Abstract
Underwater Inspection, Maintenance, and Repair operations are nowadays performed using Remotely Operated Vehicles (ROV) deployed from dynamic-positioning vessels, having high daily operational 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.
Highlights
Inspection, Maintenance, and Repair(IMR) operations at sea remain extremely costly and time-consuming, requiring the use of heavy-weight Remotely Operated Vehicles (ROV) supported by large Dynamic Positioning (DP) vessels and complex Tether Management Systems (TMS)
In the last three decades, research in autonomous underwater robots and robotic intervention has been slowly gaining speed, aiming to tackle some of the IMR tasks that could in future be performed by Intervention Autonomous Underwater Vehicles
The research started with the pioneering works of OTTER [1], ODIN [2], UNION [3] and AMADEUS [4], which contributed in developing core technologies
Summary
Inspection, Maintenance, and Repair(IMR) operations at sea remain extremely costly and time-consuming, requiring the use of heavy-weight Remotely Operated Vehicles (ROV) supported by large Dynamic Positioning (DP) vessels and complex Tether Management Systems (TMS). That paper reports experimental results obtained on autonomous manipulation in the presence of a priori unknown obstacles Another typical IMR task already demonstrated is pipe inspection [11]. MARIS was an Italian project [17] which experimentally demonstrated single-vehicle floating-base object recovery, as well as the kinematic simulation of a cooperative load transportation task. The transportation phase requires only two steps: 1) Independent optimization of the full TP hierarchies for each of the robots separately, with safety tasks at the top, based on the EE velocities required to move a transported pipe to a specific position with a specific orientation, 2) Normalization of the resulting velocities which ensures that each of the robots can achieve EE velocity in all directions (linear and angular). While the first step is equivalent in both algorithms, our velocity normalization (step 2) allows solving the problem with one TP computation only, ensuring that the desired EE velocities are possible to achieve while satisfying all the safety tasks
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