Michael, Shona; (1994) The Principles of Shaped Wheelchair Seat Cushioning Design. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The aim of this work is to determine the principles by which the optimum design of shaped wheelchair seat for an individual can be established. A system for producing individually contoured cushioning using computer-aided design and manufacturing techniques was developed and tested. Nonlinear finite element (FE) models of the seated buttock were developed from measurements of an able-bodied individual. Soft tissue force-deflection characteristics, tissue depth, body surface geometry and the weight supported through the buttock were measured during sitting. The combined soft tissues were modelled as an incompressible hyperelastic material. Interface pressure distributions calculated from the analyses were found to be similar to pressure distributions measured between corresponding shaped seat surfaces and the subject. The effects of seat shape, contour depth, interface friction and misalignment of the body on the seat were examined. The results of the FE analyses suggested that the closer the contours of the seat to the contours of the buttock prior to loading, the lower the distortional stress concentrations and hydrostatic pressure gradients in the soft tissues around the pelvis during sitting. It appeared that the stresses in the soft tissue around the sacrum are sensitive to posture and changes in position of the body on the seat. When the dorsal surface of the sacrum has a postero-inferior orientation, a lot of load is transferred through the sacrum and there is a high distortional stress concentration in the soft tissues. When the body moves about on the seat and there is a high interface friction coefficient, the soft tissues are constrained by the interface forces and additional distortional stresses develop in the soft tissue. The principles can be applied to the design of shaped seating for individuals and groups of people with similar seating needs.

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