FIELD OF THE INVENTION
The present invention relates to a system for online estimation of coil length in looper in
cold rolling mill in steel plants. More particularly, the present invention is directed to provide
a system for precise estimation of coil length in entry and exit horizontal loopers in steel
rolling mill. The system measures distance between looper trolley and fixed pulley involving
non-contact long range LASER sensors capable of measuring distance up to 200 meter with
pilot light for alignment used as primary sensor alongwith diamond grade reflector for high
sensitivity. The system estimates length in looper, indicates actual status of looper trolleys
and avoids derailment of looper trolley. The system is capable of high accuracy length
estimation and does not require regular maintenance. The system for online estimation of
coil length in looper thus allows the pickling line to run at higher speed for longer duration
of time, hence increase in productivity.
BACKGROUND OF THE INVENTION
In the applicants Cold Rolling Mill at Bokaro, the input coil is received from Hot Strip Mill,
and due to delay in processing (sometimes few weeks) the coil may have a layer of scale
(mixture of different iron oxides) with a thickness of 5-20u.The strip is de-scaled with a
combination of mechanical and chemical dissolution in pickling line. Removal of scale is
performed by chemically treating the surface of hot rolled strip at continuous pickling line of
CRM. This is done using H2SO4 at Pickling Line-1.
Pickling line-l is a continuous processing line with three independent sub-units namely
entry, process and exit sections. In entry section 300 meters and at exit section 200 meters
length of coils is stored in horizontal loopers.
The Pickling line has three sub-units or independently operated sections i.e. 1. Entry section
2. Pickling Tank and 3. Exit Section. The actual pickling process takes place in Pickling tank
and the quality of this process depends upon accuracy of speed regulation, in addition to
many other parameters. Since pickling is continuous process, the tail end of the running
coil is welded to head end of the next coil to maintain continuity, at entry section. The weld
joint is detected and cut at exit section to regain the original coil size. The coil loading &
welding at entry end, and cutting & coiling at exit end not only take time, but also employ

equipment which can breakdown and affect the process speed. This may result in the part of
coil residing in the Pickling tank to be under picked or over pickled, thus affecting the
quality.
The existing looper measurement and display was based on Russian Selsyn system[2]
having a toggle type numerical display driven by motor and governed by Selsyn signals.
This system was complex and obsolete in nature and behaved erratic at times. The incorrect
information about the storage in the loopers was leading to reduced line speed and
derailment of the looper trolley. Apart from the above problems, spares were also not
available.
To maintain the required process speed in the pickling tank, entry and exit sections are
provided with online storage facility called loopers. These loopers store strip in horizontal
fashion due to ability of looper drums (in pair) to move closer to each other or move away
from each other. Farther the looper drums, more the storage of the strip as buffer for the
process. In case of a breakdown or process halt at entry end, looper drums start moving
closer to each other thus supplying the coil to pickling tank from buffer till the inflow of
fresh material starts. Similarly at exit end, till the coiler is ready, the output strip of pickling
tank is stored in looper of exit side.
It is obvious that the required speed of pickling can be maintained only if loopers function
properly alongwith information regarding amount of strip available as buffer in loopers. To
. estimate the length correctly, a Russian selsyn based system[2] was in place which was
giving frequent problems, had limited accuracy and was difficult to maintain due to
obsolescence.
There has been therefore a persistent need in the art to overcome the aforesaid problems
relating to precise online estimation of coil length in looper in CRM to improve plant
productivity and efficiency. A solution to the stated problem is highly demanded by
introducing an improved measurement and display system based on distance measurement
of looper trolley both at entry and exit section sensors capable of measuring distance up to
200 meter with high sensitivity. The system would also provide actual status of looper
trolleys and avoid derailment.

OBJECTS OF THE INVENTION
The basic object of the present invention is directed to providing a system for online non
contact precise and correct estimation of coil length in entry and exit horizontal loopers in
steel rolling mill.
A further object of the present invention is directed to provide said a system for online non
contact estimation of coil length in loopers wherein long range laser sensors with high
sensitivity which takes care of variation due to limitation in selsysn signals are used for
desired accuracy of measurement/estimation of length of coil.
A further object of the present invention is directed to provide said a system for online non
contact estimation of coil length in loopers wherein said system indicates actual status of
looper trolleys and avoids derailment.
A still further object of the present invention is directed to provide a system for online non
contact precise estimation of coil length in entry and exit horizontal loopers wherein
sensors' performance is enhanced by installing a diamond grade reflector used to reflect the
laser light back to sensor, so that even limited amount of reflection can be sensed.
A still further object of the present invention is directed to provide a system for online non
contact precise estimation of coil length in entry and exit horizontal loopers wherein size of
the reflector is selected based on accommodating small lateral shifting of trolley that gets
magnified several times due to large distance between sensor and reflector.
A still further object of the present invention is directed to provide a system for online non
contact precise estimation of coil length in entry and exit horizontal loopers wherein sensors
are mounted on vibration free platform between entry and exit sections looper drum with
special mounting structure for vibration free installation.
A still further object of the present invention is directed to provide a system for online non
contact precise estimation of coil length in entry and exit horizontal loopers wherein
customized mounting arrangement for sensors and reflectors are adapted to avoid vibration
and provide angle.

A still further object of the present invention is directed to provide a system for online non
contact precise estimation of coil length in entry and exit horizontal loopers wherein
mounting arrangement would provide for sensor degree of freedom in horizontal as well as
vertical axis to adjust the focusing.
A still further object of the present invention is directed to provide a system for online non
contact precise estimation of coil length in entry and exit horizontal loopers wherein sensors
are also equipped with pilot RED Laser beam to assist in focusing the sensor on to the
reflector.
A still further object of the present invention is directed to provide a system for online non
contact precise estimation of coil length in entry and exit horizontal loopers wherein
continuous display of estimated length at two important pulpits for operator guidance.
A still further object of the present invention is directed to provide a system for online non
contact precise estimation of coil length in entry and exit horizontal loopers wherein
distance shown by sensor system and actual distance showed a maximum error of 500mm,
which is within tolerable limits considering the maximum range of 80 meters.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to a system for online non contact
estimation of coil length in looper at entry and exit of pickling line in Cold Rolling Mill,
comprising
said pickling line comprising (i) entry section having an entry section looper drum (ii)
pickling tank (iii) exit section having an exit section looper drum (iv) a coiler pulpit
and (v) an uncoiler pulpit,
an integrated sensor based system comprising (a) laser sensor mounted on a
vibration free platform and (b) reflector mounted on the trolley having looper drum
used to reflect the laser light back to sensor,
said integrated sensor system adapted to measure and display the trolley distance of
looper at uncoiler and/or coiler pulpits.

A further aspect of the present invention is directed to said system comprising said laser
sensor comprises laser sensors with capability of 200 meters for entry and exit looper
trolleys independently and said reflector comprises diamond grade reflector ;
means for converting the distance between the reflector and sensosr into SSI output
signal of sensor and fed to entry side pulpit for display to the operator ,means for
converting said SSI signal into 4-20mA signal and fed to the exit side pulpit.
A still further aspect of the present invention is directed to said system wherein in the exit
side pulpit the distance between the exit side trolley and sensors as well as output of entry
side sensors are displayed.
Yet another aspect of the present invention is directed to said system wherein said reflector
is of size 500mm X 500 mm (minimum) and preferably 914mm X 914mm so as not to go
out of alignment due to lateral shifting of trolley.
A further aspect of the present invention is directed to said system wherein said vibration
free platform for mounting of laser sensor comprises a rigid platform positioned in between
entry and exit sections looper drum with suitable rigid mounting structure.
A still further aspect of the present invention is directed to. said system wherein said sensor
is equipped with pilot RED Laser beam to assist in focusing the sensor on to the reflector.
A still further aspect of the present invention is directed to said system wherein mounting
arrangement of sensor has provision to provide sensor degree of freedom in horizontal as
well as vertical axis to adjust the focusing.
A still further aspect of the present invention is directed to said system wherein said signal
output of sensor of SSI type is converted using MOTRON converter cum display in entry side
uncoiler pulpit so that apart from displaying the SSI values, it converts the signal to 4-20mA
and relay forward to exit side coiler pulpit.
A still further aspect of the present invention is directed to said system wherein said power
source comprising 220 V AC power brought to sensor platform is converted to 24VDC using
DC PS module and distributed to entry and exit side pulpits.

A still further aspect of the present invention is directed to said system which is adapted to
measure and display the trolley distance of looper both at uncoiler and coiler pulpits
comprising displaying, the entry side trolley distance in the uncoiler pulpit whereas
displaying both entry and exit side looper trolley distance in the coiler pulpit.
A still further aspect of the present invention is directed to said system comprising reflecting
tapes fixed on any metal surface provided as backup for use as spare.
The objects and advantages of the present invention are described hereunder in greater
details with reference to the following accompanying non limiting illustrative drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: is the schematic illustration of conventional entry and exit sections of pickling line
provided with online storage facility called loopers showing the strip arrangement in Entry/
Exit Looper storage.
Figure 2: is the photo image of laser Sensor mounted at site according to the system of the
present invention, which is laser sensor AMS 200/200 installed having distance
measurement capability of 200 meter for entry and exit looper trolleys independently.
Figure 3: is the photographic image of Diamond grade reflector according to the system of
the present invention mounted on trolley to reflect the laser light back to sensor.
Figure 4: is the schematic wiring scheme for sensor showing the distribution from 220V
supply to sensor platform and to the pulpits.
Figure 5: is the schematic layout of Pickling line showing the entry and exit loopers with
respect to location of sensors and pulpits according to the system of the present invention.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING DRAWINGS
The present invention relates to a system for online non contact precise and correct
estimation of coil length in entry and exit horizontal loopers in pickling line of steel rolling
mill.

Accompanying Figure 1 is the schematic illustration of conventional entry and exit sections
of pickling line provided with online storage facility called loopers showing the strip
arrangement in Entry/Exit Looper storage. The components shown in Figure 1 include fixed
drum (1), rope drum(2), steel rope(3), looper trolley(4), steel strip(5), working platform(6),
fixed roll(7). To maintain the required process speed in the pickling tank, entry and exit
sections are provided with online storage facility called loopers. These loopers store strip in
horizontal fashion due to ability of looper drums (in pair, one fixed and another moving) to
move closer to each other or move away from each other. Farther the looper drums, more
the strip as buffer for the process. In case of a breakdown or process halt at entry end,
looper drums start moving closer to each other thus supplying the coil to pickling tank from
buffer till the inflow of fresh material starts. Similarly at exit end, till the coiler is ready, the
output strip of pickling tank is stored in looper of exit side. It is obvious that the required
speed of pickling can be maintained only if loopers function properly alongwith information
regarding amount of strip available as buffer in loopers. Due to variation in speed of pickling
due to malfunctioning of loopers, the part of coil residing in the Pickling tank to be under
picked or over pickled, thus affecting the quality. To estimate the length correctly,
conventionally Russian selsyn based system[2] was in place which was giving frequent
problems, had limited accuracy and was difficult to maintain due to obsolescence.
Conventional method for coil length estimation was based on selsyn[2] and for reasons
mentioned above, needed replacement. The displacement of looper drums are enacted by
motors and newer methods are based on shaft encoder mounted on the motor as primary
sensor. Results by this method have shown very good accuracy. But being a contact type
method and requiring stringent alignment, reliability of the system demands rigourous
maintenance practices.
To circumvent the aforesaid problems, design and introduction of an improved
measurement and display system based on distance measurement of looper trolley both at
entry and exit section has been implemented by way of the present invention. State of the
art LASER sensor capable of measuring distance up to 200 meter with pilot light for
alignment has been used as primary sensor alongwith diamond grade reflector for high
sensitivity. The system indicates actual status of looper trolleys and avoids derailment.
These sensors mostly work on principle of time of flight and are not prone to inaccuracy due
to magnetic interference/ slippage etc. The new installations in rolling mills having several

laser based sensors employed for various position/ distance sensing. However in case of
existing pickling line, the use of laser sensor posed several challenges.
a. The major challenge was related to distance. Though laser sensors are used
frequently now a days, but most of the application covers a distance of maximum 30
meters. In case of pickling line it was 80-100 meter (variation due to position of limit
switches). The sensors having such range are manufactured by limited laser technology
vendors. These sensors' performance is enhanced by installing a reflector so that even
limited amount of reflection can be sensed. Instead of selecting sensor with a range of 100
meter, range of 200 meter was preferred due to inherent high level sensitivity of such
sensor. Diamond grade reflectors are technically the most modern reflectors and show very
high reflectivity.
b. Another challenge was related of alignment. Since the trolley having looper drum
moves over rail track, it is obvious that during travel there would be very small lateral
shifting of trolley. However, this small amount of lateral shift gets magnified several times
due to large distance between sensor and reflector. Keeping several other mechanical issues
in consideration, it was estimated that a reflector of size 500mm * 500 mm (minimum) is
not likely to go out of alignment due to lateral shifting of trolley.
c. It is also very important that laser sensor is mounted on a vibration free platform.
A good rigid platform in between entry and exit sections looper drum was selected and
special mounting structure was designed for vibration free installation.
The system according to the present invention system has been designed and implemented
which is primarily based on Laser Sensor as the main device and reflectors, signal
converters, displays as auxiliary device.
A LEUZE [1] make laser sensor AMS 200/200 as shown in accompanying Figure 2, has
been installed having distance measurement capability of 200 meter for entry and exit
looper trolleys independently. The higher range (almost double the requirement) is selected
so that reliability can be assured. The sensor is mounted on a vertical mounting structure
especially designed for the purpose. The mounting structure takes care of vibration of
platform upto certain extent. The mounting arrangement has provision to provide sensor
degree of freedom in horizontal as well as vertical axis to adjust the focusing. The sensor is
also equipped with pilot RED Laser beam to assist in focusing the sensor on to the reflector.

Due to high distance under range, special pre-fabricated diamond reflectors as shown in
accompanying Figure 3 are used to reflect the laser light back to sensor. The size of
reflector used is 914 mmX 914mm. Reflecting tapes which can be fixed on any metal
surface are also procured as backup and to be used as spare.
The signal output of selected sensor was SSI type. Therefore MOTRON converter cum
display has been used in pulpit #3 so that apart from displaying the SSI values, it is able to
convert the signal to 4-20mA and relay forward to pulpit #4.
Accompanying Figure 4 is the schematic wiring scheme for sensor showing the distribution
from 220V supply to sensor platform and to the pulpits. 220 V AC power has been brought
from motor room#5 to sensor platform. On sensor platform 220VAC is converted to 24VDC
using DC PS module and distributed to Pulpit#3 and pulpit#4. Mounting of LASER Sensor
has been done so as no effect of vibrations is felt on the measurement.
The system finally measures and displays the trolley distance of looper both at uncoiler and
coiler pulpits. In the uncoiler pulpit, the entry side trolley distance is displayed whereas in
the coiler pulpit, both entry and exit side trolley looper trolley distance is displayed.
Accompanying Figure 5 is the schematic layout of Pickling line showing the entry and exit
loopers with respect to location of sensors and pulpits according to the system of the
present invention. The different components shown in Figure 5 include pickling tank(l),
entry looper side fixed drum(2) & moving drums(3), exit looper side fixed drum(4) &
moving drums(5), separate motors(6) to create tension, rope drums(7), sensors(8). The
integrated sensor system as shown in Figure 5 has two main parts; a. laser sensor
mounted on the platform and b. diamond grade reflector mounted on the trolley. The
distance between reflector and sensor is converted into SSI output signal of sensor and
carried to entry side pulpit, where it is displayed to the operator. This SSI signal is also
converted into 4-20mA signal and is brought to exit side pulpit. In the exit side pulpit, the
distance between exit side trolley and sensor as well as output of entry side sensor are
displayed.
Following are the advantageous features of the system for estimation of coil length in
loopers according to the present invention:

(a) implementing a non-contact type system for online estimation of coil length in a
looper based on distance measurement by long range laser sensor;
(b) providing of customized mounting arrangement for sensor and reflector to avoid
vibration and provide sensor degree of freedom in horizontal as well as vertical axis
to adjust the focusing;
(c) Schemes for automatic generation of Low and High limit;
(d) Continuous display of estimated length at two important pulpits for operator
guidance;
The new system accurately measures the distance between trolley and platform where
pulley is located. The distance shown by sensor system and actual distance showed a
maximum error of 500mm, which is within tolerable limits considering the maximum range
of 80 meters.
The accuracy expected with long range laser sensor has been achieved and the constraint of
reflectivity at long distance (>30m) was easily overcome by selection of high range sensor
and diamond grade reflectors. The improvement in productivity of 4-6 coils per day has
been achieved by installing the above described system.

We Claim:
1. A system for online non contact estimation of coil length in looper at entry and exit
of pickling line in cold rolling mill, comprising
said pickling line comprising (i) entry section having an entry section looper drum (ii)
pickling tank (iii) exit section having an exit section looper drum (iv) a coiler pulpit
and (v) an uncoiler pulpit,
an integrated sensor based system comprising (a) laser sensor mounted on a
vibration free platform and (b) reflector mounted on the trolley having looper drum
used to reflect the laser light back to sensor,
said integrated sensor system adapted to measure and display the trolley distance of
looper at uncoiler and/or coiler pulpits.
2. A system as claimed in claim 1 comprising said laser sensor comprises laser sensors
with capability of 200 meters for entry and exit looper trolleys independently and
said reflector comprises diamond grade reflector ;
Means for converting the distance between the reflector and sensosr into SSI output
signal of sensor and fed to entry side pulpit for display to the operator, means for
converting said SSI signal into 4-20mA signal and fed to the exit side pulpit.
3. A system as claimed in anyone of claims 1 or 2 wherein in the exit side pulpit the
distance between the exit side trolley and sensosr as well as output of entry side
sensors are fed.
4. A system as claimed in anyone of claims 1 to 3 wherein said reflector is of size
500mm X 500 mm (minimum) and preferably 914mm X 914mm so as not to go out
of alignment due to lateral shifting of trolley.
5. A system as claimed in anyone of claims 1 to 4 wherein said vibration free platform
for mounting of laser sensor comprises a rigid platform positioned in between entry
and exit sections looper drum with suitable rigid mounting structure.
6. A system as claimed in anyone of claims 1 to 5 wherein said sensor is equipped
with pilot RED Laser beam to assist in focusing the sensor on to the reflector.

7. A system as claimed in anyone of claims 1 to 6 wherein mounting arrangement of
sensor has provision to provide sensor degree of freedom in horizontal as well as
vertical axis to adjust the focusing.
8. A system as claimed in anyone of claims 1 to 7 wherein said signal output of sensor
of SSI type is converted using MOTRON converter cum display in entry side uncoiler
pulpit so that apart from displaying the SSI values, it converts the signal to 4-20mA
and relay forward to exit side coiler pulpit.
9. A system as claimed in anyone of claims 1 to 8 wherein said power source
comprising 220 V AC power brought to sensor platform is converted to 24VDC using
DC PS module and distributed to entry and exit side pulpits.
10. A system as claimed in anyone of claims 1 to 9 which is adapted to measure and
display the trolley distance of looper both at uncoiler and coiler pulpits comprising
displaying, the entry side trolley distance in the uncoiler pulpit whereas displaying
both entry and exit side looper trolley distance in the coiler pulpit.
11. A system as claimed in anyone of claims 1 to 9 comprising reflecting tapes fixed on
any metal surface provided as backup for use as spare.

ABSTRACT

The present invention relates to a system for online non contact estimation of coil length in
entry and exit horizontal loopers in steel rolling mill with desired accuracy. The system
measures distance between looper trolley and fixed pulley involving non-contact long range
LASER sensors capable of measuring distance up to 200 meter with pilot light for alignment
and focusing, used as primary sensor alongwith diamond grade reflector for high
sensitivity. The system estimates length in looper, indicates actual status of looper trolleys
and avoids derailment of looper trolley. The system is capable of high accuracy length
estimation and does not require regular maintenance. The system measures and displays
the trolley distance of looper both at uncoiler and coiler pulpits. The system for online
estimation of coil length in looper thus allows the pickling line to run at higher speed for
longer duration of time, hence increase in productivity.