In: Wagner W., Szekely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Vol. XXXVIII, Part 7B 
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RECOGNITION OF WINDING DISPLACEMENTS FOR STEEL COILS VIA LASER 
LIGHT SECTION TECHNIQUE 
Patrick A. Holzl, Daniel C. H. Schleicher and Bernhard G. Zagar 
Johannes Kepler University 
Institute for Measurement Technology 
Austria, Linz 4040 
patrick.hoelzl@students.jku.at, daniel.schleicher@jku.at, bemhard.zagar@jku.at 
KEY WORDS: Laser scanning, Measurement, Three-dimensional, Object, Pattern, Recognition, Segmentation, Industrial 
ABSTRACT: 
To satisfy the ever increasing quality standards of todays steel industry the basic products, in this case steel coils, must be produced 
within very small tolerances. To achive those quality limits, control systems via machine vision are getting more and more popular. For 
example the quality level of steel coils decreases due to winding displacements based on a non-ideal production process. In this paper 
a machine vision system for the recognition of winding displacements of steel coils, based on the laser light sectioning technique, will 
be presented. The introduction of the mathematical model of the laser light sectioning setup allows to compensate some influences of 
the setups inaccuracies. We show that a reliable recognition of the coil profile with an accuracy below or less than 1mm can be achieved 
by a rather simple adaptive algorithm. Finally defects can be detected accurately out of the recognized coil profile. 
1 INTRODUCTION 
Generally metal processing companies, like car manufacturer get 
their basic material in form of rolled up steel sheets, called coils. 
These metal processing companies and especially the steel indus 
try are interested in systems to detect defects and to minimize ma 
terial rejects. One of the major problems which can occur durring 
the coil manufactoring process are displacements of windings, 
due to a non-conform rolling-up process or a faulty packaging. 
These winding displacements cause a higher percentage of non 
usable material and so for quality aspects a preventive detection 
of these displacements is necessary. Figure 1 shows a model of 
the coil and winding displacements. The winding displacements 
h(r) typically are less than 5 mm, larger displacements are prob 
lematic and are aimed to be detected by our system. To achieve 
this requirement for the profil resolution the minimum detectable 
winding displacement hmin (r - ) is specified to be equal to or less 
than 1 mm. 
A-B 
Figure 1: Model of the coil with winding displacements h(r) 
indicated, di and d a are the inner and outer diameter of the coil 
respectively and b is the mean coil width. 
For the above-mentioned model we imply three assumptions which 
are realistic for further processing: 
1. An axial winding displacement h(r) on one side results in 
an inverse displacement —h{r) on the other side (implying 
b is constant for each winding). 
2. The winding displacement h(r) is constant over one wind 
ing at radius r. 
3. Winding displacements along the radius r occurs only in 
small steps. 
Due to the first assumption we only need to look for defects on 
one cylinder base. The second assumption limits the ROI to one 
radial range of zero to 2 thus improving resolution. So for the 
further recognition process the ROI will be limited to the lower 
half of the coil as indicated in Fig. 2 (red rectangle). The last as 
sumption is necessary for the recognition algorithm presented in 
Sec. 4 to work correctly. The complete detection should happen 
during the coils storage process, that means the coil will move 
during the measurement. Figure 2 shows a typical storing pro 
cess, with the coil on a transport waggon moving in axial direc 
tion with 0.5 m/s. The problem here is that the storage process 
can not be influenced or changed, so the chosen measurement 
method must be adapted to these conditions. Therfore an optical 
3D measurement method is the best choice with respect to cost 
and resolution. Due to the varying lighting conditions in the stor 
age facility, which can not be influenced, the realized measure 
ment system and furthermore the machine vision system must be 
very robust with respect to natural illumination conditions. 
Figure 2: Moving steel coil on transport waggon during the stor 
ing process, with a blurred laser line barely visible in the ROI 
(red rectangle). 
Considering the given terms a detection system based on the laser 
light sectioning technique (Kraus, 1996, Wu et al., 1993) is the 
preferred choice. Figure 3 shows the principle behind the laser 
light section technique. The elevation profile of interest is illumi 
nated from an off-center position by a line shaped laser light fan. 
So the lateral displacement d(r) of the projected line as viewed at 
from a vantage point orthogonal to the front side of the measure-