Lawrence W. Schneider

Methods for Measuring and Representing Automobile Occupant Posture

Many vehicle design and safety assessment applications use physical and virtual representations of vehicle occupants within the vehicle interior. Proper use of these human models requires accurate data concerning vehicle occupant posture and position. This paper presents techniques for characterizing vehicle occupant posture by measuring accessible body landmarks. The landmark locations are used to estimate joint locations that define a kinematic linkage representation of the human body. The resulting posture analysis techniques provide a unified method of measuring and reporting vehicle occupant postures that is suitable for use with both physical and virtual human models.

An improved seating accommodation model with application to different user populations

In this paper a new approach to driver seat position modeling is presented. The equations of the Seating Accommodation Model (SAM) separately predict parameters of the distributions of male and female fore/aft seat position in a given vehicle. These distributions are used together to predict specific percentiles of the combined male and female seat position distribution. The effects of the following vehicle parameters are reflected in the prediction of mean seat position: seat height, steering-wheel-to-accelerator pedal distance, seat cushion angle, and transmission type. The mean and standard deviation of driver population stature are included in the prediction for the mean and standard deviation of the seat position distribution, respectively. SAM represents a new, more flexible approach to predicting fore/aft seat position distributions for any driver population in passenger vehicles. Model performance is good, even at percentiles in the tails of the distribution. (A) For the covering abstract of the conference see IRRD 492369.

Fetal outcome in motor-vehicle crashes: effects of crash characteristics and maternal restraint

OBJECTIVE This project was undertaken to improve understanding of factors associated with adverse fetal outcomes of pregnant occupants involved in motor-vehicle crashes. STUDY DESIGN In-depth investigations of crashes involving 57 pregnant occupants were performed. Maternal and fetal injuries, restraint information, measures of external and internal vehicle damage, and details about the crash circumstances were collected. Crash severity was calculated using vehicle crush measurements. Chi-square analysis and logistic regression models were used to determine factors with a significant association with fetal outcome. RESULTS Fetal outcome is most strongly associated with crash severity (P < .001) and maternal injury (P = .002). Proper maternal belt-restraint use (with or without airbag deployment) is associated with acceptable fetal outcome (odds ratio = 4.5, P = .033). Approximately half of fetal losses in motor-vehicle crashes could be prevented if all pregnant women properly wore seat belts. CONCLUSION Higher crash severity, more severe maternal injury, and lack of proper seat belt use are associated with a higher risk of adverse fetal outcome. These results strongly support recommendations that pregnant women use properly positioned seatbelts.

Effects of vehicle interior geometry and anthropometric variables on automobile driving posture

The effects of vehicle package, seat, and anthropometric variables on posture were studied in a laboratory vehicle mockup. Participants (68 men and women) selected their preferred driving postures in 18 combinations of seat height, fore-aft steering wheel position, and seat cushion angle. Two seats differing in stiffness and seat back contour were used in testing. Driving postures were recorded using a sonic digitizer to measure the 3D locations of body landmarks. All test variables had significant independent effects on driving posture. Drivers were found to adapt to changes in the vehicle geometry primarily by changes in limb posture, whereas torso posture remained relatively constant. Stature accounts for most of the anthropometrically related variability in driving posture, and gender differences appear to be explained by body size variation. Large intersubject differences in torso posture, which are fairly stable across different seat and package conditions, are not closely related to standard anthropometric measures. The findings can be used to predict the effects of changes in vehicle and seat design on driving postures for populations with a wide range of anthropometric characteristics.

DEVELOPMENT OF AN IMPROVED DRIVER EYE POSITION MODEL

Society of Automotive Engineers (SAE) Recommended Practice J941 describes the eyellipse, a statistical representation of driver eye locations. Eye position data collected recently at University of Michigan Transportation Research Institute (UMTRI) suggest that the SAE J941 practice could be improved. SAE J941 currently uses the SgRP (vehicle seating reference point) location, seat track travel (L23), and design seatback angle (L40) as inputs to the eyellipse model. However, UMTRI data show that the characteristics of empirical eyellipses can be predicted more accurately using seat height, steering wheel position, and seat track rise. A series of UMTRI studies collected eye location data from groups of 50 to 120 drivers with statures spanning over 97 percent of the United States population. Data were collected in thirty-three vehicles. Significant and consistent differences were observed between eye position data collected before and after driving, indicating that actual driving is an important protocol feature for accurate measurement of driver eye position. In six vehicles, eyellipses obtained with two-way and six-way seat track travel were only slightly different. On average, drivers select seatback angles that are about 1.6 degrees more upright than design seatback angles. Stepwise regression techniques were used to identify the vehicle variables that have important effects on the distribution of driver eye locations. (A) For the covering abstract of the conference see IRRD 492369.

Automobile Occupant Posture Prediction for Use with Human Models

A new method of predicting automobile occupant posture is presented. The Cascade Prediction Model approach combines multiple independent predictions of key postural degrees of freedom with inverse kinematics guided by data-based heuristics. The new model, based on posture data collected in laboratory mockups and validated using data from actual vehicles, produces accurate posture predictions for a wide range of passenger car interior geometries. Inputs to the model include vehicle package dimensions, seat characteristics, and occupant anthropometry. The Cascade Prediction Model was developed to provide accurate posture prediction for use with any human CAD model, and is applicable to many vehicle design and safety assessment applications.

ATD POSITIONING BASED ON DRIVER POSTURE AND POSITION

Current automotive dynamic testing (ATD) positioning practices depend on seat track position, seat track travel range, and design seatback angle to determine appropriate occupant position and orientation for impact testing. In a series of studies conducted at the University of Michigans Transportation Research Institute, driver posture and position data were collected in 44 vehicles. Seat track reference points presently used to position ATDs were found to be poor predictors of the average seat positions selected by small female, midsize male, and large male drivers. Driver-selected seatback angle was not closely related to design seatback angle, the measure currently used to orient the ATD torso. A new ATD Positioning Model was developed that more accurately represents the seated posture and position of drivers who match the ATD statutes. Seat position is specified for each adult ATD size to match the mean predicted seat position of drivers matching the ATD reference stature. ATD torso orientation is set to the average driver torso orientation. The new positioning model places the ATDs in postures/positions that are more representative of drivers of similar size.

Quantifying dynamic mechanical properties of human placenta tissue using optimization techniques with specimen-specific finite-element models

Motor-vehicle crashes are the leading cause of fetal deaths resulting from maternal trauma in the United States, and placental abruption is the most common cause of these deaths. To minimize this injury, new assessment tools, such as crash-test dummies and computational models of pregnant women, are needed to evaluate vehicle restraint systems with respect to reducing the risk of placental abruption. Developing these models requires accurate material properties for tissues in the pregnant abdomen under dynamic loading conditions that can occur in crashes. A method has been developed for determining dynamic material properties of human soft tissues that combines results from uniaxial tensile tests, specimen-specific finite-element models based on laser scans that accurately capture non-uniform tissue-specimen geometry, and optimization techniques. The current study applies this method to characterizing material properties of placental tissue. For 21 placenta specimens tested at a strain rate of 12/s, the mean failure strain is 0.472+/-0.097 and the mean failure stress is 34.80+/-12.62 kPa. A first-order Ogden material model with ground-state shear modulus (mu) of 23.97+/-5.52 kPa and exponent (alpha(1)) of 3.66+/-1.90 best fits the test results. The new method provides a nearly 40% error reduction (p<0.001) compared to traditional curve-fitting methods by considering detailed specimen geometry, loading conditions, and dynamic effects from high-speed loading. The proposed method can be applied to determine mechanical properties of other soft biological tissues.

Biomechanical Investigation of Airbag-Induced Upper-Extremity Injuries

The factors that influence airbag-induced upper-extremity injuries sustained by drivers were investigated. Seven cadavers were used in 19 direct-forearm interaction static deployments. Forearm fracture was analyzed with respect to time of airbag deployment, distal forearm speed, airbag-module-to-forearm spacing, bone mineral content, and upper-extremity mass. Results suggested that airbag-module-to-forearm spacing has a substantial influence on airbag-induced upper-extremity injuries sustained by drivers. The increased initial spacing which reduces the speeds achieved by the distal forearm results to potentially mitigating injuries.

SEATED POSTURE OF VEHICLE OCCUPANTS

This paper describes the methodology and results from a project involving development of anthropometrically based design specifications for a family of advanced adult anthropomorphic dummies. Selection of family members and anthropometric criteria for subject sample selection were based on expected applications of the devices and on an analysis of U.S. population survey data. This resulted in collection of data for dummy sizes including a small female, a mid-sized male, and a large male. The three phases of data collection included: 1. In-vehicle measurements to determine seat track position and seating posture preferred by the subjects for use in development of laboratory seat bucks; 2. Measurement of subject/seat interface contours for fabrication of an average hard seat surface for use in the buck; and 3. Measurement of standard anthropometry, seated anthropometry (in the buck), and three-dimensional surface landmark coordinates using standard and photogrammetric techniques. For the covering abstract of the conference see HS-036 716. (Author/TRRL)