Study on Large Capacity Ultrasonic Motor Using Principle of Strain Wave Gearing

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In this study, aiming at development of compact, light-weight large power electrical actuators, two types of ultrasonic motors, whose operational principle differed from that of the conventional ultrasonic motors, were developed, one using multi-layr type piezoelectric devices and the other using a ring type piezoelectric device. In the proposed motors, the traveling waves were generated by the principle of the strain wave gearing and the bending wave and the rotors were driven mechanically by the friction force.The results of this study are as follows ; (1) A resonant type piezoelectric motor (ultrasonic motor) was designed and made on a trial basis using a ring type piezoelectric device with high stiffness and large output power. Moreover, the multi-layr type piezoelectric motor developed earlier was also improved for higher mechanical stiffness and better characteristics, and basic data for clarifying the problems of the motor were obtained. (2) The main circuits and its control cir … More cuits of the FET inverters with rectangular current waveforms and filtered rectangular voltage waveforms were improved for better waveform and control flexibility. (3) The measurement equipment of the motor torque versus rotational speed was improved making allowance for possible increase of the rotational speed by improvement of the motor. (4) In regard to the motor using the ring type piezoelectric device, two types of motors were made on a trial basis and compared. One was a motor using the device not divided and the other was that using the device equally divided into 6 parts. As a result, the characteristics of the motor torque versus rotational speed were not so influenced by the division of the device but by the mechanical properties of the motor stator. (5) It was clarified that the characteristics of the motor was influenced by condition of contact between the ring type piezoelectric device and the electric terminals. Especially, in the case of the divided ring type device, the characteristics were considerably influenced by the thickness of the contact layrs and, therefore, it is necessary to make the contact layr as thin as possible. (6) It was found that the higher applied voltage resulted in the considerable increase of device temperature due to the power loss in the device in the case of using the ring type device. It is necessary to reform the structure of the motor stator so as to increase the tangential speed on the surface of the stator by using the large stress of the device without the large displacement of the device. (7) In regard to the motor using the multi-layr type piezoelectric device, a new type structure which was symmetrical with respect to the motor base was employed in a trial basis in order to increase the mechanical stiffness of the motor and transmit the displacement of the device to the motor stator effectively. Less