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Examples of commonly used numerical control equipment fault detection methods
Nowadays, the use of numerical control (NC) equipment is becoming increasingly widespread across various industries. Ensuring the efficient and effective operation of such equipment is essential for maintaining productivity and minimizing downtime. When a failure occurs, it is crucial to restore the machine to normal function as quickly as possible. To achieve this, maintenance personnel must be well-trained and highly skilled. They should not only possess in-depth knowledge in areas like electromechanical integration, computer principles, NC technology, PLC systems, automatic control, motor drive principles, and hydraulic systems, but also have a solid understanding of machining processes and basic NC programming. Additionally, they need to be proficient in English to read technical documentation and communicate effectively with international suppliers or manufacturers.
Maintaining up-to-date information is equally important. This includes having access to machine diagrams, electrical schematics, system manuals, PLC ladder logic, and backup parameters. A stock of spare parts should also be available to reduce repair time. Moreover, maintenance technicians must have practical experience and be familiar with common troubleshooting techniques. Having hands-on skills allows them to diagnose and resolve issues efficiently.
Having worked in NC equipment maintenance for many years, I have developed a systematic approach to identifying and solving problems. Below are some key steps that can help in the process of fault diagnosis and resolution.
**Identifying the Fault Phenomenon**
When an NC machine fails, the first step is to understand the symptoms. It's important to speak with the operator who noticed the problem and observe the situation if possible. Documenting when and how the failure occurred, as well as its consequences, helps in narrowing down the root cause. A clear understanding of the issue makes half the battle won. Once the phenomenon is identified, the technician can analyze the machine’s working principle and NC system to locate the problem quickly and restore the equipment to normal operation.
For example, during the operation of a CNC cylindrical grinder using the American Bryant TEACHABLE III system, the grinding wheel dresser broke off during automatic machining. To investigate the failure and prevent it from happening again, the grinding wheel was removed, and the machine was run without it. The failure was observed: the grinding process was normal, but after the workpiece was finished, the dressing process caused the dresser to rotate rapidly and hit the upper limit switch. If the grinding wheel had not been removed, it would have collided with the dresser. By analyzing the machine’s mechanism, we found that the E-axis servo motor drives the dresser, and a rotary encoder provides position feedback. Normally, the Z-axis moves the dresser into position, and it swings 30° to 120° to dress the wheel. However, during the failure, the E-axis screen showed about 60°, while the actual position was around 180°. This indicated a feedback error, but neither the control board nor the encoder was at fault. After repeated observations, we discovered that the reference point was correct when the dresser was near the Z-axis, but the issue occurred when it reached the edge. Using the system’s alarm information helped us confirm the problem.
Modern NC systems now have advanced self-diagnostic capabilities. Most faults can be detected by the system, which may trigger alarms, shut down, or display error messages. These alarms often provide direct clues to the cause of the problem. For instance, a CNC channel grinder using the German SIEMENS 810 system displayed the alarm “BATTERY ALARM POWER SUPPLY†upon startup, clearly indicating a dead battery. Replacing the battery while the system was live resolved the issue. In another case, a SIEMENS 3 system did not show any display on startup. Checking the CPU board revealed a blinking LED, which, after analyzing the frequency, confirmed low power supply voltage. Replacing the battery fixed the problem.
Another example involved a FANUC 0TC system NC lathe that displayed alarm No. 2043: “HYD. PRESSURE DOWN,†indicating low hydraulic pressure. Inspecting the hydraulic system confirmed the issue, and adjusting the pressure restored the machine to normal operation.
However, not all alarms directly indicate the root cause. Some only reflect the result of the failure or other related issues. In such cases, careful analysis and inspection are necessary. Techniques like checking system logs, testing components, and comparing expected vs. actual performance can be very effective. These methods are particularly useful for diagnosing faults that do not trigger alarms. With experience and proper training, maintenance technicians can quickly identify and resolve complex issues, ensuring minimal disruption to production.