Piezoelectric actuator and lens barrel
A piezoelectric actuator includes: a plurality of first piezoelectric elements; a first member that is interposed between opposing faces of the plurality of the first piezoelectric elements and that is driven in a first direction by the plurality of the first piezoelectric elements; a second piezoelectric element that is disposed in the first member; a second member that is disposed in contact with the second piezoelectric element and that is driven in a second direction intersecting the first direction by the second piezoelectric element; and a third member that comes in contact with the second member and that is moved relative to the first member by driving the second member.
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The present invention relates to a piezoelectric actuator and a lens barrel.
Priority is claimed on Japanese Patent Application No. 2009-084113 and Japanese Patent Application No. 2009-084114, filed on Mar. 31, 2009, the contents of which are incorporated herein by reference.
BACKGROUND ARTUntil now, piezoelectric actuators (driving mechanisms) employing a piezoelectric element have been known. As such a type of piezoelectric actuator, for example, Patent Document 1 below discloses that a driven body is driven by driving plural piezoelectric elements to elliptically move a tip member coming in contact with the driven body. When an XYZ orthogonal coordinate system is set up, the piezoelectric actuator disclosed in Patent Document 1 below drives the driven body in the X axis direction due to the elliptical movement of the tip member parallel to the XZ plane.
PATENT DOCUMENT[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2007-236138
SUMMARY OF THE INVENTION Problem that the Invention is to solveHowever, the piezoelectric actuator has a problem in that vibrations in two different directions cannot be picked up as independent vibrations. In Patent Document 1 above, since the vibrations of the tip member in the X axis direction and the Z axis direction cannot be picked up as independent vibrations, plural piezoelectric elements may interfere with each other in motion. When plural piezoelectric elements are driven to interfere with each other in motion, the power of the piezoelectric actuator driving the driven member is reduced.
An object of aspects of the present invention is to provide a piezoelectric actuator which can pick up vibrations in two different directions as independent vibrations, and a lens barrel employing the piezoelectric actuator.
Means for Solving the ProblemAccording to an aspect of the present invention, there is provided a piezoelectric actuator including: a plurality of first piezoelectric elements; a first member that is interposed between opposing faces of the plurality of the first piezoelectric elements and that is driven in a first direction by the plurality of the first piezoelectric elements; a second piezoelectric element that is disposed in the first member; a second member that is disposed in contact with the second piezoelectric element and that is driven in a second direction intersecting the first direction by the second piezoelectric element; and a third member that comes in contact with the second member and that is moved relative to the first member by driving the second member.
According to another aspect of the present invention, there is provided a lens barrel including the above-mentioned piezoelectric actuator.
EFFECTS OF THE INVENTIONIn the piezoelectric actuator according to aspects of the present invention, it is possible to pick up the vibrations in two different directions as independent vibrations.
A piezoelectric actuator according to an embodiment of the present invention will be described below with reference to the accompanying drawings. The piezoelectric actuator (the driving mechanism) 1 according to this embodiment serves to drive an optical device or an electronic apparatus such as a lens barrel of a camera by performing a relative driving operation of relatively displacing a first part such as a rotor and a second part such as a driving member.
As shown in
The base member 2 is formed in a hollow cylindrical shape out of a metal material such as stainless steel and provided so as to surround the support shaft 5 by inserting the support shaft 5 therethrough.
The rotor 4 is supported (axially supported) by the support shaft 5 with a bearing 5a interposed therebetween and is disposed to be rotatable about the support shaft 5. A toothed wheel 4a used to drive a lens barrel of a camera or the like is formed on the outer circumferential surface of the rotor 4. The surface of the rotor 4 facing the base member 2 is supported by the plural driving members 3.
An end of the base member 2 is fixed to an attaching section 101a, for example, by the use of bolts not shown. A concave portion 2b is formed at the center of the surface of the base member 2 facing the attaching section 101a. A large-diameter portion 5a formed at the base end of the support shaft 5 is inserted (locked) into the concave portion 2b. The support shaft 5 is fixed to the base member 2 and the attaching section 101a by fixing the base member 2 to the attaching section 101a in this state.
Plural holding portions 2a which are concave are disposed at the other end of the base member 2 along the circumferential direction of the base member 2, that is, the rotational direction R of the rotor 4. Each holding portion 2a supports a corresponding driving member 3 from both sides in the direction (second direction) parallel to the rotational direction R of the rotor 4 so as to be perpendicular to the support shaft 5 and holds the driving member 3 so as to drive the driving member 3 in the direction (first direction) parallel to the support shaft 5.
As shown in
The depth d1 of the groove 2d is, for example, in the range of 40% to 80% of the radius r1 of the base member 2. This numerical range is only an example and the present invention is not limited to the range. The depth d1 of the groove 2d can be set to, for example, 10, 20, 30, 40, 50, 60, 70, 80, or 90% of the radius r1 of the base member 2. The width w1 of the groove 2d in the direction (the first direction) parallel to the support shaft 5 is greater than the amplitude of the vibration of the base member 2 and is greater than the amplitude of the resonant vibration of a support and drive section (structure) 1a including the first piezoelectric elements 6, the second piezoelectric elements 7, the driving members 3, and the base member 2. For example, the width w1 of the groove 2d can be set to be smaller than the radius of the base member 2.
As shown in
As shown in
The tip portion 3a includes tilted faces S2 and S3 tilted about a contact face S1. The tilted faces S2 and S3 are disposed along a direction intersecting the rotational direction of the rotor 4. The tilted faces S2 and S3 are formed continuously from the contact face S1 of the tip portion 3a in a tapered shape such that the sectional area of the tip portion 3a parallel to the contact face S1 coming in contact with the rotor 4 decreases as it gets closer to the rotor 4. That is, the tip portion 3a has a tapered shape in which the area of the contact face S1 coming in contact with the rotor 4 becomes smaller than the area of the bottom close to the base portion 3b. The tilted faces S2 and S3 may be a curved face with a concave shape or a convex shape.
As shown in
The first piezoelectric elements 6 are adhered to the base portion 3b of the driving member 3 and the holding portion 2a, for example, by the use of a conductive adhesive. Two first piezoelectric elements 6 and 6 arranged in the depth p1 direction of the driving member 3 substantially parallel to the center line CL passing through the center of the base member 2 are substantially parallel to each other. The shapes and sizes of the first piezoelectric elements 6 are substantially the same.
As shown in
The first piezoelectric elements 6 and the second piezoelectric elements 7 are formed of, for example, lead zirconate titanate (PZT) and the vibration mode thereof is a thickness-shear vibration mode. That is, the first piezoelectric elements 6 drive the corresponding driving member 3 relative to the base member 2 in the depth d2 direction of the corresponding holding portion 2a substantially parallel to the support shaft 5. The second piezoelectric elements 7 drive the tip portion 3a of the corresponding driving member 3 relative to the base portion 3b and the base member 2 in the width w3 direction (the third direction) of the driving member 3. That is, in this embodiment, the direction (the second direction) in which the driving member 3 is interposed between the first piezoelectric elements 6 and the direction (the third direction) in which the second piezoelectric elements 7 drive the tip portion 3a of the driving member 3 are substantially parallel to each other.
The first piezoelectric elements 6, the second piezoelectric elements 7, the driving members 3, and the base member 2 constitute the support and drive section 1a supporting the rotor 4 and driving the rotor 4 relative to the driving members 3 and the base member 2.
As shown in
As shown in
The support faces 2f are tilted so that the distance between the opposed support faces 2f and 2f becomes smaller as the distance from the rotor 4 supported by the tip portions 3a of the driving members 3 shown in
As shown in
Accordingly, when the base portion 3b of the driving member 3 and the pair of first piezoelectric elements 6 and 6 are held in the holding portion 2a, the base portion 3b is supported by the support faces 2f from both ends in the width w4 direction of the holding portion 2a with the pair of first piezoelectric elements 6 and 6 in a state where the bottom surface 3d of the driving member 3 is separated from the bottom 2g of the holding portion 2a, as shown in
As shown in
The driving members 31 and 32 of the sets have a uniform height from the base member 2 to the contact faces S11 and S12 so as to bring all the contact faces S11 and S12 into contact with the rotor 4 in the initial state.
In the description below, when the driving members 31 and 32 of the different sets are not distinguished from each other, they are referred to as the driving members 3. The tip portions 31a and 32a, the base portions 31b and 32b, and the contact faces S11 and S12 are similarly referred to as the tip portions 3a, the base portions 3b, and the contact faces S1.
As shown in
As shown in
As shown in
Although not shown in
As shown in
At the second terminal T2, the power supply unit 10 generates a voltage with a phase difference of 180° from the voltage generated at the first terminal T1 and with a period of eight phases similar to the voltage generated at the first terminal T1. That is, the voltage generated at the first terminal and the voltage generated at the second terminal have a phase difference of four phases, which correspond to a half period, from each other.
At the third terminal T3, the power supply unit 10 maintains a voltage in Phase 1 at 0 V, generates a voltage of −3.0 V in Phase 2, and increases the voltage by 1.0 V in the phases of Phase 3 to Phase 8. In the subsequent phases, the voltage generation pattern of Phase 1 to Phase 8 is repeated. That is, the power supply unit 10 generates the voltage with a period of eight phases at the third terminal T3.
At the fourth terminal T4, the power supply unit 10 generates a voltage with a phase difference of 180° from the voltage generated at the third terminal T3 and with a period of eight phases similar to the voltage generated at the third terminal T3. That is, the voltage generated at the third terminal and the voltage generated at the fourth terminal have a phase difference of four phases, which correspond to a half period, from each other.
In this embodiment, the frequencies of the voltages supplied to the first piezoelectric elements 6 and the second piezoelectric elements 7 from the power supply unit 10 are substantially the same as the frequency of the resonant vibration of the support and drive section (structure) 1a including the first piezoelectric elements 6, the second piezoelectric elements 7, the driving members 3, and the base member 2.
The operation of the piezoelectric actuator 1 according to this embodiment will be described below with reference to
In each parts (a) of
(Phase 0)
As shown in
As shown in parts (a) and (b) of
(Phase 1)
As shown in
As shown in
As shown in
As shown in
That is, in Phase 1, the tip portions 31a of the driving members 31 of the first set are moved in the negative Y axis direction and are separated from the rotor 4, as shown in
(Phase 2)
As shown in
As shown in
As shown in
As shown in
That is, in Phase 2, by the movement of the tip portions 32a of the driving members 32 of the second set in the positive X2 axis direction, a frictional force acts between the top surfaces of the tip portions 32a and the bottom of the rotor 4 as shown in
(Phase 3)
As shown in
As shown in
As shown in
As shown in
That is, in Phase 3, the tip portions 31a of the driving members 31 of the first set are moved in the positive X1 axis direction along the rotational direction R of the rotor 4 and in the positive Y axis direction, and come close to the rotor 4, as shown in
(Phase 4)
As shown in
As shown in
As shown in
As shown in
That is, in Phase 4, the tip portions 31a of the driving members 31 of the first set are moved in the positive X1 axis direction along the rotational direction R of the rotor 4, come in contact with the rotor 4, and supports and drives the rotor 4 in the rotational direction R, as shown in
At this time, as shown in parts (a) and (b) of
(Phase 5)
As shown in
As shown in
As shown in
As shown in
That is, in Phase 5, the tip portions 31a of the driving members 31 of the first set maintains the contact with the rotor 4, are moved in the positive X1 axis direction while supporting the rotor 4, and drives the rotor 4 in the rotational direction R, as shown in
(Phase 6)
As shown in
As shown in
As shown in
As shown in
That is, in Phase 6, the tip portions 31a of the driving members 31 of the first set maintains the contact with the rotor 4, are moved in the positive X1 axis direction while supporting the rotor 4, and drives the rotor 4 in the rotational direction R, as shown in
(Phase 7)
As shown in
As shown in
As shown in
As shown in
That is, in Phase 7, the tip portions 31a of the driving members 31 of the first set maintains the contact with the rotor 4 and drives the rotor 4 in the rotational direction R while supporting the rotor 4, as shown in
(Phase 8)
As shown in
As shown in
As shown in
As shown in
That is, in Phase 8, the tip portions 31a of the driving members 31 of the first set are moved in the positive X1 axis direction along the rotational direction R of the rotor 4 and in the negative Y axis direction, and are separated from the rotor 4, as shown in
At this time, as shown in parts (a) and (b) of
(Phase 9)
As shown in
As shown in
As shown in
As shown in
That is, in Phase 9, the tip portions 31a of the driving members 31 of the first set are moved in the negative Y axis direction and are moved in the negative X1 axis direction which is opposite to the rotational direction R of the rotor 4 while maintaining the separation from the rotor 4, as shown in
(Phase 10)
As shown in
As shown in
As shown in
As shown in
That is, in Phase 10, the tip portions 31a of the driving members 31 of the first set are further moved in the negative X1 axis direction relative to the base portions 31b and the base member 2 while maintaining the separation from the rotor 4, as shown in
In Phase 11 and the phases subsequent thereto, the same operations as described in Phase 3 to Phase 10 are repeatedly performed and the rotor 4 thus continues to rotate. Accordingly, the rotor 4 is alternately (sequentially) subjected to the support in the Y axis direction and the driving in the rotational direction R by the tip portions 31a of the driving members 31 of the first set and the tip portions 32a of the driving members 32 of the second set and the rotor 4 thus continues to rotate about the support shaft 5.
In the piezoelectric actuator 1 according to this embodiment, the first piezoelectric elements 6 driving the driving members 3 in the direction (the first direction) parallel to the support shaft 5 and the second piezoelectric elements 7 driving the tip portions 3a of the driving members 3 in the width w3 direction (the second direction) of the driving members 3 along the rotational direction R of the rotor 4 are independently disposed. Accordingly, the vibrations in the directions can be picked up as independent vibrations.
Therefore, when the rotor 4 is made to rotate by the driving members 3 and the rotor 4 and the driving members 3 are relatively driven, the rotor 4 can be made to rotate stably. Compared with the case where the first piezoelectric elements 6 interposing the base portions 3b drive the base portions 3b in different directions, it is difficult to cause the loss and it is possible to improve the energy efficiency, thereby increasing the output power of the piezoelectric actuator 1.
The first piezoelectric elements 6 interpose base portion 3b of each driving member 3 in the width w3 direction and the first piezoelectric elements 6 drive the corresponding driving member 3 in the direction parallel to the support shaft 5 and different from the width w3 direction. The sizes and shapes of the pair of first piezoelectric elements 6 and 6 interposing the base portion 3b are substantially the same. Accordingly, it is possible to unify the rigidity of the driving members 3 in the width w3 direction. As a result, it is possible to suppress the vibration of the base portions 3b of the driving members 3 in the width w3 direction. By setting all the first piezoelectric elements 6 and the second piezoelectric elements 7 to the same shape and size, it is possible to facilitate the manufacturing thereof and thus to improve the productivity.
The base member 2 includes the holding portions 2a holding the driving members 3 so as to be driven in the direction parallel to the support shaft 5. Each holding portion 2a includes the support faces 2f supporting the base portion 3b of the corresponding driving member 3 in the width w3 direction of the driving member 3. Accordingly, it is possible to support the first piezoelectric elements 6 by the use of the support faces 2f and thus to support the base portion 3b of the corresponding driving member 3 in the width w3 direction with the first piezoelectric elements 6 interposed therebetween. As a result, it is possible to enhance the rigidity of the driving members 3 in the width w3 direction and thus to suppress the vibration of the base portions 3b of the driving members 3 in the width w3 direction.
Here, each first piezoelectric element 6 has an elastic modulus in the thickness direction (longitudinal elastic modulus) greater than an elastic modulus in the deformation direction (transverse elastic modulus). Each second piezoelectric element 7 has an elastic modulus in the thickness direction (longitudinal elastic modulus) greater than an elastic modulus in the deformation direction (transverse elastic modulus). Accordingly, it is possible to enhance the rigidity of the driving members 3 in the width w3 direction and to lower the rigidity of the base portions 3b in the driving direction. As a result, it is possible to prevent any movement of the base portions 3b in the width w3 direction, thereby suppressing the vibration. It is possible to facilitate the displacement of the base portions 3b in the driving direction.
Here, each driving member 3 in this embodiment includes the tilted faces S2 and S3 disposed in the corresponding tip portion 3a and has such a tapered shape that the sectional area of the tip portion 3a parallel to the contact face S1 becomes smaller as it goes closer to the rotor 4. Accordingly, when the contact face S1 is grinded or when the contact face S1 is worn way with the lapse of time, it is possible to suppress the decrease in volume of the driving member 3, compared with the case where the tilted faces S2 and 53 are not provided. As a result, it is possible to minimize the decrease in mass of the driving member 3 and thus to reduce the variation of the natural frequency of the support and drive section 1a to a negligible extent. Therefore, it is possible to continuously drive the support and drive section 1a in the resonant state and thus to maintain the high output power of the piezoelectric actuator 1 for a long time.
As shown in
Accordingly, when the base portion 3b of each driving member 3 and the first piezoelectric elements 6 and 6 interposing the base portion are inserted to the bottom 2g of the holding portion 2a from the rotor 4 side in the direction parallel to the support shaft 5, the base portion 3b and the first piezoelectric elements 6 are interposed and supported by the support faces 2f in the width w4 direction midway in the support faces 2f. As a result, it is possible to position the driving member 3 in the direction parallel to the support shaft 5. Since the support faces 2f do not regulate the driving of the driving member 3 toward the rotor 4, it is possible to maintain the driving member 3 drivable toward the rotor 4.
The side surfaces 3c of the base portion 3b of the driving member 3 facing the support faces 2f are tilted similarly to the support faces 2f and are substantially parallel to the support faces 2f. Accordingly, when the base portion 3b of each driving member 3 and the first piezoelectric elements 6 interposing the base portion 3b are inserted toward the bottom 2g of the corresponding holding portion 2a from the rotor 4 side in the direction parallel to the support shaft 5, it is possible to bring the first piezoelectric elements 6 into close contact with the support faces 2f of the holding portion 2a and to press the first piezoelectric elements 6 to the support faces 2f. As a result, it is possible to suppress the vibration of the base portions 3b of the driving members 3 in the width w3 direction.
Since the tilt angle α of each support face 2f about the direction parallel to the support shaft 5 is in the range of 2° to 6°, it is possible to set the positioning error of the driving members 3 in the direction parallel to the support shaft 5 to an allowable error range. Here, when the tilt angle α is smaller than 2°, the positioning precision is lowered and the manufacturing becomes difficult. When the tilt angle α is greater than 6°, the driving of the driving members 3 in the direction parallel to the support shaft 5 is adversely influenced. In this embodiment, it is possible to improve the positioning precision, the productivity, and the drivability by setting the tilt angle α to 4°.
At the neutral position where the driving member 3 is positioned by the support faces 2f of the corresponding holding portion 2a, the bottom surface 3d of the base portion 3b of the driving member 3 is separated from the bottom 2g of the holding portion 2a in the direction parallel to the support shaft 5, which is the driving direction of the base portion 3b of the driving member 3. Accordingly, it is possible to drive the driving member 3 from the neutral position toward the base member 2. In this embodiment, even when the driving member 3 is driven from the neutral position toward the base member 2, the bottom surface 3d of the base portion 3b is separated from the bottom 2g of the holding portion 2a. Accordingly, when the driving member 3 is driven toward the base member 2, it is possible to prevent the bottom surface 3d of the base portion 3b from colliding with the bottom 2g of the holding portion 2a and thus to prevent any adverse influence on the driving of the driving member 3 due to the collision.
Each driving member 3 includes the tip portion 3a supporting and driving the rotor 4 in the rotational direction R and the base portion 3b held by the corresponding holding portion 2a of the base member 2 in the state where it is interposed between the pair of first piezoelectric elements 6. The driving member 3 further includes the second piezoelectric elements 7 driving the tip portion 3a in the width w3 direction of the holding portion 2a and the driving member 3 along the rotational direction R of the rotor 4 between the tip portion 3a and the base portion 3b.
Accordingly, by driving the driving member 3 in the width w3 direction, a frictional force in the tangential direction of the rotational direction R acts between the bottom surface of the rotor 4 and the tip portion 3a of the driving member 3, thereby driving the rotor 4 in the rotational direction R. It is possible to independently control the first piezoelectric elements 6 and the second piezoelectric elements 7. As a result, it is possible to independently control the driving of the tip portion 3a of the driving member 3 in the direction parallel to the support shaft 5 and the driving in the rotational direction R of the rotor 4.
By simultaneously activating the first piezoelectric elements 6 and the second piezoelectric elements 7, it is possible to simultaneously perform the driving of the tip portion 3a of the driving member 3 in the direction parallel to the support shaft 5 and the driving in the direction along the rotational direction R of the rotor 4.
As a result, as shown in
Two sets of the first set and the second set are provided, each of which includes three driving members 3 and three by two pairs of first piezoelectric elements 6 and 6 interposing the base portion 3b thereof. Accordingly, it is possible to drive the sets at different times. It is possible to support the rotor 4 at three points by the use of the tip portions 31a and 32a of the driving members 31 and 32 of the sets. As a result, it is possible to more stably support the rotor 4, compared with the support at two points or the support at four or more points.
The driving members 31 and 32 of each set are uniformly arranged in the rotational direction R of the rotor 4 and the driving members 31 of the first set and the driving members 32 of the second set are alternately and sequentially arranged in the rotational direction R. Accordingly, it is possible to support the rotor 4 with a good balance by the use of the driving members 31 and 32 of the sets and to efficiently driving the rotor 4 in the rotational direction R.
The direction in which the tip portion 3a of each driving member 3 is driven is the same as the direction in which the base portion 3b of the driving member 3 is interposed by the first piezoelectric elements 6 and the support faces 2f of the corresponding holding portion 2a. Accordingly, when the tip portion 3a of the driving member 3 performs the transfer driving and the return driving, it is possible to support the base portion 3b of the driving member 3 from before and after the driving direction. As a result, it is possible to suppress the driving member 3 from departing from the direction parallel to the support shaft 5 and to prevent the driving of the rotor 4 from being adversely influenced.
By allowing the power supply unit 10 to supply the voltages having a phase difference to the driving members 31 and 32 of the first and second sets, it is possible to drive the rotor 4 by the use of the driving members 31 and 32 of the respective sets.
By setting the voltages supplied from the power supply unit 10 to the first piezoelectric elements 6 and the second piezoelectric elements 7 of the sets to 180°, it is possible to alternately and sequentially drive the rotor 4 by the use of the driving members 31 of the first set and the driving members 32 of the second set.
By allowing the power supply unit 10 to supply the voltages to the first piezoelectric elements 6 and the second piezoelectric elements 7 of the sets so as to sequentially repeat the contact of the tip portions 3a of the driving member 3 with the rotor 4, the transfer in the width w3 direction of the driving members 3, the separation from the rotor 4, and the return in the width w3 direction of the driving members 3, it is possible to continuously perform the rotational driving of the rotor 4.
As shown in Phases 3, 7, and 14 of
As shown in
The frequency of the voltages supplied to the first piezoelectric elements 6 and the second piezoelectric elements 7 from the power supply unit 10 is substantially the same as the frequency of the resonant vibration of the support and drive section 1a including the first piezoelectric elements 6, the second piezoelectric elements 7, the driving members 3, and the base member 2. Accordingly, it is possible to enhance the amplitude of the transfer driving and the return driving of the rotor 4 by the use of the tip portions 3a of the driving members 3. The frequency of the resonant vibration of the support and drive section 1a can be adjusted by properly selecting the materials of the base member 2, the piezoelectric elements, and the tip portions 3a and the base portions 3b of the driving members 3.
In this embodiment, as shown in
The tip portion 3a of each driving member 3 has such a tapered shape that the sectional area along the rotational direction R of the rotor 4 becomes smaller as it gets closer to the rotor 4. Accordingly, compared with the case where the tip portion 3a is formed in a rectangular parallelepiped shape, it is possible to reduce the contact area of the tip portion 3a with the rotor 4, thereby reducing the volume variation of the tip portion 3a due to the abrasion of the tip portion 3a. As a result, it is possible to reduce the variation in weight of the tip portion 3a due to the abrasion of the tip portion 3a, thereby reducing the variation in the resonance frequency of the driving member 3. By setting the shape of the tip portion 3a to a hexagonal prism, it is possible to enhance the rigidity of the tip portion 3a, compared with the other shapes.
The groove 2d is formed in the side surface 2c of the base member 2 which is substantially parallel to the support shaft 5 and which intersects the width w3 direction of the driving members 3 substantially perpendicularly thereto. That is, the groove 2d is disposed to substantially perpendicularly intersect the vibration in the direction substantially parallel to the support shaft 5 propagating through the base member 2. Accordingly, it is possible to absorb the vibration by the use of the groove 2d, thereby reducing the propagation of the vibration in the base member 2.
The first piezoelectric elements 6 are disposed between the rotor 4 and the groove 2d. Accordingly, it is possible to reduce the vibration propagating over the groove 2d from the opposite side of the base member 2 about the rotor 4.
The end of the base member 2 opposite to the holding portions 2a holding the driving members 3 is fixed to the attaching section 101a and the groove 2d is disposed at a position closer to the attaching section 101a than the driving members 3. Accordingly, even when the vibration of the attaching section 101a propagates to the base member 2, it is possible to reduce the vibration at the position relatively apart from the driving members 3, thereby preventing the adverse influence of the vibration of the attaching section 101a on the driving of the driving members 3.
The width w1 of the groove 2d in the direction parallel to the support shaft 5 is set to be greater than the amplitude of the vibration of the base member 2. Accordingly, it is possible prevent the portions of the base member 2 on both sides of the groove 2d from colliding with each other.
The width w1 of the grooved 2d in the direction parallel to the support shaft 5 is set to be greater than the amplitude of the resonant vibration of the support and drive section 1a including the base member 2, the driving members 3, the first piezoelectric elements 6, and the second piezoelectric elements 7. Accordingly, even when the support and drive section 1a vibrates in the resonant state, it is possible to prevent the portions of the base member 2 on both sides of the groove 2d from colliding with each other.
By setting the depth d1 of the groove 2d to the range of 40% to 80% of the radius of the base member 2, it is possible to satisfactorily suppress the propagation of the vibration while satisfactorily guaranteeing the strength of the base member 2.
Since the clearance 2e is formed between the base member 2 and the support shaft 5, it is possible to reduce any vibration propagating from the base member 2 to the support shaft 5. It is also possible to reduce any vibration propagating from the support shaft 5 to the base member 2. Accordingly, it is possible to prevent any adverse influence on the driving of the driving members 3 and the rotor 4.
An interchangeable lens will be described below as an example of a lens barrel including the piezoelectric actuator 1 according to this embodiment. The interchangeable lens according to this embodiment constitutes a camera system along with a camera body not shown and is detachably attached to the camera body. The interchangeable lens can be switched between an AF mode where a focusing operation is carried out under a known AF (Auto Focus) control and an MF (Manual Focus) mode where the focusing operation is carried out in response to a user's manual input.
As shown in
The driving unit 104 is a unit that rotates the focusing barrel 103 about an optical axis in response to a signal from an AF controller not shown at the time of performing the AF control.
The driving unit 104 includes a support section 105, a piezoelectric actuator 1, a focus barrel gear 103a, and a cover 108.
The support section 105 is a section that supports the piezoelectric actuator 1 relative to the fixed barrel 101. The support section 105 includes an attaching section 101a and a bearing section 101b.
The attaching section 101a supports one end of the piezoelectric actuator 1. The attaching section 101a is a section formed in a needle shape to protrude from a part of the outer circumferential surface of the fixed barrel 101 in the outer diameter direction and forms a body along with the fixed barrel 101.
Similarly to the attaching section 101a, the bearing section 101b protrudes from a part of the outer circumferential surface of the fixed barrel 101 in the outer diameter direction, forms a body along with the fixed barrel 101, and serves to support the other end of a rotation shaft 106 of which one end is fixed to the rotor 4 of the piezoelectric actuator 1.
In the piezoelectric actuator 1, an end of the base member 2 is fixed to the attaching section 101a.
An output gear 107 is disposed at one end of the rotation shaft 106 and the other end thereof is fixed to the rotor 4. The rotation shaft 106 is independently disposed on the same axis as the support shaft 5 (see
The cover 108 serves to protect the piezoelectric actuator 1 and is fixed to the fixed barrel 101 by the use of screws not shown.
The interchangeable lens 100 is detachably attached to the camera body with the external barrel 102 interposed therebetween.
In the AF mode of the interchangeable lens 100, the power supply unit 10 of the piezoelectric actuator 1 operates, for example, in response to a signal from the AF controller disposed in the camera body and the rotor 4 of the piezoelectric actuator 1 rotates. The rotation shaft 106 rotates with the rotation of the rotor 4 and the focusing barrel 103 rotates about the optical axis with the rotation thereof. The focusing barrel 103 causes the lens groups used in the focusing operation to go forward and backward in the optical axis direction via the focusing cam mechanism not shown with the rotation thereof. In this way, the interchangeable lens 100 performs the AF operation.
On the other hand, in the MF mode, the focusing barrel 103 is manually made to rotate about the optical axis by the user. Similarly to the AF mode, the focusing barrel 103 causes the lens group used in the focusing operation to go forward and backward with the rotation thereof. In this way, the interchangeable lens 100 performs the MF operation.
As described above, in the interchangeable lens 100 according to this embodiment, since the piezoelectric actuator 1 which can pick up the vibrations in two different directions as independent vibrations and enhance the output power is provided, it is possible to reduce the power consumption in the AF mode.
It is possible to transmit the power of the piezoelectric actuator 1 directly to the focusing barrel 103 without using an intermediate gear or a final gear. Accordingly, it is possible to reduce any energy loss and to save energy. It is also possible to reduce the number of components.
This embodiment can be modified in various forms. For example, the base member can be divided into plural parts as long as they are disposed to surround the support shaft, or can not completely surround the support shaft. For example, the base member can be half-sided on the circumference surrounding the support shaft or can be disposed to interpose the support shaft from both sides.
In the above-mentioned embodiment, it has been described that a pair of first piezoelectric elements driving each driving member in the direction parallel to the support shaft is disposed to interpose the driving member. Instead, the first piezoelectric elements can be disposed on only one side surface of the driving member. By using a piezoelectric element which is displaced in the thickness direction as the first piezoelectric element, the first piezoelectric elements can be disposed between the bottoms of the holding portions of the base member and the bottom surfaces of the base portions of the driving members. In this case, the base portions are directly supported by the support faces of the holding portions formed in the base member from both ends in the width direction of the holding portions along the rotational direction of the rotor without using the piezoelectric elements. The support faces can serve as a guide portion holding the base portion to be slidable in the direction parallel to the support shaft.
Although it has been described in the above-mentioned embodiment that two sets of the driving members including the first piezoelectric elements and the second piezoelectric elements are provided, the number of sets of the driving members can be three or more. The number of driving members included in each set of driving members can be 1, or 2, 4, or more. For example, in the above-mentioned embodiment, three sets of driving members, each of which includes two driving members disposed on the diagonal of the base member, can be configured. In this case, the phase difference between the voltages of the voltages can be set to, for example, 120 degrees. Accordingly, it is possible to normally support and rotate the rotor by the use of two sets of driving members. The phase difference between the voltages of the sets of driving members can be set to a value obtained by dividing 360 degrees by the number of sets (that is, 180 degrees in case of two sets and 120 degrees in case of three sets).
Although it has been described in the above-mentioned embodiment that the direction (the second direction) in which the first piezoelectric elements interpose the base portion of the corresponding driving member is the same as the direction (the third direction) in which the second piezoelectric elements drive the tip portion of the corresponding driving member, the directions can be set to be different from each other. For example, by setting the third direction to a direction intersecting the width w3 direction of the driving member and being parallel to the rotational direction of the rotor, the rotor can be made to easily rotate.
The support faces of the base member can not be tilted in the direction (the first direction) parallel to the support shaft. For example, as shown in
The clearance between the base member and the support shaft can be formed up to the edge of the groove close to the holding portion, from the viewpoint of guaranteeing the strength of the base member.
The voltages supplied to the first piezoelectric elements and the second piezoelectric elements from the terminals of the power supply unit can be set to a sinusoidal voltage waveform or a voltage waveform similar to the sinusoidal waveform.
First, similarly to the above-mentioned embodiment, an example where the sets of driving members include two sets of a first set and a second set, the phase difference between the sinusoidal voltage waveforms generated at the first terminal and the second terminal of the power supply unit is 180°, and the phase difference between the sinusoidal voltage waveforms generated at the third terminal and the fourth terminal is 180° will be described below with reference to
Similarly to
When the phase difference between the sinusoidal voltage waveforms generated at the first terminal and the second terminal of the power supply unit is 180°, the tip portions of the driving members of the first set and the second set driven in the Y axis direction drawn a sinusoidal track having a phase difference of 180°, as shown in parts (a) and (b) of
Here, the track of the driving members of the first set shown in
Similarly, when the phase difference between the sinusoidal voltage waveforms generated at the second terminal and the third terminal of the power supply unit is 180°, the tip portions of the driving members of the first set and the second set driving the rotor in the X1 axis direction and the X2 axis direction draw a sinusoidal track (see
Here, as indicated by a bold line in
Accordingly, similarly to the above-mentioned embodiment, the rotor is driven in the rotational direction alternately by the driving members of the first set and the driving members of the second set (see
An example where the sets of driving members include three sets of first to third sets and sinusoidal voltage waveforms or voltage waveforms similar to the sinusoidal waveform having a phase difference of 120° are generated at the terminals of the power supply unit will be described below with reference to
When the voltage waveforms supplied to the first piezoelectric elements of the sets from the power supply unit have a phase difference of 120°, the tip portions of the driving members of the sets driven in the Y axis direction draw sinusoidal tracks having a phase difference of 120°, as shown in
Here, the tracks of the driving members of the sets shown in
Similarly, when the voltage waveforms supplied to the second piezoelectric elements of the sets from the power supply unit have the phase differences of 120°, the tip portions of the driving members of the sets driven in the X1 to X3 axis directions draw sinusoidal tracks, as shown in
Here, as indicated by the bold line in
Accordingly, similarly to the above-mentioned embodiment, the rotor is sequentially driven in the rotational direction by the driving members of the sets (see
In the above-mentioned embodiment, it has been described that the base member 2 is formed in a hollow cylindrical shape out of a metal material such as stainless steel. In another embodiment, all or a part of the base member 2 can be formed of an elastic body having elasticity. That is, at least a part of the base member 2 can have elasticity. In this embodiment, substantially all or at least the convex portions 2h and 2i (see
In this embodiment, the frequencies of the voltages supplied to the first piezoelectric elements 6 and the second piezoelectric elements 7 from the power supply unit 10 can be set to be substantially the same as the resonance frequency of the support and drive section 1a including the first piezoelectric elements 6, the second piezoelectric elements 7, the driving members 3, and the base member 2. The waveforms of the voltages supplied to the first piezoelectric elements 6 and the second piezoelectric elements 7 from the terminals of the power supply unit 10 can be set to a sinusoidal waveform. Alternatively, when the frequencies of the voltages to be supplied are substantially the same as the resonant frequency of the support and drive section 1a, other waveforms such as a rectangular waveform can be used.
The operation in the case where at least a part of the base member 2 is formed of an elastic body and the waveforms of the voltages to be supplied are sinusoidal will be described below with reference
In
In
As shown in
In
In
In
In
When the phase difference between the sinusoidal voltage waveforms generated at the first terminal and the second terminal of the power supply unit 10 is 180°, the tip portions 3a of the driving members 3 of the first set and the second set driven in the Y axis direction draw sinusoidal tracks having a phase difference of 180°, as shown in parts (a) and (b) of
At point “A” in
At point “B” in
At point “C” in
At point “D” in
Although the elastic deformation of the first convex portions 2h due to the driving of the first piezoelectric elements 6 and the second piezoelectric elements 7 and the displacement of the support faces 2f based thereon have been described, the second convex portions 2i are similarly deformed with a phase difference of 180° from the first convex portions 2h.
In this embodiment, the support faces 2f are deformed with the same period as the displacement of the driving members due to the elastic deformation of the first convex portions 2h and the second convex portions 2i. The displacement of the tip portions 3a of the driving members 3 is equal to the displacement obtained by adding the displacement based on the thickness-shear deformation of the first piezoelectric elements 6 and the second piezoelectric elements 7 to the displacement of the support faces 2f.
In this embodiment, by using the displacement based on the elastic deformation of the base member 2 in addition to the displacement based on the thickness-shear deformation of the first piezoelectric elements 6 and the second piezoelectric elements 7, the driving members are driven with higher amplitude. Accordingly, it is possible to enhance the output power of the piezoelectric actuator and to lower the voltage necessary for the driving. By causing the support and drive section 1a including the base member 2 to resonate, it is possible to maximally exhibit the advantageous effects using the in-plane deformation and the out-of-plane deformation of the convex portions formed in the base member.
Description of Reference Numerals and Signs
1: PIEZOELECTRIC ACTUATOR
1a: SUPPORT AND DRIVE SECTION (STRUCTURE)
2: BASE MEMBER (FOURTH MEMBER)
3: DRIVING MEMBER
3a: TIP PORTION (SECOND MEMBER)
3b: BASE PORTION (FIRST MEMBER)
4: ROTOR (THIRD MEMBER)
5: SUPPORT SHAFT (ROTATION AXIS)
6: FIRST PIEZOELECTRIC ELEMENT
7: SECOND PIEZOELECTRIC ELEMENT
10: POWER SUPPLY UNIT
31: DRIVING MEMBER (FIRST SET)
31a: TIP PORTION (FIRST SET)
31b: BASE PORTION (FIRST SET)
32: DRIVING MEMBER (SECOND SET)
32a: TIP PORTION (SECOND SET)
32b: BASE PORTION (SECOND SET)
61: FIRST PIEZOELECTRIC ELEMENT (FIRST SET)
62: FIRST PIEZOELECTRIC ELEMENT (SECOND SET)
71: SECOND PIEZOELECTRIC ELEMENT (FIRST SET)
72: SECOND PIEZOELECTRIC ELEMENT (SECOND SET)
100: INTERCHANGEABLE LENS (LENS BARREL)
R: ROTATIONAL DIRECTION
Claims
1. A piezoelectric actuator comprising:
- a plurality of first piezoelectric elements;
- a first member that is interposed between the plurality of first piezoelectric elements and that is driven in a first direction by the plurality of first piezoelectric elements;
- a second piezoelectric element that is disposed in the first member;
- a second member that is disposed in contact with the second piezoelectric element and that is driven in a second direction intersecting the first direction by the second piezoelectric element; and
- a third member that comes in contact with the second member and that is moved relative to the first member by driving the second member.
2. The piezoelectric actuator according to claim 1, further comprising a fourth member that has two faces coming in contact with respective faces of the plurality of first piezoelectric elements and that supports the first member with the plurality of first piezoelectric elements interposed therebetween.
3. The piezoelectric actuator according to claim 2, wherein the fourth member includes an elastic body.
4. The piezoelectric actuator according to claim 1, wherein a plurality of sets, each including the plurality of first piezoelectric elements, the second piezoelectric element, the first member, and the second member are provided.
5. The piezoelectric actuator according to claim 4, further comprising a power supply unit that supplies voltages to the first piezoelectric elements and the second piezoelectric elements,
- wherein the power supply unit supplies the voltages having a phase difference to the sets.
6. The piezoelectric actuator according to claim 5, wherein the power supply unit supplies the voltages so that the second members of the sets repeat a contact with the third member, a transfer in the second direction, a separation from the third member, and a return in the second direction.
7. The piezoelectric actuator according to claim 5, wherein each of the sets includes a fourth member that has two faces coming in contact with respective faces of the plurality of first piezoelectric elements and that supports the first member with the plurality of first piezoelectric elements interposed therebetween, and wherein a frequency of the voltages is the same as a resonance frequency of a structure including the fourth member, the first member, the second member, the first piezoelectric elements, and the second piezoelectric elements.
8. The piezoelectric actuator according to claim 5, wherein the phase difference is 360° /N (where N represents the number of the sets).
9. The piezoelectric actuator according to claim 4, wherein each set includes three pairs of the first piezoelectric elements, three of the second piezoelectric elements, three of the first members, and three of the second members.
10. The piezoelectric actuator according to claim 1, wherein the third member is disposed to be rotatable about a rotation axis parallel to the first direction, and
- wherein the second direction is a direction parallel to a rotational direction of the third member.
11. The piezoelectric actuator according to claim 10, wherein a plurality of sets each including the plurality of first piezoelectric elements, the second piezoelectric element, the first member, and the second member are provided,
- wherein the first members of each set are arranged uniformly in the rotational direction, and
- wherein the first members of the different sets are alternately arranged in the rotational direction.
12. The piezoelectric actuator according to claim 1, wherein the second member is formed in a tapered shape such that a sectional area along the second direction decreases as the sectional area approaches the third member.
13. The piezoelectric actuator according to claim 1, wherein shapes and sizes of the plurality of first piezoelectric elements are the same.
14. The piezoelectric actuator according to claim 1, wherein a longitudinal elastic modulus of the plurality of first piezoelectric elements is greater than a transverse elastic modulus of the plurality of first piezoelectric elements, and
- wherein a longitudinal elastic modulus of the second piezoelectric element is greater than a transverse elastic modulus of the second piezoelectric element.
15. A piezoelectric actuator comprising:
- a first piezoelectric element that is disposed in a base member;
- a second piezoelectric element that is disposed at a position different from a position of the first piezoelectric element in the base member;
- a first member that is driven by the first piezoelectric element;
- a second member that is driven by the second piezoelectric element;
- a third member that is disposed so as to come in contact with the first member and the second member and that is moved relative to the first member and the second member by driving the first member and the second member,
- wherein the first member and the second member include a tilted face tilted about a contact face coming in contact with the third member so that a sectional area along a direction parallel to the contact face decreases as the sectional area approaches the third member.
16. The piezoelectric actuator according to claim 15, wherein the first member is supported by the base member with the first piezoelectric element interposed therebetween and the second member is supported by the base member with the second piezoelectric element interposed therebetween.
17. The piezoelectric actuator according to claim 15, wherein the tilted face is disposed in a direction intersecting a relative movement direction of the third member.
18. A lens barrel comprising the piezoelectric actuator according to claim 1.
19. A lens barrel comprising the piezoelectric actuator according to claim 15.
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Type: Grant
Filed: Mar 31, 2010
Date of Patent: Feb 18, 2014
Patent Publication Number: 20110317292
Assignee: Nikon Corporation (Tokyo)
Inventors: Kunihiro Kuwano (Kawasaki), Hiromoto Kanamitsu (Funabashi)
Primary Examiner: Mohammed Hasan
Application Number: 13/201,058
International Classification: G02B 7/02 (20060101);
