A New Wheelchair Ergometer Designed as an Admittance-Controlled Haptic Robot

Abstract

Wheelchair ergometers aim to simulate the propulsion of a wheelchair in a controlled laboratory setup. One drawback of current ergometers is that the simulated wheelchair is always modeled as a simple unidimensional mass and friction, which do not allow a correct simulation of turning maneuvers. In this paper, we present a new design for a wheelchair ergometer based on haptic robotics. This ergometer allows us to simulate any linear or nonlinear model of the wheelchair-user system in real time, including models that implement turning maneuvers. The presented prototype was validated experimentally. The rear wheels of the ergometer match the rear wheels' velocities of the simulated wheelchair with a root-mean-square error of 0.9 %. Therefore, the ergometer's accuracy is mainly bounded by the accuracy of the wheelchair-user model, which means that future improvements of the wheelchair-user model will be directly reflected by the ergometer. The conditions for stability were also evaluated. A minimal simulated mass of 18 kg and a minimal simulated moment of inertia of 1 kg ·m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> are needed. These requirements are encountered by any wheelchair-user combination.