Step-by-step sliding mode observer for control of a walking biped robot by using only actuated variables measurement

A step-by-step observer based on second order sliding mode approach is proposed to determine the absolute orientation of a biped robot during a walking cyclic gait. The gait are composed of single support phases and impacts. The biped is underactuated in single support because there is no motor in the ankles. The observer and the control law converge in finite-time. The originality is both: firstly, the observer is based on second-order sliding mode approach and is original in biped robot context Secondly, the estimation of all state variables are derived from only actuated joint variables, which induces a minimization of the sensors number. Numerical tests are proposed to show the robustness of the observer coupled with the control.