  The environments in which the collaboration of a robot would be the most
helpful to a person are frequently uncontrolled and cluttered with many objects
present. Legible robot arm motion is crucial in tasks like these in order to
avoid possible collisions, improve the workflow and help ensure the safety of
the person. Prior work in this area, however, focuses on solutions that are
tested only in uncluttered environments and there are not many results taken
from cluttered environments. In this research we present a measure for
clutteredness based on an entropic measure of the environment, and a novel
motion planner based on potential fields. Both our measures and the planner
were tested in a cluttered environment meant to represent a more typical tool
sorting task for which the person would collaborate with a robot. The in-person
validation study with Baxter robots shows a significant improvement in
legibility of our proposed legible motion planner compared to the current
state-of-the-art legible motion planner in cluttered environments. Further, the
results show a significant difference in the performance of the planners in
cluttered and uncluttered environments, and the need to further explore legible
motion in cluttered environments. We argue that the inconsistency of our
results in cluttered environments with those obtained from uncluttered
environments points out several important issues with the current research
performed in the area of legible motion planners.
