JP2012120300A - Driving circuit and driving method of ultrasonic motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving circuit and a driving method of an ultrasonic motor, capable of dispersing timings of driving piezoelectric elements, to prevent variation in speed and effect of external force to smoothly move a driven body.SOLUTION: The driving circuit for an ultrasonic motor 101 provided with a plurality of piezoelectric elements 102 to be separately driven in an elliptic orbit in parallel along a driving direction includes a control voltage generating part 108 which generates a control voltage of pulse wave being deviated in phase for each of the piezoelectric elements 102, and a drive voltage applying part 109 which applies a drive voltage based on the control voltage. By this configuration, driving timings of the piezoelectric elements 102 are dispersed, to prevent variation in speed and effect of external force, for smoothly moving a driven object 107. Even under such condition as an external force is applied to the driven body 107, the timings at which effect is applied on the driven body 107 are dispersed, for smooth driving at a stable speed.

Description

  The present invention relates to a driving circuit and a driving method of an ultrasonic motor having a plurality of piezoelectric elements that drive a driven body by friction driving.

  The ultrasonic motor performs an expansion / contraction motion, a flexure motion, and the like by applying an AC voltage having a specific resonance frequency. In driving, a control voltage is applied from the outside to the driver as a direct current, and an alternating voltage output from the driver is applied as a drive voltage to the ultrasonic motor. This makes it possible to move and control a driven body such as a stage.

  The ultrasonic motor device described in Patent Document 1 includes an L1B4 type motor having two vibrators, a phase control device that shifts the phase of the drive voltage output from each power supply, a vibrator that holds a vibrator, And a preload mechanism that is pressed by force. Then, the phases of the two types of drive voltages output from each power source are changed, and the moving speed of the moving element is changed according to the phase difference.

JP 2004-88815 A

  However, the ultrasonic motor device described in Patent Document 1 applies a driving voltage to each piezoelectric element and controls the phase to cause resonance in the vicinity of the L1B4 mode, and each piezoelectric element is driven by an independent elliptical orbit. Not what you want. Therefore, on the premise that each piezoelectric element is driven with a predetermined phase difference, the movement speed can only be controlled by finely adjusting the phase.

  On the other hand, an ultrasonic motor is known in which a plurality of piezoelectric elements that are independently driven in an elliptical orbit are provided in parallel in the driving direction. Such an ultrasonic motor applies a pulsed control voltage to each piezoelectric element, and drives them with the same phase. The example of FIG. 8 shows a case where the drive voltage is driven by driving three piezoelectric elements with the control voltage being pulsed. 8 shows the speed of the driven body when the ultrasonic motor is driven with a pulsed control voltage.

  However, when the drive voltage is applied as in the example shown in FIG. 8, the driven body repeatedly accelerates, constant speed, decelerates, and stops, causing uneven speed. Thus, when the phase of the drive voltage applied to each piezoelectric element is equal, the contact point between the driven body and the piezoelectric element is simultaneously separated by all the piezoelectric elements, and the friction force of the driven body and the ultrasonic motor is fluctuated. It causes uneven speed. Further, when an external force is applied to the driven body, the driven body can be moved by the external force at the moment when the piezoelectric element is separated from the driven body.

  The present invention has been made in view of such circumstances, and an ultrasonic motor capable of distributing the drive timing of each piezoelectric element, preventing unevenness in speed and the influence of external force, and moving the driven body smoothly. An object of the present invention is to provide a driving circuit and a driving method.

  (1) In order to achieve the above object, an ultrasonic motor drive circuit according to the present invention is an ultrasonic motor drive circuit in which a plurality of piezoelectric elements independently driven in an elliptical orbit are provided in parallel in the drive direction. And a control voltage generation unit that generates a pulsed control voltage with a phase shifted for each piezoelectric element, and a drive voltage application unit that applies a drive voltage based on the control voltage.

  As a result, the driving timing of each piezoelectric element can be dispersed, the speed unevenness and the influence of external force can be prevented, and the driven body can be moved smoothly. Even when an external force is applied to the driven body, the timing at which the drag force is applied to the driven body can be dispersed and the drive can be smoothly performed at a stable speed.

  (2) Further, in the drive circuit for an ultrasonic motor according to the present invention, the control voltage generator applies a drive voltage to one of the piezoelectric elements at any time, and simultaneously to the other one. The control voltage is generated so as to stop the application of the drive voltage.

  Thereby, since any one of the piezoelectric elements is always stopped and the sliding tip is in contact with the driven body, a phenomenon that the driven body is moved by an external force can be prevented. Further, since all the piezoelectric elements are not turned ON / OFF at the same time, the driven body does not repeat large fluctuations in acceleration, constant speed, deceleration, and stop, and uneven speed can be prevented. Therefore, even when an external force is applied to the driven body, a uniform force is applied to the driven body, and the driven body can be smoothly driven at a stable speed.

  (3) Further, in the ultrasonic motor drive circuit of the present invention, the control voltage generation unit generates the control voltage by equalizing the phase difference of the pulsed control voltage shifted for each piezoelectric element. It is said. Thereby, a uniform force is applied to the driven body, and the driven body can be driven smoothly at a stable speed. The driving timing of each piezoelectric element due to the phase difference has an allowable range corresponding to 10 wavelengths of the resonance frequency of the piezoelectric element. In order to make the progress of wear uniform for each piezoelectric element, it is desirable that the phase difference of the pulsed control voltage shifted for each piezoelectric element is uniform.

  (4) In the ultrasonic motor drive circuit according to the present invention, the control voltage generation unit generates a control voltage so that a time average is constant for the plurality of piezoelectric elements. Thereby, it can drive smoothly at a stable speed. Further, the progress of wear for each piezoelectric element can be made uniform.

  (5) The ultrasonic motor driving method of the present invention is an ultrasonic motor driving method in which a plurality of piezoelectric elements that are independently driven in an elliptical orbit are provided in parallel in the driving direction, and each piezoelectric element has a phase. The drive voltage output by the pulsed control voltage shifted is applied.

  As a result, the driving timing of each piezoelectric element can be dispersed, the speed unevenness and the influence of external force can be prevented, and the driven body can be moved smoothly. Even when an external force is applied to the driven body, the timing at which the drag force is applied to the driven body can be dispersed and the drive can be smoothly performed at a stable speed.

  According to the present invention, the driving timing of each piezoelectric element can be dispersed, speed unevenness, the influence of external force can be prevented, and the driven body can be moved smoothly.

It is a block diagram which shows the drive circuit of the ultrasonic motor which concerns on 1st Embodiment. It is a perspective view which shows the ultrasonic motor used for 1st Embodiment. It is a perspective view which shows arrangement | positioning with an ultrasonic motor and a to-be-driven body. It is a figure which shows the pulse pattern and driven body speed of 1st Embodiment. It is the schematic which shows the pulse width by the drive method of the ultrasonic motor which concerns on 1st Embodiment, and its space | interval. It is a block diagram which shows the drive circuit of the ultrasonic motor which concerns on 2nd Embodiment. It is a perspective view which shows the ultrasonic motor used for 3rd Embodiment. It is a perspective view which shows arrangement | positioning with an ultrasonic motor and a to-be-driven body. It is a block diagram which shows the drive circuit of the ultrasonic motor of 4th Embodiment. It is a figure which shows the pulse-shaped control voltage and driven body speed of a prior art.

  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 block diagram showing an ultrasonic motor drive circuit 100. As shown in FIG. 1, the drive circuit 100 includes a control voltage generation unit 108 and a drive voltage application unit 109, and the control voltage generation unit 108 further includes a pulse generation unit 111. With such a configuration, the drive circuit 100 drives the ultrasonic motor 101. The ultrasonic motor 101 includes three piezoelectric elements 102.

  The pulse generator 111 generates a pulsed control voltage with an individual phase for each piezoelectric element 102. At that time, the phase of each piezoelectric element 102 is shifted and generated. The control voltage generation unit 108 generates pulsed control voltages Vca to Vcc using the generated pulsed control voltage, and outputs the generated voltage to the drive voltage application unit 109. As will be described later, the phase can be adjusted by providing a phase circuit in the drive voltage application unit 109. However, it is easier to control the phase by the pulse generation unit 111 and the circuit configuration is complicated. This is preferable because it is not necessary.

  The control voltage generator 108 preferably applies the drive voltage to one of the piezoelectric elements 102 and stops applying the drive voltage to the other one at any time. As a result, one of the piezoelectric elements 102 is always stopped, and at the same time, the sliding tip 103 (sliding protrusion) is in contact with the driven body 107, so that the driven body 107 can be prevented from moving due to an external force. In addition, since all the piezoelectric elements 102 are not turned ON / OFF at the same time, the driven body 107 does not repeat large fluctuations in acceleration, constant speed, deceleration, and stop, and can prevent uneven speed. Therefore, even when an external force is applied to the driven body 107, a uniform force is applied to the driven body 107, and the driven body 107 can be driven smoothly at a stable speed.

  The control voltage generator 108 preferably generates the control voltage by equalizing the phase difference between the pulsed control voltages shifted for each piezoelectric element 102. Thereby, a uniform force is applied to the driven body 107, and the driven body 107 can be driven smoothly at a stable speed. The driving timing of each piezoelectric element due to the phase difference has an allowable range corresponding to 10 wavelengths of the resonance frequency of the piezoelectric element. In order to make the progress of wear uniform for each piezoelectric element, it is desirable that the phase difference of the pulsed control voltage shifted for each piezoelectric element is uniform.

  In addition, the control voltage generation unit 108 generates a control voltage so that the time average of the plurality of piezoelectric elements 102 is constant. Thereby, it can drive smoothly at a stable speed. Further, the progress of wear for each piezoelectric element 102 can be made uniform.

  The drive voltage application unit 109 is configured as a single unit with respect to all the piezoelectric elements 102, generates the drive voltages Vda to Vdc based on the pulsed control voltages Vca to Vcc, and applies them to each piezoelectric element 102. To do. The piezoelectric elements 102 expand and contract by the application of the drive voltages Vda to Vdc, and the ultrasonic motor 101 is driven.

  FIG. 2A is a perspective view showing the ultrasonic motor 101. The ultrasonic motor 101 is incorporated so that two or more rectangular piezoelectric elements 102 are arranged inside the inner case 105 with a certain space therebetween. Specifically, a plurality of piezoelectric elements 102 that are independently driven in an elliptical orbit are provided in the inner case 105 in parallel in the driving direction. One or more drive electrodes are formed on one surface of the main surface of the piezoelectric element 102, and a common electrode held at the ground potential is formed on the other surface of the main surface. A sliding chip 103 is bonded to the side surface 104 of the piezoelectric element 102 with an epoxy resin adhesive. Here, in order to firmly bond the piezoelectric element 102 and the sliding chip 103, it is preferable to use an epoxy resin adhesive having a high adhesive strength.

  FIG. 2B is a perspective view showing the arrangement of the ultrasonic motor 101 and the driven body 107. The sliding chip 103 is preferably made of a ceramic having high hardness such as alumina in order to prevent generation of wear powder due to contact with the driven body 107. The inner case 105 is incorporated in the outer case 106, and the inner case 105 incorporating the piezoelectric element 102 is pressed by a preload mechanism (not shown) between the back surface of the inner case 105 and the outer case 106, so that the sliding chip 103 is pressed. The tip part contacts the driven body.

  When a driving voltage such as a sine wave is applied to the driving electrode of the piezoelectric element 102, the piezoelectric element 102 is driven and the tip of the sliding tip 103 moves elliptically. Thus, the driven body 107 that is in contact with the tip of the sliding chip 103 moves in the same direction as the driving direction of the piezoelectric element 102. The drive electrode is connected to a drive voltage application unit 109 (not shown).

  In FIG. 2A, three piezoelectric elements 102 are incorporated in the ultrasonic motor 101. In the ultrasonic motor 101 shown in FIG. 2A, two piezoelectric elements 102 are driven (ON) while one piezoelectric element 102 is stopped (OFF) while the control voltage is pulsed and the phase is shifted for each piezoelectric element. A state to be generated is sequentially generated for each piezoelectric element. Therefore, even when an external force is applied to the driven body 107, a uniform force is applied to the driven body 107, and the driven body 107 can be driven smoothly at a stable speed. In addition, since the three piezoelectric elements 102 are not turned ON / OFF at the same time, uneven speed can be prevented. Even when an external force is applied to the driven body 107, a uniform force is applied to the driven body, and the driven body 107 can be driven smoothly at a stable speed.

  FIG. 3 shows an example of the speed of the driven body 107 when the ultrasonic motor 101 is driven with a pulsed control voltage. This is an example in which three piezoelectric elements 102 are driven with the control voltage being pulsed and shifted, and the driven body 107 is driven. By inputting the pulse-like control voltage by shifting each piezoelectric element 102, the drive voltage applied to each piezoelectric element 102 is also shifted, creating a state where there is a constant drive and a stop. Accordingly, even when an external force is applied to the driven body 107, a uniform force is applied to the driven body 107, and the driven body 107 can be driven smoothly at a stable speed.

  FIG. 4 is a schematic diagram showing pulse widths and intervals according to the driving method of the ultrasonic motor. The application time t of the driving voltage for driving the piezoelectric element 102 is preferably 5 ms or more. In order to generate such a drive voltage, the application time of each control voltage needs to be 5 ms or more. Further, the time for which each piezoelectric element 102 is stopped is obtained by t / (n-1) where n is the number of piezoelectric elements 102. Also, the shifting interval is t / (n-1). Thereby, the drive and stop of the piezoelectric element 102 are controlled at regular intervals.

[Second Embodiment]
In the above-described embodiment, the drive voltage application unit 109 is configured as a single unit, but may be configured as a plurality according to the number of piezoelectric elements 102. FIG. 5 is a block diagram showing an ultrasonic motor drive circuit 200.

  In the ultrasonic motor drive circuit 200, a plurality of drive voltage application units 209 drive the plurality of piezoelectric elements 102 using a pulsed control voltage. A control voltage generation unit 108 having a pulse generation unit 111 inputs pulsed control voltages Vca to Vcc whose phases are shifted to the drive voltage application units 209. And according to each control voltage Vca-Vcc, each drive voltage application part 209 outputs drive voltage Vda-Vdc, and each piezoelectric element 102 expands and contracts and drives.

[Third Embodiment]
In the above embodiment, the ultrasonic motor 101 includes the three piezoelectric elements 102, but may include two. FIG. 6A is a perspective view showing the ultrasonic motor 301. FIG. 6B is a perspective view showing the arrangement of the ultrasonic motor 301 and the driven body 107.

  The basic structure of the ultrasonic motor 301 is the same as that of the ultrasonic motor 101, but the ultrasonic motor 301 incorporates three piezoelectric elements 102, whereas the ultrasonic motor 201 has two piezoelectric elements. Element 102 is incorporated. The inner case 305 is formed to accommodate the two piezoelectric elements 102, and the outer case 306 is formed to accommodate the inner case 305. In the ultrasonic motor 201, an ON / OFF operation in which one piezoelectric element 102 is driven (ON) and the other piezoelectric element 102 is stopped (OFF) by shifting the control voltage in a pulse-like manner for each piezoelectric element. Create a state in which to perform alternately. Accordingly, one of the piezoelectric elements 102 is always stopped, and the sliding tip 103 is in contact with the driven body, so that the driven body 107 can be prevented from moving due to an external force.

[Fourth Embodiment]
In the above embodiment, the control voltage generation unit 408 controls the phase of the control voltage, but the phase may be controlled by a phase circuit. FIG. 7 is a block diagram showing the drive circuit 400 of the ultrasonic motor 101. The ultrasonic motor 101 includes a piezoelectric element 102, and drives a plurality of piezoelectric elements 102 by changing the phases of the drive voltages Vda to Vdc. The control voltage is applied as a direct current, and the phase of the drive voltage applied to each piezoelectric element 102 is changed by the phase circuit 410 inside the drive voltage application unit 409, and the expansion / contraction timing of each piezoelectric element 102 is shifted.

  In the case where the three piezoelectric elements 102 are incorporated in the ultrasonic motor 101, the timing of expansion / contraction of each piezoelectric element 102 is shifted by shifting the phase of each drive voltage to the three piezoelectric elements 102 by 120 °, and the frictional force By reducing the fluctuation, the constant speed performance is improved and the driven body 107 can be driven smoothly even when an external force is applied.

DESCRIPTION OF SYMBOLS 100 Drive circuit 101 Ultrasonic motor 102 Piezoelectric element 103 Sliding chip | tip (sliding protrusion)
104 Side surface of piezoelectric element 105 Inner case 106 Outer case 107 Driven body 108 Control voltage generation unit 109 Drive voltage application unit 111 Pulse generation unit 209 Drive voltage application unit 301 Ultrasonic motor 305 Inner case 306 External case 400 Drive circuit 408 Control voltage Generation unit 409 Drive voltage application unit 410 Phase circuit

Claims (5)

A drive circuit for an ultrasonic motor in which a plurality of piezoelectric elements that are independently driven in an elliptical orbit are provided in parallel in the drive direction,
A control voltage generator for generating a pulsed control voltage with a phase shifted for each piezoelectric element;
A drive circuit for an ultrasonic motor, comprising a drive voltage application unit that applies a drive voltage based on the control voltage.   The control voltage generation unit generates the control voltage so as to stop the application of the drive voltage to the other one at the same time as applying the drive voltage to one of the piezoelectric elements at any time. 2. The drive circuit for an ultrasonic motor according to claim 1, wherein   The ultrasonic motor drive according to claim 1, wherein the control voltage generation unit generates the control voltage by equalizing a phase difference between the pulsed control voltages shifted for each of the piezoelectric elements. circuit.   4. The ultrasonic motor drive circuit according to claim 1, wherein the control voltage generation unit generates a control voltage so that a time average is constant for the plurality of piezoelectric elements. 5. . A method of driving an ultrasonic motor in which a plurality of piezoelectric elements that are independently driven in an elliptical orbit are provided in parallel in a driving direction,
A driving method of an ultrasonic motor, wherein a driving voltage is applied with a pulsed control voltage whose phase is shifted for each piezoelectric element.

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