D.B. Marco

Autonomous underwater vehicles: Hybrid control of mission and motion

This paper provides an experimental implementation and verification of a hybrid (mixed discrete state/ continuous state) controller for semi-autonomous and autonomous underwater vehicles in which the missions imply multiple task robot behavior. An overview of some of the missions being considered for this rapidly developing technology is mentioned including environmental monitoring, underwater inspection, geological survey as well as military missions in mine countermeasures.The functionalities required of such vehicles and their relation to ‘intelligent control’ technology is discussed. In particular, the use of Prolog as a computer language for the specification of the discrete event system (DES) aspects of the mission control is proposed. The connections between a Prolog specification and the more common Petri Net graphical representation of a DES are made. Links are made between activation commands, transitioning signals, and the continuous state dynamic control system (DCS) responsible for vehicle stabilization.Details are given of the NPS Phoenix vehicle implementation at the present time, together with experimental validation of the concepts outlined using a simplified example mission. The paper ends with a listing of questions and concerns for the evaluation of software controllers. A list of references is given for readers interested in this subject.

NPS Phoenix AUV software integration and in-water testing

The NPS Phoenix autonomous underwater vehicle (AUV) is a student research testbed for shallow-water minefield mapping missions. We discuss implementation of the execution, tactical and strategic levels of the rational behavior model robot architecture. Simulation-based design using an underwater virtual world has been a crucial advantage permitting rapid development of disparate software and hardware modules. Details are provided on process coordination, navigation, real-time sonar classification, path replanning around detected obstacles, networking, sonar and hydrodynamics modeling, and distributable computer graphics rendering. In-water experimental results are presented and evaluated.

Tactical/execution level coordination for hover control of the NPS AUV II using onboard sonar servoing

This paper describes work with the NPS AUV II vehicle in the further development of the execution level software to incorporate hover control behavior in the NPS hover tank. Of particular interest is the use of the ST 1000 and ST 725 high frequency sonars to provide data about the environment. Thus positioning can be accomplished without the use of beacons. Motion behaviors may be instituted that include diving and pitch control under thruster power; heading control at zero speed; lateral and longitudinal positioning, as well as the automatic initiation of filters as needed when a new target is found. A simple task level language that will be used to direct tactical level output to a port in communication with the execution level software is given.

6 DOF nonlinear AUV simulation toolbox

This paper describes the organization of 6 DOF nonlinear autonomous underwater vehicle (AUV) simulation toolbox, which is currently under development for the Ocean Explorer (OEX) series AWs developed at Florida Atlantic University. This software development is part of 5-year OM MURI effort of which its goal is to develop innovative tools and methodologies for the control of complex nonlinear dynamic systems. The purpose of this software simulation is to supply a flexible 3D-simulation platform for motion visualization, in-lab debugging and testing of mission-specific strategies as well as those related to C3 purposes. This software is currently jointly developed by the Ocean Engineering Department at Florida Atlantic University and Naval Postgraduate School for the FAU OEX and NPS Phoenix AUVs.

Evaluation of the NPS PHOENIX autonomous underwater vehicle hybrid control system

This paper describes recent work with the NPS PHOENIX vehicle in the further development of the intelligent control software incorporating hover control behaviors. Of particular interest is the use of the TRITECH ST1000 and ST725 high frequency sonars to provide data about the environment. Vehicle positioning is proposed to be based in a local relative sense, augmenting global positioning by LBL transponders. Motion behaviors around a target area have been implemented including: diving and pitch control under thruster power; heading control at zero speed; lateral and longitudinal positioning; and the automatic initiation of filters as needed for target tracking. A tri-level controller architecture is discussed as part of an ongoing evaluation for coordinating the task based control of vehicle robotic behaviors.

Strategic level mission control - an evaluation of CORAL and PROLOG implementations for mission control specifications

This paper presents the use of the software programming environments PROLOG and CORAL for the implementation of the strategic level of the NPS Phoenix vehicle. Whereas PROLOG provides a rule-based mission control specification language, CORAL builds on a graphical interface to describe mission programs using Petri nets. The paper describes the interfacing of CORAL with the tactical level of the vehicle, and details the programming and execution of a vehicle mission that was run in the NPS test tank.

Local area navigation using sonar feature extraction and model based predictive control

This paper demonstrates a method to navigate an autonomous underwater vehicle in a local area using an acoustic sensor for position information derived from feature detection. A dynamic model of the vehicle response is used for control between location updates. Favorable results have been found using this approach, and precision positioning of the vehicle to centimeters has been accomplished. Another part of the problem is the need to provide a high frequency update of vehicle position in order to close the positioning servo loops. Using sonar image feature extraction is necessarily time consuming and therefore is performed in a tactical level process providing asynchronous data to the tactical navigator. It follows that some form of fast dead reckoning must be performed in the execution level either by INS/Doppler or by water speed and heading data or by a model based predictor. This paper deals with the use of a model based predictor technique where knowledge of the dynamic model of the vehicle provides state information to the vehicle positioning control function. The model uncertainty provides errors of course, but these are corrected through asynchronous updates from the feature extracted positions in the tactical level sonar manager. This concept has been verified by both simulation studies and by experimental validation with the NPS Phoenix vehicle.

Modeling and simulation for the FAU AUVs: Ocean Explorer

This paper describes the research progress made on modeling and simulation development for the Florida Atlantic University autonomous underwater vehicles (AUV). Recent addition of simulation components include kinematic effect of longitudinal waves, inertial and position sensor dynamics so that realistic scenarios can be better accommodated. In addition, the existing FAU communication protocol used for the onboard acoustic modem has been ported to the simulation platform, thereby enabling multiple vehicle operations and communication to be simulated. At this stage acoustic propagation for the model is assumed to be ideal although a more realistic model for shallow water propagation will be developed in the near future. This research endeavor is supported by a 5-year ONR MURI project and is jointly carried out by FAU and Naval Postgraduate School.