JPH027879A - Driver of ultrasonic motor - Google Patents

Abstract

PURPOSE:To reduce the fluctuation of moving speed by providing an amplitude detection means of mechanical arm current and by correcting the detected gain of the mechanical arm current in temperature under the working environmental temperature of a motor. CONSTITUTION:An ultrasonic motor drive circuit connects a piezoelectric body 9 and a temperature sensing resistance element 5 in series to an electrode section of a motor section. At the same time it connects a capacitor 11 of a capacity equal to the capacity C0 in a working environmental maximum temperature of a piezoelectric body to a fixed resistance element 6 in series and connects them to the above series connection body in parallel. The difference 14 of each potential between the temperature sensing resistance element 5 and the fixed resistance element 6 is found and the mechanical arm current (f) is detected. This current (f) is then compared with the set value (h) with its current amplitude controller 12 through an amplitude detector 13. A voltage control frequency oscillator 1 outputs a designated driving frequency signal (a) based on the frequency control signal (i) and applies driving signals (e) and (d) to the electrode section 7, etc., through a 90 deg. phase setter 2, etc. The driving frequency is thereby decided according to the amplitude of mechanical arm current and the fluctuation of rotating speed is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an ultrasonic motor that generates driving force using a piezoelectric material.

2. Description of the Related Art In recent years, ultrasonic motors that obtain rotational or running motion by exciting various ultrasonic vibrations using electro-mechanical transducers using piezoelectric ceramics, etc., have attracted attention because of their high energy density. ing.

FIG. 3 shows an exploded perspective view of the ultrasonic motor. Tokukai 1986
As shown in Japanese Patent No. 190178, on the bottom surface of the vibrating body, a piezoelectric material 16 which is radially divided into 8 parts in a disc shape and polarized in opposite directions every 460 parts is arranged with a spatial phase of 9oO. By shifting and aligning, the piezoelectric bodies 15 and 16 each have a temporal position of 900 different values of several 10 kHz.
By applying the drive signals d and e of z, standing waves whose phases differ by 90' from each other both temporally and spatially are generated in the piezoelectric bodies 15 and 16. When the amplitudes of the two standing waves are made equal, the standing waves are combined in the vibrating body 17 to generate a bending vibration wave that travels in the circumferential direction. 19, 20
is the electrode part. Further, 21 is a spring, and 22 is a screw.

In Fig. β, point A of the vibrating body 23 is moved along the long axis 2 due to the traveling wave.
W shows an elliptical motion of the minor axis 2u, and when the movable body 24 pressurized to the vibrating body 23 comes into contact with the apex of the ellipse, V = raised in the opposite direction to the traveling wave of the wave. f-
It shows that it is moving at a speed of u (f is the frequency of the traveling wave). The movable body 22 is driven in the direction opposite to the traveling wave by the frictional force between it and the vibrating body 23, and when the work done to the outside cannot be ignored with respect to this frictional force, the movable body 22
A slip occurs between the vibrating body 23 and the vibrating body 23, and the velocity becomes smaller than V.

FIG. 2 is an electrical equivalent circuit diagram of the piezoelectric body 16 or 16, and it is thought that the capacitance C0 that does not contribute to the piezoelectric effect and the capacitance C0 that contributes to the piezoelectric effect or are coupled in parallel with C1 and R,
The current flowing through co is called electric arm current, and L, C1
, H is called the mechanical arm current. The mechanical arm current and the short axis amplitude 2u are in a proportional relationship. The admittance Y(s) of the mechanical arm is given by the following equation.

Y(s)=(s/L)/(s2+(R/L)g+(1/
LC1) (However, 8 is the Laplace operator s = j 2
πf) In the above equation, the resonance frequency is given by 1/(2πLC1). Even if the voltage and frequency applied to the piezoelectric body 11.12 are constant, the electrical admittance of the piezoelectric body 15.18 changes due to changes in ambient temperature or mechanical load (R, L, C1 change). ) Movement speed changes.

As explained above, the moving speed of the ultrasonic motor is determined by the product of the frequency W of the traveling wave and the short axis U of the elliptical motion, and the size of the short axis U is proportional to the mechanical arm current. The fluctuation range of the short axis U is larger than the fluctuation range of the frequency W, and the moving speed is determined almost by the mechanical arm current.

If the mechanical load on the piezoelectric body 15, 16 is constant, the electrical impedance is constant, and if the voltage and frequency are constant, the mechanical arm current is constant.

Problems to be Solved by the Invention However, in reality, as the moving body moves, the load on the mechanical arm fluctuates, and the electrical impedance fluctuates due to temperature changes, and as a result, the mechanical arm current changes. There is a problem that the movement speed fluctuates greatly.

In particular, there is a problem in that the capacitance of the electrical arm impedance of the piezoelectric material changes greatly due to temperature changes, making it extremely difficult to detect only the mechanical arm current, resulting in unstable motor rotation.

The present invention solves the above problems by accurately detecting the mechanical arm current regardless of the operating environment temperature of the motor and controlling the amplitude of the mechanical arm current, thereby reducing fluctuations in rotational speed. An object of the present invention is to provide an ultrasonic motor drive device that achieves stability and allows selection of rotational speed.

Means for Solving the Problem A capacitance equal to the capacitance of the electrical arm impedance of the piezoelectric body at the highest temperature in the motor operating environment is connected in series with one of the two electric signals applied to the piezoelectric body of the ultrasonic motor. A capacitor and a fixed resistance element are connected in parallel with the fixed resistance element, so that the current value flowing through the capacitor always matches the current value flowing through the electric arm of the piezoelectric body, regardless of the operating environment temperature of the motor. The mechanical arm current can be accurately measured by connecting one of the electrodes of the piezoelectric material through a temperature-sensitive resistance element having various temperature characteristics and detecting the potential difference between the fixed resistance element and the variable resistance element. can be detected.

Function As described above, by detecting the mechanical arm current flowing through the piezoelectric body of the ultrasonic motor and controlling the amplitude of the mechanical arm current to a predetermined value, the amplitude of the traveling wave of the vibrating body can be adjusted to a predetermined magnitude. Nashi,
Provided is an ultrasonic motor drive device that achieves reduction of fluctuations in rotational speed and stabilization of rotation with respect to fluctuations in mechanical load and temperature, as well as selectable rotational speed. Specific methods for controlling the amplitude of the mechanical arm current include a method of changing the frequency of the drive voltage and a method of changing the amplitude of the waveform of the drive voltage.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of an ultrasonic motor drive circuit according to the present invention. FIG. 2 shows a piezoelectric circuit. A piezoelectric body 9 and a temperature-sensitive resistance element 6 are connected in series to the electrode part, and a capacitor 11 having a capacitance equal to the capacitance C0 of the electrical arm impedance of the piezoelectric body at the maximum temperature of the motor usage environment in FIG. 2 is fixed to the electrode part. Resistance elements 6 are connected in series and connected in parallel with the series connection body consisting of the piezoelectric body and the temperature-sensitive resistance element. By determining the potential difference between the temperature-sensitive resistance element 5 and the fixed resistance element 6 using the differential amplifier 14, the electrical arm current j is canceled out and the mechanical arm current f is detected. The capacitance C0 of the electric arm impedance tends to decrease as the temperature decreases, so in order to cancel out the electric arm current j regardless of the motor environmental temperature, the current value flowing through the fixed resistance element 6 and the current value flowing through the electric arm are adjusted. A temperature-sensitive resistance element with temperature characteristics that always match is used. Since the mechanical arm current f is alternating current, the amplitude detector 13 is used to find the mechanical arm current amplitude q,
The mechanical arm current amplitude controller 12 compares the mechanical arm current amplitude with a set value. When the mechanical arm current amplitude signal q is lower than the mechanical arm current setting value, the driving frequency a is lowered and the frequency control signal i is adjusted so that the mechanical arm current amplitude signal q becomes equal to the mechanical arm current amplitude setting value. When the mechanical arm current amplitude signal q is larger than the mechanical arm current amplitude setting value, the driving frequency a is increased and the mechanical arm current amplitude signal q is output.
The frequency control signal i is outputted so that it becomes equal to the mechanical arm current amplitude setting value. The voltage controlled frequency oscillator 1 outputs a predetermined drive frequency signal based on the frequency control signal i. The 900 phase shifters 2 are 900 phase shifters 2 that are in phase with each other in time.
When different AC signals are output, an AC signal C is output. The power amplifier 3.4 amplifies the AC signal C and the AC signal C, respectively, and connects the electrode section 7, the piezoelectric body, and the electrode section 8. A drive signal e is applied to the piezoelectric body 10,
Apply d.

As described above, if the amplitude of the mechanical arm current is controlled to the mechanical arm current amplitude set value by determining the drive frequency according to the amplitude of the mechanical arm current, the amplitude of the mechanical arm current can be controlled to the mechanical arm current amplitude setting value, and the fluctuations in the mechanical load, temperature, and power supply voltage can be Fluctuations in rotational speed can be reduced. Furthermore, the magnitude of the rotation speed can be selected by changing the mechanical arm current setting value.

Although this embodiment has been explained using a disc type ultrasonic motor, the present invention is not limited to the disc type ultrasonic motor, and the present invention is not limited to the disc type ultrasonic motor. Also applicable to sonic motors.

Effects of the Invention As explained above, considering that the amplitude of the mechanical arm current of an ultrasonic motor and the rotation speed are in a proportional relationship, a means for detecting the amplitude of the mechanical arm current is provided, and the By temperature-correcting the detection gain of the mechanical arm current and controlling its amplitude to a constant value, it is possible to reduce fluctuations in the moving speed of the moving body relative to temperature fluctuations of the ultrasonic motor. Furthermore, the moving speed can be selected by selecting the amplitude setting value, which has a great practical effect.

[Brief explanation of the drawing]

Fig. 1 is a block configuration diagram of an ultrasonic motor drive device according to an embodiment of the present invention, Fig. 2 is an electrical equivalent circuit diagram of the motor, Fig. 3 is an exploded perspective view of a disc-type ultrasonic motor, and Fig. 4 The figure is an explanatory diagram of the principle of the motor. 1... Voltage controlled frequency oscillator, 2...
90° phase shifter, 3.4...Power amplifier, 9,1
o...Piezoelectric body of ultrasonic motor, 12...
・Mechanical arm current controller, 13...Amplitude detector, 1
4...Differential amplifier. Name of agent: Patent attorney Toshio Nakao and one other person

Claims (1)

[Claims] A piezoelectric driving body is formed by bonding an elastic body and a piezoelectric body having two electrode groups that are positioned out of phase with each other by an amount equivalent to a quarter wavelength, and a moving body is installed on the driving body, In the ultrasonic motor that rotates the movable body by applying two electric signals temporally different in position by 90 degrees to the two electrode groups, the piezoelectric body is connected in series with either one of the two electric signals. Connect a capacitor with a capacitance equal to the capacitance of the electric arm impedance and a fixed resistance element in parallel with the fixed resistance element, regardless of the operating environment temperature of the motor.
connected to one of the two electrode groups via a temperature-sensitive resistance element having temperature characteristics such that a current value flowing through the fixed resistance element always matches a current value flowing through the electric arm of the piezoelectric body; A mechanical arm current of the piezoelectric body is detected by detecting each potential difference between the fixed resistance element and the variable resistance element, and the amplitude of the mechanical arm current according to the electric signal is controlled to a predetermined magnitude. Ultrasonic motor drive device.