Instrumentation & Measurement Magazine 23-6 - 35
walked over the platform
and transmits this data to
the PC serially.
Calculating Center of
Pressure
Fig. 5. Functional block diagram of the system's electronic hardware.
as a slave device. The inter-block SPI communication between
the ADC and the slave microcontroller is multi-directional;
the ADC registers can be programmed, and it can also transmit digitized load cell data to the microcontroller. The master
microcontroller (Arduino Mega) controls when to request and
receive information from the four slave microcontrollers via
the industry standard RS485 communication bus. This information is then sent serially to the PC running the analysis and
plotting software. The EID reader identifies which cow has
One of the most significant variables to correctly
classify lameness is related to the position of the
force applied. The position
variables can be used to determine irregularities in
stride length, step overlap
and step abduction. These
variables provided a strong
correlation for classification [10].
To determine the center
of pressure (COP) location
on the platform, an algorithm was designed to find the X and Y positions using the
four load cell signals. When the load cells are under pressure,
reaction forces are generated. These forces, F1, F2, F3 and F4,
are shown in Fig. 6 to illustrate how the reaction forces correspond to the position of the load cells, with LC1 representing
load cell 1. The distance between LC1 and LC2 or LC3 and LC4
on the x axis is the width measurement and the distance between LC1 and LC3 or LC2 and LC4 on the y axis is the length
measurement. The total force (FT) on the platform is found using the previously calculated summation of the four load cell
signals, with these being F1 + F2 + F3 + F4. The COP is a coordinate (x, y) that can occur at any position within the dotted line
perimeter and is calculated using (1) and (2). The coordinates
for LC1 are (0, 0).
x
F 2 F 4 Width (1)
y
F 3 F 4 Length (2)
FT
FT
Recording and Plotting Weight and Position Data
Fig. 6. Center of pressure calculation.
September 2020
The software records relevant data received from all the four
platform segments and writes it to a text- file using the following format:
TIME, SLAVE, CH1, CH2, CH3, CH4, Total Weight, X-Position, Y-Position, Peak
TIME is the timestamp that the data was captured
SLAVE is the ID of the section
CH1 - 4 is the force (kg) experienced on each load cell rounded
to 2 decimal places
Total Weight is the total weight experienced on the section (kg)
X-Position/Y-Position is the center of pressure on the section
(mm)
IEEE Instrumentation & Measurement Magazine 35
Instrumentation & Measurement Magazine 23-6
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