Weaving Mechanism FM-3022 Kashif Khan Khuhro (12TE88) April 2014

Weaving Mechanism FM-3022 Kashif Khan Khuhro (12TE88)
April 2014 5th Semester1
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.

Shedding machines
The 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 shedding
o Dobby shedding
o 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 SHEDDING
This 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 maximum
eccentricity, 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 are
identical, 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 shaft
2 toothed bevel gear pairs
3 group of conjugated cams
4 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 SHEDDING
Dobbies are used for the production of plain or flat fabrics, that is of fabrics characterized by
maximum 28-32 threads in the weave repeat.
Dobbies can be divided into:
According to the working principle:
Hattersley dobbies
rotary dobbies
The 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 drive
dobbies with negative drive
The positive dobbies are dobbies in which both raising and lowering heald frames are driven
directly.
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 upper
position to avoid the intrusion of water into the mechanisms (Fig. 8485).
Fig. 84 Negative dobby (upper
position for water-jet weaving
machines)
Fig. 85
Positive dobby.

According to the card reading system:
dobbies with endless pattern card
dobbies with magnetic card
Operation principle of a dobby
Today the rotary dobby is, from the technological point of view, the most advanced dobby
available 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 180
degrees ; at this very moment the key can be controlled according to the design to be
produced.
Fig. 87 Rotary dobby: traditional
rods and quick change rods
Fig. 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 initial
position 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 SHEDDING
Jacquard machines
The 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 the
various 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 machines
Vincenzi machines
Verdol machines
At 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 system
dobbies with electronic reading system
The 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 Jacquard
In these machines the traditional hooks have been
replaced by electro-mechanically operated
modules which are driven and controlled by an
electronic program. The Jacquard machines
available on the market are double lift machines
and
have in respect to mechanical Jacquard machines
following advantages:
easy maintenance owing to following reasons:
no point needing lubrication, few moving
parts, modular construction and thus easy access;
low vibration even at high speed;
reduced setting time, as the machine is
electronically controlled and therefore no
paper is needed
Fig. 89 and 90 show the two most widely used
models of electronic Jacquard machines.
In Fig. 89 each module is composed of 48
hooks; by combining together several
modules, it is possible to attain the various
capacity loads. The hook is flexible and has
windows to allow its hooking-up to the
magnet.
The machine operates as follows: in the first
two sequences of Fig. 89, the magnet(controlled by the program) does not receive
any impulse and the double pulley maintains the warp thread in bottom position, although
the 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 a
thread 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 in
opposition 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 lean
alternatively 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 therefore
remains 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 Sley
vertical, 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.B
Shed 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 line
OB = Top shed line
OC = Bottom shed line
OA = 32cm
OE = 36cm
Sweep of sley = 15o
Bevel of reed = 90o
Height of Shuttle front = 3.5cm
Distance 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 + 0.5
OC’ 11
θ = tan-1
4/11 = 19o
50”
Stroke of front H.F:
BC = BA + AC B
BA = tan BOA O A
OA C
BA = OA tan BOA
Similarly
AC = OA tan AOC
O H
O = 90o
O’ =15o
Hence
H = 180-(90+15) = 75o
O’
In this triangle
H
C’ = 90o
H = 75o
O C’
Hence
O = 15o
We know that

OA = 32cm B
Angle BOA = 19o
50”- 15o
O A
Angle BOA = 4o
50” C
Angle 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 = BC
OE FG C G
32 = 11.36
36 FG
FG = 12.78cm
Factors on which stroke depend:
Dist of H.F from fell of cloth:
H = tan α
B
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.F
h2 = stroke of 2nd
H.F
d1 = dia of pulley which controls front H.F
d2 = 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.

Weaving Mechanism FM-3022 Kashif Khan Khuhro (12TE88) April 2014

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Weaving Mechanism FM-3022 Kashif Khan Khuhro (12TE88) April 2014