The electrical fault diagnosis of CNC machine tools has three stages: fault detection, fault judgment, isolation and fault location. Phase fault detection is to test CNC machine tools Phase fault detection is to test CNC machine tools

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 to determine whether there is a fault; the second stage is to determine the nature of the fault and separate the faulty components or modules; the third stage is to locate the fault to a replaceable module or print Circuit board to reduce repair time. In order to detect the faults in the system in time, quickly determine the location of the fault and eliminate it in time. The fault diagnosis should be as small 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:To this end, the following diagnostic methods can be used: the following diagnostic methods can be used:To this end, the following diagnostic methods can be used:

Intuitive methodIntuitive method

Use the sensory organs to pay attention to various phenomena when a fault occurs, such as whether there is spark or malfunction when the fault occurs, whether there is abnormal noise, where abnormal heat is generated, and whether there is a burnt smell. Careful observation of the surface condition of each printed circuit board that may have failed, with or without burnout and damage marks, further narrows the inspection range, which is the most basic and most common method.

Self-diagnosis function of CNC system

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

(1) Power-on self-diagnosis Power-on self-diagnosis means that the system's internal diagnostic program automatically executes modules such as CPU, memory, bus, I/O unit, and printed circuit board from the start of each power-on to the normal operational readiness state. , CRT unit, optoelectronic reader and floppy disk drive and other equipment before the functional test, to confirm whether the system's main hardware can work properly.

(2) Fault message prompt When a fault occurs during machine operation, the number and content are displayed on the CRT display. Follow the prompts and consult the service manual to confirm the cause of the malfunction and how to eliminate it. In general, the richer the fault information of the CNC machine tool diagnostic function prompt, the more convenient it is 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 the manual. The actual cause of some faults does not match the fault content prompt, or one fault indicates that there are multiple fault causes, which requires the maintenance personnel to Find out the intrinsic link between them and indirectly confirm the cause of the failure.

Data and status check

The CNC system's self-diagnosis not only displays fault alarm information on the CRT display, but also provides machine parameter and status information in the form of multiple pages of “diagnostic address” and “diagnostic data”. Common data and status checks have parameter checksums. The interface checks two.

(1) Parameter check The machine tool data of the CNC machine tool is an important parameter obtained through a series of tests and adjustments, which is the guarantee for the normal operation of the machine tool. These data include gain, acceleration, contour monitoring tolerances, backlash compensation values, and screw pitch compensation values. When external interference occurs, the data will be lost or confusing, and the machine will not work properly.

(2) Interface check The input/output interface signals between the CNC system and the machine tool include the interface input/output signals between the CNC system and the PLC, PLC and machine tool. The input/output interface diagnosis of the CNC system can display the status of all the digital signals on the CRT display. Use "1" or "0" to indicate the presence or absence of the signal. Use the status display to check whether the CNC system has output the signal to the machine. On the side, the signal on the machine side is input to the CNC system, so that the fault can be located on the machine side or in the CNC system.

Alarm indicator shows fault

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

Spare plate replacement

The use of an alternate circuit board to replace a template with a faulty point is a quick and easy way to determine the cause of the fault, and is often used for functional modules of the CNC system, such as CRT modules, memory modules, and the like. It should be noted that before the replacement board is replaced, the relevant circuit should be inspected to avoid damage to the board due to short circuit. At the same time, check whether the selection switch and jumper on the test board are consistent with the original template, and some templates should also pay attention to the template. Adjust the potentiometer. After replacing the memory board, the memory should be initialized according to the requirements of the system, otherwise the system still does not work normally.

Exchange method

In CNC machine tools, modules or units with the same function are often exchanged, and the same modules or units are exchanged to observe the fault transfer situation, so that the fault location can be quickly determined. This method is often used for fault checking of servo feed drives and for the interchange of the same modules in the CNC system.

Knocking method

The CNC system consists of a variety of boards, each with many solder joints, and any solder joint or poor contact can be faulty. When using a insulator to gently tap a circuit board, connector, or electrical component that has a problem, if the fault occurs, the fault is likely to be at the location of the tap.

Measurement comparison

For the convenience of detection, the module or the unit is provided with a detection terminal, and the level or waveform detected by these terminals is measured by using a meter such as a multimeter or an oscilloscope, and the normal value is compared with the value at the time of failure, and the cause of the failure can be analyzed. The location of the fault. Due to the comprehensive and complex nature of CNC machine tools, the factors causing the failure are multifaceted. The above-mentioned fault diagnosis methods sometimes need to be applied at the same time, comprehensively analyze the faults, and quickly diagnose the faulty parts, thereby eliminating the faults. At the same time, some fault phenomena are electrical, but the cause is mechanical; on the contrary, the fault phenomenon may be mechanical, but the cause is electrical; or both. Therefore, the fault diagnosis of it cannot often be attributed solely to electrical or mechanical aspects, but must be comprehensively and comprehensively considered.