Abstract
The objective of this thesis is to develop an understanding of the brushing process for a road sweeper so that a theoretical model of the process can be developed. The brush model has been confined to the kerb operating channel brush that usually sweeps about 80% of the debris on the road in the region of the kerb. The other 20% is swept by a roller brush beneath the vehicle. This has not been included in the study. A concept for a semi-autonomous road sweeping vehicle has also been proposed in order to sweep debris efficiently with minimum fatigue for the vehicle driver, although the debris sensing and control system have not been developed in this thesis. The metal tines of road sweeping brushes are usually rectangular in section (unlike cleaning brushes which are circular in section), giving rise to two commercial brush types. These are the flicking brush (major axis in the radial direction) and cutting brush (major axis in the tangential direction). A theoretical steady-state model of these two brushes has been developed which allows the calculation of brush axial loads, torques and tine deflection geometry as the brush rotates. The theoretical model has been validated experimentally within acceptable limits although this does require an experimental choice of the co-efficient of friction between the tines and the ground, usually between 0.6 and 0.7 for commercial brushes sweeping on concrete and tarmacadam surfaces. A dominant feature of the brush characteristics is the tine wear, as the brush stiffness increases over 120% as the tine shortens by 40%, which is the recommended minimum length taking into account brushing efficiency and damage to the road surface. The model can also be used as a tool to design new brushes so that, for example, by rotating the tine by 30 to 40° from the cutting brush configuration a 20% improvement in mechanical efficiency is predicted. In order to assess the mechanism of debris removal from the road and its subsequent collection by the vacuum unit, the brush model has been incorporated into a brush sweep-gear linkage used by commercial vehicles to track the edge of the kerb. It has been shown that a constant brush contact arc on the road can be maintained by adjusting the brush angle of attack and brush height and that this relationship is independent of the vehicle speed and brush linkage with respect to the kerb. Under these contact conditions efficient sweeping may be expected. In the case of the Johnston 600 sweeping vehicle the brush contact arc angle is 150°. This parameter is used as the output criterion for automatic control schemes that have been proposed to improve brushing efficiency and reduce driver fatigue. These will require the development of an on-line brush height sensor that can also measure brush wear.