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.

I. Introduction

A mobile robot is one of the well-know nonholonomic systems, which has attracted significant attention owing to its important application prospect in many fields, such as tube inspection robots in industrial production [1], cleaning robots meet industry and domestic needs [2], inspection robot in power system [3]. This paper introduces a double-frame mobile robot with suction cups (Fig. 1), which is mainly used for aircraft skin inspection, working on curved surface. This leads to complex nonlinearity, uncertainty and strong coupling of the system, which brings challenges to the controller design.