Disturbance adaptive control for an underactuated spherical robot based on hierarchical sliding-mode technology

An adaptive hierarchical sliding mode control (AHSMC) scheme is presented for a spherical robot, whose inner suspension is in an underactuated state driven by the motor. In this scheme, the underactuated spherical robot system is divided into sphere rolling and inner suspension subsystems according to the movement. Then a first layer sliding surface is defined for each subsystem. Based on the first layer sliding surface, a second layer surface is introduced correspondingly. Considering the unavoidable disturbance and the dynamics of the unstructured environment, we adopt an adaptive control scheme to estimate the uncertain disturbance. The adaptive control method, which can drive the subsystems´ states approaching to their sliding surface rapidly, is obtained by using Lyapunov stability theory. The simulation results demonstrate the controller´s validity and adaptive ability.