Basic method for fault diagnosis of CNC machine tools - News - Global IC Trade Starts Here.

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The diagnosis and treatment of CNC machine tool faults are generally divided into three stages, namely fault detection, fault judgment and isolation, and fault location. The first stage of fault detection is to test the CNC system to determine whether there is a fault. The second stage fault judgment and isolation is to correctly grasp the type of fault that occurs, and separate the possible parts of the fault. The third stage is to locate the fault. Replace the module or printed circuit board to repair the CNC machine tool fault in time.
1) Intuitive method Intuitive method is one of the most basic methods and one of the easiest methods. The maintenance personnel can observe the abnormal phenomena such as light, sound and taste generated when the fault occurs, and carefully check every point of the system to observe the burnt and damage marks, and often reduce the fault range to one module, or even A printed circuit board, but this requires the maintenance personnel to have a wealth of practical experience and comprehensive judgment.
2) Self-diagnostic function method The numerical control device self-diagnosis system writes a series of data called test code to the component or device being diagnosed, and then observes the corresponding output data (called check code) of the system, according to the prior knowledge. The correspondence between the test code, the check code and the fault is determined by analyzing the observation result to determine the fault original. The system white diagnosis mechanism is: after the general system is turned on, the entire hardware system is automatically diagnosed, ready for the normal operation of the system, and the other is to run or input the process of the addition process. Once an error occurs, the numerical control system automatically enters. Self-diagnosis status, locate and issue fault alarm information through fault detection.
(1) Start the diagnosis.
The startup diagnosis is a diagnosis that is automatically executed by the system internal diagnostic program every time the cNc enters the normal operation preparation state from the energization. With the startup diagnostics, most of the hardware failures of the system can be detected, so it is an effective measure to improve system reliability.
(2) Online diagnosis based on alarm information.
Online diagnosis refers to the automatic test of the automatic elbow numerical control device, servo system, external I/O and other external devices through the built-in diagnostic program of the CNC system. When the system is in normal operation, the automatic test, check, and display status information and malfunction. The system can not only display the alarm number and alarm content on the screen, but also display the status of the CNC internal key flag register and the operation unit in the plc in real time, which provides great convenience for fault diagnosis. Online diagnosis is very helpful for the operator and maintenance personnel of the CNC system to analyze the cause of the system failure and determine the fault location.
When the CNC system fails or if it is necessary to judge whether the system is really faulty, it is often necessary to stop processing and stop for inspection. This is offline diagnosis (or offline diagnosis). The main purpose of offline diagnosis is to repair the system and locate the fault, and strive to solve the fault. Position it as small as possible.
3) Parameter (machine data) inspection method There are many parameters (or machine data) addresses in the CNC system. The stored parameter values ​​are determined by the adjustment of the machine when they are shipped from the factory. They directly affect the performance of the CNC machine.
4) PLC check method (1) Use the status information of the PLC to diagnose the fault.
The mechanism for detecting faults by PLC is the PLC ladder diagram (ie program) programmed by the machine tool builder for a specific machine tool. It judges according to various logic states. If a problem is found, an alarm is generated and an alarm message is generated on the display 2S. Therefore, some PLCs generate alarms or some faults without alarms. You can diagnose the faults by analyzing the ladder diagram of the PLC, and use the trapezoidal group display function of the CNC system or the off-machine programmer to track the operation of the ladder diagram online, thus improving the diagnosis. The speed and accuracy of the fault.
(2) Diagnose faults using the trapezoidal tracking method on PI.
Most of the faults that occur in CNC machine tools are checked by the PLC program. Some faults can directly display the cause of the alarm on the screen. For some faults, although there are alarm information on the screen, it does not directly reflect the cause of the alarm. Some faults do not generate alarm information, but some actions are not performed. (http://) In the latter two cases, tracking the operation of the PLC ladder is a very effective way to diagnose a malfunction. For simple faults, the status of the input, output, and flag bits can be monitored by the status display information of the PLC according to the ladder diagram to track the operation of the program. For complex faults, the programmer must be used to track the operation of the ladder diagram.
5) Function program test method The so-called function program test method is to use the manual function or automatic programming method for the common functions of the CNC system and important special functions such as direct positioning, circular interpolation, thread cutting, fixed cycle, user macro program, etc. Compiled into a functional test program, then start the CNC system to run this functional test program. Use it to check the accuracy and reliability of the machine to perform these functions, so as to quickly determine which function of the system is not good, and then determine the cause of the failure. This method is difficult to determine whether it is a programming or operation error or a machine fault due to the long-term idle CNC machine tool and the inspection when the machine is turned on for the first time, and the machine tool processing causes no waste. Methods.
6) Exchange method This is a simple and easy method and one of the most commonly used methods for on-site judgment. The exchange method is that in the case of analyzing the general cause of the fault, the maintenance personnel can replace the suspected part with the spare printed circuit board, template, integrated circuit chip or component, even using the same existing in the system. Types of components are replaced to shrink the fault range to the printed circuit board or chip level. This is actually verifying the correctness of the analysis.
7) Single-step execution of the program to determine the point of failure The CNC system generally has a program single-step execution function, which is often used to debug machining programs. When a machining program failure occurs, the single-step execution program can quickly confirm the fault point and eliminate the fault.
8) Measurement comparison method The measurement method is the basic method for diagnosing machine tool failure. Of course, it is a common method for diagnosing faulty power of CNC machine tools. The measurement method is to measure the electronic circuit by using instruments such as multimeter, oscilloscope and logic tester.
9) Knocking method If the failure of the numerical control system is available, the tapping method can be used to check the location of the fault.
10) Principle analysis method According to the composition principle of the numerical control system, the logic level and characteristic parameters (such as voltage value or waveform) of each point can be logically analyzed, and then it is performed by a multimeter, logic, oscilloscope or logic analyzer. Measurement, analysis and comparison. Thereby locating the fault. To use this method, maintenance personnel are required to have a higher level. In addition, there are local heating methods and a variety of emerging and applied methods.