| 摘要 |
PURPOSE:To reduce the change of thrust due to the shift position of a driving coil, by providing the inner circumferential end face section of a ring-shaped pole piece, with a slanted section, and by arranging ring-shaped magnetic short- circuit members having acute angles at the tip sections, to confront a center pole via space. CONSTITUTION:Ring-shaped permanent magnets 12 are fitted on the inner peripheral face of an outer yoke 10 provided with a center pole 11 on the center of the bottom section vertically, and the inner peripheral face of the permanent magnets 12 is provided with a ring-shaped pole piece 20 to organize a magnetic circuit 1. The inner circumferential end face section of the ring-shaped pole piece 20 is provided with a slanted section 22 for reducing the height of the pole piece from the side in contact with the permanent magnets 12 to the face side confronting a space. Ring-shaped magnetic short-circuit members 30 having acute angles at the tip sections are arranged to confront the center pole 11 via space. So far as a cylindrical driving coil 2 shifting linearly in the cylindrical space 3 is concerned, the length in the axial direction is larger than the length of the magnetic pole section 14 in the same direction. |
