Technical data – Encoders

Technical Data – Encoders

Encoder/Serial encoder/Sine cosine encoder

An encoder is a measurement device which converts mechanical motion into electronic signals. Usually an encoder is a rotary device that outputs digital pulses which correspond to incremental angular motion. The encoder consists of a glass or metal wheel with alternating clear and opaque stripes that are detected by optical sensors to produce the digital outputs.

In motion terms, an encoder is used to provide digital data about a motor’s shaft position to enable the position error correction required to provide a closed loop for accurate servo control. Commonly the encoder is fitted directly to the rear of the motor shaft and can use either magnets or an optical reader to measure the increments marked on a disc fitted to the motor shaft. Typically such devices may be know as incremental encoders or optical encoders.

Serial encoders are simply those devices capable of output via a serial interface – e.g. RS232 RS422, and RS485 serial protocols. These encoders usually provide an absolute position on power up.

A sine cosine encoder outputs a sine and a cosine signal rather than a digital output. These sine/cos outputs are commonly interpolated (multiplied) either in the encoder or in the controller to give a much higher resolution output. Typically x256 to x4096.