Patent ID: 7569953

Claim:
A rotor for a hybrid type stepping motor comprising: a plurality of stack assemblies each including a pair of rotor stacks, the rotor stack having a plurality of small teeth arranged in a circumferential direction at an outer peripheral portion thereof, and a permanent magnet held between the pair of rotor stacks and magnetized so that polarity of magnetic poles appearing at the plurality of small teeth of one of the rotor stacks composing the pair of rotor stacks may be different from polarity of magnetic poles appearing at the plurality of small teeth of the other rotor stack composing the pair of rotor stacks, the plurality of stack assemblies being mounted on a rotating shaft so as to be arranged along the rotating shaft in an axial direction thereof, and one or more rotor collars made of a nonmagnetic metal material, the rotor collar being arranged between two adjacent stack assemblies among the plurality of stack assemblies so as to form a gap between the two adjacent stack assemblies, wherein two of the rotor stacks, opposing to each other in the axial direction with the rotor collar therebetween, respectively have a depressed portion for being fitted with the rotor collar, the depressed portion being formed so as to surround the rotating shaft and open toward the opposing rotor stack; wherein the rotor collars each include a central portion extending in a radial direction of the rotating shaft, and a pair of fifing portions for fitting into the depressed portions of adjacent rotor stacks disposed at both sides of the central portion in the axial direction; wherein a shape of the depressed portion of the rotor stack and a shape of the fitting portion are both defined so that no relative displacement in the radial direction of the rotating shaft may occur between the rotor stack and the rotor collar with the fitting portion fitted into the depressed portions of the adjacent rotor stacks; wherein a non-fitted depressed portion having the same shape as that of the depressed portion for being fitted with the rotor collar is formed in two rotor stacks among the rotor stacks, disposed respectively at either axial end of the rotating shaft; and wherein a cross-sectional outline of the depressed portion, as taken in a direction perpendicular to the rotating shaft, is a concentric circle with the rotating shaft; a cross-sectional outline of each of the fitting portions composing the pair of the paired fitting portions, as taken in a direction perpendicular to the rotating shaft, is a circle having almost the same diameter dimension as that of the depressed portion; and the fitting portions are respectively formed with an annular depressed portion, the annular depressed portions of the fitting portions being open in opposite directions to each other on the axial line of the rotating shaft and disposed concentrically with the rotating shaft.