Seven methods for fault diagnosis of CNC machine tools

CNC machine tools are very complex systems involving multiple application disciplines. In addition, there are many types of CNC systems and machine tools themselves 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 actual fault diagnosis, these methods should be used comprehensively.

1. Self-diagnosis function method Although the modern numerical control system has not yet reached a high degree of intelligence, it already has a strong self-diagnosis function. It can monitor the working status 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 approximate cause of the failure. The self-diagnosis function can also display the status of the interface signal between the system and the host computer, thereby determining 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, arc interpolation, spiral cutting, fixed cycles, user macro programs, etc., into a program using manual programming or automatic programming methods. The functional test program is input into the CNC system, and then the CNC system is started to run to check the accuracy and reliability of the machine tool in executing these functions, and then determine the possible cause of the failure. This method is a better method for inspecting CNC machine tools that have been idle for a long time when they are first turned on and when machine tool processing results in scrap but no alarm. It is difficult to determine whether it is a programming error or an operating error, or the cause of the machine tool failure. method of judgment.

3. Isolation method The isolation method is to disconnect some control loops, so as to achieve the purpose of narrowing down the fault area. Example: In a machining center, in JOG mode, the feed is stable, but the automatic is not normal. First of all, it is necessary to determine whether it is an NC fault or a servo system fault. First, disconnect the servo speed given signal and use the battery voltage as a signal. If the fault persists, it means there is no problem with the NC system. Further inspection is that the Y-axis clamping device is faulty.

4. Local heating method: After long-term operation of the CNC system, the components will age and the performance will deteriorate. While they are not completely broken, the failures can become sporadic. At this time, a hot hair dryer or soldering iron can be used to locally heat the suspected component and accelerate its aging, so as to completely expose the faulty component. Of course, when using this method, you must pay attention to the temperature parameters of the components and do not bake out the original good components.

5. Knocking method: When the fault of the CNC system is intermittent, the tapping 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. Boards or modules are connected through connectors and wires. Therefore, any weak soldering or poor contact may cause failure. If you tap lightly with an insulator on suspected spots with weak soldering or poor contact, the fault will definitely recur. If it does, the tapped spot is likely to be the fault location.

6． Comparison method When designing the printed circuit board, the CNC system manufacturer designed multiple detection terminals on the printed circuit board 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 measurement terminals can be detected, and the cause and 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 real fault. For this reason, maintenance personnel should accumulate the correct waveforms and voltage values of key parts or fault-prone parts of the printed circuit board during normal times. Because CNC system manufacturers often do not provide relevant information in this regard.

7. Diagnosis using alarm numbers Using alarm numbers for fault diagnosis is one of the main methods of fault diagnosis for CNC machine tools. If a machine tool fails and an alarm number is displayed on the CRT, the corresponding analysis and diagnosis must first be carried out 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 certain aspects 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 status of the travel switch (or proximity switch) is incorrect. In addition to the above commonly used fault inspection and testing methods, there are also board pulling method, voltage bias pulling method, open loop detection method and so on. Including the diagnostic methods mentioned above, 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. Only by comprehensive analysis of the fault can the scope of the fault be gradually narrowed and the fault eliminated quickly. . Once the faulty part is found, but there are no replaceable spare parts at hand, it can be solved by transplanting and borrowing as an emergency measure.