Designing optimally safe robot surface properties for minimizing the stress characteristics of human-robot collisions

Abstract

Modeling of low severity soft-tissue injury due to unwanted collisions of a robot in collaborative settings is an important aspect to be treated in safe physical Human-Robot Interaction (pHRI). Up to now, safety evaluations for pHRI were mainly conducted by using safety criteria related with impact forces and head accelerations. These indicate severe injury in the robotics context and leave out low severity injury such as contusions and lacerations. However, for the design of an intrinsically safer robot arm, a reliable evaluation of the collision between a human and a robot that is based on skin injury criteria is essential. In this paper, we propose a novel human-robot collision model with and without covering, which is based on the impact stress distribution. The reliability of the proposed collision model is verified by a comparison with various cadaver experiments taken from existing biomechanical literature. Since the stress characteristics acting on the human head can be analyzed with this new collision model, the occurrence of certain soft-tissue injury can be estimated. Furthermore, the method serves for selecting the appropriate covering parameters, as e.g. elastic modulus and thickness, by evaluating the chosen skin injury indices.

The Safety of Domestic Robotics: A Survey of Various Safety-Related Publications

“…By using Hertzian contact models to represent the impact, the proposed safety norm identifies safe design choices by evaluating the maximum stress on the skin that will occur during impact of a point on the robotic cover against a human body. Focusing on soft tissue injuries, [59] also developed a Hertz contact theory based collision model between a covered robot and a human head to analyze laceration and contusion injuries. Then by using tensile stress and energy density limits of the skin as a safety criteria, the authors proposed allowable elastic modulus and thickness for a robot covering.…”

Safe acting and manipulation in human environments: A key concept for robots in our society

“…fences or light barriers, obsolete for these interactive devices in order to enable direct physical cooperation between human and robot. For understanding the risks of this undertaking we performed a series of safety investigations [7], [8], [9], [10], [11], [12], [13], which led to fundamental insight into the potential injury a human would suffer due to a collision with a robot. Furthermore, we developed human-friendly interaction control and motion schemes that enable the robot S. Haddadin, S. Parusel, R. Belder, A. Albu-Schäffer, and G. Hirzinger are with the Institute of Robotics and Mechatronics, DLR -German Aerospace Center, Wessling, Germany, contact: sami.haddadin@dlr.de to show sophisticated real-time responses on interaction force level, motion planning, and real-time task planning [14], [4], [15], [16], [17], [18].…”

Investigation of safety in human-robot-interaction for a series elastic, tendon-driven robot arm

“…Methods for estimation of contact force and stress were presented in [15] and [16]. We extend these methods for robotic arms with joint elasticity by considering the potential energy stored in the springs.…”

“…A detailed study of a realistic collision model of a robot arm with soft covering and human head with multi-layer structure for covering design to prevent softtissue injuries was presented in [16]. To evaluate the danger of contusions, a maximum impact energy density of 2.52 J /cm 2 and for lacerations, the skin tensile strength of σ = 10 6 N /m 2 was used.…”