Miriam A. Manary

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.

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.

Evaluation of the static belt fit provided by belt-positioning booster seats

Belt-positioning booster seats are recommended for children who use vehicle seat belts as primary restraints but who are too small to obtain good belt fit. Previous research has shown that belt-positioning boosters reduce injury risk, but the belt fit produced by the wide range of boosters in the US market has not previously been assessed. The present study describes the development of a method for quantifying static belt fit with a Hybrid-III 6-year-old test dummy. The measurement method was applied in a laboratory seat mockup to 31 boosters (10 in both backless and highback modes) across a range of belt geometries obtained from in-vehicle measurements. Belt fit varied widely across boosters. Backless boosters generally produced better lap belt fit than highback boosters, largely because adding the back component moved the dummy forward with respect to the lap belt routing guides. However, highback boosters produced more consistent shoulder belt fit because of the presence of belt routing guides near the shoulder. Some boosters performed well on both lap belt and shoulder belt fit. Lap belt fit in dedicated boosters was generally better than in combination restraints that also can be used with an integrated harness. Results demonstrate that certain booster design features produce better belt fit across a wide range of belt geometries. Lap belt guides that hold the belt down, rather than up, and shoulder belt guides integrated into the booster backrest provided better belt fit.

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.

Anthropometric specification of child crash dummy pelves through statistical analysis of skeletal geometry

The pelves of the child dummies of the widely used Hybrid-III family are based on minimal data from children. Because an accurate pelvis design is critical for realistic assessments of belt restraint interactions, an analysis of medical imaging data was conducted to develop guidance for improved pelvis design. Three-dimensional polygonal meshes of the bony pelvis were generated from computed tomography (CT) data from 81 children from ages 5 to 11. After aligning to a uniform anatomical coordinate system, the meshes were resampled to create a quadrilateral mesh with 12,960 vertices for each pelvis. A principal components analysis was conducted with the mesh vertex coordinates and the locations of 31 landmarks. Over 99% of the variance in size and shape was accounted for by the first 40 components. A three-dimensional model representing the target for a new dummy pelvis was developed using bispinous breadth as the predictor variable. To obtain the appropriate geometry for the six-year-old (6YO) and 10YO Hybrid-III dummies, a regression analysis was conducted using a large sample of child anthropometry data from a previous study to obtain a target dimension for bispinous breadth, using the design stature for each dummy as input. A separate regression analysis was conducted to predict principal component scores from bispinous breadth. Reconstructing a pelvis model from the principal components scores predicted for the target bispinous breadth values yielded a three-dimensional design target for the each dummy. The new pelvis target is similar in overall size to the current pelvis components, but the location of the anterior-superior iliac spine is markedly lower, which has important implications for belt interaction.

A New Database of Child Anthropometry and Seated Posture for Automotive Safety Applications

This paper presents a laboratory study of body dimensions, seated posture, and seatbelt fit for children weighing from 40 to 100 lb (18 to 45 kg). Sixty-two boys and girls were measured in three vehicle seats with and without each of three belt-positioning boosters. In addition to standard anthropometric -measurements, three-dimensional body landmark locations were recorded with a coordinate digitizer in sitter-selected and standardized postures. This new database quantifies the vehicle-seated postures of children and provides quantitative evidence of the effects of belt-positioning boosters on belt fit. The data will provide guidance for child restraint design, crash dummy development, and crash dummy positioning procedures.

Comparison of methods for predicting automobile driver posture

Recent research in the ASPECT (Automotive Seat and Package Evaluation and Comparison Tools) program has led to the development of a new method for automobile driver posture prediction, known as the Cascade Model. The Cascade Model uses a sequential series of regression functions and inverse kinematics to predict automobile occupant posture. This paper presents an alternative method for driver posture prediction using data-guided kinematic optimization. The within-subject conditional distributions of joint angles are used to infer the internal cost functions that guide tradeoffs between joints in adapting to different vehicle configurations. The predictions from the two models are compared to invehicle driving postures.