CHAPTER I

INTRODUCTION

1.0 General

Since 1970 considerable level of emphasis is placed on operator’s comfort and safety in

design of tractors. During tractor operation, the tractor operator together with tractor forms a

man-machine system and the operator is subjected to various physical and mental stresses given

by the machine that is tractor. The stresses accelerate the fatigue of the operator and also affect

the sensitivity and reaction rate of the operator. Since optimum farm machinery management

occurs when the economic performance of the total machine system has been maximized, it is

required to give sufficient consideration to tractor operator work place (TOWP) design. This

work place design mainly includes determination of optimum positions of controls that are

usually operated by the operator during the tractor operation. If the controls, which the operators

handle during operation, are not properly adopted to his anatomy, the performance demanded of

him may quickly reach and even exceed the limits of his tolerance. Consequently, due to

excessive stress, premature fatigue and impaired health and the possibility of accidents will

increase and also the performance of the operator will not be up to the mark. That is why great

emphasis must be given on adopting the operating controls to the physical needs of the human

operator. While going for this type of optimization of control location it is necessary to be aware

of the physiological and psychological prerequisites. This knowledge should harmoniously be

integrated with technical features of design. The main aim is to obtain higher working efficiency

of the tractor-operator system, ease of operation and maximum operator safety.

As far as the safety of the tractor being operated is concerned, Roll-over

Protective Structure (ROPS) is also important. By and large tractor roll-over or turnover is the

main cause of tractor related death. Roll-over Protective Structure (ROPS), that is, nothing but a

frame or cab, made of mild steel, can prevent this sort of fatal accident, thus reducing the tractor

related death.

1.1 Justification of the present study:

For every man-machine system, human comfort and safety to the operator

without substantially affecting the cost of machines is gaining considerable importance in almost

all engineering designs. Since a past few years tractor manufacturers have also been starting to

design tractors that are taking care of operator’s comfort and safety. Before that this was not of

their concern because usually Indian farmers do not bother about comfort and safety. By and

large, they look for the machine/ tractor power performance at reasonably low price of the

1

tractors. But several researches related to man-machine system and human factor engineering

revealed that the operator performance is greatly influenced by the design and spatial locations of

the different tractor controls, the effort required in moving them, the posture adapted while

manipulating the controls and their shape, size and orientation. The inappropriate clutch and

brake pedal contributes to muscle fatigue and causes discomfort for the operator. Besides

detrimental effects to health and general feeling of discomfort after prolonged operation as well

as the higher frequency of operation, the bad posture due to the inappropriate location of tractor

controls also affects the quality and quantity of work. Therefore, there is a need to reallocate the

frequently operated controls in such a way that it can be operated without any discomfort and

minimum effort.

Along with the optimization of control locations, also safety of tractor

operator is also of great concern. The U.S. National Safety Council estimates more than 317

people were killed in 1998 while operating a tractor. About 52 percent of these deaths were the

result of a tractor roll-over. This high death rate associated with tractor roll-over is not a new

problem. Since 1970, tractor roll-over leading cause of farm operator deaths, according to the

U.S. National Safety Council. Statistics from tractor roll-over injuries show that during the past

two decades, about five people are killed each year for every 100,000 tractors in operation. So,

Roll-over Protective Structure (ROPS) are essential to be fitted with each and every tractor. The

Occupational Safety and Health Administration (OSHA) has issued regulations for ROPS

utilization in USA. According to this, except tractor operated at any conditions where ROPS

limits the use of tractor such as in an orchard, inside a building etc. each and every tractor that

has been manufactured after 1981 must be fitted with ROPS.

Keeping all these things in mind, an attempt is made in the present investigation at studying

some of the above aspects of tractor operator ergonomics and safety. The major objectives of the

project are:

1) To study the existing locations of the five most frequently operated control levers in

some commercial tractors.

2) To re-allocate the control levers mentioned above of the mini (13 hp) tractor

developed by IIT, Kharagpur.

3) To design a Roll-over Protective Structure (ROPS) for the same tractor.

2

CHAPTER II

REVIEW OF LITERATURE

This chapter embodies the most relevant literature available with respect to different aspects

of work place design, operator enclosure and roll-over protection structure (ROPS).

2.1 WORK PLACE DESIGN

2.1.1 Ergonomics in Agricultural Operations

Zander (1969) suggested that to achieve a reasonable income with a limited input of capital

and human effort for managing and operating a farm, mechanization and rationalization of farm

operations are necessary. He had emphasized that co-ordination of ergonomics research and

exchanging of information to obtain the necessary design data for the farm machinery are

essential components, in order to realize man-machine system with high capacity and a favorable

load on the worker.

Renius (1994) summarized the technical progress of tractor design in reference to Europe. He

suggested that human engineering aspect was considered as one of the best criteria in the

development trend of the tractor and their controls. According to him a successful tractor

development would make technical progress profitable for both the farmer and the tractor

manufacturer.

2.1.2 Anthropometry in Engineering Machines

Determination of the workspace for arm and foot reach is a very significant problem that

should be solved in order to get a completely correct ergonomic design because most of the

operations related to machine are either hand-operated or hand-controlled or foot-operated or

foot-controlled. This problem can be solved by using anthropometry that deals with the

measurement of the dimensions of the human body. These dimensions are specified by sex, age

and race. In designing a workplace it is not significant to consider only the consider only the

average man or the average reach of arms or the legs, all possible variations of the body and limb

sizes must be taken into account. Anthropometric database is generated for small, average and

large subjects of both sexes for a range of population. For the designing purposes, designers

frequently choose 5 percentile female and 95 percentile male dimensions as design limits. The

3

idea behind that designer has to compromise and decide that he can not economically

accommodate all the people.

Roebuck et al. (1975) quoted to design engineering anthropometry. It is concerned with the

physical measurements of human body required mainly to develop engineering standards, set

specific requirements, and desire suitability of any manufactured product intended for the human

consumer.

Sen et al. (1977) conducted a survey of 192 male workers (agricultural and industrial) of

eastern India. They concluded that the anthropometric dimensions of unorganized workers were

very similar to those of other industrial workers. They compared their study with American and

European studies (Daniels, 1962; Mcfarland et al., 1963; Stoudt et al., 1960) and observed that

the Indian values were much lower than those of Western workers.

Gupta et al. (1983) conducted a survey of farm works of Punjab state in connection with the

design of seats for machines such as tractors and combine harvesters. Forty adult male operators

(21 to 58 years) participated in the study. They reported that the workers from Punjab were taller

and heavier than those from other parts of the country. They also pointed out that there was

considerable difference between the anthropometric data of Indian and Western workers. Similar

results were also Sen (1964) and Sengupta et al. (1977).

Gite and Yadav (1989) have compiled the anthropometric data of agricultural workers from

central India and suggested use of data for farm machinery design on the basis of 5th, 50th and 95th

percentile values of the dimensions.

Prasad (1995) studied the aspect of tractor seat design with regard to Indian operators. It was

found that the tractors, manufactured in India, were based on the anthropometric measurements,

of the foreign driver population (Anonymous, 1990). He tried to modify the design of tractor seat

with regard to Indian operators considering their anthropometric data. The result was a new

tractor seat called “IITKGP 95 seat”. The seat suspension of that seat attained better vibration

attenuation and also appeared the most comfortable seat as compared to existing seats on account

of the subjective perceived comfort rating (PCR) during field operations.

Yadav and Tewari (1998) conducted some ergonomic investigation on Tractor Operator

Work Place (TOWP) design. With the anthropometric data collected from different tractor

operators from different parts of the country, a tractor operator work place simulator had been

designed and developed for studying the different tractor workplace configuration. From the

field study they found that the speed of operation of the tractor as well as the mass of the

operator had significant effect on the vibration acceleration level experienced by the operator.

4

2.1.3 Definitions of comfort and discomfort

Many research studies indicate that discomfort is primarily associated with physiological and

biomechanical factors and comfort is primarily associated with aesthetics. The transition from

discomfort to comfort and vice versa is possible. Hence, if discomfort is increased, as with

increase in time on task and fatigue, comfort will decrease.

Matthews (1964) highlighted that comfort is an abstract feeling and may obviously not be

completely defined in terms of physiological quantities, although levels of temperature, noise

and vibration are clearly important contributions to the feeling of well being or other extreme of

pain.

Shackle et al. (1969) assumed that comfort and discomfort are two opposites on a continuous

scale, ranging from extreme comfort through a neutral state to extreme discomfort.

Hertzberg (1983) first operationally defined comfort as “the absence of discomfort”.

Griffin (1995) defined comfort as “a conscious well being” and discomfort as “a conscious

unwell being corresponding to feeling such as annoyance or irritation”.

Shen and Vertiz (1997) defined comfort as “the relieving process of discomfort”.

2.1.4 Optimization of tractor operator work place

Bonney and Willims (1977) developed a software called ‘CAPABLE’ (Controls and Panel

Arrangement by Logical Evaluation) that produced good layouts in several practical situations

based on the relative importance of certain design criteria as specified by the designer. Measures

of effectiveness include separation of controls, distribution of work-load between the limbs,

distance moved and time taken to operate controls, grouping of controls, suitability for range of

percentiles of the population, comfort and some aspects of accidental operation.

Pham and Onder (1992) described a knowledge-based system for optimum work place design.

The system was constructed using a commercially available hybrid development tool. It was

interfaced with a database of anthropometric data and an optimization program. The optimization

program employed a genetic algorithm.

Yadav (1995) calculated the control locations theoretically with the help of biomechanical model

of tractor operator and the anthropometric dimensions of selected tractor operators. It was found

that the theoretical values were very close and comparable.

Yadav (1995) and Arude (1995) both used statistical techniques for optimization of the location

of various tractor controls. They used analysis of variance (ANOVA) which is one of the most

powerful and commonly used statistical tools in analyzing experimental data. The heart rate of

the operators was monitored and from this data the energy expenditure rate was calculated. The

5

evaluation of optimum workplace configuration was done on the basis of minimum energy

expenditure rate and rated perceived exertion (RPE) score of the operator.

Dhar (2001) studied the location of five most frequently used controls in some commercial

tractors and determined the optimum location of five most frequently used controls namely gear

shift lever, steering, brake pedal, clutch pedal and hydraulic lever of a tractor with the help of

experimental analysis in tractor work place simulator. He collected the data of various

biomechanical parameters that are responsible for physical and mental stresses. He used

ANNOVA for analyzing the data.

2.2 DEVELOPMENT OF ROLL-OVER PROTECTIVE STRUCTURE

2.2.1 Fatalities due to overturn

Hewitt (1998) conducted a descriptive study of the Colorado agricultural fatality experience for

the seven-year period from 1989-1995. Between this period, 107 agricultural fatalities were

investigated and analyzed. Farm machinery such as tractors, loaders, and were the most frequent

sources of fatal injury, causing 39 fatalities. Of the farm machinery deaths, 12 were due to tractor

overturn, 12 due to run over, and 9 due to collapse of equipment or loads on operators.

Letola et al. (1995) presented information about tractor accidents based on data collected and

analyzed in Iowa for the five-year period 1988-1992. This study was based on data obtained

from the news-clipping service used by the Iowa Co-operative Extension Service.

A total of 136 people were killed in 131 tractor related fatal incidents reported in Iowa

newspapers for the five year period of 1988-1992.

2.2.2 Studies on tractor overturning

Chisholm (1979) developed a mathematical model of tractor overturning and impact behavior

with ROPS. In this research the determination of typical classes of dynamic behavior in real

accidents, the development of computer program to simulate these types of behavior and

validation of program by experiments had been done. A mathematical model was developed

based on the force and displacement equations of equilibrium at each point where the tractor or

cab makes contact with the ground during overturning. This allowed incorporation of non-linear

force-deflection characteristics describing deformation of the soil, cab and parts of the tractor,

6

giving a more accurate representation than is possible if impacts are assumed to cover the

overturning phase, in addition to impact, by including tire side force relationship and jumping

terms. A computer program based on the model was written in FORTRAN IV for the simulation

of overturns down steep banks and multiple rolls on continuous slopes, the two most severe

types found in a survey of overturning accident.

He also conducted experimental validation of tractor overturning simulation. Thirty experiments

under different conditions were conducted with an instrumented experimental frame. The

experiments were done with cine film recording overturning motion. The effect of front wheel

articulation was studied. The measured values for linear and angular displacements and

velocities were compared with predicted values. Dynamic behavior and energy absorbed in the

safety frame showed good agreement with prediction of computer simulation.

In one of his studies, Chisholm (1979) found that the absorbed energy was generally more

sensitive to variation of the roll velocity component of tractor kinetic energy than to variation of

the vertical velocity component. The ROPS offered large resistance to roll couple but little to

vertical force when the tractor was more close to the ROPS impact point the ROPS has to absorb

much of the vertical energy. The magnitude of this energy was much higher than that of the roll

kinetic energy, and excessive deformations were predicted in ROPS of typical strength in these

conditions, which could result from an overturn down a bank about 3m high.

2.2.3 Design of tractor enclosure and/or Roll-over Protective Structure(ROPS)

Lamouria et al. (1964) considered fatalities due to tractor seriously and they strongly and

they strongly recommended use of safety frames on the tractors. At that time very less know-

how about safety frames was available. So, they conducted research for establishing design

criteria and testing of safety frames. For design criteria they consider impact forces involved in

tractor upset, protection of driver in a side tip of tractor, provision for normal visibility etc.

The design morphology reflects the need to halt sideward tips or backward tips at about 90

degree. The frame is capable of absorbing impact energy through metal deformation.

Field tests were made with the frame installed on tractor for two types of upset, rear tip and a

side tip. They observed that the maximum impact, and thus the maximum stress on the safety

frame occur in a side tip. Since, the impact velocity is higher for rearward tipping.

The rebound velocity of the tractor was less than 0.08m/s, so that partially all energy of the

system was observed in the initial impact. They also observed that due to tipping there was very

less or no damage to the tractor fitted with safety frame.

7

Person (1967) stated that partially all frames used in Europe are made such that they can be

converted to a cab by adding roof, windshield side windows and doors. Some frames are strong

enough to use as a platform for some implements mounted on the tractor. Independent

manufacturers generally make these protective frames and cabs. When full cabs are installed as

standard equipment, the entire frame can be discarded and the cabs build according to

automotive body design principles.

Yes et al. (1976) described an analytical procedure in support of ROPS design. The analytical

procedure is based on plastic hinge approach. It involves a piecewise linearised process with

consecutive application of incremental load.

Srivastava (1978) studied the principles of similitude modeling to develop design conditions and

predict equations to perform standard ROPS test using scale model. This method is excellent for

performing tractor roll-over test under controlled conditions. In similitude modeling, distortion

of force scale is present if the same material is used for both model and prototype. Distortion in

force scale can be compensated by distortion analysis. The static test results support the

hypothesis that the prediction equation developed to predict deflection at the yield point could be

used to predict complete elastic-plastic deformation of ROPS. It is feasible to develop scale

models of dissimilar cross sectional member by including the safe factor in the analysis.

Ayers (1994) stated that recently approved ASAE standard S519 includes an exposure criterion,

which must be satisfied by the roll-over protective structure (ROPS). The exposure criterion

describes a failure condition in which the clearance zone is exposed to the ground plane during a

tractor overturn. A FORTRAN program was developed to determine if the clearance zone is

exposed to the ground surface as the ROPS static tests to evaluate its accuracy. ROPS two-post

and one-post static tests were both conducted. Results from the two-post test showed the

clearance zone was exposed to the ground plane at a horizontal ROPS end point deflection of

316mm. The model predicted the exposure of the clearance zone at a ROPS deflection of 340

mm. This model can assist ROPS testing when evaluating the exposure criteria.

Gupta et al. (1995) designed a low-cost tractor cab with external side shades and wet pad

evaporative cooling system. It was developed to improve the working efficiency and lengthen the

effective working time of farmers during the summer who cannot afford to buy an expensive air-

conditioned cab.

Bhoi (2001) developed a Collapsible Tractor Operator Enclosure (CTOE) which can be opened

and closed hydraulically. This CTOE was well equipped with different positions required for the

all season tractor operator enclosure. The cost of the CTOE was rupees 7,500, which is much

less as compared to the canvas cabs with ROPS available in the market for 1000 US$.

8

Kumar (2001) developed a software for calculating the dimensions of ROPS. In this he analyzed

the rearward and sidewise overturn in a 3 axes co-ordinate system and the equations obtained

were used to develop the software.

9

CHAPTER III

THEORETICAL CONSIDERATIONS

This chapter presents the fundamental principles involved in work place design and in design of

Roll-over protective structure (ROPS).

3.1 THEORY INVOLVED IN WORK PLACE DESIGN

3.1.1 Design of tractor controls

Design of tractor control refers to the location of the different controls on the

operator workplace. The location of the controls should be such that these are easily accessible to

the operator. If the operations of the controls are easy then the chances of accidents are

minimized. The region in which pedals may be located (the work place envelope) is best

described by a system of co-ordinate based on seat reference point (SRP). The SRP is defined as

the mid point of the line formed by the intersection of effective planes of seat back and the seat

surface (Pheasant and Harris, 1982).

Various sources have definitions of SRP, which differ in detail. These differences

are of little importance for practical purpose. Some of them are reviewed below.

SRP is defined as the intersection of the contour lines extended from the seat and the

back cushions (SAE, 1898: 1964, revision now placed by SAE J898 APR 80)

SRP is defined as that point where the vertical line tangent to the forward point at

the longitudinal seat center line of the back and the horizontal line tangent to the highest point of

the seat cushion intersect in the longitudinal seat center line with the unloaded and adjusted to

the highest and the most rearward position (SAE J1194).

SRP is defined as the point called the locating point (LP) found by intersecting

tangent lines similar to the lines for SRP in J1194, except;

a) the seat is in the rearmost and the lowest position

b) seat suspension is deflected (backward to mid ride position)

c) seat rotational adjusts are set to the middle positions (SAE J397b).

The seat reference point need not necessarily fall on the seat surface.

Seat index point is another point which can be chosen as the origin of the co-ordinate system

mentioned above. The seat index point shall be determined in accordance with ISO 5353, with

seat adjusted to the midpoint of its adjustments. For a suspended seat, the seat shall be set to the

10

midpoint of the suspension travel, unless this is contradictory to clearly stated instructions by the

manufacturer of the seat. Where special instructions for the seat setting exist, these shall be

observed.

Control location is defined as the position of a control including the corresponding displacement,

defined from the SRP. Controls are divided into two groups:

Primary controls or frequently operated controls: Controls whose use is frequently or

continuously required to maintain operational control of the machine or its functions e.g. steering

wheel, brake, clutch, gear shift lever.

Secondary controls or infrequently operated controls: Controls that are infrequently used

by the operators such as hydraulic lever, lights, starter, and heater.

The locations of the main controls such as steering wheel, brake, clutch, and gearshift lever

are established in relation to each other. The brake and the clutch pedals are to be placed either

side of the transmission tunnel with the brake pedal on the right and clutch pedal on the left side

of the transmission tunnel. The other tractor controls should be placed where they can easily be

reached and operated in such a manner that movement of control will produce the expected

movement of control will produce the expected movement of the vehicle or the component.

3.1.2 Control resistance

Control resistance is defined as the force exerted by the operator to effect a control displacement.

Control resistance is necessary to actuate a control that has been affected by a system

malfunction may be higher than specified for normal operation resistance. The values specified

for maximum system malfunction resistance intended to provide boundary conditions for

operator activation during and the time of malfunction. Minimum control resistance shall be

sufficient to avoid inadvertent actuation by the force of the hand or foot resting on the resting on

the control during anticipated operating condition.

11

Fig. 3.1 Seat reference point

Fig. 3.2 Seat index point

12

3.1.3 Anthropometric Aspect

A control should be located where it could not cause any ambiguity regarding its

direction of motion to actuate a function. To enhance compatibility of different size of operators

with minimum adjustability of different control location with respect to the operator, the spatial

reach area of an operator has broadly been divided into two zones-

i) Zone of comfort, and

ii) Zone of reach.

Zone of comfort is defined as the preferred control location zone where both large

and small operators should be able to comfortably and quickly reach controls. Primary or

frequently used hand and foot control, including their displacements shall be located within the

zone of comfort (Fig. 3.3 and Fig.3.4).

Zone of reach is defined as the preferred control location zone where both large

and small operators should be able to reach controls from the seated positions, but the operator

may be required to rotate, lean forward, or to each side. Secondary or infrequently operated hand

and foot controls, including their displacements shall be located within the zone of reach (Fig.

3.3 and Fig.3.4).

.

3.1.4 Orthopedic Aspect

The primary support of the body in a seated posture is spine. It consists of 33 vertebrae jointed

together by the multiple ligaments and intervening cartilages. The vertebrae are divided into four

areas, which correspond to changes in the shape of spine. These areas are the topmost seven

cervical, and then twelve thoracic and five lumber vertebrae followed by five-fused sacral and

four fused coacygeal vertebrae. From the point of view of seat design, the orientation of lumber

and sacral vertebrae is important. It is the vertebrae and respective discs and the muscles, which

take most of the loads of a seated operator. Although when viewed from the front or the back, the

normal relaxed spine appears vertical (Fig.3.5), when viewed from the front or back, the normal

relaxed spine appears vertical, when viewed from side, its curved nature can be seen (Fig.3.6).

The top, vertical, curve bends forwards leading into a convex backward bend throughout the

thoracic region. The lumber region bends forward again, ending in the sacrum, which is

positioned on the pelvis.

Since the spine has evolved to this shape, it seems reasonable to suggest that

this natural shape is one, which produces both the optimum pressure distribution over the

13

Fig.3.3 Top view of the zone of comfort and reach

Fig.3.4 Front view of the zone of comfort and reach

14

Fig.3.5 Structure of the vertebral column in the upright position (Front view)

Fig.3.6 Structure of the vertebral column in the upright position (Side view)

15

cervical discs, and the optimum level of static load of the inter vertebral muscles. It follows,

therefore, that a seat in which the operator has to adopt a different spinal posture is likely to

cause misdistribution in disc pressure and will result, overtime, in lumber complaints.

3.1.5 Body Posture

The posture of a man in performing his task is largely determined by the layout of the

controls and design of seating. There are three types of design for posture. One principle decision

is whether the operator is a man or woman. The body differences between sexes make it

uneconomical to make equipment that would fit either sex.

The standing position is used where operator must be free to work. This can occur where

the control or dials are numerous or widely spaced. It may be necessary to use the standing

positions where no provisions are possible for legroom. This situation occurs where all controls

are mounted on wall or where or when the control panel has no indentation for knee room and

can not be straddled.

The seated position is superior to the standing position in several ways. There reduction

of fatigue for the operator can perform light work with the arms and the heavy work with the

legs for much longer time than when standing. There is increased stability and equilibrium in the

seated position. The operator’s body is protected against vibration, rolling and jolting, leaving

the arms and legs free to operate the controls. Another advantage of seated position is that it

enables more effective operation of pedal controls, both feet may be used simultaneously; a

greater force may be operated with either foot.

There are advantages in designing the workplace so that the operator can move between

a seated and standing position. A layout which permits the operator to seat or stand allows him to

shift posture at will, and reduces the muscular fatigue which results from prolonged effort in any

one position. In order to arrange a layout so that the operator can move between a seated and

standing position, it is necessary to provide a raised seat in order to the eye level of the operator

when seated to the same level as that when standing. The seat should be easily movable into and

out of the position, which can be done by pull out or swivel mounting.

3.1.6 Hand Operated Controls

The horizontal pushing power, which can be exerted by the arms, depends upon the

angle between the upper arm and the forearm. The maximum power that can be exerted by the

arm in sitting position and in various positions of the elbow is shown in (Fig.3.7). Pulling is

16

greater than the pushing force. So the controls demanding maximum force have to be located at a

distance of arm length.

The draft control lever should be placed within the arm reach of the tractor operator

with least changes in his alert driving posture. It must specially be ensured that operators need

not to bend forward or sideways while operating the lever. The forward or sideways movement

is likely to strain the spinal cord.

3.1.7 Foot Operated Controls

The force to be exerted by the leg in a sitting position is determined by the angle

between the upper leg and the symmetrical plane of the body. If the angle between the upper leg

and the lower leg is 155 degree on a pedal in front of the body maximum force can be exerted. It

is undesirable to design foot-operated controls too far from centerline (Fig.3.8). A distance of

zero to 80-120 mm to the left or to the right of the symmetrical plane is optimal (Dupuis, 1959).

Pedal position demanding a raised thigh or extended knee result in backward rotation of the

pelvis and a slumped spinal posture. A pedal which is lower and closer relaxes the hamstring

muscles allowing forward rotation of the maintenance of the lumbar lordosis (Fig.3.9).

3.1.8 Steering wheel

The forces that need to be exerted on the steering wheel depends on a diameter of the

steering wheel, the transmission of steering mechanism and the friction of the bearing, soil tire

friction. The minimum diameter of the steering wheel should be 400 mm. a too big steering

wheel makes the egress system difficult. The inclination between the steering column and

horizontal determines the maximum force that can be exerted.

17

Fig.3.7 Hand strength in executing six different movements (side view and top view)

Fig.3.8 Reduction in pedal thrust resulting from unfavorable location

18

Fig.3.9 Pedal positions demanding a raised thigh or extended knee

Fig. 3.10 Maximum pedal thrust in relation to height of seat above pedal

19

Fig. 3.11 Relation of maximum pedal thrust to lateral angular separation of legs

20

3.1.9 Optimization of Control Location

There are considerations of population stereotypes, comfort, safety, aesthetics, and

styling, closeness of controls for ease of use, minimum distance of controls for avoidance of

mistakes, balance of work between limbs, avoidance of operator overload conditions, the need to

satisfy a wide range of operator sizes for optimum control location. Energy expenditure rate and

rated perceived exertion score can be used as satisfactory for the optimum location of controls.

3.2 THEORY INVOLVED IN THE DESIGN OF ROPS

3.2.1 Roll-over Protective Structures

A cab or frame for the protection of operators of agricultural tractors to minimize the

possibility of serious operator injury resulting from accidental upset.

The ROPS is characterized by providing space for clearance zone, inside the envelope of the

structure or within a space bounded by a series of straight lines from the outer edge of the

structure to any part of the tractor that might come in contact with flat ground and is capable of

supporting the tractor in that position if the tractor overturns.

3.2.2 Main purpose of ROPS

i) To absorb a specified amount of energy while tractor takes sidewise overturn.

ii) To support weight of tractor in upset condition of the tractor and hence not allowing

the crushing of operator under the weight of the tractor.

21

Fig.3.12 Side view and top view of tractor workplace

22

3.2.3 Clearance Zone

Clearance zone is defined in relation to the vertical reference plane. This reference plane

shall be assumed to move horizontally with the seat and steering wheel during loading and to

remain perpendicular to the tractor or the floor of the protective structure. The clearance zone is

defined when the tractor is standing on its wheels on a horizontal surface and, and when

applicable, the steering wheel is adjusted to the mid-position for seated driving. The clearance

zone is illustrated in Figs. 3.13 and 3.14.

a. A horizontal plane (A1B1B2A2) 900 mm above the seat reference point.

b. An inclined plane (G1G2I2I1) perpendicular to the reference plane and including the rearmost

point of the seat backrest and the extension of which passes through a point 900 mm directly

above the seat reference point.

c. A cylindrical surface (A1A2I2I1) perpendicular to the reference plane, with a radius of 120

mm tangential to the planes defined in (a) and (b) above.

d. A cylindrical surface (B1C1C2B2) perpendicular to the reference plane, having a radius of

900 mm extending forward for 400 mm from and tangential to the plane defined in (a) at a point

150 mm forward of the seat reference point.

e. An inclined plane (C1D1D2C2) perpendicular to the reference plane, joining the surface

defined in (d) at its forward edge and passing 40 mm from the rim of the steering wheel

f. A vertical plane (D1E1E2D2) perpendicular to the reference plane 40 mm forward of the rim

of the steering wheel

g. A horizontal plane (E1F1F2E2) through the seat reference point

h. A surface (G1F1F2G2), curved if necessary, from the bottom lilmit of the plane defined in (b)

to the horizontal plane defined in (c) following the general direction of, and in contact with, the

rear surface of the seat backrest

i. Vertical planes (J1E1F1G1H1 and J2E2F2G2H2) not less than 250 mm on either side of the

reference plane; The distance E1E2 shall be equal to the diameter of the steering wheel plus 40

mm on each side of the rim of the wheel or 500 mm, whichever is greater

j. Parallel planes (A1B1C1D1J1H1I1 and A2B2C2D2J2H2I2) inclined so that the upper edge of

the plane on the side on which the load is applied is at least 100 mm from the reference plane.

23

Fig. 3.13 Clearance zone from the side

Fig.3.14 Clearance zone definition

24

Table 3.1 Clearance zone dimensions

DIAMENSIONS mm REMARKS

A1A0

B1B0

100 Minimum

A1A2

B1B2

C1C2

500 Minimum

D1D2

E1E2

500 Minimum or equal to the dia. of

steering wheel plus 80mm,

Whatever is greater.

F1F2

G1G2

H1H2

I1I2

J1J2

500 do

E1E0

E2E0

250 Minimum or equal to the radius

of the steering wheel plus 40 mm.

J0E0

F0G0

I0G0

C0D0

E00F0

300

-

-

-

-

depending on the tractor

25

SAE Standard defines dimensions for the minimum normal operating space envelope around

the operator enclosure (cabs) on off-road machines.

The dimensions for the recommended minimum normal operating space envelope around a

clothed operator are defined for a seated operator in Fig.3.15. The minimum operator space

envelope is measured to the interior surface without visible surface deformation of the operator

enclosure. The operator enclosure minimum space envelope may be smaller than specified in

Fig.3.15 if it can be demonstrated that the reduced operator space envelope for a particular

machine application allows for adequate operator performance. Potential modifications for the

operator enclosure space envelope include, but are not limited.

3.2.4 Design of ROPS

The ROPS must be strong and yet flexible enough to absorb the energy without intruding

into clearance zone. Sufficient flexible of ROPS is desirable and often necessary for two

important reasons namely, to prevent intolerable shocks to the operator and to avoid significant

damages to the supporting vehicle chassis. On the other hand, a ROPS with too much flexibility

may not sustain the required crush load.

There are two types of overturning of tractor:

1. Sideward overturning: In case of sideward overturning, load comes on ROPS from

side and so ROPS should absorb specified amount of energy in this case. After side loading if

tractor overturns completely then the ROPS should support weight of the tractor.

2. Rearward Overturning: In case of rearward overturning, load comes from rear and

ROPS must absorb a specified amount of energy. After this if overturning of tractor takes place

then the ROPS should support the weight of the tractor.

In each case of loading, there is some maximum limit of deflection of

ROPS, so that clearance zone should not come in contact with the ground. The value of

deflection is limited by the shape and size of the ROPS.

Therefore, ROPS should absorb different amount of energy from two

directions, and after absorbing energy either from side or rear, the same ROPS should be able to

support the weight of tractor. And in each case of loading, there is a maximum limit of deflection

for ROPS, which depends upon the shape and size of the ROPS.

26

Fig. 3.15 Minimum Operator Enclosure Dimensions for Sitting Enclosure

27

3.2.4.1Theory for geometric design of ROPS

For protection of operators, it is required that whenever overturning of tractors equipped with

ROPS occurs, clearance zone should not come in contact with ground.

As the overturning of tractor occurs whether it is sideward or rearward, ROPS deforms. In

overturned situation, tractor is supported on some points of its body of which one point is on the

ROPS. These points make the ground plane. This ground plane is called as the imaginary ground

plane. In these points, position of all points remains fixed except the point on ROPS, which

varies according to the deflection of ROPS. So, location of imaginary ground plane will vary

according to location of supporting point on ROPS, which is varying with the deflection of

ROPS.

As there will be more deflection of ROPS, the imaginary ground plane comes as nearer to the

clearance zone. So, for meeting the condition that the clearance zone should not come in contact

with the ground, there will be limitation on the deflection of ROPS. For getting more deflection,

the shape of ROPS has to be changed.

3.2.4.2 Analysis of Rearward Overturning

There may be two possibilities in case of rearward overturning. In the first case, tractor may

be obstructed to 90 degree overturn. In this condition, there will be three supports for the tractor.

Two support points will be on the two rear tires and the third one will be the crossbar of the

ROPS (Fig.3.16). All these three points will make the imaginary ground plane.

In the second phase, there will be complete overturning of the tractor. In the case, the

supporting points will be the top portion of hood and the cross-bar of the ROPS (Fig.3.17). These

points will define the imaginary ground plane.

As there are two phases in rearward overturning, there is a condition in which the supporting

point on the crossbar of the ROPS will be in common. This is the called the critical point.

Crossbar of the ROPS should not go beyond this point. Otherwise, the first imaginary ground

plane would enter into the clearance zone and if crossbar goes under the critical point, then the

second imaginary ground plane will enter into the clearance zone. With this assumption, the co-

ordinates of the critical point will be determined.

28

Convention:

X-axis: longitudinal axis of the tractor

Y-axis: transverse axis of the tractor

Z-axis: vertical axis of the tractor

Co-ordinates of the following points are required for the analysis of the rearward overturning of

the tractor (Fig.3.18):

Center Rear axle, G (Xg, Zg)

Ground contact point on the rear wheel, A (X1, Z1)

Corner point of clearance zone on plane 1, B (X2, Z2)

Corner point of clearance zone on plane 2, D (X3, Z3)

Top point on front hood of tractor, E (X4, Z4)

Critical Point, C (Xc, Zc)

Co-ordinates of points G, B, D and E are given. So, we need to obtain the co-ordinates of the

points A and C, in order to obtain the Height of ROPS and Rear extension of the ROPS.

Calculation of co-ordinates of point A:

Equation of the outer circle of the Rear Wheel with center F and diameter D is

(X - Xr)2 + (Z - Zr)2 = (D/2)2 (3.1)

Point A lies on circle (1). Hence

(X1 - Xr)2 + (Z1 - Zr)2 = (D/2)2 (3.2)

Equation of tangent to circle (1) with point of contact A is

(X - Xr)* (X1 - Xr) + (Z-Zr)*(Z1 - Zr) = (D/2)2 (3.3)

29

Line (3) passes through the point B. Hence

(X2 - Xr)*(X1 - Xr) + (Z2 - Zr)*(Z1 - Zr) = (D/2)2 (3.4)

Solving equations (3) and (4), a quadratic equation is obtained in X1. Thus, there are two

possible values for X1. It can be seen from the figure that the value of X1 that is required is the

minimum of the two solutions.

After obtaining X1; Z1 is obtained from equation (2)

Thus, the co-ordinates of the rear axle center be G (Xg, Zg). Then, from the figure, if the line GC

intersects the clearance zone, then rear extension should be provided to the ROPS. The length of

rear extension is obtained by sifting the line GC in the X-direction is the rear extension of the

ROPS. Let the rear extension be er.

Then, the height of the top point of ROPS is required for the sideward analysis of ROPS.

They are given by,

X= Xg – er, and Z= H+ Zg.

The Y- co-ordinate is obtained by the sideward analysis of overturn.

30

Fig. 3.16 Schematic diagram showing exposure of clearance one to the ground during

complete overturn of tractor

31

Fig. 3.17 Tractor overturning obstructed at 90 degree and support given by the

deformed ROPS on the ground

32

Fig. 3.18 Location of two imaginary ground planes during rearward overturning and

the critical point

33

3.2.4.3 Analysis for sideward overturning of tractor

The approach is to define the equation of a plane from three points of contact between the

tractor and the ground during the overturn. This plane is called the ground plane.

In a sideward overturn, there are two such possible ground planes. In the first case, the three

points of contact between the tractor and the tractor and the ground are outer top point of the rear

wheel, the top corner point on ROPS, and the supporting point on the front hood. In the second

case, the points of contact are the outer top point of the rear wheel, the top corner point on

ROPS, and the outer top point of the front wheel.

In the rearward overturn analysis of the tractor, the height of ROPS, and the rear deflection

of ROPS are determined. Thus, the X and Z co-ordinates remain the same for the deflected

ROPS when a side load is applied on it.

In the sideward overturn analysis, the y-co-ordinate of the deflected ROPS is determined.

Thus, the width of cross bar and side extension of ROPS are determined.

For the extreme condition, let the corner point of the clearance zone be on the ground plane.

Then, let co-ordinates of the two such possible ground planes ABC and ABD (Fig. 3.19) are:

A = (X1, Y1, Z1)

B = (X2, Y2, Z2)

C= (X3, Y3, Z3)

D = (X4, Y4, Z4)

Let the supporting point of rops on the ground plane be

E= (X5, Y5, Z5)

Its X AND Z co-ordinate that is X5 and Z5 are known.

Equation of the plane ABC is given by,

X – X1 Y – Y1 Z – Z1

X2 – X1 Y2 – Y1 Z2 – Z1 = 0 (3.5)

X3 – X1 Y3 – Y1 Z3 – Z1

Since, point E lies on the plane represented by equation (5),

34

Y5 = [(X5 – X1)*{(Y2 – Y1)*(Z3 – Z1) - (Z2 – Z1)*(Y3 - Y1)} +(Z5 –Z1){(X2 –X1)*(Y3 –

Y1) – (Y2 – Y1)*(X3 – X1)}] / [(X2 – X1)*(Z3 – Z1) – (Z2 – Z1)*(X3 – X1)]

Similarly, equation of the plane ABD is given by,

X – X1 Y – Y1 Z – Z1

X2 – X1 Y2 – Y1 Z2 – Z1 = 0 (3.6)

X4 – X1 Y4 – Y1 Z4 – Z1

Since, point E lies on the plane represented by equation (2),

Y5 = [(X5 – X1)*{(Y2 – Y1)*(Z4 – Z1) - (Z2 – Z1)*(Y4 - Y1)} +(Z5 –Z1){(X2 –X1)*(Y4 –

Y1) – (Y2 – Y1)*(X4 – X1)}] / [(X2 – X1)*(Z4 – Z1) – (Z2 – Z1)*(X4– X1)]

The maximum of (2) and (4) is assigned to Y5.

Side extension of ROPS, es = (Y5 – Y1) IF (Y5 – Y1) > 0

= 0 Otherwise

Width of the cross-bar (W) = SM+ 2*es

Where SM is the maximum distance between two points on the rear axle on which rops can be

fitted.

The height of the side extension is normally taken as 70 cm.

35

Fig. 3.19 Two possible ground planes ABC and ABD during sideward overturning

36

The following parameters of ROPS are determined using the above analysis:

Height of ROPS (H)

Top-width of Cross bar (W)

Rear extension of ROPS (er)

Side extension of ROPS (es)

Height of sideward extension (Hs)

3.2.5 Test procedure of ROPS:

The procedure for testing the strength of ROPS is described as per ASAE S383.1

FEB04.

a) Static Tests

1. A horizontal gradual increasing elemental load is applied with element length not less than

250 mm and not more than 700 mm.

2. Longitudinal Loading: The load is applied horizontally and parallel to the longitudinal

median plane of tractor (Fig.3.20 (a)). The rear load is not required on tractors having 50% or

more of the unballasted weight on the front wheels. The point of application of the load shall be

located at one-sixth of the width of the top of the ROPS. The length of the elemental load shall

not be less than one-third of the width of the ROPS and not more than 49 mm greater than this

minimum. The required energy is

Esr = 1.4*Mt (Joules). (3.7)

Where, Mt is the mass of the tractor.

3. Transverse loading: The side load shall be applied horizontally at 90 degree to the

longitudinal median plane. It shall be applied at the upper extremity of the ROPS of element

length 700 mm (Fig.3.20 (b)). The required energy is

Ess = 1.75*Mt (Joules). (3.8)

4. Crushing: A vertical force of value 20Mt (Newton) is applied on the top members of ROPS

(Fig.3.20(c)).

37

Fig.3.20 (a) Typical rear (front) load application

Fig.3.20 (b) Typical side load application

Fig.3.20 (c) Typical load application for Crush Test

38

b) Dynamic Tests

The dynamic loading shall be produced by the use of a 2000 kg mass acting as a

pendulum. The impact face of the pendulum shall be 680 mm.

1. Impact from the rear and front: For the impact test to the rear and front, the tractor shall be

positioned so that the supporting chains and the face of the pendulum block are at 20 degree to

the vertical when striking the ROPS.

1.1 Impact from the rear: The load shall be applied to the uppermost transverse structural

member of the ROPS that is, that part which is likely to strike the ground first in an overturn.

The point of application of the load shall be located at one-sixth of the width of the top of the top

of the ROPS inward from the outside corner (Fig.3.21 (a)). The height of the lift of the lift of the

pendulum block shall be calculated by choosing either of the following formulae:

Alternative 1: H = 2.165*10-2*(Mt*l2) (3.9)

Alternative 2: H = 5.74*10-2*I (3.10)

1.2 Impact from the front: The blow shall be struck as close to the corner of the top of the

ROPS as is practicable on the same side as the side impact (Fig.3.21 (b)). The lift height of the

pendulum block shall be calculated from the following formulae:

H =25 + 0.07*Mt FOR Mt = 800-2000 kg (3.11)

H = 125 + 0.02*Mt FOR Mt = 2000-6000 kg (3.12)

1.3 Impact from the side: If it is certain that any particular structural member will take the

initial impact when the tractor overturns sideways, the impact shall be struck against this

member. Otherwise, the impact shall be struck against an uppermost side member and in the

vertical plane perpendicular to the longitudinal median plane and 300 mm forward of the seat

reference point (Fig.3.21 (c)). The height of the lift of the pendulum block shall be calculated

from the following formulae:

H =25 + 0.07*Mt FOR Mt= 800-2000 kg (3.13)

H = 125 + 0.02*Mt FOR Mt= 2000-6000 kg (3.14)

39

Fig.3.21 (a) Typical rear impact application

Fig.3.21 (b) Typical front impact application

Fig.3.21 (c) Typical side impact application

40

In each case of impact loading, the maximum energy to be absorbed is,

Ei = 19.6*H (3.15)

1. Static test performance requirements will be met if structural members meet or exceed the

required rear and side energy input levels and the dimensions of the zone of clearance not

disturbed in rear and side loading.

2. Crush test performance requirements will be met if the dimensions of the clearance zone are

not disturbed while the load is applied.

3. Impact test performance requirements will be met if the dimensions of the zone of clearance

are not disturbed in both side and rear loading.

4. No sharp edges exposed to operator.

5. No parts of the ROPS shall enter the clearance zone.

3.2.6 Theory involved in determining the cross-section of the ROPS

The maximum energy that is required to absorb in each loading is the resilience or

strain energy that is to be stored in the ROPS due to external loading, within elastic limit. The

design value of the tensile or compressive stress for a particular material and for a particular

cross-section can be calculated from this by using the formula:

U = (σ2*V)/ (2*E) (3.16)

Where

U is the resilience or strain energy

σ is the design value of stress.

V is the volume of the body

E is the elastic modulus of the material.

The maximum deflection of the ROPS component can be calculated with the help of

formulae used for calculating the maximum deflection for cantilever beam (in case of side and

front loading) and for simply supported beam (in case of crushing). The formulae are:

41

δ = (W*L3)/ (3*E*I) for cantilever beam (3.17)

δ = (W*L3)/ (48*E*I) for simply supported beam (3.18)

Where

δ is the maximum deflection of the component.

W is the force or load given on the component at its free edge.

L is the length of the component.

E is the elastic modulus of the material of the component.

I is the moment of inertia of the component

I= (1/12)/ (b*h3) for solid rectangular section (3.19)

= (1/12)/ (b1*h13 – b2*h23) for hollow rectangular section (3.20)

W will be calculated from the maximum energy to be absorbed in case of dynamic loading,

using the formula,

U = W*H (3.21)

Where U is the potential energy stored in it.

As the moment of inertia is dependent on the dimensions of the cross-section, by putting

different cross-sections, the maximum deflection for the maximum energy to be absorbed, can be

found out. The cross-section for which the maximum deflection is less than the allowable one

will be the suitable cross-section.

3.3 Determination of the Center of Gravity of the Tractor with ROPS

The Centre of Gravity in present study was determined by weighing method. This involves

measuring the ground reactions in horizontal position, and when front end is lifted.

.

42

l Wt

Rr Rf

Fig.3.22(a) Determination of horizontal fore-and-aft coordinate

Fig.3.22 (b) Determination of vertical coordinate

3.3.2 Horizontal fore-and-aft coordinate (l)

43

rrrfL

h

The horizontal fore-and-aft coordinate (x) may be calculated by the following formula:

l = (Rf*L) / Wt (3.22)

Where, Rf= front reaction,

L= wheel base,

Wt = total weight

3.3.3 Vertical coordinate (H)

The vertical coordinate (H) is determined by the formula:

L’ =√ (L2 +(Δr2) –(n - Δr)2)

Δr = (rr - rf)

tanλ1 = (n -rr)/ L’

tanλ2 = Δr/ L

λ = λ1 + λ2

h = [(Wt*l – Rf’*L)/(Wt*tan λ)] – [Rf’* Δr/Wt]

H = rr + h

Where,

rr = radius of the rear wheel

rf = radius of the front wheel

λ = angle of tilt

n = the height of lift from the ground

Rf’ = the reaction at the front wheel at the lifted position

h = the height of the centre of gravity above the centre of the rear axle

H = the height of the centre of gravity above the ground

CHAPTER IV

MATERIALS AND METHODS

44

This chapter deals with the description of experiments and techniques used in the optimization of

different frequently using tractor controls locations and that employed in designing the ROPS.

4.1 Experiment 1

Study of the existing location of different controls and levers in different tractors.

4.1.1 Procedure

Six Indian tractor models were selected from the tractors available in the Farm

Machinery Shed, Agricultural and Food Engineering Department, IIT, Kharagpur. The aim was

to find out the existing locations of five most frequently operated controls on the Indian Tractors.

The five controls selected for study were brake, clutch, gear-shift lever, high-low gear, hydraulic

control lever and steering wheel.

First the tractor was kept on a leveled ground surface. The seat reference point (SRP) was

determined as defined as defined by Pheasant and Harris (Sec 3.1.1). The controls were kept on

their neutral position and their distances were measured from the SRP in X, Y and Z direction. It

was assumed that origin at SRP, Y-axis lateral, positive to the right of SRP and Z-axis fore-aft,

positive upward from of the SRP. The center of the foot pedal was taken as the location of foot

pedal. The dimensions measured for the steering were steering wheel diameter, steering column

angle with respect to the horizontal and the forward distance to the front edge of the steering

wheel. Equipments and accessories used for the measurement of dimensions were 30 cm, 1 m

steel rule, 2 m steel tape with an accuracy of 1 mm, L-square, protector with spirit level and

plum bob.

4.1.2 Data analysis

The data collected as described above for each of the tractor models studied were analyzed to

obtain the mean, range, standard deviation and co-efficient of variation values. The existing

tractor operator workplaces were designated as T1, T2, T3, T4, T5, and T6. All the measured

dimensions and respective values are presented in table 5.1. The result of these experiments are

presented and discussed in the Sec. 5.1.

4.2 Experiment 2

45

Study of the existing location of different control levers in the tractor developed by IIT,

Kharagpur.

4.2.1 Procedure

The tractor developed by IIT, Kharagpur was taken for the experiment. The aim was to find

out the existing locations of five most frequently operated controls of the tractor developed by

IIT, Kharagpur.The five controls selected for study were brake, clutch, gear-shift lever, high-low

gear, hydraulic control lever and steering wheel.

First the tractor was kept on a leveled ground surface. The seat reference point (SRP) was

determined as defined as defined by Pheasant and Harris (Sec 3.1.1). The controls were kept on

their neutral position and their distances were measured from the SRP in X, Y and Z direction. It

was assumed that origin at SRP, Y-axis lateral, positive to the right of SRP and Z-axis fore-aft,

positive upward from of the SRP. The center of the foot pedal was taken as the location of foot

pedal. The dimensions measured for the steering were steering wheel diameter, steering column

angle with respect to the horizontal and the forward distance to the front edge of the steering

wheel. Equipments and accessories used for the measurement of dimensions were 30 cm, 1 m

steel rule, 2 m steel tape with an accuracy of 1 mm, L-square, protector with spirit level and

plum bob.

4.2.2 Data analysis

The data collected as described above for the tractor models studied were analyzed to obtain

the mean, range, standard deviation and co-efficient of variation values. All the measured

dimensions and respective values are presented in table 5.2. The result of this experiment is

presented and discussed in the Sec. 5.2.

4.3 Experiment 3

Design of Roll-over protective structure

4.3.1 Procedure

The theory of design of ROPS as described in 3.2.4 was used for designing the ROPS. The

co-ordinate of different points which are required while designing the dimensions of ROPS was

taken (with respect to seat reference point). Then from this the dimensions of the ROPS was

calculated. Now for determining the suitable cross-section the maximum energy that is to be

absorbed by the ROPS was calculated as described in the section 3.2.5. Now using the theory

46

described in 3.2.6 the cross-section that is suitable for the ROPS was determined. Equipments

and accessories used for the measurement of the co-ordinate of different points were 30 cm, 1 m

steel rule, 2 m steel tape with an accuracy of 1 mm, L-square, protector with spirit level and

plum bob. The calculated value of all the dimensions are presented and discussed in the Sec. 5.3.

The calculation for designing of the dimensions of the ROPS is given in the Appendix A.

4.3.2(a) Calculation for determination of cross-section of the ROPS

Calculation is done using the formulae described in 3.2.6. Material taken into consideration

was mild steel and cross-section that used were 25*25 mm hollow square section of thickness 2

mm and 75*37.5 mm channel section of thickness 6 mm, the open side of which was covered by

welding a 3mm thick mild steel sheet. Wheel base of the tractor developed by IIT, Kharagpur

was measured. The calculation for designing of the cross-section of the ROPS is given in the

Appendix B.

4.3.2(b) Calculation for maximum deflection:

The calculation was done for determination of the maximum deflection. Load given was

calculated and then the deflection, as described in 3.2.6. Elastic modulus, E was taken as 20,

0000 N/mm2 for mild steel. The calculation was done for a cross-section of 25*25 mm hollow

square section of thickness 2mm and for a cross-section of 75*37.5 mm hollow channel section

of thickness6 mm (open side covered by 3mm thick mild steel sheet). The calculation was given

in Appendix C.

47

Work place

Vertical Post

Fig.4.1(a) The designed ROPS and workplace for the mini tractor (side view)

Fig.4.1 (b) The designed ROPS and workplace for the mini tractor (back view)

4.4 Experiment 4

48

Rearward Extension

Cross-bar

Fabrication of Roll-over protective structure

4.4.1 Procedure

The fabrication process was done in the Farm Machinery workshop, Dept. of Agricultural

and Food Engineering, IIT, Kharagpur. The two posts of the ROPS were made of 75 mm x 37.5

mm, 6 mm thick channel bar of mild steel. The support was derived from the chassis by using

nut and bolt joint (1/2” diameter). The height of the ROPS was made by welding the channel bar

as and when it is required. At the chassis horizontal plane and at the horizontal plane on which

SRP lies, the channel bars were bended at (60 degree) and (30 degree) respectively to give the

calculated length and desired shape and then the gaps were filled by putting pieces of mild steel

of the required shape. The width or the top component of the ROPS was made with a channel

bar of the width calculated in the experiment 3. At the two end of this channel bar two L-clamps

were welded. These two clamps were made of 4” wide angle iron of mild steel of thickness 8

mm. These clamps were of 1” length. At the free arms of these clamps two ½” diameter hole

(threaded inside) were made in order to fix it with the two posts with the help of nut and bolt.

The open end of the channel was covered by welding 3 mm thick and 75 mm wide mild steel

sheet. At a height 5” above the seat reference point, a 2 mm thick 1” x1” hollow square bar, both

open ends covered with 8 mm thick mild steel flat (with threaded hole of diameter 1/2”) was

jointed horizontally with the two post with the help of nut and bolt, in order to strengthen the

structure.

4.5 Experiment 5

49

Determination of Centre of gravity of the IIT Tractor with ROPS

The position of the centre of gravity of newly developed tractor was determined as per Indian

Standards (IS: 10743 - 1995). Following procedure was used to determine the CG location.

1) Tire pressure was maintained as per designed values and rolling radius was measured.

2) The tractor was parked on level ground and wheel base and track width were measured.

3) The radiator, sump, hydraulic and other reservoirs were filled to the specified levels and dead

weight of 75 kg was kept over operator’s seat.

4) Front, rear, LHS and RHS reactions as well as total weight of tractor were determined (fig.

4.2(a)).

5) The front portion of the tractor was lifted and lifting height was measured. The reaction force

coming on the rear wheel at this position was also measured.

50

Fig.4.2(a) Determination of centre of gravity of the mini tractor with designed

ROPS(leveled position )

Fig.4.2 (b) Determination of centre of gravity of the mini tractor with designed ROPS

(lifted position)

51

CHAPTER V

RESULTS AND DISCUSSION

This chapter presents analysis and interpretation of the results of the experiments conducted

during the course of investigation. It includes the comparison of the various control locations

measured on different tractor models and that measured on the tractor developed by IIT,

Kharagpur. Also the dimensions of the ROPS that has been finalized are discussed here.

5.1 Study of the existing location of different controls and levers in different tractors.

In the present study data were collected on different tractor models with regard to five

most frequently used control locations. The tractor models were designated as T1, T2, T3, T4,

T5, and T6. The picture of different tractor workplaces are shown in Figs. 5.1 through

5.6.Cartesian co ordinate system is used to define the control locations in the work place (Origin

at the SRP, X-axis – fore-aft, positive to the front of the SRP, Y-axis – lateral, positive to the

right of SRP, Z- axis – vertical, positive upward from the SRP). The tractor workplace design

parameters were measured for clutch pedal, brake pedal, gear shift lever, steering wheel and

hydraulic lever. The data collected as described above for each of the tractor models studied

were analyzed to obtain the minimum value, maximum value, mean, range, standard deviation

and co-efficient of variation values. All the measured dimensions and respective values are

presented in table 5.1.

The forward horizontal distance (X) of brake and clutch pedal from SRP was found to be

between 60 to 89.5 cm. and 60 and 85.5 cm. respectively. The respective coefficients of variation

were found to be 8.12% and 11.12% respectively. The lateral distances (Y) of brake and clutch

pedal were between 21 to 30 cm. and 23.5 to 28 cm. respectively. The respective coefficients of

variation were found to be 13.87% and 7.05% respectively. The vertical distances (Z) of brake

and clutch pedal were between 25 to 47 cm. and 25 to 49 cm. respectively. The respective

coefficients of variation were found to be 18.45% and 18.33% respectively.

The forward horizontal distance (X) of gear shift lever from SRP was found to be between 45

to 61 cm. The coefficient of variation was found to be 10.87%. The lateral distance (Y) of gear

shift lever was between 0 to 41.4 cm. The coefficient of variation was found to be 157.6%. The

vertical distance (Z) of gear shift lever was between -11 to 27 cm. The coefficient of variation

was found to be 827.22%.

52

Table 5.1 Existing Locations of the Various Frequently used Controls in Selected Indian

Tractors

Controls Co

ord

ina

te

Mean

for T1

(in

cm.)

Mean

for

T2

(in

cm.)

Mean

for T3

(in

cm.)

Mean

for T4

(in

cm.)

Mean

for T5

(in

cm.)

Mean

for T6

(in

cm.)

Grand

Mean

(in

cm.)

SD (in

cm.)

CV in

%

Gear shift

lever

x 51.5 40.3 53.7 54.5 52 55.5 51.25 5.57 10.87

y 41.4 30.5 0 0 0 0 0 18.88 157.6

z 24.5 5 -7 -7 5 -11 1.58 13.07 827.22

Clutch

Pedal

x 79 76 63.5 66.5 68 63.5 68.33 7.6 11.12

y -26.2 -24.1 -24 -24 -28 -23.5 -24.97 1.76 7.05

z -27.5 -37 -41.8 -46.5 -34 -44 -38.47 7.05 18.33

Brake

Pedal

x 83 76.1 68.5 66.5 73 71 73.02 5.93 8.12

y 21 30 23 27 29 24 25.67 3.56 13.87

z -27.5 -34 -44 -44.5 -42 -46 -39.67 7.32 18.45

Steering x 39.5 46 43.5 51.5 39 44 43.92 4.6 10.47

y 0 0 0 0 0 0 0 0 0

z 26.5 14.5 17.7 15.5 16 15 17.95 4.42 24.62

Hydraulic

lever

x 20.8 5 36.8 45.5 22 36 27.68 14.59 52.7

y 33 34.5 32 28 27 33 31.25 3.03 9.7

z 8.5 8.5 -12.6 -20.5 -16.5 -26 -9.77 14.83 151.79

The forward horizontal distance (X) of steering wheel from SRP was found to be between 33

to 58 cm. The coefficient of variation was found to be 10.47%. The lateral distance (Y) of

steering wheel was 0 cm in all case. The vertical distance (Z) of steering wheel was between 10.5

to 29 cm. The coefficient of variation was found to be 24.62%.

The forward horizontal distance (X) of hydraulic lever from SRP was found to be between 0

to 52 cm. The coefficient of variation was found to be 52.7%. The lateral distance (Y) of

hydraulic lever was between 27 to 34.5 cm. The coefficient of variation was found to be 9.7%.

The vertical distance (Z) of hydraulic lever was between -26 to 11 cm. The coefficient of

variation was found to be 151.79%.

53

The variation in the case of forward horizontal distance (X) and vertical distance (Z) of the

gear shift lever and hydraulic lever was found to be very large due to the large difference of these

coordinates in the various models.

5.2 Study of the existing location of different controls and levers in the tractor developed by

IIT, Kharagpur.

In the present study the data were collected on the tractor developed by IIT, Kharagpur

with regard to the five same control locations as was done in 5.1. The picture of the IIT tractor

workplace is shown in Fig. 5.7. Cartesian co ordinate system is used to define the control

locations in the work place (Origin at the SRP, X-axis – fore-aft, positive to the front of the SRP,

Y-axis – lateral, positive to the right of SRP, Z- axis – vertical, positive upward from the SRP).

The tractor workplace design parameters were measured for clutch pedal, brake pedal, gear shift

lever, steering wheel and hydraulic lever. The data collected as described above for the tractor

were analyzed to obtain the minimum value, maximum value, mean and finally the deviation of

the mean value from the mean value obtained from the study of other tractor models. All the

measured dimensions and respective values are presented in table 5.2.

The forward horizontal distance (X) of brake and clutch pedal from SRP was found to be

between 59.5 to 80.5 cm. and 44.5 to 65.5 cm. respectively. The deviations of the mean position

from the mean obtained from different models were found to be 3.02 cm. and 13.33 cm.

respectively. The lateral distances (Y) of brake and clutch pedal from SRP were found to be 19

cm. and 24.5 cm. respectively. The deviations of the mean position from the mean obtained from

different models were found to be 6.67cm and 0.47cm. respectively. The vertical distances (Z) of

brake and clutch pedal were between 39.7 to 42.7 cm and 47.7 to 50.7cm. respectively.

Controls CoordinateMin

value(cm.) Max. value (cm.)Mean

(cm.)Mean from the existing

models (cm.)Deviation (cm.)

Gear shift lever

x 34.5 55.5 45 51.25 6.25

y 0 0 0 11.98 11.98

z -22.5 -25.5 -24 1.58 25.58

Clutch Pedal

x 44.5 65.5 55 68.33 13.33

y -24.5 -24.5 -24.5 -24.97 0.47

z -47.7 -50.7 -49.2 -38.47 10.73

Brake Pedal

x 59.5 80.5 70 73.02 3.02

y 19 19 19 25.67 6.67

54

z -39.7 -42.7 -41.2 -39.67 1.53

Steering

x 30.5 51.5 41 43.92 2.92

y 0 0 0 0 0

z 7.5 10.5 9 17.95 8.95

Hydraulic Lever

x 29.5 50.5 40 27.68 12.32

y 33.5 33.5 33.5 31.25 2.25

z -16.5 -19.5 -18 -9.77 8.23

Table 5.2 Existing locations of the mini (13 hp) tractor developed by IIT, KGP

The deviations of the mean position from the mean obtained from different models were

found to be 1.53 cm. and 10.73 cm. respectively.

The forward horizontal distance (X) of gear shift lever from SRP was found to be between

34.5 to 55.5 cm. The deviation of the mean position from the mean obtained from different

models was found to be 6.25 cm. The lateral distance (Y) of gear shift lever from SRP was found

to be 0 cm. The deviation of the mean position from the mean obtained from different models

was found to be 11.98 cm. The vertical distance (Z) of gear shift lever was between 22.5 to 25.5

cm. The deviation of the mean position from the mean obtained from different models was found

to be 25.58 cm.

The forward horizontal distance (X) of steering wheel from SRP was found to be between

30.5 to 51.5 cm. The deviation of the mean position from the mean obtained from different

models was found to be 2.92 cm. The lateral distance (Y) of steering wheel from SRP was found

to be 0 cm. The deviation of the mean position from the mean obtained from different models

was found to be 0 cm. The vertical distance (Z) of steering wheel was between 7.5 to 10.5 cm.

The deviation of the mean position from the mean obtained from different models was found to

be 8.95 cm.

The forward horizontal distance (X) of hydraulic lever from SRP was found to be between

29.5 to 50.5 cm. The deviation of the mean position from the mean obtained from different

models was found to be 12.32 cm. The lateral distance (Y) of hydraulic lever from SRP was

found to be 33.5 cm. The deviation of the mean position from the mean obtained from different

models was found to be 2.25 cm. The vertical distance (Z) of hydraulic lever was between 16.5

to 19.5 cm. The deviation of the mean position from the mean obtained from different models

was found to be 8.23 cm.

The deviations were mainly found to be due to two reasons. Firstly, the height of the seat in

the tractor developed by IIT, Kharagpur was 125 cm. from the ground and in the other models it

55

was 100 to 105 cm. Secondly, the seat of the tractor developed by IIT, Kharagpur was 36 cm.

behind the rear axle whereas in the other models the seat was 0 to 5 cm. behind the rear axle.

5.3 Design of the ROPS:

The final specifications of ROPS were as follows:

Table 5.3 Specification of the designed ROPS

Total height 208 cm

Total width of the cross-bar 70 cm.

Sideward extension 0 cm

Rearward extension 50 cm

Material taken Mild Steel

Cross-section 75*37.5 mm channel section of thickness 6

mm, the open side of which was covered by

welding a 3mm thick mild steel sheet.

Weight of ROPS 40 kg

Maximum Deflection due to vertical loading 0.1 cm.

Maximum Deflection due to rear or front

loading

7.825 cm.

Maximum Deflection due to side loading 23.915 cm

Calculated maximum ultimate stress (σ) 1046. 53 N/mm2

These dimensions of the designed ROPS were compared with the dimensions of ROPS

computed by the software developed by Kumar (2001) and the comparisons were given in the

Table 5.4.

Table 5.4 Comparison of the dimensions of ROPS designed for IIT tractor with the

dimensions of the ROPS for Escort 355

Dimensions Escort 355 IIT Tractor

56

Total height 167 cm 208 cm

Total width of the cross-bar 89 cm 70 cm

Rearward extension 6.9 cm 50 cm

Sideward extension 0 cm 0 cm

Maximum deflection 23.915 cm 37.1 cm

It was seen from the comparison that the overall height of the ROPS of the IIT Tractor is 41 cm

more than that of escort 355. this was due to the fact that the height of the seat in the tractor

developed by IIT, Kharagpur was 125 cm. from the ground and in the Escort 355 it was 100 cm.

The width was 19 cm less for IIT Tractor as the wheel tread of the IIT Tractor was 113 cm

whereas in the Escort 355 it was 130 cm. The rearward extension was 43.1 cm more in the case

of IIT Tractor than that of in the case of Escort 355 because the seat of the tractor developed by

IIT, Kharagpur was 36 cm. behind the rear axle whereas in the Escort 355 the seat was 0 cm.

behind the rear axle. The maximum deflection of the ROPS was found to be less for the IIT

Tractor because of its less weight that is the energy to be absorbed was less than that in the case

of Escort 355.

The energy that should be absorbed by the designed ROPS and the maximum deflection for

impact loading and crushing were calculated for each type of loading and that is presented in

Table 5.5.

57

(a)

(b)

(c)

Fig.5.3 The mini tractor attached with the designed ROPS during the field testing

Table 5.5 The Energy to be absorbed by the designed ROPS and the corresponding

maximum deflection (in mm.)

58

Type of loading Energy to be absorbed Max. Deflection (in cm.)

Static Loading

Rear or front loading 1086.4 J-

Side Loading 1358 .0J-

Impact Loading

Rear loading 0740.88 J7.825

Front loading 1554.67 J7.825

Side loading 3531.92 J23.915

Crushing

Loading at front and rear edge 1552 kg.0.1

The deflection in each case is low as to prevent the clearance zone in case of rearward or

sideward overturning. A safety belt was also provided for the operator as belt is essential to be

provided with ROPS for keeping operator within the clearance zone in case of an overturning.

5.4 Determination of Centre of Gravity

59

The position of centre of gravity of the tractor was determined by the method which has already

been discussed under section 4.5. The formulae discussed in the section 3.

The point of centre of gravity was found at 45.2 cm above ground level and 60.1 cm ahead of

rear axle center.

Table 5.6 Comparison of the present position of centre of gravity with the previous position

of Centre of Gravity and some other related parameters

Sl.No Parameter Previous value Present value

1. Total weight 776 kg 938 kg

2. Weight to power

ratio

81.17 kg/kW 86.68 kg/kW

3. Static weight distribution

Front 37.7% 40.01%

Rear 62.3% 59.99%

4. Wheel base 150 cm 150 cm

5. Wheel tread 113 cm 113 cm

6. C.G. Location

Above ground level 45.2 cm 45.2 cm

Ahead rear axle

centre

56.5 cm 60.1 cm

Distance from

median plane

1.3 cm 0.1 cm

The total weight of the tractor was increased by 162 kg because of being attached with

ROPS, bonnet, mudguard, PTO and battery etc. The weight to power ratio was increased due to

the increased weight as the power of the tractor remains same. The weight coming on the front

60

wheel was increased by 2.3% because of the bonnet and the other components. Consequently,

the position of the centre of gravity ahead of the rear axle centre was shifted towards the front

axle.

61

Fig.5.4 The IIT Tractor in which the ROPS was attached

CHAPTER VI

SUMMARY AND CONCLUSION

62

There is a difference in human beings, not only as to work output, but in anatomical dimensions.

It is self evidence that any seat and control arrangement can not fit all the operators. Therefore, it

is necessary to provide adjustments for both seat and controls to accommodate individuals of

differing size. It is a wise provision of nature that the dimensions of the limbs of a grown person

are always in relation to the size of that person. Even to this rule, as to all others, there are

frequent exceptions. To ensure good body positions with respect to main tractor controls, the 5 th

and 95th percentile man as representative of Indian tractor operator, were chosen for the design of

the work place.

The study of existing locations of the controls indicated a significant difference in

placement of these from SRP in the tractor operator workplace. Cartesian coordinate system was

used to define the control locations in the tractor operator workplace (Origin at the SRP, X-axis-

fore-aft, positive in the front of the SRP, Y-axis – lateral, positive to the right of SRP, Z-axis –

vertical, positive upward from the SRP). The forward horizontal distance (X) of brake and clutch

pedal from SRP was found to be between 59.5 to 80.5 cm. and 44.5 to 65.5 cm. respectively. The

lateral distances (Y) of brake and clutch pedal were between 21 to 30 cm. and 23.5 to 28 cm.

respectively. The vertical distances (Z) of brake and clutch pedal were between 25 to 47 cm. and

25 to 49 cm. respectively. The forward horizontal distance (X) of gear shift lever from SRP was

found to be between 45 to 61 cm. The lateral distance (Y) of gear shift lever was between 0 to

41.4 cm. The vertical distance (Z) of gear shift lever was between -11 to 27 cm. The forward

horizontal distance (X) of steering wheel from SRP was found to be between 33 to 58 cm. The

lateral distance (Y) of steering wheel was 0 cm in all case. The vertical distance (Z) of steering

wheel was between 10.5 to 29 cm. The forward horizontal distance (X) of hydraulic lever from

SRP was found to be between 0 to 52 cm. The lateral distance (Y) of hydraulic lever was

between 27 to 34.5 cm. The vertical distance (Z) of hydraulic lever was between -26 to 11 cm.

The study of the tractor developed by IIT, Kharagpur showed some deviations in the

locations of the control positions from the mean positions that was obtained in the existing

models. The forward horizontal distance (X) of brake and clutch pedal from SRP was found to

be between 59.5 to 80.5 cm. and 44.5 to 65.5 cm. respectively. The deviations of the mean

position from the mean obtained from different models were found to be 3.02 cm. and 13.33 cm.

respectively. The lateral distances (Y) of brake and clutch pedal from SRP were found to be 19

cm. and 24.5 cm. respectively. The deviations of the mean position from the mean obtained from

different models were found to be 6.67cm and 0.47cm. respectively. The vertical distances (Z) of

brake and clutch pedal were between 39.7 to 42.7 cm and 47.7 to 50.7cm. respectively. The

deviations of the mean position from the mean obtained from different models were found to be

63

1.53 cm. and 10.73 cm. respectively. The forward horizontal distance (X) of gear shift lever from

SRP was found to be between 34.5 to 55.5 cm. The deviation of the mean position from the

mean obtained from different models was found to be 6.25 cm. The lateral distance (Y) of gear

shift lever from SRP was found to be 0 cm. The deviation of the mean position from the mean

obtained from different models was found to be 11.98 cm. The vertical distance (Z) of gear shift

lever was between 22.5 to 25.5 cm. The deviation of the mean position from the mean obtained

from different models was found to be 25.58 cm. The forward horizontal distance (X) of steering

wheel from SRP was found to be between 30.5 to 51.5 cm. The deviation of the mean position

from the mean obtained from different models was found to be 2.92 cm. The lateral distance (Y)

of steering wheel from SRP was found to be 0 cm. The deviation of the mean position from the

mean obtained from different models was found to be 0 cm. The vertical distance (Z) of steering

wheel was between 7.5 to 10.5 cm. The deviation of the mean position from the mean obtained

from different models was found to be 8.95 cm. The forward horizontal distance (X) of hydraulic

lever from SRP was found to be between 29.5 to 50.5 cm. The deviation of the mean position

from the mean obtained from different models was found to be 12.32 cm. The lateral distance

(Y) of hydraulic lever from SRP was found to be 33.5 cm. The deviation of the mean position

from the mean obtained from different models was found to be 2.25 cm. The vertical distance (Z)

of hydraulic lever was between 16.5 to 19.5 cm. The deviation of the mean position from the

mean obtained from different models was found to be 8.23 cm.

The deviations were mainly found to be due to two reasons. Firstly, the height of the seat in

the tractor developed by IIT, Kharagpur was 125 cm. from the ground and in the other models it

was 100 to 105 cm. Secondly, the seat of the tractor developed by IIT, Kharagpur was 36 cm.

behind the rear axle whereas in the other models the seat was 0 to 5 cm. behind the rear axle.

The arrangement of work place was done with the help of the comparison of the mean positions

of the controls obtained from the commercial tractor models and that was obtained from the

tractor developed by IIT, Kharagpur. Studying both the cases, the locations of the control

positions for the tractor developed by IIT, Kharagpur was recommended. The recommendation

was also based upon the aspects that are to be taken care of while designing the tractor operator

work place (Previously discussed in Chapter III). The final arrangement was as follows:

Table 6.1(a) Recommended locations(X, Y, Z coordinates) of the control levers for IIT

tractor

CONTROL X- Axis co ordinate Y- Axis co ordinate Z- Axis co ordinate

64

LOCATIONS (Horizontal) in cm. (Lateral) in cm. (Vertical) in cm.

Gear Shift Lever 48 to 50 0 2 to 4

Clutch Pedal 68 to 70 -23 to -25 -38 to -40

Brake Pedal 68 to 70 23 to 25 -38 to -40

Steering wheel 40 to 42 0 8 to 10

Hydraulic lever 28 to 30 30 to 32 -8 to -10

Table 6.1(b) Recommended Adjustments of the control levers and the seat for IIT tractor

Steering Angle 60 to 70 degree

Brake Pedal Angle 60 to 70 degree

Clutch Pedal Angle 50 to 60 degree

Horizontal Seat Adjustment 20 cm.

Vertical Seat Adjustment 5 cm.

The diameter of the steering wheel was almost same for every tractor and was recommended to

be 44 cm.

As far safety of the operator is concerned, ROPS (Roll over protective Structure) is one of the

most important device that is to be used in tractor. Up to 1985 nearly 20% of all work place

related fatalities in U.S.A. were tractor related. Of them, 47% was elated to tractor overturns

(National Safety Council, 1991). Many of these fatalities can be prevented if the tractors had

been equipped with ROPS and the operator were wearing the seat belts (NIOSH, 1993). The first

ROPS were made available for tractors in the 1960s, and since then included in the entire design

of many tractors.

In many cases, the ROPS are certified based on either American Society of Agricultural

Engineers (ASAE) or Society of Automotive engineers (SAE) standard tests related to ROPS.

The purpose of these standards is to define the test procedure and performance criteria for ROPS

to minimize frequency and severity of operator injury during wheeled tractor overturn. These

tests can either be a static (slow ROPS deformation) test or a dynamic (swinging pendulum) test.

Recently, the static test appears to be the most popular and primary test considered for this

research study.

65

The ROPS for the tractor developed by IIT, Kharagpur was designed with the help of a three

axes coordinate analysis (previously discussed in the Chapter III) and then the energy that should

be absorbed by the structure was calculated as per the standards. The final dimensions of the

designed ROPS were as follows:

Total height – 208 cm.

Total width – 70 cm.

Sideward extension- 0 cm

Rearward extension- 50 cm

The conclusions derived out of the investigation are as summarized below:

1. the height of the seat in the tractor developed by IIT, Kharagpur was 125 cm. from the

ground and in the other models it was 100 to 105 cm. That is why height of the ROPS of the

IIT Tractor is 35-40 cm more than that are found in the other models (Using the software

developed by Kumar 2001)

2. The seat of the tractor developed by IIT, Kharagpur was 36 cm. behind the rear axle whereas

in the other models the seat was 0 to 5 cm. behind the rear axle. That led to a rearward

extension of 50 cm whereas in general, it was found to be 7-7.5 cm.

3. The maximum deflection of the ROPS was found to be less for the IIT Tractor because of its

less weight that is the energy to be absorbed was less than that in the case of other models.

The Centre of Gravity of the tractor along with ROPS was determined. The point of centre of

gravity was found at 45.2 cm above ground level and 60.1 cm ahead of rear axle center. This

point was 0.1 cm away from the median plane towards left side that is more or less, on median

plane. The static weight distribution was found to be 40% on the front axle and 60% on the rear

axle, from which it can be concluded that with the ROPS the tractor is also stable.

REFERENCES

1. Arude, V.G., 1995. Optimization of Some Parameters of Tractor Operator Workplace Design.

Unpublished M.Tech. Thesis. Agril Engg. Dept., I.I.T., Kharagpur.

66

2. ASAE Standard, 2004. Roll-Over Protective Structures (ROPS) for Wheeled Agricultural

Tractors. ASAE S383.1 FEB04.

3. Ayers, P.D., M. Dickson, S. Warner. 1994. Model to Evaluate Exposure Criteria During Roll

over Protective Structures Testing. Transactions of the ASAE 37(6): 1763-1768.

4. Bonney, M.C., Williams, R. W., 1977. A Computer Program to Layout Controls and Panels.

Ergonomics, pp. 297-320.

5. Chishlom, C.J., 1979. The Effect of Parameter Variation on Tractor Overturning and Impact

Behaviour. J.Agric. Engg./Res/24, 417-440.

6. Griffin, M.J., 1995. The Ergonomics of Vehicle Comfort. Paper No. 95A1026. In. Proceeding

of the 3rd International Conference on Vehicle Comfort and Ergonomics. Pp. 213-221.

7. Gupta, C.P., A. Abbas, M.S. Bhutta. 1995. Thermal Comfort Inside a Tractor Cab by

Evaporative Cooling System, Transactions of the ASAE 38(6): 1667-1775.

8. Hertzberg, H. T. E., 1972. The Human Buttocks in Sitting: Pressures, Patterns and Palliatives.

SAE Technical Paper No. 720005.

9. Kiran Kumar, D. 2001. Unpublished. B.Tech thesis on Computer Aided Design of ROPS for

Wheeled Agricultural Tractors. IIT Kharagpur.

10. Lamoria, L.H., Coby Lorenzen, R. R. Parks. 1964. Design Criteria for a Driver-safe Tractor

Frame, Transactions of the ASAE : 418-419.

11. Matthews, J., 1964. Ride Comfort for Tractor Operators. I. Review of Existing Information.

J. of Agril. Engg. Res. 9(1):3-30.

12. Pham, D. T., Onder, H.H., 1992. Knowledge Based System for Optimizing Workplace

Layout Using a Generic Algorithm. Ergonomics 35(12) : 1479-1487.

13. Pheasant, S.T. and Haris, C.M., 1982, Human Strength in the Operation of Tractor Pedal.

Ergonomics, 25(1), 53-63.

14. Prasad, N., 1995. Some Investigations on Tractor Seat Design with regard to Indian

Operators. Unpublished Ph.D. thesis, Department of Agricultural and Food Engineering, I.I.T.,

Kharagpur, India.

15. Roebuck, J. A., Jr. Kroemer, K. H. E. and Thomson, W. G., 1975. Engineering

Anthropometry Methods, A Wiley-Inter Science Publication, John Willey and sons, 459p.

16. SAE Standards, 1992. Operator Space Envelope Dimensions for Off-road Machines.

SAE J154 JUN92. 40.462-40.464.

17.Sen, R. N., Nag, P.K. and Ray, G. G., 1977. Some Anthropometry of the People of the

Eastern India. J.Indian Anthrol. Soc., 12: 201-208.

67

18. Sengupta, A. K. and Sen, R. N., 1964. Body Measurements of Male Workers in Textile Mills

in Bombay. Report of Central Labour Institute, Bombay, India.

19. Shackel, B., Chidsey, K. D. and Shipley, P., 1969. The Assesment of Chair Comfort.

Ergonomics 12, 269-306.

20. Shen, W., Vertiz, A. M., 1997. Redifinig Seat Comfort. SAE Technical Paper No. 970597. In

SAE Transactions. pp- 1066-1073.

21. Singhal, Ankur. 1999. Unpublished. M.Tech Thesis on Design of ROPS for Wheeled

Agricultural Tractors. IIT Kharagpur.

22. Srivastava, A. K., G. E. Rekhular, B.J. Masemore. 1978. Similitude Modeling Applied to

ROPS Testing. Transactions of the ASAE : 663-645.

23. Tewari, V. K., 1985. Development Of Weeder from Engineering and Ergonomic

Considerations. Unpublished Ph.D. Thesis. Agril. Engg. Dept., IIT., Kharagpur.

24. Tewari, V.K., Yadav, R., 1985. 1998. Tractor Operator Workplace Design – a Review. J. of

Terramechanics 35: 41-53.

25. Yadav, R., 1995. Some Ergonomic Investigations on Tractor Operator Workplace Design.

Unpublished Ph.D. Thesis, Department of Agril. And Food Engineering, I.I.T., Kharagpur, India.

26. Yadav, R., Tewari, V.K., Prasad, N., 1997. Cab for Indian Tractors: A case Study. AMA.

28(2): 27-29.

27. Yeh, R. E., Y. Huang, E.L. Johnson. 1976. An Analytical procedure for the supports of

ROPS Design. SAE, Off Highway Vehicle Meeting, Milwaukee, Wisconsin, September. 13-16.

28. Zander, J., 1969. Ergonomics in Machine Design. Wageninge, H., Veeman and Zones, New

York, 161 p.

29. Zander, J., 1969. Ergonomics in Machine Design. Wageninge, H., Veeman and Zones, New

York, 161 p.

APPENDIX A

a) Calculation for rearward overturn

68

The X and Z axis co-ordinates are required for sideward overturn.

Name of the different points are given according to Fig.3.18.

B is (0, 70.8)

D is (55, 80.6226)

E is (200, 10)

R, (Xg, Zg) is (36,-85.5)

Rear wheel diameter is 39.5 cm.

From equations ((1), (2), (3) and (4) described in section 3.2.4), value of A obtained is

(-3.448,-84.674)

Equation of line AB is

X – 0.0209Z + 1.762 = 0

Equation of line DE is

X + 2.053Z – 220.55 = 0

Solving these two equations, the co-ordinates of critical point obtained is

C (-0.472, 107.18)

Rearward extension er required is 50 cm

Height of ROPS H is

H = [(Xc – Xg –er) 2 + (Zc – Zg) 2]1/2

The value of H is 207.3 cm. which was rounded up to 208 cm.

The top X and Z co-ordinate of ROPS that is used to determine the Y co-ordinate is

X=Xg – er =-4 and

Z = H + Zg = 122.5 cm.

b) Calculation for sideward overturn

A is (12, 25, 90)

B is (36, 70,-46)

69

C is (200, 15, 10)

D is (180,-57,-60)

E is (-4, Y5, 121.8) It is point that will touch the ground plane

From the equations of sidewise overturn the value of y was calculated.

For equation of ABC plane the value of Y5 obtained is -8.34 cm.

For equation of ABD plane the value of Y obtained is -9.22 cm.

As in both the cases the value of Y5 is < Y1, no side extension is required.

The width of cross-bar is

W = SM + 2*es

Where SM is the maximum distance between two points on the rear axle on which ROPS can be

fitted.

es is the side extension required.

SM is taken 70 cm.

W= 70 cm.

APPENDIX B

Calculation for the cross-section:

a) Calculation for the maximum energy to be absorbed

70

1. Static loading:

For rear or front loading,

Esr = 1.4*Mt = 1.4*776 = 1086.4 J

For side loading,

Ess = 1.75*Mt = 1.75*776 = 1358 J

2. Impact loading:

For rear loading,

H = 2.165*10-8*776*15002 = 37.8 mm

Ei = 19.6*37.8 = 740.88 J

For front loading,

H = 25 + 0.07*Mt = 25 + 0.07*776 = 79.32 mm

Ei = 19.6*79.32 = 1554.672 J

For side loading,

H = 25 + 0.2*Mt

= 25 + 0.2*776

= 180.2 mm

Ei = 19.6*180.2 = 3531.92 J

For crushing at front and rear edge, the vertical force,

F = 20*Mt = 20*776 = 15520 N = 1552 kg

b) Calculation for the design value of stress:

I. For a cross-section of 25*25 mm hollow square section of thickness 2mm:

Using the formula described in 3.2.6 the value of σ was calculated for each loading.

1. Static loading:

For rear or front loading,

Esr = 1.4*Mt = 1.4*776 = 1086.4 J =U

σ = √ [(Esr*2*E)/V]

= √ [(1086.4*1000*2*20, 0000)/ [1225*(252 – 212)]]

= 1338.5 N/mm2

For side loading,

Ess = 1.75*Mt = 1.75*776 = 1358 J = U

σ = √ [(Ess*2*E)/V]

71

= √ [(1358*1000*2*20, 0000)/ [1225*(252 – 212)]]

= 1552.4 N/mm2

2. Impact loading:

For rear loading,

Ei = 19.6*37.8 = 740.88 J = U

σ = √ [(Ei*2*E)/V]

= √ [(740.9*1000*2*20, 0000)/ [1225*(252 – 212)]]

= 1146.7 N/mm2

For front loading,

E = 19.6*79.32 = 1554.672 J

σ = √ [(Ei*2*E)/V]

= √ [(1554.7*1000*2*20, 0000)/ [1225*(252 – 212)]]

= 1661.02 N/mm2

For side loading,

E = 19.6*180.2 = 3531.92 J = U

σ = √ [(Ei*2*E)/V]

= √ [(3531.92*1000*2*20, 0000)/ [1225*(252 – 212)]]

= 2503.6 N/mm2

For crushing at front and rear edge, the vertical force,

F = 20*Mt = 20*776 = 15520 N

σ = 15520/ (600*25) = 1.04 N/mm2

II. For a cross-section of 75*37.5 mm hollow channel section of thickness 6 mm (open side

covered by 3mm thick mild steel sheet):

Using the formula described in 3.2.6 the value of σ was calculated for each loading.

1. Static loading:

For rear or front loading,

Esr = 1.4*Mt = 1.4*776 = 1086.4 J =U

σ = √ [(Esr*2*E)/V]

72

= √ [(1086.4*1000*2*20, 0000)/ [1225*(75*40.5 – 63*31.5)]]

= 580.42 N/mm2

For side loading,

Ess = 1.75*Mt = 1.75*776 = 1358 J = U

σ = √ [(Ess*2*E)/V]

= √ [(1358*1000*2*20, 0000)/ [1225*(75*40.5 – 63*31.5)]]

= 648.93 N/mm2

2. Impact loading:

For rear loading,

Ei = 19.6*37.8 = 740.88 J = U

σ = √ [(Ei*2*E)/V]

= √ [(740.9*1000*2*20, 0000)/ [1225*(75*40.5 – 63*31.5)]]

= 479.32 N/mm2

For front loading,

E = 19.6*79.32 = 1554.672 J

σ = √ [(Ei*2*E)/V]

= √ [(1554.7*1000*2*20, 0000)/ [1225*(75*40.5 – 63*31.5)]]

= 694.34 N/mm2

For side loading,

E = 19.6*180.2 = 3531.92 J = U

σ = √ [(Ei*2*E)/V]

= √ [(3531.92*1000*2*20, 0000)/ [1225*(75*40.5 – 63*31.5)]]

= 1046.53 N/mm2

For crushing at front and rear edge, the vertical force,

F = 20*Mt = 20*776 = 15520 N

σ = 15520/ (700*75) = 0.30 N/mm2

APPENDIX C

1. For a cross-section of 25*25 mm hollow square section of thickness 2mm:

For dynamic loading or Impact loading:

73

For rear loading,

H = 2.165*10-8*776*15002 = 37.8 mm

Ei = 19.6*37.8 = 740.88 J

W = (740.88*1000)/37.8 N = 19600 N

I = (1/12)*(b1h13 – b2h23) = 16345.33 mm4

δ = (19600*12253)/ (3*20, 0000*16345.33) = 3673.83 mm= 367.383 cm

For front loading,

H = 25 + 0.07*Mt = 25 + 0.07*776 = 79.32 mm

Ei = 19.6*79.32 = 1554.672 J

W = (1554.672*1000)/79.32 N = 19600 N

I = (1/12)*(b1*h13 – b2*h23) = 16345.33 mm4

δ = (19600*12253)/ (3*20, 0000*16345.33) = 3673.83 mm= 367.383 cm

For side loading,

H = 25 + 0.2*Mt

= 25 + 0.2*776

= 180.2 mm

Ei = 19.6*180.2 = 3531.92 J

W = (3531.92*1000)/180.2 N = 19600 N

I = (1/12)*(b1*h13 – b2*h23) = 16345.33 mm4

δ = (19600*12253)/ (3*20, 0000*16345.33) = 3673.83 mm = 367.383 cm

For crushing at front and rear edge, the vertical force,

F = 20*Mt = 20*776 = 15520 N

I = (1/12)*(b1*h13 – b2*h23) = 16345.33 mm4

δ = (19600*6003)/ (48*20, 0000*16345.33) = 26.98 mm= 2.698 cm

2. For a cross-section of 75*37.5 mm hollow channel section of thickness6 mm (open side

covered by 3mm thick mild steel sheet):

For dynamic loading or Impact loading:

For rear loading,

H = 2.165*10-8*776*15002 = 37.8 mm

74

Ei = 19.6*37.8 = 740.88 J

W = (740.88*1000)/37.8 N = 19600 N

I = (1/12)*(b1*h13 – b2*h23) = 767454.75 mm4

δ = (19600*12253)/ (3*20, 0000*767454.75) = 78.25 mm= 7.825 cm.

For front loading,

H = 25 + 0.07*Mt = 25 + 0.07*776 = 79.32 mm

Ei = 19.6*79.32 = 1554.672 J

W = (1554.672*1000)/79.32 N = 19600 N

I = (1/12)*(b1*h13 – b2*h23) = 767454.75 mm4

δ = (19600*12253)/ (3*20, 0000*767454.75) = 78.25 mm=7.825 cm.

For side loading,

H = 25 + 0.2*Mt

= 25 + 0.2*776

= 180.2 mm

Ei = 19.6*180.2 = 3531.92 J

W = (3531.92*1000)/180.2 N = 19600 N

I = (1/12)*(b1*h13 – b2*h23) = 251094.93 mm4

δ = (19600*12253)/ (3*20, 0000*251094.93) = 239.15 mm = 23.915 cm

For crushing at front and rear edge, the vertical force,

F = 20*Mt = 20*776 = 15520 N

I = (1/12)*(b1*h13 – b2*h23) = 767454.75 mm4

δ = (19600*7003)/ (48*20, 0000*767454.75) = 0.912 mm= 0.0912 cm

75