2. Machinery precedes electricity
Generally speaking, mechanical faults are easy to find, while the diagnosis of numerical control system and electrical faults is difficult. Before troubleshooting, first pay attention to eliminating mechanical faults.
3. Static before dynamic
First, understand, observe, test and analyze the static state of machine tool power failure, and confirm that it will not cause fault expansion and accidents after power failure, and then power on the machine tool. In the running state, dynamic observation, inspection and testing are carried out to find faults. However, if a crushing failure occurs after power-on, the danger can only be eliminated before power-on.
Second, the fault diagnosis technology of CNC machine tools
Numerical control system is a high-tech intensive product, and diagnostic ability is also an important index to evaluate the performance of DND numerical control system. At present, the diagnostic techniques of various DND systems can be roughly divided into the following categories:
1. Start diagnosis.
Boot diagnosis means that every time the DND system is booted, the diagnostic steps inside the system will automatically diagnose. The content of diagnosis is the most critical hardware and system control software in the system, such as DPU, memory, I/O and other unit modules, as well as MDI/DRT units, paper tape readers, floppy disk units and other devices or external devices. Only when all the items are confirmed to be correct can the whole system enter the state of preparation for normal operation. Otherwise, the fault will be indicated by an alarm on the DRT screen or LED. At this point, the process of starting diagnosis cannot be finished, and the system cannot be put into operation.
2. Online diagnosis
On-line diagnosis refers to the active diagnosis and inspection of the DND system itself and various servo units, servo motors, spindle servo units, spindle motors and external devices connected to DND equipment when the system is in normal operation. As long as the system is not powered off, online diagnosis will not stop.
3. Off-line diagnosis
Off-line diagnosis refers to the shutdown (or off-line) inspection by the CNC system manufacturer or professional maintenance center using special diagnostic software and test device after the CNC system fails. Try to locate the fault on the smallest possible scale, such as from large to small to a functional module, a part of the circuit, or even a chip or component, which is more accurate.
Three, the common troubleshooting methods of CNC machine tools
Because the faults of CNC machine tools are complex, and the self-diagnosis ability of CNC system can't detect all parts of the system, it is often difficult to explain many fault reasons from an alarm number. The following introduces the troubleshooting methods commonly used by maintenance personnel in production practice.
1. Visual inspection method
Visual inspection method is to determine the scale of the fault according to the observation of various abnormal signs such as light, sound and smell when the fault occurs, which can reduce the scale of the fault from large to a module or a circuit board and then eliminate it. Generally include:
(1) Inquiry: Ask the personnel at the scene of the fault carefully about the process, symptoms and consequences of the fault;
(2) Appearance inspection: generally check whether the working conditions of all parts of the machine tool are normal, whether the electric control device has alarm instructions, and locally check whether there is any safety burn, whether the parts have burns, cracks, wires and cables falling off, and whether the positions of all operating parts are correct;
(3) Touch: In the case of power failure of the whole machine, some faults such as broken feet, virtual welding and poor contact occur. It can be detected by touching the installation state of each main circuit board, the plugging state of each plug and socket, the connection state of each power supply and signal line, and the loose feeling of touching and shaking components by hand;
(4) Power-on: Power-on is used to check whether there is smoke, ignition, abnormal sound and peculiar smell, and whether there is overheating of motor and components when touching. Once found, power-off is immediately analyzed. If there is a comminuted fault, it must be eliminated before electrifying.
2. Initialization and reset methods
In general, the system alarm caused by instantaneous fault can be cleared by hardware reset or switching the system power supply in turn. If the working storage area of the system is chaotic due to power failure, plug-in circuit board or battery undervoltage, the system must be initialized and cleared, and the numerical copy record should be made before clearing. If the fault cannot be eliminated after initialization, hardware diagnosis should be suspended.
For example, if the CNC lathe presses its own active operation key, the microcomputer refuses to perform the processing steps, and does not display the self-check prompt of the fault, and the display screen is in the reset state (only the menu is displayed). Sometimes the manual and editing functions are normal, and the user's pace and various parameters are completely correct; Sometimes, due to the failure of the memory battery, the replacement of the memory battery, etc. , the system shows that the size in one direction exceeds the standard or all directions are qualified.
(Author: (Shandong Yantai Engineering Vocational and Technical College)