Abstract Engagement during first encounters needs both parties to comprehend each other’s intent without mutual information. A robot may fail to engage someone because people are unaware of the robot’s presence or intent to interact, or because they are uninterested in interacting with robots. In this paper, we compared three different greeting strategies for mobile social robots in first encounters with humans using the Kendon’s greeting protocol, which was derived from observations of human greeting behaviors. The theoretical protocol defines a sequence of six phases during greetings: initiation of the approach, distance salutation, head dip, approach, final approach, and close salutation. The three greeting strategies we compare in our empirical studies specifically implement the first three phases of the Kendon’s model (M1), the six phases (M2), or the six phases as a response of the human greeting phase (M3). We performed a user study during a public art exhibition in two different situations: in-the-wild and with invited participants. The results of these two experiments combined both quantitative and qualitative measures and support that people’s engagement and impressions of the robot can be enhanced when the robot employs M2 and M3, compared to M1. Our results generally support that Kendon’s greeting model is effective in human-robot first encounters for mobile social robots. We also discuss important considerations for running in-the-wild robotic experiments.
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