Anthony J. Nejman and Grant Schaffner
Space Suit Simulator, Extravehicular Activity, Kinematics, Joint Hysteresis, Workspace, Exoskeleton
A mechanical exoskeleton has the capacity to replicate the properties of a pressurized space suit with regards to motion resistance. Using such an exoskeleton for ground-based mission training and research provides a lower-cost, less operationally-complex alternative to using a space suit. To that end, NASA is supporting the development of such a device, termed a Space Suit Simulator (S3). The S3 must be designed to allow the wearer the same range of motion allowed in a space suit, and the joints must be actuated to produce the experienced resistive torques. A kinematic design of the lower-body exoskeleton was developed by using Denavit-Hartenberg notation and transformation matrices to derive the Jacobian matrix that was in turn used to identify singular configurations. The four degree-of-freedom exoskeleton design eliminates constrictive singularities by aligning human and exoskeleton joint axes. A graphical representation of the leg and S3 end-effector workspace verified that the S3 allows the human leg to move within the operational envelope anticipated during space suit use. A computational algorithm, based on the Preisach hysteresis model, was used to mimic space suit joint hysteresis behavior in knee flexion and hip abduction/adduction. The kinematic design and computational hysteresis algorithms will support the further development of a physical space suit simulator.
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