Patent ID: 7317273

Claim:
An electromagnetic actuator comprising: a cylindrical stator permanent magnet having annular end faces magnetized to a plurality of magnetic poles; a coil securely disposed inside a hollow interior of said stator; a rotary shaft put through said coil in a direction of a center axis thereof in such a way as to be rotatably supported; and a rotor of a soft magnetic material having a plurality of rotor arms facing said annular end faces of said stator and provided in such a way as to rotate together with said rotary shaft, wherein said rotor arms include at least two main rotor arms and at least one rotational-direction determining rotor arm which extend in a direction of said annular end faces of said stator from both end portions of said rotary shaft and face said annular end faces, said at least one rotational-direction determining rotor arm is less in quantity than said main rotor arms rotor, those rotor arms which are disposed at one of said annular end faces are arranged in phase with magnetic poles of the facing annular end face, those rotor arms which are disposed at the other annular end face are arranged in an opposite phase to said phase with respect to magnetic poles of the facing annular end face, and said rotational-direction determining rotor arm is so arranged as to be shifted by a given angle with respect to said magnetic poles of the facing annular end face.