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FSN WP5: Go To Formation

Andreas J. Häusler, IST

An Aspect of Multiple Marine Vehicle Path Planning

Mission Planning

• Multiple vehicle missions require the vehicles to be in formation

• An initial formation has to be established before the mission starts

• Vehicles cannot be deployed in formationNeed to get the vehicles into initial formation

Path Generation’s General Problem

• Problem description– Desired waypoints or manoeuvres– Desired AUV formation– Optimal energy expenditure or manoeuvring time

Path Generation’s General Problem

• Difficulties– Go-to-formation manoeuvre (collision-free paths)– Avoid (concave, static) obstacles– Opt. 1 – Generate non-intersecting paths– Opt. 2 – Allow for intersecting, “time-coordinated”

trajectories– Meet energy and trajectory

constraints

Path Generation• Avoid absolute timing (to cope with disturbances)• Reaching the target positions simultaneously will

ensure the required initial formation.

Decouple spatial and temporal constraints!

Step 1. Produce paths p(t) without explicit time constraints (polynomial function of t)

Step 2. Establish a timing law for = (t t t) (polynomial)τ)

Inspired by the work of Isaac Kaminer and Reza Ghabcheloo

Path Generation

Decouple spatial and temporal constraints!

• To translate between t and τ use

(adopt a polynomial approach to ( )h t )

Step 3. Use an optimization of your choice for criterion minimization.

Inspired by the work of Isaac Kaminer and Reza Ghabcheloo

Path Generation

• Polynomial equation

• Taken for all DOFs (extremely simple system!)

Inspired by the work of Oleg Yakimenko, NPS, USA

Multiple Vehicle Manoeuvres

• Most vehicles are underactuated and lack hovering capabilities

No station keeping at deployment time, no station keeping after vehicles reach mission starting positions

Mission has to start on-the-fly

• Vehicles should automatically be driven from deployment to mission start

Go To Formation• 1st part of the overall manoeuvre

• Needs to take into account initial deployment positions and orientations

• Needs to ensure simultaneous arrival at designated positions and orientations

Go To Formation• Needs to avoid collisions until mission

control takes over• Needs to consider

time, energy and vehicle constraints

• Method has been extended to deal with intersecting paths.

Go To Formation• How do we deal with “deviations from the

plan? (wind, currents, etc.)• Use cooperative

path following! (methods are available - IST, NTNU)

The Grex 2008 Azores Mission

• July 2008 in Horta, Faial (Açores)• 5 Nations, 9 Institutions

• Successful sea trials of Coordinated Path Following and Coordinated Target Tracking

Coordination and Control of

Cooperating Heterogeneous Unmanned Systems

in Uncertain Environments

The Grex 2008 Azores Mission

• The GREX System provides– Central planning for teams– Hardware/OS Abstraction– Information and command flow accross multiple

vehicles– Central and distributed mission planning– Complex coordination capability– Safety checks at several levels, transmitted via

status/emergency telegrams

The Grex Vehicle Architecture

The Grex 2008 Azores Mission

Simple Path Following• Desired Path is predefined• DELFIMX follows a

mission consisting of predefined #ARC and #POINT (line) SVPs

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The Grex 2008 Azores Mission

Coordinated Path Following• Path already

provided• Vehicles

coordinate with leader vehicle to do coordinated path-following

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The Grex 2008 Azores Mission

GoToFormation• MVP implementation

to take vehicles to a starting formation

• Will use path/trajectory planning algorithms that do spatio-temporal deconfliction

• Obstacle avoidance is also required

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The Grex 2008 Azores Mission

Simple Target Tracking• Águas Vivas

moves around while sending DELFIMX its GPS locations

• DELFIMX estimates path followed in GREX SVMP format and follows this path

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The Grex 2008 Azores Mission

Coordinated Target TrackingDELFIMX GREX-module’s estimator learns path of Águas Vivas and does a coordinated path-following with Seabee AUV using GREX MVPs

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The Grex 2008 Azores Mission• Because GREX deals with multiple vehicles, a

Go-To-Formation behaviour is necessary for each mission

• My part in the mission:– Developed an algorithm for Go-To-Formation– Helped developing the software for telegram

processing (communication on the vehicle side)– Developed software to be ready to go to sea in

Sesimbra, September 2008

Grex 2008 Azores Mission: Results• Path Following

Grex 2008 Azores Mission: Results• Target Tracking

Future Work

1. Incorporate deconfliction in time

2. Go on to three-dimensional paths

3. Finally, think about on-line path planning

during mission runtime

Thank you for your attention!

AND NOW FOR A MOVIE…