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

Jakob Reinhardt, Lorenz Prasch, Klaus Bengler

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


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 (BO) movement to communicate the intention of yielding priority to pedestrians at bottlenecks. To evaluate human sensory perception and subjective legibility, the BO is compared to three other motion strategies in a video study with 167 interviewees at the university and public spaces, where it excels regarding legibility. Implemented in a real encounter, objective motion behavior of 78 participants as a reaction to a stop-and-wait strategy, and two versions of BO (short and long), shows an improvement of the pedestrians' efficiency in the second encounter with the robot's short BO 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, BO path and time, exhibits the potential to increase the fluency of an interaction with robots at bottlenecks.

Original languageEnglish
Article number23
JournalACM Transactions on Human-Robot Interaction
Issue number3
StatePublished - Jul 2021


  • Human-robot spatial interaction
  • legibility of motion
  • metrics for human-robot interaction


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