Patent ID: 6860655

Claim:
A driving apparatus comprising: a rotatable rotor with a ring shape, said rotor having magnet portions which are divided along a circumferential direction and differently magnetized; a first magnetic pole portion, said first magnetic pole portion being formed extending in a direction perpendicular to a rotational axis of said rotor, and facing a face of said magnet portion perpendicular to the rotational axis; a second magnetic pole portion, said second magnetic pole portion sandwiching said magnet portion between said second magnetic pole portion and said first magnetic pole portion, and facing another face of said magnet portion perpendicular to the rotational axis; and a coil for magnetically exciting said first magnetic pole portion and said second magnetic pole portion, said coil being disposed radially of said rotor; wherein a condition of −0.333X+0.9<Y is satisfied where Y is a ratio of a central angle of each first magnetic pole portion relative to a central angle of each magnetized pole in said magnet portion, and X is a ratio of an outer circumferential length of each magnetized pole in said magnet portion relative to a thickness of said magnet portion in a direction of the rotational axis; and wherein a rotational position of said rotor can be selectively changed to one of three positions by selecting one of a state in which no current is supplied to said coil, a state in which current in a predetermined direction is supplied to said coil, and a state in which current in a direction opposite to the predetermined direction is supplied to said coil.