Digital Definition of the Deflected Shape of the Human Body in Seated Postures for Ergonomic Design in CAD Models

An advanced biofidelic shape of the human body is needed in computer-aided design (CAD) models for ergonomic design. To be used in seat and automotive design, this advance in biofidelity must be a 3D CAD tool that includes the deflected shape of the human body and must include skeletal landmarks, especially those related to load paths. The CAD tools must represent the range of the population and must also represent the full range of seated postures.

To develop our CAD models, a 3D anthropometric study was undertaken that used skeletal landmarks to define relative positions of transverse cross-sections that describe both the “visible” and “invisible” shape of the seated body. Data were collected on large males, average males and small females. Subjects were measured in several postures while sitting on flat foam pads. Transverse sections were measured at the center of gravity of each thigh, under the ischial tuberosities and at the S2, L4, T8 and T4 spinal levels. A coordinate measurement machine (CMM) was used in conjunction with a strain strip to measure the shape of each section. The resulting transverse sections define the deflected shape (patent pending) of the seated body for three body sizes.

The transverse section data were combined with 2D center line sections (patent pending) developed previously. Skeletal landmarks were used to define frames of reference to combine the transverse sections with the center line sections of the human body. The shape between regions was interpolated with C² continuity using the transverse sections and center line curves as controls. The resulting models of the body define the 3D biofidelic seated shape that is required to estimate the design of the optimal seat and seating package for the human occupant-driver.