FIELD OF THE INVENTION
The present invention generally relates to the design and installation of motor-
power based load measurement system in Electrical Overhead Travelling (EOT)
cranes. More particularly, the present invention relates to an improved load
assessment method in Electrical Overhead Travelling cranes to eliminate frequent
calibration of load cells of the Electrical overhead Travelling cranes.
BACKGROUND OF THE INVENTION
According to prior art, at least one rope-tension load cell is mounted on the
lifting rope of hoist motor of an EOT Crane, which measures the slackness or
tension in the rope. The rated output from the load cell is in the range of milli-
volts which is fed as input to a display unit. The electrical signal is converted
proportionally to weight of the material in tons.
The prior art system has an inherent limitation that the basis of load
measurement is the corresponding tension in the lifting rope. Due to continuous
usage and ageing, the hoisting ropes are required to be replaced, alternatively,
the tension in the rope would have undergone changes, which leads to
erroneous reading in the display unit, thereby reducing the reliability of
measurement. In order to avoid display of misleading values, the load cell needs
to be frequently calibrated, at least once in three months. It is therefore
necessary to propose an improved method which completely eliminates the
exercise of calibration, hence considerably increases the reliability of displayed
readings,
a) Patent No. DE112010006017T5-Highly exact volume weighing equipment.

Various embodiments provide a high precision belt weighing device and a high
precision belt weighing method. An exemplary high precision belt weighing
device includes a set of buffer carrier rollers provided between a first and second
belt weighing scale frames. A volume scale hopper is provided above the set of
buffer carrier rollers. A transfer conveyor is provided above the volume scale
hopper. The first and second belt weighing scale frames, the volume scale
hopper, an initial point detector, and a speedometer are connected with a
weighing control instrument by cables. Cumulative weights of bulk materials
handled by each of the first and second belt weighing scale frames, the
corrected weight of bulk materials in the volume scale hopper, and a zero point
in the length of a conveying belt detected by the initial point detector are
displayed on the weighing control instrument.
The above equipment measures volume of materials carried by a moving belt
conveyor whereas the proposed invention measures load lifted by an Electrical
Overhead Travelling crane, hence the above patent is not related to the present .
invention.
b.) Patent No. WO2013037099A1- Crane And Stabilizer Control System And
Control Method Thereof
Disclosed is a crane and stabilizer control system and control method thereof,
the control system comprising a controller (20), a switch control device (10) and
a sensor (30); the switch control device (10) is connected to the controller (20)
to receive a control signal inputted by an operator; the sensor (30) is connected
to the controller (20) to detect the extension and retraction state of each crane
stabilizer; and the controller (20) controls the extension and retraction of each
stabilizer according to the control signal, and also controls the sensor (30) to
detect and judge whether each stabilizer extends and retracts properly according

to the detection result. The control system and control method achieve a better
crane stabilizer control effect.
The above invention talks about establishment of a control system to achieve
better stabilizer control in cranes whereas the present invbention is to measure
the weight of the load lifted by a crane, hence the above patent is not related to
the present invention.
C) Patent No. US8640895B2 - Drum tensioning method and apparatus for load
hoist wire rope.
A drum tensioning method is provided for operating a crane having a
continuously reeved load hoist line, with a first end of the load hoist line
connected to a first drum and a second end of the load hoist line connected to a
second drum, with the load hoist line reeved through boom sheaves and a hook
block. The method includes the steps of applying a hold back force to the second
drum; applying a winding force to the first drum greater than the hold back force
on the second drum; and applying the winding and hold back forces while
limiting movement of the hook block, thereby spooling the load hoist line from
the second drum through the boom sheaves and hook block to the first drum
while maintaining tension in the load hoist line such that the load hoist line is
wound under more tension on the first drum than it had previously been would
on the second drum.
The above invention relates to increasing the tension in wire rope while used as
a hoist line in cranes whereas the present invention measures the load without
changing tension in the rope wire, hence the above patent is not related to the
present invention.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved load
assessment method of Electrical Overhead Travelling cranes to eliminate
frequent calibration of load cells of the Electrical overhead Travelling cranes.
A further object of the invention is to propose an improved load assessment
method of Electrical Overhead Travelling cranes to eliminate frequent calibration
of load cells of the Electrical overhead Travelling cranes, in which the weight
measurement is based exclusively on motor power which is constant for one
particular load, thereby eliminating change in the tension values in the lifting
ropes over time.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved load assessment method of Electrical
Overhead Travelling cranes to eliminate frequent calibration of load cells of the
Electrical overhead Travelling cranes. Experiments were conducted on a similar
EOT crane by individually plotting the values of load lifted versus the
corresponding motor power consumed. The motor power taken from an energy
meter is accepted as the input by an ARM (Advanced RISC Machine)
microcontroller which then assimilates the data and equates it to the
corresponding weight (in tons) by executing a polynomial function. The ARM
microcontroller processes the power data taking as reference, the speed input
from crane control panel and motor direction.

and converts this data into weight in tons and displayed in a seven segment
display unit. The present invention eliminates the drawbacks of the prior art
system which suffer from low reliability of displayed readings and frequent
requirement of load cell calibration leading to loss of manpower, time and
productivity.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
The proposed invention shall be better understood by the following description of
the accompanied drawings.
Figure 1 shows a load versus motor power line trend for a range of motor speed
(105-195 rpm)
Figure 2 shows a block schematic diagram of a load assessment system in an
EOT system.
DETAILED DESCRIPTION OF THE INVENTION
The present method involved study of power versus load characteristics of a
crane by taking note of readings from a power quality meter and simultaneously
lifting of dummy loads by the crane.
Figure 1 shows a sample line trend of load versus the motor power. As part of
the preliminary experiment conducted on the crane, the motor power was
measured with a power quality analyzer and the values recorded against
respective values of weight lifted. The weight of the load is plotted along the X-
axis and motor power along the Y-axis. The line trend indicates values

for a speed range of the motor and the results are tabulated below :

Based on the readings taken above, a system was developed which accepts
motor electrical power as input, processes the parameters and displays total
weight of the load in a 7-segment display unit.
Figure 2 shows the block schematic diagram of a load measurement system
which is adapted for load assessment of EOT cranes. A known 3 phase energy
meter (01) with RS485 communication interface accepts individual phase current
inputs (02, 03, 04) from each of three phase current transformers. The energy
meter (01) also accepts phase-to-neutral voltages taken from the input power
supply (05, 06, 07). The energy meter (01) then assimilates the voltage inputs
(05, 06, 07) and current inputs (02, 03, 04) and calculates total power consumed
in kW. An RS232/RS485 converter (08) transfers the data from RS485
communication port to RS232 serial communication port available in an ARM
Microcontroller (09). The converter (08) transfers requisite data from energy

meter (01) to an ARM Microcontroller (09). The ARM microcontroller (09)
generates a polynomial equation with the data taken from the energy meter
(01). The corresponding polynomial function is then implemented taking as
reference the two inputs - A speed input relay (10) and the motor direction (11).
A three digit large size seven segment display unit (12) is connected through
another port of the ARM microcontroller (09), which displays the corresponding
weight in tons.
The proposed method eliminates the inherent limitations of the existing method
of frequent calibration, reduced reliability and loss of manpower, time and
productivity, thereby bringing substantial improvement.

WE CLAIM :
1. An improved load assessment method of Electrical Overhead Travelling
cranes to eliminate frequent calibration of load cells of the Electrical
overhead Travelling cranes, comprising the following data processing
instruments :-
providing a known three-phase energy meter to calculate the net power
consumed by the crane motor;
providing a known Advanced RISC machine based microcontroller which
receives data from the energy meter and converts the power consumption
data to weight in tons; and
connecting a display unit with the microcontroller to convert the analog
output data from the microcontroller to digital data and display the
indicative value of the crane load lifting in tonnage.
2. The method as claimed in claim 1, wherein the energy meter (1) having a
RS485 communication interface, and wherein the energy meter is fed with
individual current inputs (02,03,04) from each of three phase current
transformers.
3. The method as claimed in claim 1, wherein the energy meter is fed with
phase-to-neutral voltages (05,06,07) taken from an input power supply.
4. The method as claimed in claim 1, wherein the processed output data
from the energy meter is converted by a converter (08) and transferred to
the microcontroller (09), and wherein the microcontroller generates a
polynomial data relationship for implementing said generated relationship
between output data processed in the energy meter (1) and weight in
tons.

5. The method as claimed in claim 1, wherein the display unit (12)
connected to the microcontroller (09) displays the indicative value of
lifting weight in tons.
6. The method as claimed in claim 1, wherein a speed input relay (10) is
optionally provided to determine the crane speed including the motor
rotational direction (11).