Control Strategy for Safety Purposes Based upon Momentum Regulation

Ensuring human safety in human-robot collaboration is an active research topic. This paper newly presented that momentum is a quantification parameter to estimate slight injury, and 17.7 N·s was considered as a threshold of the slight injury onset level. Based on this finding, a momentum observer-based control strategy for securing the safety of human body parts in the clamping scenario was originally proposed. The momentum observer and motion reshaping provided a momentum-limit function, helping to avoid the risk associated with the momentum exceeding the threshold. The part of the estimated external momentum that exceeds a predetermined momentum threshold is transformed into a motion trajectory to reshape the command motion and limit the external momentum under the injury onset criterion. Clamping experiments were conducted using a manipulator with seven degrees of freedom and a dummy with high biofidelity. The experimental results show that the external momentum was successfully limited under the momentum threshold that was set as 10 N·s, and a 5 N contact force was reduced to 0 N in the clamping situation. The study exhibits that the proposed control strategy can help avoid the risk of the momentum exceeding an injury onset threshold when the human body part is clamped and can effectively release the human body part in a clamping scenario.