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.