Encoder made of rubber material and method of manufacturing thereof

1. Field of the Invention An encoder made of rubber material in which the S-poles and the N-poles are alternately magnetized in circumference, whose magnetic force is strong and whose variation of the magnetic force is slight in the circumferential direction when it is magnetized. And a manufacturing method thereof. A ring shaped rubber compound made of unvulcanized rubber material into which magnetic powders are mixed and having thickness tof 1.5 times to 5 times thicker than the thickness t of the encoder made of rubber material as the final product is vulcanizingly molded. In this vulcanizingly molding process, the thickness of ring shaped rubber compound is reduced to one fifth ( ) to two thirds ( ) by compressing the ring shaped rubber compound in the axial direction under high temperature. And then, vulcanizingly molded one is magnetized S-poles and N-poles alternately in circumference.