Rotary encoder with commutation

Encoders with commutation are used in electric motors. These are incremental encoders with additional commutation tracks to control the motor commutation (motor feedback). Commutation is the transfer of current from one winding to the next. The timing of the commutation must be harmonised with the magnetic field of the rotor so that the electric motor works at top efficiency.

In electric motors, the pole pairs provide a direct connection between electrical and mechanical rotation. One electrical revolution always corresponds to one mechanical revolution divided by the number of pole pairs. The resolution of the commutation signals is assigned to the pole pairs of the electric motor.

With these encoders, UVW tracks are also output in addition to the ABZ tracks of the incremental encoder. In three-phase electrical machines, these are usually used for commutation. The UVW signals change during rotation according to the 3-bit Grey code, whereby the states [000] and [111] do not occur. In a three-phase machine with only one pole pair, six states are distinguished per mechanical revolution. This means that the rotor position is known to an accuracy of at least 60 degrees, which is sufficient to move the three-phase machine to the next UVW flank in field-oriented control. The exact rotor position is then known.