Obstacle surpassing and posture control of a stair-climbing robotic mechanism

In this study, we propose a new kinematic control for a robotic stair-climbing mechanism which allows successful obstacle surpassing when faced with typical architectural barriers such as curbs, ramps or staircases while maintaining the passenger's comfort and the seat's inclination within security margins. The scheme also takes into account perturbations in the system due to the fact that the environment is not perfectly known. The actuated degrees of freedom in charge of the locomotion device and the posture device are controlled in a different way. The locomotion control is achieved with a feedforward term and a standard proportional derivative (PD) control position. The posture control is obtained with a novel variant of multilevel feedback controller design via a suitable combination of a Lyapunov feedback controller design along with a multilevel generalization of the sliding mode based Sigma–Delta (Σ–ΔΣ–Δ) modulator coupled with an adequate selection of the trajectory of the center of mass. The main features of this novel kinematic control algorithm are: maintenance of the passenger comfort, high degree of perturbation rejection regarding modeling error, independence of the designed control law on the environment parameters, computational efficiency and minimal sensor requirements. Numerical simulations illustrate the performance of the proposed method when the prototype is to surpass an obstacle with different heights with the value of the height obstacle being unknown. Finally, experimental results validate the behavior of the prototype for, both, obstacle surpassing and posture control when the wheelchair prototype ascends a curb of 180 mm.