Robust Hierarchical Sliding Mode Control of Double-frame Mobile Robot with Suction Cups*

In this paper, a novel double-frame mobile robot with suction cups for aircraft skin inspection is studied. A robust hierarchical sliding mode (RHSM) scheme is presented to ensure the state stabilization of the robot system. Initially, the double-frame robot moving on the curved surface is analyzed, the nonholonomic constraint equations are established, and the dynamic model of the mobile double-frame robot is derived through Lagrange method. Then, a RHSM controller is designed, including a hierarchical sliding mode controller for sliding motor, rotating motor and leg cylinder, and an observer for estimating the total uncertainty. It is shown that the system is closed-loop stable, and the system variables are asymptotically stable. Simulation section is given to illustrate the effectiveness of the RHSM method proposed in this paper.