Design of foam covering for robotic arms to ensure human safety

Unintentional physical human-robot contact is becoming more common as robots operate in closer proximity to people. This contact may generate a large impact force and cause severe human injuries. Therefore, the ability to reduce the human-robot impact force and ensure human safety is a fundamental requirement for human-friendly robots. An easy and effective way to achieve this is using foam to cover the robot surface. We present a method for designing the stiffness and thickness of the foam covering based on a realistic safety threshold and an improved impact force model. Our model incorporates the previously neglected coupling of the human head to the torso and the coupling of the robot arm to its base. The impact model and model-based design procedure are experimentally verified for various foam properties, and robot and human velocities. The impact experiments are performed with an apparatus simulating the human head and, at lower velocity, with a human volunteer. The maximum error between the predicted and experimental peak impact force results is 8%.