José Braga

Integral Line-of-Sight Guidance and Control of Underactuated Marine Vehicles: Theory, Simulations, and Experiments

This paper presents an extensive analysis of the integral line-of-sight (ILOS) guidance method for path-following tasks of underactuated marine vehicles, operating on and below the sea surface. It is shown that due to the embedded integral action, the guidance law makes the vessels follow straight lines by compensating for the drift effect of environmental disturbances, such as currents, wind, and waves. The ILOS guidance is first applied to a 2-D model of surface vessels that includes the underactauted sway dynamics of the vehicle as well as disturbances in the form of constant irrotational ocean currents and constant dynamic, attitude dependent, and forces. The actuated dynamics are not considered at this point. A Lyapunov closed-loop analysis yields explicit bounds on the guidance law gains to guarantee uniform global asymptotic stability (UGAS) and uniform local exponential stability (ULES). The complete kinematic and dynamic closed-loop system of the 3-D ILOS guidance law is analyzed in the following and hence extending the analysis to underactuated autonomous underwater vehicles (AUVs) for the 3-D straight-line path-following applications in the presence of constant irrotational ocean currents. The actuated surge, pitch, and yaw dynamics are included in the analysis where the closed-loop system forms a cascade, and the properties of UGAS and ULES are shown. The 3-D ILOS control system is a generalization of the 2-D ILOS guidance. Finally, results from simulations and experiments are presented to validate and illustrate the theoretical results, where the 2-D ILOS guidance is applied to the cooperative autonomous robotics towing system vehicle and light AUV.

Implementation of a Control Architecture for Networked Vehicle Systems

Abstract This paper describes the layered control architecture and its software implementation developed and used at the Underwater Systems and Technology Laboratory. The architecture is implemented as a toolchain which consists on three main entities: DUNE onboard software, Neptus command and control software and a common IMC message-based communication protocol. The LSTS software toolchain has been tested throughout various field deployments where it was used to control heterogeneous autonomous vehicles like AUVs, ASVs, UAVs and ROVs in both single and multi-vehicle operations.

A feedback motion strategy applied to a UAV to work as an autonomous relay node for maritime operations

One important aspect that needs to be carefully considered in maritime operations using unmanned robotic vehicles is the communication restrictions between the vehicles and the mission controller that arises mainly due to long distances and/or low power transmissions. This paper addresses the problem of maintaining a communication link between a command station and an Unmanned Aerial Vehicle (UAV) with limited communication range during maritime operations. The proposed scheme uses an additional UAV that acts as a relay for the communication between the command station and the UAV in mission and is actively driven to maintain a desired Quality-of-Service (QoS) level, defined in this paper. Exploiting this architecture, it is possible to plan a maritime operation for a robotic vehicle without the need of considering vehicle-to-command-station communication constraints that will be satisfied by the introduction of the extra autonomous relay-UAVs. To this end, we propose a feedback strategy that has the dual task of commanding and optimizing the execution of the relay UAV motion tasks and adapting the scheduler algorithm according to a desired QoS level. The performance of the proposed strategy is illustrated through computer simulations and preliminary experimental results.

Unmanned vehicles for maritime spill response case study: Exercise Cathach.

This paper deals with two aspects, namely a historical analysis of the use of unmanned vehicles (UAVs ROVs, AUVs) in maritime spill incidents and a detailed description of a multi-agency oil and HNS incident response exercise involving the integration and analysis of unmanned vehicles environmental sensing equipment. The exercise was a first in terms of the level of robotic systems deployed to assist in survey, surveillance and inspection roles for oil spills and harmful and noxious substances.

Network enabled cooperation of autonomous vehicles: A communications perspective

In this paper we present the NECSAVE system which allows the control of heterogeneous unmanned vehicles under challenging environments by a single human operator by providing it with the desired highlevel objectives. The described software stack takes care of decomposing the high-level objectives into assignable tasks and (re)distributing the workload among team members according to their announced capabilities and eventual failures. NECSAVE is robust to system failures by supporting decentralized planning and adapting allocation in face of platform losses. The system was validated in multiple field trials where NECSAVE was used for the coordination of heterogeneous vehicles under challenged communication environments, namely the sea using radio (at surface) and acoustic communications (underwater).

Cooperation and networking in an underwater network composed by heterogeneous assets

Underwater communication and robot technologies have grown rapidly in the last decade. Systems made of underwater unmanned vehicles have moved from single vehicle deployments to systems comprising teams of assets. As of today the possibility to support cooperation and interoperability of heterogeneous platforms is a key issue. The objective of this paper is to present the SUNRISE [1] approach to overcome this limitation through the development of an abstraction layer to support the interoperability of different vehicle control software. SUNRISE also aims at integrating control software with the underwater communication and networking components to create more flexible, modular and capable underwater systems. The developed SUNRISE infrastructure has been evaluated and validated through in lab tests and at-sea experiments, in the Porto harbour, during the REP14 sea trial in the Atlantic Ocean and in the Mediterranean coast of Italy in June 2015, showing promising results. The authors gratefully acknowledge CMRE team, Sapienza team and the Portuguese Navy for their valuable feedback and for their support and help during the REP14 sea trial.

Self-triggered time coordinated deployment strategy for multiple relay UAVs to work as a point-to-point communication bridge

The use of multiple heterogeneous, low-cost, small Unmanned Aerial Vehicles (UAVs) as a tool in several application domains is becoming increasingly important. One critical aspect to enable the use of such vehicles is the coordination/planning system, whose task complexity increases with the number of vehicles and the communications constraints that arise due to their small size and large distances. In this work, we propose a control architecture for a platoon of relay UAVs that are independent of the coordination system. The platoon task consists in interconnecting the communication link between the possibly mobile command station and a UAV in a mission. The relays are actively driven to deploy, create a network and maintain a desired Quality-of-Service (QoS) level, defined in this paper. We present an architecture that is composed by a waypoint generator based on the network QoS and a Time Coordinated Path Following (TCPF) controller with a method to reduce the frequency of information exchange between the relay UAVs, through the use of a self-triggered control strategy. Exploiting this architecture, it is possible to plan a mission operation for a UAV without the need of considering vehicle-to-command-station communication constraints that will be satisfied by the introduction of the relay-UAVs platoon. Simulation results are provided to illustrate the efficacy of the developed strategy. The self-triggered approach results in significant reduction of information exchange between the relay UAVs, while maintaining the user desired network QoS.

Fault Tolerant Area Coverage Using Underwater Vehicles

Abstract Multiple autonomous underwater vehicles (AUVs) can be deployed to map large regions. For mapping, the desired motion plan must be lawn mover pattern to scan the bottom. In addition to motion plan constraints, AUVs are subject to limited sensing and communication ranges and some of the AUVs can fail while performing the assigned mission leg. Developing an efficient fault tolerant area coverage controller with these constraints is a difficult task. In this paper, we develop a consensus based fault tolerant area coverage controller that takes the uncertainty in environments, communication range constraints and AUV failures while covering the area with limited repeated coverage. Current approach is able to deal with agent faults located in the middle of a series of AUVs. Simulations are presented to validate the approach.