Ultrasonic motor

An elliptical vibration is generated by combining a longitudinal primary resonance vibration of the vibrator resulting from an expansion and a contraction of the vibrator in a direction of the central axis and a torsional resonance vibration resulting from twisting of the vibrator around the central axis as a torsional axis. The dimension ratio of the rectangle of the vibrator is chosen such that a resonance frequency of the longitudinal primary resonance vibration resulting from the expansion and the contraction of the vibrator in the direction of the central axis and a resonance frequency of the torsional resonance vibrations resulting from twisting of the vibrator around the central axis as the torsional axis match. The ultrasonic motor further includes a vibration detecting electrode layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-036338 filed on Feb. 22, 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 an ultrasonic motor.

2. Description of the Related Art

There have been proposed ultrasonic motors that generate an elliptical vibration by combining a longitudinal vibration and a torsional vibration, and rotate a rotor.

For example, in an ultrasonic vibrator disclosed in Patent Application Laid-open No. H9-85172, a pair or a plurality of pairs of multilayered piezoelectric elements is held between holding elastic bodies that are provided integrally with a basal elastic body, and that have a recessed portion in which the multilayered piezoelectric element can be inserted. Furthermore, the multilayered piezoelectric elements are fixed to the basal elastic body with screws in a state in which a compressive stress is applied with the holding elastic bodies abut on piezoelectric elements.

However, the ultrasonic vibrator disclosed in Japanese Patent Application Laid-open No. H9-85172 has various drawbacks. For example, the holding elastic bodies are required for fixing the piezoelectric elements and an oblique recessed portion must be formed in the elastic bodies for arranging the holding elastic bodies and the piezoelectric elements. Thus, the overall structure of the conventional vibrator is very complicated.

Furthermore, a plurality of the piezoelectric elements for detecting vibrations is arranged between a plurality of the pairs of the multilayered piezoelectric elements and the holding elastic bodies, and when driving such a vibrator, two wirings are required for driving a piezoelectric element for driving and two wirings are required for detecting the vibrations of the piezoelectric element for detecting vibrations, thus requiring at least eight wirings. Because of the many wirings required for driving the vibrator, downsizing the ultrasonic vibrator cannot be achieved.

SUMMARY OF THE INVENTION

The present invention is made in view of the above discussion, and it is an object of the present invention to provide an ultrasonic motor that has a simplified overall structure and less number of wirings.

To solve the above problems and to achieve the above objects, according to an aspect of the present invention, an ultrasonic motor at least includes a vibrator having a dimension ratio of a rectangle in a cross-section orthogonal to a central axis; and a rotor that is in contact with an elliptical vibration generating surface of the vibrator and that is rotated around the central axis, which is orthogonal to the elliptical vibration generating surface. 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 resonance vibration resulting from twisting of the vibrator around the central axis as a torsional axis, and the dimension ratio of the rectangle of the vibrator is chosen such that a resonance frequency of the longitudinal primary resonance vibration resulting from the expansion and the contraction of the vibrator in the direction of the central axis and a resonance frequency of the torsional resonance vibration resulting from twisting of the vibrator around the central axis as the torsional axis match. The ultrasonic motor includes a vibration detecting electrode layer.

In the ultrasonic motor according to the above aspect, it is preferable that the torsional resonance vibration is a torsional secondary resonance vibration.

In the ultrasonic motor according to the above aspect, it is preferable that the torsional resonance vibration is a torsional tertiary resonance vibration.

In the ultrasonic motor according to the above aspect, it is preferable that the vibrator is formed by stacking a plurality of piezoelectric sheets, the vibration detecting electrode layer includes a piezoelectric sheet having internal electrodes formed thereon at positions on either side of a center in a width direction thereof, and a piezoelectric sheet having internal electrodes formed thereon at positions on either side of a center in a width direction thereof that are short circuited, and polarity directions of the internal electrodes at the positions on either side of the center in the width direction of the piezoelectric sheet are the same.

In the ultrasonic motor according to the above aspect, it is preferable that the vibrator is formed by stacking a plurality of piezoelectric sheets, the vibration detecting electrode layer includes a piezoelectric sheet having internal electrodes formed thereon at positions on either side of a center in a width direction thereof, and a piezoelectric sheet having internal electrodes formed thereon at positions on either side of a center in a width direction thereof that are short circuited, and polarity directions at the positions on either side of the center in the width direction of the piezoelectric sheet are reversed.

In the ultrasonic motor according to the above aspect, it is preferable that a driving electrode layer is formed at a position including a node of at least the torsional resonance vibration, and the vibration detecting electrode layer is formed in a direction that is the same stacking direction of the driving electrode layer.

In the ultrasonic motor according to the above aspect, it is preferable that a driving electrode layer is formed at a position including a node of the torsional resonance vibration, and the vibration detecting electrode layer is formed at a position, including a node of the torsional resonance vibration, different from the node having the driving electrode layer formed thereon.

In the ultrasonic motor according to the above aspect, it is preferable that the driving electrode layer is formed at the position including a common node of the torsional resonance vibration and the longitudinal primary resonance vibration.

In the ultrasonic motor according to the above aspect, it is preferable that among external electrodes provided in the vibrator so as to be conductive with vibration detecting electrodes and driving electrodes, the external electrodes that are connected during driving and conductive with the vibration detecting electrodes and the driving electrodes are formed on the same outer surface of the vibrator, and the external electrode used only during polarization is formed on an opposing outer surface of the vibrator.

DETAILED DESCRIPTION OF THE INVENTION

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

First Embodiment

FIG. 1is a front view of a structure of an ultrasonic motor100according to a first embodiment of the present invention.

The ultrasonic motor100includes a vibrator101and a rotor102. The vibrator101is a piezoelectric element of a substantially rectangular parallelepiped shape having a dimension ratio of a rectangle in a cross-section orthogonal to its central axis100c(rotation axis). Supporting members110aand110bthat extend from a holder110arranged so as to enclose the vibrator101are fixed near a node of the vibrator101(piezoelectric element).

The rotor102is substantially disk-shaped. A bottom surface of the rotor102is in contact with friction contact members103aand103bthat are arranged on an elliptical vibration generating surface101athat is on an upper surface of the vibrator101. A shaft105extends from a center of an upper surface of the rotor102along the central axis100c. The shaft105is coupled to a bearing107held by the holder110.

A second shaft106that extends along the central axis100cabuts against a base101bof the vibrator101. One end of the second shaft106is fixed to an inner surface of the holder110and the other end passes through a spring108and a hole of a spring holding ring109.

The spring holding ring109and the second shaft106are screwed to each other. A position of the spring holding ring109on the second shaft106, that is, a pressing force of the spring108, can be adjusted by rotating the spring holding ring109. In other words, a force by which the rotor102presses the friction contact members103aand103bcan be adjusted by rotating the spring holding ring109.

When the vibrator101is driven, the rotor102is rotated around the central axis100cthat is orthogonal to the elliptical vibration generating surface101aof the vibrator101.

How individual frequencies of the vibrator101(piezoelectric element) included in the ultrasonic motor100are matched is explained below with reference toFIGS. 2A to 3.FIG. 2Ais a perspective view of a schematic structure of the vibrator101according to the first embodiment.FIG. 2Bis a perspective view that depicts with a dotted line a vibration state of the vibrator101in a torsional primary vibration mode.FIG. 2Cis a perspective view that depicts with a dotted line a vibration state of the vibrator101in a longitudinal primary vibration mode.FIG. 2Dis a perspective view that depicts with a dotted line a vibration state of the vibrator101in a torsional secondary vibration mode andFIG. 2Eis a perspective view that depicts with a dotted line a vibration state of the vibrator101in a torsional tertiary vibration mode.

As shown inFIG. 2A, the vibrator101has a substantially rectangular parallelepiped shape. A length of a short side101sof a rectangular cross-section that is orthogonal to the central axis100cis denoted by a, a length of a long side101fis denoted by b, and a height of the vibrator101along the central axis100cis denoted by c. In the following explanation, a height direction of the vibrator101is assumed to be a direction of vibrations in the 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.

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

InFIGS. 2B to 2E, 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. 2B) and the longitudinal primary vibration mode (FIG. 2C). Two nodes N are present at two positions in the height direction in the torsional secondary vibration mode (FIG. 2D). Three nodes N are present at three positions in the height direction in the torsional tertiary vibration mode (FIG. 2E).

InFIGS. 2B to 2E, 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 a shape of the vibrator101after it is subjected to vibrations.

As can be seen inFIG. 3, when a 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 about 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 about 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 0.55 and 0.65 in the longitudinal primary vibration and the torsional secondary vibration. In a multilayered piezoelectric element120shown inFIG. 6, the parameter a/b is set to approximately 0.3.

In the ultrasonic motor100, an elliptical vibration is generated by combining a longitudinal primary resonance vibration resulting from an expansion and a contraction of the vibrator101along the central axis100c(rotation axis) and a torsional secondary resonance vibration or a torsional tertiary resonance vibration resulting from twisting of the vibrator101around the central axis100cas a torsional axis. 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 axis100cand the torsional secondary resonance vibration or the torsional tertiary resonance vibration resulting from twisting of the vibrator101around the central axis100cas the torsional axis almost match.

The vibrator101includes the 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 activated regions by polarization in a thickness direction of the piezoelectric sheets.

Structures of the vibrator101and the multilayered piezoelectric element120are explained below with reference toFIGS. 4 to 7B.FIG. 4is an exploded perspective view of the structure of the multilayered piezoelectric element120.FIG. 5Ais a plan view of a structure of a second piezoelectric sheet140,FIG. 5Bis a plan view of a structure of a third piezoelectric sheet150,FIG. 5Cis a plan view of a structure of a fourth piezoelectric sheet160, andFIG. 5Dis a plan view of a structure of a fifth piezoelectric sheet170.FIG. 6is a perspective view that depicts a position at which the vibrator101is cut from the multilayered piezoelectric element120.FIG. 7Ais a perspective view, from an upper front side, of the structure of the vibrator101cut from the multilayered piezoelectric element120according to the first embodiment andFIG. 7Bis a perspective view, from an upper rear side, of the structure of the vibrator101. InFIG. 6, internal electrodes are transparently shown. InFIGS. 6 to 7B, a detailed stacking state of each of the piezoelectric sheets is omitted.

As shown inFIG. 4, the multilayered piezoelectric element120includes, stacked from the top in the height direction (a direction indicated by an arrow S1inFIG. 4), (i) a plurality of first piezoelectric sheets130, (ii) a plurality of the second piezoelectric sheets140and a plurality of the third piezoelectric sheets150, which are stacked alternately, (iii) a plurality of the first piezoelectric sheets130, (iv) a plurality of the fourth piezoelectric sheets160and a plurality of the fifth piezoelectric sheets170, which are stacked alternately, and (v) a plurality of the first piezoelectric sheets130.

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

As shown inFIGS. 5A to 5D, the second piezoelectric sheet140, the third piezoelectric sheet150, the fourth piezoelectric sheet160, and the fifth piezoelectric sheet170have an identical shape of a rectangular plate. The first piezoelectric sheet130also has the same rectangular plate shape as that of the second piezoelectric sheet140, the third piezoelectric sheet150, the fourth piezoelectric sheet160, and the fifth piezoelectric sheet170.

As the first piezoelectric sheet130, the second piezoelectric sheet140, the third piezoelectric sheet150, the fourth piezoelectric sheet160, and the fifth piezoelectric sheet170, for example, hard-type lead zirconate titanate piezoelectric elements are used. These piezoelectric ceramic sheets should preferably be made from a PZT material having a thickness of 10 micrometers (μm) to 100 μm. The internal electrodes are formed of, for example, silver-palladium (Ag—Pd) alloy having a thickness of approximately 4 μm. The second piezoelectric sheet140, the third piezoelectric sheet150, the fourth piezoelectric sheet160, and the fifth piezoelectric sheet170include internal electrodes and an activated region polarized in the thickness direction.

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

Two internal electrodes are formed by way of printing on an upper surface of the second piezoelectric sheet140, the third piezoelectric sheet150, the fourth piezoelectric sheet160, and the fifth piezoelectric sheet170.

As shown inFIG. 5A, around a center of long sides (vertical sides inFIGS. 5A to 5D) of the second piezoelectric sheet140, a first internal electrode141a(D+) and a second internal electrode142a(C+) forming a vibration detecting electrode layer for detecting the vibrations are arranged facing but isolated from each other. Furthermore, a description within parentheses given after the internal electrode indicates the name and a polarity of the electrode layer (described later) constituted by the internal electrodes.

The first internal electrode141a(D+) and the second internal electrode142a(C+) are extended such that their protrusions141band142bare, respectively, exposed to long sides140U and140L of the second piezoelectric sheet140. Moreover, the protrusions141band142bare aligned at positions facing each other along the long sides of the second piezoelectric sheet140.

As shown inFIG. 5B, around a center of long sides of the third piezoelectric sheet150, a third internal electrode151a(D−) and a fourth internal electrode152a(C−) forming a vibration detecting electrode layer for detecting the vibrations are arranged facing each other. The third internal electrode151a(D−) and the fourth internal electrode152a(C−) are short circuited to each other with a connecting electrode153arranged therebetween.

The fourth internal electrode152a(C−) is extended such that its protrusion152bis exposed to a long side150L of the third piezoelectric sheet150.

As shown inFIG. 5C, around a center of long sides of the fourth piezoelectric sheet160, a fifth internal electrode161a(B+) and a sixth internal electrode162a(A+) forming a driving electrode layer for driving are arranged facing but isolated from each other. The fifth internal electrode161a(B+) and the sixth internal electrode162a(A+) are extended such that their protrusions161band162bare, respectively, exposed to long sides160U and160L of the fourth piezoelectric sheet160. Moreover, the protrusions161band162bare aligned at positions facing each other along the long sides of the fourth piezoelectric sheet160.

As shown inFIG. 5D, around a center of long sides of the fifth piezoelectric sheet170, a seventh internal electrode171a(B−) and an eighth internal electrode172a(A−) forming a driving electrode layer for driving are arranged facing but isolated from each other.

The seventh internal electrode171a(B−) and the eighth internal electrode172a(A−) are extended such that their protrusions171band172bare, respectively, exposed to long sides170U and170L of the fifth piezoelectric sheet170. Moreover, the protrusions171band172bare aligned at positions facing each other along the long sides of the fifth piezoelectric sheet170.

The first internal electrode141a(D+) and the third internal electrode151a(D−), and the second internal electrode142a(C+) and the fourth internal electrode152a(C−) are formed on the positions facing each other when the second piezoelectric sheet140and the third piezoelectric sheet150are stacked. The first internal electrode141a(D+) and the third internal electrode151a(D−), and the second internal electrode142a(C+) and the fourth internal electrode152a(C−), respectively, form polarized regions for detecting the vibrations. These polarized regions are vibration detecting electrode layers and, respectively, denoted as Phase D and Phase C.

The fifth internal electrode161a(B+) and the seventh internal electrode171a(B−), and the sixth internal electrode162a(A+) and the eighth internal electrode172a(A−) are formed on the positions facing each other when the fourth piezoelectric sheet160and the fifth piezoelectric sheet170are stacked. The fifth internal electrode161a(B+) and the seventh internal electrode171a(B−), and the sixth internal electrode162a(A+) and the eighth internal electrode172a(A−), respectively, form polarized regions for driving. These polarized regions are driving electrode layers and, respectively, denoted as Phase B and Phase A.

The external electrodes are formed on the protrusions141b,142b,152b,161b,162b,171b, and172bof the internal electrodes, for example, by way of printing of silver paste.

A first external electrode181(C+: + electrode of Phase C) is formed on a front face101F of the vibrator101so as to short circuit the protrusion142bof each piezoelectric sheet140and a second external electrode182(CD−: common− electrode of Phase C and Phase D) is formed on the front face101F of the vibrator101so as to short circuit the protrusion152bof each piezoelectric sheet150(FIG. 7A).

A third external electrode183(D+) is formed on a rear face101R of the vibrator101so as to short circuit the protrusion141bof each piezoelectric sheet140(FIG. 7B). The first external electrode181(C+) and the third external electrode183(D+) are external electrodes that are connected to the vibration detecting electrode layer (phase C or phase D). These external electrodes are connected to an external detector (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. The second external electrode182(CD−) is used only during polarization and it is not connected when the ultrasonic motor100is being driven.

On the other hand, a fourth external electrode191(A+) is formed on the front face101F of the vibrator101so as to short circuit the protrusion162bof each piezoelectric sheet160, and a fifth external electrode192(A−) is formed on the front face101F of the vibrator101so as to short circuit the protrusion172bof each piezoelectric sheet170. Furthermore, a sixth external electrode193(B+) is formed on the rear face101R of the vibrator101so as to short circuit the protrusion161bof each piezoelectric sheet160, and a seventh external electrode194(B−) is formed on the rear face101R of the vibrator101so as to short circuit the protrusion171bof each piezoelectric sheet170.

The fourth external electrode191(A+), the fifth external electrode192(A−), the sixth external electrode193(B+), and the seventh external electrode194(B−) are external electrodes that are connected to the driving electrode layer (Phase A or Phase B). These external electrodes are connected to an external power source (not shown) of the ultrasonic motor100. As an example, an FPC is used for connection and one end of the FPC is connected to each electrode group.

The external electrodes are not shown inFIGS. 1 to 2E.

As shown inFIGS. 6 and 7A, the first external electrode181(C+), the second external electrode182(CD−), the fourth external electrode191(A+), and the fifth external electrode192(A−) are formed on the front face101F that is one of the side faces of the surface formed by stacking the first piezoelectric sheet130, the second piezoelectric sheet140, the third piezoelectric sheet150, the fourth piezoelectric sheet160, and the fifth piezoelectric sheet170. On the other hand, as shown inFIG. 7B, the third external electrode183(D+), the sixth external electrode193(B+), and the seventh external electrode194(B−) are formed on the rear face101R that is the other side face.

The vibrator101is formed by cutting the multilayered piezoelectric element120in a direction in which the central axis100cis inclined by a predetermined angle relative to the stacking direction indicated by the arrow S1of the first piezoelectric sheet130, the second piezoelectric sheet140, the third piezoelectric sheet150, the fourth piezoelectric sheet160, and the fifth piezoelectric sheet170. A long side on one side of the first piezoelectric sheet130and the long sides140U,150U,160U, and170U on one side of the second piezoelectric sheet140, the third piezoelectric sheet150, the fourth piezoelectric sheet160, and the fifth piezoelectric sheet170are aligned and a side face to which each external electrode group is exposed forms the front face101F. Moreover, a long side on the other side of the first piezoelectric sheet130and the long sides140L,150L,160L, and170L on the other side of the second piezoelectric sheet140, the third piezoelectric sheet150, the fourth piezoelectric sheet160, and the fifth piezoelectric sheet170are aligned and a side face to which each external electrode group is exposed forms the rear face101R. The friction contact members103aand103bare fixed using an adhesive to an upper surface of the cut vibrator101.

It is preferable that the vibrator101be cut from the multilayered piezoelectric element120at an angle of 45° relative to the stacking direction indicated by the arrow S1(FIG. 6). When the longitudinal vibration is to be made stronger, the vibrator101can be cut at an angle less than 45° in the stacking direction indicated by the arrow S1and when the torsional vibration is to be made stronger, the vibrator101can be cut at an angle greater than 45° relative to the stacking direction indicated by the arrow S1.

Phase A and Phase B that are the driving electrode layers are arranged at positions that correspond to the common nodal positions of the longitudinal primary resonance vibration (FIG. 2C) and the torsional tertiary resonance vibration (FIG. 2E) of the cut vibrator101, and include a central portion of the vibrator101in the long sides (in a direction of the central axis100c) where the stress during vibration is maximum.

On the contrary, Phase C and Phase D that are the vibration detecting electrode layers are arranged on extended lines in the stacking direction indicated by the arrow S1of Phase A and Phase B that are the driving electrode layers.

Operations

If a predetermined AC voltage is applied to Phase A and Phase B of the ultrasonic motor100that uses the vibrator101of the structure described above, a vibration having a displacement component in a diagonal direction within the front face101F and the rear face101R of the vibrator101is generated.

If the AC voltage of the same phase is applied to Phase A and Phase B with a frequency corresponding to the resonance frequency of the longitudinal primary vibration or the torsional tertiary vibration of the vibrator101, piezoelectric elements of Phase A and Phase B vibrate in the same phase. As a result, the vibrator101vibrates longitudinally. At this time, a potential of the same phase is generated with the same vibrational amplitude in regions of Phase C and Phase D that are the vibration detecting electrode layers. On the contrary, if the AC voltage of opposite phases) (180° is applied to Phase A and Phase B with the same frequency, the piezoelectric elements of Phase A and Phase B vibrate in reverse phases. As a result, the vibrator101vibrates torsionally. At this time, a potential of reverse phase is generated with the same vibrational amplitude in regions of Phase C and Phase D that are the vibration detecting electrode layers.

The longitudinal primary vibration and the torsional tertiary vibration of the vibrator101are simultaneously excited by applying the AC voltage having phases different from each other (for example, a phase difference of 90°) to Phase A and Phase B of the vibrator101. Due to this, elliptical vibrations are generated on the elliptical vibration generating surface101athat is the upper end face of the vibrator101, and the rotor102that is pressed and held by the vibrator101is rotated. Furthermore, a rotation direction of the elliptical vibrations generated in the vibrator101can be reversed by reversing the phase difference of the AC voltage applied to Phase A and Phase B. Thus, the rotation direction of the rotor102can be controlled.

As described above, in the regions of Phase C and Phase D that are the vibration detecting electrode layers, the potential of the same phase is generated in the longitudinal primary resonance vibration mode, and the potential of the reverse phases is generated with the same vibrational amplitude in the torsional tertiary resonance vibration mode. Thus, in the state in which the longitudinal primary resonance vibration and the torsional tertiary resonance vibration are simultaneously excited, by calculating the difference between the potentials generated in the regions of Phase C and Phase D, a longitudinal primary resonance vibration component that is an in-phase component can be cancelled and a torsional tertiary resonance vibration component only can be detected. For example, a vibration detecting signal, which is proportional to the vibrational amplitude and phase of the torsional tertiary vibration generated on the vibrator101, can be obtained by connecting the external electrode C− and external electrode D− to pick up a difference in potential between the external electrode C+ and external electrode D+.

It is known that a phase difference between the vibration detecting signal, which is obtained from the vibration detecting electrode layer in above mentioned manner, and the AC voltage applied to the driving electrode layer is a predetermined phase difference when the torsional tertiary resonance vibration is generated. By controlling the driving frequency so as to hold the phase difference to be the predetermined phase difference, the vibrator can be driven in a frequency around the resonance frequency, thereby the vibrator can be driven efficiently and stably.

Incidentally, detail description about the technique relating to a frequency tracking is omitted because the technique itself relating to the frequency tracking based on the vibration detecting signal is not involved in the characterizing portion of the present invention.

The third internal electrode151a(D−) and the fourth internal electrode152a(C−) of the third piezoelectric sheet150forming the vibration detecting electrode layer are made internally mutually conductive with the connecting electrode153. Due to this, the torsional tertiary resonance vibration component that is the difference between the potentials generated in the regions of Phase C and Phase D occurs between the first external electrode181(C+) and the third external electrode183(D+) without using an external wiring connection.

Effect

In the ultrasonic motor100described above, because the vibrator101is formed with a single member, the structure of the vibrator101can be simplified. The third internal electrode151a(D−) and the fourth internal electrode152a(C−) that are the internal electrodes for detecting the vibrations are made mutually conductive with the connecting electrode153, thus forming a conductive layer. Therefore, a torsional resonance vibration component required for tracking the frequency can be easily detected without providing wiring externally for connection between the third internal electrode151a(D−) and the fourth internal electrode152a(C−). Furthermore, because the number of wirings that need to be connected to the vibrator101when the motor is being driven can be reduced, it is beneficial for downsizing the motor. Because a signal detecting the torsional resonance vibration component is a signal from the vibration detecting electrode layers that are connected in series, a signal voltage can be increased. Thus, it is beneficial when the motor is being driven at a low speed, that is, when a vibration speed is reduced.

A polarity direction of Phase C and Phase D that are the vibration detecting electrode layers can be reversed. In this case, the longitudinal primary resonance vibration component that is the sum of the potentials generated in the regions of Phase C and Phase D can be made to occur between the first external electrode181(C+) and the third external electrode183(D+).

FIG. 8Ais a perspective view, from an upper front side, of a structure of a vibrator according to a modification of the first embodiment andFIG. 8Bis a perspective view, from an upper rear side, of the structure of the vibrator. The vibrator shown inFIGS. 8A and 8Bis a longitudinal primary torsional secondary resonance vibrator formed such that a dimension ratio of long sides (a) and short sides (b) of a rectangle in a cross-section orthogonal to the central axis100cof the multilayered piezoelectric element is approximately 0.6. In the vibrator, the driving electrode layer is provided on a position including the node portion of the torsional secondary resonance vibration, and the vibration detecting electrode layer is provided on an extended line of the stacking direction of the driving electrode layer. The same effect as that of the vibrator101shown inFIGS. 1 to 73can be obtained with the vibrator according to the modification of the first embodiment.

Second Embodiment

In an ultrasonic motor according to a second embodiment, the vibration detecting electrode layers in a vibrator are formed at different positions from that of the ultrasonic motor according to the first embodiment. Rest of the structure is similar to that of the ultrasonic motor according to the first embodiment and detailed explanation of the structure other than the vibrator is omitted.

Structures of a vibrator201and a multilayered piezoelectric element220are explained below with reference toFIGS. 9 to 12E.FIG. 9is an exploded perspective view of the structure of the multilayered piezoelectric element220according to the second embodiment.FIG. 10Ais a plan view of a structure of a second piezoelectric sheet240,FIG. 10Bis a plan view of a structure of a third piezoelectric sheet250,FIG. 10Cis a plan view of a structure of a fourth piezoelectric sheet260, andFIG. 10Dis a plan view of a structure of a fifth piezoelectric sheet270.FIG. 11is a perspective view that depicts a position at which the vibrator201is cut from the multilayered piezoelectric element220.FIG. 12Ais a perspective view, from an upper front side, of the structure of the vibrator201cut from the multilayered piezoelectric element220according to the second embodiment andFIG. 12Bis a perspective view, from an upper rear side, of the structure of the vibrator201. InFIGS. 10A to 10D, internal electrodes are transparently shown. InFIGS. 10A to 11, a detailed stacking state of each of the piezoelectric sheets is omitted.

As shown inFIG. 9, the multilayered piezoelectric element220includes, similar to that of the multilayered piezoelectric element120according to the first embodiment, stacked from the top in a height direction (a direction indicated by an arrow S2inFIG. 9), (i) a plurality of first piezoelectric sheets230, (ii) a plurality of the second piezoelectric sheets240and a plurality of the third piezoelectric sheets250, which are stacked alternately, (iii) a plurality of the first piezoelectric sheets230, (iv) a plurality of the fourth piezoelectric sheets260and a plurality of the fifth piezoelectric sheets270, which are stacked alternately, and (v) a plurality of the first piezoelectric sheets230.

As shown inFIGS. 10A to 10D, the second piezoelectric sheet240, the third piezoelectric sheet250, the fourth piezoelectric sheet260, and the fifth piezoelectric sheet270have an identical shape of a rectangular plate. The first piezoelectric sheet230also has the same rectangular plate shape as that of the second piezoelectric sheet240, the third piezoelectric sheet250, the fourth piezoelectric sheet260, and the fifth piezoelectric sheet270. A material used in these piezoelectric sheets and characteristics of the piezoelectric sheets are similar to that of the piezoelectric sheets in the first embodiment.

Internal electrodes and external electrodes are formed by a method similar to that of the first embodiment.

As shown inFIG. 10A, on a right side of long sides (vertical sides inFIGS. 10A to 10D) of the second piezoelectric sheet240, a first internal electrode241a(D+) and a second internal electrode242a(C+) forming a vibration detecting electrode layer for detecting the vibrations are arranged facing but isolated from each other.

The first internal electrode241a(D+) and the second internal electrode242a(C+) are extended such that their protrusions241band242bare, respectively, exposed to long sides240U and240L of the second piezoelectric sheet240. Moreover, the protrusions241band242bare aligned at positions facing each other along the long sides of the second piezoelectric sheet240.

As shown inFIG. 10B, on a right side of long sides of the third piezoelectric sheet250, a third internal electrode251a(D−) and a fourth internal electrode252a(C−) forming a vibration detecting electrode layer for detecting the vibrations are arranged facing each other. The third internal electrode251a(D−) and the fourth internal electrode252a(C−) are short circuited to each other with a connecting electrode253arranged therebetween.

The fourth internal electrode252a(C−) is extended such that its protrusion252bis exposed to a long side250L of the third piezoelectric sheet250.

The first internal electrode241a(D+) and the third internal electrode251a(D−), and the second internal electrode242a(C+) and the fourth internal electrode252a(C−) are formed on the positions facing each other when the second piezoelectric sheet240and the third piezoelectric sheet250are stacked. The first internal electrode241a(D+) and the third internal electrode251a(D−), and the second internal electrode242a(C+) and the fourth internal electrode252a(C−), respectively, form polarized regions for detecting the vibrations. These polarized regions are vibration detecting electrode layers and, respectively, denoted as Phase D and Phase C.

The fourth piezoelectric sheet260has the same structure as that of the fourth piezoelectric sheet160of the first embodiment. Long sides260U and260L of the fourth piezoelectric sheet260, a fifth internal electrode261a(B+), a protrusion261b, a sixth internal electrode262a(A+), and a protrusion262b, respectively, correspond to the long sides160U and160L of the fourth piezoelectric sheet160, the fifth internal electrode161a(B+), the protrusion161b, the sixth internal electrode162a(A+), and the protrusion162bof the first embodiment.

The fifth piezoelectric sheet270has the same structure as that of the fifth piezoelectric sheet170of the first embodiment. Long sides270U and270L of the fifth piezoelectric sheet270, a seventh internal electrode271a(B−), a protrusion271b, an eighth internal electrode272a(A−), and a protrusion272b, respectively, correspond to the long sides170U and170L of the fifth piezoelectric sheet170, the seventh internal electrode171a(B−), the protrusion171b, the eighth internal electrode172a(A−), and the protrusion172bof the first embodiment.

Similar to the first embodiment, the fifth internal electrode261a(B+) and the seventh internal electrode271a(B−), and the sixth internal electrode262a(A+) and the eighth internal electrode272a(A−) are formed on the positions facing each other when the fourth piezoelectric sheet260and the fifth piezoelectric sheet270are stacked. The fifth internal electrode261a(B+) and the seventh internal electrode271a(B−) and the sixth internal electrode262a(A+) and the eighth internal electrode272a(A−), respectively, form polarized regions for driving. These polarized regions are driving electrode layers and, respectively, denoted as Phase B and Phase A.

A first external electrode281(C+) is formed on a front face201F of the vibrator201so as to short circuit the protrusion242bof each piezoelectric sheet240. Moreover, a second external electrode282(CD−) is formed on the front face201F of the vibrator201so as to short circuit the protrusion252bof each piezoelectric sheet250(FIG. 12A).

A third external electrode283(D+) is formed on a rear face201R of the vibrator201so as to short circuit the protrusion241bof each piezoelectric sheet240(FIG. 12B). The first external electrode281(C+) and the third external electrode283(D+) are external electrodes that are connected to the vibration detecting electrode layer (Phase C or Phase D).

These external electrodes are connected to the external detector (not shown) of the ultrasonic motor100. As an example, the FPC is used for connection and one end of the FPC is connected to each electrode group. The second external electrode282(CD−) is used only during polarization and it is not connected when the ultrasonic motor100is being driven.

A fourth external electrode291(A+) and a fifth external electrode292(A−) formed on the front face201F of the vibrator201, respectively, correspond to the fourth external electrode191(A+) and the fifth external electrode192(A−) of the first embodiment. Furthermore, a sixth external electrode293(B+) and a seventh external electrode294(B−) formed on the rear face201R of the vibrator201, respectively, correspond to the sixth external electrode193(B+) and the seventh external electrode194(B−) of the first embodiment. The fourth external electrode291(A+), the fifth external electrode292(A−), the sixth external electrode293(B+), and the seventh external electrode294(B−) are driving electrode layers. These external electrodes are connected to the external power source (not shown) of the ultrasonic motor100. As an example, the FPC is used for connection and one end of the FPC is connected to each electrode group.

Similar to the vibrator101according to the first embodiment, the vibrator201is formed by cutting the multilayered piezoelectric element220in a direction in which a central axis200cis inclined by a predetermined angle relative to the stacking direction indicated by the arrow S2of the first piezoelectric sheet230, the second piezoelectric sheet240, the third piezoelectric sheet250, the fourth piezoelectric sheet260, and the fifth piezoelectric sheet270. A long side on one side of the first piezoelectric sheet230and the long sides240U,250U,260U, and2700on one side of the second piezoelectric sheet240, the third piezoelectric sheet250, the fourth piezoelectric sheet260, and the fifth piezoelectric sheet270are aligned and a side face to which each external electrode group is exposed forms the front face201F. Moreover, similar to the first embodiment, a long side on the other side of the first piezoelectric sheet230and the long sides240L,250L,260L, and270L on the other side are aligned and a side face to which each external electrode group is exposed forms the rear face201R. The friction contact members103aand103bare fixed using an adhesive to an upper surface of the cut vibrator201.

Similar to the first embodiment, Phase A and Phase B that are the driving electrode layers are arranged at positions that correspond to the common nodal positions of the longitudinal primary resonance vibration (FIG. 2C) and the torsional tertiary resonance vibration (FIG. 2E) of the vibrator201, and includes a central portion of the vibrator201in the long sides (in a direction of the central axis200c) where the stress during vibration is maximum.

On the contrary, Phase C and Phase D that are the vibration detecting electrode layers are arranged at positions that are not on extended lines in the stacking direction indicated by the arrow S2of Phase A and Phase B that are the driving electrode layers. Specifically, Phase C and Phase D are arranged at positions including the nodal positions (positions towards a central portion that is approximately ⅙th of a length of the long sides from an upper end face or a lower end face of the vibrator201) of the torsional tertiary vibration different from positions at which the driving electrode layers are arranged.

Effect

Because the vibration detecting electrodes are provided at nodal positions different from that of the driving electrodes, the vibration detecting electrode layers can be provided without reducing the number of layers of the driving electrodes. Furthermore, because the vibration detecting electrode layers can be stacked at positions that include the node of the torsional tertiary vibration where the stress during torsional vibration is maximum, an output of a torsional vibration detecting signal can be increased. Thus, it is beneficial for detecting the signal when the motor is being driven at a low speed, that is, when the vibrations are reduced.

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

FIG. 13Ais a perspective view, from an upper front side, of a structure of a vibrator according to a modification of the second embodiment,FIG. 13Bis a perspective view, from an upper rear side, of the structure of the vibrator. The vibrator shown inFIGS. 13A and 13Bis a longitudinal primary torsional secondary resonance vibrator formed such that a dimension ratio of long sides (a) and short sides (b) of a rectangle in a cross-section orthogonal to the central axis200cof the multilayered piezoelectric element is approximately 0.6. In the vibrator, the driving electrode layer is provided on the position including the node portion of the torsional secondary resonance vibration, and the vibration detecting electrode layer is provided on a position, which includes the node portion of the torsional secondary resonance vibration and is different from the position where the driving electrode layer is provided. The same effect as that of the vibrator201shown inFIGS. 11 to 12Bcan be obtained in the vibrator according to the modification of the second embodiment.

Third Embodiment

An ultrasonic motor according to the third embodiment differs from the ultrasonic motor100according to the first embodiment in that among external electrodes connected to driving electrode layers and vibration detecting electrode layers, all the external electrodes that need to be wired when the ultrasonic motor is being driven are formed on a front face of a multilayered piezoelectric element and the external electrodes other than these are formed on a rear face of the multilayered piezoelectric element. Rest of the structure is the same as that of the ultrasonic motor100according to the first embodiment and detailed explanation of the structure other than the vibrator is omitted.

Structures of a vibrator301and a multilayered piezoelectric element320are explained below with reference toFIGS. 14 to 17B.FIG. 14is an exploded perspective view of the structure of the multilayered piezoelectric element320according to the third embodiment.FIG. 15Ais a plan view of a structure of a second piezoelectric sheet340,FIG. 15Bis a plan view of a structure of a third piezoelectric sheet350,FIG. 15Cis a plan view of a structure of a fourth piezoelectric sheet360, andFIG. 15Dis a plan view of a structure of a fifth piezoelectric sheet370.FIG. 16is a perspective view that depicts a position at which the vibrator301is cut from the multilayered piezoelectric element320.FIG. 17Ais a perspective view, from an upper front side, of the structure of the vibrator301cut from the multilayered piezoelectric element320according to the third embodiment andFIG. 17Bis a perspective view, from an upper rear side, of the structure of the vibrator301. InFIG. 16, internal electrodes are transparently shown. InFIGS. 16 to 17B, a detailed stacking state of each of the piezoelectric sheets is omitted.

As shown inFIG. 14, the multilayered piezoelectric element320includes, similar to the multilayered piezoelectric element120according to the first embodiment, stacked from the top in a height direction (a direction indicated by an arrow S3inFIG. 14), (i) a plurality of first piezoelectric sheets330, (ii) a plurality of the second piezoelectric sheets340and a plurality of the third piezoelectric sheets350, which are stacked alternately, (iii) a plurality of the first piezoelectric sheets330, (iv) a plurality of the fourth piezoelectric sheets360and a plurality of the fifth piezoelectric sheets370, which are stacked alternately, and (v) a plurality of the first piezoelectric sheets330.

As shown inFIGS. 15A to 15D, the second piezoelectric sheet340, the third piezoelectric sheet350, the fourth piezoelectric sheet360, and the fifth piezoelectric sheet370have an identical shape of a rectangular plate. The first piezoelectric sheet330also has the same rectangular plate shape as that of the second piezoelectric sheet340, the third piezoelectric sheet350, the fourth piezoelectric sheet360, and the fifth piezoelectric sheet370. A material used in these piezoelectric sheets and characteristics of the piezoelectric sheets are similar to that of the piezoelectric sheets in the first embodiment.

Internal electrodes and external electrodes are formed by a method similar to that of the first embodiment.

As shown inFIG. 15A, on a right side of long sides (vertical sides inFIGS. 15A to 15D) of the second piezoelectric sheet340, a first internal electrode341a(D+) and a second internal electrode342a(C+) forming a vibration detecting electrode layer for detecting the vibrations are arranged facing but isolated from each other.

The first internal electrode341a(D+) that is arranged on a side of a long side340U of the second piezoelectric sheet340and whose protrusion341bis exposed to the other long side340L is guided so as not to come into contact with the second internal electrode342a(C+).

The second internal electrode342a(C+) arranged on a side of the long side340L is extended such that its protrusion342bis exposed to the long side340L of the second piezoelectric sheet340. Thus, the protrusions341band342bare arranged on the same long side340L.

As shown inFIG. 15B, on a right side of long sides of the third piezoelectric sheet350, a third internal electrode351a(D−) (on a side of a long side350U of the third piezoelectric sheet350) and a fourth internal electrode352a(C−) (on a side of a long side350L facing the long side350U) forming a vibration detecting electrode layer for detecting the vibrations are arranged facing each other. The third internal electrode351a(D−) and the fourth internal electrode352a(C−) are short circuited to each other with a connecting electrode353arranged therebetween.

The third internal electrode351a(D−) is extended such that its protrusion351bis exposed to the long side350U of the third piezoelectric sheet350.

As shown inFIG. 15C, around a center of long sides of the fourth piezoelectric sheet360, a fifth internal electrode361a(B+) and a sixth internal electrode362a(A+) forming a driving electrode layer for driving are arranged facing but isolated from each other.

The fifth internal electrode361a(B+) that is arranged on a side of a long side360U of the fourth piezoelectric sheet360and whose protrusion361bis exposed to other long side360L is guided so as not to come into contact with the sixth internal electrode362a(A+).

The sixth internal electrode362a(A+) arranged on the side of the long side360L is extended such that its protrusion362bis exposed to the long side360L of the fourth piezoelectric sheet360. Thus, the protrusions361band362bare arranged on the same long side360L.

As shown inFIG. 15D, around a center of long sides of the fifth piezoelectric sheet370, a seventh internal electrode371a(B−) and an eighth internal electrode372a(A−) forming a driving electrode layer for driving are arranged facing but isolated from each other.

The seventh internal electrode371a(B−) that is arranged on a side of a long side370U of the fifth piezoelectric sheet370and whose protrusion371bis exposed to other long side370L is guided so as not to come into contact with the eighth internal electrode372a(A−).

The eighth internal electrode372a(A−) arranged on the side of the long side370L is extended such that its protrusion372bis exposed to the long side370L of the fifth piezoelectric sheet370. Thus, the protrusions371band372bare arranged on the same long side370L.

The first internal electrode341a(D+) and the third internal electrode351a(D−), and the second internal electrode342a(D+) and the fourth internal electrode352a(C−) are formed on the positions facing each other when the second piezoelectric sheet340and the third piezoelectric sheet350are stacked. The first internal electrode341a(D+) and the third internal electrode351a(D−), and the second internal electrode342a(C+) and the fourth internal electrode352a(C−), respectively, form polarized regions for detecting the vibrations. These polarized regions are the vibration detecting electrode layers and, respectively, denoted as Phase D and Phase C.

The fifth internal electrode361a(B+) and the seventh internal electrode371a(B−), and the sixth internal electrode362a(A+) and the eighth internal electrode372a(A−) are formed on the positions facing each other when the fourth piezoelectric sheet360and the fifth piezoelectric sheet370are stacked. The fifth internal electrode361a(B+) and the seventh internal electrode371a(B−), and the sixth internal electrode362a(A+) and the eighth internal electrode372a(A−), respectively, form polarized regions for driving. These polarized regions are the driving electrode layers and, respectively, denoted as Phase B and Phase A.

A second external electrode382(D+) is formed on a front face301F of the vibrator301so as to short circuit the protrusion341bof each piezoelectric sheet340and a first external electrode381(C+) is formed on the front face301F of the vibrator301so as to short circuit the protrusion342bof each piezoelectric sheet340(FIG. 17A).

A third external electrode383(CD−) is formed on a rear face301R of the vibrator301so as to short circuit the protrusion351bof each piezoelectric sheet350(FIG. 17B). The first external electrode381(C+), the second external electrode382(D+), and the third external electrode383(CD−) are external electrodes connected to the vibration detecting electrode layer (Phase C or Phase D), These external electrodes are connected to the external detector (not shown) of the ultrasonic motor100. As an example, the FPC is used for connection and one end of the FPC is connected to each electrode group. The third external electrode383(CD−) is used only during polarization and it is not connected when the ultrasonic motor100is being driven.

A fourth external electrode391(A+) is formed on the front face301F of the vibrator301so as to short circuit the protrusion361bof each piezoelectric sheet360and a fifth external electrode392(A−) is formed on the front face301F of the vibrator301so as to short circuit the protrusion362bof each piezoelectric sheet360. Moreover, a sixth external electrode393(B+) is formed on the front face301F of the vibrator301so as to short circuit the protrusion372bof each piezoelectric sheet370and a seventh external electrode394(B−) is formed on the front face301F of the vibrator301so as to short circuit the protrusion371bof each piezoelectric sheet370(FIG. 17A).

The fourth external electrode391(A+) and the fifth external electrode392(A−), and the sixth external electrode393(B+) and the seventh external electrode394(B−) are external electrodes connected to the driving electrode layer (Phase A or Phase B). These external electrodes are connected to the external power source (not shown) of the ultrasonic motor100. As an example, the FPC is used for connection and one end of the FPC is connected to each electrode group.

As shown inFIGS. 16 and 17A, the first external electrode381(C+), the second external electrode382(D+), the fourth external electrode391(A+), the fifth external electrode392(A−), the sixth external electrode393(B+), and the seventh external electrode394(B−), in other words, all the external electrodes that need to be connected to the power source or a detecting circuit when the ultrasonic motor100is being driven are formed on the front face301F that is one of the side faces of the surface formed by stacking the first piezoelectric sheet330, the second piezoelectric sheet340, the third piezoelectric sheet350, the fourth piezoelectric sheet360, and the fifth piezoelectric sheet370. On the other hand, as shown inFIG. 17B, the third external electrode383(CD−) that is not connected when the ultrasonic motor100is being driven is formed on the rear face301R that is the other side face.

Similar to the vibrator101according to the first embodiment, the vibrator301is formed by cutting the multilayered piezoelectric element320in a direction in which a central axis300cis inclined by a predetermined angle relative to the stacking direction S3of the first piezoelectric sheet330, the second piezoelectric sheet340, the third piezoelectric sheet350, the fourth piezoelectric sheet360, and the fifth piezoelectric sheet370. A long side on one side of the first piezoelectric sheet330and the long sides340U,350U,360U, and370U on one side of the second piezoelectric sheet340, the third piezoelectric sheet350, the fourth piezoelectric sheet360, and the fifth piezoelectric sheet370are aligned and a side face to which each external electrode group is exposed forms the front face301F. Moreover, a long side on the other side of the first piezoelectric sheet330and the long sides340L,350L,360L, and370L on the other side are aligned and a side face to which each external electrode group is exposed forms the rear face301R. The friction contact members103aand103bare fixed using an adhesive to an upper surface of the cut vibrator301.

Phase A and Phase B that are the driving electrode layers are arranged at positions that correspond to the common nodal positions of the longitudinal primary resonance vibration (FIG. 2C) and the torsional tertiary resonance vibration (FIG. 2E) of the vibrator301, and include a central portion of the vibrator301in the long sides (in a direction of the central axis300c) where the stress during vibration is maximum.

On the contrary, Phase C and Phase D that are the vibration detecting electrode layers are arranged at positions that are not on extended lines in the stacking direction S3of Phase A and Phase B that are the driving electrode layers. Specifically, Phase C and Phase D are arranged at positions including the nodal positions (positions towards a central portion that is approximately ⅙th of a length of the long sides from an upper end face or a lower end face of the vibrator301) of the torsional tertiary vibration different from the positions at which the driving electrode layers are arranged. Similarly as that of the first embodiment, Phase C and Phase D that are the vibration detecting electrode layers can be arranged on extended lines in the stacking direction indicated by the arrow S3of Phase A and Phase B that are the driving electrode layers.

Effect

Because the electrodes that need to be wired when the ultrasonic motor is being operated (when the motor is being driven) are arranged on one surface of the multilayered piezoelectric element, these electrodes can be easily assembled.

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

FIG. 18Ais a perspective view, from an upper front side, of a structure of a vibrator according to a modification of the third embodiment andFIG. 18Bis a perspective view, from an upper rear side, of the structure of the vibrator. The vibrator shown inFIGS. 18A and 18Bis a longitudinal primary torsional secondary resonance vibrator formed such that a dimension ratio of long sides (a) and short sides (b) of a rectangle in a cross-section orthogonal to the central axis300cof a multilayered piezoelectric element is approximately 0.6. In the vibrator, the driving electrode layer is provided on the position including the node portion of the torsional secondary resonance vibration, and the vibration detecting electrode layer is provided on a position, which includes the node portion of the torsional secondary resonance vibration and is different from the position where the driving electrode layer is provided. The same effect as that of the vibrator301shown inFIGS. 16 to 17Bcan be obtained with the vibrator according to the modification of the third embodiment.

As described above, the ultrasonic motor according to the present invention is smaller and has a simpler structure.

In the ultrasonic motor according to the present invention, because a vibrator can be formed with a single member, a structure of the vibrator can be simplified. Furthermore, because a conductive layer of internal electrodes for detecting vibrations is formed, a torsional resonance vibration component can be easily detected without providing a specific circuit and number of wirings that need to be connected to the vibrator when the motor is being driven can be reduced. Thus, it is beneficial for downsizing the ultrasonic motor. Furthermore, because a signal detecting the torsional resonance vibration component is a signal from the vibration detecting electrode layers that are connected in series, a signal voltage can be increased. Thus, it is beneficial when the motor is being driven at a low speed, that is, when the vibration speed is reduced.