I-RIM Conference 2019 October 18 - 20, Rome, Italy ISBN: 9788894580501 Adaptive admittance control for a safe and efﬁcient human-robot interaction Federica Ferraguti, Chiara Talignani Landi, Lorenzo Sabattini, Marcello Bonf`e, Cesare Fantuzzi and Cristian Secchi Abstract— The possibility of adapting online the way a robot interacts with the environment is becoming more and more important. Nevertheless, stability problems arise when the environment (e.g. the human) the robot is interacting with gets too stiff. In this work, we present a strategy for handling the stability issues related to a change of stiffness of the human arm during the interaction with an admittance-controlled robot. I. INTRODUCTION One of the most revolutionary and challenging features of the new generation of robots is physical human-robot interaction (pHRI). In pHRI tasks, robots are designed to coexist and cooperate with humans in applications such as assisted industrial manipulation, collaborative assembly, domestic work, entertainment, rehabilitation or medical ap- plications. In these contexts, due to the desired coexistence of robotic systems and humans in the same workspace, main concerns are related to safety and dependability. A widely used approach consists in implementing interaction control strategies that guarantee a compliant behavior of the robot. In particular, admittance control is typically utilized for controlling industrial robots, that are generally characterized by a stiff and non-backdrivable mechanical structure [1]. For example, admittance control has been used to imple- ment robot manual guidance in [2] and [3], by means of the “walk-through programming” where the human operator becomes the teacher that physically guides the robot through- out the desired trajectory. When using admittance-controlled robots, instability can arise when interacting with stiff envi- ronments. Since humans are dynamic systems characterized by a time-varying impedance, they can behave in a stiff way and, consequently, give rise to instability when interacting with admittance-controlled robot. Instability induces, among other undesired effects, a deviation of the robot from the desired admittance behavior. Furthermore, it produces high amplitude oscillations of the end-effector, undermining the user safety during the interaction. The deviations have to be ﬁrst promptly detected and then canceled (or reduced) to restore the stability of the system. The adaptation of the parameters of the admittance control is a common strategy for recovering the stability of the interaction as shown, e.g., in [4], [5] and [6]. In this work we show a novel strategy F. Ferraguti, C. Talignani Landi, L. Sabattini, C. Fantuzzi and C. Secchi are with the Department of Sciences and Methods for Engineering (DISMI), University of Modena and Reggio Emilia, Italy {name.surname}@unimore.it M. Bonf`e is with the Engineering Department, University of Ferrara, Italy marcello.bonfe@unife.it for detecting the rise of oscillations during the interaction between a human and an admittance-controlled robot and a parametric adaptation of the admittance for restoring a stable behavior. The proposed adaptation allows to keep the adaptive dynamics similar to the nominal one in order to avoid unbalancing effects and to increase the usability of the system. Preliminary results have been presented in [7] and [8], while in [9] a method for automatically setting the detection threshold using a thorough statistical analysis has been introduced. Moreover, a weighted energy allocation strategy has been proposed in order to consider separately translations and rotations. In this work we present the overall framework and we show the experimental validation of the control architecture. II. ADAPTIVE ADMITTANCE CONTROL The goal of the admittance control is to force the robot to behave in a desired way when interacting with the en- vironment. In this paper, we address the case of a robotic manipulator manuall