FIELD OF THE INVENTION
The present invention relates to control system in hot strip mill and in
particular, to a looper control system in hot strip mill. Importantly, the looper
control system of the invention would favour provision of loop control involving
contact-less sensors adapted to feed accurate looper angle feed back.
Advantageously, the system of the invention is adapted for contact-less sensors
and interface of the encoder signal with analog system to favour wide scale
application and use of the same for loop control in hot strip mills.
BACKGROUND ART
It is well known that the looper and tension control is extremely important in hot
strip mills since it affects the strip quality as well as the strip threading.
Importantly, in such looper control the most difficult aspect involves the
interactions between the looper angle and the strip tension. In particular, it is
well known that the important aspect which need to be satisfied in hot rolling
mills involve the dimensional quality and the mass flow of the strip. The
dimensional quality characteristics include the thickness, width, flatness and
profile of the strip. It is further known to carry out control involving dedicated
control system such as automatic width control, automatic profile control, and
automatic gauge control. Mass flow control is intended to balance the input and
output flow of a strip in a stand. It enables smooth threading of a strip and
stable operation of the process. Control means are used to change the stored
loop length between stands by manipulating the mill motor speed and looper
angle control.
Thus, the loop control is known to play vital role in the finishing mill stands in
hot strip mills. Importantly, the loop control is directed to further control the
inter-stand strip tension. In case the strip loop is greater than the desired loop
then speed reference of preceding stand is lowered and vice versa. If loop
control is not proper in the mill, width variation in the strip takes place which can
result in excessive necking (undesired excessive, width reduction) of the strip
and lead to strip breakage inside the mill or it can also result in huge loop
formation between the two stands and lead to cobble in the mill.

Importantly, to achieve greater loop control it is essential to get an accurate
loop feed back. The loop between two stands is a function of the angle of the
looper table, which supports the loop. The angle is measured by the angle
transmitter which is fixed to the gear box of the looper table. If the angle of the
looper table is 65° then the transmitter is adapted to give 10 volts. The angle
transmitter is basically a potentiometer, which has wiper contact and wiper
contact slides over it. Depending on the wiper movement the corresponding
voltage gives the angle of the looper table, which in turn gives the loop between
the two stands.
Use of such potentiometer based angle transmitters is found to be associated
with several problems in the art. The feed back of these types of angle
transmitters are found to be inaccurate and its output does not vary smoothly
but in jerks. The failure of the wiper contact is thus found to be too high.
Whenever contact fails the feedback goes missing and this in turn results in
huge loop formation between stands and results in cobble. Considering the
feedback is not smooth, the regulation is also improper and these resulted in too
much hunting in the system with resultant width variation in the strip.
OBJECT OF THE INVENTION
It is thus the basic object of the present invention to provide for a looper control
system which would involve contact-less sensor adapted to feed accurate looper
angle feedback and thus avoid the limitations and disadvantages of contact
based sensors known for looper angle feedback.
A further object of the present invention is directed to a looper control system in
hot strip mill, which would avoid the complexities and need for potentiometer
type angle transmitters for such looper control.
A further object of the present invention is directed to a looper control system in
hot strip mill which would on one hand enable the use of contact-less sensors
and on the other hand favour integration of such contact-less sensors with
existing regulation of analog type.

A further object of the present invention is directed to a PLC based looper control
system involving contact-less sensor which would be adapted to convert the
encoder pulses to required angle and generate an analog voltage corresponding
to that angle.
A further object of this invention is directed to a looper control system adapted
such that it can be used to determine the angular movement of an object and
interface that signal to any analog system.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the invention there is provided a looper
control system in hot strip mill comprising:
means to measure the loop between two stands which is a function of the
angle of the looper table adapted to support the loop comprising contact-less
pulse encoders as sensors operatively connected and adapted to suitably
interface for feeding accurate looper angle feedback.
In accordance with a preferred aspect of the invention there is provided a
looper control system in hot strip mill comprising:
contact-less pulse encoders as sensors;
suitable interface for feeding accurate looper feed angle comprising means to
-convert the pulses sensed by the sensor to angular displacement; and means
to convert the angular displacement to analog voltage.
The above disclosed looper control system in hot strip mill of the invention
involves a PLC based system adapted to interface the pulse encoder output into
an analog output. The said PLC system is adapted to interface with said pulse
encoder output to convert the pulses to angular displacement and convert the
angular displacement to a proportional analog voltage. More specifically, the said
PLC is adapted to convert the pulses to angular displacement and corresponding
angular displacements are converted to analog voltage via an analog output
card.

In accordance with an aspect of the invention the looper control system in hot
strip mill comprises two types of pulse encoders preferably incremental type and
grey type.
In accordance with yet another preferred aspect of the invention there is
provided a looper control system in hot strip mill comprising:
five loopers;
contact-less pulse encoders as sensors wherein incremental encoders are
fixed for loopers 1 and 2 and grey type encoders are fixed for loopers 3 ,4
and 5;
suitable interface for feeding accurate looper feed angle comprising PLC
based means to convert the pulses sensed by the sensors to. angular
displacements; and PLC based means to convert the angular displacements
to analog voltages.
In particular, in the above preferred aspect of the looper control system for
incremental encoder one pulse counter card is provided in the PLC to read the
pulses from the incremental pulse encoder, the read pulses adapted to be
converted to angle in terms of degrees, means to convert the angle to
corresponding analog voltage (0 to 10 Volts) corresponding to (0 to 65
degrees) outputted through analog output card in the PLC; and for 10 bit
grey pulse encoder providing a digital input card in the PLC adapted to read
the status of the bits from the encoder and adapted to convert the grey
image to binary pattern which in turn was converted to angle and further to
corresponding analog voltage and outputted via an analog output card.
It is thus possible by way of the above discussed looper control system in hot
strip mill of the invention to achieve accurate angular movement measuring
device which would give angle feedback of looper table in terms of analog
voltage! Importantly, the looper control system is adapted to be a reliable
system, which can be calibrated according to the needs of the end user.

Also, the looper control system of the invention favour a contact-less device so
that failure of. devices due to failure of contact could be avoided and the system
would generate error free output on repeated application / use.
In the above disclosed looper control system for hot strip mill of the invention
advantageously and selectively a pulse encoder has been used for measuring the
angle of the looper table. Since the output of the pulse encoder is in pulses there
has been problem in directly interfacing such pulse encoder output with the
analog type conventional regulation system. The invention however also avoid
such problem and selectively involves the use of PLC to convert the pulses to
angular displacement and convert the angular displacement to an analog
voltage. The PLC based system is further adapted to convert the pulses to
angular displacement and corresponding angular displacement was converted to
an analog voltage via an analog output card.
In accordance with the preferred aspect of the invention the looper control
system for hot strip mills involves two types of pulse encoder (i) incremental
type pulse encoder and (ii) grey type pulse encoder. Use of both the types of
encoder for looper control system has been perfected and anyone type can be
used for looper control in hot strip mill. In particular, for the incremental encoder
a pulse counter card is provided in the PLC to read the pulses from the
incremental pulse encoder. The read pulses are converted to angle in terms of
degrees by suitable programme of the PLC. The converted angle is then
converted to corresponding analog voltage and the analog voltage (0-10 volts)
corresponding (0-65°) was outputted through analog output card in the PLC. In
case of the grey type pulse encoder digital input card is provided in the PLC
adapted to read the status of the bits from the encoder. The grey image is
converted to binary pattern by use of suitably programmed PLC. The
corresponding binary pattern is also converted to angle by a suitably
programmed PLC. The angle is finally converted to corresponding analog voltage
by the PLC system and outputted via an analog output card.
The details of the invention, its objects and advantages are explained hereunder
in greater detail in relation to the following non-limiting exemplary illustrations:

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1 is a schematic diagram of an absolute encoder based loop sensor in a
hot strip mill;
Figure 2 is a schematic illustration of the network of micro controllers for loopers
in hot strip mill
Figure 3 illustrates a module interconnection in accordance with the present
system
THE DETAILED DESCRIPTION OF THE ACCOMPANYING FIGURES
Reference is first invited to accompanying figure 1 which illustrates an absolute
encoder based loop sensor. As clearly illustrated in the said figure the system
basically involves a looper motor (LM) which is operatively connected to a
Potentiometer (POT) through gear mechanism at one end and to an absolute
encoder (AE) at its other end. The output from the encoder is fed into the digital
input card (DIC) for a PC based input, which is also provided with inputs from
the calibration switch (CS). The power supply (PS) is also adapted to supply to
the absolute encoder (AE). As shown in the figure the analog O/P card (AOC) of
PLC operatively connected to the digital input card (DIC) provides for a loop
angle feedback to the Simadyne C-drive (SCD).
Reference is now invited to accompanying figure 2 which illustrates the
arrangement for plurality of Simadyne- C for (SCD) for each of the loopers L-1
to L-5 and its operative connection to the incremental encoder (IE) for loopers 1
and 2 and to the Absolute Encoders (AE) for Loopers 3 to 5. As clearly illustrated
in the said figure in case of the incremental encoder the volt from the PLC PS is
utilized in the Simadyne C for looper L-1 and L-2 through counter module
loopers (L-1 - L-3) and analog output module to be finally transmitted as the
Simadyne C for each of the loopers L-1 - L-2.
In case of the absolute encoders (AE) the volt from PLC PS is utilized in the
Simadyne-C connected through the digital input card looper (L3-L-5) and
through the analog output module to be finally transmitted as the Simadyne C
for loopers L-3 - L-5.

Reference to now invited to accompanying figure 3 which illustrate the
mechanism of interconnection of the various components / gadgets used in the
looper control system in accordance with the present invention., As clearly
represented in the said figure for such purpose the looper motor (LM) is
operatively connected to the encoder (EN) via the coupling (CO) and the gear
box (GB). From the encoder a cable connection connects further to the junction
box (JB 5), which in turn is connected to the terminal connectors (powered by a
DC power source), counter card / digital I/P card, analog O/P card to finally
reach to the universal amplifier card via the change over switch (CS). The
provision of an existing angle transmitter (EAT) operatively connected to the
Change Over Switch (COS) is also shown in the figure. The output from the
Universal Amplifier Card is further forwarded to the Simadyn regulation.
It is thus possible by way of the present invention to provide for a looper control
system which would involve contact-less sensor adapted to feed accurate looper
angle feedback and thus avoid the limitations and disadvantages of contact
based sensors known for looper angle feedback. Importantly the above system
of the invention would avoid the complexities and need for potentiometer type
angle transmitters for such looper control. Thus the looper control system of the
invention would on one hand enable the use of contact-less sensors and on the
other hand favour integration of such contact-less sensors with existing
regulation of analog type.

WE CLAIM:
1. A looper control system in hot strip mill comprising:
means to measure the loop between two stands which is a function of the
angle of the looper table adapted to support the loop comprising contact-
less pulse encoders as sensors operatively connected and adapted to
suitably interface for feeding accurate looper angle feedback.
2. A looper control system in hot strip mill comprising:
contact-less pulse encoders as sensors;
suitable interface for feeding accurate looper feed angle comprising means
to convert the pulses sensed by the sensor to angular displacement; and
means to convert the angular displacement to analog voltage.
3. A looper control system in hot strip mill as claimed in anyone of claims 1
or 2 comprising
a PLC based system adapted to interface the pulse encoder output into an
analog output.
4. A looper control system in hot strip mill as claimed in anyone of claims 1
to 3 wherein said PLC system is adapted to interface with said pulse
encoder output to convert the pulses to angular displacement and convert
the angular displacement to analog voltage.
5. A looper control system in hot strip mill as claimed in anyone of claims 1
to 4 wherein said PLC is adapted to convert the pulses to angular
displacement and corresponding angular displacements are converted to
analog voltage via an analog output card.

6. A looper control system in hot strip mill as claimed in anyone of claims 1
to 5 comprising two types of pulse encoders preferably incremental type
and grey type.
7. A looper control system in hot strip mill comprising:
five loopers;
contact-less pulse encoders as sensors wherein incremental encoders are
fixed for loopers 1 and 2 and grey type encoders are fixed for loopers 3, 4
and 5;
suitable interface for feeding accurate looper feed angle comprising PLC
based means to. convert the pulses sensed by the sensors to angular
displacements; and PLC based means to convert the angular
displacements to analog voltages.
8. A looper control system as claimed in claim 7 wherein for incremental
encoder one pulse counter card is provided in the PLC to read the pulses
from the incremental pulse encoder, the read pulses adapted to be
converted to angle in terms of degrees, means to convert the angle to
corresponding analog voltage (0 to 10 Volts) corresponding to (0 to 65
degrees) outputted through analog output card in the PLC; and
For 10 bit grey pulse encoder providing a digital input card in the PLC
adapted to read the status of the bits from the encoder and adapted to
convert the grey image to binary pattern which in turn was converted to
angle and further to corresponding analog voltage and outputted via an
analog output card.
9. A looper control system in hot strip mill substantially as herein described
and illustrated with reference to the accompanying figures.

ABSTRACT

A LOOPER CONTROL SYSTEM IN HOT STRIP MILL
A looper control system in hot strip mill adapted to favour provision of loop
control involving contact-less sensors adapted to feed accurate looper angle
feed back. In particular the looper control system includes the looper motor
(LM) operatively connected to the encoder (EN) via the coupling (CO) and
the gear box (GB). From the encoder a cable connection connects further to
the junction box (JB 5), which in turn is connected to the terminal
connectors (powered by a DC power source), counter card / digital I/P card,
analog O/P card to finally reach to the universal amplifier card via the
change over switch (CS). The provision of an existing angle transmitter
(EAT) operatively connected to the Change Over Switch (COS) is also shown
in the figure. The output from the Universal Amplifier Card is further
forwarded to a Simadyn regulation. Advantageously, the above system of
the invention is adapted for contact-less sensors and interface of the
encoder signal with analog system to favour wide scale application and use
of the same for loop control in hot strip mills.