| 摘要 |
This invention is directed to a field piece to reduce harmonic components of magnetic flux density. A permanent magnet (20) is in contacts with a first magnetic plate (1, 3) in a direction in parallel with a rotation axis (P). The first magnetic plate (1) is provided with first and second magnetic members (10, 12) and first and second non-magnetic members (11, 13). The first magnetic member (10) includes the pole center and is in contact with one permanent magnet in the rotation axis direction. The first magnet member (10), the first non-magnetic members (11), the second magnetic member (12) and the second non-magnetic member (13) are disposed in this order in a circumferential direction starting from the pole center as a start point and centering the rotation axis. If a pole logarithm (Pn) and a not less than three odd number (i) are given, an angle (?1) defined by an edge (131) of the second non-magnetic member (13) on the pole center side with respect to a pole gap is 0<?1<180/(i Pn). Similarly, an angle (?2) defined by an edge (111) of the second non-magnetic member (11) on the pole center side with respect to a pole gap is 180/(i Pn)=?2=180 2/(i Pn). |
