JPH01198282A - Driver for supersonic motor - Google Patents

Abstract

PURPOSE:To suppress fluctuation of speed and to stabilize the operation, by driving a supersonic motor with a frequency higher than a resonant frequency and detecting the amplitude of current flowing through a mechanical arm thereafter controlling the amplitude to a predetermined level. CONSTITUTION:In the drive circuit for a supersonic motor, a piezoelectric member 9 and a resistor 5 are connected in series with an electrode section 7 and a series circuit of a capacitor 11 and a resistor element 6 is connected in parallel therewith. Potential difference between the resistor elements 5 and 6 is obtained through a differential amplifier 14 and employed for cancelling the current flowing through an electrical arm and for detecting the current (f) flowing through a mechanical arm. An amplitude controller 12 for mechanical arm current and an amplitude detector 13 are further provided, and a voltage- controlled oscillator 1 provides a predetermined drive frequency signal (a) based on a frequency control signal (i). Driving is carried out with a voltage having frequency higher than a resonant frequency except the unstable rotation area (in the vicinity of resonant frequency). When the amplitude is controlled to be constant, fluctuation of moving speed can be suppressed against fluctuation of mechanical load or temperature.

Description

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

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. 7 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 11 and a piezoelectric material 22, which are disk-shaped and radially divided into eight parts, and polarized in opposite directions every 45 degrees, are arranged so that the spatial phase of the piezoelectric material 11 and the piezoelectric material 22 are mutually adjusted. The piezoelectric bodies 21 and 22 are pasted together with a 90" difference in temporal phase by several tens of kilohertz (90").
By applying the drive signals d and e of z, standing waves whose phases differ from each other by 90'' both temporally and spatially are generated in the piezoelectric bodies 21 and 22.If the amplitudes of the two standing waves are equal, When this is done, the standing waves are synthesized in the vibrating body 23, and a bending vibration wave that propagates in the circumferential direction is generated. Reference numerals 24 and 25 are electrode parts, 26 is a spring, and 27 is a screw. .

FIG. 8 shows that point A of the vibrating body 23 is moved along the long axis by the traveling wave.
W shows an elliptical movement of the short axis 2u, and when the moving body 24, which is pressurized and installed on the vibrating body 23, comes into contact with the apex of the ellipse, the wave is raised in the opposite direction to the traveling wave v- f-
It shows that it is moving at a speed of u (f is the frequency of the traveling wave). The moving 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 moving body 2
2 and the vibrating body 23, and the speed becomes smaller than V.

FIG. 2 is an electrical equivalent circuit diagram of the piezoelectric body 21 or 22, and it is thought that the capacitance CO, which does not contribute to the piezoelectric effect, contributes to the piezoelectric effect, or is coupled in parallel with C1, R, The current flowing through Co is called electric arm current, and L, C1,
The current flowing through R 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.

(S is Laplace operator s=j 2πf) Y(s)=(
s/L)/(s2+(R/L)s+(1/LC1
)) ■ In equation (1), the resonance frequency is 1/(2πLC1
) is given by Even if the voltage and frequency applied to the piezoelectric body 11.12 are constant, the electrical admittance of the piezoelectric body 11.12 changes due to changes in ambient temperature and 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 11, 12 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. The problem is that the movement speed is large (varies), and in reality (
2) The mechanical arm current flows according to the formula (at frequencies lower than the resonant frequency, the mechanical arm current decreases significantly, and in this frequency range, the rotation speed decreases significantly or stops. Near the resonant frequency There is also a problem in that if the constants of the mechanical arm change even slightly and the resonance frequency changes, the mechanical arm current will decrease significantly, resulting in unstable rotation.

The present invention solves the above-mentioned problems by driving the ultrasonic motor with a frequency voltage higher than the resonant frequency except in the vicinity of the resonant frequency in response to changes in mechanical load and temperature. An object of the present invention is to provide an ultrasonic motor device that controls the amplitude of the current, reduces fluctuations in moving speed, stabilizes rotation, and allows the user to select the moving speed.

Means for Solving the Problems By applying a frequency voltage drive signal to a piezoelectric body and exciting an elastic wave to a vibrating body composed of the piezoelectric body and an elastic body, the piezoelectric body is brought into pressure contact with the vibrating body. An ultrasonic motor for moving an installed moving object has means for detecting the amplitude of a mechanical arm current flowing into the piezoelectric body, and detects a frequency higher than the resonance frequency except for a region near the resonance frequency of the ultrasonic motor. It is driven by a frequency voltage, and the amplitude of the mechanical arm current is controlled to a predetermined magnitude.

a mechanical arm current detection means for detecting the amplitude of a mechanical arm current flowing into the piezoelectric body, the mechanical arm being driven by a frequency voltage higher than the resonant frequency except for the vicinity of the resonant frequency of the ultrasonic motor; By controlling the amplitude of the current to a predetermined value, the amplitude of the traveling wave of the vibrating body becomes a predetermined value, reducing fluctuations in moving speed and stabilizing rotation in response to changes in mechanical load and temperature. To provide an ultrasonic motor device that achieves this goal and allows you to select the moving speed. Examples of 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.

EXAMPLES Hereinafter, examples of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of a specific circuit for driving an ultrasonic motor. FIG. 2 shows a piezoelectric equalization circuit. A piezoelectric body 9 and a resistance element 5 are connected in series to the electrode part 7, and the electric arm impedance (L,
A capacitor 11 having a capacitance equal to the capacitance CO with respect to C (series components of C□, R) and a resistor element 6 equal to the resistor element 5 are connected in series, and are connected in parallel with the series connection body consisting of the piezoelectric body and the resistor element. By determining the potential difference between the resistive elements 5 and 6 of the electrode section 7 using the differential amplifier 14, the mechanical arm current f is detected by canceling the electrical arm current j. Since the mechanical arm current f is alternating current, the amplitude detector 13 is used to determine the mechanical arm current amplitude g, and the mechanical arm current amplitude controller 12 compares it with the mechanical arm current amplitude setting value. When the mechanical arm current amplitude signal g is lower than the mechanical arm current amplitude setting value, the driving frequency a is lowered and the frequency control signal i is set so that the mechanical arm current amplitude signal g becomes equal to the mechanical arm current amplitude setting value.
is output, and when the mechanical arm current amplitude signal g is larger than the mechanical arm current amplitude setting value, the driving frequency a is increased and the frequency is increased so that the mechanical arm current amplitude signal g becomes equal to the mechanical arm current amplitude setting value. Outputs control signal i. The voltage controlled frequency oscillator 1 outputs a predetermined drive frequency signal a based on the frequency control signal i. The 90" phase shifter 2 outputs the AC signal C and the AC signal C whose phases are different from each other by 90 degrees in time. The power amplifier 3.4 amplifies the AC signal C and the AC signal C, respectively. Body and electrode part 8. Drive signals e and d are applied to the piezoelectric body 10.

FIG. 3 shows experimental values of the frequency characteristic curve of the rotation speed and the amplitude of the mechanical arm current at a constant temperature and load of the ultrasonic motor used in this example. Also, based on Equation (2), the calculated values of the frequency characteristic curve of the amplitude of the mechanical arm current calculated assuming a constant voltage are also listed. The calculated value shows that the amplitude of the mechanical arm current is symmetrical to the resonant frequency, but the experimental value shows that at frequencies lower than the resonant frequency, the mechanical arm current decreases significantly, and in this frequency range, the rotation speed decreases significantly or stops. . Even in the vicinity of the resonance frequency, each constant of the mechanical arm changes even slightly, and when the constant of the mechanical arm approaches the resonance frequency, the mechanical arm current decreases significantly, making the rotation unstable. Therefore, it rotates stably only in a frequency range where the drive frequency is higher than the resonance frequency. Therefore, in the present invention, the motor is driven with a frequency voltage higher than the resonant frequency, except in an unstable region of rotation, that is, near the resonant frequency.

The operation of this embodiment will be explained below with reference to FIG. When starting the motor, for example, if the drive start point is at point A, the amplitude of the mechanical arm current is smaller than the set value, so the driving frequency is decreased to move the operating point from point A to point B, and the mechanical arm current is changed. Match the amplitude to the mechanical arm current amplitude setting. Conversely, when the operating point is at a position such as point C and the amplitude of the mechanical arm current is larger than the set value, the driving frequency is increased to move the operating point from point C to point B, and the mechanical arm current is increased. Match the amplitude to the mechanical arm current amplitude setting value.

Eventually, the operating point converges near point B, and a mechanical arm current equal to the set value flows through the ultrasonic motor, causing the moving body to rotate at a rotational speed proportional to the mechanical arm current. Even if the impedance of the piezoelectric body changes due to variations in mechanical load, temperature, and drive voltage during rotation, automatic frequency tracking is applied so that the operating point is always at point B as described above, and the ultrasonic motor is always A mechanical arm current with an amplitude equal to the set value flows and the moving object rotates based on the 0th equation, but the frequency change width is sufficiently small compared to the fluctuation range of U, so it is proportional to the amplitude of the mechanical arm current. Rotates at the number of revolutions.

As described above, the amplitude of the mechanical arm current can be controlled by driving with a frequency voltage higher than the resonance frequency, excluding the vicinity of the resonance frequency where rotation is unstable, and by determining the driving frequency according to the amplitude of the mechanical arm current. The arm current amplitude can be controlled to the set value, and can be controlled against changes in mechanical load, temperature, and power supply voltage.
Fluctuations in rotational speed can be reduced. Further, by changing the mechanical arm current setting value, the rotation speed can be arbitrarily selected within the range shown in FIG.

FIG. 5 is a block diagram of a concrete circuit of another embodiment for realizing the ultrasonic motor driving method of the present invention. 90° phase shifter 2, mechanical arm current detector 5, mechanical arm current detector output 8
Since it is the same as the first embodiment, the explanation will be omitted.

As shown in Japanese Unexamined Patent Publication No. 60-233641, a phase detector 51 detects a phase difference k (hereinafter referred to as phase difference) between a mechanical arm current f and its applied voltage m, and determines the mechanical arm current phase. The controller 52 outputs the frequency control signal i to the voltage controlled frequency oscillator 1 so that the phase difference k becomes equal to the phase difference setting value. The variable amplification power amplifier 3.4 is a power amplifier whose amplification is variable according to the amplification control signal m.

It is assumed that the waveform amplitudes of the drive signal d and the drive signal e are the same. The mechanical arm current amplitude controller 12 outputs an amplification degree control signal m so that the mechanical arm current amplitude g and the mechanical arm current amplitude setting value are equal.

FIG. 6 is a frequency characteristic curve of the amplitude and phase difference of the mechanical arm current of the ultrasonic motor used in the second embodiment at a constant temperature and load. In a rotating state where the phase difference k is equal to the phase setting value depending on the frequency, to increase the rotation speed, increase the amplitude of the drive signals e and d to increase the amplitude of the mechanical arm current; It can be seen that the amplitude of the mechanical arm current can be reduced by lowering the amplitude of the drive signals e and d.

The operation of this embodiment will be explained below with reference to FIG. Frequency tracking by phase, for example, if the drive start point is at point E, the amplitude of the mechanical arm current is smaller than the set value, so the amplitude of the drive signals e and d is decreased to move the operating point from point E to point D. Move the mechanical arm current amplitude to match the mechanical arm current amplitude setting value.

Conversely, when the operating point is at a position such as point F and the amplitude of the mechanical arm current is larger than the set value, the amplitude of drive signals e and d is increased to move the operating point from point F to point D. Match the amplitude of the mechanical arm current to the mechanical arm current amplitude setting value.

Eventually, the operating point converges near point D, and a mechanical arm current equal to the set value flows through the ultrasonic motor, causing the moving body to rotate at a rotational speed proportional to the mechanical arm current. Even if the impedance of the piezoelectric body changes due to changes in mechanical load and temperature during rotation, the amplitudes of the drive signals A and B are controlled so that the operating point is always at point D as described above, and the amplitude of the drive signals A and B is always kept at point D. A mechanical arm current having an amplitude equal to the mechanical arm current amplitude setting value flows through the sonic motor, and the moving body rotates at a rotation speed proportional to the amplitude of the mechanical arm current.

In the second embodiment, the amplitude of the drive signal waveform was changed by changing the amplification degree of the power amplifier, but pulse width modulation (
PWM) or the like may be used to equivalently change the amplitude of the drive frequency component that contributes to the rotation.

Furthermore, although the present embodiment has been explained using a disc type ultrasonic motor, the present invention is not limited to the disc type ultrasonic motor (an annular type ultrasonic motor, a linear movement motor, etc.). It can also be applied to linear ultrasonic motors.

Effects of the Invention As explained above, rotation is stable only at frequency voltages in a frequency range higher than the resonance frequency, except near the resonance frequency, and the amplitude of the mechanical arm current of the ultrasonic motor and the rotation speed are in a proportional relationship. Taking this into consideration, a means for detecting the amplitude of the mechanical arm current is provided, and the driving frequency or the amplitude of the waveforms of the two driving signals is changed depending on the amplitude of the mechanical arm current. If the amplitude is always controlled at a constant value, the fluctuations in the moving speed of the moving object can be minimized due to changes in the mechanical load of the ultrasonic motor and temperature.Also, when controlling the amplitude of the mechanical arm current by the drive frequency, It is possible to reduce fluctuations in the rotation speed due to fluctuations in the power supply voltage.Moreover, by selecting the set value of the mechanical arm current, the moving speed can be selected, which has great practical effects.These effects make it possible to The scope of use of ultrasonic motors has expanded, and it has become possible to apply ultrasonic motors to places where voltage and temperature fluctuations are severe, such as in transportation vehicles such as automobiles, aircraft, and ships.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an ultrasonic motor driving device according to an embodiment of the present invention, FIG. 2 is an electrical equivalent circuit diagram of the motor, and FIG.
The figure shows an example frequency characteristic curve of the rotational speed of the ultrasonic motor and the amplitude of the mechanical arm current in the configuration shown in Fig. 1, and a frequency characteristic curve of the calculated value of the amplitude of the mechanical arm current, and Fig. 4 shows the rotational speed of the same motor. FIG. 5 is a block diagram of an ultrasonic motor drive device according to a different embodiment of the present invention, and FIG. 6 is a characteristic diagram showing the amplitude and phase difference frequency characteristics of the mechanical arm current. curve, Figure 7 is an exploded perspective view of a disc-type ultrasonic motor,
FIG. 8 is a diagram explaining the principle of the motor. 1... Voltage controlled frequency oscillator, 2... 90° phase shifter, 3.4... Power amplifier, 9.10... Piezoelectric body of ultrasonic motor 12... Mechanical arm current detection Vessel, 13.
... Amplitude detector, 14... Differential amplifier. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 3
h, - Tetsuhan H ■ Singing I l 4th figure 1st string I 9 Makoto group so 1st condition - Ward bag back @ - Yatou [F] Mi wo 2/, 22-10,000 electric lines? 3---Including movement zs-aIk part 23-1! 4 ffs

Claims (3)

[Claims] (1) means for applying a frequency voltage drive signal to a piezoelectric body; a vibrating body composed of the piezoelectric body and an elastic body; a movable body that is placed in pressurized contact with the vibrating body; The drive signal includes means for detecting the amplitude of the mechanical arm current flowing into the piezoelectric body based on a drive signal, and the drive signal is a frequency voltage having a frequency higher than the resonance frequency of the piezoelectric body except near the resonance frequency, and the drive signal is a frequency voltage higher than the resonance frequency of the piezoelectric body, An ultrasonic motor drive device characterized in that the amplitude of the mechanical arm current is controlled to a predetermined magnitude using a signal. (2) The ultrasonic motor drive device according to claim 1, wherein the amplitude of the mechanical arm current is controlled to a predetermined magnitude by changing the frequency of the drive signal. (3) The ultrasonic motor drive device according to claim 1, wherein the amplitude of the mechanical arm current is controlled to a predetermined magnitude by changing the amplitude of the waveform of the drive signal.