Design of soft knee exoskeleton and modeling effects of variable stiffness for advanced space suits and planetary exploration

Abstract

Existing gas-pressurized space suit designs aim to provide astronauts with a wide range of joint motion while minimizing joint torque during extra-vehicular activity (EVA). However, current space suits have stiff joints with limited range, which impede performance. Future designs should consider that some joint torque can be beneficial in storing elastic energy for locomotion in reduced gravity planetary EVAs. Though current gas-pressurized space suits restrict astronaut movement, they are capable of partially supporting their own mass and storing elastic energy in the lower body, allowing metabolic cost reduction during locomotion in reduced gravity, such as on Mars or the moon.

The BioSuit[superscript TM] developed by the Massachusetts Institute of Technology (MIT), is an advanced, skin-tight compression garment concept, which exerts mechanical counterpressure (MCP) directly on the astronaut's skin with the benefits of increasing range of motion and performance while also reducing mass when compared to gas-pressurized space suits. A BioSuit[superscript TM] soft knee exoskeleton with tunable knee stiffness was developed to minimize metabolic expenditure during locomotion in partial gravity and maximize mobility. Musculoskeletal modeling simulated predicted soft knee exoskeleton stiffness at the knee during walking in Earth and Lunar gravity. This thesis summarizes the design and development of prototype actuation in a soft exoskeleton in collaboration with the D-Air Lab (Vicenza, Italy) that applies variable knee stiffness.

Soft knee exoskeleton design criteria, fabrication techniques, and simulated impacts on joint kinematics and metabolic cost are discussed. The soft knee exoskeleton was shown to exert tunable knee stiffness via airbags. Prototypes were developed to minimize partial gravity locomotion metabolic cost and space suit inflexibility. An OpenSim software pipeline was shown to be capable of torsional spring stiffness modeling at the knee analogous with predicted soft knee exoskeleton stiffness. Integration of 1G and 0.17G walking data enabled comparison of energetics trends between exoskeleton conditions within each gravity level. The results of this thesis demonstrate the ability to integrate a soft knee exoskeleton into the BioSuit[superscript TM] to improve space suit design and enable longer, safer, and more complex EVAs in partial gravity.