Page 73 - Introduction to AI Robotics

56
6
5 2 The Hierarchical Paradigm
10
Mission
Planner

goal

Navigator

path

Pilot

path subsegment:
Turn 83 degrees
move 5 meters

Figure 2.6 Examination of planning components in the NHC architecture.

sends actuator signals, the robot polls its sensors again. The World Model
is updated. However, the entire planning cycle does not repeat. Since the
robot has a plan, it doesn’t need to rerun the Mission Planner or the Naviga-
tor. Instead, the Pilot checks the World Model to see if the robot has drifted
off the path subsegment (in which case it generates a new control signal),
has reached the waypoint, or if an obstacle has appeared. If the robot has
reached its waypoint, the Pilot informs the Navigator. If the waypoint isn’t
the goal, then there is another path subsegment for the robot to follow, and
so the Navigator passes the new subsegment to the Pilot. If the waypoint is
the goal, then the Navigator informs the Mission Planner that the robot has
reached the goal. The Mission Planner may then issue a new goal, e.g., Re-
turn to the starting place. If the robot has encountered an obstacle to its path,
the Pilot passes control back to the Navigator. The Navigator must compute
a new path, and subsegments, based on the updated World Model. Then it
gives the updated path subsegment to the Pilot to carry out.