An ultrasonic actuator includes an actuator body; and driver elements for outputting drive force, which are provided to the actuator body. The ultrasonic actuator further includes a holder which is provided to the actuator body, and which protrudes outwardly beyond principal surfaces in a direction crossing the principal surfaces of the actuator body; two supports for supporting the holder; contact rubber blocks limiting displacement of the actuator body by contacting the principal surfaces of the actuator body. The actuator body is biased toward a movable body side. A long hole extending in a biasing direction of the actuator body and into which the holder is fitted is formed in the support. At least two contact rubber blocks contact the principal surfaces of the actuator body at different positions in a longitudinal direction of the actuator body.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2009-174217 filed on Jul. 27, 2009, and the disclosure of which including the specification, the drawings, and the claims is hereby incorporated by reference in its entirety.

BACKGROUND

The present disclosure relates to a vibratory actuator including an actuator body generating stretching and bending vibrations.

In recent years, as the vibratory actuator of this type, there is a vibratory actuator disclosed in, e.g., Japanese Patent Publication No. H11-346486. The vibratory actuator includes an actuator body generating stretching and bending vibrations. Driver elements orbiting in response to the stretching and bending vibrations of the actuator body are attached to the actuator body. The vibratory actuator is arranged so that the driver elements contact a relatively-movable member. The stretching and bending vibrations are generated in the actuator body in such a state to provide the orbit motion of the driver elements, thereby relatively moving one of the relatively-movable member and the vibratory actuator with respect to the remaining one of the relatively-movable member and the vibratory actuator. In such a state, in order to increase friction force between the driver elements and the relatively-movable member, the actuator body is biased toward the relatively-movable member.

A support configuration of the actuator body will be described in more detail below. Protrusions extending in a thickness direction of the actuator body are provided in the actuator body. The protrusions are supported by supports. Specifically, a long hole extending in a biasing direction of the actuator body is formed in the support. The protrusion is fitted into the long hole of the support, and is slidable along an edge of the long hole. That is, the actuator body is supported by the supports so as to be slidable in the biasing direction.

SUMMARY

However, in the configuration in which the actuator body is supported with a certain degree of freedom, there is a possibility that noise is generated when vibrating the actuator body. For example, there is a minute clearance between the long hole of the support and the protrusion of the actuator body, which allows the slide of the protrusion. Thus, when vibrating the actuator body, the protrusion may hit a wall surface of the long hole to generate noise. Further, when vibrating the actuator body, the actuator body may hit members arranged therearound (e.g., a case in which the actuator body is accommodated and the supports) to generate noise.

The present disclosure has been made in view of the foregoing, and it is an object of the present disclosure to reduce noise when operating the vibratory actuator.

In a vibratory actuator which is movable relative to a relatively-movable member, the vibratory actuator includes an actuator body having a pair of principal surfaces facing each other, and generating stretching vibration in a longitudinal direction of the principal surface and bending vibration in a lateral direction of the principal surface; driver elements provided to the actuator body, and outputting drive force by generating orbit motion in response to the vibrations of the actuator body; protrusions provided to the actuator body, and protruding outwardly beyond the principal surfaces in a direction crossing the principal surfaces; two supports for supporting the protrusions; and contact bodies contacting one of the principal surfaces of the actuator body, and limiting displacement of the actuator body in the direction crossing the principal surfaces. The actuator body is biased toward the relatively-movable member. A long hole extending in a biasing direction of the actuator body and into which the protrusion is fitted is formed in the support. At least two contact bodies contact the principal surface of the actuator body at different positions in the longitudinal direction.

According to the vibratory actuator, the noise when operating the ultrasonic actuator can be reduced.

DETAILED DESCRIPTION

Examples of embodiments of the present disclosure will be described in detail hereinafter with reference to the drawings.

FIG. 1is a perspective view of an ultrasonic actuator of an embodiment of the present disclosure;FIG. 2is an exploded perspective view of the ultrasonic actuator; andFIG. 3is a perspective view of a drive unit in which the ultrasonic actuator is installed. A drive unit1includes an ultrasonic actuator2for outputting drive force by vibration; a movable body11which can move along a guide12; and a control unit (not shown in the figure) for driving and controlling the ultrasonic actuator2. The drive unit1is for driving the movable body11by the ultrasonic actuator2. The ultrasonic actuator2serves as a vibratory actuator, and the movable body11serves as a relatively-movable member.

The movable body11is slidably attached to the guide12fixed on a base (not shown in the figure) which is a fixed body. This allows the movable body11to move along a direction in which the guide12extends. The direction in which the guide12extends is a movable direction of the movable body11. A slide plate11amade of alumina is bonded to a bottom surface of the movable body11. Material of the slide plate11ais not limited to alumina, and the slide plate11amay be formed by using any material. The ultrasonic actuator2is arranged on the base so that driver elements3(described later) contact the slide plate11abonded to the movable body11.

The ultrasonic actuator2outputs the drive force to the movable body11in order to relatively move the movable body11with respect to the ultrasonic actuator2. The ultrasonic actuator2includes an actuator body4generating vibration, the driver elements3attached to the actuator body4to transmit the drive force of the actuator body4to the movable body11; a holder5for holding the actuator body4; supports6for supporting the holder5; and a plate spring7for biasing the actuator body4toward the movable body11.

The actuator body4includes piezoelectric elements. As illustrated inFIG. 2, the actuator body4is substantially in the form of a rectangular parallelepiped, and has a pair of substantially rectangular principal surfaces40aand40bfacing each other; a pair of long-side surfaces40cand40dfacing each other and extending in a longitudinal direction of the principal surfaces40aand40bso as to be orthogonal to the principal surfaces40aand40b; and a pair of short-side surfaces40eand40ffacing each other and extending in a lateral direction of the principal surfaces40aand40bso as to be orthogonal to both of the principal surfaces40aand40band the long-side surfaces40cand40d.

FIG. 4is an exploded perspective view of the actuator body4. As illustrated inFIG. 4, the actuator body4is provided by alternately stacking piezoelectric layers (piezoelectric elements)41and internal electrode layers42,44,43and44. The internal electrode layers42,44,43and44are a first power-feeding electrode layer42, a common electrode layer44, a second power-feeding electrode layer43, and a common electrode layer44, which are alternately stacked in this order with the piezoelectric layers41being interposed therebetween. The first power-feeding electrode layer42, the common electrode layer44, the second power-feeding electrode layer43, and the common electrode layer44are grouped as a single set, and a plurality of sets, each of which includes the internal electrode layers42,44,43, and44, are repeatedly stacked with the piezoelectric layers41being interposed therebetween. Note that the piezoelectric layers41are positioned at both ends of the actuator body4in the stacking direction. Each of the first power-feeding electrode layer42, the second power-feeding electrode layer43, and the common electrode layers44is printed on a principal surface of each of the piezoelectric layers41.

Each of the piezoelectric layers41is an insulating layer made of ceramic such as lead zirconate titanate. As in the actuator body4, the piezoelectric layer41is substantially in the form of a rectangular parallelepiped, and has a pair of principal surfaces; a pair of long-side surfaces; and a pair of short-side surfaces. Each of the long-side surfaces of the piezoelectric layer41is provided with first and second external electrodes46and47in both end portions in the longitudinal direction, and two common external electrodes48are formed on an inner side in the longitudinal direction with respect to the first and second external electrodes46and47. That is, in each of the long-side surfaces of the piezoelectric layer41, the first external electrode46, the two common external electrodes48, and the second external electrode47are arranged so as to be apart from each other in the longitudinal direction in this order.

Each of the common electrode layers44is substantially rectangular, and covers almost all the principal surface area of the piezoelectric layer41. Lead electrodes44aare formed so as to extend from long-side sections of the common electrode layer44to the common external electrodes48formed in the long-side surfaces of the piezoelectric layer41.

As illustrated inFIG. 5, the principal surface of the piezoelectric layer41is divided into quadrants, i.e., two areas in the longitudinal direction and two areas in the lateral direction. The first power-feeding electrode layer42includes a pair of first electrodes42aand42brespectively formed on one of pairs of diagonally-aligned areas of the principal surface, and the second power-feeding electrode layer43includes a pair of second electrodes43aand43bformed on the other pair of diagonally-aligned areas. The first electrodes42aand42band the second electrodes43aand43bface the common electrode layer44with the piezoelectric layer41being interposed therebetween. Lead electrodes42dare formed so as to extend from the first electrodes42aand42bto the first external electrodes46formed in adjacent portions of the long-side surfaces of the piezoelectric layer41. Lead electrodes43dare formed so as to extend from the second electrodes43aand43bto the second external electrodes47formed in adjacent portions of the long-side surfaces of the piezoelectric layer41. In the first power-feeding electrode layer42, the first electrodes42aand42bare placed in conduction through a first conduction electrode42c. In addition, in the second power-feeding electrode layer43, the second electrodes43aand43bare placed in conduction through a second conduction electrode43c.

In each of the long-side surfaces40cand40dof the actuator body4provided by alternately stacking the piezoelectric layers41and the internal electrode layers42,44,43and44, the common external electrodes48of the piezoelectric layers41are aligned in the stacking direction to function as a single external electrode. The lead electrodes44aformed in the common electrode layers44are electrically connected to the common external electrodes48. The common electrode layers44provided in the different piezoelectric layers41are placed in conduction through the common external electrodes48.

In the similar manner, in each of the long-side surfaces40cand40dof the actuator body4, the first external electrodes46of the piezoelectric layers41are aligned in the stacking direction to function as a single external electrode, and the second external electrodes47of the piezoelectric layers41are aligned in the stacking direction to function as a single external electrode. The lead electrodes42dextending from the first electrodes42aand42bare electrically connected to the first external electrodes46. In addition, the lead electrodes43dextending from the second electrodes43aand43bare electrically connected to the second external electrodes47. In this manner, the first electrodes42aand42b, and the first electrodes42aand42bprovided in the different piezoelectric layers41are placed in conduction through the first conduction electrode42cand the first external electrodes46. In addition, the second electrodes43aand43b, and the second electrodes43aand43bprovided in the different piezoelectric layers41are placed in conduction through the second conduction electrode43cand the second external electrodes47. Signal lines from the control unit are connected to the external electrodes46,47, and48. Power is fed to the actuator body4through the external electrodes46,47, and48.

Two driver elements3are attached to a long-side surface (i.e., one of a pair of surfaces facing each other along a direction of bending vibration (described later), which is hereinafter referred to as an “installation surface”)40cof the actuator body4.

The driver elements3are cylindrical members, and are made of, e.g., zirconia, alumina, silicon nitride, silicon carbide, and tungsten carbide. The driver elements3are arranged so that an axial direction thereof is along a thickness direction of the actuator body4. The driver elements3are attached to the installation surface40cwith adhesive so as to be in linear contact with the installation surface40c. The adhesive is preferably softer than the material of the actuator body4and the material of the driver elements3. Specifically, the adhesive includes, in particular, synthetic resin such as epoxy resin and silicone resin. Such material is used to possibly reduce interference with vibration (described later) of the actuator body4, thereby ensuring fixing between the driver elements3and the installation surface40c.

The driver elements3are attached to the installation surface40cat a distance of 30-35% of the length of the installation surface40cinwardly from both ends of the actuator body4in the longitudinal direction, i.e., at positions corresponding to antinodes of second-order bending vibration (described later) of the actuator body4, where the maximum vibration occurs.

In the actuator body4configured as described above, the common external electrodes48are connected to ground to apply AC voltages having predetermined frequencies to the first and second external electrodes46and47with their phases being offset by 90°, thereby applying the AC voltages which are 90° out of phase with each other, to the pair of first electrodes42aand42band the other pair of second electrodes43aand43b, which are positioned on the diagonal lines of the principal surface of the piezoelectric layer41. Consequently, stretching vibration in the longitudinal direction of the actuator body4(i.e., a so-called “longitudinal” vibration) and bending vibration in the lateral direction (i.e., a so-called “lateral” vibration) are induced.

Resonance frequencies of the stretching and bending vibrations are determined by the actuator body4, i.e., the material, shape, etc. of the actuator body4. The resonance frequencies are also varied depending on force supporting the actuator body4and positions at which the actuator body4is supported. Considering the above-described conditions, the resonance frequencies are adjusted so as to be substantially equal to each other, and AC voltages having a frequency around the adjusted resonance frequency are applied to the first and second external electrodes46and47with their phases being offset by 90°. For example, if the shape etc. of the actuator body4is designed such that the first-order stretching vibration (seeFIG. 5) and the second-order bending vibration (seeFIG. 6) have the same resonance frequency, and AC voltages having a frequency around the resonance frequency are applied with their phases being offset by 90° as described above, the first-order stretching vibration and the second-order bending vibration occur in harmony in the actuator body4. Thus, the shape of the actuator body4is varied in the order illustrated inFIGS. 8(A),8(B),8(C), and8(D).

Consequently, the driver elements3attached to the actuator body4provide substantially elliptical motion, i.e., orbit motion, on a plane parallel to the principal surface of the actuator body4(a plane parallel to the plane of the page ofFIG. 7), i.e., a plane containing the longitudinal and lateral directions (in other words, a plane containing directions of the stretching and bending vibrations).

The actuator body4configured as described above has a plurality of antinodes of vibration. The term “antinodes of vibration” refers to points where the maximum vibration displacement occurs. In the present embodiment, there are two antinodes of the longitudinal vibration positioned at the short-side surfaces of the actuator body4. In addition, there are eight antinodes of the bending vibration including four antinodes at end portions of the long-side surface40cof the actuator body4, and at end portions of the long-side surface40d; and four antinodes at a distance of 30-40% of the longitudinal length of the actuator body4inwardly from the end portions of the long-side surface40c, and from the end portions of the long-side surface40d. That is, in the ultrasonic actuator2, there are ten antinodes of vibration including the antinodes of the stretching and bending vibrations. The driver elements3are attached to the installation surface40cwhich is one of the long-side surfaces, at the points corresponding to the antinodes, i.e., at a distance of 30-35% of the length of the installation surface40cinwardly from the both end portions in the longitudinal direction.

The holder5is made of polycarbonate (containing glass fibers). As illustrated inFIG. 2, the holder5is attached to the long-side surface40dof the actuator body4, to which the driver elements3are not attached. Specifically, at a center portion of the long-side surface40dof the actuator body4in the longitudinal direction, the holder5is attached so as to sandwich the actuator body4in the thickness direction of the actuator body4. The center portion of the long-side surface40dof the actuator body4in the longitudinal direction is a portion corresponding to a node of the longitudinal vibration of the actuator body4. In addition, the holder5protrudes outwardly beyond the principal surfaces of the actuator body4, i.e., from two parallel plans including the principal surfaces, in the thickness direction of the actuator body4. The holder5serves as protrusions.

The support6includes a support body60formed in a plate-like shape; and a guide member63provided to the support body60. The supports6support the actuator body4through the holder5. The support body60is attached to a base member14fixed to the base. Specifically, the support body60is made of, e.g., stainless or general steel. Two through-holes61are formed through the support body60in the thickness direction of the support body60. The support body60is attached to the base member14with screws16inserted into the through-holes61.

In addition, at the center of the support body60, an opening62is formed through the support body60in the thickness direction of the support body60. The guide member63for supporting the holder5is provided to the opening62. The guide member63is bonded to the support body60. A long hole64extending in a direction in which the actuator body4is biased toward the movable body11(i.e., the lateral direction of the actuator body4) is formed through the guide member63. The end portion of the holder5, which protrudes in the thickness direction of the actuator body4, is inserted into the long hole64. The end portion of the holder5is slidable inside the long hole64in the extending direction of the long hole64. The guide member63is made of material having lower elasticity modulus or lower hardness than that of the support body60. In addition, the guide member63is made of material which is softer than the holder5, and which has excellent sliding properties on resin. The guide member63is made of, e.g., polyacetal. Depending on the length of the protrusion of the holder5, the long hole64may not penetrate the guide member63, and may be formed in a shape with a bottom.

Further, in a surface of the support body60, which faces the actuator body4, an arrangement hole65is formed, in which three contact rubber blocks66a,66b, and66care arranged. The arrangement hole65is formed in a shape with a bottom, and extends in the longitudinal direction of the actuator body4. In the support body60, the arrangement hole65is formed on the opposite side of the through-holes61with respect to the opening62. The contact rubber blocks66are made of silicone rubber. At approximately the center of the principal surface40a(40b) of the actuator body4to be supported by the supports6in the lateral direction, the contact rubber blocks66a,66b, and66care arranged in approximately the longitudinal direction. The first and third contact rubber blocks66aand66care arranged at a distance of approximately 13% of the longitudinal length inwardly from the both ends of the actuator body4in the longitudinal direction. The second contact rubber block66bis arranged at approximately the center in the longitudinal direction of the actuator body4. The points at a distance of approximately 13% of the length inwardly from the both ends of the actuator body4in the longitudinal direction, and the point at the center in the longitudinal direction correspond to the nodes of the second-order bending vibration of the actuator body4. In addition, the point at the center of the actuator body4in the longitudinal direction corresponds to the node of the first-order stretching vibration of the actuator body4. The arrangement hole65may not be a long hole. That is, the number of the arrangement hole(s)65can be selected based on the number of the contact rubber block(s)66, and may be a hole having a size which allows the contact rubber blocks66to fit into the arrangement hole65.

The contact rubber blocks66a,66b, and66ccontact the principal surfaces40aand40bof the actuator body4with the supports6supporting the actuator body4. The contact rubber blocks66a,66b, and66chave a function to restrict displacement of the actuator body4in a direction crossing the principal surfaces40aand40b.

The plate spring7is provided so as to face the long-side surface40dof the actuator body4, to which the holder5is attached. Specifically, the plate spring7is provided between the long-side surface40dof the actuator body4, to which the holder5is attached, and the base member14. At both end portions of the plate spring7in the longitudinal direction, openings71are formed, into which the tips of screws15inserted into the base member14are fitted. Specifically, screw holes are formed through the base member14in a direction parallel to the lateral direction of the actuator body4, and the screws15are inserted into the screw holes. The tips of the screws15protrude to the actuator body4side with respect to the base member14. The tips of the screws15are fitted into the openings71of the plate spring7. The plate spring7configured as described above contacts the holder5attached to the actuator body4. That is, the screws15of the base member14protrude to the actuator body4side, thereby allowing the plate spring7to push the actuator body4toward the movable body11side through the holder5.

Next, assembly of the ultrasonic actuator2will be described.

First, the holder5is bonded to the center portion of the long-side surface40dof the actuator body4in the longitudinal direction, to which the driver elements3are not attached. In addition, the guide member63is bonded to the support body60. Further, the contact rubber blocks66a,66b, and66care bonded to the arrangement hole65of the support body60. Note that the contact rubber blocks66a,66b, and66care not necessarily bonded to the arrangement hole65, but may be merely fitted into the arrangement hole65.

Next, one of the supports6is attached to the base member14with the screws16. Subsequently, by using jigs etc., the actuator body4is arranged at a predetermined distance from the base member14, and one of the end portions of the holder5is inserted into the long hole64of the support6attached to the base member14. Further, the long hole64of the other support6is fitted to the other end portion of the holder5, and the other support6is attached to the base member14with screws16. In such a state, the contact rubber blocks66a,66b, and66care sandwiched between each of the principal surfaces40aand40bof the actuator body4and each of the supports6to be compressed and deformed. For example, the contact rubber blocks66a,66b, and66care compressed by approximately 20%. Such an amount of compression corresponds an amount of deformation at which compression capability is ensured even when silicone rubber is plastically deformed under various environments. As described above, the other support6is attached to the base member14with the actuator body4being positioned with jigs etc., thereby precisely locating positions where the contact rubber blocks66a,66b, and66ccontact the actuator body4.

Subsequently, the plate spring7is arranged between the actuator body4and the base member14. The screws15are twisted into the screw holes of the base member14, and the tips of the screws15are fitted into the openings71of the plate spring7. By adjusting the length of the protrusions of the screws15from the base member14, the plate spring7comes into contact with the holder5.

The signal lines extending from the control unit are connected to the external electrodes46,47, and48of the ultrasonic actuator2.

In the ultrasonic actuator2assembled as described above, the base member14is attached to the base with the driver elements3contacting the slide plate11aof the movable body11. Subsequently, the screws15are adjusted to push the holder5with the plate spring7, thereby biasing the actuator body4toward the movable body11. Consequently, the driver elements3are pressed against the movable body11.

The assembly sequence of the ultrasonic actuator2, which has been described above, is an example. As long as the ultrasonic actuator2can be assembled, the order of the assembly sequence may be changed. For example, the base member14may be attached to the base before the assembly of the ultrasonic actuator2. In such a case, when the assembly of the ultrasonic actuator2is completed, the driver elements3contact the movable body11.

An operation of the ultrasonic actuator2will be described hereinafter with reference toFIG. 9.

When receiving an operation command from an external unit, the control unit applies AC voltages having frequencies corresponding to the operation command, to the first and second external electrodes46and47so as to have a phase difference corresponding to the operation command. In this manner, the control unit harmonically generates the stretching and bending vibrations in the actuator body4to cause the driver elements3to orbit as illustrated inFIGS. 8A-8D, thereby moving the movable body11. More specifically, the control unit applies AC voltages having frequencies slightly higher than a common resonance frequency for the stretching and bending vibrations of the actuator body4, to the first and second external electrodes46and47in order to reduce or prevent abnormal heat generation in the actuator body4. In such a state, the AC voltages are applied to the first and second external electrodes46and47with their phases being offset by 90°.

When generating composite vibration of the stretching and bending vibrations by the actuator body4, the driver elements3provide the substantially elliptical motion in the plane containing the longitudinal and lateral directions of the actuator body4. Thus, while the driver elements3periodically repeat an increase/decrease in friction force between the driver elements3and a contact surface of the movable body11, the drive force of the actuator body4in the longitudinal direction is provided to the movable body11through the friction force, thereby moving the movable body11along the guide12. The longitudinal direction of the actuator body4(direction coincident with the direction in which the guide12extends) is equivalent to a drive direction in which the driver elements3output the drive force.

More specifically, when expanding the actuator body4in the stretching direction (direction of the longitudinal vibration), one of the driver elements3(e.g., the driver element3on the left side as viewed inFIG. 9) is displaced while increasing the friction force between the driver element3and the movable body11as compared to the friction force before the driving of the ultrasonic actuator2(i.e., the friction force in a state in which the driver elements3simply contact the movable body11) as illustrated inFIG. 9(B). Thus, such friction force moves the movable body11toward a side to which the one of the driver elements3is displaced in the longitudinal direction (the left side as viewed inFIG. 9). In such a state, the other driver element3(the driver element3on the right side as viewed inFIG. 9) is oppositely displaced from the former driver element3in the longitudinal direction. However, such a driver element3is displaced apart from the movable body11, or is displaced while decreasing the friction force between the driver element3and the movable body11as compared to the friction force before the driving of the ultrasonic actuator2. Thus, the latter driver element3has little effect on the movement of the movable body11.

On the other hand, when contracting the actuator body4in the longitudinal direction, the latter driver element3(the driver element3on the right side as viewed inFIG. 9) is displaced while increasing the friction force between the driver element3and the movable body11as compared to the friction force before the driving of the ultrasonic actuator2(i.e., the friction force in the state in which the driver elements3simply contact the movable body11) as illustrated inFIG. 9(C). Thus, such friction force moves the movable body11toward a side to which the latter driver element3is displaced in the longitudinal direction (the left side as viewed inFIG. 9). Such a movement direction is the same as the above-described movement direction of the movable body11by the latter driver element3when expanding the actuator body4. In such a state, the former driver element3(the driver element3on the left side as viewed inFIG. 9) is oppositely displaced from the latter driver element3in the longitudinal direction. However, such a driver element3is displaced apart from the movable body11, or is displaced while decreasing the friction force between the driver element3and the movable body11as compared to the friction force before the driving of the ultrasonic actuator2. Thus, the former driver element3has little effect on the movement of the movable body11.

InFIG. 9, the driver element3having no effect on the movement of the movable body11is apart from the movable body11, but is not necessarily apart from the movable body11. That is, the driver element3may contact the movable body11with the friction force which does not allow the movement of the movable body11.

As described above, the driver elements3alternately move the movable body11in a predetermined direction with their phases being offset by 180°. The AC voltages are applied to the first and second external electrodes46and47with their phases being offset by −90° to reverse the direction of the drive force output from the driver elements3, thereby allowing the movable body11to move in the other direction.

In the ultrasonic actuator2, when vibrating the actuator body4to output the drive force, vibration swinging the actuator body4about an axis extending in approximately the lateral direction of the actuator body4(vibration swinging the actuator body4in a direction indicated by an arrow inFIG. 3) may be generated due to generation of natural vibration other than the first-order stretching vibration and the second-order bending vibration, and limitation of the movement of the actuator body4in the contact portions between the driver elements3and the movable body11and the contact portion between the holder5and the plate spring7and the like. Although the holder5attached to the actuator body4is fitted into the long holes64of the supports6, clearance which allow the slide of the holder5are formed between the holder5and the long holes64. Thus, when swinging the actuator body4about the axis extending in approximately the lateral direction, there are possibilities that the holder5attached to the actuator body4repeatedly hits wall surfaces of the long holes64formed in the guide members63, and the actuator body4repeatedly hits the supports6. In the present embodiment, the contact rubber blocks66a,66b, and66care provided. Thus, the swing of the actuator body4about the axis extending in approximately the lateral direction is attenuated by elastically deforming the contact rubber blocks66a,66b, and66c. Further, not only such swing but also the movement of the actuator body4in the direction crossing the principal surfaces40aand40bcan be absorbed by elastically deforming the contact rubber blocks66a,66b, and66c. Consequently, noise generation due to the hit of the holder5to the wall surfaces of the long holes64, and the hit of the actuator body4to the supports6can be reduced.

Thus, according to the present embodiment, at least two contact rubber blocks66contacting the principal surface40a(40b) of the actuator body4at different points in the longitudinal direction are provided, thereby reducing noise when operating the ultrasonic actuator2. That is, the contact rubber blocks66contact the principal surfaces40aand40bof the actuator body4with the actuator body4being supported by the supports6, thereby reducing the displacement of the actuator body4in the direction crossing the principal surfaces40aand40b. Further, in each of the principal surfaces40aand40b, a plurality of contact rubber blocks66are provided at different points in the longitudinal direction, thereby reducing the swing of the actuator body4about the axis extending in approximately the lateral direction. This reduces the repeated hit of the holder5attached to the actuator body4, to the guide members63of the supports6, and the repeated hit of the actuator body4to the supports6. In this manner, the noise when operating the ultrasonic actuator2can be reduced.

The contact rubber blocks66a,66b, and66care arranged so as to be symmetric with respect to a line extending in the lateral direction at the center of the principal surface40a(40b) in the longitudinal direction, and are arranged so as to be symmetric with respect to a line extending in the longitudinal direction at the center of the principal surface40a(40b) in the lateral direction, thereby ensuring symmetric vibration of the actuator body4. That is, in the portions of the actuator body4, which contact the contact rubber blocks66a,66b, and66c, the vibration is limited by the contact rubber blocks66a,66b, and66c. Thus, the contact rubber blocks66a,66b, and66care arranged as described above, thereby arranging resistors to the vibration of the actuator body4so as to be symmetric with respect to lines extending in the directions of the stretching and bending vibrations, which pass through the center of gravity of the actuator body4. Consequently, the symmetric vibration of the actuator body4can be ensured.

The contact rubber blocks66a,66b, and66care arranged at a distance of 13% of the length inwardly from the both ends of the actuator body4in the longitudinal direction, and at the center in the longitudinal direction, thereby reducing or preventing the interference with the vibration of the actuator body4by the contact rubber blocks66a,66b, and66c. That is, the points at a distance of 13% of the length inwardly from the both ends of the actuator body4in the longitudinal direction correspond to nodes of the second-order bending vibration of the actuator body4. The point at the center of the actuator body4in the longitudinal direction corresponds to the node of the first-order stretching vibration of the actuator body4. That is, at such points, the stretching and bending vibrations is generated in the actuator body4, resulting in little vibration of the actuator body4. Thus, even if the contact rubber blocks66a,66b, and66care arranged at the above-described points of the actuator body4, the contact rubber blocks66a,66b, and66chardly interfere with the vibration of the actuator body4. Consequently, degradation of vibration efficiency of the actuator body4can be reduced or prevented.

The contact bodies contacting the principal surfaces40aand40bof the actuator body4are made of rubber, thereby reducing or preventing the degradation of vibration efficiency of the actuator body4, and reducing generation of abrasion powder. That is, the contact rubber blocks66a,66b, and66ccan be elastically deformed in response to the vibration of the actuator body4. Thus, as compared to a configuration in which the actuator body4is pressed with members having high rigidity so as not to be displaced, the actuator body4can freely vibrate. Consequently, the degradation of vibration efficiency of the actuator body4can be reduced or prevented. In addition, if the contact bodies are made of the members having high rigidity, the contact bodies are hardly deformed, and therefore the actuator body4vibrates while slidingly contacting the contact bodies. Thus, there is a possibility that abrasion powder of the actuator body4and the contact bodies is generated. On the other hand, the contact bodies are made of rubber, and therefore the contact rubber blocks66a,66b, and66care deformed in response to the vibration of the actuator body4. Consequently, the contact rubber blocks66a,66b, and66cand the actuator body4hardly slide, and the abrasion powder thereof is hardly generated. In this manner, the generation of the abrasion powder can be reduced.

The contact rubber blocks66a,66b, and66care sandwiched between the supports6and the principal surfaces40aand40bof the actuator body4, thereby reducing the number of components. That is, the contact rubber blocks66a,66b, and66cmay be attached to members other than the supports6to contact the principal surfaces40aand40bof the actuator body4. On the other hand, according to the present embodiment, the contact rubber blocks66a,66b, and66care sandwiched between the supports6for supporting the actuator body4and the actuator body4, thereby realizing a configuration in which the contact rubber blocks66a,66b, and66ccome into contact with the principal surfaces40aand40bof the actuator body4with reducing the number of components. In addition, the assembly of the ultrasonic actuator2can be improved.

The guide member63is made of the material having the lower elasticity modulus than that of the support body60, thereby reducing hitting noise of the holder5to the guide members63. That is, since the support6is a member for supporting the actuator body4, the support6requires a certain degree of strength and material having higher elasticity modulus or higher hardness. Thus, the support6includes separate bodies which are the support body60and the guide member63. Consequently, the support body60can be made of the material having higher elasticity modulus to fulfill a function to support the actuator body4while the guide member63can be made of material having lower elasticity modulus than that of the support body60to reduce the hitting noise of the guide members63to the holder5. That is, the support6includes the separate bodies which are the support body60and the guide member63, thereby ensuring both of the support of the actuator body4and the reduction in hitting noise. Further, the guide member63is preferably made of material having lower hardness than that of the support body60.

In order to reduce the hitting noise of the holder5to the guide members63, the holder5may be fixed to the guide members63. However, there is a possibility that, as the driver elements3are gradually abraded, the friction force between the driver elements3and the movable body11cannot be ensured regardless of the actuator body4being biased by the plate spring7. In such a case, a drive efficiency of the ultrasonic actuator2is significantly degraded. That is, the long hole64is formed in the guide member63, and this allows the holder5to slide in the long hole64. Consequently, the friction force between the driver elements3and the movable body11is ensured, thereby maintaining the drive efficiency of the ultrasonic actuator2. For the reasons described above, flexibility for absorbing an impact from the holder5and high slide properties for sliding the holder5are required for the guide member63. In the present embodiment, the holder5is made of polycarbonate containing glass fibers, and the guide member63is made of polyacetal. However, it is not limited to the above.

Embodiments of the present disclosure may have the following configurations.

That is, the three contact rubber blocks66are provided to the principal surface40a(40b), but it is not limited to the above. In order to reduce the swing of the actuator body4about the axis extending in approximately the lateral direction, at least two contact rubber blocks66may be provided at different positions in the longitudinal direction. For example, in the foregoing embodiment, any one of the contact rubber blocks66a,66b, and66cmay be omitted. In addition, the number of contact rubber blocks66and/or positions where the contact rubber blocks66are provided may be different between the principal surfaces40aand40bof the actuator body4. However, the contact rubber blocks66are preferably arranged so as to be symmetric with respect to the lines extending in the directions of the stretching and bending vibrations, which pass through the center of gravity of the actuator body4, considering the vibration efficiency of the actuator body4. If, e.g., one of the contact rubber blocks66is omitted in the foregoing embodiment, the second contact rubber block66bin the longitudinal direction of the actuator body4is preferably omitted.

The positions of the contact rubber blocks66a,66b, and66cmay not be limited to those in the foregoing embodiment. For example, in the foregoing embodiment, the three contact rubber blocks66a,66b, and66care provided at the center of the principal surface40a(40b) of the actuator body4in the lateral direction, but it is not limited to the center in the lateral direction. Each of the contact rubber blocks66a,66b, and66cmay be arranged at a different position in the lateral direction. In addition, the contact rubber blocks66a,66b, and66cmay be provided at positions in the longitudinal direction, which are different from those in the foregoing embodiment.

In the foregoing embodiment, the contact rubber block is employed as the contact body, but it is not limited to the above. For example, steel balls may contact the principal surfaces40aand40bof the actuator body4. The contact body is a member having higher rigidity and a smaller friction coefficient, such as steel balls, thereby reducing or preventing the interference with the vibration of the actuator body4. However, the contact body is preferably made of rubber in order not to generate the abrasion powder.

The holder5protrudes outwardly beyond the principal surfaces of the actuator body4in the thickness direction of the actuator body4, but it is not limited to the above. For example, the holder5may protrude in the direction crossing the principal surfaces40aand40bof the actuator body4, e.g., may extend in a direction inclined to the thickness direction. The holder5is attached to the long-side surface40dof the actuator body4, but it is not limited to the above. The holder5may be provided so as to penetrate the actuator body4in the direction crossing the principal surfaces40aand40b. In addition, the holder5is not necessarily a single member. The holder5may include two members, and such members are provided so as to protrude outwardly beyond the principal surfaces40aand40bof the actuator body4, respectively.

The ultrasonic actuator2generates the first-order stretching vibration and the second-order bending vibration in the actuator body4, but it is not limited to the above. As long as the stretching and bending vibrations can be generated in the actuator body4, an actuator body generating any order of vibration may be employed.

In the foregoing embodiment, the ultrasonic actuator2moves the movable body11, but it is not limited to the above. For example, the ultrasonic actuator2may be attached to the movable body11with the driver elements3contacting the base member14. In such a configuration, the actuator body4vibrates to generate the orbit motion of the driver elements3, thereby moving the movable body11to which the ultrasonic actuator2is attached, with respect to the base member14. That is, in such a configuration, not the movable body11but the base member14serves as the relatively-movable member which relatively moves with respect to the ultrasonic actuator2.

In the foregoing embodiment, the actuator body4includes the piezoelectric elements, but it is not limited to the above. For example, the actuator body4may be a resonator including piezoelectric elements attached to a metal elastic body.

In the foregoing embodiment, the movable body11which is the relatively-movable member driven by the drive force of the ultrasonic actuator is formed in the rectangular parallelepiped shape, but it is not limited to the above. Any configuration may be employed as the configuration of the relatively-movable member. As illustrated in, e.g.,FIG. 10, a drive unit201may be employed, in which a movable body is a circular plate17which is rotatable about a predetermined axis X, and driver elements3of an ultrasonic actuator contact a circumferential surface17aof the circular plate17. In such a configuration, when driving the ultrasonic actuator, substantially elliptical motion of the driver elements3rotates the circular plate17about the predetermined axis X. In addition, as illustrated inFIG. 11, a drive unit301may be employed, in which a movable member is a circular plate18which is rotatable about a predetermined axis X, and driver elements3of an ultrasonic actuator contact a flat section18aof the circular plate18. In such a case, when driving the ultrasonic actuator, substantially elliptical motion of the driver elements3drives the circular plate18in a tangential direction of portions contacting the driver elements3, resulting in an rotation of the circular plate18about the predetermined axis X.

As described above, the present disclosure is useful for the vibratory actuator including the actuator body generating the stretching and bending vibrations.