International Journal of Mechanical Engineering and Technology (IJMET)
Volume 10, Issue 03, March 2019, pp. 102-109. Article ID: IJMET_10_03_010
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=3
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
Scopus Indexed
DEVELOPMENT OF BIOMECHANIC METHODS FOR
ERGONOMIC EVALUATION: COMPARISON WITH
RULA AND SES METHODS
Sajiyo and Muslimin Abdulrahim
Department of Industrial Engineering, Faculty of Engineering, University of 17 Agustus
1945, Surabaya, East Java, Indonesia
Nurul Aziza
Department of Industrial Engineering, Faculty of Engineering, University of Maarif Hasyim
Latif, Sidoarjo, East Java, Indonesia
Qomariyatus Sholihah4
Department of Industrial Engineering, Faculty of Engineering, University of Brawijaya,
Malang, East Java, Indonesia
ABSTRACT
Various methods have been developed to evaluate workload in everyday life, and
various methods of observation have been carried out. But it is still a debate until
now. In this journal, the development of biomechanical methods for evaluating
workloads which ergonomics will then be compared with the observation method. The
observation method used is the SCANIA Ergonomics Standard (SES) and Rapid Upper
Limb Assessment (RULA) methods which will be used to assess ergonomic workloads
on two simulation workstations such as tightening, loosening, or increasing the
number of pipes, and carrying out other actions. Sensors are also used to measure
biomechanical data (Inclinometers, Accelerometers, and Goniometers). The results
obtained show an assessment of the risk factors of RULA and SES according to the
final results using biomechanical methods. However, there is a mismatch in the neck
and wrist posture. In conclusion, the biomechanical approach is more appropriate
than the observation method, but several risk factors are evaluated by unmeasured
observation methods with biomechanical techniques that have been developed.
Keyword head: RULA, SES, Biomechanics, Ergonomics, MSDs.
Cite this Article: Sajiyo, Muslimin Abdulrahim, Nurul Aziza and Qomariyatus
Sholihah, Development of Biomechanic Methods for Ergonomic Evaluation:
Comparison with Rula and Ses Methods, International Journal of Mechanical
Engineering and Technology, 10(3), 2019, pp. 102-109.
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1. INTRODUCTION
As discussed in various studies, related to widespread musculoskeletal disorders in
manufacturing industries known as multi-factorial where the disease is caused by work that is
physically heavy, psychosocial, organizational and individual factors which are the most
important causes. Physical ergonomics risk factors include overly forced labor, overly rigid
postures, material lifting, material transfer and vibration which are considered to be the main
factors that are very high risk for workers, causing disorders of Musculoskeletal Disorders
(MSDs). To manage and control physical risks in ergonomics, there are several methods that
have been developed for exposure assessment and estimation of the risk of injury in various
fields of work. This method includes the paper-based observation methods such as RULA,
OCRA, REBA, etc. which are the most important techniques that are generally applied to
ergonomics which aim to assess one's posture while working [1,2].
ACGIH level index and activity strains are methods for measuring strong labor. This
manual material handling is evaluated using the NIOSH, MAC (English), ManTRA
(Australia), and code (New Zealand) equations. Various types of research have applied this
method to analyze various jobs at work stations, but their validity is still a matter of debate.
Many industrial companies develop internal methods for ergonomic analysis, and several
research articles have discussed the efficacy in using these methods. The things that need to
be considered in ergonomics and manufacturing are the accuracy and accuracy of methods
that must be applied to workplace analysis. Risk management policies related to MSDs will
not be successful without accurate ergonomic risk assessment [2,3].
In addition to observational methods, biomechanical methods (direct measurements) have
been developed by relying on sensors to record body movements. Angular measuring,
inclinometry, accelerometer, and electromyography are the most popular direct methods for
measuring power posture, movement and strength. Most of the data is precisely related to the
exposure variables that can be provided by biomechanical procedures, and developing
appropriate protocols is very important to apply. Comparing the results of the method directly
with the observation technique will provide an opportunity to increase the validity of the
observation method. Development of an accurate protocol can show which sensors should be
used and how measurements should be made before the workplace analysis is carried out
using biomechanical methods [4].
Therefore, the purpose of this study is to develop an appropriate protocol for
biomechanical measurement in manufacturing. By testing the protocol and comparing it with
two observation methods, namely SCANIA Ergonomic Standard (SES) and RULA which are
other objectives of this study. SES is an observation method at home that is used to measure
posture, strength, lifting and repetition, while RULA is a common method for assessing
posture [5].
2. METHOD
2.1. Biomechanical Measurement
First, select the sensor to measure repetition, movement and posture on the body.
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Figure 1. The placement of sensors for measurement of body movements
Inclinometers are used to measure body tendencies in certain areas, such as the head and
upper back. To measure neck posture, data was taken through a second sample of
inclinometers placed at the occipital bone (plate-shaped membrane bone located at the lower
back of the skull) and in the cervical-thoracic spine at the C7-Th1 Level. The total amount of
time when the posture head is more than 10 ° forward or back compared to the upper back is
characterized as a head posture [2,3,4].
Two triaxial accelerometers are placed along the top of the arm in the middle of the
humerus. The line rounded to the head of the acromion to the lateral epicondyle is measured
and divided into two for placement of the shumerus accelerometer. They are corrected
laterally with both hands on the Y axis vertically. The arm's height too. Therefore, a repetition
is performed. Another accelerometer is placed on L3 from the lumbar spine to assess the rear
posture. The recording is done between + 1g and -1g [1,4].
Biaxialelectro-goniometers are used to measure flexion and extension of right and left
wrist irregularities, flexion and extension of the wrist characterized in this case studying hand
postures. All sensors are small and placed above the body with double-sided adhesive tape
(Figure 1) [6].
The zero position for the head and upper back is the definition of the first data recording
when the subject stands upright in an ordinary posture and sees an eye level. The reference
position for the upper arm and lower back is established when the subject stands upright with
their hands hanging on the side of the body. After the wrist relaxes on the side of the body, it
is taken as a reference position of the wrist [1,2].
All postures and movements are recorded in the data logger and recorded in the camera
either in the reference position or when performing four simulation tasks. All data is then
transferred to the computer and actions are synchronized between movie data and loggers.
Two work stations were selected Air Component & Tie Wrapping which is a station
simulation work in truck manufacturing for operator training. As will be explained below
[3,4]:
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1. Tighten the hands with the tool (duration of 296 seconds)
2. Place the tube and wrap the Plastic Rope (duration of 462.5 seconds)
3. Loosen hands with a tool (duration of 148 seconds)
4. Another action to test the sensor limit (70 seconds duration)
2.2. Observation Method
The first observation method for evaluating ergonomic risk potential in a simulated work
station is the SCANIA inhouse Ergonomics Standard Method (SES). This method is adapted
to ergonomic risk requirements in manufacturing assembly and is designed to evaluate station
multi-task work. SES not only assesses posture but also evaluates compelling and lifting
tasks. Twenty parameters are classified into 5 categories to determine their ergonomic criteria.
To prioritize assessments, the results are sorted in the following order: Green or normal zones
that show the minimum risk of MSDs, and this type of risk is acceptable. Yellow indicates a
zone that has a moderate risk of MSDs. Tasks and yellow jobs at the Station may require
some corrective action in the future. Red is an action zone where there is a considerable risk
of MSDs for workers, and changes are needed as soon as possible. Finally, double red (DR)
shows the potential for excessive ergonomic risk for tasks assessed as DR, so they must be
stopped immediately and solutions found [1,2].
Table 1 Comparison of Priorities for Ergonomic Risks by RULA and SES
Level 1
Level 2
Level 3
RULA
Score
1-2
3-4
5-6
Level 4
7
Category
SES Colour
Definition
Green
Yellow
Red
Acceptable
More investigation is needed
Immediate modification is required
Modification is needed as soon as
possible
Double Red
The amount of yellow, red and DR is then added and the color of the work station is
determined. The worst color is considered as the final evaluation of the work station. Another
observation method used in this study is Rapid Upper Limb Assessment (RULA). This
method is widely used by ergonomics and researchers at various jobs to assess the risk of
upper limb disorders. RULA measures ergonomic risk based on posture, weight, duration and
frequency, and then provides a score that shows the risk of injury for the task to be evaluated.
The scale level for the assessment posture varies from one to seven, one shows the best and
seven shows the worst. In RULA the body is divided into two zones, A and B, which A
includes the upper arm, forearm, and wrist position, and group B neck and stem. The end of
the score produced by RULA shows posture and ergonomics containing four levels. Table I
shows the categorization of the scores produced by SES and RULA. The method of
observation is carried out by an ergonomist who is experienced and analyzed by Excel.
MATLAB software is used to analyze biomechanical data [3,4].
3. RESULT
Observations and video recordings are performed for all selected tasks. The general results of
the study show that the evaluation posture with different methods on the evaluated task
produces the same results. However, some differences occur for the position of the neck and
wrist. Furthermore, the direct method provides a variety of information that clearly reveals
different aspects of the work station for ergonomics and decision makers. The main advantage
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of the direct method is to observe whether body movements when performing tasks are
symmetrical.
3.1. Tighten by Hand and with Tools (Task One)
The neck posture score with the RULA method is 4. (20° <neck flexion) for 73% of the total
task time, while the SES Method shows that neck posture for 46% of tasks, time is red (45°
<neck flexion), and for 27% from time, the period was yellow (20° <neck flexion <45°). The
inclinometers show that for 80% of the time for this task. The neck is flexed between 10° and
20°, although it never records flexion of more than 20°. The results for the neck posture for
this task with the three methods differed better.
For 13% of the tightening duty period, the stem score was assessed as 2 with RULA (10°
<flexion return <20°). SES produces green for the rear posture, because it bends forward less
than 20° during this task. The accelerometer used as an inclinometer for the lower back
showed flexion return <20° for 81% of the time of duty. Therefore it is consistent with the
RULA and SES methods.
The upper arm score with RULA for 10% of task tightening is 2 (20° upper arm lift <45°)
and for 90% of that time 1 (upper arm lift <20°). The lower arm position of the score with
RULA is 1 during this task. The SES assessment for the static work posture of the shoulder
and arm is green, while the bending motion is forward or outward is less than 45°. There are
no criteria by the SES method for assessing the forearm. Two accelerometers on the left and
right arms indicate that the arm has never experienced flexion or abduction of more than 40°
during this task. The method reveals the same results for arm posture assessment.
Similarly, the RULA score for wrist posture is 1 (neutral) and the same results are
observed by the SES method. However, electro-goniometry of both hands shows that for 30%
of wrist postures the duration of the task is more than 15°, the results of which are not
consistent with the observation method. Repetition evaluated with SES was obtained red
because tightening by hand or tool was repeated more than 3 times per minute (according to
SES criteria). The number of repetitions is calculated with an accelerometer, and four
repetitions to tighten with the torque and eight repetitions for hand tightening are observed for
each action (Figure. 2). In total, 50 hand repetitions and 32 repetitions with the tool recorded
more than 5 minutes in this task. Although repetition is assessed as an action zone (red) with
the SES method (the same results as the direct method), it is difficult to determine the real
value of the repetition number by the observation method. The method is immediately clearly
visualized the number and pattern of repetitions.
The final RULA score for this assignment is 5, which indicates that further investigation
and changes are needed immediately. The overall color of this task with the SES method is
green, which is in the normal zone and is acceptable.
Table 2 Comparison of Ergonomic Risk Assessments by RULA, SES, and Direct Methods
Tightening
Task
Wrapping
with plastic
Neck
Backs
Arms
RULA
Score
4
2
2
Wrists
1
Green
Neck
Backs
4
3
Red
Yellow
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SES Colour
Direct Method
Red
Green
Green
Neck flexion<20°
Back flexion<20°
Arm lifting<40°
flexion and extension
>15°
Neck flexion<20°
Back flexion>45°
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strap
Loosening
task
Other tasks
Arms
2
Green
Wrists
3
Red
Neck
Backs
Arms
4
2
2
Red
Green
Green
Wrists
1
Green
Neck
Backs
Arms
1
4
5
Green
Red
Red
Wrists
3
Red
Arm lifting<40°
flexion and extension
>15°
Neck flexion<20°
20°<Back flexion<45°
Arm lifting<40°
flexion and extension
>15°
Neck flexion<20°
Flexion>45°
Arm lifting>40°
flexion and extension
>15°
3.2. Placing Tubes and Wrapping with Plastic Straps
Duration of assignments where all different actions are carried out in about 8 minutes. The
RULA score for neck posture for 51% of assignment time was 2 (10° <neck flexion <20°) and
for 19% of the assignment time was 3 (20° <neck arch). The overall score for the neck is 4
because sometimes the neck bends sideways during this task. The SES method shows red (45°
<neck flexion and sideways / rotation> 30°) for neck posture for only 10 seconds of all duty
time (2% of task time), while for most of the duration of the assignment the neck posture is
rated as yellow. Since the worst color sets the final evaluation in the SES method, because the
end for the neck posture is red. The direct method shows that the neck is flexed 10° and 20°
for 26% of the task time. In this study bending the neck side posture was not assessed by an
inclinometer. Again, for this task the results of the observation method conflict with the
inclinometer record.
The RULA score for 70% of the assignment time for rear posture 3, is defined as back
flexion more than 20° and less than 60°. Rod spinning and side bending are not observed in
this case. The stem posture is assessed by SES as yellow, which indicates forward bending
between 20° and 45°. The accelerometer at L3 shows lower back flexion between 20° and 45°
for 68% of the duration of the task, and for 13% of the time the posture of the rod is more
than 45°. Three methods provide similar results for the rear posture for this task.
The RULA score for the upper arm is 4 (the upper arm is raised> 90°) for less than 5
seconds from the total task time while for 95% of the duration of the task, this score is 2 (20°
<upper arm lifts <45°). Static posture of the shoulders and arms was assessed by SES as green
(upper arm lift <45°). Left and right arm positions are evaluated at more than 40° by the direct
method of only 1% of the task time, and this is consistent with other methods. The wrist
posture was rated as 3 by the RULA, showing flexion or extension of more than 15°, and the
results on the SES for this task were red. Electro-goniometry demonstrates that wrist posture
is more than 15° for 65% of period work. The overall RULA score in this task is 5 and the last
color for the SES method is green, as for the tightening task.
Loosening with Hands / Tools and Other Actions The results of posture assessment during
the task of loosening are the same as the tightening task, especially for the neck, back and
upper arms. However, the length of the awkward posture is shorter for tightening tasks and
the number of repetitions is also different. Table 2 shows the results of the observation
method and the direct method for these tasks. Two accelerations with the left and right arms
are given more information about hand movements and symmetry of body movements. As
shown in Table 3, although the tightening task involves the same number of jobs, with both
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tools and hands, the acceleration between the two hands for this is not the same action.
Tightening with the device is more symmetrical for both arms compared to tightening with
the hand.
Table 3 Asymmetric Movement of Arm During Manual Prevention Compare with Strength with
Tools Calculated by Acceleration (G)
Action type
Arm
RMS
0.77
0.57
0.95
0.3
0.82
0.49
Right arm
Manual
Left arm
Right arm
Tool
0.33
Left arm
0.93
RMS
1.34
1.23
1.31
1.26
4. DISCUSSION
This research was conducted to develop a biomechanical method that allows measurement
and calculation of movements and positions in plant assembly and manufacturing. We
compared the biomechanical results of measurements with two observation methods. Overall,
we did not find a big difference between the three methods. For most bodies all methods show
the same results, although biomechanical methods provide more precise information.
However, some inconsistencies occur observed, especially in the assessment of the neck and
wrist. As explained, to tighten and loosen the tasks of the second observation method for the
neck in action zones and further changes should be immediately possible, while the
inclinometer is measured at neck angles of less than 20 ° in these tasks which are in the
normal zone and accepted. One reason for this conflict might be that the observer looks at the
neck in an anatomically straight line while the inclinometer gives the neck angle to be
associated with the upper back position. Proven, flexible neck and flexible upper back [5,6].
Furthermore, several differences were found between methods for assessing wrist posture.
In contrast to the neck of the posture, the electro-gonimeter gives an angle value for both
wrists that is much worse than the results of the observation method. The position of the
reference to the wrist when measuring with a goniometer might be the reason for this
difference. Goniometers measure flexion and extension of the functional position of the hand
[3,4].
The direct method will provide the possibility of measuring precisely how many
repetitions occur during an individual task. In addition, motion symmetry is another criterion
that we can never value with observational methods. However, further investigation is needed,
especially in the actual workplace, to confirm the results of this study [7,8].
5. CONCLUSION
It can be concluded that the results obtained indicate that the sensor is more appropriate than
the observation method because it reduces the error rating. Accelerometers in the arms and
back are sufficient to assess body posture rather than inclinometers. Where it provides
complementary information about speed movement, symmetry and repetition.
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