Ergonomics evaluation

Master Seminar
on
by
AMITA GAUTAM
ID NO. -220116011
M.Tech (FMPE) Final Year
Department of Farm Machinery & Power Engineering, SVCAET & RS ,
Faculty of Agricultural Engineering Indira Gandhi Krishi Vishwavidyalaya,
Raipur(C.G)
Ergonomic Evaluation of Paddy Harvester and Thresher with
Farm Women

Rice is the staple food of Keralites and its cultivation had been the main occupation for generations.
It is reported that the area under paddy has declined by 38% within the last decade in Kerela.
The drudgery involved in cultivating rice is too intense and it calls for a decent compensation.
Studies have shown that the human body consumes 2 Kcal/min additionally if a man/woman takes a
tedious bending posture like in transplanting and harvesting; his/her heart also beats 35% faster.
And it is very common that such labourers suffer from a lot of ailments, as they grow old. It is
reported that human labour accounts for over 60% of rice production cost.
The performance of any machine especially manually operated ones could be considerably
improved if ergonomic aspects are given due consideration (Gite, 1993). Hence, there is an urgent
need to study the ergonomic aspects in detail to quantify the drudgery involved in agricultural
operations
INTRODUCTION

 Human energy measurements are important because whenever the physical capacity of a
person is exceeded, it is bound to cause considerable fatigue and a reduction in the efficiency
of operation.
 Thus, investigations on ergonomic evaluation of farm equipment can provide a rational basis
for recommendation of methods and improvement in equipment design for more output and
safety.
 Most of the operations in rice cultivation are being done by the female labourers such as
sowing the seeds, transplanting, weeding, harvesting, threshing and winnowing.

To analyze the human energy expenditure and discomfort experienced by the female
labourers during operation of a self propelled harvester and mini thresher to reduce
drudgery of farm women.
OBJECTIVES

 Selection of Subjects:
Nine subjects were selected having anthropometric dimensions conforming to
statistical requirements from the anthropometric data base of the study region.
The physiological characteristics of selected subjects are given in Table 1.
Table 1: Physiological characteristics of subjects
MATERIALS AND METHODS
Variable subjects
I II III IV V VI VII VIII IX
Age , year 40 49 42 41 49 46 40 35 48
Body weight, kg 60 60 70 62 55 65 75 60 51
Height , m 157 156 159 160 150 157 160 152 152
Resting HR ,
beats/min
74 72 73 67 68 66 74 72 69
Resting OC ,
L/min
0.239 0.196 0.245 0.136 0.166 0.232 0.149 0.259 0.19
6

 Activities
The subjects were required to do the rice farming operations namely,
• Harvesting with sickle (activity 1)
• Harvesting with self propelled harvester (activity 2),
• Manual threshing by beating on the stone (activity 3)
• Threshing with mini thresher (activity 4 ).
The trials were conducted two times a day, at different time intervals i.e., before 9 am and after 11
am in order to find out the changes in energy expended and heart rate due to environmental
condition.
A randomized field layout design was considered. The field was dry and without any lodging of
crop. The mini thresher consists of a threshing cylinder, driving mechanism and supporting frame.
The grains are separated by the combing as well as by hammering action of the threshing teeth.

 Establishing relationship between Oxygen uptake and Heart Rate
On a separate day and before performing activities, the relationship between heart
rate and oxygen uptake for each subject was determined.
This relationship is used to indirectly evaluate physiological workload. Both heart
rate and oxygen uptake have to be measured simultaneously in the laboratory at a
number of different submaximal workloads (Maritz et al., 1961).
This process is known as calibrating the heart rate-VO2 relationship for a subject.
Since the relationship between the two variables is linear during a typical
submaximal workload, a subject's heart rate measured in the field can be converted
into an estimate of oxygen uptake by referring to the laboratory data.

 The selected nine subjects were calibrated in the laboratory by measuring oxygen
consumption and heart rate simultaneously while pedalling a standard bicycle ergometer
to arrive at the relationship between heart rate and oxygen consumption.
Collection of Data
 All the nine subjects were equally trained in the operation of the self propelled harvester
and mini thresher before the actual experiment.
 After 30 minutes of resting, the subject was asked to operate the harvester (already
started by another person and engine throttle position set at required engine speed and
change lever in the required position) at the recommended speed of 2.5
km/h(Vidhu,2001).

The heart rate was measured and
recorded using computerized heart
rate monitor for the entire work
period. Each trial was carried out for
15 minutes of duration and same
procedure was repeated to replicate
the trials for all the selected subjects
The physiological response of the
subjects while harvesting with sickle
and manual threshing were also
assessed to compare the energy
expenditure in manual and
mechanized operation.
Fig1-Harvesting with Sickle
Fig2-Manual Threshing

 Analysis of Data
From the mean values of heart rate (HR) observed during the trials, the corresponding values of
oxygen consumption rate (VO2) of the subjects were predicted from the calibration curves of the
subjects.
The energy costs of the operations were computed by multiplying the value of oxygen consumption
(mean of the values of nine subjects) by the calorific value of oxygen as 20.88 kJ /lit (Nag et al., 1980)
The energy costs for all selected operations were graded as per the tentative classification of strains
in different types of jobs given in ICMR report as shown in Table 2. (Sen, 1969 and Vidhu, 2001).

Grading Physiological response
Heart rate
(beats/min)
Oxygen uptake
(lit/min)
Energy
expenditure(kcal/min)
Very light <75 < 0.35 <1.75
Light 75-100 0.35-0.70 1.75-3.5
Moderately heavy 100-125 0.70-1.05 3.5-5.25
Heavy 125-150 1.05-1.04 5.25-7.00
Very heavy 150-175 1.04-1.75 7.00-8.75
Extremely heavy >175 >1.75 >8.75
Table 2: Tentative classification of strains (ICMR) in different types of jobs
The results were statistically analyzed using an analysis of variance technique
(ANOVA) by following completely randomized design (CRD) to assess the effect of
mode of operation and time of operation on energy cost for harvesting and threshing
operations.

 Assessment of Postural Discomfort
 Assessment of postural discomfort included
• Overall discomfort rating (ODR) and
• Body part discomfort score (BPDS).
 After 30 minutes of resting, the subject was
asked to do the operations for duration of two
hours.
 Overall discomfort rating (ODR)
 For the assessment of ODR, a 10 - point
psychophysical rating scale (0 – no discomfort,
10 - extreme discomfort) was used which is an
adoption of Corlett and Bishop (1976)
technique (Fig.3).
 The overall discomfort ratings given by each of
the nine subjects were added and averaged to
get the mean rating.
Fig 3: Visual analogue discomfort scale for
assessment of overall body discomfort

 Body part discomfort score
(BPDS)
To measure localized discomfort, Corlett
and Bishop (1976) technique was used.
In this technique the subject's body is
divided into 27 regions as shown in
Fig.4.
The subject was asked to mention all
body parts with discomfort, starting with
the worst and the second worst and so on
until all parts have been mentioned. Fig 4: Regions for evaluating body part
discomfort score

 Calibration process
By using the data on heart rate and
oxygen consumption rate, calibration
chart was prepared with heart rate as the
abscissa and the oxygen uptake as the
ordinate for the selected nine subjects
(Fig.5).
It is observed that the relationship
between the heart rate and oxygen
consumption of the subjects was found to
be linear for all the subjects.
This linear relationship defers from one
individual to another due to physiological
differences of individuals.
Fig 5: Relationship between oxygen uptake and
heart rate
RESULT AND DISCUSSION

 Energy cost in harvesting operation
The results showed that mode of operation and time of operation significantly influenced the energy
cost as presented in Table 3.
It is noticed that the average energy expenditure was 17.93 kJ/min during operation of self propelled
harvester while it was increased to 20.58 kJ/min during manual harvesting, the increase being 15%.
 Here the subjects harvesting the crops with sickle in bending posture. Working in a bending posture
increased the lordative curve of the spine, thus put more strain on the back muscles and result in
increased energy expenditure.
It is further noticed that the mean energy expenditure before 9 am was 17.64 kJ/min while after 11 am
it was increased to 20.87 kJ/ min.
Based on the mean energy cost of nine subjects, the operation was graded as “moderately heavy”.

Table 3: Energy cost as influenced by mode of operation and time of operation
during harvesting
Treatments Energy cost,(kJ/min)
Mode of operation
Harvesting with self propelled
harvester
17.93
Harvesting with sickle 20.58
F(32,1) 21.79**
CD(P=0.05) 1.16
Time of operation
Before 9 am 17.64
After 11 am 20.87
F(32,1) 32.27**
CD(P=0.05) 1.16
** Significant at 1 % level of probability, F, variance ratio; CD, critical
difference; P, probability

 Energy cost in threshing operation
The results of the study show the energy cost was recorded significantly higher in manual threshing
than mini thresher operation.
 The maximum energy cost observed to be 21.55 kJ/min in manual threshing, whereas with the mini
thresher this value was 15.53 kJ/min (Table 4).
 In manual threshing, the subjects were bending over work surfaces for targets which are too low. It
may be suggested that pain rather than capacity may often be the limiting factor in such task
situations.
 In mini thresher, the subjects can comfortably do the threshing in a standing posture. The energy
expenditure after 11 am was increased by 23 % in compared to energy expenditure before 9 am.
Threshing operations are graded as " moderately heavy " as per the classification of strains
 Acceptable Workload (AWL)
Saha et al. (1979) reported that 35% of maximum oxygen uptake (also called maximum Aerobic
capacity or VO2 max) can be taken as the acceptable work load (AWL) for Indian workers which is
endorsed by Nag et al, 1980 and Nag and Chatterjee, 1981.

 To ascertain whether the operations selected for the trails were within the (acceptable workload AWL)
the oxygen uptake in terms of VO2 max (%) for each treatment was computed. Each subject's
maximum heart rate was estimated by the relationship (Bridger, 1995).
• Max. heart rate (beats/min) = 200 - 0.65 × Age(year)
The maximum aerobic capacity of the selected nine subjects varied from 1.21 to 1.51 l/min.
 For harvesting with self propelled harvester, the oxygen uptake in terms of VO2 max was 64.56 %
while it was 74.12% for manual harvesting.
Similarly VO2 max was 55.91% for threshing & with mini thresher where as it was 77.58% for manual
threshing.
 All the values were higher than that of the AWL limits of 35 % indicating that the above operations
could not be operated continuously for 8 hours without frequent rest-pauses.

 Overall Discomfort Rating (ODR)
The mean overall discomfort scores rated by nine subjects during harvesting and threshing
operations are furnished in Table 5.
Table 4: Overall discomfort rating of subjects during selected operations
S.No. Selected operations ODR ( Mean Value) Scale
1 Harvesting with Self Propelled
Harvester
6.6 Moderate discomfort
2 Harvesting with Sickle 8.0 More than moderate
discomfort
3 Threshing with Mini Thresher 6.3 Moderate discomfort
4 Manual Threshing 8.5 More than moderate
discomfort

 Body part discomfort score (BPDS)
The body discomfort score of selected operations are shown in Table 6.
Table 5: Body part discomfort score (BPDS) of the subjects for selected operations
S.No. Selected operation BPDS(Mean value)
1 Harvesting with Self Propelled
Harvester
30.90
2 Harvesting with Sickle 31.95
3 Threshing with Mini Thresher 28.50
4 Manual Threshing 33.90

There was significant difference in energy costs in machine and manual operation. The energy cost
was 20.58 kJ min-1 for harvesting with sickle, whereas for harvesting with self propelled harvester,
this value was observed to be 17.93 kJ min-1.
Harvesting after 11 am resulted in 18% more energy expenditure than harvesting before 9 am. The
average energy expenditure energy cost was 15.53 kJ min-1 for threshing with Mini Thresher; while
for manual threshing this value was 21.55 kJ min-1.
All the operations were generally graded as “Moderately Heavy”. The oxygen uptake in terms of
VO2 max was above the acceptable work load for all selected operations.
Mean overall discomfort rating on a 10 point visual analogue discomfort scale (0- no discomfort, 10-
extreme discomfort) scaled as "moderate discomfort" for machine operations whereas it was scaled
as "more than moderate discomfort" for manual operations .
CONCLUSION

Arms and shoulder regions were concerned areas of discomfort for machine operation, whereas
for manual operation, back, buttocks, thighs and legs were the concerned regions of discomfort.
The intensity of pain experienced by the subjects was more in manual operation compared to
machine operation.
The BPDS value was maximum in harvesting with sickle, where as it was minimum in
threshing with mini thresher.

1. Bridger, R. S.1995. Introduction to Ergonomics, 3rd Edn., Mc Graw-HIll, Inc, New
york
2. Corlett, E.N. and R.P.Bishop.1976. A technique for assessing postural discomfort.
Ergonomics, 19:175-182.
3. Gite, L.P. 1993. Ergonomics in Indian Agriculture – A review, Paper presented in the
International workshop on human and draught animal powered crop protection held
at Harare, Jan. 19-22.
4. Maritz,J. S., J. F.Morrison, J.Peters, N. B.Strydon, and C.H.Wyndham.1961. A
practical method of estimating an individual’s maximum oxygen uptake, Ergonomics,
4 (2):120-125.
5. Nag, P.K., Sebastian, N.C. and M.G. Malvankar.1980. Occupational workload of
Indian agricultural workers, Ergonomics, 23, 91–102.
REFERENCES

6. Saha, P. N., Datta, S. R., Banergee, P. K. and G. G. Narayanee. 1979. An
acceptable work-load for Indian workers, Ergonomics, 22(9), 1059-1071.
7. Sen, R.N. 1969.Tentative classification of strains in different types of jobs according
to the physiological responses of young Indian workers in comfortable climates,
ICMR report, Indian Council of Medical Research, New Delhi.
8. Vidhu, K. P. 2001. An investigation on ergonomic evaluation of selected rice farming
equipment, Unpublished M.E. (Ag.) Thesis, Department of Farm Machinery, Tamil
Nadu Agricultural University, Coimbatore, India

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