“…Moreover, the assembly system design [104], [195], [203] was often used to assess the level of ergonomic risk. For instance, [204] proposed a time-cost optimization model to evaluate the ergonomics difficulty index via a score sheet in the assembly system design. A different approach using the "mental model" was introduced in [205]- [207] taking into account human preferences, knowledge of the tasks, and the capabilities of the human operator and the robot to complete tasks safely and efficiently.…”