Experience in fault diagnosis of CNC machining center

With the development of computer technology, the offline diagnosis software of modern CNC is gradually integrated with CNC control software, and some systems have introduced “expert system” into fault diagnosis. This undoubtedly brings convenience to the maintenance and diagnosis of CNC machining center. With this software, the operator can diagnose the faults of CNC systems or machine tools by doing some simple session operations on THE MDI/CRT. Next xiaobian sorted out a set of self-diagnosis methods, CNC master years of work experience, very valuable worth collecting.

(1) Self-diagnosis on startup
The so-called startup self-diagnosis refers to the diagnosis automatically performed by the system internal diagnostic program when the exponential control system is powered on, which is similar to the startup diagnosis of a computer. Boot self-diagnosis can automatically check the key hardware in the system, such as CPU, memory, I/O unit, MDI/CRT unit, tape reader, floppy drive and other devices. Determine the installation, connection status and performance of specified equipment; Some systems can also diagnose some important chips, such as RAM, ROM, dedicated LSI, etc.

The self-diagnosis of CNC system is carried out when the machine is started. Only when all items are confirmed, can it enter the normal operation state. The diagnosis time depends on the NUMERICAL control system, usually only a few seconds, but some need a few minutes.

(2) Online monitoring
Online monitoring can be divided into CNC internal program monitoring and monitoring through external equipment in two forms. CNC internal program monitoring is a method of automatic diagnosis, inspection and monitoring of various parts of the state through the system internal program. The scope of online monitoring includes CNC itself and the servo unit, servo motor, spindle servo unit, spindle motor and external equipment connected to CNC. Online monitoring is always effective during the working process of the system. Numerical control system internal program monitoring includes interface signal display, internal state display and fault display.

(3) Interface signal display
It can display the current status of all interface signals between CNC and PLC, CNC and machine tools. Indicates on/off status of digital input/output signals to aid in fault analysis. Maintenance, it is necessary to understand the meaning of each signal between CNC and PLC, CNC and machine tool, as well as the various conditions that signal generation and cancellation should have, so as to carry out corresponding inspection. The “function manual” and “connection manual” provided by the NC system manufacturer and the “electrical schematic diagram of machine tool” provided by the machining center manufacturer are the technical guidelines for the above state inspection.

(4) Internal state display
In general, using the internal state display function, you can display the following aspects: the external cause of the loop instruction (process) not executing
For example: whether the CNC system is in the “in-place inspection”; Whether it is in the “machine locked” state; Whether the signal is connected in “waiting for speed to arrive”; Whether to wait for the measuring signal of “position encoder” when the spindle is programmed every turn; During thread cutting, waiting for “spindle 1 turn signal”; Whether the feed rate is set to 0, etc.

(5) Fault information display
In numerical control system, fault information is generally displayed on CRT in the form of “alarm display”. The contents of alarm display are different according to the nc system. Most of these information in the form of “alarm number” plus text, the specific content and elimination methods in the CNC system manufacturer provided by the “maintenance manual” can be consulted. Through external equipment monitoring refers to the use of computers, PLC programmers and other equipment, the state of each part of the CNC machine tool for automatic diagnosis, inspection and monitoring of a method.
Such as: through the computer, PLC programmer to PLC program in the form of ladder diagram, function diagram dynamic detection, it can be in the machine tool manufacturers did not provide PLC program, PLC program reading, inspection, so as to speed up the maintenance progress of CNC machine tools.

(6) Offline test
Offline testing is also called “offline diagnosis”, which is the test and inspection of the CNC system itself after the CNC system is separated from the machine tool. The system fault can be further located through off-line testing, and the fault range can be minimized. Off-line testing of CNC systems requires special diagnostic software or special testing equipment, so it can only be carried out in CNC system manufacturers or special maintenance departments.

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