An incremental encoder is a device used to measure the change and direction of motion. It consists of a readhead and scale. The readhead includes a specific sensor technology and light source, along with any other filtering optics required to direct the light onto the sensor.
The incremental encoder scale has a main track comprising lines of equal pitch and an index track. The main track alone does not provide absolute position information, so an index mark is added on a second track to provide a reference position. When the readhead passes over the index, an output is generated. At power up, the index track tells the controller/drive when the scale is in the zero position. This is called a homing routine. After the home or reference position is located, the controller/drive tracks incremental position changes relative to zero.
The main track is detected to measure high resolution change in position through the conversion of a light intensity signal to sine and cosine signals. By interpolating these signals, you increase the counts detected per revolution, and therefore increase the overall resolution of the encoder.
Because of the simplicity of the scale, incremental encoders require less complex sensor technology and have zero communication latency which is introduced in absolute encoders. An absolute track provides a unique signal at each location on the scale and due to this added complexity, requires a more advanced sensor technology. The simple design of an incremental encoder makes it a lower cost option for systems that do not require absolute position feedback.