Control of Industrial Sewing Machines

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Control of Industrial Sewing
Machines

very complicated process. This may not be apparent at first
glance, but a closer look at the process reveals that, due to the
flexible, often extensible nature of the materials, their handling
is a procedure that in almost all cases requires human hand.
Another important aspect is setting the machines for the great
variety of materials used currently. This can only be
accomplished by experienced sewing technicians. Machine
configuration and adjustment is an empirical, time-consuming
process that is more and more significant considering that textile
industry has been constantly moving away from massproduction
to small orders with varying materials and styles.

The sewing process is a cyclic process in which several
occurrences take place. The objective is to interlace thread(s)
with each other and through a fabric, for the purpose of joining,
finishing, protecting or decorating. Three main “sub”-processes
can be identified that ideally should be monitored and/or
controlled automatically:
-Material feeding. Seams are produced on the fabric with a
certain pattern, which is, in the simplest case, a straight line, but
may also be a complicated form such as the ones used in
embroidery operations. To form these patterns, the material has
to be transported-“fed” by a distance that is called the stitch
length. Given that industrial machines operate at very high
speeds (some of them attaining 10 000 stitches per minute), the
dynamics involved is complex and there are very often problems
with material deformation and irregular stitch length. Some of
these aspects have been addressed in [1-3, 5];
-Needle penetration. Considering again the high sewing
speeds that occur, problems with needle penetration can arise
due to the mechanical and thermal interaction between needle
and fabric. Fabric yarns may be torn by the forces acting during
needle penetration or they may fuse due to the high needle
penetration produced by friction. Systems to monitor needle
penetration forces during the process to detect defects and offline
systems to support the choice of needles and fine-tune fabric
structures and finishing to avoid these problems, would be of
high value to the industry. This kind of approach has been
studies by several authors, such as in [4-8].vs enterprises

This paper describes current work on the behavior of thread
tensions in an industrial lockstitch sewing machine using a new
measurement set-up. Methods previously investigated for
monitoring of thread tensions and establishing the correct
variable references are being ported and/or re-evaluated. The
first step is the study of the relations between material properties
and thread tensions. Some aspects are still not clear in this
regard. In [13], for instance, the authors state that the thickness
of fabric plies does not affect the needle thread tension. This is
one of the aspects to be studied in this work.
The paper will describe the measurement set-up and
experimental design in chapter II, present and discuss results in
chapter III, and summarize conclusions and future work in
chapter IV.
II. MATERIALS AND METHODS
An industrial PFAFF 1183 lockstitch (stitch 301 according
to ISO 4915) machine (Fig.1) has been instrumented with a
thread tension sensor (Fig.2) connected to a signal conditioning
circuit which in turn plugs to a National Instruments PCI-MIO-
16E-1 data acquisition board (although often called thread
tension, the parameter measured is actually a thread pulling
force). The machine’s “synchronizer” (a rotary optical encoder)
provides 512 pulses per rotation of the machine, which is used
as sample clock for signal acquisition. It is thus possible to
determine the exact angle at which each signal sample is
acquired, allowing relating the signal directly with the events
during the stitch cycle. Signals are thus represented on a
continuous angle rather than a time scale, in which the rotation
N of the machine corresponds to the angles between 360º·(N-1)
and 360º·N.
The sensor (custom-designed by Petr Skop) is a cantilever beam
with semiconductor strain gauges at the base, configured as a
complete Wheatstone bridge. A glass sphere with a rounded slot
allows a low-friction interface with the sewing thread. A thread
guide with two ceramic O-rings has been designed to guide the
thread around the thread sensor. The thread pulling force
produces deformation on the cantilever sensor that is picked up
by the strain gauges.
Thread tension is imposed to sewing threads by a device
called a tensioner This device consists
of two disks between which the thread passes. A spring holds
the two disks together.

Control of Industrial Sewing
 Machines

A typical sewing waveform of thread tension is represented
in Fig.3.
The waveform has been obtained by averaging 20 stitch
cycles.
Although several peaks are observed, the phases described
in Table I are considered the most important:
Zero degrees is the angle at which the needle is at its lowest
point. This moment is very close to the point at which thread
tensions are at its highest. For the definitions of the stitch cycle
phases, it is more convenient to split the stitch cycles from 100
to 460 degrees, as can be observed in Fig.3.
The software was set up to extract the peak values of the
measured thread force signals in these three phases, for all
stitches performed on the specimens.
A preliminary trial to observe the influence of static thread
tension was performed to compare this effect with the variation
of the number of layers. The result is presented in Fig.4.
As can be observed, the static thread tension has a significant
influence on the thread tension signals, both in the amplitude of
the attained peaks as well as in the shape of the signals.

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