Non-uniform angular velocity. This refers to rotation occurring in jerks or increments rather than smooth motion.
In an electric motor, when an armature coil enters the magnetic field produced by the field coils, it tends to speed up and slow down when leaving it. This effect becomes apparent at low speeds. The fewer the number of stator or armature poles, the more noticeable it can be.
Reducing the Effect in Electric Motors
Arrange the laminations on an armature to produce a slight twist/skew angular pattern of their slots with respect to the shaft axis. This skew or twisted pattern helps to eliminate low speed cogging effects in an armature and minimize induced vibration in a rotor as well as reduce associated noise. This can help to increase starting torque.
Increasing the number of stator and armature poles will reduce cogging.
See also: Angular Velocity.
Subjects: Mechanical Engineering