A vibration driven actuator

Abstract: A convex sliding portion (30) is provided to the driving surface of a vibrating member (1) formed with a frictional layer (31) on its surface. Inner and outer ridges (2c, 2b) of a contact portion (21) of a rotor (2) formed with a frictional layer (2a) on its surface are located at the inner and outer sides of the inner and outer edges of the sliding portion (30), respectively, so that the ridges (2b, 2c) of the contact portion (21) do not contact an effective contact portion (B) of the sliding portion (30).

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a vibration driven motor for relatively driving a movable contact member urged against a vibrating member by a vibration generated in the vibrating member, which vibrates upon reception of the vibration from the vibration generating element and, more particularly, to a structure around a frictional sliding portion. Related Background Art A vibration driven motor or actuator, especially, a vibration driven motor formed into a bar shape includes a vibrating member formed into a bar or pencil shape, and a movable member urged against the driving surface of the vibrating member, which members are coaxially arranged. Upon synthesis of bending vibrations excited upon application of AC voltages to piezoelectric elements of the vibrating member, a circular or elliptic motion is formed in surface grains of the driving surface of the vibrating member, thereby frictionally driving the movable member. Fig. 6 is a schematic sectional view of a conventional bar-shaped vibration driven motor as disclosed for example in the EP 0 420 622. In Fig. 6, the motor includes a vibrating member 1, which clamps and fixes driving piezoelectric elements 8, and the like between vibrating member structural bodies 1a and 1b, and a movable member 2 urged against the driving surface of the vibrating member structural body 1a by a spring means (not shown). Hard alumite is used as a frictional sliding material of the frictional sliding surface of the movable member, and the entire frictional sliding surface contacts the frictional driving surface of the vibrating member. In the prior art, when the motor is driven, at least one ridge of the frictional or contact sliding surface of the movable member strongly contacts the frictional driving surface of the vibrating member. This is for the following reason. That is, a contact sliding portion 2a of the movable member receives a force upon displacement of a contact sliding portion 1aa of the vibrating member. The direction of displacement of the vibrating member is not perpendicular to but inclined from the contact surface. A flange-shaped spring structure of the contact sliding portion of the movable member is also deformed, so that the contact surface is inclined. Therefore, the frictional sliding surface 2a of the movable member contacts the frictional sliding surface 1aa of the vibrating member to form a certain angle therebetween. More specifically, weak ridges 2aa and 2ab of the frictional sliding surface 2a, formed of hard alumite as an inorganic material, of the movable member strongly contact the frictional sliding surface 1aa of the vibrating member. Thus, the ridges of the hard alumite layer crack, and once the ridges crack, the cracked state is gradually worsened. For this reason, the displacement of the vibrating member can no longer be smoothly transmitted to the movable member. As a result, the starting torque is considerably lowered, or cracked alumite powder serves as an abrasive, and the frictional driving portion of the movable member is immediately worn. In addition, an output from a sensor phase for detecting the vibrating state of the vibrating member 1 becomes unstable, and feedback control is disabled. From the document US 5,013,956 an ultrasonic wave driven motor is known comprising a stator portion with a driving member and a rotor portion being in contact with the driving member via a lining material. In order to reduce the abrasion amount the lining material is made of rubber or phenol resin being disposed within a groove formed in the driving member. The contact portion of the driving member is thereby smaller than the surface of the lining material such that the edges of the lining material are not in contact with the contact portion of the driving member. Finally the document US 5,055,732 discloses an ultrasonic motor comprising a rotor having a rotating member as a contact portion and a stator a driving member thereof is in frictional contact with the contact portion of the rotor via a frictional material made of rubber. The rotor ist urged against the driving member by a plate spring. In view of this state of the art it is an object of the invention to provide a vibration driven motor which can assure a long service life. This object is solved by a vibration driven motor having the features according to the patent claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A and 1B are sectional views showing a vibration driven motor or actuator for information Fig. 2 is a sectional view of a frictional sliding portion of another vibration driven motor also for information Fig. 3 is a sectional view of a frictional sliding portion of another vibration driven motor for information Fig. 4 is a sectional view of a frictional sliding portion of a vibration driven motor according to an embodiment of the present invention; Fig. 5 is a sectional view of a frictional sliding portion of another vibration driven motor also only for information Fig. 6 is a sectional view of a conventional vibration driven motor; and Fig. 7 is a schematic sectional view of an apparatus, which adopts a vibration driven motor of the present invention as a driving source. DESCRIPTION OF THE PREFERRED EMBODIMENTS Figs. 1A and 1B show a vibration driven motor or actuator which is not an embodiment of the present invention. Fig. 1A is a longitudinal sectional view of the motor, and Fig. 1B is an enlarged sectional view of a frictional contact portion. A bar-shaped vibrating member 1 is constituted by fastening vibrating member structural bodies 1a and 1b clamping driving and sensor piezoelectric elements 8 and electrode plates 9 therebetween by a bolt 10 like in the conventional vibrating member, and an insulating sheet 11 is inserted between the vibrating member structural body 1b and the bolt 10 so as to electrically insulate them from each other. The vibrating member 1 of this embodiment is formed with a sliding portion 30 (see Fig. 1B) which has the top surface of the vibrating member structural body 1a as a driving surface, and is defined by a ring-shaped projection having a trapezoidal section. A ring-shaped or cylindrical movable member (rotor) 2 is constituted by integrally forming a contact portion 21 of a structural body having spring characteristics on the lower portion of a ring-shaped rotor main ring 20. The contact portion 21 contacts the sliding portion 30 of the vibrating member 1. Upon energization of the piezoelectric elements 8, a vibration wave is generated in the vibrating member 1, and the contact portion 21 of the rotor 2 is driven by the vibration wave, thereby rotating the rotor 2 as in a known motor. A compression spring 6 applies a compression force to the rotor 2 via a spring case 4. A gear 3 is formed with a gear portion on its outer circumferential surface, and is supported by a bearing 7. The gear 3 is engaged with the spring case 4, and rotates together with the rotor 2. A flange 5 is attached to the distal end portion of the bolt 10 to be movable in only the axial direction, and fixes the bearing 7. When the flange 5 is moved axially upward together with the gear 3, the gear 3 can be disengaged from the spring case 4. A frictional layer 2a of a frictional material is formed on the surface of the movable member 2. In this embodiment, the frictional layer 2a is formed by a 30-µm thick anodized aluminum layer as an inorganic material. A frictional layer 31 of a frictional material is formed on the surface of the vibrating member structural body of the vibrating member 1. In this embodiment, the frictional layer 31 is formed by a 35-µm thick Ni-P-SiC plating layer. In the vibration driven motor with the above-mentioned arrangement, a region indicated by B in Fig. 1B corresponds to an actual contact sliding portion. The lower end face of the contact portion 21 of the rotor 2 is formed to have a larger width than that of the region B, and the contact portion 21 contacts the sliding portion 30, so that their centers substantially coincide with each other. Therefore, an outer circumferential ridge (corner portion) 2b of the sliding portion 21 of the rotor 2 has a larger diameter than that of the outer circumferential ridge of the contact sliding surface of the vibrating member 1, and conversely, an inner circumferential ridge 2c of the rotor 2 has a smaller diameter than that of the inner circumferential ridge of the contact sliding surface of the vibrating member 1. More specifically, the two ridges 2b and 2c of the rotor never contact the contact sliding surface 30 of the vibrating member. Note that the entire vibration driven motor has a diameter of 11 mm and a length of 25 mm. Fig. 2 is an enlarged sectional view of a frictional sliding portion according to another vibration driven motor, not part of the present invention. In this motor, only an outer circumferential ridge 2b of a sliding portion 21 of a rotor 2 has a larger outer diameter than that of the contact sliding surface of a vibrating member 1, and an inner circumferential ridge 2c of the sliding portion 21 is located on the contact sliding surface of the vibrating member. However, since a frictional layer 2d having a rounded corner is formed on the end face of the sliding portion 21, the inner circumferential ridge 2c never directly contacts the sliding surface of the vibrating member. In this motor, the frictional layer 2d formed on the end face of the sliding portion 21 of the rotor 2 is constituted by a 0.5-mm thick carbon plate, which is adhered to the sliding portion 21 by an adhesive. A large number of (for example, 30) 0.05-mm deep spline knurled grooves are radially formed on the sliding surface, having an outer diameter of 8 mm, of the vibrating member 1. In these grooves, a wear powder formed by a frictional sliding operation can be deposited, and the grooves serve to suppress promotion of wear. Fig. 3 is an enlarged sectional view of a frictional sliding portion of another motor of this kind which motor is not part of the present invention. In this motor, a guide 32 as a stepped portion is formed on the driving surface of a vibrating member 1, and two projections 33 and 34 are concentrically formed on the inner peripheral portion of the guide 32. Furthermore, a groove 35 for receiving a wear powder is formed between these projections 33 and 34. The end face of a sliding portion 21 of a rotor 2 contacts the projections 33 and 34, and inner and outer circumferential ridges 2b and 2c are located above groove portions 33a and 34b formed on inner and outer peripheral portions near the projections 33 and 34. Since the sliding portion 21 is located at the inner side of the guide 32, eccentricity and rotation of the rotor 2 can be prevented. Fig. 4 is an enlarged sectional view of a frictional sliding portion according to a preferred embodiment of the present invention. In this embodiment, a frictional layer 36 formed of a 0.2-mm thick alumina plate is adhered on the sliding surface of a vibrating member 1, so that the ridge of the end face of a contact portion 21 of a rotor 2 is located within a range of the sliding surface of the vibrating member 1. A frictional layer 2e is formed by spray-coating a polyimide amide resin onto the rotor 2 formed of an aluminum alloy (A5056), and has a rounded corner portion. In this embodiment, ridges 1e and 1f of the alumina plate 36 never crack, and never cause damage to the polyimide amide resin. Fig. 5 is an enlarged sectional view of a frictional sliding portion according to a motor which is not part of the present invention. In this motor, a guide portion 22 having a stepped portion is formed on the outer peripheral portion of a contact portion 21 of a rotor 2, and a sliding portion 30 is formed on the outer peripheral portion of the driving surface of a vibrating member 1, so that a ridge 2c of the rotor 2 is located nearer the inner peripheral side than the ridge of the sliding portion 30. In this case, the ridge 2c of the frictional sliding surface of the movable member never contacts the frictional contact portion of the vibrating member. Fig. 7 is a schematic sectional view of an apparatus (in this embodiment, a camera) which adopts a vibration driven motor of the present invention as a driving source. A gear 54 coaxially has large and small gear portions 54a and 54b. The large gear portion 54a is meshed with an output gear 3 of the motor, and the small gear portion 54b is meshed with a gear portion 55a of a driven member, e.g., a lens barrel 55, thereby transmitting the rotation of the motor to the lens barrel 55. An encoder slit plate 56 is attached to the gear 54, and rotation of the motor is detected by a photocoupler 57.

Claims: A vibration driven motor comprising: a bar shaped vibrating member (1) for generating a vibration in at least a driving surface thereof in response to an electrical signal applied thereto; a contact member (2) having an effective contact portion of a driven surface frictionally contacting an effective contact portion of said driving surface of said vibrating member (1) so as to be rotatably moved relative to said vibrating member (1) by the vibration; said effective contact portion of said contact member (2) being an integrally formed portion of said contact member (2) and having spring characteristics; and at least one of said driving surface and driven surface being formed with a frictional sliding layer (2e, 36), wherein said driving surface is formed with a frictional sliding layer (36) of alumina and wherein the ridges (1e, 1f) of anyone of said at least one frictional sliding layers (2e, 36) forming one of said driving surface and said driven surface are not in contact with the effective contact portion of the respective other one of said deriving surface and said driven surface. Motor according to claim 1, characterized in that said frictional layer (2e) is formed by spray coating of a polyimide amide resin onto the rotor (2). Motor according to one of claims 1 and 2, characterized in that said frictional layer (2e) has a rounded corner portion.

Inventors: CHIBA ICHIRO, TAMAI JUN, CHIBA, ICHIRO, TAMAI, JUN, CHIBA, ICHIRO, C/O CANON KABUSHIKI KAISHA, TAMAI, JUN, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: H01L41
IPC codes: H02N2, H01L41