Too Close to Comfort ? A New Approach of Designing a Soft Cable-driven Exoskeleton for Lifting Tasks under Ergonomic Aspects

At this point of their development, available exoskeletons for industrial applications still lack broad acceptance by users on the shop floor; this is allegedly due to discomfort and restriction of movements. Exoskeletons are in close physical interaction with the user. For everyday use at work, the kinematic chain of the human and the exoskeleton must satisfy the needs of every possible user in terms of high usability and positive user experience. Focusing on aspects like the users’ wearing comfort, reduction of interaction forces and easy setup, a new concept for an exoskeleton that supports the elbow movement during lifting tasks was developed. To avoid misalignments between the exoskeleton and the human, and to allow a full range of movement, a soft cable-driven structure was chosen. In an iterative design process, a basic structure made of a rather stiff fabric with elastic inlays was developed. The cut is meant to suit a wide range of anthropometric measures while ensuring a tight fit for good transfer of forces. Using soft materials and cables poses a challenge for calculating, simulating and measuring force distributions not only in the exoskeleton, but also in the human tissue and bones. A suitable model of the kinematic human-machine-chain and a method for testing the new concept were therefore developed. Since ergonomic design and the users’ needs were of high priority in the design process, the robustness and the maximum load capacity of the system are initially left out of this concept. This paper will present the design of the soft fabric-based structure as well as the kinematic design of the cable train and the implementation.