Rack punching machine Cause of interference: EDM machine tool uses high-frequency discharge to corrode the workpiece, and high-frequency interference occurs to the intelligent error correction controller. Interference generally refers to some uncertain and harmful electrical transients that have nothing to do with signals and occur in the process of signal input, transmission and output. These transient phenomena will change the data in the NC system during transmission, increase the error, and make the local device or the whole system abnormal and cause faults.
1、 The generation of interference sources mainly includes the following situations:
1. Power interference: due to the wide coverage of the power grid, there are many kinds of equipment sharing a power grid, especially the internal changes of the power grid. The power switch operation, lightning surge, start and stop of large power equipment, harmonics caused by AC/DC drive devices, transient impact of power grid short circuit, etc. are all transmitted to the original side of the power supply through the transmission line, causing voltage transient and grid voltage fluctuation. In addition, the power line will also generate noise and fast transient pulse train during transmission, polluting the power grid.
2. Radiated interference: electromagnetic or electric field is ubiquitous in nature. In addition to being affected by electric field, the working EDM piercer is also affected by magnetic field. In the process of operation, the EDM perforator will inevitably be subject to electromagnetic interference due to the harsh working environment.
3. Interference between digital signal and analog signal: during the operation of the electric spark perforator, the whole set of equipment involves many components, including AC380V and AC220V AC signals, as well as various low-voltage DC signals of DV24V and DC5V. In the wiring process of cables used to transmit signals, sometimes misoperation occurs due to analog signal output equipment or interference generated by servo drivers or frequency converters, affecting the normal operation of equipment; The frequency used to transmit I/O input/output signals is subject to clock frequency and harmonic interference. In addition, due to improper line routing, digital signal lines and analog signal lines will inevitably be interfered by external interference signals, and various signal lines will also interfere with each other through line to line coupling.
2、 Anti interference measures: these measures mainly include shielding, isolation, filtering, grounding and software processing.
1. Shielding technology: Shielding is currently used more and more effectively. Shielding technology cuts off the transmission path of radiated electromagnetic noise. Metal materials or magnetic materials are often used to surround the area to be shielded, so that the fields inside and outside the shield are isolated from each other. The electromagnetic radiation signal is cut off to protect the shielded body from interference. Shielding is divided into electric field shielding, magnetic field shielding and electromagnetic shielding. In practical engineering applications, when electric field interference occurs, the metal shells of strong current equipment (servo drivers, frequency converters, drivers, switching power supplies, motors, etc.) in the system are reliably grounded to realize active shielding; The shell of sensitive equipment such as intelligent error correction device shall be reliably grounded to realize passive shielding; The distance between strong current equipment and sensitive equipment shall be as far as possible; High voltage and high current power line and signal line shall be routed separately, and cables with shielding layer shall be selected. For magnetic field interference, materials with high permeability, such as glass molybdenum alloy, shall be selected, and the wall thickness of shielding body shall be appropriately increased; Twist the signal wire and the grounding wire or current carrying return wire together with twisted pair and shielded wire so that the distance between the signal and the grounding wire or current carrying return wire is close; Increase the distance between lines to make the mutual inductance between the interference source and the induced line as small as possible; Sensitive equipment shall be far away from interference sources, such as strong current equipment, transformers, etc.
2. Isolation technology: isolation is to isolate the interference source with isolated components to prevent interference from entering the equipment and ensure the normal operation of the EDM machine tool. Common isolation methods include photoelectric isolation, transformer isolation and relay isolation.
(1) Photoelectric isolation: Photoelectric isolation can effectively suppress system noise and eliminate interference of grounding circuit. At the input and output ends of the intelligent error correction system, the optocoupler is used as the interface to isolate the signal and noise; In the motor drive control circuit, optocoupler is used to separate the control circuit from the motor high-voltage circuit.
(2) Transformer isolation is a widely used anti-interference component of power line. Its basic function is to realize the electrical isolation between circuits, so as to solve the interference between equipment caused by the loop current of ground wire. At the same time, the isolation transformer has a certain role in resisting common mode interference. The isolation transformer can play a very good role in restraining the transient pulse train and lightning surge interference. For the transmission of AC signals, the transformer isolation interference signal is generally used.
(3) The relay is isolated, and there is no electrical connection between the coil and contact of the relay. Therefore, the coil of the relay can be used to receive electrical signals, and the contacts can be used to send and output signals, so as to avoid the direct connection between strong current and weak current signals, and achieve anti-interference isolation.
3. Filtering technology: filtering technology is an effective measure to suppress interference. The filter is an equivalent circuit composed of lumped parameters R, L and C. It has the functions of signal separation, interference suppression, impedance transformation and impedance matching, and delay signal. Filter can be used to filter harmful components in the circuit of equipment and improve the reliability of equipment. In order to suppress the interference of high frequency on intelligent control devices on CNC machine tools. A low-pass filter can be used to filter out high-frequency components in the circuit to improve power quality. For all kinds of contacts or switches, interference caused by contact jitter at the moment of closing or opening can be eliminated by resistance capacitance filtering to suppress the reverse potential generated by inductive load at the moment of cutting off the power supply, so that the ability of the magnetic field released by the inductance coil can be converted into the energy of the electric field of the capacitor and stored to reduce energy consumption. Using L-C filter will reduce the load impedance, thus increasing the filtering effect, playing the role of filter and reducing interference.
4. Grounding treatment: connect the circuit, equipment casing, etc. with a common reference point (ground) as zero potential to achieve low impedance, which is called grounding. The grounding methods mainly include: protective grounding, working grounding, shielding grounding. Grounding has two purposes: one is to reduce interference; Second, for personal safety. In order to reduce the occurrence of safety accidents, the safety grounding protection grounding terminal and the chassis of the electrical equipment shall be well connected to the ground. In the electric cabinet of the numerical control machine tool, the thickness of the grounding bar shall not be less than 3mm (copper plate), and the grounding resistance connected to the ground shall be less than 4 ohms; The protective ground wire in the system shall be connected to the grounding bar with yellow green double color wire as thick and short as possible, and avoid forming a loop; It can reduce mutual electromagnetic interference with other equipment. In order to avoid common ground impedance interference, ground loop interference and common mode current radiation interference during the operation of CNC machine tools, working grounding is extremely important. The working grounding modes include floating grounding, single point grounding, multi-point grounding and hybrid grounding.
5. Software anti-interference: the method of identifying useful signals and interference signals with software and filtering interference signals is called software filtering. Generally, the signal time, space and attributes are used to determine whether it is a useful signal or an interfering signal.
