JPH02114869A - Control method for ultrasonic motor - Google Patents

Abstract

PURPOSE:To enable maintaining a good speed controllability even if the rotation/stop of an ultrasonic motor is repeated, by respectively supplying an apparatus with signals differing 90 deg. in phase at the time of driving and with in-phase signals at the time of stopping. CONSTITUTION:The subject apparatus has an oscillating circuit 1, 1/2 frequency divider 2 halving the frequency of a signal S1, and 1/2 frequency dividers 3, 4 halving the frequencies of signals S2, S3, and said frequency-dividing signals S4 and S5 are signals differing 90 deg. in phase. Said signal S4 is supplied to an amplifier 5 and the signal S5, to an amplifier 6 via switch SW. When a signal having a phase difference of 90 deg. is supplied to each electrode of an ultrasonic motor 7, said motor rotates as a progressive wave is generated in a piezoelectric body within the ultrasonic motor 7, and when an in-phase signal is supplied, the motor stops as a standing wave is generated. Thus, even if the rotation/stop of the ultrasonic motor 7 is repeated, it is possible to maintain a good speed controllability.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method of controlling an ultrasonic motor that can improve speed controllability.

"Conventional technology" Various ultrasonic motors using traveling waves have been developed.

In this type of ultrasonic motor, the polarization direction of the piezoelectric material constituting the stator is selected, the electrodes are divided into two electrode groups with different phases, and each electrode group has a 90' phase. A traveling wave is generated by supplying different signals. Therefore, it is necessary to create an ultrasonic motor drive circuit (1, l, two-phase AC signals with 90° different phases).The frequency of this AC signal must be set to a frequency corresponding to the desired rotation speed. Therefore, in the drive circuit, an oscillation circuit that generates a signal of such a frequency is installed. It is.

[Problems to be Solved by the Invention] By the way, an ultrasonic motor starts to generate heat when it starts rotating, and the resonant frequency of the piezoelectric body changes due to the temperature change caused by this. Therefore, the control of the ultrasonic motor is
It is necessary to perform control according to the temperature of the driving state.

On the other hand, when an ultrasonic motor is incorporated into a device,
There are many types of 7s that rotate and stop frequently. When stopped, the temperature of the ultrasonic motor decreases because there is no heat generation. Therefore, when rotation/stopping is repeated, the temperature of the ultrasonic motor may fluctuate significantly.
There was a problem that speed control became difficult.

This invention has been made in view of the circumstances in article 1-1, and is therefore a method for controlling an ultrasonic motor that can maintain good speed controllability even when the ultrasonic motor rotates/stops repeatedly. The purpose is to propose (71).

"Means for Solving the Problems" In order to solve the problems 1 and 2, the present invention supplies signals with phases different by 90 degrees during driving to each electrode group of an ultrasonic motor having two electrode groups. However, when stopping 1-, signals of the same phase are supplied to each of them.

"Operation" When signals with a phase difference of 90 degrees are supplied to each electrode of the ultrasonic motor, a traveling wave is generated in the piezoelectric body in the ultrasonic motor, causing it to rotate, and when signals of the same phase are supplied. It stops because a standing wave is created. Even when the ultrasonic motor is stopped, the ultrasonic motor is in a heat generation state because the drive signals of the same phase are supplied, and thereby the temperature of the ultrasonic motor is kept constant both during driving and when the ultrasonic motor is stopped.

``Example-1'' An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an ultrasonic motor drive circuit according to an embodiment of the present invention.

In Fig. 1, 1 is an oscillation circuit, and a signal Sl having a frequency corresponding to the desired rotation speed (see Fig. 2 (a))
will occur. 2 is 1/ which makes the frequency of signal S1 ]/2
It is a frequency divider by 2, and the signal S which is a frequency divided signal is output from the Q output terminal.
2 (see Figure 2 (0)), and a signal S3 which is an inverted signal of signal S2 from the Q output terminal (see Figure 2 (〕・)).
Output. Next, 3. /I are the signals S2. A 1/2 frequency divider is provided to halve the frequency of S3, and the frequency-divided signal S4. S5 is output respectively. Here, the signals S4 and S5 have a phase difference of 90°, as shown in FIG. 2 (d) and (po), respectively. This signal S4
is supplied to the amplifier 5, and the signal S5 is supplied to the amplifier 6 via the switch SW. Amplifier 5,
Reference numeral 6 is composed of a switching element that turns on/off based on each supplied signal, and a transformer that controls the power supply to the primary coil by this switching element, and the output signal of the secondary coil of this transformer. are supplied to electrodes 7a and 7b of the ultrasonic motor 7, respectively. Further, the double switch SW is configured to be switched to the terminal a side when driving the ultrasonic motor 7, and to be switched to the terminal A side when stopping the ultrasonic motor 7.

According to the configuration described above, when the switch SW is switched to the terminal a side, each output signal of the amplifiers 5 and 6 or the signal 34. Since the frequency and phase correspond to S5, a signal having a phase difference of 90° is supplied to the ultrasonic motor 7, and a traveling wave is generated in the piezoelectric body of the ultrasonic motor 7, which causes the moving object to rotates. At this time, since heat is generated in the ultrasonic motor 7 due to the vibration, its temperature rises and becomes a constant temperature corresponding to the vibration.

Next, when the switch SW is switched to the terminal side, the output signals of the amplifiers 5 and 6 both have a frequency and a phase corresponding to the signal S4. In other words, the currents supplied to each electrode of the ultrasonic motor 7 become in-phase signals. As a result, a standing wave is generated in the piezoelectric body of the ultrasonic motor 7, which causes the moving body to stop.

At this time, the moving body stops, but since vibrations are still occurring due to the standing waves, heat is generated in accordance with the vibrations.

As mentioned above, even when the ultrasonic motor 7 is rotating,
Even when the ultrasonic motor 7 is stopped, the heat generation state in the ultrasonic motor 7 continues. As a result, the temperature of the ultrasonic motor 7 is kept almost constant even if it is repeatedly rotated and stopped.

"Effects of the Invention" As explained above, according to the present invention, signals having a phase difference of 90° are supplied to each electrode group of the ultrasonic motor when driving the two electrode groups, and signals having the same phase when stopped are supplied to each electrode group of the ultrasonic motor. Since the signals are supplied individually, there is an advantage that good speed controllability can be maintained even when the ultrasonic motor is repeatedly rotated/stopped.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an ultrasonic motor drive circuit according to an embodiment of the present invention, and FIG. 2 is a waveform diagram showing waveforms of various parts of the circuit of the embodiment. Oscillator circuit, 24...1/2 frequency divider circuit, 5.6... amplifier, ultrasonic motor, SW switch.

Claims (1)

[Claims] A method for controlling an ultrasonic motor, characterized in that signals having phases different by 90° are supplied to each electrode group of the ultrasonic motor having two electrode groups when the motor is driven, and signals having the same phase are supplied when the motor is stopped.