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.

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

Copyright  2006 by John Wiley & Sons, Inc.

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Disciplines Contributing to Physical Ergonomics

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

Copyright  2006 by John Wiley & Sons, Inc.

Read more........

Basis of Physical Ergonomics

At its most basic level, PE is concerned with two aspects of physical effort: (1) the physical demands placed on the human and (2) the physical capabilities of the human in the situation where the demands are present. Simply, the goal is to ensure that demands do not exceed capacity, as is typical for the design of any mechanical system.

A major challenge in PE is the measurement of both demands and capacity in the wide variety of circumstances where human physical exertions are performed (or required, as in the occupational context). Physical requirements vary widely and include dimensions such as force, torque, repetition, duration, posture, etc. Similarly, human attributes vary widely across related dimensions (e.g., strength, endurance, mobility).

Along with the measurement problem is the related problem of matching. Given the variability in both demands and capacity, potential mismatches are likely (and prevalent in many cases). Occupationally, poor matching can lead to low productivity and quality, worker dissatisfaction and turnover, and in many cases musculoskeletal illness and injury.

Ongoing research is being widely conducted to address both the measurement and matching problems. In the material presented below, we have given examples of contemporary approaches, but the reader is advised that more advanced methods are currently available and the technology is rapidly advancing.

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

Copyright  2006 by John Wiley & Sons, Inc.

WHAT IS PHYSICAL ERGONOMICS?

Definitions and Brief History Ergonomics is derived from the Greek ergon (‘‘work’’) and nomos (‘‘principle’’ or ‘‘law’’). Original attribution is debated but is usually given to the Polish professor Wojciech Jastrzebowski in a treatise published in 1857 and intended to represent the ‘‘science of work.’’ The same term seems to have been reinvented in 1949 by the British professor K. F. H. Murrell with the same general intended meaning. In the past decades ergonomics as a scientific and/ or engineering discipline has seen a dramatic increase in research and application as well as attention from the general public. As such, the original term has, in cases, lost some of its original meaning. Returning to these origins and to provide a focus for this chapter, the following definition does well to encompass the current state of ergonomics as having a theoretical and multidisciplinary basis, being concerned with humans in systems and ultimately driven by real-work application (Ref. 1): Ergonomics produces and integrates knowledge from the human sciences to match jobs, products, and environments to the physical and mental abilities and limitations of people. In doing so it seeks to safeguard safety, health and well being whilst optimising efficiency and performance. As a recognized professional domain, ergonomics is quite young, becoming formalized only after the World War II. Related efforts were certainly conducted much earlier, such as Borelli’s mechanical analysis of physical efforts in the late-seventeenth century and the identification of work-related musculoskeletal illnesses by Ramazzini in the early-eighteenth century. It was only in the 1950s, however, that researchers with expertise in engineering, psychology, and physiology began to come together to realize their common goals and approaches. Ergonomics continues to be an inherently multidisciplinary and interdisciplinary field, which will be evident in the remaining material presented in this chapter. 

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