Fault Diagnosis Methods for CNC Machine Tools

Electrical fault diagnosis of CNC machine tools has three stages: fault detection, fault judgment and isolation, and fault location. The first stage of fault detection is to test the CNC machine tool to determine whether there is a fault; the second stage is to determine the nature of the fault and separate the faulty components or modules; the third stage is to locate the fault to a replaceable module or printed circuit board to shorten the repair time. In order to promptly detect faults in the system, quickly determine the location of the fault and eliminate it in time, it is required that the fault diagnosis should be as few and simple as possible, and the time required for fault diagnosis should be as short as possible. To this end, the following diagnostic methods can be used:

1. Intuitive method: Use sensory organs to pay attention to various phenomena when a fault occurs, such as whether there are sparks, bright lights, abnormal sounds, abnormal heat, and burnt smells. Carefully observe the surface condition of each printed circuit board that may have a fault, whether there are signs of burning and damage, to further narrow the scope of inspection. This is the most basic and most commonly used method.

2. Self-diagnosis function of CNC system: Relying on the ability of CNC system to process data quickly, multi-channel and fast signal acquisition and processing are carried out on the error part, and then the diagnostic program performs logical analysis and judgment to determine whether there is a fault in the system and locate the fault in time.

3. Alarm indicator light shows fault: In the CNC system of modern CNC machine tools, in addition to the above-mentioned self-diagnosis function and status display and other "software" alarms, there are many "hardware" alarm indicators, which are distributed on power supply, servo drive and input/output devices. The cause of the fault can be determined according to the indication of these alarm lights.

4. Spare board replacement method: Using spare circuit boards to replace templates with suspected faults is a quick and easy method to determine the cause of the fault. It is often used in functional modules of CNC systems, such as CRT modules, memory modules, etc. It should be noted that before replacing the spare board, the relevant circuits should be checked to avoid damage to the good board due to short circuit. At the same time, the selection switch and jumper wire on the test board should be checked to see if they are consistent with the original template. For some templates, attention should be paid to the adjustment of the potentiometer on the template. After replacing the memory board, the memory should be initialized according to the system requirements, otherwise the system still cannot work properly.

5. Exchange method: In CNC machine tools, there are often modules or units with the same functions. By exchanging the same modules or units and observing the fault transfer, the fault location can be quickly determined. This method is often used for fault inspection of servo feed drive devices, and can also be used for the interchange of the same modules in CNC systems.

6. Tapping method: The CNC system is composed of various circuit boards, and there will be many solder joints on each circuit board. Any false soldering or poor contact may cause a fault. When you gently tap the circuit board, connector or electrical component with a suspected fault with an insulating material, if a fault occurs, the fault is likely to be at the tapped location.