JPH06253557A - Driving circuit for ultrasonic motor - Google Patents

Abstract

PURPOSE:To provide a driving circuit for ultrasonic motor which can track an optimal driving frequency over a wide load range without requiring any special monitor electrode. CONSTITUTION:The driving circuit for generating AC signal VA, VB based on an electromotive force induced upon switching of transformers T1, T2 and driving an ultrasonic motor 5 by applying the AC signals to a piezoelectric element in the motor 5 comprises a comparator 3 for detecting the phase difference between a pulse signal phi2 and a signal obtained by shaping the AC signal VA with a predetermined threshold value other than zero, and an oscillation circuit 1 for controlling the frequency of the AC signal VA based on the output from the comparator 3.

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 optimally driving an ultrasonic motor.

[0002]

2. Description of the Related Art Conventionally, various drive circuits for ultrasonic motors have been proposed. For example, Japanese Patent Laid-Open No. 59-204477 discloses an output signal (monitor signal) from a monitor electrode provided in the ultrasonic motor. ) Is utilized at the resonance frequency of the vibration body of the ultrasonic motor, the voltage value of the monitor signal is monitored, and based on this voltage value, the resonance frequency or the resonance frequency A technical means for driving an ultrasonic motor in a slightly high frequency region is disclosed.

Further, in Japanese Patent Laid-Open No. 61-251490, 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 changes greatly near the resonance frequency. Disclosed is a technical means for driving an ultrasonic motor at a resonance frequency based on a phase difference between a signal and the drive voltage, or at a region slightly higher than the resonance frequency.

On the other hand, in Japanese Patent Laid-Open No. 62-92781, the optimum drive frequency of the ultrasonic motor is monitored by monitoring the phase difference between the voltage and the current of the drive signal applied to the drive electrode of the ultrasonic motor. A technical means for determining is disclosed.

[0005]

However, the above-mentioned JP-A-59-204477 and JP-A-61-2514 are known.
The technical means disclosed in Japanese Patent Publication No. 90 requires the provision of a special monitor electrode on the ultrasonic motor, which is troublesome in manufacturing and causes an increase in cost, which is not preferable.

On the other hand, the technical means disclosed in the above-mentioned JP-A-62-92781 eliminates the need for the monitor electrode, and thus the above-mentioned JP-A-59-204477 and JP-A-61-61.
The problems associated with the technical means disclosed in Japanese Patent No. 251490 are solved. However, as shown in FIG. 7, when a load is applied to the ultrasonic motor (in the figure, when the load is applied), the phase difference changes significantly depending on the load as compared to when there is no load. For this reason, when the technical means is applied to a camera having a lens with a large load change such that the entire shooting lens is extended, the load changes drastically due to posture differences during use, and it is difficult to track the optimum drive frequency. There was a problem that became.

The present invention has been made in view of the above problems, and provides an ultrasonic motor drive circuit capable of tracking an optimum drive frequency over a wide load range without disposing a special monitor electrode. The purpose is to

[0008]

In order to achieve the above object, an ultrasonic motor drive circuit according to the present invention generates an AC signal based on an induced electromotive force generated when switching an inductive element, AC signal is sent to the ultrasonic motor
In an ultrasonic motor drive circuit for driving the ultrasonic motor by applying a mechanical energy conversion element,
Phase difference detecting means for detecting a phase difference between a switching signal for switching the inductive element and a signal obtained by waveform-shaping the AC signal with a predetermined threshold value which is not zero, and based on an output of the phase difference detecting means, And a frequency control means for controlling the frequency of the AC signal.

[0009]

In the present invention, in the phase difference detecting means,
Detects the phase difference between the switching signal for switching the inductive element and the signal obtained by waveform-shaping the AC signal with a predetermined threshold value which is not zero, and induces the frequency control means based on the output of the phase difference detection means. The frequency of the alternating current signal based on the induced electromotive force generated when switching the capacitive element is controlled.

[0010]

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 drive 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 5 having two electrodes 5A and 5B, and further monitors the AC signal to monitor the AC signal. The drive control of the ultrasonic motor 5 is performed.

That is, the drive circuit is the ultrasonic motor 5
An oscillator circuit 1 for generating and outputting a pulse signal φORG having a frequency about four times as high as the AC drive signal applied to the pulse signal φORG and the pulse signal φORG output from the oscillator circuit 1.
A pulse conversion circuit 2 that divides and outputs phase-phase pulse signals φ1 to φ4, and switching transistors Q1 to Q4 that perform switching operations corresponding to the pulse signals φ1 to φ4 output from the pulse conversion circuit 2, respectively. The positive voltage of the DC power supply 10 is supplied to the primary tap on the primary side, and the primary side is turned on by the switching operation of the switching transistors Q1 and Q2.
A transformer T1 that outputs an A-phase AC signal VA to the next side,
Similarly, the switching operation of the switching transistors Q3 and Q4 causes the primary side to turn on and the secondary side to B
A transformer T2 that outputs a phase AC signal VB, a waveform shaping circuit 4 that is connected to one end (A phase side) of the output of the transformer T1 and that converts the AC signal VA into a predetermined digital signal, and the waveform shaping circuit 4 Of the digital signal and the pulse signal φ2 from the pulse conversion circuit 2
The phase comparator 3 which compares the phases of two signals and outputs the result, that is, the phase difference between the phases of the two signals, to the oscillation circuit 1 constitutes a main part.

The ultrasonic motor 5 is a well-known traveling wave type ultrasonic motor having a piezoelectric element, and as described above,
It has two electrodes 5A and 5B. That is, the electrode 5
The two-phase (A-phase and B-phase) AC signals VA and VB, which are out of phase with each other by about 90 °, are applied to A and 5B, and the rotational drive is performed by the two-phase AC signals. It is supposed to be done.

The oscillator circuit 1 has a preset optimum frequency and an output from the phase comparator 3, that is, a digital output signal of the waveform shaping circuit 4 and the pulse signal φ2.
And the phase difference between them are compared, and the oscillation frequency to be output is controlled based on this result.

FIG. 2 is an electric circuit diagram showing the waveform shaping circuit 4 in the ultrasonic motor drive circuit of the first embodiment, and FIG. 3 (a) is an AC signal which is an input signal of the waveform shaping circuit 4. A signal waveform of VA, (b) an attenuation waveform by the voltage reductions R1 and R2 in the waveform shaping circuit 4, (c) a waveform in which the voltage range is limited by the clamp diodes D1 and D2 in the waveform shaping circuit 4, (d) a waveform FIG. 6 is a diagram showing a shaping waveform of an AC signal VA which is an output signal of the shaping circuit 4, and (e) a waveform of the pulse signal φ2 corresponding to each signal of the waveform shaping circuit 4. In addition, among the waveforms shown in each figure of FIG. 3, the waveform indicated by the wavy line indicates the waveform when a predetermined load is applied to the ultrasonic motor with respect to the waveform state indicated by the solid line. The waveform shown is a waveform when a load is further applied to the ultrasonic motor.

As shown in FIG. 2, the waveform shaping circuit 4 includes resistors R1 and R2 for voltage reduction, a clamp diode D.
Inverter IV1 with 1, D2 and hysteresis
It consists of and. The input terminal of the voltage reducing resistor R1 is connected to the output terminal of the transformer T1, whereby the AC signal V generated and output by the transformer T1.
A is input to the ultrasonic motor 5 and also to the waveform shaping circuit 4.

The AC signal VA (see FIG. 3 (a)) input to the waveform shaping circuit 4 first has a voltage reducing resistor R.
1, R2 reduces the voltage (see FIG. 3 (b)),
After that, it is rectified by the clamp diodes D1 and D2 and limited to a predetermined voltage range depending on the value of the diodes (see FIG. 3C). Further, the signal is shaped into a digital signal at a predetermined threshold level of the inverter IV1 and is input as a shaped waveform (see FIG. 3D) to the phase comparator 3.

By the way, when a considerably large load is applied to the ultrasonic motor, the waveform of the AC signal for driving the ultrasonic motor changes as shown in FIG. As shown in FIG. 6, when the phase difference between the rising edge of the switching signal applied to the transformers T1 and T2 and the AC signal applied to the ultrasonic motor is Δφ, there is a change in the figure between a large load and no load. It is conceivable that the difference will be as much as the amount Δφ ′, and accurate tracking of the optimum drive frequency will not be easy.

On the other hand, in the first embodiment, as shown in FIG. 3, the voltage is reduced so that the degree of change in the waveform of the AC signal VA due to the load change becomes the smallest at the predetermined threshold level of the inverter IV1. Resistance R
The voltage values of the AC signal VA are controlled by setting the values of 1 and R2. As a result, the phase difference Δφ between the shaped waveform of the AC signal VA output from the waveform shaping circuit 4 (see FIG. 3D) and the pulse signal φ2 (see FIG. 3E) is the AC signal due to the load. It is not affected by a change in the waveform of VA in a fairly wide range.

Next, the operation of the first embodiment will be described.

FIG. 4 shows the phase difference between the AC signal VA and the pulse signal φ2 which is one output signal from the pulse conversion circuit 2 in the ultrasonic motor drive circuit of the first embodiment, and the driving of the AC signal VA. It is the diagram which showed the relationship with a frequency.

As shown in FIG. 4, the A-phase AC signal V
If the phase difference between A and the pulse signal φ2 is Δφ, the optimum driving frequency can be tracked by adjusting the driving frequency up and down so as to keep the phase difference Δφ at a predetermined value. In addition,
In the figure, the phase difference Δφ is represented by a pulse signal φ2-AC signal VA.

Specifically, the oscillation circuit 1 starts oscillating at 44 KHz, which is slightly higher than the expected optimum driving frequency, and gradually monitors the phase difference Δφ based on the output from the phase comparator 3. To lower the drive frequency. Then, the phase difference Δφ is adjusted to be a phase difference corresponding to a preset optimum driving frequency, for example, −145 °. That is, when the phase difference Δφ is larger than −145 °, the drive frequency is increased, and when the phase difference Δφ is smaller, the drive frequency is decreased. In addition, the phase difference −
In the vicinity of 145 °, there is no difference in the phase difference characteristic between the loaded state and the unloaded state.

By such an operation, it becomes possible to track the optimum driving frequency of the ultrasonic motor which has no monitor electrode and has a large load fluctuation.

Further, according to the first embodiment, the above-mentioned waveform shaping circuit can be composed of inexpensive parts, and if the voltage reducing resistor R1 is made large, the power loss of the A-phase AC signal VA hardly occurs. .

Further, as described above, the waveform shaping circuit 4
The threshold level at is set to a value that causes less waveform change due to load, and by extracting the change in the phase difference due to the change in the electrical characteristics of the ultrasonic motor, the waveform change occurs in the AC signal that drives the ultrasonic motor. Even if a large load fluctuation occurs, it is possible to track a more accurate optimum drive frequency without being affected by the load fluctuation.

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

FIG. 5 is an electric circuit diagram showing the ultrasonic motor drive circuit of the second embodiment.

The ultrasonic motor drive circuit of the second embodiment is almost the same in construction as the first embodiment, except that a memory 6 is added to the oscillator circuit 1.

By the way, in general, the characteristics of an ultrasonic motor change subtly due to variations in manufacturing dimensions and the like. Therefore, each ultrasonic motor has an optimum phase difference, that is, an optimum phase difference Δφ between the shaped waveform of the AC signal VA of the phase A and the output pulse signal φ2 from the pulse conversion circuit 2 as described above. It will be. The second embodiment is made by paying attention to the fact that each ultrasonic motor has its own optimum phase difference, and the optimum phase difference Δφ is stored in the memory 6.
Then, the same frequency control as in the first embodiment is performed.

According to the second embodiment, it is possible to correct manufacturing variations of the ultrasonic motors and more accurately track the optimum driving frequency.

In the second embodiment, it is also possible to store a plurality of phase differences Δφ in the memory 6 and select and use the plurality of phase differences Δφ based on the power supply voltage or the like.

In the first and second embodiments, the optimum drive frequency control is performed based on the phase difference between the A-phase AC signal VA and the shaped waveform of the AC signal VA. Alternatively, the phase difference between the AC signal VB and its shaped waveform or the AC signal of both phases and its shaped waveform may be used.

On the other hand, in the first and second embodiments, the oscillation circuit 1 can be constructed by using any oscillation means such as VCO or digital frequency division oscillation, and the phase shift circuit is not necessary even if the frequency is 4 times. It is possible to generate the above-mentioned pulse signals φ1 to φ4 by using the above. further,
The waveform shaping circuit 4 may be configured by using a comparator or the like, and the ultrasonic motor 5 is of a type whose impedance changes depending on the frequency or the like other than the traveling wave type, and the phase difference Δφ.
Anything that causes a change in can be used.

[0036]

As described above, according to the present invention, it is possible to track an optimum driving frequency even with an inexpensive ultrasonic motor having no monitor electrode, and an ultrasonic motor driving circuit with a small influence on large load fluctuations. Can be provided.

[Brief description of 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 a waveform shaping circuit in the ultrasonic motor drive circuit of the first embodiment.

FIG. 3 is a timing chart showing a relationship between an AC signal VA, a shaped waveform of the AC signal VA, an output pulse signal from the pulse conversion circuit, and the like in the ultrasonic motor drive circuit of the first embodiment.

FIG. 4 is a diagram showing a waveform of an AC signal VA and 1 from a pulse conversion circuit in the ultrasonic motor drive circuit of the first embodiment.
FIG. 9 is a diagram showing the relationship between the phase difference Δφ and the drive frequency, where Δφ is the phase difference from the output pulse signal.

FIG. 5 is an electric circuit diagram of an ultrasonic motor drive circuit showing a second embodiment of the present invention.

FIG. 6 is a diagram showing an example of a waveform of an AC signal applied to a conventional ultrasonic motor when a large load is applied to the ultrasonic motor.

FIG. 7 is a diagram showing an example of a relationship between a drive frequency and a current-voltage phase difference of a drive signal in a conventional ultrasonic motor with and without a load.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Oscillation circuit 2 ... Pulse conversion circuit 3 ... Phase comparator 4 ... Waveform shaping circuit 5 ... Ultrasonic motor 10 ... DC power supply

Claims (1)

[Claims] 1. An ultrasonic wave is generated by generating an AC signal based on an induced electromotive force generated when switching an inductive element and applying the AC signal to an electromechanical energy conversion element of an ultrasonic motor. In an ultrasonic motor drive circuit for driving a motor, a phase difference detecting means for detecting a phase difference between a switching signal for switching the inductive element and a signal obtained by waveform-shaping the AC signal with a predetermined threshold value which is not zero. An ultrasonic motor drive circuit comprising: a frequency control unit that controls the frequency of the AC signal based on the output of the phase difference detection unit.