Shedding types (dobby, tappet and jacquard)

Weaving Mechanism FM-3022 Kashif Khan Khuhro (12TE88)

PRIMARY MOTIONS

There are three primary motions or basic motions of loom.

Shedding motions. Beating motions. Picking motions.

SHEDDING MOTION

Warp threads are divided into two layers. Top layer is called top shed line. Bottom layer is called bottom shed line. The gap b/w two layers is called shed.

OBJECTIVES OF SHEDDING

I. To raise & lower the healed frames which carry the warp.II. To make an opening for passage of picking media.

III. To change the position of warp ends to interlace the warp & weft as per weave.

Shedding

Tappet shedding Dobby shedding Jacquard shedding

Positive Negative

Positive shedding:Raising & lowering of healed frames is with the help of Double cams.

Negative shedding:Lowering of frames is with the help of single cams & Raising is with the help of reversing media.

Reversing Media:The media which brings the frames in original position, these may be spring, pullies, & elastic etc.

SHEDDING MECHANISM

FUNCTIONS OF SHEDDING MECHANISM:

To raise & lower the healed frames, which carry the warp, ends. To make an opening for the picking media to pass trough. To change the position of warp ends to interlace warp weft as per weave.

April 2014 5th Semester1


Shedding machinesThe angle which is formed by the raising threads with the threads remaining in low position is called shed; the shed must be as wide open as to permit the easy passage of the weft insertion element.The shed can be obtained in two different ways:by moving the heald frames, the healds of which are crossed by the warp threads according to a pre-established drawing-in;by moving directly the healds through which one or several independent threads pass (figured or Jacquard weaving).

The machines used to form the shed are cam machines, dobbies and Jacquard machines.TYPES OF SHEDDING

o Tappet sheddingo Dobby sheddingo Jacquard shedding

These are the attachments which can be fitted to any loom. Therefore looms are classified as

Tappet loom Dobby loom Jacquard loom

TAPPET SHEDDINGThis kind of machine is employed for all fabrics produced with base weaves which have a pattern repeat of 10-12 threads and maximum 6-8 wefts.These machines can operate either with positive or negative shaft motion. The principle of positive motion involves that the shafts are raised as well as lowered driven by cams. The negative motion instead implies the motion of the shafts either in the upwards stroke or in the downwards stroke, while the backward movement is obtained through springs. The positive shaft motion has a conjugated structure which permits to control the shaft during all processing phases and to minimize vibrations, thus making cams suitable for any working load at high speeds.Operation of a cam machine (positive motion)This machine has conjugated cams fastened on a central shaft; the two profiles are read by small wheels mounted idle on a roller lever connected at its end with the heald frame rods.The two cams are mutually complementary, so that when a cam presents its maximumeccentricity, the other cam presents the minimum eccentricity. This characteristic permits to push upwards the right wheel and at the same time to produce the same movement with the left wheel, but in the opposite direction.The displacement of the roller lever causes the raising of the shaft.In the case of balanced weaves, i.e. plain weave, twill weave, diagonal 2/2, the two cams areidentical, but have each towards the other a phase angle which is established already during their construction.For the production of the remaining weaves, the overturning of the two cams permits to obtain the opposite effect, e.g. changing over from warp to weft twill.The cam units are as many as the working heald frames and the shaft modifies its running speed according to the weave to be produced, consequently the speed corresponds to the



revolution number of the machine/n and the figure 360/n shows the angle at which a weft of the repeat is inserted (n corresponds to the number of repeat wefts).

Fig. 81-Assembly scheme of the cam machine

Fig. 82 Conjugated cams with roller lever

Fig. 83 Cam machine:1 driving shaft2 toothed bevel gear pairs3 group of conjugated cams4 pin on which roller levers are set up.

Healed frames are operated with tappet cams. Cams are designed according to types of weave. No. of cams depend upon the weave repeat e.g. 4 cams for 3/1 twill. Tappet cam designed for one weave cannot be used for other weave. Storage of cams is necessary in the mill to change the weave. Long time for cam change is required, so cause loss in production. No. of cams for different weaves are

Design Min. cams. Max. Cams.

1/1 Plain 2 4 2/1 twill 3 6 3/1 twill 4 8 4/1 satin 5 10 etc.



ADVANTAGE OF TAPPET SHEDDING

Mechanism is simple. Initial cost is low. Maintenance is easy. No problem of design fault in fabric. No speed limitations. Plain, simple twill & Simple satin can be produced.

DOBBY SHEDDINGDobbies are used for the production of plain or flat fabrics, that is of fabrics characterized bymaximum 28-32 threads in the weave repeat.Dobbies can be divided into:According to the working principle:Hattersley dobbiesrotary dobbiesThe Hattersley dobbies are dobbies which control the movement of the heald frames through rods and rocker levers. The rotary dobbies attain the raising and lowering of the heald frame through rotating members.According to the raising motion of the heald frames:dobbies with positive drivedobbies with negative driveThe positive dobbies are dobbies in which both raising and lowering heald frames are drivendirectly.

The negative dobbies are dobbies in which the heald frames are driven directly either only in the raising phase or only in the lowering phase. The dobbies are always mounted in bottom position, both if they are with positive or negative drive.Only in the case of water jet weaving machines, the dobbies are generally mounted in upperposition to avoid the intrusion of water into the mechanisms (Fig. 84−85).

Fig. 84 Negative dobby (upperposition for water-jet weavingmachines)

Fig. 85 Positive dobby.

According to the card reading system:dobbies with endless pattern carddobbies with magnetic card

Operation principle of a dobbyToday the rotary dobby is, from the technological point of view, the most advanced dobbyavailable on the market. It consists of a central shaft on which the driving bars are positioned.



On a follower ring an eccentric plate is mounted; the plate is constrained within a block which is pivoted with the control levers of the rods.Under normal working conditions that are with the heald frames in bottom position there is no connection between the follower ring and the plate; the connection can be obtained by inserting a slider which runs in proper guides.The central shaft is driven by a modulator which has two stop times situated each other at 180degrees ; at this very moment the key can be controlled according to the design to be produced.

Fig. 87 Rotary dobby: traditionalrods and quick change rodsFig. 86 Rotary dobby

The insertion of the slider causes a 180° rotation of the plate which, thanks to the link, imparts a force on the lever controlling the rods of the heald frame, causing its passage from the initialposition to the opposite position and consequently the raising of the heald frame.As soon as such position is reached, at the subsequent shaft stop a new signal is emitted: if the heald frame has to remain in raised position, the key is pulled out, thus blocking it in upper position and leaving it motionless there till emission of a new order, which can be in same or opposite direction.If the direction of the order remains the same, the slider is taken out and the heald frame remains motionless in upper position; if the order has opposite direction, the slider is set to work andgenerates a movement in opposite direction to the previous heald frame lowering.The design is controlled by the microprocessor on board the machine, which transmits the inputs to a series of electromagnets which shift the sliders to the two said positions.The rotary dobby, which is a machine with positive drive, has replaced all other models based ondifferent operation principles.

Healed frames are operated by jacks & levers. Lifting & lowering of frames is controlled by pattern chain. It can control up to 32 healed frames depending upon the crank length. Design possibilities are crepe , honey comb , huckaback , mockleno , bedfordcord

etc.,



DISADVANTAGE OF DOBBY SHEDDING

Mechanism is complicated. Initial cost is high. Maintenance cost is high. Can produce design fault in the fabric. Limitation in loom speed.

JACQUARD SHEDDINGJacquard machinesThe name Jacquard machines originates from the designer who improved its operation; today the name ″Jacquard″is used to identify all machines with a capacity higher than 28-32 threads, which are therefore used to produce figured fabrics.The indication of the capacity of the machine, which in the past was used to differentiate thevarious machine models, has today no significance, as the hook number is no more strictly related to the mechanical structure of the machine.Jacquard machines were initially classified as follows:Jacquard machinesVincenzi machinesVerdol machinesAt present only Verdol machines and electronic Jacquard machines are still on the market.Jacquard machines can be classified as follows:According to card reading system:dobbies with endless pattern card reading systemdobbies with electronic reading systemThe endless pattern card system is gradually disappearing in favor of the electronic system.Modern Jacquards are exclusively double lift machines (which means that the thread floating over several subsequent wefts remains always in upper position and does not go down to sley level) with electronic control (with magnetic bearings).The machines with card reading system (Jacquard) or with endless pattern card system (Verdol) have practically disappeared from the market.According to machine capacity, i.e. to used hook number:Verdol type machines: 448 896 1344 hooks-electronic machine with modules permitting following load capacity: 5120-6144-8192-10240-12288 hooks.

Fig. 88 Jacquard machine with deck



Electronic JacquardIn these machines the traditional hooks have beenreplaced by electro-mechanically operatedmodules which are driven and controlled by anelectronic program. The Jacquard machines available on the market are double lift machines andhave in respect to mechanical Jacquard machines following advantages:easy maintenance owing to following reasons: no point needing lubrication, few movingparts, modular construction and thus easy access;low vibration even at high speed;reduced setting time, as the machine iselectronically controlled and therefore nopaper is neededFig. 89 and 90 show the two most widely used models of electronic Jacquard machines.In Fig. 89 each module is composed of 48hooks; by combining together severalmodules, it is possible to attain the variouscapacity loads. The hook is flexible and haswindows to allow its hooking-up to themagnet.The machine operates as follows: in the firsttwo sequences of Fig. 89, the magnet(controlled by the program) does not receiveany impulse and the double pulley maintains the warp thread in bottom position, althoughthe hooks move upwards and downwards together with the griff knives (the rotation of of the hooks). The last two sequences of Fig. 89 show that, when athread needs to be raised, the magnet receives the impulse and the flexible hook hooks-up to the magnet. This causes the lifting of the double pulley, as in this case it is not possible to make any compensation.In the model shown in Fig. 90, the elements raising the heald frames 18 and 19 operate inopposition one another. In figure A the knife 18 is positioned at the upper dead center, whereas the knife 19 is at the bottom dead center.At the end of the stroke, the movable hooks 6 connected with the suspension cable 9 leanalternatively the upper end of the check hooks 4 on the electromagnet 5.

Thre are two cases:1) The electromagnet 5 is powered (case A):- the check hook 4 remains ″stuck″to electromagnet 5.- The movable upper hook 6 goes down together with knife 18.- The lifting cord 10 goes up or remains in bottom position.2) The electromagnet 5 is not powered (case C):- owing to spring 3, the check hook 4 hooks up the movable upper hook 6, which thereforeremains in upper position.- The lifting cord 10 goes up or remains in upper position.



The body of the rocker arm 7 linked to the fixed point 11 reinstates a shifting of the lifting cord 10 equal to that of knife blades 18 and 19.

Fig. 90

Warp ends are controlled individually by harness cord. No of cord = No of ends No healed frame. Warp ends controlled by shedding mechanism. Pattern possibilities are unlimited. Complicated designs may be produced like animals, flowers, geometrical figures etc.

DISADVANTAGE OF JACQUARD SHEDDING

Mechanism contains more moving parts. Initial cost is high. Maintenance cost is high. Can produce design faults in the fabric. Design & cutting pattern cords require skilled labor. Speed limitations.

TYPES OF TAPPET SHEDDING

Positive shedding Healed frames are raised & lowered by double cams.Negative shedding Healed frames are lowered by single cams & raised by reversing

media.

NEGATIVE TAPPET SHEDDING



DEFINATION: Healed frames are lowered by single cams & raised by reversing media. (Springs, reversing pulley, elastic material).

DRIVE: It gets drive from bottom shaft.

PRINCIPLE:The rotary motion of tappet cams is converted into up & down motion of healed frames.

CONSTRUCTION:

i. Two treadle levers: One end of treadle lever is fulcrum at point F while the other to the bottom of the healed frames through connecting rod.

ii. Two treadle rollers or bowels: Fixed at the treadle levers.iii. Two tappet cams: Fixed on the bottom shaft.iv. Healed frames: These are tied at top by means of cords or leather strap;

strap is passing on reversing pulley.

WORKING:

When the bottom shaft revolves, the tappet cams fixed on it also revolves in the same direction. The tappets are adjusted at definite angles on the bottom shaft. Suppose tappet A is pressing the treadle lever A through treadle roller A, the healed frame connected to it will come down & the second frame will go up due to reversing mechanism. The warp ends passing through 1st healed frame will form bottom shed line & warp ends passing through 2nd

frame will form top shed line. The shuttle will pass through shed at that time. The treadle



lever B will be pressed by 2nd tappet & the healed frame connected to it will downward. The 1st frame will move up due to reversing mechanism. In this way shedding will continue.

STROKE:

It is the max displacement of healed frame, when it is at its max position and the on min position.

DWELL PERIOD:

The time for which reed is stationary at rare most position is known as dwell period of reed. The HF remains stationary in shed opening position and picking media is passing through shed. It has direct relation with width of m/c and indirect relation with speed of m/c. In case of sulzer it is 200-270o and for cam beat up is 220-255o.

FACTORS ON WHICH CONSTRUCTION OF TAPPET CAM DEPEND:

Type of weave Dwell period of H.F Stroke of H.F Dia of treadle bowl Nearest point of contact of tappet cam with treadle bowl (the point from where the

radius of cam is max the distance is taken as nearest point)

Arrangement of loom shafts:



WEAVING POSSIBILITIES WITH CAMS



POSITIVE TAPPET SHEDDING

DEFINATION: That type of tappet shedding in which healed frames are raised & lowered by double cams (matched cam or conjugate cams).

DRIVE: It gets drive from tappet shaft.

PRINCIPLE:The rotary motion of the double cams is converted into up & down motion of the healed frames.

CONSTRUCTION:

i. Double cams fitted on the tappet shaft.ii. Treadle lever has fulcrum point at F1; upper of it is connected with fork lever & lower

has contact with the double cam through treadle rollers.iii. Link rods: One end of it is connected to fork lever & other with the top of driving rod.iv. Driving rod: It is fulcrum at F2 & lower end of it is connected to bottom of healed

frame through harness lever, T-lever & connecting levers.v. Lock screw: It is used to connect link rod.

vi. Clamp screw: It is used for the adjustment of fork lever by moving it up and down.

WORKING: When tappet shaft is revolving, the double cams are also revolving.



HEALD FRAME MOVES DOWNWARD: Suppose lower cam A is pressing the lower treadle lever E the treadle lever will move toward the loom side. The upper portion of it will move away the loom direction. The link rod & upper of driving rod will also move in the same direction. The lower portion of the driving rod will move toward the loom side & the healed frame will be lowered through harness lever, T-lever & connecting levers.

HEALD FRAMES MOVES UPWARD: Suppose the cam B is pressing the upper treadle roller, the top of the treadle lever will move towards the loom direction. The link rods & upper of driving rod will also move in the same direction. The lower portion of the driving will move away the loom side & the healed frame will move upward through harness lever, T-lever & connecting levers.

SETTINGS:

SHED OPENING:If we move the fork lever upward with clamp screw the opening will increase & vice versa.

SHED HEIGHT:If we increase the length of link rods by lock screw, the height will increase & vice versa.

GEOMETRY OF WARP SHED

Sweep of Sley:

It is the angle subtended by the sley with the Sleyvertical, when the sley is at its rare most position (sley is used to move the reed). 12o-15o

Bevel of Reed: 87-90o Reed



It is the angle b/w the reed and race board.

R.BShed angle:

The angle b/w top shed line and bottom shed line.For shuttle looms it is 20 o and for sulzer it is 28-32o. α

Stroke of Healed frame:

The max vertical displacement of front or back H.F is known as stroke and it depends upon Height of shuttle front inside warp sheet. Position of H.F w.r.to cloth fell. Sweep of sley

Calculation for the stroke of H.F:

Consider the relative position of reed, shuttle, H.F and fell of cloth.

OA = Center lineOB = Top shed line

OC = Bottom shed line

OA = 32cmOE = 36cmSweep of sley = 15o

Bevel of reed = 90o

Height of Shuttle front = 3.5cmDistance of shuttle front from fell of cloth = 11 cm (10-20cm)Clearance b/w T.S.L and Top of shuttle front = 0.5cm

Shed Angle:

From right angle triangle OB’C’

Tan B’OC’ = B’C’ = 3.5 + 0.5OC’ 11

θ = tan-1 4/11 = 19o50”

Stroke of front H.F:

BC = BA + AC BBA = tan BOA O AOA C



BA = OA tan BOASimilarlyAC = OA tan AOC

O HO = 90o

O’ =15o

Hence H = 180-(90+15) = 75o

O’ In this triangle

HC’ = 90o

H = 75o O C’Hence O = 15o

We know thatOA = 32cm BAngle BOA = 19o50”- 15o O AAngle BOA = 4o50” CAngle COA = 15o

AC = OA tan AOC = 32 tan 15o = 8.75cm

BA = OA tan BOA = 32 tan 4o = 2.79cm

BC = BA + AC = 8.57 + 2.79 = 11.36 cm

Stroke of back H.F:

From similar triangle OFG and OBC B F

O A E

OA = BCOE FG C G

32 = 11.3636 FGFG = 12.78cm

Factors on which stroke depend:

Dist of H.F from fell of cloth:

H = tan αB

H = B tan α



Sweep of sley:

If sweep of sley is more, then stroke of H.F will be more.

Height of shuttle front:

If it is more on shed then more will be required stroke.

Dia of pulley: d2

Larger dia of pulley then more will be stroke of H.F. d1

h1 = stroke of 1st H.Fh2 = stroke of 2nd H.Fd1 = dia of pulley which controls front H.Fd2 = dia of pulley which controls back H.F

h1 α d1 h1 = const x d1

h2 α d2 h2 = const x d2

h1 = K & h2 = K d1 d2

h1 = h2 h1 = d1 d1 d2 h2 d2

This result shows that the ratio of the stroke of two H.F is always equal to ratio b/w diameters of two pullies.


Shedding types (dobby, tappet and jacquard)

Engineering

Transcript of Shedding types (dobby, tappet and jacquard)