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. Previous page next page Hole Size Mesh,Punching Hole Mesh,Punching Net Baina Wire Mesh Manufacture Co., Ltd. , http://www.bdaviarymesh.com
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 take advantage of most of the fault PLC ladder <br> <br> CNC machine tool equipment manufacturers to provide the appearance of PLC devices are checked out through the mechanism of failure is detected by the PLC to run the machine for a specific machine tool manufacturers compiled PLC ladder ( That is, the program), based on various input and output states, logically judges, 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.