Indian Journal of Textile ResearchVol. 5, March 1980, pp. 1-5

A Study of Weaving Systems by Means of Dynamic Warp and Weft TensionMeasurement

B V HOLCOMBE-, R E GRIFFITH & R POSTLESchool of Textile Technology, University of New South Wales, Kensington, Australia

Received 5 July 1979; accepted 10 September 1979

An account is given of.a.study of.Jhe within-yarn tension behaviour for three weaving looms; Dynamic tensiontraces forboth warp and weft yarns were obtained for 'three 'common looms from different manufacturers: A Picanol President tappetloom, a Northrop worsted loom and a Sulzer weaving machine. The traces'have beeninvestigat~ in detail and related to thebehaviour of the looms themselves. Some aspects of these traces have also been used to illustrate how the proportion of theweaving cycle taken up by the basic functions has changed during the development of the modern weaving loom.

The extent to which the mechanical and physicalproperties of woven fabrics are determined by loomsetting parameters is offundamental importance in theengineering of certain behavioural characteristics intothe fabric. This is an area of fabric research not yetexamined in depth, and only vaguely understood. Asmall number of papers are available on the subject,mostly dealing with the effect of changes in the averagelevel of yarn tension during weaving'-

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Tension is applied to both the warp and weft yarnsduring weaving to assist the mechanical functions ofthe cycle. These tensions and the relative alignment ofthe yarns at the moment of fabric formation have animportant influence on fabric structure. It should bepossible to derive a set of criteria which relate theseparameters to fabric properties and which areindependent of the specific mechanical means by whichthey are achieved.

Difficulties associated with the measurement ofdynamic weft yarn tensions on the running loom havetended to discourage work in this area. An earlierpaper? by the present authors gave details of thedevelopment of a system based on radio-telemetrywhich overcame many of these problems.

This paper describes a study of the dynamic warpand weft yarn tension within the weaving cycle of threedifferent looms, two of the conventional shuttle typeand one of gripper shuttle type. In each case, theprominent features of the traces of warp and wefttension have been compared and related to differencesin both the basic loom construction and the settings ofthe major mechanical parameters of the weavingprocess.

"Present address: Division of Textile Physics, CSIRO, Ryde.N.S.W. 2112. Australia.

Experimental ProcedureThe three looms investigated were: A Picanol

President Model CMC tappet loom; a NorthropModel F worsted loom; and a Sulzer gripper-shuttlemachine weaving light-weight sheeting fabric. In allcases, the fabric construction was plain weave. Weftyarn tension traces for the conventional looms wereobtained using the radio-telemetry system. Wefttension on the Sulzer machine was monitored by asmall transducer inserted on the yarn just behind thefeeder gripper. Both this transducer and that used tomonitor warp yarn tensions were based on cantileverarms fitted with semiconductor strain gauges. Thetransducers are similar in principle to the transducerdescribed for conventional shuttle looms.

The warp tension transducer was placed in the warpsheet slightly forward of the back roller on each loom.One yarn from each of the two opposing centre heddleshafts was fed into the device to produce a single-cycletrace, which averaged both upper and lower shedpositions.

The signal from each of the warp and wefttransducers was fed into separate channels of a storageoscilloscope, and a third channel was used for a timebase signal derived from a reed relay switching devicemounted on the loom mains haft. Tension calibrationlevels were also stored together with the correspondingtraces and the entire display photographed. Full detailsof the transducers used, the recording system andcalibration techniques have been given by Holcombe 7.

Analysis of the Tension TracesA typical set of traces for each of the three looms is

shown in Fig. 1, (A), (B) and (C). For clarity, theamplitude of each trace was adjusted, so that warp andweft filled the upper and lower halves of the screen

(AI Northrop Model "F"

INDIAN 1. TEXT. RES., VOL. 5, MARCH 1980

(81 Piconol CMC(CI Sulzer Gripper Shuttle

ae

180 360 540 720degrees of crankshaft rotation

leo 720360 540

Fig. I-Traces of dynamic single cycle warp and weft yarn tension for the three looms used in the experimental programme. [(a) beat-up(b) picking, (c) checking, (d) shedding starts, and (e) shedding stops]

respectively. The loom settings and levels of yarntension used on each loom were typical for the types offabric produced.

Observation of these traces shows a number ofimportant differences among the tension variations ofeach loom. Although these may be partly accounted forby yarn elasticity, there are clearly other effectsinvolved. An analysis of such differences may serve tohighlight the more critical aspects of the weavingsystem. Important parameters of the three looms havebeen summarized in Table 1 to simplify explanation ofthe features of the traces. All timing was measured asdegrees of rotation of the crankshaft from the frontcentre or beat-up position ofthe sley, which was takenas zero.

Warp Yarn TensionThe prominent within-cycle features of the warp

tens.ion traces are the response to the primary motionsof shedding and beating-up. These features are clearlyvisible for each loom. The timing of these twooperations varies slightly from loom to loom, as doesthe magnitude of the beat-up peak relative to theshedding tension. These small variations can beattributed to changes in loom technology, and in factthese three looms represent a progressive improvementin the areas of picking and shedding performance sinceabout 1900. The period of time for which the shedremains open occupies a greater percentage of the cyclein the conventional looms (Northrop 43%, Picanol42%) than in the Sulzer loom (38%). This differencereflects the higher projectile speed and considerablereductior, in projectile size in the Sulzer loom. Withmodern looms, the proportion of the cycle taken up bythe actual shedding operation has been increased,allowing a smoother interchange and a consequentiallower strain on shedding mechanisms.

Average open-shed warp yarn tensions wereapproximately 6 mN/tex for the Northrop and Picanollooms and 17 mN/tex for the Sulzer. Beat-up tensions

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Table I-Details of Loom ParametersNorthrop Picanol Sulzer

Front centre (or beat-up) 0° 0° 0°Shedding-starts 170° 210° 185°

-crosses 265° 315° 290°-stops 15° 60° 49°

Picking 95° 70° 69°Checking 290° 300° 215°Let-ofT 0-180° 180-0° 130-310°Take-up continuous 0-180° continuousWarp yarn-type 80/20 100% 50/50

wool/P.E. cotton cotton/P'E.-count (tex) 26/2 37/2 30

Weft yarn-type 80/20 100% 50/50wool/P.E. cotton cotton/P.E.

-count (tex) 20/2 30/2 30Warp denting/em 22 17.5 22Weft take up-picks/em 18.5 15 23

Maximum pick sett 19.9 16.8 25.5Maximum pick sett, % 93.2 89.1 90.2Loom speed, picks/min 103 192 267Pick duration as % of

cycle time 55 64 34

were about 1.8 times greater than the open-shedtension for toe Northrop, 1.6 for the Picanol, and 1.3for the Sulzer.

The magnitude of the beat-up peak in warp yarntension is a combination ofthe tension in the yarns dueto the state of the shed at that point and the tensionincrement resulting from extension of the warp sheet asthe new weft yarn is forced into the fell. The firstcomponent is a function of the average level of tensionset by the warp let-off, the geometric parameters whichcontrol the shape of the shed, and the timing ofshedding. Beat-up usually takes place during the laterstages of shed interchange, where the tension is risingrapidly and the timing has a significant influence on thetotal level of beat-up tension; early timing increasesthis tension, and vice versa. The variation in timingbetween looms is quite marked (Table 1). The smaller

HOLCOMBE et al.: STUDY OF WEAVING SYSTEMS BY WARP & WEFT 'fENSION MEASUREMENT

shed opening of the Sulzer loom would tend to reducethe ratio of open-shed to beat-up tension relative to theconventional looms. The second component of thebeat-up peak tension is determined by the width of thebeat-up strip and the load-elongation behaviour of theyarns. The beat-up strip is, in turn, a function of theaverage tension levels and the pick density (relative to·the maximum fabric sett). Consideration of yarncounts and loom settings indicates that pick spacingsexpressed as a percentage of the maximum sett (afterBrierly") were 93% for the Northrop, 89% for thePicanol, and 90% for the Sulzer.

In varying degrees, all the factors mentioned aboveare present in the traces. Thus, the very prominentbeat-up peak of the Northrop loom, for example, is dueto a combination of low tension, high pick density, andearly shed timing. As previously mentioned the ratio ofbeat-up peak tension to open-shed tension is about 1.3for the Sulzer loom, 1.6 for the Picanol, and 1.8 for theNorthrop. Thus, although the shed opening requiredfor weft insertion is much less for the Sulzer loom thanits conventional counterparts, a far greater level of basetension was employed, resulting in a similar order ofchange from closed to opea shed tensions for bothSulzer and Picanol. The fact that the beat-up to open-shed tension ratio was smaller in the case of the Sulzeris a result of this high base tension. A lower basetension would have still given a similar increase inbeat-up tension relative to open-shed tension, and agreater ratio of beat-up to open-shed tensions.

One final point worthy of mention is the influence ofthe warp let-off motion on the tension during the openshed. Following beat-up on the Sulzer loom, warptension undergoes a marked transient vibration in theform of a damped simple harmonic motion. Thisvibration is present to a lesser extent on the Picanolloom and does not appear at all on the Northrop loom.Such vibrations are the natural response of the springsystem comprising the mechanical components of thewarp let-off control, and the warp yarns themselves tothe impulse of beat-up.

Weft Yam TelWioD

Fundamental differences in the methods of weftinsertion and control between the conventional andgripper shuttle looms make direct comparison of theirrespective weft tension cycles meaningless. The twosystems are, therefore, discussed separately.

Conventional weft insertion-Both Northrop andPicanol weft tension traces conform to a similargeneral pattern, with slight differences in certain areaswhich may be traced back to differences in loomconstruction.

At front-centre, the shuttle is stationary and the freeweft yarn between selvedge and shuttle eye is at a

steady tension. The moment picking begins (95° for theNorthrop and 70° for the Picanol loom), the yarn isslackened and its tension drops to zero as the shuttlemoves towards the warp yarns. At some point duringshuttle flight all slack is taken up, weft tension risessharply and yarn is unwound from the pirn. The wefttension fluctuates about a high level during unwindinguntil shuttle checking takes place, when it decaysrapidly to a steady value. The level of weft tensionretained after shuttle checking is largely a function ofthe tension arrangement of the shuttle eye, althoughsuch factors as yarn over-run have some influence.

One obvious feature of the weft tension traces for theconventional looms is the difference in duration of theunwinding tension plateau between consecutive picks.This difference results from the fact that the yarnemerges from one end of the shuttle rather than thecentre. Different lengths of slack are, therefore, createdbetween selvedge and eye for each box. Since the totalpicking duration remains constant for each loom, theduration ofthe unwinding plateau varies for picks fromeach side of the loom.

Another noticeable difference between these twolooms is the proportion ofthe total cycle time taken upby the shuttle flight. The higher cyclic speed of thePicanolloom demands this, assuming similar orders ofshuttle speed. The increased proportion of cycle timefor this loom has been achieved by making refinementsin the picking and shedding systems. Closer controlover the shuttle flight has enabled more criticaltolerance of the overlap between shed interchange andthe entry and exit of the shuttle from the shed. Thus,despite shortening of the open-shed period, it has beenpossible to increase the duration of shuttle flightrelative to the total cycle.

The retained weft tension, i.e. the tension in the yarnwhile the shuttle is in either box, does not remaincompletely static between picks. There are in bothlooms tension peaks associated with the lateralcontraction of the fabric as the reed leaves the fell. Thereed forces the fell out to its full drafted width duringbeat-up, and, as it begins its return stroke, the fellcontracts a little, thereby pulling yarn from the shuttleand causing weft tension to increase. This effect may beseen in the weft tension traces, starting from the pointwhere the beat-up peak of the warp tension trace ends.The effect is quite noticeable in the case of theNorthrop loom, where contraction was much moresignificant than for the Picanol. A secondary effect hereis the withdrawal of yarn from the shuttle as the sleyundergoes its backswing, thus increasing the distancefrom selvedge to shuttle eye.

A less obvious secondary peak in weft tension resultsfrom the interaction between the yarn and the weftfork. The Northrop loom was equipped with a centre

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INDIAN J. TEXT. RES., VOL. 5, MARCH 1980

TokesYarn

~StopsStorts

Yarn Token by Shuttle Tokes Yarn

C~U'ht .""..1 Hard Broke

Starts- _Lowering_ • Lifting

Picking • • Checking

Stops Storts

fork and the timing ofcontact relative to shed cross hadno influence on the weft yarn (that could be detected astension at the shuttle). However, the Picanolloom usesa side fork (adjacent to the left-hand box) which pushesagainst the yarn close to the selvedge as they sley movesforward, thus introducing a small tension in the weftyarn. This small peak is visible immediately after theshuttle enters the left-hand box (approx. 335°).

Gripper shuttle weft insertion-The complex natureof the Sulzer weft insertion system demands a veryprecise form of yarn tension control. To simplify theexplanation of the weft tension behaviour for thisloom, a chart (Fig. 2) has been prepared setting out thetimings of those mechanical functions which have adirect influence on either the yarn or the grippershuttle.

The shuttle is in contact with the picking shoe forapproximately one-third of the distance required bythe conventional shuttles, and leaves the shoe at almosttwice the speed of a conventional shuttle. The gripper issubjected to a maximum accelerating force about 675times that due to gravity. Such a force, when imparteddirectly to one end of the yarn, would almost certainly

SelvedgeGripper

ShuttlePosition«

FeederGripper

Brake

Tensioner

Shuttle

Shedding

o 90

result in yarn breakage, particularly in the case ofrelatively fine yarns. Deceleration is also very severe,and the yam must be braked during checking toprevent over-delivery.

Control of the yam is achieved in practice throughthe action ofthe weft tensioner arm in conjunction withthe weft brake. The weft tension arm stores apredetermined length of weft which is progressivelyreleased into the system over the initial stages ofpicking. This process reduces the rate at which tensionincreases in the yam, and allows the yam unwindingfrom the package to be accelerated more slowly thanthe gripper.

The weft brake is applied during flight at two levels.The drag on the yam due to the action of the brakeprevents over-delivery during checking and straightenstwisted loops, which might lead to fault formation inthe fabric.

The transducer was mounted directly behind theweft feeder. and, therefore, information derived fromthis instrument while the jaws of the feeder are incontact with the yarn (i.e. from 2880 to 40°) is notrepresentative of the yam within the shed. The

180 270Degrees of Crankshaft Rotation

360

Relative Locations of Weft InsertionElements

FABRIC

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Fig. 2-Breakdown of the mechanical operations of the Sulzer loom which have an influence on the weft yarn

HOLCOMBE et al.: STUDY OF WEAVING SYSTEMS BY WARP & WEFT TENSION MEASUREMENT

separation of the yarn from the weft feeder at 40°represents the start of the observed tension cycle.Tension at this point was quite low, with both yarn andgripper stationary. At 50°, the tensioner arm starts tomove downwards, releasing yarn in preparation forpicking and causing weft tension to fall to zero. At 68°,the gripper is fired, although weft tension remains atzero for a few degrees as slack in the yarn released bythe tensioner is absorbed.

The initial rise from zero tension is rapid, but is soondamped by the action of the tensioner. There follows aperiod of 100° in which tension fluctuates widely asyarn loops are unwound from the package. It ispossible to see in the traces peaks superimposed on theunwinding effects which correspond to the applicationof the first, light brake and the cessation of tensionerinfluence.

At 193°, the tensioner starts to return to the storageposition. After another l O", the second, hard brake isapplied. The effect of the brake, combined with thedrawing-off of extra yarn by the tensioner, leads to asubstantial tension rise which continues until checkingtakes place. The extent of this rise in weft tensiondepends on the setting of the second brake.

Shuttle checking is followed immediately by a sharpfall in weft tension, probably due to differences betweenthe running and static frictions of the brake and otheryarn contact points, as well as a slight yarn over-delivery. This fall in tension continues until it isreversed at 240° by the accelerating upward movementofthe tensioner. At 255°, the gripper is contacted by thepositioning mechanism (which prepares it for return)and the associated backward movement slightlycounteracts the effectofthe tensioner, causing a furtherreduction in tension. A levelling off, as the gripperpositioner slows, is followed by a short rise in wefttension until the yarn is gripped by the jaws of the weftfeeder at 288°.

From this point onwards for 112°,tension variationsappearing on the trace correspond to the movement ofthe weft feeder to the reload position, and continuedmotion of the tensioner. It is interesting to observe thatthese two functions appear to be timed to minimize thefluctuations in weft yarn tension over this period andalso to prevent the yarn from becoming completelyslack.

It can be assumed that tension in the weft yarnwithin the shed remains constant following contactwith the weft feeder until beat-up, as the only externalinfluence on the yarn over this period is the affixing of

the selvedge grippers (which cause no yarn lengthchanges whatsoever). Consequently, the tension of theweft yarn as fabric formation commences may be takenas that present at the time of contact with the weftfeeder, i.e. at 288°.

ConclusionThe information available from within-cycle tension

traces for warp and weft yarns provides a means ofexamining the dynamic behaviour of the weavingprocess in detail for different types of looms. Further, itis possible, by careful choice of the time-base of acathode ray oscilloscope, and by the use of delayedtriggering, to study specific areas of the weavingoperation in even greater detail if required.

Single-cycle traces were recorded for threecommonly used weaving looms which illustrate someaspects of the development of weaving technology toits present state. The traces show how improvements inthe areas of picking and checking have enabled muchcloser control over shuttle flight to be achieved. Thus,the timing ofthe overlap between shed interchange andpicking is today more precise, and shuttle flight timehas been increased relative to the total cycle. Thesedevelopments have allowed cyclic speeds to beincreased without directly increasing the strain on themore sensitive loom components.

The traces show how the warp yarn tension at beat-up is dependent on factors such as the shed size, thewidth of the beat-up strip, and the timing of shed cross.Other lessobvious details, such as tension arising in theweft yarns due to interaction of the weft fork andcontraction of the fell, may also be observed. Clearly,the system is adaptable to suit virtually all types ofweaving looms, and provides a useful tool for loomdevelopment and tuning, as well as a basis for researchinto the influence of yarn tensions on fabric formationand properties.

ReferencesI Chamberlain N H & Snowden DC, J Text Inst, 39 (1948) T23.2 Snowden DC, M.Sc. thesis, Leeds University, 1948.3 Snowden DC, J Text Inst, 41 (1950) 237.4 Wetzel S & Backman R, Faserforsch Text Tech, 16 (1965) 233.5 Prace Instytutu Wlokiennictwa, Lodz, Poland, Rocznik 24,1974,

123.6 Holcombe B V, Griffith R E & Postle R,J Text Inst, 67 (1976) 434.7 Holcombe B V, Ph.D. thesis, University of New South Wales,

1974.8 Brierly S, Text Mfr, 78 (1952) 349, 431, 449,5::;3 & 653; 79 (1953)

293.

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