Control analysis of ultrasonic motor-equivalent circuit and mechanical internal resistance

The simple structure of ultrasonic motors enables them to be dramatically miniaturized, leading to the expectation that they can form the component of micromechanisms and the joint of miniature robots in spite Of unstable control and insufficient durability. In this study, however constant current phase control has successfully realized constant amplitude of the stator tip while maintaining a state of resonance. This report first presents a prototype constant current control circuit and the observation data on the relation between the motor current and the vibration of the stator tip. Secondly, the essential significance of the motor´s static characteristics is evaluated under the constant current mode. The study found velocity reduction proportional to the load torque under constant current drive, which depends on frictional properties such as material and surface treatment. This paper proposes a new friction model based on these findings.