US Patent 9356500 Stepper motor with adjustable detent torque

A stepper motor has a rotor having a permanent magnet, a stator housing and a plurality of stator coil assemblies disposed within the stator housing. Each coil assembly has a bobbin, a coil wound about the bobbin, and two pole plates having pole fingers extending axially inside of the bobbin. The bobbin is disposed between the two pole plates and defines a space accommodating the rotor. A number of magnetic detent plates are disposed about the permanent magnet rotor. Each magnetic detent plate has a central opening accommodating the rotor and a plurality of projections extending inwardly, spaced about the central opening. The projections interact with the magnetic field of the rotor magnet.