ah 4 mal - virginia tech

INVESTIGATION INTO AND DESIGN OF AN AUTOMATIC RESTRAINT

SYSTEM FOR ROPS-EQUIPPED OFF-ROAD VEHICLES

by

Christopher David Wyckoff

Thesis submitted to the Faculty of the

Virginia Polytechnic Institute and State University

in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

in

Agricultural Engineering

APPROVED:

Ah 4 MAL Glen H. Hetz4l, Chairman

C James H. Wilson

Arvid Myklebust

August, 1994

Blacksburg, Virginia

C2

S695 V6S5 yAS4

W435

INVESTIGATION INTO AND DESIGN OF AN AUTOMATIC RESTRAINT

SYSTEM FOR ROPS-EQUIPPED OFF-ROAD VEHICLES

by

Christopher David Wyckoff

Glen H. Hetzel, Chairman

Agricultural Engineering

(ABSTRACT)

Agriculture consistently ranks as one of the most dangerous occupations based on

an overall work death rate. Tractor overturns, by far the single largest cause of death on

farms, account for approximately 19% of all on-farm deaths. The concept of a Roll-over

Protective Structure (ROPS) came into existence in 1971 and is designed to form a

protection zone for the operator. However, the only way that the operator will stay in the

zone is by using a seatbelt or other restraint system.

A survey on tractor seatbelt usage was undertaken. Results indicate that only

13% of operators wear seatbelts half or more of the time and 61% report never wearing

one. The reasons for these practices are a combination of factors: too much

inconvenience, time consuming, an old habit of not wearing one, and a feeling that there

is no danger. However, even in the face of such negativity, the survey revealed that 65%

of the operators were neutral or approved of the idea of an automatically closing seatbelt.

An automatically closing restraint system prototype was designed and built. The

system was found to be costly ($560.00) and the potential for mass retrofitting was found

to be very limited. However, an automatically closing seatbelt seems to be a viable

solution to the problem of operators being unwilling to use the seatbelts provided.

ACKNOWLEDGEMENTS

I would like to express my sincere appreciation to everyone that has helped me in

this venture. Part of this group includes my committee members, who have not only

been helpful in this project, but in the classrooms where things truly matter, for more

than just I, and much of importance was learned. Thanks to all of my fellow graduate

students, as they have been instrumental in my learning and enjoyment. Thanks

especially to Patrick, Yanling, Dongfang, and too many others to list. Special thanks

also to my major advisor, Dr. Glen Hetzel, for his guidance, friendship, honesty, and

kind nature. He must also be creditied with the idea for this project. And last, but not

least, I would like to express my deepest appreciation and love for Amber Jamil, and the

rest of my family, who have always been there for me with patience, love, and

understanding.

1V

TABLE OF CONTENTS

CHAPTER 1 INTRODUCTION 1

OBJECTIVES 0000... .scccecsseesesseececeeesacencseceesesessecesateneaeesessessaeeessaeeesaeeseaeeeseaeesesaeesesaeecsecseeseauececseceeensaaeeersnasers 10

CHAPTER2 REVIEW OF LITERATURE 14

CHAPTER 3 METHODS AND PROCEDURES 00.0... ..csssscssssessecrscsssssscssscsssesscsssccsesssscess «17

SURVEY 0... .ecccescceseccesnecesscessecssneceaeesacecseceaeeeaeecseeeseseceessseseeenaeecsecececeseecesessaeceeeeeessscsseecserecsneeeneeeeeres 17

RESTRAINT SYSTEM .0.......cccsecccesscceessseeeesneecesseaceseeeecseneececsaaeecsuaaeeseesaeeesseaeececeausseeesseeteeeecessaaeeeeeneeiaeeeess 22

POW SOULE... oc ccccccccccceesene cee e ete e teen e eect keke eee ELD EAAAGEE EES ECCEEEEEEELLGEEGEEEE CEC EEEe08 00008 es cg pdt Dd DEDEDE Ed EEteenee een peH 23

Design LOG .....eccccceccececsceceesseceesseesesseecesssneecssneessesseeesenneeceeaeeeeeenicasessaseeesessateesesesaaenecesessaaaeserenenanes 26

FLUmman FACtOIS ccc ccc cece cect e ccc eee eee kee EEE EEE E EEE GLEE EE EA EAA EEE E EEA EERE GOAL EE GHA ERE EEA E EE OG DEES ape EE aa DERE EH EEEES 28

Component Selection ........cccceccccscnccceceecessescceceeteeeeeeseesesaeeeeeeeeesee ens censanaaaaaeaaaeeaeesqaeeeaeeeeeeaaaaaaaaaaeqaaenes 30

CHAPTER 4 RESULTS AND DISCUSSION 31

SURVEY ....ccceccssccscessceseceecesesseesecsccneesnesasasecsasensesecaeenecaesaesaesaesaaeanevsceseeaeesaseaesaseaecacerscecseesaesssecsreeneeeneaes 31

RESTRAINT SYSTEM .........:cessesecsscesceesececesecsseeceesecesecscessesesesseesaesesceaeesecsaeceeeceneseaeesaeesseersaeessessaeesseesaeens 56

System Constraints .......ccccccccccccccccccceencseeeesessneeeessensaeeeeesusaaaeeeseeseaneeeeescesueeeeeseeeesnensesnaeeeeeeeserteseeeenaas 62

System AGjUSIMEN ........cccceccessnensencensnneneacesaeceeeeceeeeeaneceeeecseeeassceaceeneceensaaaasasaceeeseesececeeeeeaaeaseeereseseeaqane 63

Actuator SYSteMs ......cccccccceccccccccesseeeeeesenscesceseneeeeesssaneeessesesseeseeeneaaeeseesenensaaaeeseesseseececieaeeeeteteseeseaeennes 63

SOLEMN... 2... eee ceccccceeensceceessnceeecenaeseesaeeecenneesecesaeeeensaaeeecsenaeceeauieaeeescenaeaeesesaeeeeseceeesaaeeeeesesceataaeeeessaneenees 63

ACU atOr .o..eeeee ccc cc ccc cececnceeeeeecesnaceeeecesaseseeececeeseaaceeeessenenneaeeeeseeesenasaaecesecenecseeesnneeaaeeeeeeeseeeesereeeereceeereeeenaes 64

Selection Of COMPONENIS....0.....cccccccccecensccceesesneeceevevececeeesssaaeeeessessnneeeeseveseeaaneeeeeeseesenensnnaaeeneceseseeeentas 69

Design Of COMPONENES .......c.cccccccccessecesseecseneceeceanecceeaseecesueessseseecsecsaeeceeniseeecsnnaeeserseanececeeeesesiaeeeeeeseas 70

Mounting and Extension Plates ..0...........cccccccceeeecscccceceeceenneeseeceeeesenaeeeeeeeeeseeecseecaaaeseceeeeeeeeeeeeesseeeseceeeeseesenpenes 72

Mounting Batt......... cc cccccccccccccceccccneeeeeeecneseeeeceeeseeeeeeeeseeeeeesaeeeecseeeeeeeeeeeeeseeeseseesaeesaeeeeeeeeeeeeeeseceeeeseeeeseenentaaas 74

Restraint Bar... ........ccccccccccccceccccccccceccceccccecccacecececessnceececceasseucecceceareeseescuaeseessuaucevevseceseeeuesecersvecerieseersateteeesers 77

List of Materials And COSt.....ccccccccccccccsctscsecscc cece cece eee e cece eee e eee e eee eee e eee e ee eee AUD IDELE DEL e ted teeeeeeeaaaneneneeeseneees 79

REE OPIL eee cece seccceenecceeeceneecenceseseeeeseesseecsceecsacecsaeeeseecseaeessaeeeeseeeeseeessieecesiaeeseeaeecseateceseieeeeenaeeey 82

Safety CONSIACrALIONS .......ccccccccccccceececnceccennneceeneeecedeceeeseaaeecseseeeesseacecsesceeeeeseuseeeececueeesevsnieneeeenteaees 8&3

CHAPTERS SUMMARY, CONCLUSIONS, AND RECOMMENDATION G........ccccccosesscsccccescsces 84

SURVEY .0....ccccccccccccceeesescccscssseusseccceccecseceusesusucuevsssesecsscecauausuvsvsevecsessscuuavseesccecueuuesssscsssuuvecccesueuseseseranasess 84

CONCIUSIONS 0. ccc cccccccccccccceeccusccnceccucccacccnseccuseccucecuscccusecsuscenscecueceauceneccucenaceeueceresarecuveeuscastescerscaresaress 84

RESTRAINT SYSTEM .o..ccccccccccccecceeceseeseeseesesteesessessccsesssessessetesssssessevecsessssevesescecececeseseeuseeusesssesecessueeueanereres 85

RECOMMENAATIONS .0...0..ccccccccccecccccceeccccusesecneeccccuseeceusecscusececsuescccuscsececenaueccuescssseeeueeseuessauecenseseenceeseesans 85

LITERATURE CITED eecccccccscscceee 87

APPENDIX A: SURVEY DATA cove 90

VITA .........ccccccccccccccscccccccssccscccccnecccccscsccscsescosccccscaccnccccocccsccccscceccccecescccecesccsccccecescccscecscccsccccesccescccccesccess 100

vi

FIGURE 1.

FIGURE 2.

FIGURE 3.

FIGURE 4.

FIGURE 5.

FIGURE 6.

FIGURE 7.

FIGURE 8.

FIGURE 9.

FIGURE 10.

FIGURE 11.

FIGURE 12.

FIGURE 13.

FIGURE 14.

FIGURE 15.

FIGURE 16.

FIGURE 17.

FIGURE 18.

FIGURE 19.

FIGURE 20.

FIGURE 21.

FIGURE 22.

FIGURE 23.

LIST OF FIGURES

WORKER DEATH RATES BY INDUSTRY DIVISION ..........:.:0cccesssseseseeeesceeseccecsesaseeeeeseeceeeeeeessaaeeeenes 3

TRACTOR OVERTURN FATALITY RATES ON THE FARM.........0ccccccccccccccccccceccceceeesceesecesesenseceeeeseses 13

SEATBELT USAGE SURVEY .......ccccccccccsesssesesseseesesssecessseecesessecesesssecesenseeesesenssesecesessssseeeesensiees 18

NUMBER OF TRACTORS PER FARM ..........ccccccccesesssssesceceeeceseccesseseeesenceseesasaeeeseeseescsestsnsaeaseneeees 32

NUMBER OF ROPS EQUIPPED TRACTORS PER FARM ........c:ccscscssccceesseseeesesececeesesseeecesetensceeeeeeeas 34

FREQUENCY OF SEATBELT USAGE .0.0.0.....ccccccccsessscsececeecescsseseseessenssanaceeaaeececaceeesececacacaesceeeeenaees 35

FREQUENCY OF REASONS FOR NOT WEARING SEATBELTS........0.0cccccccccccscccecesceeeecececceeesesessecesees 37

AGE DISTRIBUTION OF RESPONDENTS. ........0...ccccccsesssceeesseeceseteceseesseeeeeessseseeseesseeecesentneeeesenias 38

SEATBELT USAGE BASED UPON AGE GROUP ..0........ccccccsceccessecscecececsesssseasececeseseecsesstststetssecsesees 39

ATTITUDES TOWARD AN AUTOMATIC SEATBELT BASED UPON AGE ..............cccccceeeseseeeeeeeeeeeees 4]

DISTRIBUTION OF YEARS OF EXPERIENCE. ............cccccssccececcecceesceseeescsesesesesesesecenseeeeseseseseeceeees 42

SEATBELT USAGE BASED UPON YEARS OF EXPERIENCE ............cccceccceeeeceeseseneseeeceeeeeceeeesseceeeess 43

ATTITUDES TOWARD AN AUTOMATIC SEATBELT BASED UPON YEARS OF EXPERIENCE ............ 44

LAND CHARACTERIZATION RESPONSES.........:0:cccscesesseseecesssneeeeeecscenseeceeeeeeecetensenaseeeeeeeeesenes 46

SEATBELT USAGE BASED UPON SLOPE OF LAND..........cccccccesessessseeeccesescecceceeeeeseseseseseeesesenseeees 47

ATTITUDES TOWARD AN AUTOMATIC SEATBELT BASED UPON SLOPE OF LAND..................00000 48

DISTRIBUTION OF SURVEYS ACROSS THE STATE .........:cccs:ssesseeseeeseesceecceeecenseseaeasceesesssaeuaaaenees 50

SEATBELT USAGE BASED UPON AWARENESS OF ROLLOVER STATISTICS ...........0..c0eccesceeneeeeneees 51

ATTITUDES TOWARD AN AUTOMATIC SEATBELT BASED UPON AWARENESS OF ROLLOVERS..... 52

DISTRIBUTION OF FEELINGS TOWARD AN AUTOMATIC SEATBELT ..........0.c.cccccccceeescceeseeeeeerecees 54

SOLID MODEL RENDERING OF SEAT AND RESTRAINT SYSTEM...........cccccccccccscsecccecceeeseeceeeeeeeess 57

FRONT, Top, SIDE, AND ISOMETRIC VIEWS OF SEAT AND RESTRAINT SYSTEM.............00000000000 58

FRONT VIEW OF PROTOTYPE ..........c0:0ccsccscsssseessssesseseseesssesseseeeeseececeeeeeesecaaueaseeseceserstsnanaereasess 59

Vii

FIGURE 24.

FIGURE 25.

FIGURE 26.

FIGURE 27.

FIGURE 28.

FIGURE 29.

FIGURE 30.

FIGURE 31.

PRIMARY FUNCTIONAL COMPONENTS OF RESTRAINT SYSTEM..........:::0ccccescecsesesssseeeeteeeeteeenens 61

SSD SYSTEM FORCE ANALYSIS .0........ccccccccccseescsseccecsseeeecescesssseeeeseseessssseeeeeseeesesesessseeeeeeeseas 65

ELECTRICAL SCHEMATIC OF TEST CIRCUIT ...........ccccccccecccceceesseseeeeececeeeececcseeeaecesesaaeseeesesaaegess 67

STRUCTURAL COMPONENTS OF RESTRAINT SYSTEM...........:cc0cssessescececcceceeeusssaeeeseseeetasenssuaseeees 7)

LOADING ON MOUNTING PLATES...........000ccccccccccesceseseeecseeteeteesseseeseceseaesesceseaueaescscauueecessanaraes 73

LOADING ON MOUNTING BAR ........cccccccccccccsssessssssceceeeeeeecesesecesssaaeaaeaaaaeaaaeaeaessaeaaaaaageaeenaaaaeeas 75

LOADING ON RESTRAINT BAR..........cccccceeccscessececeesesssteescseceesseeseseeeseaneneeeeesesesenenssstsaeteeeeeeecees 78

Vill

TABLE 1.

TABLE 2.

TABLE 3.

TABLE 4.

TABLE 5.

TABLE 6.

TABLE 7.

TABLE 8.

LIST OF TABLES

WORK ACCIDENTS IN U.S. BY INDUSTRY, 1991] oo... cccccc cece cccccesecceceeceseuescecaeseeesaeecsteesesaeeeenaa 2

NONTRANSPORT DEATHS FROM ACCIDENTS ON FARMS BY TYPE. * ...0......00.cccccsccceeeeeecaeeseeeeeseeeenees 4

DEATH FROM MACHINERY OTHER THAN TRANSPORT VEHICLES, 1980...0.........cccccccceeseseeeecseseeeeees 6

ROPS EFFECTIVENESS ........0ccccccccccesscccessesscsesceccesceceseateesesaessesaseeesseesaeeessceaeceeseeeaeteerseeeageeees 12

POWER SOURCE ALTERNATIVES .........ccccccccccececcesesessnsnseceecesesesessesesteneususseaassaeasaaeeasaesseneeeeeenenas 24

RESULTS OF CHI-SQUARE TESTS .........ccccccsceccesssceseesesnsseecceeseseessecsesesuscaseseeeceseeesnssuceeseseeeeseneans 55

LIST OF MATERIALS AND COST FOR ACTUATOR.........cccccccccseessesseeseceseseseeeeeececsestsnesscaesesescesenenas 80

LIST OF MATERIALS AND COST FOR SSD SYSTEM ....0.......cccccceccscceeeeteeeesestaseaasaneeeeeaeaaaanseeaaaeaaee 81

1X

CHAPTER 1

INTRODUCTION

Agriculture is consistently one of the most dangerous industries in which to work

in America based on a work death rate (NSC, 1992). In addition, approximately 100

disabling injuries, serious enough to keep the victim from normal activities for at least

half a day or requiring medical attention, occurs per death. It is quite remarkable that

agriculture employs only 2-3% of the industrial work force and yet ranks fourth in total

number of fatalities. Table 1 shows the latest fatality data and injury estimates for 1991

categorized by industry (NSC, 1992). Agriculture had the highest fatality rate with 44

deaths per 100,000 workers. A historical perspective of worker death rates by industrial

division can be seen in Figure 1. These statistics show agriculture to be consistently one

of the most dangerous occupations.

Table 2 shows the total number of deaths on farms by various categories. In

1988, machinery accounted for 49% of all deaths, and has historically accounted for the

largest percentage of deaths on farms. Based on a nationwide study of farm machinery

fatalities, approximately 75% of all machinery-related deaths involved tractors

(McKnight, 1984). Of these tractor-related deaths, approximately 50% were due to

rollover incidents (NSC, 1992; McKnight, 1984). Thus, approximately 19% of all on-

farm deaths, or one out of every five, are due to tractor overturns. Tractor overturns are

the greatest cause of on-farm fatalities, and virtually all of these could be eliminated with

the use of a Roll-Over Protective Structure (ROPS) and a seatbelt.

INTRODUCTION |

Table 1. Work Accidents in U.S. by Industry, 1991

Workers Death Disabling (000) Deaths Rates” Injuries

pAll Industries 116,400 7200 4700, 000 | Agriculture* 3,200 1,400 44° 140,000

Mining, quarrying" 700 300 43 30,000

Construction 5,900 1,800 31 180,000

Manufacturing 18,200 800 4 310,000

Transportation and 6,000 1,300 22 140,000

public utilities

Trade’ 26,800 1,000 4 320,000

Services’ 37,800 1,700 4 330,000

Government 17,800 1,600 9 250,000

“Agriculture includes forestry and fishing. Mining and quarrying includes oil and gas extraction. Trade

includes wholesale and retail trade. Services includes finance, insurance and real estate.

* Agriculture rate excludes deaths of persons under 14 years of age. Rates for other industry divisions do

not require this adjustment. Deaths of persons under 14 are included in the agriculture death total.

“Deaths per 100,000 workers in each group.

Source: National Safety Council, Accident Facts, 1992 Edition.

INTRODUCTION

Death Rates by Industry Division

LE a Agriculture

Mining 01

©

| Construction

&

=)

Trans. & Pub. Util.

Manufac.

Death

Rates*

NO

Ww ©

©

—

©

HEE Bsit es te

985 1986 1987 1988 1989 1990 1991

Year Source: National Safety Council, Accident Facts, 1992

*Per 100,000 worker

a0 eit eg

1982 1983 1984 1

atti

Figure 1. Worker Death Rates by Industry Division

INTRODUCTION

Table 2. Nontransport Deaths from Accidents on Farms by Type.*

Year All Drown- | Fire- Struck | Fires, | Elec. | Anl- | Poi- | Suffo- | Light- Types ing | arms | Falls by | Burns | Curr. | mals | son- | cation | ning

Object ing 1979 | 1276 142 74 56 112 15 64 40 23 «| 38 13

1980 |1309 199 77 67 127 37 67 44 30 |46 2

1981 1192 117 93 57 11] 41 64 44 11 37 8

1982 |1219 143 78 67 108 21 82 44 30) =| 27 13

1983 | 1,089 118 80 55 92 20 36 38 34 =|24 8

1984 |989 98 73 5] 101 19 34 31 28 = |32 12

1985 | 1,006 101 86 55 102 26 27 32 17 |29 6

1986 |974 109 56 52 79 17 36 46 21 40 8

1987 |945 94 43 56 88 23 40 44 12 |22 10

1988 / 831 78 46 58 76 17 26 28 8 23 12

*Excludes farm home deaths

Source: National Safety Council, Accident Facts, 1992 Edition.

INTRODUCTION

The hazards of farm machinery can be seen in a different perspective by looking

at deaths by machinery in general, other than by transport vehicles. The Injury Fact

Book tabulated the facts and figures in Table 3 and showed that agricultural machines

accounted for 55% of all machinery-related deaths (Baker, 1984). This fact is again

quite remarkable considering the comparatively small amounts of agricultural equipment

in use compared to a// other types of machinery. Examples of these other types of

machinery include power presses, saws, and elevators, which were once problems of

serious magnitude. Baker (1984) also points out a distressing trend in the farm

machinery death rate. From 1930-1980, the farm machinery death rate increased 44%,

while the death rate of all other machinery decreased by almost 80%. Many safety

professionals conclude that these statistics depict a failure of voluntary safety standards,

and call for federal safety legislation comparable to regulations already in existence for

virtually all other consumer products sold in the United States (Karlson, 1979; Baker,

1984).

The only federal farm safety regulation in existence, known as the “General Duty

Clause,” was enacted in 1976 by the Occupational Safety and Health Administration

(OSHA). It requires that farms having more than 10 employees provide their employees

with: 1) tractors with ROPS, 2) shields on PTOs, 3) guards on certain moving parts, and

4) employee operating instructions. However, the majority of farm workers are

employed on small farms or are family members and are therefore not covered under the

OSHA regulations (Baker, 1982; Karlson, 1979). For example, in Virginia it is

estimated that only approximately 25 farms are currently employing more than 10

INTRODUCTION 5

-Table 3. Death from Machinery Other than Transport Vehicles, 1980

Type of Machinery Number Percent

Agricultural machines 814 55

Cranes, forklifts, lifting machines 239 16

Earth moving machines 101 7

Mining and earth drilling machines 78

Metalworking and woodworking machines 33 2

Other or unspecified 206 14

Total 1,471 99°

‘Percents do not add to 100 due to rounding

Source: The Injury Fact Book, 1984.

INTRODUCTION

employees and thus must abide by the OSHA requirements (Hetzel, 1994; personal

communication).

A call for strict legislation is not unjustified. From 1961 through 1983, Sweden

implemented laws requiring an enclosed protective cab (four-post ROPS) on all tractors

and had a corresponding 92% reduction in rollover fatalities (MMWR, 1993).

A point needs to be made regarding the state of the current agricultural accident

data and data collection systems. Gerberich (1991) states that "Given the overall

discrepancies among the data systems and the reporting limitations for agriculture, these

[agricultural accident statistics] would appear to be extremely conservative estimates.”

Insight into the problems of agricultural accident data collection is best presented in the

preface to the National Institute for Occupational Safety and Health's publication entitled

"Epidemiology of Farm-Related Injuries: Bibliography with Abstracts” ( Nordstrom,

1992). An excerpt cited from the preface reads:

Several factors probably account for the paucity of sound research on the etiology of farm-

related injuries. Human injury is associated with accidents, a phenomenon to which science has

devoted little attention because of a widespread belief that these events are unpredictable and

unpreventable. In addition, rural dwellers have been the subject of many negative stereotypes,

suggesting that they may be unworthy of the attention of scholars. Historically the countryside

has been portrayed as a healthier environment than the city. In any case, support for injury

research has been minimal.

The various professional disciplines working on this topic are relatively isolated from each

other. Much of the agricultural engineering work is unknown to occupational safety and health

experts, and much epidemiologic research is not regularly available to engineers and safety

INTRODUCTION 7

specialists. Another obstacle is the fact that much farm safety research is not published in the

standard periodicals and professional literature. Although some research from each discipline is

published in peer-reviewed journals that are indexed in bibliographic databases, an unusually

large proportion of farm injury work is 'fugitive' literature, appearing only in conference

proceedings, government documents, unpublished theses and dissertations, or reports by state

health departments, agricultural extension services, or other organizations.

Traditionally, efforts to reduce the toll of farm-related injuries have relied on educational

approaches of safety specialists in each state's agricultural extension office and on engineering

approaches used by farm equipment manufacturers. Recently, however, public health and

occupational safety and health specialists have increased their interest in farm-related injuries.

The increase in interest in farm-related injuries is primarily due to a

"Congressional mandate to bring to agriculture the prevention and safety effort that has

been directed at other industries for decades" (Schwab, 1993). Evidence of this increased

interest is largely in the form of several million dollars available from the National

Institute for Occupational Safety and Health (NIOSH). It is through this, and funding

from the National Institute for Farm Safety (NIFS), that the research proposed herein was

possible. NIOSH is a research branch within the Centers for Disease Control and

Prevention (CDC), which is under the Department of Human Health and Services.

With the high probability of fatality or major injury resulting from rollovers well

known, the concept of a Roll-over Protective Structure (ROPS), or anti-roll bar, was

implemented in the United States in 1965 on a John Deere 4010 tractor (Schnieder,

1990). By 1971, virtually every major tractor manufacturer had a ROPS available as

INTRODUCTION 8

optional equipment on most of their new tractors. However, it was not until 1985 that

manufacturers refused to sell a new tractor without a ROPS. This decision was made

primarily as a result of the litigious environment in which we are currently living.

Kubota has recently begun to require a ROPS on all used tractors that are sold and

financed through them.

The entire concept of a ROPS, as defined by ASAE Standard $519 (1987), is to

protect a zone in which the operator is meant to stay. Therefore, a restraint system to

hold the operator in this zone is integral to the concept and functioning of the ROPS.

However, restraint systems has not been given much attention over the last 25 years.

Although there is little empirical evidence to document the amount of seatbelt usage by

farm equipment operators, it 1s the opinion of farm safety experts, and virtually everyone

connected with the industry, that operators seldom ever wear seatbelts.

The importance of a seatbelt can not be over-emphasized. There is evidence that

a ROPS is effective in preventing a large percentage of fatalities due to rollovers, but

some fatalities and many injuries still occur when the operator is propelled from the

tractor out of the zone of protection afforded by the ROPS (Schnieder, 1990; Schnieder,

1975; Woodward, 1980). A study, conducted by Woodward (1980), explored tractor

overturn accidents with and without ROPS. There were 102 accidents investigated in

which the tractor did have a ROPS, and 101 accidents in which the tractor did not have a

ROPS. Table 4 shows a summary of the findings. The fatality rate without a ROPS was

48.5%, compared to 14.7% with a ROPS. According to this research, the percentage

could have been reduced to 1% if the operators had worn seatbelts. The percentage of

INTRODUCTION 9

accidents that reported no injury rose from 13.9% without ROPS to 37.3% with ROPS,

although there was no indication what percentage of these operators had been wearing

seatbelts. The implications of this study are that even with a ROPS, death or injury will

occur 59% of the time in the event of an overturn at current seatbelt usage levels. If

everyone wore the seatbelts provided on ROPS-equipped tractors, this number would be

significantly reduced.

Figure 2 shows that fatalities due to tractor overturns have decreased since 1969,

as would be expected with the increased usage of ROPS, increases in tractor stability,

increases in educational efforts, and the improvement of medical care of accident

victims. However, since 1980 the fatality rates have stabilized. Probably the only way

in which to significantly reduce fatality and injury rates would be to increase the

percentage of ROPS equipped tractors, and substantially increase seatbelt usage.

Research into the suitability of retrofitting older tractors with ROPS is being done at

Colorado State University by Dr. Paul Ayers (1994) and at Virginia Tech by Dongfang

Wen (1994). However, the research reported herein is focused strictly on tractor seatbelt

usage. One possible way to substantially increase seatbelt usage may be through the use

of an automatic restraint system. Based on the above discussion, this study was

undertaken with the following objectives:

Objectives

1. Quantify seatbelt usage on ROPS equipped agricultural tractors.

2. Investigate reasons for lack of seatbelt usage.

INTRODUCTION 10

3. Investigate attitudes toward an automatically closing seatbelt.

4. Develop an automated restraint system for use on off-road equipment.

INTRODUCTION 1]

Table 4. ROPS Effectiveness

With ROPS (%) Without ROPS (%) (102 accidents) (101 accidents)

No injury 37.3 13.9

Minor injury 25.5 13.9

Major injury 18.6 21.8

Fatality 14.7 48.5

Unknown 3.9 1.9

Source: Woodward, 1980.

INTRODUCTION 12

Tractor Overturn Fatality Rates on the Farm

10

8r

* ” L

& co |

Oo 6}

2 s 47

wo LL

Lu 2+

—{| of oj |

1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991

1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990

Year *Deaths per 100,000 tractors Source: National Safety Council, Accident Facts, 1992

Figure 2. Tractor Overturn Fatality Rates on the Farm

INTRODUCTION 13

CHAPTER 2

REVIEW OF LITERATURE

The most pertinent study related to off-road vehicle restraint systems was a

research project sponsored by John Deere & Company and conducted at the University of

Michigan in 1991 (Dybro, 1991). The purpose of this study was to explore restraint

system alternatives dealing with the problem of operators not wearing seatbelts.

There were four design concepts considered:

1. Seatbelt Interlock

2. Automatic Seatbelt

3. Pull-down Bar

4. Active Armrests

The pull-down bar concept was eliminated due to anthropometric considerations.

Specifically, it was concluded that “it is not possible to design a pull-down bar that is

attached to the seat that can both go around the shoulders of the operator, when it is

applied, and have a smaller width than the distance between the armpits of the same

operator” (Dybro, 1991). In addition, the pull-down bar would probably interfere with

operators turning their shoulders when viewing behind them. The seatbelt interlock

concept was considered a mediocre solution because 1t would require the operator to

manually put on the seatbelt, which is inferior to an automatic concept. Thus, the

automatic seatbelt and active armrests concepts were left after the design requirements

were analyzed. Dybro (1991) went on to further pursue the active armrests concept.

REVIEW OF LITERATURE 14

This concept consists of an overturn detection unit that closes the armrests around the

operator in the event of an overturn or other accident.

Another significant study relating to tractor seatbelt usage was undertaken at Iowa

State University (Vogel, 1993). In this study, 25 state and/or university farm employees

were asked to wear seatbelts for one week. A questionnaire about the seatbelts was

completed before and after this test period. The results indicated that operators’

perceptions about seatbelts improved with usage. The seatbelts were not found to be as

restrictive or uncomfortable as operators initially thought they would be. The study did

reveal a slight agreement in the necessity of seatbelt usage; however, there were definite

negative responses when evaluating the comfort, convenience, restrictiveness, and

remembrance of usage of seatbelts. The restrictiveness of seatbelts received the most

negative response. This study also investigated the different types of seatbelts used, and

the applicability of knowledge gained from automobile seatbelts to tractor seatbelts.

In a recent statewide safety survey of Iowa farmers, it was found that only 8% of

operators reported wearing seatbelts "always" or "often" (Schwab et al., 1993). Also

recently, while investigating the differences among aged, middle aged, and young adult

tractor operators in Pennsylvania, Ambe and Murphy (1993) found no significant

difference in usage of seatbelts among the three age groups. However, the reported mean

corresponded to an average usage of less than "never," making this statistic difficult to

interpret.


In summary, the subject of seatbelt usage on tractors has not received much

attention. Three of the four studies mentioned were published within the last year, and

only two were directly related to tractor seatbelt usage.


CHAPTER 3

METHODS AND PROCEDURES

Survey

A survey was developed to address questions relating to tractor seatbelt usage.

Some of the questions addressed were: How many tractor operators are wearing the

seatbelts provided on ROPS equipped tractors? What are the main reasons for operators

not wearing the seatbelts? Are the operators aware that tractor rollovers pose a

significant safety hazard? How would tractor operators feel toward an automatically

closing seatbelt? Are there any differences in these responses based upon age or other

such classifications?

Figure 3 is a copy of the questionnaire used to determine the answers to these and

other questions. The first question asks how many tractors are located on the farm. This

data is obtained so the percentage of tractors with ROPS can be determined. It also

provides an indicator of the size of the farming operation.

The second question asks how many tractors are equipped with a ROPS or

protective cab. This data enables comparisons to be made between national and state

averages of ROPS equipped tractors.

The third question asks how many tractors are equipped with seatbelts. This

number should be identical to those equipped with ROPS because no manufacturer has

installed a seatbelt without a ROPS, or a ROPS without a seatbelt. If the number of

tractors with ROPS is different from the number of tractors with seatbelts, then either the

METHODS AND PROCEDURES 17

PWN

Oo OND

11.

12.

13.

14.

15.

Seatbelt Usage Survey How many tractors are on your farm?

How many of these tractors are equipped with a ROPS or cab?

How many of these tractors currently have a functioning seatbelt?

When driving tractors with seatbelts/ROPS, how frequently do you wear the seatbelt?

oO Never

Oo Occasionally

O About half of the time

a Most of the time

O Always

What would you say is the biggest reason you do not wear a seatbelt?

Do not feel much danger

Too much hassle (too hard to reach, latch, etc.)

Time consuming

Old habit of not wearing one (do not think about it)

Combination of the above factors

Other OoOogagadg

What is your age?

How many years of experience do you have operating a tractor?

How many hours do you operate a tractor each year?

How many hours are spent operating a tractor with a ROPS or cab (per year)?

How would you characterize the land you farm?

0 Flat

oO Gently rolling

Oo Moderately rolling

O Fairly steep

What is the largest revenue producing operation on your farm?

O Alfalfa 0 Fruit O Small Grains

O Beef O Hogs O Soybeans

O Cow-Calf Oo Horses O Tobacco

Oo Com O Peanuts 0 Vegetable crop

O Dairy O Poultry Oo Other

In what county is your farm located?

Are you aware that agriculture is the most dangerous occupation in the U.S.?

O Yes

0 No

Are you aware that tractors account for 75% of all farm machinery related deaths, and half of these are

due to the tractor rolling over?

O Yes

Oo No

How would you feel about an automatically closing seatbelt for your ROPS equipped tractors?

(Please check only one box that most represents how you feel)

Strongly Dislike

Dislike

Neutral

Approve

Strongly Approve

Onoagqgda

Figure 3. Seatbelt Usage Survey


seatbelt or the ROPS has been removed. This question was asked to determine whether

or not the destruction of seatbelts is a problem.

The fourth question asks how frequently operators wear the seatbelts provided on

ROPS equipped tractors. A scale with five levels of usage was used so that respondents

would be able to have a halfway point in time from which to judge their usage. This

method was used to help avoid confusion over terminology such as “occasionally” or

“sometimes” or “frequently” since it is not clear which of these terms means more than

half of the time. Also, it was judged that five levels of detail were sufficient, seven

levels would be excessive, and three levels would not be enough.

The fifth question asks the greatest reason for not wearing seatbelts. The

operators were given four choices, along with an “other” blank and a choice for

“combination of above factors.” The “other” blank was introduced in the event that

something of importance was missed when it came to not using seatbelts.

The sixth question asks the operators’ ages. This data was desired so that

comparisons between age groups could be made when analyzing the responses to the

other questions in the survey. The questions of particular interest for analyzing by

different groups were question four, relating to seatbelt usage, and question fifteen,

relating to attitudes toward an automatic seatbelt.

The seventh question asks how many years of experience the operator has

operating a tractor. As with question six, this question could be used to detect

differences among the respondents.


Question eight asks how many hours are spent operating a tractor each year and

question nine asks how many hours are spent operating a ROPS equipped tractor each

year. This data was obtained so that information about exposure could be analyzed.

‘Question ten asks the respondents to characterize the land that they farm. Four

levels of detail were decided to be sufficient since it is not necessary to have a middle

value when judging land slope. This data was obtained so that comparisons between

these groups could be made when analyzing the responses to questions four and fifteen.

Question eleven asks for the largest revenue producing operation on the farm.

This data was collected to determine whether there were any differences in responses

based upon the type of farming operation.

Question twelve asks for the county in which the farm is located. This data was

obtained to give some idea of how responses were distributed over the state.

Question thirteen asks whether or not the operators are aware that agriculture is

the most dangerous occupation. Question fourteen asks whether or not the operators are

aware of the statistics pertaining to tractor overturns. These questions were also asked to

see whether there were any differences in seatbelt usage, or attitudes toward an

automatically closing seatbelt, based on awareness level.

Question fifteen asks how the operators would feel toward an automatically

closing seatbelt. A five point scale was again used because it offers a neutral position

and two levels of positive or negative feelings.

The survey was intentionally kept short (one and one-half pages) so that operators

would be willing to complete and return the survey. Responses were solicited at the


Culpeper Cooperative’s customer appreciation day, extension safety and machinery

maintenance meetings throughout the state, and from one class of Agricultural

Technology students at Virginia Tech.

‘All of the data was entered into a database program, Paradox for Windows, so

that analyses could be expedited. The differences in responses to questions four and

fifteen, based upon the different categories, were determined through the use of a Chi-

Square Test of Independence on SAS. Also, 95% confidence intervals were established

for important percentages.


Restraint System

This section covers the methods and procedures used to design the automatic

restraint system. A list of conceptual requirements for the restraint system was first

determined. It was decided that the restraint system should:

e Close automatically when the operator sits in the seat

e Have a simple release mechanism

e Meet or exceed the force requirements for cloth seatbelts

e Fit the fifth to ninety-fifth percentile sized person

e Incorporate human factors considerations

e Use standard “off-the-shelf” components

e Have the potential for retrofitting

e Be practical in terms of cost and complexity

A seat was purchased from Grammer, USA to serve as a base for mounting the

automatic restraint system. According to Grammer (Hajec, 1994; personal

communication), with the addition of a few drilled holes, this seat would fit a wide range

of tractor makes and models. This seat was therefore chosen to fulfill the design

requirement of potential retrofitting.

The restraint system was developed using the three-dimensional solid modeler in

AutoCAD™ Release 12. After full development of the 3-D model, detailed dimensional

drawings were extracted and a prototype was built.


Power Source

System requirements suggest that the operator must simply sit in the seat in order

to activate the restraint system. Therefore, several alternatives were considered as a

power source to close the mechanism. Four were considered: mechanical, hydraulic,

pneumatic, and electrical. The advantages and disadvantages of each type are listed in

Table 5.

A mechanical design would use the displacement caused by the operator sitting in

the seat to close the restraint mechanism. This design would require an elaborate linkage

mechanism and is further complicated by the fact that agricultural tractor seats are

equipped with a spring and damper system that absorbs most of the energy of the

individual while sitting down. In addition, lighter weight individuals may only displace

the seat a fraction of an inch if the seat is not adjusted properly, which could lead to

malfunctioning of the design. The only advantage in a mechanical linkage would be cost

compared to other methods.

The hydraulic design would consist of an electrohydraulic circuit controlling a

hydraulic cylinder to close or open the restraint mechanism as required. The primary

disadvantage to this system is cost. An electrohydraulic circuit would be necessary for

the automatic aspects desired of the system and therefore the price of the system would

increase. The primary advantage of the hydraulic system would be the ease of access to

hydraulic power. Most tractors are equipped with accessory ports for the hydraulic

system making access very easy.


Table 5. Power Source Alternatives

Power Sources Advantages Disadvantages

e Inexpensive Shock absorber on seat

absorbs most of the Mechanical linkage operators energy

from seat Elaborate mechanism

required

Different seat displacements

e Power source readily Must incorporate electric Hydraulic available control to automate

Expensive

No power source available

Pneumatic Expensive

Must incorporate electric

control to automate

e Power source readily Expensive

available Weatherability Electric e Electric control for

automation needed

anyway


The pneumatic design would consist of an accumulator that would be charged

when the operator sat on and displaced the seat. A pneumatic cylinder would then be

used to close or open the restraint mechanism. This design has a combination of the

problems of the previous designs. Again, there are problems with trying to use the

energy provided by the operator sitting because the shock absorbing system is integral

with agricultural tractor seats. Also, an electropneumatic system would be required for

automation, and therefore the cost of the system would be high.

A design utilizing the electrical power of the tractor would consist of either an

electrical solenoid, or an electric linear actuator to close the restraint mechanism. The

main advantage to this system is that electrical power is readily available from the tractor

electrical system. Also, the electrical power is available at all times, not just when the

tractor is running, as is the case with the hydraulic system. Automation is made easy

through the use of electrical controls. The primary disadvantage for this method would

also be cost. Linear actuators are fairly expensive, and the use of a solenoid would

require the additional use of a damper and spring adding to the cost of the entire system.

Weather might also present some concern because the system would be required to work

reliably under all conditions.

Once these design alternatives were identified, and the advantages and

disadvantages were analyzed, the next step was to decide which system to use. The

solenoid, spring, damper combination was decided as the best alternative. The solenoid

would be used to close the mechanism, the spring would open the mechanism, and the

damper would control the speed that the mechanism opened and closed.


Design Load

The next step was to analyze loading on the mechanism. The primary concern

was with tractor overturns, which would result in essentially a vertical loading on the

system. However, the restraint system must also be able to withstand a horizontal load,

as would be experienced in a collision-type of accident. How much force the system

should be able to hold was the next question. According to SAE Recommended Practice

J386 (1985), “Operator Restraint Systems for Off-Road Work Machines,” there are

different requirements for construction machines, industrial machines, and agricultural

tractors.

For construction machines, “a load of 22,200 N shall be applied to the seat belt

assembly in the forward and upward direction. The initial angle of load application shall

be that angle, between 45 deg and 75 deg from the horizontal, which produces the most

severe loading condition.”

For industrial machines, “a load of 4,450 N shall be applied to the seat belt

assembly in the forward and upward direction. A simultaneous and parallel force equal

to four times the force of gravity on the mass of the seat system shall be applied to the

center of gravity of the seat system in the forward and upward direction. The initial

angle of the load applications shall be 45 + 10 deg from the horizontal.”

For agricultural tractors, the same test as for industrial machines must be applied,

and “a load of 2,250 N shall be applied to the seat belt assembly in the rearward and

upward direction. A simultaneous and parallel force equal to two times the force of


gravity on the mass of the seat system shall be applied to the center of gravity of the seat

system in the rearward and upward direction. The initial angle of the load applications

shall be 45 + 10 deg from the horizontal.”

‘The intention of this project was to make the restraint system applicable to all off-

road equipment; however, agricultural tractors were the primary machines of interest.

Therefore, the system was designed based upon our own criteria, and based loosely upon

SAE Recommended Practice J386.

An average of the force requirements recommended by SAE J386 was decided as

a starting point for the design load. The construction machine test requires 22,200 N

(5,000 Ib) @ 45°, and the agricultural machine test requires 4,450 N (1,000 Ib) @ 45°;

therefore, it was decided to design the system for 13,325 N (3,000 Ib) @ 45°. This

loading was also suggested for a restraint system by John Deere & Company (Dybro,

1991). If this force is resolved into its horizontal and vertical components, the loading

becomes 9,422 N (2,100 Ib) in the horizontal and vertical directions. Again, one would

expect either a vertical loading on the system as a result of an overturn, or a horizontal

loading on the system as a result of a collision. In order to verify this load, a force was

calculated for a 1,110 N (250 lb) person traveling 48 km/h (30 mph) and coming

suddenly to a stop as in the result of a collision. Assuming a constant deceleration for a

duration of 0.2 seconds the resulting force is 7,600 N (1,708 lb). Therefore, a design

force of 9,000 N (2,000 Ib) in the horizontal and vertical directions was chosen as a

design loading. Due to the nature of the accidents and the restraint system, it seemed


more appropriate to establish design loads in both the horizontal and vertical directions.

Accidents occur in these directions and the most severe loading on the restraint system

also occurs in these directions.

‘After the design load was selected, a decision to design the restraint system in the

linear range of material failure was made. This creates a conservative system design,

since permanent deformation could occur without failure. This decision simplified the

design and added to the margin of safety of the system.

Human Factors

There was an attempt to incorporate applicable human factors principles into the

design. One of these principles was designing the system for a certain range of operator

sizes. The “Anthropometric Source Book” was used to obtain the needed anthropometric

measurements (NASA, 1978). The tractor seat purchased from Grammer seemed to be

designed for the ninety-fifth percentile person based upon the maximum width of the

seat. Therefore, the restraint system was designed for the fifth to ninety-fifth percentile

person. Abdominal depth and thigh clearance were the two critical measurements used

in sizing the restraint system.

The minimum height of the restraint system was determined by adding the fifth

percentile female thigh clearance, assumed to be 102 mm (4 in.), to the height of the top

of the seat cushion, minus 13 mm (0.5 in.) for seat cushion deflection. Therefore, the

lowest point of the system was located at 89 mm (3.5 in.) above the undeflected seat

cushion height.


The maximum height of the restraint system was determined by adding the

ninety-fifth percentile male thigh clearance, assumed to be 191 mm (7.5 in.), plus 13 mm

(0.5 in.) for winter clothing, minus 13 mm (0.5 in.) for seat cushion deflection, to the top

of the undeflected seat cushion. Therefore, the highest point of the system was 191 mm

(7.5 in.) above the seat cushion.

Similarly, the smallest space needed for horizontal clearance from the backrest on

the restraint system was calculated from the fifth percentile female abdominal depth,

taken to be 191 mm (7.5 in.). Seat deflection in the rearward direction was assumed to

be negligible. The armrests on the seat extended 178 mm (7 in.) beyond the front of the

backrest, thus not creating an interference problem.

The largest horizontal space needed from the backrest of the restraint system was

calculated from the ninety-fifth percentile male abdominal depth, taken to be 318 mm

(12.5 in.), plus 13 mm (0.5 in.) for heavy clothing. Thus, the maximum depth from the

restraint system to the backrest of the seat was 330 mm (13 in.).

Other human factors considerations were included when considering the type of

release mechanism. A natural position for the release mechanism is on the armrests of

the seat because if the operator is trying to get out of the seat, the first place the

individual would normally grab is the armrest. In addition, this location is probably the

most reasonable place as the operator must retract their hand for the restraint mechanism

to open. Therefore, the position chosen for mounting the release mechanism was on the

armrests of the seat. The release mechanism must also be operable by a gloved operator,

and be shielded from accidental contact. All of these factors led to a decision to use a


30-mm recessed electrical pushbutton as the release mechanism. Additionally, the

pushbutton could be color-coded green to correspond with the “release” action of the

mechanism.

Other human factors considerations that might be included in a finished product

would be a light, LCD, or audio signal to indicate to the operator that the seatbelt must

be closed if the system were integrated with a starter interlock or other safety circuit. In

addition, the study of what kind, and how much padding to put onto a ngid restraint bar,

such that the operator is not injured by being propelled into the restraint bar, is something

that would need to be addressed.

Component Selection

The strength or force requirement of each component in the system was analyzed,

and the smallest available size that met the requirements was chosen. Often, many parts

were over-designed because stock parts were used. Some components were sized very

near their maximum capabilities. All purchased components came from local stores and

suppliers.


CHAPTER 4

RESULTS AND DISCUSSION

Survey

There were 119 responses to the survey. Frequently there were incomplete

answers to particular questions, which resulted in more responses on certain questions

than others. In fact, the last three questions were added to the survey after a few surveys

had already been collected. As a result, there are approximately 100 responses for the

last three questions. However, all results account for these differences by reporting and

analyzing everything in percentage form.

There were a total of 407 tractors in the survey. ROPS or protective cabs were

reported on 38.6% of the tractors. Functioning seatbelts were availabe on 40.5% of the

tractors. There should be no difference in the percentage of tractors with ROPS and the

percentage of tractors with seatbelts because seatbelts have only been installed on ROPS-

equipped tractors. However, there was frequently a discrepancy between the number of

ROPS and the number of seatbelts reported. Most of time, more seatbelts were reported

than ROPS, suggesting that the ROPS had been removed. However, there were several

who reported fewer seatbelts than ROPS, indicating they had removed the seatbelts.

Removal, or destruction of the seatbelt, was initially thought to be somewhat of a

problem, but this data suggest that removal of the ROPS is actually a more significant

problem. Figure 4 shows a distribution of the number of tractors per farm in the survey.

There was an average number of 3.54 tractors per farm. Figure 5 shows the distribution

RESULTS AND DISCUSSION 31

Tractors per Farm Total Number in Survey = 407

Number

of Farms

1 2 3 4 5 6 7 >=8

Number of Tractors

Figure 4. Number of Tractors Per Farm


of the number of ROPS-equipped tractors per farm. There was an average of 1.39

ROPS-equipped tractors per farm.

Question four asked how frequently operators wore their seatbelts when operating

ROPS-equipped tractors. Only 13.3% + 6.5% of operators indicated they wore them half

or more of the time (using a 95% confidence interval), while 61.0% indicated “never”

wearing one. The remaining 25.7% indicated they wore the seatbelt “occasionally.” The

distribution of responses is shown in Figure 6. This data certainly justifies the need to

address the problem of tractor operators not wearing seatbelts. In Virginia, the observed

seatbelt usage in automobiles is between 50% - 60% (NSC, 1992). These statistics are

difficult to compare directly, but certainly a feel for the comparable lack of seatbelt usage

on tractors 1s evident.

When asked what the main reason was for not wearing a seatbelt, it was expected

that the most common response would be a combination of factors, which was indeed the

case, with 43.4% of the responses in this category. In hindsight, it may have been more

appropriate to ask the operators to indicate all of the reasons that apply to them not

wearing a seatbelt, and then analyze the data from this point to see if more than one

answer was commonly given. This way a more appropriate weight could have been

given to each separate response, and the most commonly identified reasons could be

discerned. However, the wording of the question suggested that a single response was

desired. It is noteworthy that the second most popular response for not wearing seatbelts

was that it was simply an old habit of not wearing one, or the operator just did not think


Tractors With ROPS per Farm Total Number in Survey = 157

10

Number

of Farms

NO

©

0 1 2 3 4 5 6 >=7

Number of ROPS Equipped Tractors

Figure 5. Number of ROPS Equipped Tractors per Farm


Frequency of Seatbelt Usage

Never

Occasionally

Half of the time

Most of the time

Always pot , I

0 10 20 30 40 50 60 70 Percentage of Respondents (%)

Figure 6. Frequency of Seatbelt Usage


about it. This result suggests that motivational techniques could be used to increase

seatbelt usage for this group of people. Motivational techniques have been used to

increase automobile seatbelt usage successfully, and something similar could be done

with tractor seatbelt usage (Geller, 1984). The "other" responses given for not wearing a

seatbelt were typically just because they do not have one. However, several people said

that it restricts their movement to look behind them. In Vogel’s (1993) study,

restrictiveness did receive the most negative rating of all the variables evaluated

concerning tractor seatbelts, which suggests another important concern. From an

ergonomic standpoint, all agricultural tractor seats should be incorporated with a swivel

base in order to take some of the stress off the back and neck when viewing to the rear.

This feature would especially be needed if operators were forced into a restraint system

that limits the rotation of their torso. Some of the other reasons given for not wearing

seatbelts were "on and off frequently," "too filthy,” and "feel unsafe with belt on."

Figure 7 shows the distribution of responses to question 5.

The age distribution of the respondents in the survey is shown in Figure 8. There

are more respondents in the age group 15-24 years old than one might expect in a

random sample of farmers. This result occured because responses were solicited from

one large class of Agricultural Technology students at Virginia Tech. Otherwise, the

distribution follows a more typical age distribution pattern. The average age of operators

was 41.0 years. A Chi-Square Test of Independence (Ott, 1988) was used to determine

whether there were any statistically significant differences, based upon age group, in

seatbelt usage or feelings toward an automatic seatbelt. Figure 9 shows the differences in


Reasons for Not Wearing Seatbelts

Feel no danger

Too much hassle

Time consuming

Old habit

Combination of above

Other

0 10 20 30 40 50

Percentage of Respondents (%)

Figure 7. Frequency of Reasons for Not Wearing Seatbelts


Age Distribution in Survey

=

= NN OO

Oo oO

Oo on oO

ON

Percentage

of Respondents

(%)

15-24 25-34 35-44 45-54 55-64 >=65

Age Group (years)

Figure 8. Age Distribution of Respondents


38

seatbelt Usage Based Upon Age Group

Never 2

O c si 0 na | ly oe ae

Half of the time

WM 15-24

Be 25-34

Be 35-44 Ee 45-54

Ee 55-64

[|] >=65

Most of the time

Al wa

y S Rescind

sd ae

0 20 40 60 £80 100

Percentage of Each Group (%)

Figure 9. Seatbelt Usage Based Upon Age Group


seatbelt usage based upon age group. With a test statistic of x’ = 22.23, df = 20, and a =

0.328, there were no significant differences among the age groups in seatbelt usage.

There were also no significant differences among the age groups in feelings toward an

automatic seatbelt (y’ = 8.92, df = 15, a = 0.882). Figure 10 shows the differences in

attitudes toward an automatic seatbelt based upon age group.

The respondents’ years of experience operating a tractor is shown in Figure 11.

The average years of experience was 24.8 years. A Chi-Square Test of Independence

was also performed on seatbelt usage by years of experience. With x’ = 27.11, df= 20,

and a = 0.138, this data set was close to having significant differences among its groups.

As Figure 12 shows, the people with the least amount of experience had a tendency to

wear the seatbelts more frequently than those with more experience. All but one of the

respondents indicating they wore their seatbelts “always” were in the 1-10 years

experience group. However, an « = 0.138 means that there would be a 13.8% chance of

being wrong if one were to conclude that there are significant differences among the

groups. A Chi-Square Test was also performed on these groups to determine whether

there were any differences in attitudes toward an automatic seatbelt based upon years of

experience driving a tractor. With a x’ = 14.86, df= 12, and a = 0.249, no significant

differences among these groups were detected when it came to attitudes toward an

automatic seatbelt. Figure 13 shows the distribution of responses toward an automatic

seatbelt based upon years of experience operating a tractor.


Feelings Toward an Automatic Seatbelt

Based Upon Age Group

ee Mi 15-24 Strongly Dislike Ee) 25-34

e 35-44

Dislike HA 45-54

Fa 55-64

Neutral L] >=65

Ap p ro

ve Ba Jo

0 10 20 30 40 50 60


Figure 10. Attitudes Toward an Automatic Seatbelt Based Upon Age

RESULTS AND DISCUSSION 4]

Years of Experience Operating a Iractor

10

Perc

enta

ge

of Re

spon

dent

s (%

)

NO

©

©

1-10

11-20 21-30 31-40 41-50

Years of Experience

Figure 11. Distribution of Years of Experience


Seatbelt Usage Based Upon

Years of Experience

Never §

Occasionally §

Half of the time

Mi 1-10 es 11-20 i 21-30 HZ 31-40 E@ 41-50

Most of the time =

Always =

a td \ jt

0 20 40 60 £80 100

Percentage of Each Group(%)

Figure 12. Seatbelt Usage Based Upon Years of Experience



Based Upon Years of Experience

Mi 1-10

fa 11-20

E 21-30

Ea 31-40

EE] 41-50

Strongly Dislike

Dislike

Neutral &

Approve Ee : | |

0 10 20 30 40 50 60 70


Figure 13. Attitudes Toward an Automatic Seatbelt Based Upon Years of

Experience


Responses to questions 8 and 9 were found to be highly variable. It seems that

farmers generally do not keep good records of how their time is spent, so the data

obtained was probably not very accurate. The reason for obtaining this data was to

establish some risk exposure data. However, Hetzel and Zhao (1993) already found that

for tractors in Virginia, the total hours of tractor usage without ROPS (280,000 hours)

was 89% higher than the hours operated on ROPS-equipped tractors (148,000 hours).

The next question in the survey asked farmers to characterize the type of land that

they farm. Figure 14 shows the land characterization distribution. The average response

fell between gently and moderately rolling. A Chi-Square Test was also performed on

the basis of land characterization in response to questions 4 and 15. Figure 15 shows the

differences in seatbelt usage based upon land type. Figure 16 shows the differences in

attitudes toward an automatic seatbelt based upon the slope of land farmed. There were

no significant differences among the groups when it came to seatbelt usage (y° = 12.03,

df = 12, a= 0.443). However, looking at the graph, there did seem to be a tendency for

people who farmed flat land to be more strongly opposed to an automatic seatbelt

compared to the other groups. The distribution of responses from people that farmed flat

land seemed almost exponential, while all of the other groups seem to follow a more

normal distribution. Nevertheless, based upon a Chi-Square Test, there could not be any

conclusion of dependence with any kind of certainty (y’ = 10.59, df = 9, a = 0.305).

Question 11 asked for the largest revenue producing operation on the farm. The

question was worded for a single response. However, typically several responses were


Land Characterization

Flat

Gently rolling

Moderately rolling Fairly steep | 1 —t eel.

0 10 20 30 40 50 Percentage of Respondents (%)

Figure 14. Land Characterization Responses



Slope of Land Farmed

Never

Occasionally Half of the time

Most of the time Baas

Always ixumms er a ee | | pt

0 10 20 30 40 50 60 70


Figure 15. Seatbelt Usage Based Upon Slope of Land



Based Upon the Slope of Land Farmed

Strongly Dislike

Dislike

Neutral

Approve

QO 10


Gently Rolling

Moderately Rolling

Fairly zi Steep

joy

20 30 40 50 60

Figure 16. Attitudes Toward an Automatic Seatbelt Based Upon Slope of


Land

48

received. Because some of the respondents only completed one category, and some of

the respondents completed several categories, the data was not analysed based upon the

type of farming operation.

Question 12 documented the county in which the farm was located. Figure 17

shows the number of surveys collected from each county. The slight bias towards the

western part of the state probably accounts for the land characterization distribution

shown in Figure 14.

The thirteenth and fourteenth questions were intended to determine awareness

levels of the operators regarding farm safety. When asked whether they were aware of

agriculture being the most dangerous occupation in which to work, 86.3% of the

operators indicated they were (+ 6.9% using a 95% confidence interval). When asked

whether they were aware of the statistics pertaining to agricultural tractor rollovers,

58.5% of the operators indicated they were (+ 10.0% using a 95% confidence interval).

Considering only 13 respondees lacked awareness that agriculture is the most dangerous

occupation, there would not be enough data to perform an analysis on seatbelt

distribution or attitudes toward an automatic seatbelt. However, an analysis was

performed on the groups of individuals indicating awareness and lack of awareness of the

rollover statistics. Figure 18 shows the distribution of seatbelt usage based upon

awareness of rollover statistics and Figure 19 shows the distribution of feelings toward an

automatic seatbelt based upon awareness of rollover statistics. A Chi-Square Test was

performed on these groups and again there were no significant differences found in


Number of Responses per County

50 RESULTS AND DISCUSSION


Awareness of Rollovers

Never

Occasionally

Half of the time

Always i ___] | a |

0 10 20 30 40 50 60 70 Percentage of Each Group (%)

Figure 18. Seatbelt Usage Based Upon Awareness of Rollover Statistics



Based Upon Awareness of Rollovers

Strongly Dislike E

Dislike

Neutra

Approve

— a ___| po

0 10 20 30 40 50 60


Figure 19. Attitudes Toward an Automatic Seatbelt Based Upon Awareness

of Rollovers


seatbelt usage or attitudes toward an automatic seatbelt (y° = 2.70, df = 4, a = .597; x° =

1.81, df= 3, a = 0.613, respectively).

The last question of the survey asked how operators would feel about an

automatically closing seatbelt. A very encouraging 61.7% were either neutral or

approved of the idea (+ 9.8% using a 95% confidence interval). Only 18.1% strongly

disliked the idea. The distribution of responses is shown in Figure 20. It is difficult to

tell from this information how many would actually be willing to pay for the system if it

was offered as an option. It is also difficult to tell how many would try to disable the

system if it were installed as standard equipment. Considering Vogel’s (1993) study,

which indicated that seatbelts are not as restrictive or uncomfortable as operators thought

they would be, the approval rating might actually be higher than what this data suggests

if the system were used. Table 6 shows a tabulation of all of the Chi-Square tests and

results.

A note should be made regarding the population of the respondents. The sample

may be slightly biased because of the method in which the surveys were collected. All

surveys were completed by farmers voluntarily attending a safety lecture, with the

exception of one group of Agricultural Technology students, and one group of farmers at

a field day. The percentage of ROPS or cab equipped tractors in this survey was 39%,

which is higher than the 27.6% of tractors reporting ROPS in Virginia (Hetzel & Zhao,

1993), but closer to the 35% reported by NIOSH which covered eight states (MMWR,

1993). This data might suggest a bias in the population; however, these discrepancies



Strongly dislike

Dislike

Neutral

Approve

Strongly Approve _ J _ |

0 10 20 30 40 50 Percentage of Respondents (%)

Figure 20. Distribution of Feelings Toward an Automatic Seatbelt


Table 6. Results of Chi-Square Tests

Test x df a

Seatbelt Usage vs. Age 22.23 20 0.328

Seatbelt Usage vs. Years of Experience 26.887 20 0.138

Seatbelt Usage vs. Slope of Land 12.034 12 0.443

Seatbelt Usage vs. Awareness Level 2.7 4 0.597

Feelings Toward Automatic Seatbelt 8.919 15 0.882

vs. Age


vs. Years of Experience


vs. Slope of Land

Feelings Toward Automatic Seatbelt 1.808 3 613

vs. Awareness Level


could also be a function of sample size. All of the raw data collected from this survey

are tabulated in Appendix A.

Restraint System

This section discusses various aspects of the restraint system. Major subtopics are

given a separate heading.

Figure 21 shows a shaded rendering of the three-dimensional solid model

developed in AutoCAD, and Figure 22 shows the top, side, front, and isometric views of

the model. Figures 23 and 24 show digital images of the constructed prototype. The

primary components of the restraint system, which are labeled in Figure 25, are a

restraint bar which closes across the lap of the operator, a locking mechanism which

locks the restraint bar when it closes, an actuator which closes the restraint bar, and a

solenoid that releases the locking mechanism. These actions, supported with an electrical

network of switches and relays, cause the unit to function.

The unit functions as follows: First the operator must adjust the device to fit

his/her size. Adjustment is accomplished by removing a pin on each side of the

mechanism and sliding the unit in or out, and then adjusting the load spring on the seat

according to the operator’s weight. The operator then sits in the seat. The restraint bar

immediately starts closing until it is locked in the horizontal position. It stays locked

until the operator depresses a pushbutton mounted on either of the armrests. The bar

then raises back to its original vertical position. After a specified amount of time, the bar

will close again if the operator has not exited the seat.


Figure 21. Solid Model Rendering of Seat and Restraint System


Figure 22. Front, Top, Side, and Isometric Views of Seat and Restraint System


Figure 23. Front View of Prototype


e de View of Proto igure 24. Si F

60 RESULTS AND DISCUSSION

Restraint Bar “7

Release Solenoid Actuator” —

Figure 25. Primary Functional Components of Restraint System


System Constraints

This section covers some of the physical constraints of the system. The design

uses a rigid bar which closes automatically when the operator sits in the seat. The rigid

bar moves from an open vertical position to a closed horizontal position. The rigid bar

must originate on the right side of the tractor, as the operator is sitting in the seat, since

most individuals mount a tractor like mounting a horse, from the left. Thus, the vertical

bar does not interfere with the posterior of the operator when attempting to sit in the seat.

There 1s a need, however, for a locking mechanism on the left side of the seat.

This mechanism serves to lock the rigid bar into place and helps distribute any load on

the system. The height of this mechanism does not rise appreciably above the armrests

so there is minimal interference with the posterior of the operator when mounting the

tractor.

The rigid bar must also close and raise in a vertical manner, because of possible

interference with the steering wheel. Also, the hydraulic and three-point hitch controls

are typically mounted on the right side of the seat which leads to possible interference

problems with the actuating unit or adjustment mechanism of the restraint system. In

addition, the fenders can present interference problems if spaced closely to the seat.

The above were the identified physical constraints on the system. The constraint

presenting the most difficulty was the hydraulic and three-point hitch controls. Possible

redesign of these controls might be the most appropriate solution to this problem when

attempting a retrofit.


System Adjustment

The system would need to adjust from the smallest operator in summer attire to

the largest operator in winter attire. It was assumed that a linear adjustment between

these points would provide an adequate fit for the majority of people. The determination

of these points was shown in the Methods and Procedures section. In order to meet these

requirements, the mechanism was made to slide on a 36° angle, starting at 89 mm (3.5

in.) above the seat cushion and 191 mm (7.5 in.) in front of the backrest, and extending

out to 191 mm (7.5 in.) above the seat cushion and 330 mm (13 in.) in front of the

backrest. Since the length of travel between these two points was 173 mm (6.8 in.) a

decision was made to make 5 adjustment positions on 44-mm (1.75-in.) centers, totaling

178 mm (7 in.) of adjustment.

Actuator Systems

Solenoid

Originally it was decided to use an electric solenoid to close the mechanism. The

solenoid would close the mechanism and produce tension on a return spring

simultaneously. When the mechanism was unlocked or released, the spring would bring

the mechanism back up to the open position. This unit would also incorporate a

hydraulic damper that acted to control the speed of closing and opening of the bar.

The primary advantage of the solenoid, spring, damper (hereafter referred to as

SSD) system was flexible control of the opening and closing speeds of the rigid bar. It is


conceivable that one would desire the system to close slowly while getting used to it, but

later desire the system to close faster. The same applies for opening of the system.

Variable speeds are possible with this system through the use of an adjustable hydraulic

damper, which could be remotely adjusted from any mounting place such as the armrests.

The SSD system can also be manually overridden. The solenoid offers no resistance if

one desires to close the bar themselves, and the release solenoid can also be released

manually in the event of a system failure.

A problem with the SSD system is that the rigid bar was to be fabricated from

steel, and therefore no solenoid was commercially available that met the resultant force

requirements. Figure 26 shows the torque requirements of the rigid bar due to its weight.

For this system to function properly, the torque from the spring must always be more

than the torque requirements of the bar, or else the spring will not lift the bar to the open

position. However, the spring force must always be less than the torque capabilities of

the solenoid, or the solenoid will not be able to push the bar closed. As Figure 26 shows,

either the bar weighed too much, or the solenoid was not strong enough. Regardless, the

system originally planned could not be enacted because of the lack of resources to either

make the rigid bar from a lightweight material, such as plastic, or special order a solenoid

that was large enough.

Actuator

Since the original design failed, a modified design was developed. This plan used

an electric linear actuator as the actuating mechanism instead of the electric solenoid. An


Linkage Analysis

NO

© ©

—

o1

©

|

Torque

(in-Ib)

S © Oo1

x

1 #15 2 2.5 Distance of travel

Solenoid Bar Spring a i io oe

3

Figure 26. SSD System Force Analysis


electric linear actuator consists of an electric motor that turns a gear extending a threaded

shaft linearly. The actuator serves to both move the restraint bar to the closed position

and reverse direction to move the restraint bar to the full open position.

‘An advantage to this system over the SSD system is its greater ability to

withstand weather. A solenoid can, however, be made to withstand the weather.

Disadvantages of this system are no possibility of manual override in the event of a

failure, and no option for speed control. Since the electric motor of the actuator turns at

a constant speed, the only way to slow the system is to reach its peak load capacity such

that the overrunning clutch activates and the actuator slips. Functionally, the actuator

would operate similarly to a hydraulic cylinder. However, speed of the hydraulic

cylinder extension and retraction could be controlled.

Due to reasons stated above, the electric linear actuator was used as the actuating

mechanism of the restraint system. The use of the actuator increased the complexity of

the control circuit slightly.

A schematic of the electrical control circuit is shown in Figure 27. Operation of

the system as designed is as follows. When the operator sits in the seat, a limit switch

(LS1) closes completing a circuit to two control relays (CR4 and CR5), which complete a

high current circuit to the electric linear actuator (RES1) that pushes the bar closed.

Another limit switch (LS2) breaks the circuit when the bar has reached its locked

position. When the operator wants to exit the seat, it is necessary to press one of the

pushbuttons (SW1 or SW2) mounted on the armrests. This action activates an off-delay

relay (CR1) which energizes two control relays (CR2 and CR3), which energize the


Electrical Schematic

LS11 - seat switch

LS2 - locked, horizontal switch

LS3 - vertical switch

SW1 - left pushbutton

SW2 - right pushbutton

RES1 - actuator

RES2 - release solenoid

+

O | eR CR4

Ls1 Ls2 0 CRS

C) CR2

LS3 CRI 5 swt CR3

|i o =_| CRI

sWw2 “oe ___ CR3

pA A, CR4 RES CRS

CR2

|___g “eo ana, CR2 RES2

CRi - time delay relay

CR2 - retract relay

CR3 - retract relay

CR4 - extend relay

CRS - extend relay

Figure 27. Electrical Schematic of Test Circuit


release solenoid (RES2) releasing the locking mechanism, and switches leads to the

actuator (RES1) reversing the direction of travel, bringing the bar back to a vertical

position. A limit switch (LS3) deenergizes the two retract relays (CR2 and CR3) when

the bar is vertical. After a specified amount of time, which in this case was variable from

0.1 - 10 seconds, the off-delay relay (CR1) resets. The cycle will repeat itself from this

point on if the operator sits in the seat. Actuation can be accomplished strictly using DC

power, but an AC-powered off-delay relay was used for convenience. An actual circuit

used on a tractor would probably not use AC power. This circuit was designed solely for

testing the system and was not intended to represent an actual circuit to be used on a

tractor.

An additional safety circuit could be designed to disable the operation of the

tractor unless the restraint system, parking brake, and/or gear selector, were in safe

positions. This type of control system is already in use on skid-steer loaders and even on

commercial mowers because these are recognized as hazardous machines. Tractors are

also hazardous machines. Something as simple as a starter interlock , however, would

probably not be a viable solution, since they were unsuccessful in automobiles.

However, a circuit that prohibited the usage of the PTO, hydraulics, or gear engagement

under certain circumstances could be developed, and many injuries and deaths could be

prevented.


Selection of Components

The first component that was selected was the electric linear actuator. The

minimum force requirement of the actuator was 378.25 N (85 Ib) with a stroke

requirement of 76 mm (3 in.). The smallest suitable actuator found was a Warner

Electric Model Electrak 2. This had a stroke of 102 mm (4 in.) and developed a force up

to1110N (250 1b). Thus, this model more than adequately met the requirements of the

designed system.

The locking mechanism consisted of a car door lock taken from a wrecked

vehicle. It was assumed that this component would be strong enough to withstand the

forces developed on it considering that the forces developed in a car accident are much

higher than would be expected in a tractor accident.

The force that was required to open the door lock was determined by loading the

lock, and measuring with a spring scale the force required to release the lock under load.

This force was found to be 22 N (5 Ib). The distance of travel required was also

measured to be 13 mm (0.5 in.) Therefore, a release solenoid was chosen that met these

requirements. A Synchro-Start Model 1502 was found to meet these requirements, and

had the additional feature of being weatherproof. Synchro Start offers a constant volume

boot for their solenoids that keeps wet and contaminated air from entering into the

solenoid cavity. Synchro-Start also offers a variety of electrical connectors, some of

which are weatherproof.


The only other components that were selected were the components of the

electrical control system. The limit switches were chosen because they are completely

sealed and rated for a temperature of -25° C (-14° F). All the electrical connections

would need to be made weatherproof if this system were to be implemented into the very

difficult environment of a farm or construction site. Most of the components could be

stored under the hood to help protect them. However, the pushbuttons, if mounted on the

armrests, would need to be sealed, similar to the limit switches. The reliability of this

system would be very critical considering that farmers’ lives are at stake, and if the

system was to fail and disable the tractor at a critical time then customer satisfaction

would suffer tremendously.

Design of Components

Structurally, there are three main components that make up the system (Figure

28). The first part is the rigid restraint bar that closes across the operator. The second

are the mounting and extension plates which, for force analysis, are treated as one unit.

The third part is the mounting bar which has the first two parts mounted to it and is

attached to the rear of the seat. Each of these components was designed to withstand a

vertical loading of 8900 N (2000 Ib) (hereafter referred to as Case 1), and a horizontal

loading of 8900 N (2000 Ib) (hereafter referred to as Case 2).


Mounting Bar

Restraint Bar

Mounting Plates

Figure 28. Structural Components of Restraint System


Mounting and Extension Plates

The first parts designed were the mounting and extension plates. Even though

these are two separate pieces, it was assumed that the forces acting upon the mounting

plate would be transmitted to the extension plates through the locking pin and grooves

into which the mounting plates slide. Therefore, the unit can be modeled as a single

cantilever beam. A diagram of the loadings is shown in Figure 29.

The maximum stress in a cantilever beam loaded as shown will be at element A.

The element is in tension due to both the moment caused by F,, and the tensile stress due

to F,. It was assumed that the shear forces caused by F, were negligible. Thus, the

maximum tensile stress in a narrow rectangular beam was computed from the following

equation (Beer & Johnston, 1981):

Om, = Me/1+F /A

where, M=F, * L= moment

c = h/2 = distance to outer fiber

I = (b*h’)/12 = moment of inertia

F =F * cos(@) = force in x-direction

F, = F * sin(Q) = force in y-direction

A = b*h = cross-sectional area


(4.1)

(4.1.1)

(4.1.2)

(4.1.3)

(4.1.4)

(4.1.5)

(4.1.6)

72

Load on Extension/Mounting Plates

Case 1 Loading = F

Case 2 Loading = P F

P

Q

™

Fy 4

4 5 > Fy

.| L

Free Body Diagram F y

M |

Figure 29. Loading on Mounting Plates


The fixed parameters were input into TK Solver! so that all of the equations could

be solved simultaneously. Various sizes of steel were then input into the equations and it

was found that ASTM-A36, 76 mm X 9.5 mm (3 in. X 3/8 in.) steel would meet the load

requirements with a safety factor of 1.1. This was deemed acceptable for the prototype

because this safety factor is based upon the yield point of the material, and yielding can

occur without failure. The safety factor becomes 1.7 if based upon the ultimate strength

of the material, not yield strength. It was also found that Case 2 produced less stress than

Case 1.

Mounting Bar

The next piece that was designed was the mounting bar. The primary loading on

this piece, as shown in Figure 30, is the torque produced from F,. The piece actually has

three-dimensional stress due to the bending of the bar from F, and F,, and additional

shear stresses from F, and F,, but these are assumed negligible compared to the stresses

caused by the torque. Thus, the piece was modeled as a thin-walled hollow section under

pure torsion. The maximum shear stress is therefore computed from the following

equation (Cook and Young, 1985):

Tom = 1 / (2tT) (4.2)

where, T = torque

T = the area enclosed by medial line of the wall cross section

t = thickness of the wall


Load on Mounting Bar

_/ Mounting Bar Fy f

—> Fx

O b

\ Lr \

IT = shaded area

Extension/Mounting Plates

Figure 30. Loading on Mounting Bar


It was found that a 51 mm X 51 mm X 6 mm (2 in X 2 in X 1/4 in) tube made of

ASTM A-36 steel would result in a safety factor of 1.62, allowing for some error due to

the assumptions stated earlier. Also, it was found that Case 1 produced the highest stress

on the object.

The welded joint that joins the mounting bar and extension plates was also

designed. It was decided to weld the square tubing around its entire perimeter to the

extension plate for an even transmission of force. The size of the weld was determined

from the following equations (Vaughan, 1992):

f=Tc/J, (4.3)

where, f = force

T = torque on weld

c = distance to outer fiber

J,, = polar moment of inertia of weld

and f, = 9,900*b

where, f,,, = allowable force

b = leg length of weld

A leg length of 5.7 mm (0.23 in.) was found to be adequate, thus the

manufacturing specifications were set to 6 mm (1/4 in.) leg length for this weld.


Restraint Bar

The last critical piece that was designed was the rigid restraint bar. For Case 1, it

was assumed that each of the bars carried half of the loading and that the bending stresses

dominated. It was also assumed that the loading occurred in the center of the bar. Thus,

the maximum tensile stress for structural tubing in bending was computed using the

following formula (Beer and Johnston, 1981):

0.4, = Me/I (4.4)

where, Mix 7 F*L/4 = moment (4.4.1)

c = h/2 = distance to outer fiber (4.4.2)

I = (b,*h,’)/12 - (b,*h,’)/12 = moment of inertia (4.4.3)

It was found that 38 mm X 38 mm X 3 mm (1.5 in. X 1.5 in. X 1/8 in.) ASTM A-

36 structural tubing was adequate for a Case | loading.

Case 2 was then analyzed. The type of loading is similar to Case 1; however, the

orientation of the load changes, which changes the moment of inertia of the bar, and the

force on the bar increases to the full 8900 N (2000 Ib). The results indicated that Case 2

produced less stress than Case 1; thus, the size of the tubing that was calculated for Case

1 is also adequate for Case 2. Figure 31 shows the loadings and cross-sections for each

case.


Case 1:

Load on Restraint Bar

Section Profile

Ra

Case 2:

Rb

Section Profile

Rb

Figure 31. Loading on Restraint Bar


The next thing that was calculated was the shear force in the pins used for the

pivot point and locking pin on the restraint bar. For a round object, the maximum shear

stress is (Beer and Johnston, 1981):

Tome = 4/3( V/A) (4.5)

where, V = shear force

A = cross-sectional area

The 13 mm (1/2 in.) diameter rounds were found to be adequate in shear strength

for all of the various loadings to which they were subjected.

List of Materials and Cost

Table 7 shows the list of materials and components and the associated costs for

the actuator system. The list of materials and selected components for the SSD system is

shown in Table 8. The cost of the systems are similar, with the linear actuator system

costing $564 and the SSD system costing $587. Therefore, cost is not much of a

consideration when choosing between the two systems. Each of the systems had a few

more parts than are listed in the tables, such as electrical wire, connectors, and small

pieces of steel. These costs are strictly material costs for the systems and do not include

labor to build the system or the cost of the seat used as a mounting base. The tractor seat

was an additional $260.00.

Even if the system could be manufactured for approximately the same cost as was

paid for all of the components, the system cost seems somewhat high. However, when

compared to the cost of a ROPS, which ranges from $600 - $4,000, the system cost is not


able 7. List of Materials and Cost for Actuator

Quantity Description Cost

1 Warner Electric Linear Actuator $180.00

1 3 in. X 3/8 in. ASTM A-36 Steel Bar 24.00

1 1.5 in. X 1.5 in. X 1/4 in. ASTM A-36 Steel Square 24.00

1 Car Doorlock 5.00

1 1502 Synchro-Start Solenoid 60.00

3 Omron Limit Switches 158.00

1 Dayton Off-Delay Relay 44.00

4 Automobile Starter Soleniod Relays 32.00

2 General Electric 30mm Recessed Pushbuttons 37.00

Total Cost "$564.00


Table 8. List of Materials and Cost for SSD System

Quantity Description Cost

1 Trombetta Q517 Solenoid $160.00

1 Enidine ADA-510 Shock Absorber 100.00

3 Bosch Industrial Torsional Springs 15.00

1 3” X 3/8” ASTM A-36 Steel Bar 24.00

1 1.5 im. X 1.5 in. X 1/4 in. ASTM A-36 Steel Square 24.00

1 Car Doorlock 5.00

1 1502 Synchro-Start Solenoid 60.00

2 Omron Limit Switches 102.00

] Dayton Off-Delay Relay 44.00

2 Automobile Starter Soleniod Relays 16.00

2 General Electric 30mm Recessed Pushbuttons 37.00

Total Cost ~ $587.00


excessive. Also, when considering that large tractors, combines, and tractor-loader-

backhoes cost from $50,000 - $150,000, an additional $500 for safety improvements is

quite small. A farmer first witnessing a demonstrated rollover with rollover protection in

1966 stated (when referring to the ROPS), “I have three tractors and three sons. I’m

putting this protection on my tractors. They’re cheaper than caskets.” (Schneider, 1990)

Hopefully this same attitude will prevail regarding restraint systems as educational

efforts about the dangers of farming continue.

Retrofit

One of the initial design requirements was for the system to have the potential for

retrofitting. An investigation of the local Ford-New Holland, John Deere, and Kubota

tractor dealerships revealed that there are a wide range of tractor seats and even wider

range of space surrounding them. Most of the tractors observed, which included many

used tractors, had severe space limitations around the tractor seat due to the fenders and

hydraulic and three-point hitch controls. Smaller horsepower tractors were especially

limited in space. However, even many of the larger horsepower tractors had severe

limitations. It would be nearly impossible to design a single retrofit system that could

accomodate a large variety of tractors, considering the extreme variability of existing

tractors. Any retrofit would probably be specific to make, model, and year, and further

modifications other than the installation of the new seat and restraint system would

probably be necessary. A restraint system such as the one proposed herein definitely


needs to be designed into the operator’s station from the beginning because placement of

all controls and other associated clearance problems shoud be addressed.

Safety Considerations

The primary safety considerations of the design were a fail-safe system and

possible injury caused by the rigid bar closing. Only the SSD system can be manually

overridden and therefore be “fail-safe.” However, on either design, the pins could be

extracted from the mounting and extension plates and the entire unit could be removed,

thus freeing the operator.

The restraint bar presents a hazard resulting from the rigid nature of the bar. The

bar must be rigid in order to reach the lock, and must have a large amount of force

applied to it in order to trip the lock. Thus an operator’s hand, arm, or head could get

caught under the bar while it 1s closing and it would not yield. However, if the bar was

padded, so that a collision type of accident would not result in significant injury, then the

only consideration would be that of pinching the operator. An accident of this nature

would not result in much injury because either the maximum force of the actuator would

be reached, or the seat would displace because it 1s incorporated with a shock absorbing

system. The system is also designed so that any time the operator pushes the release

button, even while the rigid bar is closing, the unit will open immediately. It is

acknowledged that slight injury could occur with this system; however, the injuries or

deaths this system could prevent are much more significant.


CHAPTER 5

SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS

Survey

The survey shows that tractor operators not wearing the seatbelts on ROPS-

equipped tractors is a major problem. The survey also suggests that an automatic restraint

system is a viable solution to this problem from the standpoint of user acceptance.

Conclusions

e Only 13% of operators wore their seatbelts half or more of the time, and 61%

of operators report “never” wearing their seatbelts.

e 62% of operators were neutral or approved of the idea of an automatically

closing seatbelt.

e There were no significant differences in seatbelt usage among the operators

based upon age, years of experience, slope of land farmed, or awareness of

rollover statistics.

e There were no significant differences in feelings toward an automatically

closing seatbelt among the operators based upon age, years of experience,

slope of land farmed, or awareness of rollover statistics.

If the survey sample size was larger, it may have been concluded, with a

reasonable amount of certainty, that there are differences among the various groups when

it comes to seatbelt usage or attitudes toward an automatic seatbelt.

SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS 84

Restraint System

With tractor rollovers and the lack of seatbelt usage being such a serious

problems, something should be done to address them. An automatic seatbelt seems to be

both a feasible and viable solution. A system prototype was designed, fabricated, and

evaluated; however, it is recognized that many developmental stages are still left before a

design like this prototype would be manufactured.

Recommendations

Based upon this research, a number of recommendations follow:

e Develop an automatic restraint system as an option for those operators who

are willing to pay for and use it, perhaps as standard equipment so that the

tractor is a safer machine to operate.

e Continue to educate farmers about the dangers of farming, and overturns in

particular, so that some will become motivated to wear seatbelts and to equip

their tractors with ROPS.

e Create incentive programs, such as insurance breaks, to help motivate the use

of seatbelts or the purchase of a ROPS and an automatic restraint system.

e Investigate all tractor makes and models to identify those that have the

potential of retrofitting an automatic restraint system and/or ROPS.


follow:

A number of further recommendations for the restraint system design in particular

Incorporate a more ergonomically shaped restraint bar into the system.

Create the restraint bar from low density material so that the SSD system

could be used.

Design a pin / ball-joint instead of a fixed / welded joint at the extension plate

/ mounting bar connection so that more than linear adjustment can be made

between the minimum and maximum adjustment points.

Develop a control circuit that limits the functioning of the tractor unless the

restraint system is securing the operator in the seat.

Address the safety concerns pertaining to the rigid bar closure, such as

padding on the restraint bar, fail-safe design, manual override capability, and

proper shielding of moving components.

It is hoped that this research helps justify and motivate further investigations and

solutions to the problem of operators not wearing the seatbelts provided on ROPS

equipped off-road vehicles.


LITERATURE CITED

ASAE S519. 1987. Roll-over protective structures (ROPS) for wheeled agricultural

tractors. ASAE Standard.

Ambe, F. and D.J. Murphy. 1993. Differences among aged, middle aged, and young

adult tractor operators in Pennsylvania. Technical Papers of the National Institute for Farm Safety Summer Meeting. Paper No. 93-2.

Ayers, P.D. and C.M. Johnson 1994. Testing of rollover protective structures (ROPS)

designed for pre-ROPS tractors. ASAE Paper #94-5003. St. Joseph, MI.

Baker, S.P., B. O’Neill and R.S. Karpf. 1984. The Injury Fact Book. Lexington Books,

Lexington, MA, pp. 107-111.

Beer, F.P. and E.R. Johnston, Jr. 1980. Mechanics of Materials. McGraw-Hill, Inc.

New York, NY, pp. 441-442.

Cook, R.D. and W.C. Young. 1985. Advanced Mechanics of Materials. Macmillen

Publishing Co., New York, NY, pp. 301-303.

Dybro, N. 1991. Restraint systems for rollover protection on agricultural tractors.

Unpublished Thesis. University of Michigan, Ann Arbor, MI.

Geller, E.S. 1984. Motivating safety belt use with incentives: A critical review of the

past and a look to the future. SAE Paper #840326.

Gerberich, S. G., R.W. Gibson, P.D. Gunderson, L.J. Melton IJ, L.R. French, C.M.

Renier, J.A. True, and W.P. Carr. 1991. Surveillance of injuries in agriculture.

Proceedings of Surgeon General’s Conference: Agricultural Safety and Health, April 30-

May 3. Des Moines, IA.

Hajec, S. 1994. Grammer, Inc., Oakdale, MN. Personal communication.

Hetzel, G.H. 1994. Virginia Polytechnic Institute & State University, Blacksburg, VA. Personal communication.

Hetzel, G.H. and W. Zhao. 1993. Identifying hazards and causes of accidents on

Virginia farms. Virginia Polytechnic Institute & State University, Biological Systems Engineering, Paper No. VTAHPS 3-1.

LITERATURE CITED 87

Karlson, T.A. and J. Noren. 1979. Farm tractor fatalities: the failure of voluntary safety

standards. American Journal of Public Health; 69(2): 146-149.

Ott, L. 1988. An Introduction to Statistical Methods and Data Analysis. PWS-KENT

Publishing Company, Boston, MA, pp. 249-252.

Public Health Focus: Effectiveness of Rollover Protective Structures for Preventing Injuries Associated with Agricultural Tractors. Morbidity and Mortality Weekly Report,

Jan. 29, 1993; 42 (3): 57-59.

McKnight, R.H. and G.H. Hetzel. 1984. Annual trends in farm tractor and machinery

deaths 1975-1981. ASAE Paper No. 84-5507.

NASA Anthropometric Source Book, Vol. I-III 1978. Webb Associates, Yellow

Springs, OH.

National Safety Council. Accident Facts, 1992 Edition. National Safety Council,

Chicago IL.

Nordstrom, D.L., L. Brand, and P.M. Layde. 1992. Preface. Epidemiology of farm- related injuries: Bibliography with abstracts. National Institute for Occupational Safety

and Health. Cincinnati, OH.

SAE J386. 1985. Operator restraint systems for off-road work machines. SAE

Recommended Practice.

Schnieder, R.D. 1975. Have ROPS been effective in saving lives? ASAE Paper No. 75- 1553. St. Joseph, MI.

Schnieder, R.D. 1990. An overview of ROPS related accidents, 1965-1990. ASAE

Paper No. 90-1640. St. Joseph, MI.

Schwab, C.V. and D. Anthony. 1993. Evaluation of agricultural injury notification

systems. Technical Papers of the National Institute for Farm Safety Summer Meeting.

Paper No. 93-10.

Schwab, C.V., A. Ralston, F. Lorenz, and M. Power. 1993. Methodology for evaluating

farm safety educational and awareness programs. Technical Papers of the National

Institute for Farm Safety Summer Meeting. Paper No. 93-9.

Vaughan, D.H.. 1992. AGE 4404 Class Notes-Welded Joint Specifications and Design.

Virginia Polytechnic Institute & State University, Blacksburg, VA.

LITERATURE CITED 88

Vogel, J. 1993. Criteria for increasing seatbelt use by agricultural tractor operators.

National Science Foundation Undergraduate Research Experience. Iowa State University, Agricultural and Biological Systems Engineering Department.

Wen, D. 1994. Finite element analysis of pre-ROPS tractor axle housing strength. Unpublished Dissertation. Virginia Polytechnic Institute and State University,

Blacksburg, VA.

Woodward, J.L. and S. Swan. 1980. ROPS field performance - A status report. SAE Paper No. 800679.

LITERATURE CITED 89

APPENDIX A: SURVEY DATA

YN >

=O OID

11.

12.

13.

14.

15.

Seatbelt Usage Survey

How many tractors are on your farm?

How many of these tractors are equipped with a ROPS or cab?

How many of these tractors currently have a functioning seatbelt?

When driving tractors with seatbelts/ROPS, how frequently do you wear the seatbelt?

O1 Never

C2 Occasionally

03 About half of the time

n4 Most of the time

O5 Always

What would you say is the biggest reason you do not wear a seatbelt?

01 Do not feel much danger

O12 Too much hassle (too hard to reach, latch, etc.)

03 Time consuming

04 Old habit of not wearing one (do not think about it)

O05 Combination of the above factors

06 Other

What is your age?

How many years of experience do you have operating a tractor?

How many hours do you operate a tractor each year?

How many hours are spent operating a tractor with a ROPS or cab (per year)?

How would you characterize the land you farm?

O1 Flat

O2 Gently rolling

03 Moderately rolling

04 Fairly steep

What is the largest revenue producing operation on your farm?

O1 Alfalfa 06 Fruit O11 Small Grains

02 Beef 07 Hogs 112 Soybeans

03 Cow-Calf O8 Horses O13 Tobacco

04 Com 9 Peanuts O14 Vegetable crop

O5 Dairy O10 Poultry O15 Other

In what county is your farm located?

Are you aware that agriculture is the most dangerous occupation in the U.S.?

O1 Yes

02 No

Are you aware that tractors account for 75% of all farm machinery related deaths, and half of these are

due to the tractor rolling over?

01 Yes

02 No

How would you feel about an automatically closing seatbelt for your ROPS equipped tractors?

(Please check only one box that most represents how you feel)

O1 Strongly Dislike

O12 Dislike

03 Neutral

O4 Approve

O5 Strongly Approve

APPENDIX A: SURVEY DATA 90

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_Q6 _Q7 _08 _Q9 Q10 66 60 600 600 1 14 0 0 0 2 50 40 NR NR 2 74 40 500 500 2 30 20 200 0 1 71 25 250 250 3 26 3 100 100 3 56 30 300 100 3 46 25 NR 200 1 66 50 1500 40 2 55 35 NR NR 2 70 50 250 0 4 70 43 2000 0 3 50 40 1000 800 3 59 53 1900 1500 3 50 43 2500 0 2 51 42 1300 1000 2 37 20 1500 1200 2 63 42 300 100 2 64 50 1000 500 2 35 8 200 200 1 63 40 300 150 3 4‘ 30 900 800 2 63 42 500 70 1 36 26 4500 1000 1 2/ 15 100 50 2 40 20 200 200 1 31 18 1000 1000 4 47 35 300 300 3 18 8 500 300 3 40 25 400 200 3 15 4 200 10 2 53 45 700 400 2 18 8 500 400 2 55 40 250 150 3 o7 50 NR NR 3 56 46 300 100 2 57 45 2000 0 2 42 35 200 0 3


94

_O6 Q7 O8 Q9 Q10

35 30 350 350 2 21 12 NR NR 1 61 49 500 0 4 42 40 1000 1000 3 NR 15 NR NR 2 25 13 NR NR 3 33 20 250 100 3 13 50 100 0 2 54 45 700 200 3 39 20 500 450 4 60 50 NR NR 2 26 10 NR NR 3 66 30 500 450 3 18 6 400 0 3 26 15 300 0 3 15 50 100 0 3 98 48 NR NR 3 33 25 500 400 2 39 19 NR NR 2 46 38 400 300 3 37 25 400 0 3 58 52 200 200 2 24 15 NR NR 2 49 35 400 0 2 29 20 400 400 2 25 18 150 35 1 52 5 800 0 2 52 5 150 0 1 39 10 250 200 2 41 31 150 0 3 56 35 200 0 1 62 14 200 0 3 48 31 400 200 3 55 40 500 75 3 50 NR NR NR NR 31 20 800 0 2 32 20 1000 1000 3 43 35 50 0 4 49 20 250 245 3


95

_O6 Q7 _O8 Q9 Q10

65 45 25 15 3 70 44 225 225 2 38 25 1000 400 1 39 30 120 40 4 50 12 250 250 4 62 25 250 NR 2 60 34 NR NR 1 35 25 450 400 2 41 31 100 0 4 42 30 300 200 2 50 40 300 0 3 50 9 50 0 3 53 40 500 400 3 70 30 300 200 1 24 10 40 0 2 20 1 500 500 2 18 9 1000 750 2 18 4 25 0 3 19 7 80 0 4 NR NR NR NR NR 20 6 200 NR 3 18 11 90 0 3 19 if 15 25 3 22 7 120 0 4 19 8 150 2 4 NR NR NR NR NR 22 3 NR NR NR 23 13 NR NR 2 18 7 800 500 3 25 8 2000 2000 2 19 NR NR NR 3 30 10 NR NR 2 18 7 2500 2500 3 24 3 NR NR 3 19 1 50 0 3 19 10 NR NR 2 19 4 NR NR 3 18 10 NR NR 3 18 6 100 0 2 21 10 300 100 2 20 4 NR NR 1


96

Q11 Q12 Q13 Q14 Q15 Date 2.4.11.12 Hanover NR NR NR 08/15/93

1,2,3,4,7,8,11,12 Louisa NR NR NR 08/15/93 2 Westmoreland NR NR NR 08/15/93

1,2 Fauquier NR NR NR 08/15/93 2,3 Culpeper NR NR NR 08/15/93

3 Fauquier NR NR NR 08/15/93 8 Madison NR NR NR 08/15/93

5,6 Culpeper NR NR NR 08/15/93 2,10 Shenandoah NR NR NR 08/15/93 1,2 Rappahannock NR NR NR 08/15/93 2 Culpeper NR NR NR 08/15/93 2 Orange NR NR NR 08/15/93

2,3,13 Pittsylvania 1 1 2 02/03/94 2,4,11,12,13 Pittsylvania 1 1 2 02/03/94

7 Pittsylvania 1 1 4 02/03/94

13 Pittsylvania 1 2 1 02/03/94 7,11,12,13 Pittsylvania 2 1 3 02/03/94

13 Pittsylvania 1 1 3 02/03/94 2,13 Pittsylvania 1 1 2 02/03/94

2 Pittsylvania 1 1 1 02/03/94 8 Chesapeake 2 2 1 02/15/94 9 Southampton ’ 1 3 02/15/94 9 Southampton NR NR NR 02/15/94 3 Chesapeake 1 1 3 02/15/94 9 Chesapeake NR NR NR 02/15/94

12,13 Brunswick NR NR NR 02/15/94 9.11 Southampton NR NR NR 02/15/94

5 Rockingham 1 1 3 03/10/94

1,5 Rockingham 1 1 4 03/10/94 5 Rockingham 1 2 3 03/10/94 5 Rockingham 1 2 2 03/10/94

45 Rockingham 1 1 4 03/10/94 5 Rockingham 1 1 2 03/10/94 10 Rockingham 1 1 4 03/10/94 10 Augusta 1 1 3 03/10/94

1,45 Rockingham 1 1 3 03/10/94 5 Rockingham 1 1 3 03/10/94

5,10 Rockingham 1 1 1 03/10/94 45 Rockingham 1 2 3 03/10/94


Q11 Q12 Q13 Q14 Q15 Date 5 Rockingham 1 1 4 03/10/94 5 Rockingham 1 2 4 03/10/94

3,10 Rockingham 1 1 4 03/10/94 45 Rockingham 1 1 3 03/10/94 10 Rockingham 1 1 1 03/10/94 10 Augusta 2 2 2 03/10/94 5 Rockingham 1 1 3 03/10/94

2 Rockingham 1 NR 4 03/10/94

5 Rockingham 1 1 4 03/10/94 2,3 Rockingham 1 1 2 03/10/94 5 Rockingham 1 1 3 03/10/94 4 Rockingham 1 2 2 03/10/94 3 Rockingham 1 1 2 03/10/94 5 Rockingham 1 2 4 03/10/94 5 Rockingham 1 2 4 03/10/94 15 Rockingham 1 1 3 03/10/94 10 Rockingham 1 2 3 03/10/94 5 Rockingham 1 2 2 03/10/94

5,10 Augusta 1 1 3 03/10/94 45 Rockingham 1 2 2 03/10/94 10 Rockingham 4 1 3 03/10/94

1,4,5,12,15 |Rockingham 1 1 4 03/10/94 5,10 Rockingham 1 2 3 03/10/94 10 Augusta 1 1 4 03/10/94

1,4,5,12,15 | Rockingham 1 2 3 03/10/94 5 Suffolk 1 2 1 03/10/94 10 Rockingham 1 1 4 03/10/94 10 Rockingham 4 1 3 03/10/94 10 Rockingham 1 1 3 03/10/94 2 Rockingham NR NR NR 03/10/94 10 Rockingham NR NR NR 03/10/94

2,14 Rockingham NR NR NR 03/10/94 2 Augusta NR NR NR 03/10/94

45.8 Rockingham NR NR NR 03/10/94 NR NR NR NR NR 04/27/94 2 Craig 1 2 3 04/27/94 2 Craig 1 2 3 04/27/94 2 Craig 1 1 3 04/27/94 3 Craig 1 2 3 04/27/94


Q11 Q12 Q13 Q14 Q15 Date 2 Craia 1 1 3 04/27/94 3 Craig 2 2 3 04/27/94

1,2,15 Craig 2 2 2 04/27/94 45 Craig 1 1 2 04/27/94 3 Craig 1 2 2 04/27/94 3 Craig 1 1 2 04/27/94 2 Craig 1 1 2 04/27/94 3 Craig 1 1 1 04/27/94 3 Craig 1 1 1 04/27/94 3 Craig 1 1 1 04/27/94 3 Craig 1 2 1 04/27/94 3 Craig 1 2 1 04/27/94 3 Craig 1 1 1 04/27/94

1,2 Craig 1 2 1 04/27/94 15 Loudoun NR NR NR | 04/28/94 15 Prince William 1 1 3 04/28/94 3 Page 1 2 1 04/28/94 15 Page 1 2 4 04/28/94 3 Giles 1 1 3 04/28/94

Bedford 1 1 5 04/28/94

1,4,5 Augusta 1 1 1 04/28/94 3 Bedford 1 2 3 04/28/94 3 Bedford 1 2 3 04/28/94 6 Madison 2 1 3 04/28/94 2 Augusta 2 2 2 04/28/94 NR NR 1 ¥ 3 04/28/94 14 Stafford 1 1 1 04/28/94 10 Amelia 2 2 3 04/28/94

3,15 Roanoke 2 2 3 04/28/94 Warren 1 1 4 04/28/94

3 Amherst 1 2 3 04/28/94 2,3 Pulaski { 2 3 04/28/94

2,4,12 Loudoun 1 1 2 04/28/94 8,15 Appomattox NR NR NR 04/28/94

8 Smyth 2 2 3 04/28/94 7,14 Hanover 1 2 3 04/28/94 15 Wythe 2 1 3 04/28/94 3 Pulaski 1 2 3 04/28/94

2,8 Augusta 1 1 2 04/28/94 2,3 Shenandoah 2 2 3 04/28/94 15 Southampton 2 2 4 04/28/94

APPENDIX A: SURVEY DATA 99

VITA

Chris Wyckoff was born in Luray, Virginia on June 6, 1970, to David Wyckoff

and Joanne Humphreys. He graduated from West Potomac High School in Alexandria,

Virginia in 1988. He attended Virginia Tech from August 1988 through December 1992,

when he received a Bachelor of Science degree in Agricultural Engineering. He then

began pursuing a Master of Science degree in Agricultural Engineering at Virginia Tech

in January 1993. He hopes to find employment in the agricultural equipment industry

very soon after graduating in August 1994.

LL LS by

VITA 100

ah 4 mal - virginia tech

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