ULTRASONIC MOTOR

Abstract: In an ultrasonic motor having a rotor (6,12) and a vibrating stator (43,49) wherein travelling wave is excited to drive the rotor, the vibrating stator comprises a piezoelectric member (25,26,29) and alternately-­ disposed first segment electrodes and second segment electrodes, the first segment electrodes being connected with each other to form a first intermittent ring or linear electrode train and the second segment electrodes being connected with each other to form a second intermittent ring or linear electrode train, each of the segment electrodes having a length of a quarter of wavelength of the travelling wave in the direction of the travelling wave and being to be polarized in an opposite direction to adjacent electrodes within the same segment electrode.

Description: The present invention relates to an ultrasonic motor wherein the driving force is given by an elastic travelling wave excited by an electromechanical transducer such as a piezoelectric element. FIG.1 is a perspective view showing the conventional ring-type ultrasonic motor (disclosed in US-A-4 484 099 and US-A-4 692 651). A vibrating stator 3 comprises a ring-shaped elastic member 1 which is made of an elastic material such as steel and a ring-shaped piezoelectric ceramic member 2. The piezoelectric ceramic member 2 is bonded on one surface of the elastic member 1. A rotor 6 comprises a ring-shaped elastic member 5 which is also made of an elastic material such as steel and a ring-shaped lining member 4 which is made of a wear-resistive material. The lining member 4 is bonded on one surface of the elastic member 5. The lining member 4 of the rotor 6 is in contact with another surface of the elastic member 1 with a predetermined pressure. When a voltage is applied to the piezoelectric ceramic member 2, a travelling wave of flexural vibration is excited in the circumferential direction of the vibrating stator 3, and thereby the rotor 6 rotates in a direction shown by an arrow 51. FIG.2 is a bottom view showing electrodes provided on the piezoelectric ceramic member 2 of FIG.1. In the structure shown in FIG.2, nine waves of the travelling wave travel in the circumferential direction of the piezoelectric ceramic member 2. An electrode group "A" and an electrode group "B" consist of plural segment electrodes "a" and "b", respectively. The length of each segment electrode "a" or "b" in the circumferential direction corresponds to half a wavelength of the travelling wave (wavelength of flexural vibration). The lengths of electrodes "C" and "D" in the circumferential direction correspond to three quarters and a quarter of the wavelength of the travelling wave, respectively. The electrodes "C" and "D" are disposed to have a positional difference of a quarter (π/2 radian) of a wavelength from the electrode groups "A" and "B" The directions of polarization of adjacent two regions under segment electrodes "a" or "b" within the electrode groups "A" and "B" are opposite to each other with respect to the direction of thickness of the electrode. A flat electrode (not shown) is provided all over on the reverse surface (namely the back side of the top face shown in FIG.2) of the piezoelectric ceramic member 2. The reverse surface is to be bonded with the elastic member 1 (FIG.1). For applying a voltage to the electrode groups "A" and "B", plural segment electrodes "a" and "b" are electrically connected to serve as one driving electrode, respectively. In the above-mentioned piezoelectric ceramic member 2, when the following voltages defined as V₁ = V₀·sin(ωt) (1) V₂ = V₀·cos(ωt) (2) (wherein V₀ is the amplitude of voltage, ω is the angular frequency and t is the time) are impressed on the electrode groups "A" and "B", respectively, a flexural vibration which travels in the circumferential direction is excited in the vibrating stator 3. The flexural vibration holds the relation: wherein ξ is the instantaneous value of the flexural vibration, ξ₀ is the amplitude of the flexural vibration, k is the wave number (2π/λ) , λ is the wavelength and x is the position. FIG.3 is an illustration showing the relation between the vibration of the vibrating stator 3 and the movement of the rotor 6. A point "A" on the surface of the vibrating stator 3 performs an elliptical movement with a major axis 2w and a minor axis 2u by the travelling wave. The rotor 6 touches the vibrating stator with the predetermined pressure at a position around a crest of the ellipse, thereby frictionally making a movement in a direction shown by an arrow 52 which is opposite to the travelling direction of the travelling wave shown by an arrow 53. The velocity (V) of the movement is given by the equation: V = ω x u, wherein ω is the angular frequency of vibration. FIG.4 is an illustration showing the ring-shaped vibrating stator 3 and a graph showing the distribution of displacement thereof, wherein Z is the displacement in a perpendicular direction to the vibrating stator 3 and r is the radius to a position in the radial direction. Generally, a flexural vibration mode of the first order in the radial direction and of the third order or higher in the circumferential direction are applied to the ring-type ultrasonic motor. In the above-mentioned conventional ultrasonic motor, a voltage is applied to neither of the electrodes C and D (FIG.2) which occupy one wavelength ((3/4)λ+(1/4)λ=λ) of the travelling wave in the circumferential direction on the piezoelectric ceramic member 3. Since these electrode C and D make no contribution to the driving force, they effect lowering of the output power to the ultrasonic motor. Besides, since one driving electrode A or B is provided within a half-length of the ring-shaped piezoelectric ceramic member 2, an unstableness of rotation of the rotor 6 differently affects two electrodes A and B from each other, thereby making an undesirable change of characteristic in the ultrasonic motor. FIG.5 is a partially cut-out perspective view showing the conventional disk-type ultrasonic motor. A vibrating stator 9 comprises a disk-shaped piezoelectric member 8 and a disk-shaped elastic member 7. A rotor 12 comprises an elastic member 11 and a lining member 10 which is made of wear(abrasion)-resistive material. The lining member 10 of the rotor 12 is in contact with the elastic member 7 of the vibrating stator 9 with a predetermined pressure. A travelling wave, which consists of a flexural vibration of higher order in the radial direction and of the third or higher order in the circumferential direction, is excited in the vibrating stator 9, thereby making a rotational motion of the rotor 12. FIG.6 is an illustration showing the vibrating stator 9 of FIG.5 and a graph showing the distribution of displacement in the radial direction thereof, wherein Z is the displacement in a perpendicular direction to the face of vibrating stator 9 and r is the distance to a position in the radial direction. FIG.7 is an exploded perspective view showing a conventional vibrating stator 9A of the disk-type ultrasonic motor. The vibrating stator 9A comprises an elastic member 17 and two piezoelectric members 14 and 15. The piezoelectric members 14 and 15 have thereon driving electrodes which consist of many sectors of segment electrodes 14a and 15a, respectively. The length of each segment electrode 14a or 15a in the circumferential direction corresponds to a half wavelength of the travelling wave. The piezoelectric member 15, a metal sheet 16, the piezoelectric member 14 and the elastic member 17 are stacked up in this order in the axial direction and are coaxially bonded with each other, thereby to complete the vibrating stator 9A. Each boundary of the segment electrode 14a is positioned just above each center part of the segment electrode 15a in the circumferential direction of the vibrating stator 9A. When different voltages having a phase difference of π/2 radian from each other are simultaneously impressed on the above-mentioned piezoelectric members 14 and 15 with the metal sheet 16 serving as a common terminal, two standing waves having different spatial positions from each other by a quarter (π/2 radian) of the wavelength thereof are excited. Thereby, the travelling wave is excited in the vibrating stator 9A. A projection member 18 is provided on the elastic member 17 at a position where a loop 54 (FIG.6) of vibration is formed. Mechanical output is transmitted to the rotor (not shown) through the projection member 18, thereby to rotate the rotor around a shaft 19. In the above-mentioned disk-type ultrasonic motor shown in FIG.7, the mechanical burdens seen from two piezoelectric members 14 and 15, which are coaxially bonded, are different from each other. Consequently, the impedances seen from an electrode-terminal (not shown) of two piezoelectric members 14 and 15 are different from each other. When two voltages, which have an equal amplitude to each other and different phases from each other by π/2 radian, are applied to the respective piezoelectric members 14 and 15, two standing waves having different amplitudes from each other are excited in the respective piezoelectric members 14 and 15. As a result, a travelling wave which is composed of the large standing wave is excited, thereby resulting in a declination of efficiency of the ultrasonic motor. Besides, since the change of external burden (not shown) affects the piezoelectric members 14 and 15 differently, the ultrasonic motor undesirably changes the characteristic of rotation thereof with a change of the burden. Further, it is difficult to improve the reliability of fabrication because many bonding layers of adhesive agents lie among two piezoelectric members 14, 15, the metal sheet 16 and the elastic member 17. FIG.8 is an exploded perspective view showing another conventional vibrating stator 9B of the disk-type ultrasonic motor. The vibrating stator 9B comprises an elastic member 23 and a piezoelectric member 22 to be bonded to the elastic member 23. An electrode-group 20 and an electrode-group 21 are concentrically provided on the piezoelectric member 22. The electrode-groups 20 and 21 consist of segment electrodes 20a and 21a, respectively. The length of each electrode 20a or 21a in the circumferential direction corresponds to half a wavelength of the travelling wave. These segment electrodes 20a and 21a are electrically connected with adjacent electrodes sequentially, thereby forming two circular electrode groups 20 and 21. When the voltages having a phase difference of π/2 radian from each other are impressed on the electrode groups 20 and 21, a travelling wave is excited in the vibrating stator 9B. The mechanical output is transmitted to the rotor (not shown), thereby to rotate the rotor around a shaft 24. In the above-mentioned disk-type ultrasonic motor shown in FIG.8, the characteristic of rotation is stable against a change of burden in the circumferential direction. However, when the rotor receives force in the radial direction thereof, the distribution of displacement is changed in the radial direction, thereby differently affecting the respective electrode 20 and 21 from each other. Consequently, the impedances seen from two electrode groups 20 and 21 are not balanced, and the characteristic of rotation is undesirably changed. OBJECT AND SUMMARY OF THE INVENTION The object of the present invention is to offer an ultrasonic motor which hardly changes the characteristic of motor against a change of burden and which can output large mechanical power with high efficiency. This object is solved by an ultrasonic motor having the features of claims 1 or 4, resp. Advantageous embodiments of the ultrasonic motor according to the invention are indicated in the dependent claims. In the above-mentioned ultrasonic motor, mechanical output of the motor is larger than the conventional ultrasonic motor, and rotation of the rotor is stable against the change of burden. While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings. In the drawings: FIG.1 is a perspective view showing the conventional ring-type ultrasonic motor. FIG.2 is a bottom view showing electrodes provided on the piezoelectric ceramic member 2 of FIG.1. FIG.3 is an illustration showing the relation between a vibration of the vibrating stator 3 and a movement of the rotor 6. FIG.4 is an illustration showing the ring-shaped vibrating stator 3 and the graph showing distribution of displacement thereof. FIG.5 is a partially cut-out perspective view showing the conventional disk-type ultrasonic motor. FIG.6 is an illustration showing the vibrating stator 9 of FIG.5 and the graph showing distribution of displacement thereof. FIG.7 is an exploded perspective view showing the conventional vibrating stator 9A of the disk-type ultrasonic motor. FIG.8 is an exploded perspective view showing another conventional vibrating stator 9B of the disk-type ultrasonic motor. FIG.8A is a perspective view showing a ring-type ultrasonic motor of the present invention. FIG.8B is a partially cut-out perspective view showing a disk-type ultrasonic motor of the present invention. FIG.9 is a plane view showing a piezoelectric member 25 in a ring-type ultrasonic motor of an embodiment of the present invention. FIG.10 is a graph showing the positional relation of a flexural vibration in two driving electrodes of an embodiment of the present invention. FIG.11(a) is a plane view showing a piezoelectric member 26 in a ring-type ultrasonic motor of a second embodiment of the present invention. FIG.11(b) is a bottom view of FIG.11(a). FIG.12(a) is a plane view showing a piezoelectric member 29 in a disk-type ultrasonic motor of a third embodiment of the present invention. FIG.12(b) is a bottom view of FIG.12(a). FIG.13(a) is a plane view showing a piezoelectric member 60 in a linear-type ultrasonic motor of a fourth embodiment of the present invention. FIG.13(b) is a bottom view of FIG.13(a). Hereafter, preferred embodiments of the present invention are described with reference to the accompanying drawings. FIG.8A is a perspective view showing a ring-type ultrasonic motor. A vibrating stator 43 comprises a ring-shaped elastic member 1 which is made of elastic material such as steel and a ring-shaped piezoelectric member 25 made of ceramic etc. The piezoelectric member 25 is bonded on one surface of the elastic member 1. A rotor 6 comprises a ring-shaped elastic member 5 which is also made of an elastic material such as steel and a ring-shaped lining member 4 which is made of a wear-resistive material. The lining member 4 is bonded on one surface of the elastic member 5. The lining member 4 of the rotor 6 is in contact with another surface of the elastic member 1 with a predetermined pressure. When voltage is applied to the piezoelectric member 25, a travelling wave of flexural vibration is excited in the circumferential direction of the vibrating stator 43, and thereby the rotor 6 rotates in a direction shown by an arrow 51. FIG.8B is a partially cut-out perspective view showing a disk-type ultrasonic motor. A vibrating stator 49 comprises a disk-shaped piezoelectric member 29 and a disk-shaped elastic member 7. A rotor 12 comprises an elastic member 11 and a lining member 10 which is made of a wear-resistive material. The lining member 10 of the rotor 12 is in contact with the elastic member 7 of the vibrating stator 49 with a predetermined pressure. A travelling wave, which consists of a flexural vibration of higher order in the radial direction and of third order or higher in the circumferential direction, is excited in the vibrating stator 49, thereby making a rotational motion of the rotor 12. FIG.9 is a plane view showing the piezoelectric member 25 of a first embodiment in the ring-type ultrasonic motor. Plural segment electrodes a--p are aligned on one surface (a first surface) of the piezoelectric member 25. The length of each segment electrode is selected to correspond to a quarter of wavelength of the travelling wave (wavelength of flexural vibration) which travels in the piezoelectric member 25. A flat electrode (not shown) is provided all over on the reverse surface (a second surface, namely the back of FIG.9) of the piezoelectric member 25. The directions of polarization of every two adjacent segment electrodes (e.g. the electrodes a and b and the electrodes c and d) are made opposite to each other with respect to the direction of thickness of the segment electrodes a--p. The ring-shaped vibrating stator 43 (FIG.8A) is formed by bonding the second surface of the piezoelectric member 25 with the elastic member 1 (FIG.8A). To apply voltage to the segment electrodes a--p, the segment electrodes a--p are alternately connected with next one. That is, the segment electrodes a, c, e, g, i, k, m and o are connected with each other, thereby to make a first driving electrode group (first intermittent ring), and also, the segment electrodes b, d, f, h, j, l, n and p are connected with each other, thereby to make a second driving electrode group (second intermittent ring). When two voltages having different phases from each other by π/2 radian are impressed on two driving electrodes which are disposed alternately in the circumferential direction to form a substantial continuous ring, flexural vibrations are excited in the piezoelectric member 25. FIG. 10 is a graph showing the positional relation of the flexural vibrations in two driving electrodes. The positions of two standing waves A and B of the flexural vibrations are different from each other by a quarter of wavelength thereof, and thereby the travelling wave is generated in the vibrating stator 43 (FIG.8A) and travels in the circumferential direction. FIG.11(a) is a plane view showing a piezoelectric member 26 of a second embodiment in the ring-type ultrasonic motor. Plural segment electrodes a--p are aligned on one surface (a first surface) of the piezoelectric member 26. The length of each segment electrode in the circumferential direction is selected to correspond to a quarter of wavelength of the travelling wave. The segment electrodes a, c, e, g, i, k, m and o are connected with each other through strips 56 of an electrode pattern, thereby forming a first intermittent ring. FIG.11(b) is a bottom view of FIG.11(a), showing another surface (a second surface) of the piezoelectric member 26. Plural segment electrodes q--x are provided on the second surface of the piezoelectric member 26. The length of each segment electrode in the circumferential direction corresponds to half a wavelength of the travelling wave. An occupation area of a segment electrode on the second surface corresponds to a pair of segment electrodes on the first surface. For example, the segment electrodes a and b on the first surface correspond to the segment electrode on the second surface. The directions of polarization of adjacent segment electrodes (e.g. the electrodes q and r) are opposite to each other with respect to the direction of thickness of the segment electrodes q--x. Therefore, the directions of polarization seen from adjacent pairs of segment electrodes (e.g. the electrodes a and b and the electrodes c and d) on the first surface are made opposite to each other with respect to the direction of thickness of the segment electrodes a--p, the state of which is similar to the first embodiment (FIG.9). In other words, the directions of polarization of the segment electrodes a, c, e, g, i, k, m and o are alternately reversed in the circumferential direction, and also the directions of polarization of the segment electrodes b, d, f, h, j, l, n and p are similarly reversed. When the piezoelectric member 26 is assembled into the vibrating stator 43 (FIG.8A), the second surface of the piezoelectric member 26 is bonded to the elastic member 1 (FIG.8A) made of steel or aluminum. If the elastic member 1 is made of a conductor, the segment electrodes q--x on the second surface are electrically connected by directly attaching these to the elastic member 1. If the elastic member is made of an insulator, the segment electrodes q--x are to be electrically connected by electrically connecting means (not shown). The segment electrodes b, d, f, h, j, l, n and p are electrically connected by electrically connecting means 55 such as a wire, thereby forming a second intermittent ring. A terminal 27 is led from the electrodes a, c, e, g, i, k, m and o which are integrally formed with each other, and another terminal 28 is led from the electrodes b, d, f, h, j, l, n and p which are electrically connected with each other. When two driving voltages having different phases from each other with π/2 radian are impressed on the respective terminals 27 and 28, flexural vibrations are excited in the vibrating stator 43, and the travelling wave travels in the circumferential direction. FIG.12(a) is a plane view showing a piezoelectric member 29 of a third embodiment in the disk-type ultrasonic motor. An outer-teeth-shaped electrode 30 is formed to have plural segment electrodes 30a and strips 30b of an electrode pattern which connects adjacent two segment electrodes 30a and 30a, and an inner teeth-shaped electrode 31 is formed to have plural segment electrodes 31a and strips 31b of an electrode pattern which connects adjacent two segment electrodes 31a and 31a. The electrode 30 and the electrode 31 are provided on the piezoelectric member 29 with a gap 57 therebetween, thereby to serve as two driving electrodes. The length of each segment electrode 30a or 31a in the circumferential direction is selected to correspond to a quarter of a wavelength of the travelling wave. FIG.12(b) is a bottom view of FIG.12(a), showing another surface (a second surface) of the piezoelectric member 29. Plural segment electrodes 34 are provided on the second surface of the piezoelectric member 29. The length of each segment electrode 34 in the circumferential direction is selected to correspond to half a wavelength of the travelling wave. An occupation region of the segment electrode 34 on the second surface corresponds to that of a pair of the segment electrodes 30a and 31a on the first surface. The directions of polarization of adjacent segment electrodes 34 are made opposite to each other with respect to the direction of thickness of the segment electrodes 34. Therefore, the directions of polarization seen from adjacent two pairs of segment electrodes ((30a, 31a) and (30a, 31a)) are opposite to each other with respect to the direction of thickness of the electrodes 30 and 31, the state of which is similar to the first embodiment (FIG.9) and second embodiment (FIG.11(a)). When the piezoelectric member 29 is assembled into the vibrating stator 4a (FIG.8B), the second surface of the piezoelectric member 29 is bonded to the elastic member 7 (FIG.8B) made of steel or aluminum. If the elastic member 7 is made of a conductor, the segment electrodes 34 on the second surface are electrically connected by directly attaching these to the elastic member 7. If the elastic member 7 is made of an insulator, the segment electrodes 34 are to be electrically connected by electrically connecting means (not shown). Terminals 32 and 33 are led from the electrodes 30 and 31, respectively. When two driving voltages having different phases from each other with π/2 radian are impressed on the respective terminals 32 and 33, flexural vibrations of high order in the radial direction are excited in the vibrating stator 49, and the travelling wave travels in the circumferential direction. In the above-mentioned second and third embodiments, the circumferential length of each segment electrode q--x or 34 on the second surface may be designed to have not only half a wavelength of the travelling wave, but also a quarter of a wavelength thereof, provided that each segment electrode q--x (FIG.11(b)) or 34 (FIG.12(b)) is divided into two sectors. According to the above-mentioned respective embodiments, the driving electrodes are provided to dispersively cover the whole surface of the piezoelectric element, thereby obtaining a large mechanical output. Moreover, since the driving electrodes are dispersively disposed in the circumferential direction, the characteristic of rotation hardly changes with a change of burdens of the ultrasonic motor. Although the above-mentioned embodiments have been described for a rotating machine, the present invention is also applicable to a non-rotating motor such as a linear ultrasonic motor. In the linear ultrasonic motor, two groups of the small electrodes are alternately aligned in the travelling direction of the travelling wave which travels in a linear vibrating stator as shown for instance in FIG.13(a) which corresponds to a developed view of FIG.12(a) on a straight line. In the figure, a teeth-shaped electrode 61 is formed to have plural segment electrodes 61a and strips 61b of an electrode-pattern which connect adjacent two segment electrodes 61a and 61a, and another teeth-shaped electrode 62 is formed to have plural segment electrodes 62a and strips 62b of an electrode-pattern which connect adjacent two segment electrodes 62a and 62a. The electrode 61 and the electrode 62 are provided on the piezoelectric member 60 with a gap 63 therebetween, thereby to form two intermittent train-shaped driving electrodes. The length of each segment electrode 61a or 62a in the travelling direction is selected to correspond to a quarter of wavelength of the travelling wave. FIG.13(b) is a bottom view of FIG.13(a), showing another surface (a second surface) of the piezoelectric member 60. Plural segment electrodes 63 are provided on the second surface of the piezoelectric member 60. The length of each segment electrode 63 in the circumferential direction is selected to correspond to half a wavelength of the travelling wave.

Claims: An ultrasonic motor comprising a rotor (6, 12) and a vibrating stator (43, 49) wherein a traveling wave is excited to drive the rotor frictionally held on the stator, the vibrating stator comprising: a piezoelectric member (25, 26, 29); a first driving electrode which comprises a plurality of first segment electrodes (a, c, e, g, i, k, m and o, 30) electrically connected with each other to receive a first driving signal and aligned on and in the circumferential direction of the piezoelectric member; a second driving electrode which comprises a plurality of second segment electrodes (b, d, f, h, j, l, n and p, 31) electrically connected with each other to receive a second driving signal and aligned on and in a circumferential direction of the piezoelectric member; and an elastic member (1, 7) to which the piezoelectric member is fixed, characterised in that the first segment electrodes are aligned on a first surface of the piezoelectric member (25, 26, 29) in a manner to form a first intermittent ring, each of the first segment electrodes (a, c, e, g, i, k, m and o, 30) having a length in the circumferential direction to correspond to a quarter of a wavelength of the traveling wave; the second segment electrodes (b, d, f, h, j, l, n and p, 31) are aligned on the first surface of the piezoelectric member in a manner to form a second intermittent ring, each of the second segment electrodes having a length in the circumferential direction to correspond to a quarter of a wavelength of the traveling wave, the first intermittent ring and the second intermittent ring forming one substantial continuous ring by alternately disposing each of the first segment electrodes and the second segment electrodes; a third electrode (z, q to x, 34) is provided on a second surface of the piezoelectric member, the third electrode comprising a plurality of third segment electrodes (q to x, 34), each of which has a circumferential length based on the wavelength of the traveling wave and is attached on the back of at least one segment electrode of the first segment electrodes (a, c, e, g, i, k, m and o, 30) and the second segment electrodes (b, d, f, h, j, l, n and p, 31); the respective portions of the piezoelectric member, on which the first segment electrodes (a, c, e, g, i, k, m and o, 30) are provided, are polarized in an opposite direction to each of the adjacent portions; the respective portions of the piezoelectric member, on which the second segment electrodes (b, d, f, h, j, l, n and p, 31) are provided, are polarized in an opposite direction to each of adjacent portions; and the elastic member (1, 7) is stuck on the second surface of the piezoelectric member. The ultrasonic motor in accordance with claim 1, wherein each of the third segment electrodes (z, q to x, 34) has a circumferential length corresponding to half a wavelength of the traveling wave. The ultrasonic motor in accordance with claim 1, wherein each of the third segment electrodes (z, q to x, 34) has a circumferential length corresponding to a quarter of a wavelength of the traveling wave. An ultrasonic motor comprising a movable member and a vibrating stator wherein a travelling wave is excited to drive the movable member frictionally held on the stator, the vibrating stator comprising: a piezoelectric member (60); a first driving electrode which comprises a plurality of first segment electrodes (61a) electrically connected with each other to receive a first driving signal and aligned on the piezoelectric member in a travelling direction of the travelling wave; a second driving electrode which comprises a plurality of second segment electrodes (62a) electrically connected with each other to receive a second driving signal and aligned on the piezoelectric member in a travelling direction of the travelling wave; and an elastic member (1, 7) to which the piezoelectric member is fixed, characterised in that the first segment electrodes (61a) are aligned on a first surface of the piezoelectric member in a manner to form a first intermittent train, each of the first segment electrodes having a length in the travelling direction to correspond to a quarter of a wavelength of the traveling wave; the second segment electrodes (62a) are aligned on the first surface of the piezoelectric member in a manner to form a second intermittent train, each of the second segment electrodes having a length in the travelling direction to correspond to a quarter of a wavelength of the traveling wave, the first intermittent train and the second intermittent train forming one substantial continuous train by alternately disposing each of the first segment electrodes (61a) and the second segment electrodes (62a); a third electrode (63) is provided on a second surface of the piezoelectric member, the third electrode comprising a plurality of third segment electrodes, each of which has a length in the travelling direction based on a wavelength of the travelling wave and is attached on the back of at least one segment electrode of the first segment electrodes and the second segment electrodes; the respective portions of the piezoelectric member, on which the first segment electrodes (61a) are provided, are polarized in an opposite direction to each of adjacent portions; the respective portions of the piezoelectric member, on which the second segment electrodes (62a) are provided, are polarized in an opposite direction to each of adjacent portions; and the elastic member (1, 7) is stuck on the second surface of the piezoelectric member. The ultrasonic motor in accordance with claim 4, wherein each of the third segment electrodes (63) has a length in the travelling direction corresponding to half a wavelength of the travelling wave. The ultrasonic motor in accordance with claim 4, wherein each of the third segment electrodes (63) has a length in the travelling direction corresponding to a quarter of a wavelength of the travelling wave. The ultrasonic motor in accordance with claim 1 or 4, wherein the first segment electrodes and/or the second segment electrodes are connected with adjacent electrodes through a strip (56, 30b, 31b, 61b, 62b) of electrode pattern.

Inventors: KAWASAKI, OSAMU, NISHIKURA, TAKAHIRO, TAKEDA, KATSU
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1988
Main classification: H01L41
IPC codes: H02N2, H01L41