The machine tool crawls phenomenal mechanism studies

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The mechanical model of phenomenon of crawl of machine tool of summary numerical control and kinematic description. Model of have the aid of is analysed, give out the train of thought that solves creeping problem and method. Machine tool of keyword numerical control crawls the graph in kinematic description classifies date TG519.

Crawl appears to have serious harm when 1 document label piles up low speed of system of feed of B machine tool, affect treatment precision not only, and tool of possible still attaint, produce serious noise, cause mechanical failure even, make treatment process cannot go on wheels. Crawl phenomenal generation is concerned with mechanical drive structure not only, also connect closely with the electrical system of feed part. Understanding machine tool produces creeping mechanism, the maintenance to the machine tool and improve have great real sense. One, when servo of feed of machine tool of numerical control of description of phenomenon of machine tool crawl is making low speed move or minim displacement moves, mobile component occurrence speed is inhomogenous -- when when going, stop or the phenomenon of speed. For example: Mobile component begins to cannot be started, after starting, do suddenly again move quickly, after that halt, then is done again move quickly, such go round and round, it is creeping phenomenon. 1. The mechanical model beat a drum of creeping phenomenon narrates creeping motion is a kind of very complex self-excitation brace up phenomenon, the main reason that produces this one phenomenon depends on the stiffness of the change of attrition factor and main transfer machinery be not worth. The mechanical model that can use system of sharp movement transmission will describe. In this stretch and mechanical system, main transfer machinery simplifies for a flexibility (stiffness is K) with an equivalent damp (damp coefficient is β ) driving link is made wait for fast motion, speed is V, driven with flexibility be linked together with damper, move along slideway face. In the begining driven opposite at securing fall asleep, driving link moves right make stretch compress, its flexibility power increases gradually. Exceed driven when stretch force with the biggest static friction between static slideway face when force, driven slide quickly right, right now driven the attrition force You Jing that suffers chafes kinetic friction of force Fx translate into force Fk. As a result of slideway deputy existence is moved, the difference between static friction factor, and static friction factor and itself of kinetic friction factor also are change, what can produce rate so is oscillatory. Set driving link to move in order to wait for fast + V1, after classics time T, driven displacement is X, speed is, acceleration, move equation is type in, f - α X is attrition force, move by bedspring force F and accompany speed and metabolic heft - α X composition, α is coefficient of proportionality the solution of this equation is: In type, , call damp comparing; For horny frequency; △ F is move, the difference of static friction force; S1 amends coefficient for activity, flexibility, take a cost for 1. Will (2) type undertakes differential to T, get speed and accelerometer to calculate formula: From type (4) can see, the athletic speed of executive component includes two shares: Constant V1 and Ewt of { of oscillatory quantity V1 [Cos ω T- (ξ - A) Sin ω T] } , the rate that implements a part will speed, can appear even halt, namely so called creeping phenomenon. Nextpage 2. The creeping type with the kinematic description different basis of creeping phenomenon, the creeping curve that can use different type will describe, decide creeping parameter according to creeping curve again [2] . Crawl normally but described as 3 sort. (1)x, the crawl that when going when T curve description is right, stops, x, T curve describes creeping rule OK and intuitionisticly (graph 2) . T1 is halt time, t2 is dash forward jump time, △ X is dash forward jump displacement is measured (crawl namely quantity) , f is led for creeping frequency (F=1/t=1/ (T1+t2) . Crawl the X that measure △ is the main factor that machines precision among them, it is the main parameter with creeping token. (2) V, the inhomogenous sex of speed of feed of T curve description is to cause the surface wave with treatment bigger workpiece to spend the main reason with faster face surface roughness, affected the treatment quality of the spare parts badly. To the crawl of speed, according to V, T curve (graph 3) , can get the biggest creep speed, the least creep speed. Right now relative speed differs V =vmax of δ of δ V (- the main parameter that Vmin)/vmin is descriptive crawl. (Because creeping phenomenon is relatively complex,3) deviation is described, normally X, T curve and V, T curve does not have simple and apparent regularity, cannot give the error rate of each instant machine tool. So we pass X, T curve and V, T curve decides good exercise curve (graph 4) , serve as the standard of comparison with virtual campaign curve with this. Nextpage analyses whole exercise process further, if pursue,can try a displacement error curve and speed error curve 5, crawling Dvmax of the Dxmax of error of the biggest displacement and error of the oldest rate gives out in error curve, this more reflect creeping frequency feature can clearly, systematic characteristic was mirrorred on certain level, the analysis of blemish of facilitating system motion and improve. 2, the harm with creeping machine tool 1. The influence machines precision. When machining, can make machine the surface to appear apparent knife mark, affect exterior surface roughness; 2. Affect fixed position precision. Ask in fixed position precision more expensive numerical control system is medium, realize exact location very hard, unwarrantable position precision; 3. Attaint tool. Of motion not stable, cause treatment load mutation, meeting attaint cutting tool, lower the service life of the machine tool; 4. Cause mechanical failure easily. If be in hydraulic pressure system, piston lever movement is not steady, create a system extremely easily tilt, mechanical check is dead. In addition, because move to be not stabilized, still can produce noise, affect an environment badly. 3, all sorts of element machine tools that affect machine tool crawl are mobile of the component move, the prime cause that the difference of static friction force is generation crawl, it is OK to reduce attrition from go up at all improvement is creeping. A few another elements also not allow to ignore. The element that causes a machine tool to produce creeping breakdown is OK end is 5 respects. 1. Catenary of mechanical feed drive appeared breakdown. 2. Lubricant and undesirable. 3. Feed system is electric the part appeared problem. 4. Systematic parameter setting is undeserved. 5. The integrated breakdown of mechanical part and electric part. 4, the way to deal with a situation that solves creeping problem and method 1. The place that should find out machine tool of malfunctioning place numerical control to may malfunction above all has: Device of system of drive of servo of mechanical part, electric part and part of strong report control, feed, main shaft, numerical control crawls breakdown arises to be mixed in mechanical part normally feed servo part, because count the creeping phenomenon when controlling low speed of system of machine tool feed,often depend on the character of mechanical drive part is additional, creeping problem with feed speed closely related, the speed annulus that must analyse feed servo so [3] . 2. Analysis of mechanical part breakdown is moved, the prime cause that the difference of static friction force is generation crawl, when checking mechanical part, check slideway above all deputy. Because move,the attrition instruction that component place gets basically is to come from slideway deputy, if slideway is moved deputily, static friction factor is big, and its difference value is great also, cause crawl easily. Although the slideway of numerical control machine tool deputy used roll extensively slideway, static press slideway or plastic slideway, but if adjust bad, still can cause crawl or vibration. To static press slideway deputy, should emphasize an inspection static pressure whether to build to plastic slideway, can check whether to have deputy campaign of foreign matter or slideway of eyewinker block up to scroll slideway, should check tighten measure beforehand proper, the result is favorable. Want to because be in feed system,check feed drive catenary next, arrive from servo actuating device between mobile component sure should pass the transmission chain that by nut of gear, guide screw deputy place of deputy or other drive forms. Elevate chain of this one drive effectively turn round and pull press stiffness (raise its drive stiffness namely) , to raising athletic precision, eliminate crawl very beneficial [4] . The cause that causes mobile component crawl often because be opposite nut of bearing, guide screw deputy with guide screw itself be tightened beforehand or pull beforehand pay no attention to the transmission chain that wants to cause diameter of too long, transmission shaft slants small, bearing stiffness also is not quite those who cause crawl is important, also want to consider these respects to whether have drawback when the examination. Additional, should check slideway to lubricate deputily. Deputy lubricant out of order also can cause slideway creeping [5] . 3. Closely related problem of feed servo crawl and feed speed, the not stable meeting of feed servo causes creeping phenomenon to arise, in wanting pair of servo so, each concern link item-by-item examination, classification eliminates. If inspect speed adjuster ground breakdown characteristic (whether to become scale to change like oscillatory cycle and feed speed) , check electromotor or measure fast whether does the dynamo have a problem; Still can check systematic gain whether too tall; The systematic parameter set that with the position control concerns has inerrancy; The line with speed unit control is good. CNC Milling