Hierarchical Sliding Mode Control for 7-DOF Overhead Cranes

This paper presents a hierarchical sliding mode control (HSMC) strategy for a 7-DOF crane system, incorporating three-dimensional double-pendulum dynamics and variable rope length, which has often been neglected in previous studies. The control objective is to track the reference trajectory while suppressing load vibrations. To achieve this, the system dynamics are decomposed into actuated and unactuated subsystems, each associated with a sub-sliding surface. A high order sliding surface is then constructed to integrate these subsystems, and a control law is derived to drive all system states toward the reference trajectory. Finally, simulation results confirm the effective performance of the proposed method.