Adaptive control of an underactuated spherical robot with a dynamic stable equilibrium point using hierarchical sliding mode approach

SUMMARY Unlike the traditional underactuated mechanical system, the equilibrium point of the inner swing-up suspension of a spherical robot possesses stable and dynamic characteristics. The stable dynamic equilibrium position of the underactuated suspension must agree well with the uncertain rolling resistance in practice. To overcome this special underactuated problem with dynamic equilibrium, we present an adaptive control scheme to enhance the ground adaptability using hierarchical sliding mode approach. The control method can drive the spherical robot to a desired position, and at the same time, the suspension subsystem holds on their dynamic equilibrium points rapidly. The proposed control approaches are verified to be effective by numerical simulation for a spherical robot to achieve satisfactory control performances, such as ground adaptability, rapid convergence, and disturbance rejection. Copyright © 2013 John Wiley & Sons, Ltd.