JPS622869A - Ultrasonic motor drive device - 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 Field of the Invention The present invention relates to an ultrasonic motor drive device that generates driving force using a piezoelectric body.

Conventional technology In recent years, ultrasonic motors have been announced that generate rotational, linear or curved motion by exciting ultrasonic vibrations using piezoelectric materials such as piezoelectric ceramics, and have attracted attention due to their simple structure, small size, and light weight. ing.

Hereinafter, the conventional technology of an ultrasonic motor will be explained with reference to the drawings.

Figure 5 shows an example of an ultrasonic motor, with an annular elastic body 1
An annular piezoelectric ceramic 2 is placed as a piezoelectric body on one of the annular surfaces of the
The piezoelectric driving body 3 is configured by laminating the two. 4 is a slider made of a wear-resistant material, and 6 is an elastic body, which are pasted together to form the moving body 6. The moving body 6 is in contact with the driving body 3 via the slider 4. When an electric field is applied to the piezoelectric body 2, bending vibration is excited in the circumferential direction of the driving body 3, and this becomes a traveling wave, thereby causing the moving body 6 to rotate.

FIG. 6 shows an example of the electrode structure of the piezoelectric ceramic 2 used in the ultrasonic motor of FIG. In the figure, the bending vibration has nine wavelengths in the circumferential direction. In the figure, M and B are electrode groups each consisting of a small region corresponding to a half wavelength, C is an electrode with a length of three-quarters of a wavelength, and D is an electrode with a length of a quarter of a wavelength.

Therefore, the position of the electrode group M and the electrode group B is 1/4 of each other.
There is a phase shift in wavelength (=90 degrees). Adjacent small electrode portions in the electrode group M and B are polarized oppositely to each other in the thickness direction. The bonding surface of the piezoelectric ceramic 2 with the elastic body 1 is the surface opposite to the surface shown in FIG. 6, and the electrode is a peta electrode. When in use, the electrode groups M and B are short-circuited, as indicated by diagonal lines in FIG.

The operation of the ultrasonic motor configured as above will be described below. Vo- on the electrode group of the piezoelectric body 2
When a voltage represented by sin (ωt) is applied (where vo is the instantaneous value of the voltage, ω is the angular frequency, and t is time), the driving body 3 bends and vibrates in the circumferential direction.

FIG. 7 is a perspective view of a part of the ultrasonic motor shown in FIG. This shows what it looks like when you do this.

FIG. 8 is an enlarged view of the contact situation between the moving body 6 and the driving body 3. Vo-sin (
ωt) and another electrode group BKVg-005(ωt), by applying voltages whose phases are shifted by π/2 from each other, a traveling wave of bending vibration can be created in the circumferential direction of the driving body 3. Generally speaking, if the amplitude of a traveling wave is ξ, then ξ=ξg −cos (cc
+t−kx ) ・・・−・(1) However, ξ
0: Instantaneous value of wave size: Wave number (=2π/λ) λ: Wavelength X: Can be expressed as position. Equation (1) is ξ=ξG-(Co!l(ωt)-cot(kx)+5i
n(ωt)−gin(kx)) ・−・−(2), Equation (2) is a wave whose traveling wave is temporally out of phase by π/2 with cos(ωt) and 5in(ωt), and cojs(kx) positionally out of phase by π/2 and 5in
(kx). According to the above explanation, the piezoelectric bodies 2 are positioned at π/
Since the electrode groups M and B have a phase shift of 2 (=λ/4), the temporal phase difference of π/B from the output of the oscillator with a frequency output equal to the resonant frequency of the driver 3
By creating an AC voltage shifted by 2 and applying it to the electrode group, a traveling wave of bending vibration can be created in the driving body 3.

Figure 8 shows how the point of the driving body moves in an ellipse with the long axis 2W and the short axis 2u due to the traveling wave. , it shows how the wave moves at a speed of V=ωU in the opposite direction to the direction of travel of the wave. That is, the moving body 6 is pressed against the driving body 3 with an arbitrary static pressure, contacts the surface of the driving body 3, and is driven by the frictional force between the moving body 6 and the driving body 3 at a velocity in the direction opposite to the direction of wave propagation. Ru.

If there is a gap between the two, the speed will be smaller than the above V.

The speed ma of the ultrasonic motor shown above is ma;ωtclC
ωξ0 can be expressed as (3) and is proportional to the maximum amplitude ξ0 of the bending vibration of the driving body 3. The magnitude of the amplitude of bending vibration will differ if the driving frequency is different even if the applied voltage is the same. FIG. 9 shows the frequency characteristics of the impedance and sensitivity (amplitude/applied voltage, defined as the amplitude value in units of applied voltage) of the driver 3. From the same figure, the 6th
When a piezoelectric body with the electrode structure shown in the figure is used, the resonance of the driver 3 appears as one relatively large resonance below and above the original resonant frequency fo, and the sensitivity is maximum at each resonant frequency, and the original resonance frequency is It reaches its maximum at the resonant frequency fo.

Therefore, in order to drive the ultrasonic motor efficiently, it is preferable to drive it at the resonant frequency of the drive body 3.

Problem to be solved by the invention However, as shown in FIG. Change. Generally, as the temperature of the driving body increases, the resonant frequency decreases. Since the driving body 3 generates heat due to mechanical loss during driving, the resonant frequency changes every moment due to load fluctuations and heat generation.

When the tab drive body 3 is driven using an oscillation circuit with a constant frequency as described above, it is not always possible to perform efficient and optimal driving.

The present invention has been made in view of the above points, and an object of the present invention is to provide an ultrasonic motor drive device that can always perform efficient and optimal drive even if the resonant frequency of the drive body changes.

The only way to solve the problem is to use the output of the voltage controlled oscillation circuit to drive the drive body including the piezoelectric body, detect the in-phase component of the drive voltage of the current flowing into the piezoelectric body with a detection circuit, and use the detected value as described above. The data is stored in the memory circuit at each set time, and the comparison circuit compares the memory result of the memory circuit at the previous timing with the current memory result, and based on the comparison result, the detected value becomes a dog. The oscillation frequency of the voltage controlled oscillation circuit is set by changing the voltage value of the control terminal of the oscillation circuit.

When the previous memory result is larger than the current memory result, and the control voltage at the current memory is larger than the control voltage at the previous memory of the oscillation circuit, the control voltage is On the other hand, when the control voltage during the current storage is smaller than the control voltage during the previous storage, the control voltage is increased.

In addition, if the previous memory result is smaller than the current memory result, and the control voltage at the previous memory is higher than the current one, the control voltage at the previous memory is made smaller. However, when it is smaller than the current size, it will be made even smaller.

Therefore, even if the resonant frequency of the driver changes due to load or temperature, the output frequency of the oscillation circuit is always adjusted to the resonant frequency. In other words, the piezoelectric driver can be driven at the resonant frequency at which the common-mode current is largest for the same applied voltage.

Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. FIG. 2 is an equivalent circuit near the resonance frequency when viewed from the electrode group M or B of the piezoelectric body 2 in the piezoelectric drive body 3 shown in FIGS. 5 and 6, and (a) in FIG. An equivalent circuit near the frequency; (b) shows an equivalent circuit at the resonant frequency. In the same figure, c.

represents electrical capacity, C1 is mechanical elasticity, Ll is mass, R1 is mechanical loss, Co is electric arm, CI is
+ The series circuit of Ll and R1 is called a mechanical arm. At the resonant frequency, C1 and Ll resonate. Further, is represents an electrical current, and - represents a mechanical current (Tsumari speed). Therefore, if the driver 3 is driven at the resonant frequency, the bell will flow to the maximum with the same voltage. In other words, the maximum displacement can be obtained (3)
The maximum speed of the moving body 6 can be obtained from the formula.

In FIG. 1, R1 is a resistance for detecting the inflow current to the piezoelectric ceramic 2 connected to the piezoelectric ceramic 2 of the piezoelectric driver 3, C1 and C2 are the electrode group of the piezoelectric ceramic 2, and between B and the back electrode. A capacitor with the same value as the electrical capacitance, R2
is a resistance having the same value as the resistance R1. Therefore, if the difference between the terminal voltages of resistor R1 and resistor R2 is taken by a differential amplifier 1o, the electrical current io will be canceled out and only the mechanical current m will be taken out as an output, and this - will be controlled to be maximum. Then, the amplitude ξG can be maximized with the same applied voltage, and optimal driving can be achieved.

7 is a voltage controlled oscillation circuit, and oscillation frequency control terminal 7! Depending on the voltage value of L, the oscillation frequency can be changed as shown in FIG. 8 is a 90° phase shifter that shifts the output of the oscillation circuit 7 to 90°.
phase shift. The output of the oscillator 7 and the signal phase-shifted by 900 are respectively sent to the power amplifier 9.

The signal is amplified at step 9b and input to two electrode groups B whose positions differ in phase by 90'. Memory circuits 12aL and 12b store values obtained by converting the output of the differential amplifier 10 into direct current by the rectifier circuit 11. Reference numeral 13 denotes a timing circuit that controls the storage time in the storage circuits 12& and 12b.

Now, when a control voltage is applied to the control terminal 71L by the control circuit 14 at a certain time, the oscillator 7 oscillates at a frequency determined by the control characteristics of the oscillation frequency of the oscillator shown in FIG. For example, if the voltage at the control terminal is vl, the oscillation frequency is fl. This oscillation output is inputted to a 90° phase shifter 8 and phase-shifted to eo', or directly inputted to power amplifiers ea and eb, respectively, to obtain the level required to rotate the moving object 6 at a predetermined speed. is amplified to. The amplified signal is input to the electrode group M, B, and creates a traveling wave of bending vibration in the driving body 3 as described above. The mechanical current flowing in at this time is obtained by the differential amplifier 1o, and the rectifier circuit 1
1 converts the AC value to DC and stores it in the storage circuit 121L at the timing created by the timing circuit 13.

Next, the control circuit 16 increases the control voltage applied to the terminal 71L by a set value to V in FIG. Then oscillator 7
The oscillation frequency of is f3. The mechanical current generated by this f3 is transferred to the memory circuit 12 by the timing circuit 13.
b and compares it with the memory result of the previous memory circuit 121 in the comparator 14. When the mechanical current - becomes small, the control voltage is returned to v5 to Vl, and when it becomes large, it is set to v2. is increased again by the set value, and the mechanical current at that time is stored in the memory circuit 12& and compared by the comparator 14.

In this way, when the control voltage is increased and the mechanical current increases, the control voltage is increased again by the set value, and when the control voltage is similarly increased and the mechanical current decreases, the control voltage is increased. is decreased by the set value. Also, when the control voltage is decreased and the mechanical current increases, the control voltage is further decreased by the set value, and in the same way, when the control voltage is decreased and the mechanical current decreases, the control voltage is reduced by the set value. To increase. As a result, if the variable range of the control voltage is made to match the range in which the resonant frequency of the driver 3 changes, the control circuit 16 adjusts the output frequency of the oscillator 7 so that the drive frequency of the driver 3 always matches the resonant frequency. control. Therefore, the maximum mechanical current for the same applied voltage is always −
Efficient driving is possible.

Figure 4 is another example of a circuit that draws only the mechanical current.
), step-up transformer/s 161L in parallel with piezoelectric ceramic 2,
The inductance L of 16b is selected so that this inductance L and the capacitance value co resonate in parallel near the driving frequency. As a result, a terminal voltage proportional to the mechanical current - is generated across the resistor R1.

Effects of the Invention According to the present invention, even if the impedance characteristics and resonant frequency of the piezoelectric drive body change due to changes in temperature, static load, load, etc., stable and optimum driving can be performed at all times.

[Brief explanation of the drawing]

FIG. 1 is a control characteristic diagram of the voltage controlled oscillation circuit used in the embodiment of FIG. 1, and FIG.
The figure is a block diagram showing another example of a mechanical current detection circuit flowing into a piezoelectric body, and FIG. 6 is a cross-sectional view of a conventional ultrasonic motor.
Figure 6 is a plan view showing the shape and electrode structure of the piezoelectric body used in Figure 1, Figure 7 is a model diagram showing the vibration state of the driving body of the ultrasonic motor, and Figure 8 is the ultrasonic motor. FIG. 9 is a frequency characteristic diagram of impedance and sensitivity of the driving body, and FIG. 10 is a characteristic diagram showing changes in impedance characteristics of the driving body due to load. 7...Voltage controlled oscillator, 8...9o degree phase shifter, 91L, 9b...power amplifier, 1o...
... Differential amplifier, 11 ... Rectifier circuit, 1
2a, 12b... Memory circuit, 13...
Timing circuit, 14... Comparator, 15...
...Control circuit, 161L, 16b...Step-up transformer. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 (α) C11) Figure 3 Control voltage, pressure, (v) Figure 4 Figure 5 Figure 6 Jump Figure 7 Figure 8

Claims (1)

[Claims] A piezoelectric driving body is formed by laminating an elastic body and a piezoelectric body, and by applying a voltage to the piezoelectric driving body, bending vibration is excited in the driving body to create a traveling wave, and the pasting of the elastic body is performed. In an ultrasonic motor that moves an object placed on the elastic body by elliptically moving a mass point on a surface facing the surface, the piezoelectric motor can vary the frequency by controlling a voltage applied to a control terminal. a voltage controlled oscillation circuit that generates an alternating current voltage for driving the body; a detection circuit for detecting a current component flowing into the mechanical arm of the current that flows when the drive voltage is applied to the piezoelectric body; and an output of the current detection circuit. a memory circuit that stores the current output at set time intervals, a comparison circuit that compares the previous output of the memory circuit with the current output, and a comparison circuit that constantly flows into the piezoelectric body based on the comparison result of the comparison circuit. An ultrasonic motor drive device comprising: a control circuit that controls the oscillation frequency of the oscillation circuit by a voltage applied to the control terminal so that the current component is maximized.