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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.

Virtual drivers in math models can design and evaluate the seating package in all classes of vehicles. With the driver's seated geometry constrained by vision and reach to the steering wheel and pedal, seat design is optimized to support all drivers in three back postures to operate the vehicle. The position of each virtual driver model in the seat is calculated from a biomechanical model of seated load distribution with each model represented by functionally correct positions of pelvis and spine as well as the deflected shape of the seated body in a vehicle seat. This geometry is optimized to design or evaluate seats by changing boundary conditions of select variables and functions in the math tool. The math comfort score is calculated from the physical interface between the virtual drivers and the seating package. The weighted sum of scores for all virtual drivers is the population comfort score for the vehicle seating package.

In this paper we present a method for converting the CAESAR full body scanned data into human body models for use in the ERL design software. The ERL software is a comprehensive interior automobile design tool, used in design or evaluation. The 3D CAD occupants in ERL were generated from anatomical cross sections at comparable landmarks and spinal shapes. Skeletal landmarks in the CAESAR data are used to establish segmental coordinates from which cross-sections are defined. The anatomical cross sections are used to re-generate the external shape of the body. Additional skeletal landmarks are calculated using regression equations. Segmental mass distributions are calculated based on segmental volume.

Human accommodation, has undergone rapid changes in the past few years which are outdistancing current concepts, data and design tools. This paper examines the basis of current problems in the application of these tools to the design of safe and comfortable seats. Examples of the types of new data needed are given and the discussion proposes new paths to solve current problems.