Development of pipe inspection robot; driving system and control of outer-rotor-typed spherical ultrasonic motor

In this paper we present a driving system and control method of newly developed spherical ultrasonic motor (SUSM) as a camera actuator for pipe inspection robot. The pipe inspection robot using SUSM that is very small actuator with three rotational degrees of freedom (DOF) can be inserted to the inside of pipe of 50 mm in diameter. The novel SUSM has improved the range of movement compared to previous SUSM and the robot can point a camera in any direction. The compact motor driving circuit which can be inserted in pipe was also developed. We determined a method of rotational direction and control strategy from the kinematics and characteristics of ultrasonic motor. The rotational directions were defined by the phase differences of applied voltages, and the rotational speed were changed by the frequencies from the driving circuit. In the control experiment using a small position sensing system using rotary potentiometers, the driving system composed of SUSM, driving circuit, and the sensing system have shown the returnability to the default position within 1 degree of accuracy from several specified points.