JP5571521B2 - Ultrasonic motor and driving method thereof - Google Patents

Description

  The present invention relates to an ultrasonic motor in which piezoelectric layers and electrodes are alternately stacked and driven by applying a voltage, and a driving method thereof.

  Ultrasonic motors are being studied for application in various fields because they are quiet and provide high torque. The ultrasonic motor is composed of a piezoelectric vibrator, and moves the moving body (guide plate) by being brought into pressure contact with the driving force transmission portion of the vibrating body. That is, when a high frequency voltage is input to the piezoelectric vibrator, mechanical vibration is generated in the vibrating body, and kinetic energy is propagated to the moving body by the frictional force between the vibrating body and the moving body, and as a result, the motor output can be taken out. 2. Description of the Related Art Conventionally, there is known an ultrasonic motor that simultaneously drives multiple modes by stacking segmented internal electrodes having the same pattern (see Patent Documents 1 to 3).

  For example, an ultrasonic motor described in Patent Document 1 is configured by stacking rectangular and single-plate piezoelectric vibrators to form a laminated piezoelectric vibrator, and the laminated piezoelectric vibrator has a primary expansion / contraction vibration mode and a first bending vibration. It vibrates in multiple vibration mode combined with the mode. A single-plate piezoelectric vibrator vibrates in a stretching primary vibration mode and a bending primary vibration mode, and a plurality of single-plate piezoelectric vibrators are laminated in the thickness direction.

JP 2010-104193 A JP 2005-65358 A JP 2000-116162 A

  Since the multi-mode driving of the ultrasonic motor as described above is performed at the same time, an input voltage higher than a certain level is required to start the operation. Therefore, voltage control for position control is difficult. Further, in order to reduce wear that is likely to occur due to a certain operation, it is necessary to lower the operating voltage and lower the thrust.

  The present invention has been made in view of such circumstances, and provides an ultrasonic motor and a driving method thereof capable of improving the followability of operation and friction wear characteristics by smoothly changing the operating voltage. With the goal.

  (1) In order to achieve the above object, an ultrasonic motor of the present invention is an ultrasonic motor in which piezoelectric layers and electrodes are alternately stacked and driven by application of voltage, and is driven by bending primary vibration. It is characterized by comprising a bending vibration layer and a stretching vibration layer that is laminated in parallel with the bending vibration layer and driven by stretching primary vibration.

  In this way, by configuring the stretchable vibration layer as a separate layer from the bending vibration layer, only the stretching vibration is first driven to gradually increase the bending vibration voltage and control the input voltage to the bending vibration electrode. It becomes possible to operate from substantially 0V. As a result, it is possible to smoothly change the operating voltage to improve the followability of the instruction, improve the friction wear characteristics, and extend the life of the element.

  (2) Further, the ultrasonic motor of the present invention is characterized in that a ratio of the number of drive layers of the bending vibration layer to the number of drive layers of the stretching vibration layer is 1 or more and 9 or less. Thus, an ultrasonic motor that can be driven at a high speed can be realized by adjusting the lamination ratio of the stretching vibration and the bending vibration.

  (3) The ultrasonic motor of the present invention is characterized in that a ratio of the number of driving layers of the stretching vibration layer to the number of driving layers of the bending vibration layer is 1 or more and 9 or less. Thus, an ultrasonic motor that can be driven with a large thrust can be realized by adjusting the lamination ratio of the stretching vibration and the bending vibration.

  (4) Moreover, the driving method of the ultrasonic motor of the present invention is the above-described driving method of the ultrasonic motor, firstly applying a voltage to the stretching vibration layer and gradually increasing the applied voltage; Applying voltage to the flexural vibration layer after starting voltage application to the stretching vibration layer, and gradually increasing the applied voltage, and enabling smooth driving by the two steps. Yes. With such a driving method, the operating voltage can be changed smoothly to improve the frictional wear characteristics, and the life of the ultrasonic motor can be extended.

  According to the present invention, it is possible to smoothly change the operating voltage and improve the followability of the operation and the frictional wear characteristics.

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 carrying out the expansion-contraction primary vibration. It is a figure which shows a mode that the ultrasonic motor which concerns on this invention is carrying out the bending primary vibration. 1 is a perspective view of a piezoelectric vibrator according to the present invention. It is a graph which shows the relationship between the number ratio of each of a bending vibration layer and a stretching vibration layer, and speed versus thrust. (A) It is a top view which shows the electrode pattern on a bending vibration layer. (B) It is a top view which shows the pattern of a ground electrode. (C) It is a top view which shows the electrode pattern on an expansion-contraction vibration 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 this invention. It is a graph which shows the followability to the instruction | indication of a positioning device when drive adjustment is not carried out. It is a graph which shows the followability to the instruction | indication of the positioning device when drive adjustment is carried out. It is a graph which shows the change of the number of particles with respect to time when drive adjustment is not carried out. It is a graph which shows the change of the number of particles with respect to time when drive adjustment is carried out.

  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.

  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 sliding chip 2, and a rectangular laminated piezoelectric vibrator 1 in which piezoelectric layers and electrodes are alternately laminated is formed in a multiple vibration mode. It can be driven by vibrating. The piezoelectric vibrator 1 is made of rectangular laminated piezoelectric ceramics, and each layer is polarized in the thickness direction. In addition, a sliding tip 2 for transmitting a driving force is provided at the center of the end face in the y direction of the piezoelectric vibrator 1 in the drawing.

  FIG. 2 is a diagram illustrating a state in which the ultrasonic motor is performing primary expansion and contraction vibrations. As shown in FIG. 2, the expansion / contraction direction when the piezoelectric vibrator 1 vibrates in the expansion / contraction primary vibration mode is parallel to the direction of the arrow A 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 (shearing direction) when the piezoelectric vibrator 1 vibrates in the bending primary vibration mode is parallel to the arrow A shown in FIG. 2, but as shown in FIG. The directions are opposite to each other at both ends of the child 1. By combining (degenerate) the expansion / contraction primary vibration mode shown in FIG. 2 and the bending primary vibration mode shown in FIG. 3, the sliding tip 2 performs an elliptical motion, and a driving force is generated.

  FIG. 4 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 piezoelectric vibrator 1 includes a bending vibration layer 3a and a stretching vibration layer 3b. The bending vibration layer 3a is driven by bending primary vibration. The stretchable vibration layer 3b is stacked in parallel with the bending vibration layer and is driven by the stretchable primary vibration. Thus, the piezoelectric vibrator 1 is configured such that the stretching vibration layer 3b is a separate layer independent of the bending vibration layer 3a. Therefore, only the stretching vibration is first driven by the stretching vibration layer 3b, the bending vibration voltage is gradually increased, and the input voltage to the bending vibration electrode can be controlled to operate from substantially 0V. As a result, it is possible to smoothly change the operating voltage to improve the followability of the instruction, improve the friction wear characteristics, and extend the life of the element.

  As shown in FIG. 4, the piezoelectric vibrator 1 has a multilayer structure with respect to the flexural vibration layer 3a and the stretching vibration layer 3b. However, a single layer structure may be arranged in parallel. The expansion / contraction direction when the piezoelectric vibrator 1 vibrates in the expansion / contraction primary vibration mode is parallel to the x-axis. Further, the shear direction when the piezoelectric vibrator 1 vibrates in the bending primary vibration mode is parallel to the y-axis.

  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 can change the ratio of the number of drive layers of each vibration layer according to the application. FIG. 5 is a graph showing the relationship between the number ratio of each of the bending vibration layer and the stretching vibration layer and the speed versus thrust. The relationship shown in FIG. 5 can be calculated by simulation.

  As shown in FIG. 5, for example, when the ratio of the number of driving layers of the bending vibration layer 3a to the number of driving layers of the stretching vibration layer is 1 or more and 9 or less, the influence of the bending vibration layer 3a is large, An ultrasonic motor that can be driven at a speed can be realized. On the other hand, when the ratio of the number of drive layers of the stretchable vibration layer 3b to the number of drive layers of the bending vibration layer is 1 or more and 9 or less, the influence of the stretchable vibration layer 3b is large, and ultrasonic waves that can be driven with a large thrust. The motor 10 can be realized. Thus, by adjusting the lamination ratio of the stretching vibration and the bending vibration, a desired speed and thrust can be obtained.

  FIG. 6A is a plan view showing the electrode pattern F1 on the bending vibration layer. The drive electrodes 4a and 4b are each equally divided into approximately half the area of the main surface. And it has the extraction part exposed to the side surface of the piezoelectric vibrator 1, respectively. For example, a predetermined alternating voltage is applied to the drive electrode 4a, and a voltage whose phase is different from the applied voltage to the drive electrode 4a by π / 2 is applied to the drive electrode 4b.

  FIG. 6B is a plan view showing the ground electrode pattern GND. When an electric field is generated between the ground electrode 4c and the drive electrodes 4a, 4b, or 4d, the piezoelectric layer 1b therebetween is displaced. FIG. 6C is a plan view showing the electrode pattern L1 on the stretching vibration layer. The drive electrode 4d is formed in a rectangular shape over the entire surface.

  The drive electrodes 4a, 4b, and 4d are connected to input terminals by external electrodes. The ground electrode 4c is connected to the ground terminal by an external electrode. By using 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 reduced. For example, the same voltage as that of the drive electrode 4a is applied to the drive electrode 4d.

  FIG. 7 is a diagram showing wiring for electrodes on the drive layer of the ultrasonic motor 10. As shown in FIG. 7, in the ultrasonic motor 10, the drive electrode 4a and the drive electrode 4b are provided on the drive layer so that one main surface of the rectangular piezoelectric layer 1b is divided into two. 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 a state of being insulated from 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 4d. As shown in FIG. 2, the vibration of the expansion / contraction primary vibration mode that expands and contracts in the longitudinal direction is generated.

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 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 shown in FIG. In addition, a bending primary vibration mode that bends in the width direction (shear direction) is generated.

When the resonance frequency of the expansion / contraction primary vibration mode is equal to the resonance frequency of the bending primary vibration mode, both vibration modes are combined (degenerate), and elliptical vibration is generated in the chip of the piezoelectric vibrator 1. The voltages V ₀ sin ωt and V ₀ cos ωt correspond to the first AC voltage and the second AC voltage, respectively. There is no problem even if the two are interchanged.

In the above example, the configuration of the two-phase signal input is described for the bending primary vibration mode, but the configuration of the one-phase signal input may be adopted. In this case, it is also possible to operate by applying an AC signal of V ₀ sin ωt to one drive electrode 4a by the AC voltage source 5a and opening the other drive electrode 4b.

(Drive adjustment)
The following drive adjustment is particularly suitable for the ultrasonic motor 10. First, a voltage is first applied to the stretching vibration layer 3b, and the applied voltage is gradually increased. Then, after the voltage application to the stretching vibration layer 3b is started, a voltage is applied to the bending vibration layer 3a to gradually increase the applied voltage. In this way, smooth driving is possible by two steps. As a result, the operating voltage can be changed smoothly to improve the followability of the operation, improve the frictional wear characteristics, and extend the life of the ultrasonic motor 10.

Example 1
To produce a positioning device using the ultrasonic motor 10, it was for the tracking of the current value x test to indicated value x _0, the case of when the drive adjustment not driven adjustment in the above driving method. FIG. 8 is a graph showing the followability to the instruction of the positioning device when drive adjustment is not performed. As shown in FIG. 8, when not driven adjustment, an instruction value x ₀ and the current value x is likely to deviate, deviations Δx is large.

On the other hand, FIG. 9 is a graph showing the followability to the instruction of the positioning device when the drive is adjusted. As shown in FIG. 9, by performing the drive adjustment, the current value x for the indicated value x ₀ without causing little deviation Δx matches.

(Example 2)
Further, when the positioning device was continuously operated for a predetermined time between the case where the drive adjustment was not performed and the case where the drive adjustment was performed, there was a difference in the number of particles. FIG. 10 is a graph showing changes in the number of particles with respect to time when drive adjustment is not performed. The number of particles generated was recorded for each particle diameter. As shown in FIG. 10, when driving adjustment is not performed, particles are increased by driving for about 10 minutes.

  On the other hand, FIG. 11 is a graph showing changes in the number of particles with respect to time when drive adjustment is performed. In this case, no increase in the number of particles was observed despite the operation for 20 minutes or more.

  From the above examples, it was demonstrated that driving the ultrasonic motor 10 while adjusting the driving improves the followability to the instruction, prevents the generation of particles, and improves the durability.

DESCRIPTION OF SYMBOLS 1 Piezoelectric vibrator 1b Piezoelectric layer 2 Sliding tip 3a Bending vibration layer 3b Stretching vibration layer 4a, 4b Drive electrode 4c Ground electrode 4d Drive electrode 5a, 5b AC voltage source 10 Ultrasonic motor x Current value x ₀ Indication value Δx Deviation

Claims (4)

An ultrasonic motor for a positioning device that drives a rectangular laminated piezoelectric vibrator in which piezoelectric layers and electrodes are alternately laminated in a multiple vibration mode by applying a voltage,
A bending vibration layer having two electrodes and a ground electrode arranged side by side on the main surface , driven by bending primary vibration, and laminated in parallel to the bending vibration layer, and formed over the entire surface. A piezoelectric vibrator having an extended electrode and a ground electrode, and a stretching vibration layer driven by stretching primary vibration ;
A sliding chip that is provided on an end face of the piezoelectric vibrator and transmits a driving force to a driven body;
A first AC power source that applies a first AC voltage to vibrate the bending vibration layer with respect to one of the two electrodes;
A second alternating current that vibrates the bending vibration layer by applying a second alternating voltage having a phase difference of π / 2 with respect to the first alternating voltage to the other of the two electrodes. Power supply,
An ultrasonic motor comprising: a third AC power source that applies a voltage having the same phase as the first AC voltage to the electrode formed over the one surface to vibrate the stretchable vibration layer . An ultrasonic motor for a positioning device that drives a rectangular laminated piezoelectric vibrator in which piezoelectric layers and electrodes are alternately laminated in a multiple vibration mode by applying a voltage,
A bending vibration layer having two electrodes and a ground electrode arranged side by side on the main surface , driven by bending primary vibration, an electrode and a ground electrode formed over the main surface, and the bending A piezoelectric vibrator having a stretching vibration layer stacked in parallel with the vibration layer and driven by stretching primary vibration ;
A sliding chip that is provided on an end face of the piezoelectric vibrator and transmits a driving force to a driven body;
A first AC power source that applies a first AC voltage to vibrate the bending vibration layer with respect to one of the two electrodes;
A third AC power source that applies a voltage having the same phase as the first AC voltage to the electrode formed over the one surface to vibrate the stretchable vibration layer;
The ultrasonic motor, wherein the other electrode of the two electrodes is open . The expansion and contraction of the vibration layer of the driving layer number, the ratio of the driving layer number of the bending vibration layer, according to claim 1 or ultrasonic motor according to claim 2, wherein greater than one thing. A method for driving an ultrasonic motor according to any one of claims 1 to 3,
First, applying a voltage to the stretching vibration layer, gradually increasing the applied voltage,
Applying voltage to the flexural vibration layer after starting voltage application to the stretching vibration layer, and gradually increasing the applied voltage,
A driving method of an ultrasonic motor, characterized in that smooth driving is possible by the two steps.

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