Seven methods for fault diagnosis of CNC machine tools

Numerical control machine tools are very complex systems involving multiple application disciplines. In addition to the wide variety of numerical control systems and machine tools, with different functions, it is impossible to find a universal diagnostic method suitable for all CNC machine tools and all types of faults. Here we only introduce some commonly used general methods, these methods are related to each other, in the actual fault diagnosis, these methods should be comprehensively used.

1. Self-diagnosis function method Although modern numerical control systems have not yet reached a high degree of intelligence, they already have strong self-diagnosis functions. It can monitor the working conditions of the hardware and software of the CNC system at any time. Once an abnormality is found, immediately display an alarm message on the CRT or use a light-emitting diode to indicate the general cause of the failure. With the self-diagnosis function, the status of the interface signal between the system and the host can also be displayed, so as to determine whether the fault occurs in the mechanical part or the CNC system part. This method is one of the most effective methods for current maintenance work.

2. Functional program testing method The so-called functional program testing method is to compile the common functions and special functions of the CNC system, such as linear positioning, circular interpolation, spiral cutting, canned cycles, user macro programs, etc., into a manual or automatic programming method. The function test program is input into the numerical control system, and then the numerical control system is started to run, so as to check the accuracy and reliability of the machine tool to perform these functions, and then determine the possible cause of the failure. This method is better for the inspection when the CNC machine tool is idle for a long time when it is turned on for the first time and when the machine tool processing causes waste but no alarm, it is difficult to determine whether it is a programming error or an operation error, or the cause of the machine failure. This is a good idea. Method of judgment.

3. Isolation method Isolation method is to disconnect some control loops, so as to achieve the purpose of narrowing the fault area. Example: In a machining center, in the JOG mode, the feed is stable, but the automatic is abnormal. First of all, determine whether it is NC failure or servo system failure. First, disconnect the servo speed reference signal and use battery voltage as the signal. The failure remains, indicating that there is no problem with the NC system. Further inspection is that the Y-axis clamping device is malfunctioning.

4. Local heating method After long-term operation of the CNC system, the components will age, and the performance will deteriorate. When they are not completely damaged, the failures that appear will become occasional. At this time, a hot blower or electric soldering iron can be used to locally heat up the suspected components and accelerate their aging, so as to completely expose the faulty components. Of course, when using this method, you must pay attention to the temperature parameters of the components, and do not burn out the original good components.

5. Percussion method When the failure of the CNC system appears sometimes and sometimes, the percussion method can often be used to check the location of the fault. This is because the CNC system is composed of multiple printed circuit boards, and each board has many solder joints. The boards or modules are connected by connectors and wires. Therefore, any false soldering or poor contact may cause malfunctions. When using an insulator to lightly tap the suspected spot with false soldering and poor contact, the fault will definitely reappear. If it occurs, the tapped location is likely to be the faulty location.

6. Contrast Method When designing printed circuit boards, CNC system manufacturers designed multiple detection terminals on the printed circuit boards for the convenience of adjustment and maintenance. Users can also use these terminals to compare and measure the difference between a normal printed circuit board and a faulty printed circuit board. The voltage and waveform of these measuring terminals can be detected, and the cause of the fault and the location of the fault can be analyzed. Sometimes it is even possible to artificially create "faults" on normal printed circuit boards, such as disconnecting or short-circuiting, unplugging components, etc., to determine the cause of the true failure. For this reason, maintenance personnel should accumulate the correct waveforms and voltage values of key parts or fault-prone parts on the printed circuit board at normal times. Because CNC system manufacturers often do not provide relevant information in this regard.

7. Diagnosis using alarm numbers Using alarm numbers to diagnose faults is one of the main methods of fault diagnosis for CNC machine tools. If the machine fails and there is an alarm number displayed on the CRT, firstly, perform corresponding analysis and diagnosis based on the content of the alarm number. Maintenance personnel can analyze the phenomenon pointed out by the alarm number, narrow the scope of inspection, and conduct a certain aspect of inspection purposefully. The alarm number (error code) generally includes the following fault (or error) information: (1) Programming error or operation error; (2) Memory is not working properly; (3) Servo system failure; (4) Programmable control (5) Connection failure; (6) Abnormal temperature, pressure, liquid level, etc.; (7) The state of the travel switch (or proximity switch) is incorrect. In addition to the above-mentioned commonly used fault checking and testing methods, there are pull-out method, voltage pull-off method, open-loop detection method and so on. Including the above-mentioned diagnosis methods, all these inspection methods have their own characteristics. According to different fault phenomena, several methods can be selected and applied flexibly at the same time, and comprehensive analysis of the fault can be carried out to gradually narrow the scope of the fault and eliminate the fault faster. . Once the faulty part is found, but there is no replaceable spare part at hand, the transplantation borrowing method can be used as an emergency measure to solve it.