PRODUCT DESIGN

Anthropometric Data and Use

Several large-scale anthropometric studies were conducted in the 1960s and 1970s, mostly in industrialized countries. Contemporary studies are typically of smaller scope, with the exception of the ongoing CAESAR (Civilian American and European Surface Anthropometry Resource) project (http: / / store.sae.org/ caesar / ). Anthropometric data are generally presented in tabular form, with some combination of means, standard deviations, and population percentiles. A normal statistical distribution is usually assumed, a simplification which is reasonable in most cases, though which also leads to larger magnitudes of errors at extremes

of populations (e.g., the largest and smallest individuals).

Standard statistical methods can be employed directly for a number of applications. If, for example, we wish to design the height of a doorway to allow 99% of males to pass through unimpeded, we can estimate this height from the mean ( ) and standard deviation ( ) as follows (again assuming a normal distribution). Male stature has, roughly, 175.58 and 6.68 cm. The standard normal variate, z, is then used along with a table of cumulative normal probabilities to obtain the desired value:

where zA is the z value corresponding to a cumulative area A and Y is the value to be estimated. Here, z0.99 2.326, and thus Y 191.1 cm, or the height of a 99th percentile male. Clearly, however, further consideration is needed to address a number of practical issues. These include the relevance of the tabular values, whether this static value is applicable to a functional situation, and if /how allowances should be made for clothing, gait, etc.

Percentile calculations, as given above, are straightforward only for single measures. With multiple dimensions, such as several contiguous body segments, the associated procedures become more involved. To combine anthropometric measures, it is necessary to create a new distribution for the combination. In general, means add, but variances (or standard deviations) do not. Equations are given below for two measures, X and Y (a statistics source should be consulted for methods appropriate for n 2 values):

where indicates addition if measures are to be added and subtraction otherwise, cov is the covariance, and r is the correlation coefficient. As can be seen from these equations, the variance ( 2) of the combined measure reduces to the sum of the individual variances when the two measures are independent, or cov(X,Y) rXY 0. Human measures are generally moderately correlated, however, with r on the order of 0.2–0.8 depending on the specific measures.

Maury A. Nussbaum

Industrial and Systems Engineering

Virginia Polytechnic Institute and State University

Blacksburg, Virginia

Jaap H. van Diee¨n

Faculty of Human Movement Sciences

Vrije Universiteit

Amsterdam, The Netherlands

Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.

Edited by Myer Kutz

Anthropometry

Fundamentals of Anthropometry and Measurement Anthropometry is the science that addresses the measurement and/or characterization of the human body, either individually or for populations. Engineering anthropometry is more application oriented, specifically incorporating human measures in design Examples include placement of a control so that most individuals can reach it, grip sizing for a hand-held tool, and height of a conveyor. Within ergonomics, anthropometric measures can be classified as either static or functional. The former are fundamental and generally fixed measures, such as the length of an arm or a body segment moment of inertia. Such static data are widely available from public and commercial sources. Functional measures are obtained during performance of some task or activity and may thus depend on several individual factors (e.g., training, experience, motivation). These latter measures are specific to the measurement situation and are hence relatively limited. Despite the availability of static measures, it is the functional measures that are directly relevant in design. The remainder of this section provides an overview of applied anthropometric methods. Results from anthropometry will also be critical in subsequent sections that address mechanical loading during task performance.

Static anthropometric measures are of four types: linear dimensions (e.g., body segment lengths), masses or weights, mass center locations, and moments of inertia. Linear dimensions can be obtained quite simply using tape measures or calipers, with more advanced recent approaches using three-dimensional (3D) laser scanning. A key issue with respect to linear dimensions is the differentiation between surface landmarks and underlying joint centers of rotation. The former are easily located (e.g., the lateral and medial boney ‘‘knobs’’ above the ankle joint), and methods have been developed to translate these to estimates of underlying joint centers that are required for biomechanical modeling (Section 2.4).

Mass (and/or volume) measures are often obtained using liquid immersion, though as

noted above, recent scanning methods are also being employed. Locations of segment (or whole-body) center of mass can also be obtained using liquid immersion and a number of segmental balance methods. Segment moments of inertia are usually obtained using dynamical tests, where oscillatory frequencies are obtained during natural swinging or following a quick release. Representative geometric solids (e.g., a truncated cone) can also be used to model body parts and obtain analytical estimates.

Maury A. Nussbaum

Industrial and Systems Engineering

Virginia Polytechnic Institute and State University

Blacksburg, Virginia

Jaap H. van Diee¨n

Faculty of Human Movement Sciences

Vrije Universiteit

Amsterdam, The Netherlands

Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.

Edited by Myer Kutz

PHYSICAL ERGONOMIC ANALYSES

Overview

In this section we present several of the more common ergonomic methods, tools, and procedures. A focus is maintained on material that is directly relevant to design. In each section, a review of the underlying theory is given, followed by exemplary approaches (e.g., empirical equations or models). In some sections, sample applications to occupational tasks or scenarios are given. Sources of additional information are provided at the end of the chapter.

Anthropometry

Fundamentals of Anthropometry and Measurement Anthropometry is the science that addresses the measurement and/or characterization of the human body, either individually or for populations. Engineering anthropometry is more application oriented, specifically incorporating human measures in design Examples include placement of a control so that most individuals can reach it, grip sizing for a hand-held tool,and height of a conveyor. Within ergonomics, anthropometric measures can be classified as either static or functional. The former are fundamental and generally fixed measures, such as the length of an arm or a body segment moment of inertia. Such static data are widely available from public and commercial sources. Functional measures are obtained during performance of some task or activity and may thus depend on several individual factors (e.g., training, experience, motivation). These latter measures are specific to the measurement situation

and are hence relatively limited. Despite the availability of static measures, it is the functional measures that are directly relevant in design. The remainder of this section provides an overview of applied anthropometric methods. Results from anthropometry will also be critical in subsequent sections that address mechanical loading during task performance.

above the ankle joint), and methods have been developed to translate these to estimates of underlying joint centers that are required for biomechanical modeling (Section 2.4). Mass (and/or volume) measures are often obtained using liquid immersion, though as noted above, recent scanning methods are also being employed. Locations of segment (or whole-body) center of mass can also be obtained using liquid immersion and a number of segmental balance methods. Segment moments of inertia are usually obtained using dynamical

tests, where oscillatory frequencies are obtained during natural swinging or following a quick release. Representative geometric solids (e.g., a truncated cone) can also be used to model body parts and obtain analytical estimates.

Maury A. Nussbaum

Industrial and Systems Engineering

Virginia Polytechnic Institute and State University

Blacksburg, Virginia

Jaap H. van Diee¨n

Faculty of Human Movement Sciences

Vrije Universiteit

Amsterdam, The Netherlands

Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.

Edited by Myer Kutz

Disciplines Contributing to Physical Ergonomics

As noted earlier, ergonomics is inherently a multidisciplinary field. Indeed, it can be argued that ergonomics is essentially the intersection of several more primary fields, both receiving basic information from them and providing applications, tools, and procedures to them. Among the primary disciplines contributing to ergonomics and in which the ergonomist must have a fair degree of knowledge are anatomy, physiology, and mechanics. As will be seen in the subsequent presentation of methods, all are needed at some level to adequately address the measurement and matching problems earlier noted.

Ergonomics in the Design Process

Where are ergonomists and how do they contribute to the design process? As with any profession, the answer is necessarily diverse. In smaller enterprises, if any individual has responsibility for ergonomics, it is often along with safety and other related topics. In larger enterprises, there may be one or more persons with specific ergonomics training and expertise. In the largest, such as automotive manufacturers, whole departments may exist. Ergonomics consultants are also widely employed, as are ergonomists in academic centers.

Methods by which ergonomics is part of the design process are similarly quite varied. Broadly, ergonomics in design is either proactive or reactive. In the former, procedures such as those described below are applied early in a product or process life cycle, such as in the conceptual or prototype phases. In reactive situations, ergonomics methods are employed only after a design problem has been identified (e.g., a control cannot be reached, required torques cannot be generated, or work-related injuries are prevalent).

A natural question arises as to the need for ergonomics in design. Justification comes from a range of documented case studies, formal experiments, and economic evaluations. Though somewhat oversimplified, ergonomic design attempts to optimize design by minimizing adverse physical consequences and maximizing productivity or efficiency. It should be noted that these goals are at times in conflict, but ergonomic methods provide the tools whereby an optimal balance can be achieved.

An important justification for ergonomics is provided by the high costs of mismatches between demands and capabilities. Occupational musculoskeletal illnesses and injuries (e.g., sprains, strains, low-back pain, carpal tunnel syndrome) result in tens of billions of dollars (U.S.) in worker compensation claims, additional costs related to worker absenteeism and turnover, and unnecessary human pain and suffering. Increasingly, there are legal requirements and expectations for ergonomics in design (e.g., national standards or collective bargaining contracts). With respect to economics, it has been well documented (e.g., Refs. 3 and 4) that occupational ergonomic programs have led to reductions in overall injuries and illnesses and work days missed, with concurrent improvements in morale, productivity, and work quality. Further, ergonomic controls usually require small to moderate levels of investment and resources and do not drastically change jobs, tasks, or operations.

Maury A. Nussbaum

Industrial and Systems Engineering

Virginia Polytechnic Institute and State University

Blacksburg, Virginia

Jaap H. van Diee¨n

Faculty of Human Movement Sciences

Vrije Universiteit

Amsterdam, The Netherlands

Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.

Edited by Myer Kutz