Researchers from the Department of Mechanical and Civil Engineering at California Institute of Technology have developed a robust model predictive control (MPC) framework for safe payload transfer using ship-mounted cranes. The team, led by Ersin Das and Joel W. Burdick, has tackled the unique challenges posed by the dynamic and unstructured environments in which these cranes operate.
Ship-mounted cranes face significant external disturbances due to the ship’s motion in harsh sea conditions, which can lead to robustness issues in underactuated crane dynamics. Traditional crane systems do not encounter these challenges to the same extent. The researchers aimed to ensure safe real-time control while maintaining effective payload transfer performance, even in the presence of these disturbances.
The proposed robust and safe MPC framework was demonstrated on a 5-DOF crane system. To simulate the external disturbances caused by ocean surface motions, a Stewart platform was used. The crane payload transfer operation needed to avoid obstacles and accurately place the payload within a designated target area. The researchers employed a robust zero-order control barrier function (R-ZOCBF)-based safety constraint within the nonlinear MPC to ensure safe payload positioning. Time-varying bounding boxes were utilized for collision avoidance.
One of the key innovations in this research is the introduction of an optimization-based online robustness parameter adaptation scheme. This scheme helps reduce the conservativeness of R-ZOCBFs, making the control approach more effective in real-world scenarios. The researchers conducted experimental trials on a crane prototype to demonstrate the overall performance of their safe control approach under significant perturbing motions of the crane base.
The practical applications of this research are significant for the marine sector. Ship-mounted cranes are crucial for various operations, including loading and unloading cargo, transferring supplies, and handling equipment. Ensuring safe and efficient payload transfer in dynamic environments is essential for the safety of personnel and the integrity of the cargo. The robust MPC framework developed by the researchers can enhance the safety and efficiency of these operations, even in challenging sea conditions.
Moreover, the methods developed in this research are not limited to crane-facilitated transfer. They can be applied more generally to safe robotically-assisted parts mating and parts insertion, broadening the potential impact of this work. The researchers’ focus on real-time control and safety constraints addresses critical needs in the maritime industry, where operational efficiency and safety are paramount.
This research represents a significant advancement in the field of control systems for maritime applications. By addressing the unique challenges of ship-mounted cranes, the team has developed a robust and safe control framework that can improve operational performance and safety. The experimental validation of their approach underscores the practical applicability of their methods, paving the way for broader adoption in the marine sector and beyond. Read the original research paper here.