The compass-like biped robot revisited: Nonlinear control of the disturbed passive dynamic walking

When dealing with passive walking, it has been proved in the literature that the compass-like biped robot can walk down without actuation and with a stable gait. However, the stability of gait is very sensitive to disturbances such as ground irregularity, default in manufacturing, etc. Thus, in this paper, we propose an approach to control the biped robot gait when it has disturbance. This approach benefits from the characteristics of the undisturbed passive gait, in the aim of stabilizing the disturbed one. Indeed, initially, the proposed approach considers the state variables of the passive gait as references. Next, it predicts them for every walking step. After that, the predicted model is considered by the controller to compute the joint torque. As result, The robot would generate an active dynamic walking (ADW) identical to the passive dynamic walking (PDW) and the error between the current state trajectories and the reference trajectories will be canceled. The prediction was performed by two mathematical functions which are set of Fourier series and polynomial functions. The proposed approach is based on an inverse dynamics controller, evaluated through numerical simulations and compared with another approach based on energetic control.