TWINBOT: Autonomous Underwater Cooperative Transportation
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Underwater Inspection, Maintenance, and Repair operations are nowadays performed using
Remotely Operated Vehicles (ROV) deployed from dynamic-positioning vessels, having high daily opera-
tional costs. During the last twenty years, the research community has been making an effort to design new
Intervention Autonomous Underwater Vehicles (I-AUV), which could, in the near future, replace the ROVs,
significantly decreasing these costs. Until now, the experimental work using I-AUVs has been limited to a
few single-vehicle interventions, including object search and recovery, valve turning, and hot stab operations.
More complex scenarios usually require the cooperation of multiple agents, i.e., the transportation of large
and heavy objects. Moreover, using small, autonomous vehicles requires consideration of their limited load
capacity and limited manipulation force/torque capabilities. Following the idea of multi-agent systems,
in this paper we propose a possible solution: using a group of cooperating I-AUVs, thus sharing the load
and optimizing the stress exerted on the manipulators. Specifically, we tackle the problem of transporting
a long pipe. The presented ideas are based on a decentralized Task-Priority kinematic control algorithm
adapted for the highly limited communication bandwidth available underwater. The aforementioned pipe
is transported following a sequence of poses. A path-following algorithm computes the desired velocities
for the robots’ end-effectors, and the on-board controllers ensure tracking of these setpoints, taking into
account the geometry of the pipe and the vehicles’ limitations. The utilized algorithms and their practical
implementation are discussed in detail and validated through extensive simulations and experimental trials
performed in a test tank using two 8 DOF I-AUVs