30079_15.pdf

CHAPTER 15

ERGONOMIC FACTORS IN DESIGN

Bryce G. Rutter, Ph.D., Principal

Anne Marie Becka, Editor

Metaphase Design Group, Inc.

St. Louis, Missouri

15.1 ERGONOMICS

329

15.5.5 Motion Analysis

335

15.5.6 Thermographic Imprint

Analysis

15.2 HUMANPERFORMANCE

329

336

15.2.1 Physical Ergonomics

330

15.5.7 Low-Speed Cine Analysis

336

15.2.2 Perceptual and Cognitive

Ergonomics

330

15.6 DESIGNRESEARCH

METHODS

336

15.3 THE DESIGN PROCESS

330

15.6.1 Competitive Product

Analysis

336

15.4 DESIGNRESEARCH

331

15.6.2 Product Performance

Analysis

336

15.5 ERGONOMICANALYSES

332

15.6.3 Usability Studies

336

15.5.1 Anatomical Analysis

332

15.5.2 Biomechanical Analysis

333

15.7 COST-BENEFIT ANALYSIS OF

ERGONOMICS AND DESIGN

RESEARCH

15.5.3 Task Analysis

335

15.5.4 Link Analysis

335

337

15.1 ERGONOMICS

A widespread increase in the availability of technology in the second half of the twentieth century

has meant that more and more people come in contact with a variety of product designs on a daily

basis. Regardless of this increase in the number and types of human users, many engineers still

concentrate their design efforts on the machine or system alone, forcing the user to adjust to fit the

product. Such readjustments on the part of the user can lead to discomfort and dissatisfaction with

the design, as well as more serious effects, such as safety hazards and personal injury.

Ergonomics (also called human factors) is an applied science that makes the user central to design

by improving the fit between that user and his or her tools, equipment, and environment. Key here

is that designs are developed to fit both the physiological and psychological needs of the user.

Ergonomists examine all ranges of the human interface, from static anthropometric measures and

movement ranges to users' perceptions of a product. This interface involves both software (displays,

electronic controls, etc.) and hardware (knobs, grips, physical configurations, etc.) issues.

Ergonomics grew into a distinct scientific discipline during the second world war. What began as

a form of engineering (human engineering or human factors engineering) has come to encompass a

wide range of interdisciplinary professions, including psychology, industrial design, medicine, and

computer science. Its practitioners' range in focus includes concept modeling and product design, job

performance analysis, functional analysis, workspace and equipment design, computer interfaces,

environment design, and so forth.

15.2 HUMANPERFORMANCE

The true basis of ergonomics is understanding the limitations of human performance capabilities

relative to product interaction. These limitations are either physical or cognitive/perceptual in nature,

but all address how people respond to man-made designs. Such interface analysis is crucial to estab-

lishing a safe and effective system of operation or environment for the user.

Mechanical Engineers' Handbook, 2nd ed., Edited by Myer Kutz.

Fig. 15.1 General interdisciplinary nature of human factors with selected

examples (from Ref. 1, p. 90. Reprinted by permission).

15.2.1 Physical Ergonomics

A thorough understanding of the physical characteristics of a wide range of people is essential to

any product that is designed for human use. When analyzing design relative to human performance,

ergonomists study static anthropometric data, which includes sizing percentiles (e.g., lengths, mea-

surements) of a wide range of populations, including gender, age, race, and other such factors. Ranges

of joint motions, strengths, and grips for varying human percentiles are also reviewed. These data

serve as valuable information to designers and help ensure the final product will physically fit the

targeted end-user, be it a child, the aged, or a particular racial population, and so forth.

15.2.2 Perceptual and Cognitive Ergonomics

Proper fit of a product to a user does not end with the physical interface. The perceptual and cognitive

demands a product places on a user must also be examined. Note that a great misconception under-

lying these capabilities is that they address emotive responses of the user. However, neither are

qualitative findings; both types offer fact-based, quantitative data to be used in product development.

Perceptual responses are those filtered through one or more of the five senses, such as tactile and

auditory feedback of controls. Cognitive responses are based on logic, reason, and how users process

information. Cognitive issues include intuitiveness of control features and functions as well as icon

representation and label comprehension.

15.3 THE DESIGN PROCESS

Implementing an ergonomics program can help ensure a product's successful transition from the

drawing board to the end-user. However, human factors cannot be examined in a vacuum. Ergonomists

must work directly with designers and engineers throughout the entire design development process,

each providing feedback to the other during concept development and testing. In addition to standard

ergonomic analyses, design research should be conducted with targeted end-users to identify design

problems that are often overlooked by the engineer, who examines the product only within the design

environment. Such end-user research serves to measure a design's overall efficacy on a wide range

Table 15.1 Body Dimensions of U.S. Civilian Adults, Female/Male, in cm a

Percentiles

5th

50th

95th

Heights

(f above floor, j above seat)

Stature ("height" K

Eye height /

Shoulder (acromial) height /

Elbow height 7

Wrist height 7

Crotch height 7

Height (sitting) 5

Eye height (sitting) 5

Shoulder (acromial) height (sitting) 7

Elbow height (sitting)*

Thigh height (sitting) 5

Knee height (sitting) 7

Popliteal height (sitting) 7

Depths

Forward (thumbtip) reach

Buttock-knee distance (sitting)

Buttock-popliteal distance (sitting)

Elbow-fingertip distance

Chest depth

Breadths

Forearm-forearm breadth

Hip breadth (sitting)

Head Dimensions

Head circumference

Head breadth

Interpupillary breadth

Foot Dimensions

Foot length

Foot breadth

Lateral malleolus height 7

Hand Dimensions

Circumference, metacarpale

Hand length

Hand breadth, metacarpale

Thumb breadth, interphalangeal

Weight (in kg)

152.78/ 164.69 162.94/ 175.58 173.73/ 186.65

6.36/6.68

141.52/ 152.82 151.61/ 163.39 162.13/ 174.29

6.25/6.57

124.09/ 134.16 133.36/ 144.25 143.20/ 154.56

5.79/6.20

92.63/

99.52

99.79/ 107.25 107.40/ 115.28

4.48/4.81

72.79/

77.79

79.03/

84.65

85.51/

91.52

3.86/4.15

70.02/

76.44

77.14/

83.72

84.58/

91.64 4.41/4.62

79.53/

85.45

85.20/

91.39 91.02/

97.19

3.49/3.56

68.46/

73.50

73.87/

79.20

79.43/

84.80

3.32/3.42

50.91/

54.85

55.55/

59.78

60.36/

64.63

2.86/2.96

17.57/

18.41 22.05/

23.06

26.44/

27.37

2.68/2.72

14.04/

14.86 15.89/

16.82 18.02/

18.99

1.21/1.26

47.40/

51.44 51.54/

55.88

56.02/

60.57

2.63/2.79

35.13/

39.46

38.94/

43.41 42.94/

47.63

2.37/2.49

67.67/

73.92

73.46/

80.08

79.67/

86.70

3.64/3.92

54.21/

56.90

58.89/

61.64 63.98/

66.74

2.96/2.99

44.00/

45.81 48.17/

50.04

52.77/

54.55

2.66/2.66

40.62/

44.79

44.29/

48.40

48.25/

52.42

2.34/2.33

20.86/

20.96

23.94/

24.32

27.78/

28.04

2.11/2.15

41.47/

47.74

46.85/

54.61 52.84/

62.06

3.47/4.36

34.25/

32.87

38.45/

36.68

43.22/

41.16 2.72/2.52

52.25/

54.27

54.62/

56.77 57.05/

59.35

1.46/1.54

13.66/

14.31 14.44/

15.17 15.27/

16.08

0.49/0.54

5.66/

5.88

6.23/

6.47

6.85/

7.10

0.36/0.37

22.44/

24.88

24.44/

26.97

26.46/

29.20

1.22/1.31

8.16/

9.23

8.97/

10.06

9.78/

10.95

0.49/0.53

5.23/

5.84

6.06/

6.71

6.97/

7.64

0.53/0.55

17.25/

19.85 18.62/

21.38 20.03/

23.03

0.85/0.97

16.50/

17.87 18.05/

19.38 19.69

21.06

0.97/0.98

13.8 fo /12.6 b

99.3 f c

7.34/

8.36

7.94/

9.04

8.56/

9.76

0.38/0.42

84.8 b /

1.86/

2.19

2.07/

2.41

2.29/

2.65

0.13/0.14

57.7 f c

62.01/

78.49

39.2 fc /

^Adapted from U.S. Army data reported by Gordon et al. (1989) (from K. Kroemer, H. Kroemer,

by permission of Prentice-Hall, Englewood Cliffs, NJ).

b Estimated.

Note: In this table, the entries in the 50th percentile column are actually "mean" (average) values.

The 5th and 95th percentile values are from measured data, not calculated (except for weight). Thus,

the values given may be slightly different from those obtained by subtracting 1.65 SD from the mean

(50th) percentile, or by adding 1.65 SD to it.

of user perception and knowledge levels. Resulting data can provide a tangible starting point upon

which design revisions or new product concepts can be made.

15.4 DESIGNRESEARCH

A core component of a successful product design is understanding the wants and needs of the

product's end-users. Therefore, talking with target customers to gain insight into their requirements

is a logical step in concept development. Unfortunately, most manufacturers and engineers approach

this issue through "gut-feeling" guesswork — fabricating a list of items or issues based on the

premonitions of the development team or head of manufacturing. This method of design development

is doomed from its inception, as engineers and manufacturers are often so far removed from their

customer base that the resulting products never meet users' requirements or expectations.

Other times, manufacturers circumvent actual end-user research in lieu of product assessment by

their marketing department. This form of "research" is extremely qualitative and often unsubstan-

tiated by end-user feedback. Worse yet is when manufacturers base product design requirements on

results of a survey of sales personnel. It is generally believed that because sales personnel are on the

floor daily with customers, they have insight into customers' wants and needs. However, such methods

can be disastrous, as sales representatives are not trained to observe and categorize human behavior,

as many human factors specialists are.

15.5 ERGONOMICANALYSES

Ergonomic assessments successfully define special requirements of unique user groups by providing

a comprehensive assessment of the degree of compatibility between the user, the product, and the

user's workspace. Data collected include empirical measures of workspace envelopes, task and link

analyses (used to identify inefficiencies in the conduct of work, illogical procedures, and hazards),

and definitions of anthropometric requirements (the dimensions of the human body). Several types

of ergonomic analyses are listed below.

15.5.1 Anatomical Analysis

An anatomical analysis is the study of the interaction between a product and various anatomical

features of the user's body (e.g., the musculoskeletal system, nerves, veins and arteries, joints, etc.).

The goal of this analysis is to identify biological constraints for design that, if exceeded, may lead

to user discomfort, stress, strain, pain, or occupational disability. Typically, a product's effect on the

muscular, skeletal, nervous, and circulatory systems is explored.

Design programs in which this type of analysis is especially important are those that involve large

forces being exerted, rapidly repeating body motions, and/or high pressure on a portion of the user's

anatomy. An anatomical analysis allows ergonomists to identify potentially harmful effects of the use

SHOULDER

Fig. 15.2 Selected examples of range of joint motions: upper extremities (from B. G. Rutter,

ABDUCTION

FLEXION

ELBOW/ SHOULDER

RADIAL DEVIATION

ULNAR DEVIATION

FINGER FLEXION

WRIST

Fig. 15.2 (Continued).

of a product on its users. It also provides design guidelines in the form of constraints on the user

interface. The various anatomical systems affect the level of anatomical analyses. In addition, the

type of product being designed and the nature of the interaction between the user and the product

determine what anatomical features need to be considered in the analysis. Such analysis is best when

performed by someone trained in kinesiology (the study of human movement).

15.5.2 Biomechanical Analysis

Biomechanical analysis involves modeling the human body as a mechanical system. The various

measurement tools used in biomechanical analysis all provide information about the mechanics of

the user's body when interacting with a product or performing a task. Such analysis is appropriate

when the goal is to quantitatively assess or validate the efficiency and/or safety of one or more

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