T
he beginning of the 21st century has been accompanied by ever more relentless cloth
quality specifications and requirements. One clear trend to meet these demands is the development
and implementation of suitable tools to secure process reliability and control in weaving.

In this scenario, however, it is essential that we first agree upon and understand the
aspects that determine cloth quality. Quality standards of woven fabrics have been as demanding in
recent years as the industry’s expectations with respect to productivity gains, cost-optimization
and shortened downtimes in the weaving process.

The main factors by which quality is measured are fabric properties and fabric defects. It
has become imperative to minimize faults deriving from the high-speed weaving process because
defects can usually be corrected only at considerable cost. Acceptable defect levels applied to the
majority of standard high-quality cotton fabrics throughout the world are quoted per 100 meters of
first-class fabric.

Whereas 20 years ago the tolerance was 15 non-repairable faults, the figure today is only
five. This trend will continue in the future and probably will be reduced to three permissible
faults in most instances. During the same time span, the share of seconds was brought down from a
maximum of 3 percent to 0.5 percent. Target figures for seconds in cloth manufacturing are likely
to go down to 0.3 percent of production in years to come.

Machine Downtime

Also associated with fabric quality is the necessity to drastically reduce machine downtime.
This becomes more critical in economical terms with increasing machine performance, as plant
efficiency will drop even if downtime and frequency of stops remain unchanged. Fabric manufacturers
have come to understand that normally only a few permissible defects are accepted per 100 meters of
woven fabric. This reduction was attainable, among other reasons, by drastically curbing weaving
machine stoppages.

In cotton weaving, for instance, increased machine performance has meant a reduction of
machine stops by some 50 percent over the past 20 years – as few as three to five overall stops per
100,000 picks on average now are achievable in cotton weaving on high-speed weaving machines. Even
in woolen and worsted weaving – where yarn quality aspects are even more relevant – overall stops
can be reduced significantly via optimization of the weaving process.

Looking more closely at the main causes for weaving machine stoppages, one can determine
that out of the three to five overall stops in cotton weaving achieved on average today, 20 percent
are related to problems in the filling, and 80 percent are due to deficiencies in the warp.
Generally speaking, of the main causes of warp stoppage, 20 to 30 percent emanate from yarn
defects; 30 to 40 percent are directly or indirectly related to warp and weaving preparation; and
30 to 40 percent can be attributed to influences of the weaving process itself.

Obviously, a clear split between these criteria can be established only by a proper stoppage
cause analysis of the weaving machine itself. It does, however, suggest that any measures aimed at
optimizing the overall process not only should be targeted towards the weaving machine but also
should include the weaving/technological environment.

It is quite remarkable that, despite the fact that weaving machine speeds of traditional
weft-insertion systems have more or less doubled over the past two decades, improvements in the
weaving process have ensured that the very stringent and steadily increasing quality requirements
can effectively be met. This seems to prove that neither the ongoing enhancement of fabric quality
nor increases of weaving machine speeds are suffering from a target conflict.

This progress has partly been attained through a number of quality- and
productivity-enhancing factors, such as overall improvement of yarn quality and development stages
achieved in warp and filling preparation techniques. Even more decisive, though, has been the
progress made in the technological and operational reliability of the weaving process. It is
increasingly clear that the high-speed weaving machine – with its process complexities in relation
to type of fiber, yarn characteristics, fabric styles and finishes – involves high-tech
engineering. It has to live up to the most stringent requirements in functional reliability and
adaptability.

Only by further reducing down-time and incidence of faults in the weaving process, and
thereby shifting the concentration from labor costs to capital costs, can the US weaving industry
be attracted to invest. Coming to terms with some of the physical constraints of the single-phase
weaving process means the full potential of technology must be tapped. The day will almost
certainly come when solutions are technologically possible but economically can no longer be
justified using present technology.

For a better understanding as to what weft insertion at today’s machine speeds means in
physical terms, single-phase weaving machines apply and control pick velocities exceeding 60 meters
per second (m/s) and acceleration rates of more than 20,000 meters per square second (m/s2) in a
few milliseconds. This means the filling travels through the shed at speeds of more than 200
kilometers per hour (km/h) on modern single-phase weaving machines, imposing incredible demands on
the design of mechanical movements on weaving machines. Moreover, it requires sophisticated
electronics that enable optimal control and regulation of the timing of motion sequences in the
weaving process.

Despite all the progress made in weaving technology, the main objective is to further
minimize interruptions in the weaving process and thus prevent non-repairable weaving faults, with
solutions that are technically practicable and economically advantageous.

Yarn Stresses

A major task in minimizing the stoppage rate and assuring quality is to optimize yarn
stresses, such as time-related tensions and/or elongations. Tensions occurring in the warp differ
fundamentally from those affecting the filling yarn. Optimizing (in the sense of optimum yarn
tension) means keeping yarn tensions as low as possible, but also as appropriate as necessary,
because stoppages can be caused by both over-tensioning and under-tensioning the yarn.

Weaving systems are basically expected to tackle, for instance, worsted yarns and aramid
fibers equally as well at maximum speed. The processing performance of textile materials on weaving
systems is, however, also dependent on tenacity and elongation properties of yarns. To stress this
point, the natural worsted yarn typically would possess minimal strength but a high elongation,
while the reverse is actually the case for aramid fibers.

Weft Tension

The highest weft tensions occurring at pick insertion are caused by load peaks of extremely
short duration. Weft peak loads will always rise with increasing machine speeds or filling
insertion rates under equal mechanical machine conditions – no matter whether weft yarn is being
inserted on air-jet, rapier, projectile or any other single-phase weaving machine. Figure 1
illustrates the speed-related increase in load peaks in a cotton open-end yarn that, for purposes
of comparison, was inserted with and without controlled filling yarn braking on air-jet weaving
machines. One special feature of monitoring the weft-insertion path on air-jet weaving machines is
recording of the arrival time of the weft on the receiving side of the machine. This arrival time
changes according to variations in yarn characteristics.

The signal recorded controls the main- and relay-nozzle pressures, and the yarn speed is
then corrected to the target speed if necessary. Control measures aimed at reducing tension peaks
during filling insertion include electronic weft brakes that enable the weaver to set starting and
stopping times of the braking cycle as well as the braking force to be applied to every filling
channel used on a machine.

First tests with new and special sensing devices show that an automatic on-line optimization
of the filling-insertion cycle eventually will be within the realms of economical possibility.
Measuring heads or tension-sensing devices are integrated in the weaving machine and automatically
measure the tensile force acting upon filling yarns during insertion. With this control system,
electronic weft brakes can, in the future, be automatically adjusted to preset tensile forces.

Up to now, tensile forces could be determined only with the aid of expensive laboratory
measuring instruments. Utilizing appropriate process control systems – permitting on-line
monitoring of the filling tension during weaving – latest generations of high-performance weaving
machines will provide better conditions for minimizing yarn breakages. In the future, this on-line
force recorder also will be used to monitor the whole insertion phase of filling yarns, and
mispicks can then be positively detected.

Warp Tension

During the weaving process, the warp is subjected to both frictional stresses and cyclical
elongations that create tension in the yarn. Reliable information on the forces acting on the warp
ends can be obtained only from the warp tension trace.

The weaving process is still to be blamed for disturbances of the warp flow. Whereas 20
percent of warp breaks are yarn-related, 80 percent are linked to warp preparation and the weaving
process. Unfortunately, there is no constant tensile force acting on the warp sheet in terms of
time and place, neither across the weaving machine width nor in the warp direction, and also not
from warp end to warp end.

Along with reed beat-up, the factor having a particularly high influence on the extent of
yarn elongation and force pattern is the shed geometry, which can vary considerably according to
the weave and number and position of the frames, as well as the control of the backrest roller.

Optimization efforts for equalizing the flow of warp tensile forces are mainly attached to
system improvements in shed-forming dynamics of heddle frame movements, precision of cloth take-up
and warp let-off, and positive control of warp-tensioning devices.

Special warp-tension sensing devices that are incorporated in the weaving machine for
on-line tension recordings are available. In one machine configuration, this warp let-off control
motion is based on direct measurement of absolute thread tension. The sensing heads are arranged on
the deflection roller, thus safeguarding a considerably improved precision of the warp let-off
motion.

Influencing the warp-tension pattern even further by means of positively controlled
warp-tensioning devices allows for even better adjustments to process requirements. Controlled by
cam mechanism, positive warp-tensioning devices guarantee a warp control for reaching minimum
warp-stop levels.

A positive warp control is particularly helpful for:

•    improving warp separation;

•    reducing warp tension even further;

•    minimizing load peaks for yarns with low tensile properties – thus
drastically improving the weaveability of single yarns in the warp;

•    increasing weft density;

•    directly controlling the position of the cloth fell; and

•    controlling fabric structure as well as its appearance.

For further on-line warp control improvements, automatic adjustment mechanisms for the
backrest system are being studied.

Role Of Mechatronics And Electronics

Yarn stresses that are to be tamed for best weaveability and quality require a more
scientific approach towards process control in weaving. Mechatronics are clearly gaining importance
in this respect. The benefits of gear control by such means as  servo motors are much
appreciated by weavers.

By electronically synchronizing the let-off with the take-up system, a dynamic cloth-fell
correction after a machine stop is feasible, and the intensely annoying start-mark problem will
become less of a topic in the future.

Improved process requirements in weaving derive not just from quality issues but also from
ever-increasing demands for ever-faster changeover times in plants. “Flexibility,” “quick response”
and “just-in-time” are no longer buzzwords – they are important aspects, particularly for American
weavers.

Flexibility in weaving means quick changing-over and fast-setting of weaving machines to
certain fabric parameters, as may be necessary for small-order lots and varying styles in
accordance with customer market requirements.

Through the application of state-of-the-art electronics, settings that have once been
defined for a fabric can be stored on data carriers and loaded back onto the control unit of
weaving systems. The possibilities for on-line process control mechanisms can optimally be
exploited only if machines have elements that can convert electrical signals into corresponding
weaving technological functions.

Such elements have, for quite some time now, proved successful in the form of servo, stepper
and, lately, linear motors; or as lifting and stepping magnets. Advanced solutions have been found
for controlling thread clamps of filling yarns to be presented to the rapier.

This means that on rapier machines, it is now possible to weave without any filling and warp
waste on the insertion side.

In summary, it can certainly be established that process control in weaving has become a
reality. Its degree of complexity results from the need to continuously reduce costs, and to
improve quality – but also from the limits of present technologies applied in the industry.

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Editor’s Note: Fritz Legler is president of Sultex (USA) Inc., Spartanburg, a division of
Sultex Ltd., Switzerland, and member of the Itema Group, Italy.

S
tudies in the area of “electronic textiles” or “electrotextiles” have captured
researchers’ attention worldwide. Recently, many reports and papers have been published, and
conferences and symposiums held covering this fast-growing area of research and development.

The reason for such interest is the potential to develop smart fabrics that can sense,
respond and adjust to stimuli such as pressure, temperature or electrical charge. Thermal clothing
such as blankets and jackets that  protect humans, pets and animals from cold weather, musical
jackets and a flexible foldable computer keyboard are some electrotextile products that are
commercially available today. But these are only the beginning. Material scientists, textile
engineers and technologists, computer scientists, and electrical engineers are working on combining
electronics and textile structures to come up with new products that are flexible, conformable and
lightweight; and which potentially may be produced at the speed of current traditional textile
structure manufacturing.

Research and development targets civilian and military applications such as: woven antennae;
acoustic array – a woven fabric circuit combined with an acoustic sensor that locates sources of
sound, such as gun shots or enemy vehicles; active woven fabrics with electroactive constituents to
improve the drop precision of parafoils; formation of transistors on flexible substrates, such as
thin ribbon yarns; yarn batteries and flexible and conformable solar cells to harvest and provide
electrical power to electrotextiles; and flexible textile circuitry used for fashion and design –
for example, in fabrics that can change color on demand. It is expected that electrotextile
products will find their way to new markets such as healthcare, entertainment, safety, homeland
security, computation, communication, thermal uses, protective clothing, wearable electronics and
fashion, as well as energy harvesting from tensioned structures and other large-area fabrics.

New advances in weaving technologies have led to the development of high-speed, highly
automated weaving machines. This combination and the ordered structure of woven fabrics provide new
opportunities for the weaving industry to produce woven fabric circuits and electrotextiles at high
speed.

Relevance Of Woven Structures

Due to their excellent mechanical and physical properties, woven fabrics have established
themselves in many different end-use products. Today, woven fabrics are used in countless civilian
and military applications such as apparel, upholstery, curtains, seat covers, seat belts, rugs,
wall covers, parachutes, weather balloons, tents, vehicle covers, and air-supported and tensioned
structures. They are the choice for many applications for various reasons including: high
uniformity; high strength; high tear and abrasion resistance; controllable air permeability;
dimensional stability; durability; flexibility; conformability; recovery from relatively high
stresses; and light weight.

In addition, woven fabric structures can provide a complex network that can be used as
elaborate electric circuits with numerous electrically conducting and non-conducting constituents,
and can be structured to have multiple layers and spaces to accommodate electronic devices. For
example, rigid printed circuit boards are structured with wiring layers separated by insulating
layers with vias connecting power, ground lines and wiring of different layers to process/transfer
signals. These boards, which are fabricated using the slow process of photolithography, can
potentially be replaced with flexible, stitched, multi-layered woven fabric structures that can be
produced at speeds of 40 to 100 square meters per hour depending on weaving speed, pick density and
weaving machine width
(See Figure 1). The stitches in such fabrics constitute the vias.

Currently, there are many commercial electrically conducting yarns made from metals or from
polymers coated with metals. Some examples of these are short-staple and continuous-filament steel
yarns, copper yarns, and silver-coated nylon yarns. These yarns are made from very thin fibers or
filaments that make them feel and behave like textile yarns.

Current studies indicate that researchers will meet the challenge and will succeed in
producing polymeric yarns with electrically conducting cores, solar-cell yarns, battery yarns and
electronic devices with sub-micron thicknesses built – or extruded as continuous filament – on
yarns. Furthermore, it is believed that these yarns can be produced in large quantities and may be
available on package forms similar to those for traditional textile yarns. When these 
products become a reality, complex multifunctional “electrowoven” structures – or electronic woven
structures – may be produced at high speeds. While new advances in weaving would be assets in this
vein, many other challenging developments are needed as well.

Automatic Formation Of Woven Circuits

Formation of woven circuits requires the interconnecting or welding of two or more
orthogonal yarns at selected crossover points. Because yarns in woven fabrics run from selvage to
selvage, or continuously along the fabric length, cutting of yarns may be required depending on
circuit design. The formation of interconnects and disconnects, or cutting, of today’s electrowoven
products is conducted manually post weaving. While today’s electrowoven products are simple, future
products will demand more complex circuits. To avoid human errors and provide affordable products,
automatic formation of interconnects/disconnects is essential.

Several interconnect and disconnect methods have been identified that could be automated.
Interconnect methods include resistance-welding using microprobes and air-splicing, which is used
successfully in the joining of two yarn ends in automatic yarn winding. Disconnect techniques
include cutting with microcutters and controlling the welding parameters during resistance-welding
to cut and interconnect at the same time.

To automate the formation of interconnects/disconnects, weaving machines with small robotic
devices to manipulate an air splicer, a microcutter and a resistance-welding device, or equivalent
devices, need to be developed. Existing automatic filling repair mechanisms may be modified to
include the interconnect/disconnect devices. Optical sensors may be needed to locate the positions
of interconnects and disconnects. The need for optical sensors could be eliminated by the use of
jacquard weaving, in which every warp and filling yarn location is identified – and, hence, every
crossover point location is known.

Formation Of Electrowoven

Structures At High Speeds

Ongoing research shows that producers of electrowoven structures will have to deal with
different yarns, including traditional textile yarns, conducting metallic or a combination of
polymeric/metallic yarns, battery yarns, solar-cell yarns, and yarns that have built-in electronic
devices. These yarns are expected to be of different physical and mechanical properties. Moreover,
yarns with devices may be in ribbon form, and yarn orientation is necessary. In such cases,
twisting of ribbon yarns must be avoided during weaving.

Recent advances in weaving technology meet some of these challenges. Variable-speed weaving
is an essential requirement for handling different filling yarns. In this case, since electrowoven
structures demand high quality and precise spacing of filling, the machine can run at high speeds
when weaving strong yarns and can be slowed down when weaving weaker yarns to avoid stops and
potential quality problems caused by stops. A filling selection mechanism of up to 12 colors is now
available, which provides the versatility required for electrowoven fabrics.

“Electroweaving” is expected to require modification of existing filling yarn feeders or
development of new filling feeders. It may be necessary to create filling feeders with guiding and
tensioning systems to make them suitable for feeding and maintaining orientation of ribbon yarns.
Needles and devices to introduce such filling yarns to the filling insertion may need to be
modified and/or developed. The newly developed electronic yarns may require development of new
filling feeders because of their differences in properties as compared to traditional yarns.

The same discussion can be made regarding electronic warp yarns. Because their physical and
mechanical properties are expected to be different from traditional warp yarns, differential in
yarn take-up during weaving is expected. This mandates feeding such yarns from a creel or separate
warp beam. A creel that has rotating packages and suitable guiding elements is a must to feed
electronic ribbon warp yarns to avoid yarn twisting and maintain orientation. One scenario may
require setting the traditional warp yarns on the main warp beam and feeding different electronic
yarns from a creel. The creel in this case may require rotating packages and individual automatic
setting of yarn tension. However, this type of creel does not exist today.

Filling Insertion System

For Electrowoven Fabrics

Air-jet and projectile filling insertion systems are obviously suitable for simple
electrowoven fabrics. The rapier filling insertion system seems to be the ultimate candidate for
weaving current and future electrowoven fabrics. However, novel rapier heads that are capable of
handling a broad range of traditional yarns and electronic yarns (especially ribbon yarns) are
required.

Versatility And Quality

The production of electrowoven fabrics will require short runs and a totally versatile
operation to produce different circuits of varying complexity and to manufacture fabrics with tight
specifications and high quality.

Short runs and versatile weaving operations have been made possible by many developments
that have taken place in recent years. These include quick style change, automatic pattern change
and variable pick density. Weaving machines today are modular, and weavers have full control over
their machines through digital interface. It is now possible to send woven fabric designs from a
CAD system to a weaving machine through a local area network (LAN) or from anywhere in the world
through the Internet.

Electrowoven fabrics must be of high quality and precision. Start-mark prevention mechanisms
and on-line fabric inspection are systems that would help to achieve high quality and precision.
Current start-mark prevention systems however, require operator intervention to set the system for
new styles. This is a challenging task for the operator when dealing with electrotextile fabrics of
short runs and variable pick density. Weaving machine manufacturers will have to create smarter
start-mark prevention systems that do not need operator intervention.

Weaving technologies are versatile and could automatically form complex, sophisticated,
high-quality electrotextiles with tight specifications at high speeds. They could allow weavers to
capture a large share of the present and future electrotextile markets. While there are many recent
weaving advances that are relevant to the production of electrowoven fabrics, there are many
developments that still need to be done.

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Editor’s Note: Abdelfattah M. Seyam is a professor in the department of textiles and apparel,
technology and management at North Carolina State University’s (NCSU) College of Textiles, Raleigh,
N.C. He obtained a B.S. and M.S. in textile engineering from Alexandria University, Alexandria,
Egypt, and also holds a Ph.D. in fiber and polymer science from NCSU.