Page 360 - Introduction to AI Robotics

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Hybrid Architecture
9.5 Case Study of Topological Navigation with a
As shown by the output, the Cartographer computes the path shown in
the first line. The second line shows that the current navigational task is to
move from R7 to H1. The Task Manager selects navigate-door and it begins
by looking for the door since the user did not specify where it was. By ex-
amining the database, the door is known to be to the south. Therefore, the
behavior initiates the move-ahead behavior in the south direction. When the
door is found, the initialization phase of the abstract behavior is over and the
nominal activity of moving through the door is triggered. Once the robot is
through the door, the nominal behavior is terminated, terminating the entire
abstract behavior as well.
The next navigational task is to move from H1 to H2, again in the direction
south. The task manger selects navigate-hall. The task of moving from H2
to H5 is interesting because it shows that the termination condition for hall
following is different than for H1 to H2.Since H5 is a gateway to a room of
interest, a different perceptual process is used to visually identify the room.
Once the door has been identified visually, the robot is considered at H5.
The H5-R2 connection instantiates navigate-door. However, in this case, the
ultrasonics has not yet identified the door opening and so the initialization
phase consists of wall following until the door opening is recognized. Then
the nominal behavior is activated and the robot moves into the room, suc-
cessfully completing the task.
The second simulation shown in Fig. 9.13 uses the sample topological map
provided prior to the competition. The intended path was R1-H1-F1-H8-
-H0-R0,but H8-H0 was blocked. As shown in the figure, the robot detects
that the path is blocked and uses move to goal to return to H8. The Cartogra-
pher updates the topological map and computes a new route and the robot
resumes execution, in this case H8-F1-H5-H6-H7-H0-R0. The output of the
script below shows the robot confirming the nodes H5 and H6 even though
the plan did not have them enter the associated rooms. These nodes were
kept in the path because if another blocked hall was encountered, the robot
would then be able to return to either R5 or R6 and attempt to use a route
through the door between.

9.5.2 Navigation scripts

The path planning and execution components are clearly deliberative. The
Cartographer is maintaining a map in the form of a graph and is monitoring
progress. The transition table takes the role of a high level sequencer. Scripts