Incremental Encoder

An encoder that outputs pulses for each increment of rotation, needing a count to know position.

An incremental encoder outputs a stream of pulses as the shaft turns, typically two channels, A and B, 90 degrees out of phase (a quadrature signal), plus a third Z channel that pulses once per revolution as a zero marker. The controller counts pulses to know how far the shaft has turned, and checks whether A or B leads the other to determine direction. It's mechanically simple, cheap, and easy to build at high resolution, so it's very common in motors. Its downside is that it only knows how far it has moved since power-on — losing power also loses position — so it needs to be homed at every startup, or rely on the Z pulse or a limit switch to re-establish a reference. Robot joints that use only incremental encoders typically perform a homing move at startup; avoiding that requires an absolute encoder, or a dual-encoder setup.

ExampleA 3D printer, and many desktop robot arms, bump each axis against a limit switch at startup, precisely because they rely on incremental position feedback and need to home first.

Also called

Incremental-Type Encoder

Related

Rotary Encoder · Absolute Encoder · Dual Encoder · Homing / Zero-Offset Calibration · Optical Encoder

Sources

Incremental encoder - Wikipedia