Modeling of low severity soft-tissue injury due toudunwanted collisions of a robot in collaborative settings is anudimportant aspect to be treated in safe physical Human-RobotudInteraction (pHRI). Up to now, safety evaluations for pHRIudwere mainly conducted by using safety criteria related withudimpact forces and head accelerations. These indicate severeudinjury in the robotics context and leave out low severity injuryudsuch as contusions and lacerations. However, for the design ofudan intrinsically safer robot arm, a reliable evaluation of theudcollision between a human and a robot that is based on skinudinjury criteria is essential. In this paper, we propose a noveludhuman-robot collision model with and without covering, whichudis based on the impact stress distribution. The reliability ofudthe proposed collision model is verified by a comparison withudvarious cadaver experiments taken from existing biomechanicaludliterature. Since the stress characteristics acting on theudhuman head can be analyzed with this new collision model,udthe occurrence of certain soft-tissue injury can be estimated.udFurthermore, the method serves for selecting the appropriateudcovering parameters, as e.g. elastic modulus and thickness, byudevaluating the chosen skin injury indices.
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