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K. K. Jain, A. K. Shrivastava and C. R. Mehta. “Analysis of Selected Tractor Seats for
Seating Dimensions in Laboratory”. Agricultural Engineering International: The CIGR
Ejournal. Manuscript PM 08 010. Vol. X. December, 2008.
1
Analysis of Selected Tractor Seats for Seating Dimensions in Laboratory
K.K. Jain
1, *
, A.K. Shrivastava
2
and C.R. Mehta
3
1
Research Engineer, Post Harvest Technology Scheme,
Department of Agril. Process Engineering, College of Agril. Engineering & Technology,
Junagadh Agricultural University, Junagadh (Gujarat - India)
2
Professor & Head, Deptt. of Farm Machinery and Power Engineering.
College of Agril. Engg, JNKVV, Jabalpur (M. P. - India)
3
Senior Scientist, Central Institute of Agril. Engineering, Bhopal (M. P. - India)
*email :
kjain_123@yahoo.co.in
ABSTRACT
Tractor seat is one of the important component / assembly as far as the human machine
system and comfort of tractor operator are concerned .With this in view, a field survey and
laboratory study were conducted of selected popular tractors and tractor seats, respectively,
with particular reference to seating dimensions. Dimensions for seat pan and backrest were
measured and analyzed, according to BIS recommendations. The results highlighted that seat
pan width was found 10.9% less, seat height was found 15.3% in excess, no vertical
adjustments and backrest width was also found 20.4% less. This may cause discomfort for
smaller as well as higher percentile tractor operators. Based upon the design of mounting
arrangement of different tractor seats – a common device i.e. seat base plate was developed.
This plate may serve as a base for providing isolators for vibration attenuation. Also, this
arrangement may be quite useful in testing of different tractor seats, under the constraints in
availability of different makes of tractors at a time for experimental study or testing work.
The study also highlighted that present tractor seats need minor modifications / improvements
in seating dimensions as per BIS recommendations. The development of a common seat base
plate may prove to be a step forward in the direction of long awaited tractor standardization.
The information thus obtained can be utilized in seat design, work place lay out as well as
adapted by agriculture engineers for better work environment.
Keywords: Tractor seat, seating dimensions, workplace layout, free point 3 D digitizer,
India.
1. INTRODUCTION
Mechanization in agriculture has changed the characteristics of labour and has also
influenced the work load (Salokhe et al. 1995). Presently, in India also, with a relatively good
monsoon and farmers switching over to mechanized farming, tractor volumes are picking up.
The current population of tractors in India is around 3.0 million and more than 0.25 million
tractors are added to Indian agriculture every year. India stands as the largest manufacturer of
tractors in the world (Singh and Doharey, 1999). At the same time, though tractorization has
reduced the drudgery involved in the farm operations, but it was evident that tractors had
ergonomic shortcomings (Dupuis, 1959; Fairley, 1995, Balasankari et al., 2004).
Tractor seat is one of the important components / assembly as far as human machine system
is concerned. Each tractor has its own seating arrangement in order to provide better
__________________________________________________________________________
K. K. Jain, A. K. Shrivastava and C. R. Mehta. “Analysis of Selected Tractor Seats for
Seating Dimensions in Laboratory”. Agricultural Engineering International: The CIGR
Ejournal. Manuscript PM 08 010. Vol. X. December, 2008.
2
maneuvrability, control and comfort, for example - steering of tractor, looking backward to
observe and control the machine / implement, and force required to operate clutch, brake and
hydraulic control lever. The task and workplace determine the postures and create a pattern of
loading on the structures of the body of the individual. An attempt has been made to observe
the pattern of seating dimensions as per Indian Standard 12343: 1998 (version of ISO 4253 :
1993), by mounting seats of different makes on a selected tractor. Thus, this paper describes
the analysis and comparative study of different makes of tractor seats in a field survey as well
as laboratory study.
1.1 Objectives
1. To conduct field survey and laboratory measurements for seating dimensions of
available tractor seats.
2. To compare different tractor seats for their seating dimensions, as per BIS standards.
2. MATERIALS AND METHODS
The following experiments was carried out under this study –
2.1 Field Survey
A field survey was carried out to collect information on seating dimensions and mechanisms
of different makes of new tractor seats. Relevant anthropometric seating dimensions – seat
length, seat width, seat height, back rest width and back rest height etc., feasible and suitable
for field work were measured with the help of measuring steel tape, scale etc. Fig. 1 to 3
show the mechanisms adapted for Indian tractor seats. Seating dimensions thus measured and
recorded were compiled for seating comfort as per the dimensions of the Indian standard for
comparative study.
Figure 1. View of tractor seats during field survey
2.2 Laboratory Seating Dimensions Measurement
A set up, as shown in Fig. 4, was used for measurement in the laboratory. Measurement of
various seating dimensions was made by a Freepoint 3D-digitizer instrument precisely. This
instrument works on reflection of radiations emerged from point under consideration and
__________________________________________________________________________
K. K. Jain, A. K. Shrivastava and C. R. Mehta. “Analysis of Selected Tractor Seats for
Seating Dimensions in Laboratory”. Agricultural Engineering International: The CIGR
Ejournal. Manuscript PM 08 010. Vol. X. December, 2008.
3
provides measurement in all the three coordinates. A Freepoint computer software was also
installed.
Five commonly adapted tractor seats (S1, S2, S3, S4 and S5), as shown in Fig. 5, of
different makes were procured for precise measurement with the instrument installed. The
Seat Reference Point (SRP) and Seat Index Point (SIP) (SRP & SIP were determined as per
the IS 11806, 1986 and IS 11113, 1985, respectively standards) were located by SRP device,
as shown in Fig. 6. Various angular measurements, shape, seat mounting base area etc. were
also worked out.
Figure 2. Tractor seat view showing Figure 3. Overall view of a tractor seat
suspension mechanism and inclined without open space for backrest
seat base plate
Figure 4. Setting up triangle detector array Figure 5. Selected tractors seats for
of freepoint-3D digitizer measurement set-up laboratory study
__________________________________________________________________________
K. K. Jain, A. K. Shrivastava and C. R. Mehta. “Analysis of Selected Tractor Seats for
Seating Dimensions in Laboratory”. Agricultural Engineering International: The CIGR
Ejournal. Manuscript PM 08 010. Vol. X. December, 2008.
4
Figure 6 Determining the location of
SRP as per IS:11806, 1986
2.3 Development of a Common Seat Mounting Base Plate
On the basis of seat mounting arrangement and seat type mounting dimensions, mechanism
etc., a M.S. (mild steel) plate having size 310 x 240 x 10 mm, was taken and 12 mm.
diameter holes were drilled on this plate, as per seats mounting dimensions layout, so it may
accommodate all the seats under laboratory study. On the bottom of the plate, proper nuts
were welded, so as to have easiness and rigidity in tightening seat bolts. Thus, different
makes of tractor seats could easily be fitted for comparative study and analysis.
3. RESULTS AND DISCUSSION
Results of field survey of eight tractor seats and laboratory study of five selected tractor seats
have been discussed as below –
3.1 Field Survey
Seating dimensions of eight different tractor seats were measured in a field survey as
presented in Table-1. On comparing from the prescribed anthropometric measurements as per
Indian Standards, revealed that – Seating dimensions of eight new popular commercially
available tractors at dealer’s workshop were measured in a field survey. The seating
dimensions of 8 different tractor seats are given in Table 1. The obtained results indicated,
that seat lengths of T1 and T5 tractors were found within the range as per IS 12343:1998,
while, other tractors seating dimensions were observed slightly less; i.e. 0.3 to 2.6%. Seat
width of T1 tractor was found in the range but for other tractors, seat width was found less,
i.e. 0.5 to 10.9%. This variation may lead to discomfort for tractor operators. Seat heights in
most of the tractors were found to be too high, i.e. 0.6 to 15.3%. This should be a
consideration in redesigning tractor seats. Seat pan concavity was found between 18 to 38
mm. As regards seat adjustment, longitudinally about 50 to 100 mm was provided in all the
tractor seats, while only in T2 and T8 tractor seats could be adjusted longitudinally as well as
vertically about 17 to 46 mm, by virtue of inclined seat mounting arrangement. As regards,
the back rest width, none of the tractor seats were found to be in conformance to the Indian
standards i.e. > 450 mm. Table results indicated that it was found less, i.e. 7.1 to 20.4% in all
seats. Back rest height as per IS should be independently adjustable and kept more than 260
mm. In almost all the tractor seat, it was found as per anthropometric data of Indian
operators, except in T5 seat, where there was no open space provided to accommodate the
sacrum and fleshy parts of buttocks of the operator, just above the seat pan, by which this
__________________________________________________________________________
K. K. Jain, A. K. Shrivastava and C. R. Mehta. “Analysis of Selected Tractor Seats for
Seating Dimensions in Laboratory”. Agricultural Engineering International: The CIGR
Ejournal. Manuscript PM 08 010. Vol. X. December, 2008.
5
backrest height was comparatively more as compared to other seats. Backrest concavity was
found from 18 to 36 mm.
The field survey results indicated that still there is a need for modifying tractor seat design in
the areas of seat height, seat vertical adjustment and back rest width, as per Indian standard
anthropometric considerations.
3.2 Laboratory Study
A free point 3D digitizer instrument was used to measure the seating dimensions of five
selected tractor seats. Seating dimensions of different seats were compared with the above
Indian standard. The results, as shown in Table 2, indicated that the seat lengths were found
to be almost within the range, as prescribed by the IS i.e. 350 to 450 mm. But, in case of seats
S1, S3 and S4 it was found to be slightly less then as required, i.e. -1.4 to 4.3%. Seat widths
of S2, S3 and S5 tractor seats were found within the prescribed range as per Indian standard,
while S1 and S4 seat widths were found slightly below i.e. 2.2 to 7.3%. This may contribute
to discomfort for the tractor operators, particularly those in the higher anthropometrical
percentile population. As regards, the seat adjustment, it was observed that the none of the
seats were provided with vertical adjustment facilities but have longitudinal adjustment in
between i.e. 50 to 140 mm for different seats. Seat pan cushion thickness and angle of seat
pan inclination with seat surface were found within limits.
Back rest seat widths of different seats were not found as per the Indian standard. All the
seats were found below the prescribed limit, i.e. 7.8 to 17.1%. While, back rest height of seats
were found within the range of Indian standard, by including the maximum vertical open
space above the top of the compressed seat, so as to accommodate bulged seat and fleshy
portion above the seat surface. Seat suspensions mechanisms operator’s weight range, back
rest concavity, cushion thickness, inclination of back rest axis with vertical was found within
the range. As regards mounting arrangement of different seats on a tractor and utilized space
was concerned, it was found strikingly different for the tractors under study. Above results
also revealed that seating dimensions of tractor seats for Indian operators still need
modifications by improving the tractor seat design.
6
K. K. Jain, A. K. Shrivastava and C. R. Mehta. “ Analysis of Selected Tractor Seats for Seating Dimensions in Laboratory “.
Agricultural Engineering International: The CIGR Ejournal. Manuscript PM 08 010. Vol. X. December, 2008.
Table 1. Field survey - seating dimensions of different types of tractor seats and comparison with Indian standard
S.
No.
Particulars T
1
T
2
T
3
T
4
T
5
T
6
T
7
T
8
Comments as per IS : 12343, 1998 (mm)
1. Seat length (mm) 362
(-)
341
(-2.6)
338
(-3.4)
348
(-0.6)
354
(-)
341
(-2.6)
349
(-0.3)
348
(-0.6)
Buttock popliteal length 5
th
percentile =
400 +
50
2. Seat width (mm) 455
(-)
428
(-4.9)
448
(-0.5)
441
(-2.0)
412
(-8.5)
401
(-10.9)
407
(-9.6)
428
(-4.9)
Hip breadth sitting 95
th
percentile ≥ 450
3. Seat height (mm) 555
(+2.8)
568
(+5.2)
543
(+0.6)
572
(+5.9)
458
(-)
622
(+15.2)
623
(+15.3)
520
(-)
Sitting popliteal height 5
th
percentile :
540 (maximum)
4. Seat pan concavity
(mm)
38 30 28 30 30 22 18 26 -
5. Seat adjustment -
a. Longitudinal (mm) 90 47 50 50 100 80 70 131 -
b. Vertical (mm) - 17
(inclined)
- - - - - 46
(inclined)
-
6. Back rest
a. Height (mm)
260
(-)
255
(-)
258
(-)
260
(-)
364
(-)*
260
(-)
265
(-)
262
(-)
Height should be independently
adjustable ≥ 260
b. Open space above
the
compressed seat pan
(55) (58) (52) (75) (0) (45) (50) (68)
(fix)
-
7. Back rest width (mm) 415
(-7.8)
381
(-15.3)
407
(-9.5)
402
(-10.7)
381
(-15.3)
358
(-20.4)
418
(-7.1)
377
(-16.2)
Intersey breadth of 95
th
percentile >
450
8. Back rest concavity
(mm)
36 18 28 26 32 18 28 22 -
Note : Figures in parenthesis indicated comparative percentage drop (-) or increase (+) with respect to Indian operators anthropometric dimensions.
7
K. K. Jain, A. K. Shrivastava and C. R. Mehta. “ Analysis of Selected Tractor Seats for Seating Dimensions in Laboratory “.
Agricultural Engineering International: The CIGR Ejournal. Manuscript PM 08 010. Vol. X. December, 2008.
Table 2. Laboratory measurement - Seating dimensions of selected tractor seats by Free point 3D-digitizer instrument
S.
No.
Dimension description with limits as
per IS : 12343, 1998
S
1
S
2
S
3
S
4
S
5
1. Seat length, mm
(400 +
50 mm)
343
(-2.0)
366
(-)
345
(-1.4)
335
(-4.3)
352
(-)
2. Seat width, mm
(≥ 450 mm)
417
(-7.3)
471
(-)
448
(-0.5)
440
(-2.2)
465
(-)
3. Seat pan cushion thickness, mm 48-50 55-58 38-40 45-50 55-60
4. Seat pan concavity, mm 30-32 38-40 30-32 5 30-33
5. Seat adjustment
a. Lon
g
itudinal, mm
100
90-200
140
50
50
b. Vertical, mm - - - - -
c. Type shifting sliding lever /
shifting
sliding lever nut bolts central sliding
slit hole
6. Angle of inclination of seat surface,
de
g
ree (3 to 12
o
b
ackward)
5 12 5 5 10
7. Seat base mounting space size / area
(L x W = cm
2
) and position
33 x 14 = 462
back side of
operator
16 x 9 = 144
moreoless below
the operator
31 x 7 = 217
moreoless below
the operator
25 x 23 = 575
moreoless below
the operator
32 x 24 = 768
moreoless below
the operator
8. Back rest width, mm
(≥ 450 mm)
373
(-17.1)
415
(-7.8)
408
(-9.3)
413
(-8.2)
400
(-11.1)
9. Back rest height, mm
(≥ 260 mm)
max. vertical open space
adjustment, mm (maximum)
240
75
(-7.7)
301
41
(-)
268
30
(-)
260
40
(-)
270
75
(-)
contd-
Remarks: All seats were equipped with parallelogram linkage mechanism with two helical coil springs and a shock absorber.
__________________________________________________________________________
K. K. Jain, A. K. Shrivastava and C. R. Mehta. “Analysis of Selected Tractor Seats for Seating Dimensions in Laboratory”. Agricultural
Engineering International: The CIGR Ejournal. Manuscript PM 08 010. Vol. X. December, 2008.
8
S.
No.
Dimension description with limits as
per IS : 12343, 1998
S
1
S
2
S
3
S
4
S
5
10. Back rest concavity, mm 32-35 35-38 30-32 10-12 33-35
11. Back rest cushion thickness, mm 30-35 32-35 32-35 45-48 20-22
12. Back rest inclination (degree) from
vertical (5 to 15
o
)
19
O
7
O
10
O
10
O
8
O
13. Angle of inclination between seat
pan and back rest surfaces (degree)
104
o
85
o
95
o
95
o
88
o
14. Seat suspension weight range (kg) 50-120 50-120 50-120 50-120 50-120
15. Location of SRP on seat pan
(x-axis)
38-40 mm 35-40 mm 18-20 mm extremely at the
back side of seat
pan
15-17 mm
16. Seat pan surface Apparently
medium
ribbed,
smooth
corners,
bulged sides
Apparently broad,
ribbed, smooth
corners, bulged
sides
Apparently
broad ribbed,
smooth corners,
bulged sides
Apparently flat
and
comparatively
plain, smooth
corners, slight
bulged sides
Apparently
broad, ribbed,
smooth corners,
bulged sides
17. Back rest surface ribbed plain Central portion
ribbed
plain, unribbed,
moreoless flat
plain
Note : Figures in parenthesis indicated comparative percentage drop (-) or increase (+) with respect to Indian operators anthropometric
measurements.
S indicates the different seats of tractor under study.
__________________________________________________________________________
K. K. Jain, A. K. Shrivastava and C. R. Mehta. “Analysis of Selected Tractor Seats for
Seating Dimensions in Laboratory”. Agricultural Engineering International: The CIGR
Ejournal. Manuscript PM 08 010. Vol. X. December, 2008.
9
4. CONCLUSIONS
1. Presently, all the seats (as surveyed) of Indian tractors are equipped with parallelogram
linkage mechanism with two helical coil springs and a shock absorber.
2. The comparison of measured seating dimensions of different tractor seats with the
recommendations of IS 12343 (1998) indicated that:
a) Seat pan lengths were within the recommended range of 350-450 mm.
b) The seat pan widths of some of tractor seats under the study were lower (up to 10.9%) than
minimum BIS recommendations of 450 mm.
c) Seat heights of some of the tractors exceeded the BIS recommended maximum limit of 540
mm. It may cause excessive pressure on the underside of the thigh, which can reduce blood
circulation to the lower legs.
d) Seat adjustment in longitudinal direction was within the BIS recommended range of ± 100
mm, while vertical seat adjustment was not provided in most of the seats. This may affect the
hand and leg reach, and maximum actuating force of tractor operators for operation of
frequently operated controls like brake pedals, clutch pedal, foot accelerator, steering wheel
etc.
e) The backrest heights of most of the seats were within the BIS recommendation of more or
than or equal to 260 mm. In most of the tractors seats, sufficient open area was provided
below the backrest to accommodate sacrum and fleshy parts of buttocks just above the seat
pan and to allow the lumbar region to fit firmly into the backrest.
f) The backrest widths of tractor seats under the study were lower (up to 20.4%) than
minimum BIS recommendations of 450 mm.
g) Shapes of seat pan and backrest of most of the tractor seats were found alike, but there is a
wide variation in cushion thickness, seat pan and backrest concavities and seat mounting
arrangement on tractors.
h) Seat pan and backrest inclinations as well as suspension weight range were found the same
for most of the tractor seats.
3. Tractor seats of different makes can also be fitted appropriately on the tractor by
incorporating, a properly designed simple (MS plate) seat mounting base plate.
5. ACKNOWLEDGEMENTS
Experimental laboratory work was carried out at Central Institute of Agricultural
Engineering – Bhopal, Madhy Pradesh ( India ). This is gratefully acknowledged.
6. REFERENCES
Balasankari,P.K., K. Kathirvel, R. Manian and C. R. Mehta. 2004. Anti- vibration device for
increased comfort of tractor operators, Extension Bulletin : AEC & RI, TNAU,
Publication : 87 / 2004.
Bureau of Indian Standards. 1998. Agricultural tractors – operators seat – technical
requirements IS 12343.
Dupuis, H. 1959. Effect of tractor operation on human stresses, Agricultural Engineering
40(9) : 510-519.
__________________________________________________________________________
K. K. Jain, A. K. Shrivastava and C. R. Mehta. “Analysis of Selected Tractor Seats for
Seating Dimensions in Laboratory”. Agricultural Engineering International: The CIGR
Ejournal. Manuscript PM 08 010. Vol. X. December, 2008.
10
Fairley, T. E. 1995. Predicting the discomfort caused by tractor vibration. Ergonomics 38(10)
: 2091 - 2106.
Jain, K. K. 2006. Studies on vibrational characteristics of different tractor seats and
development of vibration isolator for tractor seat, Unpublished Ph. D. Thesis,
JNKVV, Jabalpur.
Salokhe, V. M., B. Majumder and M. S. Islam. 1995. Vibration characteristics of power
tiller. Journal of Terramechanics 32(4) : 181-197.
Singh, G. and R. S. Doharey. 1999. Tractor industry in India AMA. 30(2): 9-14.
