Computer Aided Analysis of Loom Beating-up mechanisms.pdf

Textile Research Journal The online version of this article can be found at DOI 10 1177 004051759806800902 1998 68 630Textile Research Journal Youjiang Wang and Hui Sun Computer Aided Analysis of Loom Beating up Mechanisms Published by can be found at Textile Research JournalAdditional services and information for Alerts What is This Sep 1 1998Version of Record Downloaded from 630 Computer Aided Analysis of Loom Beating up Mechanisms YOUJIANG WANG AND HUI SUN School of Textile 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 weaving process 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 by the sley through which beating up is achieved has an important effect on the smoothness of shedding and picking operations In high speed weaving the relative time per cycle taken by operations other than picking should be minimized It is desirable that the reed dwell as long as possible at the rear to leave more time for weft insertion and then move swit tly to beat up the new filling yarn This is especially crucial for modern wide width looms However higher forces and vibra tions are associated with jerky movements and design compromise is necessary to achieve a balance between loom speed and smooth operation Dynamic analysis of the motion of the sley reed is therefore important for loom designers and manufacturers In general there are three basic kinds of beating up mechanisms 4 link 6 link and conjugate carn as shown in Figure 1 The 4 link mechanism is used most widely on shuttle air jet and rapier looms since it has a 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 widely in shuttleless looms due to its precise and adjustable dwell period of the sley The design of beating up mechanism particularly their mass distribution and geometry has a significant effect on the performance of the loom Traditional methods 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 a simpler way of analyzing the dynamic responses of complex structures Working Model a software product of Knowledge Revolution Inc 11 combines advanced motion sim ulation technology with sophisticated editing abilities to provide a useful tool for engineering and animation simulation A mechanism can be converted into a set of rigid bodies and constraints to build the model on the computer This software simulates the motion of the mechanism based on geometric constraints and Newtonian mechanics principles Quantities defined before the simulation can be exported during the sim Downloaded from 631 FIGURE 1 Typical beating up mechanisms a 4 link b 6 J ink and c conjugate cam ulating process for further analysis The properties of objects can be adjusted with its graphic user interface to form new models with desirable results In this study we first analyze the 4 link mechanism using the Working Model software A parametric study explores the effect of geometry on the sley s motion We also build models for the 6 link mechanism to iden tify geometric configurations that can lead to a long insertion period in a weaving cycle Finally we com pare the sley s motion for different beating up mech anisms Beating up Mechanisms FOUR LINK MECHANISM Figure 2 shows the computer model obtained dafter implementing all parts of a 4 link mechanism with Working Model according to the actual size mass and connection type Quantities measured and recorded during the simulation include the displacement of the sley X the velocity of sley V the acceleration of sley A and the force F acting on the swordpin To validate Working Model we have compared the results from the Working Model simulation and kinematics analysis and found no noticeable differences For parametric studies we have used the actual di mensions of machine parts in a shuttle loom Figure I a crankshaft length r 6 cm connecting rod length s 32 cm and sley length L 72 11 cm This geometric 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 the influence of different ratios of slr on the motion of the sley the connecting rod length varies from 17 to 102 cm while r and L are kept constant We have evaluated elevem 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 have obtained the maximum values of sley velocity V ac celeration A and the force in the connecting rod F for each model The results are shown in Figure 3 nor malized with respect to the reference model Because s r varies from 2 to 8 the maximum values of V A and F decrease significantly However there is little change in Vmax Amj and Fmax as slr increases further To ensure smooth filling yam insertion through the shed the shed should be kept large enough during the filling traverse The size of the shed is determined by the height between the two sheets of yams and the po Downloaded from 632 FIGURE 3 Effect of geometric ra tio s r on sley s motion character istics sition of the sley During a weaving cycle the filling yam 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 should stay backward most of the time for filling insertion and then move rapidly for beating up The exact range of sley positions allowing filling insertion depends on the particular design of a loom In this analysis we have assumed that the filling insertion is completed during the period when the sley is in the back zone between its 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 sley stays near its most backward position for a shorter FIGURE 4 Effect of geometric ratio sir on the displacement profile of the sley TABLE 1 Insertion periods for different 4 link models amount of time leaving less time for the filling to be inserted across the loom No matter what mechanism is discussed a lower Amax indicates a smoother movement and a higher A leads to 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 should not be handled roughly whereas a coarse staple yam may require sharp beating up to be effective There fore for light fabrics such as silk and fine cotton only very gentle beating up is required and a large sli value is suitable e g 6 For medium fabrics such as me dium density cotton a smooth beat up is needed and the slr ratio should be medium e g between 3 and 6 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 filling to be inserted a lower slr ratio should be chosen In contrast a higher slr ratio is sufficient for a narrow loom which requires a short time for filling insertion The performance map shown in Figure 5 is obtained by combining the effects of the geometric s r ratio on the sley s motion and insertion period The horizontal axis is the maximum force acting on the pin joint of the connecting rod and the sley The longitudinal axis Downloaded from 633 FIGURE 5 Performance map for the 4 link mechanism is the insertion period allowed by the geometry of the beating up mechanism It is obvious from this figure that the performance in the top left comer is desirable due to longer insertion period and lower force while the bottom right comer is undesirable because of less time allowed to insert filling and higher force As men tioned earlier for fine fabrics a higher value of s r is necessary to guarantee a low yam breakage rate during weaving However inevitably another effect of high slr is a short insertion period Therefore when a wide fine fabric is to be woven some compromise has to be made between force and insertion period SIX LINK MECHANISM We have developed a model based on the actual mechanism of a Picanol PGW4 R Z loom employing a 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 a set of trials we got the modified model also shown in Figure 6 A comparison of the angular displacement between the two models is shown in Figure 7 Here the moments when the sley is at one half its maximum displacement are marked and the periods during which the displacement is at least one half the maximum for both models are indicated It is obvious that in the mod ified model the sley stays in the back zone for a longer period of time than in the original configuration With the modification the insertion period increases from 199 or 55 of the time period in a weaving cycle to 240 or 67 of the time period This is helpful for a high speed operation COMPARISON OI SLEY S MOTION CHARACTERISTICS IN VARIOUS MECHANISMS To compare the motion of sleys driven by different mechanisms we have also developed a model for the conjugate cam beating up mechanism Figure lc r 3 J Here we compare the characteristics of the sley s motion for the conjugate cam 4 link and 6 link mechanisms Figure 8 shows the angular displacement and acceleration of 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 and dwells remains stationary at the back position for 230 exact periods depend on specific design The 4 link and 6 link driven sleys on the other had move FIGURE 6 Computer models of 6 link mechanisms original configuration left and modified configuration right Downloaded from 634 FIGURE 7 Comparison of angular displacement a linkage driven sley than with a conjugate cam mech anism because the conjugate cam allows the filling yarn to be inserted near the harnesses At higher loom speeds or higher weft insertion rates the weft carrier must 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 much longer time more than 200 of the pick cycle available for 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 the acceleration of the cam driven sley is much higher than those of the link driven sley because the cam driven sley 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 versus 360 for the link driven system The high acceleration may be acceptable for cam driven sleys which are smaller and lighter than those driven by linkage With ultra high stiffness ultra l