Resin-filled permanent-magnet stepping motor

Claim 1

A stepping motor comprising: two stator units, which comprise a pair of stator yokes, each of said stator yokes having a number of magnetic pole teeth which protrude parallel to an axial direction, and form an annular space between one of said stator yokes and the magnetic pole teeth engaged with each other, and an annular coil comprising a bobbin with magnet wire wrapped therearound disposed in said annular space, said bobbin comprising an annular core having flanges on opposite sides thereof, said two stator units being disposed in a back-to-back relation; a rotor consisting of a cylindrical magnet and a rotor shaft inserted in said cylindrical magnet, both ends thereof being extended from both ends of the magnet; a plurality of pins mounted radially in said flanges and connected to at least one magnet wire; a resin structure filled in the annular spaces and connecting integrally the stator yoke, the annular coil and the pins; an end plate formed on a first side of the stator and molded integrally with the stator; a plurality of resinous protrusions formed integrally with the resin structure on a second side of the stator yoke; a flange plate provided with retaining holes, said protrusions passing through said retaining holes and being deformed to hold said flange plate on said second side of the stator yoke; and two bearings mounted co-axially, one on the end plate and the other on the flange plate, said bearings rotatably supporting the rotor shaft.