Patent ID: 7635931

Claim:
A stepping motor comprising: two stators configured identically with each other and put together back to back, each comprising an outer yoke having a cylindrical outer frame and a plurality of pole teeth, an inner yoke having a plurality of pole teeth intermeshing with the plurality of pole teeth of the outer yoke on a same circumferential plane, and a bobbin having a coil therearound and housed in an annular hollow space formed by the outer yoke and the inner yoke; and a rotor comprising a shaft, and two magnets configured identically with each other and disposed on the shaft axially separate from each other, and rotatably disposed inside the two stators such that outer circumferences of the two magnets oppose the pole teeth of the two stators with a small air gap therebetween, wherein a first dimensional relation of Lm/Ls ranges between 0.35 inclusive and 0.45 inclusive, a second dimensional relation of d/2Lm ranges between 0.77 inclusive and 1.10 inclusive, and a third dimensional relation of d/D ranges below 0.45 inclusive, where Lm is an axial dimension of each magnet, Ls is an axial dimension of each stator, d is an outer diameter of the magnet, and D is an outer diameter of the stator.