JPH07264879A - Drive circuit for ultrasonic motor - Google Patents

Abstract

PURPOSE:To provide a drive circuit for ultrasonic motor which can accurate drive an ultrasonic motor in a short time and can quietly stop the motor. CONSTITUTION:A drive circuit for ultrasonic motor which drives an ultrasonic motor 5 which is an object to be driven by generating oscillatory waves by impressing AC signals upon an electromechanical energy converting element is provided with an oscillation circuit 1 which generates the AC signals, frequency setting circuit 2, pulse converting circuits 3 and 4, and CPU 11 (incorporating a frequency controlling means 7 and driving amount instructing means 9) which controls the speed of the motor 5 by controlling the frequency of the AC signals in accordance with the remaining driven amount of the object to be driven to an aimed position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for an ultrasonic motor, and more particularly to a drive circuit for an ultrasonic motor which applies an AC signal to the ultrasonic motor for drive control.

[0002]

2. Description of the Related Art Conventionally, various types of ultrasonic motors have been proposed and known, but it is an apparatus that requires high-precision processing technology, and it is undeniable that some errors will occur during manufacture. Absent. Therefore, variation also occurs in the resonance frequency or the like peculiar to the motor, and the drive frequency characteristic peculiar to each motor is provided. Further, it is known that the drive frequency characteristic also changes depending on the displacement of the ambient temperature of the ultrasonic motor. Due to such circumstances, it is difficult to accurately drive and control the ultrasonic motor at the optimum drive frequency.

As a technical means for solving this problem, Japanese Patent Application Laid-Open No. 62-203575 proposes an ultrasonic motor having a monitor electrode for detecting vibration. According to this technical means, first, the motor is started at a frequency sufficiently higher than the resonance point, and drive control is performed so as to gradually shift to a high efficiency / high speed drive point based on the output from the vibration detection monitor electrode. Is supposed to do. Further, based on the output from the monitor electrode, the drive frequency is controlled by feeding back so that the output becomes a predetermined amount.

On the other hand, Japanese Unexamined Patent Publication No. 63-18974 discloses a technical means for performing an accurate stop operation by controlling the speed according to the distance to the stop position of the ultrasonic motor.

All of these technical means detect the driving state of the ultrasonic motor and perform feedback control. In order to improve the stop accuracy, the feedback control is performed to shift to the low speed state. .

[0006]

However, in each of the above-mentioned technical means, since the parameter indicating the driving state is fed back so as to have a predetermined value, the following problems occur.

(1) When the responsiveness of feedback is improved, a change in the driving state due to the feedback is delayed, so that the driving frequency hunts and an abnormal noise is generated.

(2) If the follow-up operation is slowed down as a countermeasure for the problem described in the above item (1), the response becomes slower and it takes time to position the stop position.

(3) It is difficult to maintain a good operation feeling at the time of stopping, especially in the case of an apparatus where the feeling is important such as driving the lens of the camera at the time of stopping.

The present invention has been made in view of the above problems, and it is an object of the present invention to solve the above problems and provide a drive circuit for an ultrasonic motor that can be accurately driven in a short time and has a good feel when stopped. To aim.

[0011]

In order to achieve the above object, the drive circuit of the first ultrasonic motor according to the present invention generates an oscillating wave by applying an AC signal to the electromechanical energy conversion element. In an ultrasonic motor drive circuit for driving a driven body, an AC signal generating means for generating the AC signal and a frequency of the AC signal according to a remaining drive amount of the driven body to a target position are controlled. Accordingly, the control means for controlling the speed of the driven body is provided.

In order to achieve the above object, the drive circuit of the second ultrasonic motor according to the present invention is different from the drive circuit of the first ultrasonic motor in that the drive speed of the driven body is further increased. Is provided, and the control means shifts the frequency to a lower side when the drive speed detected by the speed detection means becomes a predetermined value or less.

Further, in order to achieve the above-mentioned object, the drive circuit of the third ultrasonic motor according to the present invention generates an oscillating wave by applying an AC signal to the electromechanical energy conversion element to drive the driven body. Of the ultrasonic motor that drives
In the drive circuit, a frequency signal generating means for generating a frequency signal corresponding to the frequency of the AC signal, an AC signal generating means for generating the AC signal based on the frequency signal, and a movement of the driven body. And an encoder means for generating a pulse output, and the drive frequency is shifted for each output pulse of the encoder means when the remaining drive amount of the driven body to a target position is less than or equal to a predetermined value, and the shift is performed. So that the amount varies depending on the remaining drive amount,
Control means for controlling the frequency signal generating means.

[0014]

In the drive circuit of the first ultrasonic motor according to the present invention, the AC signal is generated by the AC signal generating means, and the frequency of the AC signal is generated by the control means according to the remaining driving amount of the driven body to the target position. To control.

In the second ultrasonic motor driving circuit according to the present invention, the speed detecting means further detects the driving speed of the driven body, and the control means detects the driving speed detected by the speed detecting means. When is below a certain value, the frequency is shifted to the lower side.

Further, in the third ultrasonic motor drive circuit according to the present invention, the frequency signal generating means generates a frequency signal corresponding to the frequency of the AC signal, and the AC signal generating means performs the AC voltage based on the frequency signal. Generate a signal. Further, when the encoder means generates a pulse output corresponding to the movement of the driven body, and the remaining drive amount to the target position of the driven body becomes a predetermined value or less, each output pulse of the encoder means Then, the drive frequency is shifted, and the frequency signal generating means is controlled by the control means so that the shift amount varies depending on the remaining drive amount.

[0017]

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

FIG. 1 is a block circuit diagram showing the configuration of a drive circuit for an ultrasonic motor which is a first embodiment of the present invention.

This ultrasonic motor drive circuit has a reference signal φOS for generating an alternating current drive signal for the ultrasonic motor 5.
An oscillation circuit 1 that oscillates C, a frequency setting circuit 2 that outputs a frequency signal φUSR that is approximately four times the drive frequency of the drive AC signal, and divides the frequency signal φUSR into four-phase pulse signals φ1 to φ4. Pulse conversion circuit 3 and the 4-phase pulse signals φ1 to φ4 are input, and 2-phase drive AC signals φA and φ
And a power amplifier circuit 4 that outputs B.

The oscillation circuit 1 is composed of an oscillator such as a crystal oscillator or a ceramic oscillator, and the output signal φOSC has a high frequency of 10 MHz or more.
The frequency setting circuit 2 is composed of a presettable down counter or the like, and its preset value is input from the frequency control means 7.

FIG. 2 is a diagram showing each signal waveform in the drive circuit of the ultrasonic motor.

FIG. 3 is an electric circuit diagram showing in detail the configuration of the power amplifier circuit 4 in the first embodiment.

The power amplifier circuit 4 is, as shown in FIG.
The five-terminal transformers T1 and T2 with an intermediate tap to which the power supply voltage VE is applied are connected to switching transistors Q1 to Q4.
By switching with, two-phase AC signal φA,
φB is generated. That is, the pulse signals φ1 to φ4 from the pulse conversion circuit 3 are input to the switching transistors Q1 to Q4, respectively, and the transistors T1 to Q4 switch the transformers T1 and T2. As a result, from the transformers T1 and T2 shown in FIG.
Alternating current signals φA and φB are generated and applied to the ultrasonic motor 5.

The ultrasonic motor 5 is a traveling wave type ultrasonic motor (USM), and the alternating current signals φA and φB output from the power amplifier circuit 4 generate a vibrating wave on the surface of the vibrating body to rotate the rotor. It is supposed to be done. An encoder 6 that is mechanically coupled to the rotor and that generates a pulse according to the amount of rotation of the ultrasonic motor is disposed near the ultrasonic motor 5.

In the ultrasonic motor drive circuit according to the first embodiment, in addition to the above-mentioned components, a storage means 8 for storing the initial drive frequency of the ultrasonic motor and a temperature for detecting the temperature of the ultrasonic motor 5 are detected. The sensor 10 and the drive amount instruction means 9 for instructing the drive amount of the ultrasonic motor are provided. The encoder 6, the storage means 8, the temperature sensor 10, the drive amount instruction means 9
Is output to the frequency control means 7, the driving frequency is determined by the frequency control means 7, and a digital output signal corresponding to the determination is output to the frequency setting circuit 2. It has become. In addition,
The frequency control means 7 and the drive amount instructing means 9 in this embodiment are both formed in the CPU 11 composed of a one-chip type microcomputer.

Next, the principle of ultrasonic motor drive control in this embodiment will be described.

FIG. 4 shows high temperature (60 ° C.) and medium temperature (20 ° C.).
It is a diagram which shows the rotation speed (N) -driving frequency (F) characteristic in an ultrasonic motor at the time of (degreeC), and low temperature (-20 degreeC). In the figure, the curves LH, LM, and LL show the characteristics at 60 ° C., 20 ° C., and −20 ° C., respectively, and also fr (H), fr (M), fr ( L) is the resonance frequency at each temperature.

As shown in the figure, when the ambient temperature of the ultrasonic motor decreases, the curve of the drive frequency characteristic shifts to the high frequency side and the rotation speed as a whole decreases. Moreover, although the speed rapidly decreases near the resonance point, the change becomes gentler as the distance from the resonance point increases.

FIG. 5 is a diagram showing the relationship between the driving frequency (F) and the rotation speed (N) and the moving distance of the ultrasonic motor in the first embodiment.

In this embodiment, when the temperature is Tn, the driving frequency fF (Tn) is used when the temperature is away from the stopping point, and when the predetermined point PB (Tn) is reached, the distance from the stopping point is used as the basis. Drive frequency to increase the upper limit frequency fs
When (Tn) is reached, further frequency increase is stopped, driving is performed at the frequency, and the operation is stopped at the stop point.

In the figure, NSTOP is the maximum value of the rotational speed at which the ultrasonic motor does not overrun during braking. In the figure, the ambient temperature is T1> T2.

As shown in the figure, when the ambient temperature is T1 rather than T2, that is, when the higher temperature is lower than the lower temperature, the frequency increase is started from the front side. this is,
This is because the higher the ambient temperature, the higher the speed before deceleration.

FIG. 6 is a graph showing the relationship between the drive frequency fs (Tn) and the resonance frequency fr (Tn) in the first embodiment, with the drive frequency on the vertical axis and the temperature on the horizontal axis. Is.

As shown in the figure, the slope of the drive frequency fs (Tn) is smaller than the slope of the resonance frequency fr (Tn). This is because, as shown in FIG. 4, the rotation speed corresponding to the drive frequency fs (Tn) is made substantially the same and the stop characteristic is made constant.

Next, the operation of the CPU 11 including the frequency control means 7 in the drive circuit for the ultrasonic motor of this embodiment will be described with reference to the flowchart of FIG.

First, when it is determined that a predetermined amount of drive is necessary, C
The number of pulses is loaded into the pulse register for pulse counting in PU11, and the driving routine is entered (step S1.
01). Next, the temperature sensor 10 detects the ambient temperature of the ultrasonic motor (step S102), and subsequently the deceleration start residual pulse PB corresponding to the detected temperature, the stop upper limit frequency fs,
The normal drive frequency fF is read from the storage means 8 (step S103). Next, the data corresponding to the normal drive frequency fF is output to the frequency setting means 2 (step S1).
04), the drive circuit system is turned on to operate (step S
105). As a result, the ultrasonic motor starts driving.

Next, the pulse signal accompanying the rotation of the ultrasonic motor 5 is monitored from the output signal from the encoder 6 (step S106), and when the pulse is generated, the pulse register is counted down (step S10).
7). Then, it is detected whether or not the pulse register is zero (step S108), and if it is zero, the drive circuit system is turned off (step S112), and the drive routine is ended (step S113).

On the other hand, if the pulse register is not zero, it is judged whether or not the pulse register is below PB (step S109), and if it is larger than PB, step S109.
Returning to 106, if PB or less, proceed to step S110.
In step S110, it is checked whether or not the frequency has reached fs, and if it has reached fs, the process returns to step S106. If not, the frequency is increased by a certain amount (step S
111) and the process returns to step S106.

According to the first embodiment, since the drive control of the ultrasonic motor does not rely on the conventional feedback control based on the monitor signal or the like, it is possible to provide a device which does not respond to frequency hunting and responds well and the feeling is important. Convenient to apply. In addition, when the temperature is high, the frequency starts to increase even before the temperature is low, so even if the ambient temperature of the ultrasonic motor is high and the rotation speed increases overall (see FIG. 4), overrun is surely performed. Can be prevented. In addition, since the upper limit frequency fs is set according to the temperature, there is no overrun due to insufficient deceleration and halfway stop due to excessive deceleration, and the shift amount of the upper limit frequency fs due to temperature is smaller than the shift amount of the resonance point. Become. As a result, overrun can be prevented more reliably.

Next, a second embodiment of the present invention will be described.

The ultrasonic motor drive circuit of the second embodiment has the same construction as that of the first embodiment, but the operation of the frequency control means 7 is slightly different.

FIG. 8 is a diagram showing the relationship between the drive frequency (F) and the rotation speed (N) and the moving distance of the ultrasonic motor in the second embodiment.

As shown in the figure, in the second embodiment, the drive frequency is increased from the point where the number of remaining pulses reaches PB, which is the same as in the first embodiment, but the frequency per The change amount is not the same, and the change amount is increased as the remaining pulse number decreases. As shown in FIG. 4, there is a difference in speed change with respect to frequency change between a point near the resonance point and a point far from the resonance point. Therefore, when the frequency is uniformly increased, as shown in FIG. This is to improve the point that the speed suddenly decreases near the remaining pulse number PB and the shock at the start of control becomes large. By doing so, braking is applied almost uniformly as shown in FIG. It will be.

Next, the operation of the CPU 11 in the drive circuit for the ultrasonic motor of this embodiment will be described with reference to the flowchart of FIG.

First, when it is determined that a predetermined amount of driving is necessary, the pulse number is loaded into the pulse register for pulse counting, and the driving routine is started (step S201). Next, for each number of remaining pulses equal to or less than PB, data indicating how much the frequency should be increased is read from the storage means 8, and fs, fF, and PB are also loaded (step S203).

Hereinafter, steps S204 to S21
Since the operation of No. 3 is almost the same as the corresponding operation of the first embodiment (see FIG. 7), only different points will be described here.

In step S211, when the frequency is increased, the values read in step S203 are made to correspond to each other and the frequency is increased by different amounts according to the number of remaining pulses.

According to the second embodiment, braking can be applied more smoothly than in the first embodiment, and a good feeling can be obtained.

In the second embodiment, the storage means 8 has data as the amount of increase in frequency with respect to the number of remaining pulses, but this may have data in the form of the driving frequency itself corresponding to the number of remaining pulses. The control may be changed depending on the temperature as in the first embodiment.

Next, a third embodiment of the present invention will be described.

The drive circuit for the ultrasonic motor of the third embodiment has the same structure as that of the first embodiment, but the operation of the frequency control means 7 is slightly different.

FIG. 10 is a diagram showing the relationship between the drive frequency (F) and the rotation speed (N) and the moving distance of the ultrasonic motor in the third embodiment.

In the third embodiment, similarly to the above-described first embodiment, the drive control is performed such that the drive frequency is gradually increased from the point where the remaining pulse number becomes PB.
It is characterized in that the drive frequency is controlled to be lowered again when is less than a predetermined value NLMT.

This is to prevent the vehicle from stopping before the stop point when the load is larger than expected. That is, as shown in FIG. 10, when the rotation speed N falls below NLMT, the drive frequency is lowered again,
The rotational speed N is controlled so as to be recovered to NLMT or higher.

Next, the operation of the CPU 11 in the drive circuit for the ultrasonic motor of this embodiment will be described with reference to the flowchart of FIG.

First, when it is determined that the predetermined amount of driving is required, the pulse number is loaded into the pulse register for pulse counting, and the driving routine is started (step S301). Next, PB, fS, fF and NLMT are read from the storage means 8 (step S303). Next, the data corresponding to fF is output to the frequency setting circuit 2 (step S30
4) The drive circuit system is turned on (step S305).

Next, a timer counter (speed timer) for speed detection in the CPU 11 is started (step S306). Next, the output pulse from the encoder 6 is monitored (step S307), and when the pulse is detected, the pulse register is counted down (step S308). Next, the speed timer is read (step S309), and the speed timer is restarted (step S310).

Next, it is checked whether or not the pulse register is zero (step S311). If it is zero, the drive circuit system is turned off (step S317), and the drive routine ends.
If it is not zero, it is checked whether or not the rotation speed N is lower than NLMT (step S312). Return.

On the other hand, if the number of revolutions N is not smaller than NLMT in step S312, it is checked whether the value of the pulse register is smaller than PB (step S3).
13). If it is small, the process proceeds to step S314,
If it is not small, the process returns to step S307.

In step S314, it is checked whether or not the current frequency is the upper limit frequency fs, and if it is the frequency fS, step S3.
It returns to 07, and if it is not the same frequency fS, step S315.
Go to. In step S315, it is checked whether or not the excessive low speed flag is 1, and if it is not 1, the drive frequency is increased (step S316), and the process returns to step S307.

According to the third embodiment, in addition to the effects of the first and second embodiments, it is possible to prevent the vehicle from stopping before the stop point when the load is larger than expected. it can.

Also in the third embodiment, the first
The control may be switched based on the ambient temperature of the ultrasonic motor as in the embodiment.

In the first to third embodiments, the circuit up to the generation of the AC signals φA and φB driven by the ultrasonic motor 5 is not limited to the above-mentioned circuit system but may be another system. Further, the driving is not limited to the one in which the frequency is fixed until the number of remaining pulses PB is reached. Needless to say, the ultrasonic motor can be applied to motors other than traveling wave type motors.

According to the drive circuit of the ultrasonic motor of each of the above-mentioned embodiments, the frequency is controlled by the remaining drive amount without depending on the feedback system which is the conventional method, so that the braking response and feel are good. It is possible to realize an ultrasonic motor drive circuit that can be stopped quickly, smoothly, and with an accurate drive amount.

[Additional Notes] According to the embodiments of the present invention described in detail above, the following configurations can be obtained. That is, (1) In a drive circuit of an ultrasonic motor that drives a driven body by generating an oscillating wave by applying an AC signal to the electromechanical energy conversion element, a frequency signal corresponding to the frequency of the AC signal. A frequency signal generating means for generating a frequency signal, an alternating current signal generating means for generating the alternating current signal based on the frequency signal, and a storage means for starting a frequency shift of the frequency signal and storing a drive position of the driven body. A driving circuit for the ultrasonic motor, comprising: a control unit that refers to a stored value of the storage unit and shifts a frequency of the frequency signal according to a remaining drive amount of the driven body to a target position.

(2) AC signal generation for generating the AC signal in a drive circuit of an ultrasonic motor for driving a driven body by generating an oscillating wave by applying an AC signal to the electromechanical energy conversion element Means for driving the ultrasonic motor, and control means for controlling the speed of the driven body by controlling the frequency of the AC signal according to the remaining drive amount of the driven body to the target position circuit.

(3) In the drive circuit of the ultrasonic motor that drives the driven body by generating an oscillating wave by applying an AC signal to the electro-mechanical energy conversion element, a frequency corresponding to the frequency of the AC signal. A frequency signal generating means for generating a signal, an AC signal generating means for generating the AC signal based on the frequency signal, and a frequency of the frequency signal according to the remaining driving amount of the driven body to a target position. And a control means for controlling the ultrasonic motor.

(4) In any one of (1) to (3) above, there is further provided a means for storing an upper limit value of the frequency of the AC signal, and the control means has the frequency of the AC signal The frequency signal generating means is controlled so that the upper limit value is not exceeded.

(5) In any one of (1) to (4) above, there is further provided means for detecting the driving speed of the driven body, and the control means is for driving speed of the driven body. When is less than a predetermined value, the frequency of the AC signal is shifted to the lower side.

(6) In the above (5), the means for detecting the driving speed of the driven body is the encoder means.

(7) In the above (4), the upper limit value of the frequency varies depending on the temperature of the ultrasonic motor.

(8) In (4) above, it further comprises means for detecting the temperature of the ultrasonic motor, and the upper limit of the frequency is changed according to the detected temperature.

(9) In the above (7) or (8), the shift amount of the changed upper limit value is set smaller than the shift amount of the resonance frequency due to the temperature change of the ultrasonic motor.

(10) In the drive circuit of the ultrasonic motor that drives the driven body by generating an oscillating wave by applying an AC signal to the electromechanical energy conversion element, a frequency corresponding to the frequency of the AC signal. A frequency signal generating means for generating a signal; and a control means for shifting the frequency of the alternating current signal to a high frequency side according to the remaining drive amount of the driven body to a target position and the temperature of the ultrasonic motor. Ultrasonic motor drive circuit.

(11) In the above (10), there is further provided storage means for storing the drive position of the driven body for starting the frequency shift of the frequency signal, and the remaining drive amount is the storage means. The stored value of is referred to.

(12) In the above (10), the temperature of the ultrasonic motor is detected by the temperature detecting means.

(13) In (11) above, the stored value of the storage means is changed according to the temperature of the ultrasonic motor.

(14) In (11) above, the frequency shift start position stored in the storage means is closer to the target position as the temperature of the ultrasonic motor is higher.

(15) In the drive circuit of the ultrasonic motor which drives the driven body by generating an oscillating wave by applying an AC signal to the electromechanical energy conversion element, a frequency corresponding to the frequency of the AC signal is applied. Frequency signal generating means for generating a signal, AC signal generating means for generating the AC signal based on the frequency signal, encoder means for generating a pulse output corresponding to the movement of the driven body,
When the remaining drive amount to the target position of the driven body becomes equal to or less than a predetermined value, the drive frequency is shifted for each output pulse of the encoder means, and the shift amount is changed by the remaining drive amount. And a control means for controlling the frequency signal generating means, the drive circuit of the ultrasonic motor.

(16) In the above item (15), the shift amount of the drive frequency increases as the remaining drive amount decreases.

[0081]

As described above, according to the present invention, it is possible to provide a drive circuit for an ultrasonic motor which can be accurately driven in a short time and has a good feel when stopped.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a configuration of a drive circuit for an ultrasonic motor that is a first embodiment of the present invention.

FIG. 2 is a diagram showing each signal waveform in the drive circuit for the ultrasonic motor of the first embodiment.

FIG. 3 is an electric circuit diagram showing in detail the configuration of the power amplifier circuit in the first embodiment.

FIG. 4 is a high temperature (60 ° C.), medium temperature (20 ° C.), low temperature (-20) in the drive circuit of the ultrasonic motor of the first embodiment.
It is a diagram which shows the rotation speed (N) -driving frequency (F) characteristic in an ultrasonic motor at the time of (degreeC).

FIG. 5 is a diagram showing a relationship between a driving frequency (F) and a rotation speed (N) and a moving distance of the ultrasonic motor in the ultrasonic motor driving circuit of the first embodiment.

FIG. 6 is a diagram showing the drive frequency fs (Tn) and the resonance frequency fr (T in the drive circuit of the ultrasonic motor of the first embodiment.
FIG. 3 is a diagram showing the relationship with (n) with the drive frequency on the vertical axis and the temperature on the horizontal axis.

FIG. 7 is a flowchart showing the operation of the CPU in the drive circuit for the ultrasonic motor of the first embodiment.

FIG. 8 is a diagram showing the relationship between the drive frequency (F) and the rotation speed (N) and the moving distance of the ultrasonic motor in the ultrasonic motor drive circuit according to the second embodiment of the present invention.

FIG. 9 is a flowchart showing the operation of the CPU in the drive circuit for the ultrasonic motor of the second embodiment.

FIG. 10 is a drive frequency (F) and a rotation speed (N) in the drive circuit for the ultrasonic motor according to the third embodiment of the present invention.
It is a diagram showing the relationship between the moving distance of the ultrasonic motor.

FIG. 11 is a flowchart showing the operation of the CPU in the drive circuit for the ultrasonic motor of the third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Oscillation circuit 2 ... Frequency setting circuit 3 ... Pulse conversion circuit 4 ... Power amplification circuit 5 ... Ultrasonic motor 6 ... Encoder 7 ... Frequency control means 8 ... Storage means 9 ... Drive amount instruction means 10 ... Temperature sensor 11 ... CPU

Claims (3)

[Claims] 1. An AC signal generating means for generating the AC signal in a driving circuit of an ultrasonic motor for driving a driven body by generating an oscillating wave by applying an AC signal to an electro-mechanical energy conversion element. And control means for controlling the speed of the driven body by controlling the frequency of the AC signal according to the remaining drive amount of the driven body to the target position. Drive circuit for sonic motor. 2. A speed detecting means for detecting a driving speed of the driven body is further provided, and the control means controls the frequency when the driving speed detected by the speed detecting means becomes a predetermined value or less. Characterized by shifting to the lower side,
The drive circuit for the ultrasonic motor according to claim 1. 3. In a drive circuit of an ultrasonic motor for driving a driven body by generating an oscillating wave by applying an AC signal to an electro-mechanical energy conversion element, a frequency signal corresponding to the frequency of the AC signal. , An AC signal generating means for generating the AC signal based on the frequency signal, an encoder means for generating a pulse output corresponding to the movement of the driven body, and the driven body. When the remaining drive amount up to the target position becomes equal to or less than a predetermined value, the drive frequency is shifted for each output pulse of the encoder means, and the shift amount is changed by the remaining drive amount. A drive circuit for an ultrasonic motor, comprising: a control unit that controls the signal generation unit.