FIELD OF THE INVENTION
The present invention relates to an improved position measurement system of screw
down mechanism which is used to move up and down the backup roll in the stands
of tandem mill. More particularly, the present invention relates to a system for
position measurement and display of screw down at the two ends of the backup roll
so that balanced roll force can be applied on the ends of work roll through the
backup roll, in a 4 hi tandem mill, for desired roll gap setting for intended control on
shape/thickness of cold rolled products.
BACKGROUND OF THE INVENTION
The Tandem Mill number 1 of Cold Rolling Mill, at the applicants Steel Plant is a
2000mm , 4- High mill and 4-Stand mill was designed and installed to produce strips
with thickness from 0.4mm to 2.5mm and width from 700mm to 1850mm. This mill
is provided with electro-mechanical screw down system for roll gap setting with
electro-mechanical gauge control system. The cold reduct on of steel strip is through
electro-mechanical screw down in each stand. With the help of screw down
mechanism in the stands, the roll gap in each stands regulated as per the
requirement of rolling schedule. The screw down mechanism has two motors, one for
right screw and the other for left screw rotation in each stand. The two motors can
either be operated individually or simultaneously in synchronization. Electrical
synchronization is achieved through encoder based position display control installed
in each stand. The screw down moves the top backup roll up/down for applying the
required force on the strip through the work roll. The strip thickness reduction
through the screw down mechanism is done manually by adjusting the roll gap in
each stand for achieving the desired reduction in strip thickness. A gamma ray
thickness measurement device is installed at the exit end of the mill. The control
post near each stand has two position display units for the two screw down of each
stand.
The earlier position display system for screw down was not able to provide consistent
correct display of the screw down position in the individual stands due to various
shop logistic problems. The erroneous / mismatch in the reading of the two display

units leads to wrong adjustment of the screw down at the two ends of each stand.
This results in non-uniform roll gap across the width of the coil strip leading to Gauge
variation, Strip breakage and Roll pinch.
The present invention is directed to providing an improved position measurement
system of screw down mechanism in Tandem Cold Rolling Mill, to circumvent the
above mentioned problems. The improved position measurement system according
to the present invention would provide a correct position display of the individual
screw down to enable the operator in maintaining the uniform roll gap in the stands
and has helped in reduction in gauge variations, step breakage & roll pinch
previously experienced.
OBJECTS OF THE INVENTION
The basic of the present invention is thus directed to providing an improved position
measurement system of screw down mechanism in each stand of tandem mill for
correct position display of the individual screw down which would help the operator
in maintaining the uniform roll gap in the stands so as to educe the gauge variation,
strip breakage and roll pinch as sequel to erroneous adjustment of screw down by
the operator on the basis of inaccurate display.
A further object of the present invention is to provide an improved position
measurement system of screw down mechanism in each stand of tandem mill which
would provide the operator with the display of screw down position of each stand in
the local control post so that a balanced roll force can be applied at the two ends of
the work roll.
A still further object of the present invention is to provide an improved position
measurement system of screw down mechanism in each stand of tandem mill to
provide the operator with the display of screw down position of each stand in the exit
end control post so that the movement of screw down in ail stands can be controlled
by exit end operator.

Yet another object of the present invention is to provide an improved position
measurement system of screw down mechanism in each stand of tandem mill that
would help in storing the pass schedule for different grades of cold rolled coils and its
retrieval when required to roll the same campaign.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to a system for position
measurement of the screw down mechanism in Tandem cold rolling mill comprising :
at least two absolute encoder means in the output gear of the screw down
motors located on the two sides of each stand of Tendem Mill to measure the
screw down position at the two sides of the stand;
at least two laser sensor means selectively disposed to measure the actual
movement of screw down located on the two sides of each stand of Tandem
Mill so as to have a means of redundancy in screw position measurement in
case of failure of encoder;
control post of each stand for the operator's to have the information of screw
down position of that stand;
at least one, indicator & control unit located at the exit control post for the
operator's to have the information of anyone or more of screw down position,
roll force, inter-stand tension, stand speed, etc of all stands on the basis of
which the gauge reduction in stand can be done accurately;
at least one programmable logic controller means nstalled to in the control
room for interfacing the pulse of the encoder with indicator unit , interfacing
of the field instruments with indicator unit for indication of thickness gauge ,
roll force, inter-stand tension, mill speed and logging of these data;
at least one human machine interface means .

A further aspect of the present invention is directed to a system for position
measurement of the screw down mechanism in a four stand Tandem cold rolling mill
comprising
at least two absolute encoder means in the output gear of the screw down
motors located on the two sides of each stand of Tandem Mill to measure the
screw down position at the two sides of the stand
at least two laser sensor means above the backup roll to measure the actual
movement of screw down located on the two sides of each stand of Tandem
Mill so as to have a means of redundancy in screw position measurement in
case of failure of encoder;
at least one indicator means comprising touch paneI type digital display unit
means substantially installed in the control post of each stand for the
operator's to have the information of screw down position of that stand.
at least one master touch panel type display & control unit located at the exit
control post for the operator's to have the information of screw down position,
roll force, inter-stand tension, stand speed, etc of all the four stands on the
basis of which the gauge reduction in stand can be done accurately;
at least one programmable logic controller means installed to in the control
room for interfacing the pulse of the encoder with display unit , interfacing of
the field instruments with display unit for display of thickness gauge , roll
force, inter-stand tension, mill speed and logging of these data;
at least one human machine interface screen means installed in the PC based
Engineering workstation for the saving & retrieval of the pass schedule for a
similar campaign of Cold Roll coils ;
A still further aspect of the present invention is directed to said system which is
adapted for display of screw down position of each stand in the local control post
so that a balanced roll force can be applied at the two ends of the work roll.

A still further aspect of the present invention is direct to said system which is
adapted for the display of screw down position of each stand in the exit end control
post so that the movement of screw down in all stands car be controlled by exit end
operator.
Yet another aspect of the present invention is directed to said system that comprises
means for storing the pass schedule for different grades of cold rolled coils and its
retrieval when required to roll the same campaign.
The various features and advantages of the present invention are described in
greater details with reference to the following accompanying non limiting illustrative
drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1: illustrates the Schematic arrangement of the improved position display
system.
Figure 2: illustrates the Schematic connection of the field devices with the controller.
Figure 3: illustrates the main screen for the Engineering workstation.
Figure 4: illustrates the Screens for the operator's interface
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING DRAWINGS
The present invention relates to an improved position measurement and display
system of the screw down mechanism in Tandem cold rolling mill.
Accompanying Figure 1 illustrates the Schematic arrangement of the improved
position measurement and display system according to the present invention
consists of the absolute encoder, laser sensors, display and control unit and its
interface with programmable logic controller(PLC) and PC based human machine

interface. The absolute encoders are installed in the output shaft of spur-worm gear
of the screw down motors in each stand. The laser sensors are installed in such a
location so as to measure the linear displacement of the backup roll.
The following design parameters were taken into consideration in designing the
improved position measurement of the screw down mechanism in Tandem cold
rolling mill.
No. of Stands Four
No. of Screw down Eight ( Two/stand)
No. Of Control Post
Eight ( Two/ Stand)
Input Strip Thickness 1.80-5.00mm
Output Coil Thickness 0.40 -2.00mn
Backup Roll Dia. 1600/1460mm
Work Roll Dia. 600/570mm
Screw down speed 50mm/s (Raising)
16.6mm/s(lowering)
Motor DC Motor , Separately excited , 145kW
450rpm with 100% duty cycle.
Accompanying Figure 2 depicts the schematic connection of field devices with the
controller. Field devices like the absolute encoders and display units are connected to
PLC though communication network. The field devices like aser sensor, load cells for
roll force and inter-stand tension etc are connected through signal cable to PLC. The
laser sensors, load cell signal for inter-stand tension and roll force are connected
through signal cables.
Accompanying Figure 3 shows the main screen for the engineering workstation
which depicts the screw down position, roll force, inter-stand tension, mill speed etc.
A PC based human machine interface is installed in the room near the mill. This HMI

also acts as a engineering station for calibrating the end ler position, saving of the
pass schedule and other diagnostic functions.
The display and control unit for each stand is installed in the control post of the
respective stand. Accompanying Figure 4 shows the operator's interface (display &
control unit) installed in the control posts. The display unit shows screw down
position, roll force, inter-stand tension etc. The exit stand has the display and
control unit which has the operating data such as inter stand tension, roll force,
stand speed and screw down position of all the four stands
It is thus possible by way of the present invention to providing a system for position
measurement of the screw down mechanism in Tandem coId rolling mill adapted for
precise position measurement and display of screw down at the two ends of the
backup roll so that balanced roll force can be applied in the ends of work roll
through the backup roll, in a 4 hi tandem cold rolling mili or desired roll gap setting
for intended control on shape/thickness of cold rolled products, by enabling the
operator to maintain the uniform roll gap in the stands so as to reduce the gauge
variation, strip breakage and roll pinch in cold rolling mil ensuring improved quality
and enhanced productivity.

We Claim:
1. A system for position measurement of the screw down mechanism in Tandem
cold rolling mill comprising :
at least two absolute encoder means in the output gear of the screw down
motors located on the two sides of each stand of Tandem Mill to measure the
screw down position at the two sides of the stand;
at least two laser sensor means selectively disposed to measure the actual
movement of screw down located on the two sides of each stand of Tandem
Mill so as to have a means of redundancy in screw position measurement in
case of failure of encoder;
control post of each stand for the operator's to have the information of screw
down position of that stand;
at least one, indicator & control unit located at the exit control post for the
operator's to have the information of anyone or more of screw down position,
roll force, inter-stand tension, stand speed, etc of all stands on the basis of
which the gauge reduction in stand can be done accurately;
at least one programmable logic controller means installed to in the control
room for interfacing the pulse of the encoder with indicator unit , interfacing
of the field instruments with indicator unit for indication of thickness gauge ,
roll force, inter-stand tension, mill speed and logging of these data;
at least one human machine interface means .
2. A system as claimed in claim 1 for position measurement of the screw down
mechanism in a four stand Tandem cold rolling mil, comprising

at least two absolute encoder means in the output gear of the screw down
motors located on the two sides of each stand of Tandem Mill to measure the
screw down position at the two sides of the stand;
at least two laser sensor means above the backup roll to measure the actual
movement of screw down located on the two sides of each stand of Tandem
Mill so as to have a means of redundancy in screw position measurement in
case of failure of encoder;
at least one indicator means comprising touch penel type digital display unit
means substantially installed in the control post of each stand for the
operator's to have the information of screw down position of that stand.
at least one master touch panel type display & control unit located at the exit
control post for the operator's to have the information of screw down position,
roll force, inter-stand tension, stand speed, etc of all the four stands on the
basis of which the gauge reduction in stand can be done accurately;
at least one programmable logic controller means installed to in the control
room for interfacing the pulse of the encoder with display unit , interfacing of
the field instruments with display unit for display of thickness gauge , roll
force, inter-stand tension, mill speed and logging of these data;
at least one human machine interface screen means installed in the PC based
Engineering workstation for the saving & retrieval of the pass schedule for a
similar campaign of Cold Roll coils ;
3. System as claimed in anyone of claims 1 or 2 adapted for display of screw
down position of each stand in the local control post so tnat a balanced roll force
can be applied at the two ends of the work roll.
4. System as claimed in anyone of claims 1 to 3 adapted for the display of
screw down position of each stand in the exit end control post so that the
movement of screw down in all stands can be controlled oy exit end operator.

5. System as claimed in anyone of claims 1 to 4 comprising means for storing
the pass schedule for different grades of cold rolled coils and its retrieval when
required to roll the same campaign.

ABSTRACT

The present invention relates to an improved position measurement system of screw down mechanism which is used to move up and down the backup roll in the stands of tandem mill. The system according to the present invention favour precise position measurement and display of screw down at the two ends of the backup roll so that balanced roll force can be applied on the ends of work roll through the backup roll, in
a 4 hi tandem mill, for desired roll gap setting or intended control on shape/thickness of cold rolled products. The system thus enable maintaining the uniform roll gap in the stands so as to reduce the gauge variation, strip breakage and roll pinch in cold rolling mill.
(Figure 1)