Modeling and Estimation of Stiffness Imposed by Cable-Based Exosuits

Cable-based exosuits are one of the prevalent choices for rehabilitation, among others. These exosuits are redundant in nature and are capable of imposing a desired joint torque along with a specific impedance simultaneously due to redundancy. The exosuit imposed impedance majorly depends on the geometric routing of the cables and tension in cables. Therefore, the resulting stiffness and damping imposed onto humans could be different from what is intended for a musculoskeletal system of generalized anthropometry. Thus, modeling and estimating the impedance imposed by a cablebased exosuit is of utmost importance for the design and development of efficient and effective rehabilitation exosuits. The current work developed a framework to estimate stiffness imposed by a passive cable-based exosuit onto a human arm. To test the framework, an experiment was conducted on two participants, and the joint space and task space stiffness was estimated using the developed framework. The results indicate that during the design of routing, the geometry is more important than the cable tension. Furthermore, for the same cable routing, the imposed stiffness differed in magnitude for both participants. The developed framework can be even more beneficial in the design of complex and nonintuitive cable routing.