Preliminary Telerobotic Experiments of an Underwater Mobile Manipulator Via Sonar

Abstract

Robotic inspection of underwater infrastructures and scenarios can be enhanced when a wireless communication link is available, as the umbilical can be avoided and the mobility of the robot improved. To this end, previous experiments on sonar [1], Visual Light Communication (VLC) and Radio Frequency (RF) have been performed, which show the necessity to have a multimodal underwater communication system, as well as providing the robot with autonomous behaviors and artificial intelligence capabilities.Underwater sonar communication is a mature technology, which works fine in open waters, providing low bit rates and fluctuating delays for long distances [2] [3]. It can also be used for calculating ranges and localizing/navigating robots [3] [4]. RF modems communicate at similar bit rates, reaching short distances, and constant delays, which make it an interesting alternative for industrial scenarios where sonar might present reflections and multipath effects. VLC is already offering interesting bit rates (e.g. 2Mbps) at short distances, being necessary to have a scenario with lack of light, and also needing a special care with the spatial orientation of the modem. In the context of underwater mobile robotics for inspection, some efforts have been made in order to transmit camera or sonar images to the surface via acoustic modems [5] [6]. Compression techniques have been designed specifically to this aim [7] [8].A more challenging scenario is the use of underwater mobile manipulators for both, inspection and maintenance operations. When having a robot that physically interacts with a target having an expert in the loop, even in a supervised way, provides an extra level of safety for the intervention. As long as possible, the human presence is an extra value to the system, and sometimes really a necessity. Moreover, it requires a special care and study in order to get the most of the wireless communication system, needing the combination of compression, and telerobotic supervisory control techniques.In order to face this challenge, a preliminary study is being done in order to remotely control, in a supervised way, a G500 underwater mobile robot, provided with a Blueprint Reach Bravo robotic arm. The system includes an underwater monocular color camera, and a pair of Evologics Wise [9] acoustic modems, one installed in the robot and a second in a buoy.