FIELD OF THE INVENTION
The present invention relates to a control system for drives of Crop Cum Cobble (CCC)
Shear, Rotary Shear and Pinch Roll of Merchant Mill for stabilized rolling by adjusting field
current and armature voltage to eliminate front end hook cut/ bends and thereby improve
mill availability. More particularly, the invention is directed to providing a closed loop speed
control system for the said drives for improved accuracy of cutting implemented through
digital thyristor drives, with provision of changeover switches at drive end. Hierarchical
automation system has been used with all drives and PLCs on PROFIBUS on one level and
supporting Ethernet network on the higher level of automation, advantageously eliminating
conventional thumb wheel used for setting of roll diameter, lead speed , torque limit etc.
Digital drives have been used for controlling armature & field of Crop Cum Cobble Shear ,
Rotary Shear and Pinch Roll. All the real time field signals are accessed by a PLC system
installed in Electrical Control Room. Digital and analog values of stand motors along with
trending in user friendly formats are made available in HMI (interfaced with new as well as
old PLC) installed at ECR . The control system according to the present invention is adapted
for advantageous installation in Merchant Mill with installation of TMT production facility,
Crop-cum-Cobble shear, Slit rolling process for producing TMT bars in integrated steel
plants/rolling mills.
BACKGROUND OF THE INVENTION
Merchant Mill is one of the applicants steel plant having an installed production capacity of
2,40,000 T. Subsequently, modernization took place in Merchant Mill with installation of TMT
production facility, Crop-cum-Cobble shear, Slit rolling process for producing 16mm TMT
bars and automatic bundling and binding machine. Production capacity was enhanced to
2,80,000 T. The merchant mill is a 4 repeater continuous bar & rod mill with slit rolling
facility. The products of merchant mill are plain rods (IS 2062) & TMT bars (TMT 415 /TMT
500//TMT 550) ranging from 16 to 28 mm . Incidentally, production of merchant mill is
more than rated capacity since 2000-01.Slabs are rolled through seven number roughing
mill stands. Crop is cut at Crop-cum-Cobble shear after seventh stand. The output of
roughing stand passes though intermediate stands #8 to #11 and finally through finishing
stands #12 & #14. Rolled bars/rods pass through pinch roll, and finally get into pieces in
Rotary shear.

Problems were faced earlier mainly in crop cum cobble shear, rotary shear & pinch roll
drives due to the malfunctioning of the age old regulating cards of controller, malfunctioning
of field devices , relay logic , operator interface etc. In case of any problem related to drive,
diagnostic tools are not available leading to increased downtime. Moreover, spares
availability were almost nil for age-old electronic control unit which became obsolete
during course of time.
There has been thus a need in the existing art to developing an improved speed control
system for drives crop cum cobble shear, rotary shear & pinch roll to enable precise cutting
of rolled bars and eliminate front end hook cut/bends and thereby improve mill availability.
OBJECTS OF THE INVENTION
The basic object of the present invention is directed to providing a closed loop speed
control system for drives of Crop Cum Cobble Shear, Rotary Shear and Pinch Roll of
Merchant Mill for stabilized rolling.
Another object of the present invention is directed to providing a closed loop speed control
system to control speed of shear and stand motors by adjusting field current and armature
voltage for Precise & optimized cutting of bars, round / TMT rods in motion.
A further object of the present invention is directed to providing a closed loop speed
control system for drives of Crop Cum Cobble Shear, Rotary Shear and Pinch Roll of
Merchant Mill for improved accuracy of cutting by elimination of thumb wheel used for
setting of roll diameter, lead speed , torque limit etc.
A still further object of the present invention is directed to providing a closed loop speed
control system for drives of Crop Cum Cobble Shear, Rotary Shear and Pinch Roll of
Merchant Mill wherein digital thyristor drives, with provision of changeover switches at drive
end would be used for precise speed control of drives to ensure stabilized rolling.
A still further object of the present invention is directed to providing a closed loop control
system for the drives of Crop Cum Cobble Shear, Rotary Shear and Pinch Roll so that the

shear speed can be synchronized with the transfer bar/rod speed for precise cutting of the
bar/ rod.
A still further object of the present invention is directed to providing a closed loop speed
control system for drives of Crop Cum Cobble Shear, Rotary Shear and Pinch Roll of
Merchant Mill wherein the system ensure better speed control with fast response, optimized
cutting, better diagnostics and availability of user/operator friendly HMI.
A still further object of the present invention is directed to providing a closed loop speed
control system for drives of Crop Cum Cobble Shear, Rotary Shear and Pinch Roll of
Merchant Mill wherein armature of individual motors for CCC Shear , Rotary Shear and Pinch
Roll have been controlled by digital converters with speed feedback & emf feedback.
A still further object of the present invention is directed to providing a closed loop speed
control system for drives of Crop Cum Cobble Shear, Rotary Shear and Pinch Roll of
Merchant Mill wherein introduction of PLC with installed control logic has eliminated use of
thumb wheel switch used for settings roll diameter, lead speed, torque limit etc. which in
turn has improved the accuracy of cutting.
Yet another object of the present invention is directed to providing a closed loop speed
control system for drives of Crop Cum Cobble Shear, Rotary Shear and Pinch Roll of
Merchant Mill to ensure improved operators' safety features & equipment ( motor & gear
box) safety through introduction of logic for blade jam sensing.
A still further object the present invention is directed to providing a closed loop speed
control system for drives of Crop Cum Cobble Shear, Rotary Shear and Pinch Roll of
Merchant Mill which would be capable to generate MIS( Management Information System)
for operators' interface.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a closed loop speed control system
for drives of Crop Cum Cobble (CCC) Shear, Rotary Shear and Pinch roll of Merchant Mill
for stabilized rolling comprising
digital drives for each said CCC Shear , Rotary Shear and Pinch Roll;

incremental encoder means for measuring speed of stand and shear motors,
absolute encoder means for sensing of position of the crop shear blade and another
one for sensing position of rotary shear blade;
digital drive regulation system for each said crop shear , rotary shear and pinch roll
motors to ascertain better speed regulation of said shear motors;
a programmable controller means having a central Processing Unit, Counter Module for
processing said encoder signals, analog output module for generating corresponding
speed output;
said programmable controller means adapted for processing the output from the said
encoders of said speeds of stand motors & shear motors and shear blade positions
and scanned over a regular interval and reading the analog inputs , speed feedback
from incremental encoders , position feedback from absolute encoders and several
digital inputs including interlock information and generating references for drives and
cut command for said Rotary Shear & CCC Shear.
A further aspect of the present invention is directed to a closed loop speed control system
comprising
microprocessor based digital drive system for said CCC shear , rotary shear and
pinch roll motors for speed regulation , better speed control response and cutting
accuracy;
incremental encoders for sensing stand speeds, and absolute encoders for crop and
rotary shear blade shaft positions;
Programmable Controller means to process the analog inputs , speed feedback
from incremental encoders , position feedback from absolute encoders and several
digital inputs including interlock information and to generate said references for
drives and cut command for Rotary Shear and CCC Shear;

PLC and Drives network configuration comprising Hierarchical automation system
with all drives and PLCs on PROFIBUS on one level and supporting Ethernet
network on the higher level of automation.
A still further aspect of the present invention is directed to a closed loop speed control
system, comprising said Digital Drives of Start / Stop installed in Self Standing Panel
comprising
i) for controlling armature & field of Crop-Cum-Cobble Shear having
Microcontroller based, three phase, 6 pulse, four quadrant ( 4Q ), reversible,
regenerative, thyristorised, digital DC converter suitably rated for DC motor 380 KW
, 460V DC, 1500 rpm with built in communication , incremental encoder feedback
card (lno) as well as provision for analog tacho feedback card ( 1 no),
Microcontroller based single quadrant (1Q), thyristorised, digital DC converter for
motor field current of 14 A at voltage level of 220V DC ;
ii) for controlling armature & field of Rotary Shear Motor having Microcontroller
based, three phase, 6 pulse, four quadrant ( 4Q ), reversible, regenerative,
thyristorised, digital DC converter rated for 300 KW , 460V DC , rated armature
current 725 A , 300 rpm with built in communication , incremental encoder feedback
card ( 1 no ) as well as provision for analog tacho feedback card ( 1 no) ,
Microcontroller based, single quadrant ( 1Q ), thyristorised, digital DC converter
rated for motor field current 22.5A at voltage level of 220VDC;
iii) for controlling armature & field of Pinch Roll having Microcontroller based, three
phase, 6 pulse, four quadrant ( 4Q ), reversible, regenerative, thyristorised, digital
DC converter for DC motor of 25KW , 65Amp, 460 V DC with built in communication
and incremental encoder feedback card ( 1 no);
Microcontroller based, single quadrant ( 1Q ), thyristorised, digital DC converter for
motor field current of 5.21 Amp, at a voltage level of 220 VDC.
A still further aspect of the present invention is directed to a closed loop speed control
system, comprising
(i) One set of said Self standing panel comprising of 3 nos of digital drives for
CCC Shear , Rotary Shear and Pinch Roll;
(ii) Six nos. of said Incremental Encoder adapted for measuring speed of stand
and shear motors,

(iii) Two nos. of said Absolute Encoder , one for sensing of position of the crop
shear blade and another one for sensing position of rotary shear blade;
(iv) said three digital drive regulation system for the crop shear , rotary shear
and pinch roll motors adapted to ascertain better speed regulation of
shear motors.
(v) said programmable controller having a central Processing Unit, Counter
Module for processing the Encoder signal, Analog output module for
generating 0-10 V DC which corresponds to the speed.
A still further aspect of the present invention is directed to a closed loop speed control
system, wherein said digital drive system provides for Crop Cum Cobble Shear, rotary
shear and Pinch Roll for better speed control, optimized cutting , better diagnostics and
availability of HMI.
Yet another aspect of the present invention is directed to a closed loop speed control system
as claimed in anyone of claims 1 to 5 , wherein said programmable controller comprises
Central Processing Unit, Counter module and analog output module adapted to process the
analog inputs and several digital inputs including interlock information and generates set
points for digital drives which controls precisely the speeds of shear motors with faster
speed control response and cutting accuracy.
A further aspect of the present invention is directed to a closed loop speed control system,
wherein all said digital thyristor converters operate in closed loop mode with speed
references from PLC and speed feedback being provided by high accuracy incremental
encoder and wherein the combination of digital thyristor converter and incremental encoder
have provision of on-line trouble shooting using PC / Programmer, having provision for
feed back with CEMF (counter emf) or speed (configurable) through galvanic signal isolators
and also having provision of trending and data logging at HMI.
A still further aspect of the present invention is directed to a closed loop speed control
system wherein there are two said PLC systems housed in two PLC panels of suitable
dimensions, a 1st PLC system provides for controlling Crop Cum Cobble Shear and
associated equipment activities where as a 2nd PLC system provides for controlling Rotary
Shear & Pinch Roll and associated activities, each PLC system comprising CPU, Power
Supply, communication processor, I/O racks, and Power supply for I/O rack, I/O modules

and high speed counter modules, said counter module are capable of up / down counting of
at least 105 pulses.
A still further aspect of the present invention is directed to a closed loop speed control
system, wherein said PLCs are connected to programming station / HMI station through
Ethernet communication, with said drives connected to respective PLCs Profibus
communication and wherein the input power to PLC and interrogation supply is 24V DC.
A still further aspect of the present invention is directed to a closed loop speed control
system wherein said two PLC systems are having local I/Os as well as remote I/O station at
control pulpits.
Yet another aspect of the present invention is directed to a closed loop speed control
system, wherein all the real time field signals are accessed by a PLC system installed in
Electrical Control Room and digital and analog values of stand motors along with trending
in user friendly formats are provided in HMI (interfaced with new as well as old PLC)
installed at electrical control room.
A further aspect of the present invention is directed to a closed loop speed control system,
wherein the drive panel is provided with natural air cooling or forced air cooling by low noise
& vibration free ventilation fans at the top of cubicle / panel which sucks such air through
the modules, where the air inlet to the cubicle is allowed through suitable filter arrangement
and through the cubicle / panel vane with provision for switch for air flow monitoring.
The details of the innovation, its objects and advantages are explained in great details in
relation to non limiting exemplary embodiments of the closed loop speed control system as
illustrated in the following accompanying figures.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1: shows the Electrical Schematic Diagram of the implemented drive for Crop Cum
Cobble Shear.
Figure 2: shows the Electrical Schematic Diagram of the implemented drive for Rotary
Shear.

Figure 3: shows the Electrical Schematic Diagram of the implemented drive for Pinch Roll.
Figure 4: shows the PLC and Drives network configuration.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING FIGURES
The present invention is directed to providing a closed loop control system for drives of
Crop Cum Cobble (CCC) Shear, Rotary Shear and Pinch Roll of Merchant Mill for stabilized
rolling for controlling speed by adjusting field current and armature voltage to eliminate
front end hook cut / bends to thereby improving mill availability and to provide precise
cutting length.
The said closed loop control system according to the present invention comprises of :
1 set Self Standing IP 41 Panel comprising Digital Drives- Start / Stop type, wherein
i) for controlling armature & field of Crop-Cum-Cobble Shear having :
Microcontroller based, three phase, 6 pulse, four quadrant ( 4Q ), reversible, regenerative,
thyristorised, digital DC converter suitably rated for DC motor 380 KW , 460V DC, 1500
rpm with built in communication , incremental encoder feedback card (lno) as well as
provision for analog tacho feedback card ( 1 no);
Microcontroller based single quadrant (1Q), thyristorised, digital DC converter for motor
field current of 14 A at voltage level of 220V DC;
ii) for controlling armature & field of Rotary Shear Motor having
Microcontroller based, three phase, 6 pulse, four quadrant ( 4Q ), reversible, regenerative,
thyristorised, digital DC converter rated for 300 KW , 460V DC , rated armature current
725 A , 300 rpm of Kirloskor make with built in communication , incremental encoder
feedback card ( 1 no ) as well as provision for analog tacho feedback card ( 1 no)
Microcontroller based, single quadrant ( 1Q ), thyristorised, digital DC converter rated for
motor field current 22.5A at voltage level of 220VDC
iii) For controlling armature & field of Pinch Roll having
Microcontroller based, three phase, 6 pulse, four quadrant ( 4Q ), reversible, regenerative,
thyristorised, digital DC converter for DC motor of 25KW , 65Amp, 460 V DC with built in
communication and incremental encoder feedback card - 1 no.

Microcontroller based, single quadrant ( 1Q ), thyristorised, digital DC converter for motor
field current of 5.21 Amp, at a voltage level of 220 VDC.
With the present innovation, better speed control, optimized cutting , better diagnostics and
availability of HMI have been achieved in Merchant Mill.
The system consists of hardware and software. The following are the hardware components;
i) One set of Self standing IP 41 panel comprising of 3 nos of digital drives for CCC Shear
, Rotary Shear and Pinch Roll;
ii) Six nos. of Incremental Encoder of 1024 PPR for measuring speed of stand and
shear motors,
iii) Two nos. of Absolute Encoder of 1024 PPR , one for sensing of position of the crop
shear blade and another one for sensing position of rotary shear blade;
iv) Also three digital drive regulation system for the crop shear , rotary shear and pinch
roll motors which have been installed to ascertain better speed regulation of shear
motors,
v) A programmable controller having a central Processing Unit, Counter Module for
processing the Encoder signal, Analog output module for generating 0-10 V DC which
corresponds to the speed;
The software component consists of a program through which the output from the encoders
(speeds of stand motors & shear motors and shear blade positions ) are processed in a PLC
and scanned over a regular interval. The control software reads the analog inputs, speed
feedback from incremental encoders , position feedback from absolute encoders and several
digital inputs including interlock information and generates references for drives and cut
command for Rotary Shear & CCC Shear.
The details of the hardware components are described as below:
(A) Drive and thyristor converter:
The implemented controller is fully digital regulator based. The bridge converter
includes a 3 phase, full wave, four quadrant bridge having suitable rating for
armature control and microcontroller based single quadrant (1Q), thyristorised,

digital DC converter for field control with micro - processor based digital DC drive
regulator complete with associated interface cards and digital/analog I/Os, with PC
programmability to excite and regulate the armature & field voltage.
Thyristor converter system for DC drives is comprising of following main units:-
i) Digitally controlled thyristorised converters for armature & field.
ii) AC Power circuit devices.
iii) Meters on AC & DC side
iv) Regulation & control equipment.
v) Protection, indication & annunciation units.
vi) over voltage protection system to protect the converter in order to reduce the energy
in the field circuit if the input voltage fails.
vii) Inherent scheme for field failure protection .
All digital thyristor converters are working in closed loop mode with speed references from
PLC and speed feedback being provided by high accuracy incremental encoder. The
combination of digital thyristor converter and incremental encoder has the capability to
achieve very high degree of speed and torque control accuracies, which is demanded from
the control system. Converters have provision of on-line trouble shooting using PC /
Programmer.
The converter is also having provision for feed back with CEMF (counter emf) or speed
(configurable). The feedback is through galvanic signal isolators. Converters are also having
provision of trending and data logging at HMI
(B) PLC system (2 nosl:
There are 2 nos PLC systems housed in two PLC panels of suitable dimensions. Each PLC
system consists of CPU, Power Supply, communication processor, I/O racks, and Power
supply for I/O rack, I/O modules and high speed counter modules. The counter module
used is capable of up / down counting of at least 105 pulses. The 1st PLC system is used for
controlling Crop Cum Cobble Shear and associated equipment activities where as the 2nd
PLC system is used for controlling Rotary Shear & Pinch Roll and associated activities. The
PLCs are connected to programming station / HMI station through Ethernet

communication. Drives have been connected to respective PLCs Profibus
communication. The input power to PLC and interrogation supply is 24V DC.
The two PLC systems are having local I/Os as well as remote I/O station at CP#4 and
CP#10 respectively.



(C) DRIVE & PLC PANEL
The panels are dust and vermin proof and the degree of protection for enclosures are IP-
41.
The drive panel is provided with natural air cooling or forced air cooling by low noise &
vibration free ventilation fans at the top of cubicle / panel which sucks such air through the
modules. The air inlet to the cubicle is through suitable filter arrangement and through the
cubicle/panel vane. Switch for air flow monitoring has also been incorporated.
The software components include: PLC System software (2 sets) which are Programming
software for the PLC for configuration of the hardware and programming the PLC, HMI
Software (2 sets) for Human machine Interface with 32K tag with Run time + Development
package and HMI Software ( 2 sets ) for Human machine Interface with 32K tag with Run
time package.
The closed loop control system according to the present invention thus provides Precise &
optimized cutting of bars, round / TMT rods in motion. With the implementation of the
system the electrical downtime has reduced by 50% due to better fault diagnostics &
proper speed controls of shear and stand motors.
Reference is first invited to Figure 1 where new digital drives along with inputs and outputs
have been shown for Crop Cum Cobble (CCC) Shear with change over scheme.

Also the accompanying Figure 1, illustrates the drive functioning through armature control
and field control. Inputs like speed set point, speed feedback from encoder of CCC shear
motor, current feedback, armature voltage feedback have also been shown.
Reference is invited to Figure 2, where new digital drives along with inputs and outputs
have been shown for Rotary Shear with change over scheme.
Attention is now invited to the accompanying Figure 2, which is the illustration of the drive
functioning through armature control and field control
Reference is invited to Figure 3, where new digital drives along with inputs and outputs
have been shown for Pinch Roll with change over scheme.
Accompanying Figure 4 shows the PLC and Drives network configuration. It can be noted
that hierarchical automation system has been used with all drives and PLCs on PROFIBUS
on one level and supporting Ethernet network on the higher level of automation.
The system has been implemented successfully on trial in the Crop Cum Cobble Shear ,
Rotary Shear & Pinch roll in the Merchant Mill of applicants' Steel Plant . Weekly shutdown
day has been used for installation of self standing IP 41 panel comprising of digital drives (
start / stop type ) , PLC panel , Remote I/O panel , transducers , metering and accessories ,
incremental & absolute encoders , annunciation panel , programming & HMI terminals.
Digital drives have been used for controlling armature & field of Crop Cum Cobble Shear ,
Rotary Shear and Pinch Roll.
Under implemented scheme, analog thyristorised drives of CCC, Rotary Shear and pinch roll
drives have been replaced with digital thyristor drives, with provision of changeover
switches at drive end. Hierarchical automation system has been used with all drives and
PLCs on PROFIBUS on one level and supporting Ethernet network on the higher level of
automation.
The jobs carried out for implementing the system are the followings:
(i) Design and Development of closed loop speed control system to improve
yield, to reduce cobble generation and off-dimension in at merchant rolling
mill, using state-of-the-art digital drives, encoder, Programmable controller
and controlling devices,
(ii) Installation of encoders for sensing stand speed,
(iii) Interfacing of signals to PLC.
(iv) Programming & commissioning of digital regulators.

(v) Transferring logic of old PLC to new PLC.
(vi) Integrated trial run of the control system including ail the drives.
(vii) Fine tuning of the total control system including appropriate change in PLC
and drive logic.
(viii) Evaluation of speed control response and cutting accuracy
It is thus possible by way of the present invention system to perform closed loop speed
control with faster response which has improved cutting accuracy of bar / rod and yield of
mill , reduced cobble generation and off-dimension at Merchant Mill, thus favouring wide
industrial application.

We Claim:
1. A closed loop speed control system for drives of Crop Cum Cobble (CCC) Shear, Rotary
Shear and Pinch roll of Merchant Mill for stabilized rolling comprising
digital drives for each said CCC Shear, Rotary Shear and Pinch Roll;
incremental encoder means for measuring speed of stand and shear motors;
absolute encoder means for sensing of position of the crop shear blade and another
one for sensing position of rotary shear blade;
digital drive regulation system for each said crop shear , rotary shear and pinch roll
motors to ascertain better speed regulation of said shear motors;
a programmable controller means having a central Processing Unit, Counter Module for
processing said encoder signals, analog output module for generating corresponding
speed output;
said programmable controller means adapted for processing the output from the said
encoders of said speeds of stand motors & shear motors and shear blade positions
and scanned over a regular interval and reading the analog inputs , speed feedback
from incremental encoders , position feedback from absolute encoders and several
digital inputs including interlock information and generating references for drives and
cut command for said Rotary Shear & CCC Shear.
2. A closed loop speed control system as claimed in claim 1 comprising
microprocessor based digital drive system for said CCC shear , rotary shear and
pinch roll motors for speed regulation , better speed control response and cutting
accuracy;
incremental encoders for sensing stand speeds, and absolute encoders for crop and
rotary shear blade shaft positions;

Programmable Controller means to process the analog inputs , speed feedback
from incremental encoders , position feedback from absolute encoders and several
digital inputs including interlock information and to generate said references for
drives and cut command for Rotary Shear and CCC Shear;
PLC and Drives network configuration comprising Hierarchical automation system
with all drives and PLCs on PROFIBUS on one level and supporting Ethernet
network on the higher level of automation.
3. A closed loop speed control system as claimed in anyone of claims 1 or 2 , comprising
said Digital Drives of Start / Stop installed in Self Standing Panel comprising
i) for controlling armature & field of Crop-Cum-Cobble Shear having
Microcontroller based, three phase, 6 pulse, four quadrant ( 4Q ), reversible,
regenerative, thyristorised, digital DC converter suitably rated for DC motor 380 KW
, 460V DC, 1500 rpm with built in communication , incremental encoder feedback
card (lno) as well as provision for analog tacho feedback card ( 1 no),
Microcontroller based single quadrant (1Q), thyristorised, digital DC converter for
motor field current of 14 A at voltage level of 220V DC ;
ii) for controlling armature & field of Rotary Shear Motor having Microcontroller
based, three phase, 6 pulse, four quadrant ( 4Q ), reversible, regenerative,
thyristorised, digital DC converter rated for 300 KW , 460V DC , rated armature
current 725 A , 300 rpm with built in communication , incremental encoder feedback
card ( 1 no ) as well as provision for analog tacho feedback card ( 1 no) ,
Microcontroller based, single quadrant ( 1Q ), thyristorised, digital DC converter
rated for motor field current 22.5A at voltage level of 220VDC;
iii) for controlling armature & field of Pinch Roll having Microcontroller based, three
phase, 6 pulse, four quadrant ( 4Q ), reversible, regenerative, thyristorised, digital
DC converter for DC motor of 25KW , 65Amp, 460 V DC with built in communication
and incremental encoder feedback card ( 1 no);
Microcontroller based, single quadrant ( 1Q ), thyristorised, digital DC converter for
motor field current of 5.21 Amp, at a voltage level of 220 VDC.
4. A closed loop speed control system as claimed in anyone of claims 1 to 3, comprising
(i) One set of said Self standing panel comprising of 3 nos of digital drives for
CCC Shear , Rotary Shear and Pinch Roll;

(ii) Six nos. of said Incremental Encoder adapted for for measuring speed of
stand and shear motors,
(iii) Two nos. of said Absolute Encoder , one for sensing of position of the crop
shear blade and another one for sensing position of rotary shear blade;
(iv) said three digital drive regulation system for the crop shear , rotary shear
and pinch roll motors adapted to ascertain better speed regulation of
shear motors,
(v) said programmable controller having a central Processing Unit, Counter
Module for processing the Encoder signal, Analog output module for
generating 0-10 V DC which corresponds to the speed.
5. A closed loop speed control system as claimed in anyone of claims 1 to 4, wherein said
digital drive system provides for Crop Cum Cobble Shear, rotary shear and Pinch Roll for
better speed control, optimized cutting , better diagnostics and availability of HMI.
6. A closed loop speed control system as claimed in anyone of claims 1 to 5, wherein said
programmable controller comprises Central Processing Unit, Counter module and analog
output module adapted to process the analog inputs and several digital inputs including
interlock information and generates set points for digital drives which controls precisely
the speeds of shear motors with faster speed control response and cutting accuracy.
7. A closed loop speed control system as claimed in anyone of claims 1 or 6, wherein all
said digital thyristor converters operate in closed loop mode with speed references from
PLC and speed feedback being provided by high accuracy incremental encoder and wherein
the combination of digital thyristor converter and incremental encoder have provision of
on-line trouble shooting using PC / Programmer, having provision for feed back with CEMF
(counter emf) or speed (configurable) through galvanic signal isolators and also having
provision of trending and data logging at HMI.
8. A closed loop speed control system as claimed in anyone of claims 1 to 7 wherein there
are two said PLC systems housed in two PLC panels of suitable dimensions, a 1st PLC
system provides for controlling Crop Cum Cobble Shear and associated equipment activities
where as a 2nd PLC system provides for controlling Rotary Shear & Pinch Roll and
associated activities, each PLC system comprising CPU, Power Supply, communication
processor, I/O racks, and Power supply for I/O rack, I/O modules and high speed counter
modules, said counter module are capable of up / down counting of at least 105 pulses.

9. A closed loop speed control system as claimed in anyone of claims 1 or 8, wherein said
PLCs are connected to programming station / HMI station through Ethernet communication,
with said drives connected to respective PLCs Profibus communication and wherein the
input power to PLC and interrogation supply is 24V DC.
10. A closed loop speed control system as claimed in anyone of claims 1 to 9 wherein said
two PLC systems are having local I/Os as well as remote I/O station at control pulpits.
11. A closed loop speed control system as claimed in anyone of claims 1 to 10, wherein all
the real time field signals are accessed by a PLC system installed in Electrical Control Room
and digital and analog values of stand motors along with trending in user friendly formats
are provided in HMI (interfaced with new as well as old PLC) installed at electrical control
room.
12. A closed loop speed control system as claimed in anyone of claims 1 or 11, wherein the
drive panel is provided with natural air cooling or forced air cooling by low noise & vibration
free ventilation fans at the top of cubicle / panel which sucks such air through the modules,
where the air inlet to the cubicle is allowed through suitable filter arrangement and through
the cubicle / panel vane with provision for switch for air flow monitoring.

ABSTRACT

The present invention relates to a control system for drives of Crop Cum Cobble (CCC)
Shear, Rotary Shear and Pinch Roll of Merchant Mill for stabilized rolling by adjusting field
current and armature voltage to eliminate front end hook cut/ bends and thereby
improve mill availability. The system ensures improved accuracy of cutting implemented
through digital thyristor drives, with provision of changeover switches at drive end.
Hierarchical automation system has been used with all drives and PLCs on PROFIBUS on
one level and supporting Ethernet network on the higher level of automation. Digital drives
have been used for controlling armature & field of Crop Cum Cobble Shear , Rotary Shear
and Pinch Roll. All the real time field signals are accessed by a PLC system installed in
Electrical Control Room. Digital and analog values of stand motors along with trending in
user friendly formats are made available in HMI (interfaced with new as well as old PLC)
installed at ECR.