Multilayer piezoelectric element and vibration-wave drive device

A vibration-wave drive motor incorporating a multilayer piezoelectric element having reduced vibration damping as well as a design lending itself to reduced manufacturing costs and miniaturization. The multilayer piezoelectric element includes a piezoelectric active part formed by a plurality of piezoelectric layers having an internal electrode, and a piezoelectric inactive part formed by an integrated piezoelectric layer with no internal electrodes. The vibration-wave drive motor consists of a vibration body including the multilayer piezoelectric element, and a contact body press contacting the vibration body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a multilayer piezoelectric element, and more particularly to a vibration-wave drive device.

2. Description of the Related Art

Piezoelectric material having an electrical-mechanical energy conversion function for converting electrical energy into mechanical energy is being used for various purposes. In particular, multilayer piezoelectric elements formed by laminating, integrating and sintering multiple layers of piezoelectric material are being used. A laminated layer results in large deformation distortions and large forces with a low applied voltage as compared to a piezoelectric element consisting of a single plate-shaped piezoelectric body. Also, the thickness of a laminated layer can be larger so that a small high-performance multilayer piezoelectric element can be easily manufactured.

For example, U.S. Pat. Nos. 6,046,526 and 5,770,916 dislose manufacturing techniques for a vibration-wave motor serving as a vibration-wave drive device. In particular, disclosed is a multilayer piezoelectric element serving as a multilayer electrical-mechanical energy conversion element constituting part of a vibration body of the vibration-wave motor formed in a bar shape. For uses other than the vibration-wave motor, many techniques regarding multilayer piezoelectric elements are proposed.

The multilayer piezoelectric element consists of layers of piezoelectric material (formed by a plurality of piezoelectric ceramics) and electrode layers (hereinafter, internal electrodes) provided on the surface of the respective piezoelectric layers and formed by electrode material. The piezoelectric layers and the internal electrodes are multiply laminated and then sintered. After sintering, they are polarized to have a piezoelectric property. That is, it is generally the case for a multilayer piezoelectric element that the plurality of internal electrodes are arranged over the multilayer piezoelectric element and the piezoelectric layer is a piezoelectric active part having a piezoelectric property.

FIG. 9shows an exploded perspective view of a multilayer piezoelectric element used for a vibration body of a bar-type vibration-wave motor disclosed in U.S. Pat. No. 5,770,916.

InFIG. 9, the multilayer piezoelectric element40includes internal electrodes43provided on the surfaces of a plurality of piezoelectric layers42. Connecting electrodes43a(black parts in the figure) connected to the respective internal electrodes43and extending to outer peripheral parts of the piezoelectric layers42are formed on the surface of the piezoelectric layers42. The internal electrodes43are arranged such that the outer periphery thereof is within the outer periphery of the piezoelectric layer42, which is divided into four portions (AG, AG, BG, BG, A+, A−, B+, B+), and the respective internal electrodes43formed on the same layer are non-conductive to each other.

For every other piezoelectric layer42, the connecting electrodes43aare formed to be axially on the same phase positions of the multilayer piezoelectric element40in relation to the internal electrodes43. The connecting electrodes43aon the same phase position are connected by outside electrodes44as electrodes for continuity among the layers provided to the outer periphery of the multilayer piezoelectric element40.

A plurality of surface electrodes45are provided along the periphery arround the outer periphery of the piezoelectric surface of the top layer constructing the multilayer piezoelectric element40and are connected to the outside electrodes44provided with matching the phase positions of the connecting electrodes43a. Direct current is applied to the respective internal electrodes43via the surface electrodes45, and the surface electrode45is polarized to provide polarized polarities for enabling the following vibration-wave motor to be driven.

FIG. 10is a section view of the multilayer piezoelectric element40shown in theFIG. 9combined to a vibration body51of a bar-type vibration-wave motor50.

InFIG. 10, the multilayer piezoelectric element40with a penetrating hole in the center has the surface electrode45contacting with a flexible circuit board52and is arranged between hollow metallic members53and54constituting the vibration body51. By inserting and screwing a bolt55into the metallic member54from the metallic member53side, the multilayer piezoelectric element40and the flexible circuit board52are placed and fixed between the metallic members53and54. The flexible circuit board52is connected to the surface electrodes45connected to the outside electrodes44of the multilayer piezoelectric element40and to a drive circuit which is not shown in the figures, and high-frequency voltage for driving is applied to the multilayer piezoelectric element40.

A rotor58contacting the tip of the metallic member54by pressing via a spring56and a spring support body57is arranged on one side of the vibration body51in the axial direction, and the rotation output of the vibration-wave motor50can be extracted by a gear59rotating integrally with the rotor58.

The drive principle of the bar-type vibration-wave motor50is that two bending vibrations axially crossing the vibration body51to which the multilayer piezoelectric element40is assembled are generated with a time phase difference, so that the metallic member54moves in a swiveling manner with the tip of the metallic member54constituting the vibration body51as a drive section, and so that the rotor58as a contact member contacting the metallic member54by pressing rotates by frictional contact.

As for a linearly driven vibration-wave motor, Japanese Patent No. 3279021 and U.S. Pat. No. 5,698,930 propose using of a flat plate-shaped vibration body.

FIGS. 11A-Care schematic drawings of a linearly driven vibration-wave motor, in whichFIG. 11Ais a front view,FIG. 11Bis a right side view, andFIG. 11Cis a plan view.

InFIG. 11, two piezoelectric elements62,63that concurrently generate longitudinal vibrations and bending vibrations are arranged on one side of the metallic member61constituting part of the vibration body. Two projections64,65are formed on the other side of the metallic member61. The two piezoelectric elements62,63are adhered to an elastic body with adhesive.

High-frequency voltage A and high-frequency voltage B are respectively applied to those two piezoelectric elements62,63and the compound movements of the bending vibrations and the longitudinal vibrations are synthesized, and thereby elliptic motion or circular motion can be generated to the tips of the projections64,65. The two piezoelectric elements62,63are polarized to respectively have polarities in the same direction, and the high-frequency voltage A and the high-frequency voltage B have a time phase difference by 90 degrees.

As a result, when the tips of the projections64,65are pressed and contacted to a fixing member66, the metallic member61constituting part of the vibration body moves in relation to the fixing member66. Accordingly, by pressing and contacting other members to the vibration body, a relative displacement motion is generated therebetween, and the vibration-wave motor can be driven linearly. However, in this case, the piezoelectric elements62,63are single plate-shaped elements and not multilayer piezoelectric elements.

As the vibration-wave motor is compacted, the machining errors of the multilayer piezoelectric element40and the metallic members53,54in the vibration-wave motor as shown inFIG. 10as well as the machining errors of the metallic member61and the piezoelectric elements62,63in the vibration-wave motor as shown inFIG. 11would be larger compared to the entire size of the vibration-wave motor, and it would be difficult to produce in mass volume the vibration-wave motors with stable output because of accumulation of these errors.

It is also difficult to fully adhere a piezoelectric element with the interface or adhesive surface of a metallic member, and thereby, vibration damping is caused at the interface or adhesive surface and the performance of the vibration-wave motor was lowered.

SUMMARY OF THE INVENTION

The present invention is directed to a multilayer piezoelectric element and a vibration-wave drive motor incorporating the same, requiring a small number of parts, being simply assembled even if any needed, and for reducing the manufacturing costs of the vibration-wave motor.

In one aspect, a multilayer piezoelectric element includes a piezoelectric active part formed from a plurality of laminated layers of material having a conversion function for converting electrical quantity into mechanical quantity. The active part also includes an electrode formed on the laminated layers. The element also includes a piezoelectric inactive part laminated and integrated with the active part. The inactive part includes at least one material layer having the electrical-mechanical conversion property.

In another aspect, a vibration-wave drive motor includes a vibration body including the active and inactive parts as disclosed above. The motor also includes a contact body in press contact with the inactive part.

Further features and advantages of the present invention will become apparent from the following description of the embodiments (with reference to the attached drawings).

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

FIG. 1is a partial section view of a multilayer piezoelectric element as a laminated electrical-mechanical energy conversion element in accordance with a first embodiment of the present invention. The right half of axial line L shows a section view and the left half of the axial line L shows an outline view.FIG. 2is a perspective view showing a middle stage of manufacturing the multilayer piezoelectric element and its lamination structure. In the description below, the same reference numerals are assigned to the multilayer piezoelectric element in the middle stage of manufacturing and to that after manufacturing for convenience.

InFIGS. 1 and 2, the multilayer piezoelectric element1has a cylindrical shape with a penetrating hole in the center. The multilayer piezoelectric element1consists of a piezoelectric active part3provided between piezoelectric inactive parts4-1,4-2. The piezoelectric part3includes layers having piezoelectric properties. The part3is formed by multiply laminating layers of material having an electrical-mechanical energy conversion function for converting electrical energy (electrical quantity) into mechanical energy (mechanical quantity) and multiply divided layers of electrode material. The piezoelectric inactive part4-1is arranged on one side of the piezoelectric active part3in the axial direction. The inactive part4-1does not have piezoelectric properties and is formed by multiply laminating only the layers of material having the conversion function. The piezoelectric inactive part4-2is arranged on the other side of the piezoelectric active part3in the axial direction. Likewise, the inactive part4-2does not have piezoelectric properties and is formed by multiply laminating solely the layers of material having the electrical-mechanical energy conversion function.

The piezoelectric active part3consists of a plurality of piezoelectric layers5. Internal electrodes6-1divided into four portions A+, A−, B+, B− and internal electrodes6-2divided into four portions AG, AG, BG, BG are respectively formed on the surface of the plurality of piezoelectric layers5. Connecting electrodes6a(black parts in the figure), connected to the respective internal electrodes6-1,6-2and extending to outer peripheral parts of the piezoelectric layers5, are formed on the layers5. The connecting electrodes6ain the respective piezoelectric layers5on which the internal electrodes6-1are formed are respectively formed axially on the same phase positions of the multilayer piezoelectric element1, and the connecting electrodes6ain the respective piezoelectric layers5on which the internal electrodes6-2are formed are respectively formed axially on the same phase positions of the multilayer piezoelectric element1.

Outside electrodes7are arranged on the outer periphery of the multilayer piezoelectric element1. The outside electrodes7connect the connecting electrodes6ahaving the same phase so that there is a continuity between the layers5. In the embodiment shown inFIG. 2, for example, there are eight outside electrodes7for connecting the eight different connecting electrode6aphases.

The internal electrodes6-1of the piezoelectric active part3consist of the internal electrodes A+, A−, B+, B−, in which electrodes A+, A− and B+, B− oppose each other in the radial direction, respectively. Likewise, the internal electrodes6-2of the piezoelectric active part3consists of the internal electrodes AG, AG, BG, BG, in which electrodes AG, AG and BG, BG oppose each other in the radial direction, respectively. The piezoelectric active part3is formed by laminating the plurality of piezoelectric layers5, on which the internal electrodes6-2,6-1are formed, on top of each other.

The piezoelectric inactive part4-1and the piezoelectric inactive part4-2respectively consist of at least two integrated piezoelectric layers5having no internal electrodes. The piezoelectric inactive parts4-1,4-2can have differing thicknesses as shown inFIGS. 1 and 2.

The multilayer piezoelectric element1generally has lower resonance frequency as the total length in the multilayer direction is longer while having higher resonance frequency as the diameter is larger. The vibration energy would be larger as the piezoelectric active part3is larger, and the costs also increase. Accordingly, the shape of the piezoelectric active part1may be designed in a variety of ways according to the required torque, size, or desired frequency of the voltage supplied to the multilayer piezoelectric element1.

The multilayer piezoelectric element1in the present embodiment shows an example of the case when desiring to have an outer diameter of about 10 mm and a length of about 12 mm and has an inner diameter of about 2.8 mm, the thickness of the piezoelectric layer5of the piezoelectric active part3being about 90 μm, the thickness of the piezoelectric active part3being 2.2 mm, the thickness of the internal electrodes6-1,6-2being about 2-3 μm, and 25 layers of the internal electrodes. The outside electrode7has a length of about 2.4 mm, width of about 1 mm, and thickness of about 0.05 mm, and the thickness of the piezoelectric layers5of the piezoelectric inactive parts4-1,4-2being about 90 μm. It is also possible reduce the number of the piezoelectric inactive parts4-1,4-2by laminating thicker layers.

The multilayer piezoelectric element1, which consists of piezoelectric ceramics powder and organic binder to be formed into the piezoelectric layers5, is manufactured by using a green sheet cut out into a shape with a constant size (for example, square of 13×13 in length and width).

First, as shown inFIG. 2, for the piezoelectric inactive parts4-1,4-2, a predetermined number of green sheets are solely laminated. The piezoelectric active part3is formed by screen-printing a pattern of the internal electrodes6-1,6-2and the connecting electrodes6aon the green sheets using silver-palladium powder paste. The predetermined number of screen-printed green sheets are stacked, laminated and integrated by pressing with heating.

Next, as shown inFIG. 2, for the laminated multilayer piezoelectric element1, a penetrating hole is formed by drilling at a position corresponding to the inner diameter of the multilayer piezoelectric element1. Then, the element1is fired in a lead environment at a predetermined temperature (for example, 1100-1200° C.). After firing, both sides are lapped, and both end faces of the multilayer piezoelectric element1are smoothed.

Next, as shown inFIGS. 1 and 2, the outer diameter of the multilayer piezoelectric element is machined into a cylindrical shape so that the connecting electrodes6aare exposed on the outer periphery of the multilayer piezoelectric element1. Then, using a screen-printer for printing on the cylindrical surface, the outside electrodes7are printed on eight positions where the connecting electrodes6aare exposed on the periphery of the multilayer piezoelectric element1. After printing, the multilayer piezoelectric element is heated at a predetermined temperature (for example, approximately at 750° C.) and the outside electrodes7are baked on the outer periphery of the multilayer piezoelectric element1.

Next, as shown inFIG. 1, an annular recessed part8(recessed part) is formed by cutting the outer periphery (piezoelectric inactive part4-1) of the multilayer piezoelectric element1along the peripheral direction by machining (cutting). Also, a projecting part9is formed by cutting so as to partly enlarge the inner diameter from one of the end face sides (piezoelectric inactive part4-1) in the axial direction of the multilayer piezoelectric element1.

The recessed part8is formed for enlarging the vibration displacement. Since the part where the recessed part8is formed is rigidly weak, the upper portion above the recessed part8easily vibrates. The projecting part9is formed for positioning when a member (for example, metal or ceramics with good abrasion resistance property) is arranged on an end face contacting a rotor18(shown inFIG. 3) of the multilayer piezoelectric element1by pressing.

The recessed part8is formed solely on the piezoelectric inactive part4-1. The piezoelectric inactive part4-1is not provided with an electrode, being different from the piezoelectric active part3, and it can easily perform fine adjustment of the shape without restriction.

Finally, as shown inFIG. 2, the respective electrodes A+, A−, B+, B−, AG, AG, BG, BG divided into four portions of the internal electrodes6-1,6-2are polarized in a specific polarization direction. More specifically, a metal contact pin is pressed against eight outside electrodes7. In oil at a predetermined temperature (for example, 100-150° C.), the electrodes AG, BG are grounded G, the internal electrodes A+, B+are made positive (+), and the internal electrodes A−, B−are made negative (−). A predetermined voltage (for example, 300 V) is applied to the respective electrodes for polarization for about 10-30 minutes.

As a result, as shown inFIG. 2, the multilayer piezoelectric element1is polarized for the internal electrodes AG, BG, AG, BG corresponding to electrical grounding such that the internal electrodes A+, B+ are (+) polar and the internal electrodes A−, B− are (−) polar.

FIG. 3is a section view showing a bar-type vibration-wave motor11incorporating the multilayer piezoelectric element1.

InFIG. 3, the vibration-wave motor11(vibration-wave drive device) uses the multilayer piezoelectric element1as part of a vibration body10. The vibration body10includes a bolt12inserted into the inner diameter of the multilayer piezoelectric element1for fixing the multilayer piezoelectric element1with a flange part13of the bolt12and a nut14. A rotor part, which is the upper part of the vibration-wave motor11, is arranged on the outside of the flange part13of the bolt12. The rotor part includes a rotor18(contact body) press contacting an end face of the vibration body10via a spring16and a spring support body17, and a gear19. The rotor18is integrally with the gear19, and the rotation of the rotor18can be taken out from the gear19.

A flexible circuit board15is wound around the respective outside electrodes7of the multilayer piezoelectric element1, connecting the respective outside electrodes7to drive circuits (not shown in the drawings).

Driving of the vibration-wave motor11is performed by making the AG-phase and BG-phase a ground, the electrodes A+, A− A phase, and the electrodes B+, B− B phase having the above mentioned polarity and being in positional relation (AG and AG, BG and BG, A+ and A−, B+ and B−) of axially opposing each other, and applying the A-phase high frequency voltage approximately identical to the eigen frequency of the vibration body10and the B-phase high frequency voltage with the phase different from the A-phase by 90 degrees.

With the above application of high frequency, the electrodes A+, A− of the piezoelectric active part3alternately expands/contracts in the thickness direction, and similarly, the electrodes B+, B− of the piezoelectric active part3expands/contracts in the thickness direction. By converting the expanding/contracting actions of the piezoelectric active part3into bending vibrations by the piezoelectric inactive part4laminated and integrated on both sides in the axial direction of the multilayer active part3, two bending vibrations axially crossing the multilayer piezoelectric element1can be generated.

The conventional multilayer piezoelectric element40(refer toFIG. 9), which solely expands/contracts in the width direction, generates two bending vibrations by constituting the vibration body51by placing and fixing the multilayer piezoelectric element40between metal members53and54(though the multilayer piezoelectric element40has two piezoelectric inactive layers as the top and bottom layers which are not polarized for insulation, these layers are thin and generate one vibration or expansion/contraction solely in the thickness direction).

However, since in the multilayer piezoelectric element1of this embodiment, the piezoelectric inactive parts4-1,4-2are laminated and integrated with the piezoelectric active part3and the piezoelectric active part3is placed and fixed between the piezoelectric inactive parts4-1,4-2instead of placing and fixing the multilayer piezoelectric element between metal members as in the conventional element40. The multilayer piezoelectric element1itself is used as the vibration body10and can generate the above mentioned two bending vibrations for driving the bar-type vibration-wave motor11. Those two bending vibrations can cause swiveling using as a drive part the end face of the multilayer piezoelectric element1as the vibration body10, and the rotor18press contacting the drive part is rotated by friction.

With this embodiment, it is also possible to improve durability by arranging small parts of metal or ceramics with good abrasion resistance on the end face contacting the rotor18in the multilayer piezoelectric element1.

As described above, in this embodiment, the multilayer piezoelectric element1consists of the piezoelectric active part3being formed by multiply laminating layers of material with electrical-mechanical energy conversion function and layers of electrode material and having piezoelectric property, and the piezoelectric inactive parts4-1,4-2being formed by multiply laminating only layers of material with electrical-mechanical energy conversion function and not having piezoelectric property, and the thicknesses of the piezoelectric inactive parts4-1,4-2are set large enough to generate two bending vibrations axially crossing the multilayer piezoelectric element1, and thereby the multilayer piezoelectric element itself can have a plurality of vibration modes (two bending vibration modes).

Accordingly, it is not necessary to assemble metal members for placing and fixing the multilayer piezoelectric element to a vibration-wave motor. Accordingly, vibration damping at an interface between metal members, which reduces the performance of the vibration-wave motor, can be minimized to improve performance of the vibration-wave motor.

Furthermore, since it is not necessary to assemble the metal members to the vibration-wave motor, the vibration-wave motor can be more compact, the performance of the vibration-wave motor is improved, the manufacturing process time period for the vibration-wave motor can be shortened and the number of parts and costs can be reduced.

Furthermore, since the recessed part8is formed by machining the outer periphery of the piezoelectric inactive part4-1, coping with or changing of design specifications such as enlargement of vibration displacement can be properly done, and the piezoelectric material has good workability as compared to metal accordingly to facilitate microprocessing.

As described above, for a vibration-wave motor targeting further compactness and high output power, much effect can be expected for their performance and manufacturing.

In this embodiment, though the recessed part8for enlarging vibration displacement formed on the outer periphery of the piezoelectric inactive part4-1of the multilayer piezoelectric element1is annular, the recessed part8can have other shapes permitting enlargement of the vibration displacement.

Second Embodiment

FIG. 4is a perspective view of a multilayer piezoelectric element in accordance with a second embodiment of the present invention.FIG. 5is a perspective view showing the multilayer piezoelectric element and its lamination structure. In the description below, the same reference numerals are assigned to the multilayer piezoelectric element in the middle stage of manufacturing and to that after manufacturing for convenience.

InFIGS. 4 and 5, a vibration body2has a flat plate-shape before cutting as will be described later. The vibration body2consists of a piezoelectric active part26and a piezoelectric inactive part27. The piezoelectric inactive part27consists of a number of piezoelectric layers22(for example, 20 layers) having no internal electrodes. The piezoelectric active part26consists of alternating piezoelectric layers22having internal layers23-1,23-2formed into two portions and piezoelectric layers22having an internal electrode23-3formed entirely on the surface.

The piezoelectric active parts26and the piezoelectric inactive parts27are, for example coincidently laminated, integrated and fired and constitute a multilayer piezoelectric element20. The piezoelectric active part26is unimorph and the thickness of the piezoelectric inactive parts27is set large enough to generate bending vibrations in the multilayer piezoelectric element20. To be more specific, the thickness is set large enough for the piezoelectric inactive parts27not to come to the neutral surface of bending vibrations generated on the multilayer piezoelectric element20. When the out-of-surface bending vibrations occur on the multilayer piezoelectric element20as shown inFIG. 6, the state that the upper side of the multilayer piezoelectric element20expands and the lower side contracts and the state that the upper side contracts and the lower side expands are alternately repeated. At that time, the neutral surface with no expansion or contraction exists between the expanding portion and the contracting portion. Since reverse forces of expansion and contraction act on both sides over the neutral surface, for example when the piezoelectric active part26made of unimorph comes over the neutral surface, the force canceling the vibration by the piezoelectric active part26acts on the upper side of the neutral surface. In other words, it is necessary to set a form for arranging the piezoelectric inactive parts27on the neutral surface of the multilayer piezoelectric element20.

The internal electrodes23-1,23-2are electrically connected to the internal electrodes23-3via through holes24-1,24-2,24-3, such that they are continuous with divided surface electrodes25arranged on a rear surface of the piezoelectric layer. The electrodes are polarized as described below, and predetermined polarization polarities are provided to the respective piezoelectric layers22.

As shown inFIG. 4, two projections21(projecting parts) are formed by cutting the upper part of the piezoelectric inactive part27. That is, a vibration body20consists solely of the multilayer piezoelectric element20, which includes the piezoelectric active parts26and the piezoelectric inactive parts27. The two projections21enlarge vibration displacement.

The projections21are formed solely on the piezoelectric inactive part27. The piezoelectric active part26is not cut since the internal electrodes are formed therein, while microprocessing in the shape can be easily performed on the piezoelectric inactive part27since electrodes are not formed therein.

The multilayer piezoelectric element20can be connected to a drive circuit (not shown in the drawings) by adhering a flexible circuit board to a predetermined position on the surface after cutting off by lapping surface electrodes25arranged on the bottom surface of the multilayer piezoelectric element20. For example, similarly to the conventional art, the internal electrodes23-3of the multilayer piezoelectric element20are grounded, and high frequency voltage with time phase difference of, for example, 0-180 degrees is applied to the internal electrodes23-1,23-2,23-3, and thereby two different bending vibrations can be simultaneously generated with time phase difference by 90 degrees as shown inFIG. 6.

The bending vibrations shown inFIGS. 6A and 6Bare outside surface secondary bending vibration and outside surface primary bending vibration, and the shape of the vibration body2is designed such that the resonance frequencies of these two bending vibrations are approximately identical. The two projections21are arranged near the node of the outside surface secondary bending vibration. With this vibration, the tips of these two projections21displace in the X-direction. The two projections21are arranged near the antinode of the outside surface primary bending vibration, and with these vibrations, the tips of these two projections21displace in the Z-direction. By generating compound vibrations consisting of these two different bending vibrations, elliptic motion or circular motion can be generated to the tips of the two projections21.

As a result, when the tips of the projections21of the vibration body2are pressed and contacted to a fixing part (not shown in the drawings), the vibration body2moves by itself for the fixing part by the elliptic motion or circular motion generated on the tips. Accordingly, by pressing and contacting other members to the vibration body2, a relative displacement motion is generated therebetween, and a linearly driven vibration-wave motor can be constituted.

With this embodiment, it is also possible to increase durability by arranging very thin metal or ceramics with good abrasion resistance on the end face contacting the other members at the two projections21.

The multilayer piezoelectric element20of the present embodiment has, for example, a length of about 20 mm, width of about 5 mm and thickness of about 1.8 mm, and the thickness of the piezoelectric layer22is about 60 μm, the thickness of the internal electrode is about 1-2 μm and the diameter of the through hole is about 0.1 mm. It is also possible to use thicker sheets for the piezoelectric layers22of the piezoelectric inactive part27. The shape of the piezoelectric active part20, similarly to the multilayer piezoelectric element1, may be designed in a variety of ways according to the required torque, size, or desired frequency of the voltage supplied to the multilayer piezoelectric element1.

The manufacturing method of the multilayer piezoelectric element20, which is basically the same as the first embodiment, is described below.

First, a green sheet with no internal electrode formed thereon and a green sheet with an internal electrode formed thereon are laminated and integrated. Then, they are fired in a lead environment at a predetermined temperature (for example, 1100-1200° C.).

Next, as shown inFIG. 5, metal pins are respectively pressed against the surface electrodes25connected to the three through holes, the internal electrode23-3is grounded G, the internal electrodes23-1,23-2are made positive (+), and in oil at a predetermined temperature (for example, 100-150° C.), a predetermined voltage (for example, 200 V) is applied thereon and a polarization process is performed for about 10-30 minutes.

After the polarization process as described above, both sides of the multilayer piezoelectric element20are lapped, such that the upper and lower sides of the multilayer piezoelectric element20are smoothed and the surface electrodes25are cut off. As shown inFIG. 4, the projecting parts21are formed by cutting the surface of the piezoelectric inactive part27of the multilayer piezoelectric element20. It is also possible to first perform cutting and then polarization in the process after firing.

In this embodiment, the multilayer piezoelectric element20can be solely used as the vibration body2for the vibration-wave motor and two different bending vibrations can be simultaneously generated since the multilayer piezoelectric element20is formed by laminating and integrating the piezoelectric inactive part27with the piezoelectric active part26and that the projecting parts21for press contacting other members are formed by cutting out the surface of the piezoelectric inactive part27, which is different from the conventional art in which two different bending vibrations are generated by adhering elastic bodies as metal members and piezoelectric elements.

Since adhesion of the piezoelectric elements and thick metal members as in the conventional art is not needed, vibration damping, which reduces performance of the vibration-wave motor, can be removed and improve the performance of the vibration-wave motor.

Furthermore, since metal members are not used, the vibration-wave motor can be compacted, the performance of the vibration-wave motor is improved, the manufacturing process time period for the vibration-wave motor can be shortened and the number of parts and the costs can be reduced.

Furthermore, since the recessed part21is formed by cutting the piezoelectric inactive part27constituting the multilayer piezoelectric element20, coping with or changing of design specifications such as enlargement of vibration displacement can be properly done, and the piezoelectric material has good workability compared to metal accordingly to facilitate microprocessing.

Although in this embodiment the shape of the projections21is a rectangular parallelepiped and the number of arrangements is two, this embodiment can have other shapes and number of arrangements of the projections21that permit enlargement of the vibration displacement.

FIG. 7is a perspective view of a linear type vibration-wave motor incorporating the multilayer piezoelectric element of the second embodiment. In the multilayer piezoelectric element30shown inFIG. 7, a flat plate-type abrasion material31is adhered to the upper surface by adhesive instead of forming projections21on the upper surface as compared to the multilayer piezoelectric element20shown inFIGS. 4 and 6.

InFIG. 7, the multilayer piezoelectric element30is flat plate-shaped and consists of a piezoelectric inactive part36formed by piezoelectric layers with no internal electrode from the first layer at the top to a predetermined layer (for example, the 20th layer) and a piezoelectric active part37formed by piezoelectric layers with the internal electrodes formed similarly as inFIG. 5from the predetermined layer (for example, the 21st layer) to the bottom layer (for example, the 30th layer). Similarly as the multilayer piezoelectric element20as shown inFIG. 4or6, the piezoelectric active part36and the piezoelectric inactive part37are formed by, for example laminating, integrating and firing, and the thickness of the piezoelectric inactive part37is set large enough to generate bending vibrations in the multilayer piezoelectric element30. When the thickness of the piezoelectric inactive part37is not large enough, energy generated by the unimorph piezoelectric active part36cannot be taken out as bending vibrations.

The plate-shaped abrasion material31is connected to the upper surface of the piezoelectric inactive part37. The abrasion material31is made of material having both high frictional coefficient and abrasion durability, such as the material formed by nitriding the surface of SUS420J2 material.

The abrasion material31consists of portions31-1,31-2with uniform thickness and portions31-3,31-4that are thinner than the portions31-1,31-2. By etching the surface of the plate-shaped SUS420J2 material as abrasion material and reducing the thickness, the thin plate parts31-3,31-4are formed and the other portions are allocated as31-1,31-2. The portion31-1is formed between the portions31-3and31-4which are linearly lined up and arranged. A slider33includes a slider base part33-1and abrasion material33-2connected to the slider base part33-1, and the abrasion material33-2contacts a contact part31-1by pressing.

Since the thin plate parts31-3,31-4are recessed deeper than the contact part31-1, thin plate parts31-3,31-4do not contact the slider even when the vibration body32is vibration-excited.

The multilayer piezoelectric element30can be connected to a drive circuit (not shown in the drawings) by adhering a flexible circuit board to a predetermined position of the multilayer piezoelectric element30. Two different bending vibrations can be simultaneously generated with time phase difference by 90 degrees as shown inFIGS. 8A and 8Bby applying high frequency voltage with time phase difference to the internal electrodes of the multilayer piezoelectric element30.

The bending vibrations shown inFIG. 8Aare outside surface secondary bending vibrations similar to the bending vibrations shown inFIG. 6A. The bending vibrations shown inFIG. 8Bare outside surface primary bending vibrations similar to the bending vibrations shown inFIG. 6B. The shape of the vibration body32is designed such that the resonance frequencies of these two bending vibrations are about identical. The two contact parts31-1are arranged on similar positions as the two projections21shown inFIG. 4. By generating compound vibrations consisting of these two different bending vibrations, elliptic motion or circular motion can be generated at the surface of the two contact parts31-1of the piezoelectric inactive part37.

As a result, when the surface of the contact part31of the vibration body32is pressed and contacted to the slider33, the slider33moves linearly for the vibration body32by the elliptic motion or circular motion generated on the surface. Accordingly, by pressing and contacting the slider33to the vibration body32, a relative displacement motion is generated therebetween, and a linearly driven vibration-wave motor can be constituted.

The multilayer piezoelectric element30and the abrasion material31constituting the vibration body32as shown inFIG. 7have about the same length (X-direction) and width (Y-direction). The multilayer piezoelectric element30has a length of about 5.5 mm, width of about 3.1 mm and thickness of about 0.6 mm. The thickness of the contact part31-1of the abrasion material31and that of the portion31-2are about 0.1 mm, and the thickness of the thin plate parts31-3,31-4is about 0.05 mm. The shape of the piezoelectric active part30, similarly to the multilayer piezoelectric element1, may be designed in a variety of ways according to the required torque, size, or desired frequency of the voltage supplied to the multilayer piezoelectric element1.

In the embodiment shown inFIG. 7, the multilayer piezoelectric element30can simultaneously generate two different bending vibrations.

Furthermore, since metal members are not employed, the vibration-wave motor can be compacted, the performance of the vibration-wave motor is improved, the manufacturing process time period for the vibration-wave motor can be shortened and the number of parts and the costs can be reduced.

This application claims priority from Japanese Patent Applications No. 2003-383896 filed Nov. 13, 2003 and 2004-299072 filed Oct. 13, 2004, which are hereby incorporated by reference herein.