Dynamic model and control of six-phase spiral motor

Various industrial applications utilize linear actuators which are usually performed by rotational type motors in combination with ball screw, by hydraulic actuators, and by linear motors. The ball screw has small friction, which has bad influence on positioning accuracy. The hydraulic actuators have maintenance problem. Also the equipment of the linear motors becomes complicated it makes a lot of magnetic flux of leak. In this paper, we propose a new spiral type motor which overcome the conventional defects of these linear actuators. By using spirally shaped rotor and stator, it can transform the rotational motion to forth-and-back movement according to the screw mechanism. The friction free screw mechanism is realized by magnetic levitation of the rotor. The basic model of six-phase spiral motor is introduced. The model was analyzed by using a equivalent magnetic circuit. All interlinkage magnetic flux is given from a equivalent magnetic circuit. The thrust and torque equation is also given and the numerical examples are shown. When the spiral motor is driven, it is required to keep the displacement of gap x_g being zero in order to avoid touchdown. We applied a two-degree-of-freedom control to the gap control. The simulation results of the gap control are shown.