Parameter Design of Disturbance Observer for a Robust Control of Two-Wheeled Wheelchair System

The wheelchair system presented in this research has only two wheels. This mechanical choice increases the maneuverability of the wheelchair itself, making the system more agile and able to overcome small obstacles (e.g. step, bump, rough terrain, etc.) in different kinds of environments. In addition, the user is able to train her/his body, since it is necessary to lean the body forward and backward to drive the wheelchair along the corresponding direction. Besides these advantages, there is a big drawback: the system is naturally unstable. For this reason, a motion controller is necessary to keep the wheelchair balanced. Furthermore, it is not possible to have a direct control along the pitch direction and a stable configuration is reached only through the actuation of the wheels. In order to estimate the torque acting on the pitch direction, the synthesized pitch angle disturbance observer (SPADO) is introduced. The results collected by SPADO combined with a Lyapunov controller makes the stabilization possible. During the design phase, particular attention should be paid to the inertia parameters variation, otherwise the performance of the entire system decreases. A detailed stability analysis is carried on to identify, from a theoretical point of view, the best parameter tuning. Then, the results from the experiments on the real platform are presented to verify the theoretical results.