Task-based Variation of Active Compliance of Arm/Hand robots in Physical Human Robot Interactions Iason Sarantopoulos, Dimitrios Papageorgiou, and Zoe Doulgeri Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece iasons@auth.gr, dimpapag@eng.auth.gr, doulgeri@eng.auth.gr Abstract. In this work a control strategy combining admittance con- trol with haptic cues is proposed for varying robot arm-hand target impedances in tasks involving physical Human Robot Interaction (pHRI). External force and robot state measurements are employed to initiate task phase transitions which further involve switching to appropriate target impedances. Three tasks typical for domestic robot assistance are demonstrated experimentally showing safe and natural interactions. 1 Introduction Most of the existing arm/hand systems are usually position controlled systems that can be accurate but rigid and hence, potentially unsuitable for contact tasks with the environment and/or pHRI. Contact initiation and maintenance with the environment in the presence of uncertainties requires compliant mo- tions to ensure environmental and robot safety. Moreover, it is important for the robot to present the required compliance in order to accomplish a task which in- volves human-robot interaction forces[1][2][3]. Compliance is either built within the structure of the robot via flexible joints, links and soft covers or achieved actively by the control action. Impedance control is typically employed to com- bine accuracy in free motion and a stable equilibrium in the case of interaction. This characteristic is clearly beneficial for avoiding transitions between position and force control at contact state changes which may induce instabilities in the presence of transition delays. However, the critical issue is the specification of the appropriate desired impedance for a given task which may need to be adapted to the environment variation or the task phase requirements. For example, when handing over an object to a human, a stiff grasp is required during the object’s 1 This research is co-financed by the EU-ESF and Greek national funds through the op- erational program “Education and Lifelong Learning” of the National Strategic Ref- erence Framework (NSRF) - Research Funding Program ARISTEIA I under Grant PIROS/506.