A Novel Safety-Oriented Control Strategy for Manipulators Based on the Observation and Adjustment of the External Momentum

Human safety assurance in physical human-robot interactions (pHRIs) has become a challenge for current robotic applications. Considering the safety assurance of a pHRI validation experiment, the viscoelastic properties of a human body part were investigated in a previous study and were added in a pHRI simulation. This study focuses on a threshold momentum value as an injury criterion for momentum control strategy design. A novel safety-oriented control strategy is proposed, which consists of a conventional proportional-derivative (PD) controller, an external momentum observer-based compensator for monitoring the external momentum, and an adjustment loop for shaping the trajectory motion command to bind the external momentum within the injury criterion. The proposed control strategy can be designed without needing to obtain the mechanical properties of the environment. The strategy can also be combined with the related injury criterion. In addition, it shows the effectiveness of ensuring safety even in the worst pHRI clamping situation, where a human body part can escape from such a situation. Simulation results show that the proposed control strategy performs well in the trajectory tracking task, and the adjustment loop successfully shapes the predetermined trajectory motion command to bind the external momentum within the injury criterion.