ROBOT RENDEZVOUS: 3 OR MORE ROBOTS USING 1-DIMENSIONAL SEARCH !!!!!!! !

OVERVIEW Approaches Tested Search approaches ensuring coverage of the entire environment Final Approach Reduces problem to a 1-Dimensional Search

APPROACHES TESTED

GRID-BASED ITERATIVELY DEEPENING DEPTH FIRST SEARCH

GRID-BASED IDDFS

Based on "Symmetric Rendezvous in Planar Environments with and without Obstacles" - Isler, et. al. Decompose map into square cells of side length L Search each cell by counterclockwise perimeter circumnavigation Neighboring cells recursively searched on discovery up to a prescribed depth D. D increases each iteration by the square root of 2. Iterative deepening attempts to simulate optimality of breadth-first search.

GRID-BASED IDDFS: SIMULATION VIDEO

GRID-BASED IDDFS: CHALLENGES C-space obstacles not known beforehand. Need to use on-line wall following. Too large a cell size may cause areas to be exempt from the search For these reasons, we did not use this Corridor 1 (searched first) Corridor 3 (never searched) Corridor 2 (searched second)

LOGARITHMICALLY EXPANDING SPIRAL SEARCH

LOG SPIRAL SEARCH Based on "Spiral Search as an Efficient Mobile Robotic Search Technique" - Burlington, et. al. Generate a series of coordinates with increasing distance from origin for robot to “goto” When in contact with obstacles, wall follow using Bug2 Algorithm to navigate to next point

LOG SPIRAL SEARCH: CHALLENGES Online wall following in an unknown environment has it’s challenges Areas may be completely bypassed if robot starts in a long tunnel Future work would require a different approach to logarithmic spiraling in order to bypass this problem.

HIGHER-LEVEL RENDEZVOUS IN UNBOUNDED ENVIRONMENT LF1F3F2

HIGHER-LEVEL RENDEZVOUS IN UNBOUNDED ENVIRONMENT

R1 R2 R3 R4

R1 R2 R3 R4

R1 R2 R3 R4 INTERMEDIATE RENDEZVOUS

R1 R2 R3 R4

R1 R2 R3 R4

R1 R2 R3 R4 INTERMEDIATE RENDEZVOUS

R1 R2 R3 R4

R1 R2 R3 R4 FINAL RENDEZVOUS

R1 R2 R3 R4

1-DIMENSIONAL RENDEZVOUS IN BOUNDED ENVIRONMENT FINAL APPROACH METHODOLOGY LFFF

METHODOLOGY: SYSTEM OVERVIEW

METHODOLOGY: OUTER BOUNDARY USING DISTBUG

METHODOLOGY: 1D SEARCH

METHODOLOGY: HIGHER-LEVEL RENDEZVOUS R1 R2 R3 R4

METHODOLOGY: HIGHER-LEVEL RENDEZVOUS R1 RENDEZVOUS R3 R4 R2 COLLISION AVOIDANCE

METHODOLOGY: SIMULATION VIDEO

METHODOLOGY: COMPETITIVE RATIO

METHODOLOGY: ADVANTAGES Its a very elegant and compact algorithm Search area is greatly reduced (so we don't need to guarantee coverage of the environment) Localization isn't as crucial after the outer boundary has been found (thus much easier to apply to real world applications) Less parameter adjustment is needed to apply to real world applications

METHODOLOGY: CONSTRAINTS Method works only for bounded environment There is an upper bound on the number of robots that can perform the search with adequate "personal space" (deadlock) Rendezvous area is n*R (where R is the communication range and n is the number of robots) We can't guarantee coverage of the environment

FURTHER WORK Add communication between colliding robots to lessen the time consumed by 1D search Better search for outer bound Decrease rendezvous area Test algorithm with more robots