In the time of nc machine tool feed crawl and vibration phenomenon The key is how to solve

Published on 2017-09-04

To drive moving parts during low speed running, the numerical control machine tool feed system will appear at the beginning of the moving parts can’t start, start and then suddenly accelerated motion, then pause, and then to make accelerated motion, moving parts so the cycle stops and jump, slow and fast motion is called crawling.And when its running at high speed, moving parts and can appear obvious vibration.For nc machine tool feed system and the reason of the crawling is thought to be due to the machine tool lubrication between moving parts is bad, which resulted in increased machine table moves the static friction resistance;When the motor drive, the workbench can not move forward, make the ball screw to produce elastic deformation, the energy storage on the deformation of the motor;Motor to drive, the stored energy of elastic force is greater than the static friction force, the machine table forward peristalsis, repeatedly this movement, the crawling phenomenon.In the time of nc machine tool feed crawl and vibration phenomenon How to solve is the key in fact this is just one of the reasons, the reasons for such failure may also is malfunctioned, mechanical feed transmission chain can also be electrical part of the problem, feed system or the system parameter Settings, may also is a combination of mechanical parts and electrical parts failure.For the crawling and vibration fault of CNC machine tool, can’t jump to conclusions, and should be based on the probability of failure, lists the possible causes of the CNC machine tool crawling and vibration related factors, and then item by item, queuing, factors one by one check, analysis and positioning and troubleshooting.Check where there is a problem, he will be the place of the problem analysis, the main contradiction of the breakdowns and see whether it is, until every possible failure factors.Finally, overall consideration, the paper puts forward a comprehensive solution to the problem, the troubleshooting.Crawling out of nc machine tool feed system and the vibration fault of the specific method is as follows: (1) to analyze the failure parts crawling and vibration fault usually need in mechanical parts and feed servo system is to find problems.Because of the low speed crawl phenomenon of nc machine tool feed system often depends on the characteristics of mechanical transmission parts, when high speed vibration phenomenon and often with drive chain of the feed motion pair of pre-tightening force.In addition, the crawling and vibration problem is closely related to feed rate, and therefore to analysis of speed loop servo system and system parameters.(2) mechanical parts fault checking and removing the causes of crawl and vibration if the mechanical parts, the first thing to check guide.Because of the moving parts of the friction resistance is mainly from the guide rail pair, if guide dynamic and static friction coefficient is big, and the difference is big, will cause the crawling.Although widely used in nc machine tool guideway pair of rolling guide, hydrostatic guideway or plastic guide rail, if adjustment is not good, still can cause crawl or vibration.Hydrostatic guideway should check whether the static pressure is emphatically build;Plastic guide should check for impurities or foreign body block guide motion, rolling guide should check whether the preload is good.Crawl guide lubrication is not good can also cause problems, sometimes only crawl phenomenon is guide due to bad lubrication condition.When using resistant effect of guide rail lubricating oil is a very effective measure, the guide rail the polar additive in lubricating oil, can form a layer on the surface of guide rail is not easy to break up the oil film, thus improve the friction properties of guide rail.Second, check the feed chain.In the feed system, servo drive between moving parts must pass by or other gear, screw nut pair pair of transmission chain.Effectively improve the transmission chain of torsion and tension and compression stiffness, to improve the motion precision, eliminate crawl very beneficial.One of the reasons for crawl moving parts often because of bearing, screw nut and tighten the vice and the screw itself or pretension not ideal.Transmission chain is too long, the shaft diameter smaller, supporting and the rigidity of the bearing seat is not enough and caused the crawling factors that cannot be ignored, so also want to consider these aspects when check whether there are defects.Another bad contact of mechanical system, such as coupling damage can also cause the vibration of the machine tool and crawling.(3) feed servo system fault if checking and removing the crawling and vibration of the cause of the problem in the feed servo system, then you need to check the relevant links in the servo system respectively.Should check or tachogenerator speed regulator, servo motor, the interpolation precision of the system, system gain, related to the position control system parameter setting error, speed control unit on shorting bar set correctly, gain potentiometer to adjust the presence of deviation and speed control unit of the lines are in good condition, item by item, check the classification rule out.(1) the detection of speed regulator of speed regulator malfunction, mainly detect whether a given signal, feedback signal and speed regulator itself has a problem.A given signal can pass by the location deviation counter out by D\/A conversion to the analog signal sent by the speed regulator VCMD testing implementation, this would be if there is A vibration signal component by pins of servo board using oscilloscope to observe.If there is a cycle of vibration signal, there is no doubt that the machine tool vibration is right, this part speed regulator is no problem, but there is something wrong with the former level;And then to the D\/A converter or deviation counter to find problems, if we don’t have any periodic vibration waveform measurements, then the problem must in the feedback signal and speed regulator.(2) the motor speed feedback signal detection feedback signal with a given signal for regulator is exactly the same.So the feedback signal fluctuations, inevitably causes the speed regulator in the opposite direction adjustment, thus cause the vibration of the machine tool.In vibration due to machine tool, shows that the speed of the machine tool in the heat of the oscillation, of course tachogenerator feedback waveform also must be turmoil.At this time if the vibration frequency of machine tool and motor rotation speed is a accurate ratio relations, such as the frequency of the vibration is four times the frequency of the motor speed.When we consider the motor or tachogenerator defective problem.(3) motor inspection when the machine tool vibration frequency and speed with a certain ratio, first check the motor fault, check the carbon brush and commutator surface condition, and check the lubrication condition of ball bearing.Bad the other motor armature coil will cause vibration system.This situation can be confirmed by measuring the no-load current of the motor, if the no-load current is directly proportional to the speed increase, then motor internal short circuit phenomenon.Fault generally should first clear the commutator, check the links such as brush, measured again to confirm.If fault phenomenon still exists, could be coil turn-to-turn short circuit, deal with motor repair processing.If no problem, you should check the tachogenerator.(4) or tachogenerator testing for pulse encoder pulse encoder or tachogenerator adverse situation, according to the following method to measure.Will first position loop, speed loop disconnect, manual motor rotation, observe the speed control unit of F\/V converter voltage applied to the printed circuit board, if there is a sudden drop of waveform, then feedback bad parts.Tachogenerator is often appears a problem in store of carbon brush grinding down of charcoal powder in riser, the slot between the shorting tachogenerator commutation between patches of once appear such problem will cause vibration.5. Adjust the system parameters of a closed loop system can also be caused by unreasonable parameter setting system oscillation, the best way to eliminate the oscillation is to reduce magnification.In the system of FUNAC adjust RV1, counterclockwise rotation, then it can be seen immediately obvious better, but as a result of the RV1 adjust potentiometer range is small, sometimes don’t come over, can only change the shorting bar, also is the removal of the feedback resistance, reduce the magnification of the regulator.6. The processing of external interference in fixed interference, can check F\/V converter, the current detection terminal and synchronization of the waveform, check whether there is interference, and take corresponding measures.For random interference, it is only through effective shielding, reliable grounding, shall be avoided as much as possible.After adopting these methods, but also can’t completely eliminate the vibration, even was invalid, consider to speed regulator board replace or substituted after thorough check everywhere waveform.(the original title: how to solve the numerical control machine tool feed crawling and vibration) (source: numerical control library, headlines today)