Results of Baseline Experiments

The rst set of experiments I report here are what I call the two- and three-robot baselineexperiments. In this set of experiments, I equipped the robot teams described above with the fully functional ALLIANCE architecture, complete with explicit com-munication for allowing robots to be aware of the activities of their teammates. Using this communication system, robots broadcasted a statement of their current actions to the rest of the team at a pre-specied rate. I ran over 50 logged trials of these experiments, along with several variations reported in chapter 5, all of which allowed the study of a number of interesting cooperative robot issues. The results presented in this section for the numerous baseline experiments illustrate the ability of AL-LIANCE to meet the design requirements of robustness, reliability, exibility, and coherence.

Let us examine the results of these experiments. Figure 3-9 shows the actions se-lected by each robot on a typical trial of this experimentwith the two-robot team, and gure 3-10 shows the actions selected by each robot on a typical trial with the three-robot team. Figure 3-11 shows the trace of the three-robot movements during a typical two-robot mission⁶. Prior to both the two- and three-robot trials, the L-ALLIANCE learning system described in chapter 4 has allowed the team members to determine that GREEN (or GREEN and BLUE, in the three-robot case) cannot successfully

ac-6This movement trace data was created by hand from a videotape of a two-robot team performing this mission.

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Figure 3-9: Robot actions selected during experiment with two robots (RED and GREEN) using the ALLIANCE architecture with full awareness of other team mem-ber actions. This is one instance of many runs of this mission.

complish the task corresponding to thend-initial-nal-locations-methodical behavior set, and that RED is quicker at nding the spill.

At the beginning of a typical three-robot mission, RED has the highest moti-vation to perform behavior set nd-initial-nal-locations-methodical, causing it to initiate this action, as shown in gure 3-12. (In this and the following photographs, the starting location of the GREEN and BLUE robots (center, rear of the rst photo-graph) is the room entrance, the spill location is at the right, center of the photograph (where the small, cylindrical objects are located), and the goal location is at the near, right end of the photograph.) This causes GREEN and BLUE to be satised for a while that the initial and nal spill locations are going to be found; since no other task can currently be performed, they sit waiting for the two locations to be found.

However, they do not sit forever waiting on the locations to be found. As they wait, they become more and more impatient over time, which can cause one of BLUE or GREEN to activate its own nd-initial-nal-locations-wander if RED does not suc-cessfully locate the spill. Note that BLUE and GREEN do not activate their own nd-initial-nal-locations-methodicalbecause they have learned in previous trials that

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Figure 3-10: Robot actions selected during experiment with three robots (RED, BLUE, and GREEN) using the ALLIANCE architecture with full awareness of the current actions of other team members. This is one instance of many runs of this mission.

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Figure 3-11: A trace of the movements of a typical two-robot team performing the cleanup mission. The two robots at the left end of the picture show the robot starting locations. The square with the heavy bold outline towards the left, center of the room is the starting spill location, while the bold \X" at the right indicates the desired nal spill location. The location from which progress reports are to be given is in the vicinity of the robot starting positions. The bold trace gives the movements of GREEN; the non-bold trace indicates the movements of RED. In this example, RED rst performs thend-locationstask, followed by both GREEN and RED moving spill objects | three objects each, on three transports each. GREEN ends up reporting progress two times, while RED reports the team progress once.

Figure 3-12: The beginning of the hazardous waste cleanup mission. The left-most robot (RED) has activated its nd-initial-nal-locations-methodical behavior set, which causes it to circle the perimeter of the room. The remaining two robots (aligned with each other at the room entrance) are patiently waiting on RED to com-plete its task. Note the spill objects (small cylindrical \pucks") at the right center of the photograph.

that action does not achieve the desired eect. Indeed, as shown in gure 3-13 for a two-robot experiment, GREEN did overtake RED at this task when I intentionally interfered with RED's progress. In that case, RED acquiesced its attempt to nd the initial and nal locations to GREEN, since RED realized it was encountering diculties of some sort. In either case, the robot nding the initial and nal spill locations reports these two locations to the rest of the team.

At this point, the environmental feedback and knowledge of the initial and nal spill locations indicate to the robots that the move-spill behavior set is applicable.

Since this is a task that can be shared, the robots begin searching for a spill object in the initial spill area, as shown in gure 3-14 for a typical three-robot experiment. Once a spill object has been grasped, the robot carries it to the goal location. Figure 3-15 shows a close-up of a robot grasping a spill object and beginning its transport to the goal location. In this photograph, note the extra spill object caught in the cavity under the gripper, which allows this robot to move more than one spill object on this trip to the goal location. Figure 3-16 shows the transport from a wider perspective.

In the meantime, the robots' motivations to report the team's progress are increas-ing. Once a robot has delivered a spill object to the destination, that robot becomes motivated to report the team's progress, and thus activates the report-progress be-havior set. Figure 3-17 shows a robot (at the far, center of the photograph) reporting the team's progress at the room \entrance" during a typical mission. This reporting

3.8. EXPERIMENTAL RESULTS: HAZARDOUSWASTE CLEANUP 65

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Figure 3-13: Robot actions selected during experiment with two robots (RED and GREEN) with full awareness of other team member actions, and when RED fails in its task to nd the initial and nal spill locations. This is one instance of many runs of this mission.

Figure 3-14: Now knowing the location of the spill, the R-2 robots are attempting to nd spill objects to move to the goal location.

satises the rest of the team, so the remaining robots re-activate their move-spill behavior set. This series of actions is repeated until all of the spill is moved and the mission is complete.