Development of New Types of Small-sized Light-weight Large-power Motors Composed of Strain Wave Gearing and Multi-layer Piezoelectric Devices

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In this study, three types (synchronous type, friction type, and resonant type) of low speed high torque piezo-electric motors composed of strain wave gearing and multi-layer piezoelectric devices were developed aiming at small-sized light-weight large-power actuators (motors) for servo drive. First, basic structure of the propoed motors and mechanism to enlarge displacement of the piezoelecitric devices were studied. Next, a driving circuit for the proposed motors was made taking characteristics of the piezoelectric devices, and characteristics of prototype piezo-electric motors were investigated experimentally, Finally the characteristics of the motors were discussed theoretically based on the experimental results. Moreover, prototype motors with plastics rotor and one with ceramics rotor were also examined and thier characteristics were compared with that of the motor with iron rotor.The results of this study are as follows ;(1) The synchronous type piezoelectric motor has thin teet … More h on its strain wave gearing and the rotational speed is precisely proportional to the driving frequency independently of the applied load torque if the torque is not so large. However, the maximum torque is much smaller than that expected from the characteristics of the piezoelectric devices.(2) Although the friction type piezoelectric motor has no teeth on its strain wave gearing, the rotational speed of the motor is approximately proportional to the driving frequency in the case that the axial force applied to the rotor is constant and the applied load torque is null. The speed decreases according as the load torque increases. The stall torque, at which the speed come to stop, is considerably large in the case that the axial force of the rotor is large. Consequently this type motor is confirmed to has the property of low speed and torque.(3) The resonant type piezoelectric motor has similar characteristics of the rotational speed versus the load torque to that of the friction type motor. This type of motor is expected to have high efficiency because it can operate at lower supply voltage than the friction type motor.(4) The piezoelectric motor are confirmed to operate in the case that their rotors are made of plastics or ceramics. This fact gives possibility to realize the light-weight motor. Less