A Collaborative Robotic Screw Assembly System Using 6-PUS Parallel Mechanism

Abstract

Abstract Screw fastening is an important process in the automobile assembly line, and it is difficult to be accomplished completely by automation. Collaborative screw fastening is a practical technique in automotive assembly. In this paper, a novel collaborative robotic system for screw tightening operations based on parallel mechanism is proposed, which is more suitable for high-torque screw tightening tasks while improving operator ergonomics. To this end, a 6-PUS parallel mechanism with a central passive limb is designed. In addition, a control framework for collaborative screw tightening tasks is developed. Its main idea is that the human operator is responsible for the error-prone initial mating stage of screws, while the robot is responsible for the screw-driving stage. The two stages can be performed simultaneously, increasing productivity and reducing the labor intensity. To this end, a multi-mode active compliance controller is proposed according to stages of the screw tightening process and the feedback of a 6-axis force sensor. Furthermore, a statistics based method that helps the robot to guess the next screw position is proposed to improve the fluentness of the collaborative process. A prototype of the proposed robotic system is built. Experiments of the collaborative screw installation process of an engine part are conducted to demonstrate the effectiveness of the proposed system.