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Fault diagnosis technology of CNC machine tools

Time:2021-07-23 Views:173

Numerical control system is a high-tech intensive product. If you want to quickly and accurately find out the cause and determine the location of its fault, you must rely on diagnostic technology. With the continuous development of microprocessors, diagnosis technology has also evolved from simple diagnosis to multi-functional advanced diagnosis or intelligence. The strength of the diagnostic ability is also an important index to evaluate the performance of the CNC numerical control system. The diagnostic techniques of various CNC systems currently in use can be roughly divided into the following categories:

Start diagnosis

Startup diagnosis means that every time the CNC system is powered on, the internal diagnosis program of the system will automatically perform the diagnosis. The content of the diagnosis is the most critical hardware and system control software in the system, such as CPU, memory, I/O and other unit modules, as well as MDI/CRT units, tape readers, floppy disk units and other devices or external equipment. Only when all items are confirmed to be correct, the entire system can enter the ready state for normal operation. Otherwise, the fault information will be indicated on the CRT screen or light-emitting diode in an alarm mode. At this time, the start-up diagnosis process cannot be ended, and the system cannot be put into operation. 2.2 Online diagnosis

Fault diagnosis technology of CNC machine tools(图1)

Online diagnosis refers to the automatic diagnosis and inspection of the CNC system itself and each servo unit, servo motor, spindle servo unit and spindle motor and external equipment connected to the CNC device when the system is in normal operation through the built-in program of the CNC system. As long as the system does not power off, the online diagnosis will not stop.

On-line diagnosis generally includes thousands of status displays of self-diagnosis functions, and the status is often displayed with binary 0 and 1. For positive logic, 0 represents the off state, 1 represents the on state, and the location of the fault can be judged with the help of the status display. Commonly used are interface status and internal status display, such as using I/O interface status display, combined with PLC ladder diagram and strong current control circuit diagram, and using reasoning and elimination methods to determine the true location of the fault point. Most of the fault information appears in the form of an alarm number. Generally can be divided into the following categories: overheating alarm type; system alarm type; storage alarm type; programming/setting type; servo type; travel switch alarm type; connection failure type between printed circuit boards.

Offline diagnosis

Offline diagnosis means that after the index control system fails, the CNC system manufacturer or professional maintenance center uses special diagnostic software and testing devices to shut down (or offline) for inspection. Strive to locate the fault to the smallest possible range, such as narrowing it down to a certain functional module, a certain part of a circuit, or even a certain chip or component, this kind of fault location is more accurate.

Modern diagnostic technology

With the development of telecommunications technology and the improvement of IC and microcomputer cost performance, some new concepts and methods have been successfully applied to the field of diagnosis in foreign countries in recent years.

Communication diagnosis

It is also called remote diagnosis, that is, the CNC system with the fault is connected to the special communication diagnosis computer of the professional maintenance center through the telephone communication line for testing and diagnosis. For example, Siemens uses this diagnostic function in the CNC system diagnosis. The user connects the special "communication interface" in the CNC system to the ordinary telephone line, and the "data phone" of the special communication diagnosis computer in the maintenance center of the two subsidiaries It is also connected to the telephone line, and then the computer sends the diagnostic program to the CNC system, and the test data is sent back to the computer for analysis and conclusions, and then the user is notified of the diagnostic conclusions and handling methods.

The communication diagnosis system can also make regular preventive diagnosis for users. The maintenance personnel do not need to visit the site in person, but only need to perform a series of operation checks on the machine tool at a predetermined time. The diagnosis data can be analyzed in the maintenance center to find hidden faults in order to facilitate early Take measures. Of course, this type of CNC system must have a remote diagnostic interface and networking capabilities.

Self-healing system

It means that there is a spare module in the system, and a self-repairing program is installed in the software of the CNC system. When the software is running, once a module is found to be faulty, the system will display the fault information on the CRT on the one hand and automatically search for it. Whether there is a spare module, if there is a spare module, the system can automatically take the fault offline, and the spare module can be connected so that the system can quickly enter the normal working state. This kind of scheme is suitable for unmanned automated workplaces.

It should be noted that there are some faults in the actual use of the machine tool, and there is no alarm, and the phenomenon is not very obvious. For this situation, it is not that simple to deal with. In addition, after this equipment fails, not only there is no alarm information, but also the information required for maintenance is lacking. The diagnosis and treatment of this type of failure must be carefully checked according to the specific situation, analyzed from the subtleties of the phenomenon, and found out the real cause. To find out the cause of this type of failure, we must first find its true failure phenomenon from various surface phenomena, and then find out the cause of the occurrence from the confirmed failure phenomenon. A comprehensive analysis of a fault phenomenon is an important factor in determining whether the judgment is correct. Before finding the cause of the fault, you must first understand the following conditions: whether the fault occurred during normal operation or just after the start of the machine; whether the number of times of Shanxian occurred for the first time or has occurred multiple times; confirm the correctness of the machine tool processing program; whether there is any other people

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