Safety-Critical Steering Control for Rubber-Tired Container Gantry Cranes: A State-Interlocked CBF Approach

Abstract

The rubber-tired container gantry crane (RTG) is a type of heavy-duty lifting equipment commonly used in container yards, which is driven by two-side rubber tires and steered via differential drive. While moving along the desired path, the RTG must remain centered of the lane with restricted heading angle, as deviations may compromise the safety of subsequent yard operations. Due to its underactuated nature and the presence of external disturbances, achieving accurate lane-keeping poses a significant control challenge. To address this issue, a robust safety-critical steering control strategy integrating disturbance rejection vector field (VF) with a new state-interlocked control barrier function (SICBF) is proposed. The strategy initially employs a VF path-following method as the nominal controller. By strategically shrinking the safe set, the SICBF overcomes the limitations of traditional CBFs, such as state coupling in the inequality verification and infeasibility when the control coefficient tends to zero. Furthermore, by incorporating a disturbance observer (DOB) into the quadratic programming (QP) framework, the robustness and safety of the control system are significantly enhanced. Comprehensive simulation and experiment are conducted on a practical RTG with a 40-ton load capacity. To our best knowledge, the proposed method is one of the very few methods that have demonstrated successful application to the practical RTG systems.