Machining Material

Summary of the CNC machine tools fault diagnosis technology

Summary of the CNC machine tools fault diagnosis technology

The numerical control system is a high-tech intensive product. In order to quickly and correctly identify the cause and determine the location of its failure, it is necessary to resort to diagnostic technology. With the continuous development of microprocessors, diagnostic technology has also evolved from simple diagnosis to multifunctional advanced diagnosis or intelligentization. The strength of the diagnosis ability is also an important indicator to evaluate the performance of CNC numerical control system. The diagnostic techniques of various CNC systems currently used can be roughly divided into the following categories:

1. Online diagnosis

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 system and the CNC device when the system is in normal operation through the built-in program of the CNC system. As long as the system is not powered off, online diagnostics will not stop.

Online diagnostics generally include thousands of status displays for self-diagnostic functions, often displaying their status in binary 0 and 1. For positive logic, 0 represents the off state and 1 represents the on state. The status display can be used to determine the location of the fault. Commonly used are interface status and internal status display, such as the use of I/O interface status display, combined with PLC ladder diagram and strong power control circuit diagram, and the true location of the fault point can be determined by reasoning and elimination. The fault information mostly appears in the form of alarm number. Generally, it can be divided into the following categories: overheat alarm; system alarm; storage alarm; programming/setting; servo; travel switch alarm; connection fault between printed circuit boards.

2. Starting diagnosis

Start-up diagnosis means that every time the CNC system starts from power-on, the system’s internal diagnosis program automatically performs diagnosis. The diagnosis content 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 unit, paper tape reader, floppy disk unit and other devices or external equipment. Only after all items are confirmed to be correct, the whole system can enter the preparation state for normal operation. Otherwise, the fault information will be indicated on the CRT screen or LED by means of alarm. At this time, the startup diagnosis process cannot be ended, and the system cannot be put into operation.

3. Offline diagnosis

Offline diagnosis is that after the index control system fails, the CNC system manufacturer or professional maintenance center uses special diagnostic software and test equipment to perform shutdown (or offline) inspection. Strive to locate the fault as small as possible, such as narrowing down to a certain functional module, a certain part of the circuit, or even a certain chip or component, this fault location is more accurate.

4. Modern diagnostic technology

With the development of telecommunication technology, the cost-effectiveness of ICs and microcomputers has improved. In recent years, foreign countries have successfully introduced some new concepts and methods into the field of diagnosis.

(1) Self-healing system

That is, a backup module is set in the system, and a self-repair program is installed in the software of the CNC system. When a module is found to be faulty when the software is running, the system displays the fault information on the CRT on the one hand and automatically finds it Whether there is a spare module, if there is a spare module, the system can automatically take the fault offline, and turning on the spare module enables the system to enter the normal working state quickly. This kind of scheme is suitable for unmanned automated work occasions.

It should be noted that there are some faults in the actual use of the machine tool without alarm, and the phenomenon is not very obvious. For this situation, handling it is not that simple.

(2) Communication diagnosis

Also called remote diagnosis, that is, use the telephone communication line to connect the faulty CNC system and the special communication diagnosis computer of the professional maintenance center to test and diagnose. For example, Siemens has adopted this kind of diagnosis function in the diagnosis of CNC system. 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 of the maintenance center of the two subsidiaries It is also connected to the telephone line, and then the computer sends a diagnostic program to the CNC system, and the test data is returned to the computer for analysis and conclusion, and then the user is informed of the diagnosis conclusion and processing methods.

The communication diagnosis system can also make regular preventive diagnosis for users. Maintenance personnel do not need to visit the site in person. They only need to perform a series of running inspections on the machine tool at the scheduled time. The diagnosis data can be analyzed in the maintenance center to find the hidden troubles of the fault, so as to early Take measures. Of course, this type of CNC system must have a remote diagnostic interface and networking capabilities.

In addition, after this equipment fails, not only does it have no alarm information, but also lacks the information needed for maintenance. For the diagnosis and treatment of this type of fault, you must carefully check it according to the specific situation, analyze from the slightest part of the phenomenon, and find out its true 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.

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