JP3131520B2 - 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 driving circuit, and more particularly to an ultrasonic motor driving circuit for optimally driving an ultrasonic motor.

[0002]

2. Description of the Related Art Conventionally, various driving circuits for ultrasonic motors have been proposed. For example, Japanese Unexamined Patent Publication No. Sho 59-204477 discloses an output signal (monitor signal) from a monitor electrode provided in an ultrasonic motor. The voltage value of the monitor signal is monitored by utilizing the fact that the voltage value of ()) becomes maximum at the resonance frequency of the vibrating body of the ultrasonic motor, and based on the voltage value, the resonance frequency or the resonance frequency is calculated. Technical means for driving an ultrasonic motor in a slightly high-frequency region are disclosed.

Japanese Patent Application Laid-Open No. 61-251490 discloses that the phase difference of the monitor signal with respect to the drive voltage is determined by utilizing the fact that the phase of the monitor signal with respect to the drive voltage greatly changes near the resonance frequency. There is disclosed a technical means for monitoring and driving an ultrasonic motor in a resonance frequency or a region slightly higher than the resonance frequency based on the phase difference.

[0004]

However, Japanese Patent Application Laid-Open Nos. 59-204477 and 61-2514 describe the above.
The technical means disclosed in Japanese Patent Publication No. 90 requires an extra arrangement of a monitor electrode in the ultrasonic motor, which is not preferable because it takes time and effort to manufacture and increases the cost.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an ultrasonic motor driving circuit capable of tracking an optimum driving frequency without providing a special monitor electrode.

[0006]

In order to achieve the above object, an ultrasonic motor drive circuit according to the present invention comprises an inductive element .
An AC signal is generated based on an induced electromotive force generated when switching a flowing current, and the AC signal is used as a drive signal.
And electrodeposition electric over mechanical energy conversion element of the ultrasonic motor
By applying the electrode, in the ultrasonic motor drive circuit for driving the ultrasonic motor, as an input the driving signal
By comparing with the threshold voltage,
A waveform shaping circuit for outputting a rectangular wave that, the drive signal peptidase
Start point of voltage rise from potential b and waveform shaping circuit
Appears between the high and low signal inversion points of the output square wave
A phase difference detecting means for detecting a phase difference where is between difference, by comprising a frequency control means for controlling the frequency of the drive signal <br/> based on the output of the phase difference detecting means
Features .

[0007]

[Operation] In the present invention, the above-mentioned drive signal is input.
From high and low by comparing with the threshold voltage
Is output by a waveform shaping circuit, and the driving signal
Start point of voltage rise from potential b and waveform shaping circuit
Appears between the high and low signal inversion points of the output square wave
The phase difference, which is the difference between the two, is detected by the phase difference detecting means ,
Based on the output of the phase difference detection means ,
To control the frequency control means the frequency.

[0008]

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 driving 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 monitors the AC signal to monitor the AC signal. The drive control of the ultrasonic motor 5 is performed.

That is, the driving circuit includes the ultrasonic motor 5
An oscillation circuit 1 for generating and outputting a pulse signal φORG having a frequency approximately four times that of an AC drive signal applied to the oscillating circuit 1;
A pulse conversion circuit 2 that divides and outputs the 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 intermediate 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 for outputting an A-phase AC signal VA to the next side;
Similarly, the primary side is turned on by the switching operation of the switching transistors Q3 and Q4, and B
A transformer T2 for outputting a phase AC signal VB, a waveform shaping circuit 4 connected to one end (A phase side) of the output of the transformer T1 and converting the AC signal VA into a predetermined digital signal; , And the AC signal VA, and compares the phases of the two signals with each other. The result of the comparison, that is, the phase difference between the two signals, and the phase comparator 3 that sends the phase difference to the oscillation circuit 1 are compared. The main part is configured.

The ultrasonic motor 5 is a known traveling wave type ultrasonic motor having a piezoelectric element.
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 whose phases are shifted from each other by about 90 ° are applied to A and 5B, and the two-phase AC signals drive rotation. Is to be done.

The oscillation circuit 1 compares a preset optimum frequency with an output from the phase comparator 3, that is, a phase difference between the digital output signal of the waveform shaping circuit 4 and the AC signal VA. The oscillation frequency to be output is controlled based on the result.

FIG. 2 is an electric circuit diagram showing the waveform shaping circuit 4 in the ultrasonic motor driving circuit according to the first embodiment. FIG. 3A shows an AC signal which is an input signal of the waveform shaping circuit 4. VA signal waveform, (b) a signal waveform showing an inverted input waveform and a non-inverted input waveform of the comparator 6 in the waveform shaping circuit 4, and (c) an AC signal VA which is an output signal of the waveform shaping circuit 4. It is the diagram which each showed the signal shaping waveform. 3 (a), 3 (b) and 3 (c).
The solid, dotted, and dashed-dot waveforms
They correspond to each other .

As shown in FIG. 2, the waveform shaping circuit 4 includes a first circuit including voltage reducing resistors R1 and R2 and clamp diodes D1 and D2, and a voltage reducing resistor R1.
3, R4, clamp diodes D3, D4 and resistor R
5, a second circuit comprising an integrating circuit formed by a capacitor C1, and a comparator 6 for inputting an output signal of the first circuit to a non-inverting input terminal and inputting an output signal of the second circuit to an inverting input terminal. Have been.

The input terminals of the voltage reducing resistors R1 and R3 are connected to the output terminal of the transformer T1, and the AC signal VA output from the transformer T1 is connected to the first terminal.
And the second circuit.

The AC signal VA input to the second circuit
(See FIG. 3 (a)) is attenuated by resistors R3 and R4.
After being rectified by the clamp diodes D3 and D4 and smoothed by an integrating circuit composed of the resistor R5 and the capacitor C1, it is input to the inverting input terminal of the comparator 6 as a threshold level (see FIG. 3B). The values of the resistors R3 and R4 are equal to the values of the clamp diodes D3 and R3.
The AC signal VA is within the voltage range rectified by D4.
It is set to include the head of the waveform.

On the other hand, the AC signal VA input to the first circuit is attenuated by the resistors R1 and R2, rectified by the clamp diodes D1 and D2, and then input to the non-inverting input terminal of the comparator 6 (FIG. 3 (b)).
Note that the values of the resistors R1 and R2 indicate that the position of the AC signal VA waveform where the waveform change is most remarkable is the clamp diode
The threshold level position is set within the voltage range defined by D1 and D2.

With such a configuration, the waveform of the AC signal VA is shaped into a digital waveform at a certain threshold level (see FIG. 3C), and is output to the phase comparator 3. Has become.

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

FIG. 4 is a line showing the relationship between the phase difference between the AC signal VA and the shaped waveform of the AC signal VA in the ultrasonic motor drive circuit of the first embodiment and the drive frequency of the AC signal VA. FIG.

As shown in FIG. 4, the A-phase AC signal V
Assuming that the phase difference between A and the shaped waveform of the AC signal VA is Δφ, if the drive frequency is adjusted by raising or lowering the drive frequency so as to maintain the phase difference Δφ at a predetermined value, it is possible to track the optimum drive frequency. Note that in the figure, the phase difference Δφ is
Indicated by A.

More 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 while gradually monitoring the phase difference Δφ. Then, the driving frequency is lowered. Then, the phase difference Δφ is adjusted so as to be a phase difference corresponding to a preset optimal driving frequency, for example, −35 °. That is, if the phase difference Δφ becomes larger in absolute value than −35 °, the driving frequency is increased, and if the phase difference Δφ becomes smaller, the oscillation frequency is changed so as to decrease the driving frequency.

With such an operation, it is possible to track the optimum driving frequency of the ultrasonic motor having no monitor electrode. In addition, if the characteristic portion having little change at the time of no load and at the time of load is used, it is possible to easily track the optimum driving frequency even in an ultrasonic motor having a large load change.

Further, according to the first embodiment, the above-mentioned waveform shaping circuit can be constituted by inexpensive components, and if the voltage reducing resistors R1 and R3 are made large, the power loss of the A-phase AC signal VA is almost completely reduced. Does not occur.

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

FIG. 5 is an electric circuit diagram showing an ultrasonic motor driving circuit according to the second embodiment.

The ultrasonic motor drive circuit of the second embodiment has substantially the same structure as that of the first embodiment, and differs only in that a memory 7 is added to the oscillation circuit 1.

In general, the characteristics of an ultrasonic motor slightly change due to variations in dimensions and the like in manufacturing. Therefore, the optimum phase difference unique to each ultrasonic motor, that is, the A-phase AC signal VA and the AC signal V as described above.
A has an optimum phase difference Δφ with the shaped waveform of A. The second embodiment focuses on the fact that each ultrasonic motor has a unique optimum phase difference,
After storing the optimum phase difference Δφ in the memory 7, the first
The same frequency control as in the embodiment is performed.

According to the second embodiment, it is possible to correct variations in the manufacturing 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 7 and to select and use the plurality of phase differences Δφ based on a 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. 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, the oscillating circuit 1 can be constituted by using any oscillating means such as a VCO and a digital frequency dividing oscillator.
Even if the frequency is not four times, if the phase shift circuit or the like is used, the above-described pulse signals φ1 to φ4 can be generated. Further, the ultrasonic motor 5 has a phase difference Δ
Any type that changes φ can be used.

[0034]

As described above, according to the present invention, it is possible to provide an ultrasonic motor driving circuit which can track the optimum driving frequency even with an inexpensive ultrasonic motor having no monitor electrode.

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

FIG. 3 shows (a) an AC signal VA which is an input signal of a waveform shaping circuit in the ultrasonic motor driving circuit of the first embodiment.
(B) a signal waveform showing an inverted input waveform and a non-inverted input waveform of a comparator in the waveform shaping circuit, and (c) a signal shaping waveform of an AC signal VA which is an output signal of the waveform shaping circuit. It is the diagram respectively shown.

FIG. 4 is a diagram showing a relationship between a driving frequency and a phase difference between an AC signal VA and a shaped waveform of the AC signal VA in the ultrasonic motor driving circuit of the first embodiment.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Oscillation circuit 2 ... Pulse conversion circuit 3 ... Phase comparator 4 ... Waveform shaping circuit 5 ... Ultrasonic motor 6 ... Comparator 10 ... DC power supply

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

Claims (1)

(57) [Claims] An AC signal is generated based on an induced electromotive force generated when switching a current flowing through an inductive element , and the AC signal is used as a drive signal to be applied to an electrode of an electromechanical energy conversion element of an ultrasonic motor. By applying
In the ultrasonic motor drive circuit for driving the ultrasonic motor, the drive signal is input and compared with a threshold voltage.
Waveform that outputs a square wave consisting of high and low
Circuit, and a starting point of voltage rise from zero potential of the drive signal.
High and low signal inversion points of the square wave output from the waveform shaping circuit
A phase difference detecting means for detecting a phase difference that is a time difference appearing between: and a frequency controlling means for controlling a frequency of the drive signal based on an output of the phase difference detecting means. Ultrasonic motor drive circuit.