Transducer for high speed and large thrust ultrasonic linear motor using two sandwich-type vibrators

A transducer for an ultrasonic motor using two sandwich-type vibrators has been proposed and designed. The vibrators cross at right angles with each other at the tip. The transducer has two vibration modes; one is a symmetrical mode and the other is anti-symmetric. The normal direction motion of the transducer tip is excited by the symmetrical mode. The lateral motion of the tip is excited by the anti-symmetrical mode. The transducer is designed so that these vibration modes are degenerated. To obtain high output force and high power, materials were carefully selected. Heat-treated high strength chromium manganese steel bolts were used for binding the PZT elements. A zirconia ceramics plate was bonded on the transducer tip as frictional material. The no-load maximum speed was 3.5 m/sec. The output force was 39 N at the driving voltage of 500 V(rms) and the preload of 150 N. At this condition the maximum efficiency was 28%, and the velocity was 0.55 m/sec. The maximum output force was 51 N, which was 17 times of the transducer weight. The maximum output power per unit weight was 76 W/kg.