection portion connected to the flat plate portion and protruding from the flat plate portion. Between the electromechanical energy conversion element and the flat plate portion, the adhesive is The first adhesive layer, A vibrating actuator characterized by having a third adhesive layer adjacent to the first adhesive layer, between the first adhesive layer and the edge portion of the electromechanical energy conversion element, with a length of 100 μm to 400 μm and a thickness of 10 μm or less, wherein the thickness increases toward the edge portion.

9. The vibration-type actuator according to claim 1 or 8, characterized in that the difference between the maximum and minimum thickness of the flat plate portion is 10 μm or less.

10. A vibratory actuator according to claim 1 or 8, An optical device comprising at least one of an optical element or an image sensor, which is driven by the aforementioned vibration-type actuator.

11. Components and An electronic device comprising a vibrating actuator according to claim 1 or 8 for driving the aforementioned member.

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