analysis of anthropometric data for design and … · analysis of anthropometric data for design...
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NCADOMS-2016 Special Issue 1 Page 319
Analysis Of Anthropometric Data For Design And Development Of
Computer Workstation
Pratima.S.Joshi , Dr.Shashidhar.S.Kalashetty , Dr.S.M.Qutubuddin
Dept. of Industrial & Production, P.D.A.College of Engineering Kalaburagi,Karnataka
In this work carried for to study the Computer Workstation to establish the current practices
with reference to the use of Anthropometry. It also leads to the Re-design of the workstation
,in order to improve Productivity, Health safety and comfort of the operators in the
Workstation. Optimizing the Anthropometric data for computer workstation design can be a
complex task because of the number of design parameters that must be put into consideration.
This Problem has recently been made much easier to solve as a result of the development of
some design principles like design for extreme, design for average sizes and design for
adjustable range. Because of the nature of the selected workstations, design for adjustable
range principle is used. Anthropometric dimensions of the operators were used to design chair
and table which can accommodate 5%-95% of the operators. The workstations were examined
and analyzed under the combination of different anthropometric parameters. The analysis of
the results indicates some deficiencies in the design of the workstation based on the design
parameters and standard values from the literatures. Based on the analysis of these results the
operators and their clients may likely be exposed to fatigue, workstress and other related
diseases. For demonstration of the application of the adjustable range design approach, a
computer workstation has been redesigned as a real case. It is hoped that the new design will
contribute to improvement in Productivity, Health safety and Comfort of the operators in the
workstation. In the proposed adjustable range design approach, suggested to every
organization operating with workstation. Before any decision took on making or buying
equipments and tools, Industrial Engineers are to be consulted depending on the design factor,
for proper guidance. Anthropometric dimensions of the workers should also be considered for
any workstation that requires chair and table design. Many works were done on
anthropometry as a design factor for computer operator workstation were done on simple
system, where design for extreme and average are always resonable. The work was also done
on multiple complex systems like computer workstation in the departments and laboratories
where many people of different sitting positions of different heights were considered. In view
of these, design for adjustable range is most economical and ergonomic appropriate.
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Keywords: Anthropometry, Computer workstation, Design parameters.
Introduction:
The word ergonomic was derived from the Greek word, ergon, meaning work, and nomos, meaning law
or usage. The literature suggests that the word “Ergonomics” was independently used in 1949 by a British
Scientist, K.R.H. Murrell (Kroemer, 2003).During the past decade, research in ergonomics had led to
heightened interest in the technology of work and furniture design based on biomechanics of the human
body. These researches were focused on the development of new principles for the design of chairs and
desks in the workplace (Parcells et al, 1999).Bridger (1995) and Chou and Hsiao (2005) believed
anthropometry is a research area in ergonomics dealing with the measurement of human body dimensions
and certain physical characteristics. Anthropometric data can be used in ergonomics to specify the
physical dimensions of workspaces, workstations, and equipment as well as applied to product
design.Presently, the importance of safety and ergonomic in the design and manufacture of consumer
products had grown significantly. The latest technology had increased the option to broaden the
ergonomic and safety features of certain consumer products. However, it will also pose new risks which
are more complicated to manage. Therefore, it is important for the product designer and manufacturer to
use anthropometric data and ergonomic knowledge in making decision during designing of machines,
equipment, products and systems (Mattila, 1996).
Visual discomfort and musculoskeletal discomfort, particularly in the neck and shoulders, are
occupational health concerns for people who work with computers (Bergqvist and Knave, 1994;
Bergqvist et al, 1995; Hunting et al, 1981). In terms of ergonomics, comfort integrates a sense of
wellbeing with health and safety; conversely, discomfort could be related to biomechanical factors
involving muscular and skeletal systems (Zhang et al, 1996).Over the last two decades, ergonomics in
work environments has gained much attention from researchers; this is because ergonomics had played a
very important role in preventing and controlling work-related injuries and illnesses (Piegorsh et al,
2006). According to Wang et al. (1999) anthropometry has been considered as the very basic core of
ergonomics in an attempt to resolve the dilemma of “fitting people to machines” .
Computers have almost totally replaced typing machines, and facilitated intensive research
activities of various sorts through their screens using keyboard and mouse. Therefore, continuous and
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repetitive nature of computer applications, normally involving long hours of work for on the job usage or
for leisure, engaging mostly one hand (and about three middle fingers of the right hand in the case of
using mouse)[1] in almost hanging situation, and sewing the eyes to shiny jungle of shambles and
hieroglyphs on the improperly proportioned screens, etc… are bound to inflict multitude of very
complicated injuries, mostly of persisting kind, to the user. Carpal tunnel syndrome [2-4], eyestrains [5-
7], and musculoskeletal complaints [8-11] are known major problems ensuing from the repetitive use of
computers involving several components. In the opinion of the present authors, by the increased and
flooding use of computers, as time goes by, will aggravate injuries and human force will greatly suffer to
the point of permanent disability in its major organs, unless a critical remedying action be taken by
introducing engineering design principles and practice in the corresponding educational and industrial
establishments. That is, the hardware and software should be designed by professionals who have passed
courses on total engineering design at relevant institutions. As far as the present authors are aware, such
courses are non-existing in computer and electronics engineering and science courses in even major
universities or colleges around the world. In order to give the matter a heavier degree of due importance,
advice of lawsuits to computer-use-inflicted injuries are suggested. Although, not a frequent computer
user as such, but one or more hours of continuous sessions at the desk is enough to give eye fatigue and
dryness, musculoskeletal fatigue, pain on my hand and wrist, dry fingers, back and spine hump, and
headache. Moreover, as a trained eye for beauty of shapes and color and characters matching, looking at
aesthetically non-proportioned components, specially the screen gives me mental unease, recovery from
which need some extra effort. We therefore feel the gravity of bad design effects on the user to the bone.
Although the present authors do not claim to have succeeded in developing a completely effective desk
design, because we did not fully follow engineering design principles, but we hereby propose our
concerned points in the form of a geometry which may arise some further thoughts to assist in the future
developments.
Applying practical interviews, and remembering the tilt angle that draftspersons used to provide
for themselves of their drawing boards, we have proposed a totally different angle for the screen in
respect to the desk surface, and a stepped desk, which can include useful components that lack in most
present designs. There are good directives to the frequent user in the literature who can benefit from
them as injury preventive measures. All the same, good design certainly eliminates or, at least can
alleviate the use inflicted problems to a great extent. New conceptual look and redesign of certain items,
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such the seat, mouse, keyboard, etc. using advantages of developments in the science of mechatronics is a
vital necessity before too late.
Fig. 1 Continuous step desk design
Figure 2(a): Computer workstation Figure 2(b): Computer workstations in laboratories
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Desk design
In order to alleviate hand, wrist, arm and back strains, we have been approved by the interviewees to locate the mouse and keyboard at a lower height than the desk’s main surface
(Fig. 1). This lower desk surface is considered continuous lengthwise, in our design, to provide enough free space for some of the periphery to be moved about. Considering the anthropometrics standards our proposed design also facilitates serial arrangements of desks (Fig. 2), which are
suitable for most of the work environments as generally practiced now. The height of the desk step provides just enough room for some compartmentalization purposes (Fig. 1). These
compartments, though limited in size, facilitate design of lockers for the user, space for writing paper, CDs, etc. The best location of the tower for right-handed users, which is an established practice now, is underneath the desk at the right hand.
PC screen issues
Due to the most PC terminals being notoriously too voluminous and bulky, and the trend of development seemingly is toward monitors of the LCD type, we have concentrated our study on the latter type of designs. Most of the on-the-job and frequent users tend to adjust the screen
angle of their bulky terminals to about 75 degrees plus to the desk, due to the positional restrictions imposed by their stand designs. Our department secretaries hard at work in front of
the screen of their voluminous PCs interviewed, despite their tendencies to first defend their habit of using the aforementioned large angle, gradually came to agree with the suggestion of 30-35 degrees screen angle to the desk giving their sight, head, and back a more comfortable
position. According to the interviews, position of the reference material was preferred aligned with the screen angle. The screen center at their 75 degrees plus terminal orientation, they were
more at ease, not at the center portion, but at a slightly lower section of the proposed 30-35 degrees angle screen. At this position screen top is viewed even more comfortably. In all the interviews, the approximately perpendicular viewing distance to the screen was about 50 cm.
Figure (3) shows a proposed rough angular position of the bulky and LCD kind of terminals and corresponding viewing angles in respect to horizon. Dimensions given by the manufactures of
LCD 15 and 17 inch terminals and the provision of some of them for adjustability of tilt angle,
we find that the lower surface of the proposed desk is approximately a favorable base for these
kinds of terminals (Fig. 4). When not in use terminals can be locked in the left hand compartment underneath the desk (Fig. 1). All wiring would be hidden from the scene, which is a measure to remedy the wires syndrome.
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Fig 3: Proposed screen position Figure 4: Proposed desk design
Ergonomic Chair Design Computer chair is the most important part of computer work station. The chair has to fit user and
suit the tasks that is been done. One style of chair may not suit every worker. For example, the average chair is designed in some instances to fit the average male and may not suit other users. A chair is only ergonomic if it can be adjusted to fit the user. The following features are part of a
good computer chair: I. 5 – Caster Swivel base
II. Arm rest III. Height adjustable seat pan IV. Tilt adjustable back rest
V. Ability to make adjustments easily while sitting in the chair VI. Firm padding covered with non slip, breathable fabric
The special features include: Seat Pan: the seat pan should be the type with rounded front edge, wide and deep enough to fit the user Comfort ability, and with adjustable in angle.
Back rest: the back rest contains padding for the low back area that is curved to fit the shape of the back of the user. It must be of adjustable height and angle with locking mechanism, wide and
high enough to fit the back of the user. It should be noted that, when seated, the back tends to lose some of its natural curvature. An effective lumber support of a chair is designed to help maintain the natural curvature of the spine when sitting. It is important to provide appropriate
support for the spine so that there is no discomfort or pain.
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Figure 5: Chair with Lumber support
The arm rest should be designed in such a way to eliminate interference with the work surface and will provide height and width adjustability.
The chair height is designed in a way that allows the feet of the user to rest comfortably on the floor and even pressure is felt from the seat pan both on the back of the seat (buttock region) and
under the thighs (near the knees). To carter for the chair range of motion, the seat and back rest should allow for varied seated postures. This can be accomplished by allowing a rearward tilt on
the back. A minimum of 100
rearward tilt (between 900
and 1150
) is preferable [13]. The only
guidelines for seat tilt measurement is to ensure the torso-to thigh angle is not less than 900
, and
that the seat angle is between 0- 40
rearward tilt.
Figurer 6: Measurements for Ergonomic Chair
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Table 1 Specific Chair design guideline Measurements (all dimensions in cm)
Measurement Guideline (cm) All Steel Sum Chair (cm)
Seat Height A Popliteal Height + Shoe allowance
15.0 - 19.9 15.0 – 22.25
Seat Depth B Buttock- Popliteal
length- Clearance allowance
No deeper than 16.9
(fixed), 16.9 include (adjustable)
15.0 – 18.0
Seat Width C Hip breadth,
Sitting + Clothing allowance
No less than 18.0 18.0
Back rest Height
D None At least 12.2 24.0
Back rest
Width
E Waist breadth 14.2 16.0
Back rest Lumber
F None Most prominent point 5.9 – 9.8 from seat pan,
in and out1
Infinite through
height of back
Arm rest
Height
G Elbow rest Height
6.9 – 10.8 7.9 – 9.8
7.0 – 11.0
Arm rest
Length
H None None 10.5
Distance between Arm
rest
I Hip breath, Sitting + Clothing
allowance
18 (fixed) 18 (adjustable)
16.5 – 19.0
Methodology Designing a computer workstation requires more than just putting a computer on a standard office desk and providing an adjustable chair. The design of computer workstation includes the
work envelope (range of movement), work surfaces (such as desks, tables, etc.), and seats as well as the design and location of computer screen, keyboard, and mouse. The design of the computer
workstation should clearly be rooted in the use of anthropometric data. In this study, we have specifically developed a questionnaire based on the occupational Safety and Health (NIOSH) Symptoms Survey and the Nordic Musculoskeletal Questionnaire to gather
data on upper limb symptoms. The questionnaire covers the usual background information (age, sex, occupational history), the present job position, the nature of symptoms (ache, numbness,
tingling, burning, pain, weakness, cramping, swelling, loss of color, stiffness), trouble and discomfort areas (neck, shoulders, elbows, wrists/hands, upper back, lower back,
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hips/thighs/buttocks, knees, ankles/feet), the notification and duration of the problems, plus
medical history asking about any medical treatment for the problem.
Figure7: Seated body dimensions computer user
Anthropometric Dimensions for Desk and Chair Design The data was collected under the following body dimensions: 1. Sitting Height: with the subject sitting erect, distance from sit to vertex of the hair pressed down.
2. Shoulder Width: the distance from the edge of one shoulder to the next in the sitting position. 3. Hip Width (Seat Width): distance between the outer part of the right and left hips in a seated
position.
4. Elbow Rest Height (Arm rest Height): with subject sitting erect, distance from seat to bottom of elbow.
5. Knee Height (Seat Height): distance from the knee to the sole in sitting position.
6. Buttock-Knee Length (Seat Depth): distance from the back of the buttocks to the foremost point of the patellar.
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7. Thigh Clearance: with subject sitting, distance between the right and left thigh.
8. Eye Height: with subject sitting erect, distance from the seat to the eye level.
9. Lower Arm-Hand Length (Arm rest Length): in sitting position, distance from the elbow to the
mid finger tip.
10. Back rest Lumber: distance between the lower back rest curvature to the tip of the seat pan.
11. Back rest Height: distance between the topmost edge and bottom edge of the back rest.
12. Back rest Width: distance between the top most right side to the top most left side of the back rest.
13. Distance between the Arms rests: in sitting position, hip width with clothing allowance.
Selection of statistic and Error Rate The primary statistical procedure used was one - way analysis of variance (ANOVA). The general
linear model in SPSS 16.0 was used for analyzing data. The SPSS 16.0 Software program includes an
additional column labeled sig. for significance. Several assumptions were made for the one -way ANOVA statistical procedures in the study. (a) Samples were randomly collected from the
population and randomly assigned to group (b) There was homogeneity of variance (c) the error rate
selected was 0.05 type 1
Figure 8: The computer workstations Desk & PC dimensions in AutoCAD
As shown in above figure it explains about the computer workstation dimensions in AutoCAD. The proper ergonomic positioning with the body positioned using a static seated posture with the
body positioned using the 90-90-90 rule in which the back-thigh angle was 90 degrees, the thigh-leg angle 90 degrees, and the leg-foot angle was 90 degrees. Movement, such as leaving your workstation at least once an hour for 5-10 minutes , needed to be performed since frequent
position changes help prevent work-related musculoskeletal disorders. Today, good ergonomics
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practice dictates that some computer workers should work in a variety of postures to include
sitting. Some of the awkward postures as shown in below figures:
Figure 9(a): Wrist pain Figure 9(b): Height of footrest
Figure 9 (c): Unreached of the hand (can’t reach due to collapse with wall)
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Figure 9(d): The touching of knees to the keyboard platform
Figure 9(e): No foot rest
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Figure 9(f): No armrest
WORKING CONDITIONS
The workstation is designed or arranged for doing VDT, video display terminal, tasks so it allows the employee’s,students,lecturers,professors . . .
Yes No
A. Head and neck are about upright (not bent down/back).
B. Head, neck and trunk face forward (not twisted).
C. Trunk is about perpendicular to floor (not leaning forward/backward).
D. Shoulders and upper arms are about perpendicular to the floor (not stretched
Forward) and relaxed (not elevated).
E. Upper arms and elbows are close to the body (not extended outward).
F. Forearms, wrists, and hands are straight and parallel to the floor (not
Pointing up/down).
G. Wrists and hands are straight (not bent up/down or sideways toward little
Finger).
H. Thighs are about parallel to the floor and lower legs are about perpendicular to
Floor.
I. Feet rest flat on the floor or are supported by a stable footrest.
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J. VDT tasks are organized in a way that allows the employee to vary VDT tasks
with other work activities, or to take micro-breaks or recovery pauses while at
the VDT workstation
. 2. SEATING The chair . . .
Yes No
1. Backrest provides support for employee’s lower back (lumbar area).
2. Seat width and depth accommodate specific employee (seat pan not too
big/small).
3. Seat front does not press against the back of employee’s knees and lower legs
(seat pan not too long).
4. Seat has cushioning and is rounded/has a “waterfall” front (no sharp edge).
5. Armrests support both forearms while employee performs VDT tasks and do
not interfere with movement. 3.KEYBOARD/INPUT DEVICE
The keyboard/input device is designed or arranged for doing VDT tasks so that . . . Yes No
6. Keyboard/input device platform(s) is stable and large enough to hold
keyboard and input device.
7. Input device (mouse or trackball) is located right next to keyboard so it can be
operated without reaching.
8. Input device is easy to activate and the shape and size fit the hand of the
specific employee (not too big/small).
9. Wrists and hands do not rest on sharp or hard edge.
4.MONITOR The monitor is designed or arranged for VDT tasks so that . . .
Yes No
10. Top line of the screen is at or below eye level so the employee is able to read
it without bending head or neck down/back. (For employees with
bifocals/trifocals, see next item).
11. Employee with bifocals/trifocals is able to read screen without leaning head,
neck or trunk forward/backward.
12. Monitor distance allows employee to read screen without leaning head, neck
or trunk forward/backward.
13. Monitor position is directly in front of employee so employee does not have
to twist head or neck.
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14. No glare (e.g., from windows, lights) is present on the screen that might cause
employee to assume an awkward posture to read screen.
5.WORK AREA The work area is designed or arranged for doing VDT tasks so that . . .
Yes No
15. Thighs have clearance space between chair and VDT table/keyboard platform
(thighs are not trapped).
16. Legs and feet have clearance space under VDT table so employee is able to
get close enough to keyboard/input device. 6.ACCESSORIES
Yes No
17. Document holder, if provided, is stable and large enough to hold documents
that are used.
18. Document holder, if provided, is placed at about the same height and distance
as monitor screen so there is little head movement when employee looks from
document to screen.
19. Wrist rest, if provided, is padded and free of sharp and square edges.
20. Wrist rest, if provided, allows employee to keep forearms, wrists and hands
straight and parallel to ground when using keyboard/input device.
21. Telephone can be used with head upright (not bent) and shoulders relaxed (not
elevated) if employee does VDT tasks at the same time.
7.GENERAL Yes No
22. Workstation and equipment have sufficient adjustability so that the employee
is able to be in a safe working posture and to make occasional changes in
posture while performing VDT tasks.
23. VDT workstation, equipment and accessories are maintained in serviceable
condition and function properly. PASSING SCORE = “Yes” answer on all “working postures” items A-J and no more than two
“No” answers on remainder of checklist (items 1-23).
Figure 10 shown below explains about the exact computer workstations after the approach
of questionnaire.
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Figure 10: The exact dimension of computer workstation after questionnaire
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The survey exercise was 100% response; all the questionnaires given out were attended to. The
majority of the respondents were male, which was 53.33% while the female was 46.67%. The age limit of most of the respondents fell in between 20 – 30 years with a percentage of 33.33%, followed
by the age limit between 30 – 40years with a percentage of 30%. Age 40 – 50 years limit was
16.67%, 50 years and above was 13.33% and 20% of the respondents were below 20 years. Most of the respondents were 56.67% and 50% in height and weight respectively. The extremely tall
respondents of above 1.7meters were 23.33%, followed by those respondents below 1.5 meters with
20% quota. All the respondents were frequent computer user, so 100% computer operators were recorded. In the area of daily working hour of the respondents, the highest number of the respondents
uses computer between 3 – 6hours per day with 50% quota, while the least users were below 3 hours per day. Full working hour respondents fell in between the two, with 26.67%. Almost half of the
respondents experiences pain sometimes during and after work with 43.33%. ‘Always’ and “rarely’
pain experience user were both 20%, 16.67% of the respondents neither experience pain during nor after work. All the respondents preferred sitting position while at work on computer. The
respondents’ experiences pain mostly o the buttock, neck region, spinal cord and shoulder with
18.42%, 17.11%, 15.79% and 13.16% respectively. The thigh and hand muscles both shared the same level of 9.2%, while hips, leg muscles and elbow/forearm were 3.95%. The respondents rarely
experience pain on the legs and wrist with 2.63%. None of the respondent experience pain on the
finger. In the ergonomic awareness part of the result from the questionnaire, 36.67% of the respondent
sometimes experiences fatigue at work, mostly at the neck region with 33.33%, while 26.67% rarely experience fatigue. 20% always experience, and 16.67% never experience at all. The percentage of
respondents that also experienced fatigue causing pain on the spinal cord, buttocks, leg muscles and
hand muscles were 24.24%, 15.15%, 12.12% and 9.10% respectively. The level of implementation of ergonomic in the existing design was evaluated by the respondents using liker scale. 23% of the
respondents agreed to moderately conformed, 30% agreed to slightly conformed, 16.67% consented
to strongly conformed, while only 6.67% chose not conformed. The respondents rated their
productivity and efficiency on the existing design. 40% consented to be good, 33.33% consented to
be average performance, 20% believed to be excellent, and only 6.67% agreed to not conform.