JP2001078472A - Device and method for driving ultrasonic motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drive an ultrasonic motor at the resonance frequency of a vibrating body. SOLUTION: In an ultrasonic motor drive device 1, an external inductor 20 for impedance compensation is connected to the vibrating body of an ultrasonic motor 2. The drive device 1 detects the phase difference between a drive voltage(v) and a drive current (i) supplied to the motor 2 and makes servo-control on the frequency of the drive, voltage(v) so that the phase difference becomes zero. In addition, the device 1 also detects the rotational speed of the motor 2 and makes servo-control on the speed by controlling the drive voltage(v).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ultrasonic motor driving apparatus and an ultrasonic motor driving method.

[0002]

2. Description of the Related Art At present, ultrasonic motors for converting high-frequency elastic vibration generated by a piezoelectric element or the like into mechanical output using frictional force have been put into practical use. This ultrasonic motor has attracted attention as a next-generation actuator because it can obtain a high torque at a low speed and has a high response speed as compared with a conventional electromagnetic motor.

FIG. 7 shows a disk-type ultrasonic motor as an example, and the basic operation principle of the ultrasonic motor will be described using this disk-type ultrasonic motor.

As shown in FIG. 7, a disk-type ultrasonic motor 100 is a vibrating body formed by bonding a piezoelectric element 102 such as a piezoelectric ceramic to an elastic body 101 formed of a metal or the like formed in a ring shape. The moving body 103 includes a friction member 104 provided on a contact surface with the vibration body 103.

As shown in FIG. 8, the piezoelectric element 102 is polarized in the thickness direction of the vibrating body 103 (the direction of arrow A in FIG. 8). The piezoelectric element 102 is provided with a plurality of electrodes 106 having a length corresponding to a half wavelength of the flexural vibration. When two AC powers whose positions are shifted by 1/4 wavelength are applied to such a piezoelectric element 102, two standing waves of flexural vibration shifted by 1/4 wavelength are excited in the vibrating body 103.

When two standing waves are excited in the vibrating body 103, as shown in FIG. 9, an arbitrary point on the surface of the vibrating body 103 moves so as to draw an elliptical trajectory. A traveling wave is excited. Therefore, when the moving body 105 is pressed against the vibrating body 103 in which the traveling wave is generated in a pseudo manner, the vibrating body 1
05 rotates in the direction opposite to the traveling direction of the traveling wave.

As described above, the ultrasonic motor 100 has a 1/4
Drive electrodes 10 of a plurality of piezoelectric elements formed with wavelength shift
6 is applied with two-phase AC voltages having a phase shift of 90 °, the vibrating body 103 excites a traveling wave of flexural vibration, and the moving body 105 rotates and moves in accordance with the vibration of the vibrating body 103. .

Further, as shown in FIG. 10, the equivalent circuit viewed from the drive terminal of the vibrating body 103 is an electric arm 121 which is a circuit showing the electric property of the piezoelectric element 102 alone, and the mechanical property of the ultrasonic motor 100. Arm 122 which is a circuit representing
And a parallel circuit. The electric arm 121 is represented by a capacitance Cd. The mechanical arm 122 is represented by a capacitance Cm, an inductance Lm, and a resistance Rm.

The frequency characteristics of admittance viewed from the drive terminal of the vibrating body 103 are as shown in FIG. 11, for example. The magnitude of the vibration of the vibrating body 103 is proportional to the magnitude of the current flowing to the drive terminal. If driven at the same voltage, the current will be proportional to the admittance. Therefore, if the driving is performed in the vicinity of the resonance frequency of the vibrating body 103 as shown in FIG. 11B, a vibration having a large amplitude can be obtained with a relatively low driving voltage.

As described above, in the ultrasonic motor 100, high efficiency can be obtained by driving the vibrating body 103 near the resonance frequency.

[0011]

By the way, the vibrating body 10
The resonance frequency of No. 3 changes depending on temperature, load, and the like. Therefore, a drive circuit for the ultrasonic motor requires a servo circuit for driving the ultrasonic motor 100 at a frequency near the resonance frequency together with a basic drive circuit.

A conventional ultrasonic motor drive circuit employs a method of detecting a drive current and servo-controlling the frequency so that the drive current has a constant value.

However, at the peak point of the amplitude of the drive current, as shown in FIG. 12, the amplitude level decreases even if the frequency moves in the direction of increasing the frequency or the direction of decreasing the frequency. I will. Therefore, in the method in which the drive current is fixed, the servo lock cannot be performed at the peak of the amplitude of the drive current, and the servo lock is performed at a position where the level is lower than the peak of the amplitude. The ultrasonic motor could not be driven at the resonance frequency. Further, in such a system, a servo system having a narrow servo range, a level fluctuation centered on the reference frequency is asymmetric on the left and right, and an area having a small level fluctuation width is generated on one side, so that it is difficult to pull in and easily deviate. Had become.

In the method of keeping the driving current constant, the operating range may be deviated due to the characteristics of the ultrasonic motor changing over time, so that the driving control may not be performed thereafter.

The present invention has been made in view of such circumstances, and provides an ultrasonic motor driving apparatus and an ultrasonic motor driving method capable of driving an ultrasonic motor at a resonance frequency of a vibrating body. The purpose is to do.

[0016]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a driving apparatus for an ultrasonic motor according to the present invention is provided with a vibrator which is supplied with an alternating voltage and vibrates by the alternating voltage, and which generates the vibrator. A driving device for an ultrasonic motor that drives an ultrasonic motor having a moving body that moves in accordance with the vibration that is generated, and an impedance compensating unit connected to the vibrating body, and supplying an AC voltage to the vibrating body. Driving means for driving the ultrasonic motor, phase difference detecting means for detecting a phase difference between a voltage applied to the vibrating body and a current flowing through the vibrating body, and a phase difference detected by the phase difference detecting means. And a frequency control unit for controlling the frequency of the AC voltage supplied by the driving unit.

In this ultrasonic motor driving device, impedance compensation is performed on the vibrating body, and at the time of resonance,
By eliminating the inductance component and the capacitance component, the phase difference between the voltage and the current changes linearly when the frequency is changed in a servo range around the resonance frequency. In the ultrasonic motor driving device, the frequency of the AC voltage applied to the vibrating body is made to follow the resonance frequency of the vibrating body based on the phase difference between the voltage applied to the vibrating body and the current flowing through the vibrating body. .

The ultrasonic motor driving device according to the present invention is characterized in that it comprises a driving voltage control means for controlling a driving voltage level to be supplied to the vibrator according to the speed of the ultrasonic motor.

In the ultrasonic motor driving device, the voltage of the voltage applied to the vibrating body is controlled while the frequency of the AC voltage applied to the vibrating body follows the resonance frequency of the vibrating body. Control the speed of the motor. In this ultrasonic motor driving device, the speed of the ultrasonic motor is controlled using, for example, a current flowing through the vibrating body, an encoder, or the like.

The ultrasonic motor driving apparatus according to the present invention is characterized in that the driving means applies a predetermined level of AC voltage to the vibrating body when the ultrasonic motor is stopped.

The ultrasonic motor generates no torque unless a voltage higher than a certain level is supplied to the vibrator. In other words, the ultrasonic motor does not operate even when a voltage lower than a certain level is supplied to the vibrator. For this reason, in the ultrasonic motor driving device, even when the ultrasonic motor is stopped, a predetermined level of the AC voltage is continuously applied, and the frequency of the AC voltage applied to the vibrating body is continuously made to follow the resonance frequency of the vibrating body.

A method of driving an ultrasonic motor according to the present invention is directed to an ultrasonic motor having a vibrating body supplied with an AC voltage and vibrating by the AC voltage, and a moving body that moves in accordance with the vibration generated by the vibrating body. A method of driving an ultrasonic motor that drives the ultrasonic motor, wherein the impedance of the vibrating body is compensated, a phase difference between a voltage applied to the vibrating body and a current flowing through the vibrating body is detected, and the detected phase difference is determined. The frequency of the AC voltage supplied to the vibrator is controlled.

In this ultrasonic motor driving method, impedance compensation is performed on the vibrating body so that the inductance component and the capacitance component are eliminated at the time of resonance, and the frequency is varied in a servo range centered on the resonance frequency. At the same time, the phase difference between the voltage and the current changes linearly. In the ultrasonic motor driving method, the frequency of the AC voltage applied to the vibrating body is made to follow the resonance frequency of the vibrating body based on the phase difference between the voltage applied to the vibrating body and the current flowing through the vibrating body. .

A driving method of an ultrasonic motor according to the present invention is characterized in that a driving voltage level supplied to the vibrator is controlled according to a speed of the ultrasonic motor.

In the method of driving the ultrasonic motor, the voltage value of the voltage applied to the vibrating body is controlled while the frequency of the AC voltage applied to the vibrating body follows the resonance frequency of the vibrating body. Control the speed of the motor. In this ultrasonic motor driving device, for example, the current flowing through the vibrating body and the speed of the ultrasonic motor are detected, and the voltage value applied to the vibrating body is controlled to control the speed of the ultrasonic motor. I do.

A method of driving an ultrasonic motor according to the present invention is characterized in that a predetermined level of an AC voltage is applied to the vibrator when the ultrasonic motor is stopped.

The ultrasonic motor generates no torque unless a voltage higher than a certain level is supplied to the vibrator. In other words, the ultrasonic motor does not operate even when a voltage lower than a certain level is supplied to the vibrator. Therefore, in the driving method of the ultrasonic motor, the AC voltage of the predetermined level is continuously applied even when the ultrasonic motor is stopped, and the frequency of the AC voltage applied to the vibrating body continues to follow the resonance frequency of the vibrating body.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, as an embodiment of the present invention, an ultrasonic motor driving apparatus to which the present invention is applied will be described.

FIG. 1 shows a driving device of an ultrasonic motor to which the present invention is applied.

The driving device 1 for an ultrasonic motor shown in FIG.
This is a device that generates torque in the ultrasonic motor 2 and drives the ultrasonic motor 2.

The ultrasonic motor driving device 1 comprises a driving voltage detecting section 3, a driving current detecting section 4, a first amplifier 5, a second amplifier 6, a first comparator 7, a second Comparator 8, first monomultivibrator 9, second monomultivibrator 10, flip-flop circuit 11, integration circuit 12, and VCO (Voltage Controller)
lled Ocillator) 13, a first waveform generator 14, a second waveform generator 15, a first power amplifier 16, a second power amplifier 17, a peak hold circuit 18,
It has a gain control circuit 19 and an external inductor 20.

The ultrasonic motor 2 has an external inductor 20 mounted thereon to compensate for impedance of a vibrating body of the ultrasonic motor 2. As described in the conventional example, the electrical equivalent circuit of the ultrasonic motor 2 is represented by a parallel circuit of an electric arm composed of a capacitance component Cd and a mechanical arm representing the mechanical properties of the ultrasonic motor. Ultrasonic motor drive 1
Then, as shown in FIG. 2, an external inductor 20 is connected in parallel with the capacitance component Cd of the equivalent circuit of the ultrasonic motor 2, and the capacitance component Cd is absorbed as a tank circuit. The value of the inductance Ld of the external inductor 20 is determined as follows.

Ω ₀ = 1 / √ (Ld · Cd) = 1 / √ (Lm · Cm) Ld = 1 / {Cd (2πf ₀ ) ² } = (Lm · Cm) / C
d f ₀ = resonant frequency of vibrator Lm = inductance of machine arm Cm = capacitance of machine arm

The drive voltage detector 3 is configured to supply an AC drive voltage v supplied to a piezoelectric element forming a vibrating body of the ultrasonic motor 2.
Is detected. The drive voltage detector 3 detects the detected drive voltage v
And outputs a voltage detection signal corresponding to. This voltage detection signal is supplied to the first amplifier 5. When two sine wave voltages having phases shifted by 90 ° are supplied to the piezoelectric element as the drive voltage, at least one of the sine wave voltages may be detected.

The drive current detector 4 detects an AC drive current i flowing through the piezoelectric element based on an AC drive voltage v supplied to the piezoelectric element constituting the vibrating body of the ultrasonic motor 2. The drive current detector 4 outputs a current detection signal corresponding to the detected drive current i. This current detection signal is
To the amplifier 6. When two sine wave voltages having phases shifted by 90 ° are supplied to the piezoelectric element as the drive voltage v, a current flowing by at least one of the sine wave voltages may be detected.

The first amplifier 5 amplifies the voltage detection signal output from the drive voltage detector 3 to a saturation level,
Is supplied to the comparator 7. First comparator 7
Generates a pulse signal that is turned on and off at a zero cross point of the voltage detection signal by comparing the voltage detection signal amplified to the saturation level with a power supply voltage (for example, 5 volts). As described above, by amplifying the voltage detection signal to the saturation level and detecting the zero cross point, the signal level of the voltage detection signal output from the drive voltage detection unit 3 is not affected,
The phase can be detected by detecting the zero-cross point of the drive voltage v supplied to the vibrating body. The pulse signal output from the first comparator 7 is supplied to a first mono multivibrator 9.

The second amplifier 6 amplifies the current detection signal output from the drive current detection unit 4 to a saturation level, and
Is supplied to the comparator 8. Second comparator 8
Generates a pulse signal that is turned on and off at a zero cross point of the current detection signal by comparing the current detection signal amplified to the saturation level with the power supply voltage. As described above, by amplifying the current detection signal to the saturation level and detecting the zero-cross point, the drive current i supplied to the vibrator is not affected by the signal level of the current detection signal output from the drive current detection unit 3. Can be detected to detect the phase. The pulse signal output from the second comparator 8 is supplied to a second mono multivibrator 10.

The first mono-multi vibrator 9 has the first
A trigger pulse is generated at the timing of the rising edge of the pulse signal output from the comparator 7. This trigger pulse is a trigger pulse indicating the phase of the drive voltage v supplied to the vibrating body, and is hereinafter referred to as a voltage phase trigger pulse. The voltage phase trigger pulse output from the first mono multivibrator 9 is supplied to the flip-flop circuit 11.

The second mono-multivibrator 10 generates a trigger pulse at the timing of the rising edge of the pulse signal output from the second comparator 8.
This trigger pulse is a trigger pulse representing the phase of the drive current i supplied to the vibrating body, and is hereinafter referred to as a current phase trigger pulse. The current phase trigger pulse output from the second mono multivibrator 10 is supplied to the flip-flop circuit 11.

The flip-flop circuit 11 generates a pulse signal having a time width corresponding to the phase difference between the voltage phase trigger pulse and the current phase trigger pulse. For example, the flip-flop circuit 11 includes an RS flip-flop, and a voltage phase trigger pulse is input to a set terminal and a current phase trigger pulse is input to a reset terminal. The RS flip-flop outputs a pulse that is turned on at the timing when the voltage phase trigger pulse is supplied and turned off at the timing when the current phase trigger pulse is supplied.

Note that this flip-flop circuit 11
When the timing of the voltage phase trigger pulse coincides with the timing of the current phase trigger pulse, that is, the phase difference between the driving voltage v supplied to the vibrating body and the driving current i flowing through the vibrating body becomes zero.
At this time, a pulse having a predetermined time width (t ₀ ) is output. Then, the flip-flop circuit 11
Outputs a signal having a pulse width (t ₀ + t ₊ δ) obtained by adding a predetermined time width (t ₀ ) by this advance time (t ₊ δ) when the phase of the voltage phase trigger pulse is advanced. the delay time when the direction of current phase trigger pulse phase delayed _- to output a signal (t [delta]) by subtracting the pulse width from a predetermined time width _{(t 0) (t 0 +} t + δ) To The predetermined time width (t ₀ ) is a time width during which the reference voltage Vref is output when integration is performed by the integration circuit 12 at the subsequent stage. The reference voltage Vref is a voltage at which the center frequency is output from the VCO 13 at the subsequent stage. For example,
As shown in FIG. 1, a reference voltage Vref may be applied to the integration circuit 12. Further, for example, when the flip-flop circuit 11 is configured by an RS flip-flop, in order to output a pulse of a predetermined time width (t ₀ ) when the phase difference is 0, the current phase trigger pulse is set to this value. It may be delayed by a predetermined time width (t ₀ ) and supplied to the reset terminal.

The integration circuit 12 is a flip-flop circuit 1
The pulse signal output from 1 is integrated and smoothed, and an analog control voltage to be supplied to the VCO 13 at the subsequent stage is generated. When a pulse having a time width (t ₀ ) is continuously output from the flip-flop circuit 11, the integration circuit 12 outputs a control voltage having a voltage value of the reference voltage Vref. Then, when the supplied pulse signal fluctuates around the time width (t ₀ ), the integration circuit 12 outputs a control voltage that increases or decreases around the reference voltage Vref. The control voltage output from the integration circuit 12 is VCO1
2 is supplied.

The VCO 12 generates a clock signal whose frequency is changed according to the input analog control voltage. The center frequency of the VCO 12 generates a clock signal having a frequency n times the resonance frequency f ₀ of the vibrating body of the ultrasonic motor 2 (for example, n = 90). This VCO 12
Around the center frequency n · f ₀ of the output clock signal, the n times the frequency of the lower limit frequency f _1, the upper limit frequency f ₂
Is varied in the range up to n times the frequency. Lower limit frequency f
₁ and the upper limit frequency f ₂ are the frequency at a point 3 dB lower than the amplitude value obtained at the resonance frequency f ₀ in FIGS. The VCO 12 outputs a clock signal whose frequency is controlled in accordance with the control voltage to the first waveform generator 14.
And to the second waveform generator 15.

The first waveform generator 14 stores amplitude data for one wavelength of a sine wave in correspondence with addresses from 0 to (n-1). Specifically, one wavelength of the sine wave is divided into n and sampled, and the sampled value is stored in correspondence with addresses 0 to (n-1). The first waveform generation unit 14 periodically counts the values of 0 to (n-1) by the clock supplied from the VCO 12, and reads out the amplitude data of the address of the counted value. Then, the first waveform generation unit 14 performs D / A conversion on the read amplitude data and outputs an analog signal.

The analog signal output from the first waveform generator 14 is a sine wave signal having a frequency 1 / n of the frequency of the clock signal output from the VCO 12. Therefore, the first waveform generating section 14 outputs the resonance frequency f
₀ around the, outputs a sine wave signal varying from the lower limit frequency f ₁ to the upper limit frequency f _2. That is, the first waveform generator 14 controls the frequency of the analog signal to be output in accordance with the control voltage output from the integration circuit 12, and the frequency thereof is set at the lower limit frequency f centered on the resonance frequency f _0. It varies from ₁ to the upper limit frequency f _2.

In order to generate a sinusoidal signal varying from the lower limit frequency f ₁ to the upper limit frequency f ₂ according to the control voltage output from the integration circuit 12, the VCO whose center frequency matches the resonance frequency f ₀ is generated. After generating a pulse signal by using, the pulse signal can be generated by filtering. However, in this method, since a sine wave is generated from a rectangular wave, the waveform distortion is large, and the jitter of the VCO is directly affected. Therefore, the zero cross point for detecting the phase difference is not stably detected. However, in the method of setting the frequency of the clock signal generated by the VCO to n times the resonance frequency f ₀ and reading out the sine wave sampling data stored in the memory by the clock having the frequency of n times,
The effect of the jitter of the VCO becomes 1 / n, and the waveform distortion becomes very small.

The second waveform generator 15 converts the amplitude data for one wavelength of the cosine wave, which is 90 ° out of phase with respect to the sine wave, stored in the first waveform generator 14 into 0- ( n-
It is stored in correspondence with the addresses up to 1). Specifically, one wavelength of the cosine wave is divided into n and sampled,
The sampled values are stored in correspondence with addresses 0 to (n-1). The second waveform generator 15 outputs V
By the clock supplied from the CO 12, 0 to (n−
The value of 1) is counted periodically, and the amplitude data at the address of the counted value is read. Then, the second waveform generator 15 D / A converts the read amplitude data and outputs an analog signal.

As described above, the analog signal output from the second waveform generator 15 has the same period as the analog signal output from the first waveform generator
The cosine wave signal is shifted in phase by 0 °.

The first power amplifier 16 amplifies the power of the sine wave signal output from the first waveform generator 14 and supplies the amplified signal to the vibrating body of the ultrasonic motor 2. Then, the driving voltage v applied to the vibrating body from the first power amplifier 16 is detected by the voltage detection unit 3, and the driving current i supplied to the vibrating body from the first power amplifier 16 is detected by the current detection. This is detected by the unit 4.

The second power amplifier 17 amplifies the power of the cosine wave signal output from the second waveform generator 15 and supplies the amplified signal to the vibrating body of the ultrasonic motor 2.

The peak hold circuit 18 holds the peak of the detection signal detected by the drive current detector 4, and detects the peak value. The peak hold circuit 18 supplies the detected peak value to the gain control circuit 19.

The gain control circuit 19 compares the peak value supplied from the peak hold circuit 18 with a reference voltage for speed control, and according to the error signal, the first power amplifier 16 and the second The power amplifier 17 is controlled to vary the drive voltage.

Next, the operation of the ultrasonic motor driving device 1 will be described with reference to the waveform diagram shown in FIG.

First, the drive voltage detector 3 detects the drive voltage v applied to the vibrating body, and as shown in FIG.
Outputs a sine wave voltage detection signal. The voltage detection signal is saturated and amplified by the first amplifier 5 and is converted by the first comparator 7 into a pulse signal indicating a zero cross point as shown in FIG. Then, the first monomultivibrator 9 outputs a voltage phase trigger pulse generated at the timing of the rising edge of the zero-cross point as shown in FIG.

The drive current detector 4 detects the drive current i flowing through the vibrator, and outputs a sine wave current detection signal as shown in FIG. This current detection signal is
, And is converted into a pulse signal indicating a zero-cross point as shown in FIG. Then, the second mono-multi vibrator 10 outputs a current phase trigger pulse generated at the timing of the rising edge of the zero cross point as shown in FIG.

Both the voltage phase trigger pulse and the current phase trigger pulse are supplied to a flip-flop circuit 11, which calculates the phase difference as shown in FIG. 3 (G). The obtained phase difference is
As shown in FIG. 3H, the signal is smoothed by the integration circuit 12 and supplied to the VCO 13 as an analog control voltage. The integrator circuit 12 outputs the reference voltage Vref when the phase difference is 0, and outputs an analog control voltage that increases and decreases around the Vref.

As shown in FIG. 3 (I), the clock signal output from the VCO 13 has a center frequency n times the resonance frequency f ₀ when the input voltage is Vref (the phase difference is 0). Is n · f ₁ according to the fluctuation of the input voltage.
To n · f ₂ . Then, as shown in FIG. 3 (J), the frequency of the first power amplifier 16 is varied in the range of f _{1 to} f ₂ according to the change of the input voltage, and the phase difference between the current and the current is 0. A drive voltage v locked at a certain frequency is supplied to the vibrating body of the ultrasonic motor 2.

As described above, in the ultrasonic motor driving device 1, the driving voltage v applied to the vibrating body of the ultrasonic motor 2
And the phase difference between the driving current i flowing through the vibrating body and
The frequency of the drive voltage v is servo-controlled so that the phase difference becomes zero.

For this reason, in the ultrasonic motor driving device 1, the ultrasonic motor 2 can be driven at the frequency with the highest driving efficiency, and the control can be easily performed. Furthermore, even if the characteristics of the ultrasonic motor 2 change over time due to temperature or other influences, it is possible to follow the changed resonance frequency f ₀ , so that the operation range is not deviated and control is possible. The time is longer and the service life is longer.

In the ultrasonic motor driving apparatus 1, an external inductor 20 is connected to the ultrasonic motor 2,
Implements impedance compensation. When impedance compensation is performed by the external inductor 20 in this manner, a phase change between the voltage and the current becomes linear with respect to a frequency change near the resonance frequency f ₀ , and the stability of servo control is increased.

The difference in control stability between when there is no compensation by the external inductor 20 and when there is compensation will be described below.

FIG. 4 shows a vector diagram and a phase characteristic of admittance (reciprocal of the impedance of the circuit shown in FIG. 11) as viewed from the drive terminal of the moving body of the ultrasonic motor 2 when the external inductor 20 is not provided. FIG.
2 shows a vector diagram of admittance (reciprocal of the impedance of the circuit shown in FIG. 2) and a phase characteristic as viewed from the drive terminal of the moving body of the ultrasonic motor 2 when the external inductor 20 is connected. 4 (A) and FIG.
The horizontal axis of the vector diagram shown in (A) indicates the real component of admittance, and the vertical axis indicates the imaginary component of admittance. The resonance point is f ₀ , the lower limit frequency is f ₁ , and the upper limit frequency is f
Indicated by ₂ . 4B and 5B, the horizontal axis represents frequency, and the vertical axis represents phase.

The admittance vector when there is no external inductor 20 is, as shown in FIG.
When the frequency is increased from 0, the trajectory linearly rises on the imaginary axis and is drawn to the position of point O '. This is an effect due to only the capacitance Cd of the electric arm. Then, from the position of the O 'points on the imaginary axis, caused the influence of mechanical arms, draw the circumference of one rotation while through f _1, f _0, f ₂ in clockwise, O on the imaginary axis Return to point '. And
When the frequency further increases, the vector locus further increases on the imaginary axis due to the influence of the electric arm.

As shown in FIG. 5A, when the frequency is increased from 0, the locus of the admittance when the external inductor 20 is connected increases linearly on the imaginary axis. It is drawn up to the position of the origin O. Subsequently, from the position of the origin O, clockwise, f ₁ , f ₀ , f ₂
Draw a circumference of one rotation while passing through and return to the position of the origin O. When the frequency further increases, the vector locus further increases on the imaginary axis.

Here, the circumference drawn by the vector locus indicates the resonance state by the mechanical arm, and the length from the O 'point or the origin to each point on the circumference is the resonance amplitude (motor speed).
Is proportional to The phase of the drive current i with respect to the drive voltage v is represented by the angle between the line segment O-fx and the X axis, as indicated by φ. When controlling the phase by changing the frequency,
Since it is more efficient to use the portion where the amplitude increases, control is performed using the right half of the circumference.

In the case of admittance when there is no external inductor 20, as shown in FIG. 4B, the phase change from the lower limit frequency f ₁ to the resonance frequency f ₀ and the resonance frequency f ₀
The phase change from ₀ to the upper limit frequency f ₂ is significantly asymmetric. Further, the amount of phase change from the resonance frequency f ₀ to the upper limit frequency f ₂ is very small.

On the other hand, in the admittance when the external inductor 20 is connected, as shown in FIG. 5B, the phase changes from the lower limit frequency f ₁ to the resonance frequency f ₀ and the admittance changes from the resonance frequency f ₀ to the upper limit. The phase change to the frequency f ₂ is contrasting and linear.

Thus, the ultrasonic motor driving device 1
It can be seen that by connecting the external inductor 20 to the ultrasonic motor 2 and performing impedance compensation, it is possible to obtain a high loop gain when performing phase control, thereby improving stability. Further, even if the circumference of the admittance becomes small or the resonance frequency f ₀ fluctuates due to the influence of a temperature change or the like, the phase control is not affected. In addition, since the phase change is symmetrical around the resonance frequency f ₀ , the servo can be pulled in from a higher frequency or a lower frequency, so that the start frequency and the sweep processing can be simplified. It can be.

The VCO of the ultrasonic motor driving device 1
As done in 13, by using the VCO to output a signal in the range of frequencies from a lower limit frequency f ₁ to the upper limit frequency f _2, without the need for pull-in circuit special servo lock, pull can be performed . That is, the lower limit frequency f ₁ from the upper limit frequency f ranges always resonance frequency f up to ₂
Since ₀ is, by starting the servo control at an arbitrary frequency from the lower limit frequency f ₁ to the upper limit frequency f _2, the resonance frequency f
_{A value} of ₀ enables servo lock.

The ultrasonic motor driving device 1 detects the speed of the ultrasonic motor 2 and varies the level of the driving voltage v supplied to the vibrating body of the ultrasonic motor 2 according to the detected speed. Thus, the speed servo control is performed. In the ultrasonic motor driving device 1, the ultrasonic motor 2
Is proportional to the drive current i flowing through the moving body, the peak hold circuit 18 detects the peak value of the drive current i, and performs speed servo based on the detected peak value. In addition, the speed detection is not limited to the detection of the drive current i as described above, and may be directly detected by, for example, attaching an encoder or the like to the moving body.

Further, in the ultrasonic motor driving apparatus 1, even when the ultrasonic motor 2 is stopped, the driving voltage v having a predetermined voltage value is continuously applied, and the servo loop of the phase control is always turned on. As shown in FIG. 6, the ultrasonic motor 2 does not generate torque unless the applied driving voltage v is equal to or higher than a certain voltage. That is, there is a dead zone where the movement does not start even when the driving voltage v is applied. In the ultrasonic motor drive device 1, the drive voltage v in the dead zone is supplied at the time of stop, so that the servo pull-in operation does not need to be performed again at the time of restart, so that the response speed can be increased. it can.

[0072]

According to the present invention, the impedance is compensated for the vibrating body so that the inductance component and the capacitance component are eliminated at the time of resonance, and the frequency is changed in the servo range centered on the resonance frequency. ,
The phase difference between the voltage and the current changes linearly. In the ultrasonic motor driving device, the frequency of the AC voltage applied to the vibrating body is made to follow the resonance frequency of the vibrating body based on the phase difference between the voltage applied to the vibrating body and the current flowing through the vibrating body. .

As a result, according to the present invention, the ultrasonic motor can be driven at the most efficient frequency.
Control can also be simplified. Furthermore, even if the characteristics of the ultrasonic motor change with time, the resonance frequency can follow the changed resonance frequency, so that the operating range is not deviated and the life is extended. Further, according to the present invention, servo control can be performed stably, and servo pull-in is simplified, and servo is less likely to come off.

Further, according to the present invention, while making the frequency of the AC voltage applied to the vibrating body follow the resonance frequency of the vibrating body, the voltage value of the voltage applied to the vibrating body is controlled to control the speed of the ultrasonic motor. Control. As a result, the speed control and the control of the resonance frequency can be made independent of each other, and the control system is simplified.

Further, in the present invention, even when the ultrasonic motor is stopped, a predetermined level of the AC voltage is continuously applied, and the frequency of the AC voltage applied to the vibrating body is made to follow the resonance frequency of the vibrating body. As a result, in the present invention, even when the ultrasonic motor is stopped, the frequency control can be continuously performed, and it is not necessary to perform the control pull-in operation at the start of the operation of the ultrasonic motor. Can be.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a driving device of an ultrasonic motor to which the present invention is applied.

FIG. 2 is a diagram showing an equivalent circuit of an ultrasonic motor to which an external inductor is connected.

FIG. 3 is a waveform diagram for explaining the operation of the ultrasonic motor driving device.

FIG. 4 is a vector diagram and a phase characteristic diagram of admittance of an ultrasonic motor to which no external inductor is connected.

FIG. 5 is a vector diagram and a phase characteristic diagram of an admittance of the ultrasonic motor to which an external inductor is connected.

FIG. 6 is a diagram showing characteristics of torque with respect to drive voltage of an ultrasonic motor.

FIG. 7 is a diagram illustrating an example of an ultrasonic motor.

FIG. 8 shows electrodes provided on the piezoelectric element of the ultrasonic motor,
FIG. 4 is a diagram illustrating a relationship between voltages applied to piezoelectric elements.

FIG. 9 is a diagram illustrating a traveling wave generated in a vibrating body of an ultrasonic motor.

FIG. 10 is an equivalent circuit diagram of a vibrating body of the ultrasonic motor.

FIG. 11 is a diagram showing frequency characteristics of admittance of the vibrating body.

FIG. 12 is a diagram illustrating a servo lock point at a resonance point of a current flowing through the vibrating body.

[Explanation of symbols]

1 Ultrasonic motor drive device, 2 Ultrasonic motor, 3
Drive voltage detector, 4 drive current detector, 11 flip-flop circuit, 12 integration circuit, 13 VCO, 14, 1
5 Waveform generator, 16, 17 power amplifier, 19 gain controller, 20 external inductor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H680 AA00 AA06 BB03 BB16 CC02 CC06 CC07 CC10 DD01 DD02 DD15 DD23 DD27 DD53 DD66 DD87 DD92 EE21 EE24 FF08 FF21 FF23 FF26 FF27 FF30 FF33 FF36 FF38

Claims (10)

[Claims] An ultrasonic motor driving apparatus for driving an ultrasonic motor having an oscillator supplied with an AC voltage and vibrating by the AC voltage, and a moving body moving in accordance with the vibration generated by the oscillator. An impedance compensating means connected to the vibrating body; a driving means for supplying an AC voltage to the vibrating body to drive the ultrasonic motor; and a voltage applied to the vibrating body and a current flowing through the vibrating body. Drive of an ultrasonic motor, comprising: a phase difference detecting unit that detects a phase difference between the two; and a frequency control unit that controls a frequency of an AC voltage supplied by the driving unit in accordance with the phase difference detected by the phase difference detecting unit. apparatus. 2. The ultrasonic motor driving device according to claim 1, further comprising: a driving voltage control unit that controls a driving voltage level supplied to the vibrator according to a speed of the ultrasonic motor. 3. The driving apparatus for an ultrasonic motor according to claim 1, wherein said driving means applies a predetermined level of AC voltage to said vibrator when said ultrasonic motor is stopped. 4. An ultrasonic wave according to claim 1, wherein said frequency control means outputs an AC voltage generated by changing a frequency around a resonance frequency of the vibrator according to the phase difference. Motor drive. 5. The AC voltage according to claim 4, wherein the frequency control means generates the AC voltage by changing a frequency from a lower limit frequency of the resonance to an upper limit frequency around a resonance frequency of the vibrating body. Ultrasonic motor drive. 6. An oscillator for generating a clock signal whose frequency is fluctuated around a frequency n times the resonance frequency of the vibrating body in accordance with the phase difference, and an oscillator for generating one wavelength of a sine wave. A storage unit for storing data sampled by being divided by the division number n, wherein the storage unit sequentially outputs the sampled data according to a clock signal from the oscillator. Item 4
A driving device for the ultrasonic motor according to the above. 7. An ultrasonic motor driving method for driving an ultrasonic motor having an oscillator supplied with an AC voltage and vibrating by the AC voltage, and a moving body moving in accordance with the vibration generated by the oscillator. The impedance of the vibrating body is compensated, a phase difference between a voltage applied to the vibrating body and a current flowing through the vibrating body is detected, and a frequency of an AC voltage to be supplied to the vibrating body according to the detected phase difference. A driving method for an ultrasonic motor, comprising: 8. The driving method of an ultrasonic motor according to claim 7, wherein a driving voltage level supplied to said vibrator is controlled according to a speed of said ultrasonic motor. 9. The ultrasonic motor driving method according to claim 7, wherein a predetermined level of an AC voltage is applied to said vibrator when said ultrasonic motor is stopped. 10. The ultrasonic motor driving method according to claim 7, wherein the impedance of the vibrator is compensated.