1

A Plug Assembly Line: An Assessment of Workstation Design and

Working Posture

Adi Saptari, Seri Rahayu Kamat, Wan Hasrulnizzam Wan Mahmood, Isa Halim

Faculty of Manufacturing Engineering, Kolej Universiti Teknikal Kebangsaan Malaysia

e-mail: adi@kutkm.edu.my

I. Introduction Workstation design is one of the major areas in which human factors or Ergonomics

professional can help improve the fit between human, machine and environment. Good

design of workstation considering the human factor anthrophometry data to make

workstation that is comfortable and support productivity improvement.

Productivity in assembly line determined by many variables, among others:

a. Skill of the workers;

b. Design of equipment or tools;

c. Design of workstation; and

d. Design of assembly process.

Productivity improvement can be made by upgrading or enhancing by controlling

variables, which contribute to the productivity. In most industry, assembly line job

environments such as workstation design including working position such as: standing or

sitting, the use of tools such as jig and the height of working table are influencing

workers’ performance. Meanwhile, working posture such as: position of body: arm and

wrist, neck, trunk and leg determine comfortability and safe posture while working.

These aspects also play a significant role in productivity.

Most job environment in industry applies standing or seated work. Standing workstations

are usually applies when job requires workers to do activities that need frequents

movements, handle heavy or large objects or exert large forces. Whereas seated

workstation is chosen usually for long-term duration job. A seated workstation allows

better controlled on arm movements provides a stronger sense and balance. Standing

posture, however prolonged standing could be stressful that put excessive load to the

body and may lead to body accumulation in the legs (Wickens et.al. 2004).

Additional tool, such as jig, is designed to help workers’ performance to do the job easier,

faster and more comfortable. However, jig may also hinder some workers in doing their

job, if the design of the jig is not suitable to the workers. Design of jig should such that

help worker in performing their job and more productive.

Table height of an assembly line may contribute to performance of workers when

position is either standing or sitting. There are researches regarding the types of works

and the height ideally for workers. Grandjean, 1988, has made exploration work surface

height for different kinds of jobs. He proposed precision work for men should be set at

100-110 cm, Light work around 90-95 cm and Heavier work around 75-90 cm.

Workers who have experience backaches, neck aches, and shoulder pains at work can be

traced that the height of a work surface can lead to such aches and pain. If a work surface

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is too low, the back of worker bend over the certain degree. Surface work means in this

research is the height of the top surface of the table to the floor. On the other hand if

worker work surface too high, the shoulder must be raised so that worker can perform the

job, this will trigger shoulder and neck discomfort (Sanders, 1993).

Previous studies showed that there are numerous problems in workstations design have

been studied, Table 1.shows research area and its focus.

Table 1: Researches have been carried-out relating to workstation design

Research Work Research Applied Focus

Krzysztof, S. and

Grzegorz, K., 1996

Workstation design for textile

industry in Poland.

Improving working posture through

modification workstation design

using computer aided facility.

Biman, D. and

Arijit, K. S., 1996

The conceptual basis of

workstation design in general

industry.

Improving working posture by

designing the workstation according

anthropometry of workers.

Nico, J. D. and Jan,

D., 2002

Workstation design for

sewing operation.

Improving working posture through

proper arrangement of workstation

such as desk height, desk slope and

pedal position.

Richard, W. M. and

Jeremy, R. W. et al.,

1996

Improving workstation design

for lifting capacitors at

satellite storeroom, draining

oil task and packaging electric

meters.

Priority is given on the working

posture by providing appropriate

working height and introducing

suitable handling equipment.

Tissot, F. et al.,

2005

Creating a workstation design

for standing and sitting

posture.

Improving working posture for

standing and sitting to prevent lower

back pain.

Kamal, K. and

Berman, K., 2001

Workstation design for

manual handling activities in

manufacturing, retail and

service industry.

The research focused on muscular

strain in seated manual handling

tasks.

Goossens, R. H. M.

et al., 2003

Workstation design for

sedentary tasks in office.

Introducing lumbar support to

reduced loading on back muscle.

Thomas, R. W. et

al., 1998

Workstation design for

manual lifting in grocery

warehouse.

To optimize the oxygen

consumption of workers during

manual lifting.

Mohammad Iqbal, et

al., 2004

Optimization of workstation

design for semi-automated

printing workstation at

electronic industry in

Malaysia.

Consideration was given to four

factors, cycle time, energy

consumption, working posture and

lifting limitation of worker while

performing task.

Isa Halim, 2006 Improvement on workstation

design for manual material

handling task in metal

stamping industry under

Malaysian SMIs.

Improvement on working posture,

reduce muscles loading and

optimize the oxygen consumption of

workers while performing manual

materials handling.

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II. Objective The objective of this research is to explore:

i. The effect of different workstation design i.e. different height of the table and

different position of the worker standing or sitting to the response time;

ii. The effect of using jig and without jig in assembly line to the response time;

iii. Analyze working posture for different workstation designs.

This experiment will analyze how different design of workstation will contribute to

variety of workers’ productivity. A special designed jig is also analyzed whether

contribute to better productivity. Last but not least, working posture for different design

of workstation also is investigated. The latter is to study whether the working posture is

safe. The research uses an assembly line for small scale industry particularly in electrical

appliances industry. A plug product is used for the purpose of this research.

III. Method

3.1 Design of Experiment

There are three factors to be tested to see the effect of each factor in the productivity in

this case the time needed to finish the job (assembly time). These factors are: 1) Table

height; 2) Position of subjects, standing or sitting; and 3) Tools, using Jig and without Jig.

For table height we applied to different height i.e. 91 cm and 103 cm. These sets were

based on literatures on working environment needed for light work and precision work

based on study recommended by Grandjean, 1988.

The design of experiment for this particular setting is 2x2x2 (23). Each factor has two

level sets, Table height is set either 91 cm or 103 cm, Tools use Jig or without Jig, and

Position either standing or sitting.

3.2 Subjects

Two subjects participated in these experiments. They were chosen based on their past

performance, they have been showing a constant quality of work during their period of

jobs, both of them are still young age around 28 years old. The average height is 170 cm.

They were trained first before doing the experiment begins, so that they were familiar

with the equipment. They have been using this equipment, so is not something new for

them to use.

3.3 Experiment Task

Every subject performs 288 experiments i.e. produce 288 plugs. Number of experiments

for each different level and set (Table, Tool, and Position) are 36 experiments. There are

8 different ways of doing the experiments. Every plug has 7 components. The process of

assemble has been designed such that the sequence of picking the components follows

the order.

The response time, time needed to finish the assembly, is recorded by using stopwatch.

The first data recorded is when subject has done certain amount of experiments such that

the subject already comfortable in doing his job, and the time also shows a constant rate.

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3.4 Tools:

List of tools used for this research as follows:

1) Screw driver powered by air pressure. This Screw driver can be operated to move

clock wise and anti clock wise;

2) A stop watch to record assembly time of a plug;

3) Digital camera to record the working posture;

4) CATIA software;

5) A pen and table paper to document the response time.

6) Adjusted table height.

7) A chair for subject to seat while working;

8) A jig designed to accommodate four plugs at a time, see Figure 1;

9) Compartments, for holding the components of a plug. There are 7 compartments

holding 7 type of components;

10) A compartment or bag to collect finished product.

Figure 1: Design of Jig

3.5 Image Capturing

A digital camera was utilized to capture the working posture of subjects while they

performing the task. The digital camera is set at the appropriate distance so that the

images of subjects can be captured clearly, as shown in Figure 2. Two angles of view:

both side and front views of images were captured. The objective of image capturing is to

obtain the magnitudes of working posture such as neck angle, trunk angle and the angle

of other body parts.

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Figure 2: An image of digital camera capturing

3.6 Measurement of Working Posture

After the images of working posture were captured, they are transferred onto Computer

Aided Design (CAD) software to determine the magnitudes of working posture. For

example, to determine the forearm angle of a subject while sitting position, firstly the

image of digital camera is transferred onto Computer Aided Design (CAD) software.

Using facilities in CAD software, two lines were constructed, the first line is sketched

vertically as a reference line, and the second line is sketched respective to subject’s

forearm. As illustrated in Figure 2, the magnitude of these two lines (104º) is the angle of

forearm for this specific posture. The information will be used as the input data for

further analysis. Through this technique, the data can be acquired easily. Thus, the result

of this particular working posture can be obtained accurately. Figure 2 shows the

integrated image from digital camera and CAD Software to determine the forearm and

wrist angles of a subject while he assembling electrical parts.

3.7 Standing Position

Figure 3 and Figure 4 show the isometric, front, side and top views as well as vision of a

subject (inset) while performing the task in standing position. In both positions, the table

height is adjusted to 91 cm and 103 cm.

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Figure 3: Standing position, isometric view (left) and front view (right)

Figure 4: Standing position, side view (left) and top view (right)

3.8 Sitting Position

Figure 5 and Figure 6 illustrate the isometric, front, side and top views as well as vision

(inset) of a subject performing the task in sitting position. The table height is adjusted to

91 cm and 103 cm in both positions.

Figure 5: Sitting position, isometric view (left) and front view (right)

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Figure 6: Sitting position, side view (left) and top view (right)

IV. Results

There are two categories of results for this research:

1) Analysis of statistics regarding different setting of workstation design as: Table,

Tools, and Position. The purpose of this assessment to verify which factors

contribute significantly to the productivity.

2) Analysis of working posture. This evaluation is more to observe whether the

working posture of the subject while doing different sets of workstation design are

safe.

4.1 Workstation Design Analysis

The First test is to verify whether two subjects have different quality of work, or

performance. This is necessary to make sure the inferences made from the results may

work for both subjects. The t test and Analysis of Variance (ANOVA) for single factor

were conducted to see any significant different between two subjects. Both tests show

that there is not any significant different between two subjects mean performance and

also the variance. T Stat (0.5438) < T Critical one tail 1.65 or t critical two tail (1.968),

see Table 2. Analysis of Variance of single factor to observe whether there is a significant

different between two subjects also shows the same result, no significant different of two

subjects, F test (0.292) < F critical (3.857), see Table 3.

Table 4 shows result of different setting workstation design for subject # 1. It points up

that different sets present a range of mean and standard deviation. First assessment of the

results may conclude that position of subject either standing or sitting (assuming other

factors Table and Tools in the same set) does not provide significant different. For

example at position Table 91 cm and No Jig, standing and sitting provides 30.69 sec and

30.24, while with jig standing and sitting gives 27.09 sec and 23.62 sec. First evaluation

shows the present of tool gives significant different to the assembly time. For instance the

average of using No Jig and Jig 30.46 sec compare to 25.35 sec. for Table set 91 cm, and

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35.06 sec compare to 26.67 sec for Table 103 cm. While different set of Table i.e. Table

91 cm and 103 cm provides mean 27.91 sec compare to 30.86 sec.

Table 2: t-Test: Paired Two Sample Means

Subject#2 Subject#1

Mean 29.66451 29.38656

Variance 30.38457 45.73449

Observations 288 288

Pearson Correlation 0.011985 Hypothesized Mean Difference 0

Df 287

t Stat 0.543854

P(T<=t) one-tail 0.293482

t Critical one-tail 1.65018

P(T<=t) two-tail 0.586964

t Critical two-tail 1.968264

Table 3: Anova: Single Factor

SUMMARY

Groups Count Sum Average Variance

Subject#2 288 8543.38 29.66451 30.38457

Subject#1 288 8463.33 29.38656 45.73449

ANOVA

Source of Variation SS Df MS F P-value F crit

Between Groups 11.125 1 11.125 0.292305 0.588957 3.85771

Within Groups 21846.17 574 38.05953

Total 21857.3 575

Table 4 Descriptive statistics of Results Subject #1

F-1 f-2 F-3 F-4 F-5 F-6 F-7 F-8 All

Mean 30.69 30.24 27.09 23.62 38.07 32.05 26.00 27.33 29.39

Standard Error 1.19 1.25 0.39 0.27 1.29 0.95 0.75 0.36 0.40

Median 29.01 27.82 27.35 24.03 37.84 31.78 27.21 26.94 27.81

Standard Deviation 7.12 7.47 2.33 1.61 7.73 5.68 4.52 2.19 6.76

Sample Variance 50.71 55.85 5.44 2.61 59.76 32.28 20.40 4.79 45.73

Kurtosis 5.11 1.70 0.19 -0.75 -1.08 1.75 1.68 -0.70 2.54

Skewness 1.91 1.34 0.70 -0.51 0.15 0.95 -1.40 -0.51 1.41

Range 36.45 30.49 8.27 5.16 27.57 28.94 16.20 6.99 42.54

Minimum 21.19 20.97 23.78 20.54 24.26 21.12 15.10 23.14 15.10

Maximum 57.64 51.46 32.05 25.70 51.83 50.06 31.30 30.13 57.64

Sum 1104.99 1088.70 975.40 850.16 1370.49 1153.85 935.90 983.84 8463.33

Count 36.00 36.00 36.00 36.00 36.00 36.00 36.00 36.00 288.00

Confidence Level(95.0%) 2.41 2.53 0.79 0.55 2.62 1.92 1.53 0.74 0.78

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For subject # 2, the results are rather different compare to subject # 1. For example the

Mean for various setting of table and without jig, standing and sitting position provides

22.88 sec compare to 25.55 sec. While using jig, standing and sitting provides 35.52 sec

compare to 27.41 sec. These two results show non consistent for position, on the first set

sitting is slower compare to the second one, this may be due to using jig and no jig.

Further investigation should be carried on which factors contribute more in reducing or

increasing assembly time.

Table 5 shows descriptive statistics results of Subject #2. It shows more consistent in

terms of assembly time, it can be seen from the standard of deviation, there are not much

different.

Table 5 Descriptive statistics of Results Subject #2

A-1 A-2 A-3 A-4 A-5 A-6 A-7 A-8 All

Mean 22.88 25.88 32.52 27.41 31.61 29.68 31.90 35.42 29.66

Standard Error 0.61 0.61 0.82 0.51 0.92 0.88 0.43 0.36 0.32

Median 22.44 25.55 31.43 26.27 30.70 28.97 32.35 35.93 29.36

Standard Deviation 3.67 3.65 4.91 3.04 5.53 5.31 2.58 2.19 5.51

Sample Variance 13.49 13.33 24.07 9.25 30.61 28.17 6.65 4.79 30.38

Kurtosis -0.38 -0.57 -0.42 -0.81 1.07 2.18 -1.26 -0.96 0.17

Skewness 0.04 -0.16 0.97 0.87 0.94 1.00 -0.08 0.31 0.22

Range 14.68 14.26 14.53 8.59 25.04 26.09 7.30 7.01 32.10

Minimum 15.39 18.19 27.29 24.70 22.45 19.46 28.42 32.35 15.39

Maximum 30.07 32.45 41.82 33.29 47.49 45.55 35.72 39.36 47.49

Sum 823.83 931.60 1170.88 986.84 1138.05 1068.54 1148.48 1275.16 8543.38

Count 36.00 36.00 36.00 36.00 36.00 36.00 36.00 36.00 288.00

Confidence Level(95.0%) 1.24 1.24 1.66 1.03 1.87 1.80 0.87 0.74 0.64

Figure 7 and Figure 8 illustrates the mean and standard deviation for every set of

workstation design for each subjects. Subject #1 (F) and subject#2 (A), the Mean for each

set of workstation design is not much significant, however most of the standard deviation

for subject #2 (A) are less than Subjects# 1, it shows more consistent in assembly time.

Further investigation is to observe whether there is a significant different among the

setting of experiments, Analysis of Variance (ANOVA) for with single factor for first

subject (Subject #1) and also subject #2 were used. The F Test for both subjects show

there exist a significant different among the setting of the experiments, meaning different

position, the height of table and the use of Jig and no Jig, contribute to significant

different to the response time (assembly time). Table 6 and 7 shows the ANOVA analysis

for single factor of subject t#1 and #2.

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Figure 7 Mean of two subjects for different set of factors (in second)

Mean

0.00

10.00

20.00

30.00

40.00

50.00

Mean

Mean 22.8 30.625.8 30.2 32.5 27.027.4 23.6 31.638.0 29.632.0 31.9 26.0 35.427.3

A-1 F-1 A-2 f-2 A-3 F-3 A-4 F-4 A-5 F-5 A-6 F-6 A-7 F-7 A-8 F-8

Figure 8 Standard errors of two subjects for different set of factors (in second)

Standard Error

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

Standard Error

Standard Error 0.61 1.19 0.61 1.25 0.82 0.39 0.51 0.27 0.92 1.29 0.88 0.95 0.43 0.75 0.36 0.36

A-1 F-1 A-2 f-2 A-3 F-3 A-4 F-4 A-5 F-5 A-6 F-6 A-7 F-7 A-8 F-8

Further analysis to investigate which factors contribute more significant than the others,

3-way ANOVA is applied. Table 8 for subject#1 illustrates each factors Table, Tool, and

Position are significantly contribute to the various response time (assembly time). Among

three factors, Tools is the most significant, Table height the second, and last is the

Position whether standing or sitting. Combination factors of Tools and Table also shows

significant effect to the assembly time, whereas combination of Table - Position and

Tools - Position are not significantly contributes to assembly time. This information

provides evidence that the existence of Tools in this case the use of Jig has an effect on

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assembly time. It means also the design of Jig is help the workers’ productivity. Subject

#2 has slightly different results compare to #1.

Table 6 ANOVA of Single Factor for Subject#1

Anova: Single Factor combination of Table-Tools and Position

Subject # 1

SUMMARY

Groups Count Sum Average Variance

F-1 36 1104.99 30.69417 50.7076

F-2 36 1088.7 30.24167 55.84857

F-3 36 975.4 27.09444 5.4411

F-4 36 850.16 23.61556 2.607043

F-5 36 1370.49 38.06917 59.76303

F-6 36 1153.85 32.05139 32.28432

F-7 36 935.9 25.99722 20.39859

F-8 36 983.84 27.32889 4.785222

ANOVA

Source of Variation SS Df MS F

P-value F crit

Between Groups 5011.557 7 715.9367 24.70499 3.81E-

26 2.042359

Within Groups 8114.241 280 28.97943

Total 13125.8 287

Table 7: Anova: Single Factor

Subject #2

SUMMARY

Groups Count Sum Average Variance

A-1 36 823.83 22.88417 13.48785

A-2 36 931.6 25.87778 13.32894

A-3 36 1170.88 32.52444 24.0651

A-4 36 986.84 27.41222 9.248635

A-5 36 1138.05 31.6125 30.60869

A-6 36 1068.54 29.68167 28.17377

A-7 36 1148.48 31.90222 6.646349

A-8 36 1275.16 35.42111 4.788833

ANOVA

Source of Variation SS Df MS F P-value F crit

Between Groups 4158.187 7 594.0267 36.45785 4.69E-

36 2.042358

Within Groups 4562.186 280 16.29352

Total 8720.373 287

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Table 8: 3 way ANOVA for Assembly of Electric tool

Subject # 1

Source Df SS MS F Stat F-crit

Table 1 626.67 626.67 21.62 3.87441

Tool 1 3285.43 3285.43 113.37 3.87441

Position 1 334.18 334.18 11.53 3.87441

Tab-tool 1 194.16 194.16 6.70 3.87441

Tab-pos 1 2.56 2.56 0.09 3.87441

tool-pos 1 84.10 84.10 2.90 3.87441

3-way 1 484.46 484.46 16.72 3.87441

Error 280 8114.24 28.98

Total 287 13125.80

Table 9 illustrates 3 way ANOVA results for Subject # 2, Table height is the most

significant factor effect to the assembly time, while Tools (with Jig and without Jig) is the

second factor, and position (standing or sitting) does not contribute significantly the

assembly time. Second subject has relatively shorter than the first subject. That might be

the reason the height of table does has an effect to the response time. The combination

Table and Tool have significantly effect to the assembly time, this may be understood

since both factors are significant. However, the other two combinations i.e. Table-

Position, and Tools-Position combinations do not significantly contribute to results.

Table 9: 3 way ANOVA for Assembly Time

Subject # 2

Source df SS MS F Stat F-crit

Table 1 1785.43 1785.43 109.58 3.87441

Tool 1 1331.88 1331.88 81.74 3.87441

Position 1 1.27 1.27 0.08 3.87441

Tab-tool 1 119.15 119.15 7.31 3.87441

Tab-pos 1 61.83 61.83 3.79 3.87441

tool-pos 1 31.75 31.75 1.95 3.87441

3-way 1 826.89 826.89 50.75 3.87441

Error 280 4562.19 16.29

Totals 287 8720.37

As mention earlier there are 8 different positions of working, every position was analyzed

to determine whether the posture is safe or exposed to hazards. RULA Software was used

as a tool to generate the results. According to RULA Software, the lowest of RULA score

indicates that the particular working posture is safe. The results of every working posture

adopted by the subjects in various condition of workstation are presented in the following

sections.

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4.2 Analyses of Working Posture

In a workstation, a subject may perform a task in various working posture. Sometimes the

working posture is safe to the subject and sometimes it can be exposed to the hazards.

Improper workstation design will expose to occupational hazards associated with

awkward working posture. For example, if the working height is not properly adjusted or

positioned too low, subject needs to perform the task in bending posture. Marras, W. S.

(2000) identified that the awkward working postures such as bending, twisting and static

are the main contributors to occupational hazards associated lower back pain in variety of

industries. Therefore, the attention on working posture has to be given priority to ensure

it is safe to the subject. There are various tools that have been introduced to analyze

working posture; one of the common tools is RULA analysis (McAtamney, L. and

Corlett, E. N., 1993). RULA analysis may be an effective tool that can be used in the

current research.

Before the posture of a subject being analyzed, the researchers have to consider the

condition of workstation and anthropometry of subjects. The workstation was designed

using CATIA Part Design according to the actual dimensions of real workstation.

Meanwhile, the researchers were measured the anthropometry of subjects using an

antropolometer. The specific dimensions of subjects’ anthropometry, as shown in Table

10 were adapted to create a manikin in RULA Software as shown in Figure 9.

Consequently the drawing of workstation is transferred into RULA Software and the

created manikin was positioned at the workstation. This is done by referring to the real

situation to ensure RULA Software generates an accurate result. The orientation of

subjects is set based on magnitudes of working posture such as neck angle, trunk angle of

the subjects, as shown in Table 11. A complete analysis of working posture using RULA

Software is shown in Figure 10.

Table 10: Anthropometry data for the subjects

Body parts Subject 1 Subject 2

Stature 1702 mm 1721 mm

Axilla 1270 mm 1280 mm

Chest (standing) 1230 mm 1240 mm

Waist (standing) 956 mm 970 mm

Crotch (standing) 764 mm 750 mm

Acromion-radiale length 300 mm 290 mm

Radiale-stylion length 250 mm 240 mm

Chest breadth 320 mm 290 mm

Waist breadth 290 mm 264 mm

Hip breadth (standing) 340 mm 324 mm

Elbow height (standing) 1050 mm 1050 mm

Elbow height (sitting) 900 mm 800 mm

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Figure 9: A manikin was created based on anthropometry of subject

Table 11: Magnitudes of working posture of subjects

Workstation Position Subject

Upper Arm Angle

Forearm

Angle

Wrist Angle Neck Angle

Trunk Angle

L R L R L R

Table height: 91 cm

(without jig) Standing

1 30º 17º 75º 70º 12º 10º 18º 14º

2 13º 12º 95º 94º 10º 7º 17º 18º

Table height: 91 cm

(without jig) Sitting

1 55º 54º 88º 93º 17º 16º 20º 15º

2 18º 15º 70º 80º 16º 10º 12º 18º

Table height: 91 cm

(with jig) Standing

1 9º 30º 61º 98º 8º 9º 18º 25º

2 15º 17º 80º 85º 5º 9º 15º 16º

Table height: 91 cm

(with jig) Sitting

1 17º 14º 62º 77º 5º 10º 12º 16º

2 17º 10º 98º 96º 6º 5º 10º 20º

Table height: 103 cm

(without jig) Standing

1 7º 13º 62º 83º 3º 6º 5º 10º

2 10º 11º 84º 84º 9º 10º 10º 0º

Table height: 103 cm

(without jig) Sitting

1 65º 55º 98º 88º 16º 16º 14º 18º

2 60º 55º 102º 90º 5º 8º 17º 15º

Table height: 103 cm (with jig)

Standing 1 8º 5º 44º 60º 12º 10º 13º 10º

2 3º 3º 60º 62º 7º 5º 17º 0º

Table height: 103 cm (with jig)

Sitting 1 6º 30º 88º 91º 18º 17º 12º 12º

2 6º 31º 90º 80º 4º 7º 20º 16º

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Figure 10 illustrates the example of one results of posture analysis. As depicted in the

figures, the column at the right hand side of dialogue box, it states the posture score of

every body part. In the left hand side, the dialogue box recorded condition of posture

(static, intermittent, and repeated); repeat frequency of the posture (< 4 times/minute or >

4 times/minute); condition of arm (supported, across body midline, and balance) amount

of load handled by the subject; and the RULA Score. From the presented results, the

posture score for every body part is in the rage of 1 to 3. Orientation of upper arm,

forearm, wrist, muscles, neck, trunk and legs are considered safe, if the posture score 1 or

2. Meanwhile, further investigation should be carried-out if the posture score reaches 3.

As illustrated in Figure 10, the score of wrist posture is 3 when the subject flexed his

wrist at 30 while performing task in standing position.

Table 12 summarizes the results of working posture for the subjects while they perform

the task in various condition of workstation. The workstation is adjusted to two different

heights, 91 cm and 103 cm respectively, with/out a tool (jig) and subjects positions,

standing and sitting. Table 11 describes in detail the conditions of workstation and the

positions of subjects perform the task. From the various condition of workstation, it can

be summarized that 69% of working posture adopted by the subjects is acceptable, and

31% need to be investigated further, as recommended by RULA Score.

Observing those working postures further for RULA score 3, one of the explanation is

that Subject #1has height 172 cm and the position of Table at 91 cm. In this case the

height of table is too low for him to perform the job.

Figure 10: Result of RULA analysis generated by RULA Software

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Table 12: RULA Score for different table heights and positions, as well as with/out tool

Table

height Tool Position Subject

RULA

Result Indication Score

91 cm without

jig Standing 1 3

Working posture

needs further

investigation

Wrist is flexed at

17

2 2 Working posture

is acceptable

91 cm without

jig Sitting

1 2 Working posture

is acceptable

2 3

Working posture

needs further

investigation

Wrist is flexed at

16

91 cm with jig Standing

1 3

Working posture

needs further

investigation

Trunk is flexed at

25º

2 2 Working posture

is acceptable

91 cm with jig Sitting

1 2 Working posture

is acceptable

2 2 Working posture

is acceptable

103 cm without

jig Standing

1 2 Working posture

is acceptable

2 2 Working posture

is acceptable

103 cm without

jig Sitting

1 3

Working posture

needs further

investigation

Wrist is flexed at

16 and upper arm

is flexed at 65º

2 2 Working posture

is acceptable

103 cm with jig Standing

1 2 Working posture

is acceptable

2 2 Working posture

is acceptable

103 cm with jig Sitting

1 3

Working posture

needs further

investigation

Wrist is flexed at

18

2 2 Working posture

is acceptable

17

V. Conclusion and Further Research

Significant findings pertinent to the impact of various condition of workstation design to

response time (assembly time) and to the working posture have been generated from this

research. The following findings are concluded:

(i) The design of jig has significantly help subjects in performing their jobs. It has

shown statistically this factor is significant contributes to the Response time

(assembly time) of the plug assembly line.

(ii) The design of the jig does not have any implication in working posture. Either

provided or not provided with the jig, both subjects show a safe working posture.

However, appropriate design of tool needs to ensure the wrist posture of subject

within safe limit.

(iii) The position: standing and sitting while performing task does not contribute

significantly to the response time, both position of working posture are safe.

Subjects adopt safe working posture when they perform the task in standing

position with working height is slightly high. Correspondingly, their posture is

safe when perform the task in sitting position with working height is slightly low.

(iv) The Table height also has significant factor to the response time. Two sets of table

height, one is for precision job, the other for non-precision job. It turns out that

table height of 91 cm (non-precision) is more suitable for the job, it shown by the

response time shorter than the 103 cm (precision). This job does not require

precision position of the table.

(v) The table height of working also plays an important role to determine the safe

posture of a subject. When the table height is adjusted appropriately to subject’s

height or, when a subject manipulating the task in elbow height, the posture

adopted will be safe.

There are some areas need to explore further, among others are:

1) Design of jig was chosen can handle 4 plugs at the same time, the optimum number

should be investigated, how many is the optimum plugs that give the shortest

assembly time;

2) Design of assembly process, can be explored further whether two or three series of

subjects would be better than single subject finish the job.

3) Design of product itself can be further investigated, the number of components would

play significant contribution the response time.

18

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