Encoder: channels A and B, phase shift and direction of rotation

Incremental encoder do have two lines (channels A and B). Why and what is the relative phase shift depending on the direction of rotation?

Incremental encoders, as used by maxon, produce a series of electrical high-low pulses. From these pulses the electronics gains information such as

• by how much (which angle) has the motor shaft rotated (counting the number of pulses)
• how fast is the motor shaft rotating (e.g. number of pulses per millisecond)

Unfortunately with one line only the signal looks the same if rotating clockwise (cw) or counter clockwise (ccw). Therefore, a second line (channel B) is needed having its signal shifted by 90 electrical degrees (°e) with respect to channel A.

This phase shift is needed to determine the direction of rotation. Depending on direction of rotation the signal of channel A is preceeding channel B or vice versa.

For maxon catalog encoder the following definition applies (if not specified otherwise):

• If the motor shaft rotates clockwise (CW), channel A leads channel B.
• If the motor shaft rotates counter clockwise (CCW), channel B leads channel A.

Definition of direction of rotation of maxon motors

The same as the direction of the shaft seen from outside onto the mounting flange (load side) of the motor.

Quadcounts enhance resolution

maxon controller evaluate the signal edges of the encoder signals. This results in a four times higher positioning resolution relative to the counts per turn of the encoder. The technical term for this is quadcounts or states.