JP4593737B2 - Ultrasonic motor drive circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control circuit for driving an ultrasonic motor, and more particularly, to control an ultrasonic motor that uses a mechanical vibration wave for an electro-mechanical energy conversion element such as an electrostrictive element, a piezoelectric element, or a magnetostrictive element. Regarding the circuit.
[0002]
[Prior art]
Conventionally, an ultrasonic motor using ultrasonic vibration as a driving force is known. The amplitude of the mechanical vibration generated in the piezoelectric body is maximum when the frequency of the drive signal is the resonance frequency, but in a predetermined frequency band including the resonance frequency, abnormal vibration of audible sound occurs in the elastic body, and the rotational speed of the rotor And the efficiency of an ultrasonic motor may fall. For this reason, it is necessary to drive the ultrasonic motor in a frequency band higher than the audible sound generation band.
[0003]
By the way, the audible sound generation band and the drive frequency band of the ultrasonic motor vary depending on the individual ultrasonic motor, the ambient temperature of the ultrasonic motor, and the load applied to the ultrasonic motor. Therefore, the appropriate frequency of the drive signal is not constant and needs to be changed according to the individual motor, ambient temperature, load, and the like.
[0004]
As an example of audible sound detection means, Japanese Patent Application Laid-Open No. 3-159583 monitors the disturbance of the waveform of the detection signal output from the piezoelectric element, and reduces the drive frequency when the waveform is not disturbed. A technique is disclosed in which when the waveform is disturbed, the frequency of the drive signal is determined to have entered the audible sound generation band and the frequency is increased.
[0005]
[Problems to be solved by the invention]
However, the technical means disclosed in Japanese Patent Laid-Open No. 3-159583 requires that a monitor electrode for waveform detection be disposed on the piezoelectric element of the ultrasonic motor, which is troublesome in production and increases costs.
[0006]
Further, since the amplitude of the voltage waveform detected from the monitor electrode varies greatly depending on the frequency of the drive signal, it is difficult to detect the waveform disturbance because the circuit becomes complicated.
[0007]
Further, in the case of an ultrasonic motor that does not generate audible sound, the detected waveform from the monitor electrode is not disturbed, so that the drive frequency may be reduced beyond the resonance frequency, and the rotational speed of the rotor may be rapidly reduced. Moreover, there is a risk of destruction of the components of the ultrasonic motor and the ultrasonic motor drive circuit due to overcurrent.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, in the ultrasonic motor driving circuit according to the present invention, a current waveform detecting means, a waveform shaping means for converting the detected current waveform into a digital signal, and an output of the waveform shaping means are used. By providing the frequency control means for controlling the drive frequency, by detecting the generation of audible sound from the disturbance of the current waveform, the arrangement of the monitor electrode becomes unnecessary, and the change in the amplitude due to the frequency of the drive signal can be ignored.
[0009]
In an ultrasonic motor that does not generate audible sound, the current waveform is not disturbed, but the amount of current increases as it approaches the resonance point. Therefore, by setting a predetermined threshold in the waveform shaping circuit, waveform shaping is performed. By detecting the cycle of the output of the circuit, overcurrent can be detected without using a special element.
[0010]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0011]
FIG. 1 is a circuit diagram of an ultrasonic motor driving circuit showing an embodiment of the present invention. In the figure, reference numeral 1 denotes a microcomputer, which determines the drive frequency of the ultrasonic motor 8 according to the output of the waveform shaping unit 5, and sets the frequency of the output of the oscillation unit 3 by the frequency setting unit 2. The signal output from the oscillation unit 3 by the pulse control unit 4 generates a control signal φ1~φ4 for switching the switching transistor Q1 to Q4.
[0012]
This ultrasonic motor drive circuit applies a two-phase AC signal of A phase and B phase having a phase difference of 90 degrees to a known ultrasonic motor 8 having two electrodes 8a and 8b.
[0013]
φ1 and φ2, φ3 and φ4 each have a phase difference of 180 degrees, φ1 and φ3, φ2 and φ4 are pulse signals each having a phase difference of 90 degrees, and φ1 to φ4 are switching transistors Q1 to Q4 that perform a switching operation. Each corresponds. A positive voltage of the DC power source 7 is supplied to the intermediate tap on the primary side of the transformers T1 and T2, and the primary side of the transformer T1 is turned on by the switching operation of the switching transistors Q1 and Q2, and accordingly, the A-phase AC is supplied to the secondary side. Output a signal. Similarly, the primary side of the transformer T2 is turned on by the switching operation of the switching transistors Q3 and Q4, and accordingly, a B-phase AC signal is output to the secondary side. The resistor Rs is connected in series with the DC power source 7 and the primary side of the transformers T1 and T2, and a current waveform is detected by obtaining a potential difference between both ends of the resistor Rs. Since the potential difference between both ends of the resistor Rs is very small, it is amplified by the differential amplifier circuit in the current waveform detector 6. The output signal from the differential amplifier circuit and the waveform shaping unit 5 for converting a predetermined digital signal, controlling the driving frequency by the microcomputer 1 when the cycle of the digital output signal of the waveform shaping section 5 becomes a specific period It is the composition to do.
[0014]
FIG. 2 is a timing chart of the pulse control unit, and φ1 to φ4 are control signals for switching the switching transistors Q1 to Q4.
[0015]
FIG. 3 shows output waveforms of the current waveform detection unit 6 and the waveform shaping unit 5 during normal rotation. The output of the current waveform detector 6 is a current waveform detected by the detection resistor Rs. This waveform is a current waveform when the switching transistors Q1 to Q4 turn on / off the DC power source 1 applied to the primary side windings of the transformers T1 and T2. The output of the waveform shaping unit 5 is a waveform obtained by shaping the detection waveform of the current waveform detection unit 6 into a digital signal. Since this waveform is the cycle of the switching waveform of the switching transistors Q1 to Q4, the cycle is four times the drive frequency.
[0016]
FIG. 4 shows output waveforms of the current waveform detection unit 6 and the waveform shaping unit 5 when an audible sound is generated. The output of the current waveform detector 6 is a current waveform detected by the detection resistor Rs. The output of the waveform shaping unit 5 is a waveform obtained by shaping the detection waveform of the current waveform detection unit 6 into a digital signal. When this waveform deviates significantly from a period four times the drive frequency, the microcomputer 1 determines that the current waveform is disturbed.
[0017]
Next, the operation of one embodiment will be described.
[0018]
The waveform output from the differential amplifier circuit in the current waveform detector 6 is a switching waveform of Q1 to Q4 shown in FIG. 2, that is, a frequency four times the drive frequency. The detected waveform is shaped into a digital signal by the waveform shaping unit 5 having hysteresis characteristics, and the period is obtained from the shaped digital signal. When the detection result has a period greatly changed from four times the driving frequency, it is determined that the waveform is disturbed, and it is determined that an audible sound is generated, and the driving frequency is increased and corrected. Also, when the current amount exceeds a predetermined amount, the cycle changes depending on the output of the waveform shaping unit 5 due to the increase in the current amount, so that it is determined as an overcurrent and the drive frequency is increased and corrected.
[0019]
【The invention's effect】
As described above, according to the present invention, the generation of audible sound can be detected even with an ultrasonic motor that does not include a monitor electrode. In addition, even an ultrasonic motor that does not generate an audible sound can simultaneously detect an overcurrent, thereby preventing damage to the motor and circuit components due to the overcurrent.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an ultrasonic motor driving circuit to which the present invention is applied.
FIG. 2 is a timing chart of a pulse control unit.
FIG. 3 is an output waveform diagram showing outputs of a current waveform detection unit and a waveform shaping unit in a normal state.
FIG. 4 is an output waveform diagram showing outputs of a current waveform detection unit and a waveform shaping unit when an audible sound is generated.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Microcomputer 2 Frequency setting part 3 Transmission part 4 Pulse control part 5 Waveform shaping part 6 Current waveform detection part 7 DC power supply 8 Ultrasonic motor

Claims (1)

Detecting means for detecting a power supply current supplied to the ultrasonic motor ;
Waveform shaping means having a predetermined hysteresis characteristic and converting the current waveform detected by the detection means into a digital waveform ;
Drive frequency control means for determining the drive frequency of the ultrasonic motor;
Have
The driving frequency control unit, when the digital waveform 2n times the driving frequency (n is a positive integer) are out of the consisting cycle, increasing the driving frequency is determined that generation of audible sound or overcurrent ultrasonic motor drive circuit, wherein the you modify.

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