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Working principle of incremental rotary encoder

The information comes from:the Internet posted on:2023-06-27

The incremental rotary encoder converts the timing and phase relationship of its angle code disk through two internal photosensitive receivers, and obtains an increase (positive direction) or decrease (negative direction) in the angular displacement of its angle code disk. After integrating digital circuits, especially microcontrollers, incremental rotary encoders have the advantage of being cheaper and simpler in angle measurement and angular velocity measurement compared to absolute rotary encoders.
Internal working principle of incremental rotary encoder
A. Two points B correspond to two photosensitive receivers, with a spacing of S2 between points A and B, and a grating spacing of S0 and S1 for the angle encoder, respectively.
When the angle code disk rotates at a constant speed, it can be seen that the S0: S1: S2 ratio in the output waveform is the same as the S0: S1: S2 ratio in the actual graph. Similarly, when the angle code disk rotates at other speeds, the S0: S1: S2 ratio in the output waveform is still the same as the S0: S1: S2 ratio in the actual graph. If the angle encoder performs variable speed motion and considers it as a combination of multiple motion cycles (defined below), then the S0: S1: S2 ratio in the output waveform of each motion cycle remains the same as the S0: S1: S2 ratio in the actual graph. By outputting the waveform, it can be seen that the timing of each motion cycle is clockwise and counterclockwise
We save the current output values of A and B and compare them with the next output values of A and B to easily determine the direction of movement of the angle code disk,
If the light grid S0 is equal to S1, which means that the angle between S0 and S1 radians is the same, and S2 is equal to 1/2 of S0, then the displacement angle of the angle code disk movement can be obtained as 1/2 of the angle between S0 radians. Divided by the time consumed, the displacement angular velocity of the angle code disk movement can be obtained.
When S0 is equal to S1 and S2 is equal to 1/2 of S0, the motion direction position and displacement angle can be obtained by 1/4 motion cycles. If S0 is not equal to S1 and S2 is not equal to 1/2 of S0, then it takes 1 motion cycle to obtain the motion direction position and displacement angle.
Is there only two types of rotary encoders: incremental and absolute? How can these two types of rotary encoders be distinguished? How does the working principle differ?
There are only incremental and absolute types. The incremental type only measures the increment of angular displacement (indirectly angular velocity), with the previous moment as the base point. The absolute type measures the angular displacement from the start of work. The incremental type measures small angles accurately, but large angles have accumulated errors. The absolute type measures small angles relatively accurately, but large angles have no accumulated errors
The Principle and Application of Encoder
Encoder is a rotary sensor that converts angular displacement into a series of electrical digital pulses, which can be used to control angular displacement. If the encoder is combined with a rack or helical rod, it can also be used to control linear displacement. The conversion of angular displacement in the encoder adopts the principle of photoelectric scanning. The reading system is based on the rotation of a radial dial, which is composed of alternating transparent and opaque windows. This system uses an infrared light source to illuminate vertically, so that light projects the plate and image onto the surface of the receiver. The receiver is covered with a layer of grating, called a collimator, which has a light source