Back-off: Evaluation of Robot Motion Strategies to Facilitate Human-Robot Spatial Interaction

Standstill behavior by a robot is deemed to be ineffective and inefficient to convey a robot's intention to yield priority to another party in spatial interaction. Instead, robots could convey their intention and, thus, their next action via motion. We developed a back-off movement to communicate the intention of yielding priority to pedestrians at bottlenecks. To evaluate human sensory perception and subjective legibility, the back-off is compared to three other motion strategies in a video study with N = 167 interviewees at the university and public spaces, where it excels regarding legibility. Implemented in a real encounter, objective motion behavior of N = 78 participants as a reaction to a stop & wait strategy, and two versions of back-off (short and long) shows an improvement of the pedestrians' efficiency in the second encounter with the robot's short back-off version compared to the stop strategy. Eventually, in the third encounter with all motion strategies, interaction causes only a small time consumption still required by the cognitive process of perceiving an object in the visual field. Hence, the design of kinematic parameters, back-off path and time, exhibits the potential to increase the fluency of an interaction with robots at bottlenecks.