UBC Theses and Dissertations
Finite element analysis of a wheelchair when used with a front-attached mobility add-on Ogilvie, Colleen
Over the past two decades, a variety of mobility add-ons for manual wheelchairs have emerged in the assistive technology industry, including pushrim-actuated power-assist wheelchairs, motorized propulsion aids, manual and motorized front-end drive attachments, and passive attachable wheels. These technologies are typically used by long-term lightweight manual wheelchair users including those from spinal cord injury populations, and increase the mobility capabilities of the wheelchair, such as through the addition of all-terrain wheels or power-assistance. Currently, little is known about how mobility add-ons affect the durability, strength, and lifespan of manual wheelchairs, and whether they increase the risk of component failures. In particular, very little research has assessed the likelihood of failures associated with front-attached mobility add-ons. Component failures can lead to wheelchair rider injuries or leave users stranded. Additionally, repairing or replacing damaged frames can incur significant costs. Finite element analysis (FEA) is a technique frequently used in structural analysis. The goal of this thesis is to develop a finite element model of a wheelchair when used with a passive, front-attached mobility add-on that attaches at the footplate. The FEA model was physically validated using strain gauges under static loading scenarios. The validated model was then used to assess stresses and displacements under static loading considering several different design variables and dynamic loads based on experimental use cases, and considers how these factors impact number of cycles to fatigue failure in the system and therefore the overall lifespan of the wheelchair. Results found that the use of a footplate-mounted mobility add-on increased stresses in the horizontal portion near the tube intersections of a D-shaped footplate. The thickness of the tubing in the footplate and the location of the rear axle created high stresses in the footplate under particular customizations. Furthermore, it was found that user mass and increased frontal impacts greatly reduced the hours of use to failure for the chair. Through identifying the location and magnitudes of points of failure, design guidelines such as changes to attachment location or recommendations for reinforcement in manual frames can be provided to minimize risks of component failures.
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