Abstract: The process of investigating, analyzing, and diagnosing faults in the electrical systems of CNC machine tools is also the process of troubleshooting. Once the cause is identified, the fault is almost eliminated. Therefore, the methods of fault analysis and diagnosis are very important. Keywords: CNC machine tool , fault troubleshooting, analysis I. Fault Investigation and Analysis This is the first and crucial stage of troubleshooting. The following tasks should be performed: 1. Inquiry and Investigation: Upon receiving information about a fault at the machine tool site requiring troubleshooting, the operator should be instructed to maintain the fault state at the site as much as possible without taking any action. This facilitates a rapid and accurate analysis of the fault cause. 2. On-site Inspection: Upon arrival at the site, the accuracy and completeness of the information provided by the operator should be verified to confirm the accuracy of the preliminary judgment. Due to the operator's skill level, there are often instances where the description of the fault condition is unclear or even completely inaccurate. Therefore, upon arrival at the site, one should not rush to take action but carefully re-investigate all situations to avoid damaging the site and increasing the difficulty of troubleshooting. 3. Fault Analysis: Based on the known fault conditions, the fault type should be analyzed according to the fault classification method described in the previous section to determine the troubleshooting principles. Since most faults are indicated, under normal circumstances, by referring to the diagnostic manual and instruction manual of the CNC system that the machine tool is equipped with, we can list a variety of possible causes of the fault. 4. Determine the cause. Investigate the various possible causes to find the real cause of the fault. This is a comprehensive test of the maintenance personnel’s familiarity with the machine tool, knowledge level, practical experience and analytical judgment ability. 5. Troubleshooting preparation. Some faults may be easy to troubleshoot, while others are more complex and require a series of preparatory work, such as the preparation of tools and instruments, partial disassembly, repair of parts, procurement of components and even the formulation of troubleshooting plan steps. The commonly used diagnostic methods for electrical faults are summarized below. (1) Visual inspection method. This is a method that must be used at the beginning of fault analysis, which is to use sensory inspection. ① Inquiry. Carefully inquire about the process of fault generation, fault symptoms and fault consequences from the personnel at the fault site, and may need to be asked multiple times throughout the analysis and judgment process. ② Visually inspect the overall working status of each part of the machine tool to see if it is in normal condition (e.g., the position of each coordinate axis, the status of the spindle, the tool magazine, the position of the robot, etc.), whether each electrical control device (such as the CNC system, the temperature control device, the lubrication device, etc.) has an alarm indication, check locally whether the fuse is burnt, whether the components are charred or cracked, whether the wires and cables are detached, whether the position of each operating element is correct, etc. (2) Instrument inspection method Use conventional electrical instruments to measure the voltage of each AC and DC power supply, and measure the relevant DC and pulse signals, etc., to find possible faults. For example, use a multimeter to check the power supply status, and measure the relevant signal status measurement points set on certain circuit boards, use an oscilloscope to observe the amplitude, phase, and even presence or absence of the relevant pulse signals, and use a PLC programmer to find the fault location and cause in the PLC program, etc. (3) Signal and alarm indication analysis method ① Hardware alarm indication This refers to the various status and fault indicator lights on each electronic and electrical device, including the CNC system and the servo system. By combining the indicator light status and the corresponding function description, the indication content, fault cause, and troubleshooting method can be obtained. ② Software alarm indication As mentioned above, faults in system software, PLC programs and machining programs are usually equipped with alarm displays. By referring to the corresponding diagnostic manual based on the displayed alarm number, the possible causes of the fault and the troubleshooting methods can be found. (4) Interface status check method Modern CNC systems often integrate PLCs, and the CNC and PLC communicate with each other through a series of interface signals. Some faults are related to interface signal errors or loss. Some of these interface signals can be displayed by indicator lights on the corresponding interface board and input/output board, and some can be displayed on the CRT screen through simple operation. All interface signals can be retrieved by the PLC programmer. (5) Parameter adjustment method CNC systems, PLCs and servo drive systems are equipped with many modifiable parameters to adapt to the requirements of different machine tools and different working states. These parameters not only enable each electrical system to match with the specific machine tool, but are also necessary to optimize the various functions of the machine tool. Therefore, any change in parameters (especially analog parameters) or even loss is not allowed; and the changes in mechanical or electrical performance caused by the long-term operation of the machine tool will break the initial matching state and optimization state. This type of fault usually refers to the latter type of fault in the fault classification section, which requires readjustment of one or more related parameters to eliminate the fault. (6) Spare parts replacement method When the fault analysis results are concentrated on a certain printed circuit board, it is very difficult to pinpoint the fault to a certain area or even a certain component due to the continuous expansion of circuit integration. In order to shorten the downtime, if there are spare parts available, the spare parts can be replaced first, and then the faulty board can be checked and repaired. Given the above conditions, before removing the old board and replacing it with a new board, you must carefully read the relevant information, understand the requirements and operating procedures before taking action, so as to avoid causing a bigger fault. (7) Cross-swapping method When a faulty board is found or it is not certain whether it is a faulty board and there are no spare parts, two identical or compatible boards in the system can be swapped for inspection, such as the swapping of two coordinate instruction boards or servo boards to determine the faulty board or faulty part. This cross-swap method requires special attention. Not only should the hardware wiring be correctly swapped, but a series of corresponding parameters should also be swapped. Otherwise, not only will the purpose not be achieved, but new faults will be generated, causing confusion in thinking. It is necessary to consider everything in advance, design a software and hardware swapping scheme, and then swap and check it accurately. (8) Special handling method Today's CNC systems have entered the PC-based and open development stage. The software content is becoming richer and richer, including system software, machine tool manufacturer software, and even user-owned software. Due to some unavoidable problems in the design of software logic, some fault states are impossible to analyze, such as the phenomenon of system crash. For such fault phenomena, special means can be used to deal with them, such as powering off the whole machine, pausing for a while, and then turning it on again. Sometimes this may eliminate the fault. Maintenance personnel can explore its rules or other effective methods in their long-term practice. II. Electrical maintenance and fault elimination The process of electrical fault analysis is also the process of fault elimination. Therefore, some common methods of electrical fault elimination have been comprehensively introduced in the analysis methods in the previous section. This section lists a few common electrical faults for a brief introduction for maintenance personnel to refer to. 1. Power Supply: The power supply is the energy source for the normal operation of the maintenance system and even the entire machine tool. Its failure or malfunction can result in data loss and downtime, or even damage to parts or the entire system. Western countries, with their abundant power and high-quality power grids, have less consideration for power supply design in their electrical systems. This is somewhat inadequate for my country's power grid, which experiences significant fluctuations and high harmonics. Combined with certain human factors, power supply-related failures are inevitable. 2. CNC System Position Loop Faults: ① Position loop alarm: This could be due to an open circuit in the position measurement loop; damaged measuring elements; or the absence of the interface signal for position control. ② Coordinate axis movement without command: This could be due to excessive drift; positive feedback in the position or speed loop; an open circuit in the feedback wiring; or damaged measuring elements. 3. Machine Tool Coordinates Cannot Find Zero: This could be due to the zero direction being far from zero; a damaged encoder or open circuit in the wiring; a shifted grating zero-point mark; or a malfunctioning zero-return deceleration switch. 4. Deterioration of Machine Tool Dynamic Characteristics, Reduced Workpiece Machining Quality, and Even Machine Tool Vibration at Certain Speeds. One major possibility is that the mechanical transmission system has excessive clearance or severe wear, or that the guide rails are not adequately lubricated or are also worn. For the electrical control system, the speed loop, position loop, and related parameters may not be optimally matched. Optimization adjustments should be made after the mechanical fault has been largely eliminated. 5. Intermittent shutdowns. There are two possible scenarios: one is that, as mentioned earlier, problems in the related software design cause shutdowns under certain combinations of operations and functions. Generally, these will disappear after the machine tool is powered off and then powered on again. The other scenario is caused by environmental conditions, such as strong interference (power grid or peripheral equipment), excessively high temperature, or excessive humidity. These environmental factors are often overlooked. For example, in southern regions, machine tools may be placed in ordinary factory buildings or even near open doors, with the electrical cabinet running for extended periods, or near equipment that generates a large amount of dust, metal shavings, or water mist. These factors can not only cause malfunctions but can also damage the system and machine tool in severe cases, so it is essential to address these issues.