Compact high-Tc superconducting actuator system design

This paper describes the system design of centimeter-sized YBCO superconducting linear and rotary actuators and their appropriate bearings that have been developed since 1989. An MPMG-YBCO superconductor tile of the linear actuator driven by two solenoids is guided and levitated over two magnetic bearings. Its position, measured by a laser sensor, is satisfactorily well controlled by linear feedback with biased currents applied to the solenoids. A disk-shaped rotor of the same superconductor for the rotary actuator with two poles magnetized by field cooling was stably driven by four solenoids arranged evenly around the rotor up to about 400rpm, levitating over a disk-shaped permanent magnet. The rotation angle is detected by the laser sensor and a lab made absolute encoder. The control system of both types of actuator were designed by computer simulations with a simple repulsion force model, developed by the author. Damped oscillations can occur dependent on feedback gains for the rotary actuator, but this drawback will be improved by generating uniform torque based on current control depending on the position of the actuator. The hysteretic torque dependent on the angle for this actuator should be reduced in future work.