Patent ID: 7436094

Claim:
A rotary actuator comprising: a stator having plural permanent magnets; a rotor having a rotor core which two salient poles are formed at, and one or more rotor coils are wound around; an electro-magnetic torque generating portion comprising the stator and the rotor between which electro-magnetic torque is generated by supplying an electric current to the rotor coils, which, in approximate proportion to the magnitude of the electric current, displaces a relative angle position of the rotor and the stator; and an elastic member biased in approximate proportion to the magnitude of the relative angle displacement of the rotor and the stator and thereby generating a torque in the direction opposite to the direction of the electro-magnetic torque, wherein the permanent magnet having two circumferential end portions and one circumferential center portion, and the radial thickness of the permanent magnet at the circumferential end portions being smaller than the radial thickness of the permanent magnet at the circumferential center portion, wherein the distance from the radial outline of the circumferential center portion of the salient pole to the rotation center of the rotor core being smaller than the distance from the radial outline of the circumferential end portions of the salient pole to the rotation center of the rotor core, and wherein the angle between the line connecting one of circumferential outlines of a salient pole and the rotation center of the rotor core and the line connecting the other circumferential outline of the same salient pole and the rotation center of the rotor core being an obtuse angle.