This paper discusses a new control method for an ultrasonic motor (USM). An USM has the capability of generating a resistant torque against an external one even under power-off which is well known as self-locking characteristic and conveniently utilized to save energy while maintaining rotor position. The goal of the paper is to relax the self-locking characteristic and to widely change it between lock and free states. In order to achieve this, we newly propose the two d.o.f. PWM control, in which OFF command is included in addition to CW and CCW commands. By applying this, we can also control the torque of USM in open loop without using any complicated circuit. In this paper, we first demonstrate the basic structure of the two d.o.f PWM control, and then show several experimental results to verify the effectiveness of the scheme proposed.

Three-axis force sensors based on the principle of the pressure pick-up device are characterized by their manufacturability, simple structure, and miniature size. Their use, however, has not been explored due to the insufficient force information they provide. To make the most of the three-axis force sensor, the authors have proposed a new six-axis force sensors composed of two three-axis force sensors and a connector [twin-head (TH) six-axis force sensor] and examined the possibility of realization for sensors using two identical three-axis force sensors. This paper discusses TH force sensors constructed from two different types of three-axis sensors. While fifteen types of combinations are theoretically conceivable, it is proved that nine types can result in a characteristic matrix with full rank.