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      Fault Diagnosis Method Of Machine Tool

      Release:rhqqzmkm Browse:39

        The electrical fault diagnosis of CNC machine tools has three stages: fault detection, fault judgment, isolation and fault location. The first stage of fault detection is to test the CNC machine tool to determine whether there is a fault; the second stage is to determine the nature of the fault and isolate the faulty component or module; the third stage is to locate the fault to a replaceable module or print Circuit board to shorten repair time. In order to find the fault in the system in time, quickly determine the location of the fault and eliminate it in time, it is required that fault diagnosis should be as few and simple as possible, and the time required for fault diagnosis should be as short as possible. To this end, the following diagnostic methods can be used:

        Intuitive method

        Using the sensory organs, pay attention to various phenomena when the failure occurs, such as whether there are sparks, bright lights, abnormal noise, abnormal heat, and burning smell during the failure. Carefully observe the surface condition of each printed circuit board that may be malfunctioning, and whether there are burnt and damage traces to further narrow the inspection scope. This is a basic and commonly used method.

        CNC system self-diagnosis function

        Relying on the ability of the CNC system to quickly process data, multi-channel and fast signal acquisition and processing of the error location, and then logical analysis and judgment by the diagnostic program, to determine whether the system has a fault, and to locate the fault in time. The self-diagnosis function of modern CNC system can be divided into the following two categories:

        (1) Power-on self-diagnosis The power-on self-diagnosis refers to the automatic execution of the internal diagnostic program of the system from the start of each power-on to the normal operation preparation state. The CPU, memory, bus, I/O unit and other modules, printed circuit boards , CRT unit, photoelectric reader and floppy disk drive and other equipment before operating the functional test to confirm whether the main hardware of the system can work normally.

        (2) The fault message prompts when a fault occurs during the operation of the machine tool, the number and content will be displayed on the CRT display. Follow the prompts and consult the relevant maintenance manual to confirm the cause of the failure and the troubleshooting method. Generally speaking, the richer the fault information prompted by the CNC machine tool diagnostic function, the more convenient it will be for fault diagnosis. However, it should be noted that some faults can directly confirm the cause of the fault according to the fault content prompt and refer to the manual; while the real cause of some faults does not match the fault content prompt, or a fault shows multiple fault causes, which requires maintenance personnel to Find out the internal connection between them and indirectly confirm the cause of the failure.

        Data and status check

        The self-diagnosis of the CNC system can not only display fault alarm information on the CRT display, but also provide machine parameter and status information in the form of multiple pages of "diagnostic address" and "diagnostic data". Common data and status checks include parameter checking and Two kinds of interface checks.

        (1) Parameter check The machine data of CNC machine tools is an important parameter obtained after a series of tests and adjustments, and is a guarantee for the normal operation of the machine tool. These data include gain, acceleration, contour monitoring tolerance, backlash compensation value and screw pitch compensation value. When subjected to external interference, data will be lost or confused, and the machine tool will not work normally.

        (2) Interface check The input/output interface signals between the CNC system and the machine tool include the input/output signals between the CNC system and the PLC, and between the PLC and the machine tool. The input/output interface diagnosis of the CNC system can display the status of all digital signals on the CRT display. Use "1" or "0" to indicate whether the signal is present or not. Use the status display to check whether the CNC system has output the signal to the machine tool. Whether the switch value and other signals of the machine tool side have been input to the CNC system, so that the fault can be located on the machine tool side or in the CNC system.

        Alarm indicator shows failure

        In the CNC system of modern CNC machine tools, in addition to the above-mentioned “software” alarms such as the self-diagnosis function and status display, there are also many “hardware” alarm indicators, which are distributed on the power supply, servo drive and input/output devices. The indication of these warning lights can determine the cause of the failure.

        Spare board replacement method

        Using a spare circuit board to replace a template with a faulty point is a quick and easy way to determine the cause of the fault. It is often used in the functional modules of the CNC system, such as CRT modules, memory modules, etc. It should be noted that before replacement of the spare board, the relevant circuit should be checked to avoid damage to the good board due to a short circuit. At the same time, it should be checked whether the selector switch and jumper on the test board are consistent with the original template. Adjustment of the upper potentiometer. After replacing the memory board, the memory should be initialized according to the requirements of the system, otherwise the system still cannot work normally.

        Exchange method

        In CNC machine tools, there are often modules or units with the same function. By exchanging the same modules or units with each other and observing the failure transfer situation, the fault location can be quickly determined. This method is often used for fault checking of servo feed drives, and it can also be used for the interchange of the same modules in CNC systems.


        The CNC system is composed of various circuit boards, and each circuit board has many solder joints. Any false soldering or poor contact may cause malfunction. When using an insulator to gently tap the circuit board, connector or electrical component with the suspected fault, if a fault occurs, the fault is likely to be in the knocked part.

        Measurement comparison method

        In order to facilitate detection, the module or unit is equipped with detection terminals. Using multimeters, oscilloscopes and other instruments, compare the normal value with the value at the time of the failure through the level or waveform detected by these terminals, and analyze the cause of the failure and The location of the fault. Due to the comprehensiveness and complexity of CNC machine tools, there are many factors that cause failures. The above-mentioned fault diagnosis methods sometimes require several simultaneous applications to perform a comprehensive analysis of the fault, and quickly diagnose the faulty part to eliminate the fault. At the same time, some failure phenomena are electrical, but the cause is mechanical; conversely, the failure phenomenon may be mechanical but the cause is electrical; or both. Therefore, the fault diagnosis cannot be attributed solely to electrical or mechanical aspects, but must be integrated and comprehensively considered.

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