Due to the wide variety of machine tool control systems, various equipment configurations, various design methods, and various fault phenomena, it is difficult to maintain a good number of CNC equipment. While mastering the mechanical structure and electrical control principle, it must be analyzed rationally, used flexibly, and good at summing up to achieve a multiplier effect. Based on the principle, from easy to difficult to narrow the fault and rule out. In order to ensure the safe operation of the machine tool, the linear axis of the machine tool is usually provided with two sets of “defending lines”: soft limit (parameter limit setting) and hard limit (travel limit switch). The limitation problem is one of the common faults of CNC machine tools, and there are few related materials. The following are some of the main reasons for the "limit alarm".
I. Corruption of the related control circuit breaker or limit switch This causes a relatively high incidence of “limit alarms” due to the influence of external components on the environment, such as mechanical impact, dust accumulation, corrosion, friction, etc. It is easy to cause the related limit switch itself to be damaged and the control circuit to be disconnected, and at the same time generate a "limit alarm" message. Also encountered the situation that the over-travel switch cannot be reset after pressing. The handling of such failures is relatively straightforward, and the damaged switches and wires can be repaired or replaced. When the wire is broken or poorly contacted, the line must be carefully checked and observed.
Second, the operation is not standardized, misoperation or machine out of control which, mainly to cause hard limit alarm mainly, in general, through direct remedial measures can be restored, the use of the machine's own over-travel release function or short-circuit method is daily The usual method of maintenance. In order to win precious production time, we should firmly grasp the individual characteristics of equipment and systems in the process of processing, and look for reliable shortcuts to solve problems flexibly and quickly.
1, according to the characteristics of machine tool structure processing Most of the machine tools are equipped with "overrange release" contacts, once the "hard limit" alarm, after confirming that the hard limit switch is pressed, so that the contact is closed and in Manually remove the limit position in the opposite direction, that is to release the alarm; also a few do not set the button, this time should take equivalent short-circuit measures at the corresponding point, that is to force the conditions to meet, and then move the machine out of the limit position.
2. Grasping the limitations and features of the CNC system In routine maintenance, we also encountered special circumstances due to the limitations of the CNC design software. For the treatment of such problems, we must fully grasp the individual characteristics and performance of a CNC system. While exploring and summarizing, it is necessary to make a good record. There are conditions that should receive some necessary technical training.
(1) Due to improper operation, the lower left corner of the machine panel shows Y direction "hard limit", the Y travel switch has been pressed, and the hard limit red indicator light is on. In the manual mode, the limit position cannot be moved in the opposite direction.
Processing method and reason: The conventional removal and short-circuiting methods cannot eliminate the fault, because the alarm is not cleared and the Y-axis movement operation has been invalid in the manual or handwheel mode. In the absence of other possible causes, the NC system was suspected. However, at this time, the CNC system did not show any sign of panic or disorder, and all other axes were able to move normally. Decided to short-circuit the Y stroke limit switch, turn off the machine power and wait a moment, then restart the machine and find that the alarm message disappears, the red indicator light goes out, the machine tool is moved out of the limit position, and finally the short circuit is cancelled and everything is back to normal In fact, after the failure occurred several times, we realized that the fault was due to the fact that the CNC system had the function of keeping the memory when the previous coordinate position was energized.
(2) The alarm information in the lower left corner of the machine control panel CRT is displayed as “hard limit”, the hard limit red indicator light is not on, and the actual position of the machine tool is far away from the hardware limit switch. At the same time, the machine coordinate value is close to the maximum value of 99999999, and the axis cannot move.
Processing method: In view of the above phenomenon, firstly, it is judged that the data overflow of the coordinate value has exceeded the limit value of the machine memory. In the case where the accumulation is larger and larger, the coordinate data must be cleared completely. The system mechanical coordinate zeroing procedure is as follows: 1 In the main page, enter the "monitor" menu; 2 page content part without any category display, do not bother (hidden), enter the second "slave monitoring"; 3 next According to the third item “F3”, it can be seen that the axis machine coordinates are all zero and the alarm has been cleared. In particular, the machine tool must be referenced again to establish the machine coordinate system. This is due to the limitation of the CNC function program. The characteristics of point (1) above should be combined when processing.
Third, back to the reference point process failure, caused by relatively high-end limit of the numerical control system can usually use the convenient and flexible parameter correction function to maintain the machine, if the actual position of the machine does not exceed the limit position and limit alarm occurs, you should first carefully check whether Loss or change of parameters due to travel. For the parameters, the most typical case is that some machine tools are vulnerable to soft limit alarms when they return to the reference point, and the actual position of the machine tool is a certain distance from the reference point. At this time, if the machine hardware limit function is in good condition, modify the soft limit parameter value appropriately according to the stop point of the machine tool when the alarm is reported and the displacement of the reference point mark (sometimes need to be set to the maximum value or cancel, according to which Situation)) The soft limit setting needs to be restored after the standby bed returns to the normal reference point. In addition, after the replacement of some devices involved in the trip (such as motors, shaft couplings, screws, etc.), the gap, displacement is subject to certain changes, there may be failure to refer back to the same time, resulting in "limit alarm."
Fourth, the machine parameters are changed or lost due to outside interference, and soft limit parameters are common. Poor quality of the workshop power supply, poor processing environment, lightning, and inadequate shielding measures are very likely to cause various parameters of the CNC machine tool to change or be lost. While restoring the parameters, it is necessary to find out the direct cause of the failure and take remedial measures.
5. Influence of Coordinate System and Numerical Control Program The preparation of machining programs must strictly consider the processing scope of the machine tool. During the machining process, once the tool enters the forbidden area, a limit alarm of the travel (soft stroke and hard stroke) occurs. In one case, the program coordinate value is changed due to improper operation (the software filter simulation check does not exist for the program filter type check), and on the other hand, the relative coordinates are taken due to improper setting of the machine tool coordinate system (G54~G59) parameters. When it is out of range.
