Marine Robotic Platforms Research Articles

Gain-scheduled steering control for a wave-propelled unmanned surface vehicle

The persistent observation of oceanographic phenomena is nowadays hampered by technological limitations, that prevent marine robotic platforms to autonomously execute scientific surveys for extended periods of time. The propulsion and course-over-ground (COG) of wave-propelled unmanned surface vehicles (USVs) rely primarily on the forces exerted by the environment and, for this reason, ensuring an intended navigational behavior at sea is a challenging task. In this article we discuss the design and experimental validation of a gain-scheduled steering control system that governs the course of a wave-propelled USV subject to different sea surface currents. A theoretical investigation of the vehicle nonlinear dynamics identifies in a scalar scheduling variable γ the major source of model nonlinearities due to vehicle’s and ocean current velocities. The impact of such nonlinearities on the control of the course-over-ground is investigated with a quasi-linear model analysis in the frequency domain. This provides a basis for the design of a gain-scheduled steering controller, whose theoretical assumptions are supported and validated by extensive simulations and experimental results. Moreover, we show that scheduling of the autopilot gains can still be achieved despite the lack of sea current measurements onboard the USV. Finally, it is demonstrated that the navigation and course-keeping performances improve significantly when the gain-scheduled controller is employed, as compared to the nominal fixed-gain autopilot.The presented control system is assessed with simulations and validated on a series of field experiences meant to quantify the autopilot robustness and the vehicle course-keeping capabilities.

Towards Posidonia Meadows Detection, Mapping and Automatic recognition using Unmanned Marine Vehicles

This paper reports the development of a new methodology for automatic detection and mapping of underwater vegetation by means of highly autonomous marine robotic platforms. In particular, the work describes the exploitation of a Remotely Operated Vehicle (ROV), equipped with a multi-parametric sensors package, for the exploration and characterization of sea-bottoms interested by the presence of the Posidonia oceanica seagrass, which represents a valuable indicator of the environmental health. The proposed methodology relies on the systematic exploration of the sea-bottom by means of the ROV acquiring acoustic data and video imagery of the seabed, in order to reconstruct a 2.5D model of the environment (i.e. an elevation map of the sea-bottom). The data collection is achieved by the employment of a single beam echosounder for seabed range measurements and a down-looking underwater camera. Furthermore, an acoustic data procedural analysis is developed to automatically detect the Posidonia presence, so that in future works it will be possible to operate also in low-visibility conditions. Data acquisition was carried out over different seafloor types in coastal area near Biograd Na Moru (Croatia) and the results are reported in the paper.

Low cost underwater acoustic localization

Over the course of the last decade, the cost of marine robotic platforms has significantly decreased. In part this has lowered the barriers to entry of exploring and monitoring larger areas of the earth's oceans. However, these advances have been mostly focused on autonomous surface vehicles (ASVs) or shallow water autonomous underwater vehicles (AUVs). One of the main drivers for high cost in the deep water domain is the challenge of localizing such vehicles using acoustics. Here we propose a novel low cost underwater modem design to assist in localizing deep water submersibles. The system will consist of location aware anchor buoys at the surface and underwater nodes. We present a comparison of methods, simulation of the proposed algorithms as well as experimental results, together with details on the physical implementation to allow its integration into a novel deep sea AUV currently in development.

Testing the Waters: Design of Replicable Experiments for Performance Assessment of Marine Robotic Platforms

Robotics is becoming part of our daily life through home automation (called domotic) and assistive applications that are taking place in habitations, up to industrial and service employments. With this strict cooperation between humans and robots, it is of absolute necessity to assess the robotic systems' capabilities and performance to ensure safety and reliability according to actual and significant criteria and parameters. Within this context, there are delays in technology transfer from research frameworks toward actual applicative scenarios. These delays are caused by the lack of methodologies and standardized procedures for the experiment execution and result comparison. A further restraint to the needed process of technology transfer is due to the inability to understand the actual capabilities of the systems and to be aware and confident (or not) about what they can be realistically employed for. In many cases, this can also turn into the inability to define specific regulations for the employment of robotic platforms to comply with the current laws. This is the case for marine robotics. Tethered vehicles [e.g., remotely operated vehicles (ROVs)] are considered part of the vessel equipment when they are operated from a ship (because of the physical connection provided by the cable). Conversely, whenever autonomous systems, such as unmanned surface vehicles (USVs) or autonomous underwater vehicles are commanded through an acoustic or Wi-Fi/radio communication link, they are considered as navigating platforms and are subject to the regulation in force. For the commercial employment of these vehicles, it is then necessary to strongly assess the vehicle's capabilities in a standardized way, to guarantee the operating performance and evaluate limitations of the target system.

Multi-vehicle cooperative path-following guidance system for diver operation support

This paper focuses on the development of a cooperative guidance system allowing two marine robotic platforms, one on the surface and the other operating underwater, to coordinate their motion in order to fulfil the goal of supporting diver operations during dive campaigns. In the scope of EU FP7 CADDY Project, the proposed paper deals with the specific problem of the “guide” functionality, allowing the diver to rely on robotic platforms to be guided along the desired dive spots. A cooperative path-following technique based on the virtual-target approach is developed and validated through simulation results.