1, According to the principle of the signal point: incremental encoders, absolute encoders, hybrid encoder
1) Incremental encoder
    Direct use of photoelectric conversion principle square wave pulse output three groups A, B and Z phase; A, B groups skew 90º, which can easily determine the direction of rotation, and a Z phase pulses per revolution for the reference point Location. The advantage is that the principle of simple structure, mechanical average life of more than tens of thousands of hours, anti-interference ability, high reliability, suitable for long distance transmission. The disadvantage is that the absolute position information can not be output shaft rotation.
2) absolute encoder
    Using natural binary or binary cycle (Gray) mode photoelectric conversion. The difference absolute encoder and incremental encoder that the disc translucent, opaque line graphics, the absolute encoder can have several codes, according to the coding read code on the disc, to detect the absolute position. The design can be encoded binary code, cyclic code, twos complement, and the like. It is characterized by:
(1) can be directly read out the absolute angular coordinates;
(2) no cumulative error;
(3) after removal of the power position information is not lost. But the resolution is determined by the binary digits, that accuracy depends on the number of bits, there are 10, 14, and other.
3) Hybrid absolute encoder
    It outputs two sets of information: a set of information for detecting the magnetic pole position with absolute information function; the other group complete with incremental encoder output.