. firs; ,u 3: .11: .145. ... am.” a kl... .. a “any“. v. ‘? - L . flu): I r, h ‘ . ... Q: My: xi...” ”NM“. . awn 4m... «u, ‘ an“ . . 3:5,, ,2 . $352. . ...§§%§$fi .. . ‘ n.1,? .. a? :35 LIBRARY ‘ L004 Michigan State University This is to certify that the dissertation entitled MEASUREMENT AND ANALYSIS OF HUMAN POSTERIOR BACK AND THIGH CONTOURS FOR AUTOMOTIVE SEAT DESIGN presented by Zhenyu Liu has been accepted towards fulfillment of the requirements for the Doctoral degree in EngLneering Mechanics Major Professor’s Signhture IX riI 1005 Date MSU is an Aflinnative Action/Equal Opportunity Institution PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. MAY BE RECALLED with earlier due date if requested. DATE DUE DATE DUE DATE DUE I ._.. 11% a “gag 2/05 c:EIFlC/Date0ue.indd-p. I 5 MEASUREMENT AND ANALYSIS OF HUMAN POSTERIOR BACK AND THIGH CONTOURS FOR AUTOMOTIVE SEAT DESIGN By Zhenyu Liu A DISSERTATION Submitted to Michigan State University In partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Mechanical Engineering 2005 ABSTRACT MEASUREMENT AND ANALYSIS OF HUMAN POSTERIOR BACK AND THIGH CONTOURS FOR AUTOMOTIVE SEAT DESIGN By Zhenyu Liu To better understand and represent the seated human posterior back, buttocks, and thigh contours, three groups of human subjects (5th percentile small females, 50th percentile mid-sized males, and 95th percentile large males) (Entire measured in a specially designed contour chair within typical automotive interior environment. The postures were acquired by a human motion measurement system. I The data were analyzed, and then representative seated mid-sized male posterior back, buttocks, and thigh contours were developed for both physical hardware and computer program software for automotive seating design and validation. To explore the relations among contours of people with different anthropometric dimensions and the possibility to relate the contours of different anthropometric groups of people, a method was developed to scale the mid- sized male contours to large male or small female subjects’ contours. Potentially it could be used to generate the contours for people in different groups other than small female and large male. For the first time, the scaling methodology of scaling contours of mid-sized male to small female or large male was verified by experimental data. The coefficient of correlation analysis produced very high agreements between the scaled and measured data of the contours. Both the hardware and software from this research are being utilized in the automotive seating industries. The data collected in this research are having significant influences on the seating design and validation. Copyright by Zhenyu Liu 2005 Dedication I would like to dedicate this dissertation to my parents and my sisters, my parents-in-law, for their guidance and encouragement in everything and every way, even in my pursuing beautiful dreams. I would like to dedicate this dissertation to my family, my wife, Lan, our wonderful children Alice Yiyang, Christine Yihuan, and Daniel Yikang, for their inspiration, support, and sacrifices. ACKNOWLEDGEMENTS The author would like to express his sincerest gratitude to the following people for their assistance, and encouragement in the course of preparing this dissertation. To my advisor and mentor, Dr. Robert Hubbard, for your guiding and assisting me in every way possible. Your advice and encouragement will be with me well beyond the scope of this dissertation. Thank you. To my graduate committee: Dr. Gary Cloud, Dr. Hongyu Tsai, and Dr. Joseph Vorro, thank you for reviewing my work. Special thanks to Cliff Beckett, for helping me with every detail in the contour chair building, and keeping experimental equipments in excellent condition. To Chris and Melissa Gedraitis, Bob Boughner, Richard Setyabudhy, and Akram Ali, for your effort and time put into this work. To Automotive Seat and Package Evaluation and Comparison Tools program (ASPECT) and Human Solution, Inc., for their generous funding of my research. vi TABLE OF CONTENTS LIST OF FIGURES ............................................................................................... x LIST OF TABLES ................................................................................................ xv CHAPTERI INTRODUCTION ............................................................................. 1 1.1 Background and Literature Review ...................................................... 1 1.2 Statement of The Problem ................................................................. 13 1.3 Objectives .......................................................................................... 13 CHAPTER 2 ANATOMICAL BASICS AND TARGETED BONY LANDMARKS..15 2.1 Introduction ........................................................................................ 15 2.2 Posture Descriptions .......................................................................... 15 2.3 Positional Terminologies .................................................................... 19 2.4 Upper Limb ......................................................................................... 19 2.5 Spine .................................................................................................. 20 2.6 Thorax ................................................................................................ 23 2.7 Pelvis .................................................................................................. 24 2.8 The Lower Limbs ................................................................................ 25 CHAPTER 3 MEASUREMENT OF SEATED HUMAN CONTOURS AND POSTURES ................................................................................... 27 3.1 Introduction ........................................................................................ 27 3.2 Experimental Device and Setup ......................................................... 27 3.2.1 Contour Test Chair ................................................................. 27 3.2.1.1 Seat Pan ..................................................................... 29 3.2.1.2 Seat Back .................................................................... 31 3.2.1.4 Measurement Contour Chair Accuracy ....................... 32 3.2.1.5 Seat Foam Stiffness Selection .................................... 32 3.2.2 Test Lab Space ...................................................................... 35 3.2.3 Measurement Targets and Probe ........................................... 35 vii 3.2.5 Reference Chair ...................................................................... 38 3.2.6 Contour Data Acquisition ........................................................ 40 3.2.7 Posture Data Collection .......................................................... 41 3.3 Testing Protocol ................................................................................. 43 3.4 Subject Selection Criteria ................................................................... 45 3.5 Subject Anthropometric Data Acquisition ........................................... 46 CHAPTER 4 DATA ANALYSIS APPROACHES AND RESULTS ...................... 49 4.1 Introduction ........................................................................................ 49 4.2 Initial Raw Data Treatment ................................................................. 49 4.2.1 Data Transformation Among Coordinate Systems ................. 50 4.2.1.1 Translation ................................................... . ............... 53 4.2.1.2 Rotation ....................................................................... 54 4.2.2 Generating Contour Surface from Measurement Data Points 55 4.3 Seated Posture Calculations ........................................ , ...................... 56 4.3.1 Lower Neck Joint .................................................................... 57 4.3.2 Shoulder Joints ....................................................................... 58 4.3.3 Upper Lumbar Joint ................................................................ 59 4.3.4 Lower Lumbar and Hip Joints ................................................. 60 4.3.5 Knee Joints ............................................................................. 62 4.3.6 Ankle Joints ............................................................................ 63 4.3.7 Wrist Joints ............................................................................. 63 4.3.8 Elbow Joints ........................................................................... 64 4.4 Deformed Contours Data Analysis ..................................................... 65 4.4.1 Methods .................................................................................. 65 4.4.1.1 Analyzing the Thigh and Buttocks Data Surface ......... 66 4.4.1.2 Analyzing the Back Data Surfaces .............................. 68 4.4.2 Comparing Measured Data and J826 H-point Machine. ......... 69 4.4.2.1 The Thigh and Buttocks Data ...................................... 69 4.4.2.2 The Back Contour Data ............................................... 73 4.5 Defining Mid-male Contour ................................................................. 81 4.5.1 Defining The ASPECT Mid-male Contours ............................. 81 4.5.1.1 Thigh and Buttocks Contours ...................................... 82 4.5.1.2 Back Contour .............................................................. 83 4.5.2 Defining The RAMSIS Mid-male Contours ............................. 93 CHAPTER 5 CONTOUR SCALING FOR LARGE MALE AND SMALL FEMALE ...................................................................................................... 95 5.1 Introduction ........................................................................................ 95 5.2 Development of Scaling Factors ........................................................ 96 5.2.1 Thoracic .................................................................................. 97 5.2.2 Lumbar ................................................................................... 97 5.2.3 Pelvis ...................................................................................... 98 5.2.4 Thigh ....................................................................................... 99 5.3 Scaling Procedures and Results ........................................................ 99 5.3.1 Small Female ........................................................................ 100 5.3.2 Large Male ............................................................................ 113 5.4 Correlation Comparison Between Measured and Scaled Contours .126 5.4.1 Methods ................................................................................ 126 5.4.2 Correlation of Large Male and Small Female Contours ........ 127 5.4.2.1 Differences ................................................................ 127 5.4.2.2 Coefficients of Correlation ......................................... 141 5.4.2.3 Corridors ................................................................... 145 5.5 Discussion of Scaling Results .......................................................... 154 5.5.1 Thorax .......................... 154 5.5.2 Lumbar ......................................................................... 155 5.5.3 Pelvis ........................................................................... 155 5.5.4 Thigh ............................................................................ 156 CHAPTER 6 CONCLUSIONS ........................................................................... 158 APPENDICES ................................................................................................... 162 APPENDIX A Scaling Factors Used for Scaling Procedures ........................................ 163 APPENDIX B Scaled and Measured Small Females Results ....................................... 166 APPENDIX C Scaled and Measured Large Males Results ........................................... 199 LIST OF REFERENCES ................................................................................... 223 ix LIST OF FIGURES Images in this dissertation are presented in color. Figure 1 J826 Two-Dimensional H-point Template and Three-Dimensional H-point Machine ..................................................................................... 3 Figure 2 Two—Dimensional JOHN Model ............................................................... 6 Figure 3 Definition of TRA ................................................................................... 11 Figure 4 TLC ....................................................................................................... 12 Figure 5 A Typical Posture Model ....................................................................... 17 Figure 6 Subject in Contour Measurement Chair ................................................ 18 Figure 7 Targets at Lateral Epicondyle, Mid-wrist, and Acromion Probed .......... 20 Figure 8 The Spine Column, Adapted from Chaffin [13] ..................................... 22 Figure 9 Targeted at Manubrium and Xiphoid Process ....................................... 23 Figure 10 Pelvis: illium, ischium, pubic symphysis .............................................. 25 Figure 11 Targets on Lower Limbs ..................................................................... 26 Figure 12 Contour Chair with Targets for Local Coordinate System ................... 28 Figure 13 Light Box ............................................................................................. 30 Figure 14 Same Subject Measured on Stiff and Soft Foams .............................. 33 Figure 15 Measurement Target ........................................................................... 36 Figure 16 Measurement Probe ........................................................................... 37 Figure 17 Reference Chair .................................................................................. 39 Figure 18 Transformed Data Points .................................................................... 51 Figure 19 Lofted Data Surface ............................................................................ 52 Figure 20 From Coordinate System Ox1x2x3 Translated to Ox1’x2’x3’ .................. 53 Figure 21 Cartesian Coordinate System Ox1x2x3 Rotated to Ox1’x2'x3’ ............... 55 Figure 22 Calculation of Lower Neck Joint .......................................................... 57 Figure 23 Calculation of Shoulder Joint .............................................................. 58 Figure 24 Calculation of Upper Lumbar Joint ...................................................... 59 Figure 25 Pelvis Coordinate System ................................................................... 61 Figure 26 Calculation of Lower Limbs Joints ...................................................... 63 Figure 27 Calculation of Upper Limbs Joints ...................................................... 64 Figure 28 Sliced Thigh Curves (Relative to Left Femur Axis) and Back Curves .65 Figure 29 Contour Surface Analyzing Scheme ................................................... 67 Figure 30 Sections of J826 H-point Machine and Subjects Contours ................. 71 Figure 31 Sections of J826 H-point Machine and Subjects Contours ................. 72 Figure 32 Sections Through the ASPECT and UMTRI Contours with Postures and Contact Edges .............................................................................. 74 Figure 33 Measured Back Contours ................................................................... 75 Figure 34 Contour Sections Up the Seat Back ................................................... 76 Figure 35 Comparison between ASEPCT and UMTRI Back Contour ................. 80 Figure 36 ASPECT Symmetrical Buttocks and Thigh Contours .......................... 82 Figure 37 Torso Length Scaled In Z-Direction .................................................... 84 Figure 38 Measured Contour Curves .................................................................. 87 Figure 39 Measured Back Contours Between Upper Lumbar Joint .................... 88 Figure 40 Average Back Contour And Posture Side View .................................. 89 Figure 41 Average Back Contour Left Rear View ............................................... 90 Figure 42 ASPECT Back, Buttocks and Thigh Contour Surfaces ....................... 91 Figure 43 ASPECT Manikin ................................................................................ 92 Figure 44 Tested and Scaled Subject 1’s Contour Curves, rear view ............... 102 Figure 45 Tested and Scaled Subject 1’s Contour Curves, oblique view .......... 103 xi Figure 46 Tested and Scaled Contour Curves at Each Section of Small Female Subject 1 ............................................................................................ 104 Figure 47 Measured and Scaled Subject 1’s Contour ....................................... 115 Figure 48 Measured and Scaled Subject 1’s Contour ....................................... 116 Figure 49 Tested and Scaled Contour Curves at Each Section of Large Male Subject 1 ............................................................................................ 117 Figure 50 Typical Difference Curves between Scaled and Measured Contour. 129 Figure 51 Typical Difference Curves between Scaled and Measured Contour.133 Figure 52 Typical Bar Charts of Coefficient of Correlation ................................ 142 Figure 53 Typical Corridor Plots at Mid Thorax, Lumbar, Pelvis, and Thigh of Large Males ....................................................................................... 146 Figure 54 Typical Corridor Plots at Mid Thorax, Lumbar, Pelvis, and Thigh of Small Female ..................................................................................... 150 Figure 55 Pelvis Region Not Well Supported in Seat ........................................ 156 Figure 56 Female Subject 2 Rear View ............................................................ 167 Figure 57 Small Female Subject 2 lso View ..................................................... 167 Figure 58 Scaled and Measured Curves of Small Female Subject 2 ................ 168 Figure 59 Small Female Subject 3 Rear View .................................................. 171 Figure 60 Small Female Subject 3 Iso View ..................................................... 171 Figure 61 Scaled and Measured Curves of Small Female Subject 3 ................ 172 Figure 62 Small Female Subject 4 Rear View .................................................. 175 Figure 63 Small Female Subject 4 lso View ..................................................... 175 Figure 64 Scaled and Measured Curves of Small Female 4 ............................. 176 Figure 65 SmaIFemale Subject 5 Rear View .................................................... 179 Figure 66 Small Female Subject 5 lso View ..................................................... 179 Figure 67 Scaled and Measured Curves of Small Female Subject 5 ................ 180 Figure 68 Small Female Subject 6 Rear View .................................................. 183 xii Figure 69 Small Female Subject 6 lso View ..................................................... 183 Figure 70 Scaled and Measured Curves of Small Female Subject 6 ................ 184 Figure 71 Small Female Subject 7 Rear View ...... 187 Figure 72 Small Female Subject 7 lso \fiew ..................................................... 187 Figure 73 Scaled and Measured Curves of Small Female Subject 7 ................ 188 Figure 74 Small Female Subject 8 Rear View .................................................. 191 Figure 75 Small Female Subject 8 lso View ..................................................... 191 Figure 76 Scaled and. Measured Curves of Small Female Subject 8 ................ 192 Figure 77 Small Female Subject 9 Rear View .................................................. 195 Figure 78 Small Female Subject 9 lso View ..................................................... 195 Figure 79 Scaled and Measured Curves of Small Female Subject 9 ................ 196 Figure 80 Large Male Subject 2 Rear View ...................................................... 200 Figure 81 Large Male Subject 2 lso View ......................................................... 200 Figure 82 Scaled and Measured Curves of Large Male Subject 2 .................... 201 Figure 83 Large Male Subject 3 Rear View ...................................................... 204 Figure 84 Large Male Subject 3 lso View ......................................................... 204 Figure 85 Scaled and Measured Curves of Large Male Subject 3 .................... 205 Figure 86 Large Male Subject 4 Rear View ...................................................... 207 Figure 87 Large Male Subject 4 lso \fiew ......................................................... 207 Figure 88 Scaled and Measured Curves of Large Male Subject 4 .................... 208 Figure 89 Large Male Subject 5 Rear View ...................................................... 211 Figure 90 Large Male Subject 5 lso View ......................................................... 211 Figure 91 Scaled and Measured Curves of Large Male Subject 5 .................... 212 Figure 92 Large Male Subject 6 Rear View ...................................................... 215 Figure 93 Large Male Subject 6 lso View ......................................................... 215 xiii Figure 94 Scaled and Measured Curves of Large Male Subject 6 .................... 216 Figure 95 Large Male Subject 7 Rear View ...................................................... 219 Figure 96 Large Male Subject 7 lso View ......................................................... 219 Figure 97 Scaled and Measured Curves of Large Male Subject 7 .................... 220 xiv LIST OF TABLES Table 1 Specifications of the Contour Chair ...................................................... 29 Table 2 Subjects Feet Positions ....................................................................... 32 Table 3 Subjects Selection Criteria ................................................................... 46 Table 4 Calculation of Hip Joint Center ............................................................ 60 Table 5 Calculation of Lower Lumbar Joint ....................................................... 62 Table 6 Average Differences (mm) between Scaled and Measured Data ...... 137 Table 7 Standard Deviations (mm) of the Differences .................................... 138 Table 8 Average Differences (mm) between Scaled and Measured Data ...... 139 Table 9 Standard Deviations (mm) of the Differences .................................... 140 Table 10 Coefficients of Correlation .................................................................. 143 Table 11 Coefficients of Correlation .................................................................. 144 Table 12 Body Dimensions for Large Male Scaling .......................................... 164 Table 13 Body Dimensions for Small Female Scaling ...................................... 165 CHAPTER 1 INTRODUCTION 1.1 Background and Literature Review Seating comfort is a growing issue in both automotive and office seat design. Comfort is also a vague and ubiquitous term, and comfort has no clear and operational definition. Comfort is influenced by several factors such as vehicle package factors, seat factors, an occupant’s sitting posture, and seat contour. Seat factors include the geometric dimensions and mechanical responses of seats to test manikins and to human beings, as well as the layout of the vehicle interior components, also called vehicle package factors. The positions of the vehicle components affect a driver’s location in the vehicle seat and can also affect the driver’s postures. Therefore, a driver's posture results from compromises between comfort and restrictions from interior layouts and driving tasks. During driving, a driver may change his posture from time to time in order to make himself comfortable. When sitting, a person’s body contours either conform to the seat contours or the seat will not be in contact with and support the person's body. The contours of the seat determine the possible contours of the body and the compatibility of seat and body contours influence contact pressures and sitting posture. Hence, seating comfort is directly related to seat contour, including lumbar support location and amount of lumbar prominence, associated with permissible ranges of sitting postures. To achieve desired seat comfort, accurate and efficient tools are needed for both seat design and evaluation. To comply with the Society of Automobile Engineer (SAE) Handbook Recommended Practice J826 [1] used since the early 1960’s, seat dimensions and shapes are determined by using an SAE J826 two- dimensional H-point template, and an SAE J826 three-dimensional H-point Figure 1 J826 Two-Dimensional H-point Template and Three-Dimensional H-point Machine machine, known as the J826 manikin (Figure 1). The H-point in the SAE J826 tools is a representation of the average man’s hip joint center (HJC). The SAE handbook also specifies measurements for dimensions, adjustability, and configuration of auto seating. It is simple and practical to use physical tools in designing, confirming and evaluating the desired comfort. The survey [2] conducted by the Automotive Seat and Package Evaluation and Comparison Tools (ASPECT) program found a strong need for a physical tool like the J826 H-point machine. However, the J826 2-D H-point template and 3-D H-point machine were originally developed for locating occupants in an automobile seat within a vehicle interior. Hubbard [3] pointed out that the misuse of the J826 2-D H-point template and 3-D H-point machine resulted in a slumped posture and affected the comfort of seated occupants for more than two decades. The J826 machines simulate the mid-size male body segments by simulating the combined pelvis and thighs, a segment of combined thorax and lumbar, and the two feet and legs, which can be adjusted to the 10‘“, 50th and 95th percentile male adult’s leg and thigh lengths. The torso and butt-thigh segments can articulate about a lateral axis through the H-points. The 3-D H- point machine is usually used to determine the H-point of a seat and seat back angle following methods specified in the SAE Handbook. Normal human motion in a seat is very complicated, and includes, among other factors, lumbar curvature changes as well as, thorax and pelvis articulation around spinal joints, associated with changes in spinal curvature. The structure of the 3-D H-point machine has a slumped posture with a straight lower back does not represent a normal human postures change in vehicle seats. The 3-D H-point machine does not fit into seats that have highly contoured shapes with large amount of lumbar prominence. If the J826 manikin is placed in a contoured automobile seat with lumbar support and its lower lumbar and pelvis area is held against-the seat back, its upper torso is in a fonrvard position without contacting the seat back. If its upper torso is pushed against the seat back, its H-pOint slides cut away from the seat back. From the point view of seating design and analysis, it is very important to describe human posture and contour as precisely and correctly as possible. There were two very important studies in this area. One was conducted by Haas and Hubbard at Michigan State University. They developed a two dimensional, sagittal computer model [4], which represents the average adult male’s geometry, including the shape and relative position of the head, thorax and pelvis, and spinal motion. The head, thorax, and pelvis in the Haas model were connected by a series points representing joint centers in the cervical, thoracic, and lumbar spinal regions, as seen in Figure 2. In this model, the thorax and pelvis articulate around upper and lower lumbar joints respectively, with oneto- one opposite rotation. This computer model program is known as JOHN to recognize the support from Johnson Controls, Inc. Figure 2 Two-Dimensional JOHN Model Another important anthropometric study was performed at the University of Michigan Transportation Research Institute (UMTRI) [5] for crash dummy development by determining how a driver is positioned within an automobile. It was the best data resource at that time and was partially adopted in the JOHN program. In their study, UMTRI placed subjects in production auto seats in car interior layout environments. A combination of seat surface casting strips and photographs of external landmarks on subjects’ skin was used to determine both exterior contour and landmark locations. Subjects were placed into three subgroups: mid-sized male, small female, and large male. The limitations of UMTRI contours are as follows: 1) the production seats were used in the study and the shape of the seat affected subject’s contours, especially in the posterior thigh area, where soft tissue deformed substantially. The production seats were designed and evaluated by the 2-D H-point template and 3-D H-point machine, therefore, the shortcomings of the tools still influenced the UMTRI data; 2) the study did not consider the lumbar curvature and foot positions, which are crucial for seating design; 3) in Haas’s study he pointed that the UMTRI contour’s pelvis was positioned too high. Apparently the 46 mm soft tissue under ischial tuberosities on the bottom of the pelvis when one sits in a seat was unreasonable. Development of computer model programs has rapidly advanced and cannot be overstressed in the area of seat design and computer-aided evaluation to achieve optimal design. Also, computer modeling can reduce expensive design and validation cycles. There are several available anthropometric computer models for possible application to automotive seating design, which are briefly described below. {:RAMSIS [6] is a three-dimensional, ergonomic computer program developed by TecMath (now Human Solutions), GmbH in Kaiserslautern, Germany, to represent people seated within automotive interior layouts for analysis and design. RAMSIS includes a posture prediction algorithm based on data of subjects seated in vehicle packages. The human sizes and shapes are fit to video images of individual subjects, and they are based on anthropometric data. Thus, the RAMSIS model is positioned in a seat based on the video images of individual subjects. Because video cameras are incapable of capturing the deformed body segments that are contacting a seat surface, the contour is not realistic. Therefore RAMSIS is not being used for seat comfort design or evaluation. This present study is being performed to provide TecMath the deformed back, buttocks, and posterior thigh contou‘rE\ JOHN has been developed under the direction of Professor Hubbard at Michigan State University with the support of the Automotive Systems Group of Johnson Controls, Inc. JOHN program is based upon Haas’s human model [4], which represents the movement between the ribcage and pelvis with selected values of lumbar curvature and the torso recline angle to describe seated postures. JOHN represents the geometry of the skeleton, major muscles, and back skin surfaces of a 50th percentile male. There were several major phases in JOHN development worth mentioning here. For his model [4], Hass defined two geometric variables to determine the relative positions of body segments. Torso recline angle (T RA) was defined as the angle measured from a vertical line passing through the twelfth thoracic/first lumbar vertebrae (T 1 2/L1) and the fifth lumbar/first sacral (L5/S1) spinal joint centers. Total Lumbar Curvature (TLC) was defined as the total amount of curvature of the lumbar region in the sagittal plane. TLC is zero when the lumbar joints are aligned on a straight line. TLC is the angular position change of the thorax relative to the pelvis and is positive with lordosis (concave lumbar curvature). Both TRA and TLC are as shown in Figure 3 and Figure 4. Boughner [7] created a three-dimensional model program for the 50th percentile adult male using solid modeling techniques. The models of major skeletal structures were established by using the data from several anatomy texts and the data from the UMTRI study [5]. This model also represents the posterior thigh muscle geometry to calculate hamstring muscle length. Bush [8] modeled the shapes of the erector spinae muscles and the external skin contours of the JOHN program by using data from the cadaver studies of Koritké and Sick [9]. Bush rotated the 0° TLC contours about the lumbar spinal joint centers to achieve other contours with respect to selected values of TLC, -10°, 0°, 10°, 20°, 30°, and 40°. Frost [10] developed new contours for the JOHN models by using both the Bush and UMTRI data [5]. These contours could be articulated to any specified amount of TRA and TLC in the sagittal plane. Then, by using scaling factors for the individual dimensions of the thoracic, lumbar, and pelvic segments, Frost created back skin contours for 5th percentile adult females as well as 50‘", and 95th percentile adult males. 10 TRA Figure 3 Definition of TRA 11 7 Figure 4 TLC 12 TLC is positive when lumbar dorlosis 1.2 Statement of The Problem The shape of the seat has a strong influence on the posture and comfort of the seat user. Because the body articulates when a person sits in a seat, his body changes posture so that his body surfaces against the seat conform to the seat shape. Thus, the shape of the seat strongly influences the shape and posture of the seat user. If the seat shape is not compatible with possible or preferred shapes of the person, then there is geometric mismatch between the seat and sitter. Ellis mismatch can reduce the area of contact, increase local 0(’ pressures, and be perceived as discomfortTIJSome postures may be preferred by the seat user to function in the seated environment, such as seeing instruments or operating controls in an automobile. Also, some postures are more healthful, such as postures with some concave lumbar curvature (lordosis), which allows the upper torso to rotate rearward and the head to be over the base of the neck. This lumbar curvature reduces spinal disc pressures, and this head position reduces neck and shoulder muscle tension to maintain head position. The shape of the interface surface between the seat and the user is significant for comfort support and posture. 1.3 Objectives The general goal is to define seated contours for people in typical driving postures. The more specific objectives of this study are as follows: 13 r/ 1. l {1‘- Collect data of seat contact surface contours and postures for representative subjects of the 5"1 percentile small adult female, 50th percentile average adult male and 95th percentile large adult male. 2. Develop contours based on analyzed measurement data that could be used for the JOHN and RAMSIS programs. 3: Develop a methodology to represent seated contact surface contours for I . . /I diverse drrver populations. 3 _,__.—$ 14 CHAPTER 2 ANATOMICAL BASICS AND TARGETED BONY LANDMARKS 2.1 Introduction In a sitting position, human body weight is mainly transferred to certain areas of ischial tuberosities of the pelvis and their surrounding soft tissues, and also the feet [11, 12]. The weight distribution is related to seating comfort, and soft tissue fatigue and is usually determined by sitting posture and the supporting seat contour. To better understand sitting posture and comfort, a brief review of the anatomy of spine, pelvis, and thigh is presented. 2.2 Posture Descriptions The representation of sitting posture adopted in this research was developed in the ASPECT program [2]. ' It is based on a kinematical model of the human body, in which the human body is modeled as an open chain of straight- Iine segments connected at major joints [4]. The segment lengths, the orientation of the segments, and the location of the joints have to be determined by means of a combination of photography and calculation [2], as seen in Figure 5. To collect posture data, the choice of appropriate bony landmarks has to be made based upon both the data acquisition method and human anatomy [2]. 0 The bony landmarks of interest have to be palpable and easily located. It is crucial for targets at the selected landmark locations to be visible to multiple 15 video cameras so that their positions can be recorded and calculated to determine the joint centers of interests. A typical presentation of a targeted subject and his posture data is shown in Figure 5 and Figure 6. 16 Lower Neck Joint Wrist Joints / |\Shoulder \ Elbow J7'nt Jornts pper Lumbar Knee Joints Joint \ Front of Pelvis A b Lower Lum ar Joint / Hip Joint Centers Ankle Joints Figure 5 A Typical Posture Model 17 Steering whee Figure 6 Subject in Contour Measurement Chair 2.3 Positional Terminologies The term “superior” is used to express the direction toward the top of the head, and “inferior” toward the feet. The direction toward the front of the body is defined as “anterior", and toward the back of the body as “posterior”. There is a central mid-sagittal plane of symmetry passing through the head and trunk that separates the right from left sides. On either side of the central plane, the direction pointing to the plane is referred to as “medial”, and the direction away from the plane is referred to as “lateral”. A plane perpendicular to the long axis of the body and dividing its superior portions from inferior is named the transverse or horizontal plane. 2.4 Upper Limb In the performance of tasks and reaching controls, the positions of the shoulders and the upper limbs influence spinal postures and comfort during driving. Therefore, arm and shoulder positions must be taken into account for posture [7, 13]. The three bony landmarks targeted or probed on each side were the acromian process, lateral epicondyle, and mid-wrist (a midpoint of styloid process of radius and ulna) to locate the shoulder joint, elbow joint, and mid-wrist skin points, respectively. Figure 7 shows that the acromion process, lateral epicondyle, and mid wrist were targeted or probed. 19 ‘ ACromion Process probed O Mid—wrist Lateral Epicondyle Figure 7 Targets at Lateral Epicondyle, Mid-wrist, and Acromion Probed 2.5 Spine The spine is very important in biomechanical aspects of sitting, especially the lumbar region. The spinal column consists of five segments of cervical, thoracic, lumbar, sacral, and coccygeal vertebrae, as shown in Figure 8. There normally are thirty-three vertebrae stacked on top of one another in a spinal column for a normal person. Each vertebra is named with respect to its relative position in the spine column from top to bottom, such as C1-C7 for the seven 20 vertebrae in the cervical region, T1 -T12 in the thoracic region, and L1-L5 in the lumbar region. Among these five segments, only cervical and lumbar vertebrae have significant mobility. Because the cervical vertebrae are responsible for head movement, they are of less importance for sitting postures. In the thoracic spine, the mobility is limited because of the connection to the rib cage [13]. The sacrum is effectively part of the pelvis with 5 vertebrae fused together, and the coccyx (4 vertebrae) does not have meaningful function for seating posture. There are natural curvatures in the vertebral column: cervical lordosis, thoracic kyphosis, and lumbar lordosis resulting from the vertebrae and discs structural characteristics when standing erect, as shown in Figure 8. In this study, markers of the spinous processes of C7, T8, and sacrum were used to determine the spine posture. By palpating the most posterior aspect of the spinous process, these vertebral landmarks can be found, especially the prominent C7 vertebral process. 21 Cervical (Lodorsis) Thoracic i (Kyphosis) Lumbar (Lordosis) Sacrum Coccygeal Figure 8 The Spine Column, Adapted from Chaffin [13] 22 2.6 Thorax Thoracic vertebrae articulate with each other and with the rib cage, so their mobility is limited [13]. This is why the thorax is considered to be a rigid body in posture analysis [2]. The top end of the sternum is named the manubrium. The inferior tip of the stemum is called the Xiphoid process, Figure 9. Together with the landmarks on the vertebral column, these two stemal landmarks are used to determine the thoracic shape and position in posture analysis. Figure 9 Targeted at Manubrium and Xiphoid Process 23 2.7 Pelvis When seated, the body is mainly supported in the area of the ischial tuberosities of the pelvis and their surrounding soft tissues [13]. In this sense, the pelvis is really a base for the trunk when sitting. The sacrum transfers most of the weight from the lumbar spine through the pelvis to the ischial tuberosities and its surrounding soft tissues when a person sits. The pelvis also articulates at hip joint centers with the femurs of the thighs. The pelvis consists of two hipbones, or coxal bones. Each hipbone derives from three separate irregular bones: the illium, ischium, and pubis. The illiac crest is anteriorly prominent at the right and left anterior superior illiac spines (ASIS), which can be palpated and targeted easily. The most inferior prominence of each ischium is known as ischial tuberosity, which supports the pelvis in the sitting position. The pubic symphysis is located where the two pubic bones connect the left and right hipbones anteriorly. During the tests, the pubic symphysis was probed to determine its location. Also, the mid-point of two posterior superior illiac spine (PSIS) was targeted as shown in Figure 10. 24 Figure 10 Pelvis: illium, ischium, pubic symphysis 2.8 The Lower Limbs The spherical head of the femur inserts into the acetabulum of the pelvis to form the hip joint center. The neck of the femur then extends to the greater 25 and lesser trochanters. At the distal end of the femur, there are the medial and lateral femoral condyles of the knee. The tibia is the shinbone, which transfers the forces between the knee and the ankle. The fibula is the slender bone lateral to the tibia. At the distal end of the fibula, the lateral malleolus is easily seen and palpated. The lateral femoral condyle, lateral malleolus, and approximate ball of foot were selected as bony landmarks to determine the locations of the ankle joint, knee joint, and foot position, as shown in Figure 11. 7,. ateral . 0006938.- Figure 11 Targets on Lower Limbs 26 CHAPTER 3 MEASUREMENT OF SEATED HUMAN CONTOURS AND POSTURES 3.1 Introduction The goal of this research is to experimentally determine seat contact surface contours for selected subgroups of driver populations in certain permissible ranges of sitting postures within typical vehicle interior geometries. To simplify anthropometric issues, two measurements that account for most of the variance of body dimensions (height and weight) [14,15] were chosen to classify the subgroups of driver populations. In this section, the. details related to measurement will be discussed. 3.2 Experimental Device and Setup 3.2.1 Contour Test Chair /To acquire the seat/sitter contact surface data, a special contour test chair was designed and built, Figure 12. To represent a typical mid-sized sedan, the specifications of the contour chair were used. See Table 1. The seat pan angle and the seat back angle were measured by following the SAE J826 procedure described in [1]\ . \l / I/V 27 f Wires & their pat ii 1‘ .‘ 2: 4L. _ 3.. Light box for seat pan 1, I Figure 12 Contour Chair with Targets for Local Coordinate System 28 Table 1 Specifications of the Contour Chair Seat height 280 mm from foot support surface to H-point Seat angle 15° with respect to horizontal Seat back angle 23° with respect to vertical Steering wheel angle 20° with respect to vertical 500 mm X 500 mm X 100 mm Cushion foam size - (Width by Depth by Thickness) Seat back size 580 mm X 650 mm X 100 mm 3.2.1.1 Seat Pan In the contour chair, there was a flat seat pan with a foam block having dimensions of 500 mm by 500 mm by 100 mm. A hundred stainless steel wire cables were evenly distributed over the 500 mm x 500 mm area in a matrix of 10x10 with the wires 45 mm apart. These wires moved smoothly within plastic tubes when one of the cable ends was displaced via soft plastic discs of 25 mm in diameter that were on the foam surface. The other ends of these wires were led through the plastic tubes to channels in a light box where they were aligned in parallel channels. By means of video cameras and computer interface, the positions of the wire ends in the light box shown in Figure 13 could be digitized 29 accurately and rapidly with a Visual Basic program. An original reference position file (before deformation) of these ends was taken separately with respect to the displaced position file (after deformation). Thus the deformation of the seat pan and seat back can be recorded and further processed. Figure 13 Light Box 30 3.2.1.2 Seat Back On the seat back there is a 13 x 16 matrix of steel cables, 45 mm apart. A maximum of four inches of working distance can be set for the wires on the seat back. No foam pad was needed for the seat back because there was sufficient friction in the matrix of measurement wires to support the torso in the selected posture. The seat back was flat to eliminate the influence on the measured back contour from the shape of the back support. The data acquisition principles were the same as those for the seat pan. 3.2.1.3 Foot Support Plate and Steering Wheel 60 fit the different sized groups, the foot support plate and steering wheel were adjustable in the fore-aft direction. However, the angles were fixed. The selected angle value was 20 degrees with respect to horizontal for foot support plate, vertical for steering wheel, respectively. Refer to Figure 6. The horizontal distance from the heel to H-point could be changed to adjust the relative deformation of the thighs into the seat foam, and let the subject determine his preferred position by altering the horizontal position of the foot support plate. Also, the design foot position was analyzed. The distances for small size female, mid size male, and large male were listed in the Table 2. The steering wheel was adjusted horizontally and vertically for the subject to feel comfortable as in his normal driving condition, and the angle of the \ steering wheel was fixed. Refer to Figure 6 31 Table 2 Subject’s Feet Positions Mid-male Small Female Large Male Foot Position 900 mm 800 mm 1000 mm 3.2.1.4 Measurement Contour Chair Accuracy To determine the accuracy of the contour chair, two methods were employed to obtain the outer shape of the SAE manikin. F i_rst,_thg sheflgf the SAE manikinfiwflas‘scanned by a probe?" This shell could be considered as an ‘ .M‘h- - V- . L...— accurate one. Secondly, the SAE manikin was put into the measurement contour chair and the shape was recorded in the system. Then, the second shell shape was compared to the first measurement from the scanning at the same locations. The results showed the system error was within 3 to 5 mm. 3.2.1.5 Seat Foam Stiffness Selection (After the primary mechanism of the contour test seat was built, a preliminary comparison study between softer and stiffer foams was performed for the same subjects to evaluate the effects of foam properties on measured thigh contours. The results are shown in Figure 14. In the regions directly under the femurs, the deformed thigh shapes were almost the same for both stiffer and softer foams owing to the mechanical restrictions from the femur and the presence of the hamstring muscles. For the softer foam, more of the subjects’ 32 Data from stiffer foam .0 ‘1' r . / // / Figure 14 Same Subject Measured on Stiff and Soft Foams 33 body shapes were recorded because the foam deformed more. These findings were also verified by Setyabudhy’s finite element model [16]. On the other hand, the foam shape itself as a seat factor was also considered. A flat, soft block of foam was selected 'as seat pan cushion to minimize the influence of seat pan shape on the contour shape and to obtain more of the subjects’ body shapes) 3.2.2 Test Lab Space The testing space was approximately 6m X 6m X 3m. A five-camera MacReflex Qualysis high-speed video system [17] was carefully set up in the space so that each target could be visible simultaneously at least for two cameras, as required by the software used for calculation of the three dimensional coordinates [17]. Through calibration of the camera system, a right- handed SAE vehicle Cartesian system was defined in the space, with positive X- axis pointing rear ward, Y-axis from subject’s left to right, and the Z-axis upward vertically. 3.2.3 Measurement Targets and Probe Measurement targets were spherical wooden beads of 16 mm diameter covered with 3M retro-reflective tape [18], shown in Figure 15, as required by the camera system. The reflective bead was then glued to a square piece of vinyl with approximate 20 mm by 20 mm in dimension. By means of double-sided tape and medical tape, the target was secured to the subject’s skin over the skeletal landmark of interest. 35 A /Tape-covered Bead » /Vinyl Backing Figure 15 Measurement Target iii, \/ A measurement probe used in the testing is shown in Figure 16. There were two targets fixed on a steel rod of 4 mm diameter. The centers of the targets were on the rod centerline. Whenever it is difficult to apply the targets in some region or for two cameras to capture a target, the probe can be used to locate the skeletal landmark. The landmark location could be calculated from the measured centers of bead 1 and bead 2, and the lengths of the steel rod as follow. Ln = In. —x.)2 +(y. -y.)2 +(z. —z.)2 (1) 36 _ L-X2 +(L-L12)x1 X L12 {,2 Y = L'Yz +(L—L12)YI ,‘i (2) L12 _L-zz+(L—L,2)z1 Z I-12 Bead 2 at (XL-N117) Steel Rod \ \ Landmark (XXX) Figure 16 Measurement Probe 37 3.2.5 Reference Chair When a subject sits in the contour chair, any targets on his [FEBJVJJIILQK be visible to the cameras. To collect the position data of C7, and T8, a non- deforrnable thorax was assumed. This makes it possible to gather the position data of C7 and T8 relative to the manubrium and xyphoid in a so-called reference seat, or hard seat as presented in Figure 17. There is a 70 mm opening down the centerline on the seat back, which provides visibility to the targets on the subject’s spine for the cameras. The seat angles were determined based on SAE standards J826 [1]. The first target on the edge is 120 mm fonrvard of the seat back, and the second target 225 mm apart from the first one in the rearward direction. The two targets provided a I “r reference coordinate system. 38 1" - r /' / , I . Figure 17 Reference Chair 39 3.2.6 Contour Data Acquisition A reference position of the contour chair was collected to record the initial positions of the ends of the steel cables when the seat pan foam was not deformed. While the subject was sitting on the contour chair, the positions of the displaced ends of the steel cables were gathered. The differences between the two positions of the steel cables illustrated the deformed interface between the seat foam surface and the subject. In the collected seat contour data, only the contact region between a subject and the seat can be taken for a subject’s body contour. To differentiate the subject’s body contour from the non-contact part of the seat surface, a testing probe was used to trace the border of the contact areas of a subject and the seat. The positions of the two balls on the probe were recorded, since the lengths of the probe were known, the tip positions of the probe could be computed. Ten mid-sized male subjects were measured and 9 out of 10 subjects' data analyzed for the ASPECT manikin contour [16]. Ten of small female and another ten large male subjects were measured and the data were analyzed. The testing protocol is attached. The subject measurement is pictured in Figure 6. 4O 3.2.7 Posture Data Collection The representation of sitting posture adopted in this experiment was developed in the ASPECT program [2]. This kinematic model of the human body is modeled as an open chain of straight-line segments connected at major joints. The segment length, the orientation of the segments and the location of the joints have to be determined by means of a combination of photography and calcirlation. Reflective balls of 16 mm diameter were placed at the selected skin landmarks on subjects. The posture data were collected in both the reference hard seat (Figure 16) and the contour test chair in Figure 6 or 11. A five-camera MacReflex Qualysis high-speed video system was used to gather the motion measurement data in the approximately 6 m x 6 m x 3 m testing space [17]. Each camera contains an optical filter, which cuts off the visible part of the light spectrum. Each camera is equipped with an infrared light to illuminate the measurement area, and light is reflected from the targets back to the camera. These infrared lights help to suppress the ambient light and only the target balls can be seen and recorded. There is a video processor to calculate the center of the ball coming with each camera. The MacReflex software provides the tool to read data from the camera system and to distinguiSh one target from another among all the targets in the image by using direct linear '1 transformation from the object space to the image space. Each camera car: only readjonly two of the’three coordinates in a three-dimensional space,“ so any marker must be seen by two cameras to form an over-deterrnined system of four equations for the three coordinates in the three-dimensional space. Before data 41 collection, all the cameras were calibrated to gather all the set-up constants for the direct linear transformation. Finally the MacReflex converts the data to a format proper for the subsequent processing, such as a CSV format in] our case. Y During the measurement, the acromions were probed because of the visibility to the cameras. Owing to the personal privacy and sensitivity concern, the pubic symphysis was probed by the subject after instructions was given. 42 3.3 Testing Protocol 1) Instruct a subject about the measurement procedures. Have the subject sign the consent form (lRB#96-765) approved by University Committee on Research Involving Human Subjects (UCHRIS). 2) Target subject for the reference chair The landmarks C7, T8, T12, Sacrum, stemal notch, xyphoid process; right and left ASIS, right and left lateral femoral condyle, maleolous, ball of foot on left side were targeted by the taped wooden beads on vinyl backing. The pubic symphysis will be probed by the subject. 3) Take the reference file of the body in the reference chair in Figure 16. Measure the distance between the ball of foot target and heel point for the calculation purpose. 4) Target subject for contour chair Surface landmarks stemal notch, xyphoid process; right and left lateral humeral condyle, right and left Wrist, right and left ASIS, right and left femoral lateral condyle, right and left maleolous and ball of foot on left [side and two seat i I pan targets, two seatback targets and M93?! frame targets. Surface landmark acromion will be probed by a tester and pubic symphysis will be probed separately by the subject during the measurement process. 5) Decide steering wheel position 43 Position subject at the desired distance between H-point and foot support bar, placing hands at 3 and 9 o’clock position (during all measurements), adjust the steering wheel fore or aft for a comfortable position by the subject. 6) Decide preferred foot position Set the distance between manikin H-point and foot support bar to designed distance 1, let subject sit in the contour chair and select a comfortable position 1 by moving foot rest forward, then subject leaves chair. Set the distance between manikin H-point and foot support bar to designed distance 2, let subject sit in the chair and select a comfortable position 2 by moving foot rest reanrvard. Decide Preferred foot position (the mid-point 3 between positions 1 & 2). 7) Gather posterior contour of thigh and buttocks“; ' 1" Set the distance between manikin H-point and foot support bar to designed driving distance with the seat pan in normal position, let subject sit into the chair with back flat against seat back. At designed driving position, wait for 20 sec., and then gather the data for contour and posture (one file with Acromian probed, the another with Pubic Symphysis probed). Move the foot support to designed driving position 2, wait for 20 sec.; gather the data of contour, posture, and perimeter. Move the foot support to preferred position, wait for 20 sec., gather the data of contour, posture. Move the foot support to designed driving position 3, wait for 20 sec., gather the data of contour, posture. Redo step 7) twice. 8) Gather posterior contour of back, thigh and buttocks With 0 lumbar prominence, pull the back wires out and set the distance between manikin H-point and foot support bar to designed driving position with the seat pan in a fonrvard position, let subject sit on the seat pan, move the seat pan back into the seat back support using power track, have subject sit in the chair with back flat against seat back and wait for 20 sec., gather data of contour, posture. Redo step 8) twice. 3.4 Subject Selection Criteria Based upon data from U. 8. population study by Abraham, [15], body mass and stature range from 5‘" percentile small female values are 47 kg (104 lbs.) and 151 cm (59.5 in.) to 95‘" percentile large male values of 102 kg (225 lbs.) and 187 cm (73.5 in.), respectively. A decision was made that three size groups would be used, they are 5‘“ percentile small female, 50th percentile average male, and 95‘" percentile large male within the U. S. population,. The ranges of mass and stature are given in the Table 3. 45 Table 3 Subjects Selection Criteria / i S”°j°°.t Large Male (95%) Mid-sized Male (50%) Small Female (5%) Categorles Range Min Max Min Max Min Max 32:: 76.5 108 67.5 78.75 45 56.25 mm,» (170) (240) (150) (175) (100) (125) Stature (height) 178.9 186.2 164.2 171.5 144.8 151.9 . (73) (75) (67) (70) (59) (62) cm I (In) 3.5 Subject Anthropometric Data Acquisition To detail information of participating subjects’ body dimensions, it was necessarily to obtain anthropometric data. These data were collected by using the definitions and methodologies specified in 1988 Anthropometric Survey Of US. Army Personnel [14]. The list of the following anthropometric items was gathered. ANTHROPOMETRIC DIMENSIONS MEASURED Definitions cited from ANSUR [18], as follow. Stature (99, reference number in [18]) 46 Weight (124) Sitting Height (93) Biacromial Breadth (10) Mid—shoulder Height, Sitting (78) Hip Breadth, Sitting (66) Waist Height, sitting (121) Bispinous Breadth (14)--------- Inter-ASIS Width Waist Breadth (1 12) . Chest Breadth (32) Chest Depth (36) lnterscye ll (70) lnterscye l (71) Waist Depth (115) Waist Back Length (Natural indentation)(1 10) Waist Back Length (Omphalion)(111) Waist Height,sitting (Natural lndentation)(120) Waist Height,asitting (Omphalion)(121) Chest Circumference (33) Chest Circumference at Scye (34) Chest Circumference below Breast (35) Waist Circumference (Natural indentation)(113) Waist Circumference (Omphalion)(114) lnter-PSIS Wldth 47 Hip Breadth (65) Hip Breadth,sitting (66) Buttock Depth (24) Buttock Circumference (23) Thigh Circumference (103) Knee Circumference (71) Buttock height (25) Buttock-knee length (26) Buttock-popliteal length (27) 48 CHAPTER 4 DATA ANALYSIS APPROACHES AND RESULTS 4.1 Introduction The recorded posture data were tracked by using MacReflex software [17] and exported in a format of CSV files. During data processing, the data were transformed from intermediate coordinate systems to the global coordinate system. Because of the complexity of comparing the three-dimension data plots, the contour data were converted into two dimension curves for analysis purposes by creating planes relative to skeletal landmarks to intersect the contour surfaces. In this section the methods of data analysis are discussed. Some of the representative results are presented and discussed. 4.2 Initial Raw Data Treatment Based on the posture descriptors defined by the ASPECT program [2], key skin landmarks on both sides of the subjects were targeted to reflect the subject’s real sitting postures in the present study. The tracked data for target location were input to the spreadsheet program [19] that has been revised for this application to calculate the joint centers coordinates of interest. After coordinate transformation and the contour surface data file format was changed to IGES files, the data were imported into the IDEAS program package [20]. First, the data points (see Figure 18) from the seat pan and seat back were splined into 49 curves, then these curves were lofted to create the three-dimensional contour surface as seen in Figure 19. 4.2.1 Data Transformation Among Coordinate Systems There were four coordinate systems used: 1) a global coordinate system in the testing space set by the camera system, 2) one local coordinate system on , the seat pan, 3) one local coordinate system located on the seat back, and 4) a local coordinate system on the contour chair frame. The systems 2, 3 and 4 are as shown in the Figure 12. All the back, buttocks and posterior thigh data from the local coordinate systems on the seat back and seat pan were transformed into the global coordinate system [21]. 50 Figure 18 Transformed Data Points 51 Figure 19 Lofted Data Surface 52 4.2.1.1 Translation x1 Data point [U] = x2 in coordinate system Ox1x2x3 was translated to 6 x3 x,’ new coordinate system O’xl’xz’x3’ as [U'] = x2 . See F igue 20. The distance x3’ a between the two origins O and O’ are [D]: b , and the following relation will c hold: x1 a U'=U+D= x2 + b (3) x3 c X3 X3 X2 D 0' X1 X2 0 X1 Figure 20 From Coordinate System Ox1x2x3 Translated to Ox1’x2’x3’ 53 4.2.1.2 Rotation Suppose that two rectangular Cartesian coordinate systems ox1x2x3 and 0x1 ’xz’xa’ originate at the same point 0, as shown in Figure 21, and the angle between unprimed and primed axes is defined by Ail=(Xi'. Xi) i.i=1.2.3 (4) and the direction cosines 3]] are given by at]: cos(xi’, Xj) i,j=1,2,3 (5) so the transformation matrix [ajj] is an 312 813 [an]: 321 a22 a23 iri=1v2r3 (6) a31 a32 333 x1 Write translated position vector U’ as [U'] = x2 and the rotated same point U as x3' x1 [0]: x2 , the following relation will hold, X3 [U]: [aili' [U] i,j=1,2,3 (7) 54 x3' Figure 21 Cartesian Coordinate System Ox1x2x3 Rotated to Ox1’x2’x3’ 4.2.2 Generating Contour Surface from Measurement Data Points ( A contour surface was generated from the measurement data points of a subject after the raw data were initially treated, including file format change, coordinate system transformation, etc. The l-DEAS program was employed in the surface generation. First, the primary curves were in the lateral direction, as in Figure 19. The measurement points in the lateral direction were B-splined into curves. These primary curves describe the major features of the contour [14]. The secondary direction in surface generation was engaged in lofting the primary curves into a contour surface, as shown in Figure 1b 55 4.3 Seated Posture Calculations One of the goals of this study was to represent subjects’ seated surface contours relative to their bone structures. To accomplish this goal, the subjects’ sitting postures were estimated by using both targeting landmarks and available scaling data [2]. Once the locations of target centers were recorded, actual bony landmark locations could be calculated by constructing a vector from the center of the target to the location of the actual bony landmark on the skin surface. The length of this vector LT..>L was as follow: 1 LT->L = ‘Z’Dt + Tb + Ti (8) Where 0:: the diameter of the target, Tb: the thickness of the target backing, R: the tissue thickness at the targeted location. To determine the direction of the vector from the target center to a joint center, another adjacent landmark target was chosen to create a line between the two target centers. Usually the direction of the vector would be toward the joint under the skin landmark and perpendicular to the line. For a second method to determine a joint center, three landmark targets were needed to yield a plane with three points. The direction of the vector was chosen to be perpendicular to the plane, and pointing to the joint by the landmark. 56 4.3.1 Lower Neck Joint 'The location of the lower neck joint was determined using the C7 and suprastemal surface landmarks. See Figure 22. The vector R from C7 to suprastemal was rotated counter clockwise 8° and became R’. The lower neck joint was the point on vector R’, away from C7 at 55 percent of the R length. R’=0.55R C7 / Lower Neck Joint Suprasternal Figure 22 Calculation of Lower Neck Joint 57 C7 Acromion Suprasternal / 0.42R Shoulder Joint Figure 23 Calculation of Shoulder Joint 4.3.2 Shoulder Joints The surface landmarks C7, suprastemal, and acromion were used to calculate the shoulder joint. The Y coordinate of the shoulder is the same as that of the acromian landmark. Through the acromion, a vector A was created to form an angle of 67° with the vector R, as shown in Figure 23. The shoulder joint is located on the vector A at P, which is 42 percent of the length of C7 to suprastemal from the acromian. From the position of this point, the joint coordinate X and Z could be decided. Because the ASPECT posture was defined as sagittal symmetry, another shoulder joint could be reflected in the 3-D space. 58 4.3.3 Upper Lumbar Joint The upper lumbar joint was calculated from the T8 and T12 positions, as shown in Figure 24. The vector T8-T12 was rotated counter-clockwise 94° to form vector UL, and the upper lumbar joint was located on the vector UL at 52 percent of the length of C7 to suprastemal from the T12. T8 94° E Upper Lumbar Joint T12 Figure 24 Calculation of Upper Lumbar Joint 59 4.3.4 Lower Lumbar and Hip Joints The right and left anterior-superior iliac spine (ASIS) landmarks, the pubic symphysis (PS) landmark, and the posterior-superior iliac spine landmark (PSIS) were used to calculate the lower lumbarjoint and hip joint centers. A pelvis coordinate system was created to calculate the lower lumbar joint and hip joint centers, as shown in Figure 25. The Y-axis passes through both right and left ASIS on bone. The Z-axis was perpendicular to Y-axis and passes through the pubic symphysis and the mid-point of right and left ASIS. The X-axis was mutually perpendicular to the Y and Z-axes. To locate the hip joint center (HJC) in the pelvis coordinate system, the method exploited by Seidel, et al [22], was adopted in this study. The HJC coordinates were scaled from subjects’ pelvic width (PW), pelvic height (PH), and pelvic depth (PD) as tabulated in the Table 4. The computed HJC coordinates were then transformed into the global coordinate system for further analysis. Table 4 Calculation of Hip Joint Center Coordinate Measurement Calculation X Pelvic depth PD 0.34*PD Y Pelvic width PW i 0.36*PW Z Pelvic height PH - 0.79*PH 6O Mmmumrrrv '1")V"r . 3.“.1 can t .1"ng- Figure 25 Pelvis Coordinate System 61 The method developed by Reynolds, et al [23] was used to locate the lower lumbarjoint center in the bone pelvis coordinate system [2] as illustrated in Table 5. Table 5 Calculation of Lower Lumbar Joint Coordinate Measurement Calculation X Pelvic depth PD 0.399*PD Y Pelvic width PW 0 Z Pelvic height PH 0.432*PH 4.3.5 Knee Joints To determine the knee joint locations, the landmarks at the lateral maleolus and lateral condyle along with the calculated hip joint location were utilized to create a plane. At the measured lateral femoral condyle landmark, a vector was constructed perpendicular to this plane. The knee joint location was on the vector medial to the landmark by a distance of 11.8 percent of the measured length between lateral maleolus and the lateral femoral condyle landmarks. See Figure 26. 62 4.3.6 Ankle Joints The ankle joint could be calculated from Figure 26. At the lateral maleolus landmark, a vector was created perpendicular to the described plane. The ankle joint was located medial to the landmark by a distance equal to 8.5 percent of the distance between the lateral maleolus and the lateral femoral condyle landmarks. Lateral Femoral Condyle 0.118 P Knee joint Lateral Malleolus Hip Joint Medial Ankle joint 0.085 P Figure 26 Calculation of Lower Limbs Joints 4.3.7 Wrist Joints For this application, the wrist landmarks were adequate for accuracy. The measured wrist point was just a mid skin point between the radial and ulnar styloid process. 63 4.3.8 Elbow Joints In Figure 27, the landmark on the lateral humeral condyle, mid wrist, and calculated shoulderjoint were used to yield a plane for calculating the elbow joint. A vector was created passing through the lateral humeral condyle landmark, perpendicular to the plane mentioned above. The elbow joint was located on the vector medial to the lateral humeral condyle a distance at 15.5 percent of the length between the lateral humeral condyle and wrist landmarks. Shoulreroint Wrist Landmark Medial Lateral Elbow Joint 0.1550 Figure 27 Calculation of Upper Limbs Joints 64 4.4 Deformed Contours Data Analysis 4.4.1 Methods To compare different subjects’ body shapes, the three-dimensional data were converted to two-dimensional curves as shown in Figure 28. . “ 1' \"x 3' .13 if. , «x. Figure 28 Sliced Thigh Curves (Relative to Left Femur Axis) and Back Curves 65 4.4.1.1 Analyzing the Thigh and Buttocks Data Surface After examining the left and right sides of the measured data, it was found that the differences between both sides were within the resolution range of the contour chair, which is 5 mm. So a decision was made to section the left thigh. A local coordinate system was created with its origin at left HJC and x-axis through the knee joint center after the transform of the HJC together and alignment of the left thigh axes for this purpose. Although the subjects were from the same mid-size male subgroup, each of their body parts was not exactly proportional to their stature. Therefore, the thigh axis was defined as from HJC to knee joint center on the same side of the body, and evenly divided into 10 sections for the comparison. Planes that were perpendicular to the left thigh axis started from the left HJC towards knee joint center were created at ten percent of their thigh length (HJC to knee joint) apart from each other to intersect the three- dimensional contour surface. See Figure 29. Because of the limitation of the length of the seat pan of the contour chair, there was seven sections on each subjects’ data, and the seventh usually is not long enough to provide all the information needed. The other way to section the contour surface is by using the vertical plane through the thigh axis to intersect the contour surface to investigate the shape change in the longitudinal direction of the thigh. The same procedure was applied to the data of the J826 H-Point machine. 66 Lower Neck Joint :l I - WW5!!!" n _. I “ ~‘“‘-.-- flu.) E: ,~ - 988.8921: . .. \ Upper LumbarJoint gi‘l‘.’ . . . I I K . try-*A x9 , . ‘t'lrrlil’s‘sgt'rw - ' . . ‘gIIV Lower LumbarJornt (,K ~~€~'~\ ‘ Sectioning planes . _ _ I (I! *4/ch 1, It,» .317.» were perpendicular to the linkages f H-point \\ / \ W‘s“ Figure 29 Contour Surface Analyzing Scheme 67 4.4.1.2 Analyzing the Back Data Surfaces The anatomical aspects of the back and its motion are much more complicated than the thigh. Future applications of the processed back contour data for input into JOHN program were considered. Sectioning planes were created to intersect the back contour surfaces that were perpendicular to the joint linkages, such as the linkage between lower neck joint and upper lumbar joint of the thorax, or the linkage between upper lumbar joint and lower lumbar joint of the lumbar region. In the pelvic region, the linkage of the hip joint center (the mid-point of right and left HJC and lower lumbar was used as the intersection planes were created. The intersection planes were spaced at a distance of ten percent of the linkage length as seen in Figure 29. Due to the differences in linkage orientations caused by the different postures, using this sectioning method sometimes left a gap between two adjacent regions as can be seen in Figure 28. According to the thoracic and pelvis shape and their relative position to the joint centers, the linkages were extended and a few more planes were created to intersect the back surface to fill the gaps in such a case. Meanwhile these planes also intersected the skeletal links in the torso and lumbar to create the points of intersection with the torso and lumbar links. 68 4.4.2 Comparing Measured Data and J826 H-point Machine Based on the measurement data of nine mid-male subjects, a comparison between the J826 machine and measurement data was conducted. 4.4.2.1 The Thigh and Buttocks Data At each thigh section, there were typically nine curves (from nine mid- sized male subjects) together with the intersection points of the thigh axis to be analyzed. In order to compare the thigh shape relative to the skeletal linkage, the lowest points on the curves to the left buttocks and thigh were determined by creating straight horizontal lines tangent to the curves at the lowest 2 position in the coordinate Y-Z plane in the thigh coordinates where X was along the thigh axis. One of the nine lowest points was chosen as a reference point (usually one near the center of the distribution). Then all the curves along with the corresponding intersection points on the thigh axes were translated to coincide with all the lowest points on the curves. From here the relative positions of the intersection points on the thigh axes was calculated and further statistic analysis performed. . These sectioning and analysis methods were employed to compare the measured data of the mid-sized subjects and J826 H-Point machine. The following are the brief results of that part of the study as an example here. In Figure 30, (A) are the sections under the hip joint center (HJC). The H- point of J826 H-point machine and the average HJC of human subjects were positioned on the same 2 level. There is 5 mm difference between the lowest 69 points on the curves of J826 H-point machine and subjects, i.e., the H-point location of J826 H-point machine is 5 mm higher than the mean location of the subjects’ HJC. From (B) and (C) it can be seen that the subject’s thigh contours were more symmetrical, flatter and the thigh axes closer to the bottom of the curves compared to the J826 H-point machine. Moreover, the subjects’ contours are more prominent under the ischial tuberosities in the medial region. To study the contours along the length of the thigh, the thigh axes and HJC of all subjects and the J826 H-point machine were overlaid. After the lowest points on all curves were determined and marked, all curves were translated to coincide with the mean lowest point and the marks left in the original positions (Figure 31). This data verified that the H-point of J826 H-point machine was higher than the mean HJC location of human subjects. There is a 10 mm vertical distance between the lowest points of the J826 H-point machine and the mean location of subject contours. The bigger difference occurred near the knees on the curves. The main reason for this is that the subjects’ leg lengths are different. The shorter the subjects’ lower leg, the more the thigh penetrates the seat pan. The testing protocol controlled the horizontal distance between the H- point and toe-bar on the contour chair. 70 Z J826 H-point Subjects’ Average H-point /\ More prominent under ischial tuberosities (A) Sections Right Under H-point J826 Thigh Reference Point Subjects’ Thigh Average Reference Point -. / (B) The Fourth Sections from H-point Figure 30 Sections of J826 H-point Machine and Subjects Contours (Planes perpendicular to thigh axes) 71 J826 Thigh Reference Point Z + Subjects’ Average Thigh \ Y + Reference Point More symmetrical and flatter (C) The Sixth Sections from H-point Figure 30 Continued Thigh Axes Mean Lowest Point of Subject J826 Lowest Point Figure 31 Sections of J826 H-point Machine and Subjects Contours (Planes vertical through the thigh axes) 72 4.4.2.2 The Back Contour Data The approach used to analyze the thigh and buttocks contours was also applied to the back contours. The comparisons between human subject data, the J826 H-point machine, and the UMTRI data [5] were performed. Figure 32 shows a view from the left upper front of sections at 30 mm intervals above the HJC of the average data from this study for the ASPECT program (so named as ASPECT contour data) and the UMTRI back contours with the limits of seat contact marked for each contour. The limit of seat contact for the UMTRI contours was selected at the divergence of the UMTRI shell and seat contours measured in this study. The region of measured seat contact for the ASPECT contour was wider than with the UMTRI back (Figure 32). The side views of the ASPECT and SAE back contours are very close (Figure 33). Compared to the ASPECT back contour, the side view of the UMTRI crash dummy seat-shell contour was convex (Figure 33). Compared to the average posture of the ASPECT subjects, the angle from UL to LN in UMTRI posture was 6 degrees forward. The UMTRI torso seat-shell shape was rotated rearward about its UL joint to provide a composite back contour such that the original UMTRI contour was rearmost below the UL and the rotated UMTRI contour was rearmost above the UL. The side view of this adjusted UMTRI back contour was very close (within a few millimeters) to the ASPECT and the J826 back contours (Figure 34). 73 ASPECT seat back (red ASPECT contact border gr - ASPECT back (green) 16. 480mm 15, 450mm ’ 14,420mm UMTRI dummy shell (blu = ,3. 390mm UMTRI contact border (blue) ‘ 12. 360mm ‘ - 11, 330mm -_ \l' 10. 300mm ASPECT average posture (red W, UMTRI dummy posture (blu - ‘\—z “. 9. 270mm “.___ . ' 8. 240mm 1“ 7, 210mm ’ l 6, 180mm ’ i . 5. 150mm /7 I 4. 120mm / \ 3. 90mm i 2, 60mm 0. at HJC Figure 32 Sections Through the ASPECT and UMTRI Contours with Postures and Contact Edges V A ‘x l . "1| ASPECT average posture (green) rJ ' x, R. . t]. "l. \5'1'1 ix - . 'l J826 (red), offset rearward by . 5 'l - ~. 5% i difference between H-pt. and HJC I specr( green) UMTRI posture I rm 8. Rotated back 6° to be parallel i| UMTRI ‘0 ASPECT thorax (p'nk) i a. Parallel to ASPECT thorax b. Original position (blue) I (pink) I b. Original position (blue) Figure 33 Measured Back Contours Between Upper Lumbar and Lower Neck Joint 75 ASPECT measured (green) UMTRI dummy (gold) ASPECT splined (black) J826(pink) l H '\ i + .\ \ ‘2‘ . "a "\ \ \ El E {E 5 l lg: . i I ‘ ‘ . ‘ __ > J' . ._ .. I. _. J Section 2, 60mm above HJC 3. 90mm 4, 120mm 5, 150mm 6, 180mm 100mm ASPECT measured (green) UMTRI dummy (gold and blue - rotated 6° back) ASPECT splined (black) J826(pink \ + + , 4'. u \ \t (l t I ‘. I l \. l mfi/I'c— I,” "#0.“— ..-—-u M— .- - ‘2 f , Cl ‘1- ’ :- . i i 1 ‘i :1“. E I I I . I l.‘ ‘5‘ 47' h J" I W .1 _ ‘ 45 Section 7, 210mm above HJC 8, 240mm 9, 270mm 10, 300mm Figure 34 Contour Sections up the Seat Back 76 ASPECT measured (green) UMTRI dummy (blue - rotated 6° back) / ASPECT MW) \\ / J826(plnk) x + .__.__,+ I I I i ,5 4L . " i 17, 510mm . +’ 4 ' g Section 12. 360mm above HJC 13. 390mm 14, 420mm 15. 450mm 16. 480mm 100mm Figure 34 Continued With the side view back contours aligned as above, X-Y (transverse) sections of the ASPECT back contour were compared to sections of the UMTRI composite torso. A series of sections at 30 mm intervals above the H-point or HJC through the ASPECT, UMTRI, and SAE back contours are shown in Figure 34. Section 2 is the first section shown and it is 60 mm above HJC. For Sections 3 - 7 and 14 — 16, the sides of the UMTRI sections generally appeared to be continuous with lateral parts of the ASPECT contours near the 50 mm X-direction limit of the ASPECT back measurements. In the region of the shoulder on the 77 sides of Sections 8 — 13, the UMTRI contours were fonrvard of the ASPECT contours probably because of difference in arm placement. For the UMTRI contours the hands were on a steering wheel while the ASPECT contours were measured with the arms closer to the torso. The middle part of the ASPECT measured contours (within approximately Y = :90 mm) were nearly flat because of the flat seat back of the measurement chair, while the UMTRI contours were more rounded (Figure 34). In the sections of Figures 34 and 35, the sides of the J826 back contour become apparent in section 4, which is 120 mm above H-point and HJC. Up to section 8 at 240 mm above HJC, just above the upper lumbar pivot, the J826 is more rounded than the ASPECT measured contour or the UMTRI dummy shell, yet the widths of the J826 and UMTRI contours are similar. Above the upper lumbar pivot, the J826 contours continue to be more rounded than the ASPECT contours and the UMTRI contours are generally between J826 and ASPECT. As stated above, the difference between the shape of the ASPECT and UMTRI contours above section 10 was probably due to the fonlvard UMTRI hand position to reach the steering wheel. As described in the next section, the sides of the UMTRI dummy shell torso were added to the measured ASPECT back contours to provide the ASPECT manikin torso contour. The following is a comparison of the back widths of the J826 torso and ASPECT torso (which uses the sides of the UMTRI dummy shell torso). 78 The narrowest part of the J826 back is 306 mm at 230 mm above H-point. Comparable dimensions of the UMTRI dummy shell are the width lateral to the bottom of the 10th rib which is 312 mm at 160 mm above HJC and the abdominal breadth of 325 mm and waist breadth at the umbilicus 314 mm. These dimensions indicate that J826 is approximately 6 mm narrower than the new ASPECT back. The widest part of the J826 back is 392 mm at 430 mm above H-point. On the UMTRI dummy shell, the width between the rear upper margins of the armpit (posterior Scye landmark) is 394 mm wide at 370 above HJC. This is nearly the same as the J826 widest part. The dimensional differences between J826 and UMTRI back widths are small, and the ASPECT back is flatter in cross- section (seen below in Figure 35). 79 _ xx--. Splined ASPECT contour (black) (green) UMTRI Rotated Back _ an”: ‘9: 171 510mm, above HJC 6° (blue) "5;:16 480mm UMTRI (maize) 15 450mm ' 14, 420mm 13. 390mm 12, 360mm 11, 330mm 10, 300mm 9, 270mm 8, 240mm 7, 210mm 6, 180mm . 5, 150mm 4, 120mm 3, 90mm 1 “x 2, 60mm above HJC X direction, forward right side Figure 35 Comparison between ASEPCT and UMTRI Back Contour 80 4.5 Defining Mid-male Contour Even though humans are not precisely symmetrical, the posture and contours for manikins or the computer models ought to be symmetrically defined [24]. By creating a central, mid-sagittal plane of symmetry, the contour surfaces were separated into right and left sides. The right side and its reflection were used for the development of the manikin contours. After the right side of the contour was reflected about the plane of symmetry, the right and left sides were nearly identical, with a difference of only approximately :1 mm. This small difference is less than measurement accuracy and supports the decision to develop symmetrical contours. There were two versions of mid-male contours that were defined in this section, and they were ASPECT mid-male and TecMath mid-male contours. 4.5.1 Defining The ASPECT Mid-male Contours In the ASPECT program, there was a need to reevaluate and revise the J826 hardware and procedures as stated earlier in the Chapter 1. Because the contact contours of the new manikin were very important in determining the interactions with seat pans and resulting measurements of H-point location and seat pan angle, a study of the contact contours between subjects and the seat support surface was carefully conducted, which resulted in the creation of the new ASPECT manikin contour of mid-male size. 81 4.5.1.1 Thigh and Buttocks Contours The thigh and buttocks surface contour of the new manikin was defined by selecting one of the mid-male subject’s contours that was consistently in the middle of the small range of variation of the nine subjects’ contours. The contour then was separated right from left; the right side and its reflection were used in the ASPECT thigh and buttocks contours. An averaged contour would have been similar to, yet may not be as realistic as, this single subject’s contour. The ASPECT thigh and buttocks contours are shown in Figure 36. Figure 36 ASPECT Symmetrical Buttocks and Thigh Contours 82 4.5.1.2 Back Contour Compared to the buttocks and thigh, back posture and contours are more complex because there are a greater number of mobile segments, leading to greater potential for postural and contour variability. Although the subjects were chosen to be mid-size males, there were variations in their skeletal anthropometric dimensions and postures. To reduce the effects of these variations and to analyze the subjects’ back contours for the generation of the single manikin contour being developed, the following analysis steps were accomplished: 1. The measured back contour data for each subject were splined to yield a surface. 2. The splined back contour for each subject was rotated and translated so that the mid-HJC was aligned on the same axis and the LN was in the same plane. 3. A coordinate system was established (Figure 37) such that: a. The X-axis was fonrvard and perpendicular to the seat back plane of the measurement chair. The posture data for each subject was positioned so that the point midway between the hip joint centers (mid-HJC) was on the X-axis. The origin of the axis system was in the plane of the seat back of the measurement chair. b. The Z-axis was upward in the seat back plane. The posture data for each subject was positioned so that the perpendicular projection 83 2, up the seat back I \ Lower neck joints at Z = 507mm —- Upper lumbar joints — Lower lumbar joints Hip joint centers Figure 37 Torso Length Scaled In Z-Direction of the lower neck joint (LN) to the seat back plane was on the Z- axis. c. The Y-axis was perpendicular to X and Z, in the seat back plane, and to the left. In this coordinate system, the mid-HJC of each subject was placed on the X-axis and the lower neck joint (LN) was placed in the X-Z plane. 4. The Z distance from the mid-HJC to the LN was averaged (Zav = 507 mm), and the Z values of the posture and splined contour data for each subject were scaled to the average. By these steps, the mid-HJC of each subject was at (X., 0, 0) where Xi was X-coordinate value of each subject’s HJC. The LN of each subject was (xi, 0, 23‘.) where X,- was the X-coordinate value of each subject’s LN and Zav is the average Z coordinate value for all the subjects. The Y coordinate values were not altered but were within a few millimeters of zero. The X values of the HJC and LN were averaged and the X, Y, and Z values of the LL and UL were averaged to yield an average torso posture for the back contour subjects. The lower backs of the subjects’ were all against the flat seat back of the measurement chair so that their measured contours in this region were very similar (Figure 38). In the upper torso (Figure 39), the contours varied because 85 the upper torso postures of the subjects varied primarily due to different angles of their thorax from vertical. The depth of ASPECT back contour measurements was limited to 50 mm in the X direction perpendicular from the flat seat back. The measured and splined seat back contours for each subject were sectioned with X-Y (transverse) planes that were 30 mm apart in the Z-direction starting 60 mm above HJC, which was near the bottom of the measured back data. At seventeen points (sixteen segments) equally spaced along each contour section, the X and Y values of the contours for each section were averaged to generate an average back contour. There were very small differences within two millimeters in the Y values between subjects, and these were averaged by this procedure. The average contour sections are shown in Figures 40 and 41. The ASPECT back, buttocks, and thigh contours are shown in Figure 42. ASPECT manikin is illustrated in Figure 43. 86 Z, up the seat back Middle and lower torso contours are very similar between subjects. Figure 38 Measured Contour Curves from Mid Thorax to End of Lumbar 87 . \~i‘;\ \Ievel lower neck joint Measured back contours differ probably due to differences in upper torso postures shown in Figure 41. f right side ._ \ \ \ a) -" left side \ \ ‘>\ 4] ._ X direction. fonrvard ’ \ ’ level upper , , lumbar jomt Figure 39 Measured Back Contours between Upper Lumbar Joint And Lower Neck Joint 88 A Z 17, 507mm 16, 480mm 15, 450mm 14,420mm 13, 390mm 12, 360mm 1, 330mm —— 0, 300mm 9, 270mm 8, 240mm 7, 210mm 6, 180mm 5, 150mm 4, 120mm 3, 90mm 2, 60mm 1 0 Lower neck joint upper lumbar joint lower lumbarjoint hip joint center Figure 40 Average Back Contour And Posture Side Vlew 89 left side right side Figure 41 Average Back Contour Left Rear View 90 Figure 42 ASPECT Back, Buttocks and Thigh Contour Surfaces 91 Figure 43 ASPECT Manikin 92 To define the edge of contact between the seat and body, points on the contour sections were chosen that were the first points from the sides with an X value that was clearly less the maximum X value for that section. The X-value of the chosen point was typically near 40 mm. Actual contact was between this chosen point and the next point to the side, which was at the maximum measurable X value (near 50 mm). The contours lateral to these chosen points would be affected by inclusion of some points that were not in contact with the subject. However, contours splined to the edge of known contact were found to be less than 1 mm different in X-value when compared to contours splined with points beyond the contact edge. The contact edge for the average ASPECT back contours is shown in Figure 32 with the edge of seat back contact for the UMTRI dummy shells. 4.5.2 Defining The RAMSIS Mid-male Contours Boughner [7] developed a three-dimensional skeleton that represented mid-size males and was based on the UMTRI dummy anthropometrics [5] and articulated according to the work of Haas [4]. To his skeletal model, Boughner added shapes to represent major muscle groups. To represent the mid-size male, Frost [10] added skin surfaces to the Boughner model so the skin surfaces articulated with the skeletal linkage. In developing this contour, Frost considered both the skeletal and muscle geometries of Boughner [7] and the surface contours of UMTRI [5]. So, the Frost contours included transverse section curvatures that were believed to be more representative of people’s back than 93 the flatter UMTRI contour that was based on the shape of an automobile seat in contact with their human subjects. Frost also scaled the mid-male contour based on anthropometric dimensions to represent small women and large men. Because the ASPECT contour of this study was based on data measured in a flat-backed seat fixture, the resulting contours appeared to be flat. For aesthetics in the development in this study of the contours for the RAMSIS model [6], the ASPECT contours were adjusted by a few millimeters, less than measurement variability. For this, the contours from Frost [10] and UMTRI [5] and the APSECT contours from this study were Considered. The side view (sagittal plane) shape of the Frost and UMTRI contours were nearly identical but the Frost contour was thought to have more human-like transverse contours, so the Frost contour was selected. To develop the RAMSIS contour, the postural linkages for the Frost and ASPECT contours were aligned and the differences between these contours were averaged to produce the RAMSIS contour. 94 CHAPTER 5 CONTOUR SCALING FOR LARGE MALE AND SMALL FEMALE 5.1 Introduction Since the early 1960s, both physical and digital models of mid-sized males, such as SAE practice J826 [1] and the JOHN model [7], have been extensively used in seat design and evaluation. However, there are needs for tools representing other groups of people in different height and weight ranges. Among those most needed are models of 5th percentile small female and 95th percentile large male for applications to confirm that seats will accommodate these extreme sizes of people. Because of the extensive and prevailing application of the mid-sized male models, it became very meaningful to explore the correlations or the relations between mid-male and small female, and mid- male and large male. Frost [10] and Robbins [5] used the scaling method to create contour models for small females and large males from the mid-male data, but the scaling method was never validated by data from human subjects. Therefore in this study, mid-male contours from experimental data were employed to create contours for small females and large males by scaling. Furthermore, the measured data of large males and small females were utilized to validate the scaling methodology. If a feasible scaling system could be established, then the contours of any percentiles could be created from the mid-sized male contours by using the scaling method. This would be a very efficient way to create a contour for any size individual. 95 5.2 Development of Scaling Factors The seat contact contours of three groups of human subjects (small women, mid-size men, and large men) were measured in this study along with anthropometric dimensions for these three size groups. As described previously, a seat contact contour was developed to represent mid-size men and was used in the development of the ASPECT manikin and for RAMSIS model development [6]. In computer modeling, it is easily possible to scale the size of shapes so that seat contact contours for different size people could be generated based on their sizes. In this section, scaling factors are described for the purpose of scaling the mid-size male contours to the size of the contours for small women and large men. These scaling factors were based on values of anthropometric dimensions measured on the surfaces of the human subjects and internal skeletal linkage dimensions that were based on the external anthropometric dimensions. The approach to evaluating agreement between the contours scaled from the mid-size male to the other size people was to compare the scaled contour for each individual subject to the measured contour for that subject. Scaling factor F in one specific body direction was defined as the individual subject’s body dimension D, divided by mid-sized male body corresponding dimension Dm, i.e., D8 F = a” , (9) m 96 There were three scaling factors for each body segment corresponding to scaling in length, depth, and breadth directions, for instance, F., F... and Fb, respectively. 5.2.1 Thoracic In the thorax area, three scaling factors are defined for body dimensions in breadth as Fm, in depth as Ftd, and in length as F". n=Dm um Dmtb D8 Feb—0m: (11) 0 F =—s" 12 u D"... ( ) Where Dab, Dstd, and Dst. are subject’s chest breadth (reference number 32 in [14]), chest depth (36), and chest length, respectively. The chest length here is the average distance between the lower neck joint and upper lumbarjoint. Dmtb, Dmtd, and Dmu are the chest breadth, chest depth, and distance between the lower neck and upper lumbar joint of the mid-male contour, respectively. 5.2.2 Lumbar To scale the mid-sized male contour to the desired subject’s contour in this area, scaling factors Flb, Fld, and F.. are used for the lumbar area scaling. 97 F = 13 l. D... < ) 0 F = w 14 .. D... ( > D F-uJi 15 .. D ( ) mll In equations 13 to 15, 05",, Dsld, and D," stand for subject’s waist breadth (112), waist depth (115), and length between the upper and lower lumbar joints, Dmlb, Dmtd, and Dmu for the waist breadth (112), waist depth (115), and the distance between the upper and lower lumbarjoints of the mid-male contour in that order. 5.2.3 Pelvis In the same fashion as for the thorax and lumbar areas, three scaling factors are defined for the pelvic area as F», de, and Fpl. o 3,: ”° 06) Dmpb o l=',,,,=spd 07) 0m,d F —D” 08) PI — Dmpl Where 0,», Dspd, and Dsp. are used for subject’s sitting hip breadth (66), buttocks depth (24), and the distance between the lower lumbar joint and the midpoint of HJCs, and Dmpb, Dmpd, and Dmp. for the sitting hip breadth (66), buttocks depth (24), and distance between the lower lumbar joint and midpoint of HJCs of the mid-male contour, correspondingly. 98 5.2.4 Thigh For the thighs, scaling factors Fm, Fm, and Fm are defined for the thigh breadth, depth, and length in the following way: D F . = —3°” 19 D5 Fthid = 6:: (20) D . F . = stl'lll 21 mthil In the equations 17-19, Dam. is the average distance between the HJCs and knee joints of a subject, Dmthi. is the distance between the HJC and knee joint of the mid-male contour. For the thigh region, the pelvis’s breadth and depth are utilized to scale the thigh shape for both the subject and the RAMSIS mid-male. 5.3 Scaling Procedures and Results Once the scaling factors for each body segment had been defined, the values of the scaling factors were calculated and are tabulated in Table 12 for large males and in Table 13 for small females in Appendix A. Before the scaling procedures started, there were four local coordinate systems to be defined. 1) Thorax coordinate system was originated at upper lumbar joint, positive X- axis pointing to lower neck joint, positive Y-axis from left to right. The Z- axis was determined by the existing axes by the right-hand rule. 99 2) Lumbar coordinate system started with the X-axis from lower lumbarjoint toward upper lumbar joint, Y-axis pointing to right from left, and the X and Y directions decided the Z-axis by the right-hand rule. 3) Pelvic coordinate system origin was located midway between the two hip joint centers with X-axis pointing to lower lumbar joint, Y-axis pointing from left to right, and the Z-axis was then decided by these two X and Y axes. 4) Thigh coordinate system was originated at the mid point between right and left hip joints. Positive X-axis pointing toward the midway of the two knee joint centers, positive Y-axis pointing from left to right, and Z-axis was decided by the X- and Y-axes. 5.3.1 Small Female In the scaling process, the RAMSIS mid-sized male contour and posture were scaled down to each small female subject’s contours. First the thorax contour of the RAMSIS mid-male was translated to coincide with the upper lumbar joint for the subject. Then the mid-male thorax contour and the skeletal linkage were scaled down to the small subject’s contour in the local thorax coordinate system using the previously defined scaling factors. 100 Finally the scaled body segment and the posture linkage were aligned with the subject’s linkage connecting lower neck joint and upper lumbarjoint. The lumbar contour of the RAMSIS mid-male contour was repositioned at the lower lumbar joint of the small female subject. In the local lumbar coordinate system, the lumbar contour of the mid-male then was scaled down according to the small female subject’s anthropometric data. The scaled lumbar and the posture were then rotated to the subject’s posture linkage. The pelvic contour and the posture linkage of the RAMSIS mid-male was relocated at the center of the right and left H-points. The pelvic contour and posture were scaled down to the small female subject’s dimension. The contour and linkage were also rotated to align to the small subject’s. All of the scaled contour curves from small female subject 1 are presented together with the curves from measured contours for that subject in Figure 44 for a back view and in Figure 45 for an oblique view. The curve at each individual section is illustrated in Figure 46 in detail. By visual inspection, the differences between the two sets of contour curves are within less than 10 mm. Considering the accuracy of contour and skeletal landmark measurement, the two sets of curves match with each other to an acceptable degree. The rest of the small female subjects’ results are documented in the Appendix B. The similarity of these curves is analyzed and discussed in section 5.4 below. 101 Subject 1 Figure 44 Tested and Scaled Subject 1’s Contour Curves, rear view 102 caled ETA/UPS Figure 45 Tested and Scaled Subject 1’s Contour Curves, oblique view 103 _— SF1 Thorax 2"d SF1 Thorax 3rd SF 1 Thorax 4" Figure 46 Tested and Scaled Contour Curves at Each Section of Small Female Subject 1 104 '\ " ‘ “—— ~.——-—— _———-' SF1 Thorax 5m SF1 Thorax 6th Figure 46 Continued 105 SF1 Lumbar 18t SF1 Lumbar 2"‘1 SF1 Lumbar 3rd Figure 46 Continued 106 SF1 Lumbar 4th I \ W —-— ——_ _‘_— SF1 Lumbar 5m SF1 Lumbar 6"1 Figure 46 Continued 107 SF1 Pelvic 15‘ .I ‘ _ . _.." SF‘IPericZ"d - ~ —_ —.—.—.—4’ - SF1Pe|vic4th Figure 46 Continued 108 SF1 Pelvic 5th SF1 Pelvic 6th Figure 46 Continued 109 SF1 Thigh 1st SF1 Thigh 2"d sr=1 Thigh 3rd Figure 46 Continued 110 SF1 Thigh 4“" SF1 Thigh 5th SF1 Thigh 6'“ Figure 46 Continued 111 l \. SF1 Thigh 7th E . \ _g__ ° // *Qézffiff SF1 Thigh 8”1 Figure 46 Continued 112 5.3.2 Large Male In the scaling process, the RAMSIS mid-sized male contour and posture were scaled to each large male subject’s contours. First the thorax contour of the RAMSIS mid-male was translated to coincide with the upper lumbar joint of the subject. A local thorax coordinate system was created at upper lumbar joint, X-axis pointing from upper lumbar joint towards lower neck joint and Y axis in lateral direction. Then the mid-male thorax contour was scaled up to the large male subject’s contour in the local thorax coordinate system, using the previously defined scaling factors. After this the scaled contour and posture were then aligned with the subject’s thoracic skeletal axis system. The lumbar contour of the RAMSIS mid-male contour was repositioned at the lower lumbarjoint of the large male subject. In the local lumbar coordinate system, which was originated at lower lumbar joint and with X axis pointed from lower to upper lumbar joint center and Y axis goes laterally. The lumbar contour of the mid-male was then scaled up according to the large male subject’s anthropometric data. The scaled lumbar and the posture were rotated to line up with the subject’s posture linkage. The pelvic contour of the RAMSIS mid-male was relocated at the center of the right and left H-points. Next, the pelvic contour was scaled up to the large male subject’s dimension in the local pelvic coordinate system. The mid-point of the right and left H-points was the center of the local pelvic coordinate system, and its X-axis was in the direction of the mid point to lower lumbar joint, Y in the 113 lateral direction. Then the scaled pelvic contour and the posture were brought into the line of subject’s posture linkage. The rest of the other large males’ results are documented in the Appendix 114 \ __// : } Tested :F ,. W (I f¥ ‘ § Scaled V E L .) ETD/UPS Figure 47 Measured and Scaled Subject 1’s Contour 115 Scaled .417 7' , 4414111114,] 1' ' TeSted / 'Wgw 2 l<: ETA/UPS Figure 48 Measured and Scaled Subject 1’s Contour 116 LM1 Thorax 1” \ / \ / wh ‘_’_——~_—-—‘§__’ LM1 Thorax 2"° LM1 Thorax 3” Figure 49 Tested and Scaled Contour Curves at Each Section of Large Male Subject 1 117 LM1 Thorax 4‘" LM1 Thorax 5m LM1 Thorax 6"1 Figure 49 Continued 118 LM1 Lumbar 1“ LM1 Lumbar 2"" I \ /.-——- \ LM1 Lumbar 3'" Figure 49 Continued 119 LM1 Lumbar 4'" LM1 Lumbar 5m LM1 Lumbar 6‘" Figure 49 Continued 120 \\ // LM1 Pelvis 1” l l I l l l \ / \ / \ / \\ // \\ \\ ———————— //// LM1 Pelvis 2"“ LM1 Pelvis 3'“ Figure 49 Continued 121 LM1 Pelvis 4m l I I I \ / \~ / \ / \\\\\ /// W LM1 Pelvis 5m l I I I \ / \ / LM1 Pelvis 6m Figure 49 Continued 122 \ ‘~—~._—.——-fl-’ LM1 Thigh 1" LM1 Thigh 2'“I LM1 Thigh 3'“ Figure 49 Continued 123 LM1 Thigh 4m LM1 Thigh 5‘" i ' ‘ . I \ / a”-\\' / ” ~\_/ LM1 Thigh 6tn Figure 49 Continued 124 LM1 Thigh 7‘n Figure 49 Continued 125 5.4 Correlation Comparison Between Measured and Scaled Contours When comparing each pair of curves of measured and scaled contours, the scaled curves typically matched to the measured contours within less than 15 mm. A further numerical correlation analysis [25] was performed to assess the quantitative resemblance between the scaled and the tested contour curves at selected sections of the contours. 5.4.1 Methods Three aspects of the geometric resemblance between the scaled and tested curves of the contours were considered. They were differences between scaled and tested curves, shape resemblances, and corridors with one and two standard deviations [26, 27]. The differences showed how far apart the curves were from each other numerically and graphically. The coefficient of the correlation was employed in the analysis of the shape resemblance as defined in the following section. The corridors with standard deviations described how closely the scaled contour curves were distributed in the space. The scaled and tested curves have respective magnitudes X3, and XM. So the coefficient of the correlation between the scaled and tested curves was SR defined as follows [26, 27]: ]:x,dex R = b b (22) Jjaxgdx L xadx or, 126 _ ZXSXMox R ’ ,5; 73px: xgax (23) If SR =1, the curves with magnitudes of X3 and XM had identical shapes. The values of SR were between 1 and 0. When SR = 0, it means that the two compared are not related to each other. For simplicity of comparisons and reduction of the amount of computational work, curves from sections 3, 4, and 6 in the thoracic region, 2, 4, and 6 in the lumbar region, and 4, 5, and 6 in the pelvis region, and 1, 4, and 7 in the thigh region were quantitatively analyzed. The procedures (MatLab program) [28] were used to perform the correlation analysis. 5.4.2 Correlation of Large Male and Small Female Contours 5.4.2.1 Differences The first comparison was to find out the difference, d, in the X direction between tested and scaled contoUr curves. Figure 50 and Figure 51 show typical plots of the difference (cl) in the midsections of thorax, lumbar, pelvis, and thigh for large males and small females. In the measured region of the body contour, the contour data were linearly interpolated every millimeter apart to provide a continuous curve. Then, at the same corresponding locations, the differences between points on the measured contours and the scaled contours were found and plotted. Almost all the differences (d) were within 10 to 12 mm. The rest of 127 the difference results are in the Table 6 for large males and Table 8 for small females, and the standard deviations of the differences can be found in the Table 7 and Table 9 for large males and small females, respectively. 128 20 l l l l T l l 15* 10- Difference (mm) 0 '5 + subj.1 + sub]. 2 -10 _ I . + subj. 3 — + subj. 4 * -¢— subj. 5 -15 i subj. 6 - ‘ > + subj. 7 l l l 50 1 00 1 50 200 _2 l 1 l 300 -150 -100 -50 0 Y (mm) (A) At Mid Thorax — Large Males Figure 50 Typical Difference Curves between Scaled and Measured Contour at Mid sections of Large Males 129 Difference (mm) Lumbar 20 l l l l I l l o~ -0- subj. 1 + subj. 2 + subj. 3 -5 “ + subj. 4 + subj. 5 + subj. 6 '10 ” + subj. 7 'ggoo -150 -100 -50 o 50 100 150 200 (B) At Mid Lumbar — Large Males Figure 50 Continued 130 Difference (mm) Pelvis 20 I l l l l l l 15- 1 — 10 _ + subj. 2 g ' j ->— subj. 3 ‘ —a— sub]. 4 _ - ' + subj. 5 _ 15 sub]. 6 —+— sub]. 7 _2 L I l 300 -150 -100 -50 0 50 100 150 200 Y (mm) (C) At Pelvis — Large Males Figure 50 Continued 131 Thigh 25 i i l l T l l Difference (mm) Y (mm) (D) At Mid Thigh — Large Males Figure 50 Continued 132 30 l l W i i -O- subj. 1 25’ + subj. 2 J ->- sub]. 3 20~ + subj.4 ‘ + subj. 5 15] subj. 6 ~ - —f- '. 7 1o '- 8 '. 9 Difference (mm) 01 0 -5 -10 I -15 [ 1 _ -2 I l l l I - 50 -100 -50 50 100 150 (A) At Mid Thorax — Small Females Figure 51 Typical Difference Curves between Scaled and Measured Contour at Mid sections of Small Females 133 Difference (mm) Lumbar 20 T fir T l 1 15 ._ . ‘ I . . . . ._ 10— . _ xi ’ 4‘ \ 5- _ 0- _ -5 — _ —0— _ 1 -1o — , —<— .2 - " + sub]. 3 * -15 — + subj. 4 _ + sub]. 5 _ _ + subj. 6 _ 20 -i- subj. 7 -+ sub]. 8 '25 h -x- subj.9 “ "3950 -100 -50 0 50 100 150 Y (mm) (B) At Mid Lumbar - Small Females Figure 51 Continued Difference (mm) Pelvis , “"’"’ -O- subj. 1 -5- ‘ +subj.2 * -- ->— subj. 3 + subj.4 '10 ‘ + subj. 5 subj. 6 —i— subj. 7 -e- subj. 8 -x- subj. 9 - 50 -100 -50 0 50 100 ' 150 (C) At Mid Pelvis — Small Females Figure 51 Continued 135 Difference (mm) Thigh 20 l T l l i 15- - 10 1 1 5 0 + sub]. 1 -5 r + sub]. 2 ~ ->- sub]. 3 ‘ + sub]. 4 -1° _ + subj. 5 ‘ subj. 6 _1 5 _ —i— subj. 7 _ i -O- subj. 8 . -*- subj. 9 _2 1 1 r r 4 r - 50 -100 -50 0 50 100 150 Y (mm) (D) At Mid Thigh — Small Females Figure 51 Continued 136 o m m m a m s o sushi N m N m N 2 o N N 5%: o o m N w a o o v 59.: N m N N 2 N v N N 5:: o m. 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N_>_Nn_ NNNN NNNN NNNN NNNN NNNN NNNN NNNN NNNN NNNN NNNN N253 NNNN NNNN NNNN NNNN NNNN NNNNN NNNN NNNN NNNN NNNN N253 83 N86 83 33 N86 N30 ammo mamd mag mmmd N .253 253 22.35 N .833 :8.sz N523 28.35 38.35 N 2.35 N .835 22.35 $00.33 0.0EON =0Ewi 530.0560 No 256580 NN 038. 144 5.4.2.3 Corridors There were always differences even though the contour curves were at the same relative sections and in one subgroup of subjects. Because the anthropometric dimensions were different from each other for the different subjects, the variability necessitates that corridors be created to represent the range of contour shapes at the interested sections. The average of the tested contour curves were first calculated at each section of interest. Then at each point (1 mm apart), the standard deviations of the tested data were computed, and were added to the average curves to construct the corridors. For the most of the scaled contour curves, they were within the corridors of tested average with i- 0'. See Figures 53, (A), (B), (C), (D), and Figure 54, (A), (B). (C). (D)- 145 (A) Scaled Curves and Corridors at Mid Thoraxes - Large Males Figure 53 Typical Corridor Plots at Mid Thorax, Lumbar, Pelvis, and Thigh of Large Males 146 (B) Scaled Curves and Corridors at Mid Lumbar -— Large Males Figure 53 Continued 147 ‘é’ (C) Scaled Curves and Corridors at Mid Pelvis — Large Males Figure 53 Continued 148 X (mm) (D) Scaled Curves and Corridors at Mid Thighs — Large Males Figure 53 Continued 149 (A) Scaled Curves and Corridors at Mid Thoraxes - Small Females Figure 54 Typical Corridor Plots at Mid Thorax, Lumbar, Pelvis, and Thigh of Small Female 150 I d .5 O r _'. N o T .‘a. .5 o r .13 0| 0 r L a o r .3 N O r (B) Scaled Curves and Corridors at Mid Lumbars - Small Females Figure 54 Continued 151 X (mm) -50 O 50 100 150 Y (mm) (C) Scaled Curves and Corridors at Mid Pelvis — Small Females Figure 54 Continued 152 '60” ."-e-Mean -- subj.1 . -- subj.2 £0- 3. . , __ SUbj.3 ._ ; . _ > 2 -- subj.4 , g g -- subj.5 , g _ ,. , i , -- subj.6 , . _ .. S . . 100 ' i -- subj.7 7 ---- subj.8 ---- subj.9 '12-’950 400 -50 o 50 100 150 Y (mm) (D) Scaled Curves and Corridors at Mid Thighs — Small Females Figure 54 Continued 153 5.5.1 Thorax In this region, the subjects’ backs came into contact with the chair usually after the 3rd section from the lower neck joints in this study. This is basically decided by the position of the lower neck joint with respect to the chair back. If the position of the lower neck joint is far away from the chair back, the subject’s back starts contacting the chair back at a lower point vertically on the chair back. After the 4"1 section, the contour shapes were less affected by the sitting postures of the subjects as can be observed in the Figures 44,45, 46, 47, 48, 49, and the rest of the figures in Appendices B and C. From the correlation analysis of the scaled and measured contour data, very good results could be seen from the 4th section down to the 6th section, which was the last section in this region. The average difference (d) of between the scaled and measured contour curves, presented in the Table 6, and Table 8, show that the contour data agree within 15 mm with standard deviation less than 10 mm after the 4th section. Table 10 and Table 11 list all the coefficients of the correlation of the correlation analysis between the swled and measured data. For the thorax region, all the coefficients are more than 0.95, which means that the curves are very highly related or resemble to each other. In the Figure 53 (A) and Figure 54 (A), most of the scaled contour curves are very close to the average measured curve within one standard deviation 0' . 154 5.5.2 Lumbar Because the bodies were in full contact with the chair back in the lumbar region, the back deformed shapes were well measured and well defined in this area, and the contour results were close to each other from the scaling and the testing. The differences between the scaled and measured contour curves were less than 12 mm and deviations less than 7 mm (Table 6 and 8). The correlation analysis results show that the contour curves have excellent resemblance, with the coefficient of correlation within the range of 0.989 to 0.999 (Table 10 and 11). The scaled contour cUrves were all within the corridors with 2 0'. 5.5.3 Pelvis In the current seat, the body segment in this region is not well supported by the seat. Orin this region, the body is not contacting the seat. See Figure 55. Obviously the body shapes were not well recorded and defined. Only after the 5th section in this area did the contour curves reflect subjects’ body shapes. That is why the coefficient of correlation started becoming close to 1 after the 4th sections as can be seen in the Table 10 and 11 for the small female data. 155 5.5.4 Thigh Seat back Sitter and seat surface i terface ’ ” I’ ’ In this region the boo was not well contacting Undeformed seat surface the seat surface Figure 55 Pelvis Region Not Well Supported in Seat In this area, the interface between the chair and sitter were in good contact conditions for most of the contours because of the presence of the foam. See the Figures 44, 45, 46, 47, 48, 49, and the rest of the figures in Appendices B and C. The differences (d) were less than 13 mm with maximum standard deviation 9 mm for large males, and the differences were less than 10 mm with maximum standard deviation 6 mm for the small females. However, at the front of the chair, the thigh postures affected the deformed thigh shape measurement simply because the thigh might not fully 156 contact the seat surface. So at the last sections of the contour curves, some deviation could be seen. In Table 10 and 11, some of the coefficients of correlation were below 0.9. 157 CHAPTER 6 CONCLUSIONS Both seating postures and seat contours are very important to seat design and seating comfort. The focus of this study was to determine (relative to a skeletal linkage) the contours between people and seats that are deformed by contact for a useful range of human subject sizes and postures. For this study, three representative human subject groups were chosen: 5"1 percentile small adult female, 50"1 percentile average adult male, and 95th percentile large adult male. Ten subjects from each anthropometric group were measured. To determine the seated contours, the subject’s posterior contours, including back, buttocks, and thighs, were acquired in a specially designed contour chair simultaneously with supporting force data from several load cells and posture data from a video system. The contour data from average size males were analyzed by section'ng splined surfaces into two—dimensional curves based on axes systems in major anatomical segments, thorax, lumbar, pelvis, and thigh. Even though human beings are not exactly symmetrical, the measured postures and contours were interpreted to provide symmetrical contours for development of the ASPECT manikin and RAMSIS computer models. These contours were compared to contours of the J826 SAE manikin. The thigh and buttocks surface contour of the ASPECT manikin was defined by selecting one subject’s contour, which was consistently nearthe middle of the nine subjects’ contours at each of several cross-sections of the thigh and 158 buttocks region; this was done to provide a contour that was realistic because the variation between subjects was small. Because of the greater number of mobile segments in the torso compared to the thigh and buttocks region, there are greater postural and contour variability in the back area. After the data were transformed, and scaled to the average distance between lower neck joint and mid-HJC, the back data and postures were averaged in the X direction (generally posterior to anterior direction) in each local segmental coordinate system to better represent the range of the variation. For the aesthetics in the development in the back contours for the RAMSIS model, the ASPECT back contours were adjusted a few millimeters, less than measurement variability. To develop the RAMSIS contour, the postural linkages of the contours by Frost and ASPECT contours were aligned and the differences between these contours were averaged to generate the RAMSIS contour. Both ASPECT and RAMSIS contours could be used for the applications of the seat design and all purposes of dummy design. Representations of mid-size males have been extensively used as the basis and starting point for design and evaluation of seating. Thus, it is very useful to explore the relationships between mid-size males and other commonly used human sizes, which are small females and large males. The present study is the first to scale mid-male contours to the anthropometric dimensions of small females and large males and to validate these scaled contours with the measurement data from small females and large males. A system was established in this study to scale the contours of mid-size males to represent 159 contours for small females and large males. In the scaling process, the body regions of mid-male’s thorax, lumbar, pelvis, and thigh were separately scaled to the anthropometric dimension of each individual subject in the small female or large male subgroups, and then rotated to align with the body postural linkage of the subject. Verified by the analysis of correlation, the scaling results were in very close agreement with the measurement data and most of the coefficients of correlation were within 0.95-0.99. The corridors were created to illustrate the possible range of contour shapes at the interesting sections. First, the average of the measurement contour curve was found at each section, and then the standard deviations of the measured data were computed, and were used to calculate the corridors. For most of the scaled contour curves, they were within the corridors of the measured average with :t a. In a few extreme cases, the maximum average difference between the scaled and measured contour curves was within 15 mm, and maximum standard deviations were 9 mm. Because of the closeness of the scaled contours to measured contours for this broad range of human sizes, the contours developed in this work for average size males can be used with confidence in computer models for scaling to represent people of different sizes such as small females and large males based on anthropometric dimension. This is a very useful result of a very simple scaling process to represent various human back contours. The sample sizes in the present study are limited, and future work could add confidence to representing and scaling human back contours. However, the contours and scaling provided- 160 in this study can be easily and usefully implemented in computer models such a RAMSIS. The contours provided by this study represent the interface between two deformable objects: seats and people. The back shape of the torso is highly dependant on posture, and these can be represented by the contours and skeletal linkage of this study. Consideration should be given to regional deformability. For a particular posture, the back of the torso (where the skeletal structures are close to the contact surface) is not highly deformable relative to regions beneath the buttocks and thighs (where pelvis and femurs are prominent only in the central regions). Also, the deformability of seats varies from place to place. So, the contours of this study should be used and interpreted with consideration of seat and body deformability. Future work could add useful represent of the defonnability of the human soft tissues and seats. 161 APPENDICES 162 APPENDIX A Scaling Factors Used for Scaling Procedures 163 NNN NNN NNN NNN NNN NNN NNN NNN 5.50 52.8 NNN NNN NNN NNN NNN NNN. NNN NNN £525 528 NNN NNN NNN NNN NNN NNN NN NN 59.3 533 NNN NNN NNN NNN NNN NNN NNN NNN 520 55.5 NNN NNN NNN NNN NNN NNN vNN NNN 5.505 55.5 NNN NNN NNN NNN NNN NNN NNN NNN 59.3 55; NNN NNN NNN VNN NNN NNN NNN NNN £20 520 NNN NNN NNN NNN NNN NNN NNN NNN 5525 520 NNN NNN NNN NNN NNN NNN NNN NNN 59.3 520 .55. .55. .55. .55. .55. .55. .55. .55. 5.22055 .13 N N... N 23 N 8:. N 3% N E: N 6.2. N 55.2-55. . Noam 5......sz 50.2w .8..sz .855 505% .855 50.35 50%.... 95.08 0.5.). 093 .3 30.20.55 zoom NN 0355 164 8. 3. SN «Pu SN mmm mmm 58 new 8N 2.80 0.88m $5 :5 55 :5 35 $5 «on 53, N8 85 “wwmhm 8 x. 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Es. .55. .55. .55. .55. .55. .55. 585885 0.2:. 2...... .0...» Cam 8me :0: f0; .00? .053 85.2-2.2 . >80 .8530 .8530 .8530 .8530 .8530 .8530 .8530 .8530 .8530 Swim... 9.30m .2560". =me .0. 0co_mc0E_o .68 m? 035... 165 APPENDIX B Scaled and Measured Small Females Results 166 ~- —. —-—-’a-.’/’ Figure 56 Female Subject 2 Rear View Figure 57 Small Female Subject 2 lso View 167 \ ‘.\ W W - \ --”’ SF2 Thorax 2"(1 SF2 Thorax 3" N - x l \‘\ J” ’/ \ ,fi" ' ‘ t “—- ..—— I, SF2 Thorax 4"1 SF2 Thorax 5" SF2 Thorax 6"1 SF2 Lumbar 1“ SF2 Lumbar 2"“ \ _ \j , . \§\\~——‘///\i SF2 Lumbar 3" Figure 58 Scaled and Measured Curves of Small Female Subject 2 SF2 Lumbar 4‘" . nd SF2 Pelvnc 2 \ / ‘ / “k [m ‘\ ll \Q 7/ \\ / WI/ \\\ ’x/ W SF2 Lumbar 5'“ SF2 Pelvic 3'“ -A \‘ I, _ l j \ \\ [I’m \\_\ - L'r‘. \ ‘ 2” v / SF2 Lumbar 6th SF2 Pelvic 4m ’ l A I | “\‘l . I ‘K 1' r... \K /./N \ \‘. ,. \ / W/ \\ -------- ”/ m SF2 Pelvic 1“ SF2 Pam 5 Figure 58 Continued 169 SF1 Thigh 4m \ / SF2 Thigh 5'" SF2 Thigh 6‘" \\ , Wk SF2 Thigh 7'h l \ ' " ' I / \ —————— // x W / SF2 Thioh 8‘" Figure 58 Continued 170 J... k i“? M) Figure 59 Small Female Subject 3 Rear View Figure 60 Small Female Subject 3 lso View 171 \ | I II \ \X x/ I W’, ~— SF3 Thorax 4m \\ I \\\ SF3 Thorax 5‘" SF3 Thorax 6"‘ I l _ ' 'N— k / \ / ’/ ~-.—-—--—’ SF3 Pelvic 1" l i i —\i\ - if.— I." \t I \ l \W SF3 Lumbar 2'” SF 3 Lumbar 3'“ Figure 61 Scaled and Measured Curves of Small Female Subject 3 \“ / w”! SF3 Lumbar 4" SF3 Pelvic 3'" ‘ I fl ‘\ ' [If-‘— WW, SF3 Lumbar 5" SF3 Pelvic 4'" \ “\‘X‘ . I; |\ I! \ \ ‘ —— ‘\§‘\‘\ W SF3 Lumbar 6m SF3 Pelvic 5“ l . , H ‘ ‘ I, \ I ‘x.\ 12‘.— I \§\\ // \\\\ \—-// SF3 Pelvic 1“ SF3 Pelvic 6" l‘ l _\ \ I c \\ //"~ \\ /) \\“__._ ____ ’// \\\\‘\‘ SF3 Pelvic 2"“ SF3 Thigh 1“ Figure 61 Continued 173 SF3 Thigh 2"1 SF3 Thigh 3" _—--- ‘ SF3 Thigh 4" SF3 Thigh 5" SF3 Thigh 6‘” SF3 Thigh 7‘h '—~. \-_—’ \ I \c——.—’ SF3 Thigh 8" Figure 61 Continue Figure 62 Small Female Subject 4 Rear View / i/-, - . / / / ‘1.“ /W Figure 63 Small Female Subject 4 lso View 175 ‘fi-p". \’ s ’ SF4 Thorax 1" SF4 Thorax 2"“ /"—‘\ , \\\____, sr=4 Thorax 3'" '- ~—’ sr=4 Thorax 4'" SF4 Thorax 5‘“ SF4 Lumbar 1" SF4 Lumbar 2‘” SF4 Lumbar 3'‘1 l l . \J SF4 Lumbar 4" -———fi 1 l \\ \\ sr=4 Lumbar 5" Figure 64 Scaled and Measured Curves of Small Female 4 "\X //‘“ .w SF4 Lumbar 6"1 SF4 Pelvic 6th : I \‘i . if. K I) \X / \\\\\\ ’I’l 14W ~ _-—— SF4 Fame 1“ SF4 Thigh 1:: l i i K I. at l LIE ‘\ i I \ \x X SF4 Pelvic 2"" SF4 Thigh 2nd I. \ \ // k g/ “2%— ‘ ‘\~ - -” SF4 POMC 5m SF 4 Thigh 3rd \ LE ‘\\\\ //l \\ ’1, ‘ \Vty/ SF4 Pelvic 3rd Figure 64 Continued 177 SF4 Thigh 5m \\ , SF4 Thigh 6"" \ \ ——————— / I v SF4 Thigh 7‘" \ '__‘ // SF4 Thigh 8'" Figure 64 Continued 178 Figure 65 SmalFemale Subject 5 Rear View 4 I l /” I z/I’ 1/1/ x /’ " ' ' ' I // ,/’/’ I / I [I I 1’ , / II a“ ’ I, I Figure 66 Small Female Subject 5 lso View 179 / ~ \ / \\ ,7/l \ / Th “ SF5 Lumbar 1" SF5 orax 1 “I: l: M _\\{ I, \ 4:'/ \\ “’// SF5 Lumbar 2"“ SF5 Thorax 2"6 SF5 Thorax 3'“ SF5 Lumbar 3'“ l l ._\\ _ I, —\ j j \\\ 1:1, / \~ -..-.._..-/ SF5 Thorax 5‘" SF5 Lumbar 4'h fi' . /————— —_\\ ' \\\\ I //’ M ‘W' ”'1 SF5 Thorax 4 SF5 Lumbar 5‘" Figure 67 Scaled and Measured Curves of Small Female Subject 5 180 —\\\\ I’l/ ._ __ SF5 Lumbar 6'” SF5 peMc 5th a: I: ,/"~_— \ // \\ //’/ ‘; I’II’, SF5 Pelvic 1st SF5 Pelvic 6'“ SF5 Pelvic 2"0 SF5 Thigh 1st I \ ia— \ - th SF5 Pelvrc 4 SF5 Thigh 2nd Figure 67 Continued 181 SF5 Thigh 3'“ SF5 Thigh 6‘“ W“‘—T‘J SF5 Thigh 7'“ SF5 Thigh 4th SF5 Thigh 8‘" SF5 Thigh 5m Figure 67 Continued 182 Figure 68 Small Female Subject 6 Rear View at \_ 2 7 75 Figure 69 Small Female Subject 6 lso View 183 \ 11,/P— \\ -- SF6 Thorax 1" i: : \‘ I‘, f“— 4, \-_ / SP6 Thorax 2"d \ ir— SF6 Thorax 3'‘1 ~— /' SF6 Thorax 4m SF6 Thorax 5"1 l l I l . [rm—— ’1 SF6 Lumbar 11“ SP6 Lumbar 2"“ SF6 Lumbar 3'6 SF6 Lumbar 4'h SF6 Lumbar 5th Figure 70 Scaled and Measured Curves of Small Female Subject 6 184 SF6 Lumbar 6th SF6 Pelvic 1st SF6 Pdvic 2"6 x ” ‘—_—_—-" SF6 Pelvic 3“1 SF5 Pelvic 4th SF6 Pelvic 5'h SP6 Pelvic 6'” SF6 Thigh 2"“ SF6 Thigh 3" Figure 70 Continued 185 SF6 Thigh 4m SF6 Thigh 7'" / \‘ ’ W x I ’ ‘ SP6 Thigh 6'" SF6 Thigh 5‘" .0...“ ’/ SF6 Thigh 6th SF6 Thigh 9'" Figure 70 Continued 186 Figure 71 Small Female Subject 7 Rear View Figure 72 Small Female Subject 7 lso View 187 SF7 Thorax 1“ SF7 Thorax 3rd I l \ \\\ / “A " SF7 Thorax 4'" ‘R SF7 Thorax 5m SF7 Lumbar 1" SP7 Lumbar 2"“ SF7 Lumbar 3'" SF7 Lumbar 4‘" SF7 Lumbar 5m Figure 73 Scaled and Measured Curves of Small Female Subject 7 SF7 Lumbar 6m \\ r“— \\ / \ W-.. ——-- ’ SF7 Pelvic 18t SF7 Pelvic 2"d SF 7 Pelvic 4‘" SF7 Pelvic 5'" SF7 Pelvic 6‘" L.— SF7 Thigh 1"t ' l \\ /’ SF7 Thigh 2"“ Figure 73 Continued 189 l ' ' - l I \\ \~\/\/ . rd SF7 Thigh 3 SF7 Thigh 7a.. . 4m 1‘ . . ' I W \\ /"-.‘\ //’ SF7 Thigh 5‘" . m SF7 Thigh 9 \ \\‘~ ””””” \ / SF7 Thigh 6'h Figure 73 Continued 190 Figure 74 Small Female Subject 8 Rear View . Figure 75 Small Female Subject 8 lso View 191 SF7 Thorax 1“ ___\‘ _ \\ /’/ RN ,- _ SF7 Thorax 2"d \LQJ \ SF7 Thorax 3'u 0 ———~‘ \ I; 1 I ~V’ /, SF7 Thorax 4'" SF7 Thorax 5‘" fi‘ . ’ \\ ‘ SF7 Lumbar 18t SF7 Lumbar 2"“ __~__'—\ \ . ‘. '\‘ / SF7 Lumbar 3'“ M b , ”M SF7 Lumbar 4'’1 SF7 Lumbar 5'“ Figure 76 Scaled and Measured Curves of Small Female Subject 8 _ \.‘ . N— \\ . ,’ .‘ t ,' \ l x \\ I / ’ \‘\ ’ // \——-- SF7 Lumbar 6"1 SF7 Pelvic 4th _.\ . fl \ . \ ’ SF7 Pelvic 1’" SF8 Pelvic 5m fl \i 8 'I’ . V - nd SF7 Pe'V'C 7- SF8 Pelvic 6'" \\|\ "I '\\ [I x _________ ;’//"— \‘ -—__ ,2 I - h SF7 P6|VIC 3‘ SF8 Thigh 15: Figure 76 Continued 193 r— _ or SF8 Thigh 2"(1 SP8 Thigh 6th SFB Thigh 3rd SFB Thigh 71h - m SP8 Thigh 4 SF8 Thigh 8‘“ \\ — ”// \\\\‘WM SP8 Th' h 51” '9 SP8 Thigh 9'“ Figure 76 Continued 194 Figure 77 Small Female Subject 9 Rear View \ /, .}‘ - __—_-g-fl-IP r’ .i. LM2 Pelvis 3'" LM2 Lumbii‘r 4“ I i ‘ l \ I 4 . / . x} \ LM2 Pelvis 4" LM2 Lamb?!r 5.. \‘ —l—— ”I \ . A, i f,"— ‘77 \ / q . 7‘wzu’l \\x\\.\~ a. // LM2 Pelvis 5... LM2 Lumbl‘ir 6“ I ‘ \ i I \ \ I, x “I \ ‘7‘» ..-r;.”’ J‘V + // ,——- \w:-':-'::"’ \ // ________ LM2 POWis 6“ LM2 PelViS 1“ \\ LM2 T1139h 1“ LM2 pelvis 2"“ Figure 82 Continued 202 C-‘ \ x «fl‘o- 4 ~‘_" 2. .—2’ x ...... ' ~~~~~ 0 \‘ \ ;’ \\~—u— ”-\ \v”’ ‘_._--—__t “_—” \‘-_” LM2 Thigh 2"“ LM2 Thigh 5" J I / i l l/ \ . '—‘~ I ,‘ ‘§ \‘. / \“\\__-" ‘~- -11" \ N“ I"\ -- .— z - rd LM2 Tr“9h 3 LM2 Thigh 6'“ i I I I i \ \ \ / I I I | \ \ \ . Ju'ul-j. .“J; - 3| LM2 Thigh 4" LM2 “"9" 7 Figure 82 Continued 203 Figure 83 Large Male Subject 3 Rear View Figure 84 Large Male Subject 3 lso View 204 LM3 Thorax 2"“ LM3 Thorax 6m LM3 Lumbar 1" LM3 Thorax 3" LM3 Lumbar 2"“ LM3 Thorax 4'” m LM3 Lumbar 3” LM3 Thorax 5 Figure 85 Scaled and Measured Curves of Large Male Subject 3 205 \x / \ _ l / I " v '\“‘...—_._——u—’" ‘~- \‘ .’- 4* ’..i‘ s ’ “ %—-_—_——‘M" "I LM3 Lumbar 6'" LM3 Thigh 5" l | I . ‘\ v \ ‘ l l ‘. ._\ ,. \ ' ' . I u} .I \ ,_.—: I \ 'I"~. / \\ ,-' ’1 ’/ ‘—' -A‘- ’9 ‘ur \ 1“ I ’ \‘-—--———-" ‘*~~_')~".~’ N""/' ' It ’ -~~‘~. \ I \ K ‘s ./ '~. \ I", I \p ’_ ""--"-" “-‘_>-t—" ‘3': ‘7' LM3 Thigh 2"“ LM3 Thigh 7m LM3 Thigh 3'“ Figure 85 Continued 206 Figure 86 Large Male Subject 4 Rear Wew Figure 87 Large Male Subject 4 lso View 207 LM4 Thorax 3"l LM4 Thorax 4m , \ / / W’ LM4 Thorax 6‘“ l l l l A \\ I ‘l\“\\\\_____._.——\_//// LM4 Lumbar 1st W70 LM4 Lumbar 2'” LM4 Lumbar 3 Figure 88 Scaled and Measured Curves of Large Male Subject 4 208 LM4 Lumbar 4"1 l l l l l l - I l l \ / \\ // \\ ————————— //// LM4 Pelvic 2"d \‘\\ /; \‘M/ LM4 Lumbar 5‘“ LM Pelvic 1“ LM4 Pelvic 3'“ LM4 Pelvic 4‘" l I \ / \ / A\§\ // / \\\\\_’/ LM4 Pelvic 5'" ‘~-————" LM4 Pelvic 6'“ Figure 88 Continue 209 LM4 Thigh 2"“ LM4 Thigh 5'" - ill LM4 Thigh 3'd LM4 ““9“ 6 LM4 Thigh 4th Figure 88 Continued 210 Figure 89 Large Male Subject 5 Rear View ”3 fl " , c/ATW/I/IW ’- \ 44.22/60 :« . I - ‘ . , - a Figure 90 Large Male Subject 5 lso View 211 \\ / "—‘\ //-———-/ W LM5 Thorax 2"“ l l i l I .. / \\\\ ///// ' LM5 Thorax 3’d / \ l l l\ I ‘\ \\ //,// \\“~- J LM5 Thorax 4'” I -— \ l - l \ / ‘7‘» \ / /—- “~\ / . ‘¥ 4,/ LM5 Thorax 5" I '\ .fi \ . \ ,1/ \\ \W LM5 Thorax 6'" LM5 Lmbar 1“ LM5 Lumbar 2"“ LM5 Lumbar 3'“ Figure 91 Scaled and Measured Curves of Large Male Subject 5 i I l i I \ - I \ ’/"/—‘ \ /’ Kw _//{l \\ ’1/ ‘ \\\\~_-”"”/ LM4 Lumbar 4‘" LM5 Pelvic 2'“1 i \ LM5 Pelvic 3”1 LM5 Lumbar 6m LM5 Pelvic 4m ' i ask [II /~_ \\\\ l/II/ LM5 Pelvic 1“t I-Nl5 Pelvic 5'" Figure 91 Continue 213 l I r . . l l \ . I \ I . \ / \ / / \ —— / ‘ \ / \ J \\ I I’ ‘ ~ _, " .. LM5 Thigh 5" LM5 Thigh 1" ’_———‘ LM5 Thigh 2“‘1 LM5 Thigh 6'h LM5 Thigh 3'" LM5 Thigh 7‘" LM5 Thigh 4‘" Figure 91 Continued 214 Figure 92 Large Male Subject 6 Rear View '--/ 4714'”- 1.. _ Figure 93 Large Male Subject 6 lso View 215 ‘ \ \‘\ é/ // \_.—_-”” LM6 Thorax 3n1 LM6 Lumbar 1“ LM6 Lumbar 2"d LM6 Thorax 4'“ Figure 94 Scaled and Measured Curves of Large Male Subject 6 216 / LM6 Pelvic 2nd ' I ‘ I W// \ I, \\ I LM6 LUmbar 4m \:\\ // QQ‘”?=_// LM6 Pelvic 3rd \\.\ . III l\ ll LM6 Lumbar 51h \ \\ / t\\:‘\\ /H/ W LM6 '38ch 41!: i i . l I'— + I” \\ /// LM6 Lumbar 6m LM6 Pelvic 5‘" Figure 94 Continued 217 \ \\\\“‘~ -- ””/y \_‘\\ /,/ \\\ Ill \ ___ ”/,/’ \ v” LM6 Thigh 1x LM6 Thigh 5'" i ll . | //,. \\ _ // \ "’ “ ‘ ‘9’; LM6 Thigh 2"“ LM6 Thigh 6" \\ . I, LM6 Thigh 3m LM6 Thigh 7‘" Figure 94 Continued 218 Figure 95 Large Male Subject 7 Rear View Figure 96 Large Male Subject 7 lso View 219 ‘-,.——"" ~’_~‘_ fl" LM7 Thorax 4" ’\ LM7 Thorax 6'" //_' \\ / / LM7 Lumbar 1“t LM7 Lumbar 2"“ LM7 Lumbar 3rd Figure 97 Scaled and Measured Curves of Large Male Subject 7 220 LM7 Lumbar 4'" LM7 Lumbar 5‘" I \ I i . II / \‘\\ 7/ w LM7 Lumbar 6'" LM7 Pelvic 1“t LM7 Pelvic 3'“ LM7 Pelvic 4" LM7 Pelvic 5'" Figure 97 Continued 221 LM7 Pelvic 6‘" I . t i I \\ l ' x/ \\ 4/ LM7 Thigh 1" \\ // LM7 Thigh 3" l I i I \\ I \ \ // W’” LM7 Thigh 2"d \\‘\\ "— ’/”//, LM7 Thigh 4'h \ - , / \\ // \\\ ’,/’ ~\ \\\\ 7 LM7 Thigh 5‘" LM7 Thigh 6m LM7 Thigh 7‘" Figure 97 Continued 222 LIST OF REFERENCES 1 S.A.E. Handbook 1980 - Part 2, Society of Automotive Engineers, Warrendale, PA. 2 Hubbard, R. P., M. P. Reed, etc., “ASPECT Task 1: Foundational Activities, Interim Report”, February 1997. 3 Hubbard, R. P., W. A. Haas, R. L. Boughner, R. A. Canole and N. J. 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