
An optical encoder is an electromechanical device which produces electrical output and is proportionate to the angular state of the input shaft. The optical encoder operates on the principle of optics which converts angular displacementor mechanical rotary motion of an input shaft into a digital signal. A light source from an infra-red or LED is passed through a rotating high-resolution code disk or encoded disk which contains a binary code or grey code. Photo sensors, which could be a phototransistor, photovoltaic cell, or silicon photodiode on the other side of the disc scans the rotating encoded disk and generates the output electric signal. The output signal from the photo sensors is a series of voltage pulses since the light from infra-red or LED source is interrupted by opaque areas of the encoder disc. Incremental encoders and absolute encoders are two basic types of optical encoders. Incremental encoder also known as relative rotary encoder produces the square wave pulses output signal. On the other hand, absolute encoders produce the unique output code for every rotating position of the input shaft and are more complex than incremental encoders. Optical encoders are usually used to monitor and control motion parameters including position, distance, direction, rate, and speed