US Patent 7129610 Commutator for an electric motor

A commutator includes a support ring and a plurality of conducting segments arranged over a circumference of the support ring. Some of the conducting segments have an electrically insulating portion. The commutator is employed with a device that measures rotation of an electric motor rotor shaft. The commutator is fitted onto the electric motor rotor shaft. A commutator housing includes at least three brushes and comes into contact with the conducting segments of the commutator. At least one of the brushes contacts the electrically insulating portions of the commutator segments to provide an electrical measurement that enables the speed, the direction of rotation and the angular position of the electric motor rotor shaft to be determined.