Direct Drive and Vibration Analysis of Ultrasonic Motor for Robot Hand

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Ultrasonic motors (USMs) have many excellent features compared to the electric-magnetic motors, such as simple structure without coils, a quick response, and high torque at low speed, etc. These advantages of USM are, therefore, very hopeful for robot manipulators to be downsized and light weighted.This research proposes a technique for a cylinder-shaped ultrasonic motor (USM) to be driven by a single-phase electric source. The state of vibration was examined from both the theoretical and the experimental aspects. The following conclusions are summarized from the experiments and the discussions.(1)The proposed arrangement of the electrodes enables the cylinder-shaped USM to be driven by a single-phase electric power source. An ingenious arrangement of the inside and outside electrodes produces the extensional vibration that includes not only the standing wave but also the traveling wave.(2)The extensional vibration of the USM under single-phase drive is composed of the standing and the traveling waves, that have two wavelengths on the circumference. Vibrating surface consists in the combination of standing wave and traveling wave.(3)The rotor in contact with the stator at two crests of the wave rotates resulting from the cooperation of both wave types. This moving mechanism can be explained by the separation of the degeneration mode by a perturbation.(4)The vibration of the USM under single-phase drive can be explained consistently by superimposing two vibration modes with azimuthal lag of π/4 and with the phase lag of π/8,which are produced by the electrodes on both inner and outer sides of the cylinder.(5)The torque characteristic by single-phase drive is similar to one by the conventional driving method.The possibility of single-phase drive would promise the robot manipulators that employ the USM to be downsized and light weighted in near future.