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New models are being developed to represent the geometry and movements of people in seated postures. The positions and motions of the torso skeletal structures for different amounts of lumbar curvature have been studied and represented in side view, two dimensional computer models of the average man, small woman, and large man. Some further developments for the average man include: 1. two dimensional, articulated drafting template, 2. three dimensional computer model of the skeletal system with soft tissue thicknesses added to represent the external body contours on the back of the torso, and 3. model of forces and moments between body segments based on seated posture, body segment masses, and seat surface forces. This paper describes these new biomechanical models and their potential uses in designing seats that more comfortably fit and move with people.

A need to develop methodologies to obtain objective measurements of the effects of different seat contours on people is evident. In an effort to monitor muscle activity during static seated postures, electromyography (EMG) was employed. In an experimental setting, fatigue was induced in back extensor muscles for different seated postures. The resultant EMG signals were then sampled bilaterally for three different vertebral levels and the effects of the different seating systems on posture were evaluated. In preliminary tests involving 4 subjects of similar size and build, utilizing three differently contoured seats, findings support the use of EMG to quantify muscular fatigue as a viable means of objectively measuring the effects of different seat contours.

Deformations of soft tissues and seat cushion foam are significant factors in determining the interface contours between the seat and the back of the thigh. This paper describes the measurement of forces, deformations, and contours of people's thighs and seat cushion materials. The goal of this work is to represent the human interactions with seats. A two-dimensional, plane strain finite element method was used to develop a contact model between the cross section of the human mid-thigh and flat surfaces, which can be a flat, rigid surface or a flat, foam cushion of various thicknesses and densities. Results of human and seat interactions for various subjects were measured, modeled, and compared. The present work showed a good agreement between experiments and models for various subjects and foam densities. The important results showed that the stiffness of the foam does not depend on the foam thickness.

Driver and passenger comfort, as related to automotive seats, is a growing issue in the automotive industry. As this trend continues, automotive seat designers and developers are generating a greater need for more anthropometrically accurate tools to aid them in their work. One tool being developed is the JOHN software program that utilizes three-dimensional solid objects to represent humans in seated postures. Contours have been developed to represent the outside skin surfaces of three different body types in a variety of postures in the sagittal plane. These body types include: the small female, the average male, and the large male.

To assist automotive seat development and evaluation, a technique for predicting the posture of seated occupants has been developed. The method involved modeling the torso geometry and articulation of a mid-size male, based on information presented in SAE paper number 930110 [1]. This mid-size male model, known as 2-D JOHN, was developed in a commercial kinetic modeling software and used in a comparative seat evaluation study between a current production automotive seat and a prototype articulating seat. The 2-D JOHN model was supported a greater range of postures, defined as Total Lumbar Curvature (TLC) and Torso Recline Angle (TRA), in the prototype seat than the automotive seat.

The geometric, inertial, and joint characteristics of two Part 572 crash test dummies were measured to provide input to the MVMA 2-D occupant model. Segments of the dummies were defined which correspond to the links of the model and coordinate axes were defined for each segment. The center of gravity of each segment was located and its coordinates were measured along with the locations of joint centers, instrument mounts, and other significant geometric features. The mass moment of inertia for each segment about a lateral axis through its center of gravity was measured. The geometric and inertial measurements are presented on summary sheets for each segment with the hardware definition, coordinate system, and special notes for that particular segment. These summary sheets present the data in a format that is readily usable for defining computer model input.

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.

The design and evaluation of seating has been limited by the available technologies to measure the mechanical interaction between a seat and its user. For many years, representation of the seated torso has been by two standardized measurement manikins from the American National Standards Institute (ANSI)1 for office seating and the Society of Automotive Engineers (SAE)2 for vehicle seating. Most office and automotive seat backs recline about a single point; this motion can be measured with the available manikins. However, both the ANSI and the SAE manikins do not represent the natural anatomical movements of the upper torso (thorax) relative to the lower torso (pelvis) that occur with spinal articulation. Current tools that are useful for seat design and evaluation include the biomechanical models3,4 and experimental test methods5, 6,7 that have been developed at Michigan State University's (MSU) Biomechanical Design Research Laboratory (BDRL).

The ASPECT program was conducted to develop new Automotive Seat and Package Evaluation and Comparison Tools. This paper presents a summary of the objectives, methods, and results of the program. The primary goal of ASPECT was to create a new generation of the SAE J826 H-point machine. The new ASPECT manikin has an articulated torso linkage, revised seat contact contours, a new weighting scheme, and a simpler, more user-friendly installation procedure. The ASPECT manikin simultaneously measures the H-point location, seat cushion angle, seatback angle, and lumbar support prominence of a seat, and can be used to make measures of seat stiffness. In addition to the physical manikin, the ASPECT program developed new tools for computer-aided design (CAD) of vehicle interiors. The postures and positions of hundreds of vehicle occupants with a wide range of body size were measured in many different vehicle conditions.

The ASPECT (Automotive Seat and Package Evaluation and Comparison Tools) Program has developed the next generation SAE 3-D H-Point testing manikin. During the development of the ASPECT manikin, new data were collected on how people loaded different regions of a seat and how these loads varied with different postures. These data, along with a computer model of the ASPECT manikin, were used to assist in the development of a human-like weight distribution for the new seating device, the ASPECT manikin.

Auto and boat racers suffer fatigue and injury from loading of their necks. While racing, a driver's neck often becomes fatigued because it must support the weight of the head and helmet. In crashes, extreme motions of a driver's unrestrained head relative to the restrained torso cause excessive loads in the driver's neck. These neck loads between the head and torso can cause severe or fatal injuries such as spinal dislocations and basilar skull fractures. A new type of head and neck support has been developed that restrains the driver's head relative to their torso to reduce undesirable head motions and neck loads that cause fatigue and injury. This paper describes recent work, using computer crash simulations, crash dummy tests, and driver experiences, to better understand head and neck injury in racing and to evaluate the performance of a new head and neck support.