Decision processes in Artificial Intelligence are often organized hierarchically. One example is robot navigation with a global path planner and a local executor. This paper examines whether a shift from optimizing the two typical modules in navigation towards a dynamic interaction of more, not necessarily hierarchically linked, modules leads to robust navigation behavior. We empirically evaluate different organizations of modules for navigation in a simulated household with a simulated PR2 robot.
MotivationRobot navigation in household environments is still a challenge. Navigation in general is difficult because of the high variety of situations. In addition, households are more narrow and less structured than classical test environments such as museums or office spaces, and the movement should be legible 1 to people. Kirsch [15] introduces a heuristics-based local navigation method that moves a robot safely, efficiently and legibly inside single rooms, being able to circumvent obstacles without the need of a map or a planner.However, moving into other rooms or in very cluttered rooms requires planning. The standard approach is to calculate a global trajectory (represented by a list of intermediate points) with a global path planner and then to trace it with a local planner (also called controller) by moving the robot from one trajectory point to the next. In human-aware robot navigation, the global planner has received more research effort than the local planner [17], but the interaction of global and local planner faces some fundamental challenges: 1) When the environment changes (possibly because humans or pets are moving), a new global plan is calculated. The recalculation can be done efficiently, but the impression of goal-directed behavior is lost, the legibility of the trajectory suffers [20,16]. 2) Global planners abstract the state space and thus ignore some details. As an example, the reachability of points may be estimated by the line of sight. With a simple local planner, the planned trajectory may not be executable without * This research is funded by Deutsche Forschungsgemeinschaft and the Bavarian Academy of Sciences and Humanities.1 According to Lichtenthäler et al. [20] "Robot behavior is legible, if a human can infer the next actions, goals and intentions of the robot with high accuracy and confidence." C. Benzmüller, C.