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Examples of commonly used numerical control equipment fault detection methods
In today's rapidly evolving industrial landscape, the application of numerical control (NC) equipment is becoming increasingly widespread. Ensuring the efficient and effective use of such equipment is crucial for maintaining productivity and minimizing downtime. When a failure occurs, it's essential to restore the machine to normal operation as quickly as possible. To achieve this, maintenance personnel must be well-trained and equipped with both technical expertise and practical skills.
Maintenance staff should not only possess in-depth knowledge in areas like electromechanical integration, computer principles, NC technology, PLC systems, automatic control, motor drives, and hydraulic systems, but also have a solid understanding of machining processes and basic NC programming. In addition, they need a good command of English to read and interpret technical documentation. They must also have access to essential information, such as machine diagrams, electrical schematics, parameter backups, system manuals, and PLC ladder logic. Having an inventory of spare parts is equally important for quick repairs.
Moreover, experienced maintenance technicians should be familiar with various troubleshooting techniques. The author has spent many years working on NC equipment and has developed a set of effective maintenance methods, which are outlined below for reference.
**Identifying the Fault Phenomenon**
When a CNC machine fails, the first step is to thoroughly understand the fault. It's important to communicate with the operator to learn when the issue first occurred, what conditions were present, and how the problem manifested. Observing the fault during operation can provide valuable clues. Understanding the exact nature of the problem is key to resolving it efficiently. Once the issue is clearly defined, the technician can use the machine's working principles and the NC system’s functionality to diagnose and fix the problem effectively.
For example, consider a CNC cylindrical grinder using the American Bryant TEACHABLE III system. During automatic machining, the grinding wheel dresser broke off. To analyze the situation, the grinding wheel was removed, and the machine was run again. The fault was observed: while the grinding process was normal, the dressing action caused the dresser to move too quickly and hit the upper limit switch. By analyzing the E-axis movement and its position feedback, it became clear that there was a discrepancy between the displayed and actual positions. After checking the encoder and control board without success, further testing revealed that the reference point and swing mechanism were functioning correctly under certain conditions. Using the system’s alarm data helped pinpoint the issue.
Modern NC systems are now equipped with advanced self-diagnosis capabilities. Most systems can detect faults and respond accordingly, such as by stopping the machine or displaying an alarm. These alarms may appear on the screen or be indicated through the NC unit, PLC, or drive system. By consulting the manual and analyzing the alarm information, technicians can often identify the root cause directly. For instance, a CNC channel grinder using the Siemens 810 system displayed the alarm “BATTERY ALARM POWER SUPPLY†upon startup. This clearly indicated a dead backup battery, which was replaced while the system was still powered. The machine was then reset and returned to service.
Another case involved a Siemens 3 system where no display appeared after powering on. Upon inspection, a blinking LED on the CPU board was noted. By analyzing the blink frequency, it was determined that the power supply voltage was low. Replacing the battery resolved the issue, and the system resumed normal operation.
In some cases, the alarm message does not directly indicate the root cause but reflects the consequences of the fault. In such situations, careful analysis and hands-on inspection are necessary. For example, a FANUC 0TC-controlled lathe displayed alarm number 2043: “HYD. PRESSURE DOWN,†indicating low hydraulic pressure. After inspecting the hydraulic system and adjusting the pressure, the machine was restored to full functionality.
Some faults do not trigger any alarms, making them more challenging to detect. In these cases, systematic testing and experience become invaluable tools for identifying and resolving the issue.