Ultrasonic motor

In an ultrasonic motor, an elliptical vibration is generated by combining a longitudinal primary resonance vibration resulting from an expansion and a contraction of a vibrator in a direction of a central axis and a torsional secondary resonance vibration or a torsional tertiary resonance vibration resulting from twisting around the central axis. A dimension ratio of a rectangle of the vibrator is chosen such that a resonance frequency of the longitudinal primary resonance vibration and a resonance frequency of the torsional secondary resonance vibration or the torsional tertiary resonance vibration match. The vibrator includes a plurality of regions in a surface orthogonal to the central axis, and deformations of the regions adjacent to each other along the direction of the central axis are mutually different. The vibrator expands and contracts in a direction orthogonal to a polarization direction thereof.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-021047 filed on Feb. 2, 2010; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to ultrasonic motors.

2. Description of the Related Art

Japanese Patent Application Laid-open No. H9-117168, for example, discloses an ultrasonic motor that generates an elliptical vibration by combining a longitudinal vibration and a torsional vibration, and rotation drives a rotor.FIG. 1of Japanese Patent Application Laid-open No. H9-117168 depicts an exploded perspective view of a vibrator. The vibrator has a structure in which a plurality of piezoelectric elements is arranged between elastic bodies that are cut obliquely with respect to an axis of the vibrator. Positive electrodes of the piezoelectric elements are divided into two groups. These groups will be called Phase A and Phase B electrodes.

The longitudinal vibration can be generated in a bar-shaped vibrator by applying alternating voltages of the same phase to both Phase A and Phase B electrodes. On the other hand, the torsional vibration can be generated in the bar-shaped vibrator by applying alternating voltages of opposite phases to both Phase A and Phase B electrodes. A position of a groove in the vibrator is adjusted such that a resonance frequency of the longitudinal vibration and a resonance frequency of the torsional vibration substantially match. When alternating voltages that differ by π/2 phase are applied to Phase A and Phase B electrodes, the longitudinal vibration and the torsional vibration are generated simultaneously, thereby generating an elliptical vibration on a top surface of a bar-shaped elastic body. In this state, by pressing the rotor on the top surface of the bar-shaped elastic body, the rotor can be rotation driven in a clockwise direction (CW direction) or a counterclockwise direction (CCW direction).

The ultrasonic motor disclosed in Japanese Patent Application Laid-open No. H9-117168 has various drawbacks. For example, as shown inFIG. 1, both the piezoelectric element and the elastic body are necessary, the elastic body must be cut obliquely, and the groove must be made in a portion of the elastic body to match the resonance frequencies of the longitudinal vibration and the torsional vibration. Thus, the overall structure of the conventional vibrator is very complicated.

SUMMARY OF THE INVENTION

The present invention is made in view of the above discussion. It is an object of the present invention to provide an ultrasonic motor that can generate a torsional resonance vibration efficiently by positively employing the bending movement of the piezoelectric element. It is another object of the present invention to provide an ultrasonic motor that includes a single part, has a simple structure without a groove etc., can generate a longitudinal vibration and a torsional vibration easily, can generate an elliptical vibration by combining the longitudinal vibration and the torsional vibration, and can rotate a rotor by the elliptical vibration.

To solve the above problems and to achieve the above objects, according to an aspect of the present invention, an ultrasonic motor includes a vibrator having a dimension ratio of a rectangle in a cross-section orthogonal to a central axis; and a rotor that contacts an elliptical vibration generating surface of the vibrator and that is rotation driven around the central axis that is orthogonal to the elliptical vibration generating surface of the vibrator. An elliptical vibration is generated by combining a longitudinal primary resonance vibration resulting from an expansion and a contraction of the vibrator in a direction of the central axis and a torsional secondary resonance vibration or a torsional tertiary resonance vibration resulting from twisting around the central axis. The dimension ratio of the rectangle of the vibrator is chosen such that a resonance frequency of the longitudinal primary resonance vibration and a resonance frequency of the torsional secondary resonance vibration or the torsional tertiary resonance vibration match. The vibrator includes a plurality of regions in a surface orthogonal to the central axis. Deformations of the regions adjacent to each other along the direction of the central axis are mutually different in the regions. The vibrator expands and contracts in a direction orthogonal to a polarization direction thereof.

In the ultrasonic motor mechanism according to the present invention, it is preferable that each of the regions among the regions is deformed in a single direction to generate the torsional secondary resonance vibration.

In the ultrasonic motor mechanism according to the present invention, it is preferable that each of the regions among the regions is deformed in a mutually different direction to generate the torsional tertiary resonance vibration.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments of an ultrasonic motor according to the present invention are explained in detail below by using the accompanying drawings. The present invention is not limited by the following embodiments.

First Embodiment

An ultrasonic motor100according to the first embodiment of the present invention generates an elliptical vibration by combining a longitudinal primary resonance vibration and a torsional secondary resonance vibration. As shown inFIGS. 1 and 2, the ultrasonic motor100includes a vibrator101and a rotor102.

The vibrator101is a piezoelectric element of a substantially right-angled parallelepiped shape having a dimension ratio of a rectangle in a cross-section orthogonal to its central axis100C (rotation axis). The rotor102is substantially disk-shaped. A bottom surface of the rotor102contacts with friction contact members103aand103bthat are arranged on an elliptical vibration generating surface101aof the vibrator101. The rotor102is rotation driven around the central axis1000that is orthogonal to the elliptical vibration generating surface101aof the vibrator101.

A structure for coupling the rotor102to the vibrator101is explained below.

A holder110is fixed near a node of the vibrator101(piezoelectric element). A shaft105, the rotor102, a bearing107, a spring108, and a cap ring109are arranged in this order between the elliptical vibration generating surface101aof the vibrator101and the holder110. All these members are concentrically arranged on the central axis100C.

The bearing107is engaged with a central hole102aof the rotor102. The shaft105passes through the central hole102aof the rotor102and a hole of the bearing107along the central axis100C. A base of the shaft105rests on the elliptical vibration generating surface101aof the vibrator101.

The shaft105, which penetrates the central hole102aof the rotor102and the hole of the bearing107, passes through the spring108and a hole of the cap ring109in this order, and then passes through a through hole110aprovided in an upper part of the holder110. A ring111is threadably mounted on an upper tip of the shaft105that comes out of the through hole110a. The shaft105is thus fixed to the holder110.

The cap ring109and the shaft105are provided with threads, and the cap ring109is threadably mounted on the shaft105. A position of the cap ring109on the shaft105, i.e., a pressing force of the spring108, can be adjusted by rotating the cap ring109. In other words, a force by which the rotor102presses the friction contact members103aand103bcan be adjusted by rotating the cap ring109.

How resonance frequencies are matched in the vibrator101(piezoelectric element) included in the ultrasonic motor100is explained below referring toFIGS. 3A to 3EandFIG. 4.

As shown inFIG. 3A, the vibrator101has a substantially right-angled parallelepiped shape. A length of a short side101sof a rectangular cross-section that is orthogonal to the central axis100C is denoted by a, a length of a long side101f is denoted by b, and a height of the vibrator101along the central axis100C is denoted by c. In the following explanation, a height direction of the vibrator101is assumed to be a direction of vibrations in a longitudinal primary vibration mode as well as an axis direction of torsion in the torsional vibration. Moreover, a, b, and c satisfy a<b<c.

The resonance frequency in the longitudinal primary vibration mode and the resonance frequency in a torsional secondary vibration mode, or the resonance frequency in the longitudinal primary vibration mode and the resonance frequency in a torsional tertiary vibration mode can be matched by appropriately choosing a, b, and c in the vibrator101.

InFIGS. 3B to 3E, directions of the torsional vibration are shown by p1and p2, a direction of the longitudinal vibration is shown by q, and a node of the vibrations is shown by N. One node N is present at central positions in a height direction in each of the torsional primary vibration mode (FIG. 3B) and the longitudinal primary vibration mode (FIG. 3C). Two nodes N are present at two positions in the height direction in the torsional secondary vibration mode (FIG. 3D). Three nodes N are present at three positions in the height direction in the torsional tertiary vibration mode (FIG. 3E).

InFIGS. 3B to 3E, a continuous line is used to show a shape of the vibrator101before it is subjected to vibrations and a dotted line is used to show the shape of the vibrator101after it is subjected to vibrations.

As can be seen inFIG. 4, when the parameter a/b is varied, although the resonance frequency of the longitudinal primary vibration mode stays constant without depending on the parameter a/b, the resonance frequencies of the torsional vibration increase with an increase in the parameter a/b.

Furthermore, the resonance frequency of the torsional primary vibration mode never matches with the resonance frequency of the longitudinal primary vibration mode irrespective of the value of the parameter a/b. On the contrary, the resonance frequency of the torsional secondary vibration mode matches with the resonance frequency of the longitudinal primary vibration mode near a position where the parameter a/b is 0.6. Moreover, the resonance frequency of the torsional tertiary vibration mode matches with the resonance frequency of the longitudinal primary vibration mode near a position where the parameter a/b is near 0.3. Therefore, the lengths a and b are chosen in the vibrator101according to the first embodiment such that the parameter a/b falls between 0.25 and 0.35 in the longitudinal primary vibration and the torsional tertiary vibration, and falls between 0.5 and 0.6 in the longitudinal primary vibration and the torsional secondary vibration.

In the ultrasonic motor100, the elliptical vibration is generated by combining the longitudinal primary resonance vibration resulting from an expansion and a contraction of the vibrator101along the central axis100C (rotation axis) and the torsional secondary resonance vibration or a torsional tertiary resonance vibration resulting from twisting of the vibrator101around the central axis100C. A ratio (proportion) of the lengths a and b is chosen such that the resonance frequencies of the longitudinal primary resonance vibration resulting from the expansion and the contraction of the vibrator101along the central axis100C and the torsional secondary resonance vibration or the torsional tertiary resonance vibration resulting from twisting of the vibrator101around the central axis100C almost match.

The vibrator101includes a multilayered piezoelectric element120in which a plurality of piezoelectric sheets is stacked. The longitudinal primary resonance vibration and the torsional secondary resonance vibration or the torsional tertiary resonance vibration are generated in the vibrator101because of formation of activation regions by polarization in a thickness direction of the piezoelectric sheets. A structure of the multilayered piezoelectric element120forming the vibrator101is explained below referring toFIGS. 5 to 8B.FIG. 5is an exploded perspective view of the structure of the multilayered piezoelectric element120.FIG. 6Ais a plan view of a structure of a first piezoelectric sheet130,FIG. 6Bis a plan view of a structure of a second piezoelectric sheet140, andFIG. 6Cis a plan view of a structure of a third piezoelectric sheet150.FIG. 7is a perspective view from an upper front side of the multilayered piezoelectric element120.FIG. 8Ais a left side view of the multilayered piezoelectric element120shown inFIG. 7, andFIG. 8Bis a right side view of the multilayered piezoelectric element120shown inFIG. 7.

As shown inFIG. 5, the multilayered piezoelectric element120includes, stacked from this side to the other side in the thickness direction (a direction indicated by an arrow S1inFIG. 5), two first piezoelectric sheets130, two pairs of the second piezoelectric sheets140and the third piezoelectric sheets150alternately layered, two first piezoelectric sheets130, two pairs of the second piezoelectric sheets140and the third piezoelectric sheets150alternately layered, and two first piezoelectric sheets130.

The number and arrangement of the piezoelectric sheets included in the multilayered piezoelectric element120can be varied depending on the specification of the vibrator101.

As shown inFIGS. 6A to 6C, the first piezoelectric sheet130, the second piezoelectric sheet140, and the third piezoelectric sheet150have an identical shape of a rectangular plate. As the first piezoelectric sheet130, the second piezoelectric sheet140, and the third piezoelectric sheet150, for example, hard-type lead zirconate titanate piezoelectric elements are used. The piezoelectric element consisting of the second piezoelectric sheet140and the third piezoelectric sheet150includes an internal electrode and an activated area polarized in the thickness direction.

Two internal electrodes are formed by way of printing on an upper surface of each second piezoelectric sheet140. Two internal electrodes are formed by way of printing also on a surface of each of the third piezoelectric sheet150.

Concrete structures of the internal electrodes and external electrodes are explained below.

As shown inFIG. 6B, around centers of long sides (vertical sides inFIGS. 6A to 6C) of the second piezoelectric sheet140, a first internal electrode141aof +phase and a second internal electrode142aof +phase are arranged facing to and isolated from each other.

The first internal electrode141aof +phase and the second internal electrode142aof +phase are extended such that their protrusions141band142bare exposed to an upper part of long sides140L and140R of the second piezoelectric sheet140. Moreover, the protrusions141band142bare arranged at a position facing to each other along the long sides of the second piezoelectric sheet140.

As shown inFIG. 6C, a first internal electrode151aof −phase and a second internal electrode152aof −phase are arranged around a center of long sides of the third piezoelectric sheet150facing to and isolated from each other.

The first internal electrode151aof −phase and the second internal electrode152aof −phase are extended such that their protrusions151band152bare respectively exposed to a lower part of long sides150L and150R of the third piezoelectric sheet150. Moreover, the protrusions151band152bare also arranged at a position facing to and isolated from each other along the long sides of the third piezoelectric sheet150.

The first internal electrode141aof +phase and the first internal electrode151aof −phase are formed on the position facing to each other when the second piezoelectric sheet140and the third piezoelectric sheet150are stacked. Moreover, the second internal electrode142aof +phase and the second internal electrode152aof −phase are formed on the position facing to each other when the second piezoelectric sheet140and the third piezoelectric sheet150are stacked.

The external electrodes are formed on the protrusions141b,142b,151b, and152bof internal electrodes, for example, by way of printing of silver paste.

The external electrodes formed on the protrusions141bcompose a first external electrode group121L of +phase and a third external electrode group123L of +phase on a left surface120L of the multilayered piezoelectric element120. The external electrodes formed on the protrusions142bcompose a first external electrode group121R of +phase and a third external electrode group123R of +phase on a right surface120R of the multilayered piezoelectric element120(FIG. 7andFIGS. 8A to 8B).

The external electrodes formed on the protrusions151bcompose a second external electrode group122L of −phase and a fourth external electrode group124L of −phase on the left surface120L of the multilayered piezoelectric element120. The external electrodes formed on the protrusion152bcompose a second external electrode group122R of −phase and a fourth external electrode group124R of −phase on the right surface120R of the multilayered piezoelectric element120(FIG. 7andFIGS. 8A to 8B). Meanwhile, the external electrodes are not shown inFIGS. 1 and 2.

The external electrodes are respectively connected to an external power supply (not shown) of the ultrasonic motor100. As an example, an FPC (flexible print circuit) is used for connection and one end of the FPC is connected to each electrode group.

Eight external electrodes formed on the surfaces of the multilayered piezoelectric element120compose four pairs of phases by respectively coupling the first external electrode group121L of +phase and the second external electrode group122L of −phase as a pair, the third external electrode group123L of +phase and the fourth external electrode group124L of −phase as a pair, the first external electrode group121R of +phase and the second external electrode group122R of −phase as a pair, and the third external electrode group123R of +phase and the fourth external electrode group124R of −phase as a pair.

From another aspect, the multilayered piezoelectric element120consists of four regions120A,120B,120C, and120D with an angle of 90 degrees for each, separated by orthogonal surfaces around the central axis100C (FIG. 7andFIGS. 8A to 8B).

The region120A corresponds to the phases of the first external electrode group121R of +phase and the second external electrode group122R of −phase, the region120B corresponds to the phases of the third external electrode group123R of +phase and the fourth external electrode group124R of −phase, the region1200corresponds to the phases of the first external electrode group121L of +phase and the second external electrode group122L of −phase, and the region120D corresponds to the phases of the third external electrode group123L of +phase and the fourth external electrode group124L of −phase, respectively. By this structure, each region is deformed to a single direction in response to a signal applied from the external power supply.

An operation of the vibrator101and the multilayered piezoelectric element120is explained below referring to FIG.9andFIGS. 10A to 10D.FIG. 9is a figure that shows the deformation of each region of the multilayered piezoelectric element120and it is an exploded view from an upper front side.FIG. 10Ais a left side view of the multilayered piezoelectric element120shown inFIG. 9,FIG. 10Bis a left side view of the deformation of the multilayered piezoelectric element120shown inFIG. 9,FIG. 10Cis a right side view of the multilayered piezoelectric element120shown inFIG. 9, andFIG. 10Dis a right side view of the deformation of the multilayered piezoelectric element120shown inFIG. 9. The external electrodes are not shown inFIG. 9andFIGS. 10A to 10D.

In the examples shown inFIG. 9andFIGS. 10A to 10D, a signal is applied from the external power supply to each phase between the first external electrode group121R and the second external electrode group122R, between the third external electrode group123R and the fourth external electrode group124R, between the first external electrode group121L and the second external electrode group122L, and between the third external electrode group123L and the fourth external electrode group124L, respectively. By this application of power, the regions120A and120D are deformed so that they are expanded along the central axis100C, and the regions120B and120C are deformed so that they are contracted along the central axis100C. That is, the adjacent regions of the multilayered piezoelectric element120are deformed along the central axis100C to the opposite directions and the directions of deformation are vertical to a direction of polarization (direction S1of stacking). Meanwhile, the directions of deformation of the regions can be different from the directions shown inFIG. 9andFIGS. 10A to 10Das far as the directions of deformation of the adjacent regions are opposite from each other.

As shown here, when four regions are deformed, by combining the longitudinal primary resonance vibration (FIG. 3C) and the torsional secondary resonance vibration (FIG. 3D) along the central axis100C, the elliptical vibration is generated on both sides of the height direction of the vibrator101. Accordingly, elliptical vibration is propagated to the rotor102through the friction contact members103aand103b.In addition, a torsional secondary resonance vibration to the opposite direction can be generated by applying signals to each phase so that each region is deformed to the directions opposite to the directions shown above.

With the structure explained above, the vibrator101that consists of a single part of a simple structure without a groove etc., can be obtained. The cost of the ultrasonic motor100that includes this vibrator101can be reduced because it requires only a small number of parts and can be easily assembled. Furthermore, the ultrasonic motor100can easily generate the longitudinal vibration and the torsional vibration, and rotate the rotor102using the elliptical vibration by combining the longitudinal vibration and the torsional vibration.

Second Embodiment

An ultrasonic motor according to the second embodiment of the present invention differs from the ultrasonic motor100according to the first embodiment in the point that an elliptical vibration is generated by combining a longitudinal primary resonance vibration and a torsional tertiary resonance vibration. Structures are the same as those of the first embodiment excepting the piezoelectric sheets and accordingly, the same reference symbols will be used and the descriptions of the items other than the piezoelectric sheets are not shown.

A vibrator in the second embodiment includes a multilayered piezoelectric element220formed by a plurality of piezoelectric sheets stacked together and that generates the longitudinal primary resonance vibration and the torsional tertiary resonance vibration by an activated area polarized in a thickness direction of the piezoelectric sheets. A structure of the multilayered piezoelectric element220forming the vibrator is explained below usingFIGS. 11 to 14B.FIG. 11is an exploded perspective view of the structure of the multilayered piezoelectric element220.FIG. 12Ais a plan view of a structure of a first piezoelectric sheet230.FIG. 12Bis a plan view of a structure of a second piezoelectric sheet240.FIG. 12Cis a plan view of a structure of a third piezoelectric sheet250.FIG. 13is a perspective view from an upper front side of the multilayered piezoelectric element220.FIG. 14Ais a left side view of the multilayered piezoelectric element220shown inFIG. 13.FIG. 14Bis a right side view of the multilayered piezoelectric element220shown inFIG. 13.

As shown inFIG. 11, the multilayered piezoelectric element220includes, stacked from this side to the other side in the thickness direction (a direction indicated by an arrow S2inFIG. 11), two first piezoelectric sheets230, two pairs of the second piezoelectric sheets240and the third piezoelectric sheets250alternately layered, two first piezoelectric sheets230, two pairs of the second piezoelectric sheets240and the third piezoelectric sheets250alternately layered, and two first piezoelectric sheets230.

As shown inFIGS. 12A to 12C, the first piezoelectric sheet230, the second piezoelectric sheet240, and the third piezoelectric sheet250have an identical shape of a rectangular plate. As the first piezoelectric sheet230, the second piezoelectric sheet240, and the third piezoelectric sheet250, for example, hard-type lead zirconate titanate piezoelectric elements are used. The piezoelectric element consisting of the second piezoelectric sheet240and the third piezoelectric sheet250includes an internal electrode and an activated area polarized in the thickness direction.

The concrete structures of the internal electrode and an external electrode are explained below.

As shown inFIG. 12B, a first internal electrode241aof +phase, a second internal electrode242aof +phase, a third internal electrode243aof +phase, and a fourth internal electrode244aof +phase are formed on the second piezoelectric sheet240. The first internal electrode241aof +phase and the third internal electrode243aof +phase are placed at a top position, facing to and isolated from each other along long sides (vertical direction inFIGS. 12A to 12C) of the second piezoelectric sheet240. The second internal electrode242aof +phase and the fourth internal electrode244aof +phase are arranged at a bottom position, facing to and isolated from each other along the long sides of the second piezoelectric sheet240.

The first internal electrode241aof +phase and the third internal electrode243aof +phase are extended so that their protrusions241band243bare respectively exposed to an upper part of long sides240L and240R of the second piezoelectric sheet240. The second internal electrode242aof +phase and the fourth internal electrode244aof +phase are extended so that their protrusions242band244bare respectively exposed to a lower part of the long sides240L and240R of the second piezoelectric sheet240. The protrusions241band243bare arranged at positions facing to each other along the long side of the second piezoelectric sheet240. The protrusions242band244bare also arranged at positions facing to each other.

Similarly, as shown inFIG. 12C, a first internal electrode251aof −phase, a second internal electrode252aof −phase, a third internal electrode253aof −phase, and a fourth internal electrode254aof −phase are formed on the third piezoelectric sheet250. The first internal electrode251aof −phase and the third internal electrode253aof −phase are placed at the top position mutually facing to and isolated from each other along the long sides of the third piezoelectric sheet250. The second internal electrode252aof −phase and the fourth internal electrode254aof −phase are arranged at the bottom position facing to and isolated from each other along the long sides of the third piezoelectric sheet250.

The first internal electrode251aof −phase and the third internal electrode253aof −phase are extended such that their protrusions251band253bare respectively exposed to an upper part of long sides250L and250R of the third piezoelectric sheet250. The second internal electrode252aof −phase and the fourth internal electrode254aof −phase are extended so that their protrusions252band254bare respectively exposed to a lower part of the long sides250L and250R of the third piezoelectric sheet250. The protrusions251band253bare arranged at the positions facing to each other along the long side of the third piezoelectric sheet250. The protrusions252band254bare also arranged at the positions facing to each other.

The first internal electrode241aof +phase and the first internal electrode251aof −phase, the second internal electrode242aof +phase and the second internal electrode252aof −phase, the third internal electrode243aof +phase and the third internal electrode253aof −phase, and the fourth internal electrode244aof +phase and the fourth internal electrode254aof −phase, are respectively formed on a position facing to each other when the second piezoelectric sheet240and the third piezoelectric sheet250are stacked.

The external electrodes are formed on the protrusions241b,242b,243b,244b,251b,252b,253b, and254bof the internal electrodes, for example, by way of printing of silver paste.

The external electrodes formed on the protrusion241bcompose a first external electrode group221L of +phase and a fifth external electrode group225L of +phase on a left surface220L of the multilayered piezoelectric element220. The external electrodes formed on the protrusion242bcompose a fourth external electrode group224L of +phase and an eighth external electrode group228L of +phase on the left surface220L of the multilayered piezoelectric element220.

Moreover, the external electrodes formed on the protrusion243bcompose a first external electrode group221R of +phase and a fifth external electrode group225R of +phase on a right surface220R of the multilayered piezoelectric element220. The external electrodes formed on the protrusion244bcompose a fourth external electrode group224R of +phase and an eighth external electrode group228R of +phase on the right surface220R of the multilayered piezoelectric element220(FIG. 13andFIGS. 14A to 14B).

The external electrodes formed on the protrusion251bcompose a second external electrode group222L of −phase and a sixth external electrode group226L of −phase on the left surface220L of the multilayered piezoelectric element220. The external electrodes formed on the protrusion252bcompose a third external electrode group223L of −phase and a seventh external electrode group227L of −phase on the left surface220L of the multilayered piezoelectric element220.

Moreover, the external electrodes formed on the protrusion253bcompose a second external electrode group222R of −phase and a sixth external electrode group226R of −phase on the right surface220R of the multilayered piezoelectric element220. The external electrodes formed on the protrusion254bcompose a third external electrode group223R of −phase and a seventh external electrode group227R of −phase on the right surface220R of the multilayered piezoelectric element220(FIG. 13andFIGS. 14A to 14B).

Sixteen external electrodes formed on the multilayered piezoelectric element220are coupled into four pairs of phases on each of the left surface220L and the right surface220R of the multilayered piezoelectric element220. In the concrete, the first external electrode group221L of +phase and the second external electrode group222L of −phase as a pair, the third external electrode group223L of −phase and the fourth external electrode group224L of +phase as a pair, the fifth external electrode group225L of +phase and the sixth external electrode group226L of −phase as a pair, and the seventh external electrode group227L of −phase and the eighth external electrode group228L of +phase as a pair, respectively, compose the four pairs of phases on the left surface220L of the multilayered piezoelectric element220. The first external electrode group221R of +phase and the second external electrode group222R of −phase as a pair, the third external electrode group223R of phase and the fourth external electrode group224R of +phase as a pair, the fifth external electrode group225R of +phase and the sixth external electrode group226R of −phase as a pair, and the seventh external electrode group227R of −phase and the eighth external electrode group228R of +phase as a pair, respectively, compose the four pairs of phases on the right surface220R of the multilayered piezoelectric element220.

From another aspect, the multilayered piezoelectric element220consists of four regions220A,220B,220C, and220D with an angle of 90 degrees for each, separated by orthogonal surfaces around a central axis200C (FIG. 13andFIGS. 14A to 14B).

The region220A corresponds to the pairs of the first external electrode group221R of +phase and the second external electrode group222R of −phase, and the pairs of the third external electrode group223R of −phase and the fourth external electrode group224R of +phase. The region220B corresponds to the pairs of the fifth external electrode group225R of +phase and the sixth external electrode group226R of −phase, and the pairs of the seventh external electrode group227R of −phase and the eighth external electrode group228R of +phase. The region220C corresponds to the pairs of the first external electrode group221L of +phase and the second external electrode group222L of −phase, and the pairs of the third external electrode group223L of −phase and the fourth external electrode group224L of +phase. The region220D corresponds to the pairs of the fifth external electrode group225L of +phase and the sixth external electrode group226L of −phase, and the pairs of the seventh external electrode group227L of −phase and the eighth external electrode group228L of +phase.

By this structure, each part is deformed reacting to a signal when the signal is applied to each phase from the external power supply. Since each region includes two pairs of phases, a part corresponding to each phase can be deformed to different directions even in the same region.

An operation of the vibrator101and the multilayered piezoelectric element220is explained below referring toFIG. 15andFIGS. 16A to 16D.FIG. 15shows deformations of each region of the multilayered piezoelectric element220and it is a view from the upper front side.FIG. 16Ais a left side view of the multilayered piezoelectric element220shown inFIG. 15.FIG. 16Bis a left side view of the deformation of the multilayered piezoelectric element220shown inFIG. 15.FIG. 16Cis a right side view of the multilayered piezoelectric element220shown inFIG. 15.FIG. 16Dis a right side view of the deformation of the multilayered piezoelectric element220shown inFIG. 15. The external power supply is not shown inFIG. 15andFIGS. 16A to 16D.

In the examples shown inFIG. 15andFIGS. 16A to 16D, a signal is respectively applied to the pairs of the external electrode groups of each region from the external power supply. As the effect, in the region220A, the deformation occurs so that, a section facing to the first external electrode group221R and the second external electrode group222R expands to a direction along the central axis200C, and a portion facing to the third external electrode group223R and the fourth external electrode group224R contracts to the direction along the central axis2000. Likewise, in the region220B, deformation occurs so that, a section facing to the fifth external electrode group225R and the sixth external electrode group226R contracts to the direction along the central axis200C, and a section facing to the seventh external electrode group227R and the eighth external electrode group228R expands to the direction along the central axis200C. Moreover, in the region220C, deformation occurs so that, a section facing to the first external electrode group221L and the second external electrode group222L contracts to the direction along the central axis2000, and a section facing to the third external electrode group223L and the fourth external electrode group224L expands to the direction along the central axis2000. Likewise, in the region220D, deformation occurs so that, a section facing to the fifth external electrode group225L and the sixth external electrode group226L expands to the direction along the central axis200C, and a section facing to the seventh external electrode group227L and the eighth external electrode group228L contracts to the direction along the central axis2000.

Accordingly, the multilayered piezoelectric element220deforms to the direction along the central axis200C so that the adjacent regions or the adjacent portions deform to opposite directions and the directions of deformations are vertical to a direction of polarization (direction S2of stacking). Meanwhile, the directions of deformations of each region can differ from those shown inFIG. 15andFIGS. 16A to 16Das far as the directions of deformations of the adjacent regions are opposite.

As explained above, by deforming the four regions, the elliptical vibration is generated on both surfaces of the height direction of the vibrator101by combining the longitudinal primary resonance vibration (FIG. 3C) and the torsional tertiary resonance vibration (FIG. 3E) around the central axis200C as an axis of twisting. Accordingly, the elliptical vibration is transmitted to the rotor102through the friction contact members103aand103b. Likewise, the torsional tertiary vibration to an opposite direction can be generated by applying a signal so that each portion of each region will deform to the opposite direction.

With the structure mentioned above, the vibrator101that consists of a single part of a simple structure without a groove etc., can be obtained. The cost of the ultrasonic motor100that includes this vibrator101can be reduced because it requires only a small number of parts and can be easily assembled. Furthermore, the ultrasonic motor100can easily generate the longitudinal vibration and the torsional vibration, and rotate the rotor102using the elliptical vibration by combining these vibrations.

Furthermore, other structures, operations, and advantages are the same as those of the first embodiment.

Third Embodiment

An ultrasonic motor according to the third embodiment of the present invention generates an elliptical vibration by combining a longitudinal primary resonance vibration and a torsional secondary resonance vibration. It differs from the ultrasonic motor100according to the first embodiment in the point that it includes an internal electrode pattern that enables an external electrode group to be arranged on a bottom surface of a multilayered piezoelectric element320. Other structures are the same as those of the ultrasonic motor100of the first embodiment and accordingly, the same reference symbols will be used and the descriptions of the items other than those of the piezoelectric sheets are not shown in the diagrams.

A vibrator in the third embodiment includes the multilayered piezoelectric element320formed by a plurality of piezoelectric sheets stacked together and that generates the longitudinal primary resonance vibration and the torsional secondary resonance vibration by an activated area polarized in the thickness direction of the piezoelectric sheets. A structure of the multilayered piezoelectric element320forming the vibrator is explained below usingFIGS. 17 to 20.FIG. 17is an exploded perspective view of the structure of the multilayered piezoelectric element320.FIG. 18Ais a plan view of a structure of a first piezoelectric sheet330.FIG. 18Bis a plan view of a structure of a second piezoelectric sheet340.FIG. 18Cis a plan view of a structure of a third piezoelectric sheet350.FIG. 19is a perspective view from an upper front side of the multilayered piezoelectric element320.FIG. 20is a bottom view of the multilayered piezoelectric element320shown inFIG. 19.

As shown inFIG. 17, the multilayered piezoelectric element320includes, stacked from this side to the other side in a thickness direction (a direction indicated by an arrow S3inFIG. 17), two first piezoelectric sheets330, two pairs of the second piezoelectric sheets340and the third piezoelectric sheets350alternately layered, two first piezoelectric sheets330, two pairs of the second piezoelectric sheets340and the third piezoelectric sheets350alternately layered, and two first piezoelectric sheets330.

As shown inFIGS. 18A to 18C, the first piezoelectric sheet330, the second piezoelectric sheet340, and the third piezoelectric sheet350have an identical shape of a rectangular plate. As the first piezoelectric sheet330, the second piezoelectric sheet340, and the third piezoelectric sheet350, for example, hard-type lead zirconate titanate piezoelectric elements are used. The piezoelectric element consisting of the second piezoelectric sheet340and the third piezoelectric sheet350includes an internal electrode and an activated area polarized in the thickness direction.

Concrete structures of the internal electrodes and external electrodes are explained below.

As shown inFIG. 18B, around centers of long sides (orthogonal sides inFIGS. 18A to 18C) of the second piezoelectric sheet340, a first internal electrode341aof +phase and a second internal electrode342aof +phase are arranged facing to and isolated from each other.

The first internal electrode341aof +phase and the second internal electrode342aof +phase are extended such that their protrusions341band342bare exposed to a bottom surface340U of the second piezoelectric sheet340. The protrusions341band342bare arranged at a position isolated from each other at the bottom surface340U of the second piezoelectric sheet340.

As shown inFIG. 18C, a first internal electrode351aof −phase and a second internal electrode352aof −phase are arranged facing to each other around a center of long sides of the third piezoelectric sheet350.

The first internal electrode351aof −phase and the second internal electrode352aof −phase are extended so that their protrusions351band352bare exposed to a bottom surface350U of the third piezoelectric sheet350. The protrusions351band352bare arranged at positions inner than the corresponding positions of the protrusions341band342b, and isolated from each other.

External electrodes formed on the protrusion341bcompose a first external electrode group321L of +phase and a third external electrode group323L of +phase on a bottom surface320U of the multilayered piezoelectric element320. External electrodes formed on the protrusions342bcompose a first external electrode group321R of +phase and a third external electrode group323R of +phase on the bottom surface320U of the multilayered piezoelectric element320(FIG. 20).

External electrodes formed on the protrusion351bcompose a second external electrode group322L of −phase and a fourth external electrode group324L of −phase on the bottom surface320U of the multilayered piezoelectric element320. External electrodes formed on the protrusion352bcompose a second external electrode group322R of −phase and a fourth external electrode group324R of −phase on the bottom surface320U of the multilayered piezoelectric element320(FIG. 20).

Eight external electrodes formed on the bottom surface320U of the multilayered piezoelectric element320compose four groups of phases by respectively coupling the first external electrode group321L of +phase and the second external electrode group322L of −phase as a pair, the third external electrode group323L of +phase and the fourth external electrode group324L of −phase as a pair, the first external electrode group321R of +phase and the second external electrode group322R of −phase as a pair, and the third external electrode group323R of +phase and the fourth external electrode group324R of −phase as a pair.

From another aspect, the multilayered piezoelectric element320consists of four regions320A,320B,320C, and320D with an angle of 90 degrees for each, separated by vertical surfaces around a central axis300C (FIGS. 19 and 20).

The regions320A,3203,320C, and320D, respectively, correspond to the first external electrode group321R of +phase and the second external electrode group322R of −phase, the third external electrode group323R of +phase and the fourth external electrode group324R of −phase, the first external electrode group321L of +phase and the second external electrode group322L of −phase, and the third external electrode group323L of +phase and the fourth external electrode group324L of −phase. By this structure, each region is deformed to a single direction reacting to a signal applied from the external power supply, just like the multilayered piezoelectric element120in the first embodiment. Furthermore, other structures, operations, and advantages are the same as those of the first embodiment.

Fourth Embodiment

An ultrasonic motor according to the fourth embodiment of the present invention generates an elliptical vibration by combining a longitudinal primary resonance vibration and a torsional tertiary resonance vibration. It differs from the ultrasonic motor according to the second embodiment in the point that it includes an internal electrode pattern that enables an external electrode group to be arranged on a bottom surface of a multilayered piezoelectric element420. Other structures are the same as those of the ultrasonic motor of the second embodiment and accordingly, the same reference symbols will be used and the descriptions of the parts other than the piezoelectric sheets are not shown in the diagrams.

A vibrator according to the fourth embodiment includes the multilayered piezoelectric element420formed by a plurality of piezoelectric sheets stacked together and that generates the longitudinal primary resonance vibration and the torsional tertiary resonance vibration by an activated area polarized in a thickness direction of the piezoelectric sheets. A structure of the multilayered piezoelectric element420forming the vibrator is explained below usingFIGS. 21 to 24. In the explanation,FIG. 21is an exploded perspective view of the structure of the multilayered piezoelectric element420.FIG. 22Ais a plan view of a structure of a first piezoelectric sheet430.FIG. 22Bis a plan view of a structure of a second piezoelectric sheet440.FIG. 22Cis a plan view of a structure of a third piezoelectric sheet450.FIG. 23is a perspective view from an upper front side of the multilayered piezoelectric element420.FIG. 24is a bottom view of the multilayered piezoelectric element420shown in.FIG. 23.

As shown inFIG. 21, the multilayered piezoelectric element420includes, stacked from this side to the other side in the thickness direction (a direction indicated by an arrow S4inFIG. 21), two first piezoelectric sheets430, two pairs of the second piezoelectric sheets440and the third piezoelectric sheets450alternately layered, two first piezoelectric sheets430, two pairs of the second piezoelectric sheets440and the third piezoelectric sheets450alternately layered, and two first piezoelectric sheets430.

As shown inFIGS. 22A to 22C, the first piezoelectric sheet430, the second piezoelectric sheet440, and the third piezoelectric sheet450have an identical shape of a rectangular plate. As the first piezoelectric sheet430, the second piezoelectric sheet440, and the third piezoelectric sheet450, for example, hard-type lead zirconate titanate piezoelectric elements are used. The piezoelectric element consisting of the second piezoelectric sheet440and the third piezoelectric sheet450include internal electrodes and an activated area polarized in the thickness direction.

Concrete structures of the internal electrodes and external electrodes are explained below.

As shown inFIG. 22B, a first internal electrode441aof +phase, a second internal electrode442aof +phase, and a fourth internal electrode444aof +phase are formed on the second piezoelectric sheet440. The second internal electrode442aof +phase and the fourth internal electrode444aof +phase are arranged on a lower part of the second piezoelectric sheet440along a longer side (vertical direction inFIGS. 22A to 22C) facing to and isolated from each other. The first internal electrode441aof +phase is arranged on an upper position isolated from the second internal electrode442aof +phase.

The second internal electrode442aof +phase is extended such that its protrusion442bis exposed to a bottom surface440U of the second piezoelectric sheet440. The first internal electrode441aof +phase is extended to the fourth internal electrode444aof +phase. The fourth internal electrode444ais extended so that its protrusion444bis exposed to the bottom surface440U of the second piezoelectric sheet440. The protrusions442band444bare arranged at a position isolated from each other at the bottom surface440U of the second piezoelectric sheet440.

Meanwhile, as shown inFIG. 22C, a first internal electrode451aof −phase, a second internal electrode452aof −phase, a wiring electrode453a, and a fourth internal electrode454aof −phase are formed on the third piezoelectric sheet450. The first internal electrode451aof −phase and the wiring electrode453aare arranged on a higher part of the third piezoelectric sheet450along a longer side, facing to and isolated from each other. The second internal electrode452aof −phase and the fourth internal electrode454aof −phase are arranged on a lower part of the third piezoelectric sheet450along the longer side, facing to and isolated from each other.

The second internal electrode452aof −phase is extended such that its protrusion452bis exposed to a bottom surface450U of the third piezoelectric sheet450. The first internal electrode451aof −phase is connected to the fourth internal electrode454aof −phase through the wiring electrode453a.Furthermore, the fourth internal electrode454aof −phase is extended so that its protrusion454bis exposed to the bottom surface450U of the third piezoelectric sheet450. The protrusions452band454bare arranged on positions inner than the corresponding positions of the protrusions442band444band are isolated from each other on the bottom surface450U of the third piezoelectric sheet450.

External electrodes formed on the protrusion442bcompose a first external electrode group421L of +phase and a third external electrode group423L of +phase on a bottom surface420U of the multilayered piezoelectric element420. External electrodes formed on the protrusion444bcompose a first external electrode group421R of +phase and a third external electrode group423R of +phase on the bottom surface420U of the multilayered piezoelectric element420(FIG. 24).

External electrodes formed on the protrusion452bcompose a second external electrode group422L of −phase and a fourth external electrode group424L of −phase on the bottom surface420U of the multilayered piezoelectric element420. External electrodes formed on the protrusion454bcompose a second external electrode group422R of −phase and a fourth external electrode group424R of −phase on the bottom surface420U of the multilayered piezoelectric element420(FIG. 24).

Eight external electrodes formed on the bottom surface420U of the multilayered piezoelectric element420compose four pairs of phases by respectively coupling the first external electrode group421L of +phase and the second external electrode group422L of −phase as a pair, the third external electrode group423L of +phase and the fourth external electrode group424L of −phase as a pair, the first external electrode group421R of +phase and the second external electrode group422R of −phase as a pair, and the third external electrode group423R of +phase and the fourth external electrode group424R of −phase as a pair.

From another aspect, the multilayered piezoelectric element420consists of four regions420A,420B,420C, and420D with an angle of 90 degrees for each, separated by vertical surfaces around a central axis400C (FIGS. 23 and 24).

The regions420A,420B,420C, and420D, respectively, correspond to the first external electrode group421R of +phase and the second external electrode group422R of −phase, the third external electrode group423R of +phase and the fourth external electrode group424R of −phase, the first external electrode group421L of +phase and the second external electrode group422L of −phase, and the third external electrode group423L of +phase and the fourth external electrode group424L of −phase.

According to this structure, each region is deformed reacting to a signal applied from the external power supply. Specifically, the deformation can be generated to different directions even in one region because a pair of the first internal electrode441aof +phase and the first internal electrode451aof −phase, and a pair of the second internal electrode442aof +phase and the second internal electrode452aof −phase are of different phases. Furthermore, other structures, operations, and advantages are the same as those of the first embodiment.

As explained above, the ultrasonic motor according to the present invention is appropriate for the ultrasonic motor that rotates the rotor by generating the elliptical vibration by combining the longitudinal vibration and the torsional vibration.

The ultrasonic motor according to the present invention can generate the torsional resonance vibration efficiently by positively applying the bending movement of the piezoelectric element. Moreover, the ultrasonic motor according to the present invention consists of a single part, has a simple structure without a groove etc., can generate the longitudinal vibration and the torsional vibration easily, can generate the elliptical vibration by combining the longitudinal vibration and the torsional vibration, and can rotate the rotor by the elliptical vibration.