Fault one
One CNC lathe of our company uses Siemens 802D numerical control system, the spindle is controlled by frequency converter, and the gear shift is realized by hydraulic cylinder pushing the gear. A failure occurred during use. The “CNC Start†button of the machine fails; the spindle rotation function is missing; the manual pulse generator fails; the automatic and manual tool change functions are missing. There is no alarm display on the machine panel, there is no alarm for the spindle drive and each feed axis drive, and the machine cannot operate normally.
The author conducted the following tests: 1 The reverse reference point function is normal. 2 “CNC Start†button fails in “Auto†mode and “MDI†mode. 3 The machine tool moves the feed axis normally with the JOG method.
The machine has many faults. According to the principle of easy and difficult, the fault is easier to handle first. The author chooses the fault of the “CNC start†button as a breakthrough. According to the electrical schematic diagram, find the address of the “CNC start†button corresponding to the input port of the machine PLC, and press the CNC start button to input the signal 0, 1 to change normally. The button is not faulty and the line is normal. Is it because of the failure caused by the spindle rotation? The CNC machine tool panel is displayed as 1st gear, and the MDI mode input M42 becomes 2nd gear. Press the “CNC start†button, the machine has no shifting action. The spindle of the machine tool is jogged, the spindle motor of the machine tool rotates, and the spindle does not rotate. Check the output of the PLC spindle shifting part of the PLC, all zero, which means that the machine does not have a shifting action. Disassemble the top cover of the headstock and find that the slip gear of the 3-axis of the machine headstock is stopped in the middle position, and the torque transmission cannot be realized. Analyze the tool change program of the machine PLC program. It is found that the tool change program is stopped. Check the PLC input point "CNC stop" button address is 1. The signal of the address pressed by the "CNC stop" key does not change. Use the multimeter to detect the “CNC Stop†button. This key is effective. Replace the button. The "CNC start" key function of the machine tool is restored; the spindle shifting is more normal, the rotation function is normal; the manual pulse generator is normal; the automatic and manual tool change functions are normal. Machine troubleshooting.
The surface of the machine fault is seen more, in fact, it is caused by the effect of a "CNC stop" key. Because of its failure, the CNC system has been in the state of NC stop; so the "CNC start" button does not work. Automatic and manual tool change does not work, and the manual pulse generator fails.
2. Fault 2
A Siemens 802 CNC machine tool has a spindle failure during the electrical commissioning after the mechanical overhaul is completed. The phenomenon is that the spindle can only be jogged, the main and reverse motions of the spindle are missing, the spindle rotates in the MDI state, the motion is missing, and the spindle rotates and the motion is missing in the automatic mode. There is no alarm in the CNC system of the machine tool, the anti-reference point is normal, and there is no alarm on the spindle drive. Check that the PLC input point address 0, 1 of the spindle punctual and reverse button changes normally. Since the machine tool failure occurred during the mechanical overhaul process, during the mechanical overhaul process, the electrical circuit was understood, and the author carefully examined the disconnected part of the wiring, but there was no error. The analysis PLC program found that the spindle rotation program was reset, and the PLC input address of the "spindle stop" button of the machine tool was often 0. Use the multimeter to check the machine's "spindle stop" button, which is normal. The test line found that the connection line of the button was soldered. After the repair, the machine is tested and the machine is trouble-shooting and normal operation.
3. Conclusion
(1) For the "set" fault of CNC machine tools, you can directly monitor the PLC set address to see if the "set" button is together with the line. If it is normal, look at the "reset" address signal is normal.
(2) PLC program analysis method is especially suitable for machine tools without any alarm number and alarm information. The machine tool has no action and abnormal function. This method requires maintenance personnel to have an understanding of the commonly used PLC language. In this way, in the process of analyzing the PLC program, it can be targeted and quickly find the fault point of the machine tool.
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