Patent ID: 6719463
Filing Date: 2004-04-13
Classification: G03B,H02K

Abstract:
A drive apparatus comprising:a rotor that has a magnet portion having a cylindrical shape whose outer peripheral surface is circumferentially divided into sections that are magnetized to have different poles, and is capable of rotating about an axis; at least one outer magnetic pole portion that is formed so as to protrude and extend parallel to the axis and opposes the outer peripheral surface of the magnet portion; an inner magnetic pole portion disposed at a position opposing the outer magnetic pole portion so as to oppose an inner peripheral surface of the magnet portion; and a coil that is disposed in an axis direction of the rotor and excites the outer magnetic pole portion and the inner magnetic pole portion, wherein the rotor is maintained at two stoppage positions, and when a value of a ratio of a central angle of the outer magnetic pole portion to a central angle of each magnetized pole of the magnet portion is referred to as Y, and a value of a ratio of a thickness of the magnet portion in a diameter direction to a circumferential length of each magnetized pole of the magnet portion is referred to as X, the following condition is satisfied: âˆ’0.3X+0.63>Y.