A rotary encoder is a device used to convert the angular position or motion of a shaft or axle into an analog or digital signal. There are two main types of rotary encoders: absolute and incremental.

Incremental Encoder: This type of encoder generates a series of pulses as the shaft rotates. It doesn’t provide absolute position information on its own; instead, it measures changes in position relative to a starting point. To determine absolute position, additional circuitry or counting logic is needed to track the position from a known reference point.

Absolute Encoder: An absolute encoder provides unique digital code for each position of the shaft within a single revolution. This means it can directly report the exact position of the shaft without needing a reference point or initialization. The output of an absolute encoder typically represents the absolute position of the shaft in either binary or Gray code.

Binary Absolute Encoder: In a binary absolute encoder, each shaft position corresponds to a unique binary code. For example, a 10-bit encoder can represent 1024 unique positions.

Gray Code Absolute Encoder: Gray code is a binary numeral system where two consecutive values differ in only one bit. Gray code is used in some absolute encoders to prevent errors during transition between positions, as only one bit changes at a time.

In summary, while both incremental and absolute encoders measure shaft position, absolute encoders directly provide the exact position without requiring additional tracking logic or reference points. They are useful in applications where knowing the precise position of a shaft is critical, such as in robotics, CNC machines, or industrial automation systems.