Seven methods for fault diagnosis of CNC machine tools
CNC machine tools are very complex systems involving multiple application disciplines. In addition, the CNC system and the machine tool itself have a wide variety of functions and functions. It is impossible to find a general 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 applied.
1. Self-diagnostic function method Although the modern numerical control system has not yet reached a high degree of intelligence, it has already possessed a strong self-diagnosis function. The hardware and software of the CNC system can be monitored at any time. Once an anomaly is detected, an alarm message is displayed on the CRT or the LED is used to indicate the approximate cause of the fault. The self-diagnosis function can also display the status of the interface signal between the system and the host to determine whether the fault occurred in the mechanical part or the CNC system. This method is one of the most effective methods of current maintenance work.
2. Functional program test method The so-called function program test method is to use the manual function or special programming method of the common functions and special functions of the numerical control system, such as linear positioning, circular interpolation, spiral cutting, fixed cycle, user macro program, etc. The function test program is input into the numerical control system, and then the numerical control system is started to operate, thereby checking the accuracy and reliability of the machine performing these functions, thereby judging the possible cause of the failure. This method is difficult to determine whether it is a programming error or an operation error, or a machine fault, for the long-time idle CNC machine inspection when the machine is turned on for the first time and the machine tool processing causes waste without alarm. The method of judgment.
3. Isolation method Isolation method is to break some control loops to reduce the search for fault areas. Example: In a machining center, in the JOG mode, the feed is stable, but the automatic is not normal. First of all, to determine whether it is an NC fault or a servo system fault, first disconnect the servo speed reference signal, use the battery voltage as a signal, the fault remains, indicating that the NC system has no problem. Further inspection revealed that the Y-axis clamping device had failed.
4. Local heating method After the long-term operation of the CNC system, the components are aging and the performance will deteriorate. When they are not completely damaged, the failures that occur will become unavailable sometimes. At this time, a hot hair dryer or a soldering iron can be used to locally heat up the suspected components to 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, do not burn the original good devices.
5. Knocking method When the failure of the CNC system is manifested as sometimes, there is no time. 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, each of which has many solder joints. The inter-board or module is connected by connectors and wires. Therefore, any solder joint or poor contact may cause a malfunction. When the insulator is used to gently tap the suspected point of solder joint and poor contact, the fault will be repeated repeatedly. If it occurs, the tap is likely to be the fault location.
6. Contrast method When the CNC system manufacturer designs the printed circuit board, a plurality of detection terminals are designed on the printed circuit board for the convenience of adjustment and maintenance. Users can also use these terminals to compare 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 to analyze the cause of the fault and the location of the fault. It is sometimes possible to artificially create "faults" on normal printed circuit boards, such as disconnecting or shorting, unplugging components, etc., to determine the cause of a true fault. To this end, the maintenance personnel should accumulate the correct waveform and voltage value of the key parts of the printed circuit board or the faulty parts at normal times. Because CNC system manufacturers often do not provide information on this.
7. Diagnosing with the alarm number Using the alarm number for fault diagnosis is one of the main methods for fault diagnosis of CNC machine tools. If the machine tool fails and the alarm number is displayed on the CRT, the corresponding analysis and diagnosis should be performed according to the content of the alarm number. The maintenance personnel can analyze according to the phenomenon indicated by the alarm number, narrow the scope of the inspection, and conduct a certain inspection in a targeted manner. 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 test methods, there are also drawing method, voltage pull method, open loop detection method and so on. Including the above mentioned diagnostic methods, all of these inspection methods have their own characteristics. According to different fault phenomena, several methods can be selected at the same time for flexible application. Comprehensive analysis of faults can gradually reduce the fault range and eliminate faults faster. . Once the fault location is found, but there is no spare parts available at hand, the transplant borrowing method can be used as an emergency measure.
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