International Journal of Social Robotics manuscript No. (will be inserted by the editor) Exploiting the robot kinematic redundancy for emotion conveyance to humans as a lower priority task Josep-Arnau Claret · Gentiane Venture · Luis Basa ˜ nez Received: date / Accepted: date Abstract Current approaches do not allow robots to execute a task and simultaneously convey emotions to users using their body motions. This paper explores the capabilities of the Jacobian null space of a humanoid robot to convey emo- tions. A task priority formulation has been implemented in a Pepper robot which allows the specification of a primary task (waving gesture, transportation of an object, etc.) and exploits the kinematic redundancy of the robot to convey emotions to humans as a lower priority task. The emotions, defined by Mehrabian as points in the Pleasure - Arousal - Dominance space, generate intermediate motion features (jerkiness, activity and gaze) that carry the emotional infor- mation. A map from this features to the joints of the robot is presented. A user study has been conducted in which emo- tional motions have been shown to 30 participants. The re- sults show that happiness and sadness are very well con- veyed to the user, calm is moderately well conveyed, and fear is not well conveyed. An analysis on the dependencies between the motion features and the emotions perceived by This work has been partially supported by the Spanish MINECO projects DPI2011-22471, DPI2013-40882-P and DPI2014-57757-R, the Spanish predoctoral grant BES-2012-054899, and the Japanese challenging exploratory research grant 15K12124. The authors would like to thank the members of the GVLab for their invaluable support with the translations and attending the local participants during the user study. Josep-Arnau Claret Institute of Industrial and Control Engineering, Technical University of Catalonia (UPC), BarcelonaTECH, Barcelona, Catalonia, Spain E-mail: josep.arnau.claret@upc.edu Gentiane Venture Tokyo University of Agriculture and Technology, Tokyo, Japan E-mail: venture@cc.tuat.ac.jp Luis Basa ˜ nez Institute of Industrial and Control Engineering, Technical University of Catalonia (UPC), BarcelonaTECH, Barcelona, Catalonia, Spain E-mail: luis.basanez@upc.edu the participants shows that activity correlates positively with arousal, jerkiness is not perceived by the user, and gaze con- veys dominance when activity is low. The results indicate a strong influence of the most energetic motions of the emo- tional task and point out new directions for further research. Overall, the results show that the null space approach can be regarded as a promising mean to convey emotions as a lower priority task. Keywords Human-robot interaction · Social robotics · Emotion conveyance · Robot kinematics · Task priority · Pepper robot Abbreviation DOF Degree of Freedom JVG Jerkiness - Activity - Gaze PAD Pleasure - Arousal - Dominance 1 Introduction Robotics is moving from cells of industrial manipulators to shared environments where humans and robots have to inter- act [10, 44]. The increasing interest in Human-Robot Inter- action and social robotics [4] has naturally lead to the ques- tion of whether robots should be endowed with emotions [11] and emphatic behaviours [3, 43]. In this regard, a future is devised in which humans and robots interact on a daily basis. Several studies show a link between productivity and the emotional state of the workers, for example, happiness raises productivity [36], and anxiety impairs cognitive performance, which may ultimately lead to fatigue and degrade productivity [18]. In order to increase the probability that the operator succeeds in his/her task, a