1. The relevant control circuit is broken or the limit switch is damaged. The cause of the "limit alarm" is relatively high. Because external components are greatly affected by the environment, such as mechanical collision, dust, corrosion, friction and other factors, It is easy to cause damage to the relevant limit switch itself and the control circuit is broken, and at the same time generate "limit alarm" information. Also encountered when the overtravel switch is pressed and cannot be reset. The handling of such faults is relatively straightforward, and the damaged switches and wires can be repaired or replaced. Care should be taken to observe and observe the wire when the wire is broken or the contact is poor. Such as: an XK755 CNC milling machine, using FANUC 0-M CNC system. During the machining process, the “X+, X-, Y+, Y-hard limit†alarm suddenly appears, but the machine tool is actually in the normal processing range. According to the above phenomenon, it is estimated that the line contact is poor or the possibility of disconnection is the greatest. The 24V voltage of the supply limit circuit on the terminal block of the electrical cabinet is measured, and the pressure value is normal. According to the route direction, one by one, when a line connector on the right side of the bed is rotated by hand, it is found that the alarm on the screen disappears instantaneously, and the alarm is reproduced in the hand. Therefore, the joint is removed, and it is found that the two wires welded inside have been detached, and the two ends of the wire break can be touched during the process of turning by hand, so the above change phenomenon occurs. After re-welding the joint, the machine returns to normal. Second, the operation is not standardized, the malfunction or the machine tool is out of control Among them, mainly to cause the hardware limit alarm, in general, through direct remedial measures can be restored, using the machine tool's over-travel function or short-circuit method is the usual method of routine maintenance. In order to win valuable production time, we should firmly grasp the individual characteristics of equipment and systems in the process of processing, find shortcuts with reliability, and solve problems flexibly and quickly. 1, according to the characteristics of the machine structure Most machine tools are equipped with an “overtravel release†contact. Once the “hard limit†alarm occurs, after confirming that the hardware limit switch is pressed, the contact is closed and the limit is removed in the manual direction in the manual mode. The position is set to cancel the alarm; there are also a few that are not set. In this case, the equivalent shorting action should be taken at the corresponding point, that is, the condition is forcibly satisfied, and then the machine is moved out of the limit position. Such as: an imported HX-151 vertical five-axis machining center. The “X-axis hard limit†alarm appears, and the “Overtravel Release†button is not set in the machining center. Due to the structure of the machine tool, the X+-direction limit switch installation position is “hiddenâ€, and it is necessary to remove the pedal and remove the guard plate, which requires a lot of time and effort to delay production. Therefore, the shorting of the corresponding terminal number and other potential points on the wiring board in the electrical cabinet, that is, shorting the 3230 and 3232 points on the machine wiring board (also directly at the input points of the plc A305.3 and A306. 6 short circuits), and move the machine back to the range of travel, troubleshooting. 2, grasp the limitations and characteristics of the CNC system In daily maintenance, we also encountered a special situation due to the limitations of the CNC system design software. For the treatment of such problems, it is necessary to fully grasp the individual characteristics and performance of a certain CNC system. While exploring and summarizing, we must make a good record and have the necessary technical training. For example, the blade shot peening economical CNC machine tool designed by our technicians controls X, Y, Z, A four axes (where A axis is the rotary axis), and the numerical control system is developed by Southwest Automation Research Institute (Swai). ) M2000, using open loop control. The following two representative fault phenomena occur: (1) Due to improper operation, the left lower corner of the machine panel is displayed as Y-hard limit, the +Y travel switch has been pressed, and the hard limit red indicator light is on. In manual mode, the limit position cannot be moved in the opposite direction. Treatment method and reason: The conventional removal and shorting method cannot eliminate the fault. Because the alarm is not cleared, the Y-axis movement operation is invalid in the manual or handwheel mode. In the absence of other possible causes, the CNC system problem was suspected. However, at this time, the CNC system did not have any signs of crash or disorder, and all other axes could move normally. Decide to short the +Y travel limit switch, turn off the machine power and wait for a while, then restart the machine, find the alarm message disappears, the red indicator light goes out, then move the machine out of the limit position, and finally cancel the short wiring, everything is restored Normally, in fact, after the fault occurred multiple times, we realized that the fault is due to the fact that the CNC system has the function of keeping the memory in the case where the previous coordinate position is energized. (2) The alarm information of the lower left corner of the CRT of the machine tool panel is displayed as “hard limitâ€. The red limit indicator of the hardware limit is not bright. The actual position of the machine tool is far away from the hardware limit switch. At the same time, the machine coordinate number is close to the maximum value of 99999999, and the axis cannot move. Processing method: For the above phenomenon, firstly, it is judged that the data overflow has occurred in the coordinate value, which exceeds the limit value of the machine memory. In the case where the accumulation is getting larger and larger, the coordinate data must be completely cleared. The steps of clearing the mechanical coordinates of the system are as follows: 1 Enter the “Monitor†menu under the main page; 2 The content part of the page has no class display, ignore it (hidden), and enter the second “slave monitoringâ€; 3 next According to the third item “F3â€, it can be seen that the coordinates of each axis machine are zero and the alarm has been cleared. It is important to note that the machine tool must be re-referenced to establish the machine coordinate system. This situation is due to the limitations of the CNC system function program. The characteristics of point (1) above should be combined with the processing. Third, the reference point return process failed, causing the limit More high-end CNC systems 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 the limit alarm occurs, you should first carefully check whether the parameters of the stroke are lost or changed. For the parameters, the most typical example is that some machine tools are prone 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, in the case that the hard limit function of the machine tool is intact, the value of the soft limit parameter is modified according to the stop point of the machine tool alarm from the reference mark mark displacement (sometimes it needs to be set to the maximum value or canceled, it should be regarded as Situation), the soft limit setting must be restored after the standby bed is returned to the reference point. In addition, after replacing some equipment involved in the stroke (such as motor, shaft coupling, lead screw, etc.), the gap and displacement are subject to certain changes, and there may be a failure of the reference point return and a "limit alarm". Such as: a THM6350 horizontal machining center manufactured by Ningjiang Machine Tool Co., Ltd., the numerical control system is FANUC 0i-MA. During the reference point return, the alarm message of the Y axis is “507 OVER TRAVEL +Xâ€, there is a deceleration process, the repeated operation can not return to the reference point, and the same alarm information appears. The machining center uses the stop mode to refer to the reference point. . Analysis and processing: It can be seen that the root cause of the fault is not the hard limit itself. Then, is the reference point mark pulse not appearing after deceleration? If this is the case, there are two possibilities: one is that the grating does not find the reference point pulse signal during the return to the reference point, or the reference point mark fails, or the reference point pulse selected by the reference point mark is in the process of transmission or processing. Loss, or measurement system hardware failure, has no discrimination or processing capability for the reference point pulse signal. Second, the deceleration switch and the reference point mark position are misaligned. After the deceleration switch is reset, the reference point mark does not appear. Check the relevant parameters one by one without change and loss. Press the switch directly by hand. In the PMC address X1009. 0, the deceleration signal is changed from “0†to “1â€, indicating that the function is intact. According to the fault phenomenon, the overtravel signal is also intact. The key point should be to check the reference point signal and eliminate it. Due to loss of signal or damage to components. The distance between the deceleration switch and the reference point switch has been set by the manufacturer's standard. The reference counter capacity and the standard are the same. Generally, no changes or modifications are made during the maintenance process. First, do not use the tracking method to determine the first reason for the above analysis, first consider the principle of easy to difficult to consider the problem. See if the recognition ability of the benchmark mark has been reduced or lost? Decided to change the X value of parameter 1425 (FL speed after bumping stop) from 100 to 100. To ensure the balance of motion of each axis, set the FL speed of other axes to 100 at the same time, try to return to the reference point, and the machine will recover. Normal, this idea has been verified. Therefore, the cause of the failure is that the reference point mark recognition capability has been lowered, causing the machine tool to return to the reference point until the hard limit is pressed. Fourth, machine tool parameters are changed or lost due to external interference In this respect, the soft limit parameters are mainly used. External factors such as poor power quality, poor processing environment, lightning, and inadequate shielding measures can easily lead to changes or loss of various parameters of CNC machine tools. While restoring the parameters, it is necessary to find out the direct cause of the failure and take remedial measures. A horizontal machining center adopts the FANUC 0i-MA numerical control system. During the machining process, “501 OVER TRAVEL –X†appears, that is, the negative overtravel. The numerical value of the mechanical coordinate of the machine tool far exceeds the set value -99999999~ The range of +99999999 (unit: μm), while the actual machine tool is within the travel range. Treatment method: As can be seen from the above phenomenon, the digital display data of the machine tool has changed due to interference and exceeded the software limit setting range. Enter the parameter screen modification parameters 1320, 1321 (the coordinate value of the Y-axis stored stroke detection negative direction boundary). Next, the parameter 1320 is set to be smaller than the parameter 1321, the stroke is considered to be infinite, and the detection of the stored stroke detection 1 is not performed. Shut down Restart the machine and return to the reference point, then restore the parameters of 1320 and 1321 to the coordinates before the modification. On the other hand, the direct cause of the data change must be found and eliminated immediately to prevent the recurrence of the failure and cause more serious consequences. The fault was finally confirmed to be caused by lightning interference. Fifth, the influence of coordinate system and NC program The machining program must be strictly considered in the machining range of the machine. During the machining process, once the tool enters the prohibited area, the stroke (soft stroke and hard stroke) limit alarm occurs. In one case, the program coordinate value is changed due to improper operation (the software filter does not exist through the strict simulation of the program), and on the other hand, the machining coordinate system (G54~G59) parameter of the machine tool is improperly set, and the relative coordinates are taken. When it is out of range. For example: a VMC1000C vertical machining center, after setting the machining coordinate system and each compensation parameter, the “OVER TRAVEL –Y†alarm appears in the machine running program, that is, the Y-axis negative hard limit. At the same time, if the tool change statement (M06) is not executed, the interpolation statement is executed directly, and the tool path is incorrect. Processing: Obviously, the hardware limit alarm here is only a kind of prompt. After confirming that the system parameters and the machining program have no abnormalities, it is decided to further confirm whether the position loop is intact. The empty running with G54 is another NC program of the machining coordinate system. The machine works normally, which eliminates the possibility of fault in the position loop. The fault range is reduced to the machining coordinate system. Set the coordinate value set on G58 to G54, and change the G54 in the original program to G58. The program after modifying the machining coordinate system is normal. At this point, the basic judgment is that there is a problem with G58. Generally, there are few faults in the function of establishing coordinate system of G54~G59. According to the principle of easy to difficult, it is first considered that the coordinate system set in G58 is not accepted by the system, but the memory becomes another data, which can be seen from the path. Therefore, we use the method of clearing data and re-entering, and the trial running machine returns to normal, and the judgment is correct. This fault is due to the non-standard input data, which affects the machine coordinate system data, resulting in over-travel alarm on the machine.
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