JP2008172885A - Ultrasonic actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic actuator which can stably obtain high output and a high driving efficiency without preventing miniaturization. <P>SOLUTION: In the ultrasonic actuator including a vibrator equipped with a piezoelectric displacement part expanding/contracting by an electric signal, and with an abutting part which causes elliptical motion by resonance-exciting longitudinal vibration and bending vibration by the displacement of the piezoelectric displacement part, and also including a driven body which is press-contacted by the abutting part to cause relative movement to the vibrator, the gravity of one side part in the longitudinal vibration, where the node position of the longitudinal vibration in the vibrator is set as a boundary, is located closer to the abutting part than the center position of the full length in the longitudinal vibration of the one side part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultrasonic actuator, and more particularly, to an ultrasonic actuator that generates a relative movement by bringing a vibrating body into pressure contact with a driven body.

  In the past, attempts have been made to use ultrasonic actuators in various mobile devices. An ultrasonic actuator is generally composed of a vibrating body including a piezoelectric element that is an electro-mechanical energy conversion element, a driven body (moving body) that contacts the vibrating body in a pressurized state, and the like. The ultrasonic actuator is brought into pressure contact with the vibrating body by inputting a drive signal to the vibrating body, causing the vibrating body to expand and contract, and causing part of the vibrating body to perform elliptical vibration (hereinafter, including circular vibration). A relative motion is generated between the driven body and the driven body by a frictional force.

  Since the ultrasonic actuator is small and excellent in quietness, it has been used as a drive mechanism for electronic equipment such as an electronic camera, and its application is expanding further.

  On the other hand, in recent years, with the progress of miniaturization and high performance of electronic cameras and the like, there has been a demand for better driving performance of ultrasonic actuators used as the driving mechanism.

  In order to meet such demands, various studies have been conducted to increase the driving efficiency of the ultrasonic actuator.

For example, by providing a protrusion (contact portion) on a vibrating body that performs elliptical vibration by resonantly exciting the longitudinal (stretching) primary vibration mode and the bending secondary vibration mode, and making the longitudinal dimension longer than the width dimension. The center of gravity of the protrusion is moved away from the vibration node to increase the moment of inertia, thereby amplifying the amplitude of lateral vibration at the tip of the protrusion during bending vibration (see, for example, Patent Document 1). Also known are those using a vibrating body that excites an elliptical vibration by exciting a longitudinal (stretching) primary vibration and a bending primary vibration (for example, see Patent Document 2).
JP 2005-86991 A JP-A-6-121552

  However, in Patent Document 1, since the mass of the protrusion itself is small, in order to obtain a sufficient effect, it is necessary to lengthen the dimension of the protrusion, and there is a problem in that downsizing of the vibrating body is hindered.

  Further, in order to increase the amplitude of the longitudinal vibration, it is necessary to lengthen the longitudinal dimension of the rectangular portion (piezoelectric portion) of the vibrating body. However, as described above, in Patent Document 1, since it is necessary to increase the size of the protruding portion, the ratio of the length of the protruding portion to the entire length of the vibrating body becomes large, particularly when mounted on a small device. The length of the piezoelectric portion is shortened. For this reason, there is a problem that it is difficult to increase the amplitude of the longitudinal vibration.

  In addition, the longitudinal vibration is symmetrically expanded and contracted with the center of the vibrating body as a node, and can be represented by a dynamic model in which weights are attached to both ends of the spring. However, in patent document 1, since the dimension of a projection part becomes long, the gravity center position of the one side part bordering on the node position of a longitudinal vibration will become near the center (node) of a vibrating body. For this reason, the above-described dynamic model is similar to the model in which the spring length is shortened, and the amplitude of vibration is reduced.

  As described above, in Patent Document 1, the amplitude of the longitudinal vibration tends to be small, and in the configuration in which the vibrator is arranged so that the direction of the longitudinal vibration is the normal direction of the driven body, the thrust becomes small, There is a problem that driving stability is lowered.

  Here, the relationship between elliptical vibration and drive performance will be described. The elliptical vibration trajectory is the driving characteristic of an ultrasonic actuator that generates relative motion by frictional force with a driven body that is in pressure contact with the vibrating body by causing the part of the vibrating body to elliptically vibrate. The speed changes depending on the diameter (amplitude) in the tangential direction in contact with the body, and the thrust changes depending on the diameter (amplitude) in the normal direction.

  The larger the diameter in the tangential direction, the higher the speed in the tangential direction at the driving point, so the speed of the driven body that is friction driven increases. On the other hand, since the thrust is determined by the frictional force, it is sufficient to increase the vertical drag, that is, the pressing force. However, as the vibrating body is pressurized, the elastic deformation of the driven body and peripheral mechanism parts, the driven body And elastic deformation of the contact portion surface of the vibrating body (hereinafter collectively referred to as micro elastic deformation) increases. Since the amplitude of the elliptical vibration of the vibrating body is several μm or less, the driving performance is greatly affected by this minute elastic deformation.

  FIG. 17 schematically shows the state of driving by elliptical vibration. In FIG. 17, the minute elastic deformation is represented as the deformation of the driven body. FIG. 17A shows the driving state when the amplitude of the elliptical vibration is sufficiently large with respect to the minute elastic deformation, and FIG. 17B shows the driving state when the amplitude of the elliptical vibration is smaller than the minute elastic deformation.

  In the case of FIG. 17 (a), the contact portion contacts the driven body only when moving in the driving direction, and separates from the driven body when moving in the counter driving direction, but in FIG. 17 (b). In this case, since the amplitude of the elliptical vibration is small, even when the abutting portion moves in the non-driving direction, it comes into contact with the driven body and becomes a brake. For this reason, the driving force of the ultrasonic actuator is reduced, and the driving stability is reduced such as the occurrence of speed unevenness and the reproducibility. In addition, abnormal noise may occur.

  Therefore, in order to increase the driving force and stabilize the driving state, it is necessary to make the elliptical diameter in the normal direction sufficiently larger than the minute elastic deformation amount.

  Further, in Patent Document 2, it is necessary to substantially match the resonance frequencies of both the longitudinal (stretching) primary vibration and the bending primary vibration, but in this case, there is no choice but to adjust the aspect ratio of the dimensions of the vibrator. Also, since the aspect ratio is uniquely determined, it greatly affects the degree of freedom in designing the shape of the vibrating body. Further, the vertical / horizontal value at that time is about 0.7, and there is a problem that the amplitude of flexural vibration is reduced because the lateral width is increased and the bending rigidity is increased.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an ultrasonic actuator capable of stably obtaining high output and high drive efficiency without hindering downsizing.

  The above object is achieved by the invention described in any one of 1 to 7 below.

1. A piezoelectric displacement part that expands and contracts by an electrical signal;
A vibrating body comprising: an abutting portion that generates an elliptical motion by resonantly exciting longitudinal vibration and bending vibration by displacement of the piezoelectric displacement portion;
In an ultrasonic actuator having a driven body that is in pressure contact with the abutting portion and causes relative movement with respect to the vibrating body,
The center of gravity of one side portion in the longitudinal vibration direction with the node position of the longitudinal vibration in the vibrating body as a boundary is located closer to the contact portion than the center position of the full length of the one side portion in the longitudinal vibration direction. Ultrasonic actuator.

  2. 2. The ultrasonic actuator according to claim 1, wherein the piezoelectric displacement portion has weight members having a specific gravity greater than that of the piezoelectric displacement portion at both ends in the longitudinal vibration direction.

  3. 3. The ultrasonic actuator according to 2 above, wherein the material of the weight member is any one of tungsten, a tungsten alloy, a tungsten resin obtained by combining tungsten powder and a resin, or a tungsten carbide cemented carbide.

4). The material of the weight member is a tungsten carbide cemented carbide,
4. The ultrasonic actuator according to 2 or 3, wherein the weight member and the contact portion are formed integrally.

  5. 5. The ultrasonic actuator according to claim 1, wherein the piezoelectric displacement portion has a laminated structure, and a metal layer is laminated on at least one end portion in a longitudinal vibration direction.

  6). Any one of 1 to 5 above, wherein the vibration mode used for resonance of the piezoelectric displacement portion is a longitudinal primary vibration mode and a bending primary vibration mode, or a longitudinal primary vibration mode and a bending secondary vibration mode. 2. The ultrasonic actuator according to item 1.

7). The piezoelectric displacement portion has a weight member A provided with the contact portion at one end in the longitudinal vibration direction, and a weight member B at the other end,
Any one of 1 to 6 above, wherein when the weight of the weight member A is Wa and the weight of the weight member B is Wb, Wa / Wb satisfies the following condition (Equation 1). The ultrasonic actuator according to item.
0.1 ≦ Wa / Wb <1 (Formula 1)

  According to the present invention, the center of gravity of one side portion in the longitudinal vibration direction at the node position of the longitudinal vibration in the vibrating body is positioned closer to the contact portion than the center position of the entire length of the one side portion in the longitudinal vibration direction. I made it. That is, since the center of gravity of each one side portion of the vibrating body is closer to the contact portion that contacts the driven body, the longitudinal vibration increases the spring length and weight mass in the above-described dynamic model of the spring and weight. This is equivalent to this, and the amount of displacement increases. Also in the bending vibration, the amount of displacement becomes large because the moment of inertia around the node position of the bending vibration becomes large. Thereby, since the amplitudes of both longitudinal vibration and bending vibration can be increased, high output and high driving efficiency can be stably obtained.

  Embodiments of an ultrasonic actuator according to the present invention will be described below with reference to the drawings. In addition, although this invention is demonstrated based on embodiment of illustration, this invention is not limited to this embodiment.

Embodiment 1
Initially, the structure of the ultrasonic actuator 1 by Embodiment 1 is demonstrated using FIG. FIG. 1A is a front view showing an outline of the overall configuration of the ultrasonic actuator 1, FIG. 1B is a side view, and FIG. 1C is a view from the AA ′ direction in FIG. FIG.

  As shown in FIG. 1A, the ultrasonic actuator 1 includes a vibrating body 10, guide members 21, 22, a pressure member 30, and the like.

  The vibrating body 10 is disposed between two guide members 21 and 22 corresponding to a driven body in the present invention, and is guided by contact portions 105 and 106 provided at one end in the longitudinal vibration direction described later. The guide 21 is brought into contact with the member 21 and the contact portion 104 provided at the other end. The vibrating body 10 expands and contracts by a drive signal applied by a drive circuit (not shown), and the contact portions 105 and 106 and the contact portion 104 perform elliptical vibrations in opposite directions to each other. , And the guide members 21 and 22 that are in pressure contact with the contact portion 104, respectively, to perform relative movement by frictional force.

  As shown in FIG. 1A, the guide member 21 partially protrudes in the lateral direction, and is incorporated and fixed to the apparatus with the protrusions 21a and 21b as a reference. As the vibrating body 10 moves, the guide member 22 is slightly inclined. However, since the contact portion 104 is located between the contact portions 105 and 106 with respect to the moving direction, the guide member 21 is vibrated. The posture of the body 10 does not always change, and highly accurate position control and speed control can be performed.

  A pressure member 30 is coupled to the guide members 21 and 22 to bring the vibrating body 10 into pressure contact with the guide members 21 and 22. At both ends of the pressure member 30, spring constituent portions 30a are provided, and the vibrating body 10 is sandwiched with a predetermined amount of force by the elasticity of the spring constituent portions 30a.

  The pressurizing member 30 is made of a resin material such as PC (polycarbonate), POM (polyacetal), etc., and as shown in FIG. 22 unnecessary vibration is prevented.

  The guide members 21 and 22 may be excited by the vibration of the vibrating body 10 as an excitation force. When the natural vibration is excited in the guide members 21 and 22, the transmission efficiency of the elliptic vibration is greatly reduced due to the frequency and phase relationship between the elliptical vibration of the vibrating body 10 and the natural vibration of the guide members 21 and 22, and the thrust force is reduced. Problems such as reduction and abnormal noise occur.

  Since the pressure member 30 is coupled over substantially the entire length of the guide members 21 and 22 and is made of a resin material having a large vibration damping effect, when the natural vibration starts to be excited in the guide members 21 and 22, the pressure member 30. The natural vibration of the guide members 21 and 22 is attenuated and suppressed by converting vibration energy into heat at the coupling portion.

  The guide members 21 and 22 and the pressure member 30 are integrally formed by insert molding or the like, thereby ensuring adhesion and efficiently exhibiting a damping effect. Further, the guide members 21 and 22 and the pressure member 30 may be coupled with an adhesive such as epoxy.

  In addition, as shown in FIG. 1C, the pressing member 30 is provided with side walls 30 b and 30 c that regulate the vibration of the vibrating body 30 in the thickness direction.

  The guide members 21 and 22 are long parts having a circular or quadrangular cross-sectional shape, and a metal part such as stainless steel that is inexpensive and easy to manufacture is used as the material. The surface is subjected to surface hardening treatment such as quenching and nitriding treatment in order to prevent abrasion with the vibrating body 10. Ceramic coating such as CrN or TiCN may be performed. Moreover, wear resistance can be further improved by using ceramics, such as an alumina and a zirconia.

  Here, a method of connecting the vibrating body 10 and the lens block 60 when, for example, the lens block 60 is driven using the ultrasonic actuator 1 will be described with reference to FIG. FIG. 2 shows an example of a method of coupling the vibrating body 10 and the lens block 60, and is a plan sectional view as seen from the BB ′ direction in FIG.

  The lens block 60 moves along a guide member (not shown), and sandwiches the vicinity of the center in the vertical direction of the vibrating body 10 by the two leaf springs 50 fixed to the lens block 60. As the vibrating body 10 moves, a driving force is transmitted to the lens block 60 via the leaf spring 50. The strength of the leaf spring 50 is set to a strength that does not inhibit the vibration of the vibrating body 10. In order to prevent wear between the leaf spring 50 and the vibrating body 10, the leaf spring 50 and the vibrating body 10 may be fixed with a soft adhesive such as rubber.

  Next, the configuration of the vibrating body 10 according to the first embodiment will be described with reference to FIG. FIG. 3A is a front view showing the configuration of the vibrating body 10, and FIG. 3B is a side view.

  As shown in FIG. 3A, the vibrating body 10 includes a piezoelectric displacement portion 101, weight members 102 and 103, contact portions 104, 105, and 106.

  The piezoelectric displacement portion 101 is displaced by power supply from a drive circuit (not shown), and further resonates with the displacement as an excitation force to generate elliptical vibration. The weight members 102 and 103 are provided at both ends of the piezoelectric displacement portion 101, and expand the vibration amplitude at the later-described resonance. The contact portions 105 and 106 and the contact portion 104 are in contact with the above-described guide members 21 and 22, respectively, and transmit elliptical vibrations to the guide members 21 and 22 by a frictional force.

  Here, the structure of the piezoelectric displacement part 101 is demonstrated using FIG. FIG. 4 is a plan sectional view showing the internal electrode configuration of the piezoelectric displacement portion 101 and viewed from the CC ′ direction in FIG.

  The piezoelectric displacement portion 101 includes a rectangular piezoelectric ceramic thin plate (hereinafter also referred to as a piezoelectric thin plate) having piezoelectric characteristics such as PZT, internal electrodes a2 and b2 shown in FIG. 4A, and an internal electrode shown in FIG. a1 and b1 are alternately stacked. Further, the internal electrodes a2 and b2 and the internal electrodes a1 and b1 are divided into two on the left and right sides of the vibrating body 10.

  External electrodes A1 and B1 and external electrodes A2 and B2 are provided on the front surface and the back surface of the vibrating body 10, respectively, and are connected to the internal electrodes a1 and b1 and the internal electrodes a2 and b2 protruding from the end surfaces. Also, lead wires and FPC (flexible printed wiring board) (not shown) are connected to the external electrodes A1 and B1 and the external electrodes A2 and B2, and are connected to a drive circuit.

  The piezoelectric thin plate is polarized in the same direction through the external electrodes A1 and A2 and the external electrodes B1 and B2 in the internal electrode a1-a2 direction and the internal electrode b1-b2 direction.

  When a voltage of the same polarity (for example, A1 = B1 = 0V, A2 = B2 = 10V) is applied between the external electrodes A1-A2 and the external electrodes B1-B2, all the piezoelectric thin plates expand (or contract), and as a whole Stretch (or shrink). Further, when a voltage of opposite polarity (for example, A1 = B2 = 10V, A2 = B1 = 0V) is applied between A1 and A2 and between the external electrodes B1 and B2, the left half of the piezoelectric thin plate expands (or contracts), and the right Half is shrunk (or stretched), and bending deformation occurs in the piezoelectric portion as a whole.

  Returning to FIG. 3, the weight members 102 and 103 are fixed to both ends of the piezoelectric displacement portion 101 in the stacking direction by an adhesive having a relatively high elastic modulus such as epoxy. As will be described later, a material having a large specific gravity is effective as the material of the weight members 102 and 103. Therefore, tungsten (specific gravity ≈ 19), tungsten alloy using nickel, copper, iron or the like as a binder (specific gravity ≈ 18), Tungsten carbide cemented carbide (specific gravity ≈ 15), tungsten resin composite with tungsten powder and resin (specific gravity ≈ 10 to 13) or the like is used.

  The piezoelectric displacement portion 101 is manufactured by stacking in units of blocks sufficiently larger than the vibrating body 10 and then cutting out to the size of the vibrating body 10 with a dicer or the like. In addition, since the weight members 102 and 103 are also laminated and bonded at the same time in the laminating process, it is not necessary to perform the pasting work for each vibrating body, so that the manufacturing process can be greatly simplified and the cost can be reduced. it can.

  As the material of the contact portions 104, 105, 106, cemented carbide, ceramics such as alumina and zirconia are used in order to prevent wear. The contact portion 104 and the contact portions 105 and 106 are fixed to the weight members 103 and 102 using an adhesive having a relatively high elastic modulus such as epoxy, respectively.

  FIG. 5 shows an example in which a cemented carbide is used as the material for the weight members 102 and 103 and the contact portions 104, 105, and 106 to integrate them. 5A is a front view showing the configuration of the contact portion 104 and the vibrating body 10 in which the contact portions 105 and 106 and the weight members 103 and 102 are integrated, and FIG. 5B is a side view. is there.

  Since the cemented carbide has a high specific gravity (about 15) and a high hardness (Hv≈1500), a displacement expansion effect and a wear resistance effect can be obtained simultaneously. Furthermore, since the joining process of the contact part 104 and the contact parts 105 and 106 and the weight members 103 and 102 can be omitted, the manufacturing process can be simplified and the cost can be reduced.

  Here, the elliptical vibration excited by the vibrating body 10 having such a configuration will be described with reference to FIG. The vibrating body 10 is driven using resonance. 6A and 6B show a state of deformation of the vibrating body 10 due to the natural mode used for resonance driving. FIG. 6A shows the longitudinal (stretching) primary vibration mode, and FIG. 6B shows the bending primary vibration mode. is there.

  In the longitudinal primary vibration mode, as shown in FIG. 6A, stretching vibration is performed with the central portion P of the vibrating body 10 as a node, and the contact portions 104 to 106 are displaced in the longitudinal direction (Y direction). In the bending primary vibration mode, as shown in FIG. 6B, the first bending deformation is performed with the nodes P1 and P2 as nodes, and the tips of the contact portions 104 to 106 are in the lateral direction (X direction). It is displaced to.

  The longitudinal primary vibration mode can be excited by applying a drive signal having the same phase between the external electrodes A1 and A2 and between the external electrodes B1 and B2 at the resonance frequency. The bending primary vibration mode can be excited by applying a drive signal having an opposite phase between the external electrodes A1 and A2 and between the external electrodes B1 and B2 at the resonance frequency.

  By substantially matching these two modes and applying a drive signal having a phase difference of 90 degrees between the external electrodes A1 and A2 and between the external electrodes B1 and B2 at the resonance frequency, both modes are excited and the vibrating body Elliptical vibrations are generated at both ends of 10. When a drive signal having a phase advanced by 90 degrees with respect to the space between the external electrodes B1 and B2 is applied between the external electrodes A1 and A2, the end surfaces of the contact portions 104 are counterclockwise and end surfaces of the contact portions 105 and 106 Is excited by an elliptical vibration that rotates clockwise. When the phase of the drive signal to be applied is reversed (-90 degrees), the rotational direction of the elliptical vibration at each contact point is reversed.

  Next, the relationship between the specific gravity of the weight members 102 and 103 and the vibration amplitude of the contact portions 104 to 106 will be described with reference to FIG. FIG. 7 is a diagram illustrating the relationship between the specific gravity of the weight members 102 and 103 and the vibration amplitude of the tip of the contact portion 104 when the vibration body 10 is excited in the longitudinal primary vibration mode and the bending primary vibration mode, respectively. It is. The amplitude of the bending vibration of the abutting portions 105 and 106 is slightly different from that of the abutting portion 104, but the relationship between the specific gravity of the weight members 102 and 103 and the amplitude of the bending vibration of the abutting portions 105 and 106 is as follows. It shows the same tendency as.

  In FIG. 7, point a is when the specific gravity of the weight member 102 (103) and the piezoelectric displacement portion 101 is the same, that is, on one side of the longitudinal vibration node P of the vibrating body 10 in FIG. It shows the amplitude of longitudinal vibration and bending vibration when the center of gravity G1 (G2) is located at the center C1 (C2) of the total length (2 × L) in the longitudinal vibration direction of one side portion, and the weight member 102 ( As the specific gravity of 103) increases, the amplitude of both longitudinal vibration and bending vibration increases.

  When the specific gravity of the weight member 102 (103) increases, the mass in the vicinity of the tip of the vibrating body 10 increases, and the gravity center position G1 (G2) also has a contact portion 104 more than the center C1 (C2) position of one side portion of the vibrating body 10. Since it becomes closer to (105, 106), the longitudinal vibration is equivalent to the increase in the spring length and the mass of the mass in the above-described dynamic model of the spring and the mass, so that the amount of displacement increases. In bending vibration, the amount of displacement increases because the moment of inertia around the node P1 (P2) of bending vibration increases.

  On the other hand, by providing the weight member 102 (103), the ratio of the piezoelectric displacement portion 101 to the entire length of the vibrating body 10 is reduced by the amount of the weight member 102 (103), and there is a concern about a decrease in the amount of displacement. However, since the vibration expansion rate at the time of resonance increases, the displacement amount equal to or larger than that can be obtained as a result, and the resonance frequency is lowered, so that the drive circuit such as the oscillation circuit can be simplified. And cost can be reduced.

  Further, as described above, in order to make the resonance frequencies of both modes coincide with each other, it is usually performed by adjusting the vertical / horizontal dimension ratio of the vibrating body 10. Since it increases and the rigidity increases, the amplitude of flexural vibration decreases. Further, since the aspect ratio is determined almost uniquely, there is a problem that the degree of freedom in design is reduced.

  From the node P1 (P2) in the bending primary vibration mode, the tip side performs a rotation operation around the node P1 (P2). In the first embodiment, since the weight member 103 (102) is disposed near the tip, the moment of inertia around the node P1 (P2) is increased. Accordingly, the sensitivity to the resonance frequency of the bending primary vibration mode with respect to the shape change (change in the moment of inertia) near the tip is increased, and the width of the vibrating body 10 is made relatively narrow by adjusting the shape in a direction to reduce the moment of inertia. It is possible to design. An example is shown in FIG. By dropping both corners 103a (102a) of the weight member 103 (102) far from the node P1 (P2), the moment of inertia is lowered, the resonance frequency of the bending primary vibration mode is increased, and the longitudinal (stretching) primary The resonance frequency of the vibration mode is matched. As a result, the lateral width can be reduced. As a result, the rigidity in the bending direction is lowered, and the amount of displacement is also increased.

  In addition, if the deviation of the resonance frequency of both modes becomes large due to a dimensional error at the time of manufacturing the vibrating body 10 or the like, the driving performance is deteriorated. In the first embodiment, the resonance frequency can be adjusted by additionally processing the weight member 102 (103). After the assembly is completed, the resonance frequency of both modes is measured by an inspection process, and the resonance frequency can be adjusted by removing a part of the weight member 102 (103) with a laser or the like according to the error amount. Variation can be suppressed.

  As described above, in the ultrasonic actuator 1 according to the first embodiment of the present invention, the center of gravity G1 (G2) of the one side portion in the longitudinal vibration direction at the node P of the longitudinal vibration in the vibrating body 10 is used as the longitudinal vibration of the one side portion. It was made to be located closer to the contact part 104 (contact part 105, 106) than the center C1 (C2) position of the total length (2 × L) in the direction. That is, since the center of gravity G1 (G2) of one side portion of the vibrating body 10 is closer to the contact portion 104 (105, 106) that contacts the driven body (guide members 22, 21), the longitudinal vibration is caused by the above-described spring. In the dynamic model of the weight, the amount of displacement is large because it is equivalent to an increase in the spring length and weight mass. Also in the bending vibration, the amount of displacement increases because the moment of inertia around the node P1 (P2) of the bending vibration increases. Thereby, since the amplitudes of both longitudinal vibration and bending vibration can be increased, high output and high driving efficiency can be stably obtained.

(Modification 1 of Embodiment 1)
A configuration of the vibrating body 10 according to Modification 1 will be described with reference to FIGS. 9 and 10. FIG. 9A is a front view showing the configuration of the vibrating body 10, and FIG. 9B is a side view. FIG. 10 shows the internal electrode configuration of the piezoelectric displacement portion 101, and is a front cross-sectional view seen from the DD ′ direction in FIG. 9B.

  As in the case of the first embodiment, the piezoelectric displacement portion 101 according to the modified example 1 has the piezoelectric thin film laminated thereon, but the lamination direction is different, and as shown in FIG. They are stacked in the direction. The internal electrodes a1 and b1 and the internal electrodes a2 and b2 have the configurations shown in FIGS. 10A and 10B, respectively, and are divided into two on the left and right sides of the vibrating body 10 as in the first embodiment. Has been. The external electrodes A1 and A2 and the external electrodes B1 and B2 are provided on the left and right side surfaces of the vibrating body 10, respectively.

  In the piezoelectric displacement portion 101 having such a configuration, the displacement extraction direction (longitudinal vibration direction) is 31 directions (direction perpendicular to the stacking direction). Compared to the case where the displacement is taken out in the 33 direction (stacking direction) as in Embodiment 1 described with reference to FIG. 3, the amount of displacement is reduced, but the number of stacks can be reduced, so productivity is reduced. Can be increased. In addition, since the piezoelectric element is weak against the pulling force in the stacking direction, the strength is increased as compared with the configuration in the first embodiment.

(Modification 2 of Embodiment 1)
The structure of the vibrating body 10 by the modification 2 is demonstrated using FIG. 10A is a front view showing the configuration of the vibrating body 10, FIG. 10B is a side view, and FIG. 10C is a rear view.

  The piezoelectric displacement part 101 according to the modification 2 is formed of a single-phase (bulk) piezoelectric body, and electrodes are provided on the front surface and the back surface of the vibrating body 10 respectively. As shown in FIGS. 10A to 10C, the electrodes on the front side of the vibrating body 10 are divided into two electrodes A and B on the left and right sides of the vibrating body 10 in the same manner as in the first embodiment. The electrode on the back surface may be a common electrode G (GND) without being divided. In this case, the drive voltage becomes high, but the structure is very simple, so that productivity can be improved and cost can be reduced.

[Embodiment 2]
Next, the configuration of the vibrator 10 according to the second embodiment will be described with reference to FIG. 12A is a front view showing the configuration of the vibrating body 10, and FIG. 12B is a side view.

  As shown in FIG. 12A, the piezoelectric displacement portion according to the second embodiment is composed of a piezoelectric displacement portion 111 and a piezoelectric displacement portion 112 that are separated into two on the left and right, and two rectangular parallelepiped laminated piezoelectric elements. Are arranged in parallel.

  The laminated piezoelectric element has substantially the same material and configuration as in the first embodiment, but the internal electrodes are not divided in each plane, and are so-called general laminated piezoelectric elements. Moreover, you may use the roll-type piezoelectric element currently disclosed by Unexamined-Japanese-Patent No. 2002-185055 for the piezoelectric displacement parts 111 and 112. FIG.

  The weight members 103 and 102 in which the contact portion 104 and the contact portions 105 and 106 are integrated respectively connect both ends of the two piezoelectric displacement portions 111 and 112. For bonding to the piezoelectric displacement portions 111 and 112, a relatively high elastic adhesive such as epoxy is used. Other configurations are the same as in the case of the first embodiment, and the generation principle of elliptical vibration is also the same. Therefore, the state of deformation of the vibrating body 10 by the eigenmode used for resonance driving is shown in FIG. To do. Here, FIG. 13A shows the longitudinal (stretching) primary vibration mode, and FIG. 13B shows the bending primary vibration mode.

[Embodiment 3]
Next, the configuration of the vibrating body 10 according to the third embodiment will be described with reference to FIG. FIG. 14 is a front view illustrating the configuration of the vibrating body 10.

  As in the case of the second embodiment, the piezoelectric displacement portion according to the third embodiment includes a piezoelectric displacement portion 111 and a piezoelectric displacement portion 112 that are separated into left and right as shown in FIG. The stacked piezoelectric elements having a shape are arranged in parallel, but the masses of the weight member 102 (hereinafter referred to as weight member B) and the weight member 103 (hereinafter referred to as weight member B) are different. Other configurations and operation principles are the same as those in the second embodiment. Note that the mass configuration of the weight member B and the weight member A according to the third embodiment can also be used in the case of the first embodiment.

  By making the mass Wb of the weight member B larger than the mass Wa of the weight member A, the vibration becomes asymmetric, the displacement amount of the weight member B decreases, and the displacement amount of the weight member A increases. FIG. 15 shows a state of deformation of the longitudinal vibration of the vibrating body 10. The vibration node is at the position indicated by P in FIG. FIG. 16 shows changes in the longitudinal vibration amplitude of the weight member A and the weight member B with respect to the mass ratio Wa / Wb of the weight member A and the weight member B.

  When the mass ratio Wa / Wb changes, the position of the node P of the longitudinal vibration shown in FIG. 15 changes, but the position of the node P can be obtained by simulation.

  In FIG. 16, the point of mass ratio 1 vibrates symmetrically as in the first and second embodiments, the amplitude on the weight member A side increases as the mass ratio decreases, and the mass ratio is around 0.25. Maximum. On the other hand, on the weight member B side, the amplitude decreases as the mass ratio decreases. Therefore, by setting the mass ratio Wa / Wb between the weight member A and the weight member B to 0.1 or more and less than 1, the amplitude on the weight member A side is increased as compared with the case of oscillating symmetrically. By setting it to about 25, the largest displacement amount and amplitude can be obtained.

  The vibrating body 10 having such a configuration is suitable for the case where driving is performed by bringing only the weight member A side into contact with the driven body. Elliptical vibration is enlarged, and output and efficiency can be improved.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be changed or improved as appropriate.

  For example, in the first to third embodiments described above, the vibrating body that performs the longitudinal primary vibration and the bending primary vibration is shown as an example. However, the longitudinal primary vibration and the bending secondary as disclosed in Patent Document 1 are illustrated. Even if a vibrating body that vibrates is used, the same effect can be obtained.

  In the above-described first to third embodiments, a driving method in which elliptical vibration is excited by applying a two-phase driving signal has been described, but the resonance frequency of the two modes is shifted by a predetermined value, A single-phase driving method that generates an elliptical vibration by applying a driving signal only to one piezoelectric displacement portion may be used. Even in the single-phase driving method, the same effect can be obtained because the vibration synthesis of each mode remains the same.

1 is an overall configuration diagram of an ultrasonic actuator according to Embodiment 1 of the present invention. 6 is a diagram illustrating an example of a method for coupling a vibrating body and a lens block according to Embodiment 1. FIG. 5 is a diagram illustrating a configuration of a vibrating body according to Embodiment 1. FIG. FIG. 3 is a diagram illustrating an internal electrode configuration of a piezoelectric displacement unit according to Embodiment 1. It is the figure which made the weight member and contact part by Embodiment 1 integrated. FIG. 6 is a diagram illustrating a state of deformation in the natural mode of the vibrator according to the first embodiment. It is a figure which shows the relationship between the specific gravity of the weight member by Embodiment 1, and a vibration amplitude. FIG. 6 is a diagram showing a shape of a weight member according to another example of the first embodiment. 6 is a diagram illustrating a configuration of a vibrating body according to another example of Embodiment 1. FIG. 6 is a diagram illustrating an internal electrode configuration of a displacement portion according to another example of Embodiment 1. FIG. 6 is a diagram illustrating a configuration of a vibrating body according to another example of Embodiment 1. FIG. 6 is a diagram illustrating a configuration of a vibrating body according to Embodiment 2. FIG. FIG. 10 is a diagram illustrating a state of deformation in the natural mode of the vibrator according to the second embodiment. 6 is a diagram illustrating a configuration of a vibrating body according to Embodiment 3. FIG. FIG. 10 is a diagram illustrating a state of deformation in an eigenmode of a vibrating body according to a third embodiment. It is a figure which shows the relationship between the mass ratio of the weight member by Embodiment 3, and a vibration amplitude. It is a schematic diagram which shows the mode of the drive by elliptical vibration.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic actuator 10 Vibrating body 101,111,112 Piezoelectric displacement part 102,103 Weight member 104,105,106 Contact part 21,22 Guide member 30 Pressure member 50 Leaf spring 60 Lens block A1, A2, B1, B2 , G External electrode a1, a2, b1, b2 Internal electrode

Claims (7)

A piezoelectric displacement part that expands and contracts by an electrical signal;
A vibrating body comprising: an abutting portion that generates an elliptical motion by resonantly exciting longitudinal vibration and bending vibration by displacement of the piezoelectric displacement portion;
In an ultrasonic actuator having a driven body that is in pressure contact with the abutting portion and causes relative movement with respect to the vibrating body,
The center of gravity of one side portion in the longitudinal vibration direction with the node position of the longitudinal vibration in the vibrating body as a boundary is located closer to the contact portion than the center position of the full length of the one side portion in the longitudinal vibration direction. Ultrasonic actuator. The ultrasonic actuator according to claim 1, wherein the piezoelectric displacement portion has weight members having a specific gravity greater than that of the piezoelectric displacement portion at both ends in the longitudinal vibration direction. 3. The ultrasonic actuator according to claim 2, wherein the material of the weight member is any one of tungsten, a tungsten alloy, a tungsten resin obtained by combining tungsten powder and a resin, or a tungsten carbide cemented carbide. The material of the weight member is a tungsten carbide cemented carbide,
The ultrasonic actuator according to claim 2, wherein the weight member and the contact portion are integrally formed. 5. The ultrasonic actuator according to claim 1, wherein the piezoelectric displacement portion has a laminated structure, and a metal layer is laminated on at least one end portion in a longitudinal vibration direction. 6. . 6. The vibration mode used for resonance of the piezoelectric displacement portion is a longitudinal primary vibration mode and a bending primary vibration mode, or a longitudinal primary vibration mode and a bending secondary vibration mode. The ultrasonic actuator of Claim 1. The piezoelectric displacement portion has a weight member A provided with the contact portion at one end in the longitudinal vibration direction, and a weight member B at the other end,
7. The weight of the weight member A is Wa and the weight of the weight member B is Wb, and Wa / Wb satisfies the following condition (Formula 1). 2. The ultrasonic actuator according to item 1.
0.1 ≦ Wa / Wb <1 (Formula 1)

Images