Indian Journal of Fibre & Textil e Research Vol. 24, December 1999, pp. 258-263

A comparative study on the performance of electronically- and mechanically­controlled warp yarn let-off systems

Ali A A Jeddi , H Nosraty, D Ordoukhany & M Rashidian

Textile Engineering Department, Amirkabir University of Technology. Tehran IS!) 14. Iran

Received 28 Decelllber 1998; revised received and accepted 24 M{(v 1999

The perrormance or a mechanically-controlled warp yarn let-oil (a Hunt type) is compared with that or the conve ned system employing an electron ic contro l system. The results indicate that the electronica ll y-contro ll ed system pcrforms hCli cr in compensating the warp yarn tension di sturbances , thereby increasing weaving machine elTici ency and I 'cs llitin ~ in improved fabri c qu alit y.

Keywords: El ectronic warp let-o IT, Loom, Mechani ca l warp let-oil, Warp yarn tension

1 Introduction

rn recent years, several weaving machine makers have designed and developed the e lectronically­controlled warp yarn let-off system. The drive of this system is activated by an independentl y regulated e lectric motor which is controlled by an e lectronic regulator. Sulzer Ruti I designed a warp yarn let-off system with a variable speed electric motor for weaving machine model P7100. The speed of the motor is contro ll ed by detecting the displacement of the back rest roller by means of an inductive analogue sensor. Picanol 2 fo r GTM and PA T -A looms suggested a let-off mechani sm with an independently regulated e lectric motor whic h is controlled by an e lectronic regulator. Registering the warp tension can be achieved by detecting the displacement of the back rest roller by means of an e lectronic sensor. Other companies, viz. Somet, Toyoda and Tsudacoma, have also designed and app lied the e lectronic warp let-off system for their weavi ng mac hines . In sp ite of the extensive use of e lectronic warp let-off units instead of mechanical system, there are a few pape rs which consider the advantages in the working performance of e lectronic let-off compared to mechanical let-off units. Lunenschloss and Schlichter' suggested that the use of e lectronic warp let-off is ad vantageous over the use of mechanical let-off system in weaving filament sty le. They also analyzed the new possibilities in the des ign of warp yarn tension measuri ng e lements for their suitabili ty for use as warp let-off unit to control input quantities .

This study focuses on monitoring and documenting the variation inherent in the warp yarn tension during

the weaving process by e mpl oy ing e icc troni c anu mechanical warp ya rn le t-off mechani sms 0 11 the same machine.

2 Control System of Warp Let-off Devices Smith weaving machine moue l NOUVO

PIGNONE TP400 w ith fl ex ibl e ra pi e r wert in serti on was used to compare the mec han ica l anu e lectroni c warp let-off devi ces. This mac hine h,IS HU T mechani cal regul ator and the mac hine ' s speed is ~()()

rpm.

2.1 Mechanical Control System In thi s system, the di sp lacement o f back rest ro ll e r

represents the diffe rences be tween the warp yarn tension and the des ired warp ya rn te ns ion that is ri sed from weight and spring loaded tens ion. These differences are transferred to the PIV co nt ro lle r to dri ve the warp beam to a position correspondin g to

compensate the difference be twee n these two tensions.

The bl ock d iagram of a c losed-l oop sys te m anci the schematic diagram of mechanical wa rp let-o ff sys te m are shown in Fig. I where P I and P2 arc the eyc l ic and disturbance tens ions respect ive ly; and F and W , the spring and we ight loaded te nsions to displace the back rest roller in M2 value. Warp ya rn tensi o n displaces the same ro ller in M, va lue so that the final movement of back rest rolle r is resu ltant nf these two di splacements.

2.2 Electronic Control System The control function and the sc he matic diagram or

converted e lectron ic warp let-off are sh o wn in Fig .2.

r

"

JEDDI et al.: WARP YARN LET-OFF SYSTEMS 259

pI p2

-:( I

(a)

we.vezon'] ~

;---: b:=f-~9., ",".' ,_.,,-,", ICf J and :;pnng lenglh change

rest beam

51

L-_ _ _ np-4r--=mo=-~o-,:::-' , ~r I

PIV

(b)

Fig. I - Block diagram of a closcd loop syslem for mcchani ca l warp Iet-olT (a). and schemati c diagram of mcchanical warp ICl­off on loom (b) [I- Back res t ro ll er; 2- Load spring; 3-Dri vG from loom; 4 - P I Y mcch ani sm; 5-Levers for PlY di amcter controL 6-Worm gcar: 7 - Wcight: and 8 - Warp bC3ml

Similar to mechanical system, di fferent forces cause the back rest roller di splacement. Thi s movement is measured continuously by a linear inducti ve analogue sensor at 7S degree of running cyc le of main shaft drive by means of a trigger in an electri ca l vo ltage and is transmitted to an AID carel. The measurement values are processed by a processor computer and then the output signal is transmitted to a DC motor via a DIA card, amplifier (Op Amp), and a motor con troller to control warp let-off units as a C0mpensating function . The block diagram for thi s system is shown in Fig. 3. The assemblage of PC computer and DC motor controller is the auto mati c control system that applies the required vo ltage to the DC motor based on the comparison between input signal and the required set point value. Therefore, it is necessary to determine the relationship between the output of automati c control system and the actuating error signal , i.e. suitable type of cont ro ller should be selected. Lunenschloss.J showed that the combination of proportional , integral and derivati ve controller (PID) can be used as a control system fo r weaving machine. The gain values of each controller would depend on

",,1

(a)

(b)

gear bor

I

~-w

Ml f -- "'2 .. - I ~

i- - I _ T

lodsdlSI)lacemcnl 'L' ­lll!11 sf'lflnQ length chang& i

,eSlqbeam _ sl i'" I

sensor L- I

Iriger ~_. _~_ - - VI

~~~A aLI

Fig. 2- Block d iagram of a clOSGd loop syslcm ror eicclro nic:!1 warp Ict-olT (a). and schcmalic diagra m " I' e icCl J'lllli cal warp ICl ­oil 0 11 loum (b) II-Back reSl ro liG r: 2 - Lo,ld sp rin),! : 7 - Weight: 8 - Warp bcam: l) - Sell ,or: IO - Co lllplJl er:

I 1 - DC motor dri vc r: 12 - DC Illotor: alld I.' - C..iear h(l\ I

set pointvaluEt

~ loom

DC motor controlle r

- ---- -J Sensor ... ~

back rest roller dlsplace mt!111

J- ~

Fig. 3 - Block di agram oi' e lcc lro lli ca ll y-co il lroll ed warp le i-o il

the machine spec ifications In thi s wurk, a PID controller was des igned fo r DC motor. In order to obtain a required control syste ll1 , a computer programme was written to operate as a controll er.

3 Computer Pmgramme to Contml Warp Let-off Motion For a propol1ional , integral and de ri val i ve controll er.

260 INDIAN J. FIBRE TEXT. RES .. DECEMBER I lJ99

the output of the contro lle r 11(1) is de fined by the following equation6

:

u(t) =K e(/ ) + K ITJ 'e( / )dl + K T .de( / )ldl ... ( I ) p r I I I P d

where e(t) is the actuating e rror signal; K,h the proportional gai n; Tj , the integral time; and Ttl , the derivative ti me. Each of the va lues of K",Tj and Ttl is adjustab le and shou ld be dete rmined for the contro l system. At the first tri al, it was assumed that the re is on ly the proportiona l part of equation for controller

and other two parts are zero i.e. Tj = 00 and Ttl = O. Based on thi s assumpt ion, a compute r programme was written for proportional controlle r. The experimental works showed that the proportional controlle r on sys tem performance continued to osci ll ate inde finit e ly. Contro l syste m ex hibiting such response c haracteri stics is not des irable . Therefore, we modified the computer programme based on a proportional plus integra l controlle r.

The integral time adju sts the integral cont ro lle r, whi le a change in the va lue o f K" affects both the proportional and integral parts of the contro lle r. The integration of input vo ltage (lVOLT) to the AID card o f contro l system, which represents the warp yarn tension in each cycle of weav ing, in the inte rva l Tj

(the integral time) g ives the area (S) bounded by the x ax is at the inte rval (Tj ) as fo ll ow ing :

S=TJ:', IVOLT (/ )dl (2)

or 5 ITj =IJT

j L~' I VOLT(/)dl (3)

where A VE=SIT;=average o f input data at inte rval

time. Therefore,

AVE-SP= IITj L ~; e(1 )dl ... (4)

where

SP=set point valuc= IIT)t~' SPdl (5)

e (t)=IVOLT ( I ) - SP (6)

The experimental work) showed that with the decrease of K" the osci llati on o f control sys tem is decreased. Thus, with Kp = 0, minimum osc illati on is obtained i.e. controlle r becomes onl y integra l contro ll er. With the above programme 100 readings, that equal s to s ix comple te cyc les of weaving operation, were taken. The integral time at the beginning was chosen arbitrary. Traynard

2 , in hi s

work on warp le t-off motion of Tsudakuma weaving machine, expressed that to contro l the speed of warp let-off motor, the measurement o f warp tension during nine successive weaving cyc les is required, while in this control programme, it is poss ible to measure warp tension during only two success ive weaving cycles

and control the let-off system. The ex periments also show severe va ri ati on in wa rp yarn tens ion w he n the machine is stopped for mainte nance or during weekend , because the response or con troll e r is ve ry slow. However, this situati on does not ;Irise in normal weavi ng operati on. Conseque ntl y. the de ri va ti ve pa rt of equation for contro ll e r is not necess;try. because thi s part increases the osci ll ation or th e bad res t roll e r during negli g ible variation or wa rp ya rn tension.

To acce lerate the contro l sys te m to reac h the se t point , a large va lue of proporti o nal ga lll is selec ted instead of using the de ri vative part or contro ll e r) . Numerous ex periments were exa illined on dirferent

~/ I k=~ ~yes

yes-- p=O.9

. yes -.-_-~=~~

_ -yes---- '_ p=O.6 I

P=O~~

>--- yes - C' p=O .2

::::>-~yes out=250

Fig. 4-Flowchan o r co mput er progr;lI11mc ror UHlIrol or \\,;trp lel-o lT selling time

JEDDI et al.: WARP YARN LET-OFF SYSTEMS 26 1

values of proporti onal gain and intervals of actuating error signal. The final fl owchart of computer programme to control the warp yarn let-off motion is shown in FigA.

4 Comparison of Warp Yarn Tension in Electronically- and Mechanically-Controlled Warp Let-off Devices The following experiments were designed and

performed on two mechanicall y- and electronicall y­controlled let-off dev ices to compare them with each other in working performance, particul arl y in warp yarn tension. For thi s purpose, the generati on of warp yarn tension and the bac k rest ro ller di splacement should be same fo r both devices. To measure the back rest roller di splacement, a computer programme was written) and the warp yarn tension was obtained by means of ROTHSCHILD Tension Meter during weaving operati on. For each examinati on, the tension of more than 40 warp yarns across the width of the machine was measured between back res t roller and drop wires. A plain weave structure with 20/2 Ne cotton warp yarn and 30/2 Ne cotton-polyes ter weft yarn was used during the current experiments.

4.1 Comparison of Setting Time of the two Control Systems

Systems with energy storage cannot respond instantaneously and will exhibit transient response

8

7 Mechanically controlled

E 6 E

5 0-

0:: 4

0:: III

2

0 0 ~ 70 100 leo 22IJ 280 3«l

88

77 MechanicaUv controlled

Z 66 0 ...------~: 55

>- 4-4 :: 33

22

11

0

0 40 70 100 160 220 280 ~

whenever they are subjected to in puts or di sturbances. The setting time is one of the transient response characteri stics of a contro l system and is defined as the time required fo r the response curves to reac h and stay within a range around the fin al va lue of size specified by the abso lute percentage of the fi nal value, usuall y 2% or 5% (ref.6) . The setting time is related to the largest time constant of the control sys tem.

~

~

For the convenience in compari ng setting ti me of these two dev ices, the back rest roll er is set at a certain distance from the set poi nt and the machine is started. Fig. 5 shows the response curves of the back rest roller di spl acement and warp ya rn tens ion for mechanicall y- and electroni call y-controll ed warp ya rn let-off moti ons respecti vely. It is seen in this fi gure that the setting time of both bac k res! ro lle r and ya rn tension response curves fo r mechani ca l dev ice is obtained nearl y after 220 weav in g cycles while for electronic device, it is obtained nearl y after 11 0 cycles . Therefore, it may be concluded th at the sett ing time of the electronic cont ro ll er is nearl y half of the mechanical one.

4.2 Compensation for Sudden Inuease in Warp Ya rn Te nsion In thi s experiment , I kg weight is added to the

weight loaded mechani sm of back res t roll er for 20s and then it is removed. Fig.6 shows that the mechanica ll y-operated dev ice requ i res more than two

Electronically controlled

0 ~ 60 1~ 220' 300 380

Electronically controlled

t-

1

0 30 60 110 140 200 260 320 380

Pick frequency

Fig. 5 - Mechanicall y- and electroni cally-cont ro lled warp let-off [RRRD- Back rest roll er di spi:lce lllcll t: and WYT - Warp yarn tension)

262 INDIA J. FIBRE TEXT. RES .. DECEMBER 1999

8

Mechanically controlled Electronically controlled

E 6

E. 5 0 a: 4

a: 3

CO

0 1 I

0 40 eo 130 170 210 2$) 340 o 40 110 130 170 210 2eO 340

88

n Mecha nically controltlld Electronically controlled Z

66 l)

~ 55 -->-?: 44

33

22

11

0

0 90 140 . 180 220 28Q 360 o 80 130 170 21 0

-Pick frequ e ncy

Fig. 6 - The co mpensati on of sudden increasing of warp tension by mechani cally- and eiectl"<l ni c;dlv-c(1ll!ru l kd warp let-o lT I BRR D- Back rest ro ller displacement: and WYT - Warp yarn tCIl , iolll

12 11 10

Mechanically controlled Etectronically controlled

E 9 ·

E 0" 0:: 0:: CD

0 0 30 eo 90 130 160 190 220 2!lO 320 :leO 0 30 I!O 90 ~30-· 1 60 190 220 260 320 360

~f Mechanically controlled

f Z 66

Electronica lly controlled

l)

.1-- 55

>- 44 ?:

33

22

11

0 40 80 130 170 210 260 340 40 80 130 170 210 260 340

Pick frequency

Fi g. 7 - The compensati on of sudden decreasing of warp tension by mechanica lly alld clectr() ni ca ll y cll ll!ro lkd II .111' ic'! -,)rt [B RRD - Back res t ro lle r di splacemellt: ;lnd WYT - Warp y<l rll tellsiolll

ti mes as long as the electronic let-off to compensate the di sturbances due to sudden increase in warp yarn tension. The curves show that the max imum overshoot i.e. the max imum peak value of the response curves of the back res t ro ller di splacement, and the warp ya rn ten -ion of the mechanical device are about six and three time respecti vely compared to that fo r the electronic dev ice.

4.3 Compensa tion 1'01' Sudd en Decrease ill War p Yar ll Tension

When the weavi ng mac hine is working norm,tll y. the fabric take-up ro ller is d isconnec ted for fi ve seconds. Therefo re, the let-oil Illoti on suddenly decreases and consequentl y, the contro lk r de\'iees react to compensate the decrease in warp yarn tension. Fig. 7 shows that the electronicall y-contro ll ed system

JEDDI el a l.: W ARP Y ARN LET-OFF SYSTEMS 263

compensates di sturbances about two times rapidly than the mechanically-controlled system. The variation of back rest roller di splacement in electronic system is also nearly half of the mechanical one.

5 Conclusion

The electronic warp let-off system with independent DC motor and the installation of a suitable computer programme as an automatic controller offer advantages over the use of mechanical let-off system (type HUNT regulator) in a weaving machine. The electronically­operated device responses more rapidly than the mechanical device to regu late the disturbances created in warp yam tension . Yam tension variation in electronical controller is about two times less than that in mechanical

contro ller. The control programme designed in this work has ability to measure the warp yarn tensiull during onl y two success ive weaving cyc les.

References I Sulzer Rut i Corporation. Functi onal Description o j" KS A 213.2

Contro ller, Eleclrica l Calalog lle of P710() Sll /~.n Rllfi Wl'{{\ 'ing M achine, 1997.

2 Traynard 0 , Ind TexI, (1989) 51 .

3 Lunenschloss J & Schiichter S. M ellialld. I I ( I 'JX7 ) lQ I . 4 Schiichter S & Lunenschloss J . M ellialld. 67(.\) ( l lJX6) 160. 5 Ordoukhani D. The al1a /vsis or re/(I{iollshil l In'III 'N'1I IIwll r(l m

lens ion and warp beam mfaliOIl ill IIIl'CIWllicli1 lI lId e/eclronica / wall } ya rn lel .ofT IVI.Sc. thesis. Amirkabir Uni versit y of Technology, Tehran . Iran. IlJlJ6.

6 Ogata K, Modem cOll lrol l' lIg ill('('/'ill ,~. (Prenti ce Hall Internati onal Editions, USA), IlJlJO. I X2· l lJO. 2:i6-26(,.