Abstract:
This thesis reports on the development of a double inclined plane (DIP) transducer
system based upon the principles of force reaction. This transducer had a design
specification to measure the true mass of “free” flowing granular materials, primarily
agricultural crops, with an accuracy of ± 2 % on total mass flowed for flow rates
between 1 and 10 kg/s. Two absolute values are used to assess accuracy in this study,
(i) the total mass flowed (kg), a measure of the mass accumulation and, (ii) the mass
flow rate (kg/s), a ‘spot’ reading of flow rate. The performance of the novel system has
been evaluated through theoretical, laboratory and field studies and consideration has
been given to the commercial and business aspects of the manufacture, marketing and
further development of the device.
Following mathematical and laboratory studies of the sponsors current force reaction
transducer - a single reaction device, angular variations were highlighted as having a
significant effect upon output. A further study found that the least sensitive reaction
plate angle was 55° To overcome this problem, the double inclined plane (DIP)
concept was developed, 2 single reaction plates, joined along their apexes, angled at 55
degrees to the horizontal, mounted upon a horizontal strain gauged beam. Angular
compensation when tilting the transducer was provided by generating a higher force
from the shallower face and a lower force from the steeper face. A mathematical model
of the new transducer allowed the output to be predicted to within 1.7 %. Initial
calibration was undertaken in the laboratory and tested using a combine clean grain
system simulation apparatus. In-situ machine studies were performed by mounting the
transducer in a New Holland TF42 combine, firstly on an extended bubble up auger
and finally in the drop box, between the clean grain elevator and bubble up auger.
Initial pilot studies were conducted with the combine static to calibrate the system and
finally a full harvest field trial was undertaken.
Over the harvest field trial, the accuracy on accumulated mass was better than 0.9 %
over 127 tonnes. Tramline effects upon transducer output were found to be self
cancelling, as the resulting positive and negative ‘spikes’ in the signal, when summed
over time approximated to zero. Changes in pitch angle, up to 10 degree caused
between 1.5 and -2.8 % randomly distributed error. Roll angles up to 7.5 degrees,
caused between -0.9 % and 1.7 % randomly distributed error in static trials. Field beans
and oilseed rape required calibration constants 6.8 % and 3.1 % lower than that for
12.5 % moisture content wheat, but with adjusted calibration constants, gave excellent
repeatable results. Increasing moisture contents of up to 30 % in wheat resulted in the
transducer under reading by, on average, 1.6 %.
An assessment of manufacturing costs was made and the unit cost was £154.12 each
for 30 units reducing to £109.59 each for 3000 units. It is recommended a pricing
objective of maximising sales growth is used which will position the device at the less
expensive end of the market. Due to commercial sensitivity, a draft patent has been
written to protect the DIP concept. The first stages of commercial adoption already
being undertaken by a major multi-national agricultural machinery company, who are
evaluating a pre-production prototype.
This thesis provides the systems, data and principles required to create a novel,
commercially practical transducer system, based upon the principles of force reaction.
The problem of angular compensation has been overcome in a simple and effective
manner offering a relatively inexpensive but accurate method of measuring mass flow
rate, which has already received commercial interest.