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

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 ·m² are needed. These requirements are encountered by any wheelchair-user combination.