Nowadays, the use of numerical control equipment is more and more extensive, and it is followed how to ensure the effective utilization of the equipment. When the equipment fails, it is necessary to restore the equipment to normal use as soon as possible. In order to solve this problem, first of all, maintenance personnel should have high quality, not only require rich professional knowledge, such as mechatronics technology, computer principle, numerical control technology, plc technology, automatic control technology, drag principle, hydraulic technology, etc. It is also necessary to master the common knowledge of machining and the simple programming of numerical control devices. In addition, it must have a certain level of English and be able to read English technical materials. Have sufficient information, including machine, electricity, liquid drawings, machine parameter backup, system use maintenance manual, PLC ladder diagram and so on. There is also a certain amount of spare parts. In addition, maintenance personnel need to have certain experience and master certain maintenance methods. The author has been engaged in the maintenance of CNC equipment for many years, accumulated a certain amount of experience, summed up a set of methods for repairing CNC equipment, which is now introduced for reference.
To find out the fault phenomenon
When the numerical control equipment fails, first understand the fault phenomenon, understand the situation of the first fault, and observe the process of the fault when possible, and observe under what circumstances the fault occurs. How does it happen? What caused the consequences. Only by understanding the first-hand situation will it be beneficial to eliminate the fault and clear the fault process, and the problem will be solved halfway. After clearing the fault phenomenon, and then according to the working principle of the machine tool and the numerical control system, the problem can be quickly diagnosed and the fault can be eliminated, so that the equipment can be restored to normal use.
For example, in a CNC cylindrical grinding machine using the American BRYANT TEACHABLE III system, the grinding wheel wears off the dresser during automatic machining. In order to observe the fault phenomenon and prevent the accident from happening again, remove the grinding wheel and run the machine tool. Then observe the fault phenomenon and find that there is no problem in the grinding during the automatic grinding process. After the workpiece is ground, the grinding wheel is normal when the grinding wheel is finished. Feeding, and the wheel dresser rotates very fast, and the upper limit switch is pressed very quickly. If the grinding wheel is not removed at this time, the grinding wheel must hit the dresser again. According to the working principle of the machine tool, the wheel dresser is driven by the E-axis servo motor, and the rotary encoder is used as the position feedback component. Under normal circumstances, when the dresser trims the grinding wheel, the Z-axis slide moves the E-axis dresser to the trimming position, and the trimmer performs a swing of 30°~120° to trim the grinding wheel. We observed the fault phenomenon many times and found that when the E-axis is at the upper limit switch, the coordinate value of the E-axis on the screen is only about 60°, and the actual position is about 180°. Obviously, there is a problem with the position feedback, but the position is changed. Both the control board and the encoder did not solve the problem. After repeated observations and experiments, we found that when the E-axis dresser is at the edge of the Z-axis, there is no problem with the reference point and the rotary swing, and the system's alarm information is used.
Now the self-diagnosis capability of the CNC system is getting stronger and stronger, most of the faulty CNC systems of the equipment can be diagnosed, and corresponding measures, such as shutdown, can be used to generate an alarm display. When the numerical control equipment fails, the alarm information is sometimes displayed on the display, and sometimes there is an alarm indication on the numerical control device, the PLC device, and the drive device. At this time, the alarm information should be analyzed according to the manual. Some alarms can directly confirm the cause of the fault. As long as the contents of the alarm information are clarified, the fault of the numerical control device can be eliminated.
For example, a CNC channel grinder with German SIEMENS 810 system will generate “BATTERY ALARM POWER SUPPLY†when it is turned on, which obviously indicates that the CNC system is powered off and the battery is dead. After replacing the new battery (Note: Be sure to replace the battery with the system charged, reset the fault, and return the machine to use. Another CNC grinding machine with SIEMENS 3 system, the screen is not displayed after booting, check the numerical control device, and find that one LED on the CPU board flashes. According to the manual, analyze the flashing frequency, confirm that the battery voltage is low after the power is off. After replacing the battery. , restart the system failure disappears.
For example, a CNC lathe using the Japanese FANUC 0TC system, the No. 2043 alarm appears, showing “HYD. PRESSURE DOWNâ€, indicating that the hydraulic system pressure is low. According to the alarm information, the hydraulic system was inspected and found that the hydraulic pressure was indeed low, and the hydraulic pressure was adjusted to restore the machine to normal use.
The alarm information of other faults does not reflect the root cause of the fault, but reflects the result of the fault or other problems caused by it. At this time, careful analysis and inspection are required to determine the cause of the fault. The following methods apply to such faults and The detection of some faults without an alarm is effective.
To use the PLC status display function of the CNC system
Many CNC systems have PLC status display functions, such as PC STATUS under the PC menu of Siemens 3 system, PLC STATUS function under the DIAGNOSIS menu of Siemens 810 system, and PMC status display function of DGNOS PARAM function of FANUC 0T system. The function displays the immediate status and contents of the PLC's inputs, outputs, timers, counters, and more. According to the working principle of the machine tool and the electrical schematic diagram provided by the machine tool manufacturer, some faults can be diagnosed by monitoring the corresponding state.
For example, a CNC lathe using FANUC 0TC in Japan, once a fault occurs, the alarm No. 2041 appears on the power-on, indicating the alarm of the X-axis over-limit, but the X-axis does not have an over-limit, and the X-axis limit switch is also Without pressing, but using the PMC status display function of the NC system, check that the state of the PMC input X0.0 of the X-axis limit switch is "1", the switch contact is indeed turned on, indicating that there is a problem with the switch, replacing the new one. After the switch, the machine fault is eliminated.
For example, a CNC lathe that uses the Japanese MITSUBINSHI MELDAS L3 system fails once and the turret does not rotate. According to the working principle of the turret, when the turret rotates, the turret is first floated by the hydraulic cylinder before it can rotate. Observing the fault phenomenon, when the button of the turret rotation is manually pressed, the turret does not react at all, that is, the turret does not float. According to the electrical schematic diagram, the output of the PLC Y4.4 controls the relay K44 to control the solenoid valve. The solenoid valve controls the hydraulic cylinder to make the turret float. First, the PLC status display function of the NC system is used to observe the state of Y4.4. When the manual turret rotation button is pressed, its status becomes "1", no problem, continue. The inspection found that the contact of the DC relay K44 controlled by it was damaged, the new relay was replaced, and the turret was restored to normal operation.
To use the PLC ladder provided by the machine tool manufacturer
Most of the faults that occur in CNC equipment are checked by the PLC device. The mechanism of PLC fault detection is to run the PLC ladder diagram (ie program) programmed by the machine tool builder for a specific machine tool, and make logic judgment according to various input and output states. If a problem is found, an alarm is generated and an alarm message is generated on the display. Therefore, for some PLCs to generate alarm faults, or some faults without alarms, you can diagnose the faults by analyzing the ladder diagram of the PLC, and use the ladder diagram display function of the NC system or the off-machine programmer to track the operation of the ladder diagram online. Diagnose the speed and accuracy of the fault.
For example, a CNC grinding machine with SIEMENS 810 system has a fault. After starting the machine, the machine does not return to the reference point and there is no fault display. Check the control panel and find that the indicator light of the indexing device is not lit. For safety reasons, this machine only needs to be safe. The indexing device does not fall and the feed axis of the machine cannot move. But checking the indexing device has fallen without problems. According to the PLC ladder diagram provided by the machine tool manufacturer, the output of the PLC A7.3 control panel on the control panel drops the indicator light. Using the programmer to observe the operation of the ladder diagram online, it is found that F143.4 is not closed, resulting in the state of A7.3 being "0". F143.4 indicates that the workpiece indexing table is in the drop position. Continue to check that the state of F143.4 is "0" due to the absence of the input E13.2. According to the electrical schematic diagram, the PLC input E13.2 is connected to the proximity switch 36PS13 which detects the falling of the workpiece indexing device, disassembles the indexing device, finds that the mechanical device has a problem, and cannot drive the mechanical device that drives the proximity switch, so E13. 2 can't always close. After the mechanical device is repaired, the machine tool is restored to normal use.
A CNC milling machine with SIEMENS 3TT system, in the process of automatic cycle machining, the workpiece has been processed, the worktable is about to rotate, the spindle has not retracted, then the second station spindle stops, the automatic cycle is interrupted, and an alarm is generated. F97 "SPINDLE1 SPEED NOT OK STATION2" and F98 "SPINDLE2 SPEED NOT OK STATION2" indicate that the two spindle speeds of the second station are abnormal. However, no problems were found in the inspection of the spindle system. In order to determine the cause of the fault, the external PLC is used to dynamically monitor the operation of the PLC ladder diagram of the machine tool, and check according to the logic relationship. Finally, it is found that the workpiece of the second station is clamped to the hydraulic pressure switch, and the state of E21.1 at the moment of failure When a change occurs, the "1" signal instantly changes to a "0" signal, which in turn becomes a "1" signal. E21.1 is connected to a pressure switch P21.1, and its state becomes "0", indicating the workpiece. There is no clamping, so the spindle stops and the automatic cycle stops. Since the clamping of the workpiece is done by hydraulic pressure, the hydraulic system is inspected and the pressure is found to be somewhat unstable. The hydraulic system is adjusted to make it stable and the machine tool resumes normal operation. The alarm information of this fault reflects the phenomenon that the spindle is stopped due to hydraulic instability, and does not reflect the root cause of the hydraulic instability.
The above two methods are very effective for detecting machine side faults, because these faults are nothing more than detection of switches, relays, solenoid valves or mechanical execution structures. These problems can basically be detected according to the PLC program. Status to confirm the point of failure. In the case of some system failures, sometimes the situation is more complicated. The following methods and detection principles can be used to quickly confirm the fault point.
Accurately locate fault points using exchange method
For some faults involving the control system, it is sometimes not easy to confirm which part has a problem. To ensure that there is no further damage, replacing the suspected control panel with the standby control board is an effective way to accurately locate the fault point. Sometimes the control panel interchange with the same type of control system on other machine tools will diagnose the fault more quickly (in this case, it will ensure that the good board will not be damaged).
For example, a CNC internal grinding machine using the American BRYANT TEACHABLE III system has a fault. When the E-axis moves, an alarm occurs: "E AXIS EXCESS FOLLOWING ERROR". The meaning of this alarm is that the following error of the E-axis displacement is exceeded. Predetermined area. Since the E axis generates this alarm, the E axis cannot return to the reference point. Manually move the E-axis to observe the fault phenomenon. When the E-axis moves, the E-axis displacement changes on the screen. When going from 0 to 14, the value on the screen suddenly jumps to 471. The same is true for reverse motion, and when it reaches -14, it also jumps to 471. At this time, the above alarm occurs and the feed stops. The analysis may be a problem of the E-axis position feedback system, including the E-axis encoder, the connecting cable, the position control board of the numerical control system, and the CPU board of the numerical control system. In order to find the problem as soon as possible, the principle of simplicity and complexity is first. Replace the position control board and the fault is eliminated. This machine has another alarm on the X axis. First, the position control board is replaced. The fault is not eliminated. Therefore, it is suspected that the encoder is more likely to be damaged. When the encoder is removed, the coupling is disconnected and replaced. The coupling is eliminated and the fault is eliminated.
It is necessary to check the faults in the principle of first, after, after, after, after, after, after, after, after, after, after, after, after, after, after, after, after, after, after, after, after,
For more complex faults in CNC equipment, especially when it comes to control systems, applying these principles simplifies the fault diagnosis process and avoids detours. Sometimes these principles should be combined so that the fault can be eliminated as quickly as possible.
For example, a CNC grinding machine using SIEMENS 3 system, when returning to the reference point, the X axis can not find the reference point, and finally the X axis over limit alarm occurs. In the first principle of the external and internal, first check the zero point of the X axis. Switch, normal no problem, observe the fault phenomenon, X-axis pressure upper limit switch, can also slow down; then according to the simple and complex principle, first check the NC system's position control board, because the feedback hardware uses the grating ruler, so On the position control board, an X-axis and Y-axis are each added with an EXE processing board. First, the X-axis and the Y-axis EXE board are interchanged. At this time, the power-on test, the X-axis returns to the reference point, and the fault is transferred to the Y-axis. The Y axis can not find the reference point, the fault phenomenon is the same, thus confirming that there is a problem with the EXE board, and the replacement of the EXE board is eliminated.
For example, a CNC quenching machine with SIEMENS 810 system has a fault, and when it is turned back to the reference point, when the X axis is taken, the alarm 1680 “SERVO ENABLE TRAV. AXIS X†appears. This alarm is also generated when the X axis is manually taken. The device was found to have an overload alarm indication. According to the Siemens manual, the cause of this fault is that the mechanical load is too large, the servo control power supply is faulty, the servo motor is faulty, etc. In the principle of mechanical and electrical first, the X-axis slide table is first detected, and the X-axis slide table is manually driven. It was found to be very heavy and the disk did not move. It was definitely a problem in the mechanical part. The X-axis ball screw was removed and found to be rusted. The original slide was not well sealed, and the quenching liquid entered the ball screw, causing the ball screw to rust and replacing the new ball screw.
For example, a CNC grinding machine with SIEMENS 3 system, during the automatic machining process for a period of time, often stops the automatic cycle midway, and the alarm 114 "SERVO LOOP HARDWARE" appears, indicating a problem with the Y-axis servo system. According to the manual, it is the servo. Measuring the problem with the feedback system. In order to further confirm the fault, in accordance with the principle of first static and then moving, after the machine is turned back to the reference point, the machine does not perform any operation in the waiting state. At this time, the machine does not have an alarm. When automatic machining is performed, this alarm occurs occasionally. And every time it is moving to about 190mm, an alarm occurs because the position feedback of the X-axis and Y-axis of this machine is a grating scale, and the lead cable moves together with the slide table, so the cable is suspected to be moving frequently. Some signal lines are broken, and an alarm is generated when the motion is moved to a certain position. This judgment is confirmed by the inspection, and the fault is eliminated after replacing the new cable. This machine has this fault again, and this alarm appears when it is still. Therefore, if there is any problem with the control board, replace the XY board of the Y-axis on the position control board with the X-axis. At this time, start the test and fail over to On the X-axis, the EXE board of the original Y-axis is damaged, and the replacement of the new EXE board is eliminated.
The above describes several common methods for detecting faults in CNC equipment. There are many other methods. However, the most important and important thing to solve the problems of CNC equipment is to master the working principle of the CNC system and the working principle of the machine tool. When dealing with the problems of the numerical control equipment, it can be handy, on the basis of the observation, thinking, inspection, analysis, diagnosis, and finally troubleshooting. Manual rotation occurs when the dresser moves into the middle of the Z-axis slide. According to this phenomenon, it may be concluded that the encoder of the E-axis often moves back and forth with the trimmer on the Z-axis, and some lines in the cable of the encoder are broken, resulting in different positions of the cable with the trimmer, at the edge of the Z-axis. The contact is good and there is no fault, and in the middle of the Z-axis, some signal lines are disconnected, and the feedback pulse is lost. Based on this judgment, we started the calibration line. At this time, we found that there were several bad line contacts. After finding the broken part, we welded the broken wire and took anti-folding measures. The test was restarted, the fault was eliminated, and the machine tool resumed normal use. .
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