JPH0322873A - Starting device for ultrasonic motor - Google Patents

Abstract

PURPOSE:To prevent the generation of uncomfortable abnormal sound upon starting an ultrasonic motor by a method wherein the frequency of a voltage, impressed on a piezoelectric body, is set so as to be higher than a predetermined driving frequency and, then, the frequency of the voltage is reduced sequentially. CONSTITUTION:A microcomputer 3 reads a data from an A/D converter 25, determines a driving frequency for an ultrasonic motor in accordance with the value of the read data, outputs a data in reference to the driving frequency to a D/A converter 5 and drives the ultrasonic motor. The frequency of a voltage, impressed on a piezoelectric body upon starting the motor, is set so as to be higher than predetermined driving frequency and resonance frequency but so as to be lower than a subsequent resonance frequency and the frequency of the voltage, outputted thereafter, is reduced sequentially. According to this method, a coincidence between the frequency of the voltage, impressed on the piezoelectric body upon starting the ultrasonic motor, and the resonance frequency may be avoided and the generation of uncomfortable abnormal sound upon starting the same may be prevented.

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention relates to a method and device for starting an ultrasonic motor,
In particular, the present invention relates to a method and apparatus for starting an ultrasonic motor that can appropriately start the ultrasonic motor without causing unpleasant noises from the ultrasonic motor.

(Prior Art) In recent years, various so-called ultrasonic motors that obtain driving force through ultrasonic vibrations have been developed and put into practical use.

Such an ultrasonic motor has a simple configuration, generates stable high torque in a low rotational speed range, and has many advantages such as high responsiveness and high holding torque.

As a conventional drive device for driving such an ultrasonic motor, the one shown in FIG. 11 is known.

On the surface of the stator 101, electrostrictive elements having a plurality of polarized sections A and B are arranged. The electrostrictive elements of these sections A and B are arranged so that their phases differ by 90 degrees from each other.

Furthermore, electrodes 101a and 10lb are provided on the electrostrictive elements of section A and section B, respectively. This electrode 10
Frequency voltages having a phase difference of 900 degrees are applied to 1a and 10lb. Further, the electrode 101c is a monitor electrode for detecting vibration waves on the electrostrictive element.

VCO (voltage controlled oscillator) 105 has a duty ratio of 50
This is an oscillator for outputting a rectangular pulse of %, and the frequency of this output rectangular pulse is determined by a low-pass filter]04
It is controlled according to the signal voltage from the microcomputer 106 or the signal from the microcomputer 106. This voltage controlled oscillator 10
The rectangular pulse from 5 is connected to amplifier 107 and coil 110.
It is applied to the electrode 101a via. Further, the rectangular pulse from the voltage controlled oscillator 105 is shifted in phase by 90'' by the shift register 116 and then applied to the other electrode 10lb via the amplifier 108 and the coil 111.

Monitor electrode】-0 1. The detection signal from c is applied to terminal R of phase comparator 112 via comparator 102. Further, the frequency voltage applied to the electrode 101a is converted into a pulse signal by a comparator 117. This pulse signal is changed in phase by 90 degrees by the shift register 125.
'After the delay, the phase comparator 1
12 terminal S.

The phase comparator 112 detects a phase difference between both signals input to terminals R and S, and outputs a signal corresponding to the detected phase difference. The signal from phase comparator 112 is applied to voltage controlled oscillator 105 via multiplexer 126 and low-pass filter 104. Voltage controlled oscillator 1
05 controls the oscillation frequency according to this input signal, thereby controlling the phase difference between the frequency voltages applied to the electrode 101a and the electrode 101C to 90°.

Next, the operation of the conventional example shown in FIG. 11 will be explained with reference to FIG. 12.

When the power switch is turned on in step 201, the output port of the microcomputer 106 is turned on.
An L level signal is output from o to multiplexer 126. Subsequently, in step 203, the voltage controlled oscillator 105
The microcomputer 106 outputs data written in a binary code for determining the oscillation frequency of the oscillation frequency. That is, the output port PA of the microcomputer 106
L-level signals are output from O, PA1, PA2, and PA3, respectively. Thereby, the voltage controlled oscillator 105 performs an oscillation operation at the lowest oscillation frequency among the oscillation frequencies within a preset variable range.

Also, the multiplexer 126 is connected to the microcomputer 10.
Terminal 126c is selected based on the L level signal from 6, and the output pulse from voltage controlled oscillator 105 is output to low pass filter 104.

Therefore, the low-pass filter 104 and the voltage-controlled oscillator 105 form a closed circuit via the multiplexer 126, and the oscillation frequency of the voltage-controlled oscillator 105 is determined by data from the microcomputer 106.

Next, in step 205, the microcomputer 106
It has a register A inside, which stores a detection signal from the drive detection circuit 109 input via the input port PBO, that is, a signal indicating whether or not the ultrasonic motor is driven.

Next, in step 207, the microcomputer 106 has a register B, and a constant n is set in this register B.

Next, in step 209, it is determined whether the data input manually via the input boat PBO and the data stored in register A match, and if the content of both matches, that is, the ultrasonic If the motor is not being driven, the process advances to step 211 and 1 is subtracted from the contents of register B.

Subsequently, in step 213, it is determined whether the contents of register B are 0 or not. If not, the process proceeds to step 209 again, and the data input via the manual port PBO is compared with the contents of register A. This comparison operation is repeated n times.

The series of operations from step 209 to step 213 shown below is for detecting whether or not the ultrasonic motor is driven for a certain period of time, and this series of operations determines whether the ultrasonic motor is not being driven. When it is determined that
Increase the value of 戊 by 1 using the pinary code output from AI, PA2, and PA3.

This increases the oscillation frequency of voltage controlled oscillator 105. Further, the process returns to step 207 from step 215, and the series of operations described above are repeated.

As described above, when the output state from the drive detection circuit 109 does not change for a certain period of time, the microcomputer 106 increases the oscillation frequency of the voltage-controlled oscillator 105 at predetermined time intervals, and converts the oscillation frequency from the voltage-controlled oscillator 105 into an ultrasonic wave. Bring it closer to the motor's resonant frequency.

The drive detection circuit 10 inputs the data stored in the register A and the manual boat PBO in step 209.
9 is different from the detection signal from the output port P, that is, when the oscillation frequency of the voltage controlled oscillator 105 approaches the resonant frequency of the ultrasonic motor, the process proceeds to step 217, and the output port P
Set the CO output level to H level. This prohibits updating of the output data from the output ports PAO, PAI, PA2, and PA3, and also
passes the signal from the phase comparator 112 to the low-pass filter 10
Output to 4. Therefore, P L L (Phase
Frequency control is performed using Locked Loop), and the phase difference between the frequency voltages applied to the electrodes 101a and 101b is set to 90°.

As described above, when the phase difference between the frequency voltages applied to the electrodes 101a and 101b is set to 90', the driving frequency of this frequency voltage is set to a value slightly higher than the resonance frequency of the ultrasonic motor. And the ultrasonic motor maintains the rotation driving state.

(Problems to be Solved by the Invention) FIG. 13 is a graph showing changes in the impedance of the ultrasonic motor with respect to the frequency of the frequency voltage applied to the electrodes 101a and 101b.

The first resonant frequency f at which the impedance becomes low as shown in FIG. ．． and a second resonant frequency f. , is recognized. Further, when the ultrasonic motor is in an optimal driving state, the driving frequency of the frequency voltage applied to the electrodes 101a and 101b is the above-mentioned first resonance frequency f. ．． The frequency fl is slightly higher than the frequency f3 of the anti-resonance point and lower than the antiresonance point frequency f3.
, for example 40K. It is set to Hz.

By the way, the conventional device shown in FIG. 11 sets the drive frequency to the first '(oscillation frequency f
. ．． The driving frequency is set to a lower value (OHz) than the ultrasonic motor, and the driving frequency is successively increased until the ultrasonic motor starts driving. Therefore, the driving frequency of the frequency voltage applied to the electrodes 101a and 101b is always the first resonance frequency f. ．．
The driving frequency f1 is controlled to the optimum driving frequency f1.

As shown in FIG. 14, when the value of the driving frequency is sequentially increased from the stopped state, the number of revolutions and 1·L of the ultrasonic motor are also sequentially increased. Further, the value of the driving frequency is the first resonance frequency f
. ．． As the value approaches , a vibration wave with a frequency that is doubled or divided from this first resonant frequency foe is generated in the electrostrictive element of the ultrasonic motor, and the vibration due to this doubled or divided wave causes unpleasant vibrations. An abnormal noise occurs.

The present invention has been made in view of the above two problems, and an object of the present invention is to provide an ultrasonic motor drive device that prevents the generation of unpleasant abnormal noises when starting an ultrasonic motor.

[Structure of the Invention] (Means for Solving the Problems) -1 In order to achieve the first object, the present invention provides a piezoelectric body with a voltage having a drive frequency near an arbitrary resonance frequency and higher than the resonance frequency. In an ultrasonic motor starting device that drives an ultrasonic motor by ultrasonic vibrations generated in the piezoelectric body, the frequency of the voltage applied to the piezoelectric body is set to be higher than the expected driving frequency, and the frequency is set to the resonant frequency. The resonant frequency is set to a lower frequency than the next resonant frequency at a higher frequency, and a starting means is provided for sequentially lowering and outputting the frequency.

(Function) The ultrasonic motor of the present invention is driven by ultrasonic vibrations generated in the piezoelectric body by applying a voltage at a predetermined driving frequency slightly higher than the resonance frequency to the piezoelectric body.

Therefore, in the ultrasonic motor starting device of the present invention, the frequency of the voltage applied by the starting means to the piezoelectric body at the time of starting is higher than the expected driving frequency and higher than the resonant frequency. The output is set to a frequency lower than the resonant frequency, and then the output frequency is successively lowered.

As described above, in the present invention, when the ultrasonic motor is started, the frequency of the voltage applied to the piezoelectric body does not become the same as the resonance frequency, so that no unpleasant noise is generated.

(Example) Hereinafter, an example according to the present invention will be described in detail with reference to the drawings.

First, the structure will be explained with reference to FIG.

A plurality of electrostrictive elements polarized as piezoelectric bodies are arranged on the surface of a stator 1 of an ultrasonic motor. These plurality of electrostrictive elements form two groups of electrostrictive elements consisting of section A and section B, and the electrostrictive elements of section A and section ■ have a phase of 90'.
are arranged differently.

Further, as shown in FIG. 3, the electrostrictive element of category A has an electrode 1a.
The electrostrictive element in the other section B is provided with an electrode 1b. These electrodes 1a (!: electrode 1b are applied with frequency voltages having a phase difference of 90'' from each other. For example, a sinusoidal frequency voltage is applied to the electrode 1a, and a frequency voltage of a sine wave is applied to the electrode 1b. A frequency voltage with a cosine waveform is applied.The electrode 1c is placed on an electrostrictive element that is insulated from the electrodes 1a and 1b mentioned above (7), and outputs a detection signal according to the vibration state of the electrostrictive element. Further, electrode 1d is a common electrode for electrodes 1aS'4b and 1c.

Referring to Figure 2 again, microphone 1 and microphone 3 are A.
It is connected to the A/D converter 25 and the D/A converter 5, reads the output data from the A/D converter 25, and adjusts the driving frequency of the ultrasonic motor according to the read value. is determined, and data regarding the drive frequency is output to the D/A converter 5. Therefore, the driving frequency of the ultrasonic motor is determined based on the output data from the microcomputer 3.

Furthermore, at the start of starting the ultrasonic motor, the microcomputer 3 outputs data such that the driving frequency is at the upper limit value among the driving frequency values within a preset variable range.

The D/A converter 5 is connected to a voltage controlled oscillator 7,
The digital signal data input from the microcomputer 3 is converted into analog signal data and output to the voltage controlled oscillator 7.

The voltage controlled oscillator 7 changes the oscillation frequency according to the input signal voltage, and the value of the oscillation frequency that can be changed is limited to a value within a predetermined range that includes the optimum driving frequency of the ultrasonic motor. There is.

Further, the voltage controlled oscillator 7 is configured to output a rectangular pulse having an oscillation frequency of, for example, 1.28 MHz in the optimal driving state of the ultrasonic motor.

Frequency divider 9 is connected to voltage controlled oscillator 7, and is also connected to electrode 1a via amplifier 11 and coil 13. The frequency divider 9 divides the frequency of the rectangular pulse outputted from the voltage controlled oscillator 7 by ]/32 and outputs the divided frequency. The pulse signal frequency-divided by the frequency divider 9 is amplified by the amplifier 11 and then applied to the electrode 1a via the coil 13.

The clock input terminal V of the shift 1 register 15 is connected to the voltage controlled oscillator 7, and the data input terminal D is connected to the frequency divider 9. Further, the output terminal Q8 of the shift register 15 is connected to the electrode 1b via the amplifier 17 and the coil 19. The phase of the pulse signal is delayed by 90'' and output from the output terminal Q8. The pulse signal from the shift register 15 is amplified by the amplifier 17 and then applied to the electrode 1b via the coil 19.

Therefore, the phase of the frequency voltage applied to the electrode 1a is 90
Frequency voltages with phases different by .degree. are applied to the voltage i1b.

The bandpass filter (B, P.F) 21 is connected to the electrode 1c, and among the vibration wave components obtained through the electrode IC, the resonance frequency f at which the impedance of the ultrasonic motor shown in FIG. 13 is the minimum . ．． This is a filter that allows only harmonics that are integral multiples of . Moreover, this band pass filter 21 has a resonance frequency f among the vibration wave components obtained through the electrode IC. ．． It may be configured using a filter that passes only the frequency-divided wave. That is, the bandpass filter 21 extracts only the signal due to the harmonics or frequency division waves of the resonant frequency from among the vibration wave components obtained through the electrode IC.

The rectifier 23 is connected to the bandpass filter 21 and also to the microcomputer 3 via the A/D converter 25. The rectifier 23 rectifies the output from the bandpass filter 21 and converts it into a DC voltage. Also A
/D converter 25 converts the output voltage from rectifier 23 into a digital signal and outputs it to microcomputer 3.

Next, the action will be explained.

In step S1 shown in FIG. 4, when a power switch (not shown) is turned on, the microcomputer 3 starts operating and outputs data regarding the upper limit driving frequency to the voltage controlled oscillator 7 via the D/A converter 5. do. As a result, as shown in FIG. 5(A), a frequency voltage having the upper limit drive frequency is applied to the electrode 1a at time t1. At the same time, a frequency voltage that is different in phase by 90 degrees from the phase of the frequency voltage applied to the electrode 1a is applied to the electrode 1b.

Here, the upper limit driving frequency at the start of activation of the ultrasonic motor will be explained with reference to FIG. 13.

As shown in Figure 13, the first stage has a lower impedance value.
The resonant frequency f. ．． and this first resonant frequency f. , a second resonance frequency f that is the next resonance point after the resonance point having .

, exists. Here, the optimum drive frequency f1 when driving the ultrasonic motor is the first resonance frequency f. ．． a value slightly higher than and lower than the frequency f of the anti-resonance point,
For example, in the case of 40 KHz, the value is higher than this optimum drive frequency f1 and the second resonance frequency f. , the drive frequency f, which is lower than , is set as the upper limit drive frequency at the start of startup. In other words, any frequency from the resonance frequency at the specified minimum temperature of the resonance point to be used to the resonance frequency at the specified maximum temperature of the next resonance point on the high frequency side of the resonance point is set as the upper limit drive frequency at the start of startup. Set. The specification maximum temperature and specification minimum temperature are, for example, when the temperature specification of this ultrasonic motor is -3
When the temperature range is 0°C to 100°C, 100°C is the specified maximum temperature, and -30°C is the specified minimum temperature.

Referring again to FIG. 4, in step S3, the signal from the bandpass filter 21 is read. Here, as shown in FIG. 13, even if a frequency voltage of drive frequency f is applied to the ultrasonic motor at the start of startup, the value of drive frequency f is set to the optimum drive frequency f. The ultrasonic motor does not drive because the distance is much greater than that. Therefore, electrode 1C
Since no signal is obtained from the filter, the bandpass filter 21 outputs a 0-level signal as shown in FIG. 5(B).

In step S5, the output value from the band pass filter 21 is compared with a predetermined reference value Ds, and since the ultrasonic motor is not driven, if the output value from the band pass filter 21 is less than the reference value Ds, Proceed to step S7. In step S7, the value of the drive frequency is set to a value lower than the upper limit drive frequency f by 0.1 KHz.

Subsequently, in step S9, data regarding the new drive frequency set in step S7 is transferred to the D/A converter 5.
Output to. This causes the voltage controlled oscillator 7 to reach 3.2KH.
Outputs a rectangular pulse with an oscillation frequency lower by z (0.1 KHz x 32). The rectangular pulse output from this voltage controlled oscillation 7 is frequency-divided by a frequency divider 9 and then applied to the electrode 1a via an amplifier 11 and a coil 13. Similarly, the rectangular pulse output from the voltage controlled oscillator 7 is shifted in phase by 90'' by the shift register 15, and then sent to the other electrode 1b via the amplifier 17 and the coil 19.
is applied to.

Returning from step S9 to step S3, the above-described operations are repeated, and the value of the driving frequency of the frequency voltage applied to the electrodes 1a and 1b is sequentially changed to 0. Lower the IKHz step by step.

As described above, when the driving frequency of the frequency voltage applied to the electrodes 1a and 1b is successively lowered, FIGS.
), the ultrasonic motor starts driving at time t3.

During the period from time t3 when the ultrasonic motor starts driving to time t4, the output value from the bandpass filter 21 is a value lower than the reference value Ds, so the process returns to step S7 and step S9, and further driving is performed. Set the frequency value to 0. Lower the IKHz step by step.

In this way, by gradually lowering the drive frequency toward the frequency f, the rotation speed of the ultrasonic motor gradually increases as shown in FIG. The output value also increases gradually.

If the value of the driving frequency of the frequency voltage applied to the electrodes 1a and 1b jumps over the optimal driving frequency f1 and is set to an even lower value, the first Resonant frequency f. A so-called harmonic signal having a frequency that is an integer multiple of , is outputted via the electrode IC together with the fundamental wave signal shown by curve a.

In step S5, when the output value from the bandpass filter 21 exceeds the reference value Ds due to such a harmonic signal, the process proceeds to step 811, and the value of the driving frequency is changed to Q. l
Increase by KHz.

Thereby, the value of the driving frequency of the frequency voltage applied to the electrodes 1a and 1b becomes the first resonance frequency f. , and this first resonance frequency f. ．． For example, 40 KHz is set as the optimum driving frequency f1.

When the value of the actual driving frequency applied to electrodes 1a and 1b is set to the optimum driving frequency f1 in this way, harmonic waves are generated in the electrode IC as shown in curve b of FIG. 6(A). is reduced.

Next, an explanation will be given of the operation when the value of the actually applied driving frequency changes due to load conditions or aging due to wear between the rotor and stator.

As described above, the driving frequency applied to the electrodes 1a and 1b decreases from the optimum frequency f1 due to aging or the like, and becomes lower than the frequency f1 and reaches the first resonance frequency f. ．． When the value of f changes to a value close to that of f, the first resonant frequency f changes as shown by curve b in FIG. 6(B). ．． A harmonic signal that is an integral multiple of is output from the electrode IC. Therefore step S
If the output value from the band pass filter 21 exceeds the reference value DS by 2 times in Step 5, the process proceeds to step Sll, where the value of the drive frequency is increased by 0.1 KHz. As a result, the actual driving frequency of the frequency voltage applied to the electrodes 1a and 1b is the first resonance frequency f. ．． even higher than,
For example, the drive frequency f is corrected to the optimum value.

Note that the bandpass filter 21 has a first resonant frequency fo. Even in the case where a filter is used to pass only the divided wave component of can be controlled to a specific value.

As described above, only the signal resulting from the harmonic or divided wave of the resonant frequency of the ultrasonic motor is extracted, and the drive frequency is controlled based on this extracted value, so the device configuration can be simplified. , it is possible to reduce costs.

Next, another embodiment of the present invention will be described with reference to FIG.

In this embodiment, the microcomputer 3 is used to set the drive frequency at the start of driving the ultrasonic motor to an arbitrary frequency within the range described in the previous embodiment, and the drive frequency is set at an arbitrary frequency within the range described in the previous embodiment. The value of is gradually decreased.

Further, after the ultrasonic motor starts to start, the phase of the frequency voltage applied to the electrode 1a and the phase of the frequency voltage applied to the electrode 1b are made to differ by 906 based on the output from the phase comparator 33. It is characterized in that the driving frequency is controlled.

Specifically, the microcomputer 3 is connected to the drive detection circuit 2, the multiplexer 4, and the D/A converter 5, respectively.

The drive detection circuit 2 includes, for example, a rotary encoder, detects that the ultrasonic motor is driven, and outputs a detection signal to the microcomputer 3. Also, the multiplexer 4 is the output port PC of the microcomputer 3.
When a signal from O to L level is input manually, the terminal 4b is selected and the output signal from the D/A converter 5 is outputted to the low-pass filter 6 via the terminal 4d.

Furthermore, when the multiplexer 4 receives an H level signal from the output port PCO of the microcomputer 3, it selects the terminal 4C and sends the output signal from the phase comparator 33 to the low-pass filter 6 via the terminal 4d.

The low-pass filter 6 smoothes the human input signal from the multiplexer 4 and outputs it to the voltage controlled oscillator 7.

The detection signal from the electrode 1c is converted into a pulse signal by the comparator 31 and applied to the terminal R of the phase comparator 33.

Further, the signal from the electrode 1a is converted into a pulse signal by the converter 35 and is applied to the data input terminal D of the shift register 37.

The shift register 37 inputs the output from the voltage controlled oscillator 7 as a clock signal to the clock input terminal V.
When the pulse signal from the comparator 35 is inputted to the data input terminal D as shown in FIG. 8(A), as shown in FIG. 8(B).
The phase of the pulse signal from the comparator 35 is delayed by 90'' as shown in FIG. It is applied to the terminal S of the comparator 33.

In the phase comparator 33, as shown in FIG.
Compare the phases of both pulse signals input to the Specifically, as shown in Figure 9, if the positive pulse signal to terminal R is input earlier than the positive pulse signal to terminal S, that is, the phase of the pulse signal input to @FR is advanced. In this case, H is maintained for a period corresponding to this phase difference.
Outputs a level signal. In addition, if a positive pulse to terminal f'-RS of both input terminals is input earlier than a positive pulse to terminal R, an L level signal is output for a period corresponding to this phase difference. . During other periods, the output terminal of the phase comparator 33 is set to a high impedance state.

It should be noted that the device structure other than the circuit section described above is the same as that of the embodiment shown in FIG. 2, so the same reference numerals are given and detailed explanation is omitted.

Next, the operation of the embodiment shown in FIG. 7 will be explained with reference to FIG. 10.

When a power switch (not shown) is turned on, the microcomputer 3 starts operating. In step 321, an L level signal is output from the output port/PCO to the multiplexer 4.

Subsequently, in step S23, the output boats PAO, PA
L, PA2, and PA3 output pinary code data at H level to the D/A converter 5, respectively.

Multiplexer 4 selects input terminal 4b and outputs the signal from D/A converter 5 via terminal 4d. Therefore, the oscillation frequency of the voltage controlled oscillator 7 is
output data from the output boats PAO, PAI,
It is determined by the binary code data from PA2 and PA3.

Therefore, at the start of driving the ultrasonic motor, as shown in FIG.
, is set to . Since the ultrasonic motor does not operate at such an upper limit drive frequency f, the drive detection circuit 2 outputs an L level signal. Therefore, in step S25, an L level signal is input to the manual boat PBO.

Subsequently, in step 827, a preset constant n is set in register B built into the microcomputer 3.

In step S29, it is determined whether the signal inputted to the manual boat PBO is at L level or not. If there is a signal at L level, the process proceeds to step S31 and the value of the constant set in register B is subtracted by 1.

Subsequently, in step 833, it is determined whether or not the value set in register B is 0. If it is not 0, the process proceeds to step S29 again, and the above-described operations are repeated.

If the series of operations from step S29 to step S33 is repeated and the value set in register B becomes 0, the process advances from step 833 to step S35.

In step S35, the output boats PAO, PA1, PA2
, decreases by 1 the value of the data consisting of the pinary code output from PA3.

Subsequently, the process returns from step S35 to step S27, and the above-described operations are repeated.

That is, the value of the driving frequency is gradually decreased from the upper limit frequency f, to approach the optimum driving frequency f.

As described above, when the ultrasonic motor operates by decreasing the drive frequency sequentially, the drive detection circuit 2 detects this and
A level signal is output to the microcomputer 3. This causes the process to proceed from step S29 to step S37.
An H level signal is output from the output port PCO to the multiplexer 4.

When the multiplexer 4 receives an H level signal from the microcomputer 3, it selects the terminal 4c and sends out the signal from the phase comparator 33 via the terminal 4d (7).

Therefore, voltage controlled oscillator 7 changes its oscillation frequency based on the signal from phase comparator 3B. As a result, electrode 1c
The phase difference between the detection signal from the electrode 1a and the frequency voltage applied to the electrode 1a is controlled to be 90°.

As described above, the embodiment shown in FIG. 7 is configured to immediately execute phase control using PLL when it is detected that the ultrasonic motor has started, so that the drive frequency value is set to the optimum value. can be controlled.

[Effects of the Invention] As explained above, according to the present invention, when starting the ultrasonic motor, a voltage with a frequency higher than the optimum drive frequency is applied, and the frequency of this voltage is gradually lowered. With this structure, the generation of unpleasant abnormal noise can be reliably prevented without passing through the resonance point of the ultrasonic motor.

[Brief explanation of the drawing]

Fig. 1 is a diagram corresponding to claims, Fig. 2 is a block diagram showing an embodiment of the present invention, Fig. 3 is an explanatory drawing showing the electrode configuration of an ultrasonic motor, and Fig. 4 is an operation of Fig. 2. FIG. 5 is a graph showing the operating state of the ultrasonic motor in response to changes in the drive frequency, FIG. 6 is a signal waveform diagram generated from the monitoring electrode, and FIG. A block diagram, FIGS. 8 and 9, showing another embodiment is shown in FIG. 7; a signal waveform diagram of each part of the embodiment, and FIG. FIG. 11 is a block diagram showing the conventional example, FIG. 12 is a flow chart showing the operation of the conventional example shown in FIG. FIG. 14 is a graph showing the rotation speed of the ultrasonic motor with respect to the change in drive frequency. 1... Stator 3... Microcomputer 7... Voltage controlled oscillator 33... Phase comparator

Claims (1)

[Claims] (1) An ultrasonic motor starting device that applies a voltage with a drive frequency near a given resonance frequency and higher than the resonance frequency to a piezoelectric body, and drives the ultrasonic motor by the ultrasonic vibrations generated in the piezoelectric body. The frequency of the voltage applied to the piezoelectric body is set to a frequency higher than the expected driving frequency, higher than the resonant frequency, and lower than the next resonant frequency, and
A starting device for an ultrasonic motor, comprising a starting means for sequentially lowering and outputting the frequency.