| 摘要 |
PROBLEM TO BE SOLVED: To form a low-cost and precise magnet pole and to detect a speed of rotation with high accuracy, by a method wherein the size in the axial direction of a metal ring which is composed of a cylindrical part and a funnel-shaped flange part is set at a size which is slightly longer than the size in the axial direction of a molding mold, the metal ring and an elastic magnet material are charged into the molding mold, and an encoder is formed. SOLUTION: When this cylindrical encoder is formed, a metal ring 3 is charged into a molding mold 4 which has a size (h') in the axial direction which is slightly shorter than the size in the axial direction of the metal ring 3. The metal ring 3 is mold-tightened and compressed by an upper mold 4a and a lower mold 4b which come into contact with both end faces of the metal ring 3. By a spring action due to the funnel shape of a flange part 3b connected from a cylindrical part 3a, both end faces are brought strongly into close contact with the upper mold 4a and the lower mold 4b. After that, an elastic magnet material is filled to the outer circumference of the metal ring 3 inside the molding mold 4. The metal ring 3 and an elastic magnet 2 are molded integrally. Since the metal ring 3 is brought into close contact with the molding mold 4, the elastic magnet material does not creep to the inner circumferential side of the metal ring 3, and the cylindrical encoder can be shaped precisely.
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