FIELD OF THE INVENTION
The present invention relates to shear blade gap measurement system for side trimming
shear in a plate mill and) ,in particular, to a system for a PLC and digital encoder based
system for measurement of horizontal and vertical blade gaps of 4 side trimming shear
in a rolling mill. The system is adapted for trimming shear of any variety of rolling mills
including side trimming shear in plate mill and advantageously, includes digital pulse
encode (incremental) for sensing the linear displacement of the shear blade of the
trimming shear. More specifically and also advantageously, the measured gap signal in
the system of the invention is processed involving PLC and is adapted to be displayed
appropriately for the operator purposes. The system is adapted for wide scale
application and use in diverse industrial processes involving cutting of plates, sheets
with the help of side trimming shear. The invention is further directed to a simple and
effective method of measurement of shear blade gaps for adjustment, to cut (shear)
plates of different thickness and sizes. Advantageously, the system apart from being
effective in the blade gap measurement is found to be highly reliable, easy to maintain
and user friendly.
BACKGROUND ART
It is well known that plate mills of steel plants have side trimming shear to trim the
plates from the side for producing the customer required plate width. The trim plates are
finished products for shipments. The measurement of the horizontal and vertical gaps of
the shear blades is essential to operate the shear property.
It is presently known in the art to follow a very old and conventional gap measurement
invobring a system based on the System technology. In such known system four
numbers of seisyn are required for measuring the shear blade gap and the measured
value are displayed in the circular electro. mechanical dials. Two horizontal and two
vertical measuremets for each of the sides i.e. slide "A" and side "8" respectively are
provided. Corresponding to each selsyn a gap reading dial is provided in the pulpit for
the operator for necessary control and adjustment to the trimming shear operations.
The above discussed conventional gap measurement system involving the selsyn
technology is found to have limitations on account of the mechanical wear and tear and
the inherent tendency to develop backlash in due course of selsyn operation due to its
nature i.e. the same being an electro-mechanical device. Moreover, the above gap

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measurement system is found to be very obsolete and accordingly, the availability of
spare parts is also very poor and its used is thus found economically non-viable.
OBJECTS OF THE INVENTION
It is thus the basic object of the present invention to develop an advanced measurement
system using digital encoders and PLC system and provide digital display of the
measured gap value to the operators with better resolution and reliability.
Another object of the present invention is directed to the development of PLC and digital
encoder based shear blade measurement gap system far side trimming shear in variety
of rolling mills which would avoid the limitations and problems associated with the
mechanical wear and tear and the inherent tendency of developing backlash experienced
in the use of electro-mechanical devices.
Yet further object of the present invention is directed to providing digital encoder and
PLC based system for shear blade gap measurement which would be economically viable
and readilly obtained/installed for wide scale application and use in measurement of the
shear blade gap in variety of rowing mills.
Yet further object of the present invention is directed to the development of PLC and
digital encoder based shear blade gap measurement. system for side trimming shear in a
rolling mill which would provide for gap measurement and display of measure values to
the operators promptly and effectively for proper cutting of plates, sheets involving side
trimming shear.
Yet further object of the present invention is directed to method of measurement of
shear blades gaps for adjustment to cut (shear) plates of different thickness and sizes by
way of 3 reliable, easy to maintain and user friendly method.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a system
for measurement of horizontal & vertical blade gaps of a side trimming shear in a rolling
mill comprising:
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atleast one horizontal gap measuring encoder and atleast one vertical gap measuring
encoder means provided at each of the two sides ;
said encoder means operatively connected/interfaced to a Programmable Logic
Controller (PLC) means adapted to measured gap values and to the operators with better
resolution and reliability.
The above system for measurement of horizontal & vertical blade gaps of a side
trimming shear in a rolling mill thus basically comprises of PLC panel with PLC processor
I/Os, Encoder input processing cards, communication card, PLC power supply,
interrogating power supply of 24V DC and other operative panel components,
lmportartly, the output of the encoders is interfaced with the PLC encoder input cards,
the data is processed by the PLC for and the blade gaps are displayed in the digital
display units by transferring the data from PLC to these units using RS-487 unitelway
data network of the Schneider make PLC.
Advantageously the system for measurement of horizontal 8 vertical blade gaps of a
side trimming comprises of flexible shaft for measuring vertical gaps while the horizontal
gaps are measured with the help of mounting the encoders directly on the shear body
rthe output or the encoders are taken to PLC through control cabies wherein the encoder
output is processed by special encoder I/Os called "Counter Modules'. The flexible shaft is
adapted to transmit the movement of the blade gap measurement screw to the encoder.
Preferably, the flexible shaft's back end is interfaced with the blade gap measuring
screw of the shear.
In accordance with another aspect the system for mesurement of horizontal & vertical
blade gaps of a side trimming shear in a rolling mill includes limit switches for sensing
the maximum and minimum travel (movement) of the shear blades preferably two limit
switches are used for detecting these melts which as inputs are taken 35 digital inputs to
the PLC and processed.
In accordance with an aspect the said PLC comprises 3 suitable PLC processor, 2 nos. of
encoder input cards, and one no. of 32 channels digital input card , One UNITEL WAY
network on which four nos. of ASCI display units are connected said four unit display
the four measured values of Horizontal Gap of one side (Side - A), Vertical Gap of said
one side (Side - A) and Horizontal Gap of the other side (Side - B), Vertical Gap of the
another side (Side - B)respectively.
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The said processor is adapted to support (a) communication modules for remote digital
display units, (b) Operator interface for data viewing and control (c) Advance
mathematical instructions and (d)PID instructions.
The said incremental encoders are provided with required specifications and operative
connections for said horizontal and vertical gap measurement.
in accordance with another aspect of the invention there, is provided a method for
measurement of horizontal and vertical gap using the system as discussed above
comprising:
identifying the least count constant (KFs) value for the Horizontal and vertical gaps;
obtaining based thereof the gaps measured value at any point which is = dynamic value
of the encoder counter x KFs; and
displaying the processed values of all the four gaps in the digital display units in the
control pulpit of the trimming Shear Unit.
In accordance with a preferred aspect the values of least count for Horizontal Gaps = (-
) 0.0062 and for Vertical Gaps = (+) 0.051.The horizontal encoder moves in anti clock,
wise direction as the gap increases therefore the encoder starts down-counting giving
negative pulses and to get the positive value for the gap the least count constants are
made negetive.
In the above method for the shear blade gap measurement calculations the incremental
cnnnected for Screw is adapted to move the shear blades after the necessary gear
reduction train moves around 200 - 220 degrees for the entire range of measurement,
for the two Horizontal gaps this span is from 0.4 mm 4.0 mm and for Vertical gaps it
is 4.0mm to 45mm.
It is thus possible by way of time above disclosed PLC and digital encoder based shear
blade gap measurment system which would enable effective and advantageous digital
pulse encoder (incremental) based sensing of the linear displacement of the shear blade
of the trimming shear and thereby avoid the complexities and problems associated with
conventional electro-mechanical device. The measured gap signal in the system is
further processed using the PLC and is adapted to be appropriately displayed for the

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operator which would favour avoiding the drawbacks of the conventional sluggish dial
based gap indicator. The system of the invention would thus favour wide scale
application and use in diverse industrial processes involving cutting of plates, sheets with
the help of side trimming shear. The system favours the following of a method of
measurement of shear blade gap for adjustment to cut (shear) plates of different
thicknesses and sizes, which would be reliable, easy and user friendly.
The system thus favour as a much required advance measurement system using digital
encoder and PLC and provide digital display of the measured gap values to the operators
with better resolution and reliability. The gap mesurement system of the invention thus
further avoids the problems of the existing gap measurement and its display means. The
accuracy of the present system is found to be same but the present system achieve
increased resolution by involving the encoder mesurement and its necessarily more
acceptable to the operators since it would enable the operators to read better values to
the order of +/- 0.01 mm. and +/- 0.1mm for horizontal and vertical gaps vis-à-vis the
conventional display with resolution of +/- 0.1mm. and+/- 1.0mm. respectively.
Advantageously, the present system of the invention achieves substantially increased
throughput and also the shear down lime since the usual selsyn failure has been avoided
and its problems attended, importantly, further the system of the invention would favour
reducing shear down time ans improve the plate cutting equality with trimmed edges
mealing required customers satisfaction.
The details of the invention, its object and advantages are explained hereunder in
greater detail in relation to non-limiting exemplary illustrations as per the following
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE
Figure 1: illustrates the block schematic of the system to accordance with this invention;

Figure 2: illustrates the flexible shaft and its connectivity with the encoder on the front
side in accordance with the system of the present invention;
Figure 3: illustrates in greater detail the connectivity of the back end of the flexible shaft
to the shear blade gap adjustment screw to entrap the linear movement of the blades in
accordance with the system of the present invention; and
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Figure.4 : illustrates, the flexible shaft and collate that is used for interfacing the encoder
with the blade gap measurement screw of trimming shear in accordance with the system
of the invention.
Reference is first invited to Figure1 which illustrates the block schematic of the complete
system comprising of PLC panel with PLC, processor, 1/Osa,Encoder input processing
cards, communication card, PLC power supply, interrogating power supply of 24V DC and
other panel components Four no. of incremental encoders are used, the output of these
encoders is interfaced with the PLC encoder input cards. The data is processed by the
PLC for algebric manipulations and the blade gaps are displayed in the digital display
units by transferring the data from PLC to these units using a data network, Two
encoders are used for measuring horizontal gaps of side 'A' and side 'B' respectively.
Two encoders are used for measuring vertical gaps of slide 'A' and side 'B' respectively.
importantly, the flexible shaft is selectively provided for measuring vertical gaps. The
horizontal gaps are measured with the help of mounting the encoders directly on the
shear body by fitting the encoders onto the exiting flange of the selsysn.
The output of the encoders is taken to PLC through control cables. The encoder output
is processed by special encoder 1/Os called 'Counter Modules'. The maximum and
minimum travel (movement) of the shear blades is sensed with the help of limit
switches. Two limit switches are used for detecting these limits. These inputs are taken
as digital inputs to the PLC and processed.
Reference is now invited to accompanying Figure 2 which illustrates in detail the flexible
shaft that is selecetively applied to transmit the movement of the blade gap measurement
screw to the encoder. importantly and most advantageously this is a clear deviation
form the old system wherein the selsyn (old technology) was directly mounted over this
screw which was subject to direct impact and heavy vibrations of the plate cutting stokes
leading to damaging selsyn very often. In this figure the details of the front side of the
flexible shaft and its connectivity with the encoder is illustrated.
Reference is now invited to accompanying fig.3 which illustrates the details of the
flexible staft's back end and its interface (connectivity) with the blade gap measuring
screw of the shear. Some preferred forms of the components and configurations
thereof provided in the system of the invention are detailed hereunder:
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PLC system:
The PLC system used involves a PLC processor, 2 nos. of encoder input cards, and one
no. of 32 channel digital input card. One RS 485 based UNITTEL WAY network on which
four nos. of ASCI display units are connected. These four unit display the four measured
gaps Horizontal Gap Side - A, Vertical Gap Side - A and horizontal Gap Side - Bt
Vertical Gap Side - B respectively. The PLC specifications can be as follows:
PLC Processor Specs:
The PLC proessor is modular Rack mounted type with following specifications:
Scan time: not more than 0.5ms/ K of PLC program,Digital I/O handling capacity;
auto transfer.
importantly, the processor is adapted to support (a) communications modules for remote
digital display units, (b) Operator interface for data viewing and control(c) Advance
mathematical instructions viz. and (d) PID instructions.
in accordance with an embodiment the processor specifications can include RAM
capacity: 48K Words, with battery back-up,Networking; Ethernet port along with RS 232
and RS-435 ports,The PLC rack has 10 slots, one PLC processor, one Power supply and
other I/O cards on the Rack,The PLC has watching timer,The PLC has real time
dock.The system has 256 software counters / timers,Ambient temperature for reliable
working Of PLC is 60 oC.
Encoders:
Two encoders are used for measuring two gaps on each side Horizontal and
Vertical respectively comprising of four encoders in all. The incremental encoder
can have the following specifications as per Table t.
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Table: 1- Incremental Encoder Specifications

The Method of Shear Blade Gap Measurement Using the Above Discussed System Of the
invention is Further Discussed Hereunder:
The Shear blade gap measurement calculations are as follows: The incremental
connected for Screw which moves the shear blades after the necessary gear reduction
train moves around 200 - 220 degrees for the entire range of measurement for the two
horizontal gaps this span is from 0.4 mm to 4.0 mm and for Vertical gaps it is 4.0 mm to
45mm.
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For a given day with a set of shear blades the minimum and maximum gaps were
measured and least count factor was calculated after many trials. This least count factor
is calculated completely manually and confirmed later with the PLC system calculated
values.
Least count for Horizontal gap: LCbg

Similarly the Least count for Vertical gap: LCvg

Example of the Case:
Calculation Data for calculating least counts for all four gaps of two sides of the shear.
Table 2: Calibration data for Vertical Gaps

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Table 3: Calibration data for Horizontal Gaps

The least count constants are termed as KFs the notation provided in the PLC
terminotogy
The values of least count for Horizontal Gap KF1, KF3 = (-) 0.0062 and for Vertical Gap
KF2, KF4 = (+)0.05i
Horizontal encoder moves in anti clock wise direction as the gap increases therefore the
encoder starts down-counting giving negative pulses. To get the positive value for the
gap the least count constants are made negative.
The gap measured value at any point = dynamic value of the encoder counter x KFs
Now suppose at a point the encoder for horizontal gap side A has moved 355 pulses men
the measured and displayed value with be = 355 x 0.0062= 2.201 mm. This value will
be direrctly displayed in the pulpit of the trimming shear which is located a 100 m away
from the PLC.
It is thus possible by way of the present invention to provide an advanced measurement
system using digital encoders and PLC system and provide digital display of the
measured gap value to the operators with better resolution and reliability. The system is
directed to the development of PLC and digital encoder based shear blade measurement
gap system for side trimming shear in variety of rolling mills which would avoid the
limitations and problems associated with the mechanical wear and tear and the inherent
tendency of developing backlash experienced in the use of conventional electro-
mechanical devices, the PLC based system of the invention would be economically viable
and readily obtained ( installed for wide scale application and use to measurement of the
shear blade gap in variety of rolling mills.
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WE CLAIM:
1. A system for measurement of horizontal & vertical blade gaps of a side trimming
shear in a rolling mill comprising:
at least one horizontal gap measuring encoder and atleast one vertical gap measuring
encoder means provided at each of the two sides ;
said encoder means operatively connecterd/interfaced to a programmable logic
Controller (PLC) means adapted to measured gap values and to the operators with better
resolution and reliability.
2. A system for measurement of horizontal & vertical blade gaps of a side trimming
shear in a rolling mill as claimed in claim 1 comprising of PLC panel with PLC processor,
1/Os, Encoder input processing cards, communications card, PLC power supply,
interrogating powder supply of 24V DC and other operative panel components.
3 A system for measurement of horizontal & vertical blade gaps of a side trimming shear
in a rolling mill as claimed in anyone of claims 1 or 2 wherein the output of the encoders
is interfaced with the PLC encoder input cards, the data is processed by the PLC for and
the blade gaps are displayed in the digital display units by transferring the data from PLC
to these units using cooperative data network.
4. A system for measurement of horizontal & vertical blade gaps of a slide trimming
shear in a rolling mill as claimed in anyone of claims 1 to 3 comprising flexible shaft for
measuring vertical gaps while the horizontal gaps are measured with the help of
mounting the encoders directly on the shear body the output of the encoders are taken
to PLC through control cables wherein the encoder output is processed by special
encoder I/Os called 'Counter Modules'.
5. A system for measurement of horizontal & vertical blade gaps of a side trimming
shear in a rolling mill as claimed in anyone of claims 1 to 4 comprising limit switches for
sensing the maximum and minimum travel (movement) of the shear blades preferably
tea limit switches are used for detecting these limits which as inputs are taken as digital
inputs to the PLC and processed.
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5. A system for measurement of horizontal & vertical blade gaps of a side trimming
shear in a rolling mill as claimed in anyone of claims 1 to 5 wherein a flexible shaft is
adapted to transmit the movement of the blade gap measurement screw to the encoder.
7. A system for measurement of horizontal & vertical blade gaps of a side trimming
shear in a rolling mill as claimed in anyone of claims 1 to 6 wherein the flexible shaft's
back end is interface with the blade gap measuring screw of the shear.
8. A system for measurement of horizontal & vertical blade gaps of a side trimming
shear in a rolling mill as claimed in anyone of claims 1 to 6 wherein said PLC comprises
a suitable PLC processor, 2 nos. of encoder input cards, and one no. of 32 channel digital
input card , One UNITEL WAY network on which four nos. of ASCI display units are
connected said four unit display the four measured gaps Horizontal Gap of one side
(Side - A). Vertical Gap of said one side (Side - A) and Horizontal Gap of the other side
(Side - B), Vertical Gap of the another side (Side - B )respectively.
9. A system for measurement of horizontal & vertical blade gaps of a side trimming
shear in a rolling mill as claimed in anyone of claims 1 to 8 wherein said processor is
adapted to support (3) communication modules for remote digital display units, (b)
Operator interface for data viewing and control (c) Advance mathematical instructions
and (d)PLD instructions.
10. A system for measurement of horizontal & vertical blade gaps of a side trimming
shear in a rolling mill as claimed in anyone of claims 1 to 9 wherein said incremental
encoders are provided with required specifications and operative connections for said
horizontal and vertical gap measurement.
11. A method for measurement of horizontal and vertical gap using the system as
claimed in anyone of claims 1 to 10 comprising:
identifying the least count constant (KFs) values for the Horizontal and Vertical gaps;
obtaining based thereon the gap measured value at any point which is = dynamic value
of the encoder counter xKFs;. and
displaying the processed values of all the four gaps in the digital display units in the
control pulpit of the Trimming Shear Unit.
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12. A method as claimed in claim 11 wherein the values of least count for Horizontal
Gaps = (-) 0.0062 and for Vertical Gaps = (+) 0.051.
13. A method as claimed in anyone of claims 11 or 13 wherein the horizontal encoder
moves in anti clock wise direction as the gap increases therefore the encoder starts
down-counting giving negative pulses and to get the positive value for the gap the least
count constants are made negative.
14. A method as claimed in anyone of claims 11 to 13 wherein for the shear blade gap
measurement calculations the incremental connected for Screw is adapted to move the
shear blades after the necessary gear reduction train moves around 200 - 220 degrees
for the entire range of measurement, for the two Horizontal gaps this span is from 0.4
mm to 4.0 mm and for Vertical gaps it is 4.0mm to 45mm.
15. A system for mesurement of horizontal & vertical blade gaps of a side trimming
shear in a rolling mill and a method for said horizontal and vertical gap measurements
using the system substantially as herein described and illustrated with reference to the

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A PLC and digital encoder based system for measurement of horizontal and vertical
blade gaps of a side trimming shear in a rolling mill. The system is adapted for
trimming shear of any variety of rolling mills including side trimming shear in plate
mill and advantageously, includes digital pulse encoder (incremental) for sensing the
linear displacement of the shear blade of the trimming shear. More specifically and
also advantageously, the measured gap signal in the system of the invention is
processed involving PLC and is adapted to be displayed appropriately for the
operators purposes. The system is adapted for wide scale application and use in
diverse industrial processes involving cutting of plates, sheets with the help of side
trimming shear. The invention is further directed to a simple and effective method of
measurement of shear blade gaps for adjustment to cut (shear) plates of different
thickness and sizes. Advantageously, the system apart from being effective in the
blade gap measurement is found to be highly reliable, easy to maintain and user
friendly.