FIELD OF THE INVENTION
The present invention relates to an illumination system for real-time detection of
strip surface abnormalities in a hot strip mill producing flat or shaped metal
products.
BACKGROUND OF THE INVENTION
Known illumination systems for application in bottom side surface inspection
system for hot mill and metal production unit use halogen/HPS based lighting
devices. These illumination systems project a relatively strong beam of light on
the surface and the abnormalities are detected by an imaging device.
Operational control and/or adjustment of light beam intensity or spectrum
projected by the known lighting devices is quite difficult. In other words, the
prior art lighting devices fail to produce and maintain a constant and uniform
high power light beam over the entire width of a metal strip under inspection.
Normally these illumination devices are installed inside a (conditioned) room
constructed below the surface/roller table of the mill. In some metal rolling mills,
due to space-constraint, provision of a room (especially at the bottom side) is
not always feasible. Accordingly, there is a need to propose an illumination
system that does not require a room like structure to be built below the roller
table.
The prior art solution of providing a bottom illumination device is not sufficient
enough for projecting a powerful, uniform beam of light over the full width of a
moving hot rolled strip, so as to accurately conduct a surface inspection. One of

the several disadvantages of prior art, is that the bottom light box fails to project
light beam powerful and uniform enough to conduct an accurate surface
inspection of a hot-rolled strip in a Hot strip Mill. Further, in prior art, halogen
lamps are used which frequently fail, making it difficult to remove and repair the
lamps due to space and design constraints. Further, the light beam, at least after
a brief period of use, becomes insufficient as dust and water accumulate over
the light box. This results in poor detection of the surface abnormalities due to
poor image quality, high down time and high maintenance. Internally the light
system is not affected by dust/water and the controlling unit adapts to the
situation and allows a certain amount of dust/water.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an illumination system for
surface inspection of hot metal strip in hot strip mill, which eliminates the
disadvantages of prior art.
Another object of the invention is to propose an illumination system for surface
inspection of hot metal strip in hot strip mill, which is enabled to provide
accurate detection results under harsh environmental conditions for example,
high temperature, high humidity, and highly corrosive conditions.
A still another object of the invention is to propose an illumination system for
surface inspection of hot metal strip in hot strip mill, which is operable under
limited space-availability constraints.

Yet another object of the invention is to propose an illumination system for
surface inspection of hot metal strip in hot strip mill, which is capable of
projecting light beam on the rolling strip at high speed, high intensity and
optimum beam-width.
A further object of the invention is to propose an illumination system for surface
inspection of hot metal strip in hot strip mill, in which the light source is
controllable through a micro-controller in respect of light intensity, contrast of
the reflected light, beam width, and temperature.
A still further object of the invention is to propose an illumination system for
surface inspection of hot metal strip in hot strip mill, which is provided with
cooling arrangement to ensure continuous operation, damage-prevention, and
accuracy of results.
SUMMARY OF THE INVENTION
Accordingly, there is provided an illumination system for surface inspection of hot
rolled metal strip in hot strip mill, the hot strip mill having a roller table
conveying the metal strip, a roller grider with a plurality of rollers disposed below
the roller table, a c-notch to allow the illumination system to be inclinedly
mounted, and a host computer connected through a fibre optic communication
cable to the illumination system, the system comprising a plurality of power light
emitting devices forming an array and installed inside a first box which is housed
inside a second pressurized box, the second box internally accommodating
several metallic tubes circulating chilled water for heat dissipation; a thin high
conductive layer disposed at the interfacing surface of the first box and the

metallic tubes, wherein the second box is mounted below the roller table on the
roll girder conveying said roll strip, wherein the positional relationship of the light
array with respect to a camera is maintained such that the light emitting devices
are enabled to project a beam of light on the rolled strip surface at a high speed,
and wherein the host-computer of the mill communicates with a micro-controller
disposed under the first box having the light source, via a fibre optic
communication interface disposed for controlling illumination level to achieve a
desired dynamic detection level and contrast into the camera. The camera
captures the image of the moving metal strip via a funnel channelising the
reflected light beam.
The first box comprising said power light emitting devices is comprised of a first
heat resistant glass window to prevent internal contamination of light emitting
devices installed inside the first box which is housed inside the second box.
The second box housing the first box with power light emitting devices further
comprises a second heat resistant glass window to prevent external
contamination and provided with water inlet and outlet ports.
For surface inspection of the hot rolled metal strip, it is essential to have a high
intensity and uniform profile. A software interface program is adopted to
communicate with the microcontroller to operably control the light emitting
devices through the fibre optic communication interface thereby set and display
the intensity of each individual light emitting diode of the array and further to
control the junction temperatures. To protect the light emitting diodes from high
temperature from any abnormal behaviour, the cut-off temperature is set
through the software program.

The system is enabled to perform corresponding to any change in light emitting
devices, and maintain the same illumination level and control.
The 'controller' is a known controller. Only the interface software program as
incorporated accesses the controller, fetches temperature and intensity data of
the LEDs. As per decided profile, the software sets the intensity level of the
LEDs. The operating steps of the system are described hereinafter.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows the illumination system of the invention installed in the hot strip
mill below the rollers.
Figure 2 shows the illumination system of Figure 1 with first and second box
housings.
Figure 3 shows a configuration of a metallic tube mesh formed of the plurality of
metal tube inside the second box according to the invention.
Figure 4 shows the illumination system of Figure 1 inclinedly installed below the
rollers so that the reflected light beam reaches the camera having light sensitive
elements.
Figures 5A and 5B depicts a flow-chart illustrating the operation of the
illumination system of the invention.

DETAILED DESCRIPTION OF THE INVENTION
As shown in figures 1 and 4, a hot rolling mill having at least a roller table (not
shown) conveying a hot metal strip which is under surface inspection. A roll
grider (12) is disposed below the roller table and holding a plurality of roller (2).
As shown in figure 2, the illumination System (IS) comprising a first box (6) and
having a light source consisting of a plurality of light emitting diodes arranged to
form an array. A second box (7) accommodates the first box (6) and is mounted
on the roller grider (12). A plurality of metallic tubes formed as a tube mesh (14)
is disposed into the second box (7) to circulate chilled water for dissipiation of
heat, the second box (7) is provided with at least one each ports (10, 11) for
ingress and egress of the chilled water. A camera (5) with light sensitive
elements is distally disposed from the light source such that the camera (5) is
enabled to capture a clean image with optimum contrast of the surface
conditions of the rolling metal strip for detecting surface abnormalities. The
rolling mill further comprises a host computer with software means. The
illumination system having a fibre optic communication interface (not shown)
which is operably connected via a microcomputer to the host-computer.
Illumination level including contrast of the light beam is controlled by the host
computer through the microcontroller so that the camera (5) is enabled to
receive dynamic level of reflected light for accurate detection. A thin high
conductive layer is provided at the interfacing surface of the first box (6) and
the tube mesh (14). The first box (6) is provided with a first heat resistant
window to prevent any damage to the light emitting devices, and wherein the
second box (7) is equipped with a second heat resistant window to prevent
external damage of the illumination system. Reference numerals (8,9) shows the
cable inlet (11) and outlet (10) for the light source including optical cable
configured on the second box (7). The host computer is enabled to disable the

light source through the micro-controller once the temperature measured by a
disposed temperature sensor (not shown) exceeds 65 to 70°C. Figure 4 shows
that the illumination system is inclinedly positioned and further adjustable
through a C-notch (not shown) to eliminate obstruction of the projected light
beam (13) by the rollers (2). The micro-controller is disposed below the first box
(6).
According to the invention the illumination system (IS) provides a projected
beam of light (13) with a width of about 45 mm which is wide enough to handle
movement of the hot metal strip (1) and detection of surface irregularity. The
projected light beam (13) is having an intensity of at least 100,000 Lux at 1
meter distance, with wavelength range of 400 to 800 nanometer. At this high
enough wavelength range, a high contrast images can be obtained. Although,
the peak power occurs at 450 nanometer, an increased Lux level however,
creates an optimum reflected Lux level at the line scan camera (5) having light
sensitive elements. The intensity of the light beam (13) is controlled through a
software running on the host computer and connected to the illumination system
(IS) through a fiber optic interface (not shown). The camera (5) with light
sensitive elements is capable to capture a good image quality with sufficient
dynamic detection level and contrast for optimal abnormalitie detection.
According to the invention, the illumination system (IS) has been configured for
being installed within a limited space below the rollers (2). The reflected light
from the strip surface reaches the camera - (5) with light sensors through a
funnel (4).

A micro controller is provided inside the second box (7) accommodating the light
emitting devices box (6) and cold water is circulated through the inlet and outlet
ports (10,11).
The tube mesh (14) is designed to have high contrast level with light emitting
devices Heat sink. A highly conductive graphite film is placed between the
metallic mesh (14) and the second box (7) to have a higher heat conductivity.
Figures 5A and 5B shows the operating steps followed by the inventive
illuminating system.
Further improvement of the invention is achieved by adding a diffuser to make
the projected beam more parallel. Also due to working in harsh environment, the
prior art disadvantages of frequent cleaning of the system is avoided by adding
an automatic cleaning device.
PRIOR ART TAKEN ON RECORD.
US 2007/01478271 Al (pub. Date June 37, 2007) Gaessler et al. "Device and
method for optically inspecting a surface"
US 2007/0206182 Al (pub Date Sep.6, 2007) Ishikawa et al. "Surface defect
inspection method and device".
US 2007/0222974 Al (pub. Date Sep. 27, 2007) Zhao et al "Method and system
for inspecting surface with improved light efficiency"

US 2010/0002244 Al (pub Date Jan 7, 2010) lino et al, "Method and system for
inspecting the surface"
US 2011/0013013 Al (pub Date Jan 20, 2011) Lee et al. "Water inspection
apparatus"

WE CLAIM :
1. An illumination system for surface inspection of hot rolled metal strip in
hot strip mill, the hot strip mill having a roller table conveying the metal
strip, a roller grider with a plurality of rollers disposed below the roller
table, a c-notch to allow the illumination system to be inclinedly mounted,
and a host computer connected through a fibre optic communication cable
to the illumination system, the system comprising a plurality of power
light emitting devices (LEDs) forming an array and installed inside a first
box which is housed inside a second pressurized box, the second box
internally accommodating several metallic tubes circulating chilled water
for heat dissipation; a thin high conductive layer disposed at the
interfacing surface of the first box and the metallic tubes, wherein the
second box is mounted below the roller table on the roll girder conveying
said roll strip, wherein the positional relationship of the light array with
respect to a camera is maintained such that the light emitting devices are
enabled to project a beam of light on the rolled strip surface at a high
speed, and wherein the host-computer of the mill communicates with a
micro-controller disposed under the first box having the light source, via a
fibre optic communication interface disposed for controlling illumination
level to achieve a desired dynamic detection level and contrast into the
camera.
2. The system as claimed in claim 1, wherein the first box housing comprises
at least one first heat resistant glass window.
3. The system as claimed in claim 1, wherein the second box housing
comprises a second heat-resistant glass window.

4. The system as claimed in claim 1, wherein the high conducting film for
example a graphite layer is enabled to transfer heat generated by the light
source to the plurality of metal tubes.
5. The system as claimed in any of the preceding claims, wherein the speed
of the strip is compatable to a Hot Strip mill.
6. The system as claimed in any of the preceding claims, wherein the width
of the projected light beam is about 45mm.
7. The system as claimed in any of the proceeding claims, wherein intensity
of the projected light is at least 100,-000 Lux at 1 metre distance.
8. The system as claimed in any of the preceding claims, wherein the wave
length of the projected light beam is between 400 to 800 nanometer.
9. The system as claimed in any of the preceding claims, wherein the
optimum intensity of the light reflected at the camera is about 15000 lux.

The invention relates to an illumination system for surface inspection of
hot rolled metal strip in hot strip mill, the hot strip mill having a roller
table conveying the metal strip, a roller grider with a plurality of rollers
disposed below the roller table, a c-notch to allow the illumination system
to be inclinedly mounted, and a host computer connected through a fibre
optic communication cable to the illumination system, the system
comprising a plurality of power light emitting devices (LEDs) forming an
array and installed inside a first box which is housed inside a second
pressurized box, the second box internally accommodating several metallic
tubes circulating chilled water for heat dissipation; a thin high conductive
layer disposed at the interfacing surface of the first box and the metallic
tubes, wherein the second box is mounted below the roller table on the
roll girder conveying said roll strip, wherein the positional relationship of
the light array with respect to a camera is maintained such that the LEDs
are enabled to project a beam of light on the rolled strip surface at a high
speed, and wherein the host-computer of the mill communicates with a
micro-controller disposed under the first box having the light source, via a
fibre optic communication interface disposed for controlling illumination
level to achieve a desired dynamic detection level and contrast into the
camera.