Multivariate Anthropometric Models for Soldier System Design, Testing, and Validation

1. Multivariate Anthropometric Models for Soldier System Design, Testing, and Validation Dr. Claire C. Gordon, Office of the Director Dr. Brian D. Corner, Science & Technology Directorate U.S. Army Natick Soldier Center (NSC) Soldier clothing, equipment, workspaces, and vehicles are increasingly treated as systems within systems. Integration of system components developed independently by different teams, contractors, and organizations is thus critical to successful performance at the system level. Engineering anthropometry is the study of human body dimensions for application to the design and sizing of clothing, equipment, crewstations and other work environments that must fit their human users well in order to meet performance expectations. In anthropometric terms, system integration means that each component, and the system as a whole, needs to fit its intended users. In order to achieve system level “fit”, it is important that requirements statements, design criteria, and the humans or human models used in testing & evaluations validly represent the same range of variation in body sizes and shapes expected in the systems’ users.   Using examples drawn from work done for the US Army Future Force Warrior and Future Combat System programs, this paper illustrates the need for multivariate statistical approaches in setting system wide anthropometric requirements, and demonstrates a valid method for establishing the extremes of body size and shape needed to specify design limits for complex systems such as those the Future Force will wear, drive, fly, and use. Methods for expressing these statistically valid (but two-dimensional) design specifications in three-dimensional tools used by engineers and designers are reviewed, including a discussion of the shortcomings of current parameterized human modeling systems, and of the possibilities and difficulties offered when statistically derived models are integrated with actual 3D human scans to represent design criteria. Soldier clothing, equipment, workspaces, and vehicles are increasingly treated as systems within systems. Integration of system components developed independently by different teams, contractors, and organizations is thus critical to successful performance at the system level. Engineering anthropometry is the study of human body dimensions for application to the design and sizing of clothing, equipment, crewstations and other work environments that must fit their human users well in order to meet performance expectations. In anthropometric terms, system integration means that each component, and the system as a whole, needs to fit its intended users. In order to achieve system level “fit”, it is important that requirements statements, design criteria, and the humans or human models used in testing & evaluations validly represent the same range of variation in body sizes and shapes expected in the systems’ users.   Using examples drawn from work done for the US Army Future Force Warrior and Future Combat System programs, this paper illustrates the need for multivariate statistical approaches in setting system wide anthropometric requirements, and demonstrates a valid method for establishing the extremes of body size and shape needed to specify design limits for complex systems such as those the Future Force will wear, drive, fly, and use. Methods for expressing these statistically valid (but two-dimensional) design specifications in three-dimensional tools used by engineers and designers are reviewed, including a discussion of the shortcomings of current parameterized human modeling systems, and of the possibilities and difficulties offered when statistically derived models are integrated with actual 3D human scans to represent design criteria.

2. 2/1/2012 2 Anthropometry for the Soldier

3. 2/1/2012 3 Anthropometric Design Process Measurements relevant to product design Samples representative of the intended users Clearly defined accommodation targets Statistically valid models of body size variation Systematic application of the anthropometric data Early and ongoing design & sizing evaluations

4. 2/1/2012 4 Deriving Design Values What percentage of users must you fit? higher rates require adjustability and/or more size categories lower rates influence user performance, safety and satisfaction US Army targets 98% for life support equipment; 90% all other A serious but common mistake: relying on 5th to 95th percentiles Why use multivariate methods? to ensure valid accommodation rates to identify true “worst case” sizes and shapes to provide additive and proportionally realistic design values

5. 2/1/2012 5 Sequential Reduction in Accommodation Using Percentiles*

6. 2/1/2012 6 Non-Additivity of Percentiles*

7. 2/1/2012 7 5th/95th Percentiles Fail to Capture Shape Extremes Zehner GF, Meindl RS, and Hudson JA (1992) A Multivariate Anthropometric Method for Crew Station Design: Abridged. Technical Report AL-TR-1992-0164, Wright-Patterson Air Force Base, OH. AD A274 588. Zehner GF, Meindl RS, and Hudson JA (1992) A Multivariate Anthropometric Method for Crew Station Design: Abridged. Technical Report AL-TR-1992-0164, Wright-Patterson Air Force Base, OH. AD A274 588.

8. 2/1/2012 8 A Multivariate Alternative

9. 2/1/2012 9 FCS Common Crewstation

10. 2/1/2012 10 Principal Components Analysis ANSUR data demographically weighted; adjusted to 2015 Sexes analyzed separately (n=3458 females, 5077 males) PCA conducted on the correlation matrix Three components retained for each sex The male and female PC models each explain 91% of original variation

11. 2/1/2012 11 Male PCA for FCS Crewstations

12. 2/1/2012 12 Understanding the PCA

13. 2/1/2012 13 Defining Extreme Forms

14. 2/1/2012 14 Model Specifications Both theoretical values and actual body dimensions of nearest neighbors can be used The body dimensions of theoretical extremes are calculated using the eigenvectors Nearest neighbors capture more variety than theoretical extreme forms because the PCA model accounts for < 100% variation Nearest neighbors represent “real people” - nothing smoothed or estimated Scanning technology can provide solid models of neighbors or statistical values can be used to create parameterized models In a recent application, we used NBR median values to expand the PCA model to include some 30 variables needed by a commercial manikin manufacturer to build custom manikins for clothing designers. Both theoretical values and actual body dimensions of nearest neighbors can be used The body dimensions of theoretical extremes are calculated using the eigenvectors Nearest neighbors capture more variety than theoretical extreme forms because the PCA model accounts for < 100% variation Nearest neighbors represent “real people” - nothing smoothed or estimated Scanning technology can provide solid models of neighbors or statistical values can be used to create parameterized models In a recent application, we used NBR median values to expand the PCA model to include some 30 variables needed by a commercial manikin manufacturer to build custom manikins for clothing designers.

15. 2/1/2012 15 How are the PCA Models Used? Central Forms Represent multivariate center of the distribution of critical dimensions Optimal center for both sizing systems and equipment adjustments Starting point for concept development and component integration Boundary Forms Represent worst case scenarios of size and shape Establish limits of sizing systems & ranges of adjustment Establish the body dimension ranges required of test subjects Distributed Samples from within the Ellipsoid Virtual fit testing Sampling strategies for test subjects

16. 2/1/2012 16 Physical Models: Manikins

17. 2/1/2012 17 Crewstation Design & Modeling Blackhawk & Comanche Crewstations Live accommodation testing subjects plotted within PC space to estimate % of population accommodated vs. cost of revisions to reach boundary envelopeBlackhawk & Comanche Crewstations Live accommodation testing subjects plotted within PC space to estimate % of population accommodated vs. cost of revisions to reach boundary envelope

18. 2/1/2012 18 FCS Modeling

19. 2/1/2012 19 FFW Modeling

20. 2/1/2012 20 Advantages of the PCA Method Direct relationship between rate of accommodation desired and models used for design & testing Shape extremes are addressed directly Boundary Forms have realistic body proportions Enables a powerful synergy between multivariate statistics & 3D technologies to optimize design & sizing

21. 2/1/2012 21 Methodological Remarks Requires relatively large sample sizes, access to individual data Methodological decisions critical to technique success require sophisticated knowledge of human variation and its application to sizing and design Central & Boundary form information alone is not usually sufficient to optimize an ergonomic design, which can be misleading to naïve users In short, this is a method best used by experts Critical Decisions Variable selection Separate male & female PCAs Form selection from multiple PCAs What Central & Boundary Models alone can’t do… Determine how many sizes are needed to properly fit the subjects inside the accommodation boundary – this depends on the item & its function Determine optimal grade rules for critical pattern dimensions Determine optimal relationships among workstation adjustments for different body dimensions Determine how fine the adjustments need to be to properly fit the subjects inside the accommodation boundary – again this depends on the item & its function Critical Decisions Variable selection Separate male & female PCAs Form selection from multiple PCAs What Central & Boundary Models alone can’t do… Determine how many sizes are needed to properly fit the subjects inside the accommodation boundary – this depends on the item & its function Determine optimal grade rules for critical pattern dimensions Determine optimal relationships among workstation adjustments for different body dimensions Determine how fine the adjustments need to be to properly fit the subjects inside the accommodation boundary – again this depends on the item & its function

22. 2/1/2012 22 For Further Information Bittner AC, Glenn FA, Harris RM, Iavecchia HP, and Wherry RJ (1987) CADRE: A family of manikins for workstation design. In SS Asfour (ed.) Trends in Ergonomics/Human Factors IV. North Holland: Elsevier, pp. 733-740. Gordon, C.C. (2002) “Multivariate Anthropometric Models for Seated Workstation Design”. In Paul T. McCabe (ed): Contemporary Ergonomics 2002, pp 582-589. London: Taylor & Francis. Gordon, C.C., Corner, B.D., & Brantley, J.D. (1997) Defining Extreme Forms for Designing Body Armor and Load Bearing Systems: Multivariate Analysis of Army Torso Data. NATICK/TR-97/012. Natick, MA: U.S. Army Soldier Systems Command, Natick Research, Development, and Engineering Center. (AD A324 730)

23. 2/1/2012 23 For Further Information HFES 300 Committee: M. Dainoff, C.C. Gordon, K. Robinette, & M. Strauss (2004) Guidelines for Using Anthropometric Data in Product Design. Santa Monica CA: Human Factors and Ergonomics Society. Kozycki, R. & Gordon, C.C. (2002) “Applying human figure modeling tools to the RAH-66 Comanche Crewstation Design”. Proceedings of the 2002 SAE Digital Human Modeling Conference, pp. 191-200. Warrendale, PA: Society of Automotive Engineers. Zehner G.F., Meindl R.S., & Hudson J.A. (1992) A Multivariate Anthropometric Method for Crew Station Design: Abridged, AL-TR-1992-0164. Wright-Patterson Air Force Base, OH: Armstrong Laboratory. (AD A274 588)