JPH04222477A - Ultrasonic motor power circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides an inverter circuit for supplying high-frequency power to the piezoelectric body of a traveling wave type ultrasonic motor equipped with an elastic body and a vibrating body made of a piezoelectric body that excites the elastic body. This invention relates to a power supply circuit for an ultrasonic motor.

0002

[Prior Art] Conventionally, a power supply circuit for this type of ultrasonic motor includes a switching element that variably controls the voltage applied to a piezoelectric material in order to drive the ultrasonic motor stably regardless of temperature and load fluctuations. It consisted of a cascade connection of a chopper circuit made up of diodes, inductance, etc., and an inverter circuit made up of switching elements, capacitors, etc. that variably controlled the frequency and phase difference of the voltage applied to the piezoelectric body.

0003

[Problem to be solved by the invention] Ultrasonic motors have low speed and
It takes advantage of the characteristics that a drive transmission mechanism is not required because it is a high-torque drive, and that since the vibrating body and the moving body are in pressurized contact, the holding torque at the time of stopping is large due to the frictional force between them. , are used in various small actuators, but in terms of packaging, it is desired that not only the motor but also the attached parts such as the power supply circuit be made smaller and lower in price. However, in order to drive the ultrasonic motor stably regardless of changes in temperature and load, the above-mentioned functions are essential, and there is a problem in that it is not easy to reduce the size and cost of the ultrasonic motor. An object of the present invention is to eliminate the above-mentioned conventional drawbacks.

0004

[Means for Solving the Problem] In order to achieve this object, the characteristic configuration of the power supply circuit for the ultrasonic motor according to the present invention is as follows.
A duty cycle control means is provided for variably controlling the duty cycle of the output pulses of the inverter circuit. It is preferable that the duty cycle control means is variably controlled based on the output of the vibration state detection means for detecting the vibration state of the vibrating body.

[0005]

[Operation] As shown in Fig. 4, when the duty cycle of the output pulse of the inverter circuit is variably controlled, the voltage value applied to the piezoelectric body is constant, but the application time, that is, the amount of power supplied can be variably controlled. By variably controlling the voltage value, substantially the same effect as variably controlling the amount of supplied power can be obtained. For example, as shown in Figure 4A, if the motor drive speed decreases, the duty cycle is increased to increase the amount of power supplied, and as shown in Figure 4C, if the motor drive speed increases, the duty cycle is decreased. Reduce power supply. By variably controlling the duty cycle based on the output of the vibration state detection means for detecting the vibration state of the vibrating body, stable driving can be achieved even with load fluctuations.

[0006]

[Effects of the Invention] A chopper circuit is no longer necessary, and the power supply circuit can be made smaller and lower in price.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. As shown in FIGS. 2 and 3, the ultrasonic motor M is
A stator 3 as a vibrating body 3 which generates a traveling wave of ultrasonic waves by fixing an elastic body 2 to a piezoelectric body 1, and a rotor 4 as a moving body that rotates in pressurized contact with the stator 3. It is configured. The piezoelectric body 1 is divided into two piezoelectric body groups A and B in the circumferential direction, and each area A and B is divided into adjacent sections alternately in the thickness direction at an interval of one half of the wavelength λ. In addition to polarization processing, the regions A and B are arranged with a three-quarter wavelength shift. By applying high frequency voltages having a phase difference of 90° to the regions A and B, the standing waves generated in the stator 3 corresponding to the regions A and B interfere with each other and are combined to form a traveling wave. That is, the rotor 4 rotates due to the frictional force with the stator 3 based on the traveling waves generated in the stator 3. By setting the phase of the high frequency voltage to 270°, the rotation direction can be switched.

The power supply circuit 5 of the ultrasonic motor M is shown in FIG.
, an inverter circuit 6 that supplies high-frequency power to the piezoelectric body 1, a frequency control means 7 that variably controls the output frequency of the inverter circuit 6, and an inverter circuit 6.
and a duty cycle control means 8 for variably controlling the duty cycle of the output pulses. The inverter circuit 6 is a combination of two power-split half-bridge inverters that output two-phase square waves with a phase shift, and each outputs a maximum of approximately 100 volts to the regions A and B via a vertical transformer. Frequency around 40kHz before and after
It is connected to apply a voltage of z. A vibration state detection means 9 made of a piezoelectric material is attached to the vibrating body 3 to detect the vibration state of the vibration state, and the frequency control means 7 controls the output voltage of the vibration state detection means 9 and the piezoelectric material 1. The output frequency of the inverter circuit 6 is variably controlled so that the phase difference between the voltages applied to the inverter circuit 6 becomes the set value, and the duty cycle control means 8 controls the output voltage of the vibration state detection means 9 so that the output voltage becomes the set value. The duty cycle of the output pulse of the inverter circuit 6 is variably controlled. In other words, the frequency control means 7 adjusts the output frequency of the inverter circuit 6 to the resonant frequency of the vibrating body 3 in order to correct the fluctuation in the driving speed caused by the fluctuation of the mechanical resonance frequency due to the temperature change of the vibrating body 3. control to maintain a relationship that deviates by a certain value from On the other hand, the duty cycle control means 8
This is to correct fluctuations in drive speed due to load disturbances. More specifically, the frequency control means 7 includes a phase comparator PC that compares the phase difference between the output voltage of the vibration state detection means 9 and the voltage applied to the piezoelectric body 1, and an output of the phase comparator PC at a low frequency. It consists of a low-pass filter LPF that can pass a band, and a voltage-controlled oscillator VCO that outputs a square wave whose oscillation frequency changes according to the output of the low-pass filter LPF. The duty cycle control means 8 includes:
An absolute value circuit 8a that full-wave rectifies and smoothes the output voltage of the vibration state detection means 9, a speed setting circuit 8b that sets the driving speed of the motor M, and an input from the frequency control means 7 according to the difference between these voltages. The modulator 8c makes the pulse width of the square wave variable. The frequency variable switches S1...S4 of the inverter circuit 6 are switched by the output signal of the duty cycle control means 8.

[0009] This allows the ultrasonic motor M to operate at a constant power supply frequency with good electrical/mechanical energy conversion efficiency, regardless of changes in the mechanical resonance frequency due to temperature and load fluctuation characteristics of the ultrasonic motor M itself. Control the output voltage value to obtain a stable speed.

In the above embodiment, the vibration state detection means 9 is constituted by a piezoelectric body provided on the vibrating body 3. It may also be a means for detecting. Inverter circuit 6
The high-speed response can be further improved by pulse width modulating the output pulses at a frequency higher than the switching frequency. In other words, the ON time of the output pulse of the inverter circuit 6 is variably divided into several pulses. The voltage and frequency applied to the piezoelectric groups A and B are not limited to these, but can be arbitrarily set according to the characteristics of the motor. The inverter circuit 6 is not limited to the previous embodiment and is optional. Incidentally, although reference numerals are written in the claims section for convenient comparison with the drawings, the present invention is not limited to the structure shown in the accompanying drawings.

[Brief explanation of the drawing]

[Figure 1] Schematic configuration diagram of power supply circuit

[Figure 2] Schematic plan view explaining the operating principle of an ultrasonic motor

[Figure 3] Schematic side view explaining the operating principle of an ultrasonic motor

[Figure 4] Waveform diagram of voltage applied to piezoelectric body

[Explanation of symbols]

1 Piezoelectric body 2 Elastic body 3 Vibrating body 6 Inverter circuit 8 Duty cycle control means

Claims (2)

[Claims] 1. A traveling wave type ultrasonic motor including a vibrating body (3) made of an elastic body (2) and a piezoelectric body (1) that excites the elastic body (2). A power supply circuit for an ultrasonic motor, which is provided with an inverter circuit (6) for supplying high-frequency power, and includes a duty cycle control means (8) for variably controlling the duty cycle of output pulses of the inverter circuit (6). Power supply circuit for an ultrasonic motor. 2. The duty cycle control means (8
2. The power supply circuit for an ultrasonic motor according to claim 1, wherein the power supply circuit for an ultrasonic motor is variably controlled based on the output of a vibration state detection means (9) for detecting the vibration state of the vibrating body (3).