Ultrasonic motor having high drive efficiency

Abstract: An ultrasonic motor has a stator (100) having a piezoelectric member (102) vibrated by a drive signal, and an elastic member for generating a traveling vibration wave in a drive surface (P1) thereof upon vibration of the piezoelectric member, a rotor (20) which is urged against the drive surface of the elastic member and is driven by the generated traveling vibration wave, a support member (30, 33, 36, 300, 303, 306, 309, 313) integrally molded on the elastic member, and a fixing member for holding the support member. In the ultrasonic motor, one end face (P3) of the support member is formed at the same level as the drive surface (P1) or the junction surface (P2) of the elastic member, an electrode (13) of the piezoelectric member is grounded through the support member, a plurality of holes (312, 316) are regularly formed in the circumferential direction of the support member, or the support member is fixed to the fixing member by an adhesive (400), thereby improving drive efficiency.

Description: BACKGROUND OF THE INVENTION : Field of the Invention The present invention relates to an ultrasonic motor having high drive efficiency, which causes a stator to generate a traveling vibration wave, thereby driving a rotor. More particularly, the present invention relates to an ultrasonic motor having high drive efficiency, which causes an elastic member to generate a traveling vibration wave upon vibration having a vibration frequency in an ultrasonic range of a piezoelectric member, thereby driving a rotor. Related Background Art The structure of a conventional ultrasonic motor is disclosed in, e.g., JP-A-62-77068. Fig. 1 is a sectional view of the ultrasonic motor. A stator 1 is constituted by integrally fixing a piezoelectric member 1b to an elastic member 1a. A radial support member 3 is integrally molded on an inner peripheral surface of the elastic member 1a near a neutral axis of the stator 1 as a whole. The support member 3 has a thin plate portion 3a provided to the inner peripheral surface of the elastic member 1a, and a thick portion 3b provided on the peripheral edge of the thin plate portion 3a and having a larger thickness than that of the thin plate portion 3a. A technique for integrally molding the support member to the elastic member in this manner is also disclosed in, e.g., JP-A-59-213286. The thick portion 3b is fixed in a case 5 which receives a bearing 4. A flange portion 6a radially projects from the inner periphery of the rotor 2, and a thick portion 6b is integrally molded on the peripheral edge of the flange portion 6a. A compression force by a given means (not shown) is applied to the thick portion 6b through a bearing 7, so that a lower surface 8 of the rotor 2 is urged against a drive surface 1c of the elastic member 1a. When an AC voltage is applied to the piezoelectric member 1b, the piezoelectric member 1b causes bending vibration, and a traveling vibration wave is generated in the elastic member 1a. This vibration wave frictionally drives the rotor 2. The generation mechanism of the traveling vibration wave is described in detail in JP-A-60-24582, and a description thereof will be omitted. The structure of a conventional stator is disclosed in, e.g., JP-A-60-245482. Figs. 5 and 6 show this structure. A stator 10 is constituted by adhering an annular elastic member 11 and an annular piezoelectric member 12. A plurality of electrodes 13 (Fig. 6) are formed on the upper surface of the piezoelectric member 12, and electrodes 14a to 14d are also formed on its lower surface. The elastic member 11 is adhered to the piezoelectric member 12 so as to be electrically connected to all the electrodes 13. These electrodes are magnetized to alternately have opposite polarities. One-end portions of lead wires 15 and 16 are respectively soldered to the electrodes 14a and 14b. An AC voltage is applied to the electrodes 14a and 14b through these lead wires 15 and 16. The other end of a lead wire 17, one end of which is grounded, is soldered to the electrode 14c. The electrode 14c is electrically connected to the elastic member 11 through a conductive adhesive 18. In the above-mentioned structure, all the electrodes 13 are grounded through the elastic member 11, the conductive adhesive 18, the electrode 14c, and the lead wire 17. Therefore, when an AC voltage is applied to the electrodes 14a and 14b, this is equivalent to apply a voltage to the widthwise direction of the piezoelectric member 12. When a predetermined AC voltage is applied to the electrode 14a through the lead wire 15, and an AC voltage having a 90° phase difference from the predetermined voltage is applied to the electrode 14b through the lead wire 16, the piezoelectric member 12 is vibrated by these applied voltages. Upon this vibration, a traveling vibration wave is generated in a drive surface 11a of the electric member 11. However, in this structure, the elastic member 11 and the electrode 14c are electrically connected through the conductive adhesive 18 to ground the electrodes 13. Therefore, the adhesive 18 is degraded by vibration of the elastic member 11 in use, resulting in a grounding error of the electrodes 13. Since ultrasonic vibration has a high frequency, it has a peeling effect as demonstrated in ultrasonic washing. Thus, the ground lead wire 17 may be directly connected to the elastic member 11 through a screw or the like so as not to disconnect the lead wire 17. However, undesirable vibration occurs in the connected portion due to the weight of the screw, and as a result, smooth driving is disturbed. SUMMARY OF THE INVENTION: It would be desirable to improve drive efficiency of an ultrasonic motor by preventing a grounding error of electrodes formed on a stator caused by unnecessary vibration generated in an elastic member. The present invention is set out in the appended claims. According to an embodiment of the present invention, there is provided an ultrasonic motor in which a first electrode is arranged on a surface of a piezoelectric member on a side contacting an elastic member, a second electrode is arranged on an opposite surface, the first electrode is grounded through the elastic member, and an AC voltage is applied to the second electrode to vibrate the piezoelectric member, comprising grounding means for grounding the first electrode through a support member integrally formed on the outer or inner peripheral surface of the elastic member. With this structure, when the piezoelectric member vibrates and a travelling vibration wave is generated in the elastic member, a grounding error of the first electrode can be prevented, thus improving drive efficiency of the ultrasonic motor. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a sectional view showing a structure of a conventional ultrasonic motor; Fig. 2 is a sectional view showing an embodiment of an ultrasonic motor according to the present invention; Fig. 3 is a sectional view showing another embodiment of a stator, a support member, and a fixing member constituting the ultrasonic motor according to the present invention; Fig. 4 is a sectional view showing still another embodiment of an ultrasonic motor according to the present invention; Figs. 5 and 6 show a structure of a conventional stator, in which Fig. 5 is a perspective view thereof, and Fig. 6 is a sectional view thereof; DESCRIPTION OF THE PREFERRED EMBODIMENTS: Embodiments of the present invention will be described below with reference to Figs. 2 to 4. Fig. 2 is a sectional view showing an ultrasonic motor according to the present invention. A first electrode 13 is formed on an upper surface of a piezoelectric member 12 constituting a stator 10, and second electrodes 14a and 14b are formed on its lower surface. A conductive elastic member 11 is coupled to the piezoelectric member 12 so as to be electrically connected to the electrode 13. The electrodes 14a and 14b are connected to lead wires 15 and 16 in the same manner as in Figs. 5 and 6. The elastic member 11 is formed of a conductive material such as phosphor bronze, stainless steel, or invar. A flange-like support member 300 radially extends from the outer peripheral surface of the elastic member 11 near a neutral surface of the stator 10 as a whole by integral molding. The support member 300 has a thin plate portion 301 contiguous with the outer peripheral surface of the elastic member 11 and having a thickness of about 0.3 mm, and a thick portion 302 contiguous with the thin plate portion 301. The thickness of the thick portion 302 is sufficiently larger than that of the thin plate portion 301. A male thread is formed on the peripheral surface of the thick portion 302, and is threadably engaged with a female thread formed on the inner peripheral surface of an annular fixing member 53, thereby fixing and holding the elastic member 11. The other end of a lead wire 17, one end of which is grounded, is mounted on the upper surface of the thick portion 302 by a screw 52. A rotor 20 is constituted by adhering an annular slider member 22 to an annular rotor base 21. A flange portion 21a radially projects from a portion of the rotor base 21 near a neutral surface of the rotor as a whole, and a support member 54 is integrally molded on the peripheral edge of the flange portion 21a. A compression force generated by a compression means (not shown) is transmitted to the rotor 20 through the support member 54, thereby urging the lower surface of the slider member 22 against a drive surface 11a of the elastic member 11. In the above structure, the electrode 13 is grounded through the elastic member 11, its support member 300, and the lead wire 17. As described above, a predetermined AC voltage is applied to the electrodes 14a through the lead wire 15, and an AC voltage having a 90° phase difference from the predetermined voltage is applied to the electrode 14b through the lead wire 16. Upon application of these voltages, the piezoelectric member 12 vibrates, and a traveling vibration wave is generated on the drive surface 11a of the elastic member 11. As a result, the rotor 20 is driven. In this case, the thick portion 302 of the support member 300 is not vibrated since it is fixed to the fixing member 53. As described above, the support member 300 and the elastic member 11 are integrally formed, and the lead wire 17 is connected to the thick portion 302 of the support member 300 to ground the electrode 13. Therefore, no conductive adhesive 18 (Fig. 5) is necessary. The thick portion 302 is not almost influenced by the vibration of the piezoelectric member 12, and does not cause a grounding error due to vibration of the elastic member 11 unlike in the conventional structure. In addition, no undesirable vibration acts on the elastic member. The thick portion 302 is not always necessary to prevent a grounding error of electrodes as an object of the present invention. That is, the distal end of the thin plate portion 301 may be fixed and held by a fixing member. In the above structure, the lead wire 17 and the screw 52 constitute a grounding means. As shown in Fig. 3, a fixing member 55 may be formed of a conductive material, the grounding lead wire 17 may be fixed to the fixing member 55 by the screw 52, and the electrode 13 may be grounded through the elastic member 11, a support member 303, the fixing member 55, and the lead wire 17. In the above structures, the lead wire 17 is connected to the thick portion 302 or the fixing member 55 by the screw 52 but may be soldered thereto. A printed circuit board may be used in place of the lead wire 17. In addition, the male thread is formed on the peripheral edge of the thick portion 302 or 305, and the threaded portion is threadably engaged with the fixing member. However, the thick portion 302 or 305 may be fixed to be vertically clamped by a pair of fixing members. In the above structures, the support member 300 or 303 is formed on the outer peripheral surface of the elastic member 11. However, as shown in Fig. 4, a support member 306 may be formed on the inner peripheral surface of the elastic member 11, and the support member may be fixed by a fixing member 56 inside the elastic member 11.

Claims: An ultrasonic motor which has a first electrode for grounding and a second electrode for applying an AC voltage, comprising: a piezoelectric member (12) on one surface of which the first electrode (13) is formed and on the other surface of which the second electrode (14a, 14b) is formed; a conductive elastic member (11) which is coupled to said piezoelectric member, which is electrically connected to said first electrode and which generates a vibration in a drive surface (11a) thereof upon vibration of said piezoelectric member; a rotor (20) which is in contact with the drive surface of said elastic member and is driven by the travelling vibration wave; grounding means (17, 52) for grounding said first electrode; and a support member (300, 303, 306) for supporting said elastic member, characterised in that said support member is integrally formed on an inner or outer peripheral surface of said elastic member, and in that said first electrode is grounded through said elastic member and said support member. An ultrasonic motor according to claim 1, wherein said support member comprises a thin plate portion (301, 304, 307) which damps said vibration and a thick portion (302, 305, 308) for fixing the ultrasonic motor to a device in which the ultrasonic motor is incorporated. An ultrasonic motor according to claim 2, wherein said support member is conductive and in which said thin plate portion, said thick portion and said elastic member are integrally formed. An ultrasonic motor according to claim 3, further comprising a conductive fixing member (53, 55, 56) to which said thick portion is fixed, said grounding means being attached to said fixing member. An ultrasonic motor according to any of claims 2 to 4, wherein said grounding means is attached at a location where the vibrations of the elastic member have been damped via said support member. An ultrasonic motor according to any preceding claim, wherein said first electrode (13) is interposed between the conductive elastic member (11) and the piezoelectric member (12). An ultrasonic motor according to any of claims 1 to 3, wherein said grounding means (17, 52) is attached directly to said support member. An ultrasonic motor according to any preceding claim, wherein said grounding means is a grounding lead wire, or a printed circuit board. An ultrasonic motor according to any preceding claim, wherein said rotor includes an insulating slider member on a surface thereof in contact with the drive surface of said elastic member. An ultrasonic motor according to claim 4, wherein said thick portion has an external thread portion and wherein said fixing member has an internal thread portion, said thick portion being screwed into said fixing member. An ultrasonic motor according to any preceding claim, wherein a third electrode (14a, 14b) is formed on the same surface of the piezoelectric member as the second electrode. An ultrasonic motor according to any preceding claim, wherein said vibration is a travelling vibration wave.

Inventors: NEMOTO SHIGEHISA, SAYA DAISUKE, TAKAGI TADAO, NEMOTO, SHIGEHISA, SAYA, DAISUKE, TAKAGI, TADAO
Applicants: NIPPON KOGAKU KK, NIKON CORPORATION
Application year: 1990
Main classification: H01L41
IPC codes: H01L41, H02N2