Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-11-30
2001-10-23
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S321000, C310S323020
Reexamination Certificate
active
06307299
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of correcting a resonance frequency of a small rotary actuator which is used as a power means for clocks, cameras, tools, automatic assembling devices, accurate X-Y stages or the like.
Conventionally, in the case of manufacturing a small rotary actuator having a plurality of oscillators, in order to reduce a variation in a resonance frequency of the respective oscillators, there has been applied a method in which an accuracy in machining of the oscillators is improved and in which a piezoelectric element is improved through a higher accuracy process technology, or a manner in which only an excellent performing rotary actuator is selected from a plurality of rotary actuators. However, there is a limit to improving a machining accuracy, and also there arises a problem in that a yield is lowered to deteriorate productivity in the manner where only the most accurate rotary actuator is selected.
In the case where the oscillator is driven by using a piezoelectric element such as a PZT, the efficiency is the highest when the oscillator is driven with an a.c. voltage a frequency of which is identical with its resonance frequency. When the oscillator is driven with an a.c. voltage a frequency of which is different from the resonance frequency of the oscillator, a very large voltage must be applied to the oscillator, thus providing a low efficiency. When the frequency of the a.c. voltage is largely different from the resonance frequency of the oscillator, it is impossible to drive the oscillator.
In a rotary actuator of the type in which a rotary torque is produced due to continuous impact caused by the vibrations of the oscillator to drive a rotor, a large rotary torque can be obtained by providing and driving a plurality of oscillators at the same time. However, in the prior art, it is difficult to obtain an oscillator having an accurate desired resonance frequency when a small rotary actuator having a plurality of vibrators is fabricated, because the resonance frequencies are largely varied among the respective oscillators. As a result, when the oscillators are intended to be driven with an a.c. voltage a frequency of which is suitable for one oscillator, other oscillators different in resonance frequency cannot be driven, and thus the efficiency of rotation cannot be improved.
In order to reduce a variation in resonance frequency of the oscillators by improving the machining accuracy of the oscillators and the piezoelectric element, the manufactured devices and the manufacturing processes need to be improved, and the costs cannot be prevented from largely increasing. As a result, it is difficult to manufacture a highly efficient actuator.
SUMMARY OF THE INVENTION
The present invention has been made in order to solve the above problems, and therefore an object of the present invention is to provide a method of correcting a resonance frequency of a small rotary actuator which efficiently generates a large torque.
In order to achieve the above object, according to the present invention, there is provided a method of correcting a resonance frequency of a small rotary actuator in which the frequency is corrected by cutting a piezoelectric element using a laser beam, an ion beam or plasma to reduce a variation in the resonance frequencies of a plurality of oscillators.
Also, according to the present invention, the resonance frequency is corrected while measuring the resonance frequency of the oscillators by conducting electric measurement through an impedance analyzer of measurement through a laser Doppler vibrometer.
REFERENCES:
patent: 3716828 (1973-02-01), Massa
patent: 4004166 (1977-01-01), Nakata
patent: 4379244 (1983-04-01), Dinger
patent: 4385473 (1983-05-01), Aoki
patent: 4455500 (1984-06-01), Savit et al.
patent: 4505014 (1985-03-01), McNeel et al.
patent: 5414320 (1995-05-01), Mashio
patent: 5850117 (1998-12-01), Tobe et al.
patent: 5986385 (1999-11-01), Atsuta
patent: 60-123106 (1985-07-01), None
patent: 03-285575 (1991-12-01), None
Suzuki Mizuaki
Tani Kazuo
Adams & Wilks
Budd Mark O.
Seiko Instruments Inc.
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