Revisited adaptive sliding mode control of underactuated mechanical systems with real-time experiments

In this paper, the stabilisation problem of a second-order underactuated mechanical system, namely the inertia wheel inverted pendulum, is addressed. Stabilising control design for this system is quite challenging since the control approaches designed for fully actuated systems could not be straightforwardly applied to such a system. We propose a new approach based on a first robust sliding mode controller (SMC) and an adaptation law that does not require the knowledge of uncertainties and perturbations bound and guarantees sufficiently small gain. To resolve the problem of underactuation, the proposed approach is based on a global change of coordinates, transforming the system into a cascade interconnection of linear and nonlinear subsystems. Through this transformation, two new desired trajectories are proposed for the design of the controller. Extensive real-time experiments are conducted to validate the effectiveness of this approach, where the first-order sliding mode controller and the adaptive sliding mode scheme are compared. The experimental results show that the proposed adaptive approach outperforms the original sliding mode controller in terms of external disturbance rejection.