Forces applied and space required relationship for four caster vehicle manoeuvres

Abstract

Four-caster manually manoeuvred vehicles are ubiquitous with functions varying from goods movement to transport devices for disabled people. Manual handling related health and safety concerns have been raised but no theoretical study has been published. The few empirical studies which exist have not related dynamics to kinematics and no substantive guidance exists for disability adaptation planning for these vehicles. A novel graphical method of inspecting the kinematics is developed: the vehicle translational velocity regions in which di erent combinations of wheel angular velocity directions occur are identi ed. Theory predicts that these varying combinations of wheel angular velocity directions, along with the caster orientations which arise from them, result in 1) di erent motion resistance reactions at each of the four caster assembly contacts with the vehicle-frame, 2) a variation in the proportion of the summation of those reactions to the resulting moment acting on the vehicle-frame and 3) substantial variation in the handle-forces required to balance these two motion resistance e ects. An empirical study is devised from the theory. Sixteen subjects made planar manoeuvres from static equilibrium with a maximum comfortable load while attempting to maintain eleven (maximum) di erent centres of zero velocity which related to the velocity regions. Results showed substantial inter-manoeuvre di erences in maximum comfortable load: the loads of the manoeuvres with the two largest maximum comfortable loads are approximately 100% greater than the loads of the two manoeuvres with the smallest maximum comfortable load. The four-caster manually manoeuvred vehicle is mechanically omni-directional but the human operator is e ectively constrained. The results con rm the predictions for the rst-order e ect. The results are important for adaptation planning: environments can be planned to maximise the operator's load capacity. As the study is based on the relative di erence between manoeuvres the results are applicable to various oor coverings and vehicles. The forces-applied and space-required relationship for these vehicles is not intuitive but the results are presented graphically and are therefore accessible to those in adaptation planning services. Further work includes investigation of second-order e ects and the e ects of wall constraints rather than maintenance of centres of zero velocity. In loose but concise terms this work shows how the architectural spaces which make manoeuvres easy or di cult can be identi ed.