Mutual trust-based subtask allocation for human-robot collaboration in flexible lightweight assembly in manufacturing

A human-robot hybrid cell is developed for flexible assembly in manufacturing through the collaboration between a human and a robot. The selected task is to assemble a few LEGO blocks (parts) into a final product following specified sequence and instructions. The task is divided into several subtasks. A two-level feedforward optimization strategy is developed that determines optimum subtask allocation between the human and the robot before the assembly starts. Human's trust in robot and robot's trust in human are considered, computational models of the trust are derived and real-time trust measurement and display methods are developed. A feedback approach is integrated into the feedforward subtask allocation in the form of subtask re-allocation if trust levels reduce to below specified thresholds. It is hypothesized that subtask re-allocation may help regain trust and maintain satisfactory performance. Experiment results prove that (i) the integrated (feedforward + feedback) optimum subtask allocation is effective to maintain satisfactory trust levels of human and robot that result in satisfactory human-robot interactions (HRI) and assembly performance, and (ii) consideration of two-way trust (human's trust in robot and robot's trust in human) produces better HRI and assembly performance than that produced when one-way trust (human's trust in robot) or no trust is considered.