A COMPARISON OF DIFFERENT ASSISTANCE STRATEGIES IN POWER ASSISTED WHEELCHAIRS USING AN OPTIMAL CONTROL FORMULATION

摘要

Power assisted wheelchairs are a promising solution tornovercome problems associated with manual wheelchairrnpropulsion, such as the incidence of upper limbs injuriesrnand muscle fatigue. However, there are still open questionsrnregarding the most appropriate assistance strategy. Thernmain goal of this paper is to compare three different typesrnof assistance in power assisted wheelchairs: constant force,rnproportional force and a novel type of assistance inspiredrnon the impedance control theory. The comparison was performedrnusing a simple model and an optimal control formulationrnthat searched for optimal user actuation and controllerrnparameters so as to minimize the user effort. Thernfairness of the comparison was ensured by imposing an upperrnbound on the energy consumption by the motors. Thernresults show that the proportional and impedance controlbasedrnstrategies are the most appropriate steady state conditions.rnIn typical daily activities such as obstacle avoidance,rnthe impedance control has advantage as it permits a fasterrnsystem’s response.