JPH01107672A - Driving gear for ultrasonic wave motor - Google Patents

Abstract

PURPOSE:To exactly control rotational frequency, by controlling a driving circuit via a variable oscillator, with signal detecting the current level of a piezoelectric unit, and each signal due to the phase difference of the current and applied voltage. CONSTITUTION:The driving gear of an ultrasonic wave motor is composed of a current detecting circuit 35, a voltage detecting circuit 36, a phase detecting circuit 37, an error amplifier 43, a variable oscillator 44, and the like. Then, to the input side of a current level detecting circuit 51, the output of the current detecting circuit 35 is connected, and the output is connected to the one side input side of an operational amplifier 54 via a resistor 52, and to the other side input side of the amplifier 54, a reference voltage source 55 is connected, and an error amplifier 56 is composed. Then, the amplitude integrating value of current in proportion to mechanical system oscillation, flowing to a piezoelectric unit 2 is compared with the reference voltage source 55, and by comparing the phase difference of output generated from a phase difference detector 50 with a reference voltage source 41, rotational frequency can be exactly controlled with the phase difference.

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 body, and more particularly to a drive device that drives a piezoelectric body that excites an elastic body.

2. Description of the Related Art In recent years, ultrasonic motors that obtain rotational or running motion by exciting various ultrasonic vibrations using electromechanical transducers such as piezoelectric ceramics have attracted attention because of their high energy density. There is.

For example, an ultrasonic motor having a structure as shown in FIG. 4 has been proposed. That is, two circular piezoelectric bodies 1. A stator 4 is constructed by stacking a piezoelectric body 2 and a circular elastic body 3 in the thickness direction, a lining 6 is bonded to the lower surface of the stator 4 in surface contact with the stator 4, and a fastening shaft 7 for pressure contact is formed at the lower part. death,
At the top is a mechanical output shaft 8 that transmits rotation to an external rotated body.
The rotor base 5 is formed of a rotor base 5, a bearing 9, a spring 10 and a fastening ring 11 for pressurizing and assembling the rotor base 5 and the stator 4 with a desired fastening torque. It has a ring-shaped protrusion 3a for applying vibrational energy, and a rotational force is obtained by applying electrical signals out of phase with each other to the piezoelectric bodies 1 and 2.

As a driving device for such an ultrasonic motor, a configuration as shown in FIG. 5 has been proposed.

The operating principle of the ultrasonic motor shown in FIG. 5 will be explained below.

First, the output signal oscillated by the oscillator 15 at the drive frequency fm determined by the stator 4 is branched, and one is input directly to the amplifier 16 and the other is input to the amplifier 18 via the phase shifter 17 . The phase shifter 17 shapes a signal whose phase is shifted within a range of ±10° to ±170°, which is used for forward or reverse rotation. The output signal of the oscillator 15 is directly input to the amplifier 16 and the amplified signal is applied to the first piezoelectric body 1 through lead wires 19 and 20. As a result, the stator 4 has 8 poles in the circumferential direction and 4 wavelengths of excitation corresponding to 4 sets of vibrators, with each wavelength being a pair of regions in which the polarization directions of the first piezoelectric body 1 have different positive polarity or negative polarity. waves are generated. The second piezoelectric body 2 is similarly driven by applying the output of the amplifier 18 via the lead wires 20, 21.

These phase shifters 17 and amplifiers 16 and 18 constitute a drive circuit 22.

When the stator 4 is driven as described above, the apex of the vibration on the side of the stator 4 facing the rotor 14 comes into contact with the rotor 14, and since the apex mainly moves with time,
A force having a lateral component will be applied to the rotor 14. In this way, the rotor 14 can obtain rotational motion as a result of repeating positional movement by the traveling wave of the lateral component at the drive frequency fm determined by the stator 4.

However, the oscillation frequency fd of the output signal oscillated by the oscillator is the resonant frequency fr of the stator 4.

Even if the drive frequency fm is set to match the drive frequency fm determined by fro and driving frequency f
m changes and the drive frequency fm becomes the oscillation frequency fro
It deviates significantly from

Therefore, the efficiency of generating traveling waves decreases, the driving efficiency of the motor decreases, and in extreme cases, the motor may stop.

For this reason, an ultrasonic motor drive device as shown in FIG. 6 has been proposed.

In FIG. 6, reference numeral 23 indicates an electrical circuit diagram of the first piezoelectric body 1 and the second piezoelectric body 2 that constitute the ultrasonic motor. Reference numeral 35 denotes the piezoelectric body 2, a resistor 24 connected in series to the piezoelectric body 2, and a capacitor 26 whose one terminal is connected to the terminal 2'Oa on the opposite side from the connection terminal A of the piezoelectric body 2 with the resistor 24. , one terminal is connected to the other terminal of the capacitor, and the other terminal is connected to the piezoelectric body 2 of the resistor 24.
It is equipped with a resistor 25 connected to the terminal 19a on the opposite side of the connecting terminal A, and a differential amplifier circuit 42 composed of resistors 30 to 33 and an operational amplifier 34, This is a current detection circuit that detects a proportional current.

Here, a little more current detection circuit 35 proportional to mechanical system vibration
I will explain in detail. An equivalent electrical circuit of the piezoelectric body 2 is shown in FIGS. 8(a) and 8(b). (Ohmsha, Takube Ikeda, “Basics of Piezoelectric Material Science” P99-P1
02)) If the total current flowing through the piezoelectric body 2 is IT, then I
T is the current I which is proportional to the vibration of the mechanical system as shown in Figure 8(b).
It is the sum of m and Ic, which flows through the capacitance Co of the piezoelectric body 2 and includes harmonic components. Therefore, the current IT flowing through the piezoelectric body 2
Of these, by subtracting the current IO flowing through the capacitance Co of the piezoelectric body 2, a current Im proportional to the mechanical vibration is obtained.

Therefore, if the capacitance of the capacitor 26 is set equal to the capacitance of the piezoelectric body 2, and the resistors 24 and 25 are set equally, the differential amplifier circuit 42 converts the total current IT flowing through the piezoelectric body 2 into a piezoelectric Current 1o flowing through capacitance Co of body 2
An output waveform corresponding to the current proportional to the mechanical vibration obtained by subtracting the current flowing through the capacitor 26 which is equal to 1 is obtained. That is, a current Im proportional to mechanical system vibration can be detected. FIG. 9 shows points A and B shown in FIG.

The waveform at point 0 is shown. Point A as you will see from now on.

At point B, a distorted waveform due to harmonic components is obtained, but at point 0, a waveform of current In proportional to mechanical system vibration is obtained, whose phase can be compared with the voltage waveform.

36 is a voltage detection circuit that detects the voltage applied to the piezoelectric body 2. A phase difference detection circuit 37 compares the phases of the output waveforms of the current detection circuit 35 and the voltage detection circuit 36, which are proportional to mechanical system vibration, and outputs a DC voltage according to the phase difference.

43 is an error amplifier that compares the output voltage of the phase difference detection circuit 37 and the voltage of the reference voltage source 41, and outputs a voltage according to the difference voltage.

44 is a variable oscillator whose oscillation frequency is varied according to the output voltage of the error amplifier 43.

In addition, in FIG. 6, resistors 28, 29 and capacitor 2
7 is inserted to balance the voltage applied to the piezoelectric body. This will be explained in detail below.

A resistor 28 having the same resistance value as the resistor 24 connected in series to the piezoelectric body 1 is connected in series to the piezoelectric body 1, and a capacitor 2 is connected in series to the piezoelectric body 1.
A series circuit consisting of a capacitor 27 and a resistor 29, each equal to the value of the piezoelectric body 2 and the resistor 25, is connected between the lines 21a and 20a, and the piezoelectric body 2 and the resistor 24 constitute a current detection circuit proportional to the vibration of the mechanical system. and resistor 25 and capacitor 26
The piezoelectric body 1, the resistor 28, the resistor 29, and the capacitor 27 are inserted so as to have a symmetrical configuration along the line 20a. By having the symmetrical configuration, when the voltage level applied between lines 21a and 20a and the voltage level applied between lines 20a and 19a are equal (but different in phase), the piezoelectric material 1 and piezoelectric body 2
The voltage levels applied to both are also equal. Therefore, problems caused by the difference in the voltage levels applied to the piezoelectric body 1 and the piezoelectric body 2 (for example, a decrease in motor efficiency) will not occur. This provides stable motor rotation.

In the drive circuit for the ultrasonic motor configured as described above, as shown in FIG.
If the drive frequency fm1 is set at a phase difference ΔP, fd=fm+ (1) The environment in which the ultrasonic motor is driven changes, temperature changes due to self-heating, and changes over time occur, causing the stator 4 to Even if the mechanical system resonance frequency frol and the drive frequency f1 at a phase difference ΔP from it change to from l fm2, the frequency fd of the output signal oscillated by the oscillator, that is, the output signal of the ultrasonic motor drive circuit 22, is It is controlled by fd=fm2. That is, with respect to a change in the mechanical system resonance frequency fro of the stator 4, the frequency fd of the output signal of the ultrasonic motor drive circuit 22 always follows fro and fm.

Problems to be Solved by the Invention However, in such an ultrasonic motor drive circuit,
When the driving frequency f1 is above the resonance point, the rotational speed of the ultrasonic motor is inversely proportional to the driving frequency f1 as shown in FIG. 10, but the phase difference between the current and voltage is proportional to the mechanical vibration of the piezoelectric body 1.2. is inversely proportional when the driving frequency fml is low, and the change is small when the driving frequency fit is high, so
When the driving frequency fII11 is high (the number of revolutions is low), the variation in the phase difference causes a large change in the number of revolutions, posing a problem that accurate control is difficult.

The present invention solves the above problems and provides an ultrasonic motor drive device that can accurately control rotation even when the drive frequency is high (low rotation).

Means for Solving the Problems In order to solve these conventional problems, the present invention provides current detection means for detecting a current proportional to mechanical system vibration flowing through a piezoelectric body, voltage detection means for detecting voltage; phase difference detection means for detecting a phase difference between a signal from the current detection means and a signal from the voltage detection means;
current level detection means for detecting the current level of the current detected by the current detection means and comparing the current level with a reference voltage source; and oscillation by a signal from the phase difference detection means and a signal from the current level detection means. It is composed of a variable oscillator that varies the frequency, and a drive circuit that supplies a current proportional to the mechanical vibration flowing through the piezoelectric body based on a signal from the variable oscillator and a drive voltage that keeps the phase difference constant. It is something.

Operation With the above configuration, the present invention uses the current level detection means to compare the current level of the current proportional to the mechanical imaging flowing through the piezoelectric body with a reference voltage source, and also uses the phase difference detection means to compare the current level of the current proportional to the mechanical imaging flowing through the piezoelectric body. The drive circuit is controlled via a variable oscillator by the signal from the current level detection means and the signal from the phase difference detection means. The current proportional to the vibration of the mechanical system flowing through the current and the phase difference are controlled to be constant. In other words, the rotation speed is controlled to be constant. Here, the current level is as shown in Figure 2 (
As shown in a), it is inversely proportional to the driving frequency of the ultrasonic motor, and even when the driving frequency is high, it can follow the characteristics of the driving frequency and rotation speed of the ultrasonic motor, and is stable in the high driving frequency range. can be controlled. Further, even in a low drive frequency range, for example, around 70 kHz as shown in FIG. 2(a), since control is performed using a phase difference, stable and accurate rotation speed control can be performed.

EXAMPLE Hereinafter, an example of the present invention will be described based on FIGS. 1 to 3.

Note that the same parts as the conventional example (Figs. 4 to 9)
The same reference numerals as in Figure) are given, and the explanation thereof will be omitted.

FIG. 1 is a circuit diagram of a driving device according to a first embodiment of the present invention, 51 is a current level detection circuit, and the output of the current detection circuit 35 is connected to the input side of this current level detection circuit 51. . The output of the current level detection circuit 51 is connected to one input side of an operational amplifier 54 via a resistor 52, and one input side of the operational amplifier 54 is connected to the resistor 5.
3 to the output side of the operational amplifier 54.

A reference voltage source 55 is connected to the other input side of the operational amplifier 54.
are connected, and an error amplifier 56 is configured by the resistors 52 and 53 and the operational amplifier 54. In addition, the drive circuit 22
The primary side of a transformer (not shown) for boosting the drive voltage within is connected to one input side (111II connected to resistor 52) of operational amplifier 54 via resistor 57.

Then, a current proportional to the mechanical vibration flowing through the piezoelectric body 2 is detected by the current detection circuit 35, and this detected current (
A signal having an amplitude) is input to the current level detection circuit 51. This current level detection circuit 51 performs half-wave rectification of the input current, then refines it, and outputs this integrated value. The output signal of this current level detection circuit 51 is converted into a voltage signal by a resistor 52, and then compared with a reference voltage source 55 having a reference voltage by an operational amplifier 54 to amplify the error. The output of this operational amplifier 54 is input to the variable oscillator 44.

Further, the output of the phase difference detector 50 is also input to the variable oscillator 44. The oscillation frequency of the variable oscillator 44 is varied according to each of these signals, and the rotation speed of the ultrasonic motor is controlled to be constant via the drive circuit 22. At this time,
The reference voltage of each of the reference voltage sources 41.55 needs to be set in accordance with the desired rotation speed.

As described above, in this embodiment, the integrated amplitude value of the current proportional to the mechanical system vibration flowing through the piezoelectric body 2 shown in FIG. 2(a) output from the current level detection circuit 51 is compared with the reference voltage source 55, By comparing the phase difference shown in FIG. 2(a) outputted from the phase difference detector 50 with the reference voltage source 41, the amplitude integral value of the current can be determined even in a high driving frequency range. As shown in Figure 2 (a)), it is possible to accurately control the rotation speed in the high drive frequency range (low rotation), and it is also possible to accurately control the rotation speed in the low drive frequency range (for example, 7
The rotation speed (near 0kHz, at high rotation) can be accurately controlled by the phase difference.

In addition, the signal input to the transformer of the drive circuit 22 is input to the operational amplifier 54 via the resistor 57, so that the drive voltage can be feedback-controlled, and the rotation speed for each drive voltage is as shown in FIG. - Torque characteristics can be changed. Therefore, by changing the voltage input to the transformer, the rotation speed-torque characteristics can be changed, making it easy to adapt to various specifications. As a comparative example, the conventional rotation speed-torque characteristic is shown in Figure 2 (C
).

Next, FIG. 3 shows another embodiment of the present invention. In this embodiment, a piezoelectric sensor 58 provided near the piezoelectric body 2 and a signal from the piezoelectric sensor 58 are inputted to the piezoelectric body 2. A current detection circuit 35a is constituted by a detector 59 that detects a current signal proportional to the flowing mechanical system vibration. Note that the piezoelectric sensor 58
The relationship between the output signal and drive frequency is shown in FIG. 2(a). When the piezoelectric sensor 58 is mounted on a stator (not shown), the magnitude of the detected signal (a current signal proportional to the mechanical vibration flowing through the piezoelectric body 2) changes depending on the position. By using this, the capacitors 26 and 27 for detecting current signals can be omitted, and the output of the drive circuit 22 can be applied to the piezoelectric body 23 in a larger amount than in the first embodiment.

Effects of the Invention As is clear from the above explanation, the present invention detects the current level of a current proportional to mechanical vibration flowing through a piezoelectric body, and compares the current level with a reference voltage source. , the drive circuit is controlled via a variable oscillator by each signal from a phase difference detection means that compares the phase difference between a current proportional to mechanical vibration flowing through the piezoelectric body and a voltage applied to the piezoelectric body with a reference voltage source. By doing this, it is possible to use the phase difference and current level to respond to the characteristics of the rotation speed relative to the drive frequency when the drive frequency is low (at high rotations), and when the drive frequency is high (at low rotations). can be met using the current level as compensation, so
Stable and accurate rotation speed control can be performed in any drive frequency range.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the ultrasonic motor drive device according to the first embodiment of the present invention, and FIG. 2(a) shows the integrated amplitude value of a current signal proportional to mechanical system vibration, and the amplitude of the current signal generated by the piezoelectric sensor. Integral value 9 Figure 2 (b) is a graph showing the relationship between the phase difference between current and voltage proportional to mechanical system vibration, drive frequency, and rotation speed and drive frequency. (C) is a graph showing the relationship between torque and rotational speed for each input voltage to the transformer, (b) is for the present invention, (C) is for the conventional one, and Fig. 3 is for another implementation of the present invention. FIG. 4 is an exploded perspective view of a conventional ultrasonic motor, FIG. 5 is a block diagram of a conventional ultrasonic motor drive device, and FIG. 6 is a block diagram of a conventional ultrasonic motor drive device. A block diagram of the drive device, Fig. 7 is an admittance characteristic diagram of the piezoelectric material that makes up the ultrasonic motor, Fig. 8 is an equivalent circuit diagram of the piezoelectric material that makes up the ultrasonic motor, and Fig. 9 is proportional to mechanical system vibration. The waveform diagram at points A, B, and C of the current detection circuit, and Figure 10 is a graph showing the relationship between the phase difference between the current and voltage, the drive frequency, and the rotation speed and drive frequency, which are proportional to the mechanical vibration of the ultrasonic motor. be. 1.2...Piezoelectric body, 4...Stator,
14... Rotor, 22... Drive circuit,
24.25... Resistance, 26.27...
Capacitor, 28, 29.30. 31.32.33・
... Resistor, 34... Operational amplifier, 35.
35a...Current detection circuit proportional to mechanical system vibration, 36...Voltage detection circuit, 37...Phase difference detection circuit, 38.39...Resistance , 40...
...Operation amplifier, 41...Reference voltage source, 4
2... Differential amplifier circuit, 43... Error amplifier, 44... Variable oscillator, 50...
Phase difference detector, 51... Current level detection circuit,
52.53... Resistor, 54... Operational amplifier, 55... Reference voltage source, 56...
Error amplifier, 57...Resistor, 58...
Piezoelectric sensor, 59...detector. Name of agent: Patent attorney Toshio Nakao and one other person Figure 4 [F] -/ l l Figure 7 Figure 8 Figure 9

Claims (5)

[Claims] (1) Current detection means for detecting a current proportional to mechanical vibration flowing through a piezoelectric body constituting an ultrasonic motor; voltage detection means for detecting a voltage applied to the piezoelectric body; phase difference detection means for detecting a phase difference between the signal and the signal from the voltage detection means; and current level detection means for detecting the current level of the current detected by the current detection means and comparing the current level with a reference voltage source. , a variable oscillator that varies an oscillation frequency so that a current proportional to mechanical vibration flowing through the piezoelectric body and the phase difference are kept constant based on a signal from the phase difference detection means and a signal from the current level detection means; An ultrasonic motor drive device comprising a drive circuit that supplies a drive voltage based on a signal from the variable oscillator. (2) The current level detection means is composed of a current level detection circuit connected to the current detection means, a reference voltage source, and an error amplifier having input terminals connected to the current level detection circuit and the reference voltage source, respectively. An ultrasonic motor drive device according to claim 1. (3) According to the magnitude of the drive voltage applied to the piezoelectric body from a drive circuit, the setting of a current proportional to the mechanical system vibration flowing through the piezoelectric body, which should be kept constant, is changed. 2. The ultrasonic motor drive device according to item 2. (4) The ultrasonic motor drive device according to claim 3, further comprising a resistor for connecting the input terminal of the error amplifier of the current level detection means and the drive circuit. (5) The ultrasonic motor drive device according to any one of claims 1 to 4, wherein the current detection means is a piezoelectric sensor that receives mechanical vibration of a piezoelectric body as input.