Presentation on theme: "Assessment and Design Anthropometry Physiology of Work Ergonomic/Anthropometric Assessment Design of Work."— Presentation transcript:
Assessment and Design Anthropometry Physiology of Work Ergonomic/Anthropometric Assessment Design of Work
Anthropometry The science of measurement and the art of application that establishes the physical geometry, mass properties, and strength capabilities of the human body (Roebuck, 1993) Anthropos = human metricos = measurement Uses/applications for measurement Design, criminology, medical practice, personnel selection
What defines the human being anthropometrically? Physical Measurements Wide range of sizes Proportions of various body dimensions Mobility Strengths Human Sensing and Performance Capabilities Physiology Psychology of Comfort and Perception e.g., three dimensional spatial locations of the eyes so as to determine what can be seen and thereby identify obstructions that limit vision and cause error
Anthropometry helps to Evaluate postures and distances to reach controls Specify clearances separating the body from hazards such as surrounding equipment Identify objects or elements that constrict movement Assess the biomechanical forces and torques during manual material handling, operator fit in vehicles, accommodation comfort, and general human performance Assist in the design of tools to be grasped and handles that can be grasped or readily operated Help clothing designers develop better fitting garments and make it easier for clothing buyers and military quartermasters to know how many of what sizes to procure Provide numerical data permitting a person’s body dimensions to seat heights, breadths, depths, and support angles (studies have shown that ranges of these values correlate closely with comfort/discomfort according to the activity performed in the seat.
History of Anthropometry An outgrowth of physical anthropology Developed 200 years ago to distinguish among the races and ethnic groups of humans, identify criminals, and aid in medical diagnosis More recently used in developing engineering design requirements and evaluation of modern vehicles, work sites, equipment, and clothing (Roebuck, Kroemer, and Thompson, 1975), evaluations of cockpits and clothing were strongly supported and determined by military needs during and following World War II (Hertzberg, 1955) Many modern applications are to commercial and civilian equipment, vehicles, and clothing (CAD Modelling, 1992; Czaja, 1984; Roe, 1992; Sanders and Shaw, 1985).
History of Anthropometry Anthropometric studies are fairly infrequent and lack the prominence in academic anthropology – tend to be more technical papers Considered a developing science where certain aspects of he subject matter of anthropometry qualify it as an historical science (anthropometric surveys are in many ways historical events and can never be repeated in exactly the same way, even on the same people due to developmental changes. Consequently, populations are frequently identified by year of measurement, by occupation, and by ethnic group. Body dimension surveys serve as benchmarks against which new survey data can be compared and can be used to trace and predict the microevolution of human groups.
Electronic Modeling and New Measurement Technologies Technological innovations are changing the use of anthropometry in engineering applications Computer modeling of people as substitutes for living humans in computer-aided design (CAD) for human factors applications Use of new electronic imaging methods for measurement 3-D visualization and statistical manipulation of body sizes and shapes Widespread attempts to develop graphical computer models of the human body forms and functions Becoming a new design approach called “concurrent design” or “simultaneous engineering” (Boyle, Ianni, Easterly, Harper, and Korna, 1991; Majoros, 1990; Roebuck, 1991) Major goal is to complete engineering analyses before spending a large percentage of the project funds on construction of physical mockups, prototypes, or products (e.g., Boeing 777 and 787) Ergonomics today cannot rely as heavily on the responses and fit of living subjects in mockups Leading to models of human responses and size variations into electronic models of humans
Electronic measurement and modeling Focusing attention on past and current deficiencies of anthropometric data gathering, reporting and application methods Creating new demands for more comprehensive, integrated data 3-D measurements of body surface contours and landmarks Location of internal joint centers of rotation Determination of interjoint link lengths and orientations Need for data on the effects of changes in orientation, pressures on external surfaces on body flesh, environmental effects, clothing shape, and new concepts for body support
Computer Modeling Historically, it has been common to have different sets of data and models for each application area (e.g., work space or clothing) Developments in computer models and data-handling technologies offers new opportunities for using large, central mathematical databases and more integrated, comprehensive representations of the human form Potentially useful for design of clothing, work space, tools, and equipment Frequently require more data than available from most surveys Data need to be in three dimensions and to describe ranges of movement for joints When a great deal of contour data are known (up to 5000 points), it has generally not been at the key cross-sections desired (passing through joints or a specified percentages of distance between joints) or related to internal links and joint centers Lack of data and large individual differences result in contour data cannot be readily analyzed using conventional statistics
New Approaches Development of typical sets of equations that describe general form functions common to many different people Standard sets of internal coordinate systems related to joint centers and vectors connecting them Modelers hope to more completely specify body shape, size, and postures without incurring excessive cost to gather, analyze, and publish data Potential to improve our understanding how the geometry of human bodies may be defined in terms of statistical variables and functional mechanisms
Benefits Computer modeling offer enhancements to: Sports performance Design of personal protective gear Design of clothing Design of medical prostheses and medical equipment Design of tools and assembly jigs Design of vehicle interiors
Measurement Technology Started as simple body measurements Standardization required focus on body landmarks Usefulness required understanding of joint movements, associated torques and stresses New measurement techniques include use of lasers, stereo video, structured light, flying-spot light beam, magnetic resonance imaging (MRI), computer aided tomography (CAT) scanning, special X-ray methods, ultrasonic visualization, sonic digitization, movement measurement methods Most new methods couple computers to sensors in ways that produce digitized data, points, and pixels located in three- dimensional space. Significantly more data than single or two dimension methods. New measurement capabilities complement new data needs but pose problems for comparing/understanding data produced by older, manual methods
Knowledge and Skill Requirements Traditional measurement requires knowledge of anatomy, especially locations, names, and shapes of bones and muscles Understanding of how to read measurement scales, how to measure weights, how to handle instruments. Advanced technologies require understanding principles of electronics, lasers, photography, video devices necessary Statistics knowledge to plan measurement surveys, reduce data and analyze data, forcast and estimate values Helpful to have successful planning experience dealing with prioritization of time and processes in an efficient and effective order Artistic, line-drawing skills to depict measurement equipment and how it is used for scientific illustration
Knowledge and Skill Requirements Knowledge of mathematics (algebra, geometry, and trigonometry), mechanical aspects of physics, mechanical engineering principles and practices Need to be able to read engineering orthographic drawings and understand the concepts of mass properties, force, and torque Talent for visualizing geometric relationships and performing elementary design work for planning mockup evaluations Ability to perform hands-on construction of models, special measurement devices, full-scale mockups from a variety of materials Since many techniques require touching people and directing their movements to assume certain postures, need to be able to explain your activity in a credible manner Must be able to develop a friendly relationship with subjects while maintaining a professional attitude
Planning for Measurements Fundamental requirement when selecting measurements and methods is to plan ahead to satisfy users of the data produced Imagine future applications Perform task analyses on future uses of the data Ask potential users what they need (face to face or use of questionaire After list of perceived needs is compiled, creative methods to estimate some dimensions may be developed to help limit the number and kind of dimensions to be measured (use the systems approach)
Remember that most anthropometric measurements represent samples taken at one point in time (cross-sectional survey). Rarely are individuals tracked in a longitudinal survey Sequential surveys will reveal changes in means, variabilities, correlations, and proportions of body parts that may be caused by attrition from death, illness, disinterest, aging, selection, or dietary changes. Remember there are significant changes in proportions of different racial and ethnic groups surveyed at different times that may affect body proportion averages Remember to consider these changes not only when deciding on sampling procedures but also when assessing the accuracy and meaning of available anthropometric data. This is especially important with regard to age brackets because of relatively rapid changes during youth and extreme age
Elements of a Measurement Plan Varying degrees of planning required Facilities, subjects, paperwork to recruit subjects, legal release of data, purchasing or building instruments/equipment, obtaining services of those who will measure/analyze data Scheduling transport, arranging for housing, feeding, sanitation, and thermal comfort of subjects; scheduling and distribution of work of the measurers, checking data before entry into records, recording data efficiently
Facilities Private space for disrobing Adequate room for stands, jigs, chairs, desks, and other furnishings Storage of instruments and supplies Workload and time required at each station (if more than one) for balanced, smooth flow of subjects through facility To limit confusion caused by audible reading of instructions and measurements, recommend use of separate rooms when more than one subject being tested at the same time
Equipment Measuring team must obtain/have available anthropometric instruments and chairs, tables, jigs, and fixtures in a sufficient number for each measuring site plus spares Computers at each station for checking and recording data (eliminates transcription of data Forms, recording sheets, other supplies may also be needed
Checking Software and Procedures Remember, every measurement instrument made by human beings is subject to error. Misread scales Transposed digits Judgment/rounding Subjects may make inadvertent motions or measures may be inconsistent based on the pressure applied (Gavan, 1950). There are tables of expected and acceptable variations in measurement for each dimension (Gordon, 1988; Gordon and Bradmiller, 1992) as well as accuracy summaries of various scales
Procedures (continued) Desirable to perform each measurement twice and compare the results to see if the readings are the same or acceptably close Computers and some software available allow comparison of detected measurements against detected measurements to identify potential errors. Software may also accumulate data as measuring proceeds and develop a continually updated prediction of expected population statistical extremes (e.g., 2-3 standard deviations) for each dimension measured. As collection continues, software may be able to calculate dispersion values around average trends (regressions of one dimension on one or more others). (Churchill, et al., 1988). May consider regression formulas to test for outliers or deviant measures to be expected in a population of measures
Personnel Each measuring site typically requires two people: one to record and one to conduct measurements. If complicated adjustments are required, a third technician may be needed. Best if a female measurer works with female subjects and a male conducts measurements on male subjects especially when measurements are made in sex-sensitive areas May consider a receptionist to manage scheduling and appearance times, for paperwork management, and for answering questions at the beginning of the measuring process. Subject selection is a key concern and may require several recruiters.
Training Measurers need to be trained in proper techniques and tested to assure the principal investigator that all are using the same techniques Consistancy among measures requires hours of practice. PI needs to check that each measurer will obtain the same results with repeated measures. Training time will depend on new skills to be learned and personnel background. May consider preparing a videotape of the measurement methods as a more feasible and cost effective method of training Video taped records of measuring may also serve as an effective supplement to written documentation of methods used in the survey and can be very helpful in standardizing data (Gordon et al., 1989a, 1989b). This becomes increasingly important with large surveys.
Scheduling The number and relative complexity of measurements should be divided equitably among the measuring teams to make efficient use of their time and ensure a smooth flow of subjects Commonly the measurer and recorder alternate tasks after a suitable period (say an hour) to reduce fatigue and boredom Scheduling should consider procedures for ensuring health and safety. When direct contact methods are used, provisions should be made to prevent the transmission of disease. Instruments should be wiped with alcohol before each use Consider giving subjects disposable paper slippers and washable shorts
Administrative Concerns Need to consider and resolve and problems with: pay (unless volunteers are used) Lines of authority Permission to use buildings and rooms Scheduling of work hours Ensure that the planning efforts are carried out through effective and timely actions by all involved in the surveys
What to Measure? When planning an anthropometric survey, developers are faced with conflicting goals in deciding what parts and attributes to measure. Industrial Applications – workplace design Body segment lengths and heights Some breadths Some depths Few circumferences Clothing Design/Size Distributions Circumferences Surface areas Few lengths and heights
Physiological Studies Volumes Densities Areas Computer Modeling – workspace design/manual materials handling Joint centers of rotation Inter-joint link lengths relative to skin surfaces Offsets in relation to consistent, 3D coordinate systems
Regardless of the measurement devices/media used, the question of what to measure for engineering anthropometry MUST include postures Standing posture Standard upright sitting posture Certain postures that permit maximum reach with the arms and legs Future needs for the location of joint centers may dictate several different postures for each joint that can be flexed or extended in order to locate effective centers of joint rotation. Ideally, a full set of contours for the entire body should be scanned in several postures to provide details of body cross- sections so that joint centers of rotation can be derived. Models incorporating a full set of contours for the whole body may prove useful in many different applications These ideas have rarely been achieved due to the constraints of time, money, and available technology If contour data are not gathered, measures should obtain many more depths, breadths, and offsets than is typical of current practice.
Historical Practice and Measuring Standards Standard measurements needed for comparative purposes and forecasting trends Ideas about which dimensions should be standard have gradually changed with purposes of anthropometric measurements Major shift in goals for the use of data away from purely scientific studies of differences among peoples of various parts of the world toward engineering applications (which are also changing
Surveys done by/for the USAF present high quality documentation Good for teaching about commonly used measurement methods and instruments Frequently include text and illustrations of techniques with line drawings and photographs Anthropometric Standardization Reference Manual (Lohman, Roche, and Martorell, 1988) is a more readily accessible commercial publication Book includes pictures and illustrations Emphasizes measurements of interest for sports medicine and performance rather than design of work space and clothing
“What are the accepted standards for measurement naming, measurement selection, and measurement methodology?” Titles of landmarks and measurement methods written in German by Martin (1928) and later revised (Martin and Knussman, 1988; Martin and Saller, 1957) (out of print). Certain general approaches to establishing names for dimensions have evolved and appear consistently throughout the literature on physical and engineering anthropometry. Various compilations but little consensus “Anthropometric Source Book” (NASA, 1978a,b,c) Electronic Human Modeling (CSERIAC, 1991) workshop but mainly concerned with medical imaging and software communication standards rather than anthropometry for design
Society of Automotive Engineers (SAE) held meetings (1990) for setting standards and naming anthropometric dimensions, performing measurements, and selecting a preferred minimum list of measurements Various source books (Donelson and Gordon, 1991; Gordon et al., 1989a,b; Clauser et al., 1987) illustrate the various landmarks (key features marked on the body prior to measurement) used to identify locations of underlying bone features Although many measurements are common to all past large-scale military surveys, some notable exceptions influence applications of data to design (e.g., Waist Height and Buttock-Heel Length)
Waist Height Either of two easily confusable measurements may sometimes be erroneously listed simply as Waist Height Dimension name should indicate which of two common landmarks was used for the Waist Height measurement Naval (omphalion in some reports) Natural Indentation – place where the middle portion of the trunk is narrowest (as seen from front or back) and where the circumference is generally smallest). Difficult to locate on very obese persons (often resulting in arbitrary decision Often easy to locate on military personnel Can be defined as half the between the 10 th rib and top of the pelvis (iliocristale) Place an elastic cord with round cross section, adjust its length to apply moderate tension, release tension, cord will see the height with the smallest circumference) – height then marked and circumference measured with a tape.
Buttock – Heel Length A subtle problem relating to definition of measurement and postures used in measuring and the ultimate use of the data used. Buttock-leg length, buttock-heel length, functional leg length, total leg length. CAD generate models and drafting manikins is a theoretical upright sitting posture with legs fully extended forward at the knee would be desirable (note, upper and lower legs in alignment and the sum of the distances from heel to hip joint (approximately equal to Trochanteric Height) could be subtracted from Buttock- Leg length to determine horizontal location of the hip joint Knee bent posture is more realistic when back is upright Men cannot actually achieve the extended posture when sitting with a hip angle of 90 degrees (mean is 2.3 cm longer than the theoretical length with sd of.64 greater
Clauser is yet another solution but introduces error in average length of perhaps 2.2 cm depending on the angle of the leg from horizontal Perhaps consider Idealized Buttock-Heel length by adding Buttock-knee length to Flexed knee-heel length, standing (which can be either difference between Stature and Kneeling Height to determine Flexed Knee-heel Length standing. Issues of sitting heights are lack of weight on the heal pads and joints and subtle leaning postures involved in stable standing orientations that can produce small changes in overall length. Joints measured landmark to landmark are often slightly longer With increased accuracy requirements come more careful and detailed attention to effects of posture and gravitational load on differences between landmarks.
Summary For each population, you must read the descriptions of how the measurements were made Researchers and writers dealing with anthropometry should Attempt to use standard methods when possible Accurately describe each measurement method used, especially if it is unusual or if no commonly recognized standard is available; Locate all such descriptions together in reports and handbooks so that they can be readily compared.
Assignment Next time we meet, be prepared to conduct some anthropometric dimension measurements Each of you should be dressed or be prepared to change into some athletic clothing, preferably thin cloth (like running pants) You should be prepared to be both a “Subject”, a “Measurer”, and a “Data Collection Agent” We will shift roles as we measure various anthropometric dimensions