JP3131519B2 - Ultrasonic motor drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor drive circuit, and more particularly to an ultrasonic motor drive circuit for controlling the speed of an ultrasonic motor by controlling the frequency of an applied AC drive signal.

[0002]

2. Description of the Related Art Conventionally, there are known various technical means for optimizing a driving frequency by detecting a phase difference between an output signal (monitor signal) of a monitor electrode provided in an ultrasonic motor and an applied AC driving signal. For example, JP-A-61-25
Japanese Patent Application Publication No. 1490 discloses that the phase of the monitor signal is monitored by utilizing the fact that the phase of the monitor signal with respect to the drive voltage greatly changes near the resonance frequency, and the resonance frequency or the resonance frequency is determined based on the phase. Technical means for driving an ultrasonic motor in a region slightly higher in frequency than the frequency is disclosed.

On the other hand, Japanese Patent Application Laid-Open No. 63-209482 discloses that a drive frequency is prevented from lowering when an ultrasonic motor enters a resonance state based on a phase difference between the monitor signal and an applied AC drive signal. A technical means for adjusting the speed of an ultrasonic motor by changing the frequency in a frequency range higher than the resonance point is disclosed.

[0004]

However, in the technical means disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 63-209482,
In order to specify the drive frequency region, a phase difference output between the monitor signal and the applied AC drive signal, and a pulse detection output of the ultrasonic motor obtained from a pulse interval of an encoder signal indicating the rotational speed of the ultrasonic motor, It is necessary to always monitor these two outputs (the phase difference output and the speed detection output) simultaneously.

[0005] However, when the ultrasonic motor is rotated at a high speed, a CPU which performs monitor control of the above-described phase difference output and speed detection output is required to have a considerable processing speed, thereby increasing costs and increasing machine cycles. There is a problem that power consumption increases due to the above.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and realizes an ultrasonic motor drive which realizes low cost and low power consumption and can control the speed by the frequency while maintaining the ultrasonic motor in a stable frequency range. It is intended to provide a circuit.

[0007]

In order to achieve the above object, a first ultrasonic motor drive circuit according to the present invention uses a DC power supply and converts an AC signal generated by switching an inductive element into an electro-mechanical signal. Monitoring means for detecting a driving state of the ultrasonic motor in an ultrasonic motor driving circuit for driving an ultrasonic motor in which the electro-mechanical energy converting element is disposed by applying the ultrasonic motor to the energy converting element; Drive speed detection means for detecting the drive speed of the ultrasonic motor, and drive amount for detecting the drive amount of the ultrasonic motor
The output from the detecting means and the driving amount detecting means is a predetermined value.
Reach the, on the basis of the output of said monitor means, a first frequency control means for follow-up control of the frequency of the AC signal to the resonant frequency of the ultrasonic motor, the drive detection hand
When the output from the stage reaches a predetermined value, the AC signal
Lower limit frequency storage means for storing the frequency of
After the output from the detection means reaches a predetermined value, based on the output of the driving speed detecting means at the stored frequency higher frequency range to the lower limit frequency storage means, the frequency of the AC signal a second frequency control means for controlling, the ingredients
It is characterized by having.

In order to achieve the above object, a second ultrasonic motor drive circuit according to the present invention uses a DC power supply and switches an inductive element to convert an AC signal generated to an electro-mechanical energy conversion element. By applying
In an ultrasonic motor drive circuit for driving an ultrasonic motor in which the electro-mechanical energy conversion element is arranged, a monitor for detecting a drive state of the ultrasonic motor, and a drive for detecting a drive speed of the ultrasonic motor Speed detection means, and a drive time detection for detecting a drive time of the ultrasonic motor.
Output means and the output from the drive time detecting means are a predetermined value
To reach based on the output of said monitor means, a first frequency control means for follow-up control of the frequency of the AC signal to the resonant frequency of the ultrasonic motor, the drive time detector
When the output from the means reaches a predetermined value,
A lower frequency limit storage means for storing a frequency of issue, the drive
After the output from the time detecting means reaches a predetermined value, based on the output of the driving speed detecting means, at a high frequency range than the stored frequency in the lower frequency storage means, the frequency of the AC signal a second frequency control means for controlling,
It is characterized by having.

[0009]

[0010]

[0011]

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

FIG. 1 is an electric circuit diagram of an ultrasonic motor driving circuit showing a first embodiment of the present invention.

The ultrasonic motor drive circuit according to the first embodiment applies a predetermined two-phase AC signal to a known ultrasonic motor 7 having two drive electrodes 7A and 7B and a monitor electrode 7M. The drive control of the ultrasonic motor 7 is performed by monitoring a monitor signal from 7M.

That is, the drive circuit controls the drive circuit and controls a drive frequency control switching means 3, a first frequency control means 4, a second frequency control means 5, a drive speed detection means 12, a drive amount detection means CPU 14 having means 13
An oscillation circuit 1 for generating and outputting a pulse signal φUSR having a frequency approximately four times that of an AC signal applied to the ultrasonic motor 7, and converting the pulse signal φUSR output from the oscillation circuit 1 into a four-phase pulse signal a pulse conversion circuit 2 for dividing the frequency into φ1 to φ4 for output, and a switching transistor Q1 for performing a switching operation in response to the pulse signals φ1 to φ4 output from the pulse conversion circuit 2, respectively.
To Q4 and the intermediate tap on the primary side are supplied with the positive voltage of the DC power supply 10, and the primary side is turned on by the switching operation of the switching transistors Q1 and Q2.
Accordingly, a transformer T1 for outputting an A-phase AC signal VA to the secondary side, and the switching transistor Q3
And the switching operation of Q4, the primary side is turned on, and the transformer T outputs the B-phase AC signal VB to the secondary side.
2, a waveform shaping circuit 9 for converting a monitor signal from the monitor electrode 7M of the ultrasonic motor 7 into a predetermined digital signal, and a digital output signal of the waveform shaping circuit 9 and one output from the pulse converting circuit 2. A certain pulse signal φ1 is input, the phases of the two signals are compared and counted, and the result, that is, the phase difference between the phases of the two signals is transmitted to the first frequency control means 4 in the CPU 14. A phase difference counter 8, a rotation encoder 11 that detects the rotation of the ultrasonic motor 7, generates a predetermined pulse, and sends the pulse to the drive speed detection means 12 and the drive amount detection means 13 in the CPU 14; The memory 6 for storing information of the drive frequency control switching means 3 constitutes a main part.

The ultrasonic motor 7 is a known traveling wave type ultrasonic motor having a piezoelectric element.
There are two driving electrodes 7A and 7B. That is,
The two-phase (A-phase and B-phase) AC signals VA and VB whose phases are shifted from each other by about 90 ° are applied to the electrodes 7A and 7B, and the two-phase AC signals rotate. Driving is performed. The ultrasonic motor 7 has a monitor electrode 7M.
The output signal (monitor signal) VM from M is input to the waveform shaping circuit 9 as described above.

FIG. 2 is an electric circuit diagram showing the configuration of the oscillation circuit 1 and the pulse conversion circuit 2 of the first embodiment.

The oscillating circuit 1 receives an oscillator 33 for outputting a predetermined clock signal, a latch 31 for latching a predetermined output from the CPU 14, and a clock from the oscillator 33. Ultrasonic motor 7
And a down counter 32 that generates and outputs a pulse signal φUSR having a frequency approximately four times that of the AC signal applied to the power supply. The output waveform of the pulse signal φUSR is as shown in the timing chart of FIG.

The pulse conversion circuit 2 has four D
It has a 4-bit shift register composed of a flip-flop 51. The output signal from the oscillation circuit 1 and the pulse signal φUSR are frequency-divided into four-phase pulse signals φ1 to φ4 (see FIG. 4). Q1
To Q4.

FIG. 3 is an electric circuit diagram showing the phase difference counter 8 and the waveform shaping circuit 9 in the first embodiment.

The waveform shaping circuit 9 comprises a pressure reducing resistor 94, clamp diodes 92 and 93, and an inverter 91 having hysteresis. The above resistor 94
Is connected to the monitor electrode 7M for detecting the vibration state provided on the ultrasonic motor 7 so that the monitor signal VM from the ultrasonic motor 7 is input to the waveform shaping circuit 9. It has become. The monitor signal VM (see FIG. 4) input to the waveform shaping circuit 9 is decompressed by the decompression resistor 94, rectified by the clamp diodes 92 and 93, and further rectified by the inverter 9
The signal is shaped into a digital signal by 1 (see FIG. 4) and output to the phase difference counter 8.

The phase difference counter 8 calculates a phase difference between an output signal from the waveform shaping circuit 9, that is, a waveform-shaped monitor signal VM and a pulse signal φ 1 which is one output from the pulse conversion circuit 2. Upon receiving an RS flip-flop 81 to be detected and a clock from the oscillator 33,
An up-counter 82 counts the output from the RS flip-flop 81, that is, the phase difference between the monitor signal VM and the pulse signal φ1 and outputs the result to the first frequency control means 4 in the CPU 14. ing.

The rotary encoder 11 is composed of, for example, a known photo interrupter or MR sensor, and is disposed near the ultrasonic motor 7.
A pulse signal Spls proportional to the rotation amount of the motor 7 is generated and sent to the driving speed detecting means 12 and the driving amount detecting means 13.

On the other hand, the CPU 14 controls the drive circuit as described above and controls the drive frequency control switching means 3, the first frequency control means 4, the second frequency control means 5, the drive speed detection means 12, the drive amount It has a detecting means 13.

The drive speed detecting means 12 receives the pulse signal Spls from the rotary encoder 11, recognizes the rotational speed of the ultrasonic motor 7, and sends the result to the second frequency control means 5. In addition, the drive amount detecting means 13 recognizes the drive amount of the ultrasonic motor 7 from the pulse signal Spls, and sends the result to the drive frequency control switching means 3.

The first frequency control means 4 outputs the output from the phase difference counter 8, that is, the monitor signal VM.
Receiving the count information of the phase difference between the ultrasonic motor 7 and the pulse signal φ1, starting the oscillation of the frequency of the AC signal applied to the ultrasonic motor 7 from a frequency higher than the resonator frequency of the ultrasonic motor 7, Is controlled so as to follow the resonance frequency.

The second frequency control means 5 operates based on an output from the drive speed detection means 12 to store a frequency range higher than the lower limit frequency of the ultrasonic motor 7 stored in the memory 6 at a timing described later. Controls the frequency of the AC signal.

The drive frequency control switching means 3 receives the output result from the drive amount detection means 13 and selectively operates the first and second frequency control means 4 and 5, and outputs the result to the oscillation circuit 1 To be communicated to. That is, when the output from the drive amount detecting means 13 reaches a predetermined switching drive amount, the operation of the first frequency control means 4 is prohibited, and the frequency of the AC signal at this time is set as a lower limit frequency. Stored in the memory 6, and
The operation of the second frequency control means 5 is permitted.

The memory 6 is connected to the drive frequency control switching means 3, and as described above, when the output from the drive amount detection means 13 reaches a predetermined switching drive amount,
The frequency of the AC signal applied to the ultrasonic motor 7 is stored, and can be read at any time by the drive frequency control switching means 3.

[0029]

In the first embodiment, the driving frequency control switching means 3, the first frequency control means 4, the second frequency control means 5, the driving speed detecting means 12, the driving amount detecting means 13
Each block is constituted by software or hardware included in the CPU 14.

Next, the operation of the ultrasonic motor driving circuit according to the first embodiment will be described with reference to a flowchart shown in FIG. 5 and a diagram shown in FIG.

FIG. 6 is a diagram showing changes in speed, frequency and the like of the ultrasonic motor 7 in the first embodiment. In the figure, reference numeral Np denotes the target speed, and reference numeral Nr denotes the ultrasonic motor 7. This is the number of revolutions at the resonance frequency fr.

First, an operation button or the like (not shown) is operated to start the drive mode (step S101). Next, the initial frequency f of the AC signal applied to the ultrasonic motor 7
s is set (step S102). Note that, as shown in FIG.
Is a relatively low output signal having a frequency higher than the resonance frequency fr. This is because, as is well known, the ultrasonic motor can operate more stably in a frequency region higher than the resonance frequency fr. The setting of the initial frequency fs is performed by setting the frequency division number of the corresponding oscillator 33 (see FIG.
This is performed by writing “1”.

Next, by operating the pulse conversion circuit 2, AC signals VA and VB are generated, and the driving of the ultrasonic motor 7 is started (step S103). After the ultrasonic motor 7 starts to drive, the first frequency control means 4 is started (shown as a first frequency control area in FIG. 6). That is, the count value from the phase difference counter 8 is read (step S104), and the frequency of the AC signal is changed depending on whether the value is larger or smaller than the reference value (step S10).
5, Step S106, Step S107).

Steps S105, S106, S10
With the repetition of 7, the drive frequency gradually approaches the resonance frequency fr of the ultrasonic motor 7, and the rotational speed of the ultrasonic motor 7 increases (see FIG. 6).

On the other hand, the drive amount detecting means 13 determines whether or not the ultrasonic motor 7 has driven the predetermined number of pulses n1 based on the output signal Spls from the rotary encoder 11 (step S108). , Predetermined pulse number n
If it has been driven for about one minute, the frequency of the AC signal at this time is stored in the memory 6 as the lower limit frequency (step S
109). Then, the operation in the first frequency control means 4 ends, and the operation shifts to the operation in the second frequency control means 5. If the drive for the predetermined number of pulses n1 has not been completed, the process returns to step S104.

In step S108, whether or not the drive for the predetermined pulse number n1 has been performed is determined by, for example, connecting the output signal Spls of the rotary encoder 11 to a predetermined interrupt processing terminal and generating a pulse. This can be realized by counting down the register in which the pulse number n1 has been loaded in advance. Alternatively, a predetermined counter in the CPU 14 set so that a carry is output when the pulse number n1 is reached may be used.

Next, the second frequency control means 5 is started (shown as a second frequency control area in FIG. 6), and the drive speed detecting means 12 receives the output signal Spls from the rotary encoder 11 or not. Whether or not it is detected (step S110), every time one pulse is input, the drive speed of the ultrasonic motor is read by measuring the time from the previous pulse (step S111). Thereafter, the driving speed is compared with a reference speed preset as a target value (step S112). If the driving speed is higher than the reference speed, the frequency is increased to reduce the driving speed ( If the frequency is not the lower limit (step S113), the frequency is lowered (step S115) only if the frequency is not the lower limit (step S114). At this time, the judgment is made by comparing the current frequency value with the value stored in the memory 6.

Thereafter, the operation returns to step S110 if the drive permission signal input to the CPU 14 is continued by operating an operation button or the like (not shown). If not, the pulse conversion circuit 2 is disabled. The driving is stopped (step S117), and the constant speed driving flow is ended (step S118).

According to the ultrasonic motor driving circuit of the first embodiment, as shown in FIG. 6, since the frequency control is performed in a frequency range higher than the resonance frequency fr, the driving speed of the ultrasonic motor 7 is reduced. It is kept almost at Np. Further, since the operation of the first frequency control means 4 and the operation of the second frequency control means 5 are switched based on the output of the drive amount detection means 13, a low-speed and inexpensive CPU is used as compared with the case where both processes are performed simultaneously.
And power consumption can be reduced because of the constant speed driving. Further, since the above control is switched after the pulse signal Spls of a predetermined number of pulses is output from the rotary encoder 11, the drive at the high output resonance frequency fr is performed until the start is reliably performed, and the start does not fail. Also has the effect.

Next, an ultrasonic motor driving circuit according to a second embodiment of the present invention will be described.

The structure of the second embodiment is substantially the same as that of the first embodiment, except that the target drive speed is variable, and the switching drive amount of the ultrasonic motor changes in accordance with the drive speed. It is characterized by doing.

FIG. 8 is a diagram showing the switching drive amount with respect to the target drive speed of the ultrasonic motor in the ultrasonic motor drive circuit of the second embodiment.

As shown in this figure, for example, when the target drive speed is 0 to Np1, the switching drive amount n1 is changed to n11.
Hereafter, when the target drive speed is Np1 to Np2, the switching drive amount is set to n12, and when the target drive speed is Np2 or more, the switch drive amount is set to n13.

FIG. 9 is a diagram showing changes in frequency and driving speed (indicated as the number of revolutions in the figure) when the respective switching driving amounts are set as shown in FIG. 8 in the second embodiment. It is.

According to the second embodiment, when the ultrasonic motor is driven at a low speed, excessively high drive speed, that is, hunting, can be reduced, and the target drive speed can be reached quickly and reliably.

Next, an ultrasonic motor driving circuit according to a third embodiment of the present invention will be described.

The third embodiment is substantially the same as the first embodiment except that the total drive amount from the start to the stop of the drive is set. The difference is that the switching drive amount is changed.

The operation of the third embodiment will be described with reference to flowcharts shown in FIGS. 10 and 11 and diagrams shown in FIGS. In addition, in FIG. 10, (*)
The flow is connected to (*) inside.

FIG. 12 is a diagram showing the switching drive amount with respect to the total drive amount of the ultrasonic motor in the ultrasonic motor drive circuit of the third embodiment.

As shown in this figure, for example, when the total driving amount is 0 to Dp1, the switching driving amount n1 is set to n11, and when the total driving amount is Dp1 to Dp2, the switching driving amount is set to n12. When the total drive amount is equal to or greater than Dp2, the switching drive amount is set to n13.

FIG. 13 is a graph showing changes in the frequency and the driving speed (indicated as the number of rotations in the figure) when the respective switching drive amounts are set as shown in FIG. 12 in the third embodiment. FIG. In the drawing, reference numeral Np denotes an intended speed, and reference numeral Nr denotes the number of revolutions of the ultrasonic motor 7 at the resonance frequency fr.

In FIGS. 10 and 11, step S20
1, Step S205 to Step S212, Step S
227 and S228 are performed in steps S101 and S102 to S102 shown in FIG.
109, step S117, and step S118, respectively.

Steps S213 and S215
Steps S219, S220, and S2
Steps 22 to S226 also correspond to steps S110 to S115 shown in FIG. 5, respectively, and thus description thereof will be omitted.

First, in step S202 in FIG. 10, the number of pulses Dp (total driving amount) corresponding to the amount to be driven
Set. Next, the switching drive amount n1 of the ultrasonic motor corresponding to the total drive amount Dp is read based on the value read from the diagram shown in FIG. 12, and the number obtained by subtracting the switch drive amount n1 from the total drive amount Dp is obtained. The number of remaining switching pulses is stored in the memory 6 (step S203).

Further, even from the rotational speed Nr, a sufficient rotational speed Ns can be obtained.
The number of deceleration pulses that can be decelerated to t is subtracted from the total drive amount Dp to set the number of remaining deceleration pulses (step S204). If this value is larger than the number of remaining pulses for switching, the value is set to one smaller than the number of remaining pulses for switching.

Then, after setting the initial frequency fs (step S205) as in the first embodiment, step S20 is performed.
6, the ultrasonic motor 7 based on the first frequency control means 4.
Is driven to reach the remaining switching pulse (step S2).
11) Switch to the second frequency control means 5, but initially set the high speed as the reference speed Np, and when reaching the deceleration region in step S214, switch the reference speed to Nst and drive, and in step S221 the remaining pulses When the number becomes 0, the driving of the ultrasonic motor 7 is stopped.

FIG. 13 shows how the speed and frequency of the ultrasonic motor 7 change in the operation described above.

In FIG. 13, reference symbol A denotes the first frequency control means 4.
Is an operation section of the second frequency control means 5 and a section in which the reference speed is Np of high speed,
Reference numeral 2 denotes an operation section of the second frequency control means 5 in which the reference speed is Nst.

When the first frequency control means 4 is operated with a large amount of drive as described above, the drive speed of the ultrasonic motor becomes too high, and the first motor can be stopped without fail. If the drive speed is set to Nst, the drive amount may exceed the amount to be driven while the drive speed is being reduced to Nst, which may cause a problem that the ultrasonic motor overruns. However, according to the third embodiment, the switching drive amount n1 can be reduced at the time of minute driving, so that the above-described inconvenience does not occur.

According to the present embodiment, the CP of the low-speed processing
Since U can be used and an accurate driving amount can be achieved, the present invention can also be applied to auto-focus driving of a photographing lens of a camera. Note that, in this case, the reference speed may not be two steps but may be multiple steps.

Next, an ultrasonic motor driving circuit according to a fourth embodiment of the present invention will be described.

FIG. 14 is a block diagram showing the configuration of the ultrasonic motor driving circuit according to the fourth embodiment.

The structure of the fourth embodiment is substantially the same as that of the first embodiment (see FIG. 1), but the driving time detecting means 1 is replaced with the driving amount detecting means 13 in the first embodiment.
3 'is provided. In the fourth embodiment, a hardware timer or the like built in the CPU 14 is used as the driving time detecting means 13 '.

The operation of the fourth embodiment is shown in the flowchart of FIG. 15, but instead of step S108 (see FIG. 5) in the first embodiment, the operation proceeds to step S30.
8 is different only in that the operations of steps S301 to S307 and S30 are performed.
The operations in steps 9 to S318 correspond to steps S101 to S10 in the flowchart shown in FIG.
7 and steps S109 to S118, and a description thereof will not be repeated.

In step S308, the driving time from the start of driving is read out from the driving time detecting means 13 'and monitored, and when the predetermined time has been reached, the flow proceeds to step S309. The driving state of the ultrasonic motor 7 is almost the same as that shown in FIG.

The fourth embodiment is particularly effective when the pulse pitch of the rotary encoder 11 used in the first embodiment is wide.

Further, with the same configuration as that of the fourth embodiment, the switching drive time can be controlled according to the target speed and the total number of drive pulses as shown in the second and third embodiments. It is.

In the first to fourth embodiments, the oscillating circuit 1 may be an analog oscillator such as a VCO, and the pulse conversion circuit 2 and the AC waveform generator may be of any known type, regardless of the configuration of these embodiments. Various circuits may be employed. Also, the phase difference between the monitor signal VM from the monitor electrode 7M and the pulse signal φ1 is used as the monitor means. The amplitude of the monitor signal VM, the phase difference between the current and the voltage, and the difference between the pulse signal φ1 and the AC signal VA are used. Other methods such as a phase difference may be used. Further, a part of the configuration inside the CPU 14 may be configured by a hardware digital circuit or the like.

[0070]

As described above, according to the present invention, since the frequency control based on the monitoring means and the frequency control based on the speed detecting means are not performed simultaneously, a low-speed and low-cost C
It is possible to provide an ultrasonic motor drive circuit that can use a PU, can control high-speed rotation with low power consumption, and can control the speed by frequency change.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of an ultrasonic motor drive circuit showing a first embodiment of the present invention.

FIG. 2 is an electric circuit diagram showing a configuration of an oscillation circuit and a pulse conversion circuit in the ultrasonic motor drive circuit of the first embodiment.

FIG. 3 is an electric circuit diagram showing a phase difference counter and a waveform shaping circuit in the ultrasonic motor drive circuit of the first embodiment.

FIG. 4 is a timing chart showing signal waveforms at various parts of the ultrasonic motor drive circuit according to the first embodiment.

FIG. 5 is a flowchart showing the operation of the ultrasonic motor drive circuit of the first embodiment.

FIG. 6 is a diagram showing changes in speed, frequency, and the like of the ultrasonic motor in the first embodiment.

FIG. 7 is a diagram showing the relationship between the number of rotations and the frequency of the ultrasonic motor in the first embodiment.

FIG. 8 is a diagram illustrating a switching drive amount with respect to a target drive speed of an ultrasonic motor in an ultrasonic motor drive circuit according to a second embodiment of the present invention.

FIG. 9 is a diagram showing changes in frequency and drive speed (indicated as the number of revolutions in the figure) when each switching drive amount is set as shown in FIG. 8 in the second embodiment. .

FIG. 10 is a flowchart showing the operation of the ultrasonic motor drive circuit of the first embodiment.

FIG. 11 is a flowchart showing the operation of the ultrasonic motor drive circuit according to the first embodiment.

FIG. 12 is a diagram showing a switching drive amount with respect to a total drive amount of an ultrasonic motor in an ultrasonic motor drive circuit according to a third embodiment of the present invention.

FIG. 13 shows changes in frequency and drive speed (indicated as a rotational speed in the figure) when the respective switching drive amounts are set as shown in FIG. 12 in the ultrasonic motor drive circuit of the third embodiment. FIG.

FIG. 14 is an electric circuit diagram of an ultrasonic motor driving circuit showing a fourth embodiment of the present invention.

FIG. 15 is a flowchart showing the operation of the ultrasonic motor drive circuit according to the fourth embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 oscillation circuit 2 pulse conversion circuit 3 drive frequency control switching means 4 first frequency control means 5 second frequency control means 6 memory 7 ultrasonic motor 8 phase difference counter 9 waveform shaping circuit 10 DC power supply 11 ... Rotary encoder 12 ... Drive speed detecting means 13 ... Drive time detecting means

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02N 2/16

Claims (2)

(57) [Claims] 1. An ultrasonic motor in which an electric-mechanical energy conversion element is disposed by applying an AC signal generated by switching an inductive element to an electro-mechanical energy conversion element using a DC power supply. In the ultrasonic motor driving circuit, a monitoring means for detecting a driving state of the ultrasonic motor, a driving speed detecting means for detecting a driving speed of the ultrasonic motor, and a drive for detecting a driving amount of the ultrasonic motor Amount detection means
If, until the output from the drive detection means reaches a predetermined value
Based on the output of said monitor means, a first frequency control means for follow-up control of the frequency of the AC signal to the resonant frequency of the ultrasonic motor, it reaches the value output predetermined from the drive detection means When
And a lower limit frequency storage means for storing the frequency of the AC signal, after the output from the drive amount detection means reaches a predetermined value.
Shall be based on the output of the driving speed detecting means at the stored frequency higher frequency range to the lower limit frequency storage means, equipped with the second frequency control means for controlling the frequency of the AC signal, the An ultrasonic motor drive circuit characterized by the following. 2. An ultrasonic motor in which the electro-mechanical energy conversion element is disposed by applying an alternating-current signal generated by switching an inductive element to the electro-mechanical energy conversion element using a DC power supply. In the ultrasonic motor driving circuit, a monitoring means for detecting a driving state of the ultrasonic motor, a driving speed detecting means for detecting a driving speed of the ultrasonic motor, and a drive for detecting a driving time of the ultrasonic motor Time detector
And the output from the drive time detecting means reaches a predetermined value.
In, on the basis of the output of said monitor means, a first frequency control means for follow-up control of the frequency of the AC signal to the resonant frequency of the ultrasonic motor, reaches the value output predetermined from the driving time detecting means I did
The lower limit frequency storage means for storing the frequency of the AC signal, and after the output from the drive time detection means reaches a predetermined value.
Shall be based on the output of the driving speed detecting means at the stored frequency higher frequency range to the lower limit frequency storage means, equipped with the second frequency control means for controlling the frequency of the AC signal, the An ultrasonic motor drive circuit characterized by the following.