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Working principle of incremental encoder
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Working principle of incremental encoder

2020-12-30 21:25

The incremental encoder converts the displacement into a periodic electric signal, and then converts this electric signal into a counting pulse, and the number of pulses is used to indicate the magnitude of the displacement. Encoder is a device that converts angular displacement or linear displacement into electrical signals. The former becomes a code wheel, and the latter is called a yardstick. Encoders can be divided into contact type and non-contact type according to the reading mode. The contact type uses a brush to output, and the brush touches the conductive area or the insulating area to indicate whether the state of the code is "1" or "0"; the non-contact type receiving sensitive element is a photosensitive element or a magnetic sensitive element. The light-transmitting area and the opaque area indicate whether the state of the code is "1" or "0". According to the working principle, encoders can be divided into two types: incremental and absolute. The incremental encoder converts the displacement into a periodic electrical signal, and then converts the electrical signal into a counting pulse. The number of pulses is used to indicate the magnitude of the displacement. Each position of the absolute encoder corresponds to a certain digital code. , So its indication is only related to the start and end positions of the measurement, and has nothing to do with the middle process of the measurement. Rotary incremental encoder outputs pulses while rotating, and knows its position through counting equipment. When the encoder is not moving or the power is cut off, it relies on the internal memory of the counting equipment to remember the position. In this way, when the power is off, the encoder cannot move. When the power is on, the encoder cannot lose the pulse due to interference during the pulse output. Otherwise, the zero point of the counting device will shift, and this deviation There is no way to know the amount of shift, only after the wrong production results appear. The solution is to increase the reference point. Every time the encoder passes the reference point, the reference position is corrected into the memory position of the counting device. Before the reference point, the accuracy of the position cannot be guaranteed. For this reason, in industrial control, there are methods such as first finding the reference point for each operation, turning on the machine and making change. For example, the positioning of the printer scanner is based on the principle of incremental encoder. Every time we turn it on, we can hear a crackling noise. It is looking for the reference zero point before it works.

Incremental rotary encoder converts the timing and phase relationship of the angle code disc through two internal photosensitive receiving tubes, and obtains the increase (positive direction) or decrease (negative direction) of the angular displacement of the angle code disc. After joining the digital circuit, especially the single-chip microcomputer, the incremental rotary encoder has the advantages of cheaper and simpler than the absolute rotary encoder in angle measurement and angular velocity measurement.

Incremental encoders directly use the principle of photoelectric conversion to output three sets of square wave pulses A, B and Z phase; A and B two sets of pulses have a phase difference of 90º, so that the direction of rotation can be easily judged, and the Z phase is one per revolution. Pulse, used for reference point positioning. Its advantages are simple structure, average mechanical life of more than tens of thousands of hours, strong anti-interference ability, high reliability, and suitable for long-distance transmission. The disadvantage is that the absolute position information of the shaft rotation cannot be output. 

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