Designing a Fractional Order Back-Stepping Controller Based on GPI Observer for a 3D Biped Robot

This paper proposes an active disturbance rejection control (ADRC) method based on generalized proportional integral (GPI) observer to control of a biped robot while considering its complicated structure and possible disturbances. These observers are used to estimate time-varying disturbances and possible uncertainties. Generally, implying GPI observer on robotic systems is accompanied by a PD-controller in feedback, which is not efficient enough due to abrupt velocity changes of the biped in impact phase, and consequently, a higher level of input torque is required. Thus, applying the back-stepping technique to the mentioned method is suggested. In this study, a two-nested control loop is designed for a 3D biped robot. The back-stepping method with a GPI observer is used in the inner control loop to improve the custom method. Joint trajectories are designed by an offline method and modified by an online method in the outer loop to maintain the stability of the biped. The efficiency of the proposed control strategy is depicted for the biped in the presence of time-varying disturbances through MATLAB simulation.