Satellite-based tele-operation of an underwater vehicle-manipulator system. Preliminary experimental results Paolo Di Lillo, Daniele Di Vito, Enrico Simetti, Giuseppe Casalino, Gianluca Antonelli Abstract—Within the European project DexROV the topic of underwater intervention is addressed. In particular, a remote control room is connected through a satellite communication link to surface vessel, which is in turn connected to an UVMS (Underwater Vehicle-Manipulator System) with an umbilical cable. The operator may interact with the system using a joy- stick or exoskeleton. Since a direct teleoperation is not feasible, a cognitive engine is in charge of handling communication latency or interruptions caused by the satellite link, and the UVMS should have sufficient autonomy in dealing with low level constraints or secondary objectives. To this purpose, a task- priority-based inverse kinematics algorithm has been developed in order to allow the operator to control only the end effector, while the algorithm is in charge of handling both operative and joint-space constraints. This paper describes some preliminary experimental results achieved during the DexROV campaign of July 2017 in Marseilles (France), where most of the components have been successfully integrated and the inverse kinematics nicely run. I. I NTRODUCTION Underwater intervention is needed by several applications ranging from interaction with structures belonging to the oil & gas industry to archaeology, from mining applications to collections of biological samples. Several national (MARIS [1], RAUVI [2]) and international (TRIDENT [3], PAN- DORA [4], ROBUST [5]) projects have been funded in the last few years on this important topic. Within the European H2020 project DexROV [6], [7], the researchers are investigating the possibility to reduce the number of crew on board of the vessel by creating a remote control room linked by satellite communication to the UVMS (Underwater Vehicle-Manipulator System). The operator may interact with the system by joystick or exoskeleton and a proper cognitive tool is in charge of handling communication latency or interruptions caused by the satellite link. The time delay and the satellite communication low band- width force the operator to share the control with the UVMS, that has to be capable of performing autonomously part of the needed operations. While the operator controls the end- effector motion, the UVMS control system takes care of all the safety-related tasks, both in operative and joint space. This kind of control is achieved by resorting to a multi- task-priority inverse kinematics framework that allows to perform multiple tasks simultaneously. The key aspect of P. Di Lillo, D. Di Vito and G. Antonelli are with the University of Cassino and Southern Lazio, via Di Biasio 43, 03043, Cassino, Italy {pa.dilillo,d.divito,antonelli}@unicas.it E. Simetti and G. Casalino are with the University of Genoa, Via All’Opera Pia 13, 16145 Genova, Italy {simetti,casalino}@unige.it this approach is to define a priority among tasks, creating a hierarchy in which the position of a task is relative to its importance. Usually the highest-priority tasks related to the safety of the system, e.g. avoiding obstacles or mechanical joint limits, leaving the operational tasks such as the end- effector position and orientation at a lower priority level. These considerations lead to solutions as in [8], [9] [10], where secondary control objectives were defined and handled in priority using the null-space projector, later extended in [11] to multiple tasks. In [12] a different approach is pre- sented that is robust to the algorithmic singularities occurring when tasks are incompatible with each other. Such a work has been then extended to multiple tasks in the singularity robust multi-task priority inverse kinematics framework in [13] [14], [15]. The aforementioned framework has been developed to handle control objectives in which the goal is to bring the task value to a specific one, e.g. moving the arm end-effector to a target position. This kind of tasks are usually referred as equality-based. However, several control objectives may require their value to lie in an interval, i.e. above a lower threshold and below an upper threshold. These are usually called set-based tasks. Classic examples of set- based tasks for a robotic manipulator are the mechanical joint limits, the obstacle avoidance and arm manipulability tasks. In the last years, a great effort has been made in order to extend task-priority frameworks to handle set-based tasks, as for example done in [16]. In particular, the singularity- robust multi-task priority inverse kinematic framework has been extended to handle set-based tasks in [17], [18]. In this paper some positive, preliminary experimental results achieved during the DexROV campaign of July 2017 in Marseilles (France) are shown. Figure 1 shows the UVMS during deployment and Fig. 2 depicts a graphical rendering of the two manipulators. Most of the components have been successfully integrated and the inverse kinematics nicely run. In particular, during the wet tests, the following constraints were simultaneously handled: mechanical joint limits and smart joint-space velocity saturation [19]. The robot has fol- lowed both pre-programmed and joystick-driven trajectories generated on board the vessel (Marseilles), and trajectory generated with the exoskeleton in Brussels (Belgium). Fi- nally, some tests were designed to intentionally move the arm to reach kinematic singularities. II. DEXROV CONCEPT DexROV is an EC (European Commission) Horizon 2020 funded project that aims to develop a system able to perform underwater operations using a novel paradigm that allows