JP2006304425A - Operation method of ultrasonic motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a stable and high motor output by efficiently generating each vibration mode, in an ultrasonic motor that simultaneously generates a plurality of the vibration modes. <P>SOLUTION: This operation method operates the ultrasonic motor that comprises an ultrasonic vibrator that is provided with a driving electromechanical conversion element and a vibration detecting electromechanical element, and generates almost elliptical vibration at an output end by simultaneously generating the two different vibration modes by feeding a two-phase alternating voltage of a prescribed phase difference and a prescribed vibration frequency to the driving electromechanical conversion element. A pressing force that presses the output end of the ultrasonic vibrator against a driven body is set so that mechanical resonant frequencies of the two vibration modes coincide with other on the basis of a signal outputted from the vibration detecting electromechanical conversion element. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for operating an ultrasonic motor.

In recent years, ultrasonic motors have attracted attention as new motors that replace electromagnetic motors. This ultrasonic motor has the following advantages over conventional electromagnetic motors.
(1) High torque can be obtained without gears.
(2) There is holding power when electricity is OFF.
(3) High resolution.
(4) Rich in silence.
(5) Magnetic noise is not generated and is not affected by noise.

As a conventional ultrasonic motor, there is one having a structure disclosed in Patent Document 1. The ultrasonic motor disclosed in Patent Document 1 has a configuration in which an ultrasonic transducer is pressed against a driven body by a pressing spring with a predetermined pressing force. In Patent Document 1, the pressing force is set to a value less than the pressing force at which the longitudinal vibration resonance frequency and the bending vibration resonance frequency match, and the drive frequency is a frequency between the longitudinal vibration resonance frequency and the bending vibration resonance frequency. Was set to. Under such conditions, longitudinal vibration and bending vibration are excited in the ultrasonic vibrator, and the driven body is driven leftward or rightward.
Japanese Patent Laid-Open No. 9-224385

  However, in the ultrasonic motor of Patent Document 1, the pressing force is set to a value less than the pressing force at which the longitudinal vibration resonance frequency and the bending vibration resonance frequency match, and the resonance frequency of the longitudinal vibration and the resonance frequency of the bending vibration are equal. Since this is not done, the maximum vibration amplitude in both vibration modes cannot be used, and there is a disadvantage that sufficient characteristics cannot be obtained as a motor output. In addition, since the drive frequency is a frequency between the resonance frequency of the longitudinal vibration mode and the resonance frequency of the bending vibration mode, it cannot be used at the maximum vibration amplitude of both vibration modes, and is also sufficient as a motor output. There was a problem that it was not possible to obtain proper characteristics.

  The present invention has been made in view of the above circumstances, and in an ultrasonic motor that simultaneously generates a plurality of vibration modes, each vibration mode can be efficiently generated to stably obtain a high motor output. An object of the present invention is to provide a method for operating an ultrasonic motor.

In order to achieve the above object, the present invention provides the following means.
The present invention includes an electromechanical transducer for driving and an electromechanical transducer for detecting vibration, and supplies a two-phase alternating voltage having a predetermined phase difference and a predetermined driving frequency to the driving electromechanical transducer. An operating method of an ultrasonic motor including an ultrasonic vibrator that simultaneously generates two different vibration modes and generates substantially elliptical vibration at an output end, wherein the output end of the ultrasonic vibrator is connected to a driven body. The pressing force to be pressed is set to match the mechanical resonance frequencies of the two vibration modes based on the signal output from the vibration detecting electromechanical transducer.
According to the present invention, two different vibration modes are generated simultaneously by supplying a two-phase alternating voltage having a predetermined phase difference and a predetermined vibration frequency to the driving electromechanical transducer, and the ultrasonic transducer A substantially elliptical vibration is generated at the output end. By pressing the output end against the driven body by the operation of the pressing means, the driven body is driven in the tangential direction of the elliptical vibration of the output end by the frictional force generated between the output end and the driven body. .
In this case, the mechanical resonance frequency of the two vibration modes is set to match by appropriately adjusting the pressing force by the pressing means based on the signal output from the electromechanical transducer for vibration detection. Therefore, in driving the driven body, it is possible to use substantially the maximum vibration amplitude of the two vibration modes at the same time. As a result, a high motor output can be obtained and the driven body can be driven efficiently.

In addition, the present invention includes an electromechanical conversion element, and supplies two different alternating modes with a predetermined phase difference and a predetermined drive frequency to the electromechanical conversion element to simultaneously generate two different vibration modes. An operation method of an ultrasonic motor including an ultrasonic vibrator that generates substantially elliptical vibration at an output end, wherein a pressing force pressing the output end of the ultrasonic vibrator against a driven body is a vibration speed in the vicinity of the output end. The mechanical resonance frequencies of the two vibration modes are set to coincide with each other based on the signal output from the vibration meter that measures the vibration.
According to the present invention, two different vibration modes are generated simultaneously by supplying a two-phase alternating voltage having a predetermined phase difference and a predetermined vibration frequency to the electromechanical transducer, and the output end of the ultrasonic transducer is generated. Substantially elliptical vibration occurs. By pressing the output end against the driven body by the operation of the pressing means, the driven body is driven in the tangential direction of the elliptical vibration of the output end by the frictional force generated between the output end and the driven body. .
In this case, the pressing force by the pressing means is appropriately adjusted based on the output from the three-dimensional Doppler vibrometer, for example, so that the mechanical resonance frequencies of the two vibration modes are set to coincide with each other. In driving the driving body, it is possible to simultaneously use substantially the maximum vibration amplitude of the two vibration modes. As a result, a high motor output can be obtained and the driven body can be driven efficiently.

  According to the present invention, in an ultrasonic motor that simultaneously generates a plurality of vibration modes, each vibration mode can be generated efficiently, and a high motor output can be obtained stably.

Hereinafter, an ultrasonic motor according to a first embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 1, the ultrasonic motor 1 according to the present embodiment includes an ultrasonic transducer 3 that is placed in contact with the driven body 2 and a pressing unit that presses the ultrasonic transducer 3 against the driven body 2. 4 is provided. The driven body 2 is fixed to the movable portion 7 of the linear motion bearing 6 fixed to the base 5. In addition, a sliding plate 8 made of, for example, zirconia ceramics is bonded to the driven body 2 on the surface in contact with the ultrasonic vibrator 3. Reference numeral 9 in the drawing denotes a screw for fixing the fixing portion 10 of the linear motion bearing 6 to the base 5.

  As shown in FIGS. 2 to 4, the ultrasonic transducer 3 is provided with a sheet-like internal electrode 12 (see FIG. 4) on one side of a rectangular plate-shaped piezoelectric ceramic sheet 11 (electromechanical transducer). A rectangular parallelepiped piezoelectric laminate 13 formed by laminating a plurality of objects, two friction contacts 14 (output ends) bonded to one side surface of the piezoelectric laminate 13, and the friction contacts 14 are provided. And a vibrator holding member 16 for projecting the pin 15 from the side surface adjacent to the side surface.

As shown in FIG. 3, the piezoelectric laminate 13 has external dimensions of, for example, a length of 18 mm, a width of 4.4 mm, and a thickness of 2 mm.
The piezoelectric ceramic sheet 11 constituting the piezoelectric laminate 13 is, for example, a lead zirconate titanate-based piezoelectric ceramic element (hereinafter referred to as PZT) having a thickness of about 80 μm, as shown in FIG. As PZT, a hard material having a large Qm value was selected. The Qm value is about 1800.
The internal electrode 12 is made of, for example, a silver palladium alloy having a thickness of about 4 μm. The piezoelectric ceramic sheet 11 a disposed at one end in the stacking direction does not include the internal electrode 12. The other piezoelectric ceramic sheet 11 includes two types of internal electrodes 12 as shown in FIG.

  The piezoelectric ceramic sheet 11 shown in FIG. 4A includes an internal electrode 12 on almost the entire surface. The internal electrodes 12 have approximately the same size with an insulation distance of about 0.4 mm in the length direction of the piezoelectric ceramic sheet 11 and an insulation distance of about 0.4 mm in the width direction of the piezoelectric ceramic sheet 11. Are arranged in two rows in the length direction and three rows in the width direction. Each internal electrode 12 is disposed with a gap of about 0.4 mm from the periphery of the piezoelectric ceramic sheet 11, and a part thereof extends to the periphery of the piezoelectric ceramic sheet 11.

  In the piezoelectric ceramic sheet 11 shown in FIG. 4B, the length in the width direction of the internal electrode 12 located in the center in the width direction of the internal electrodes 12 shown in FIG. It has been done.

  The piezoelectric ceramic sheet 11 provided with these internal electrodes 12 is formed by laminating a plurality of sheets each having a large internal electrode 12 shown in FIG. 4A and a small internal electrode 12 shown in FIG. 4B. As a result, a rectangular parallelepiped piezoelectric laminate 13 is formed.

  A total of twelve external electrodes 17 are provided on each of both end faces in the length direction of the piezoelectric laminate 13, six each. All the internal electrodes 12 arranged at the same position of the same kind of piezoelectric ceramic sheet 11 are connected to each external electrode 17. Thereby, the internal electrodes 12 arranged at the same position of the same type of piezoelectric ceramic sheet 11 are set to the same potential. Each of the external electrodes 17 is connected to a controller (not shown) via wiring (not shown). The wiring may be any wiring as long as it is flexible, such as a lead wire or a flexible substrate.

The piezoelectric laminate 13 is manufactured as follows, for example.
In order to manufacture the piezoelectric laminate 13, first, the piezoelectric ceramic sheet 11 is manufactured. The piezoelectric ceramic sheet 11 is manufactured by, for example, drying a slurry prepared by mixing a calcined powder of PZT and a predetermined binder on a film by a doctor blade method and then peeling the slurry from the film.

  An internal electrode material is printed on each of the manufactured piezoelectric ceramic sheets 11 using a mask having a pattern of internal electrodes 12. First, the piezoelectric ceramic sheets 11a not having the internal electrodes 12 are arranged, and then the piezoelectric ceramic sheets 11 having the internal electrodes 12 having different shapes are alternately laminated while the internal electrodes 12 are positioned accurately downward. I will do it. The laminated piezoelectric ceramic sheets 11 are thermocompression bonded, then cut into a predetermined shape, and fired at a temperature of about 1200 ° C., whereby the piezoelectric laminated body 13 is manufactured.

After that, the external electrodes 17 are formed by baking silver serving as the external electrodes 17 so as to connect the internal electrodes 12 exposed on the periphery of the piezoelectric ceramic sheet 11.
Finally, the piezoelectric ceramic sheet 11 is polarized by applying a direct current high voltage between the opposed internal electrodes 12 to be piezoelectrically activated.

Next, the operation of the thus configured piezoelectric laminate 13 will be described.
The six external electrodes 17 formed at one end in the longitudinal direction of the piezoelectric laminate 13 are connected to the A phase (A +, A−) and the C phase (C +, C) from the other side of the piezoelectric laminate 13 (upper side in the drawing). C-), B phase (B +, B-), and six external electrodes 17 formed at the other end are connected to the B phase (B +, B-) from the other side of the piezoelectric laminate 13 (upper side in the figure). , D phase (D +, D−), and A phase (A +, A−). A phase and B phase are internal electrodes for driving, and C phase and D phase are internal electrodes for vibration detection.

When an alternating voltage having the same phase and corresponding to the resonance frequency is applied to the A phase and the B phase, the primary longitudinal vibration as shown in FIG. 5 is excited. Further, when an alternating voltage corresponding to the resonance frequency is applied to the A phase and the B phase in opposite phases, a secondary bending vibration as shown in FIG. 6 is excited. 5 and 6 are diagrams showing computer analysis results by the finite element method.
On the other hand, the sum of the signals output from the C phase and the D phase is proportional to the longitudinal vibration, and the difference between the signals output from the C phase and the D phase is proportional to the bending vibration. These calculations are performed by the controller described above.

The frictional contacts 14 are bonded to two positions that become antinodes of secondary bending vibration of the piezoelectric laminate 13. Thereby, when primary longitudinal vibration is generated in the piezoelectric laminate 13, the friction vibrator 14 is displaced in the length direction of the piezoelectric laminate 13 (X direction shown in FIG. 2). On the other hand, when secondary bending vibration is generated in the piezoelectric laminate 13, the frictional contact 14 is displaced in the width direction of the piezoelectric laminate 13 (Z direction shown in FIG. 2).
Therefore, by applying an alternating voltage corresponding to a resonance frequency whose phase is shifted by 90 ° to the A phase and the B phase of the ultrasonic transducer 3, primary longitudinal vibration and secondary bending vibration are generated simultaneously. Thus, as indicated by an arrow C in FIG. 2, a substantially elliptical vibration in the clockwise direction or the counterclockwise direction is generated at the position of the friction contact 14.

  The vibrator holding member 16 includes a holding portion 16a having a substantially U-shaped cross section, and a pin 15 integral with the holding portion 16a protruding vertically from both side surfaces of the holding portion 16a. The holding portion 16a is bonded to the piezoelectric laminate 13 with, for example, a silicone resin or an epoxy resin so as to surround the piezoelectric laminate 13 from one side in the width direction of the piezoelectric laminate 13. In a state where the holding portion 16a is bonded to the piezoelectric laminate 13, the two pins 15 provided integrally on both side surfaces of the holding portion 16a serve as a common node for longitudinal vibration and bending vibration of the piezoelectric laminate 13. It is arranged coaxially at the position.

  As shown in FIG. 1, the pressing means 4 is fixed to the base 5 at a position away from the friction contact 14 in the width direction (Z direction) with respect to the ultrasonic transducer 3. A bracket 18 that is supported, a pressing member 19 that is supported by the bracket 18 so as to be movable in the width direction of the ultrasonic transducer 3, and a coil spring 20 that applies a pressing force to the pressing member 19. An adjustment screw 21 for adjusting the pressing force by the coil spring 20 and a guide bush 22 for guiding the movement of the pressing member 19 with respect to the bracket 18 are provided. Reference numeral 23 denotes a screw for fixing the bracket 18 to the base 5.

  The pressing member 19 includes two holding plates 24 that sandwich the ultrasonic transducer 3 in the thickness direction. Each holding plate 24 is provided with a through hole 25 through which each of the two pins 15 of the vibrator holding member 16 passes. The pressing force applied to the pressing member 19 is transmitted to the ultrasonic transducer 3 through the holding plate 24 and the pin 15 that penetrates the through hole 25.

  The coil spring 20 is a compression coil spring and is sandwiched between the adjustment screw 21 and the pressing member 19. Therefore, by changing the fastening position of the adjustment screw 21 with respect to the bracket 18, the amount of elastic deformation can be changed to change the pressing force that urges the pressing member 19 toward the ultrasonic transducer 3. Yes.

In the ultrasonic motor 1 according to this embodiment, the adjustment screw 21 is adjusted as follows.
That is, the phase difference between the voltages applied to the A phase and the B phase of the ultrasonic vibrator 3 is set to 90 ° or −90 °, and the vibration speed in the vicinity of the friction contact 3 is output from the C phase and the D phase. FIG. 7 shows the result of measurement using the obtained signals (that is, the sum signal and difference signal obtained by the controller). FIG. 7A shows the resonance characteristics when the adjusting screw 21 is completely loosened and no pressing force is applied to the pressing member 19. 7B and 7C show the resonance characteristics when the fastening position of the adjusting screw 21 is changed, respectively, and the case of FIG. 7C is more than the case of FIG. 7B. The pressing force is high.

  7A to 7C, in the state of FIG. 7A in which no pressing force is applied, the mechanical vibration frequency at which the mechanical vibration speed becomes the maximum value is the machine in the longitudinal vibration mode. The mechanical vibration frequency (fl) is larger than the mechanical vibration frequency (ff) in the flexural vibration mode, but when the pressing force is applied, they gradually approach each other (FIG. 7 (b)), When the pressure is further increased, as shown in FIG. 7C, both are reversed, and the mechanical resonance frequency (fl) in the longitudinal vibration mode is higher than the mechanical resonance frequency (ff) in the bending vibration mode. Is also low.

  In the ultrasonic motor 1 according to the present embodiment, based on signals output from the C phase and the D phase, the mechanical resonance frequency (fl) in the longitudinal vibration mode and the mechanical resonance frequency (ff) in the bending vibration mode. The adjustment screw 21 is adjusted so as to be in the state of FIG. The procedure is as follows.

As shown in FIG. 8, first, the adjustment screw 21 is set so that a predetermined pressing force (a certain value of pressing (force)) is applied to the pressing member 19.
Next, the mechanical resonance frequency (fl) in the longitudinal vibration mode and the mechanical resonance frequency (ff) in the bending vibration mode are obtained based on the signals output from the C phase and the D phase, and the machine in the longitudinal vibration mode is obtained. The adjustment screw 21 is adjusted so that the mechanical resonance frequency (fl) matches the mechanical resonance frequency (ff) of the bending vibration mode.
That is, as a result of the determination, when the mechanical resonance frequency (fl) in the longitudinal vibration mode is higher than the mechanical resonance frequency (ff) in the bending vibration mode (the state in FIG. 7A), the adjustment screw 21 is tightened. The pressing force applied to the pressing member 19 is increased. Conversely, when the mechanical resonance frequency (fl) in the longitudinal vibration mode is smaller than the mechanical resonance frequency (ff) in the bending vibration mode (the state shown in FIG. 7C), the adjustment screw 21 is loosened and the pressing member The pressing force applied to 19 is reduced. Then, when the mechanical resonance frequency (fl) in the longitudinal vibration mode matches the mechanical resonance frequency (ff) in the bending vibration mode, the adjustment work of the adjustment screw 21 is finished.

  Adjustment of the adjusting screw 21 is a display screen on which the relationship between the mechanical resonance frequency (fl) in the longitudinal vibration mode and the mechanical resonance frequency (ff) in the bending vibration mode (that is, the relationship shown in FIG. 7) is displayed. The operator is manually performed while looking at the (display), or is automatically performed by a signal from the controller.

The operation of the ultrasonic motor 1 according to this embodiment configured as described above will be described.
In order to operate the ultrasonic motor 1 according to the present embodiment, high-frequency voltages (A phase and B phase) whose phases are different by 90 ° are supplied via wiring connected to the external electrode 17.
As a result, a substantially elliptical vibration in which the longitudinal vibration mode and the bending vibration mode are mixed is generated in the frictional contactor 14 bonded to the ultrasonic transducer 3, and the driven body is driven along the tangential direction of the elliptical vibration mode. The driven body 2 is propelled by the frictional force generated between the two sliding plates 8.

In this case, according to the ultrasonic motor 1 according to the present embodiment, the pressing force is applied so that the mechanical resonance frequencies (fl, ff) of the longitudinal vibration mode and the bending vibration mode simultaneously generated in the ultrasonic vibrator 3 coincide with each other. Since it is adjusted, the maximum vibration amplitude of each vibration mode can be used for propulsion of the driven body 2, and an effect is obtained that a high output can be obtained.
Even if each member constituting the pressing means 4 has a variation in the spring coefficient or the like, the pressing force can be finely adjusted while monitoring the actual vibration, so that the optimal pressing force can be set. Thus, it is possible to obtain stable motor characteristics.

An ultrasonic motor according to a second embodiment of the present invention will be described below with reference to FIGS. 9 and 10.
As shown in FIG. 10, the ultrasonic motor according to the present embodiment includes an ultrasonic transducer 30 in which an internal electrode for vibration detection is omitted, and the vibration speed in the vicinity of the ultrasonic transducer 30 is included. However, it is different from the ultrasonic motor 1 according to the first embodiment described above in that it is measured using a three-dimensional Doppler vibrometer 31 as shown in FIG.

According to the ultrasonic motor according to the present embodiment, it is not necessary to provide an internal electrode for vibration detection on the piezoelectric ceramic sheet 11, so that the configuration of the piezoelectric ceramic sheet 11 can be simplified and the ultrasonic vibrator 30. The configuration can be simplified.
Since other operations and effects are the same as those of the first embodiment described above, description thereof is omitted here.

In each of the above embodiments, PZT is used as the piezoelectric ceramic sheet. However, the present invention is not limited to this, and any piezoelectric element other than PZT may be used as long as it exhibits piezoelectricity.
In each of the above embodiments, the silver-palladium alloy is used as the material of the internal electrode, but silver, nickel, platinum, or gold may be used instead.
Furthermore, instead of adhering a sliding plate made of zirconia ceramics to the surface of the driven body 2, zirconia ceramics may be adhered to the surface of the driven body 2 by a thermal spraying method.
Furthermore, in the second embodiment, the three-dimensional Doppler vibrometer 31 is used as the vibrometer, but the present invention is not limited to this, and an electrostatic vibrometer can be used. Various vibrometers using the above principle can also be used.

1 is an overall configuration diagram showing an ultrasonic motor according to a first embodiment of the present invention. It is a perspective view which shows the ultrasonic transducer | vibrator of the ultrasonic motor of FIG. It is a perspective view which shows the piezoelectric laminated body which comprises the ultrasonic transducer | vibrator of FIG. It is a perspective view which shows the piezoelectric ceramic sheet which comprises the piezoelectric laminated body of FIG. It is a figure which shows a mode that the piezoelectric laminated body of FIG. 2 vibrates in the primary longitudinal vibration mode by computer analysis. It is a figure which shows a mode that the piezoelectric laminated body of FIG. 2 vibrates in a secondary bending vibration mode by computer analysis. It is a graph which shows the change of the frequency characteristic according to the pressing force of the vibration speed of the ultrasonic transducer | vibrator of FIG. It is a flowchart which shows the process in which the mechanical resonance frequency in two vibration modes of an ultrasonic transducer | vibrator is matched like FIG.7 (b). It is a perspective view which shows the ultrasonic transducer | vibrator of the ultrasonic motor which concerns on the 2nd Embodiment of this invention. It is a perspective view which shows the piezoelectric ceramic sheet which comprises the piezoelectric laminated body of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic motor 2 Driven body 3 Ultrasonic vibrator 11 Piezoelectric ceramic sheet (electromechanical transducer)
14 Friction contact (output end)
30 Ultrasonic vibrator 31 3D Doppler vibrometer ff Bending vibration mode mechanical resonance frequency fl Longitudinal vibration mode mechanical resonance frequency

Claims (2)

The electromechanical transducer for driving and the electromechanical transducer for detecting vibration are different by supplying a two-phase alternating voltage having a predetermined phase difference and a predetermined driving frequency to the electromechanical transducer for driving. An operation method of an ultrasonic motor including an ultrasonic vibrator that generates two elliptical vibrations at the output end by generating two vibration modes simultaneously,
The pressing force pressing the output end of the ultrasonic transducer against the driven body is made to match the mechanical resonance frequencies of the two vibration modes based on the signal output from the electromechanical transducer for vibration detection. The set ultrasonic motor operation method. An electromechanical conversion element is provided, and by supplying a two-phase alternating voltage having a predetermined phase difference and a predetermined drive frequency to the electromechanical conversion element, two different vibration modes are generated at the same time, and substantially elliptical vibration is generated at the output end. A method of operating an ultrasonic motor including an ultrasonic vibrator that generates
The pressing force pressing the output end of the ultrasonic transducer against the driven body matches the mechanical resonance frequency of the two vibration modes based on the signal output from the vibrometer that measures the vibration velocity in the vicinity of the output end. The operation method of the ultrasonic motor that is set to be

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