Indian Journal of Fibre & Textile Research Vol. 25, June 2000, pp. 1 08- 1 1 4

Modified tappet shedding mechanism for improved performance of jute loom : Part I-Design, operation and heald movement analysis

of the mechanism

S K Neogi, A K Bandyopadhyay & N C Banerjee

Indian Jute Industries' Research Association, 17 Taratola Road, Calcutta 700 088, India

Received 2 February 1 999; revised received 26 May 1 999; accepted 2 July 1 999

A positive tappet shedding mechanism with simple design and 35% less number of components than in the existing system has been developed for weaving plain cloths. In this mechanism, only one grooved tappet actuates the two healds in both upward and downward directions. The mechanism is so designed and fitted on the loom that it enables easy and quick setting and produces much improved nature of heald movement which is expected to minimize the warp breakages at weaving.

Keywords : Grooved tappet . . Heald displacement, Heald velocity, Jute loom, Tappet profile, Tappet shedding mechanism

1 Introduction

The formation of warp shed in each pick cycle causes rapid cyclic stretching and relaxation, and thereby imposes strain on the warp yarns. The strain on the yarns is directly proportional to the speed of shed formation or speed of loom and to the square of the depth of shed l . In jute weaving, a fairly large shed is required to accommodate the jute shuttles of bigger dimensions. The conventional jute fabrics (hessian and sacking) are produced with plain and 3-end twi ll weaves and the jute looms are, therefore, equipped with the conventional tappet shedding mechanism of negative type. Irrespective of the type of weave, each heald shaft is actuated by a separate set of tappet, treadle lever, treadle bowl and reversing roller. This type of shedding mechanism is, however, often found to produce faulty and jerky movements of the heald shafts because of the errors in the profi les and dimen­sions of the tappets, settings of the treadle fulcrum, diameters of the reversing rollers and so on2-5 . :rhe erratic movements of heald shafts, in addition to large depth of shed, cause increased warp breakages and significant loss in weaving efficiency4 of the jute yarns wl1ich have a low breaking extension6 of the order of 1 .2% only.

Considering the shortcomings of the conventional negative tappet shedding mechanism and also the fact that the shedding motion of a loom plays a key role in achieving the desired performance at weaving, a modified system of shedding with grooved (i.e. posi-

tive) tappet has been designed and developed for jute looms.

2 Materials and Methods 2.1 Design Consideration of the Modified Shedding

Mechanism In designing the modified tappet shedding mecha­

nism, the main criteria taken into consideration were as fol lows : - the mechanism should exercise the precise 'and

positive control on the heald shafts throughout their movements so that they can move smoothly in simple harmonic motion (SHM),

- the mechanism should be simple in design with less number of components to reduce the mainte­nance ana spare costs,

- the mechanism should be so located on the loom that it is easily accessible for carrying out the nec­essary setting and tuning operations, and

- the mechanism should be mechanically reliable for operating successfully under the actual production condition in the jute mills.

The major portion of the jute fabrics produced is of hessian and sacking qualities. The entire hessian and some of the sacking cloths are woven in plain ( I up -I down) weave. The shedding mechanism has, there­fore, been designed and developed for weaving plain cloth and its derivatives. It is wel l known that the ba­sic need for producing a plain weave is two heald shafts only, which should reciprocate simultaneously in the simi lar manner but in the reverse directions in

NEOGlel al. : MODIFIED TAPPET SHEDDING MECHANISM FOR IMPROVED PERFORMANCE OF JUTE LOOM: PART I 1 09

each pick cycle. It may, therefore, be possible that with the suitably designed link mechanism between the treadle lever and the heald shafts, the oscil latory movement of one treadle tever generated by one shedding tappet can be util ized to move the two heald shafts simultaneously in the reverse directions with­out the aid of a heald reversing mechanism. Positive control of heald movements with necessary dwells can be achieved by the grooved, summation or matched (i.e. conjugate) cams7. Of these, the first one has been considered in the modified shedding mecha­nism reported here because it gives the simplest posi­tive control of heald shaft motion. The novelty of the modified system of shedding designed for weaving plain construction thus lies in the consideration that only one grooved tappet-treadle lever assembly has been employed to actuate the two heald shafts in both the directions without any reversing mechanism.

2.2 Brief Description and Operation of the Mechanism

Fig. 1 shows the general view of the modified shedding mechanism fitted on a conventional hessian loom and Fig. 2 shows the diagrammatic view of the modified mechanism with various components incor­porated in it. The two heald shafts are governed by one grooved tappet, keyed at one end of the existing bottom shaft of the loom outside the loom frames. The tappet transmits motion to heald shafts by one

treadle lever, fulcrumed at a suitable place on the outer face of the loom frame. The other end of the treadle lever is connected to a heald actuating lever by a link rod. The heald actuating lever is fitted on an auxil iary shaft which runs across the loom and is car­ried by two pummer blocks and a bush. Figs 1 and 2 indicate that all the components from the tappet to the heald actuating lever, employed in transmitting the rotational movement of the tappet to the reciprocating movement of the lever required for driving the heald shafts, are mounted on the available space outside one of the loom frames and located in an easily accessible position. This provides the scope for quick setting and tuning of the shedding mechanism without dis­turbing the warp yarns, which is not possible with the conventional negative tappet shedding mechanism.

On the auxiliary shaft and inside the loom frames are fitted two crank levers (Figs 1 and 2) . These lev­ers are connected to the bottom of the metal heald frames with sliding wire healds through adjustable tie rods. Since the heald shafts are controlled from the bottom only, all metal heald frames, instead of the cotton heald shafts used in the conventional shedding mechanism, have been employed. The connection between the crank levers and the heald frames has been made at the two ends of the frames. To enable the heald frames to reciprocate smoothly during op­eration, they are guided by two nylon guides at two

Fig. I -MoJ i ficJ tappet shcJJi ng mcchanism fillcJ on a jutc loom

1 10 INDIAN J.FIBRE TEXT. RES., JUNE 2000

Fig. 2-Diagrammatic view of the modi tied shedding mechanism showing different components

ends. The guides are rigidly mounted on two side frames of the loom. As shown in Fig. 2, the compo­nents from the crank levers to the guides of the heald shafts, whose functions are only to move the shafts steadily and which would n�t require frequent atten­tion, are located inside the loom frames.

During the operation of the loom, as the grooved tappet rotates with the bottom shaft, the treadle lever reciprocates and moves the heald shafts both upward and downward (without the aid of any heald reversing mechanism) through the connecting l ink, heald actu­ating lever, crank levers and tie rods. S ince the two heald shafts are connected to the two arms of the crank levers and actuated by one grooved tappet, they traverse in the similar manner but in reverse direc­tions in each pick cycle.

It is worth noting from Fig. 2 that if the points of attachment of the l ink with the treadle lever and / or heald actuating lever are altered, the different extents of heald movements or shed depth can be achieved by the tappet of a given shape and dimensions, which is not possible with the conventional negative tappet shedding mechanism used in jute looms. Because of the elimination of the heald reversing arrangement and employment of one set of tappet and treadle lever for the two heald shafts, 35% less number of compo­nents can be used in the modified shedding mecha­nism in comparison to those of the conventional mechanism (Table I ) .

Table I -Components used in two shedding mechanisms for plain weave construction

Component

Shedding tappet Treadle lever Treadle bowl Treadle fulcrum Fulcrum bracket Grid bar for treadle lever Metal hook (long) Wooden lam Connecting l ink Heald actuating lever Auxiliary shaft Bushing for auxiliary shaft Pummer block Crank lever Tie rods Heald shaft fixing block Heald shaft Heald shaft guide Guide brackets Metal hook (short) Leather strap Rope Reversing roller Reversing roller shaft Reversing roller bracket Cross rail

. Total components Reduction, %

Shedding mechanism Conventional Moditied

2 (negative) 2 2 I 2 I

2 2

2 (cotton)

4 4 8 4

2

40

I (grooved-positive) I I I

2 2 4 4

2 (metal) 2 2

26 35

NEOGI et al. : MODIFIED T APPEf SHEDDING MECHANISM FOR IMPROVED PERFORMANCE OF JU1E LOOM: PART I 1 1 1

2.3 Operational Advantages of the Modified Shedding Mechanism over the Conventional System

The description of the modified shedding mecha­nism clearly indicates that from the mechanical and operational points of view it has some distinct ad­vantages over the conventional system, as enumerated below : -- Grooved tappet of correct design and dimensions

can exercise precise and positive control on the'

heald shafts . -- Similar nature of the movement of two heald

shafts (for plain weave) can be achieved as the heald shafts are actuated by one shedding tappet.

-- Quick and easy settings of shed timing are possi­ble because the tappet and treadle lever assembly is located outside the loom frame.

-- The modified system offers the possibility for ob­taining different shed depths from a given shed­ding tappet.

-- Maintenance and spare costs of the modified mechanism are l ikely to be much reduced because of the less number of components employed.

As pointed out earlier, the modified shedding mechanism has, however, one l imitation i .e . it is suit­able for weaving plain ( 1 up - 1 down) construction only.

2.4 Nature of Heald Movements Before discussing the working performance of the

modified shedding mechanism, it is more appropriate to examine the nature of heald movements obtained with the grooved tappet of the newly developed sys­tem and compare the same with those obtained with the negatiave tappets of the conventional shedding

I · 1 ,

DWELL , 6HF ' 550 TOP SHEP LINE 1 ,.. Z ,. I � t: =- -:- -: :� _ _ _ _ L-::-_

-� _ _

I I I I E I � I N I � ;; I

I I , I ,

..J ., I ........ m I 1-P.- 9 . 50 � ��-- - - T�---- - - - - - ---1;; � ..J I , 9 .. '" x '"

I : I I I I I

mechanism. For this purpose, the heald movements of the modified as well as of a typical conventional mechanism used for the production of the same type of fabric on the same loom have been recorded by a simple instrument developed earlier by one of the authors4 and analysed.

The nature of heald movements has been shown in Figs 3 and 4 for the conventional and modified shed­ding mechanisms respectively and the important findings are shown in Table 2. From the tracings of heald movement, the displacements and velocities of the heald shafts while traversing from one dwell to the next have also been studied to examine how far they conform to the SHM. The results are shown in Figs 5 and 6 and Table 3 for the two types of shed­ding mechanism. The heald velocities have been cal­culated by the standard formulae8 .

3 Results and Discussion 3.1 Heald Movement Analysis

• From the tracings of the heald movements of the conventional shedding mechanism (Fig. 3), it is ob­served that all the dwell periods of two tappets vary widely from each other and none is equal to the re­quired value of 60°. The maximum difference be­tween the two heald dwells is 24° (Table 2) . Because of the inequality in the dwell periods, the two heald shafts in either pick cycle do not enter or leave the dwells simultaneously. This causes undue slackness and tightness in the shedding mechanism and jerky movements to the heald shafts. For both the tappets, the dwell periods at the top shed position are appre­ciably less than those at the bottom. Because of the

DWELL,6HBZ' 46° I" II "; l

BACK HEALD I I I

. I I

'-'-- 80 I _ _ _ _ _ _ _ _ _ _ _ -1 --' _ _ _ _ ..l. _ _ _ _ _ _

FRONT HEALD

: I I

-- - - - -,- - - - -- -I _ _ _ _ _ _ _ _ I BOTTOM I I I - f - - - - l - - - - i - - - - - - -

I SHED I DWELL SHB ' 690'" �,c�ID�mmL-�U�NE�----�I�----------�,. �I. __ ----------------------�,. , P I C K CYCLE , P, ' 189 0 PICK CYCLE , PZ ' 1 7 1 0

Fig. 3-Heald movement diagram of conventional shedding mechanism

1 12

Shedding mechanism

Conventional

Modified

1 2

INDIAN J.FIBRE TEXT. RES. , JUNE 2000

Table 2-Heald movement analysis for conventional and modified shedding mechanisms

Heald l ift, mm Heald dwell, 0° Pick ci:cle duration, 0° Front Back DitTerence Front Back Max P,

R ISE

1 1 8

1 1 3

1 2 1

1 1 3

E E

3

0

I OWELL,BHFZ' 60"., ,.. �I , 1

� � u. :; , '" "

Top Bottom Top Bottom difference shed shed shed shed

55 70 46 69 24

60 64 64 60 4

, DWELL, BHBZ' 64° I ,.... ...., _ _ _ _ Tr:.P .:�� L�N! _ _ � ___ � __ ... '

"'-BliCK H E ALD ' ,

1 89

1 80

o ..J <t _ _ _ _ _ w :r <XI ...... ,.- 30 �- - - - - � '- - - - - - - - - - -'" ,

, , I I .1 I - - - - - - - - - - - - 1- - - - - - - - - - -

'" U <t � Z o a: u.

u. ..J

I , FRDNT HEALD

/

I

.:-..,c-----+-----f'- - - - - - +- - - -- - - -:::--.�, ----+---.-,<' , I I.. .. . : BOTTO M , S H ED L I N E '" .. I ,

, ' DWELL,QHB,'BOO, I : DWELL,6HFI , 64° : : �� .. ---------------� .. ..- II_--r"------------------------� __ � I , PICK CYCLE , � , 180° I PICK CYCLE, P2, 1800 I

Fig. 4--Heald movement diagram of modified shedding mechanism

FALL

90

60 � E u .. ...

30 g J ... >

, �

9

BACK HEALD - RISE FRONT HEALD - FALL

P2

1 7 1

1 80

Difference

1 8

0

90

60 � b )­I­U 30 0 J ... > o 30 60 90 115 1 t-20--9TO--"60--3"0-':�0.J.0 �-�---r---r--�O

E u ,: z '" ,. 6 ... u " � "' o 3

o 30 60 90 12� 120 90 TAPPET ROTATJON,deg

60 30

90 '" "-60 E u ,: l­i)

30 � ... >

Fig. 5-Heald displacement and velocity diagrams with conven­tional tappet [(-) actual, and (- - - ) theoretical (SHM)]

o 30 60 90 116 120 90 60 30 o TAPP E T ROTAT I O N , dog

Fig. 6-Heald displacement and velocity diagrams with modified (grooved) tappet [(-) actual, and (- - -) theoretical (SHM)]

errors in the dwell periods, the heald dwells at the top and bottom shed lines in a pick cycle do not coincide and the mis-alignment in the dwell varies from 8° to 9.5° . It is also observed from Fig. 3 that none of the dwell periods of either heald shaft is smooth and uni­form with the result that the heald shafts do not re­main absolutely at rest at the dwells. This is because of errors in the profiles of the shedding tappets .

NEOGI e/ al. : MODIAED TAPPET SHEDDING MECHANISM FOR IMPROVED PERFORMANCE OF JlITE LOOM: PART I 1 1 3

Table :'I-Deviation of heald displacement and velocity from SHM for conventional and modified shedding mechanisms

Shedding Maximum deviation mecha- Dis�lacement, cm Velocit�, cmls nism Rise Fall Rise Fall

Start Middle End Start Middle End Start Middle End Start Middle End

Front +2.2 +2.0 +0.9 -0.3 -0.2 -0. 1 + 1 8.2 - 1 2.2 - 1 2.0 +7.8 + 1 .0 +4.0 Conven- heald tional

Back +0.7 + 1 .0 +0.4 -0.2 +0.5 +0.6 +5.3 -5.6 -5.5 +6. 1 - 1 .8 + 1 1 .6 heald

Front +0.4 -0.3 -0.3 +0.3 +0.4 -0. 1 + 1 0. 1 +0.8 +4.7 +3.4 + 1 .6 +4.0 Modi- heald fied

Back +0.3 +0.4 -0. 1 +0.4 -0.3 -0.3 +3.4 + 1 .6 +4.0 + 1 0. 1 +0.8 +4.7 heald

Note : (+) indicates the higher and (-) indicates the lower actual values than theoretical (SHM)

It is also observed from Fig. 3 that the heald level position does not occur at the interval of 1 80° rotation of the tappets and the duration of two successive pick cycles differs by 1 8° in one rotation of the tappet (Table 2) or by 36° in one rotation of the crank shaft of the loom.

Fig. 3 further shows that while the heald shafts form the top shed lines, the front heald moves further up than the back one which is contrary to what should have been and the difference between the shed heights at the top position is - 7 mm. As a result, the difference between the lifts of the two heald shafts is only 3 mm (Table 2) which is not at all adequate for proper formation of the warp shed.

As regards the modified system of shedding devel­oped, even a cursory look at the heald movements in Fig. 4 clearly reveals their superiority over those ob­tained with the conventional shedding mechanism and shown in Fig. 3. As expected, both the heald shafts of the modified mechanism remain at dwell for exactly the same period of time in a pick cycle. Although the dwell periods in the pick cycle P2 are not exactly 60°, they are very close to it and the maximum difference between the heald dwells in two pick cycles is 4° only (Fig. 4 and Table 2). Since both the heald shafts, in any case, move in unison, this small difference in dwell is hardly l ikely to have any adverse effect on the performance of the mechanism. From Fig. 4, it is also observed that each dwell of the grooved tappet is fairly smooth and each heald shaft, therefore, remains absolutely stationary during this period.

Fig. 4 and Table 2 further show that unlike the conventional shedding, the heald shafts of the modi-

fied system become level at the desired interval of 1 80° rotation of the tappet, thus enabling each pick cycle to occupy the same length of time.

It is also observed from Fig. 4 and Table 2 that both the heald shafts have identical lift of 1 1 3 mm. Because of the absence of the heald reversing mecha­nism, it has been possible to place the two heald shafts of the modified system of shedding so close to each other that the amount of excess lift required for the back heald shaft over that of the front is too small to have any practical significance and the same lift has been maintained for both the heald shafts. Same lift of the back heald as that of the front is expected to reduce the strain and thereby the chances of breakage of the warp yarns.

3.2 Heald Displacement and Velocity From the displacements and velocities of the two

heald shafts of the conventional shedding mechanism (Fig. 5), it is observed that the nature of their move­ments while traversing from one position to other does not strictly fol low the desired path of SHM, par­ticularly when they are ascending to form the top shed lines. For both the heald shafts, the amount of angular rotation of the tappet for their upward and downward traverses is not the same with the result that the maximum velocity of a heald shaft while ris­ing is different from that when it is fall ing. It is also observed from Fig. 5 that during the upward move­ment, the maximum velocity of either shaft does not occur at the theoretically correct angular position of the corresponding shedding tappet.

The deviations of the actual heald displacements and velocities from the normal in the case of conven-

/'

1 14 INDIAN J.FIBRE TEXT. RES. , JUNE 2000

tional shedding mechanism (Table 3) reveal that the displacements and velocities of both the heald shafts are either higher or lower than the corresponding cor­rect values and in many cases, the extent of deviation is quite appreciable. The maximum deviations of 2.2 cm in displacement and 1 8 .2 cm/s in velocity have been observed during the rise of the front heald shaft.

The diagrams of the heald displacements and ve­locities of the modified shedding mechanism (Fig. 6), on the contrary, clearly indicate that the nature of the movement of both the heald shafts in either directicn is much superior to that of the conventional mecha­nism and is in close agreement with SHM, although there are some discrepancies� Because of the method of drive to the heald shafts, the various values of the displacement and velocity of the front heald shaft while rising are identical to those of the back heald shaft while falling and vice-versa. It is observed from

. Fig. 6 that in the case of the grooved tappet also, the angular rotation occupied by a heald shaft while moving up and down is not the same and there is a difference of about 40 . The angular rotation of the tappet at which the maximum heald velocity occurs also differs by about 5.50 during the fall of the front heald shaft ( or the rise of the back heald shaft) .

Nevertheless, the extents of deviation in heald dis­placement and velocity with grooved tappet are much less compared to those observed in case of the con­ventional tappet (Table 3). The maximum deviation in displacement is only 0.4 cm and that in velocity it is 10. 1 cm/s during the rise of the front heald shaft (or the fal l of the back heald shaft).

From the comparative study of heald movements obtained with the two types of tappet shedding mechanism, the modified system of positive shedding is expected to perform better and reduce the warp breakages at weaving.

4 Conclusions 4.1 The modified shedding mechanism contains

35% less number of components than the conven­tional system because of the elimination of the heald reversing mechanism and employment of one set of tappet and treadle lever for two heald shafts, which is expected to minimize the spare and maintenance costs of the 100m.

4.2 The modified shedding mechanism is fairly simple in design and construction with the tappet­treadle lever assembly mounted on the available space outside one of the loom frames and located at an easily accessible position for easy and quick set­ting of the mechanism.

4.3 Compared to the conventional shedding mecha­nism, the modified system produces much improved nature of heald movement with desired dwell periods and this is expected to reduce the warp breakages at weaving.

Acknowledgement The authors are thankful to Dr K J ayachandran,

Director, IJIRA, and to Mr D P Khatua, Dy. Director, IJIRA, for valuable criticism and help during the study.

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