Modular modeling and coordination control scheme for an underwater cooperative transportation performed by two I-AUVs

Intervention Autonomous Underwater Vehicles (I-AUVs), also known as Underwater Vehicle Manipulator Systems (UVMSs), are an alternative for reducing costs and increasing safety in underwater operations which require dexterous manipulation. Beyond the well-posed and currently studied manipulation scenarios, the cooperative underwater transportation is a promising and challenging task, still not extensively explored. This paper aims to contribute to this latter problem by addressing the modeling and control system design of a cooperative underwater transportation performed by two planar I-AUVs, each of them composed by an AUV linked to a 2-Degrees of Freedom (DoFs) serial manipulator. A hierarchical approach for deriving the equations of motion through the Modular Modeling Methodology (MMM) is presented. Also, a complete coordination scheme composed of the Inverse Kinematics (IK) and motion control modules is proposed. A new IK control is formulated on the jerk level with the Super-Twisting Algorithm (STA) to prevent numerical drift and uncertainties while considering secondary objectives. The low-level motion control is synthesized within a continuous Sliding Mode Control (SMC) algorithm to compensate for the modeling errors and external disturbances. The coordination scheme is verified through numerical simulation considering a scenario in which an object is transported by the two I-AUVs over a predefined path. The analysis is made more realistic by considering the thrusters and motors dynamics along with sensors measurements, sampling effects and an optimal state estimator. Modeling errors and external disturbances are also considered in the analysis. The results reveal the suitability of the proposed modeling and coordination approaches for numerical simulation and control of the I-AUVs during underwater transportation.