JP5486255B2 - Ultrasonic motor - Google Patents

Description

  The present invention relates to an ultrasonic motor that vibrates a rectangular laminated piezoelectric vibrator in a multiple vibration mode.

  2. Description of the Related Art Conventionally, a technique is known in which an electrode for a sensor is provided on an ultrasonic motor or actuator using a multilayer piezoelectric element, and the operation of the multilayer piezoelectric element is controlled by a signal extracted therefrom (Patent Document 1). 2, 3).

  The actuator described in Patent Document 1 includes an actuator portion and a sensor portion that are integrally laminated with an insulating material layer interposed therebetween. Piezoelectric ceramics that have been subjected to polarization treatment in the thickness direction as a piezoelectric material layer are used for the sensor portion. It has been. Then, when the actuator part is displaced in the thickness direction, the electric field of the sensor part is displaced according to the displacement amount, and the displacement amount of this electric field is sampled and held as a voltage signal and fed back to the control unit. Sensing sensitivity is improved by detecting non-linear stress fluctuations.

  The laminated piezoelectric element described in Patent Document 2 is a laminated piezoelectric element in which a plurality of piezoelectric element plates each having an electrode formed on one side of a piezoelectric ceramic are laminated in the thickness direction, and a part of the piezoelectric ceramic layer is used as a sensor phase. An electrode for extracting a sensor phase signal is provided on the piezoelectric element plate. A sensor electrode having one wavelength width is provided in non-contact with the conduction hole, while the uppermost piezoelectric element plate is formed with an electrode that conducts with the sensor electrode by a through hole or the like. The drive control of the drive device is going to be performed with high accuracy.

  In the vibration wave motor described in Patent Document 3, the surface electrode layer is disposed in the first layer and the piezoelectric layer is disposed in the second layer in the laminated piezoelectric element. In the layers from the third layer to the Nth layer, different piezoelectric layers are alternately arranged, and an internal electrode divided into four is formed on the surface of the piezoelectric layer. On the surface of the piezoelectric layer, four internal electrodes are formed, and in each piezoelectric layer, only the internal electrode which is the sensor phase and the internal electrode arranged in the same phase are exposed to the outside of the piezoelectric layer. Thus, the traveling wave unevenness of a small vibration wave motor is reduced.

Japanese Patent No. 3059038 Japanese Patent No. 3729781 JP 2007-13039 A

  As described above, there is a piezoelectric actuator provided with an electrode for a sensor, but in an ultrasonic motor driven in multiple modes by longitudinal vibration and bending vibration, a configuration for sensing by an electrode has not been developed, There is no efficient detection and control of the drive.

  The present invention has been made in view of such circumstances, and in an ultrasonic motor that is driven in multiple modes by longitudinal vibration and bending vibration, an ultrasonic motor that enables efficient detection and control of the drive with a compact configuration. An object is to provide a sonic motor.

  (1) In order to achieve the above object, an ultrasonic motor of the present invention is a rectangular ultrasonic motor used for vibration in a multiple vibration mode, and is formed by stacking piezoelectric layers and the stacked piezoelectric layers. Drive electrodes and ground electrodes that are alternately layered, and a sensing electrode that is layered in a plane where the drive electrode is layered on one main surface side of the stacked piezoelectric layers that are used for drive detection. Provided that the length in the stretching direction in the primary longitudinal vibration mode is L and the length in the shear direction in the secondary bending vibration mode is w, the resonance frequency and the secondary bending in the primary longitudinal vibration mode It is characterized in that it is formed based on w / L that substantially matches the resonance frequency of the vibration mode.

  Thus, the inactive layer volume ratio that does not contribute to the operation can be reduced by providing the drive electrode and the sensing electrode in the same plane. An ultrasonic motor that utilizes 31 lateral effect vibration by vibrating a rectangular laminated piezoelectric vibrator in the L1F2 multimode can be configured compactly. As a result, since the ratio of the piezoelectric active layer is larger than when the sensing layer is separate from the drive layer, it is possible to provide an efficient high performance ultrasonic motor.

  (2) Further, the ultrasonic motor of the present invention is characterized in that two sensing electrodes are provided at symmetrical positions. As a result, the structure is symmetrical to eliminate the bias of operation.

  (3) Further, in the ultrasonic motor of the present invention, the sensing electrode has a quarter electrode area, and the drive electrode in the plane in which the sensing electrode is installed has a quarter electrode area. It is characterized by having. As a result, the driving state can be detected while driving the ultrasonic motor, without being disturbed by the sensing layer.

  (4) Further, the ultrasonic motor of the present invention is characterized in that the inner layered drive electrode, ground electrode and sensing electrode are connected to input, ground and detection terminals by external electrodes, respectively. As described above, the volume ratio of the inactive layer that does not contribute to the operation can be reduced by increasing the volume ratio of the active layer by using the external connection without using the through hole.

  (5) In the ultrasonic motor of the present invention, the piezoelectric layer is polarized in two polarization directions in the same layer, and a one-phase driving voltage is applied to the inner layer driving electrode. It is characterized by that. As described above, even in the case of one-phase driving, the operation can be sensed by obtaining a constant voltage waveform in the operation direction voltage using the sensing electrode. Therefore, the sensor circuit can be simplified if only a certain voltage waveform can be sensed without sensing the phase difference.

  ADVANTAGE OF THE INVENTION According to this invention, the efficient detection and control of a drive are enabled by the compact structure in the ultrasonic motor driven by multiple modes by a longitudinal vibration and a bending vibration.

It is a front view of the ultrasonic motor concerning the present invention. It is a figure which shows the mode of the primary longitudinal vibration of the ultrasonic motor which concerns on this invention. It is a figure which shows the mode of the secondary bending vibration of the ultrasonic motor which concerns on this invention. It is a figure which shows a mode that the ultrasonic motor which concerns on this invention drives a to-be-driven body rightward in a figure. It is a figure which shows a frequency spectrum when a rectangular-shaped piezoelectric vibrator is vibrated in a plurality of types of vibration modes. It is a figure which shows an example of a structure of the sheet | seat lamination at the time of preparation of a piezoelectric vibrator. 1 is a perspective view of a piezoelectric vibrator according to the present invention. It is a top view which shows the electrode pattern on a drive layer. It is a top view which shows the pattern of a ground electrode. It is a top view which shows the electrode pattern on a sensing layer. It is a top view which shows the electrode pattern on a sensing layer. It is a figure which shows the wiring with respect to the electrode on the drive layer of the ultrasonic motor which concerns on 1st Embodiment. It is a figure which shows the wiring with respect to the electrode on the sensing layer of the ultrasonic motor which concerns on 1st Embodiment. It is a graph which shows the input voltage with respect to time in 1st Embodiment. It is a graph which shows the sensing voltage with respect to time in 1st Embodiment. It is a graph which shows the sensing voltage with respect to time in 1st Embodiment. It is a figure which shows schematic structure of the ultrasonic motor which concerns on 2nd Embodiment. It is a graph which shows the input voltage with respect to time in 2nd implementation. It is a graph which shows the sensing voltage with respect to form time in 2nd Embodiment.

  Next, embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same components in the respective drawings, and duplicate descriptions are omitted.

[First Embodiment]
FIG. 1 is a front view of the ultrasonic motor 10. As shown in FIG. 1, the ultrasonic motor 10 includes a piezoelectric vibrator 1 and a chip 1a, and can be driven by vibrating the rectangular laminated piezoelectric vibrator 1 in a multiple vibration mode.

  FIG. 2 is a diagram illustrating a state of the primary longitudinal vibration of the ultrasonic motor 10. The primary longitudinal vibration is generated by repeatedly expanding and contracting in the longitudinal direction of the piezoelectric vibrator 1 as indicated by arrows A and B in FIG. FIG. 3 is a diagram showing a state of secondary bending vibration of the ultrasonic motor 10. As shown by an arrow C in FIG. 3, the secondary bending vibration is generated by repeatedly bending in the thickness direction of the piezoelectric vibrator 1 by shearing forces having different directions. By synthesizing (degenerate) these primary longitudinal vibrations and secondary bending vibrations, the chip provided in the piezoelectric vibrator 1 performs an elliptical motion to generate a driving force.

  FIG. 4 is a diagram showing stepwise how the piezoelectric vibrator 1 drives the driven body 2 in the right direction in the drawing. In FIG. 4, the piezoelectric vibrator 1 includes a chip 1a. By synthesizing the primary longitudinal vibration and the secondary bending vibration of the piezoelectric vibrator 1, the piezoelectric vibrator 1 repeats expansion and contraction and bending, and the driven body is moved by the distance l in one cycle. The piezoelectric vibrator 1 generates a driving force based on such a principle.

  FIG. 5 is a diagram illustrating a frequency spectrum when the rectangular piezoelectric vibrator 1 is vibrated in a plurality of types of vibration modes. In FIG. 5, L = 20 mm is fixed, and only w is changed. FIG. 5 shows the relationship between w / L and the resonance frequency of the primary longitudinal vibration mode (L1) of the piezoelectric vibrator, w / L and the secondary bending vibration mode (F2), with w / L as a variable. The relationship with the resonance frequency can be seen.

  When w / L is small, the resonance frequency of the primary longitudinal vibration mode is higher than the resonance frequency of the secondary bending vibration mode. When w / L is 0.27, the resonance frequency of the primary longitudinal vibration mode substantially coincides with the resonance frequency of the secondary bending vibration mode. When w / L exceeds 0.27, the resonance frequency of the secondary bending vibration mode becomes higher than the resonance frequency of the primary longitudinal vibration mode. Note that the fact that the resonance frequencies substantially match means that both vibration modes are combined (degenerate) and elliptic vibrations are generated, and there is a certain range of numerical values for the matching w / L.

  When w / L is further increased, the resonance frequency of the primary longitudinal vibration mode becomes higher than the resonance frequency of the secondary bending vibration mode. That is, the subtraction value obtained by subtracting the value of the resonance frequency of the secondary bending vibration mode from the value of the resonance frequency of the primary longitudinal vibration mode for the same value of w / L corresponds to the increase of w / L. Change from a negative number to a positive number. That is, also at this point, the resonance frequency of the primary longitudinal vibration mode substantially matches the resonance frequency of the secondary bending vibration mode. It is preferable to configure the piezoelectric vibrator 1 with a dimension in which the value of w / L at that time is 0.55 or more and 0.65 or less. The value of w / L is particularly preferably 0.63.

  When w / L is 0.63, the piezoelectric vibrator 1 is so-called thicker and has a smaller length in the longitudinal direction than when the side ratio w / L is near 0.27. As a result, downsizing can be achieved. Moreover, since it becomes thick, it becomes difficult to produce the damage by fatigue and excessive input, and it becomes possible to improve durability.

  FIG. 6 is a diagram illustrating an example of a configuration of sheet lamination when the piezoelectric vibrator 1 is manufactured. In the figure, the sheet number indicates the number of sheets to be laminated, the sheet thickness indicates the thickness of each sheet, and the type of inner layer printing indicates the pattern of inner layer printing. The print patterns J1, GND, S1, and S2 correspond to electrode patterns that will be described later. In the example shown in FIG. 6, the third to sixth sheets, the 11th to 14th sheets, the 25th to 28th sheets, and the 33rd to 36th sheets of the piezoelectric vibrator are sheets serving as a driving layer, and the third sheet and the 11th sheet. Driving electrodes are printed on the 29th and 37th sheets. The drive layer is a piezoelectric layer that causes displacement when a voltage is applied.

  A ground electrode is printed on the seventh, fifteenth, twenty-fifth, and thirty-third sheets. Further, the 15th to 18th sheets and the 21st to 24th sheets are sheets that become sensing layers, and sensing electrodes and drive electrodes are printed in the same plane on the layers. The piezoelectric vibrator 1 is obtained by firing the formed body formed by laminating the sheets in this way. The sensing layer is a piezoelectric layer for detecting driving. Note that the above laminated structure is an example, and the order is not necessarily in this order, but the electrode patterns are preferably laminated so that the positions of the electrode patterns are centrosymmetric.

  FIG. 7 is a perspective view of the piezoelectric vibrator 1. The piezoelectric vibrator 1 is made of rectangular laminated piezoelectric ceramics, and the polarization direction of each layer coincides with either positive or negative in the z-axis direction of the coordinate axis shown in FIG. The expansion / contraction direction when the piezoelectric vibrator 1 vibrates in the primary longitudinal vibration mode is parallel to the x axis, and the length of the piezoelectric vibrator 1 in the x axis direction is L. Further, the shearing direction when the piezoelectric vibrator 1 vibrates in the second bending vibration mode is parallel to the y-axis, and the length of the piezoelectric vibrator 1 in the y-axis direction is w.

  The piezoelectric vibrator 1 has a ground electrode and a drive electrode that are alternately provided on the surface or between layers of the stacked piezoelectric layers. The piezoelectric vibrator 1 includes a sensing electrode that is provided in the same plane as the drive electrode and detects the operation of the piezoelectric vibrator 1 as a signal. That is, the sensing electrode is layered on the one main surface side of the drive layer in a plane on which the drive electrode is layered.

  FIG. 8A is a plan view showing an electrode pattern J1 on the drive layer. The drive electrodes 4a and 4b are each equally divided into approximately an area of a quarter of the main surface. And it has the extraction part exposed to the side surface of the piezoelectric vibrator 1, respectively. A predetermined alternating voltage is applied to each of the drive electrodes 4a and 4b having a diagonal relationship in the electrode pattern, and a voltage having a phase different by π / 2 from the voltage applied to the drive electrode 4a is applied to the drive electrode 4b.

  FIG. 8B is a plan view showing a ground electrode pattern GND. When an electric field is generated between the ground electrode 4c and the drive electrodes 4a, 4b, 4d, and 4f, the piezoelectric layer 1b therebetween is displaced. Further, when the piezoelectric layer 1b between the ground electrode 4c and the sensing electrodes 4e and 4g is displaced, a voltage is generated in the sensing electrodes 4e and 4g, and the driving of the piezoelectric vibrator 1 can be detected.

  8C and 8D are plan views showing electrode patterns S1 and S2 on the sensing layer, respectively. The sensing layer is used for driving detection among the stacked piezoelectric layers. The sensing electrodes 4e and 4g are formed in one rectangular shape when the entire main surface is divided into four, and have a quarter electrode area. The drive electrodes 4d and 4f are formed in three rectangular shapes when the entire main surface is divided into four and have a three-quarter electrode area. As a result, the driving state can be detected while driving the ultrasonic motor, without being disturbed by the sensing layer.

  Thus, the drive electrodes 4d and 4f are provided on the same plane as the sensing electrodes 4e and 4g. Thereby, the volume ratio of the inactive layer that does not contribute to the operation can be reduced, and the external extraction electrode can be configured in a compact manner. An ultrasonic motor that utilizes the 31 lateral effect vibration by vibrating the rectangular laminated piezoelectric vibrator 1 in the L1F2 multimode can be configured in a compact manner. As a result, since the ratio of the piezoelectric active layer is larger than when the sensing layer is separate from the driving layer, the ultrasonic motor 10 can be provided with a sensing layer and have high performance.

  The drive electrodes 4a, 4b, 4d, and 4f are connected to input terminals by external electrodes. The ground electrode 4c is connected to the ground terminal by an external electrode. Each sensing electrode 4e, 4g is also connected to the detection part 6 mentioned later via the detection terminal by the external electrode. In this way, by making external connection without using a through hole, the volume ratio of the active layer can be increased, and the volume ratio of the inactive layer that does not contribute to the operation can be decreased.

  The same voltage as that of the drive electrode 4b is applied to the drive electrodes 4d and 4f. The two sensing electrodes 4e and 4g are provided at symmetrical positions in the thickness direction and the longitudinal direction of the piezoelectric vibrator 1, respectively. It is preferable that they are provided at symmetrical positions. As a result, the structure is symmetrical to eliminate the bias of operation. The drive electrodes 4a, 4b, 4d, and 4f are preferably provided symmetrically with respect to the center.

  FIG. 9 is a diagram showing wiring for electrodes on the drive layer of the ultrasonic motor 10. In FIG. 9, the electrode surface on the drive layer of the piezoelectric vibrator 1 is schematically cut out. On the drive layer, a pair of drive electrodes 4a and a set of drive electrodes 4b that are diagonally opposed to each other are provided so that one main surface of the rectangular piezoelectric layer 1b is divided into four. A ground electrode 4c is provided on the other main surface of the drive layer and is grounded. The drive electrodes 4a and 4b are individually provided in an insulated state, and then the electrodes 4a and 4b positioned diagonally to each other are electrically connected to each other.

The drive circuit of the ultrasonic motor 10 is composed of two AC voltage sources 5a and 5b. The AC voltage source 5a applies a voltage of V ₀ sin ωt to the drive electrode 4a, and the AC voltage source 5b applies a voltage of V ₀ cos ωt to the drive electrode 4b. As described above, when the voltages V ₀ sin ωt and V ₀ cos ωt having a phase shift of π / 2 with respect to the drive electrodes 4a and 4b of the piezoelectric vibrator 1 are applied, the piezoelectric vibrator 1 is applied with FIGS. As shown in FIG. 2, vibrations in the primary longitudinal vibration mode that expands and contracts in the longitudinal direction and vibrations in the secondary bending vibration mode that flexes in the shear direction are generated. When the resonance frequency of the primary longitudinal vibration mode is equal to the resonance frequency of the secondary bending vibration mode, both vibration modes are combined (degenerate), and the chip of the piezoelectric vibrator 1 (not shown in FIG. 9). No.) generates elliptical vibration.

Although FIG. 9 shows the configuration of the two-phase signal input, the AC signal V ₀ sinωt is applied to a pair of diagonally opposed drive electrodes 4a, and the other set of drive electrodes 4b is opened. By doing so, it can be operated in one phase.

  FIG. 10 is a diagram illustrating wiring for electrodes on the sensing layer of the ultrasonic motor 10. As shown in FIG. 10, the same voltage as that of the drive electrode 4a shown in FIG. 9 is applied to the drive electrode 4d. As a result, the sensing layer is displaced in the same manner as the driving layer, and efficient driving is possible. On the other hand, the voltage generated in the sensing electrode 4e by driving is detected by the detection unit 6 connected to the sensing electrode 4e. Similarly, the voltage generated at the sensing electrode 4g is detected by the detection unit 6 connected to the sensing electrode 4g.

Next, the operation when the ultrasonic motor 10 is driven in two phases will be described. FIG. 11A is a graph showing the input voltage with respect to time. A voltage Va shown in FIG. 11A is a voltage applied to the drive electrode 4a by the AC voltage source 5a and can be expressed as Va = V ₀ sin ωt. The voltage Vb is a voltage applied to the drive electrode 4b by the AC voltage source 5b and can be expressed as Vb = V ₀ cos ωt.

11B and 11C are graphs showing the sensing voltage with respect to time, respectively. A voltage V _S1 shown in FIG. 11B is a detection voltage generated at the sensing electrode 4e. Further, the voltage V _S2 shown in FIG. 11B is a detection voltage generated at the sensing electrode 4g. In the example shown in FIGS. 11B and 11C, the detection voltage V _S1 is a sine wave having a wave phase obtained by combining the drive voltages Va and Vb. The detection voltage V _S2 is a sine wave whose phase is changed by π from the detection voltage V _S1 . These indicate that the driving of the ultrasonic motor is normal. For example, if the phase of the detection voltage V _S1 and the detection voltage V _S2 is opposite to that in the above case, it is understood that a malfunction has occurred. In that case, the phases of the drive voltages Va and Vb are reversed and the magnitude of the voltage is adjusted to adjust the drive of the ultrasonic motor 10 to be normal.

[Second Embodiment]
In the above embodiment, voltages having different phases are applied to the drive electrodes 4a and 4b, but voltages having the same phase as b may be applied. In that case, the piezoelectric layer between each drive electrode 4a, 4b and the ground electrode is previously polarized in the opposite direction. Thus, the piezoelectric layer is polarized in two polarization directions in the same layer, and a one-phase driving voltage is applied to the driving electrode.

  As described above, when the one-phase driving is performed, the operation of the ultrasonic motor 10 can be sensed by obtaining a constant voltage waveform in the operation direction voltage using the two sensing electrodes. Therefore, it is sufficient that only a certain voltage waveform can be sensed without sensing the phase difference, and the sensor circuit can be simplified.

FIG. 12 is a diagram showing wiring for the drive layer of the ultrasonic motor 10. The wiring for the sensing layer is the same as in the above embodiment. 13A and 13B are graphs showing the input voltage with respect to time. Voltages V _S1 and V _S2 shown in FIG. 13B are detection voltages generated at the sensing electrodes 4e and 4g. In the example illustrated in FIG. 13B, the detection voltage V _S1 is a sine wave having a wave phase obtained by combining the drive voltages Va and Vb. This indicates that the driving of the ultrasonic motor is normal. For example, if the phase of the detection voltage V _S1 and the detection voltage V _S2 is opposite to that in the above case, it is understood that a malfunction has occurred. In that case, the drive voltages Va and Vb are reversed in phase, and the magnitude of the voltage is adjusted to adjust the drive of the ultrasonic motor 10 to normal.

DESCRIPTION OF SYMBOLS 1 Piezoelectric vibrator 1a Chip 1b Piezoelectric layer 2 Driven body 4a, 4b, 4d, 4f Drive electrode 4c Ground electrode 4e, 4g Sensing electrode 5a, 5b AC voltage source 6 Detection part 10 Ultrasonic motor Va, Vb Drive voltage V _S1 , V _S2 detection voltage

Claims (5)

A rectangular ultrasonic motor used for vibration in multiple vibration mode,
Laminated piezoelectric layers;
Drive electrodes and ground electrodes alternately layered between the laminated piezoelectric layers;
On one main surface side of the laminated piezoelectric layer used for drive detection, the sensing electrode is provided in an inner layer in the surface on which the drive electrode is provided,
When the length in the expansion / contraction direction in the primary longitudinal vibration mode is L and the length in the shear direction in the secondary bending vibration mode is w, the value of w / L is 0.55 or more and 0.65 or less. An ultrasonic motor characterized by being formed as described above .   The ultrasonic motor according to claim 1, wherein two sensing electrodes are provided at symmetrical positions. The sensing electrode has a quarter electrode area;
3. The ultrasonic motor according to claim 1, wherein the drive electrode in a plane in which the sensing electrode is provided has a three-fourth electrode area. 4.   The ultrasonic wave according to any one of claims 1 to 3, wherein the driving electrode, the ground electrode, and the sensing electrode that are inner layers are connected to input, ground, and detection terminals by external electrodes, respectively. motor. The piezoelectric layer is polarized in two polarization directions within the same layer,
5. The ultrasonic motor according to claim 1, wherein a one-phase driving voltage is applied to the inner layered driving electrode. 6.

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