Hug and Haul: Object Transport by Tube-Connected Robots
Cooperative object transportation by mobile robots has applications in logistics, manufacturing, and service robotics. In this project, we developed Hug and Haul, a complete path-planning and tracking-control framework for multiple mobile robots interconnected by deformable tubes. The tube connections allow the robots to enclose and transport both single large objects and multiple small objects without grasping them. The transportation task is divided into three stages: approaching the objects, enclosing them, and transporting them to the desired location.
We first construct collision-free travelling corridors around paths generated by RRT*. Within these corridors, smooth minimum-jerk Bézier paths are generated and reparametrized to maintain suitable inter-robot spacing. Centralized and distributed controllers then drive the robots along the planned paths while preserving the tube-connected formation. An adaptive compensation term addresses unknown object and environmental resistance during transport, without requiring measurements of contact forces or prior knowledge of object mass and friction coefficients. Input-to-state stability analysis shows that robot position errors remain bounded while the reference curve evolves and converge to zero after it stops changing. Numerical simulations and hardware experiments with objects of different shapes, quantities, and spatial distributions demonstrate collision-free motion, stable tracking, and successful transportation of single, clustered, and sparse objects under both control schemes.
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