Incremental encoder introduce！

The incremental encoder is a device which provides electrical pulses if its
shaft is rotating [1], [2], [4]. The number of the generated pulses is proportionalto the angular position of the shaft. The incremental encoder is one of the most
frequently used position transducers. The principle of an optical incremental
encoder is presented in Fig. 1. Together with the shaft there is rotating a
transparent (usually glass) rotor disc with a circular graduation-track realized as
a periodic sequence of transparent and non-transparent radial zones which
modulates the light beams emitted by a light source placed on one side of the
disc on the fix part (stator) of the encoder. On the opposite side the modulated
light beams are sensed by two groups of optical sensors and processed by
electronic circuits. Each of the two outputs of the encoder (noted A and B) will generate one pulse when the shaft rotates an angle equal to the angular step of
graduation θp, i.e. the angle according to one successive transparent and non transparent zone. The number of pulses (counted usually by external electronic
counters) is proportional to the angular position of the shaft. Due to the fact that
the light beams are placed shifted to each other with an angle equal to the
quarter of angular step of graduation θp/4, the pulses of the two outputs will be
also shifted, making possible the determination of the rotation sense. A third
light beam is modulated by another track with a single graduation. The output
signal (named Z) associated to this third beam provides a single pulse in the
course of a complete (360°) rotation. The shaft position corresponding to this
pulse may be considered as reference position. Fig. 2 shows the output pulses of
the encoder

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