An ultrasonic driving device

Abstract: In the present invention, an electrode (2,3) in both end portions of a piezoelectric vibrator (1) is respectively divided in two (2a,2b,3a,3b), alternative current voltage is supplied to each of electrodes of the both end portions, whereby reversible circumferential progressive wave arises on the both end portions or side portion of a state consisting of the piezoelectric vibrator (1). A member to be driven is composed on each of the both end portions or the side portion of the stator (4).

Description: Background of the Invention : The present invention relates to an ultrasonic driving device comprising a stator consisting of a columnar piezoelectric vibrator having divided electrodes at each end portion of said vibrator. In a known ultrasonic motor using a piezoelectric vibrator, two groups of electrodes are attached to one end of a ring type piezoelectric ceramic, the two group of electrodes are so positioned that standing waves respectively generated by the two groups of electrodes are sifted every π/2 in each position. The parts of the ring type piezoelectric vibrator corresponding to the electrode are alternately polarized in reverse. Also, the two groups of the electrodes are respectively connected to two oscillators for respectively generating alternating current voltages having π/2 phase shift each other. When the alternating current voltages from the two oscillators are respectively applied to the two groups of electrodes, the two standing waves having π/2 phase shift each other generate on the surfaces of the ring type piezoelectric vibrator and then progressive waves owing to an compound of the two standing waves generate on the surfaces of the ring type piezoelectric vibrator. Therefore, when a rotary member is put on the ring type piezoelectric vibrator and the rotary member is strongly pressed to the ring type piezoelectric vibrator, the rotary member is rotated by the progressive waves. In the prior ultrasonic motor, since the ring type piezoelectric vibrator must be polarized in the many portion thereof and the two oscillators must be connected to the electrodes, the composition of the ring type piezoelectric vibrator is complex and the cost of the ultrasonic motor becomes expensive. US-A-4 645 964 discloses a vibration wave motor which drives a movable member having a plurality of electrostrictive elementes arranged in order to have a phase difference therebetween. The electrostrictive elements are ring-shaped and polarized around its circumference at a constant pitch. The electrostrictive members are distributed on a first and a second surface on the inner peripheral portion of vibration member. Summary of the Invention : It is, therefore, the primary object of the present invention to provide an ultrasonic driving device having a simple composition. In order to accomplish the above object, the present invention provides an ultrasonic driving device as described in claim 1. Further embodiments of the invention and the advantages thereof appear from the dependent claims and the following description. Brief Description of the Drawings : Fig.1 shows a sectional view of an ultrasonic motor in the prior art. Fig. 2 shows a plane view of a form of a piezoelectric vibrator and a composition of electrodes of the piezoelectric vibrator in the ultrasonic motor in Fig. 1. Fig.3 shows a perspective view of a stator of an ultrasonic driving device of an embodiment in the present invention. Fig.4 shows a view of explaining an operation of a stator in Fig.3. Fig.5 shows a simple side view of an ultrasonic driving device of the embodiment in the present invention. Fig.6 shows a front view of a fan of an ultrasonic driving device according to the present invention. Fig.7 shows a side view of the fan of Fig.6. Fig.8 shows a sectional view of one part of the fan in Fig.6. Figs.9 shows a side sectional view of a fan of the other ultrasonic driving device using according to the present invention. Description of the Preferred Embodiments : Referring to the prior art in Fig. 1, a ring type piezoelectric vibrator B is attached to a ring type resilient member A and the piezoelectric vibrator B vibrates with the resilient member. The piezoelectric vibrator B is divided in 17 parts by the ratio of e.g. 22.5° or 11.25°. The respective neighbouring portions in the 17 parts of the piezoelectric vibrator B are polarized by the reverse polarity each other as shown in Fig. 2. The two portions C and D in the one side of the piezoelectric vibrator B are respectively attached as an electrode by conductive paint as shown in Fig.2. The portion G in Fig.2 shows an earth electrode. The member F to be driven to which slider E is attached is mounted on the resilient member A. In the ultrasonic motor in the prior art, the alternating current voltage of V₀sinωt is applied to the one electrode C and the alternating current voltage V₀cosωt is applied to the other electrode D, where V₀ is instantaneous value, ω is radian frequency and t is time. The phases of these voltages shift by π/2 each other. Thereby, the divided portions of the piezoelectric vibrator B alternately arise expantion and contraction and thus, the resilient member A arises bending vibration. Therefore, standing wave is generated in the resilient member A and progressive wave is generated on the resilient member A. Thus, the driven member F having the slider E is rotated on the resilient member A. However, in the prior ultrasonic motor, because the divided portions of the ring type piezoelectric vibrator B must be alternately polarized and the divided electrodes must be formed on the divided portion of the piezoelectric vibrator B, the composition of the prior ultrasonic motor is complex. Referring to Fig. 3, in a stator consisting of a columnar piezoelectric vibrator in the embodiment of the present invention, divided electrodes 2a and 2b are provided with one end of a piezoelectric vibrator 1 and divided electrodes 3a and 3b are provided with the other end of the piezoelectric vibrator 1. Gaps 2c and 3c are respectively formed between the divided electrodes 2a, 2b and 3a, 3b and are shifted each other(about 90° in this embodiment). In the above stator 4, when alternative current voltage is applied to the divided electrode 2a and electrode 3a, circumferential progressive wave progressing to one direction arises on the end portions and side portion of the stator 4 as shown by an arrow A in Fig.4. When alternative current voltage is applied to the divided electrode 2b and electrode 3a, circumferential progressive wave progressing to the reverse direction arises on the end portions and side portion of the stator 4 as shown by an arrow B in Fig.4. Explaining the principle for generating the circumferential progressive wave on the stator 4, when the alternative current voltage having the resonance frequency of the piezoelectric vibrator 1 is applied to the electrodes 2a and 3a, since the gaps 2c and 3c are shifted by about 90°, the voltage is obliquely exerted in the stator 4 as shown by an arrow C in Fig.3. Therefore, thickness vibration is changed to torsion vibration in the stator 4 and circumferential progressive wave to the direction of the arrow A may arise on the end and side portions of the stator 4 as shown in Fig.4. When the voltage is applied to the electrodes 2b and 3b, also the circumferential progressive wave arises to the direction of the arrow A as same as the above composition. When the alternative current voltage having the resonance frequency of the piezoelectric vibrator is applied to the electrodes 2b and 3a, the voltage is obliquely exerted in the stator 4 as shown by an arrow D in Fig.3. Therefore, thickness vibration is chaged to torsion vibration in the stator 4 and circumferential progressive wave to the direction the arrow B may arise on the end and side portions of the stator 4 as shown in Fig.4. When the voltage is applied to the electrodes 2a and 3b, also the circumferential progressive wave arises to the direction of the arrow B. In the above instance, even if the gaps 2c and 3c are shifted by 90°, the shift of these gaps 2c and 3c may be 45° or the gaps 2c and 3c may be slightly shifted. The shift of the gaps 2c and 3c is not strictly set and the voltage may be obliquely exerted on the stator by the electrodes. In the above instance, if the gaps 2c and 3c is set in parallel and the voltage is applied to the electrodes 2a and 3a or 2a and 3b, the direction of the circumferential progressive wave on the stator becomes unstable, and the circumferential progressive wave generates to the arrow A or B by the slight change of the frequency of the resonance of the stator 4. Referring to Fig.5, when a member 5 to be driven is pressed on the end portion of a stator 4 consisting of a columnar type piezoelectric vibrator, the member 5 is rotated very smoothly. Also, if the side portion of the member is pressed on the side portion of stator 4, the member 5 is rotated very smoothly. Referring to Fig.6, Fig.7 and Fig.8, a stator 4 and a supporting plate 7 are fixed with a base 6 by a screw 8. A cylindric member 5 to be driven is mounted on a circumferential portion of the stator 4 and a stopper 10 is fixed on the end portion of the stator 4 by a screw 9. The ends of a plurality of vanes 11 are fixed on the member 5. As shown in Fig.8, one ends of the springs 12 are fixed on the inside of the member 5 and the other ends of the springs 12 are pressed on the stator 4. As shown in Fig. 3, when the alternative current voltage having resonance frequency of the piezoelectric vibrator is applied to two of the electrodes 2a or 2b and 3a or 3b, the member 5 is rotated and this device can be used as a fan. Referring to Fig.9, the one end the stator 4 and a cylindric supporting member 7 are fixed with a base 6 by a screw 8. A space is provided between the stator 4 and the cylindric supporting member 7 and a plurality of balls 13 supported by a member 5 to be driven are put between the stator 4 and the cylindric supporting member 7 and are inserted in grooves of the member 7. A bearing 15 of the member 5 is rotatably supported by a screw 14 fixed with the other end of the stator 4 and a plurality vanes are fixed with the outside of the member 5. In the fun having the above composition, the balls 13 of the member 5 are rotated by the circumferential progressive wave generated on the stator 4 and make rolled in the grooves of the cylindric supporting member 7. In this fan, if lubricating oil is supplied to the balls 13, the supporting member 7 and balls 13 is protected from these wear. Also, since the balls 13 are contacted with the hard side portion of the piezoelectric vibrator ceramics 1, the piezoelectric vibrator and its electrodes need not have protective members. In the above embodiment, though the electrodes of the end portions of the piezoelectric vibrator 1 are respectively divided in two, the electrodes may be divided in three or more and then if the alternative voltage is supplied to one or more of the electrodes of the one end of the piezoelectric vibrator, the circumferential progressive wave can be arisen on the stator 4.

Claims: Ultrasonic driving device comprising a stator (4) and a driven member (5) characterized in that the stator (4) consists of a columnar piezoelectric vibrator and groups of electrodes (2a, 2b, 3a, 3b), one group positioned at each end portion of the piezoelectric vibrator, said end portions are essentially flat and parallel surfaces, each group of electrodes is comprised by at least two electrodes, each pair of said electrodes is spaced by a straight gap (2c, 3c), the line defined by the direction of a gap positioned at one end portion is twisted with respect to the line defined by the direction of a gap positioned at the other end portion. the driven member (5) is connected to one end portion or side portion of the stator (4), and alternative current voltage is supplied to the two or more electrodes (2a, 2b, 3a, 3b). Ultrasonic driving device according to claim 1, cha racterized in that the gaps (2c, 3c) of the electrodes (2a, 2b, 3a, 3b) are slightly twisted with respect to each other. Ultrasonic driving device according to claim 1, cha racterized in that the gaps (2c, 3c) of the electrodes (2a, 2b, 3a, 3b) are twisted with respect to each other by 45°. Ultrasonic driving device according to claim 1, cha racterized in that the gaps (2c, 3c) of the electrodes (2a, 2b, 3a, 3b) are twisted with respect to each other by 90°. Ultrasonic driving device according to one of the foregoing claims, characterized in that the stator (4) is fixed to a base (6). Ultrasonic driving device according to claim 5, cha racterized by a plate (7) which is fixed with the base (6), a spring (12), which is fixed with one end with the inside of the driven member (5) and with the other end contacted to the side portion of the stator (4), and a plurality of vanes (11) which are fixed with the driven member (5). Ultrasonic driving device according to claim 5, cha racterized by a cylindric supporting member (7) which is fixed with the base (6), balls (13) which are rotatably supported in the driven member (5) and which are positioned between the cylindric supporting member (7) and the stator (4), and a plurality of vanes (11) which are fixed with the driven member (5).

Inventors: HONDA KEISUKE, HONDA, KEISUKE
Applicants: HONDA ELECTRONIC, HONDA ELECTRONIC CO., LTD.
Application year: 1988
Main classification: H01L41
IPC codes: H01L41, H02N2