  Robots must move legibly around people for safety reasons, especially for
tasks where physical contact is possible. One such task is handovers, which
requires implicit communication on where and when physical contact (object
transfer) occurs. In this work, we study whether the trajectory model used by a
robot during the reaching phase affects the subjective perceptions of receivers
for robot-to-human handovers. We conducted a user study where 32 participants
were handed over three objects with four trajectory models: three were versions
of a minimum jerk trajectory, and one was an ellipse-fitting-based trajectory.
The start position of the handover was fixed for all trajectories, and the end
position was allowed to vary randomly around a fixed position by $\pm$3 cm in
all axis. The user study found no significant differences among the handover
trajectories in survey questions relating to safety, predictability,
naturalness, and other subjective metrics. While these results seemingly reject
the hypothesis that the trajectory affects human perceptions of a handover, it
prompts future research to investigate the effect of other variables, such as
robot speed, object transfer position, object orientation at the transfer
point, and explicit communication signals such as gaze and speech.
