A SYSTEM FOR AUTOMATIC CONTROL OF SIDE GUIDE MOVEMENT IN
THE FINISHING STANDS OF THE ROLLING MILLS
FIELD OF INVENTION
The present invention relates to a system for automatic control of side guide
movement in the finishing stands of the rolling mill for achieving optimum guide
gap for the hot bars / strips of different widths. More particularly, the invention
relates to the Design and development of a system for automatic control of side
guide movement in the finishing stands of the rolling mill using VWF (Variable
voltage Variable frequency) based digital drive system for individual guide motors.
BACKGROUND ART
In a Hot Strip Mill, slabs are rolled into strips and final product is in coil form. A
slab is first rolled in roughing stands and then it passes through a delay table and
then it enters into the finishing stands. The coil box and crop shear are located at
the end of the delay table. A crop shear is used to cut the head end and tail end
of transfer bar. The shear is located after coil box and before entry to finishing
stand F1. After finishing stands (F1 to F6) Strip passes through Runout table and
then finally goes to Coiler.
Side guides of finishing stands of HSM, RSP were operated by pushbuttons, relay
logic system and driven by three phase, 415 V, 180 L frame size, 10 KW AC slip
ring Induction motors. Encoders are connected with all guide motors those are
used to measure the guide gaps. By this system, guide operator is able to
achieve desired guide gap from strip edge within a range of -40 and + 40 mm
from the centre line. Based on existing hardware, precise control of side guide
movement is not possible. The operation of guide is solely manual, working on
contactor logic.
The limitation of the existing system is that the desirable gap cannot be adjusted
by the operator by any means. The only commands of guide open and guide
close works on contactor logic and it is very difficult to stop the guide motors in
absence of braking system. The encoders mounted with the motors are to be
used for calculating the guide gap. Both the side guides of any stand are
mechanically coupled with one shaft, which is finally coupled with the motor
through a gearbox arrangement.

It has been found that there are difficulties in opening and closing the guides
manually for required bar width because of the absence of close loop automation
system. Always Guide gap remains much higher than the desirable gap. It results
generation of Cobbles in the mill and a tendency of wobbling and telescopicity
build up in the coil. Most of the time there is a long chew end appears in the coil
resulting in the loss of metal. Also there are chances of delays in the mill due to
improper guide movement operation.
Automatic control of side guide movement in the finishing stands of the rolling mill
has been envisaged by development of automatic control system based on
installation of seven nos. of inverter grade squirrel cage induction motors, VVVF
based digital drives for individual motors, Encoders of 1024 PPR for all the
motors, New Mechanical couplings for all the motors with existing system etc.
In the existing mill at RSP (Rourkela steel plant), side guides of finishing stands of
HSM, RSP are operated by pushbuttons, relay logic system and driven by three
phase, 415 V, 180 L frame size, 10 KW AC slip ring Induction motors. The
movement of guide motors is manual and totally dependent on the operator. The
operator uses the pushbutton for opening and closing of the guides and the guide
motor is finally driven by the relay logic based system. Encoders are connected
with all guide motors to know the speed of motors those are used to measure the
guide gaps after certain calibration. By this system, guide operator is able to
achieve desired guide gap from strip edge within a range of -40 and + 40 mm
from the centre line. Based on existing hardware, precise control of side guide
movement is not possible.
Present speed of guide travel is 19.16 mm/sec. No braking system exists and
maximum distance of guide from centre is 855 mm on each side.
Such conventional Side guide movement system suffers from drawbacks /
disadvantages which are discussed hereunder:
A. Online correction of Side guide gap during rolling is not possible because
the motors cannot be stopped at the particular position precisely.
B. It is very difficult to control the Side guide movement as per the required
width of bar.

C. Desired position of Side guide is not possible due to absence of speed
control of guide motors.
OBJECTS OF THE INVENTION
It is therefore the principle object of the present invention is to precisely control
the side guide movement as per required width of bar / strip.
Another object of the present innovation is to sense the speed of guide motor and
know the position of the guide with great precision.
Yet another object of the present invention is the establishment of closed loop
feedback system to ensure proper opening and closing operation of guide.
Further object of invention is network design of different types of signals and to
generate MIS (Management Information System) for operator's interface. That is
to be achieved in the HMI (Human machine interface).
SUMMARY OF THE INVENTION
Thus, according to the present invention there is provided a system for Automatic
control of side guide movement in the finishing stands of the rolling mills, which is
reliable and provides precise guide gap as desired for rolling the slabs of
particular width.
Such as herein described is a system for Automatic control of side guide
movement in the finishing stands of the rolling mills comprises of: A plurality of
Inverter grade squirrel cage motors for all the guides. Same number of coupling
set matching to existing gearboxes and new motors with proper alignment; a
plurality of VVVF based digital drives with electrical braking for all the side guide
motors of finishing stands; a plurality of incremental encoders of 1024 PPR which
has been installed at the non drive end of the motors for sensing the motor speed
and finally the position of the guides; position control feature of the AC drive has
been used in this system for the automatic control of side guide movement and
guide gap adjustment; at least one programmable logic controller has been used
for processing of encoder signals and sending the reference signal to the drive
through the profibus.
With the present invention the Automatic control of side guide movement in the
finishing stands of the rolling mills has been possible with great precision.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1 illustrates the requirement of guide movement in accordance with the
present invention;
Fig 2 illustrates a block diagram of Automatic Side Guide Gap movement control
system in accordance with the present invention;
Fig 3 illustrates schematic of automatic control of Side guide movement in
accordance with the present invention;
DETAILED DESCRIPTION
Herein disclosed is a system for automatic control of side guide movement in the
finishing stands of the rolling mill for achieving optimum guide gap for the hot bars
/ strips of different widths.
Fig 1 shows the requirement of guide movement showing if planned slab width is
1250 mm, initially guides of all stands shall be opened for 1325 mm. As soon as
the head end of the bar bites F1 stand (to be known from F1 roll force), the guide
gap will be reduced to 1270 mm .Once strip is passed the stand the guide gap
again widen to 1325mm.This is repeated in all stands of finishing mill.
The system has been implemented in the crop shear stand guide and finishing
stand guide in the Hot Strip Mill of Rourkela Steel Plant of Steel Authority of India
Limited, which consists of hardware and software. The following are the hardware
components used for the disclosed automatic control of the side guide movement
in the finishing stands:
i) Seven numbers of three phase, 415 V , 8 pole , 11 KW , 180L frame size ,
inverter duty TEFC (totally enclosed fan cooled) squirrel cage induction motors
with extended shaft at non drive end for encoder mounting,
ii) Seven numbers of Self standing IP 41 VVVF drive panel having same
numbers of 46 A microcontrollers based three phase, inverter grade reversible,
digital variable voltage variable frequency drive with built in communication and
encoder feedback card. Drives also have dynamic braking resistances along with
suitable punch grid resistances. Line chokes shall also be considered for each
drive since motors are located at distances about 200m from drives,
iii) Seven numbers of hollow shaft incremental encoders with 1024 PPR
fitted at the non drive end of the motors.

iv) Seven numbers of mechanical coupling set matching to existing
gearboxes and motors with proper alignment.
v) A programmable logic controller having a central Processing Unit,
standard IO modules, Counter Module for processing the encoder signal, profibus
communication processor for communicating with drive profibus ports, profibus
connectors at drive and PLC ends.
The number of the hardware components may increase and/or decrease as per
the posed requirement in the rolling mill. The numbers has been provided only for
the purpose of explanation only. A person skilled in the art will be able to
understand the enhanced and distinguishing effect made through the said
automatic control and the usefulness of the disclosed system. It will be
appreciated by the person of skill in the art that various addition / alteration may
be made to the above described embodiments without departing from the scope
of the present disclosure.
New inverter grade motors have been used as the driving mechanism for the
shaft of individual guides. New encoders have been installed for measuring speed
of the motors. Digital drive regulation system for auto control of side guide motors
has been introduced for faster and precise response of the system. The control
logic for automatic control of side guide movement has been developed in-house
in the drive and PLC (Programmable logic Controller).
The software component consists of recent software like CT Soft used for
programming the drive parameters and Sypt pro for position control operation of
drive. The WinCC has been used for the HMI purposes in which datalogging and
operator display screens have been designed.
The communication between the drive and PLC is through profibus. The number
of commands from PLC to drives and then feedback to PLC takes place with the
said profibus only. The Ethernet communication has also been done for PC
connectivity with the network. All Three phase power cables, shielded encoder
cables and communication cables are laid and Gl conduits have been provided at
all vulnerable points. Effective dynamic braking has been introduced for braking
of motors in which punch grid type steel resistances have been used. The system

is able to rotate the guide motors in both the directions and stop them so that
precise opening and closing of guide may be achieved. The improved Guide gap
control system has highly enhanced the reliability of the guide operation during
rolling of hot coils.
The Guide gap control is possible during rolling. As shown in Fig 3, the new
system basically consists of WVF based digital drive system using new three
phase squirrel cage induction motors which will have speed feedback from
incremental encoder mounted on Non Drive End of the new squirrel cage
induction motor. The existing control desks are to be used for the new system. In
the new scheme, suppose if planned slab width is 1250 mm, initially guides of all
stands shall be opened for 1325 mm. As soon as the head end of the bar bites F1
stand (to be known from F1 roll force), the guide gap will be reduced to 1270 mm
.Once strip is passed the stand the guide gap again widen to 1325mm.This is
repeated in all stands of finishing mill.
The major components of the system are as follows:
WVF Digital Drive: The proposed drive is fully digital regulator based suitable
for 15 KW inverter duty motor for finishing stand guide and for crop shear guide
with profibus interface. A micro - processor based digital VVVF drive regulator
complete with associated interface cards and digital/analog l/Os, with PC
programmability including all standard protection features is there. Distance
between drive and motor is approx 200 m. Appropriate electrical accessories like
electrical chokes of suitable ratings are considered for fail proof operation of
drives. Reference to drive is position set points from PLC, jog switches etc and
output from drive are current, voltage, position actual, speed, faults etc.
Emergency switches to drives at panels and at operator desks at speed cabins
are the part of new system. Emerson make SP 3403 drives have been used for
this application.
The drive has following features:-
• Input frequency : 50 +/- 5 %
• Overload 150 % for 60 seconds.
• Overvoltage, Over current , phase loss protection , phase imbalance
protection and power wiring fault features

• Closed loop flux vector control
• Speed dependent current limit.
• Standard Inbuilt I Os module
• Drive able to work in position control mode
• Line choke of suitable rating at input side
• Sine filter of suitable rating at output.
• Able to work in Ambient temperature of 50 deg C
• Communication - profibus as well as Ethernet
• Encoder feedback technology box
• Door mounted LCD screen for program / monitor drive parameters
• Provision of programming the drive from local as well as remote.
• Able to communicate with Siemens S7-300 PLC ( Processor 314)
• PC based programming & status monitoring
• Once parameterized, drive is able to retain the parameters even in case of
power failure.
Squirrel Cage Induction Motor
Three Phase, 415 V, 8 poles, 11 KW, 180 L frame size, inverter duty TEFC
Squirrel cage induction motor for finishing stands guide and 01 no. three phase
415 V ,6 pole ,132 M ,5.5 KW Squirrel cage induction motor for crop shear guide.
Motor shaft is extended at NDE for encoder mounting. Motors have following
features.
• Motor winding - Copper
• Degree of protection - IP-55
• Cooling-IC-411
• Ambient temperature - 50 deg C
• Insulation- F class (Minimum)
• duty cycle - S4
The inverter duty motors have been selected because they can generally run full
torque at low speed and can operate well above standard motor base speeds
reliably. There are possibilities of premature failures of motor insulation system
with the introduction of fast switching drives. These can be avoided by using
inverter duty motors. ABB make special motors have been used for this purpose.

Incremental Encoder
Optical incremental hollow shaft type encoders - with resolution 1024 PPR
having cable and connector outputs have been used. Matching housing diameter
and shaft diameter of encoders have been mounted with the extended shaft of
the supplied motors. Operating temperature of encoders is to be upto + 100 Deg
C and protection class to be IP 65. Hubner make encoder has been used for this
purpose.
The schematic block diagram of the system is shown in Fig 2. Three types of
cables namely power cable, encoder cable and profibus cable have been used as
shown. CTnet and Ethernet cable are also used for drive and PC communication.
Programmable Controller System:
Programmable Controller system consists of Central Processing Unit, Counter
module and Standard input output modules. Programmable Controller of any
make shall serve the purpose. The counter module should be bidirectional i.e. it
should have provision to connect Direct Pulse (0°), Quadrature Pulse (90°),
Marker Pulse (N) and Inverted pulses of all. The profibus communication
processor has been used for communicating with drive profibus ports .Siemens
make S7-300 PLC (314 processor) with 342-5 profibus communication module
has been used for this particular invention.
Two numbers of programming terminals (PCs with second generation Intel
processors) have been used for different purposes. One PC has been used for
programming the digital drives. The drive programming software CT Soft has
been loaded for the purpose of programming the drive parameters and Software
like sypt pro has been loaded for position control operation of the drive. A
program for position control for the auto movement of side guide has been written
in high level languages. A suitable OPC platform has also been used for proper
communication.
The other computer has been loaded with Siemens make SCADA called WinCC
that has been used for the HMI purposes in which data logging and operator
display screens have been designed. However any other SCADA may work for
this purpose.

Transducers, metering accessories for sensing current, voltage and RPM are
used in the system for the display of different indications.
Usefulness of the Invention
The system thus provides precise speed control of Side guide motors. Further
electrical braking has been introduced with the introduction of new VVVF drives
as per the demand of the system. Open and close operation of the Side guides is
possible automatically for required bar width. The response of the system has
become faster due to digital drive regulation. Guide Operator is able to achieve
desired guide gap from strip edge within the desired +/-10 mm or even less from
centre.
In summary, Side Guide Auto movement System has better control and braking
as dynamic braking has been introduced. Introduction of WVF based digital
drive enables the position control of guides to operate in a closed loop manner. A
Plant now has a complete freedom to close / open the guide as per their process
requirements with the new side guide gap position control system. The HMI
screen displays all the necessary features of the guides on one page. The
number of delay hours and cobbles in the finishing mill area that were generated
due to improper guide operation is expected to be reduced with the new system.
A significant reduction in tail end chew has been resulted in the strip with the new
system.
Industrial Applicability
A system has been designed and developed in house for the Side guides of
finishing stands as well as crop shear of hot strip mill at Rourkela steel plant of
SAIL (Steel authority of India Ltd). Procurement of Miscellaneous equipments of
different make, software etc used has been done by Research and development
centre of Iron and steel, SAIL and System has been installed and commissioned
at Hot strip mill, Rourkela steel plant.
Numerous modifications may be made to the present invention, which still fall
within the intended scope hereof. Thus, it should be apparent that there has been
provided in accordance with the present invention a system for automatic control
of side guide movement in the finishing stands of the rolling mills that fully
satisfies the objectives and advantages set forth above. Although the invention

has been described in conjunction with specific embodiments thereof, it is evident
that many alternatives, modifications and variations will be apparent to those
skilled in the art. Accordingly, it is intended to embrace all such alternatives,
modifications and variations that fall within the spirit and broad scope of the
appended claims.

WE CLAIM:
1. A system for automatic control of side guide movement in the finishing
stands of the rolling mills comprises of:
a plurality of inverter grade squirrel cage motors for all the guides with same
number of coupling sets matching to gearboxes and motors with proper
alignment;
a plurality of VWF based digital drives with electrical braking for all the side guide
motors of finishing stands;
a plurality of incremental encoders of 1024 PPR installed at the non-drive end of
the motors for sensing the motor speed and finally the position of the guides; and
at least one programmable logic controller configured for processing of encoder
signals and sending the reference signal to the drive through the profibus.
2. A system for automatic control of side guide movement in the finishing
stands of the rolling mills as claimed in claim 1, wherein the VWF based digital
drives ensures controlled movements of guide motors and the inverter grade
squirrel cage motors ensures better control and fail proof operation.
3. A system for automatic control of side guide movement in the finishing
stands of the rolling mills as claimed in claim 1, further includes digital encoders
for a closed loop feedback system.
4. A system for automatic control of side guide movement in the finishing
stands of the rolling mills as claimed in claim 1, wherein the position control
feature of the AC drive controls of side guide movement and guide gap
adjustment.
5. A system for automatic control of side guide movement in the finishing
stands of the rolling mills as claimed in claim 1, wherein position control loop of
the drive ensures improved regulation of guide movement.
6. A system for automatic control of side guide movement in the finishing
stands of the rolling mills as claimed in claim 1, wherein the programmable
controller further comprises Central Processing Unit, Counter module and
standard input output modules and profibus modules.

7. A system for automatic control of side guide movement in the finishing
stands of the rolling mills as claimed in claim 1, wherein the programmable
controller processes the encoder outputs in counter module to determine the
speed and position of the drive.
8. A system for automatic control of side guide movement in the finishing
stands of the rolling mills as claimed in claim 1, wherein the data transfer from
drive to controller happens through the profibus instantly.
9. A system for automatic control of side guide movement in the finishing
stands of the rolling mills as claimed in claim 1, wherein the reference signals and
acknowledgment signals are transmitted simultaneously.
10. A system for automatic control of side guide movement in the finishing
stands of the rolling mills as claimed in preceding claims, wherein an Ethernet
network is provided between drives and programming units.

ABSTRACT

A system for automatic control of side guide movement in the finishing stands of the rolling mills comprises of: a plurality of inverter grade squirrel cage motors for all the guides with same number of coupling sets, matching to gearboxes and motors with proper alignment; a plurality of VVVF based digital drives with
electrical braking for all the side guide motors of finishing stands; a plurality of incremental encoders of 1024 PPR installed at the non-drive end of the motors for sensing the motor speed and finally the position of the guides; and at least one programmable logic controller configured for processing of encoder signals and
sending the reference signal to the drive through the profibus.