JP2011211795A - Ultrasonic motor and method of driving the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic motor which can get a high thrust and control the generation of particles by reducing a friction with a driven body at drive.SOLUTION: The rectangular ultrasonic motor 10 used for vibration in multiple vibration mode includes: a piezoelectric layer 11b; two-segmented driving electrodes 14a and 14b which are provided on one main face side of the piezoelectric layer 11b; and a ground electrode which is provided on the other main face of the piezoelectric layer 11b. It is driven at a frequency equal to or higher than an anti-resonant frequency in multiple vibration mode by a driving circuit 18 of single phase drive which applies a voltage to either of the two-segmented driving electrodes and opens the other. By driving the rectangular ultrasonic motor 10 by single-phase drive at a frequency equal to or higher than an anti-resonant frequency in multiple vibration mode, a high thrust can be obtained; and the generation of particles can be controlled by reducing the friction with the driven body at drive.

Description

  The present invention relates to a rectangular ultrasonic motor used for vibration in a multiple vibration mode and a driving method thereof.

  2. Description of the Related Art Conventionally, an ultrasonic motor that generates a driving force by forming a piezoelectric element in a rectangular shape and vibrating in a multiple vibration mode combining a longitudinal vibration mode and a bending vibration mode is known (for example, Patent Documents 1 to 3). reference). Patent Document 1 discloses an ultrasonic transducer in which a plurality of piezoelectric bodies are stacked and driven in an L1F2 resonance mode that is a combination of a primary longitudinal vibration mode and a secondary bending vibration mode.

  The ultrasonic transducer includes piezoelectric elements and internal electrodes that are alternately stacked, and includes an internal electrode group that is substantially divided into four along a second direction and a third direction orthogonal to the stacking direction. ing. In addition, the first external electrode group and the second external electrode group that are electrically connected to the internal electrode group, respectively. Then, by applying a voltage to the first and second external electrode groups, the longitudinal vibration mode generated in the second direction and the bending vibration mode generated in the third direction are excited simultaneously, thereby causing an elliptical Generate vibration.

  Patent Document 2 discloses a driving method using a two-phase signal input method and a one-phase signal input method. In the two-phase signal input method, a first AC voltage is applied to one of the electrodes, and a second AC voltage whose phase is shifted by π / 2 from the first AC voltage is applied to any one of the electrodes. It is a method. The one-phase signal input method is a method in which an AC voltage is applied to one of the electrodes and either one of the other electrodes is opened. Patent Document 3 discloses a driving method using a two-phase signal input method.

JP 2006-094597 A JP 2009-240148 A JP 2009-225655 A

  However, even if the ultrasonic motor is caused to elliptically vibrate simply by the method as described above, a high thrust force to the driven body is not necessarily obtained. Further, friction is generated between the ultrasonic motor and the driven body during driving, and generation of particles cannot be suppressed. The present invention has been made in view of such circumstances, an ultrasonic motor capable of obtaining high thrust, reducing friction with a driven body during driving, and suppressing generation of particles, and a driving method thereof The purpose is to provide.

  (1) In order to achieve the above object, an ultrasonic motor according to the present invention is a rectangular ultrasonic motor used for vibration in a multiple vibration mode, and includes a piezoelectric layer and one main surface side of the piezoelectric layer. Single-phase drive comprising a provided two-section drive electrode and a ground electrode provided on the other main surface side of the piezoelectric layer, applying a voltage to one of the two-section drive electrodes and opening the other The drive circuit is driven at a frequency equal to or higher than the anti-resonance frequency of the multiple vibration mode.

  Thus, the ultrasonic motor of the present invention is driven at a frequency equal to or higher than the anti-resonance frequency of the multiple vibration mode by single-phase driving. Thereby, high thrust can be obtained, friction with the driven body during driving can be reduced, and generation of particles can be suppressed.

  (2) The ultrasonic motor driving method of the present invention is an ultrasonic motor driving method for driving a rectangular ultrasonic motor by applying a single-phase voltage, and includes two driving electrodes and a ground electrode. For a rectangular ultrasonic motor having a piezoelectric layer in between, drive at a frequency equal to or higher than the anti-resonance frequency of the multiple vibration mode by applying a voltage to one of the two drive electrodes and opening the other. It is characterized by letting.

  As described above, according to the driving method of the ultrasonic motor of the present invention, the rectangular ultrasonic motor is driven at a frequency equal to or higher than the anti-resonance frequency of the multiple vibration mode by single-phase driving. Thereby, high thrust can be obtained, friction with the driven body during driving can be reduced, and generation of particles can be suppressed.

  (3) Further, the driving method of the ultrasonic motor of the present invention is characterized in that it is driven in a multiple vibration mode of a primary longitudinal vibration mode and a primary or secondary bending vibration mode. As a result, high thrust can be obtained, and the ultrasonic motor can be driven in a track that is not easily rubbed against the driven body during driving.

  (4) The ultrasonic motor driving method of the present invention is characterized in that the ultrasonic motor is driven at a frequency of 100% to 110% of the anti-resonance frequency of the multiple vibration mode. By driving at a frequency in such a range, particularly high thrust can be obtained compared to driving at a frequency outside the range, and friction with the driven body at the time of driving is reduced, and particles are generated. Can be suppressed.

  (5) Further, the ultrasonic motor driving method of the present invention is characterized in that the ultrasonic motor has a structure in which a plurality of the driving electrodes, piezoelectric layers and ground electrodes are laminated. With such a laminated structure, a large displacement can be obtained and a higher thrust can be obtained.

  According to the present invention, high thrust can be obtained, friction with a driven body during driving can be reduced, and generation of particles can be suppressed.

It is a front view of the ultrasonic motor concerning the present invention. It is a figure which shows a mode that the ultrasonic motor which concerns on this invention is performing the primary longitudinal vibration. It is a figure which shows a mode that the ultrasonic motor which concerns on this invention is performing the primary bending vibration. It is a figure which shows the wiring with respect to the electrode on the drive layer of the ultrasonic motor which concerns on this invention. 1 is a perspective view of an ultrasonic motor 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 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. The wiring with respect to the electrode on the drive layer of the ultrasonic motor which concerns on this invention is shown. 1 is a perspective view of an ultrasonic motor 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. FIG. It is a graph which shows the relationship between the frequency of each vibration, and impedance. It is a graph which shows the relationship between the frequency of elliptical motion, and impedance. It is a graph which shows the relationship between a drive frequency and the speed of a to-be-driven body. It is a graph which shows the particle count number by the ultrasonic motor which concerns on this invention.

  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. The ultrasonic motor 10 can be elliptically moved by the primary longitudinal vibration and the primary bending vibration. As shown in FIG. 1, the ultrasonic motor 10 includes a piezoelectric vibrator 11 and a sliding chip 12, and can be driven by vibrating the rectangular laminated piezoelectric vibrator 11 in a multiple vibration mode. The piezoelectric vibrator 11 is formed of rectangular laminated piezoelectric ceramics, and each layer is polarized in a direction perpendicular to the paper surface. The length in the expansion / contraction direction in the primary longitudinal vibration mode is L1, and the length in the shear direction in the primary bending vibration mode is w1. In addition, a sliding tip 12 for transmitting a driving force is provided at the center of the end surface of the piezoelectric vibrator 11 in the y direction in the figure.

  FIG. 2 is a diagram illustrating a state in which the ultrasonic motor is performing primary longitudinal vibration. As shown in FIG. 2, the expansion / contraction direction when the piezoelectric vibrator 11 vibrates in the primary longitudinal vibration mode is parallel to the direction of the arrow A1 in FIG. FIG. 3 is a diagram illustrating a state in which the ultrasonic motor is performing primary bending vibration. As shown in FIG. 3, the direction (shear direction) when the piezoelectric vibrator 11 vibrates in the first bending vibration mode is parallel to the arrow A1 shown in FIG. 2, but the arrows B1 and C1 in FIG. As shown, the directions are opposite to each other at both ends of the piezoelectric vibrator 11. The first longitudinal vibration mode shown in FIG. 2 and the first bending vibration mode shown in FIG. 3 are combined (degenerated), so that the sliding tip 12 performs an elliptical motion, and a driving force is generated.

  FIG. 4 is a diagram showing wiring for electrodes on the drive layer of the ultrasonic motor 10. In FIG. 4, the electrode surface on the drive layer of the piezoelectric vibrator 11 is schematically cut out. As shown in FIG. 4, in the ultrasonic motor 10, on the drive layer, the drive electrode 14a and the drive electrode 14b are divided into two sections so that one main surface of the rectangular piezoelectric layer 11b is divided into two. It is provided as. A ground electrode (not shown) is provided on the other main surface of the drive layer and is grounded. The drive electrodes 14a and 14b are individually provided in a state of being insulated from each other.

The drive circuit 18 of the ultrasonic motor 10 is configured such that an AC voltage source 15a is connected to one drive electrode 14a, and the other drive electrode 14b is opened. The AC voltage source 15a applies a voltage of V ₀ sin ωt to the drive electrode 14a. As described above, when the voltage V ₀ sin ωt is applied to the drive electrode 14a of the piezoelectric vibrator 11 and single-phase driving is performed, the piezoelectric vibrator 11 has a longitudinal direction as shown in FIGS. Vibration in the first longitudinal vibration mode that expands and contracts in the first direction, and vibration in the first bending vibration mode that bends in the width direction (shear direction).

When the resonance frequency of the primary longitudinal vibration mode is equal to the resonance frequency of the primary bending vibration mode, both vibration modes are combined (degenerate), and the chip of the piezoelectric vibrator 11 (not shown in FIG. 4). No.) generates elliptical vibration. The voltage V ₀ sin ωt may be applied to the drive electrode 14b, and the applied voltage of each electrode may be switched.

  In this single phase drive, the ultrasonic motor 10 is driven at a frequency equal to or higher than the antiresonance frequency. Thereby, high thrust can be obtained, friction with the driven body during driving can be reduced, and generation of particles can be suppressed. The ultrasonic motor 10 is driven at the highest frequency or higher among the anti-resonance frequencies of the respective vibration modes. In particular, it is preferable to drive the ultrasonic motor 10 at a frequency of 100% or more and 110% or less of the anti-resonance frequency of the multiple vibration mode. By driving at a frequency in such a range, high thrust can be obtained compared to driving at a frequency outside the range, and friction with the driven body during driving can be reduced, and generation of particles can be suppressed. .

[Second Embodiment]
FIG. 5 is a perspective view of the ultrasonic motor 20. The piezoelectric vibrator 21 constituting the ultrasonic motor 20 is formed 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 21 vibrates in the primary longitudinal vibration mode is parallel to the x-axis, and the length of the piezoelectric vibrator 21 in the x-axis direction is L2. Further, the shear direction when the piezoelectric vibrator 21 vibrates in the secondary bending vibration mode is parallel to the y-axis, and the length of the piezoelectric vibrator 21 in the y-axis direction is w2.

  The piezoelectric vibrator 21 has drive electrodes 24a and 24b and a ground electrode 24c that are alternately provided between the surfaces or layers of the laminated piezoelectric layers 21b. The ultrasonic motor 20 preferably has such a structure in which a plurality of layers are laminated. With such a laminated structure, a large displacement can be obtained and a higher thrust can be obtained.

  FIG. 6 is a plan view showing the electrode pattern J2 on the drive layer. The drive electrodes 24a and 24b are each equally divided into two-segment drive electrodes so that the area is approximately one half of the main surface. And it has the extraction part exposed to the side surface of the piezoelectric vibrator 21, respectively. A predetermined alternating voltage is applied to the drive electrode 24a having a diagonal relationship in the electrode pattern, and the drive electrode 24b is opened. Using such a single-phase driving circuit, driving is performed at a frequency equal to or higher than the anti-resonance frequency. In particular, it is preferable to drive the ultrasonic motor 20 at a frequency of 100% or more and 110% or less of the anti-resonance frequency of the multiple vibration mode.

  FIG. 7 is a plan view showing a ground electrode pattern GND2. When an electric field is generated between the ground electrode 24c and the drive electrodes 24a and 24b, the piezoelectric layer 21b therebetween is displaced.

[Third Embodiment]
FIG. 8 is a front view of the ultrasonic motor 30. As shown in FIG. 8, the ultrasonic motor 30 includes a piezoelectric vibrator 31 and a chip 31a, and can be driven by vibrating the rectangular piezoelectric vibrator 31 in a multiple vibration mode. The length (x direction) of the ultrasonic motor 30 is L3, and the width (y direction) is w3.

  FIG. 9 is a diagram illustrating a state of the primary longitudinal vibration of the ultrasonic motor 30. The primary longitudinal vibration is generated by repeatedly expanding and contracting in the longitudinal direction of the piezoelectric vibrator 31, as indicated by arrows A3 and B3 in FIG. FIG. 10 is a diagram illustrating a state of secondary bending vibration of the ultrasonic motor 30. The secondary bending vibration is generated by repeatedly bending in the thickness direction of the piezoelectric vibrator 31 with shearing forces having different directions, as indicated by an arrow C3 in FIG. By synthesizing (degenerate) these primary longitudinal vibrations and secondary bending vibrations, the chip provided on the piezoelectric vibrator 31 performs an elliptical motion to generate a driving force.

  FIG. 11 is a diagram showing stepwise how the piezoelectric vibrator 31 drives the driven body 32 in the right direction in the drawing. As shown in FIG. 11, the piezoelectric vibrator 31 includes a chip 31a. By synthesizing the primary longitudinal vibration and the secondary bending vibration of the piezoelectric vibrator 31, the piezoelectric vibrator 31 repeats expansion and contraction and bending, and the driven body is moved by the distance l3 in one cycle. The piezoelectric vibrator 31 generates a driving force based on such a principle.

  FIG. 12 is a diagram illustrating wiring for the drive electrodes of the ultrasonic motor 30. In FIG. 12, the main surface of the piezoelectric vibrator 31 is schematically shown. On the main surface, a pair of drive electrodes 34a and a set of drive electrodes 34b that are diagonally opposed to each other are provided so that one main surface of the rectangular piezoelectric vibrator 31 is divided into four. The set of drive electrodes 34a and the set of drive electrodes 34b constitutes two sections of drive electrodes. A ground electrode (not shown) is provided on the other main surface of the piezoelectric vibrator 31 and is grounded. The drive electrodes 34a and 34b are individually provided in a state of being insulated from each other, and the drive electrodes 34a and 34b positioned diagonally to each other are electrically connected to each other.

The drive circuit 38 of the ultrasonic motor 30 is configured by connecting the AC voltage source 15a to a pair of diagonally opposed drive electrodes 34a and opening the other set of drive electrodes 34b. The AC voltage source 15a applies a voltage of V ₀ sin ωt to the drive electrode 34a. As described above, when the voltage V ₀ sin ωt is applied to the drive electrode 34a of the piezoelectric vibrator 31, the piezoelectric vibrator 31 is primarily expanded and contracted in the longitudinal direction as shown in FIGS. The vibration in the longitudinal vibration mode and the vibration in the second bending vibration mode that bends 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 synthesized (degenerate), and the chip of the piezoelectric vibrator 31 (not shown in FIG. 12). O) elliptical vibration occurs.

  In such single-phase driving, the ultrasonic motor 30 is driven at a frequency equal to or higher than the antiresonance frequency. Thereby, high thrust can be obtained, friction with the driven body during driving can be reduced, and generation of particles can be suppressed. Note that the ultrasonic motor 30 is driven at the highest frequency or higher among the anti-resonance frequencies of the respective vibration modes. In particular, it is preferable to drive the ultrasonic motor 10 at a frequency of 100% or more and 110% or less of the anti-resonance frequency of the multiple vibration mode. By driving at a frequency in such a range, high thrust can be obtained compared to driving at a frequency outside the range, and friction with the driven body during driving can be reduced, and generation of particles can be suppressed. .

[Fourth Embodiment]
FIG. 13 is a perspective view of the ultrasonic motor 40. The piezoelectric vibrator 41 constituting the ultrasonic motor 40 is formed 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 41 vibrates in the primary longitudinal vibration mode is parallel to the x-axis, and the length of the piezoelectric vibrator 41 in the x-axis direction is L4. Further, the shear direction when the piezoelectric vibrator 41 vibrates in the secondary bending vibration mode is parallel to the y-axis, and the length of the piezoelectric vibrator 41 in the y-axis direction is w4. The piezoelectric vibrator 41 includes drive electrodes 44a and 44b and a ground electrode 44c that are alternately provided between the surfaces or layers of the stacked piezoelectric layers 41b.

  FIG. 14 is a plan view showing an electrode pattern J4 on the drive layer. The drive electrodes 44a and 44b are each equally divided into a quarter of the main surface. Each of the piezoelectric vibrators 41 has an extraction portion exposed on the side surface. A predetermined alternating voltage is applied to a pair of drive electrodes 44a that are in a diagonal relationship in the electrode pattern, and the other set of drive electrodes 44b is open. The one set of drive electrodes 44a and the one set of drive electrodes 44b constitute two sections of drive electrodes. Using such a single-phase driving circuit, driving is performed at a frequency equal to or higher than the anti-resonance frequency.

  FIG. 15 is a plan view showing a ground electrode pattern GND4. When an electric field is generated between the ground electrode 44c and the drive electrodes 44a and 44b, the piezoelectric layer 41b therebetween is displaced. The ultrasonic motor 40 preferably has such a structure in which a plurality of layers are laminated. With such a laminated structure, a large displacement can be obtained and a higher thrust can be obtained.

  As described above, the rectangular ultrasonic motor is preferably driven in the multiple vibration mode including the primary longitudinal vibration mode and the primary or secondary bending vibration mode. As a result, high thrust can be obtained, and the ultrasonic motor can be driven in a track that is not easily rubbed against the driven body during driving.

  Next, an experiment using the ultrasonic motor 10 in the first embodiment will be described. First, the ultrasonic motor 10 was driven in a single phase, and the relationship between frequency and impedance was measured for bending vibration and stretching vibration. FIG. 16 is a graph showing the relationship between the frequency and impedance of each vibration. As shown in FIG. 16, in the bending vibration and the stretching vibration, a resonance frequency peak and an anti-resonance frequency peak appear, respectively. The peak protruding downward on the side where the frequency is small is the peak of the resonance frequency. Further, the peak that protrudes upward on the higher frequency side is the peak of the antiresonance frequency.

  Further, the relationship between the frequency and the impedance of the elliptical motion by the single phase driving of the ultrasonic motor 10 was examined. FIG. 17 is a graph showing the relationship between the frequency of the elliptical motion and the impedance. The graph of the elliptical motion is similar to the behavior of bending vibration and stretching vibration. At this time, it was found that the highest frequency among anti-resonance peaks was 77.5 kHz.

  Therefore, the relationship between the driving frequency in the forward direction and the reverse direction and the speed of the driven body was measured for a frequency range including 77.5 kHz or more. FIG. 18 is a graph showing the relationship between the drive frequency and the speed of the driven body. As shown in FIG. 18, when the frequency is about 77.3 kHz, the speed is 50 mm / s or less, while at 77.5 kHz, the speed reaches 120 mm / s or more, and the speed is remarkably increased. On the other hand, when the frequency exceeds 78.5 kHz, the speed is lower than 100 mm / s, and the speed is remarkably different in these points. Therefore, it was proved that the speed becomes particularly large at a frequency of 100% to 110% at 77.5 kHz.

  Further, the ultrasonic motor 10 was driven at 78 kHz to count the number of particles. FIG. 19 is a graph showing the particle count by the ultrasonic motor. There were very few particles having a size in the range of 0.1 μm or more and 0.5 μm or less, and almost no particles were generated from the start to the end of the operation. In this way, it has been demonstrated that almost no particles are generated when single-phase driving is performed at a frequency higher than the antiresonance frequency.

DESCRIPTION OF SYMBOLS 10 Ultrasonic motor 11 Piezoelectric vibrator 11b Piezoelectric layer 12 Sliding chip 14a, 14b Drive electrode 15a AC voltage source 18 Drive circuit 20 Ultrasonic motor 21 Piezoelectric vibrator 21b Piezoelectric layer 24a, 24b Drive electrode 24c Ground electrode 30 Ultrasonic motor 31 Piezoelectric vibrator 31a Chip 32 Driven bodies 34a and 34b Drive electrode 38 Drive circuit 40 Ultrasonic motor 41 Piezoelectric vibrator 41b Piezoelectric layers 44a and 44b Drive electrode 44c Ground electrode

Claims (5)

A rectangular ultrasonic motor used for vibration in multiple vibration mode,
A piezoelectric layer;
Two sections of drive electrodes provided on one main surface side of the piezoelectric layer;
A ground electrode provided on the other main surface side of the piezoelectric layer,
An ultrasonic motor driven by a single-phase drive drive circuit that applies a voltage to one of the two drive electrodes and opens the other, at a frequency equal to or higher than the anti-resonance frequency of the multiple vibration mode. A method of driving an ultrasonic motor that drives a rectangular ultrasonic motor by applying a single-phase voltage,
For a rectangular ultrasonic motor having a piezoelectric layer between a drive electrode of two sections and a ground electrode, multiple vibrations are applied by applying a voltage to one of the drive electrodes of the two sections and opening the other. A method for driving an ultrasonic motor, wherein the driving is performed at a frequency equal to or higher than the antiresonance frequency of the mode.   3. The method of driving an ultrasonic motor according to claim 2, wherein the driving is performed in a multiple vibration mode of a primary longitudinal vibration mode and a primary or secondary bending vibration mode.   4. The method of driving an ultrasonic motor according to claim 2, wherein the ultrasonic motor is driven at a frequency of 100% to 110% of an anti-resonance frequency of the multiple vibration mode.   5. The method of driving an ultrasonic motor according to claim 2, wherein the ultrasonic motor has a structure in which a plurality of the drive electrodes, piezoelectric layers, and ground electrodes are stacked.

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