Experimental Comparison of Kinematic Task-Priority Control Methods for an Articulated Intervention-AUV

Abstract

This work revisits two classical closed-loop inverse kinematics (CLIK) formulations for hierarchical control and investigates their differences in the context of articulated intervention-autonomous underwater vehicles (AIAUVs). The class of AIAUVs consists of free-floating, slender, multi-link vehicles with distributed thrusters and no distinct base, allowing the entire vehicle to be modeled and controlled as a manipulator. The concept of body-velocity sharing, a phenomenon where different tasks depend on overlapping body-frame motions, is introduced and formalized through the notion of body-sensitivity subspaces. Changing the location of the system’s body-frame is shown to directly affect both controllers’ closed-loop performance, and it shown that due to body-velocity sharing, tasks for AIAUVs most often fall into an intermediate regime between orthogonal and strictly incompatible tasks, causing the two task-priority formulations to differ. The theory is validated through open-water field trials with the Eelume-M, a 6-meter-long AIAUV, comparing the two control laws. The experiments confirm the theoretical predictions: the projected-residual law improves secondary-task tracking but is more sensitive to algorithmic singularities, whereas the post-projection law remains robust to such singularities at the cost of reduced secondary-task performance. These results provide practical guidelines for selecting kinematic task-priority control laws and body-frame placement for AIAUVs.