With the development of computer technology, off-line diagnostic software of modern CNC is gradually integrated with CNC control software. 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 system or machine tool as long as he makes some simple conversational operations on MDI/CRT. Next, Dongguan Kaicheng Precision Hardware Co., Ltd. sorted out a set of self-diagnostic methods. The work experience of CNC master for many years is very valuable and worth collecting.
1. Start-up self-diagnosis
The so-called boot-up self-diagnosis refers to the diagnosis automatically executed by the internal diagnostic program of the system when the CNC system is powered on. It is similar to the computer boot-up diagnosis. Start-up self-diagnosis can automatically check the key hardware in the system, such as CPU, memory, I/O unit, MDI/CRT unit, tape reader, floppy driver, etc. It can determine the installation, connection status and performance of designated equipment. Some systems can also diagnose some important chips, such as RAM, ROM, special LSI, etc.
The self-diagnosis of NC system is carried out at the start of the machine. Only when all the items are confirmed correctly, can they enter the normal operation state. The time of diagnosis depends on the CNC system, usually only a few seconds, but some need several minutes.
2. On-line monitoring
Online monitoring can be divided into two forms: CNC internal program monitoring and external equipment monitoring. CNC internal program monitoring is a method to automatically diagnose, check and monitor the status of each part through the internal program of the system. On-line monitoring scope includes CNC itself and the servo units connected with CNC, servo motors, spindle servo units, spindle motors, external equipment, etc. Online monitoring is always effective in the process of system work. The internal program monitoring of CNC system includes three aspects: interface signal display, internal status 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 the on-off status of digital input/output signals and helps to analyze faults. During maintenance, it is necessary to understand the significance of signals between CNC and PLC, CNC and machine tools, as well as the various conditions for signal generation and cancellation, so as to carry out the corresponding inspection. The "Function Instructions", "Connection Instructions" and "Machine Tool Electrical Principle Diagram" provided by NC System Manufacturers are the technical guides for the above condition checks.
4. Internal status display
Generally speaking, using the internal state display function, the following aspects can be displayed: the external reasons for the non-execution of circular instructions (processing programs)
For example: whether CNC system is in the "in-place check", "latch-in" state; whether it is in the "waiting speed arrival" signal connection; whether it is waiting for the "position encoder" measurement signal when the spindle is programmed; whether it is waiting for the "spindle 1 turning signal" when the thread is cut; whether the feed rate is set to 0, and so on.
5. Fault Information Display
In CNC system, fault information is usually displayed on CRT in the form of "alarm display". The contents of alarm display are different according to the different CNC systems. Most of these information appears in the form of "alarm number" plus text. The specific contents and exclusion methods can be consulted on the "maintenance instructions" provided by CNC system manufacturers. Monitoring through external equipment is a method of automatically diagnosing, inspecting and monitoring the state of various parts of NC machine tools by using computer, PLC programmer and other equipment.
For example, through computer and PLC programmer, the PLC program can be dynamically tested in the form of ladder diagram and function diagram. It can read and check the PLC program when the machine tool manufacturer does not provide the PLC program, so as to speed up the maintenance progress of NC machine tools.
6. Offline Testing
Off-line testing, also known as "off-line diagnosis", is the test and inspection of the CNC system itself after separating the CNC system from the machine tool. Through off-line testing, the fault of the system can be further positioned and the fault scope can be minimized. The off-line test of CNC system needs special diagnostic software or special testing device, so it can only be carried out in the manufacturer or special maintenance department of CNC system.
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