1. Routine Inspection Method The routine inspection method is one of the most fundamental approaches used in fault diagnosis, relying on human senses such as sight, hearing, touch, and smell to detect unusual phenomena like light, sound, or odor during a malfunction. This method involves a systematic examination of all parts of the system, following the principle of "from outside to inside" to narrow down the fault to a specific module or printed circuit board. It requires maintenance personnel to have extensive hands-on experience, broad technical knowledge, and strong analytical skills. For example, if a CNC machine suddenly stops during operation, opening the control cabinet and visually inspecting the Y-axis motor’s main circuit might reveal that the motor’s power cable has worn out and caused a short circuit. Replacing the damaged cable typically resolves the issue and restores normal operation.
2. Self-Diagnostic Function Method Modern CNC systems are equipped with powerful self-diagnosis capabilities that continuously monitor hardware and software components. When an anomaly occurs, the system displays error messages on the CRT or uses LED indicators to signal the approximate cause of the fault. Additionally, it can display interface signals between the system and the machine, helping determine whether the problem lies in the mechanical part or the CNC system itself. This method is highly effective for current maintenance tasks, as it significantly reduces the time needed to identify and resolve issues.
3. Functional Program Test Method This method involves using manual or automated programming to test common and special functions of the CNC system, such as linear positioning, circular interpolation, and fixed cycles. These functions are compiled into a test program and run on the system to evaluate its performance and reliability. While this approach helps identify potential causes of failure, it may not always distinguish between programming errors, operational mistakes, or actual machine faults. It is especially useful when testing long-idle machines or when no alarms are triggered during the first startup.
4. Spare Parts Replacement Method Replacing faulty components with known good ones is a widely used technique in field troubleshooting. The process involves identifying a suspect component and swapping it with a spare to see if the fault is resolved. Before replacement, it is essential to verify that the spare part matches the original in terms of specifications, settings, and configuration. For instance, replacing a memory board in a FANUC FS-6 system may require reinitializing the system and resetting parameters. Similarly, other systems may need specific operations after a motherboard swap. Always follow the manufacturer's guidelines to avoid further complications.
5. Transfer Method This method involves swapping identical components, such as printed circuit boards or integrated circuits, between two systems to observe if the fault transfers. If it does, the faulty component can be identified quickly. This approach is essentially a variation of the spare parts replacement method, so similar precautions apply, including checking compatibility and ensuring proper installation.
6. Parameter Inspection Method CNC parameters play a crucial role in system performance. These parameters are stored in memory and can be lost or altered due to battery failure, electrical interference, or long periods of inactivity. Correcting these parameters can often restore normal operation. Regular checks and updates are necessary, especially after prolonged downtime or when unexplained issues arise without alarm signals. Adjustments may also be required due to wear or changes in system components over time.
7. Measurement and Comparison Method Manufacturers often include test points on PCBs to facilitate troubleshooting. By comparing voltages and waveforms between a working and a faulty board, technicians can pinpoint the source of the issue. In some cases, artificial faults may be created on a functioning board (e.g., by disconnecting or shorting components) to simulate real-world conditions. Maintaining records of normal readings is essential, as manufacturers rarely provide this information.
8. Tapping Method If a fault appears intermittently, gently tapping suspected areas with a non-conductive tool can help locate the issue. This method is effective because poor solder joints or loose connections can cause intermittent failures. Tapping may trigger the fault, revealing the problematic component.
9. Local Heating Method Over time, components may degrade without fully failing. Using a hair dryer or soldering iron to heat up suspected parts can accelerate aging and expose the faulty component. However, care must be taken to avoid overheating and damaging good parts.
10. Principle Analysis Method By understanding the system’s design and analyzing logic levels, voltage values, and waveforms, technicians can logically diagnose faults. This method requires in-depth knowledge of the system’s architecture and the ability to interpret measurements from tools like multimeters, oscilloscopes, and logic analyzers.
11. Integrated Mechanical, Electrical, and Fluid Analysis Method CNC machines combine mechanical, electrical, and fluid systems. Diagnosing faults from multiple perspectives ensures a comprehensive approach, avoiding misdiagnosis. Identifying which system is at fault allows for targeted troubleshooting and faster resolution.
In addition to the above methods, techniques such as drawing analysis, voltage pull, and open-loop detection are also used. Each method has its strengths, and combining them based on the fault symptoms improves efficiency. By applying these techniques flexibly, technicians can quickly narrow down the fault and restore machine functionality.
CNC machines integrate mechanical, electrical, hydraulic, and electronic technologies. Therefore, focusing on key interface points between these systems is vital for efficient fault diagnosis. When a fault is suspected, it is important to determine whether it originates from the CNC system, PLC, MT, or hydraulic components. If spare parts are unavailable, emergency measures such as component borrowing can be employed. For example, unused sections of a faulty IC can be repurposed to keep the machine running temporarily. This involves cutting off damaged pins and rerouting signals to functional ones, allowing the machine to resume operation quickly.
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