JPH0870587A - Driving apparatus for ultrasonic motor - Google Patents

Abstract

PURPOSE: To provide a driving apparatus for ultrasonic motors wherein driving frequency is capable of being varied so that phase difference between voltage applied to a plurality of laminated piezoelectric elements and current passing through them will fall within a specified range, and being thereby optimized. CONSTITUTION: An ultrasonic motor includes an elastic body and an ultrasonic piezoelectric transducer composed of a plurality of laminated piezoelectric elements secured on the elastic body. A driving apparatus for ultrasonic motors moves a mobile body by applying a.c. voltages, different in phase from each other, to these laminated piezoelectric elements by means of a two-phase oscillator 1 and thereby generating ultrasonic oscillation. In the driving apparatus one of the plurality of the laminated piezoelectric elements 113A, 113B is selected according to the direction of the movement of the mobile body. The driving apparatus is provided with means 4, 5, 6, 7, 8, 9 for so controlling the frequency of a.c. voltage that phase difference between the a.c. voltage applied to a selected laminated piezoelectric element and current passing through the piezoelectric element will be a specified value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention applies an AC voltage to an electro-mechanical energy conversion element to generate ultrasonic vibration.
The present invention relates to a drive device for an ultrasonic motor using this as an energy source.

[0002]

2. Description of the Related Art Conventionally, regarding an ultrasonic motor for moving a moving body by applying an AC voltage to a plurality of electro-mechanical energy conversion elements fixed to an elastic body, an ultrasonic motor for moving a moving body has been previously described by the present applicant. Filed by JP-A-6-10557
The technology (conventional technology 1) described in the publication No. 1 is disclosed.

FIG. 8 is a perspective view of an ultrasonic transducer which is a mechanical-electrical energy conversion element which constitutes an essential part of the ultrasonic motor of the prior art 1. In this ultrasonic transducer 110, three holding elastic bodies 112 are fixed to the upper surface of a basic elastic body 111, and the laminated piezoelectric element 11 is provided between the holding elastic bodies 112.
3A and 113B are sandwiched and fixed.

The basic elastic body 111 is formed by processing a brass material into a rectangular parallelepiped shape, and has three parts (2
The elastic body 11 for holding is provided at the portion corresponding to the node of the next bending vibration).
2 is fixed with epoxy adhesive and screw 114
I have stopped. Then, the laminated piezoelectric elements 113A and 113B are abutted and held between the respective holding elastic bodies 112. That is, the laminated piezoelectric elements 113A and 113B are arranged so that the holding elastic body 11 does not come into contact with the basic elastic body 111.
It is adhesively fixed to 2. In addition, the laminated piezoelectric element 113
The side surfaces of A and 113B are resin-coated. Here, the electrodes to the laminated piezoelectric element 113A on the left side of FIG. 8 are referred to as A and G and are referred to as A phase. Similarly, electrodes to the laminated piezoelectric element 113B on the right side are referred to as B and G and are referred to as B phase.

Sliding members 115 are adhered to both ends of the bottom surface of the basic elastic body 111. The sliding member 115 is made of polyimide mixed with carbon fiber (20% by weight) and mica (30% by weight) as a filler, and has a thickness of about 0.1 mm.

Incidentally, referring to the specifications of the ultrasonic transducer 110, the dimensions of the basic elastic body 111 are 30 mm in width and 8 m in height.
The length of the holding elastic body 112 is 4 m.
m, height 3 mm, depth 4 mm, laminated piezoelectric element 113
Is NL-2 × 3 × 9 from Tokin Co., Ltd., and the size is 2 mm ×
It is 3.1 mm x 9 mm.

Next, the operation of the ultrasonic transducer will be described. According to the computer simulation, the ultrasonic transducer having the above dimensions can excite the primary resonant longitudinal vibration as shown in FIG. 9 and the secondary resonant bending vibration as shown in FIG. 10 at substantially the same frequency. Its frequency is 53.5 kHz
Is. Therefore, a direct current voltage of 30 V is applied to the A phase and the B phase to apply compression preload to the laminated piezoelectric elements 113A and 113B, and the A phase and the B phase have a frequency of 53.5 kHz and an amplitude of 1
An alternating voltage of 0 Vp-p is applied. Here, if the phases of the A phase and the B phase are made to be the same phase, primary resonant longitudinal vibration as shown in FIG. 9 is excited. Next, when the phases of the A phase and the B phase are made opposite to each other, secondary resonant bending vibration as shown in FIG. 10 is excited. Next, by shifting the phases of the A phase and the B phase by 90 degrees, ultrasonic elliptical vibration can be excited near the sliding member 115.

By the ultrasonic elliptical motion excited on the sliding member 115, the moving body in contact therewith is moved. The moving direction of the moving body is changed by setting the phase difference between the voltages applied to the electrodes A phase and B phase of the laminated piezoelectric elements 113A and 113B to +90 degrees or -90 degrees.

According to the prior art 1, since the piezoelectric longitudinal effect is utilized by using the laminated piezoelectric element, the electromechanical conversion efficiency is improved and the low voltage driving becomes possible. Further, it is possible to obtain an ultrasonic linear motor having a large output with a very simple structure and being compact, and since the laminated piezoelectric element is used while being preloaded, the durability of the motor can be improved.

On the other hand, in order to optimize the driving frequency of the ultrasonic motor, the AC voltage is controlled so that the phase difference between the voltage applied to the electro-mechanical energy conversion element and the current flowing therethrough falls within a predetermined range. A technique (prior art 2) disclosed in Japanese Patent Publication No. 5-38552 is disclosed as an ultrasonic motor device for controlling the frequency.

FIG. 11 is a functional block diagram of an ultrasonic motor device of the prior art 2. In the figure, 207 is a variable oscillator that generates an AC signal for driving the piezoelectric driver 203. The output of the variable oscillator 207 is divided into two, one of which is 9
After being 90 ° phase-shifted by the 0 ° phase shifter 208, the other is directly input to the power amplifiers 209 and 209 ′,
It is amplified to a predetermined level and applied to the piezoelectric driver 203.

R ₁ is a resistance element for detecting current,
Current detection is performed by the current detector 210 based on the voltage across the resistor R ₁ . At the same time, the voltage detector 211 detects the voltage applied to the piezoelectric ceramic forming the piezoelectric driver 203.
The outputs of the current detector 210 and the voltage detector 211 are output after being waveform-shaped into a logic level. Although the voltage / current of the output of the power amplifier 209 ′ is detected here, the same applies to the output of the power amplifier 209.

At the resonance frequency of the driver 203, the applied voltage and the current are in phase with each other, so that the driver 203 can be driven efficiently if it is driven in the vicinity of the frequency having the minimum phase difference. At this time, the motor speed is maximum.

[0014] 212 is an exclusive OR circuit output V ₂ of the output V ₁ and the voltage detector 211 of the current detector 210 is inputted (abbreviated as Ex-OR). FIG. 12 shows outputs V ₁ and V ₂
It is a chart figure which shows the relationship between the phase difference of (4) and the output of Ex-OR212. V ₃ is the output waveform of the Ex-OR 212, and V ₄ is the output of the rectifying circuit composed of the resistance element R ₂ and the capacitance element C ₂ . FIG. 12A shows the waveform of each part when the current waveform V ₁ and the voltage waveform V ₂ are in phase with each other, and the output V _{4 of the} rectifier circuit is zero. (B) is when the phases are out of phase, and the output V ₄ has a certain value instead of 0. That is, depending on the level of the output V _4, the piezoelectric driver 203
You can see the voltage / current phase difference.

A voltage comparator 213 in FIG. 11 compares the output V ₄ with the set voltage V _ref . Voltage comparator 213
When the output V ₄ is larger than the set voltage V _ref , the output of is at the logic level H, and at the opposite, it becomes L. When the allowable phase difference is determined, the corresponding set voltage V _ref is set, and when the output of the voltage comparator becomes H, the control circuit 214 is operated to change the output frequency of the variable oscillator 207 and the voltage comparator 13 Is controlled to be L, that is, the phase difference between the applied voltage and the current is smaller than the phase difference corresponding to the set voltage V _ref .

According to the prior art 2, the ultrasonic motor can be always driven in the vicinity of the resonance frequency even at the time of starting and during the operation, and at the time of the fluctuation of the temperature and the load, with the simple structure, so that the operation is stable. , Efficient.

[0017]

However, according to the experiment, in order to set the driving frequency of the ultrasonic transducer described in the prior art 1 to the optimum value, the voltage applied to the laminated piezoelectric element and the voltage applied to it are applied. When it is attempted to change the frequency so that the phase difference between the currents becomes a predetermined value, the phase difference between the current and the voltage is completely different between the two laminated piezoelectric elements.
Further, it was discovered that the phase difference between the current and the voltage is changed by reversing the moving direction of the moving body.

On the other hand, the circuit for detecting the phase difference between the voltage applied to the piezoelectric driving body and the current flowing therein according to the prior art 2 detects only one of the piezoelectric driving bodies and the other is the same. From the above experimental results, it is clear that it is difficult to determine the optimum driving frequency by detecting only one of the piezoelectric driving bodies.

The present invention has been made in view of the above conventional problems, and an object of the invention according to claim 1 or 2 is to provide a phase difference between a voltage applied to a plurality of laminated piezoelectric elements and a current flowing therethrough. So that it falls within a predetermined range, the ultrasonic frequency can be changed by changing the drive frequency.
It is to provide a drive device for a motor.

[0020]

In order to solve the above-mentioned problems, the invention according to claim 1 or 2 is an ultrasonic transducer comprising an elastic body and a plurality of laminated piezoelectric elements fixed to the elastic body. In the ultrasonic motor provided with, in the driving device of the ultrasonic motor for moving the moving body by applying alternating voltages having different phases to the plurality of laminated piezoelectric elements by a two-phase oscillator, generating ultrasonic vibrations, One is selected from the plurality of laminated piezoelectric elements according to the moving direction of the moving body, and applied so that the alternating voltage applied to the selected laminated piezoelectric element and the flowing current have a predetermined phase difference. It is characterized in that means for controlling the frequency of the AC voltage is provided.

[0021]

In the invention according to claim 1 or 2, one of a plurality of laminated piezoelectric elements is selected according to the moving direction of the moving body,
By controlling the frequency of the alternating voltage so that the alternating voltage applied to the selected laminated piezoelectric element and the flowing current have a predetermined phase difference, it is possible to keep the driving frequency of the ultrasonic motor in the optimum frequency range. Have. In addition to the above-mentioned action, the action of the invention according to claim 2 detects the phase difference between the voltage and the current by detecting the phase difference between the voltage and the current when the moving direction of the moving body is reversed in an extremely short time by the program of the microcomputer. The operation is stabilized by temporarily stopping the controlled operation and fixing the frequency immediately before that.

[0022]

Embodiment 1 FIGS. 1 to 5 show a first embodiment, FIG. 1 is a block diagram of a driving device for an ultrasonic motor, FIG. 2 is a front view of the ultrasonic motor, and FIGS. It is a chart which shows the waveform of the voltage and current of a phase. The ultrasonic oscillator 110 of the ultrasonic motor shown in FIG. 2 is the same as that of the conventional technique 1 shown in FIG. 8, and the same members are designated by the same reference numerals and the description thereof will be omitted. In the present embodiment, the moving body 20 that is in pressure contact with the sliding member 115 of the ultrasonic transducer 110 is movably held in the left-right direction by means (not shown) to form an ultrasonic motor.

In FIG. 1, reference numeral 1 denotes a two-phase oscillator for generating two-phase AC voltages having different phases by 90 degrees, one output of which is power-amplified by a power amplifier 2 and one of the laminated piezoelectric elements of the ultrasonic vibrator 110. Electric power is supplied to the electrode of the element 113A (hereinafter referred to as A phase). Further, the other output of the two-phase oscillator 1 is power-amplified by the power amplifier 3 and is supplied to the electrode (hereinafter referred to as B-phase) of the other laminated piezoelectric element 113B of the ultrasonic transducer 110. Detection resistors 8 and 9 for converting the current into a voltage are connected to both the A phase and the B phase.

The A-phase or B-phase voltage and current are input to the phase detector 4 by selecting one of the A-phase or B-phase by the switching means (FET, relay, analog switch, etc.) 6 and 7, respectively. Phase difference between current and current
Is converted into an electric signal for controlling the frequency of, and this electric signal is input to the frequency control terminal of the two-phase oscillator 1. The phase difference between the two outputs of the two-phase oscillator 1 is the switching means (FET,
+9 to each other by 5)
Switches to 0 degrees or -90 degrees. The three switch means 5, 6, 7 are switched in conjunction with each other.

3 to 5 show the measurement results of the voltage and current waveforms of the A and B phases. 3 shows a waveform at a frequency lower than the optimum drive frequency of the ultrasonic motor, FIG. 4 shows a waveform at the optimum drive frequency, and FIG. 5 shows a waveform at a frequency higher than the optimum drive frequency. In the case of the optimum drive frequency of FIG. 4, when the phase difference between the A phase voltage and the B phase voltage is +90 degrees, the phase difference between the A phase voltage and the current is several tens degrees, and the phase difference between the B phase voltage and the current is The phase difference is almost 0 degree. However, the phase difference between the A phase voltage and the B phase voltage is-
When the movement direction is reversed at 90 degrees, the phase difference between the A-phase voltage and current is approximately 0 degrees, while the phase difference between the B-phase voltage and current is several tens degrees. Further, in FIGS. 3 and 5, it can be seen that the phase difference between the voltage and the current is different from that in FIG.

From the above measurement results, it is understood that the optimum drive frequency can be obtained by controlling the frequency so that the phase difference between the voltage and the current of either the A phase or the B phase is approximately 0 degrees.
Further, at this time, when the moving direction of the moving body 20 changes, the phase in which the phase difference between the voltage and the current is substantially 0 degree is inverted between the A phase and the B phase, so that the phase for detecting the phase difference between the voltage and the current is changed. It will be necessary to change. According to the experiment, when the moving body 20 shown in FIG.
3A, it is known that the laminated piezoelectric element 113B should be selected when the moving body 20 moves to the left.

As is apparent from the above description, in the ultrasonic motor driving device shown in FIG. 1, the phase for detecting the phase difference between the voltage and the current is switched at the same time when the moving direction is switched,
When the frequency is controlled so that the phase difference becomes a predetermined value, the ultrasonic motor shown in FIG. 2 is driven at the optimum driving frequency.

The effects of this embodiment will be described. Depending on the moving direction of the moving body, either one of the two laminated piezoelectric elements of the ultrasonic motor is selected, and the frequency is controlled so that the phase difference between the voltage applied to this laminated piezoelectric element and the flowing current is within a predetermined range. By doing so, the AC voltage supplied to the ultrasonic motor can be automatically set to the optimum frequency.

In the measurement results of this embodiment, the optimum phase difference between the voltage and the current is approximately 0 degrees, but the optimum phase difference is not necessarily 0 degrees depending on the configuration of the motor. When there is a difference in electrical performance between the two laminated piezoelectric elements due to an error, it may be optimal to have a slight phase difference. Therefore, the predetermined phase difference is not limited to 0 degree, and it is desirable that the predetermined phase difference be adjustable.

[0030]

Second Embodiment FIGS. 6 to 7 show a second embodiment, FIG. 6 is a block diagram of an ultrasonic motor driving device, and FIG. 7 is a table showing a relationship between a target position and time. Also in this embodiment, the ultrasonic motor to be driven is the same as that shown in FIG. 2 of the first embodiment and shown in FIG.

In FIG. 6, reference numeral 21 is a two-phase oscillator for generating two-phase AC voltages having different phases by 90 degrees, one output of which is power-amplified by a power amplifier 22 and one of the laminated piezoelectric elements of the ultrasonic transducer 110. Electric power is supplied to the electrode of the element 113A (hereinafter referred to as A phase). The other output of the two-phase oscillator 21 is power-amplified by the power amplifier 23, and the ultrasonic transducer 1
Electric power is supplied to the electrode (hereinafter referred to as B phase) of the other laminated piezoelectric element 113B of 10. Detection resistors 28 and 29 for converting the current into a voltage are connected to both the A phase and the B phase.

The A-phase or B-phase voltage and current are input to the phase detector 4 by selecting one of the A-phase or B-phase by the switching means (FET, relay, analog switch, etc.) 26 and 27, respectively. And the phase difference of the current is converted into an electric signal. This phase difference signal is sent to the microcomputer 2
5, the microcomputer 25 can control the phase difference between the two outputs of the two-phase oscillator 21 to +90 degrees or −90 degrees based on the phase difference signal by the program, and change the phase difference. Sometimes, the two switch means 26, 27 are also switched.

Generally, when controlling a motor, closed-loop control is frequently performed using a movement amount detection sensor such as an encoder. Then, as shown in FIG. 7, the driving direction (moving direction) is controlled so that the moving amount increases with respect to the target position when the moving amount is insufficient and decreases when the moving amount is too large. Therefore, as shown in FIG. 7, a phenomenon in which the driving direction (moving direction) of the motor is frequently reversed can occur near the target position.

By the way, this phenomenon also occurs in the case of the first embodiment, and when the phase of the laminated piezoelectric element for detecting the phase difference between the voltage and the current is switched, a predetermined frequency is maintained until the frequency becomes stable at the switching moment. Takes time. Further, also in the present embodiment, when the moving direction is frequently changed in a relatively short time, the phase of the laminated piezoelectric element is switched to change the voltage-
If the frequency is controlled so that the current phase difference becomes a predetermined amount, it takes time until the frequency stabilizes, and the optimum drive frequency cannot be determined in a short time.

Therefore, in this embodiment, when the movement direction is reversed in a very short time, the program of the microcomputer 25 temporarily stops the operation of detecting the phase difference between the voltage and the current and controlling the frequency. Then, I decided to fix the frequency just before that. This stabilizes the operation of the ultrasonic motor. According to the experiment, it was confirmed that the change of the resonance frequency due to the heat generation of the ultrasonic motor does not pose a problem in a short time of about several seconds, and even if the drive frequency is fixed, it does not largely deviate from the optimum frequency. .

In this embodiment, frequency control can be programmed by a microcomputer, and when the moving direction of the moving body is reversed in a relatively short time as compared with the first embodiment, the voltage of the laminated piezoelectric element is not always required. It is not necessary to determine the frequency only by the phase difference between the current and the current, and even in the application where the moving direction is frequently changed like the positioning of the moving body shown in FIG. 7, the ultrasonic motor can be stably driven with the optimum driving frequency. Can be driven.

[0037]

According to the present invention, the driving frequency is changed so that the phase difference between the voltage applied to the plurality of laminated piezoelectric elements and the current flowing therethrough falls within a predetermined range. It is possible to provide a driving device for an ultrasonic motor having an optimum driving frequency. According to the invention of claim 2, in addition to the above effect, even in a case where the moving direction is frequently switched,
It is possible to stably drive the ultrasonic motor at an optimum drive frequency.

[Brief description of drawings]

FIG. 1 is a block diagram showing a drive device for an ultrasonic motor according to a first embodiment.

FIG. 2 is a front view showing the ultrasonic motor according to the first embodiment.

FIG. 3 is a table showing waveforms of voltage and current of A phase and B phase of the first embodiment.

FIG. 4 is a chart showing voltage and current waveforms of the A phase and B phase of the first embodiment.

FIG. 5 is a chart showing waveforms of voltage and current of A phase and B phase of the first embodiment.

FIG. 6 is a block diagram showing a drive device for an ultrasonic motor according to a second embodiment.

FIG. 7 is a table for explaining the operation of the second embodiment.

FIG. 8 is a perspective view showing an ultrasonic transducer of prior art 1.

FIG. 9 is a perspective view showing an operation of an ultrasonic transducer of prior art 1.

FIG. 10 is a perspective view showing an operation of the ultrasonic transducer of the related art 1.

FIG. 11 is a block diagram showing an ultrasonic motor device of prior art 2.

FIG. 12 is a chart diagram for explaining a voltage / current phase comparison unit according to Related Art 2;

[Explanation of symbols]

 1 Two-Phase Oscillator 2 Power Amplifier 3 Power Amplifier 4 Phase Detector 5 Switch Means 6 Switch Means 7 Switch Means 8 Detecting Resistor 9 Detecting Resistor 113A Multilayer Piezoelectric Element 113B Multilayer Piezoelectric Element

Claims (2)

[Claims] 1. An ultrasonic motor comprising an ultrasonic vibrator including an elastic body and a plurality of laminated piezoelectric elements fixed to the elastic body, and alternating voltages having different phases to the plurality of laminated piezoelectric elements. Is applied by a two-phase oscillator to generate ultrasonic vibrations to move the moving body. In the driving apparatus of the ultrasonic motor, one is selected from the plurality of laminated piezoelectric elements according to the moving direction of the moving body. A driving device for an ultrasonic motor comprising means for controlling the frequency of the applied AC voltage so that the AC voltage applied to the selected laminated piezoelectric element and the flowing current have a predetermined phase difference. . 2. The means for controlling the frequency of the applied AC voltage selects one of the plurality of laminated piezoelectric elements and a detection resistor for converting a current flowing through the plurality of laminated piezoelectric elements into a voltage. 2. The ultrasonic motor according to claim 1, further comprising: switch means for switching, a phase detector connected to the switch means, a two-phase oscillator, a microcomputer connected to the switch means and the phase detector. Drive.