Development of a Passive Lower Body Exoskeleton with Novel Compliant Joints for Walking Assistance
Authors
Hole, Roger ; Bjoner, Jørgen
Term
4. term
Education
Publication year
2020
Submitted on
2020-06-03
Pages
89
Abstract
This thesis presents the development of a passive lower-limb exoskeleton with novel compliant joints for walking assistance, aimed at post-stroke gait rehabilitation. The work responds to the need for lighter, more compact devices than many existing systems. The project focuses on compensating gravitational and inertial effects during walking. A simplified dynamic design tool, developed by the authors previously, was used to estimate hip and knee joint torque requirements; the model was refined to better represent ground reaction forces during stance, though these effects were not used in the exoskeleton design itself. The proposed passive mechanism is a pulley-based system that converts the tension in built-in springs into balanced joint torques; its configuration was optimized with respect to torque demands. Analysis showed the need for high-stiffness springs with substantial pretension, leading to the choice of practical linear tension springs. Both hip and knee modules use aluminum frames with springs placed alongside the frame for a compact and safe layout. Structural analysis identified frame deformation as the most critical design factor; a topology-optimized outer frame reduced weight by 58% (hip) and 49% (knee). Multibody simulations of the full CAD model attached to a humanoid leg indicated average driving torque reductions of approximately 66% at the hip and 72% at the knee. Due to COVID-19 constraints, the study is purely theoretical with no physical testing.
Denne afhandling omhandler udviklingen af et passivt underekstremitets-eksoskelet med nye eftergivelige (compliant) led til gangassistance, målrettet rehabilitering efter apopleksi. Udgangspunktet er behovet for lettere og mere kompakte løsninger end mange eksisterende systemer. Projektets scope er at kompensere for tyngde- og inertialkræfter under gang. Et simplificeret dynamisk designværktøj, udviklet af forfatterne tidligere, blev anvendt til at estimere momentkrav i hofte- og knæled; modellen blev udvidet for bedre at repræsentere underlagsreaktionskræfter i standfasen, men disse blev ikke indarbejdet i selve eksoskeletdesignet. Den foreslåede passive mekanisme er et remskivesystem, der omsætter trækkraften i indbyggede fjedre til balancerede ledmomenter; konfigurationen blev optimeret i forhold til momentkravene. Analysen viste behov for højstive fjedre med betydelig forspænding, og lineære trækfjedre blev valgt. Hofte- og knæmodulerne er opbygget omkring aluminiumsrammer med fjedre anbragt langs rammen for en kompakt og sikker løsning. Strukturanalyse identificerede rammedeformation som den mest kritiske faktor; derfor blev yderrammen topologioptimeret, hvilket reducerede vægten med 58 % for hofterammen og 49 % for knærammen. Multilegemes-simuleringer med CAD-modellen af det komplette eksoskelet koblet til en humanoid benmodel indikerede, at det gennemsnitlige drivmoment kunne reduceres med cirka 66 % i hoften og 72 % i knæet. Arbejdet var rent teoretisk som følge af COVID-19, og der blev ikke gennemført fysiske forsøg.
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