TITLE OF THE INVENITON
Photosensor based system for measuring torque up to elastic limit of spindle in rolling
mill.
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a design and development of photosensor based system
for measuring torque experienced by rolls of rolling stand of mill at the time of byte.
More particularly, the invention is concerned about developing a simple, low cost but
highly reliable optics based system for measuring torque up to elastic limit of spindle
which connects motor and roll of rolling stand of steel plant.
BACKGROUND AND THE PRIOR ART
In rolls of rolling mill of steel plants, a heavy torque is generated at the time of byte and
sometimes it crosses the permissible limit which results into breakage of spindle and mill
remains down for few shifts to replace the shaft on the cost of production loss.
Earlier attempts taken to overcome this breakage problem of spindle by (i) sensing the
motor load current or (ii) putting coppers rings at two places around the spindle (iii)
breaking of a thin wire which is tightened on two ends of spindle and many more but
could not predict reliably the breakage of spindle every instant the times.
(i) Sensing the motor load current: A. C. / D.C. motor current is sensed by current
transformer. The instantaneous power factor is determined by knowing the phase
difference of voltage and current.

US4356443 discloses a method is provided for detecting the existence of arcing faults in
the phase windings of a polyphase electric machine and for simultaneously identifying
the specific phase winding in which the arcing fault exists. Arcing faults in phase
windings of electric machines cause high frequency currents to flow through all phase
windings of the machine with a drastically higher magnitude in the phase winding in
which the arcing fault exists. These currents can thus be measured to determine the
existence of the arcing fault and selectively determine which phase is affected.
US4851766 discloses a system for fault diagnosis for a rotor winding of rotary electric
machines is disclosed, in which the rotor winding of rotary field type is excited in DC
fashion by an excitation circuit, on which an AC voltage is superposed, the impedance of
the rotor winding is calculated from the current and voltage of the AC portion flowing in
the rotor winding, and the resulting impedance is compared with a reference impedance
thereby to decide a fault, if any, of the rotor winding, thus making possible accurate
diagnosis of a rotary electric machine even while it is running.
US4978909 discloses a motor current analysis method for the remote, noninvasive
inspection of electric motor-operated systems. Synchronous amplitude demodulation and
phase demodulation circuits are used singly and in combination along with a frequency
analyzer to produce improved spectral analysis of load-induced frequencies present in the
electric current flowing in a motor-driven system.
US5028804 discloses an energy conversion generation system which receives energy
from a resource and converts the energy into electrical power for supply to a polyphase
electric power grid operating at a system frequency. A prime mover driven by the
resource energy and a converter, such as a power electronic converter, for produces
excitation power from power received from a converter power source. A brushless
doubly-fed generator has a rotor with rotor windings and a stator with stator windings
comprising first and second polyphase stator systems. The rotor is driven by the prime
mover. The first stator system supplies the electrical power to the grid, and the second
stator system receives the excitation power from the converter. A sensor senses a

parameter of the electrical power output supplied to the grid and produces a sensor signal
corresponding to the sensed parameter. A controller controls the converter in response to
the sensor signal. This invention was made with government support under Grant No. 79-
85BP24332, awarded by the Bonneville Power Administration. The United States
government has certain rights in this invention.
US5430362 discloses a control for operating an electromagnetic machine in a starting
mode of operation wherein the main armature winding of the machine receives electrical
power from a controllable power source during the starting mode of operation, comprises
a circuit for detecting a magnitude of a parameter of power applied to the main armature
winding relative to a stationary frame of reference, a position sensor for detecting rotor
position of the electromagnetic machine, a converter responsive to angular position
indication for converting the detected parameter magnitude into field and torque
producing components relative to a rotating frame of reference, and a circuit responsive
to the field and torque producing components for controlling the power source during
operation in the starting mode. This control includes an igniter for igniting a prime
mover. Further, the control is operable during a first phase prior to ignition of the prime
mover for causing the electromagnetic machine to provide motive power to the prime
mover so as to accelerate the prime mover at a first predetermined rate, is operable during
a second phase subsequent to the first phase so as to accelerate the prime mover at a
second predetermined rate, is operable during this second phase for providing fuel to the
prime mover to facilitate ignition thereof, and is operable during a third phase subsequent
to the ignition of the prime mover so as to accelerate the prime mover at a third
predetermined rate to a self-sustaining speed. This is an indirect method, and in such
methods no necessary measures are found for controlling torque. Moreover, there is
problem of variation in current due to varying load also. Method is not reliable for
measuring the twisting of spindle.
(ii) Coppers rings at two places: In 1985, in blooming mills in steel plants coppers rings
at two places around the shaft were put and its relative twisting was supposed to be
measured by strain gauge and its signal were transmit on wireless . In the system even

strain gauge could not be put on the shaft. Such a system is not a feasible system.
(iii) Breaking of a thin wire tightened on two ends: A piano wire was tightened in
between two places along the spindle. Due to relative twist, the wire was supposed to
break. Many times wire was broken but could not provide the signal. This is not a
feasible system.
With this background, a very low cost photosensor based system has been developed for
measuring the torque by using two perforated annular rings.
OBJECTS OF THE INVENTION
Thus, an object of the present invention is to design and develop a photosensor based
system for measuring torque thereby avoiding the problem of spindle breakage and
production loss.
Another object of the present invention is to provide an audio/video alarm to prevent
breakage of spindle.
Further object of the present invention is to provide a direct method for contact-less
torque measurement.
Yet another object of the present invention is to reduce the complexity associated with
the earlier technologies.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a photosensor based
system for measuring torque up to elastic limit of a spindle of rolls of rolling stand of
mill, said system comprising:

a pair of shafts;
at least a pair of rolling means being mounted on said shafts, said rolling means include a
top roll and a bottom roll,
at least one driving means being operatively coupled to said shafts so as to drive said
rolling means; wherein said shafts comprise a plurality of annular strips, said strips being
circumferentially located on the shafts and having predetermined distance between two
such strips; and
wherein said strips comprise two or more sensing means disposed on either side of each
annular strips wherein said sensing means measure the torque generated due to twisting
of the shaft on the basis of counting the interruption of light by opaque portion such that
when the measured torque exceeds a certain preset value an audio / video alarm means is
set off thereby indicating that corrective actions need to be taken.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates the blooming mills of steel plant.
Figure 2 illustrates the least count of said system 4 mm is achieved by making 220 holes
in each annular strip having 0.7 m diameter.
Figure 3 illustrates a light emitting diode (LED) and a phototransistor placed on either
side of each annular strip in the system of the present invention.
Figure 4 illustrates isometric view of the system along with the photosensor means.
DETAILED DESCRIPTION OF THE INVENTION
In rolling mills the torque is generated at the time of byte sometimes it exceeds the
threshold limit, resulting in the breakage of the spindle along with loss in time as well as
extra cost is needed to replace the spindle.

In blooming mill of a steel plant in India; hot ingots (dimension 1760 mm x 600 mm x
600 mm) are converted into blooms (cross section 340 mm x300 mm) by rolling through
1150 mm diameter reversible rolling stand. Either excessive draft on top roll by screw
down mechanism in different rolling passes or cold metal at the time of byte, forces
momentary stillness in the one end of shaft and the linear segment across the shaft
gradually increases towards driving end side. If degree of twisting (stress/strain) crosses
the permissible limit which is governed by of Hook's law then connecting shaft breaks at
its end and the mill remains down for few shifts to replace a new shaft.



Thus, the present invention provides a design and development of a very simple, low cost
but highly reliable optics based system for measuring the torque developed by rolling
mill motor at the time of byte. The system describes the use of photosensor for measuring
the torque up to elastic limit of long heavy spindle in rolling mill of steel plant. Heavy
torque is generated at the time of byte and sometimes it crosses the permissible limit and
results into breakage of spindle and mill remains down for few shifts to replace the shaft
on the cost of production loss. Earlier attempts were made to overcome on shaft-breakage
problem but could not predict reliably at every such instance. With this background, a
very low cost system has been developed for measuring the torque. If the measured value
of the torque exceeds a certain value, an alarm is generated which acts as a warning and
the main drive motors are switched off manually.
In accordance with the above objects, the present invention provides a novel photosensor
based system for measuring the torque up to the elastic limit to prevent the breakage of
spindle in rolling mills. The system comprises a pair of shafts of unequal length but
having equal diameter which is in turn coupled to a 8 MW motor which helps drive a set
of rolling means for the functioning of a rolling mill. The present invention is
characterized by the presence of two annular strips which have incorporated in them
photosensors for the measurement of torque. If this measured values exceeds a certain
preset value then an alarm is generated and the motors are to be shut down manually for
preventing shaft (spindle ) breakage.

The shafts being of equal diameter of 0.7 m but unequal length viz. the top one being 15
m long and the bottom one having a length of 11 m. A DC motors of 8 MW drives the
individual roll therefore two motors are put to dive the top and bottom rolls respectively.
The strips are made of soft and flexible material like paper sheets, tin sheets, plastic
sheet. The paper sheet used, has a thickness of around 0.2 mm and the tin sheet used
having thickness of 24 gauge are wound around the shaft at an interval of 4 m. The least
count of system 4 mm and it is achieved by making 220 holes in each annular strip which
are wrapped around the shaft of 0.7 m diameter as shown in Fig-2. Both side of strip a
pair of phototransistor and its illuminating light source (LED light emitting diode). On
rotation of shaft , the annular strip is also rotates . Therefore system can sense two holes
which are apart by 4 mm. Phototransistors function as sensing means in the present
invention. The differential twist at two different places along the shaft is achieved by
counting the interruption of light by opaque portion of disk with the help the
photosensors. On exceeding the preset value, alarms are activated by way of the light
emitting diode which functions as a video alarm along with audio alarms. The alarm
indicates that the corrective measures need to be taken by manually shutting down the
motor to avoid the breakage of the shaft. The alarm is generated if relative twisting
exceeds 4 count i.e. 4x 4 mm (least count) = 16 mm and it matches with theoretical
calculation. So timely prediction avoids the breakage of spindle by keeping threshold
value of count difference (between two annular perforated strip) by 14mm.
Presently the system of taking the necessary action after the alarm is generated and it
works in manual mode.
Efforts are in progress to make the system fully automate. For this a control relay is
actuated and its potential free contact (normally open) is used for shutting down the
drive. After adjusting the screw down ( spacing of top and bottom rolls ), the system gets
ready for accepting next pass of bloom.
The theoretical twisting angle is 0.0231534° (16.2052 mm) while trial results also match

i.e. up to 16 mm difference in angular shift at two points which are apart by 4 m, is safe
to operate the motor and rolls. Total length of shaft is 11 m i.e. angular deflection might
be 44 mm. The difference in the theoretical value and the practical value might be due to
different site condition i.e. a load applied on other end of shaft while one end of shaft is
free in theoretical calculation.
A prototype of the present invention has been designed and developed and the same was
tested for accurate and reliable results. The experimental details have been provided
before to substantiate the working of the above system.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In figure 4 the system comprises a pair of shafts (1) which is coupled to a motor (2)
which helps to drive a set of rolling means (3) for the functioning of a rolling mill. The
annular strips (4) have photo-sensors (5) for the measurement of torque.
EXPERIMENTAL RESULTS
On twisting of shaft due to increased torque, the number of pulse count in CI counter
related to drive side increases w.r.t. driving side counter C2 .

WE CLAIM
1. A photosensor based system for measuring torque up to elastic limit of a spindle
in a rolling mill, said system comprising:
a pair of shafts;
at least a pair of rolling means being mounted on said shafts, said rolling means
include a top roll and a bottom roll;
at least one driving means being operatively coupled to said shafts so as to drive
said rolling means; wherein said shafts comprise a plurality of annular strips, said
strips being circumferentially located on the shafts and having predetermined
distance between two such strips; and
wherein said strips comprise two or more sensing means disposed on either side
of each annular strips wherein said sensing means measure the torque generated
due to twisting of the shaft on the basis of counting the interruption of light by
opaque portion such that when the measured torque exceeds a certain preset value
an audio/video alarm means is activated thereby indicating that corrective actions
need to be taken.
2. The system as claimed in claim 1 wherein the torque is measured by measuring
the differential twist at two different places along said shaft by counting the
interruption of light by opaque portion of said strip.
3. The system as claimed in claim 1-2 wherein said rolling means comprises rollers.
4. The system as claimed in claim 1-3 wherein said driving means comprises 8 MW
twin motors.
5. The system as claimed in claim 1-4 wherein said shafts are of equal diameter of

about 0.7 m.
6. The system as claimed in claim 1-5 wherein said shafts have unequal length.
7. The system as claimed in claim 1-6 wherein said annular strips comprise soft and
flexible material selected from paper sheet, tin sheet and the like.
8. The system as claimed in claim 1-7 wherein said sensing means comprises at least
one phototransistor.
9. The system as claimed in claim 1-8 wherein said video alarm means comprises
light emitting diodes for emitting light signals for shutting down the motor. .
10. The photosensor based system for measuring torque upto elastic limit of a spindle
in a rolling mill as substantially described hereinbefore with reference to
accompanying drawings.

The present invention relates to a photosensor based system for measuring torque up to
elastic limit of a spindle in a rolling mill. The system comprises a pair of shafts (1), at
least a pair of rolling means (3) mounted on the shafts (1), at least one driving means
being operatively coupled to said shafts so as to drive said rolling means; wherein said
shafts comprise a plurality of annular strips (4) circumferentially located on the shafts (1)
and having predetermined distance between two such strips. The strips comprise two or
more sensing means (5) disposed on either side of each annular strips. The sensing means
measure the torque generated due to twisting of the shaft on the basis of counting the
interruption of light by opaque portion such that when the measured torque exceeds a
certain preset value an audio/video alarm means is activated thereby indicating that
corrective actions need to be taken.