Robust Swing-Up and Balancing Control Using a Nonlinear Disturbance Observer for the Pendubot System With Dynamic Friction

This paper proposes the robust swing-up and balancing control method using a nonlinear disturbance observer for the pendubot system in the presence of dynamic friction. First, the uncertainties in the pendubot system are verified through the experiment to take the form of a continuous and differentiable friction model. Then, the uncertainties present in both actuated and unactuated dynamics are shown to have the coupled form between them through the analysis, such that they can be compensated by estimating only one of them. In order to compensate for the uncertainties, the robust swing-up control is proposed. Then, the limit-cycle phenomenon, which appears around the unstable equilibrium point due to the uncertainties is compensated in the robust balancing control using the nonlinear disturbance observer, and the disturbance estimation errors are shown through the stability analysis to converge to zero. Finally, the performance and the validity of the proposed method are verified through both simulation and experimental results.