Cooperative robotic sentry vehicles

ABSTRACT As part of a project for the Defense Advanced Research Projects Agency, Sandia National Laboratories' Intelligent Systems& Robotics Center is developing and testing the feasibility of a cooperative team of robotic sentry vehicles to guard a pe-rimeter and to perform a surround task. This paper describes on-going activities in the development of these robotic sentryvehicles. To date, we have developed a robotic perimeter detection system which consists of eight "Roving All Terrain Lu-nar Explorer Rovers" (RATLERTh), a laptop-based base-station, and several Miniature Intrusion Detection Sensors (MIDS).A radio frequency receiver on each of the RATLER vehicles alerts the sentry vehicles of alarms from the hidden MIDS.When an alarm is received, each vehicle decides whether it should investigate the alarm based on the proximity of itself andthe other vehicles to the alarm. As one vehicle attends an alarm, the other vehicles adjust their position around the perimeterto better prepare for another alarm. For the surround task, both potential field and A* search path planners have been addedto the base-station and vehicles. At the base-station, the operator specifies goal and exclusion regions on a GIS map. Thepath planner generates vehicle paths that are previewed by the operator. Once the operator has validated the path, the appro-priate information is downloaded to the vehicles. For the potential field path planner, the polygons and line segments thatrepresent the obstacles and goals are downloaded to the vehicles, instead of the simulated paths. On board the vehicles, thesame potential field path planner generates the path except that it uses the true location of itself and the nearest neighboringvehicle. For the A* path planner, the actual path is downloaded to the vehicles because of limited on-board computationalpower.Keywords: Mobile Robots, Cooperative Control, Distributed Autonomous Systems1. INTRODUCTIONThe field of mobile robotics is quite advanced. The ability to build robotic vehicles that can navigate over long distances ei-ther using tele-operation or atitonomous control has been demonstrated by a number of researchers, see for instance [1]. Inrecent years, this field has expanded to consider large numbers or squads of vehicles [2]. The underlying goal of multi-vehicle systems is expanded capability through cooperation. Methods for controlling groups of vehicles range from distrib-uted autonomy [3] to intelligent squad control and general purpose cooperative mission planning [4]. The types of tasks un-der study range from moving large objects [5] to troop hunting behaviors [6]. Conceptually, large groups of mobile vehiclesouffitted with sensors should be able to automatically perform military tasks like formation following, localization of chemi-cal sources, de-mining, perimeter control, surveillance, and search and rescue missions [7- 1 0]. In simulation, it has beenshown that by sharing concurrent sensory information the group can better estimate the shape of a chemical plume and there-fore localize its source [1 1]. Similarly, for a search and rescue operation a moving target is more easily found using an or-ganized team [12-13]. Simulation has also shown that enhanced perimeter control can be achieved by dispersing the groupuniformly and by communicating when possible intrusions occur.As a proof-of-concept, Sandia National Laboratories is developing a squad of semi-autonomous all terrain vehicles for re-mote cooperative sensing applications, (see Figure 1). This system serves as a test platform to verify communications, con-