Design of elastomeric foam-covered robotic manipulators to enhance human safety

Unintentional physical human–robot contact is becoming more common as robotic manipulators operate in closer proximity to people. In this paper, we investigate the use of compliant foam covering to reduce impact severity and enhance human safety. An improved analytical impact dynamic model is introduced. The impact model conservatively approximates the impact force and resulting head acceleration; and incorporates the configuration-dependent manipulator dynamics and the coupling between the human head and moving torso. It is applicable to head impacts with impact velocities that do not exceed 1.25 m/s. Based on this model, the most important manipulator parameter for reducing the impact severity is the effective mass. Furthermore, the foam stiffness has a greater reduction effect than any of the manipulator parameters. A procedure to properly design the foam in accordance with a force-based or acceleration-based safety criterion and a foam thickness constraint is proposed. The impact model and model-based design procedure are tested experimentally. Impact experiments are performed with an apparatus simulating the human head–neck–torso. The maximum error between the predicted and experimental maximum head acceleration results is less than 7%.