114 WEAVING FUNDAMENTALS

FIGURE 5.8 Motion diagrams of harnesses.

Figure 5.10 shows various types of open-end loop 5.1.3 Filling Insertion
heddles for riderless frames and Figure 5.11 shows
After each shed change, the filling yarn is inserted
heddles with closed end loops for normal frames.
through the shed as shown in Figure 5.12. It is
Automatic harness leveling devices are used on
possible to select and insert different filling yarns
weaving machines with cam motions to equalize
one after another. These filling yarns can be of
tension on warp yarns during a machine stop. This
different color, weight, etc., and a selection
eliminates start up marks in the fabric. It also makes
mechanism is used for this purpose. Depending on
warp yarn repairs easier.
the machine type, several different filling yarns can
Shedding mechanisms of major weaving machine
be used in the same fabric. The selection mechanism
types are included in the following chapters.
presents the proper filling yarn to the yarn carrier
for insertion of each yarn.
Weaving machines are usually classified according
to the filling insertion mechanism. Figure 5.13 shows
various classifications of weaving machines. The
major filling insertion systems that are used today
are air-jet, rapier, projectile and water-jet which are
called shuttleless weaving machines (Figure 5.14).
M8300 is a multiphase air-jet weaving machine
(Chapter 11).
A gripper projectile transports a single filling yarn
into the shed (Figure 9.2). Energy required for
picking is built up by twisting a torsion rod. On
release, the rod immediately returns to its initial
position, smoothly accelerating the projectile
through a picking lever. The projectile glides through
FIGURE 5.9 Carbon composite frame slat profiles for the shed in a rake-shaped guide, braked in the
harnesses (courtesy of Burckle). receiving unit, the projectile is then conveyed to its

© 2001 By Sulzer Textil Limited Switzerland

 FIGURE 5.10 Open end loop heddles (courtesy of Burckle).

FIGURE 5.11 Closed end loops (courtesy of Burckle).

FIGURE 5.12 Selection and insertion of filling yarns.

115
© 2001 By Sulzer Textil Limited Switzerland
116 WEAVING FUNDAMENTALS

FIGURE 5.13 Classification of weaving machines.

original position by a transport device installed In the shed, the tapes move without guides. The
under the shed. The projectile’s small size makes grippers assume the correct clamping position
shedding motions shorter which increases operating automatically. Different versions of rapier insertion
speeds over wide widths of fabric, often weaving systems are explained in Chapter 10.
more than one panel of fabric with one insertion The most popular method of filling insertion is
mechanism. illustrated in Figure 8.1 where a jet of air is used to
Figure 10.4 illustrates filling insertion by two “blow” the filling yarn into the shed. This small mass
flexible rapiers with filling carriers, a giver and a of insertion fluid enables the mechanism to operate
taker. The filling is inserted half way into the shed at extremely high insertion rates. The picks are
by one carrier and taken over in the center by the continuously measured and drawn from a supply
other carrier and drawn out to the opposite side of package, given their initial acceleration by the main
the fabric. A spatial crank gear drives the oscillating air nozzle and zboosted or assisted across the fabric
tape wheels to which the rapier tapes are attached. width by timed groups of relay air nozzles. The other

FIGURE 5.14 Major shuttleless weaving systems.

© 2001 By Sulzer Textil Limited Switzerland

 5.1 Basic Weaving Motions 117

fluid system uses water as the insertion medium, but

the use of a water-jet is generally limited to
hydrophobic yarns such as nylon or polyester
filament.
A shuttle loom uses a shuttle to store and carry
the yarn back and forth across the loom (Chapter
7). Shuttle looms have become obsolete in
manufacturing of traditional woven fabrics due to
several reasons, including low production rate, high
noise, safety concerns, limited capabilities, etc.
Nevertheless, the shuttle loom is still used as a
reference point for the modern shuttleless weaving
machines. Besides, some industrial woven fabrics are
still being made on specially designed shuttle looms.
Filling insertion mechanisms of major weaving
machine types are included in the following chapters.

Yarn Feeders
Yarn feeders or accumulators are used to wind a
predetermined yarn length to make it ready for
insertion. Their main purpose is to supply filling yarn
to the weaving machine smoothly and at a constant
and proper tension. There are various types of
feeders used (Figure 5.15). Typical characteristics
of these machines are:

• one-step pneumatic threading up

• integrated yarn break sensor
• floating element yarn store sensors
• stepless yarn separation adjustment
• microprocessor controlled speed and motor
effect FIGURE 5.15 Yarn feeders for rapier and projectile
• sealed spool body weaving machines (courtesy of Nuova Roj Electrotex).
• S/Z rotation shifting
• insertion speeds up to 2000 m/min through the feeder can be done manually or
• serial communication interface pneumatically. The tensioning of the yarn is
controlled by a breaking device which can be of
The selection of a feeder depends on several factors: different types including bristle, metal amella, flex
brake and coaxial output tensioner (CAT). Figure
• maximum speed delivered
5.16 shows the membrane and the endless beryllium
• yarn count
copper tensioning strip. The flex is used to replace
• winding direction (S or Z)
the brush ring and output tensioner in conventional
• yarn reserve control
brake systems. In CAT system (Figure 5.17), the yarn
Maximum speed depends on the yarn count range. travels through two tensioning discs mounted in the
Reserve control can be done mechanically or feeder nose. An adjustable tensioning spring
electronically by means of photocells. The threading regulates the base force exerted by the discs which

© 2001 By Sulzer Textil Limited Switzerland

118 WEAVING FUNDAMENTALS

FIGURE 5.18 Schematic of feed detector to stop the

weaving machine (courtesy of Nuova Roj Electrotex).

feeder as shown in Figure 5.21 which allows an even

FIGURE 5.16 Flex brake (courtesy of IRO). distribution of liquids, wax, oil, moisturizers and
anti-static lubricants on filling yarns during weaving.
allows the setting and maintaining of tension levels. The filling yarn is coated when it passes over a motor
During the filling insertion process, the CAT driven rotating cylinder that is immersed in a liquid
compensates yarn tension fluctuations. Filling reservoir.
breakage at the feeder entry is detected electronically To improve the fabric appearance, i.e., to
to stop the weaving machine (Figure 5.18). compensate yarn count fluctuations and color
For heavy yarns, a balloon breaker can be fitted irregularities, a 1–1 filling insertion from two
in front of the feeder instead of the normal eyelet bobbins instead of filling insertion from only one
(Figure 5.19). Figure 5.20 shows the path of the yarn bobbin is recommended.
inside a typical feeder.
During weaving of fine woolens and linen yarns,
5.1.4 Beat-Up
usually a lubricant is used which is supplied by a
liquid dispenser. The purpose of the lubricant is to When the filling yarn is inserted through the shed,
reduce filling breakages and increase weaving it lies relatively far from its final position. This is
machine speed and weaving efficiency. A liquid because the insertion device (air-jet, projectile, rapier,
dispenser is placed between filling package and etc.) cannot physically fit at the acute angle of the
shed opening. This final position is called fell which
is the imaginary line where the fabric starts.
Therefore, the newly inserted filling yarn needs to
be brought to its final position by pushing through

FIGURE 5.19 Balloon breaker for heavy yarns (courtesy

FIGURE 5.17 Coaxial output tensioner (courtesy of IRO) of Nuova Roj Electrotex)

© 2001 By Sulzer Textil Limited Switzerland

 FIGURE 5.20 Yarn path inside a feeder (courtesy of Nuova Roj Electrotex).

FIGURE 5.21 Liquid dispenser (courtesy of Savitec).

119
© 2001 By Sulzer Textil Limited Switzerland
120 WEAVING FUNDAMENTALS

loom will be higher than in the reed; generally about

5% higher depending on the weave, tensions and
yarn sizes involved.
There is a close interaction between shedding and
beating which may be dictated by the yarn type and
weave. The shedding and beating actions need to be
properly timed and synchronized for the most
effective filling insertion with minimum warp tension.
In general, the beat-up is done on an open shed for
filament yarns as shown in Figure 5.24 which also
shows that the beat-up is usually done on a crossed
FIGURE 5.22 Schematic of beat-up process. shed with staple fiber warp yarns. It is rare to beat-
up the filling yarn at the time the warp sheets cross.
the warp sheet. Beat-up is the process of pushing the Figure 5.25 shows the beating mechanism of a
last inserted filling yarn to the cloth fell by using a projectile weaving machine. For high speed
device called reed as shown in Figure 5.22. For all operation, light-weight parts are used for beating
practical purposes, the fabric is not formed until motion. The rigidity of the parts should be high and
beat-up occurs. the beating stroke should be short. In some terry
Reed is a closed comb of flat metal strips (wires).
These metal strips are uniformly spaced at intervals
that correspond to the spacing of warp ends in the
fabric; therefore, the reed is also used to control warp
yarn density (closeness) in the fabric. Warp density
is expressed as either ends per inch (epi) or ends per
centimeter (epc), which affects the weight of the
fabric. The spaces between the metal strips are called
“dents”. The reed holds one or more warp yarn(s)
in each dent and pushes them to the cloth fell. After
beating up the filling, the reed is withdrawn to its
original rest position before the insertion of the next
pick. Figure 5.23 shows a regular reed and a profiled
reed. Profiled reed is used in air-jet weaving
machines. In shuttle looms, the reed also guides the
shuttle.
The shape and thickness of the metal wires used
in the reed are important. Reed selection depends
on several considerations including fabric
appearance, fabric weight (ends per unit width),
beat-up force, air space requirement and weave
design.
Reeds are identified by a “reed number” which
is the number of dents per unit width. Specifying
the number of ends per dent with a certain reed
number dictates the construction (density) of ends
per inch in the fabric on the loom. It should be noted
that interlacing causes a natural contraction of yarns FIGURE 5.23 Regular reed (bottom) and profiled reed
in the fabric such that density of warp ends off the (courtesy of Burckle).

© 2001 By Sulzer Textil Limited Switzerland

 5.1 Basic Weaving Motions 121

frictional force depends on the coefficient of friction

between the warp and filling. Another reaction arises
from the bending of warp and filling yarns due to
crimp interchange. In order to overcome these
reactions, the pushing of the filling yarn into the
cloth fell is done in a rather harsh manner which
gives the action its name, i.e. beating-up. The beat-
up force increases as the beating proceeds towards
the cloth fell.
The beat-up process is very complex. The warp
tension increases and the fabric tension decreases
as the filling yarn is being pushed into the cloth fell.
Figure 5.27 shows the movement of yarns during
beat-up. The fabric area near the cloth fell does not
represent the actual fabric structure because the
distances between the yarns are not uniform. When
the reed returns after beat-up, warp tension exerts
FIGURE 5.24 Types of beating-up.
a force on the last few picks and these picks tend to
go back toward the warp beam. This is balanced
machines, the technique of two beat-up positions of out by the frictional restraint of the filling yarns.
the reed is used as shown in Figure 5.26. When the next beat-up cycle occurs, the new filling
During beat-up, the filling yarn is pushed against yarn is inserted and pushed into the cloth fell by the
frictional forces of the warp. Beating-up of filling reed. The yarns which have previously slipped back
yarn requires considerable amount of force. The are pushed into the fell again. The shed is unbalanced

FIGURE 5.25 Beating mechanism of a projectile machine.

© 2001 By Sulzer Textil Limited Switzerland

122 WEAVING FUNDAMENTALS

FIGURE 5.26 Double beat-up position for terry weaving.

in most situations to obtain closer pick spacing and Normally, the fabric fell is in equilibrium and the
a better fabric appearance. This unbalanced shed position of the fell does not change from pick to
develops different tensions in the upper and lower pick. However, any interruption in weaving will
sheds. The yarns in the upper shed are shorter and cause the fell position to change and this in turn
have less tension and the yarns in the lower shed distorts the motion of beat-up. Variations in the cloth
are longer which creates more tension. This could fell cause irregularities in the pick spacing in woven
ultimately affect the quality of the fabric. fabrics, causing a defect.
Several factors tend to affect the position of the
cloth fell during beat-up. These include warp and
fabric tensions, weaving machine speed and shed
motion during beat-up. Also, there are forces that
evolve during the beat-up process. Some of these
are the beat-up force, warp and fabric tensions and
weaving resistance.
Figure 5.28 shows the forces in beating [2]. T1
and T2 are the tension forces on the warp yarn. R is
the reaction force. R’ is the reactions from the
opposite interlacings. As the filling moves towards
the fell, the angle ß steepens, the magnitudes of R
and R’ increase, and α gets smaller. When the filling
is moved far enough into the fell, the angle a becomes
so acute that the filling would be squeezed out if it
FIGURE 5.27 Filling yarn spacing during beat-up [1]. were not restrained. Thus, there is a critical value

© 2001 By Sulzer Textil Limited Switzerland

 5.1 Basic Weaving Motions 123

tension will lead to an increase in the amount of

energy required for beat-up. Also, the shed timing is
important in determining the required energy. It
determines the tension distribution between the top
and the bottom sheds. The closer the distribution is
to being equal the more energy required [3].
Spun warps are timed to interlace the filling yarn
earlier, increasing the force of beat-up and the stress
on warp yarns to enhance fabric appearance (Figure
5.29). These extra stresses generally are not applied
to filament warp yarns since the uniformity of yarn
dyeability would be detrimentally affected.
Pick spacing is an important factor in beatup. As
stated earlier, irregular pick spacing caused by
variations in the fabric fell causes defects. These
defects result from loom stoppages. If a loom stops
for some reason such as a broken end, and, if it is
started without the fell being corrected, a start-up
line may be developed. This is where the previous
picks were not fully beaten into the fabric fell [1]. It
was also shown that beat-up force increases when
FIGURE 5.28 Forces in beating on an open shed [2]. pick spacing decreases [4].

for α beyond which the filling yarn cannot be pushed

5.1.5 Take-Up
any more forward in case of open shed. This critical
value depends on the coefficient of friction between As the fabric is woven, it should be removed from
the filling and warp and it determines the minimum the weaving area. This is achieved by the take-up
pick spacing that can be obtained by beating on an motion. The fabric take-up removes cloth at a rate
open shed. When beating is done on a crossed shed, that controls filling density [picks per inch (ppi) or
there is a smaller reaction to squeeze the filling yarn picks per centimeter (ppc)]. Two factors determine
out. As a result, closer pick spacings can be obtained filling density: weaving machine speed and rate of
in a cross shed. fabric take-up. Generally, the pick insertion rate of
The beat-up forces are affected by crimp levels,
the yarn dimensions and the filling spacing. As the
filling yarn is forced into the cloth fell, the beat-up
becomes more and more difficult. If the beat-up force
is increased beyond a certain magnitude to obtain a
close pick spacing, the beat-up force is taken by the
warp and the fabric becomes slack. This situation is
known as “bumping” which indicates a “jammed”
fabric. If jamming condition is reached, the pick
spacing cannot be reduced any further.
In beat-up, energy is required to beat the last pick
into position. The energy required is dependent upon
many factors. The main factors are fabric
construction and width, but tension is also an
important factor. An increase in the warp or filling FIGURE 5.29 Early shed timing.

© 2001 By Sulzer Textil Limited Switzerland

124 WEAVING FUNDAMENTALS

a weaving machine is fixed at the time of purchase changes in the fabric construction which must be
based on the range of fabrics it is intended to considered in setting up loom specifications.
produce, the type of insertion mechanism and the Take-up mechanisms of major weaving machine
weaving machine width. Weaving machine speed is types are included in the following chapters.
expressed as picks per minute (ppm) and rate of take-
up as inches per minute (ipm) or centimeter per
5.2 AUXILIARY FUNCTIONS
minute (cm/min). Warp density and filling density
together are referred to as the “construction” of the In addition to the five basic motions of a loom, there
fabric. Figure 5.30 shows the main parameters of are many other mechanisms on typical weaving
fabric construction and manufacturing. The machines to accomplish other functions. These
following relations exist: include:

• a drop wire assembly, one wire for each warp

yarn, to stop the machine when a warp end
is slack or broken (Chapter 4)
• a tension sensing and compensating whip roll
assembly to maintain tension in the warp
sheet
• a mechanism to stop the machine when a
filling yarn breaks
• automatic pick finding device reduces
machine downtimes in case of filling yarn
breakages
It should be emphasized that both the ends and picks • filling feeders to control tension on each pick
contract because of interlacing causing construction • pick mixers to blend alternate picks from two
on the loom and off the loom to be different. or more packages
Subsequent fabric finishing steps also introduce

FIGURE 5.30 Fabric construction and manufacturing parameters (courtesy of Johnston Industries).

© 2001 By Sulzer Textil Limited Switzerland

 5.1 Basic Weaving Motions 125

• filling selection mechanism for feeding multi- weave design affects the crimp level in the fabric
type filling patterns and crimp on the filling yarn causes the fabric to
• filling selvage devices such as trimmers, contract in width direction. Fabric construction, i.e.,
tuckers, holders and special weave harnesses the number of weft and warp yarns per unit length,
for selvage warp ends also affects fabric crimp and therefore fabric width.
• filling replenishment system to provide High weaving tensions, especially in the warp yarns,
uninterrupted filling insertion by switching cause fabric to shrink. Warp yarns closest to the
from a depleted to a full package selvages of the fabric undergo more stress due to
• a temple assembly on each selvage to keep widthwise contraction of the fabric toward the
fabric width at the beat-up as near the width center, causing linear angular displacement of these
of the warp in the reed as possible outermost yarns.
• sensors to stop the machine in the event of The narrowing of fabric width should be
mechanical failure prevented, by using a temple on each side of the
• a centralized lubrication control and machine. Control of fabric contraction by the
dispensing system temples of the machine is another critical aspect of
• a reversing mechanism to avoid bad start ups good weaving performance. A temple is a metallic
after a machine stop device that keeps the fabric stretched by applying a
• a color coded light signal device to indicate force along the filling direction. There are various
the type of machine stop from a distance temple types as shown in Figure 5.32. It is also
• a production recording system possible to have a temple across the full width of
the fabric as shown in Figure 5.33. Full width
These auxiliary functions are described for each type temples ensure uniform fabric quality over the entire
of weaving machine in the following chapters. weaving width with delicate fabrics and easier
operation. The full temple has the following
advantages:
5.3 FABRIC CONTROL
• uniform warp and weft tension over the entire
5.3.1 Fabric Width width
• uniform fabric characteristics over the entire
At the moment it is woven, the fabric width is equal
width
to the reed width as shown in Figure 5.31. However,
• no fabric drawing defect
as the weaving continues and fabric gets away from
• no damage to fabric by needle rings
the reed, the fabric starts narrowing due to several
• rapid changeover from full width to
factors (it should be noted that there are certain
cylindrical temples
fabrics which do not get narrower, e.g. glass fabrics).
These are weave design, fabric construction and Appendix 4 shows more temple types used in the
weaving tensions. The interlacing pattern of the industry.

FIGURE 5.31 Temple function in weaving.

© 2001 By Sulzer Textil Limited Switzerland

126 WEAVING FUNDAMENTALS

sides of the fabric (Figure 5.34). In this case, special

selvages are needed to prevent slipping of outside
warp yarns out of the fabric. There are several types
of selvage designs that are used for this purpose with
shuttleless looms.
In tucked-in selvage, the fringed edges of the filling
yarns are woven back into the body of the fabric
using a special tuck-in mechanism. As a result, the
filling density is doubled in the selvage area (Figure
5.34). Tucked-in selvage was being only used for
projectile weaving machines in the past, however, it
is now also applied to other shuttleless weaving
machines. Pneumatic tucking units are also available.
When setting up for the selvages on a projectile
weaving machine, the following points must be
noted.
• The selvage must be drawn into the reed 15
mm wide.
FIGURE 5.32 Examples of temples used in weaving • The selvage must not be thinned too much.
machines (courtesy of Broll). • The reed must be filled with yarns up to the
last dent.
5.3.2 Selvages
If possible, the selvages are always drawn-in on
Selvages (also called selvedges) provide strength to
separate harnesses. The selvage harnesses are always
fabric for safe handling of the fabric. Selvage should
behind the ground harnesses, so that the front shed
not curl. In shuttle looms, there is no need for special
is shorter. This arrangement enables the shed to be
selvage; since the yarn is not cut after each filling
adjusted smaller.
insertion, the edges of the fabric are smooth and
In leno selvage, a leno design at the edges of the
strong (Figure 5.34).
fabric locks the warp yarns in (Figure 5.34). Half
In shuttleless weaving, since the pick yarn is cut
cross leno weave fabrics have excellent shear
after every insertion, there is fringe selvage on both
resistance. They are made with special leno weaving
harnesses.
Electronically controlled thermal cutters are used
to cut and fuse selvages of synthetic fabrics on
weaving machines. The temperature of the cutters
is reduced when the machine is stopped. Figure 5.35
shows schematic of a thermal cutter application.

Fabric Inspection Lines

After weaving, some fabrics are inspected on the
weaving machine for quality purposes (Figure 5.36).
Inspection speed can be varied between 0 to 100
linear meters per minute. Inspection machines have
a lighted diffusion screen. Fabric alignment is
controlled by a mobile trolley operated by photocells
FIGURE 5.33 Full width temple. to sense the cloth.

© 2001 By Sulzer Textil Limited Switzerland

 FIGURE 5.34 Fabric selvages.

FIGURE 5.35 Thermal cutter (courtesy of Loepfe).

127
© 2001 By Sulzer Textil Limited Switzerland
128 WEAVING FUNDAMENTALS

FIGURE 5.36 Fabric inspection (courtesy of Formia Nuova s.r.i.).

REFERENCES Weaving with the Aid of a High Speed Video

System”, Textil Praxis International, September
1. Zhang, Z., and Mohamed, M.H.,
1992.
“Theoretical Investigations of Beat-up”,
Textile Research Journal, July 1989.
2. Lord, P., and Mohamed, M.H., Weaving: REVIEW QUESTIONS
Conversion of Yarn To Fabric, Merrow
1. Explain the advantages and disadvantages
Technical Library, 1982.
between negative and positive let-off
3. Greenwood, K., and McLoughlin, W.T., “The
mechanisms.
Design and Operation of a Loom with
2. Derive the formula for harness lifts in an
Negative Beat-up”, Shirley Institute Memoirs,
unsymmetric shed.
Vol. XXXVIII, Shirley Institute, Didesbury,
3. What are the effects of the position of the zero
Manchester, 1965.
line on fabric properties? Explain.
4. Shih, Y. et al, “Analysis of Beat-up Force
4. Explain how order of entering and order of
During Weaving”, Textile Research Journal,
lifting affect the fabric structure on a weaving
December 1995.
machine.
5. Why are the yarn feeders necessary? Explain.
SUGGESTED READING 6. Derive a formula to calculate the beat-up force.
Make the necessary assumptions.
• Marks, R., and Robinson, A., Principles of
7. Name five auxiliary motions in a typical
Weaving, The Textile Institute, 1976.
weaving machine.
• Weinsdorfer, H., and Salama, M., “Measuring
8. Why does a fabric continuously narrow on a
the Movement of the Fell of the Cloth During
weaving machine if no temple is used? Explain.

© 2001 By Sulzer Textil Limited Switzerland

6

Shedding Systems

Every weaving machine provides a control device 6.1 CRANK (TREADLE) SHEDDING
for each warp yarn. Heddles controlling warp yarns
that always follow the same interlacing pattern are This is the simplest and least expensive shedding
grouped together into a common frame called a system. In this system, the harness motion is
harness. There must be a different harness provided provided by the crank shaft of the weaving
for each group of warp yarns that follow a different machine. A wheel is rotated a half turn for each
weaving pattern. In the case where every end weaves crank shaft revolution. The harness is linked to the
a different pattern, a harness cord is provided for wheel through a lever arm and a drive pin. In each
each heddle. weaving cycle, the harness changes its position,
There are four systems used to provide therefore, this system is used only for plain weave
manipulation to the warp yarns: and its derivatives. These systems are used in air-
jet and water-jet machines where speed is generally
• crank shedding high.
• cam (tappet) shedding
• dobby shedding 6.2 CAM SHEDDING
• jacquard shedding
Cams with weave pattern profiles rotate to deliver
Crank, cam and dobby mechanisms control the lifting and/or lowering instructions to harnesses. A
harnesses; jacquard system provides control of typical cam system can handle weave patterns with
individual warp yarns. Each shedding mechanism can up to 14 different harnesses. Cam shedding
be mounted on any weaving machine. Dobby and mechanisms are relatively simple and inexpensive
jacquard systems can be mechanical or electronic. to design and maintain, they are more reliable for
There are many variations of cam, dobby and producing fault free fabric and they do not restrict
jacquard shedding mechanisms. For the purpose of the weaving machine speed. A pair of cams is
this book, only the major groups of these mechanisms sufficient to weave a plain fabric. The main
will be discussed which will be limited to the disadvantage of the cam shedding mechanisms is
elementary principles of these shedding mechanisms. their restricted patterning possibilities. Another
Table 6.1 shows the major characteristics of the most disadvantage is that, when the weave has to be
common shedding systems. changed, it is usually necessary to change or

129
© 2001 By Sulzer Textil Limited Switzerland
130 SHEDDING SYSTEMS

TABLE 6.1 Characteristics of shedding mechanisms (Staubli).

rearrange the cams which is time-consuming and not The design and functions of cams are extensively
practical for frequent pattern changes. explained in mechanical engineering literature [1],
therefore, the discussion of cam design will be limited
to the weaving machines only for the purpose of
6.2.1 Cam Design this book.
A cam is a disk that transforms a rotational motion The size of the weave repeat in cam shedding is
of its own to a reciprocating motion of a follower. limited by the maximum practicable number of picks
The transfer is done by means of the cam’s edge or a to the repeat. This can be explained using Figure
groove cut in its surface as shown in Figure 6.1. 6.2. Assuming that a fabric with eight yarns in a
unit cell will be woven with a negative cam system,
a total of eight cams will be required which will be
mounted on a shaft as shown in the figure. In the
diagram, one pick occupies one-eighth of the
revolution or 45°. If the number of cams is increased,

FIGURE 6.1 Cam design. FIGURE 6.2 Arrangements of cams on a shaft.

© 2001 By Sulzer Textil Limited Switzerland

 6.2 Cam Shedding 131

of some external device. Figure 6.3 shows the

principle of a negative cam mechanism. In negative
cam shedding mechanisms, some form of spring
reversing motion is used with separate springs for
each harness. Negative cam shedding is being used
less and less in modern weaving machines.

6.2.3 Positive Cam Shedding

In positive cam shedding, the harnesses are both
raised and lowered by the cams. There are two main
types of positive cams. In the first type, a frictionless
roller follows a groove machined in the face of the
cam (Figure 6.1). The cam follower, which is
attached to one end of a lever, moves up and down
and the lower end of the lever moves back and forth
in the horizontal direction. Then the motion is
carried to the harness frame with various levers. This
type of mechanism is not used much any more.
In the second type of positive-cam shedding, a
pair of matched cams are used for each harness
FIGURE 6.3 Schematic principle of negative cam (Figure 6.4). The frictionless rollers, which are in
shedding. contact with the cam faces, oscillate the lever about
its fulcrum. As a result, a reciprocating movement
is obtained in the lever. This type of mechanism is
then there would be less space for each cam for dwell. common in modern weaving machines.
This also means that the slope of the cam contour Figure 6.5 shows positive cam mechanisms that
will increase which will increase the maximum force can be adapted for all weaving machines. Figure 6.6
acting in the system. In the figure, to produce a
vertical force F to lift the harness, the cam must apply
a force R on the cam follower. As the slope of the
cam contour increases, the force R also increases.
The cams are designed to give a simple harmonic
motion to the cam follower for a smooth operation.
The cam follower moves in a vertical imaginary line
that passes through the axis of the cam shaft. To
avoid excessive force in the system, for a given cam
size, the maximum slope of the cam contour should
be minimized which requires low number of yarns
per unit cell in the fabric.
There are two types of cam mechanism in weaving
machines: negative cam and positive cam systems.

6.2.2 Negative Cam Shedding

The harnesses are either raised or lowered by the FIGURE 6.4 Positive cam system with two negative cams
cam mechanism but they are returned by the action (courtesy of Fimtextile).

© 2001 By Sulzer Textil Limited Switzerland

132 SHEDDING SYSTEMS

FIGURE 6.5 Positive cam mechanisms (courtesy of Staubli).

shows the inside schematic of a positive cam The current trend is to mount the cam mechanism
mechanism. Figure 6.1 shows weaving possibilities on the floor next to the machine.
with cams. Figure 6.8 shows mounting possibilities Automatic harness leveling devices are used in
of positive cam mechanisms on weaving machines. cam shedding to provide even tension on warp yarn
during machine stops. The device also helps with
eliminating the start-up marks. In modern machines,
all moving parts of the cam mechanisms are
immersed in an oil bath. The cams are usually made
of hardened steel.

6.3 DOBBY SHEDDING

Dobby mechanisms are more complicated than cam
systems. They usually have higher initial and
maintenance costs. They are normally built to
control up to 30 harnesses. Picks per repeat are
virtually unlimited in dobby shedding. Due to their
complexity, dobby mechanisms are more liable to
produce fabric faults than cam systems.
Basically there are two separate functions in a
FIGURE 6.6 Inside schematic of positive cam mechanism dobby mechanism: 1) power transmission, 2)
(courtesy of Staubli). connection and disconnection of the harnesses to

© 2001 By Sulzer Textil Limited Switzerland

 6.3 Dobby Shedding 133

FIGURE 6.7 Weaving possibilities with cams (courtesy of Staubli).

and from the power source at the proper time. each harness (single lift dobbies, which have become
Dobby mechanisms are classified as negative, obsolete, had only one knife per harness). The double
positive and rotary dobbies, they can be mechanical lift dobby’s cycle occupies two picks and therefore
or electronic. The first wooden lag dobby was made most of its motions occur at half the loom speed
commercial in 1898 (Figure 6.9). which allows higher running speeds. All modern
negative dobbies are double lift dobbies. Negative
dobbies tend to be simpler than the positive dobbies.
6.3.1 Negative Dobby Shedding
Referring to the figure, the knives (K1 and K2)
In negative dobby shedding, the harnesses are lifted reciprocate in slots along a fixed path (the
by the dobby and lowered by a spring motion. Figure mechanism to move the knives is not shown). They
6.10 shows the schematic of a basic double lift, complete one reciprocation every two picks. When
negative dobby mechanism in which a baulk and a peg in the lag forming part of the pattern chain
pairs of feelers, pegs, hooks and knives are used for raises the right end of feeler F1, the rod C is lowered

© 2001 By Sulzer Textil Limited Switzerland

134 SHEDDING SYSTEMS

FIGURE 6.9 First wooden lag dobby mechanisms circa

1898 (courtesy of Staubli).
FIGURE 6.8 Mounting possibilities of positive cam
mechanisms (courtesy of Staubli). The stop (S2) acts as a fulcrum. As a result, the jack
is moved through the central link. The motion of D
which in turn causes the hook (H1) to be lowered is magnified by the lever action of the jack and is
and engaged with the knife K1. Then, the knife K1 is transmitted to the harness via straps.
moved to the right carrying the hook H1 with it. Figure 6.10 shows the method of lag-and-peg for
This movement is transmitted to D on the baulk (AB). a 3/1/2/1 twill design. Each lag corresponds to two

FIGURE 6.10 Schematic of a negative dobby mechanism.

© 2001 By Sulzer Textil Limited Switzerland

 6.3 Dobby Shedding 135

FIGURE 6.11 Card cylinder for a modern dobby mechanism (courtesy of Staubli).

picks. The holes in the lags are positioned such that Figure 6.12 shows a negative dobby with
they correspond with the location of the feelers. The electronic control. It operates in correct pick sequence
pattern chain is turned intermittently by a wheel so synchronously with the weaving machine during
that a new lag is presented every second pick. A filled normal operation as well as during the pick finding
circle represents a peg in the lag. Figure 6.11 shows process. The electronic control is comprised of an
a card cylinder for a mechanically programmable electromagnet for each lifting unit and a control unit
dobby shedding machine. or “controller” that activates the electromagnets of
As an alternative to the lag-and-peg chains, the dobby and starts the control functions of the
punched paper or plastic pattern cards are used. A weaving machine according to the weave data. The
punched hole in the paper corresponds to a peg in electronically controlled weave data program
the lag, thus a hole causes the corresponding shaft controls the retention hooks via intermediate
to be lifted. Light feelers such as needles are used to elements and initiates a harness frame motion as soon
detect the presence or absence of a hole. The force as the selected baulk hook enters the range of the
needed to move the hooks is not supplied by feelers. controlled retention hook. The internal parts consist
Auxiliary knives and hooks are used to engage and of baulks to which short hooks are hinged (Figure
disengage main knives and hooks. Holes on paper 6.13). The push bars are directly driven by
or plastic cards are punched on special punching complementary cams via balance levers pushing the
machines. These cards are especially suitable for very baulks. In the mechanical version of this machine
long patterns. (Figure 6.14), programming takes place by lag-and-
In the early mechanical dobby mechanisms, the peg cards which are made of lightweight, reusable
knives were actuated from a crank mounted on the plastics.
end of the bottom shaft on the loom. In modern Figure 6.15 shows a computer programming
dobbies, the knives are actuated from cams mounted system for dobby weaving. Weaving programs can
on a shaft in the dobby. be prepared and archived with computer aided
Recently, more modern dobbies utilize electronic systems for both electronically and card controlled
systems for input of the harness lifting and lowering dobbies. With the programming systems, data can
patterns. These dobbies can weave patterns requiring be prepared, stored or transferred according to
up to about 30 harnesses and repeating on as many requirements utilizing program carrying cards and/
as 6400 picks. or floppy disks.

© 2001 By Sulzer Textil Limited Switzerland

136 SHEDDING SYSTEMS

FIGURE 6.12 Negative dobby with electronic control (courtesy of Staubli).

Card cutting and copying machines are used for (Figure 6.17). Figure 6.18 shows a cylinder with
cutting, copying and pasting pattern cards for reading plate which acts as holder for the point paper
dobbies, color and function control devices and and facilitates the reading and transferring of the
name weaving machines. Figure 6.16 shows a motor point paper onto the keyboard.
driven card cutting and copying machine, which can As stated earlier, the negative dobby mechanisms
cut and copy paper and plastic cards. The machine raise the harnesses but can not lower them; spring
consists of keyboard, quick reading plate for point undermotion mechanisms are used to lower the
paper, drive, copying device, pasting device, setting harnesses. Figure 6.19 shows the application of
dial for card transport wheels and cutting device negative dobby.

© 2001 By Sulzer Textil Limited Switzerland

 6.3 Dobby Shedding 137

FIGURE 6.13 Functional principle of negative electronic

dobby (courtesy of Staubli).

6.3.2 Positive Dobby Shedding

In positive dobby shedding, the harnesses are both
raised and lowered by the dobby mechanism which FIGURE 6.14 Mechanical negative dobby (Staubli).
eliminates the need for a spring undermotion.
Therefore, in any positive dobby some kind of selection. The harness frames move throughout the
mechanism is necessary to return the ends of the entire cycle without play, regardless of load or speed.
baulks to their stop bars and to hold them there. A Although this machine is developed specifically for
locking bar is used for this purpose. A sample rapier machines, under specific conditions, it can
mechanism to achieve this is shown in Figure 6.20. also be used for projectile machines. The dobby is
Push bars B1 and B2 and the knives K1 and K2
reciprocate together. When the knife returns after
displacing the hook, it pushes the end of the baulk
against its stop bar. Then, the locking bar, L1 engages
a notch in the hook which is pushed up by the
selection mechanism. Therefore, the baulk is
prevented from moving until the next selection. The
locking bar L1 will hold the baulk against its stop
while the knife K1 and the push bar B1 make one
complete cycle.
Figure 6.21 shows a high performance positive
dobby machine. This double lift open shed dobby
operates according to the Hattersley principle. There
are two separate units in the system: a drive unit for FIGURE 6.15 Computer programming system for dobby
harness frame motion and a reading unit for hook weaving (courtesy of Staubli).

© 2001 By Sulzer Textil Limited Switzerland

138 SHEDDING SYSTEMS

FIGURE 6.16 Motor driven card cutting and copying machine: left, front of the machine; right, back of the machine
(courtesy of Staubli).

driven either directly by the main shaft of the weaving control unit for the hooks have two functions directly
machine or by a back-gear shaft. The reading unit related to the harness frame movement: positive hook
reads the pattern card and transmits the selection to control without springs and movement and
the traction hooks. The cylinder movement is positioning of harness frames in their end positions
continuous for precise pattern card feed and the in upper or lower shed. Four pairs of complementary
cylinder swings out for pattern card changes. cams provide these functions. Figure 6.23 shows the
Figure 6.22 shows the functional principle of placement of positive dobby systems on weaving
double lift positive dobby machine. The drive and machine.

FIGURE 6.17 Copying (left) and pasting devices (courtesy of Staubli).

© 2001 By Sulzer Textil Limited Switzerland

 6.3 Dobby Shedding 139

FIGURE 6.18 Cylinder with point paper and reading plate (courtesy of Staubli).
6.3.3 Rotary Dobby

Figure 6.24 shows a rotary dobby with electronic

control. It is a positive machine operating according
to the rotary principle. The dobby is composed of
the following units:
• main drive with modulator and
complementary cams
• drive block with cam units for harness frame
motion
• control unit with magnet block for
transformation of electronic signals
• electronic control box
The dobby is driven either by the weaving machine’s
main drive shaft or back-gear shaft.

FIGURE 6.19 Placement of negative dobby (courtesy of

Staubli).

FIGURE 6.21 Double lift open shed positive dobby

FIGURE 6.20 Schematic principle of positive dobby [2]. (courtesy of Staubli).

© 2001 By Sulzer Textil Limited Switzerland

140 SHEDDING SYSTEMS

FIGURE 6.22 Functional principle of double lift open shed positive dobby (courtesy of Staubli).

The control is composed of a magnet bar with 20 or • leveling of harness frames in lower, middle
28 electromagnets and a controller which activates and upper shed
the electromagnets of the dobby and starts the • individual lifting of each harness frame
control functions of the weaving machine according • separation of warp threads
to the weave data. The controller carries out the
following operational functions: The rotary dobby with electronic control operates
according to the rotary principle and is founded on

© 2001 By Sulzer Textil Limited Switzerland

 FIGURE 6.23 Mounting positions of positive dobbies (courtesy of Staubli).

FIGURE 6.24 Rotary dobby with electronic control (courtesy of Staubli).

141
© 2001 By Sulzer Textil Limited Switzerland
142 SHEDDING SYSTEMS

FIGURE 6.25 Functional principle of rotary dobby (courtesy of Staubli).

two elements: cam unit and modulator (Figure 6.25). from the weaving machine into an irregular rotary
Each harness frame is controlled by a cam unit only motion. By the use of complementary cams precise
12 mm wide. This cam unit converts the irregular laws of motion result. Figure 6.27 shows the possible
rotary motion of the main drive shaft directly into mounting locations of rotary dobby on weaving
the linear motion required for the harness frame machines.
drive. The essential element is a crank mechanism
enclosing a cam with ball bearings (Figure 6.26). A
High Performance Rotary Dobby
ratchet placed on the outside of the cam connects it
with the driver, and by a 180° rotation of the cam Figure 6.28 shows a positive dobby machine that
causes a lifting motion. The ratchet is controlled operates on the rotary principle with pattern card
according to the pattern by the control unit. The control. This system can be used for high speed
modulator transforms the regular rotary motion rapier, projectile and air-jet weaving machines. In

© 2001 By Sulzer Textil Limited Switzerland

 FIGURE 6.26 Rotary dobby arm (courtesy of Fimtextile).

FIGURE 6.27 Possible mounting locations of rotary dobbies (courtesy of Staubli).

143
© 2001 By Sulzer Textil Limited Switzerland