Electrical fault diagnosis and maintenance of CNC machine tools (2)

3.2 CNC machine tool simple fault alarm processing method.

Generally, the CNC machine tool has a strong self-alarm function, which can monitor the working state of the system hardware and software at any time. Most of the faults of the CNC machine tool can be alarmed. The fault of the machine tool can be determined according to the fault prompt, and the fault can be processed and eliminated in time. Machine integrity and efficiency.

3.3 Direct observation method.

The direct observation method is a method of using a human sensory organ to pay attention to various external phenomena at the time of failure (or after a failure) and to determine possible parts of the failure. This is the primary entry point for dealing with CNC system faults, and is often the most direct and effective method. For the simple case, the "simple" fault can solve the problem through this direct observation.

3.4 Method of judging the fault by using the status display diagnostic function.

Modern CNC systems not only display fault diagnosis information, but also provide diagnostic status in the form of diagnostic addresses and diagnostic data.

3.5 The method of judging the fault of the numerical control system parameters in time for failure.

The parameter changes of the numerical control system of the CNC machine tool will directly affect the performance of the CNC machine tool, causing the CNC machine tool to malfunction, and even the whole machine can not work normally. Therefore, in the process of analyzing and diagnosing the fault, although some measures have been taken, the problem cannot be solved, the fault is eliminated, or the fault is not clear enough, the idea should be changed, starting from what people call a "soft" fault. Checking the parameters of the CNC system is because the fault caused by the change of the parameters of the CNC system is often a slight anomaly, which is the crux of the problem.

4 fault examples

4.1 CNC machine chip conveyor fault analysis and improvement.

After the field worker removes the motor and conducts trial operation, the result shows that the operation is normal, so the cause of the motor failure can be eliminated, and the key on the motor drive shaft can be observed not on the keyway, so the direct cause of the fault can be initially diagnosed. For the motor shaft to separate from the chip auger, further analysis, because the transmission key is subjected to the instantaneous and constant force of the load, if the transmission key is divided at this time, each part of the segment can be regarded as a beam, so it can be It performs vibration analysis and its force is as shown in Figure 1:

After the analysis of the force situation, the transmission key has the condition of fretting wear, so the wear of the transmission key is fretting wear, and the search reveals that the key has fallen into the hole of the screw rod, and it can be concluded that the key is intact and only slightly worn, so It can eliminate the key crushing and the cause of the key wear. Finally, it can be concluded that the direct cause of the fault is that the key is detached, causing the spiral chip removing rod to disengage from the motor shaft and losing the driving force. After the key is installed and the motor is reassembled, the troubleshooting works fine.

4.2 Vibration and creep processing of CNC machine tools.

The oscillation phenomenon of the numerical control system has become a common problem of the numerical control full-closed system. When the system oscillates, it will cause crawling and vibration faults in the machine. The oscillation fault of the machine usually occurs in the mechanical part and the feed servo system. There are many reasons for the oscillation. In addition to the mechanical non-removable transmission gap, elastic deformation, frictional resistance and other factors, the influence of the relevant parameters of the servo system is also an important aspect. Sometimes the numerical control system will generate high-frequency harmonics in the feedback signal due to some oscillations in the expansion, which makes the output torque undetermined and generates vibration. For this high-frequency oscillation, a first-order low-pass filter can be added to the speed loop, which is a torque filter.

The speed command and the speed feedback signal are converted into a torque signal by the speed controller, and the torque signal is cut off by the first-order filtering link to obtain an effective torque control signal. By adjusting the parameters, the mechanically generated frequencies above 100 Hz can be cut off, thereby achieving the effect of eliminating high frequency oscillations.

5 Troubleshooting and aftercare work

After the troubleshooting, the maintenance work can not be completed. It is necessary to analyze the deep-seated causes of the fault from the technical and management aspects, and take appropriate measures to prevent the fault from happening again. If necessary, the equipment can be modified and improved according to the site conditions using mature technology. Confirmation of troubleshooting, troubleshooting completed. Finish the line, test all the movements of the machine, and then deliver it normally, and let the operator continue to observe the operation. After a period of time, ask about the operating conditions of the operator's machine tool and perform a full inspection of the point of failure again. Finally, make a maintenance record, detailing the entire process of maintenance, including repair time, replacement part model specifications and failure cause analysis. Find out what you lack from the process of troubleshooting, develop a learning plan, and finally enrich yourself.

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