Robot perceived as a threat: very much relating to the previous point robot navigation is considered generally safe. For a roboticist that means that the robot will not actively drive into a person and usually researchers in robotics are very much satisfied by robots efficiently navigating between places while not bumping into things and people; however, utilizing such traditional state of the art navigation approaches might well cause a robot to drive up very close to humans or plan paths that conflict with the human intention to walk along, which are situations in which the robot could be perceived as threatening.
Navigation in humans is determined by many factors, such as conventions (e. g. passing people on the right or left depending on the cultural preference), establishing eye contact to convey intention and even assessment of others abilities. In a sense, humans negotiate non-verbally when they manage space in the proximity of other people. Enabling a robot to master this challenge even close to the way humans do it is still on-going research in the field of human-aware navigation with all its different facets [
15]. Within the STRANDS project this challenge is also tackled by enabling the robot to continuously adapt to the appropriate navigation methods [
5] taking the past experience of encounters with humans into account. One key challenge for this is also perception, i. e. to be able to see and recognize people in the vicinity of the robot [
4], which becomes even trickier if people sit in wheelchairs or are of greatly varying posture or body height and also has to be taken into consideration. As a general policy, robots are usually designed to be very obedient to humans and if in any doubt to stop and let any humans pass first [
17]. This, however, often leads to situations identified earlier where the robot does not move for a while, as it is waiting for situations that are considered to be safe to move. Consequently, it might also result in a stuttering motion, while it continuously tries to find a safe and comfortable way to move among humans, while these at the same time move as well. In a way what we observe in human-robot joint navigation is not that different to a situation we all know when humans do a little “dance” when trying to pass each other in a narrow door or corridor, while negotiating who passes on which side.