Transcript Constraint

WORK PERFORMANCE
COMPARISONS OF
ERGONOMICALLY AND
NON- ERGONOMICALLY
SCREW DRIVERS
By
Abdullah AL-Shehri
(422000373)
INTRODUCTION
Any business interested in controlling costs needs to consider those
related to employee injury and illness
 Causes of Musculoskeletal Disorders :
The scope of this problem has lead to intense interest in
understanding the causes of MSDs and their associated solutions
 Posture as a Physical Risk Factor:
All of these risk factors have been subject to empirical research
(in isolation and in numerous combinations) concerning their
contribution to work-related MSDs
Problem Description
It is important to remember that MSDs are a
result of complex interaction among the elements
described above
• It is often convenient to provide general
guidelines for the design of work.
• A review of a number of textbooks that
specifically address hand/wrist posture and the
design of hand-tools leads to the ubiquitous
recommendation to “bend the tool, not the wrist.”
•
There are
Screw driver
12 conditions
Ergonomic
Horizontal
Vertical
Constraint unconstraint
Non-Ergonomic
Slanted
Horizontal
Constraint unconstraint
Constraint unconstraint
Vertical
Slanted
Constraint unconstraint
Constraint unconstraint
Constraint unconstraint
Methodology
Apparatus
(1) hand-held stopwatch.
2) EMG device.
3) Screw driver sets
Independent Variables
1) Screw driver
Two levels of screw drivers will be applied
i) straight-handle
ii) bent–handle
2) Constraint
constraint conditions (palm)
unconstrained condition (any manner desired)
3) Work Surface Orientation
Three different work surface orientations will be
used in this experiment:* Horizontal
* Vertical
* Slanted at a 45° angle.
Dependent Variables:
Productivity
Productivity will be measured as the time (measured to
the hundredth of a second) taken to complete three cycles
for each given condition.
EMG activity analysis
(electromyography=EMG) EMG values such as root mean
square (RMS) and rectified absolute mean (RAM) were
measured during the twelve treatments.
To measure the differences in the twelve treatments,
Palmaris longus muscles on the right side of the
body were considered for the analysis.
Three maximum contractions were executed in
order to normalize the signals.
Muscular activity (EMG) were recorded for
the entire treatment using disposable pregelled surface electrodes.
The two electrodes were attached to the body
on the long muscle to the hand.
The signals of the EMG values attained were recorded using
“CASSY Sensor, Ag/AgCl” as shown down, with an
inter-electrode center distance of 30 mm.
Palmaris longus muscles
As shown in the Figure, one of the Cassy-Lab
screens shows analyzing the muscular
activity while the subject was performing
the task.
Experimental Design:
Each subject was performed twelve treatments in a
random order. Time, subjective ratings and muscular
contraction were the main dependent variables. Three
factors that represent the main independent factors
which are: screw type, orientation and constraint.
The levels of screw type were straight and bent
handle (ergonomically). And, the levels of orientation
were: horizontal, vertical and inclined and the level of
constraint were constraint and unconstraint.
Finally, the numbers of the participated students
were 12 subjects. SPSS for MS Windows 10.0
was employed to analysis the time, subjective
ratings as well as EMGs data. A within subject
design in the form of “screw type by work
surface orientation by constraint )” was
implemented. Only absolute mean and root
mean square of the EMGs signals for Palmaris
longus muscles were considered.
Controlled Variable
Working Height
An important consideration in this experiment was the
working height for the different experimental conditions,
since working height had a direct effect on the dependent
variables (particularly posture).
Subjects
Twelve male subjects were recruited from the
general university population.
Protocol
1- Anthropometry
Anthropometric data (stature, height to right acromion
process and right lateral epicondyle of the humerus) were
collected.
Student Dimension
Mean
SD
Min.
Max.
1. Age (years)
2. Weight (kg.)
3. Stature (cm.)
4. Shoulder height (cm.)
5.Elbow height (cm.)
24.25
80.24
170.4
147.8
109.86
2.6
7.03
7.48
7.83
7.83
20
70
158
133
102
28
90
180
160
121
2- Trial Randomization
All subjects were performed all twelve conditions
(screw driver by orientation by constraint).
3- Subject Instructions
The particular task was explained to the subject.
The subject was told that he was free to position
himself in a standing position in front of the work
surface whatever he felt comfortable.
4- Subject Practice
practice session during which they complete a
minimum of two cycles of the task in the vertical,
horizontal orientation and slanted condition with
both types of screw drivers.
5- Trial Data Collection
During performance of the twelve conditions (two screw
drivers x three orientations x two constraints), data will be
collected at standing in front of the work surface
The subject will be asked if he was ready, if so, he had
instructed to begin completion of three cycles of the task.
Data collection form
In a random order
Results:
1) Root Mean Square of the arm Muscular Activity:
To assess the effect of the independent variables on arm
muscular activity, MANOVA was performed. Only one of
the main variables had significant effect on arm muscular
activity that was constraint variable, F(1,11) = 5.777,
p<0.035. Also, one of the second-order interactions had
significant effect on the arm performance; screw type by
orientation, F(2,22)=11.407, p<0.001; Also, the threeorder interaction had a significant effect on the arm
muscular activity, F(2,22)=5.508, p<0.011 .
As shown down at constraint variable, the muscle activity was
higher non-significantly in a case of straight screw driver relative
to ergonometric screw driver in working at vertical surface.
However, there were significantly higher in a case of straight
screw driver relative to ergonometric screw driver in working at
both inclined and horizontal surfaces, p<0.000.
0.4
Root mean square
0.39
0.38
0.37
0.36
straight
0.35
ergonomic
0.34
0.33
0.32
0.31
0.3
Horizantal
Vertical
Constraint
Inclined
As shown down at unconstraint variable, The muscle activity was
higher significantly in a case of ergonometric screw driver relative
to straight screw driver in working at horizontal surface, p<0.000.
However, there were non-significantly higher in a case of
ergonometric screw driver relative to straight screw driver in
working at both inclined and vertical surfaces,
0.7
Root mean square
0.6
0.5
0.4
straight
0.3
ergonomic
0.2
0.1
0
Horizantal
Vertical
unconstraint
Inclined
2) Absolute Mean of the arm Muscular Activity:
To assess the effect of the independent variables on arm
muscular activity, MANOVA was performed. None of
the independent variables had significant effect on arm
muscular activity at p<0.05.
3) Execution Time:
To assess the effect of the independent variables on
execution time, MANOVA was performed. The result
showed that Screw types were significantly different,
F(1,11)=94.539, p<0.000. Also, orientation surfaces were
significantly different, F(2,22)=19.348, p<0.000.
As shown down subjects reacted significantly faster in
straight screw driver (e.g., 6.685 sec./screw) compared to
ergonometric screw driver (e.g., 16.069 sec./screw).
18
16
execution time
14
12
10
8
6
4
2
0
straight
ergonomic
screw type
To assess the effect of the orientation variable on execution
time, One Way ANOVA was performed. The result
showed that there was only a significant different
between horizontal and inclined orientation surfaces,
p<0.015. On other wards, subject reacted significantly
slowly at inclined surface compared to horizontal
surface. In addition to, subject reacted non-significantly
slowly at inclined surface compared to vertical surface;
subject reacted non-significantly slowly at vertical
surface compared to horizontal surface.
14
execution time
12
10
8
6
4
2
0
Horizantal
Vertical
Orientation
Inclined
4) Subjective Measures:
The discomfort ratings were analyzed using Friedman's
two-way ANOVA by ranks, which yielded a statistically
significant result for screw driver types, χ2 =72, df =1,
p<0.000; orientations, χ2 =62.81, df = 2, p<0.000;
constraint variable, χ2 = 12.3, df =1, p<0.000.
Table 4.1 summarizes the mean and standard deviation of the discomfort
ratings for all treatments during execution different activities.
Mean
Standard deviation
7.25
16.10
1.02
2.15
Orientation
Horizontal
Vertical
Inclined
10.56
11.66
12.79
4.37
4.45
5.22
Constraint
Constraint
Unconstraint
11.86
11.49
4.84
4.67
Screw driver type
Straight
Ergonomic
subjective measure
As shown down, subjects rated ergonometric screw driver as the most
uncomfortable screw driver compared to the straight one. This
finding does not agreed with the knowledge of ergonomics.
20
18
16
14
12
10
8
6
4
2
0
st.dev, 2.15
st.dev
mean, 16.1
st.dev, 1.02
mean, 7.25
straight
ergonomic
screw type
mean
As shown down, subjects rated the working at horizontal surfaces as
least uncomfortable compared to vertical and inclined surfaces.
Also, the subjects rated the inclined as the most uncomfortable
subjective maesure
feelings toward working in horizontal or vertical surfaces.
20
18
16
14
12
10
8
6
4
2
0
st.dev; 5.22
st.dev; 4.37
st.dev; 4.45
st.dev
mean
mean; 10.56
mean; 11.66
mean; 12.79
Horizantal
Vertical
Inclined
Orientation
As shown down, subjects rated the working at unconstraint condition
as least uncomfortable compared to constraint condition. This
finding does agreed with the psychological knowledge.
18
subjective measure
16
14
st.dev, 4.84
st.dev, 4.67
12
10
st.dev
8
mean
6
mean, 11.86
mean, 11.49
constraint
unconstraint
4
2
0
Constraint
CONCLUSION
At constraint variable, the Root Mean Square of the EMG
muscular activity was higher non-significantly in a case
of straight screw driver relative to bent-handle screw
driver in working at inclined surface; and there was
significantly higher in a case of straight screw driver
relative to bent-handle screw driver in working at both
horizontal and vertical surfaces. At unconstraint variable,
the muscular activity was higher significantly in a case of
bent-handle screw driver relative to straight screw driver
in working at horizontal surface; and there was nonsignificantly higher in a case of bent-handle screw driver
relative to straight screw driver in working at both
inclined and vertical surfaces
Subjects reacted significantly faster in straight
screw driver compared to bent-handle screw
driver. In addition to, there was only a
significant difference between horizontal and
inclined orientation surfaces in terms of
execution time; subjects reacted significantly
slowly at inclined surface compared to
horizontal surface
Subjects rated bent-handle screw driver as the
most uncomfortable screw driver compared to
the straight one. Also, subjects rated the
working at horizontal surfaces as least
uncomfortable compared to vertical and
inclined surfaces. In addition, subjects rated the
inclined as the most uncomfortable feelings in
working at horizontal or vertical surfaces.
Finally, subjects rated the working at
unconstraint condition as least uncomfortable
feelings compared to their feelings at constraint
condition.

Thank You