Vibration actuator

A vibration actuator has a vibration member for generating a vibration, and a contact member which contacts the vibration member and moves relative thereto when the vibration member vibrates. A portion of the vibration member, which is in sliding-contact with the contact member, is formed as a separate first member which is coupled to rest of the vibration member.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a vibration actuator for relatively moving
 a contact body by a vibration produced in a vibrator.
 2. Related Background Art
 FIGS. 10A and 10B are sectional views of a rod-shaped ultrasonic wave motor
 described in U.S. Ser. No. 340,469 as the prior art of the present
 invention. A vibration member 1 generates an oscillating vibration upon
 application of AC voltages to a piezoelectric member 3, and the surface
 particles of a sliding portion B make an elliptic motion. On the other
 hand, a movable member 2 is in press-contact with the sliding portion B
 and receives a frictional driving force from the vibration member. At this
 time, a friction layer 1a on the vibration member side is an Ni-P-SiC
 composite galvanized layer, and is formed on the entire surface of the
 vibration member 1.
 In this prior art, the function required of the friction layer is given by
 the composite galvanized layer. However, the galvanized layer must be
 formed on a portion that is not associated with the required function.
 When the galvanized layer itself can be uniformly and smoothly formed on
 the entire surface, this problem is concluded as only a wasteful
 treatment. However, a post-treatment is required after the galvanizing
 treatment due to the nonuniformity of the thickness, surface roughness,
 and warp of the galvanized layer. As a first example, since a sliding
 layer 1a' of the vibration member must effectively receive a minute
 displacement of the piezoelectric member, it must be finished to have a
 surface precision as high as that obtained by cutting or grinding. Thus,
 the sliding surface is subjected to lapping after the galvanizing
 treatment, in practice. The same applies to an actuator of a type in which
 a piezoelectric member is adhered to a vibration member. As a second
 example, since the resonance frequency of a vibration mode used for
 frictional driving must fall within a predetermined range, the galvanized
 portion must be removed in the post-treatment. More specifically, in the
 prior art shown in FIG. 10, the galvanized layer attached to a constricted
 portion 1d' of the vibration member 1 must be locally removed to adjust
 the resonance frequency to a predetermined value. This process is
 discussed in detail in Japanese Laid-Open Patent Application No. 5-300768,
 and a detailed description thereof will be omitted.
 On the other hand, some attempts have been made to utilize a resin, rubber,
 or the like as the friction layer. However, with this method, since the
 resin or rubber has a low rigidity, a molded member consisting of such a
 material cannot maintain a predetermined shape, and it becomes difficult
 to maintain high positional precision if such a member is coupled to the
 vibration member. On the other hand, when the molded member whose rigidity
 is increased by increasing its thickness is coupled to the vibration
 member, since the resin or rubber has large vibration attenuation, the
 energy loss of the motor becomes undesirably large.
 SUMMARY OF THE INVENTION
 The present invention has as its object to solve the above-mentioned
 conventional problems. As means for achieving the object of the present
 invention, a single conventional member is divided into two or more
 members, these members are separately manufactured in advance, and the
 members are coupled to obtain a member for a vibration member.
 In other words, a functional portion required for a sliding friction layer,
 a portion required for magnifying a displacement of a sliding portion, and
 a structural portion required for a vibration member are separately formed
 in advance, and are then coupled to each other without disturbing the
 vibration performance of the vibration member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 First Embodiment
 FIG. 1 shows an ultrasonic wave motor as a vibration wave actuator serving
 as the presupposition of the first embodiment according to the present
 invention. FIG. 1 is a longitudinal sectional view of the entire motor.
 A vibration member as a vibrator is constituted by sandwiching driving and
 sensor piezoelectric members (electro-mechanical or mechano-electrical
 energy conversion members) 3 and electrode plates 4 between upper and
 lower vibration member structural bodies 1 and 5, and then fastening them
 using a bolt 6. In order to electrically isolate the upper vibration
 member structural body 1 from the bolt 6, an insulating sheet 7 is
 inserted therebetween. The magnitude of a vibration displacement produced
 on a sliding surface 1b of the vibration member is adjusted by the
 diameter of a constricted portion 1d. A sliding surface 2b of a movable
 member 2 as a contact body is pressed against the sliding surface 1b by
 the expanding force of a coil spring 8. A displacement produced on the
 sliding surface 1b of the vibration member is transmitted to the movable
 member 2 via friction, and is output to an external portion via a gear 9.
 Note that the rotation of the gear 9 is transmitted to a gear X
 constituting a portion of a system.
 FIGS. 2A to 2H show the first embodiment. FIG. 2A shows an example wherein
 a sliding member 10-1 as a separate member is press-fitted on and coupled
 to the upper vibration member structural body 1. Conventionally, an
 Ni-P-SiC galvanized layer is formed on the entire surface of the upper
 vibration member structural body 1. However, in this embodiment, brass
 (JIS C3604) is directly used without any surface treatment. The sliding
 member 10-1 was manufactured by punching a precipitation hardening
 stainless steel plate into a ring shape by press working, and removing
 burrs, corner slopes, and the like by barrel finishing. Since such a shape
 can be easily manufactured by press working, the number of processes can
 be greatly reduced as compared to a working method such as cutting. The
 hardness of the stainless steel used was about 480 Hv (Vickers hardness),
 but could be increased to about 580 Hv (Vickers hardness) by performing an
 aging treatment of the stainless steel at a low temperature of 475.degree.
 C. In this manner, when a precipitation hardening material is used, it can
 be easily worked since it is relatively soft. In addition, since a
 hardening treatment for reducing the sliding wear amount is performed at a
 low temperature which causes almost no residual distortion, deformation
 and scaling are hard to occur.
 Of course, martensitic stainless steel may be used, or austenitic stainless
 steel may be used after it is subjected to cold rolling to form a
 working-induced martensitic texture. Furthermore, austenitic stainless
 steel (JIS SUS316) with a high corrosion resistance may be used after its
 surface is subjected to a nitriding treatment. On the other hand, the
 movable member is manufactured by hard-anodizing an aluminum alloy (JIS
 A5056H34).
 FIG. 2B shows an example wherein a projection having a trapezoidal section
 is formed on the end face of a sliding member. This sliding member 10-2
 including the projection can be formed by cutting, sintering, press
 working, or the like. In the case of press working, the projection can be
 easily formed by pressing in the surface opposite to the projection.
 Due to the presence of this projection, since the fragile anodized aluminum
 edge of the movable member side does not contact the sliding surface of
 the vibration member, the wear resistance can be improved. Since this
 projection is located outside the edge portion of the vibration member
 structural body 1, this sliding surface can be subjected to lapping (a
 treatment for pressing a rotating smooth disk against a sample to improve
 the flatness and surface roughness of the sample; since the disk surface
 contacts only the outermost surface of the sample, a recess portion cannot
 be subjected to lapping) after coupling.
 The sliding member may be press-fitted on the upper vibration member
 structural body 1 or may be expansion- or shrinkage-fitted thereon. In
 addition, an adhesion force by an adhesive may also be used. In this
 embodiment, coupling surfaces include a surface 1f parallel to the motor
 shaft and a surface 1e perpendicular to the motor shaft, and a gap 11-1 is
 formed between these surfaces so that the two surface do not cross each
 other. The coupling surface 1f serves to hold the sliding member 10-2 to
 be satisfactorily coaxial with the center of the motor shaft, and the
 coupling surface 1e serves to maintain high positional precision, in the
 motor shaft direction, of the sliding member 10-2. These two roles are
 common to the structure shown in FIG. 2A. In FIG. 2B, since the gap 11-1
 is additionally formed, coupling (contact) on the coupling surface 1e is
 assured, and the positional precision, in the motor shaft direction, of
 the sliding member 10-2 is further improved. The coupling surface 1e may
 be located immediately below the trapezoidal portion. FIG. 2C shows an
 example wherein the outer circumferential side of a sliding member 10-3 is
 coupled to the vibration member structural body 1. The material of the
 sliding member includes ceramics such as alumina, silicon carbide, silicon
 nitride, SIALON, aluminum nitride, and the like; a material prepared by
 anodizing an aluminum alloy; inorganic materials such as graphite, glass,
 and the like; and cermets such as extra hard metals (carbide). Most of
 these materials are hard and can be good frictional members. In this case,
 since the breaking stress due to compression is relatively larger than the
 tensile stress, the outer circumferential surface side of the sliding
 member is used as one of the coupling surfaces. The sliding member
 consisting of any of the above-mentioned materials not only can provide a
 high frictional force but also can assure a high wear resistance. For this
 reason, the sliding member can satisfactorily serve as that for an
 ultrasonic wave motor. In addition, since the sliding member has small
 vibration attenuation unlike rubber or resin materials, it does not
 interfere with any vibration. However, such materials are not easy to work
 as compared to metals, and it is not practical to form the entire
 vibration member structural body using these materials. In this
 embodiment, it suffices to work a material which is not easy to work into
 a simple ring shape.
 In FIG. 2D, the sliding surface of a sliding member 10-4 is subjected to
 lapping in advance, and then, the sliding member 10-4 is coupled to the
 vibration member structural body 1. The press-contact position with the
 movable member 2 is a lower position in FIG. 2D. In this example,
 frictional driving is attained at a position where the vibration direction
 of the sliding surface particles of the vibration member is changed.
 In FIG. 2E, a member having a width corresponding to the upper bottom
 surface of the trapezoidal projection shown in FIG. 2B, i.e., a sliding
 member 10-5 obtained by cutting a thin pipe into a ring shape is
 press-fitted on the vibration member structural body 1. In order to assure
 the coupled state between the sliding member 10-5 and the vibration member
 structural body 1, a gap 11-2 is formed. In order to press-contact a
 coupling portion 1f against the sliding member 10-5, a groove 12 is formed
 in the vibration member structural body 1, so that a support portion 1g
 has a spring restoration force, thereby assuring the firmly coupled state.
 In FIG. 2F, a ring member whose sectional shape, cut along a plane
 including the center of the motor shaft, is an L shape, is press-fitted.
 The above-mentioned spring restoration force is provided to a sliding
 member 10-6 by forming grooves 10a in the sliding member 10-6 (see FIG.
 2G). The sliding surface is defined by a portion near the ridge of the
 L-shaped section. Note that the sectional shape may be defined by a
 portion of an arc, a portion of a curve, a portion of a polygon, or a
 combination of a curve and a straight line in addition to the L shape. The
 objective of this shape is to improve the startability of the motor in
 addition to the effects described with reference to FIG. 2B. More
 specifically, since the sliding portion is defined by the ridge of a
 polygon or a portion of a curved surface, i.e., has a small width, the
 start performance of the motor can be improved. That is, in a
 high-humidity environment, the water content condenses into water in the
 narrow gap between the sliding surfaces of the movable member and the
 vibration member, and makes these members tightly contact each other. If
 the sliding surface is large, the tight contact force increases.
 In FIG. 2H, a ring-shaped sliding member 10-7 having an L-shaped section is
 press-fitted, and a surface corresponding to its thickness is used as a
 sliding surface.
 FIG. 3 shows an ultrasonic wave motor as a basis of the second embodiment.
 In FIG. 3, a groove 1h is formed in a portion, near the sliding surface,
 of the vibration member structural body 1 to provide rigid flexibility to
 the sliding surface of the vibration member. With this structure, the
 design of the movable member 2 requires only a groove 2c with a simple
 shape. Since a flange portion 2d of the movable member with this shape has
 no undercut portion unlike in FIG. 1, the movable member can be formed by
 press working.
 FIGS. 4A to 4F show the second embodiment. FIG. 4A is an enlarged view of a
 portion near a sliding portion. In FIG. 4A, a separately formed sliding
 member 10-8 is press-fitted on the vibration member structural body 1.
 In FIG. 4B, a sliding member 10-9 prepared by press working is welded to
 the vibration member structural body 1 using a projection 1i. Since the
 welding can assure reliable metal coupling, a vibration is not disturbed.
 A groove 1j is formed to stabilize the degree of rigid flexibility of the
 above-mentioned sliding surface.
 In FIG. 4C, a sliding member 10-10 is coupled by a screw. The screw
 coupling can assure the most reliable coupling. A projection 10b is an
 example of the projection described with reference to FIG. 2B, and is
 formed by press working. When the movable member 2 is divided into two
 members, as shown in FIG. 4C, an optimal sliding member can be selected
 without disturbing practicality upon working. In this embodiment, a member
 2d consists of stainless steel, and the sliding member 10-10 consists of
 an aluminum alloy subjected to an anodizing treatment.
 FIGS. 4D and 4E show an example wherein recesses 10e are formed in a
 surface 10b, which is in sliding contact with the movable member, of a
 sliding member 10-11. With this structure, the above-mentioned
 startability can be improved. On the contrary, when projections 10c are
 used as sliding portions, as shown in FIG. 4E, the same effect can be
 expected. Holes may be formed in place of the recesses, and each recess
 may extend between the inner and outer circumferential surfaces.
 FIG. 4F shows an example wherein slits 10d are formed to provide the
 above-mentioned rigid flexibility to a sliding member 10-12. In this case,
 portions 10b serve as a sliding surface with the movable member 2. In FIG.
 4F, the sliding member 10-12 has an L sectional shape, but may have a
 linear shape.
 FIGS. 5A to 5E also show the second embodiment. FIG. 5A shows an example of
 a two-end support or fixing structure while the examples described so far
 provide the rigid flexibility using a cantilever shape. Since the
 direction of displacement is close to the direction of the center of the
 motor shaft, the structure shown in FIG. 5A is effective when a vibration
 displacement in this direction is required. A recess 10f of a sliding
 member 10-13 is formed to prevent the movable member from being decentered
 upon rotation.
 In FIG. 5B, unlike in the examples explained so far, the outer
 circumferential surface side of a sliding member 10-14 is coupled to the
 vibration member structural body. As in the example shown in FIG. 5A, this
 structure is selected depending on the direction of vibration
 displacement. A sliding surface 10b is curled by press working. The
 effects of this structure are the same as those described with reference
 to FIG. 2B.
 In FIG. 5C, a sliding member 10-15 is coupled to the vibration member
 structural body 1 by flattening and caulking a portion 1k. When the
 material used for the vibration member structural body 1 has a high
 ductility, this coupling method becomes a simple but reliable method. In
 this example, the sliding member 10-15 consists of phosphor bronze, and
 its surface is subjected to Ni-P galvanizing. In this example, after the
 sliding member 10-15 is formed, a surface treatment or surface coating
 such as galvanizing is performed.
 In an example shown in FIG. 5D, unlike in FIG. 5C, a sliding member 10-16
 is prepared by punching a material, which is subjected to a surface
 treatment or surface coating beforehand, by press working. With this
 process, since a treatment need not be performed for each member, the
 number of processes of the surface treatment or surface coating can be
 greatly reduced. For example, a pure aluminum or aluminum alloy plate is
 formed into the shape of the sliding member 10-16 by press progressive
 working. In this case, a large number of members are not disconnected but
 are kept connected via beams. After this material is subjected to an
 anodizing treatment, the respective members are disconnected from the
 beams to obtain individual sliding members. As the surface treatment, in
 addition to the anodizing treatment for aluminum, an iron alloy, a copper
 alloy, or the like selected as the material of the sliding member may be
 subjected to galvanizing of Cr, Ni alloy, Co, or the like, or stainless
 steel may be subjected to a nitriding treatment. As surface coating, resin
 coating, spray coating, or the like may be used. In this example, a recess
 portion serves as a sliding surface with respect to the movable member,
 contrary to the example shown in FIG. 5C. This is to not only suppress the
 above-mentioned decentering but also to expect the following effect. For
 example, as in the example of performing resin coating or spray coating,
 the thickness of a recess portion of a film in a molten state immediately
 after coating becomes larger than that of a flat portion due to its
 surface tension, as shown in FIG. 5D. That is, the thickness of only a
 film portion used as the frictional sliding member increases, and the
 durability of the motor can be improved.
 In FIG. 5E, a sliding member has radial projections 10h formed at three
 positions by press working. Only these projections 10h contact the sliding
 portion of the movable member. Since there are three contact portions and
 they can define a plane, these projections can attain a uniform contact
 state with the sliding surface of the movable member without being
 subjected to lapping. The shape of each projection is not limited to a
 linear shape but may be a dot shape. On the other hand, each projection
 may form a certain angle with the radial direction of this member when it
 is formed into a linear shape. That is, each projection need not extend in
 the radial direction.
 FIGS. 6A to 6C show the third embodiment. FIG. 6A shows an example wherein
 a flange member 2d for lowering the rigidity on the sliding surface is
 obliquely formed to achieve a deformation direction equivalent to that in
 FIG. 2F. In this example, the flange member 2d of the movable member
 consists of aging hardening stainless steel, and a sliding member 10-18 of
 the vibration member consists of an extra hard material. Stainless steel
 suffers a larger wear amount than the extra hard material. However, as the
 distal end of the flange member 2d is worn, the contact position of the
 sliding member (the ultra hard material) with the distal end of the flange
 member moves toward its outer circumferential surface, and both the
 materials are uniformly worn, thus improving the durability of the motor.
 FIG. 6B shows a structure wherein both the vibration member and the
 movable member have resiliency. Even when the distal end of the flange
 member 2d is considerably worn, the function as the motor can be
 maintained. In order to further improve the durability of the motor, the
 axial dimension of the flange member 2d is preferably increased. In this
 structure, a sliding member 10-19 of the vibration member preferably
 consists of a material having a higher wear resistance than that of the
 flange member 2d. FIG. 6C shows a disposition opposite to that shown in
 FIG. 6B.
 Many materials of the flange member 2d and the sliding members 10-18 to
 10-20 of the vibration member in FIGS. 6A to 6C were tested. As a result,
 the combinations shown in FIG. 7 exhibited good results in terms of wear
 resistance.
 FIG. 8 shows a ring-shaped ultrasonic wave motor as a basis of the fourth
 embodiment. The details such as the driving principle of this motor are
 described in U.S. Pat. No. 4,831,305 and the like. In an ultrasonic wave
 motor of this type, a vibration member is constituted by adhering a
 piezoelectric member 3 to a vibration member structural body 1. A movable
 member 2 contacts the vibrator. A large number of grooves 1i are formed in
 the vibration member, and magnify the vibration displacement.
 Conventionally, since the grooves 1i must be formed by cutting or
 grinding, a large number of processes are required. In order to solve this
 problem, in the fourth embodiment, a plate 20-1 in which a plurality of
 holes 20d are formed by press working or etching, as shown in FIG. 9A, is
 press-molded, as shown in FIG. 9B, and is then firmly coupled to the
 vibration member structural body 1 by adhesion or welding. Since the
 vibration member has the above-mentioned structure, a bending vibration
 deformation produced in the vibration member structural body 1 can be
 reliably transmitted to the press-molded member, and the sliding member
 20-1 can consist of a material which cannot be worked by cutting or
 grinding, thus greatly reducing the number of processes.
 FIG. 9C shows a structure from which the vibration member structural body 1
 is omitted. The piezoelectric member 3 is directly adhered to a sliding
 member 20-2 of the vibration member. FIG. 9D shows a press blank for the
 sliding member 20-2. As shown in FIG. 9D, holes 20d are formed in a
 ring-shaped member.
 FIG. 9E shows a mold structure used when the member 20-2 is molded by press
 working.
 Note that the mold structure includes stationary molds 31 and 32, and by
 pressing a movable mold 30 downward in FIG. 9E, the member 20-2 can be
 press-worked into the shape shown in FIG. 9C.
 FIGS. 11 and 12 respectively show the fifth and sixth embodiments. A
 substantially ring-shaped sliding member 10-21 is fitted in a vibration
 member structural body 1 at its inner circumferential surface (A) side,
 and is also fitted in the vibration member structural body 1 at its outer
 circumferential surface (B) side. The advantage of fitting at both the
 inner and outer circumferential surfaces will be explained below.
 When the sliding member consisting of a different material is fitted in the
 vibration member structural body for the purpose of preventing a wear of
 the vibration member, the vibration member structural body and the sliding
 member consist of different materials (thermal expansion coefficients).
 For this reason, due to a change in environment such as a change in
 temperature, humidity, and the like, the fitting state changes, and a gap
 may be formed between the sliding member and the vibration member
 structural body. In such a case, upon rotation of the motor, the sliding
 member may rotate together with the movable member, which is in
 press-contact with the sliding member, due to the gap and the influence
 of, e.g., a vibration. As shown in FIGS. 13A to 14B, for example, when the
 vibration member structural body 1 consists of brass (BS) and the sliding
 member 2 consists of stainless steel (JIS SUS440C), since the thermal
 expansion coefficient of brass is higher than that of stainless steel, a
 gap is undesirably formed between the vibration member structural body and
 the sliding member (FIGS. 13A and 14B) in a low-temperature (-20.degree.
 C.) environment in the case of fitting at only the inner diameter side and
 in a high-temperature (45.degree. C.) environment in the case of fitting
 at only the outer diameter side, and the sliding member 2 may be
 undesirably rotated.
 In the cases of FIGS. 13B and 14A, the two members change in a direction to
 eliminate the gap.
 For example, when a substantially ring-shaped sliding member which has an
 inner diameter of about 8.5 mm and consists of SUS440C is subjected to a
 temperature change from 45.degree. C. to -20.degree. C., it is calculated
 that a gap of about 4 .mu.m be formed between itself and a vibration
 member structural body consisting of a BS base material. Note that the
 sliding member may be fixed to the vibration member structural body by an
 adhesive. However, since the adhesive application position is in the
 vicinity of the contact portion between the vibration member and the
 movable member, the adhesion position and the adhesive amount must be
 strictly controlled, resulting in an increase in cost as a whole.
 As shown in FIG. 11, the substantially ring-shaped sliding member 10-21 is
 fitted in the vibration member structural body 1 at its inner
 circumferential surface (A) side, and is also fitted in the vibration
 member structural body 1 at its outer circumferential surface (B) side.
 With this structure, even when a gap is formed at the (A) side due to a
 change in environment, no gap is formed at the (B) side in this case (and
 vice versa).
 More specifically, when the sliding member 10-21 is fitted so that both its
 inner and outer circumferential surfaces contact the vibration member
 structural body 1, these members change in a direction to eliminate a gap
 at one side even when the environment (temperature) changes. For this
 reason, the sliding member 10-21 can be prevented from rotating with
 respect to the vibration member structural body 1 without using any
 adhesive.
 In FIG. 12, the fitting state of the sliding member to the vibration member
 structural body is reversed to that shown in FIG. 11, and the same effect
 as in FIG. 11 is obtained. Note that the ring-shaped sliding member in
 FIGS. 11 and 12 has an L-shaped section. However, the present invention is
 not limited to the L-shaped section as long as the sliding member 10-21 is
 fitted in the vibration member structural body at both its inner and outer
 circumferential surfaces.
 FIG. 15 is an explanatory view of the seventh embodiment. In the seventh
 embodiment, a fitting bottom surface portion, to be inserted in a
 vibration member structural body 1, of a substantially ring-shaped sliding
 member 10-22 is slanted into a wedge shape.
 In this case, as in the fifth and sixth embodiments, in an environment for
 forming a gap at a portion (A), a portion (B) acts in a direction to be in
 tight contact with the vibration member structural body; in an environment
 for forming a gap at the portion (B), a portion (A) acts in a direction to
 be in tight contact with the vibration member structural body. For this
 reason, the sliding member can be prevented from rotating.
 In the seventh embodiment, as shown in FIGS. 15 and 16, the compression
 force from the movable member 2 is divided into components a and b, and
 the component a acts to take up the formed gap.
 The operation will be described below with reference to FIGS. 19 and 20. In
 the structure shown in FIG. 19, the compression force from the movable
 member 2 does not have a function of taking up a gap. However, as shown in
 FIG. 20, when the sliding member is formed into a wedge shape and is
 inserted, the component a moves the sliding member to take up a gap formed
 by a change in temperature.
 Therefore, with this effect, as long as the sliding member 10-22 is always
 compressed by the movable member 2, the sliding member moves in a
 direction to eliminate the gap, thus obtaining a simple fitting structure.
 FIGS. 16, 17, and 18 respectively show the eighth, ninth, and 10th
 embodiments. In these embodiments, the relationship between the inner and
 outer circumferential surfaces of a vibration member structural body and a
 sliding member are reversed.
 FIG. 21 is an explanatory view of the 11th embodiment. In the 11th
 embodiment, projections 101 are formed on the inner circumferential
 surface of a sliding member 10-23, and the sliding member 10-23 is coupled
 to a vibration member structural body so that these projections 101 are
 press-fitted in and mesh with the vibration member structural body with a
 low hardness, thus attaining a firm fixed state. The shape of each
 projection is not particularly limited, and may be a mountain shape,
 three-dimensional shape, round shape, and the like. Also, an appropriate
 number of projections are formed in both the axial and circumferential
 directions.
 FIG. 22 shows the 12th embodiment. In the 12th embodiment, projections 101
 are formed on the outer circumferential surface of a sliding member 10-23.
 With this structure, a large frictional force in the circumferential
 direction can be assured between a vibration member structural body 1 and
 a sliding member 10-23, and the rotation of the sliding member 10-23 can
 be prevented independently of a change in environment.
 FIG. 23 shows a ring-shaped ultrasonic wave motor according to the 13th
 embodiment. A substantially ring-shaped sliding member 20-3 is formed by
 press working as in the embodiment shown in FIG. 9. In the 13th
 embodiment, a recess is formed in a vibration member structural body 1 to
 receive the sliding member 20-3 at both the inner and outer
 circumferential surfaces. With this structure, at room temperature shown
 in FIG. 24A, the sliding member 20-3 is fitted in the vibration member
 structural body 1 at both the inner circumferential surface (A) and the
 outer circumferential surface (B). Even when the vibration member
 structural body 1 consists of brass (BS) and the sliding member 20-3
 consists of stainless steel (SUS), the inner circumferential surface (A)
 is strongly fitted in a high-temperature state shown in FIG. 24B, and the
 outer circumferential surface (B) is strongly fitted in a low-temperature
 state shown in FIG. 24C. Therefore, even when the two members have a
 thermal expansion coefficient difference based on a change in temperature,
 the sliding member 20-3 is strongly coupled to the vibration member
 structural body 1, and can be prevented from rotating or disengaging from
 the vibration member structural body 1.
 In the fifth to 13th embodiments described above, the vibration member
 structural body undergoes a larger expansion than the sliding member in a
 high-temperature state. Even when this relationship is reversed, the same
 effect can be expected.
 In each of the above-mentioned embodiments, the vibration member is fixed
 in position, and the movable member is moved. Alternatively, the movable
 member (contact member) may be fixed in position, and the vibration member
 may be moved. According to the present invention, the vibration member and
 the contact member need only be moved relative to each other by a
 vibration produced in the vibration member.
 As described above, according to each of the above embodiments, a vibration
 actuator with high durability, high efficiency, and good startability can
 be provided by working a vibration member or contact member with simple
 working means.
 Since a separate member attached to a vibration member defines the
 outermost surface, a post-treatment such as lapping is facilitated.
 Since grooves or holes are formed in the separate member attached to the
 vibration member, it is easy to increase the magnitude of a vibration and
 to obtain a required vibration displacement.
 Since projections or recesses are formed on the separate member attached to
 the vibration member, the motor startability can be improved.
 When the separate member attached to the vibration member is formed by
 press working, workability can be improved, and grooves, holes,
 projections, or recesses can be easily worked.
 Since the separate member attached to the vibration member is formed into a
 ring shape, the coupling process is facilitated, and the fitting portion
 upon coupling is set at its inner or outer diameter portion, thus solving
 problems caused by the characteristics and drawbacks of specific materials
 used.