As the core part of some automation equipment, the reliability and stability of the motion control system directly affect the performance of the equipment, and one of the main factors affecting its reliability and stability is the problem of anti-interference. Therefore, how to effectively solve the interference problem is a problem that cannot be ignored in the design of the motion control system.
1. Interference phenomenon
In the application, the following main interference phenomena are often encountered:
1. When the control system does not issue a command, the motor rotates irregularly.
2. When the servo motor stops moving and the motion controller reads the position of the motor, the value fed back by the photoelectric encoder at the end of the motor jumps randomly.
3. When the servo motor is running, the value of the encoder read does not match the value of the command issued, and the error value is random and irregular.
4. When the servo motor is running, the difference between the read encoder value and the issued command value is a stable value or changes periodically.
5. The equipment that shares the same power supply with the AC servo system (such as a display, etc.) does not work properly.
2. Interference source analysis
There are two main types of channels that interfere with entering the motion control system:
1, signal transmission channel interference, interference enters through the signal input channel and output channel connected to the system;
2, power supply system interference.
The signal transmission channel is the way for the control system or driver to receive feedback signals and send out control signals, because the pulse wave will be delayed and distorted on the transmission line, attenuation and channel interference, in the transmission process, long-term interference is the main factor.
There are internal resistances in any power supply and transmission lines. It is these internal resistances that cause the noise interference of the power supply. If there is no internal resistance, no matter what kind of noise will be absorbed by the power supply short-circuit, no interference voltage will be established in the line. , AC servo system driver itself is also a strong source of interference, it can interfere with other equipment through the power supply.
Motion Control System
Three, anti-interference measures
1. Anti-interference design of power supply system
(1) Implement power supply in groups, for example, separate the drive power of the motor from the control power to prevent interference between devices.
(2) The use of noise filters can also effectively suppress the interference of AC servo drives to other equipment. This measure can effectively suppress the above-mentioned interference phenomena.
(3) The isolation transformer is adopted. Considering that high-frequency noise passes through the transformer mainly not by the mutual inductance coupling of the primary and secondary coils, but by the coupling of the primary and secondary parasitic capacitances, the primary and secondary sides of the isolation transformer are isolated by shielding layers to reduce their Distributed capacitance to improve the ability to resist common mode interference.
2. Anti-interference design of signal transmission channel
(1) Photoelectric coupling isolation measures
In the process of long-distance transmission, the use of photocouplers can cut off the connection between the control system and the input channel, output channel, and the input and output channels of the servo drive. If the photoelectric isolation is not used in the circuit, the external spike interference signal will enter the system or directly enter the servo drive device, causing the first interference phenomenon.
The main advantage of photoelectric coupling is that it can effectively suppress spikes and various noise interference,
Therefore, the signal-to-noise ratio in the signal transmission process is greatly improved. The main reason is: Although the interference noise has a large voltage amplitude, its energy is small and can only form a weak current. The light-emitting diode of the input part of the photocoupler works under current state, and the general conduction current is 10-15mA, so Even if there is a high amplitude interference, it is suppressed because it cannot provide enough current.
(2) Twisted-pair shielded wire and long-wire transmission
The signal will be affected by interference factors such as electric field, magnetic field and ground impedance during transmission. The use of grounded shielding wire can reduce the interference of electric field.
Compared with coaxial cable, twisted-pair cable has a lower frequency band, but has high wave impedance and strong resistance to common mode noise, which can cancel each other’s electromagnetic induction interference.
In addition, in the process of long-distance transmission, differential signal transmission is generally used to improve the anti-interference performance. The use of twisted-pair shielded wire for long-wire transmission can effectively suppress the second, third, and fourth interference phenomena.
(3) Ground
Grounding can eliminate the noise voltage generated when current flows through the ground wire. In addition to connecting the servo system to the ground, the signal shielding wire should also be grounded to prevent electrostatic induction and electromagnetic interference. If it is not properly grounded, the second interference phenomenon may occur.
Post time: Mar-06-2021