New type of piezoelectric ultrasonic motor

The authors describe a newly developed motor concept which allows a bidirectional piezoelectric ultrasonic motor to be operated with only a single voltage feed and thus only one power amplifier. The motor concept is based on the superposition of a longitudinal and a flexural oscillation of a rod-shaped resonator. In a way analogous to the generation of a Lissajous figure, this superposition produces a rotary movement of the resonator end by means of which a rotor is directly driven. By selecting the relative phase of the electrical stimulations of both modes, the speed can be continuously varied in both directions. The motor can be driven in both right and left directions with speeds of 0 to 300 r/min, and a freewheeling state can be set up by means of a suitable phase between the oscillation modes. In the off state, the motor blocks the motion.