Rotary encoder anti-interference principle, how to judge it is encoder interference2021

Rotary encoder is a kind of precision electronic components, which requires anti-interference for the environment of use. Today, I will take you to understand the design principle of anti-interference system of rotary encoder. How to judge whether it is the fault of the encoder itself? Still interference.

Design principle of anti-jamming system of rotary encoder

A rotary encoder is a rotary displacement sensor that is rotated into a series of digital pulse signals that can be used to control angular displacement. So how does the motion control system in the rotary encoder interfere with the anti-jamming design? Signal transmission channel: shielded twisted pair transmission, the signal will be affected by the impedance of the electric field, magnetic field and interference factors in the transmission process. Compared with coaxial cable, although the frequency band is poor, the impedance is large and the common mode noise is strong, so that every small part of electromagnetic interference can cancel each other. Photoelectric coupling isolation measures In long-distance transmission, the optocoupler can cut off the circuit connection between the control system and the input channel, as well as the output channel and the input and output channels of the servo drive. The main advantage of photoelectric coupling is that it can effectively suppress peak pulses and noise interference, thereby greatly improving the signal-to-noise ratio (SNR). Although the noise voltage is large, the energy is small, and there is only a weak current, and the input part of the light-emitting diode photocoupler works in the current state, and the general conduction current is 10-15mA, so even if it cannot provide enough current, it is suppressed, so the interference is very serious. Big. Anti-interference design of power system: implement power supply group, for example, will implement motor drive power supply and control power supply to prevent interference between devices. Using an isolation transformer, considering that the high-frequency noise of mutual inductance coupling does not depend on the secondary winding of the transformer in the early stage, but starts between the primary and secondary auxiliary parasitic capacitive coupling, so the transformer is isolated from the shielding layer to reduce the capacitance. Improve the ability to resist common mode interference. The noise filter can effectively suppress the interference to other AC servo drives.

In many cases, the rotary encoder is not broken, but it is only the cause of interference, resulting in a bad wave pattern and inaccurate counting.

Rotary encoders are precision components. This is mainly because of the serious interference around the encoder, such as whether there is interference caused by frequent starting of large motors and electric welding machines, and whether it is transmitted in the same pipeline as the power line.

It is also important to choose what kind of output to resist interference. Generally, the anti-jamming output with reverse signal is better, namely A+~A-, B+~B-, Z+~Z-, which is characterized by the addition of 8 power lines, and Not 5 lines (total zero). The transmission in the cable with the reverse signal is symmetrical, and the interference is small. It can also be judged in the receiving device (for example, the signal of the receiving device uses the 90° phase difference of the A and B signals to read the level 10, , 01, 00 four states, count as a valid pulse, this program can effectively improve the system's anti-interference performance (accurate counting)).

How to judge whether it is the fault of the encoder itself?

1. Eliminate (move away, close, isolate) sources of interference;

2. Determine whether it is the cumulative error of the mechanical gap;

3. Determine whether the circuit interface of the control system and the encoder does not match (encoder selection error);

1,2,3 After the failure phenomenon is eliminated after the method is tried, preliminary judgment can be made, if it is not eliminated, further analysis is required.

The simple way to judge whether it is the fault of the encoder itself is the elimination method.

The specific method of elimination is: replace it with an encoder of the same model. If the fault phenomenon is the same, the encoder fault problem can be basically eliminated, because the occurrence of a small probability event that two encoders fail at the same time may be very small. Seen as 0. If you change to an encoder of the same model, and the fault is eliminated immediately, you can basically determine that the encoder is faulty.