Common faults and maintenance methods of the NC sy

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And the training course of the society for advanced molding technology (the participants attended the training course on July 13)

common faults and maintenance methods of the plastic machine numerical control system

the following are some experience summarized by the Engineer in the actual maintenance work for your reference. I hope it can be helpful to you.

1, common fault analysis

(1) position ring

this is the control command issued by the numerical control system and compared with the feedback value of the position detection system, The key link to further complete the control task has a high working frequency and is connected with peripherals, so it is prone to failure. Common faults include:

· position control ring alarm, which may be the open circuit of the measurement circuit; The measuring system is damaged, and the position control unit is internally damaged

· move without sending instructions, which may be due to high drift, positive feedback, and position control unit failure; The measuring element is damaged

· measuring element failure, generally manifested as no feedback value; The machine tool cannot return to the reference point; The possible reasons for the alarm of high-speed time leakage pulse are that the bulb in the grating measuring element is broken, the grating or reading head is dirty or the grating is damaged

(2) servo drive system association

servo drive system is associated with power supply, electrical and mechanical systems, and has been in frequent startup and operation states in work, so this is also the part with more faults

the main faults are:

· system damage is generally caused by too large network voltage fluctuation or voltage shock. Poor power quality in most parts of China will bring voltage overrun to machine tools, especially instantaneous overrun. If there is no special voltage monitor, it is difficult to detect it. When looking for the cause of the fault, we should pay attention to it. There are also some damages caused by special reasons, such as the damage of multiple machine tool servo systems caused by lightning strike in a factory substation in North China

· no control command, but the motor runs at high speed. The cause of this failure is speed loop open-loop or positive feedback. For example, in a factory in Northeast China, during the commissioning of the rotor milling machine imported from Wotan company in West Germany, the x-axis of the machine tool operates at a high speed without instructions. After analysis, we believe that it is caused by positive feedback. Because of the zero drift of the system, in the case of positive feedback, it will quickly accumulate to make the motor operate at high speed. After we checked the line according to the label, it was completely correct. The technicians of the machine tool factory thought it impossible to connect it wrong. After full analysis and detection, we connected the feedback line in reverse, and the machine tool operated normally. The technicians of the machine tool factory have to admit that the German side made mistakes

· another example is the maintenance of a precision grinder that has been unable to work normally. The fault is that the motor runs as soon as the machine tool is started, and it becomes faster and faster until the maximum speed. According to the customer's description, our analysis believes that it is caused by the open circuit of the speed loop and the uncontrollable system drift. After inspection, it is caused by the speed feedback line connected to the ground wire

· when machining, the workpiece surface cannot meet the requirements, and there is a boss when reversing the circular interpolation shaft, or the motor crawls or vibrates at low speed. Such faults are generally caused by improper adjustment of the servo system, unequal gain systems of each axis, or improper matching with the motor. The solution is to carry out optimal adjustment

· the fuse is burnt out or the motor is overheated, which may be caused by excessive mechanical load or jamming

(3) power supply part

power supply part is the energy support part to maintain the normal operation of the system. The direct result of its failure or failure is the shutdown of the system or the destruction of the whole system. Generally, in developed countries in Europe and the United States, the power supply is sufficient and the power quality is relatively good. Such problems are relatively few, so there are not many factors considered in the design. In China, due to the power shortage, the power supply fluctuates greatly, and the quality is poor. There are also hidden disturbances such as high-frequency pulses, and some human factors, such as sudden switching off

in addition, some operating data, setting data and processing programs of the CNC system are generally stored in RAM memory. After the system is powered off, they are maintained by the backup battery or lithium battery of the power supply. Therefore, the downtime is relatively long, and unplugging the power supply or memory may cause data loss, making the system unable to operate

(4) PLC logic interface

logic control of CNC system, such as tool magazine management, hydraulic startup, etc., is mainly realized by PLC. To complete these controls, it is necessary to collect the status information of each control point, such as circuit breakers, servo valves, indicator lights, etc. Therefore, it is connected with a wide variety of external signal sources and actuators, and changes frequently, so the possibility of failure is more, and the types of failure are also variable

(5) other

due to environmental conditions, such as interference, temperature, humidity exceeding the allowable range, improper operation, improper parameter setting, may also cause shutdown or failure. The numerical control equipment in one factory lost the numerical control ready signal soon after starting up, and the system could not work. After inspection, it was found that the body temperature was very high, because the ventilation and filtration had been blocked, causing the temperature sensor to act. After replacing the filter, the system works normally

failure to plug and unplug the circuit board according to the operating procedures, or no electrostatic protection measures, etc., may cause shutdown faults and even damage the system

generally, in the design, use and maintenance of numerical control system, we must consider giving an alarm to the parts that often fail. After the alarm circuit works, on the one hand, it will give alarm information on the screen or operation panel, on the other hand, it will send protective interruption instructions to stop the system from working, so as to find out the fault and carry out maintenance

2. Troubleshooting methods

previously, we introduced the fault diagnosis methods, and now we introduce the troubleshooting methods from several aspects

(1) initialization reset method

generally, the system alarm caused by transient fault can be cleared by hardware reset or switching the system power supply in turn. If the working storage area of the system is confused due to power failure, plugging in and unplugging of the circuit board or undervoltage of the battery, the system must be initialized and cleared. Before clearing, pay attention to make a copy of the data and record. If the fault still cannot be eliminated after initialization, carry out hardware diagnosis

(2) parameter change she indicates that the program correction method

system parameters are the basis for determining the system function, and the wrong parameter setting may cause system failure or invalid function. For example, the rotor milling machine adopts a measurement cycle system, which requires a background memory. During debugging, it is found that this function cannot be realized. After checking, it is found that the data that determines the existence of the background memory is not set, and after setting, the function is normal. Sometimes, due to user program errors, it can also cause fault downtime. For this, the block search function of the system can be used to check and correct all errors to ensure its normal operation

(3) optimization adjustment method

adjustment is the simplest and easiest method. Correct the system fault by adjusting the potentiometer. The display screen of the system is disordered and normal after adjustment. The belt slips when the main shaft is started and braked. The reason is that the load torque of the main shaft is large, and the setting of the ramp time of the driving device is too small. After adjustment, it is normal

optimization adjustment is a comprehensive adjustment method to systematically achieve the best match between the servo drive system and the driven mechanical system. The method is very simple. Use a multi line recorder or a dual trace oscilloscope with storage function to observe the response relationship between command and speed feedback or current feedback respectively. By adjusting the proportional coefficient and integration time of the speed regulator, the servo system can achieve the existing high dynamic response characteristics, Without oscillation. When there is no oscilloscope or recorder on site, an empirical method can be adopted, that is, adjust to make the motor vibrate, and then slowly adjust in the opposite direction until the vibration is eliminated

(4) spare parts replacement method

replace the diagnosed bad circuit board with good spare parts and do the corresponding initialization startup, so that the machine tool can be quickly put into normal operation, and then repair or repair the bad board, which is the most commonly used troubleshooting method at present

(5) method of improving power quality

at present, the quality of power supply in China is poor. The way to solve this problem is generally to use regulated power supply to improve power fluctuation. For high-frequency interference, capacitance filtering method can be used to reduce the failure of the power board through these preventive measures

(6) maintenance information tracking method

some large manufacturing companies constantly modify and improve the system software or hardware according to the accidental faults caused by design defects in actual work. These modifications are constantly provided to maintenance personnel in the form of maintenance information. These information can be used as the basis for troubleshooting, so as to correct and completely eliminate the fault

3. Precautions in maintenance

(1) when taking out a circuit board from the whole machine, pay attention to record its corresponding position and connected cable number. For the fixed installed circuit board, the corresponding crimping parts and screws should also be removed before and after to make a record. The removed crimping parts and screws should be placed in a special box to avoid loss. After assembly, everything in the box should be used, otherwise the assembly will be incomplete

(2) the electric soldering iron should be placed in front of the hand and away from the maintenance circuit board. The soldering iron head should be properly trimmed to adapt to the welding of integrated circuits and avoid bumping other components during welding

(3) when the production and sales of industrial robots in 2017 will exceed the resistance value between 120000 sets, the power supply should be cut off. When measuring the resistance value, the red and black probes shall be interchanged for measurement twice, and the one with a large resistance value shall be taken as the reference value

(4) most of the circuit boards are brushed with solder mask, so the corresponding solder joint should be found as the test point during measurement, and do not remove the solder mask. Some boards are all brushed with insulating layer, so only scrape the insulating layer at the solder joint with a blade

(5) printing should not be cut off at will to drive allied enterprises to achieve green development. Some maintenance personnel have some experience in home appliance maintenance and are used to wire breaking inspection. However, most of the circuit boards on CNC equipment are double-sided metal perforated plates or multi-layer perforated plates. The printing lines are thin and dense. Once cut, it is not easy to weld, and it is easy to cut off adjacent lines when cutting. In addition, some points, when cutting a line, it cannot be separated from the line, You need to cut several wires at the same time

(6) components and parts should not be removed and replaced at will. Some maintenance personnel should remove and replace immediately just by feeling which component is broken without determining the faulty component. In this way, the misjudgment rate is high, and the artificial damage rate of the removed components is also high

(7) when disassembling components, use a tin suction device and a tin suction rope, and do not take them hard. The same pad should not be heated for a long time and disassembled repeatedly to avoid damaging the pad

(8) when replacing new devices, their pins should be properly treated, and acid welding oil should not be used in welding

(9) record the positions of switches and jumpers on the line, which cannot be changed at will. For the comparison inspection or exchange of components and parts above the two poles, pay attention to marking the components on each board to avoid confusion, so that the good board can not work

(10) check the power configuration and type of the circuit board. According to the needs of inspection, power can be supplied separately or completely. Attention should be paid to high voltage. Some circuit boards are directly connected to high voltage, or there is a high voltage generator in the board, so proper insulation is required. Special attention should be paid to operation

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