FIELD OF THE INVENTION:
The present invention is directed to a PLC based control system for multiple stand tandem
finishing mill of hot strip mill such as a six stand tandem finishing mill of Hot Strip Mill to
facilitate data entry related to the process parameters with ease and with reliability of
flexible and adaptable automation in operation/functioning of the system. More specifically,
the system of the invention is directed to a distributed control system based on Controllers,
Human Machine -Interface (HMI) systems, communication controllers and the like whereby
the sub-systems can be effectively and beneficially integrated for better user friendly
purposes to the operator of the system. The system of the present invention is adapted to
favour data entry in WinCC, calculations in WinCC as well as PLC with adaptability for
changeover to existing system to ensure minimal shut down and maximum plant output.
The system is directed to improve uptime and better diagnostic facility and favour
stabilization of finishing mill controls and elimination of mill interruptions and cobbles arising
out of malfunctioning of computer systems and is thus reliable with better availability, ease
of trouble shooting and effective interface with other automation equipment to achieve
overall integration of HSM operations.
BACKGROUND ART:
It is well known in the art of finishing stands operation of steel rolling mills that the speed
control of individual stand motors in the tandem rolling mill, plays an important role for
achieving necessary mechanical and metallurgical properties of the rolled product. The
speed reference is initially decided based on the material specification, material properties
at input to the tandem mill and the target parameters to be achieved in the rolled steel strip
product. Once the initial set points are calculated, the controller at the Level-I usually
carries out the dynamic speed control. Prevailing facility until recent past, included a First
Generation Computer(Siemens-R30) installed for speed control of the six stand tandem
finishing mill. The existing computer system having multi-programming, real time operating
System used to control the Speed of finishing Mill motors and the inter-stand loopers by
direct Digital Control. With the passage of time, various parts of the existing automation
and visualisation systems had become obsolete and reached their performance limits or the
due service dates had expired running the risk of plant breakdown or failing to meet the
customers' demand or quality compliance resulting in situations prone to incur substantial
financial loss.
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Importantly, the existing R30 Computer systems have become obsolete because no new
spare parts were made available by the original equipment manufacturer; The prospects of
maintenance and reliability of plant operation were very much unpredictable due to the
uncertainty in availability of critical spares like CPUs, Analog input cards and Counter cards
etc. Any failure of parts/components of the system crippled the production of HSM. In
addition to the non-availability of critical spares, usual depletion of skilled manpower due to
normal separation/turnover in respect of both operation and maintenance, prolonged the
downtime and the trouble shooting became an event of trial and error sequences.
There has thus been a persistent need to develop a new speed control system for finishing
stand motors, replacing the existing obsolete computer system and HMI interface, with an
efficient flexible and adaptable automation system as well as structured application software
fulfilling the functionalities of the existing system and other benefit attributes, more so in
terms of: (a) increased Plant availability and productivity; (b) Easy trouble shooting and
maintenance;(c) Interface with other automation equipment/subsystems in the HSM.
OBJECTS OF THE INVENTION:
It is thus the basic object of the present invention to provide for a PLC based control
system for speed control of multiple stand Tandem Finishing Mill motors of HSM,
eliminating down time due to want of obsolete spares and equipments experienced in the
existing R30 computer system, while providing all functions of the existing facility.
A further object of the present invention is to provide for a PLC based control system for
speed control of multiple stand Tandem Finishing Mill motors of HSM involving easier and
direct ways and means for troubleshooting and maintenance of the system.
A still further object of the present invention is directed to providing for a PLC based control
system for speed control of multiple stand Tandem Finishing Mill motors of HSM having
provision for speed control of finishing stand motors advantageously adapted to facilitate
future expansion and up-gradation of the system.
Another important object of the present invention is directed to integrating the speed
control system for the individual finishing stand motors with other subsystems in the HSM
plant, for favoured integrated control on product quality and economic operation.
3

A still further object of the present invention directed to speed control system for six stand
tandem finishing mill is to achieve low risk implementation of the new automation system,
switch over unit means installed in change over cabinets, for easy switch back to
conventional R30 automation system.
A further objective of the invention is directed to change over units in the new system,
which when implemented would activate the shadow mode of the new automation system,
parallel to actual production in order to verify functionalities like tracking, sequencing and
visualization, correct reception and distribution of parallel setup data, simulation of
functions and controls, communications with external systems.
A still further object of the present invention is directed to a speed control system for
finishing stand is to provide a switch over unit capable of duplication of the existing signals
without falsification of signal level with regard to the existing automation inputs.
A still further object of the present invention is directed to providing change over units for
desired speed control of finishing stand motors such as to ensure minimal shut down and
maximum plant availability during the conversion or change over.
According to a further object of the present invention directed to a new improved speed
control system for the finishing stand motors of the Hot strip mill is to stabilize the finishing
mill controls and elimination of mill interruptions and formation of cobbles due to
malfunctioning of faulty computer system.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a PLC based
speed control system for multiple stand tandem finishing mill of hot strip mill comprising:
A distributed control system comprising
control means involving a PLC system comprising Digital, Analog input & output
cards, Counter Cards and communication processors preferably adapted for TCP-IP
and PROFIBUS based communication; and
4

Human-machine-interface involving SIMANTIC WinCC, such as to impart flexible and
adaptable automation and structured application to favour availability, ease of
troubleshooting and interface with other automation equipments.
A further aspect of the present invention is directed to said PLC based speed control system
for multiple stand tandem finishing mill of hot strip mill wherein said distributed control
system is adapted to carry out the following functions:
a) data entry of process parameter variables and processing of such inputs;
b) calculating set points for speed reference to finishing mill motors and
parameters for the looper drives;
c) receiving process signals for mill operation status and reference change
requirements from process and modifying process output signals accordingly;
d) display important rolling parameters for operators guidance; and
e) data transfer to other systems through digital outputs as parallel data.
According to a still further aspect of the present invention directed to a PLC based speed
control system for multiple stand tandem finishing mill of hot strip mill wherein the system
is adapted to be structured to into different modules for data entry in WinCC, calculations in
WinCC as well as PLC , all process signal inputs and outputs through PLC with selective
algorithms to further support desired functionalities.
Another important aspect of the present invention is directed to said PLC based speed
control system for multiple stand tandem finishing mill of hot strip mill comprising switch
over units for desired switch over to and from existing automation (R30 automation).
5

A still further aspect of the present invention is directed to said PLC based speed control
system for multiple stand tandem finishing mill of hot strip mill adapted for shadow mode
operation parallel to actual production such as to verify:
i) tracking, sequencing and visualization;
ii) correct reception and distribution of parallel setup data;
iii) simulation of functions and controls; and
iv) communications with external systems.
According to yet another aspect of the present invention directed to said PLC based speed
control system for multiple stand tandem finishing mill of hot strip mill wherein all the
output signals are wired involving miniature relays and adapted to facilitate said change
over to and from the existing automation (R30 automation).
A still further aspect of the present invention directed to said PLC based speed control
system for multiple stand tandem finishing mill of hot strip mill wherein TCP/IP protocol
based communication is provided for interfacing PLC & HMI system.
The present invention and its objectives and advantages are described in greater details
with reference to the accompanying figures.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE:
Figure 1: is the Schematic Illustration of the system according to the present invention
involving PLC based speed control of motors for six stand tandem finishing mills, including
the change over unit for conversion to existing R30 control system or vice versa to achieve
controlled quality of steel strip product.
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DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING FIGURES
The present invention is directed to the PLC based new speed control system of individual
motors for the six stand tandem finishing mills of the Hot Strip Mill, providing same
functionality as of the conventional R30 system. As already described that the speed control
of individual stand motors is a vital function for achieving necessary mechanical and
metallurgical properties of the rolled product obtained at the output. The speed reference is
initially decided by based on the material specifications, material properties at input to the
tandem mill and the target parameters to be achieved. After the initial set points are
calculated, the dynamic control of the speed is usually done by the controllers at Level-I.
The purpose of the present computer control system is to achieve the same functionality of
R 30 computer having multi-programming, leal time Operating System used to control the
speed of finishing stand motors and inter-stand Loopers by a PLC based distributed control
system involving a PLC system comprising Digital, Analog input & output cards, Counter
Cards and communication processors preferably adapted for TCP-IP and PROFIBUS based
communication; and
Human-machine-Interface involving SIMANTIC WinCC, such as to impart flexible and
adaptable automation and structured application to favour availability, ease of
troubleshooting and interface with other automation equipments. The new PLC based
flexible and adaptable automation system is enabled with structured application software
developed for meeting the functional requirements of the existing system in operation for
speed control and looper position/angle control.
The present invention directed to said PLC based speed control system involving distributed
processing of data and HMI interfaced operators' input, for multiple stand tandem finishing
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mill of hot strip mill wherein said distributed control system is adapted to carry out the
following functions:
a) data entry of process parameter variables and processing of such inputs;
b) calculating set points for speed reference to finishing mill motors and
parameters for the looper drives;
c) receiving process signals for mill operation status and reference change
requirements from process and modifying process output signals accordingly;
d) display important rolling parameters for operators guidance; and
e) data transfer to other systems through digital outputs as parallel data.
Reference is now invited to the accompanying Figure 1, that illustrates the schematic
arrangement of the components and their interdependence, of the new system of
distributed processing to achieve the above functions, as well as a change over unit
interfaced with the present system to switch over to the existing conventional R30 system
of speed control of finishing stand motors or vice versa.
All the functions performed by the existing R30 system are achieved in the new PLC based
speed control system by transforming to a distributed control system based on controllers,
Human-Machine-Interface (HMI) systems. Communication Controllers etc. so that the
subsystems are integrated to provide the operator a synergistic view to the desired control
of parameters for attaining selective product attributes. PLC based speed control system
according to the present invention for multiple stand tandem finishing mili of hot strip mill
wherein the system is adapted to be operated on software developed and structured into
different modules For data entry in WinCC, calculations in WinCC as well as PLC , all process
signal inputs and outputs through PLC with special algorithms to further support desired
functionalities.
8

To comply with low risk implementation of the new PLC based speed control/automation
system for multiple stand tandem finishing mill of hot strip mill switch over units installed in
change over cabinet were provided for easy switch back to conventional R30 system such
that on activation of said unit is adaptec for shadow mode operation of new system parallel
to actual production, avoiding falsification of signal levels in regard to the existing
automation inputs, such as to verify:
v) tracking, sequencing and visualization;
vi) correct reception and distribution of parallel setup data;
vii) simulation of functions and controls; and
viii) communications with external systems.
The change over units ensured minimal shutdown and maximum plant availability by
effective and timely switchover from one system to the other. This included temporary
installation of both old and new controls as well as parallel operation via the same pulpit
desk attended by a single operator. All the output signals were wired using miniature relays
to facilitate change over from old system to new system and vice versa.
For interfacing the PLC based distributed control system and HMI system for operators data
input and visualization, TCP/IP protocol based communication has been used. Software
development and up-gradation was carried out according to the process requirements, with
flexibility of expansion and further improvement and achieve interfacing with other
subsystems in the HSM. The present system thus led to the stabilization of finishing mill
controls and elimination of mill interruptions. Also the occurrences of cobbles due to
variation of speed of rolls or mill interruption in any form, as a consequence of failure/fault
of the computer system are substantially controlled/minimized.
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It can be seen from the accompanying Figure 1, illustrating the new system of the speed
control of individual motors of the six stand tandem finishing mill in HSM, the raw field data
relating to Roll force, HMD signal, speed higher or lower signals and other process related
inputs are fed to the S7 400 PLC via a Input isolator corresponding to each stand for multi-
stand finishing rolling mill. Also the data relating to process variables such as the speed set
up, looper tension, Working Roll and Backup Roll Diameter, Pass Line etc are fed by the
operator as inputs to the WinCC HMI at operator's cabin interfaced to the same PLC, for
analysis and control for desired optimum product quality. The output from the PLC is fed to
the Finishing drive motors Fl to F6 on respective stands and inter-stand loopers 1 to 5 for
implementing desired control, via the change over unit, which in turn send data
corresponding to Speed reference to Drive Fl to F6 to SIMADYN-C panel, the looper control
parameters to the SIMADYN-C panel and relevant data to coiler computer. It is however,
possible by the operation of said change over unit to switch over to the existing R30 system
of computer control and to the PLC system for executing speed control of motors and looper
position based on control on process parameters, or vice versa, in the event of any fault
occurring in either system of control. As already stated that on activation of said change
over unit, shadow mode operation of new system runs parallel to actual production,
avoiding falsification of signal levels in regard to the existing automation inputs, such as to
verify tracking, sequencing and visualization; correct reception and distribution of parallel
setup data; simulation of functions and controls; and communications with external
systems.
It is thus possible by way of this invention to obtain a PLC based control system for speed
control of individual motors of multi stand tandem finishing mill of HSM to control rolling
speed of strips through different stands with a given starting material, such that desired
quality characteristics is maintained in terms of geometry and grade/metallurgical
properties of rolled product, by administering optimized process parameters. Further
10

according to the present system the trouble shooting and maintenance and reliability of the
entire plant or any subsystem thereof become easier with readily available spares. The
changeover unit provided and interfaced to both the existing R30 as well as the present PLC
provide more flexibility in operation reducing further the down time of plant. The system
developed is a low-cost solution based on currently available and popular platform and as
such the risk of obsolescence is minimized, providing the flexibility in the system for future
expansion and incremental improvement, after installation. The distributed PLC based
control system of the present invention can thus be adapted to any tandem rolling mill with
loopers with possible adaptability for the requirement of modifications depending on the
state of technology available at a particular plant and thus having immense potential for
wide industrial application for low cost control of HSM plants.
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WE CLAIM:
1. A PLC based speed control system for multiple stand tandem finishing mill of hot
strip mill(HSM) comprising:
A distributed control system comprising
control means involving a PLC system comprising Digital, Analog input & output
cards, Counter Cards and communication processors preferably adapted for TCP-IP
and PROFIBUS based communication; and
Human-machine-Interface involving SIMANTIC WinCC, such as to impart flexible and
adaptable automation and structured application to favour availability, ease of
troubleshooting and interface with other automation equipments.
2. A PLC based speed control system for multiple stand tandem finishing mill of hot
strip mill as claimed in claim 1 wherein said distributed control system is adapted to
carry out the following functions:
a) data entry of process parameter variables and processing of such inputs;
b) calculating set points for speed reference to finishing mill motors and
parameters for the looper drives;
c) receiving process signals for mill operation status and reference change
requirements from process and modifying process output signals accordingly;
d) display important rolling parameters for operators guidance; and
e)data transfer to other systems through digital outputs as parallel data.
3. A PLC based speed control system for multiple stand tandem finishing mil! of hot
strip mill as claimed in anyone of claims 1 to 2 wherein the system is adapted to be
structured to into different modules for data entry in WinCC, calculations in WinCC as
well as PLC , all process signal inputs and outputs through PLC with selective
algorithms to further support desired functionalities.
12

4. A PLC based speed control system for multiple stand tandem finishing mill of hot
strip mill as claimed in anyone of claims 1 to 3 comprising switch over units for
desired switch over to and from existing automation (R30 automation).
5. A PLC based speed control system for multiple stand tandem finishing mill of hot
strip mill as claimed in claim 4 adapted for shadow mode operation parallel to actual
productivity such as to verify :
a. tracking, sequencing and visualization;
b. correct reception and distribution of parallel setup data;
c. simulation of functions and controls; and
d. communications with external systems.
13
6. A PLC based speed control system for multiple stand tandem finishing mill of hot
strip mill as claimed in anyone of claims 1 to 5 wherein all the output signals are
wired involving miniature relays and adapted to facilitate said change over to and
from the existing automation (R30 automation) and vice versa.
7. A PLC based speed control system for multiple stand tandem finishing mill of hot
strip mill as claimed in anyone of claims 1 to 6 wherein TCP/IP protocol based
communication is provided for interfacing PLC & HMI system.
8. A PLC based speed control system for multiple stand tandem finishing mill of hot
strip mill substantially as hereindescribed and illustrated with reference to the
accompanying figures.

A PLC based speed control system for multiple stand tandem finishing mill of hot strip mill
(HSM), such as a six stand tandem finishing mill of Hot Strip Mill to facilitate data entry
related to the process parameters with ease and with reliability of flexible and adaptable
automation in functioning of the system. The system of the invention involves a distributed
control system comprising Controllers, Human Machine Interface (HMI) systems,
communication controllers and the like whereby the sub-systems can be effectively and
beneficially integrated for better user friendly purposes to the operator of the system. The
present invention is adapted to favour data entry in WinCC, calculations in WinCC as well as
PLC with adaptability for switchover to and from existing system to ensure minimal shut
down and maximum plant output. The system is capable to improve uptime and better
diagnostic facility and favour stabilization of finishing mill controls on cobbles arising out of
failure of computer systems.