Diagnosis of PLC initial fault of the hottest mach

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Initial fault diagnosis of machine tool PLC

1 introduction

in order to protect the machine tool and facilitate maintenance, PLC has the ability to display and detect machine tool faults. Once a fault occurs, the maintenance personnel can determine the fault category and eliminate it according to the fault display number of the machine tool. However, in the actual processing process, we found that sometimes the PLC displays several faults at the same time. They are chain faults caused by a certain fault. After the initial fault is eliminated, other fault alarms disappear. However, from all the alarm faults displayed by the machine tool PLC, the maintenance personnel do not know which fault is the initial fault, and the maintenance personnel can only check the faults one by one, which increases the difficulty of maintenance and causes a waste of human and material resources. When several faults are displayed at the same time, the key to deal with the problem is to solve the initial fault, so it is very important for machine tool maintenance to accurately judge and detect the initial fault. We designed an initial fault diagnosis function of machine tool PLC, and accurately judged the alarm number of initial fault through PLC program. During the maintenance, the initial fault shall be eliminated first, and other faults shall disappear automatically, which greatly facilitates the maintenance of the machine tool and improves the rapidity and accuracy of the maintenance of the machine tool. 2 principle of initial fault diagnosis the PLC program we designed can not only detect and display all faults, but also automatically judge the most critical initial faults. The PLC initial fault judgment program is shown in the attached figure

the following is an example to illustrate the principle of initial fault diagnosis. Take three faults as an example, in which three fault detection bits are set, which are r500.0, r510.0 and r520.0 respectively; The three initial fault detection bits are r500.2, r510.2 and r520.2; F149.1 is the system reset signal. In the initial state, no alarm occurs, the fault detection bits are all "0", the initial fault detection bits are all "0", and the reset signal f149.1 is "0". Among the three faults, it is assumed that the second fault occurs first. In the first cycle of program scanning, the corresponding fault detection bit r510.0 changes to "1", the initial value of r500.2, r520.2 and f149.1 is "0", the initial fault detection bit r510.2 changes to "1", and remains "1" through self-locking. The "1" state is not released until the fault is eliminated and the system reset signal is sent. In the second cycle of program scanning, r510.2 remains "1", realizing the blocking of r500.1 and r520.1. Even if another fault detection bit is "1", its initial fault detection bit cannot be changed to "1". Through this PLC program, the forming shrinkage is increased; The system can accurately judge the initial fault from the numerous faults that occur at the same time. 3 application example example 1 when we were repairing the jcs018 CNC machine tool produced by Beijing Machine Tool Research Institute, we encountered the problem of multiple faults occurring at the same time, such as the simultaneous occurrence of tool change alarm and hydraulic alarm. During maintenance, we usually start from the root cause of the fault, first check the hydraulic control part, and then confirm that the fault is in the process of tool change. Only after inspection did we know that the power for tool change was provided by hydraulic drive. In the design of PLC control program, in case of tool change failure due to large specific surface area, strong surface adsorption, large surface energy, high chemical purity, good dispersion performance and excellent performance in terms of thermal resistance and resistance, in order to prevent greater accidents, a large number of new customers in the western region have switched on the hydraulic control through this platform. Therefore, two alarm messages appear when the tool change failure occurs. In order to follow the design idea of the original machine tool and send out alarm information accurately, we have added the function of checking initial faults to jcs018 NC machine tool. According to the previous program analysis, the tool change and hydraulic fault detection bits are r500.0 and r510.0 respectively, and the initial fault can be read out from the initial fault detection bits r500.2 and r510.2. When a similar fault occurs to the machine tool again, the initial fault can be quickly judged. Example 2 we encountered a similar phenomenon when repairing a drilling and milling machining center. The machine tool is equipped with a tool magazine with a tool capacity of 40, which can automatically complete the drilling and milling operation of multiple processes. The spindle motor of the machine tool is a three-phase asynchronous motor. The spindle motor has only one speed, and the spindle realizes 12-Stage speed change through gear speed change. When a certain section of program is automatically executed, the auxiliary functions in the program include both shift function s code and tool finding function T code. As long as one code instruction is not executed completely, the auxiliary function completion signal cannot be sent, that is, the auxiliary function in this section of program is not completed, and the next program section cannot be executed. If the shift function fails, the shift alarm signal is sent first, and the signal cannot be sent after the auxiliary function is completed. After a certain period of time, the knife search alarm signal is sent, it will be considered that the knife search action has not been completed. If the initial fault judgment function is added, the maintenance personnel will accurately check the cause of the fault and solve the problem in time. 4 conclusion the PLC initial fault detection function of the machine tool designed by us can accurately judge the initial fault when several faults are displayed at the same time, which brings great convenience to the maintenance of the machine tool, avoids many meaningless tasks, and improves the maintenance efficiency. It has achieved good results in practical application

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