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Physical human–robot interaction implies the intersection of human and robot workspaces and intrinsically favors collision. The robustness of the most exposed parts, such as the hands, is crucial for effective and complete task execution of a robot. Considering the scales, we think that the robustness can only be achieved by the use of energy storage mechanisms, e.g. in elastic elements. The use of variable stiffness drives provides a low-pass filtering of impacts and allows stiffness adjustments depending on the task. However, using these drive principles does not guarantee the safety of the human due to the dramatically increased dynamics of such system. The design methodology of an antagonistically tendon-driven hand is explained. The resulting hand, very close to its human archetype in terms of size, weight, and, in particular, grasping performance, robustness, and dynamics, is presented. The hyper-actuated hand is a research platform that will also be used to investigate the importance of mechanical couplings and, in future projects, be the basis of a simplified hand that would still perform daily manipulation tasks.

The DLR Hand Arm System is a highly dynamic and fully integrated mechatronic system which uses an anthropomorphic design. It exhibits impressive robustness by using a complete variable stiffness actuation paradigm. It aims at reaching the human archetype in most of its performances and its design. The methodology consists in understanding the human archetype on a functional basis rather than to copy it. However, the design is driven by two antipodal concepts: On one hand, the design has to be simple, robust, and easy to maintain. On the other hand it must be anthropomorphic in shape and size but also, more importantly, in functionality.The paper presents a finger design that combines a reduced diversity of parts with the need to build five kinematically different fingers. The fingers are protected against overload by allowing subluxation of the joints. The tendon routing allows for an antagonistic actuation and is optimized to minimize friction and wear. The resulting combination of the link design and the antagonistic actuation is shown to be robust against impacts as well as highly dynamic. They achieve the targeted maximum fingertip force of 30 N in stretched out configuration. The use of antagonistic drives enables to tackle problems of tendon overstretching and slackening that commonly encounter in tendon driven mechanisms. Due to the enhanced capabilities and, in especial, its robustness, the application developers can focus on the use of innovative grasping and manipulation strategies instead of worrying about the integrity of a costly robotic systems. The possibility of storing energy in the elastic elements of the drive opens new opportunities to perform dynamics based actions (e.g, snapping fingers).

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