Permanent magnet type stepping motor

Claim 1

A permanent magnet type stepping motor having a rotor that defines an axis and comprises a substantially disc-like permanent magnet coaxially sandwiched between a pair of pole pieces each of which as cicumferentially spaced rotor pole teeth around its periphery, and a stator having a core that comprises a cylindrical yoke and magnetic poles projecting radially inwardly from said yoke, each having circumferentially spaced stator pole teeth at its radially inner tip that radially oppose said rotor pole teeth across a gap, and a winding around each of said magnetic poles, said stepping motor being characterized by: A. said magnetic poles having a thickness, measured parallel to said axis, that is substantially equal to the sum of the axial lengths of the two pole pieces; B. the stator pole teeth being disposed in two groups substantially similar to one another, (1) each said group comprising circumferentially spaced stator pole teeth that are axially outwardly offset in relation to the magnetic poles, and (2) said groups being spaced apart axially by a distance substantially equal to the axial length of the permanent magnet so that the stator pole teeth of each group oppose the rotor pole teeth of one of the pole pieces; and C. the stator pole teeth of each group having a thickness, measured parallel to said axis, which is substantially equal to that of the rotor pole teeth opposing them.