Design optimization of dosa making works
Journal of Scientific
& Industrial Research
SOMASUNDARAM
& SRINIVASAN: DESIGN OPTIMIZATION OF DOSA MAKING WORKSTATION
Vol. 69, March 2010, pp. 221-224
221
Design optimization of dosa making workstation for smooth
ergonomic interface
A Somasundaram1* and P S S Srinivasan2
1
Department of Mechanical Engineering, Kongu Engineering College, Perundurai, Erode 638 052, India
2
K S Rangasamy College of Technology, Tiruchengode 637 209, India
Received 12 August 2008; revised 21 December 2009; accepted 08 January 2010
This study presents design optimization of Dosa making workstation (DMW) used in preparation of South Indian food,
dosa. Anthropometry of South Indian user population is considered in ergonomic interface analysis. Design of Experiments
(DOE) was used for optimization of DMW. Four control parameters (shoulder height, arm length of worker, table width and table
height of DMW) were considered in design optimization. Proposed parameters (height, 1150 mm; width, 750 mm) reduced risk
of musculoskeletal disorder for users and enhanced quality of work at DMW.
Keywords: Design of Experiments, Dosa Making Workstation, Ergonomics, Musculoskeletal disorder
Introduction
Dosa making workstation (DMW) is highly engaged
to prepare dosa - a South Indian food item. Ergonomic
studies identified risk factors and reduced
musculoskeletal disorder (MSD) in task specific
applications. Attwood1 indicated that particular type of
discomfort could be linked to specific aspects of
workstation design. Fogleman et al2 identified risk
factors associated with self reported MSD in a population
of visual display terminals operators. Sarma et al3 studied
height of workstation of tyre-changer considering
anthropometry of user groups. Gallagher et al4 observed
that repetitive works can increase stresses on spine.
Bernard5 found that MSD is associated with perceptions
of intensified work load, monotonous work, limited job
control, low job clarity, and low social support.
This study on Indian hotel kitchen ergonomics
enhances safety and comfort for workers.
Experimental
A preliminary survey was conducted to identify
problems in hotel kitchen environment (HKE) by
interviewing 350 persons working in HKE in Erode and
Coimbatore districts of Tamilnadu, India. Dosa making
section in South Indian hotel kitchen contributes 20-27%
*Author for correspondence
E-mail: somas789@yahoo.com
of total sales in middle class hotels. User’s perception
of existence of discomfort in HKE reflect poor interface
between men in work and HKE (Fig. 1). Workers average
dissatisfaction was recorded using a ten point scale. Dosa
making has been found to involve repetitive arm and
wrist rotation, trunk bending, arm stretching and
prolonged standing; all of these ergonomic risk factors
lead to discomfort and MSD for workers.
Work Schedule and Capacity Utilization
Each worker prepares 350-500 dosa in average. In
semi urban hotels, only one worker is made to work the
whole day with a rest of about 6 h in between shifts.
Peak hour load leads to MSD because of repetitive arm
motion and improper interface between workers in
DMW.
Risk Assessment Method and Workstation Parameters
Experimental analysis was carried out on six workers
working in dosa making section of hotel kitchens in
Erode. Each worker was asked to work in workstation
of model 1, model 2 and model 3 for 3 days each in
same set of working conditions. Data were collected on
a five point scale about pain experienced during
operation (Table 1) at the end of peak hours. All workers
participated in experimentation were men
(age, 27-45 yrs).
222
J SCI IND RES VOL 69 MARCH 2010
Control Parameters-Anova Results
6
95
5
4
4
3
S/N, Ratio
Intensity
5
3
2
2
1
85
75
0
Ch in es e
D osa
S team
Veg et able
food
m aking
co oking
c ut ting
65
1
S h o u lde r H e i g h t
Department
Table 1— Risk factor perceptions surveyed from HKE
Factors
Neck pain
Shoulder pain
Wrist/hand pain
Low back pain
Low leg pain
Finger pain
Elbow/ forearm
Eye strain
Skin dryness
Body dehydration
Range
1-5
2-4
3-5
2-4
2-5
2-4
1-3
1-3
2-4
2-4
3
A rm L e n g t h
Ta b le W id th
T a b l e H e ig h t
Fig. 2—S/N ratio
Fig. 1—HKE problem intensity chart
S.No
1
2
3
4
5
6
7
8
9
10
2
Le ve l
Average
4
3
4
3
4
3
2
2
3
3
(5-Very high, 4-High, 3-Moderate, 2-Low, 1-None)
Height, length, breadth of workstation, shoulder
height, arm length and heat inside kitchen were factors
leading to MSD. Based on variations in workstation
parameters, workstation is broadly classified into model
1, model 2 and model 3 (Table 2). Among 30 kitchens
surveyed, dosa workstation used models as follows:
model 1, 60%; model 2, 25%; and model 3, 15%.
Average temperature around workplace of a DMW was
36°C.
Solution Methodology
Risk factors causing MSD were observed mainly
due to anthropometry and work posture. Shoulder height
and arm length of cook engaged in dosa making largely
influenced arm reach over dosa plate in preparing dosa.
Also, width and height of work surface of DMW had
large impact on arm reach. All four parameters were
considered as critical input parameters in design
optimization of DMW. Arm reach over surface of dosa
plate in preparing dosa was output of experiment.
Design Optimization using Design of Experiments (DOE)
Any change in height and width of DMW affects
worker’s efficiency. Any change in table length
Table 2—Dimensions of DMW grouped from actual observations
Model
1
2
3
Height, mm
1250
1150
900
Length, mm
1300
1200
1100
Breadth, mm
750
600
500
Table 3—Three levels of variation in critical parameters
Parameter
Shoulder height (A)
Arm length (B)
Table width (C)
Table height (D)
L1
1320
670
680
950
Dimension, mm
L2
1430
750
750
1050
L3
1540
840
830
1150
negligibly affected worker’s efficiency as worker can
move along the length of DMW. Increase in height of
DMW leads to raised arms during dosa making and this
increased risk of MSD. Increase in width of DMW made
worker to lean forward while reaching outermost edges.
Trunk angle (> 15-20° leads to lower back disorder, a
type of MSD.
Selection of Variation Levels
Anthropometry data follows normal distribution for
a given population. Three levels of shoulder height and
arm length of users (for 5th, 50th and 95th percentile) data
was considered. Also, three levels of DMW’s width and
height were considered. These four parameters highly
influenced response or arm reach (R) of worker over
DMW (Table 3).
Orthogonal Array
Orthogonal array was used for ergonomic interface
analysis. For four control parameters with three levels
of variation (with no noise factors), minimum number of
conventional experiments required was 34 *1=81. Using
Taguchi’s DOE technique, number of experiments was
calculated using degrees of freedom approach. An
223
SOMASUNDARAM & SRINIVASAN: DESIGN OPTIMIZATION OF DOSA MAKING WORKSTATION
Table 4-—L9 Orthogonal array indicating dimensions of critical parameters, reach and S/N ratio
Run
A
cm
B
cm
C
cm
D
cm
Arm reach (R)
cm
S/N
ratio
1
2
3
4
5
6
7
8
9
132
132
132
143
143
143
154
154
154
67
75
84
67
75
84
67
75
84
68
75
83
75
83
68
83
68
75
95
105
115
115
95
105
105
115
95
26
20
15
29
39
08
52
18
31
28
26
24
29
32
18
34
25
30
Total
238
246
Table 5—Sum of squares (SS), variation and optimum design values for “nominal the best”
Factor
A
B
C
D
Dimension, cm
SS
L1
L2
L3
78
92
72
90
79
83
85
78
89
71
90
78
SS
25
70
60
32
187
orthogonal array (L9) for three levels, four control
parameter and no noise level along with response factors
and S/N (signal to noise) ratio is tabulated (Table 4).
Theoretical response (arm reach, R) was calculated as
2
2
Theoretical response, R (mm)= [C+150]-[B -(A-D) ]
…(1)
Eq. (1) was used in interfacing of human body
dimensions with DMW parameters. Preferred clearance
between worker and workstation was found to be 150
mm. R is maximum distance that worker stretches his
arm to reach outer edge of DMW. Worker bends his trunk
forward while reaching edges, when engaged in dosa
preparation. Eq. (1) may be suitably modified for other
application also depending on variables considered in
interface.
Even though there were no noise parameters, S/N
ratio were calculated in order to identify optimum design
parameters and variation of control parameter as
S/N Ratio=10 log [(1/n) R2]
Variation
%
…(2)
13
37
33
17
Optimum design values for
“nominal the best”
Optimum
Value
level
mm
2
1430
2
750
2
750
2,3
1150
where, n, number of levels (assumed to be 1); R, response
Results and Discussion
Results
Experimental output values (R over width of table
and S/N ratio) under nine experiments for four critical
input parameters (shoulder height, arm length of worker
engaged in dosa making, dosa plate surface width and
table height of DMW) were calculated (Fig.2, Table 4).
Calculation of Variation and Sum of Least Squares of Control
Parameters
Sum of squares (SS) value and variation were
obtained as
SS= [(A12/3) + (A22/3) + (A32/3)] – (R 2/9) …(3)
Variation (%) = SSB/SS
…(4)
where A, summation of responses of each parameter for
various level; SS B, summation of squares of
corresponding control parameters; SS, summation of
squares.
224
J SCI IND RES VOL 69 MARCH 2010
Optimization settings for each of control parameters
(Table 5) indicated holds good for 50 th percentile
population (level 2). Optimum parameter values were:
shoulder height, 1430 mm; arm length, 750 mm; dosa
plate width, 750 mm; and table height, 1150 mm.
in physical stresses for optimum design values of DMW.
Back pain, shoulder pain and neck pain rating have gone
down to 3, 2, and 2 respectively from previously
respective reported levels of 3, 3, and 4, indicating
improvement.
Discussion
Acknowledgement
Authors thank DST for funding research work (DST
reference No. SP/WS/066/2006).
Arm length and table width contributed more to the
performance. Table height had significant influence over
performance. “Nominal the best” - Level 2 parameters
holds good for 50th percentile population to reduce
discomfort and enhance safety. 95th percentile user group
also found level 2 parameters suitable but 5th percentile
user group did not find it suitable. So “Nominal the best”
parameters considered for new design of DMW that suit
most users. However, 5th percentile users may be advised
to stand on a platform (height, up to 100 mm) to make
use of same workstation.
Conclusions
From ergonomic interface analysis using DOE, 50th
and 95th percentile workers were recommended to use a
workstation (height, 1150 mm; width, 750 mm). 5th
percentile anthropometry workers were advised to use
dosa maker of height 1050 mm. Worker’s productivity
was enhanced from 38 dosa/h to 42 dosa/h, due to relief
References
1
2
3
4
5
Attwood D, Comparison of discomfort experienced at CADD,
word processing and traditional drafting workstations, Int J
Ind Ergon, 4 (1989) 39-50.
Fogleman M & Guimaraes L, Factors associated with self
reported musculoskeletal discomforts in vedio display terminal
(VDT) users, Int J Ind Ergon, 29 (2002) 311-318.
Sarma D V & Panneerselvam S, Ergonomics in redesign of
Tyre-Changer, Int Ergon J, 27 (2) (1998) 6-11.
Gallagher S, Marras W S, Litsky A & Burr D, Torso flexion
loads and the fatigue failure of human lumbosacral motion
segments, Spine, 30 (2005) 2265-2273.
Bernard B, Musculoskeletal disorders and workplace factors:
a critical review of epidemiologic evidence for work-related
musculoskeletal disorders of the neck, upper extremity and low
back [US Department of Health and Human Services, National
Institute for Occupational Safety and Health (NIOSH), USA]
1997.
& Industrial Research
SOMASUNDARAM
& SRINIVASAN: DESIGN OPTIMIZATION OF DOSA MAKING WORKSTATION
Vol. 69, March 2010, pp. 221-224
221
Design optimization of dosa making workstation for smooth
ergonomic interface
A Somasundaram1* and P S S Srinivasan2
1
Department of Mechanical Engineering, Kongu Engineering College, Perundurai, Erode 638 052, India
2
K S Rangasamy College of Technology, Tiruchengode 637 209, India
Received 12 August 2008; revised 21 December 2009; accepted 08 January 2010
This study presents design optimization of Dosa making workstation (DMW) used in preparation of South Indian food,
dosa. Anthropometry of South Indian user population is considered in ergonomic interface analysis. Design of Experiments
(DOE) was used for optimization of DMW. Four control parameters (shoulder height, arm length of worker, table width and table
height of DMW) were considered in design optimization. Proposed parameters (height, 1150 mm; width, 750 mm) reduced risk
of musculoskeletal disorder for users and enhanced quality of work at DMW.
Keywords: Design of Experiments, Dosa Making Workstation, Ergonomics, Musculoskeletal disorder
Introduction
Dosa making workstation (DMW) is highly engaged
to prepare dosa - a South Indian food item. Ergonomic
studies identified risk factors and reduced
musculoskeletal disorder (MSD) in task specific
applications. Attwood1 indicated that particular type of
discomfort could be linked to specific aspects of
workstation design. Fogleman et al2 identified risk
factors associated with self reported MSD in a population
of visual display terminals operators. Sarma et al3 studied
height of workstation of tyre-changer considering
anthropometry of user groups. Gallagher et al4 observed
that repetitive works can increase stresses on spine.
Bernard5 found that MSD is associated with perceptions
of intensified work load, monotonous work, limited job
control, low job clarity, and low social support.
This study on Indian hotel kitchen ergonomics
enhances safety and comfort for workers.
Experimental
A preliminary survey was conducted to identify
problems in hotel kitchen environment (HKE) by
interviewing 350 persons working in HKE in Erode and
Coimbatore districts of Tamilnadu, India. Dosa making
section in South Indian hotel kitchen contributes 20-27%
*Author for correspondence
E-mail: somas789@yahoo.com
of total sales in middle class hotels. User’s perception
of existence of discomfort in HKE reflect poor interface
between men in work and HKE (Fig. 1). Workers average
dissatisfaction was recorded using a ten point scale. Dosa
making has been found to involve repetitive arm and
wrist rotation, trunk bending, arm stretching and
prolonged standing; all of these ergonomic risk factors
lead to discomfort and MSD for workers.
Work Schedule and Capacity Utilization
Each worker prepares 350-500 dosa in average. In
semi urban hotels, only one worker is made to work the
whole day with a rest of about 6 h in between shifts.
Peak hour load leads to MSD because of repetitive arm
motion and improper interface between workers in
DMW.
Risk Assessment Method and Workstation Parameters
Experimental analysis was carried out on six workers
working in dosa making section of hotel kitchens in
Erode. Each worker was asked to work in workstation
of model 1, model 2 and model 3 for 3 days each in
same set of working conditions. Data were collected on
a five point scale about pain experienced during
operation (Table 1) at the end of peak hours. All workers
participated in experimentation were men
(age, 27-45 yrs).
222
J SCI IND RES VOL 69 MARCH 2010
Control Parameters-Anova Results
6
95
5
4
4
3
S/N, Ratio
Intensity
5
3
2
2
1
85
75
0
Ch in es e
D osa
S team
Veg et able
food
m aking
co oking
c ut ting
65
1
S h o u lde r H e i g h t
Department
Table 1— Risk factor perceptions surveyed from HKE
Factors
Neck pain
Shoulder pain
Wrist/hand pain
Low back pain
Low leg pain
Finger pain
Elbow/ forearm
Eye strain
Skin dryness
Body dehydration
Range
1-5
2-4
3-5
2-4
2-5
2-4
1-3
1-3
2-4
2-4
3
A rm L e n g t h
Ta b le W id th
T a b l e H e ig h t
Fig. 2—S/N ratio
Fig. 1—HKE problem intensity chart
S.No
1
2
3
4
5
6
7
8
9
10
2
Le ve l
Average
4
3
4
3
4
3
2
2
3
3
(5-Very high, 4-High, 3-Moderate, 2-Low, 1-None)
Height, length, breadth of workstation, shoulder
height, arm length and heat inside kitchen were factors
leading to MSD. Based on variations in workstation
parameters, workstation is broadly classified into model
1, model 2 and model 3 (Table 2). Among 30 kitchens
surveyed, dosa workstation used models as follows:
model 1, 60%; model 2, 25%; and model 3, 15%.
Average temperature around workplace of a DMW was
36°C.
Solution Methodology
Risk factors causing MSD were observed mainly
due to anthropometry and work posture. Shoulder height
and arm length of cook engaged in dosa making largely
influenced arm reach over dosa plate in preparing dosa.
Also, width and height of work surface of DMW had
large impact on arm reach. All four parameters were
considered as critical input parameters in design
optimization of DMW. Arm reach over surface of dosa
plate in preparing dosa was output of experiment.
Design Optimization using Design of Experiments (DOE)
Any change in height and width of DMW affects
worker’s efficiency. Any change in table length
Table 2—Dimensions of DMW grouped from actual observations
Model
1
2
3
Height, mm
1250
1150
900
Length, mm
1300
1200
1100
Breadth, mm
750
600
500
Table 3—Three levels of variation in critical parameters
Parameter
Shoulder height (A)
Arm length (B)
Table width (C)
Table height (D)
L1
1320
670
680
950
Dimension, mm
L2
1430
750
750
1050
L3
1540
840
830
1150
negligibly affected worker’s efficiency as worker can
move along the length of DMW. Increase in height of
DMW leads to raised arms during dosa making and this
increased risk of MSD. Increase in width of DMW made
worker to lean forward while reaching outermost edges.
Trunk angle (> 15-20° leads to lower back disorder, a
type of MSD.
Selection of Variation Levels
Anthropometry data follows normal distribution for
a given population. Three levels of shoulder height and
arm length of users (for 5th, 50th and 95th percentile) data
was considered. Also, three levels of DMW’s width and
height were considered. These four parameters highly
influenced response or arm reach (R) of worker over
DMW (Table 3).
Orthogonal Array
Orthogonal array was used for ergonomic interface
analysis. For four control parameters with three levels
of variation (with no noise factors), minimum number of
conventional experiments required was 34 *1=81. Using
Taguchi’s DOE technique, number of experiments was
calculated using degrees of freedom approach. An
223
SOMASUNDARAM & SRINIVASAN: DESIGN OPTIMIZATION OF DOSA MAKING WORKSTATION
Table 4-—L9 Orthogonal array indicating dimensions of critical parameters, reach and S/N ratio
Run
A
cm
B
cm
C
cm
D
cm
Arm reach (R)
cm
S/N
ratio
1
2
3
4
5
6
7
8
9
132
132
132
143
143
143
154
154
154
67
75
84
67
75
84
67
75
84
68
75
83
75
83
68
83
68
75
95
105
115
115
95
105
105
115
95
26
20
15
29
39
08
52
18
31
28
26
24
29
32
18
34
25
30
Total
238
246
Table 5—Sum of squares (SS), variation and optimum design values for “nominal the best”
Factor
A
B
C
D
Dimension, cm
SS
L1
L2
L3
78
92
72
90
79
83
85
78
89
71
90
78
SS
25
70
60
32
187
orthogonal array (L9) for three levels, four control
parameter and no noise level along with response factors
and S/N (signal to noise) ratio is tabulated (Table 4).
Theoretical response (arm reach, R) was calculated as
2
2
Theoretical response, R (mm)= [C+150]-[B -(A-D) ]
…(1)
Eq. (1) was used in interfacing of human body
dimensions with DMW parameters. Preferred clearance
between worker and workstation was found to be 150
mm. R is maximum distance that worker stretches his
arm to reach outer edge of DMW. Worker bends his trunk
forward while reaching edges, when engaged in dosa
preparation. Eq. (1) may be suitably modified for other
application also depending on variables considered in
interface.
Even though there were no noise parameters, S/N
ratio were calculated in order to identify optimum design
parameters and variation of control parameter as
S/N Ratio=10 log [(1/n) R2]
Variation
%
…(2)
13
37
33
17
Optimum design values for
“nominal the best”
Optimum
Value
level
mm
2
1430
2
750
2
750
2,3
1150
where, n, number of levels (assumed to be 1); R, response
Results and Discussion
Results
Experimental output values (R over width of table
and S/N ratio) under nine experiments for four critical
input parameters (shoulder height, arm length of worker
engaged in dosa making, dosa plate surface width and
table height of DMW) were calculated (Fig.2, Table 4).
Calculation of Variation and Sum of Least Squares of Control
Parameters
Sum of squares (SS) value and variation were
obtained as
SS= [(A12/3) + (A22/3) + (A32/3)] – (R 2/9) …(3)
Variation (%) = SSB/SS
…(4)
where A, summation of responses of each parameter for
various level; SS B, summation of squares of
corresponding control parameters; SS, summation of
squares.
224
J SCI IND RES VOL 69 MARCH 2010
Optimization settings for each of control parameters
(Table 5) indicated holds good for 50 th percentile
population (level 2). Optimum parameter values were:
shoulder height, 1430 mm; arm length, 750 mm; dosa
plate width, 750 mm; and table height, 1150 mm.
in physical stresses for optimum design values of DMW.
Back pain, shoulder pain and neck pain rating have gone
down to 3, 2, and 2 respectively from previously
respective reported levels of 3, 3, and 4, indicating
improvement.
Discussion
Acknowledgement
Authors thank DST for funding research work (DST
reference No. SP/WS/066/2006).
Arm length and table width contributed more to the
performance. Table height had significant influence over
performance. “Nominal the best” - Level 2 parameters
holds good for 50th percentile population to reduce
discomfort and enhance safety. 95th percentile user group
also found level 2 parameters suitable but 5th percentile
user group did not find it suitable. So “Nominal the best”
parameters considered for new design of DMW that suit
most users. However, 5th percentile users may be advised
to stand on a platform (height, up to 100 mm) to make
use of same workstation.
Conclusions
From ergonomic interface analysis using DOE, 50th
and 95th percentile workers were recommended to use a
workstation (height, 1150 mm; width, 750 mm). 5th
percentile anthropometry workers were advised to use
dosa maker of height 1050 mm. Worker’s productivity
was enhanced from 38 dosa/h to 42 dosa/h, due to relief
References
1
2
3
4
5
Attwood D, Comparison of discomfort experienced at CADD,
word processing and traditional drafting workstations, Int J
Ind Ergon, 4 (1989) 39-50.
Fogleman M & Guimaraes L, Factors associated with self
reported musculoskeletal discomforts in vedio display terminal
(VDT) users, Int J Ind Ergon, 29 (2002) 311-318.
Sarma D V & Panneerselvam S, Ergonomics in redesign of
Tyre-Changer, Int Ergon J, 27 (2) (1998) 6-11.
Gallagher S, Marras W S, Litsky A & Burr D, Torso flexion
loads and the fatigue failure of human lumbosacral motion
segments, Spine, 30 (2005) 2265-2273.
Bernard B, Musculoskeletal disorders and workplace factors:
a critical review of epidemiologic evidence for work-related
musculoskeletal disorders of the neck, upper extremity and low
back [US Department of Health and Human Services, National
Institute for Occupational Safety and Health (NIOSH), USA]
1997.