Process control in weaving

© Woodhead Publishing Limited, 2013
265
11
Process control in weaving
V. K. KOTHARI, Indian Institute of
Technology Delhi, India
DOI: 10.1533/9780857095633.3.265
Abstract:A weaving unit must have a satisfactory system of process
control that focuses on loom production, quality monitoring and the cost
of fabric production in order to achieve quality and production targets
at the lowest possible cost.This chapter discusses factors that affect loom
productivity and efficiency and what needs to be done to optimise these
factors to produce fabric of required quality at the lowest cost. Online
quality and process control in weaving are discussed and factors affecting
the weaving cost are analysed.
Key words: weaving process control, productivity and weaving efficiency,
fabric defects, online process monitoring and control, weaving cost.
11.1 Introduction
Woven fabric consists of two sets of yarns called ‘warp’ and ‘weft’ as shown
in Fig. 11.1.The fundamental processes involved in weaving are:
Shedding, that is, dividing the longitudinal ‘warp’ yarns into two sheets•
to create a space called a ‘shed’.
Picking, that is, insertion of the transverse ‘weft’ or ‘filling’ yarn into the•
space created by the division of the warp yarns.
Beating, that is, pushing the inserted weft yarns.•
These basic processes have remained unchanged over centuries, whether
the technology is a handloom, power loom, automatic loom or shuttleless
loom. Shuttleless looms have been developed to overcome the inherent
problems created by the dynamics of the picking mechanism on conventional
shuttle looms and make use of entirely different method of weft insertion.
Air jet, water jet, rapier and projectile looms are the various types of shut-
tleless weaving machines, named after the method employed for weft inser-
tion. Shuttleless looms have a very high productivity; in the case of a single
phase jet loom,weft insertion rates can exceed 2000 m/min.Since shuttleless
machines have a much higher production rate and are more costly, process
control in weaving using these machines is even more important, as any loss

266 Process control in textile manufacturing
in production or quality would have a much higher influence on the eco-
nomic viability of the production process.
Fabric production is a very competitive industry, and the principal objec-
tive of any weaving unit is to produce fabric of suitable quality at an accept-
able cost. For this to be achieved, a thorough understanding of processes,
machines, materials and staff is required.The mill’s success also depends on
the choice of product mix and the marketing skills of the management. To
achieve quality and production targets at the lowest possible cost, a weaving
unit must have a satisfactory system of process control, namely one which
focuses on loom production, quality monitoring and the cost of fabric pro-
duction (Fig. 11.2).
The practical parameters for any given woven fabric are the warp and weft
threads per unit length and the crimp of the yarn used. Each of these param-
eters, together with the type of fibre, will have an influence on the quality of
the fabric.If the loom is running under normal conditions,the weft density of
the grey fabric should be consistent. However, the process can be affected by
various disturbances, leading to variations in weft density. Disturbances dur-
ing weaving can usually be traced back to the take-up of fabric and the let-
off of warp ends. During weaving, the warp and weft yarns enter the system
and grey fabric comes out; for quality fabrics, this process should be contin-
uous and dynamically balanced.This balance is primarily determined by the
fabric specifications, and dictates the set-up of the loom. Any interference
with the balance could lead to an alteration of the fabric’s characteristics,
which, in turn, could lead to a fault in the fabric. It is therefore crucial that
Warp
Woven
fabric
Weft
11.1 Weaving as a system for producing fabrics.

Process control in weaving 267
the appropriate conditions are maintained during weaving; in particular, that
beat-up distance and the level of warp tension remain constant.1
11.2 Controlling loom productivity, efficiency and
fabric quality
Control of loom productivity, efficiency and fabric quality are essential for
producing fabrics at acceptable cost with selected yarns and to succeed in
the competitive environment.
11.2.1 Loom productivity and efficiency
The productivity of a loom is reliant on loom speed, loom width, and pick
density.2
The theoretical production levels that these factors would facilitate,
however, are rarely achieved, due to such issues as yarn breakages, machine
failures or necessary changes of the warp beam,all of which may cause loom
stoppages.The weaving efficiency, therefore, influences the actual loom pro-
duction. Efficiency, which can be quantified as the ratio of actual production
to potential production, is affected by the following factors:
1. loom type, speed and width,
2. yarn type, quality and yarn preparation,
3. fabric structure, density and style,
4. weave room conditions,
5. weaver’s skill and workload.
Productivity
and efficiency
Cost Quality
Process
control
11.2 Main elements of process control in weaving.

Warp breakage rate is an extremely important factor in loom efficiency.
According to a number of studies, warp breakage rate is largely governed
by yarn quality, yarn clearing and sizing.3
Looking more closely at the main
causes of weaving machine stoppages in cotton yarn weaving, a rate of 3–5
overall stops per 100 000 picks is achievable on modern shuttleless machines.
Of these breaks, roughly 20% are related to problems in weft while the
remaining 80% are due to deficiencies in the warp. Generally speaking,
most warp stoppages are the result of either yarn defects (20–30%) or warp
and weaving preparation (30–40%); the remaining 30–40% are related to
weaving process itself.4
A detailed understanding of reasons for warp stop-
pages can be obtained only by a proper stoppage cause analysis at the loom
itself, but it is clear the overall process can be improved by optimising yarn
quality, yarn preparation along with loom parameters, and weave room
conditions.
A major task in minimising the stoppage rate is to optimise yarn stresses
so that they are kept as low as is necessary. During the weaving process,
warp is subjected to both static tension and frictional stresses, along with
cyclic elongations that create tension peaks in the yarn. Reliable informa-
tion about the forces acting on the warp ends can be obtained only through
a warp tension trace, for which specialist warp-tension sensing devices
that create online tension recordings are now available. Though such warp
tension measurements are useful in controlling warp let-off, more precise
control of the warp tension can be achieved through the use of positively
controlled warp tension devices.These are particularly useful for the follow-
ing processes:
1. improving warp separation,
2. reducing warp tension,
3. minimising tension peaks for yarns thus improving the performance of
weak yarns,
4. increasing weft density,
5. controlling the position of the cloth fell,
6. controlling fabric structure and its appearance.
During pick insertion, the peaks in weft tension are extremely brief, but
become more frequent with higher machine speed or weft insertion rate
on any given machine. Optimisation of peak tension during weft insertion
could result in fewer weft breaks. By utilising the appropriate process con-
trol systems to monitor weft tension online during the weaving process, a
new generation of high-performance weaving machines is now being devel-
oped, providing better conditions for minimising yarn breaks.
Weaving efficiency also depends on the number of looms per weaver;
this can vary from 4 to 150, depending on the number of loom stops per

hour and the repair time of each stop. A lower loom allocation increases
idle labour time and thus the overall labour cost, while higher loom allo-
cation increases idle machine time and thus overall machine cost. Loom
allocation is thus dictated by the appropriate balance between these two
costs, which, in turn, is dependent on conditions such as temperature and
humidity.
11.2.2 Control of fabric quality
The quality of any given fabric is usually measured by both its defects and its
general properties. These include fabric specifications such as fabric width,
ends and picks per unit length, weight per unit area, as well as the required
functional properties of the fabric. The process of yarn preparation should
minimise yarn faults, which could otherwise result in unacceptable fabric
appearance or defects. Defects incurred during the weaving process itself
must also be kept to a minimum, as the cost of fabric defects can be very
high, with potentially substantial reductions in the value of the product.The
tolerance limit of non-repairable faults per 100 m of fabric has been consid-
erably reduced (from 15 to 5) in recent years, and is forecast to reach as low
as 3 in the future.4
11.3 Online process control, quality control and
monitoring in weaving
Manual process and quality control systems in fabric production are costly,
inefficient and not suitable in a competitive environment. In the context
of high speed machines and technological developments, online monitoring
and controls are increasingly used during the fabric production.
11.3.1 Online process control
To maximise both the quality and weavability of the fabric, yarn stresses
must be kept to a minimum.With careful assessment of the weaving process,
the appropriate technological development of the loom can be identified
and adopted. By electronically synchronising the let-off with the take-up
system, for example, it becomes possible to ensure a dynamic cloth fell cor-
rection after each machine stop, and thus avoid leaving starting marks in the
fabric. Electronically controlled warp let-off and cloth take-up units ensure
a high degree of fabric regularity, while electronic monitoring systems have
made it easier to identify any problems, allowing swift, corrective action to
be taken. Settings for a fabric can be stored and loaded back on the control
unit of the weaving system when required.

The possibilities offered by online process control mechanisms can only
be exploited if the machines are able to convert electrical signals into the
corresponding technological functions of the weaving itself. This is usually
achieved with the use of elements such as servo-, stepper- and linear motors,
or alternatively lifting and stepping magnets. Advanced solutions, such as
the use of highly accurate linear motors, have been found for controlling
thread clamps of weft yarns to be presented to the rapier.
Many weaving machine manufacturers offer a quick style change (QSC)
system.The basic principle of this system is to prepare a module outside the
weave room, so as to replace the empty module inside the weaving machine
as quickly as possible. With the QSC system, German company Lindauer
Dornier GmbH are known to have operated changes from a fine worsted
fabric to a cashmere fabric in less than 30 min. Almost all major manu-
facturers offer their own version of the system. Dornier also offers a Fast
Dobby Change (FDC) system, which allows a mill to exchange a positive
cam motion for a dobby so as to increase versatility and increase shedding
machine speeds. The exchange time in an FDC system is usually no more
than 1.5 h.
In rapier machines, electronically controlled weft tension devices can
reduce yarn tension during insertion,while the opening and closing time can
be selected – usually at yarn pick up – according to the material used. In the
event of a weft break between the package and the weft feeder, automatic
package switching devices prevent the machine from stopping mid-process.
Another important development is the emergence of new, pneumatic tuck
in motions. This involves the use of air to first hold the weft end in place,
before forcing it to be tucked in the next shed.The elimination of the tuck in
needle with the use of a pneumatic tuck in motion enables the loom to run
much faster in comparison with purely mechanical devices. These numer-
ous technological developments have, in short, allowed mills to increase
machine productivity, improve system controls, reduce breakages and ulti-
mately facilitate a rise in quality. It is safe to conclude that, with the rise of
new generation machines, process control is becoming considerably easier.
11.3.2 Quality control and monitoring
Visual inspection is a necessary but costly process for textile manufacturers.
It is undertaken at a number of stages during the production of a textile,
with different commercial justifications at each stage.The final inspection is
carried out for quality control purposes, whereas inspection at other stages
is generally used to identify defective material, so that it can be either
mended or removed from the production process before unnecessary costs
are incurred. Figure 11.3 shows an example of a visual inspection unit; such

systems may vary from simple inspection tables to semi-automatic inspec-
tion tables with automated fabric movement and fault marking.
With regard to articles, colours, pattern and structure, manual cloth inspec-
tion remains the ideal method for judging fabric, as an inspector can utilise
his or her own experience and expertise to subjectively judge the severity of a
given fault. Manual visual inspection of textiles does have a number of widely
acknowledged limitations, however.The subjective nature of the process gives
rise to inconsistencies from one inspector to the next, while basic human error
is, from time to time, inevitable, meaning that all faults may not be detected.
These limitations can be overcome by automatic fabric inspection sys-
tems, which provide consistently objective and reproducible assessment of
the fabrics. The inspection data is provided directly in electronic form and
can therefore be processed quickly and the analysis can be immediately
transmitted to the people concerned.
Fabric inspection, though, has proven to be one of the most difﬁcult of
all textile processes to automate. It has taken decades for computer and
scanning technology to develop to the extent that practical, consistent and
reasonably user-friendly systems can be produced. Automatic inspection
systems are designed to increase the accuracy, consistency and speed of the
detection of defects in the manufacturing process of fabrics.
In the last 20 years progress in the design of the textile machinery has been
remarkable, most notably in the improvement of productivity, automation
and efﬁciency. On modern, high speed machines, constant monitoring of the
machine, the weaving process and the fabric quality is highly desirable, so as
11.3 Fabric inspection unit.

to avoid faults and defects, achieve a high level of efficiency, and reduce the
production of inferior quality fabric to a minimum.
To ensure quality, fabric inspection should ideally be both fast and exact.
For this reason, high speed automatic inspection systems have increasingly
become the focus in terms of development. Fabricscan (Zellweger Uster),
I-TEX (Elbit Vision Systems Ltd.) and Cyclops (Barco) are all examples of
systems based on machine vision, and in some cases, fabric inspection sta-
tions can be integrated with loom monitoring system allowing for the auto-
matic recall of weaving data. I-TEX, Cyclops, Zellweger Uster, among other
companies, now offer on-loom inspection systems for all types of weaving
machines.5
This rise in the commercial availability of such automatic fabric
inspection systems is largely due to the following reasons:
Image acquisition systems have vastly improved and are now available•
at a reasonable cost.
High-performance parallel processors are now available.•
Image processing systems have become more advanced and more•
versatile.
Large data storage capacity is now easily available at very low cost.•
The inspection system is operated from an operating terminal, where arti-
cle-specific inspection criteria and the necessary individual data are entered
or read in via a bar code reader. The reports can also be called up via the
operating terminal. Detected faults can, at any time, be called up on the
screen and analysed quickly and easily. This is particularly useful in assess-
ing whether a problem is recurring, frequent or anomalous. Ultimately, the
visual display makes the assessment and the implementation of corrective
measures considerably easier.
Automatic cloth inspection, with the advantage of quick, objective and
reproducible measurements of the fabric characteristics, provides us with an
effective instrument of modern quality management in the following ways:
The continuous process optimisation; a system which allows the user•
to quickly identify and adjust any weaving machines that produce an
increasing number of disturbing faults.
The process control function is provided with a complementary alarm•
system, ensuring that deviations from the specified limit values are
directly indicated and recorded.
The determination of fabric quality, through common quality param-•
eters such as the number of faults per piece or unit of length, or the so-
called demerit point system.The systems allocate point values according
to the size of a fault (with the Uster Fabriclass system, the faults can be
classified based on the length and intensity of deviations in the direction
of the warp or weft).

The automatic fabric inspection system from Zellweger Uster shown
in Fig. 11.4 uses a neural network to learn the characteristics of the flaw-
less fabric.6
The system then detects marks, records and classifies the faults
automatically. The fabric passes over a two-component, illumination mod-
ule, which allows for an inspection in reflected or transmitted light. The
selection of the illumination type depends on the fabric density, the special
fault types or the textile process stage at which the inspection is carried out.
Depending on the inspection width, there are between 2 and 8 special CCD
high-resolution line cameras installed above the light source.With these,it is
possible to inspect fabrics which fall between the standard widths of 110 and
440 cm.The cameras continuously scan the fabric for deviations. During the
normal inspection process, the system, with speeds of up to 120 m/min, looks
for local deviations from the normal fabric appearance; the characteristics
of these local deviations are then analysed. Depending on the conclusions
of the analysis, the system initiates a marking of the fabric, records the event
or carries out a fault classification.
The entire learning phase of the neural network,and its subsequent trans-
mission to the evaluation unit, takes approximately one minute, and has to
be carried out once for each article. All following pieces of that particular
article will then be inspected according to the same standard.
The company’s current system, Fabricscan, can inspect fabric at speeds
up to 120 m/min while offline (the inspection speed of an online system is
11.4 Uster Fabriscan inspection system.

approximately 30 m/min), and can detect defects down to a resolution of
0.3 mm.The Uster Fabriscan is available for both transmitted and reflective
light, allowing it to recognise a wide range of faults (oil spots, e.g. can only
be seen in reflective light whereas start marks can only be seen in transmit-
ted light).
I-TEX from Elbit Vision Systems Ltd. (EVS) is a well-established auto-
matic fabric inspection system. The system consists of an image acquisition
unit,computers and a post-inspection evaluation work station for review and
analysis of defect report, along with a video album of all defects.The system
can detect defects as small as 0.5 mm on fabric widths of up to 330 cm,and at
speeds of up to 100 m/min. On any unicolour fabric, I-TEX detects diverse
spinning, weaving, dyeing, finishing and coating defects.Virtually any visible
defect, from yarn and weaving faults (holes, missing threads, starting marks,
broken yarns), to water and dyestuff stains, can be detected by the system.
For grey and technical fabric inspection, I-TEX can be configured for extra-
high resolution and extra-wide fabrics, while for unicolour, dyed finished
fabric inspection it uses both transmitted and reflected light, as well as two
sets of cameras.
EVS also offer an in-line system called Shade Variation Analyser (SVA),
which utilises a calibrated, travelling spectrophotometer to measure shade
consistency in textiles during fabric flow. The spectrophotometer readings
are compared to a reading at the beginning of the roll to detect side-to-
side and beginning-to-end shade variation.The SVA can be integrated with
an EVS I-TEX system or can operate as an independent, standalone unit.
For printed designs, EVS has developed the in-line fabric monitoring and
defect detection system PRIN-TEX, which can be mounted on a rotary
screen printing machine.This enables online detection of recurring printing
defects. Upon detection, an alarm is raised and the fabric fault and its loca-
tion are displayed in real-time on a video monitor, enabling swift corrective
action and an overall improvement in quality.Figure 11.5 shows the on loom
Inspection system of Elbit Vision System.7
The Cyclops automatic loom inspection system from Barco detects warp
and weft defects by means of one or two mobile scanning heads.These heads
consist of a CMOS camera and infrared LED illumination unit, installed
either on the off-loom take-up or above the cloth roll.At a number of posi-
tions, an image of the fabric is taken and transferred to the image processing
unit. The software analyses the texture of the fabric and detects deviation
from the normal texture. Any detected defect is signalled to the loom. All
defect information is also sent to a fabric quality data base through the
Barco Sycotex loom monitoring systems (Fig. 11.6), allowing the produc-
tion of defect maps and various types of quality reports. Based on the defect
analysis, the grey inspection may or may not be bypassed (a fabric judged to
be first grade, for example, can be sent directly for further processing).

Setting up the Cyclops system is very simple. The scanning range adjusts
itself to the fabric position and width through automatic detection of the
fabric boundaries. Illumination and camera settings are optimised by the
calibration software module in accordance with the optical characteris-
tics of the fabric. Furthermore, the structure of the fabric is automatically
identiﬁed, so as to calculate the algorithm parameters for optimal defect
detection.8
The latest version of the Cyclops system (Fig. 11.7) has now also been
optimised for the inspection of carbon,Kevlar and glass fabrics.BarcoVision
has also launched a brand new sensor for air jet weaving looms, entitled the
To the central P.C. Ethernet LAN
I/O
DC power
I/O Box
AC power
Loom panel
Fluorescent lamp + Electronic ballast
Camera bridge
SVC (smart video camera)
11.5 On-loom inspection system of Elbit Vision System.
Weaving
Data unit
DU5P
Data unit
DU5P
Server
SYCOTEX Client - Server system concept
Planning
Production
Quality control
Ethernet
Ethernet
CIM - server
Direct link to machine
microprocessor
Preparation
VT520Monitor Scoreboard
9 3.1
Fabric inspection
Touch screen
11.6 Barco automatic loom inspection and monitoring systems.

Kinky Filling Detector (KFD). This detector, a combination of laser and
camera technology, continuously checks the fabric for the presence of kinky
weft yarns (loops) and can stop the loom in case of excessive occurrence of
these defects within a certain length of the fabric.8
Online detection not only reduces the amount of defective produce, it
also reduces the amount of required handling. If a roll being removed from
the machine is of high quality, the roll might be immediately prepared for
shipment, and thus undergo minimal handling. If the roll has one section
that is defective, moreover, the operator will, with the help of online detec-
tion, know precisely where to find it, thus minimising the time it takes for
removal, resulting in a significant reduction in cost. As machine production
increases every year, so does the importance of online quality monitoring.
Effective fabric inspection can reduce the fabric defects in the final fabric
and is thus highly advantageous for process control in weaving.
11.4 Cost control in weaving
The ultimate aim of any mill is to make profit,a goal dependent both on sales
income and production expenditure. While sale price depends on product
positioning, supply and demand and other factors, a product is rarely able
to dictate price in a competitive market. It is, therefore, necessary to opti-
mise the production costs, the key factors of which are the respective costs
of raw materials and weaving itself. More than two-thirds of all production
cost derives from the cost of raw materials, which can vary considerably
depending on market conditions, and are thus somewhat difficult to control.
It is therefore essential that a mill optimises weaving cost in order to remain
11.7 New Cyclops automatic on loom fabric inspection system.

competitive in the market. Weaving cost per metre of the fabric produced
may be divided into the following three main elements: (a) labour cost, (b)
fixed cost, and (c) other costs.
Labour cost is the sum of cost of all personnel directly involved in oper-
ations from preparation to inspection of the final fabric. The labour cost
depends on the type of work, skill and efficiency of the operator, the extent
of the automation and condition of the machines, and finally the work allo-
cation. In high wage countries, labour cost can be a significant component
of conversion cost while in low wage countries, the proportion of the total
conversion cost dedicated to labour cost will be smaller. A higher number
of looms per worker reduces the labour cost, but will also decrease loom
efficiency and thus reduce production and increase the fixed cost.There has
to be a compromise, then, to achieve the lowest overall cost.
Fixed costs are those that do not depend on the production and include
interest, depreciation, overhead, maintenance, space, air-conditioning and
management costs.With more expensive machinery and other installations,
it becomes necessary to spread the fixed cost over a higher production.Any
increase in fixed costs should be accompanied by increased productivity and
machine efficiency otherwise the weaving cost will rise.To operate looms at
higher speed while also ensuring a low end breakage rate, production can
be increased; to achieve this, though, it is necessary to spend money on good
preparation and better quality yarn. Once again, a compromise is necessary
to achieve the lowest possible cost.
There may be costs associated with the inventory which will add to the
production cost.To minimise such costs, it is necessary to reduce the inven-
tory to the lowest level practicable. Continuous monitoring of loom data,
proper planning of yarn inventory and other preparatory processes can
provide more accurate predictions of such factors as the time when a new
beam will be required on a given loom, which will in turn reduce the down
time otherwise caused by the beam change, and ultimately increase the
efficiency.
Control of hard waste is another essential step in minimising the conver-
sion cost. All areas of a weaving mill will create certain amount of waste
during the processing of material. This waste can be divided into two types
(i) process waste, and (ii) incidental waste. Process waste is unavoidable
waste linked to the type of equipment and the nature of the process; it can-
not be reduced below a certain level unless equipment changes and major
process changes are adopted. All other waste is incidental and completely
avoidable. Waste resulting from poor package quality, work practices and
material handling must be eliminated or reduced to bare minimum.A good
example would be the need for extra ends in a beam to take care of miss-
ing ends. Better control of lappers at sizing will reduce missing ends and
thus the necessity for large numbers of replacements. Proper setting of the

loom and even tension in warp ends can further help in reducing the end
breaks. In the case of formation of cloth with fringe selvedge, optimisation
of the weft insertion system can also help to reduce waste.A higher number
of fabric defects not only affects the fabric quality and leads to a drop in
value, but can also lead to a higher quantity of hard waste. Savings through
waste reduction can be substantial and can reduce the overall cost of fabric
production.
11.5 References
1. Chen, X., Characteristics of Cloth Formation in Weaving and Their Inﬂuence
on Fabric Parameters, Textile Research Journal,April 2005, 281–7.
2. Lord, P.R. and M.H. Mohamed, Weaving: Conversion of Yarns to Fabrics,
Chapter 17: Weave Room Management, Woodhead Publishing Co., Cambridge,
England, 2001.
3. Paliwal, M.C. and P.D. Kimothi, Process Control in Weaving, ATIRA,
Ahmedabad, 1983.
4. Legler, F., Is process control in weaving possible or just a dream?, Textile World,
February 2003, 26–9.
5. Dockery, A. ‘Automated Fabric Inspection: Assessing the Current State
of the Art’, 2001. Available from: http://www.techexchange.com/library/
Automated%20Fabric%20Inspection%20-%20Assessing%20The%20
Current%20State%20of%20the%20Art.pdf
6. Jose Fuster, S.A., ‘Uster Fabriscan Product Catalogue’, 2011. Available from:
www.fuster.com
7. Elbit Vision Systems Ltd. (EVS), 2012. Available from: http://www.evs.co.il/
index.php?
8. Belgium Monitoring Systems (BMS) Vision, ‘Cyclops Automatic on-loom fab-
ric inspection’, 2012. Available from: http://www.visionbms.com/textiles/en/
products/product.asp?element=1315

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