Vibration driven motor

Abstract: In a vibration driven motor, a support member for supporting one end of a pressing member which presses a vibration member and a moving member receiving a drive force from the vibration member is fixed to a fixing member, with a result that the vibration member is indirectly supported.

Description: This invention relates to an ultrasonic motor in which electric energy is supplied to an electro-mechanical energy conversion element provided on a bar-like resilient member to thereby vibrate the resilient member as a bar-like vibration member and cause circular or elliptical motion at the material point of the vibration member, thus frictionally driving a moving member pressed against the vibration member, and particularly to a supporting method for an ultrasonic motor suitable for use in an optical instrument such as a camera and a business machine such as a printer. Ultrasonic motors of the type in which a bending vibration is caused in a circular ring-like resilient member and a moving member for driving a lens is driven by a frictional force have heretofore been put into practical use in AF mechanisms for cameras. However, the ultrasonic motors of this conventional type are ring-shaped and therefore are relatively costly as a unit including a pressing mechanism, and are disadvantageous in cost as motors which need not be hollow. So, a motor of the type which is solid and for which it is easy to construct the pressing system, etc. has been recently proposed in Japanese Patent Application No. 1-173528 or U.S. Application Serial No. 533,534 (filed on June 5, 1990) by the present applicant. Figures 5 and 6 of the accompanying drawings show the ultrasonic motor thus proposed, and the supporting of the vibrator 1 of this proposed bar-like ultrasonic motor has been accomplished by sandwiching a supporting electrode plate 22 between two piezo-electric elements (for example, PZTs) 4 as electro-mechanical energy conversion elements and a sandwiching member 2 which cooperates with the vibrator 1 to constitute a vibration member, and fixing the electrode plate 22 to a fixed member 25 by means of screws 26 or the like. The reference numeral 3 designates a bolt for bringing the vibrator 1 and the sandwiching member 2 into engagement with each other with the piezo-electric elements 4 and the electrode plate 22 interposed therebetween, and the reference numeral 24 denotes springs for urging washers 23 against the electrode plate 22. The shape of the supporting electrode plate 22 is a shape having flange portions on the end portions thereof as shown in Figure 5, and holes into which the screws 26 are fitted are of a diameter larger than the outer diameter of the screws 26. Now, in the case of an ultrasonic motor of the construction as described above, it is necessary to endow the direction of vibration, chiefly the direction perpendicular to the axis of the vibration member 1, 2, with a degree of freedom in order to maintain the vibration characteristic of the vibration member 1, 2 and for this reason, the screws 26 for fixing the vibration member cannot be completely fastened. As a result, there has been the problem that during the driving of the motor, the supporting electrode plate 22 shifts to right and left (the direction perpendicular to the axis of the vibration member 1, 2) and the efficiency of the motor is reduced due to the friction created between the electrode 22 and the washers 23 when the shift takes place. EP-A-0365231 discloses a vibration motor having a vibration member, a contact member, a piezo-electric vibrator, a pressing member, and means for supporting the pressing member and securing it to a fixed position. The vibrator includes two independent electrode patterns, each producing mechanical vibrations which, when combined, cause relative movement between the vibration member and the contact member. A concern of the present invention is to provide a vibration driven motor which solves the above-noted problem. Another concern of the present invention is to provide a vibration driven motor in which impairment of the efficiency of the motor is reduced or eliminated. According to the invention there is provided a vibration driven motor comprising: a vibration member; an electro-mechanical energy conversion member functionally coupled to said vibration member for generating in said vibration member at least one vibration wave in response to an applied signal; a bar-like member for coupling said conversion member to said vibration member; a contact member arranged to be driven by said vibration wave; and a resilient supporting member for applying a force relatively urging said vibration member against said contact member; characterised in that said vibration member has a bore therethrough, in that said supporting member is located on, or substantially on, an axis of said vibration member and in that said bar-like member is connected through said bore to a fixed member via said resilient supporting member. In this manner, the vibration member is indirectly supported. In the accompanying drawings:- Figure 1 is a plan view of an embodiment of the ultrasonic motor of the present invention. Figure 2 shows the construction of the essential portions of the motor shown in Figure 1. Figure 3 shows the arrangement of the piezo-electric elements and electrodes of the motor shown in Figure 1. Figure 4 shows the waveforms of AC voltages applied to the piezo-electric elements shown in Figure 3. Figures 5 and 6 are a plan view of an ultrasonic motor according to the prior art and a construction view, respectively, of the essential portions thereof. Figures 7 and 8 are a plan view of an ultrasonic motor according to another embodiment of the present invention and a construction view, respectively, of the essential portions thereof. Figures 9 and 10 are a plan view of an ultrasonic motor according to still another embodiment of the present invention and a construction view, respectively, of the essential portions thereof. Figures 11 to 19 are plan views of ultrasonic motors according to still further embodiments of the present invention and construction views, respectively, of the essential portions thereof. Figures 20 and 21 show the construction of the essential portions of a camera to which the bar-like ultrasonic motor of the present invention is applied. Figure 1 is a plan view of an ultrasonic motor (vibration driven motor) for a camera according to a first embodiment of the present invention, and Figure 2 shows the construction of portions of the Figure 1 motor. The motor will now be described, but in each of the following embodiments, elements functionally similar to those of the motor shown in Figures 5 and 6 are given similar reference numerals and need not be described. The reference numeral 1 designates a metallic cylindrical vibrator functionally similar to the vibrator shown in Figure 6 and having an inclined portion 1 a for transmitting a drive force to the inclined portion 9 a of a rotational member 9, and a threaded portion 1b with which a bolt 3 is threadably engaged. The reference numeral 2 denotes a metallic cylindrical sandwiching member functionally similar to the sandwiching member shown in Figure 6 and also having a thread portion 2 a with which the bolt 3 is threadably engaged. The bolt 3 is one for enabling two piezo-electric elements 4 to be sandwiched between the vibrator 1 and the sandwiching member 2, and the head 3a of the bolt 3 is formed with a hole of a predetermined depth, to the end of which is fixed the tip end of a bolt fixing pin 6. The pin 6 cooperates with a detent 12 fixed to a predetermined member of a camera to restrict the rotation of the vibration member 1, 2 within a predetermined range. When the diameter of the vibration member 1, 2 is 10 mm, the diameter of the pin 6 is 1 mm and the diameter of the tip end portion 3 b of the pin 6 is made as small as 1.4 - 2.0 mm, and the structure of this portion is designed not to adversely affect the vibration characteristic of the vibration member 1, 2. The construction of the aforementioned two piezo-electric elements 4 is as shown in Figure 3. The piezo-electric elements 4 are comprised of two piezo-electric elements 4A and 4B (or alternatively may be comprised of four piezo-electric elements), and in each of the piezo-electric elements 4A and 4B, two electrodes (plus electrode a and minus electrode b ) differing in the direction of polarization from each other and polarized in the direction of thickness are symmetrically formed on one side thereof at the opposite sides of an insulating portion d formed at the center axis position and the common electrode c of the plus electrode a and the minus electrode b is formed on the other side thereof, and these piezo-electric elements 4A and 4B are disposed with a positional phase difference of 90° therebetween with respect to the axis of the vibration member 1, 2. The reference numeral 5 designates a spring as a pressing member having one end thereof fixed to the end of the bolt 3 and having the other end thereof fixed to a fixing flange 7. By the biasing force of the spring 5, the vibration member 1, 2 is rotatably brought into frictional contact with the rotational member 9 as a moving member with the inclined portions 1 a and 9 a as the point of contact. The reference numeral 8 denotes screws for fastening the fixing flange 7 as a support member to a fixing member 13 which is a portion of the camera, the reference numeral 10 designates a gear for transmitting the rotational force of the rotational member 9 to the spool of the camera, and the reference numeral 11 denotes bearings for cutting off the transmission between the rotational member 9 and the fixing flange 7 and for preventing the fixing of the motor by the fixing flange 7, the screws 8 and the fixing member 13 from affecting the vibration member 1, 2. The operation of the motor constructed as described above will now be described. A voltage V 1 is applied from an AC voltage source V 1 to between an electrode plate 4D and an electrode plate 4C and a voltage V 2 is applied from an AC voltage source V 2 to between the electrode plate 4D and an electrode plate 4E, whereby there are generated a vibration by the expansion and contraction displacement of the piezo-electric element 4A in the direction of thickness thereof and a vibration by the expansion and contraction displacement of the piezo-electric element 4B in the direction of thickness thereof, and these vibrations are combined by the vibration member 1, 2, which is thus vibrated. In other words, said first energy conversion member 4A generates a first bending vibration having a first direction in said vibration member 1, 2 in response to an applied first electrical signal V 1 and said second energy conversion member 4B generates a second bending vibration having a second direction different from said first bending vibration in response to an applied second electrical signal V 2 , whereby a combined vibration of the first bending vibration and the second bending vibration is caused in said vibration member 1, 2. The AC voltage V 1 and the AC voltage V 2 , as shown in Figure 4, are the same in amplitude and frequency and has a time phase difference of 90° therebetween. Thus, the vibration member, as previously described, makes circular motion like the bending and stretching rope of rope skipping (hereinafter referred to as the rope skipping vibration). The principle on which this circular motion is created is known and need not be described herein. In the case of this embodiment, the vibration member is indirectly fixed at a predetermined position and therefore, even if the motor is firmly fixed by the screws 8, the loss of the motor is small, or in other words, there is provided a motor of good efficiency. Figures 7 and 8 are a plan view of an ultrasonic motor for a camera according to a second embodiment of the present invention and a view showing the construction of portions thereof, respectively, and this embodiment is one in which a parallel pin 14 is used as the tip end side hook of the spring 5, thereby increasing the strength of the portion to which the hook is secured. The fixing flange 7 in this embodiment has therein apertures 7 a and 7 b similar to apertures 7 a and 7 b formed in the fixing flange 7 shown in Figure 1, and an aperture 7 c through which the spring 5 is passed, and the parallel pin 14 is extended from the aperture 7 a to the aperture 7 b . Also, the fixing flange 7 is made of resin from the viewpoint of the attenuation characteristic of vibration and prevents the wear and damage of the portion thereof to which the hook is secured. As a detent for the vibration member 1, 2, use is made of a detent electrode 15 sandwiched between the sandwiching member 2 and the piezo-electric element 4. In the other points, the construction and operation of this embodiment are similar to those of the motor of the first embodiment and need not be described. Figures 9 and 10 are a plan view of an ultrasonic motor according to a third embodiment of the present invention and a view showing the construction of portions thereof, respectively. Regarding this and further embodiments, only the differences thereof from the aforedescribed embodiments will be described chiefly. In this third embodiment, the spring for pressing the rotational member is changed from a tension coil spring to a compression coil spring 5A. Thereby the assemblage of the motor becomes much easier. Because of the spring 5A being used, the fixing flange 7 has a level difference portion 7 a against which the spring 5A bears, as shown in Figure 10. The reference numeral 17 designates a washer against which one end of the spring 5A bears, the reference numeral 18 denotes an E-shaped ring, and the reference character 3A designates a bolt having the function of the aforedescribed bolt 3 and the function of transmitting the spring force of the spring 5A, to the rotational member 9 through the fixing flange 7 and bringing the rotational member 9 into frictional engagement with the vibration member 1, 2. Figures 11 and 12 are a plan view of an ultrasonic motor according to another embodiment of the present invention and a view showing the construction of portions thereof, respectively, and this embodiment adopts a combination of the system of the Figure 10 embodiment in which the pressing force is created by the compression spring 5A and the detent system by the electrode plate 15 shown in Figures 7 and 8. Figures 13 and 14 are a plan view of an ultrasonic motor according to still another embodiment of the present invention and a view showing the construction of portions thereof, respectively, and this embodiment is one in which a circular soft rubber ring 19 is wound on the mode position which seems to be least in affecting the vibration of the vibration member and a fixing member 20 provided at a predetermined position is fixed so as to embrace the rubber ring 19. By the soft rubber ring 19 being employed, a degree of freedom is given in the other directions than the direction of rotation of the vibration member. Figures 15 and 16 are a plan view of an ultrasonic motor according to another embodiment of the present invention and a view showing the construction of portions thereof, respectively, and this embodiment is one substantially similar to the embodiment of Figures 9 and 10 and in which a belleville spring 21 is employed in lieu of the compression coil spring 5A shown in Figure 10 to thereby achieve a reduction in cost. Figures 17 to 19 are a plan view of an ultrasonic motor according to another embodiment of the present invention, a view showing the construction of portions thereof and a fragmentary perspective view of a pin shown in Figure 18, respectively. This embodiment is one in which the bolt 3A in the embodiment of Figure 10 is constructed of a bolt 3 (see Figure 18) and a pin 27 threadably engaged with the threaded portion of the bolt 3. The pin 27, as shown in Figure 19, has a diametrically protruding projection 28 in the intermediate portion thereof, and this projection 28 is constructed so as to mesh with the projection 7b of the fixing flange 7. The rotation of the vibration member 1, 2 is restricted by this meshing. Figure 20 is a view showing the construction of portions of an ultrasonic motor for a camera according to another embodiment of the present invention. In Figure 20, the reference numeral 7 designates a fixing flange secured to the ground plate 40 of a camera by means of a screw 8, and the reference numeral 9 denotes a rotational member rotated by the drive force of a vibrator 1. The rotational force of the rotational member 9 is transmitted to the rotary cylinder 33 of the camera through a gear 10 rotated with the rotational member 9, a gear 30 meshing with the gear 10, a gear 31 meshing with the gear 30, and a gear 32 fitted to the gear 31. The reference numeral 36 designates a gear meshing with the gear 31 and having secured thereto a pulse plate 35 for detecting the position and speed of said rotary cylinder. The reference numeral 37 denotes a conventional photocoupler for detecting the position and speed of the pulse plate 35. The reference numeral 38 designates a lead wire connected to the photocoupler 37. The lead wire 38 is connected to the lens control circuit (not shown) of the camera. The operation of the motor of the above-described construction will now be described. When AC voltages are applied from a conventional driving circuit, not shown, to four piezo-electric elements 4, the vibration member 1, 2 is given a vibration conforming to the electrical phase difference between the applied AC voltages in a plurality of planes conforming to the polarized states of the piezo-electric elements 4 by the piezo-electric elements 4 and therefore, rotational motion is caused to the surface particles of the vibration member 1, 2 and as a result, the rotational member 9 receives a drive force from the inclined portion of the vibrator 1 and is rotated. Therefore, the gear 32 is rotated through the gears 10, 30 and 31, and the rotary cylinder 33 meshing with the gear 32 is also rotated, and with the rotation of the rotary cylinder 33, the optical system (not shown) of the photo-taking lens of the camera, not shown, is moved for focus adjustment. Figure 21 is a view showing the construction of portions of the photo-taking lens of a camera to which the ultrasonic motor of one embodiment of the present invention is applied. This embodiment is substantially the same as the camera of the embodiment shown in Figure 20, and is designed such that the aforedescribed rotary cylinder 33 meshes with a gear 32 operatively associated with the rotation of the rotational member 9 and the helicoid portion 33a thereof is helicoid-coupled to the helicoid portion 34a of a fixed cylinder 34. Also, this embodiment is one in which the rotary cylinder 33 is rotated in response to the rotation of the rotational member 9, whereby the focusing optical system 1 of the photo-taking lens is moved along the optical axis thereof. Since the vibration member is indirectly supported as described above, there is provided an ultrasonic motor in which the reduction in efficiency by the supporting of the vibration member is eliminated and which is of good efficiency.

Claims: A vibration driven motor comprising: a vibration member (1,2); an electro-mechanical energy conversion member (4) coupled to said vibration member (1,2) for generating in said vibration member (1,2) at least one vibration wave in response to an applied signal; a bar-like member (3,3A) for coupling said conversion member (4) to said vibration member (1,2); a contact member (9) arranged to be driven by said vibration wave; and a resilient supporting member (5, 5A, 21) for urging said vibration member (1,2) against said contact member (9); characterised in that said vibration member (1,2) has a bore therethrough, in that said supporting member (5,5A,21) is located on, or substantially on, an axis of said vibration member (1,2) and in that said bar-like member (3,3A) is connected through said bore to a fixed member (7) via said resilient supporting member (5,5A,21). A vibration driven motor as claimed in claim 1, characterised in that said supporting member (5,5A,21) comprises a compression spring (5A) arranged between said fixed member (7) and an abutment member (17) on said bar-like member (3A). A vibration driven motor as claimed in claim 1, characterised in that said supporting member (5,5A,21) is a tension coil spring (5). A vibration driven motor as claimed in claim 1, 2 or 3, characterised in that said conversion member (4) generates a first bending vibration having a first direction and a second bending vibration having a second direction different from said first bending vibration, whereby a combined vibration of said first and second bending vibration is generated in said vibration member (1,2). A vibration driven motor as claimed in any one of claims 1 to 4, characterised in that said vibration member (1,2) is substantially cylindrical in shape. A vibration driven motor as claimed in any one of claims 1 to 5, characterised in that said bar-like member (3,3A) is a threaded bolt which engages a thread in said bore to secure said conversion member (4) to said vibration member (1,2). A system having a driven member (30-36) and including a motor as claimed in any one of claims 1-6, wherein said contact member (9) is in driving connection with said driven member (30-36). A camera having a lens system movable for focus adjustment by transmission means (30, 32), and a motor as claimed in any one of claims 1-6, wherein said contact member (9) is in driving connection with said transmission means (30-32).

Inventors: FUJIMOTO KAZUKI, SUZUKI RYUJI, TAMAI JUN, FUJIMOTO, KAZUKI, SUZUKI, RYUJI, TAMAI, JUN, Fujimoto, Kazuki, c/o Canon Kabushiki Kaisha, Suzuki, Ryuji, c/o Canon Kabushiki Kaisha, TAMAI, JUN, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: H01L41
IPC codes: H02N2, H01L41