| 摘要 |
PURPOSE:To improve magnetic pole density by preparing n pieces of magnetic rings of substantially the same size which are magnetized in such a way that a magnetic material can form m pieces of magnetic poles equidistantly at a spacing t along the circumferential direction thereof and stacking the magnetic rings concentrically to one body in such a way that the magnetic pole positions deviate by a spacing t/n. CONSTITUTION:When the width of a magnetic material 13 is designated as 2d, said material is divided to two upper and lower stages 13A and 13B, and the magnetic material is magnetized in such a way that the magnetic material parts 13A, 13B in each stage have m pieces of magnetic poles 14A and 14B equidistantly at a spacing t along the circumferential direction and that the positions of the magnetic poles in each stage deviate from each other at a spacing t/2. If gap 21 are provided and the length thereof is made larger than the entire width 2d of a magnetic ring 13 and the magnetic poles 14A, 14B of the parts 13A, 13B are read successively, m+m=2m pieces of magnetic poles are read in one circumference. Therefore, even if the number of the magnetic poles encoded per round of the respective parts 13A, 13B is m pieces, the number of the magnetic poles read per round of a magnetic drum 10 is 2m pieces and the apparent magnetic pole density is doubled. The rotation is controlled with correspondingly high accuracy. |
