The disturbance in the CNC system is often caused by a "soft" failure, which is an aspect that is frequently overlooked. To eliminate such interference, it's essential to address it from several key areas:
First and foremost, ensure proper grounding of both the machine tool and the CNC system. The CNC machine should use point grounding (as shown in Figure 1-3), not just for convenience or time-saving. Grounding should be done near each part of the machine, avoiding multiple grounding loops. The grounding wire must meet the system’s specifications, with sufficient diameter, especially when shielding is required. Shielded cables should be used where necessary, and the shielding must be properly connected according to the system guidelines to prevent unwanted interference.
CNC machines typically have strict requirements for interfacing with their environment. The incoming power lines to the workshop or factory must have a complete and well-designed grounding network that meets all installation standards. This is a fundamental requirement for ensuring safe and reliable operation, and it should not be ignored.
Second, prevent strong electrical interference. Components like contactors, relays, and AC motors in the power cabinet can cause frequent switching, leading to voltage spikes, surges, and other disturbances that affect the CNC control system. To reduce this, the following measures are recommended:
1) Install parallel RC snubbers across the coil of the AC contactor and the three-phase output of the AC motor.
2) Add a freewheeling diode across the coil of DC contactors or solenoid valves.
3) Use surge suppressors and filters on the input power lines of the CNC system.
4) Use shielded cables for the three-phase armature of the servo motor (commonly used with Siemens drives).
These methods can effectively suppress interference, but it's important to note that the connection lines should be as short as possible, ideally no longer than 20 cm, to minimize the impact of the interference source.
Third, manage interference from the power supply line L. In cases where the power supply is unstable—such as voltage fluctuations, frequency drift, phase shifts, waveform distortion, or common-mode and normal-mode noise—this can disrupt the CNC system’s operation. To reduce such issues:
1) Install electronic voltage regulators in areas with significant grid voltage fluctuations.
2) Ensure the power line has sufficient capacity to meet the machine's power requirements.
3) Avoid sharing the main power line with high-power equipment that frequently starts and stops, such as CNC machines and EDM devices.
4) When installing the CNC machine, place it as far away as possible from devices like medium-frequency furnaces and high-frequency induction furnaces to reduce electromagnetic interference.
By addressing these factors, you can significantly improve the stability and performance of the CNC system. It’s crucial to take a proactive approach in identifying and mitigating potential sources of interference, as even small oversights can lead to major operational problems.
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