WP6 “Control architecture” focuses on the whole-body control of the overall underwater vehicle manipulator system (UVMS). The control system is in charge of executing a bathymetric survey of an area of interest, on the basis of which the UVMS autonomously chooses the most promising area where the mining nodules could be found. Then, the UVMS performs a successive, low altitude survey, where optical sensors can detect the nodules. Whenever a possible nodule is found, the control system guides the UVMS to land on the seafloor, and then moves the LIBS attached to the manipulator close to the detected nodule.
The control system developed in WP6 follows a hierarchical approach (Fig. 1), where a kinematic control layer generates reference velocities for an underlying dynamic control layer.
Owing to the modular structure of the ROBUST UVMS, the dynamic control layer exploits a specific dynamic model developed within WP6, based on the composition of the dynamic models of basic elements, as shown in Fig. 2.
Finally, the Kinematic control layer implements a task priority inverse kinematics framework. This framework allows the UVMS to take care of many concurrent control objectives, such as following the survey path, while maintaining a given altitude from the seafloor, aligning to the desired velocity to reduce energy consumption (i.e. avoiding later translations), and so on. As an example of multi objective behaviour, Fig. 3 shows the control system aligning the vehicle to the nodule, and keeping the vehicle at a distance within two predetermined thresholds, before the final landing is accomplished. This is necessary to make sure that the nodule to be inspected is within the manipulator’s workspace during the subsequent manipulation phase, which is occurring when the vehicle has landed.