On direct-drive motion of a spiral motor

Spiral motor, a novel high-thrust linear actuator with high backdrivability, consists of a helical structure stator and mover. Under proper gap control against the load fluctuation, the mover moves helically in the stator and the linear motion is extracted to drive the load. Thus, the motor realizes direct-drive motion without mechanical gears. In this paper, an exact feedback linearization engaged with disturbance observer (DOB) is used to achieve full direct-drive motion of a spiral motor. Through the use of high gain feedback time scale separation is artificially introduced and the overall closed-loop system is transformed into a singular perturbation one. Then, using tools from singular perturbation theory, the proposed method ensures arbitrary disturbance attenuation, small tracking error, and boundness of all closed loop signals. Simulation and experimental results are given to verify the theoretical one.