  Physical interaction between humans and robots can help robots learn to
perform complex tasks. The robot arm gains information by observing how the
human kinesthetically guides it throughout the task. While prior works focus on
how the robot learns, it is equally important that this learning is transparent
to the human teacher. Visual displays that show the robot's uncertainty can
potentially communicate this information; however, we hypothesize that visual
feedback mechanisms miss out on the physical connection between the human and
robot. In this work we present a soft haptic display that wraps around and
conforms to the surface of a robot arm, adding a haptic signal at an existing
point of contact without significantly affecting the interaction. We
demonstrate how soft actuation creates a salient haptic signal while still
allowing flexibility in device mounting. Using a psychophysics experiment, we
show that users can accurately distinguish inflation levels of the wrapped
display with an average Weber fraction of 11.4%. When we place the wrapped
display around the arm of a robotic manipulator, users are able to interpret
and leverage the haptic signal in sample robot learning tasks, improving
identification of areas where the robot needs more training and enabling the
user to provide better demonstrations. See videos of our device and user
studies here: https://youtu.be/tX-2Tqeb9Nw
