uMan: A Low-Impedance Manipulator for Human-Robot Cooperation Based on Underactuated Redundancy

This paper revisits the concept of underactuated manipulator in order to significantly improve physical human-robot cooperation for the assembly industry. The main focus is to achieve intuitive and minimum effort fine manipulation, regardless of the payload's shape and weight. An underactuated manipulator-referred to as uMan-based on a macro-mini architecture is designed with a novel passive mini mechanism, which aims at minimizing the impedance, eliminating the nonlinear impedance, and decoupling the human and robot dynamics. A specific control strategy is developed to achieve these objectives, while handling the underactuated nature of the robot for cooperative and autonomous assistance. Experimental validations are provided to assess the ease of fine manipulation using a peg-in-hole task to demonstrate the safety of the device using an effective collision detection and to establish the viability of the concept for practical industrial assembly tasks.