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Fault analysis of automatic machine tool
Automatic machine tool is an important material basis for modern enterprises to produce and an important technical means to complete the production process. Strengthening management is the key, and the combination of "prevention" and "treatment" is the only way to solve the "difficult use and maintenance" of CNC machine tools.
I. Fault Investigation and Analysis
This is the first stage of troubleshooting, and it is also a very critical stage. The following work should be done:
1, Asking and Investigating When receiving the information that the on-site fault of the machine tool needs to be eliminated, the operator should be required to keep the on-site fault state as far as possible without any treatment, which is conducive to quickly and accurately analyzing the cause of the fault.
2. After the on-site inspection arrives at the site, the accuracy and completeness of various situations provided by the operators should be verified first to verify the accuracy of the preliminary judgment. Due to the level of operators, there are many cases where the fault situation is unclear or even completely inaccurate. Therefore, after arriving at the scene, don't rush to deal with it, and carefully investigate all kinds of situations again, so as not to destroy the scene and increase the difficulty of troubleshooting.
3. Fault analysis According to the known fault conditions, the fault types are analyzed according to the fault classification method described in the previous section, so as to determine the troubleshooting principle. Because most faults are explained, generally speaking, according to the diagnosis manual and instruction manual of CNC system equipped with machine tools, various possible causes of faults can be listed.
4. Determine the reason. Investigate all possible causes and find out the real cause of this fault. At this time, it is a comprehensive test of the maintenance personnel's familiarity with this machine tool, knowledge level, practical experience and analytical judgment ability.
5. Troubleshooting preparation Some troubleshooting methods may be simple, while some faults are often complex, which requires a series of preparatory work, such as preparing tools and meters, partially disassembling, repairing parts, purchasing parts and even making troubleshooting plan steps.
Common electrical fault diagnosis methods are as follows.
(1) Visual inspection This is a necessary method at the beginning of fault analysis, that is, using sensory inspection.
(1) Ask the personnel at the scene of the fault to carefully ask about the process, symptoms and consequences of the fault, which may be asked many times during the whole analysis and judgment process.
② Visually check whether all parts of the machine tool are in normal state (such as the positions of coordinate axes, spindle, tool magazine and manipulator). ), whether there are electrical control devices (such as numerical control system, temperature control device, lubrication device, etc. ) with alarm instructions, on-site check whether there is any safe burning, whether there is any burning and cracking of components, whether there is any loss of wires and cables, and whether the positions of various operating components are correct.
(2) Instrument inspection method uses conventional electrical instruments to measure AC and DC power supply voltages and related DC and pulse signals of each group to find possible faults. For example, use multimeter to check the power supply situation, and measure some related signal state measuring points set on circuit boards, use oscilloscope to observe the amplitude, phase and even presence of related pulse signals, and use PLC programmer to find the fault parts and causes in PLC programs.
(3) signal and alarm indication analysis method
(1) Hardware alarm indicator This refers to various status and fault indicators on various electronic and electrical equipment, including numerical control systems and servo systems. Combined with the status of indicator light and the corresponding function description, we can get the indication content, fault reason and troubleshooting method.
(2) Software alarm indication As mentioned above, faults in system software, PLC program and processing program usually have alarm display. According to the displayed alarm number and the corresponding diagnosis instruction manual, possible fault causes and troubleshooting methods can be known.
(4) Inspection method of interface state Modern CNC systems mostly integrate PLC, and CNC and PLC communicate with each other in the form of 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 CRT screen through simple operation. All interface signals can be called out by PLC programmers.
(5) Parameter adjustment method Many modifiable parameters are set in the CNC system, PLC and servo drive system to meet the requirements of different machine tools and different working conditions. These parameters can not only match each electrical system with a specific machine tool, but also be necessary to optimize the function of the machine tool. Therefore, it is not allowed to change or even lose any parameters (especially analog parameters); However, the change of mechanical or electrical properties caused by long-term operation of random bed will break the initial matching state and optimization state. This kind of fault mostly refers to the latter fault in the fault classification part, and one or more related parameters need to be readjusted to eliminate it.
(6) Spare parts replacement method When the failure analysis results are concentrated on a printed circuit board, it is difficult to implement the failure of a certain area or even a certain component due to the continuous expansion of circuit integration. In order to shorten the downtime, in the case of the same spare parts, the spare parts can be replaced first, and then the faulty board can be inspected and repaired.
In view of the above situation, before pulling out the old board and replacing it with a new one, you must read the relevant materials carefully, understand the requirements and operation steps before starting work, so as to avoid causing greater failures.
(7) Cross-transposition method When a faulty board is found or it is uncertain whether there is a fault or not, and there are no spare parts, two identical or compatible boards in the system can be interchanged for inspection, such as the command board or the servo board with two coordinates, so that the faulty board or the faulty part can be judged. This cross transposition method should not only pay special attention to the correct interchange of hardware wiring, but also pay attention to a series of corresponding parameters. Otherwise, it will not only fail to achieve the goal, but will cause new faults and confusion of thinking. Be sure to think carefully in advance, design a good software and hardware exchange scheme, and check the exchange after it is accurate.
(8) Special treatment methods Today's CNC system has entered a PC-based and open development stage, in which the software content is more and more abundant, including system software, machine tool manufacturer software and even users' own software. Due to some inevitable problems in software logic design, some fault states cannot be analyzed, such as crash. For this kind of fault phenomenon, special measures can be taken to deal with it, such as power failure, restart after a short pause, and sometimes the fault may be eliminated. Maintenance personnel can explore its laws or other effective methods in long-term practice.
Second, the electrical maintenance and troubleshooting
The process of electrical fault analysis is also the process of troubleshooting, so some common electrical fault troubleshooting methods have been comprehensively introduced in the analysis method in the previous section. This section briefly introduces several common electrical faults for maintenance personnel's reference.
1. Power supply is the energy source to maintain the normal operation of the system and even the whole machine tool. If it fails or fails slightly, it will lose data and cause downtime. In severe cases, it will destroy some or even all systems. Due to the abundant power and high quality of power grid in western countries, the power supply design of their electrical systems is less considered, which is slightly insufficient for China's power supply network with large fluctuations and high harmonics. Coupled with some human factors, it is inevitable that there will be failures caused by power supply.
2, CNC system position ring fault
(1) position rings the alarm. It may be that the position measurement loop is open; The measuring element is damaged; The interface signal established by position control does not exist, etc.
② Axis moves without instructions. It may be that the drift is too large; Position loop or speed loop is connected with positive feedback; The feedback line is open; The measuring element is damaged.
3. The machine tool coordinates can't find the zero point. It may be that the zero direction is far from the zero point; The encoder is damaged or the line is open; Grating zero drift; Zero deceleration switch failure.
4. The dynamic characteristics of the machine tool become worse, the machining quality of the workpiece decreases, and even the machine tool vibrates at a certain speed. The gap of mechanical transmission system is too large or even seriously worn, or the guide rail is not fully lubricated or even worn. For the electrical control system, it may be that the speed loop, position loop and related parameters are no longer in the best matching state, and they should be optimized after the mechanical failure is basically eliminated.
5. Stop the machine occasionally. There are two possible situations here: one is that the above-mentioned problems in related software design lead to the failure of shutdown under some specific operation and functional operation combinations, and in general, the machine tool will disappear when it is powered off and then on; Another situation is caused by environmental conditions, such as strong interference (power grid or peripheral equipment), excessive temperature and humidity, etc. This kind of environmental factor is often ignored by people. For example, in the south of China, machine tools are placed near ordinary factories or even open doors, electrical cabinets are left open for a long time, and there are a large number of devices that produce dust, metal chips or water mist nearby. These factors will not only cause failures, but also seriously damage the system and machine tools, so we must pay attention to improvement.
Abstract: The process of fault investigation, analysis and diagnosis of electrical system of CNC machine tools is also the process of fault elimination. Once the cause is found out, the fault is almost eliminated. Therefore, the method of fault analysis and diagnosis is very important.
Keywords: CNC machine tool fault analysis
I. Fault Investigation and Analysis
This is the first stage of troubleshooting, and it is also a very critical stage. The following work should be done:
1, Asking and Investigating When receiving the information that the on-site fault of the machine tool needs to be eliminated, the operator should be required to keep the on-site fault state as far as possible without any treatment, which is conducive to quickly and accurately analyzing the cause of the fault.
2. After the on-site inspection arrives at the site, the accuracy and completeness of various situations provided by the operators should be verified first to verify the accuracy of the preliminary judgment. Due to the level of operators, there are many cases where the fault situation is unclear or even completely inaccurate. Therefore, after arriving at the scene, don't rush to deal with it, and carefully investigate all kinds of situations again, so as not to destroy the scene and increase the difficulty of troubleshooting.
3. Fault analysis According to the known fault conditions, the fault types are analyzed according to the fault classification method described in the previous section, so as to determine the troubleshooting principle. Because most faults are explained, generally speaking, according to the diagnosis manual and instruction manual of CNC system equipped with machine tools, various possible causes of faults can be listed.
4. Determine the reason. Investigate all possible causes and find out the real cause of this fault. At this time, it is a comprehensive test of the maintenance personnel's familiarity with this machine tool, knowledge level, practical experience and analytical judgment ability.
5. Troubleshooting preparation Some troubleshooting methods may be simple, while some faults are often complex, which requires a series of preparatory work, such as preparing tools and meters, partially disassembling, repairing parts, purchasing parts and even making troubleshooting plan steps.
Common electrical fault diagnosis methods are as follows.
(1) Visual inspection This is a necessary method at the beginning of fault analysis, that is, using sensory inspection.
(1) Ask the personnel at the scene of the fault to carefully ask about the process, symptoms and consequences of the fault, which may be asked many times during the whole analysis and judgment process.
② Visually check whether all parts of the machine tool are in normal state (such as the positions of coordinate axes, spindle, tool magazine and manipulator). ), whether there are electrical control devices (such as numerical control system, temperature control device, lubrication device, etc. ) with alarm instructions, on-site check whether there is any safe burning, whether there is any burning and cracking of components, whether there is any loss of wires and cables, and whether the positions of various operating components are correct.
(2) Instrument inspection method uses conventional electrical instruments to measure AC and DC power supply voltages and related DC and pulse signals of each group to find possible faults. For example, use multimeter to check the power supply situation, and measure some related signal state measuring points set on circuit boards, use oscilloscope to observe the amplitude, phase and even presence of related pulse signals, and use PLC programmer to find the fault parts and causes in PLC programs.
(3) signal and alarm indication analysis method
(1) Hardware alarm indicator This refers to various status and fault indicators on various electronic and electrical equipment, including numerical control systems and servo systems. Combined with the status of indicator light and the corresponding function description, we can get the indication content, fault reason and troubleshooting method.
(2) Software alarm indication As mentioned above, faults in system software, PLC program and processing program usually have alarm display. According to the displayed alarm number and the corresponding diagnosis instruction manual, possible fault causes and troubleshooting methods can be known.
(4) Inspection method of interface state Modern CNC systems mostly integrate PLC, and CNC and PLC communicate with each other in the form of 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 CRT screen through simple operation. All interface signals can be called out by PLC programmers.
(5) Parameter adjustment method Many modifiable parameters are set in the CNC system, PLC and servo drive system to meet the requirements of different machine tools and different working conditions. These parameters can not only match each electrical system with a specific machine tool, but also be necessary to optimize the function of the machine tool. Therefore, it is not allowed to change or even lose any parameters (especially analog parameters); However, the change of mechanical or electrical properties caused by long-term operation of random bed will break the initial matching state and optimization state. This kind of fault mostly refers to the latter fault in the fault classification part, and one or more related parameters need to be readjusted to eliminate it.
(6) Spare parts replacement method When the failure analysis results are concentrated on a printed circuit board, it is difficult to implement the failure of a certain area or even a certain component due to the continuous expansion of circuit integration. In order to shorten the downtime, in the case of the same spare parts, the spare parts can be replaced first, and then the faulty board can be inspected and repaired.
In view of the above situation, before pulling out the old board and replacing it with a new one, you must read the relevant materials carefully, understand the requirements and operation steps before starting work, so as to avoid causing greater failures.
(7) Cross-transposition method When a faulty board is found or it is uncertain whether there is a fault or not, and there are no spare parts, two identical or compatible boards in the system can be interchanged for inspection, such as the command board or the servo board with two coordinates, so that the faulty board or the faulty part can be judged. This cross transposition method should not only pay special attention to the correct interchange of hardware wiring, but also pay attention to a series of corresponding parameters. Otherwise, it will not only fail to achieve the goal, but will cause new faults and confusion of thinking. Be sure to think carefully in advance, design a good software and hardware exchange scheme, and check the exchange after it is accurate.
(8) Special treatment methods Today's CNC system has entered a PC-based and open development stage, in which the software content is more and more abundant, including system software, machine tool manufacturer software and even users' own software. Due to some inevitable problems in software logic design, some fault states cannot be analyzed, such as crash. For this kind of fault phenomenon, special measures can be taken to deal with it, such as power failure, restart after a short pause, and sometimes the fault may be eliminated. Maintenance personnel can explore its laws or other effective methods in long-term practice.
Second, the electrical maintenance and troubleshooting
The process of electrical fault analysis is also the process of troubleshooting, so some common electrical fault troubleshooting methods have been comprehensively introduced in the analysis method in the previous section. This section briefly introduces several common electrical faults for maintenance personnel's reference.
1. Power supply is the energy source to maintain the normal operation of the system and even the whole machine tool. If it fails or fails slightly, it will lose data and cause downtime. In severe cases, it will destroy some or even all systems. Due to the abundant power and high quality of power grid in western countries, the power supply design of their electrical systems is less considered, which is slightly insufficient for China's power supply network with large fluctuations and high harmonics. Coupled with some human factors, it is inevitable that there will be failures caused by power supply. 2, CNC system position ring fault
(1) position rings the alarm. It may be that the position measurement loop is open; The measuring element is damaged; The interface signal established by position control does not exist, etc.
② Axis moves without instructions. It may be that the drift is too large; Position loop or speed loop is connected with positive feedback; The feedback line is open; The measuring element is damaged.
3. The machine tool coordinates can't find the zero point. It may be that the zero direction is far from the zero point; The encoder is damaged or the line is open; Grating zero drift; Zero deceleration switch failure.
4. The dynamic characteristics of the machine tool become worse, the machining quality of the workpiece decreases, and even the machine tool vibrates at a certain speed. The gap of mechanical transmission system is too large or even seriously worn, or the guide rail is not fully lubricated or even worn. For the electrical control system, it may be that the speed loop, position loop and related parameters are no longer in the best matching state, and they should be optimized after the mechanical failure is basically eliminated.
5. Stop the machine occasionally. There are two possible situations here: one is that the above-mentioned problems in related software design lead to the failure of shutdown under some specific operation and functional operation combinations, and in general, the machine tool will disappear when it is powered off and then on; Another situation is caused by environmental conditions, such as strong interference (power grid or peripheral equipment), excessive temperature and humidity, etc. This kind of environmental factor is often ignored by people. For example, in the south of China, machine tools are placed near ordinary factories or even open doors, electrical cabinets are left open for a long time, and there are a large number of devices that produce dust, metal chips or water mist nearby. These factors will not only cause failures, but also seriously damage the system and machine tools, so we must pay attention to improvement.