Compliant gripper with force estimation for physical human–robot interaction

Despite the major interest in the field of Human–Robot Interaction (HRI) in recent years, not much work has been presented on physical HRI (pHRI), especially for robot-initiated contact. Although pHRI is a key skill in areas like assistive or rescue robots, advances are limited by hard constraints in safety and compliance that require specific hardware features and force estimation capabilities. This work presents a new compliant gripper with four underactuated fingers and force-sensing capabilities designed to manipulate a human forearm. Fingers are based on the rigid-link approach, where one of the links has been replaced by a compression spring. High-resolution angular sensors at the passive joints allow computing the spring compression and the actuator torque. Then grasping forces are estimated through the kinetostatic model of the fingers. The gripper has been built and tested. Compliance and grasping force estimation and control have been successfully evaluated. Results prove that the proposed finger arrangement offers good performance, making our design suitable for pHRI applications.