Assessing the effects of the design population on seat dimensions

Dimensional recommendations for automotive seat design are often based on populations different from the intended user population. Military data are commonly used to provide guidance for seats used by civilians, for example, because detailed military data are more readily obtained. Even when data from an anthropometric study of civilians are available, target dimensions for automotive seats are often selected under the assumption that the design population is the same as the population measured in the anthropometric study. This report examines the consequences of these assumptions by comparing target values for key anthropometric dimensions for the general U.S. population with estimates for specific populations that may be of interest for seat design. The focus of the investigation is on the importance of gender mix, ethnicity, and market country in selecting target dimensions for seat design. Data from CAESAR, NHANES, the U.S. Census, and ISO 7250-2 were used. The report analysis demonstrates that population definition is important in computing distributions of anthropometric dimensions to be used to guide seat design. In the U.S., gender mix has the potential to be more important than ethnicity distributions across regions.The University of Michigan Transportation Research Institutehttp://deepblue.lib.umich.edu/bitstream/2027.42/89869/1/102815.pd

Analysis of Body Movement Patterns and Subjective Discomfort Ratings in Long-Duration Sitting

Technical Report FinalA laboratory study was conducted to evaluate the hypothesis that discomfort in long-duration sitting is associated with more frequent posture changes. Two nominally identical production automobile driver seats were obtained for testing and one was modified in ways that were expected to increase discomfort. Twenty-four men and women with a wide range of age and body size sat in each of the seats for one hour on two different days while watching videos and completing a discomfort questionnaire every five minutes. Posture was monitored using a video, pressure sensors in the seats, and a Microsoft Kinect depth sensor. A variety of posture change metrics were computed from each data source. The modified seat produced significantly higher discomfort ratings. However, no difference in movement frequency was observed between the seats, and no relationship between maximum discomfort and movement frequency was observed.Magna Seatinghttps://deepblue.lib.umich.edu/bitstream/2027.42/153990/1/UMTRI-2020-1.pd

Analysis of Driver Knee Contours for Vehicle Interior Design

An analysis of knee contours was conducted to provide design guidelines to prevent inadvertent actuation of switches located in the lower part of the driver compartment. A programmatic analysis of 3D laser scan data from 181 men and women was conducted. The results quantified the maximum level of penetration into a circular opening that could be expected. The maximum penetration was generally observed in the lateral patella area. A statistical model of the data was used to generate plots of the distributions of penetrations that would be observed for circular holes of various size. A verification study was conducted using manual measurements on a convenience sample of 42 people. The results of the manual measurements were generally consistent with the programmatic measurements from 3D scans, with discrepancies typically less than 3 mm for holes up to 50 mm.General Motorshttps://deepblue.lib.umich.edu/bitstream/2027.42/145591/1/UMTRI-2018-1 final.pdfDescription of UMTRI-2018-1 final.pdf : Technical Repor

Occupant Dynamics During Crash Avoidance Maneuvers

Technical Report FinalA test-track study was conducted to assess the effects of initial posture and position on the head motions of front-seat passengers in abrupt vehicle maneuvers. A pilot study with 12 participants was conducted in a sedan, a minivan, and a pickup truck to assess whether head excursions differed across vehicles. Each participant experienced two abrupt braking events, two lane changes, and turn-and-brake maneuvers. Peak vehicle accelerations were about 1 g and 0.7 g in the braking and lane-change events, respectively. Head position was tracked using a custom, semi-automated system that uses a single depth camera. Head center of gravity (CG) location was estimated from landmarks identified on a three-dimensional scan of the participant’s head and face. Forward head excursion was slightly smaller in the passenger car than in the other two vehicles. No explanation for this finding was apparent; the vehicle kinematics were similar. A larger study was then conducted using a passenger sedan and an SUV. A total of 90 men and women with a wide range of age and body size were assigned to test-condition blocks that addressed a variety of initial conditions. The factors investigated were seat position, foot placement, seat back recline angle, retractor locking, vehicle differences, and the effects of leaning inboard on the console armrest or leaning forward while reaching. Each participant experienced two braking events, a right-going lane change, a left-going lane change, and a turn-and-brake maneuver. The two vehicles performed similarly, and the acceleration profiles were similar to both the pilot study and a 2018 study at the same facility. Greater forward head excursion relative to the seat was observed when the seat was further rearward or reclined, or the feet were placed flat rather than resting on the heels. No difference in forward excursion was noted across vehicles. Forward leaning reduced forward head excursion during braking events, but the head position was more forward than when starting from a standard posture. Younger participants exhibited slightly larger forward excursions, but overall anthropometric effects were small. Forward lean produced much larger lateral excursions than the standard posture. Recline reduced lateral excursions, as did resting the feet on the heels rather than flat on the soles. Greater outboard excursion was observed in the SUV during the left lane change, possibly because greater space was available than in the sedan. Higher BMI and younger age were associated with slightly larger lateral excursions in some conditions, but anthropometric effects were small compared with the effects of test conditions. A functional regression analysis of head CG trajectories on the primary axes of motion was conducted. The results provide insight into the effects of test and occupant variables on head motion. Parametric corridors were developed that can be used to tune and validate computational models of occupant responses in pre-crash maneuvers. Overall, the results suggest that a wide range of occupant head locations can be produced by abrupt vehicle maneuvers. More research is needed to assess the robustness of occupant protection systems to this wide range of postures.National Highway Traffic Safety Administrationhttp://deepblue.lib.umich.edu/bitstream/2027.42/168421/1/UMTRI-2020-10 final.pdfDescription of UMTRI-2020-10 final.pdf : Technical Report Fina

Whole-body center of mass location in seated posture

The location of the body center of mass (CM) is useful for a wide range of biomechanics analyses relevant to the design of seats, chairs, restraint systems, and other products and environments intended for human use. The body CM is usually estimated by summing the contributions of individual body segments, often using on cadaver-based estimates calculated from regression equations, using standard anthropometric variables as inputs. However, torso CM location may not be well estimated by these methods for seated postures, in which the torso is in a markedly different posture than the supine in which cadavers are segmented. For the current analysis, whole-body laser scan data were analyzed to estimate the location of the center of mass in relaxed seated postures. Scan data from 447 women and 315 men were analyzed by computing the center of volume of horizontal slices through the body from the knees through the top of the head, excluding the upper extremities. Constant density was assumed. Estimates of the mass of the legs and upper extremities were applied at the knees and elbows, respectively. The fore-aft CM location was significantly related to body weight. In the measured posture, the CM is about 220 mm forward of the back of the buttocks for adult men of median body mass (about 77 kg). The average fore-aft CM location for a person with a body mass of 140 kg (308 lb) is about 273 mm forward of the back of the buttocks, a difference of 63 mm.http://deepblue.lib.umich.edu/bitstream/2027.42/110772/1/103146.pd

Evaluation of the seat index point tool for military seats

This study evaluated the ISO 5353 Seat Index Point Tool (SIPT) as an alternative to the SAE J826 H-point manikin for measuring military seats. A tool was fabricated based on the ISO specification and a custom backangle measurement probe was designed and fitted to the SIPT. Comparisons between the two tools in a wide range of seating conditions showed that the mean SIP location was 5 mm aft of the H-point, with a standard deviation of 7.8 mm. Vertical location was not significantly different between the two tools (mean -0.7 mm, sd 4.0 mm). A high correlation (r=0.9) was observed between the back angle measurements from the two tools. The SIPT was slightly more repeatable across installations and installers than the J826 manikin, with most of the discrepancy arising from situations with flat seat cushion angles and either unusually upright or reclined back angles that caused the J826 manikin to be unstable. The investigators who performed the measurements indicated that the SIPT was easier to use. The data show that the SIPT is a reasonable substitute for the SAE J826 manikin when ease-of-use considerations favor the SIPT, such as restricted space around the seat, low seat heights, or low cushion angles. Human posture measurements in seats with large discrepancies between the tools will be needed to determine which provides a better prediction of sitter position.U.S. Army TARDEChttp://deepblue.lib.umich.edu/bitstream/2027.42/111823/1/103190.pd

Elderly occupants: posture, body shape, and belt fit

A laboratory study was conducted to quantify the posture, body shape, and safety belt fit of 200 adults with a wide range of age, stature, and body weight. Body and belt landmark data were gathered as participants sat in a driver mockup that was adjusted to represent nine vehicle packages spanning a large range of the vehicle fleet and in a mockup of a rear passenger seat. Whole-body surface shape data were gathered in 22 postures using a laser scanner. The data analysis showed significant effects of occupant attributes on posture and belt fit. Vehicle and seat variables had important effects on posture and position but did not have strong effects on belt fit relative to occupant attributes, particularly body mass index. Age had significant effects on both posture and belt fit, although the effect of age was smaller than the effect of body mass index across the ranges in the participant population.National Highway Traffic Safety Administrationhttp://deepblue.lib.umich.edu/bitstream/2027.42/134392/1/103250.pdfDescription of 103250.pdf : Final repor

The seated soldier study: posture and body shape in vehicle seats

Dates covered (From - To) September 2011- October 2013Final ReportDesigning vehicles for the safety and comfort of occupants requires detailed information on posture, position, and body shape. This report presents the methods and results of a study of soldiers as drivers and passengers in vehicle seats. A total of 257 male and 53 female soldiers were measured at three Army posts while minimally clad, wearing the Advanced Combat Uniform (ACU), with the addition of personal protective equipment (PPE), composed of the Improved Outer Tactical Vest (IOTV) and Advanced Combat Helmet (ACH), and with encumbrance (ENC) simulating the gear of either a rifleman or SAW-gunner. Standard anthropometric data, such as stature and body weight, were recorded. Participants were measured as either drivers or crew. Five driver workstation configurations (packages) were produced in a vehicle mockup by varying the steering wheel position relative to the pedals. The participants adjusted the seat to obtain a comfortable driving posture. The three-dimensional locations of body landmarks were measured using a FARO Arm coordinate digitizer. In the crew conditions, the experimenters varied the seat height and back angle and conditions included a simulated protective footrest. A whole-body laser scanner was used to record body shape at each garb level. A statistical analysis of the body landmark data was conducted to obtain models to predict soldier posture as a function of vehicle factors, such as seat height, and soldier attributes, such as stature, and garb level (ACU, PPE, or ENC). Driver posture was strongly affected by steering wheel position and crew posture by seat back angle. Adding PPE and ENC resulted in more-upright postures, but the effects on spine posture were small. Statistical models of both seated and standing body shape were developed from the scan data, including the effects of PPE and ENC on space claim. The effects of ENC on space claim were largely independent of body size. The results of this study have broad applicability for the design and assessment of military vehicles. Approved for public release.US Army Tank Automotive Research, Development, and Engineering Centerhttp://deepblue.lib.umich.edu/bitstream/2027.42/109725/1/103143.pdfDescription of 103143.pdf : Final Repor

Evaluation of Hybrid-III 6YO ATD chest jacket shape and position

In previous work, belt fit on the Hybrid-III six-year-old (6YO) anthropomorphic test device (ATD) was found to depend on the positioning of the chest jacket of the ATD. Moreover, differences were noted between jackets manufactured by Denton-ATD and First Technology Safety Systems (FTSS). The objective of this study was to quantify differences between the manufacturers’ jackets by detailed measurements of exemplar jackets and to assess the effects of jacket installation procedure on jacket position. A custom fixture was designed to hold rigidly the thorax, pelvis, and head of a 6YO ATD while allowing the chest jacket to be installed and removed. Testing was conducted with two jackets from FTSS and one from Denton. In pilot testing, jacket position was affected by the installation procedure and by the initial position of the shoulder components. Detailed measurements were made using a portable surface measurement device (laser scanner) with each jacket in six conditions defined by initial shoulder position and the manner in which the jacket was installed. Quantitative comparisons in jacket position and shape were conducted in software using the laserscan data. Notable differences in jacket shape were observed between the FTSS and Denton jackets, with the FTSS jacket having a wider, flatter profile in the lateral shoulder area and the Denton jacket extending more forward in the upper chest area. However, the effects of jacket positioning were much larger than differences between manufacturers in jacket shape. Pulling the jacket down firmly resulted in jacket shoulder positions relative to the spine differing by more than 25 mm from those obtained by pulling the jacket down lightly, with results dependent on the initial positions of the shoulder components. The results of this study indicate that careful attention to jacket positioning is needed to obtain a consistent relationship between the chest and shoulder surfaces and the ATD skeleton. Pulling the jacket down firmly after initially placing the shoulder components in a downward/rearward position is suggested. Monitoring and adjusting the location of reference points on the jacket relative to specified hard points on the ATD skeletonprovides a means for ensuring that the jacket is consistently placed for static or dynamic testing.National Highway Traffic Safety Administrationhttp://deepblue.lib.umich.edu/bitstream/2027.42/89865/1/102811.pd

Development of a methodology for simulating seat back interaction using realistic body contours

Seat comfort is driven in part by the fit between the sitter and seat. Traditional anthropometric data provide little information about the size and shape of the torso that can be used for backrest design. This report introduces a methodology for using three-dimensional computer models of the human torso based on a statistical analysis of body shapes for conducting automated fit assessments. Surface scan data from 296 men and 417 women in a seated posture were analyzed to create a body shape model that can be adjusted to a range of postures spanning those typical of vehicle occupants. A parameterized finite-element model of an auto seat surface was created, along with custom software that generates body models and postures them in the seat. A simple simulation technique was developed to rapidly assess the fit of the torso relative to the seat back. Further refinement of the method will allow prediction of seat surface pressure distribution, which may be usefully related to subjective assessment of seat fit.The University of Michigan Transportation Research Institutehttp://deepblue.lib.umich.edu/bitstream/2027.42/89868/1/102814.pd