Diagnosis and maintenance method of no alarm fault

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Diagnosis and maintenance methods for alarm free faults of CNC machine tools

in practical work, we have encountered many alarm free faults, which makes maintenance more difficult. Combined with examples, the diagnosis and maintenance methods of this kind of fault are introduced as follows

1. The x-axis does not perform the action of automatically returning to the reference point

the machine tool is a JCS-018 vertical machining center produced by a research institute, and the CNC system is fanuc-besk7m. After the failure occurs and according to the conservative estimation, check that there is no alarm prompt on the CRT and no alarm indication on all parts of the machine tool. However, the manual X-axis can move. After moving the x-axis to the reference point manually, the machine tool can carry out normal processing again, and the above phenomenon is repeated after processing

according to the above situation, we can judge that the NC system and servo system have no fault. Considering that the fault occurred in the process of x-axis returning to the reference point, it is suspected that the fault is related to the change of parameters of x-axis reference point. However, when we call out the parameters related to X-axis reference point with address f in TE mode for inspection, we find that these parameters are normal

according to the working principle of CNC machine tool, the axis reference point is not only related to parameters, but also related to the origin position and reference point position of the axis. Check the limit switch of the x-axis reference point on the machine tool and find that it has failed due to oil contamination, that is, it is always in the on state. Therefore, when the processing program is completed, the system considers that it has returned to the reference point, so the x-axis does not return to the reference point. After cleaning and repairing the travel switch, the fault is eliminated

2. In the process of automatic machining, there is no exchange action between worktables A and B

the machine tool is mkc-500 horizontal machining center produced in Hungary, and the numerical control system is Siemens 820m. When the fault occurs, the machine tool processing program has executed the M06 function in the L60 subroutine, the door curtain has been opened, but there is no exchange action between worktables A and B, the program is in the stopped state, and there is no alarm display on the NC system

it can be seen from the flow chart of machine tool workbench exchange: when workbench A and B are exchanged, two conditions must be met: first, the door curtain must be opened; Second, the workbench should be in a relaxed state and raised. Check the above two conditions: (1) the door curtain has been opened and the conditions are met. (2) The workbench is not raised, and the conditions are not met, that is, the workbench is still in the clamping state. It is known from the operating instructions of the machine tool that the clamping and loosening of the rotating workbench are related to the sp03 pressure. In order to understand this decision, it is necessary to review the history of electrical appliances, and the PLC input point corresponding to the sp03 pressure relay is e9.0. When the machine tool is in the normal processing state, the rotating workbench is clamped, e9.0=1; When the machine tool is in the exchange state, the rotating worktable is relaxed, e9.0=0, and ready for the exchange of worktables A and B. According to its working principle, in order to exchange the worktable, e9.0=0 must be made, and the worktable must be relaxed, even if the sp03 pressure relay is disconnected

we found that the sp03 pressure relay failed due to oil contamination. After cleaning and repairing it, when it is adjusted to the workbench exchange, e9.0=0; When the workbench is processed, e9.0=1. Troubleshooting

3. The manipulator does not change the tool in automatic machining

the machine tool is a kt1400 vertical machining center produced by a research institute, and the numerical control system is fanuc0 system. The inspection found that the manipulator did not change the knife under the automatic control mode, and there was no alarm. In the manual mode, the tool can be changed, and then the automatic machining can continue

according to the above inspection, we judge that the CNC system and servo system are free of faults. Considering that the actions of the magazine motor and manipulator are controlled by Fuji frequency converter alone, the inspection focus is on the frequency converter. When observing the manual state, the tool magazine and tool change action are accurate. Observe the automatic state, the rotation of the tool magazine is normal, but the tool change is abnormal. Check that the NC control signal has been sent out and the control contactor has been closed, indicating that the tool change signal has been sent to the frequency converter. Check the working condition of the frequency converter and find that its working frequency is 35Hz when changing the tool manually, but only 2Hz when changing the tool automatically. At such a low frequency, the manipulator certainly cannot perform the normal tool change action. The reason for the failure is that when the manipulator is changing tools, the substation suddenly cuts off power, causing the manipulator to get stuck when changing tools. After the power supply is restored, the above failure occurs and finds out the best temperature and pressure conditions. After resetting its frequency to 35Hz, the fault is eliminated and the manipulator returns to normal

4. During the lifting or rotating process of the rotating workbench, the odd number positioning is correct, and the even number positioning is inaccurate

the machine tool and system are described in fault 2. After the fault occurs, the machine tool has no alarm. When the positioning is not on time, the machine tool cannot work, but after the workbench is lifted and lowered again, the positioning is correct again, and the machine tool can continue to work. According to this fault phenomenon, we suspect that it is caused by the loose rotary encoder on the motor of the rotary workbench. 3. The selection reference movement or inaccurate positioning of the rubber tensile testing machine of the experimenter. However, repeatedly adjusting the rotary encoder and modifying the parameters related to the rotary encoder cannot eliminate the fault

the drive system is the same as the motor drive system of the tool magazine, and we use the replacement method to exchange. When the drive system of the tool magazine is changed to the rotary workbench, the fault is eliminated. When the drive system of the rotary table is changed to the tool magazine, the tool magazine fails to find the correct tool number. Through this inspection, we can confirm that the workbench drive system has failed. The drive system is simodrive611-a feed drive. By consulting the manual of the drive system and analyzing the faults of the drive system, it is agreed that there is no hardware fault in the drive device. The above failures are mainly caused by the wear of mechanical moving parts after long-term operation, the performance changes of electrical components and other reasons, resulting in the servo system and the dragged mechanical system did not achieve the best match. According to the technical data, in this case, the servo system can reach the best working state with high dynamic response characteristics and no oscillation by adjusting the proportional coefficient Kp and integral time TN of the speed controller. We refer to the KP scale and TN scale on the motor drive device of the tool magazine to fine tune the driving system of the rotating workbench, and the fault is eliminated

no alarm fault accounts for a large proportion of the faults of CNC machine tools. The failure is usually caused by the influence of external conditions such as power supply voltage, hydraulic pressure, pneumatic pressure, oil stain and ambient temperature. As described in faults 1, 2 and 3 in this article. In addition, after the CNC machine tool is used for a long time, due to the aging of components and mechanical parts, the matching between the system and the mechanical part will also cause problems, resulting in no alarm fault, as shown in this

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