JPH06101940B2 - Ultrasonic motor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ultrasonic motor having an elastic body and a piezoelectric body that excites the elastic body.

(Prior Art) As a conventional ultrasonic motor, in order to obtain an efficient drive, for example, as shown in FIG. 4, the voltage values of two AC signals input to a piezoelectric body are made equal to each other. Some are in control.

That is, in the conventional example shown in FIG. 4, the first AC signal is applied to the electrode 2a of the piezoelectric body 2 forming a part of the ultrasonic motor 1 via the oscillator 3, the sine wave generator 4a and the amplifier 5a. It is inputted to the electrode 2b of the piezoelectric body 2 via the oscillator 3, the sine wave generator 4b and the amplifier 5b, and is separated from the first AC signal by π.
The second AC signal with a phase difference of / 2 is input,
A voltage for detecting and comparing the voltage of the first AC signal input to the electrode 2a from one end A of the coil 6a and the voltage of the second AC signal input to the electrode 2b from one end B of the coil 6b. The voltage comparison circuit 7 is provided with a comparator circuit 7, and the voltage comparison circuit 7 is an amplifier so that the potential at the one end A and the potential at the one end B become equal.
5a and 5b are controlled so that the voltage values of the two AC signals input to the electrodes 2a and 2b are controlled to be equal to each other.

(Problems to be Solved by the Invention) However, in such a conventional ultrasonic motor,
The impedances of the respective piezoelectric portions of the electrodes 2a and 2b inevitably differ from each other in manufacturing, and as a result, even if the voltage values of the two AC signals input to the electrodes 2a and 2b are controlled to be equal to each other, the piezoelectric body The magnitude of the current flowing through the electrode 2 is 2a
Is different from the part of the electrode 2b, and as shown in FIG. 5, when the current flowing through the piezoelectric body 2 is large,
Because of the characteristic of the piezoelectric body that the generated ultrasonic vibration is also large, the amplitude of the ultrasonic vibration generated at each piezoelectric body portion of the electrodes 2a and 2b is different. For example, as shown in FIG. 3, it is assumed that a standing wave 30a having an amplitude α is generated in the piezoelectric portion of the electrode 2a and a standing wave 30b having an amplitude α / 2 is generated in the piezoelectric portion of the electrode 2b.

It should be noted that FIG. 3 shows the generation of surface waves over time, with the horizontal axis representing the phase and the vertical axis representing the amplitude α.
The surface wave 30 is a combination of a waveform 30a of ultrasonic vibration generated in the piezoelectric portion of the electrode 2a and a waveform 30b of ultrasonic vibration generated in the piezoelectric portion of the electrode 2b. Further, FIG. 3 (a) shows a state at a certain time T = 0 °, and FIG. 3 (b) shows a state at a time T = 45 °, which is 1/8 cycle after the time T = 0 °. In FIG. 3 (c), time T = 90 when time has elapsed by 1/4 cycle from time T = 0 °
FIG. 3 (d) shows the state at time T = 135 ° after 3/8 cycles have elapsed from the time T = 0 °.
FIG. 6E shows a state at time T = 180 °, which is a time period corresponding to 1/2 cycle from time T = 0 °. Third
The figure (a) shows a standing wave 30a of amplitude α in the piezoelectric portion of the electrode 2a.
Is generated and a standing wave 30b having an amplitude of 0 is generated in the piezoelectric portion of the electrode 2b.
Is generated, and this composite wave 30 is the standing wave 30a.
Is equal to FIG. 3 (b) shows a state in which T = 45 ° has elapsed and the phase is shifted by 45 ° from the state of FIG. 3 (a), and a standing wave of amplitude α is applied to the piezoelectric portion of the electrode 2a. 30a is generated and the standing wave 30b having the amplitude α / 2 is generated in the piezoelectric portion of the electrode 2b, and the combined wave 30 is a combined wave of the standing wave 30a and the standing wave 30b. is there. FIG. 3 (c) shows that T = 90 ° has elapsed and the phase is 90 ° from the state of FIG. 3 (a).
In this case, the standing wave 30a having an amplitude of 0 is generated in the piezoelectric body portion of the electrode 2a and the standing wave 30b having an amplitude of α / 2 is generated in the piezoelectric body portion of the electrode 2b. This composite wave 30 is equal to the standing wave 30b. The same applies to FIGS. 3 (d) and 3 (e).

Therefore, in the above conventional ultrasonic motor, the electrodes 2a, 2
As shown in FIGS. 3 (a) to 3 (e), the surface wave generated by the combination of the ultrasonic vibrations generated in each piezoelectric body portion of b is time T
At the same time, the propagation velocity and the amplitude α change, which makes the contact between the elastic body and the rotor pressed against the elastic body incomplete, which makes the operation of the ultrasonic motor unstable and reduces the efficiency. There was a problem that it did.

The present invention has been made in view of such conventional problems, and it is possible to generate a surface wave whose propagation velocity and amplitude are always constant, which improves efficiency and stability of operation. The purpose is to provide a sonic motor.

(Means for Solving Problems) The gist of the present invention for achieving such an object is to provide an elastic body, a piezoelectric body that excites the elastic body, and two alternating currents input to the piezoelectric body. In an ultrasonic motor including a detection unit that detects each current of a signal, a holding unit that holds a reference current value to be input to the piezoelectric body, and an amount related to each detection result of the detection unit and the An ultrasonic motor comprising: a control unit that compares the amount related to the reference current value of the holding unit and controls the current values of the two input AC signals to be substantially equal to each other. Exist.

(Operation) In the ultrasonic motor 1, the currents of the two alternating current signals h and i input to the piezoelectric body 2 are controlled by alternating current control means (current value comparison circuit 9).
a, 9b) so that a surface wave whose propagation velocity and amplitude are always constant is generated in the piezoelectric body 2.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. The same parts as those of the conventional example are designated by the same reference numerals.

1 and 2 show an embodiment of the present invention.

As shown in FIG. 1, the ultrasonic motor 1 has a stator composed of an elastic body (not shown) and a piezoelectric body 2 for exciting the elastic body, and a rotor (not shown) rotated by the stator. The surface wave is generated in the elastic body by the excitation of the piezoelectric body 2, and the rotor is rotated by the surface wave.

Electrodes 2a, 2b, 2c and 2d are formed on one surface of the piezoelectric body 2, and the drive system of the ultrasonic motor 1 is connected to the electrodes 2a, 2b.

The drive system of the ultrasonic motor 1 is an oscillator 3, a sine wave generator 4
a, 4b, amplifiers 50a, 50b, coils 6a, 6b, current value detection resistor 8a,
8b and current value comparison circuits 9a and 9b.

The oscillator 3 has first and second signals whose phases are different from each other by π / 2.
It outputs a and b.

The sine wave generators 4a and 4b synchronize with the first and second signals a and b, respectively.
The second sine wave signals c and d are output respectively.

The amplifiers 50a and 50b are configured to amplify the first and second sine wave signals c and d input to one input terminal and the amplification factor signals e and f input to the other input terminal.
The first and second AC signals h and i amplified in accordance with the above are respectively output.

One output terminal of the amplifier 50a is connected to the electrode 2a through the current value detecting resistor 8a, and the other output terminal is grounded to the electrode 2c.
Respectively connected to. Similarly, one output terminal of the amplifier 50b is connected to the electrode 2b via the current value detection resistor 8b, and the other output terminal is connected to the electrode 2c.

One end of the coil 6a is connected to the amplifier 50 via the resistor 8a for current value detection.
The other end of the coil 6a is connected to one output terminal of a and the other output terminal of the amplifier 50a. Similarly, one end of the coil 6b is connected to one output terminal of the amplifier 50b through the current value detecting resistor 8b, and the other end of the coil 6b is connected to the other output terminal of the amplifier 50b.

The current value comparison circuit 9a detects the terminal voltage of the current value detection resistor 8a, compares the current value converted from the detected voltage with a reference current value g, and outputs an amplification factor signal e corresponding to the comparison result. Is output to the other input terminal of the amplifier 50a. Similarly, the current value comparison circuit 9b detects the terminal voltage of the current value detection resistor 8b, compares the current value converted from the detected voltage with the reference current value g, and amplifies according to the comparison result. The rate signal f is output to the other input terminal of the amplifier 50b.

The operation will be described below.

The first and second signals that differ in phase by π / 2 from the oscillator 3
When a and b are output to the sine wave generators 4a and 4b, respectively, the sine wave generators 4a and 4b output the first and second sine wave signals c and d to the amplifiers 50a,
Output to one input terminal of 50b respectively.

As a result, a first AC signal h corresponding to the amplification factor signal e is output from one output terminal of the amplifier 50a, and the first AC signal h is transmitted through the current value detecting resistor 8a to the electrode 2a.
Flow into. Further, the second AC signal i corresponding to the amplification factor signal f is output from one output terminal of the amplifier 50b by a phase difference of π / 2 from the first AC signal h. The signal i flows into the electrode 2b through the current value detecting resistor 8b.

At this time, the current value comparison circuit 9a detects the terminal voltage of the current value detection resistor 8a, and converts the current value of the first AC signal h flowing into the electrode 2a converted from the detected terminal voltage to the reference current value. Compared with g, if the current value is larger than the reference current value g, it works to decrease the amplification factor signal e, and in the opposite case, it works to increase the amplification factor signal e.

Similarly, the current value comparison circuit 9b detects the terminal voltage of the current value detection resistor 8b, and converts the current value of the second AC signal i flowing into the electrode 2b converted from the detected terminal voltage into the reference current value. Compared with g, when the current value is larger than the reference current value g, the amplification factor signal f is decreased, and in the opposite case, the amplification factor signal f is increased.

Therefore, the current value flowing into the electrodes 2a, 2b is controlled to be the same as the reference current value g.

In this way, since a constant current, which is the same as the reference current value g, always flows through the electrodes 2a, 2b, the amplitude of the ultrasonic vibration generated in the piezoelectric body portion of the electrode 2a exceeds that generated in the piezoelectric body portion of the electrode 2b. It is always equal to the amplitude of sonic vibration.

Therefore, in the ultrasonic motor 1, as shown in FIGS. 2 (a) to 2 (e), the surface wave generated by the combination of the ultrasonic vibrations generated in the piezoelectric portions of the electrodes 2a and 2b is The amplitude is always constant, so that the contact between the elastic body (not shown) and the rotor pressed against the elastic body is complete, and stable operation and highly efficient driving can be obtained.

Here, FIG. 2 shows a state of generation of a surface wave over time, in which the horizontal axis represents the phase and the vertical axis represents the amplitude. The waveform 20a of ultrasonic vibration generated in the piezoelectric portion of the electrode 2a and the waveform 20b of ultrasonic vibration generated in the piezoelectric portion of the electrode 2a are combined. Further, FIG. 2 (a) shows a state at a certain time T = 0 °, and FIG. 2 (b) shows a state at a time T = 45 °, which is 1/8 cycle after the time T = 0 °. 2 (c) shows time T = 90 when time has elapsed by 1/4 cycle from time T = 0 °.
FIG. 2 (d) shows the state at time T = 135 °, which is the time when 3/8 cycles have elapsed from time T = 0 °.
FIG. 6E shows a state at time T = 180 °, which is a time period corresponding to 1/2 cycle from time T = 0 °. Second
The figure (a) shows a standing wave 20a of amplitude α in the piezoelectric portion of the electrode 2a.
And a standing wave 20b with zero amplitude is generated in the piezoelectric portion of the electrode 2b.
Is generated, and the composite wave 20 is the standing wave 20a.
Is equal to FIG. 2 (b) shows a state in which T = 45 ° has elapsed and the phase is shifted by 45 ° from the state of FIG. 2 (a), and a standing wave of amplitude α is applied to the piezoelectric portion of the electrode 2a. 20a is generated and a standing wave 20b having an amplitude α / 2 is generated in the piezoelectric body portion of the electrode 2b, and the composite wave 20 is a composite wave of the standing wave 20a and the standing wave 20b. is there. FIG. 2 (c) shows that T = 90 ° has elapsed from the state of FIG. 2 (a) and the phase is 90 °.
In this case, the standing wave 20a having an amplitude of 0 is generated in the piezoelectric portion of the electrode 2a and the standing wave 20b having an amplitude of α / 2 is generated in the piezoelectric portion of the electrode 2b. This composite wave 20 is equal to the standing wave 20b. The same applies to FIGS. 2 (d) and 2 (e).

It should be noted that in the above-described embodiment, an alternating current that detects the currents of the two alternating current signals h, i input to the piezoelectric body 2 and controls the currents of the two alternating current signals h, i so that the current values become equal to each other. The current control means is composed of current value comparison circuits 9a and 9b.

Further, in the above embodiment, the alternating current control means,
The currents flowing into the electrodes 2a and 2b may be compared with each other, and the current values may be controlled to be equal to each other.

(Effects of the Invention) According to the ultrasonic motor of the present invention, the currents of the two AC signals input to the piezoelectric body are controlled by the AC current control means so that the current values thereof are equal to each other. The propagation velocity and amplitude of the surface wave generated by the synthesis of ultrasonic vibrations generated in the body are always constant, which makes the contact between the elastic body and the rotor pressed against the elastic body perfect, and the efficiency and operation are stable. The property is improved.

Further, when the alternating current control means is configured to constantly compare the current flowing through the piezoelectric body with the reference current value, a constant current that is the same as the reference current value always flows through the piezoelectric body. Does not flow into the piezoelectric body, and it is possible to prevent the piezoelectric body from being destroyed by an excessive current.

[Brief description of drawings]

1 and 2 show one embodiment of the present invention,
FIG. 1 is a block diagram showing an ultrasonic motor and its drive system, and FIGS. 2 (a) to 2 (e) are explanatory views showing the generation of surface waves over time, FIG. 3 and FIG. Shows a conventional example, FIGS. 3 (a) to 3 (e) are explanatory views showing generation of surface waves over time, and FIG. 4 is a block diagram showing an ultrasonic motor and its drive system. 5 is a characteristic diagram showing the relationship between the current flowing through the piezoelectric body and the amplitude of ultrasonic vibration. 1 ... Ultrasonic motor, 2 ... Piezoelectric body 9a, 9b ... Current value comparison circuit (AC current control means) h, i ... Two AC signals

Claims (1)

[Claims] 1. An ultrasonic motor comprising: an elastic body; a piezoelectric body that excites the elastic body; and a detection unit that detects respective currents of two alternating current signals input to the piezoelectric body. Holding means for holding a reference current value to be input to the input means, and an amount relating to each detection result of the detecting means and an amount relating to the reference current value of the holding means are compared, and the input two values are input. An ultrasonic motor comprising control means for controlling so that respective current values of AC signals are substantially equal.