The Role of Closed-Loop Hand Control in Handshaking Interactions

In this letter, we investigate the role of haptic feedback in human-robot handshaking by comparing different force controllers. The basic hypothesis is that in human handshaking force control there is a balance between an intrinsic (open-loop) and extrinsic (closed-loop) contributions. We use an underactuated anthropomorphic robotic hand, the Pisa/IIT hand, instrumented with a set of pressure sensors estimating the grip force applied by humans. In a first set of experiments, we ask subjects to mimic a given force profile applied by the robot hand, to understand how human perceive and are able to reproduce a handshaking force. Using the obtained results, we implement three different handshaking controllers, in which we varied the intrinsic and extrinsic contributions and in a second set of experiments, we ask participants to evaluate them in a user study. We show that a sensorimotor delay mimicking the reaction time of the central nervous system is beneficial for making interactions more human-like. Moreover, we demonstrate that humans exploit closed-loop control for handshaking. By varying the controller we show that we can change the perceived handshake quality and also influence personality traits attributed to the robot.