Principle and application of incremental encoder

Encoder is a device that converts angular displacement or linear displacement into electrical signal According to the working principle, the encoder can be divided into two types: incremental type (SPC) and incremental type (APC) Incremental encoder is to convert displacement into periodic electrical signal, and then convert this electrical signal into count pulse The number of pulses is used to express the displacement Here are some introductions of incremental encoder 1 Working principle: the working principle of the photoelectric incremental encoder is as follows: there is a grating on the pulse code disk which rotates with the rotation axis, and there are several light transmission sections and light shielding sections evenly distributed on the code disk The incremental encoder does not have a fixed starting zero It outputs pulses that are proportional to the increment of the rotation angle It needs a counter to count the number of pulses Every time a light transmission area is turned, a pulse signal is sent out The current value of the counter is increased by 1, and the counting result corresponds to the increment of the corner The incremental encoder has the advantages of simple manufacturing process, low price and sometimes used to measure the angle of rotation 2 Classification of incremental encoder (1) there is only a pair of optocouplers in the single channel incremental encoder, and only one pulse sequence can be generated (2) There are two pairs of optocouplers in the AB phase encoder, and the output phase difference is 90 ° The relationship between the lead and lag of the two pulses is just opposite It can be seen from the figure below that the level of phase a pulse is just opposite when the phase B pulse is on the rising edge, positive rotation and reverse rotation Therefore, using phase AB encoder, PLC can easily identify the rotation direction of the shaft When the measurement accuracy needs to be increased, the frequency multiplication method can be used, i.e counting the rising edge and falling edge of a and B phase waveforms respectively The resolution can be increased by 4 times, but the Zui high frequency of the measured signal will be reduced accordingly (3) In addition to two pairs of optocouplers of the two channel incremental encoder, the other channel of the pulse code disk has one light transmission section, which outputs one pulse every revolution The pulse is called z-phase zero pulse, which is used as the system zero signal or the origin of the benchmark to reduce the accumulated error of measurement The incremental encoder has the advantages of simple structure, long average life, strong anti-interference ability, high reliability, suitable for continuous operation and high-precision positioning control Its disadvantage is that it is unable to output the position information of shaft rotation 3 Encoder selection: first, select the encoder type according to the measurement requirements, and the number of pulses per revolution of incremental encoder is equal to the number of lines of its grating In the design, the number of lines of the encoder shall be determined according to the degree requirements of speed measurement or positioning and the speed of the encoder The encoder is installed on the motor shaft, or on a certain shaft after deceleration The speed of the encoder is very different It should also be considered whether the Zui high frequency of the pulse it sends is within the allowable range of the PLC high-speed counter 3 The matching problem of encoder and PLC high-speed counter take S7-200 as an example When using single channel incremental encoder, the single add / subtract counter mode (mode 0-5) of high-speed counter can be selected, which can be subdivided into with / without external direction input signal, with / without reset input and with / without start input signal When the AB phase encoder is used, the A / B phase orthogonal counter mode (mode 9-11) should be selected for the high-speed counter, which can increase and decrease the count during the forward rotation and the reverse rotation 4 How to judge whether the AB phase encoder is forward or reverse? The high-speed counter of S7-200 uses the current counting direction status bit in SM area to indicate the rotation direction of the encoder If the period of the encoder output pulse is more than twice of the scanning cycle time of PLC, the encoder rotation direction can be determined by judging the 0 and 1 state of the A-phase pulse signal at the rising edge of the B-phase pulse Information from: