Discussion on common diagnostic methods for electrical faults of CNC machine tools

The process of investigation, analysis and diagnosis of faults in the electrical system of CNC machine tools is also the process of troubleshooting. Once the cause is identified, the fault is almost equal to the elimination. Therefore, the method of fault analysis and diagnosis becomes very important. The common diagnostic methods are as follows:

(1) Visual inspection method This is a method that must be used at the beginning of failure analysis, that is, the use of sensory inspection.

1 Inquire the personnel at the fault site to inquire carefully about the process of the fault, the fault phenomenon and the consequences of the fault, and may ask multiple times during the entire analysis and judgment process.

2 Visually check whether the working status of each part of the machine tool is in a normal state (such as each coordinate axis position, spindle state, tool magazine, robot position, etc.), and each electronic control device (such as numerical control system, temperature control device, lubrication device, etc.) has No alarm indication, partial inspection of whether there is insurance burnt, component burnt, cracking, wire and cable fall off, the position of each operating component is correct or so.

3 Touch can be found under the condition of power failure of the whole machine by touching the installation status of each main circuit board, the plugging status of each plug, the connection status of each power and signal wires (such as servo and motor contactor wiring). The cause of the failure.

4 Power-on This refers to the power-on analysis in order to check for smoke, fire, abnormal sound, odor, and presence or absence of overheating of the motor and components.

(2) Instrument inspection method Use conventional electrician instrument to measure the AC and DC power supply voltage of each group, and measure related DC and pulse signals to find possible faults. For example, use a multimeter to check the status of each power supply, and measure the relevant signal state measurement points set on some boards. Use an oscilloscope to observe the amplitude, phase, or even the relevant ripple signal. Use the PLC programmer to find the PLC program. The location and cause of the fault.

(3) Signal and alarm indication analysis

1 hardware alarm indication This refers to various states and fault indicators on various electronic and electrical devices including numerical control system and servo system. Combined with the indicator status and corresponding function description, the indication content and the cause of the fault and the elimination can be obtained. method.

2 Software alarm indication The faults in the system software, PLC program and machining program as mentioned above are usually provided with alarm display. According to the displayed alarm number, the corresponding fault description and troubleshooting method can be obtained by comparing the corresponding diagnosis manual.

(4) Interface state check method Modern CNC system integrates PLC in it, and CNC and PLC communicate with each other in a series of interface signals. Some faults are related to the error or loss of interface signals. Some of these interface signals can be displayed on the corresponding interface board and input/output board, and some can be displayed on the CRT screen by simple operation, and all interfaces The signal can be called up with the PLC programmer. This inspection method requires the maintenance personnel to be familiar with the interface signals of the machine and to be familiar with the application of the PLC programmer.

(5) Parameter adjustment method The numerical control system, PLC and servo drive system are all equipped with many modifiable parameters to adapt to different machine tools and different working conditions. These parameters not only match the electrical system to the specific machine, but are also necessary to optimize the machine's functions. Therefore, any change in parameters (especially analog parameters) or even loss is not allowed; and changes in mechanical or electrical properties caused by long-term operation of the random bed will break the initial matching state and optimization state. Such faults refer to the latter type of faults in the fault classification section, and one or more related parameters need to be re-adjusted to be excluded. This method has high requirements for maintenance personnel. It is not only necessary to understand the main parameters of the specific system, but also knows that its address is familiar with its function, and it has to have rich experience in electrical debugging.

(6) Spare parts replacement method When the fault analysis results are concentrated on a certain printed circuit board, it is very difficult to implement the fault in a certain area or even a certain component due to the continuous expansion of the circuit integration degree, in order to shorten For downtime, you can replace the spare parts before you have the same spare parts, and then check the repaired fault board. Pay attention to the following problems when replacing spare parts boards.

1 Replacement of any spare parts must be carried out in the event of a power failure.

2 Many printed circuit boards have some switches or shorting bars to match the actual needs. Therefore, the original switch position and setting state must be recorded on the replacement spare board, and the new board should be the same. Set, otherwise an alarm will be generated and it will not work.

3 Some printed circuit board replacements also need to perform certain operations after replacement to complete the establishment of software and parameters. This requires careful reading of the instructions for the appropriate board.

4 Some printed circuit boards cannot be easily removed, such as boards containing working memory, or spare boards, which can lose useful parameters or programs. You must follow the instructions when you have to replace it. In view of the above conditions, before you remove the old board to replace the new board, you must carefully read the relevant information, understand the requirements and operating procedures before you start, so as not to cause more problems.

(7) Cross-transposition method When the faulty board is found or the faulty board cannot be determined and there is no spare part, the same or compatible two boards in the system can be interchanged and checked, for example, two coordinate command boards or servos. The exchange of the board determines the fault board or the fault location. This cross-transposition method should pay special attention to not only the correct exchange of hardware wiring, but also a series of corresponding parameters exchange, otherwise it will not achieve the purpose, but will create new faults causing confusion of thinking, must be considered in advance , design a good software and hardware exchange program, and then exchange and check accurately.

(8) Special processing method Today's CNC system has entered the development stage of PC-based and open-ended, in which the software content is more and more abundant, there are system software, machine tool builder software, and even the user's own software, due to software logic. Some of the inevitable problems in the design will make some fault states unrecognizable, such as crashes. For this kind of fault phenomenon, special measures can be taken to deal with it. For example, the whole machine is powered off, and then restarted after a pause, and sometimes the fault may be eliminated. Maintenance personnel can explore their laws or other effective methods in their long-term practice.