Patent ID: 8421293

Claim:
A manufacturing method of a rare earth-iron based annular magnet, comprising the steps of: arranging a predetermined number of U-shaped segments at a molded cavity, the U-shaped segments being as an aggregated body of fragments in magnetic fields Hex in which to retain an inner-and-outer peripheral section providing variation of H θ corresponding to a mechanical radian φ when H θ is an angle defined by a uniform direction of external magnetic fields Hex and a tangent line in inner and outer peripheral directions that corresponds to optional mechanical radians φ of an annular magnet; making the segments fragmented and transporting the fragments to an annular cavity that opens in an inverse direction relative to the segments, the fragments being transported along with rotation satisfying H θ≈Mθ when H θ is set to the angle defined relative to the tangent line in the inner and outer peripheral direction that corresponds to the optional mechanical radians φ of the annular magnet, and when a direction of anisotropy is set to M θ; recompressing the fragments at the annular cavity so as to recombine each of the fragments; and making anisotropic direction M θ to be continuously varied relative to the mechanical radian φ of magnetic poles.