The measurement of the cargo weight on semi-trailer trucks is required to several
stakeholders in the logistics market, for this information can reduce expenses
on vehicle maintenance, risk for load traffic fines and ensures safer driving of
the vehicle. The state-of-the-art on on-board weighing systems of semi-trailers
with leaf spring suspension adopt several techniques to estimate the load:
solutions based on load cells, vibrating-wires force transducers or strain
gauges on the chassis, on the suspension springs or on the axles of the vehicle.
In this work, a new system based on hall effect sensor was developed and tested
for measurement of the axle load in semi-trailers through the linear movement
that occurs between the trailer axle and its chassis. This solution has low
sensitivity to environmental phenomena not caused by human intervention, such as
humidity or temperature variations. A lab test was made to compare some
arrangements of magnets and hall effect sensors to find out which interaction
provides the best linear response for the displacement range. Next, a mechanical
prototype and an embedded hardware were designed and assembled into a tank
semi-trailer to test the system at the facilities of Librelato Semi-trailers
factory. The test routine consisted of several known water loads in the tank of
the semi-trailer, which would repeatedly position its axles over a certified
weighbridge. A data acquisition software was developed to capture measure points
during loading and unloading processes. When comparing to the weighbridge, the
system response presented variations that goes from 15%, with an empty tank, to
2% error, with a fully load tank. The proposed system accomplished good results
within the tests conditions and the traffic legislation and presents a
competitive development cost, indicating that a further development could be
done in order to reach the market.