機(jī)械外文文獻(xiàn)翻譯-織機(jī)打緯機(jī)構(gòu)的計(jì)算機(jī)輔助分析【中文4000字】【PDF+中文WORD】

機(jī)械外文文獻(xiàn)翻譯-織機(jī)打緯機(jī)構(gòu)的計(jì)算機(jī)輔助分析【中文4000字】【PDF+中文WORD】,中文4000字,PDF+中文WORD,機(jī)械,外文,文獻(xiàn),翻譯,織機(jī),打緯,機(jī)構(gòu),計(jì)算機(jī)輔助,分析,中文,4000,PDF,WORD http:/ Research Journal http:/ online version of this article can be found at:DOI:10.1177/004051759806800902 1998 68:630Textile Research JournalYoujiang Wang and Hui SunComputer Aided Analysis of Loom Beating-up Mechanisms Published by:http:/ can be found at:Textile Research JournalAdditional services and information for http:/ Alerts:http:/ is This?-Sep 1,1998Version of Record Downloaded from 630Computer Aided Analysis of Loom Beating-up MechanismsYOUJIANG WANG AND HUI SUN School of Textile&Fiber Engineering,Georgia Institute of Technology,Atlanta,Georgia 30332,U.S.A.ABSTRACTAnalysis and design of the beating-up mechanism is of great importance for im-proving loom performance.Computer aided design and analysis tools are used to studydifferent kinds of beating-up mechanisms,including the 4-link and 6-link systems,andtheir characteristics are compared with those of the conjugate-cam mechanism.Resultsfrom models with varying geometric parameters are presented,revealing that the com-puter tools are effective and useful in analyzing and designing beating-up mechanisms with smoother operation,lower noise and vibration,and higher speeds.The last decade has witnessed the transformation of,the textile industry from a labor intensive one into ahigh productivity,capital intensive industry.In manu-facturing woven fabrics,there is a constant desire forhigh performance looms that are fast,energy efficient,reliable,highly automated,quiet,durable,and lowmaintenance.Over the last few decades,the production rate of looms has increased tremendously,with maxi-mum weft insertion rates moving from about 200.towell over 2000 m/min.Such a significant improvementin performance is a result of technological innovations(e.g.,shuttleless weaving),employment of new tech-nologies(e.R.,computers and materials),and bettermachinery designs.Regardless of the kind of loom,its technologicalstate,or the pattern to be woven,the basic weavingoperations consists of four steps:shedding,picking,beating-up,and taking-up/letting-off 2 J.The shed-.ding operation raises and lowers specific warp yarns bymeans of harnesses to form a shed.During the pickingstep,the new filling yam is inserted through the shed.Beating-up occurs when the newly inserted filling yarnis pushed firmly in place by means of the reed mountedon the sley.Finally,the finished fabric is wound on the;cloth beam.while more warp yarn is released from the:warp beam.These four operations are performed in a.constantly repeated sequence.Beating-up is of great importance to the weavingprocess and the quality of the product.A normal beat-ing-up operation will give a firm,uniform fabric struc-ture.In addition,the movement of the reed carried bythe sley,through which beating-up is achieved,has animportant effect on the.smoothness of shedding andpicking operations.In high speed weaving,the relativetime per cycle taken by operations other than pickingshould be minimized.It is desirable that the reed dwell;as long as possible at the rear to leave more time forweft insertion,and then move swittly to beat up thenew filling yarn.This is especially crucial for modernwide-width looms.However,higher forces and vibra-tions are associated with jerky movements,and designcompromise is necessary to achieve a balance betweenloom speed and smooth operation.Dynamic analysisof the motion of the sley(reed)is therefore importantfor loom designers and manufacturers.In general,there are three basic kinds of beating-upmechanisms:4-link.6-link,and conjugate-carn,asshown in Figure 1.The 4-link mechanism is used mostwidely on shuttle,air-jet,and rapier looms.since it hasa simple structure and is easy to manufacture.The 6-link mechanism,which may provide a longer dwell pe-riod,is mainly used in air-jet looms.The conjugate-cam mechanism is being used more and more widelyin shuttleless looms due to its precise and adjustabledwell period of the sley.The design of beating-up mechanism;,particularlytheir mass distribution and geometry,has a significanteffect on the performance of the loom.Traditionalmethods for analyzing these mechanisms based on ki-nematic and dynamic principles are well established,but often involve lengthy mathematical derivations.Computer aided design and analysis tools provide asimpler way of analyzing the dynamic responses ofcomplex structures.Working Model,a software product of KnowledgeRevolution,Ibines advanced motion sim-ulation technology with sophisticated editing abilitiesto provide a useful tool for engineering and animationsimulation.A mechanism can be converted into a setof rigid bodies and constraints to build the model onthe computer.This software simulates the motion ofthe mechanism based on geometric constraints andNewtonian mechanics.principles.Quantities definedbefore the simulation can be exported during the sim-Downloaded from 631FIGURE 1.Typical beating-up mechanisms:(a)4-link,(b)6-J.ink.and(c)conjugate-camulating process for further analysis.The properties ofobjects can be adjusted with its graphic user interfaceto form new models with desirable results.In this study,we first analyze the 4-link mechanismusing the Working Model software.A parametric studyexplores the effect of geometry on the sleys motion.We also build models for the 6-link mechanism to iden-tify geometric configurations that can lead to a longinsertion period in a weaving cycle.Finally,we com-pare the sleys motion for different beating-up mech-anisms.Beating-up MechanismsFOUR-LINK MECHANISMFigure 2 shows the computer model obtained dafterimplementing all parts of a 4-link mechanism withWorking Model,according to the actual size;mass,andconnection type.Quantities measured and recordedduring the simulation include the displacement of thesley(X),the velocity of sley(V),the acceleration ofsley(A),and the force(F)acting on the swordpin.Tovalidate Working Model,we have compared the resultsfrom the Working Model simulation and kinematicsanalysis and found no noticeable differences.For parametric studies,we have used the actual di-mensions of machine parts in a shuttle loom(FigureI a)-crankshaft length r=6 cm,connecting rodlength s=32 cm,and sley length L=72.11 cm.Thisgeometric configuration is the reference for the perfor-mance comparison with other models.We have as-sumed that the loom speed is 200 rpm.To observe theinfluence of different ratios of slr on the motion of thesley,the connecting rod length varies from 17 to 102cm,while r and L are kept constant.We have evaluatedelevem models with s/r ratios from 2.83 to 17.FIGURE 2.Computer model of 4-link beating-up mechanism.From the Working Model simulation data,we haveobtained the maximum values of sley velocity V,ac-celeration A,and the force in the connecting rod F,foreach model.The results are shown in Figure 3,nor-malized with respect to the reference model.Becauses/r varies from 2 to 8,the maximum values of V,A.and F decrease significantly.However.there is littlechange in Vmax,Amj,and Fmax as slr increases further.To ensure smooth filling yam insertion through theshed,the shed should be kept large enough during thefilling traverse.The size of the shed is determined bythe height between the two sheets of yams and the po-Downloaded from 632FIGURE 3.Effect of geometric ra-tio.s/r on sleys motion character-istics.sition of the sley.During a weaving cycle,the fillingyam can only be inserted when the sley stays close to.;the backward position and the shed opening is suffi-cient.Thus,for fast loom operation,the sley shouldstay backward most of the time for filling insertion,andthen move rapidly for beating-up.The exact range ofsley positions allowing filling insertion depends on theparticular design of a loom.In this analysis,we haveassumed that the filling insertion is completed duringthe period when the sley is in the&dquo;back zone&dquo;betweenits original(most backward)position and one-half of.its maximum displacement(Figure 4).The corre-:.sponding period is refered to as the insertion period.From the simulation data on the displacement of the.sley.,we see that the sley reaches one half its maximum.displacement at different degrees of the crank rotation,depending on the geometry of the 4-link mechanism,.as summarized in Table I.With increased s/r,the sleystays near its most backward position for a shorterFIGURE 4.Effect of geometric ratio sir on thedisplacement profile of the sley.TABLE 1.Insertion periods for different 4-link models.amount of time,leaving less time for the filling to beinserted across the loom.No matter what mechanism is discussed,a lower Amaxindicates a smoother movement and a higher A,leadsto a jerky action.For a loom in particular,the move-ment of the sley affects the efficiency of beating-up.For different fabrics,however,different actions of beat-ing-up are desired 2.A fine,delicate fabric shouldnot be handled roughly,whereas a coarse staple yammay require sharp beating-up to be effective.There-fore,for light fabrics such as silk and fine cotton,onlyvery gentle beating-up is required and a large sli-valueis suitable(e.g.,6).For medium fabrics such as me-dium density cotton,a smooth beat-up is needed,andthe slr ratio should be medium(e.g.,between 3 and6).For heavy fabrics such as jeans or industrial ma-terials,an impulsive,jerky sort of beat-up is necessary,and a small slr ratio is more appropriate(e.g.,3).For a wide loom,which needs a long time for the fillingto be inserted,a lower slr ratio should be chosen.Incontrast,a higher slr ratio is sufficient for a narrowloom,which requires a short time for filling insertion.The performance map shown in Figure 5 is obtainedby combining the effects of the geometric.s/r ratio onthe sleys motion and insertion period.The horizontalaxis is the maximum force acting on the pin joint ofthe connecting rod and the sley.The longitudinal Downloaded from 633FIGURE 5.Performance map for the 4-link mechanism.is the insertion period allowed by the geometry of thebeating-up mechanism.It is obvious from this figurethat the performance in the top left comer is desirabledue to longer insertion period and lower force,whilethe bottom right comer is undesirable because of lesstime allowed to insert filling and higher force.As men-tioned earlier,for fine fabrics,a higher value of s/r isnecessary to guarantee a low yam breakage rate duringweaving.However,inevitably,another effect of highslr is a short insertion period.Therefore,when a wide,fine fabric is to be woven,some compromise has to bemade between force and insertion period.SIX-LINK MECHANISMWe have developed a model based on the actualmechanism of a Picanol PGW4-R/Z loom employinga 6-link driven sley,as shown in Figure 6.We at-tempted to increase the filling insertion period by ad-justing some of the geometric parameters,and after aset of trials,we got the modified model.also shown inFigure 6.A comparison of the angular displacementbetween the two models is shown in.Figure 7.Here,the moments when the sley is at one-half its maximumdisplacement are marked,and the periods during whichthe displacement is at least one-half the maximum forboth models are indicated.It is obvious that in the mod-ified model,the sley stays in the back zone for a longerperiod of time than in the original configuration.Withthe modification,the insertion period increases from199,or 55%of the time period in a weaving cycle,to240,or 67%of the time period.This is helpful for ahigh speed operation.COMPARISON OI SLEY S MOTION CHARACTERISTICS INVARIOUS MECHANISMSTo compare the motion of sleys driven by differentmechanisms,we have also developed a model for theconjugate-cam beating-up mechanism(Figure lc)r 3 J.Here we compare the characteristics of the sleys motionfor the conjugate-cam,4-link.and 6-link mechanisms.Figure 8 shows the angular displacement and accelerationof the sley for the three different driving mechanisms.In Figure 8,we see that the cam-driven sley com-pletes its movement in 130 of the pick cycle,anddwells(remains stationary)at the back position for230(exact periods depend on specific design)The 4-link and 6-link driven sleys.on the other had.moveFIGURE 6.Computer models of 6-link mechanisms:original configuration(left),and modified configuration(right)Downloaded from 634.FIGURE 7.Comparison of angular displacementa linkage-driven sley than with a conjugate-cam mech-anism,because the conjugate-cam allows the fillingyarn to be inserted near the harnesses.At higher loomspeeds or higher weft-insertion rates,the weft carriermust cross the shed in a shorter period.Thus the link-driven sleys restrict the weft insertion interval and be-come an obstacle to increasing loom speed and weft-insertion rate.The cam-driven sley leaves a muchlonger time,more than 200 of the pick cycle,availablefor weft insertion,which permits a higher loom speed,shorter harness lift distance,and lower warp tension.On the other hand,it is clear from Figure 8 that theacceleration of the cam-driven sley is much higher thanthose of the link-driven sley,because the cam-drivensley has to complete the forward and backward move-ments within less than half the time used in a link-driven sley(130 for the cam-driven system versus360 for the link-driven system).The high accelerationmay be acceptable for cam-driven sleys,which aresmaller and lighter than those driven by linkage.Withultra high stiffness,ultra light composites,the mass in-ertia for the sley mechanisms can be further reduced,promising even higher loom speeds.ConclusionsA high speed loom speed calls for a swift weft insertionand fast shedding and beating-up actions.A sophisticatedengineering design of the loom system is required for fast,smooth,efficient operation of the loom.Computer aideddesign tools provide a rapid and reliable means of studyingthe dynamic characteristics of machine mechanisms.In thispaper,we use the Working Model software to analyze the4-link and 6-link beating-up mechanisms.We analyzed theeffect of geometric parameters on the motion characteris-tics of the sley,and we demonstrate that by adjusting cer-tain geometric parameters in the computer model,the sys-tem can be easily fine tuned to allow for a relatively longerfilling insertion period in a weaving cycle.We also com-pare the motion characteristics of the linkage mechanismswith that of a conjugate-cam driven mechanism.Literature Cited1.Knowledge Revolution.Working Model Users Manual,1992.2.Lord,P.R.,and Mohamed,M.H.,Weaving:Conversionof Yarn to Fabric,2nd ed.,Merrow Publishing Co.Ltd.,1982.3.Sun,H.,Computer Aided Design and Analysis of Loom Beat-ing-up Mechanisms,Masters thesis,School of Textile&FiberEngineering,Georgia Institute of Technology,1997.AMtMrrf/MrfOfh/trf72/./997;f/.Sfw/7/.#o,/WDownloaded from