.
I"H

ugn‘

0-169

 

 

This 1. to certify that the

thesis entitled

"A Control W for the Power
hnipuletion of e Blueberry finder"

presented by
mm P. I.”

has been accepted towards fulfillment
of the requirements for

__‘a_fl.u_ degree inth
Engineering

Major professor

Date ‘2 5-

 

 

 

..- 1'“

A CONTROL SYSTEM FOR THE POhER MENIPULATION
OF A BLUEBERRY KEEDER ‘

By
Dwight Frederick.§3mpe

AN ABSTRACT
Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Agricultural Engineering

Year 1953

I D ‘““ "’ ' - Ah}-

Approved_

"HERE

to work
bushes
result
to work
the row
Th
minis

is the

k;- w
mg

be

The cultural practice of setting bushes on a four by ten foot Spacing
used in the growing of blueberries has kept growers from.satisfactorily
mechanizing the weeding of the row area and has forced them to rely
principally on hand hoeing to keep this area free of weeds.

A mechanical weeder was developed by Hall of Michigan State College
to work in this area but the system for maneuvering the weeding head around
bushes required a considerable amount of effort from the operator. As a
result it was only partially satisfactory and this project was undertaken
to work out a system of automatic controls for manipulating the head in
the row area.

The method selected was to maneuver the head by means of a hydraulic
cylinder which would be controlled by a bumper that contacted each bush
as the weeder came to it. This system.would retract the weeding head out
of the row when the bumper contacted a bush and extend it back into the
rOW'again when the bumper had moved past the bush. This would maneuver the
head around each bush and do it without any assistance from.the Operator.

The first control system.tested utilized only two conditions for
control of the weeding head. ‘When the bumper was in contact with a bush
the weeding head would be retracted out of the row and when the bumper
moved away from.the bush the head would extend back into the row again.
This system was adequate to maneuver the weeding head without any assistance
from.the operator but, having only two positions, it would cycle between
them.and this cycling proved to be objectionable.

The depth regulation on Hall's weeder, on which the first system was
tested, proved to be inadequate for automatic control and only a limited

amount of test work could be done.

A n1
centers
control
also in:
was encc
of the I

able to

A new weeder was built to overcome the difficulties that were en-
countered when using Hall's weeder with an automatic control and a second
control system was developed that had a higher speed of retraction and
also incorporated a hold position for improved stability. Some difficulty
was encountered in achieving the additional stability due to overtravel
of the weeding head but after making corrections to the system it was
able to control the weeding head more smoothly than the first system.

The system, however, could not be operated above a tractor speed of
600 engine r.p.m, without becoming unstable due to the overtravel and
had to be kept below this speed for satisfactory operation.

Either of these control systems was adequate to maneuver the weeding
head around bushes but the one incorporating the hold position was more
satisfactory as long as it was operated so that the factors affecting

overtravel were not prominent enough to affect stability.

A CONTROL SYSTEM FOR THE POWER MANIPULATION
OF A BLUEBERRY WEEDER

By
Dwight Frederick Kampe

A THESIS
Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Agricultural Engineering

1953

The
Carleton

counsel,

He
Agnew

this in

on the

Cannes

Gest 01'

ACKNOWLEDGMENTS

The author wishes to express his sincere thanks to Doctor Walter
Carleton, under whose guidance this project was conducted, for his

counsel, encouragement, and helpfulness in making this project a reality.

He is also deeply indebted to Professor Arthur Farrell and the
Agricultural Engineering Department of Michigan State College for making

this investigation possible.

The author wishes to commend Doctor Carl Hall for his initial work

on the blueberry hoe and to thank him for his most helpful counsel.

He also wishes to thank Mr. J. Levin and Mr. H. Gaston for their
counsel and expresses his appreciation to Mr. H. Hootman and Mr. H.

Gaston for making their facilities available for field testing.

ACQIOLL]
LIST 017

L11

TABLE OF CONTENTS

ACKNO‘VLIIIIG ”N T S 0 O O O O O O O O O O O O O O O O 0

LIST OF FIGURE 0 O O O O O O O 0 O O O O O O O O O

I.

II.

III.

IV.

INTRODUCTION . . . . . . . . . . . . . . . .
Present Status of Blueberry weeding . . . .
Source of the Problem - Blueberry Culture .
Present mechanical Weeding thhods . . . . .
Need for a Power Operated Machine . . . . .

SELECTION OF A SYSTEM FOR TEST . . . . . . .
Need for Automatic Control . . . . . . . . .
Requirements of an Automatic Control System
The Basic Type of System . . . . . . . . . .
Details of the Systemu . . . . . . . . . . .

THE FIRST EXPERIMENTAL MACHINE . . . . . . .
Preliminary Considerations . . . . . . . . .
Design of the Control Elements . . . . . . .
Incorporation of the Control Elements . . .
Preliminary Test . . . . . . . . . . . . . .
Field Test . . . . . . . . . . . . . . . . .
Evaluation of the Machine . . . . . . . . .

THE SECOND ECPERIAFNTAL MACHINE . . . . . . .
Preliminary Considerations . . . . . . . . .

The New heeder . . . . . . . . . . . . . . .

earn
'10.?

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A) A) A) #4 F4 k1 F1 p4 P‘ F‘
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\J’I

FIELD}

The New Control System . .

Preliminary Test on Stakes

First Field Test . . . . .

Second Test on Stakes . .

Second Field Test

Evaluation of the Machine

V. SUMMARY .

Conclusions

Recommendations for Further Study

BIBLIOGRAPHY

O

Page
29

AD

46
48
A8
A9
50

 

Figure 1.

Figure
Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure
Figure
Figure

Figure

Figure

Figure

Figure

Figure

2.
3.
h.

5.

6.

7.

8.

9.
10.
ll.

12.

13.
lb.

15.

16.

17.

LIST OF FIGURES

Typical planting of blueberries . . . . . . . . . .
Diagram.of area worked by'a grape hoe . . . . . . .
EXperimental blueberry weeder . . . . . . . . . . .

Diagram of the area worked by Hall's eXperimental
menine O O O C O O O O O O O C O O O O O O O O O

Hydraulic circuit selected to control the
weedingheadeeeeeeeeeeeeeeeoee

Diagram showing how the path of the weeding
head across the ground would determine the
bumper's location and shape . . . . . . . . . . .

Diagram.showing pressure balance on the
c0ntrolvalve..................

Hall's weeder with the automatic control
elements incorporated . . . . z . . . . . . . . .

Weeder positioned between the rows . . . . . . . .
Path of retraction on the approach side of a bush .
Path of extension on the back side of a bush . . .

Weeder working the second side of the row with
an overlap at the center . . . . . . . . . . . .

Row area after working both sides . . . . . . . . .

New weeder used for testing the automatic
control system . . . . . . . . . . . . . . . . .

Weeding head of the new machine . . . . . . . . . .

Upper section of the frame showing the hydraulic
cylinder and the Springs used to extend the head

New circuit incorporating a hold position used
to control the weeding head . . . . . . . . . . .

ll

12

l7

18
20

20

26
28

28

30

Figure

Figure

Figure

Figure

Figure

Figure

Figure
Figure
F‘ie'llre

Fié‘Ure

Figure

Figure

Figure

Figure

Figure

Figure

Figure
Figure

Figure
Figure

Figure

Figure

18.

19.

21.

22.

23.

25.
26.

27.

28.

29.

Weeding head showing marker and string
attaChed to the bumper e e e e e e e e 0

Trace made by marker on the weeding head
while maneuvering around a stake with
machine in original condition . . . . . .

Trace made by marker on the weeding head
during a full retraction stroke . . . . .

Trace made by marker on the weeding head
with increased weight on the depth shoe .

Trace made by marker on the weeding head
with increased spread on the control
positions, metering slots in the valve
Spool, and increased load in the extension
springSeeeeeeeeeeeeeeeee

The new weeder being driven between rows
Ofbushes................

Row area before any weeding was done . . .
Row area after being weeded from one side .

Row area after being fully weeded . . . . .

Path of the weeding head on the approach side

of a bush showing the improved ground coverage

Trace made by the marker on the weeding head

with intermediate springs and metering slots

Weeder being operated with the extended bumper

vii

Page

33

3h

35

37

$51515

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trend i
made in
berry c
rily be
Special
with th.
Plantin!
until a

recJ-lir‘e;

INTRODUCTION

Present Status of Blueberry Weeding

The mechanical weeding of blueberries has lagged behind the general
trend in farm mechanization and to date only limited progress has been
made in this field. This lag has been due to the fact that the blue-
berry culture presents a special weeding problem.that cannot satisfacto-
rily be handled by regular cultivating equipment and there has been no
Special equipment develOped to fill this gap. This has left the grower
with the necessity of using large amounts of hand labor to keep his
planting free of weeds and he will be required to continue this practice
until a satisfactory weeder can be developed that will meet the Special

requirements of this weeding problem.

Source of the Problem - Blueberry Culture

Natgge ofgrowthA The blueberry is a shallow rooted perennial that
grows to a height of about four feet in eight years and may reach a
height of six to eight feet at full growth. The bottom.branches are from
eight to twelve inches from the ground with the bush having approximately
Na hemiSpherical shape. The stump consists of several shoots forming a
stump approximately six inches in diameter.

Blueberries in Michigan are grown on predominantly sandy soil with
a pH h-0 -5.5. The young plants are started in nursery beds and are

set out into the field at about two or three years of age. Common practice

f 01101

r013 .
fire A

Q.

 

 

Fig. 1. Typical planting of blueberries. Rows are ten
feet apart and bushes are on four foot centers.
is to set them.in rows 10 feet apart and with a spacing of A feet within

the row (r13 1).

The weedigg problem. The weeding problem consists of keeping the
entire area free of weeds and unwanted plants. Part of this problem.is
the removal of a cover crop that is planted in the fall and removed the
following spring.

The ten foot spacing between rows allows the grower to drive between
rows with his tractor and any tillage implement be selects to work this
area. The four foot Spacing within rows, however, prevents the use of

conventional tillage methods between bushes and requires that a band of

3011 be
this be
is in 1
for we:
A
free 0
there

pense

have 1
but t,

to PE

soil be left untouched that contains the row of bushes. The width of
this band varies with the type of tillage used between the rows but it
is in this area that growers have had to rely principally on hand hoeing
for'weed removal.

Although it is the most effective means of keeping the row of bushes
free of weeds, the cost of this hand hoeing is $25 - $35 per acre and
‘there has been considerable interest among growers in reducing this 8X9
pense by some other means of weed removal.

Chemicals, fire, grazing, fallowing, and mulching are methods that
have been advocated to reduce the cost of weed removal in the row area
but these methods have not been very successful and growers still have

to rely on mechanical working for.most of their weeding.

Present Mechanical Weeding Methods
The grapg hoe. One mechanical weeding method used in the row area
consists of a Special blade that is set so that as it is pulled down the
row it scrapes the soil out of the row for one cultivation and pushes it
. back for the next. This implement, known as a grape hoe, is manipulated
'by a set of handles to move it out of the row, around the bush, and back

into the row again after the bush has been passed (fig 2). This works

Till - I-BUSH _
' ./ « 'I 'l/K’ / ' / - //// l,///’/ /
, " ‘ ’///// / / '// /
‘ ' /‘ ” ' IéD
~— e a
, \ \ \
\\ \‘N‘x \\\\ \\\\\\\\\\‘\ ‘ \ \ \\ \

w? ‘5
. 90a
43 \ \ ~ WORKEQ AREA

 

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Fig. 2. Diagram.of area worked by a grape hoe.

part of
present
still L
in a de.
£__x
the row
of Mich
driven
were us
blade.
and has
that e:

Shaft ;

part of the row area and cuts down on the required hand hoeing. At the
present time this hoe is the standby of the blueberry growers but it
still leaves a large area for hand hoeing and after prolonged use results
in a definite billing of the rows.

gaperimental Equipment. In order to provide a weeder especially for
the row area in blueberries, an experimental weeder was built by Hall
of Michigan State College. This machine (fig. 3) consisted of a power
driven weeding head (fig. 3,A) in the form of a cylinder with knives that
were used to work the soil rather than rely on the forward motion of a
blade. This head was driven by belts (fig. 3,B) from.the tractor p.t.o.
and was supported on a frame by means of a long horizontal shaft (fig. 3,0)
that extended out to the side of the tractor. The head rotated on this

shaft and was mounted so it could be moved in and out by means of cables

r.)
I

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iihmi

}
1

I
H-

l.

4.4

A ‘ '

 

Fig. 3. Experimental blueberry weeder. Weeding head
was moved in and out of the row by means of a

hand lever (not shown).

-"

 

and a l
Operat‘
the bu
row un‘

T
no for
the bu

and wh

at the

 

    

and a hand lever. As the tractor moved along between the rows, the
Operator manipulated the head so that it worked in the row area between
the bushes. When a bush was reached, the head was retracted out of the
row until the bush was passed, and then returned to the row area again.
This power driven head did a more vigorous job of weeding and since
no forward motion was necessary, the head could be maneuvered in close to
the bush. The row was worked from both Sides with an overlap in the center
and when the Operation was completed, only a small area remained unweeded

at the base of each bush (fig. 4).

- :. X :A’.f_\

,,-~- BUSH

  

 

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WORKED AREA

,- , > _ _ ‘_

Fig. 4. Diagram of the area worked by Hall's
experimental machine.
Need for a Power Operated Machine

The field test of Hall's machine proved that the basic principle
of weeding was sound but that the hand lever as a means of moving the
. head in and out of the row was not satisfactory as moving the head re-
quired too much effort fromthe operator. Hall listed this as the out-
standing limit of the weeder and recommended that a system of power
operation be incorporated.

Since the system for maneuvering the weeding head in the row area

was the limiting factor in the use of either of these weeders, this

proje

project was undertaken to work out a system of power operation for man-
ipulating the head of Hall's machine that would make this weeder more
satisfactory and could also serve as a basis for power operation of

other machines of this type.

flag
it was :1
the weed
and how
a tractc
each 2.1
this 81.:
and the
touli b1
Miami.-
°Perati.

G‘r
for the

PESSed

SELECTION OF A SYSTEM FOR TEST

Need for Automatic Control

The time factor. In the prelindnary consideration of power operation
it was necessary not only to consider a means of applying power to move
the weeding head but to also consider the means of controlling this power
and how power operation would fit into the use of the weeder. At 1 m.p.h.
a tractor moving down a row would move past a bush on four foot centers
each 2.7 seconds and move past the six inch stump in .3 second. Even at
this slow tractor speed, the weeder would move between bushes so fast,
and the time at the bush would be so short, that timing the Operation
would be a critical factor. Even with some form of power operation,
manipulation by the Operator with a hand control would make continuous
Operation difficult to achieve. .

Ground coverage. Not only would it be difficult, by hand control,
for the Operator to cope with the Speed at which the bushes would be
passed but it would be equally difficult, at this Speed, for him to
maneuver the weeding head for good ground coverage so that only a small
area would be left unweeded at the base of each bush. In order to avoid
, colliding with a bush, he would have to give it a wide berth and leave
a large area unweeded around the base. Only after he became quite Skill-
ful could he work in close and do the best possible job.

Since inability to Operate continuously down a row would reduce the

capacity of any machine using this control system, and the poor ground

 

the j
Sensc
accol
such

weed

coverage of a hand control would reduce it's effectiveness, it was decided
to by-pass hand control by the operator and try to avoid these limitations
with some type of an automatic control system. This automatic control
system would take over the job of moving the weeding head out of the row,
around the bush, and back into the row again. This would leave the

operator with only the job of guiding the tractor and watching the weeder.

Requirements of an Automatic Control System

Sensing. If the control of the weeding head was to be automatic,
the first requirement of the control system would be that it be able to
sense each bush as the weeder came to it. This sensing would have to be
accomplished regardless of the size, shape, or age of the bush and be of
such a nature that it could be translated into the proper movement of the
weeding head so as to move around each bush without damaging it.

Ground cqyerggg; In translating the sensing of a bush into head
movement the contrOl system would have to perform so as to give the best
possible ground coverage around the base of each bush. The control system.
would have to move the weeding head so as to be sure of clearing each
bush but, at the same time, move out of the row only as far as necessary.
The weeding head would have to be kept in the row as long as possible
and, during retraction, be kept close to the base Of the bush at all tines.

ReliabilityLI Both in sensing each bush and translating this sensing
into head movement the control system would have to possess a high degree
Of reliability. Irregular shaped bushes, trash, dirt, stones, and other
Obstacles would have to be handled without difficulty. Since any failure

to maneuver the head around a bush would result in serious damage to it,

m “0'.

chem

syste
bushe
to pe
Tris

and:

and
be u
Ther

aVaj

in normal operation the control system.would have to perform.with no
chance of malfunction.

Durability. Along with the operating requirements of the control
system would be the general requirement of durability. There are 1,089
bushes to an acre with four by ten spacing so the system.would be required
to perform 2,178 cycles for each acre in working both sides of the row.
This would require a very durable system to stand up under extensive use

and all components would have to be selected with this in mind.

The Basic Type of System

Izpe of power. In selecting the basic type of system to be built
and tested the type of power was selected on the basis of how it could
be used as the core for an intergrated automatic power control system.
There were three ways, mechanical, electrical, and hydraulic generally
available in which the power of the tractor could have been utilized.
A.lechanical system.would have required some sort of clutching arrangment
for control and, since these clutches would require a large force to
~Operate them, a mechanical system.did not lend itself to automatic control.
An electrical system, although easy to control in small amperages, would
have been difficult to control when supplying enough power to maneuver
the weeding head and would have been hard to adapt to the in and out type
I motion that was needed. A hydraulic system using a cylinder would produce
the type of motion that was needed and would be capable of all the power
that was necessary. It's valves offered a fair ease of control so a
hydraulic system.was selected as the most likely swans of utilizing the

power of the tractor in an automatic control system.

10

Sensing method. Since control of the power source would be by means
of a control valve, the method selected as the simplest means of sensing
each bush and translating this sensing into head movement was to mount the
valve on the weeding head so that the bush would operate it by making
contact with a bumper that would act as the valve handle. This bumper
would be mounted in front of the weeding head so that the forward motion
of the weeder would bring it into contact with each bush and move the
control valve so as to retract the head out of the row. This type of
sensing would be positive for large bushes and would be limited only by
the resistance of the shoots on small ones. Since blueberries have a
rather stiff shoot, this system would require only that the load required
to move the valve be kept low in order to make the system work on bushes

of almost any size.

Details of the System

The control circuit. After selecting the type of power and the
sensing method, the control circuit was selected to conform with the
pattern of Operation of the weeding head over the ground. Since the
weeder would Operate with the head fully extended into the row most of
the time (fig. 4), power to move the head would be needed only when it
was being retracted to maneuver around a bush. By using a spring to ex?
I tend the weeding head and hold it in this position, the hydraulic system
could be relieved of pressure while the head was extended which would
be the greater part of the cycle. This pressure relief would be necessary
in order to keep from generating too much heat within the oil by working

the pump against pressure and doing no external work. The hydraulic

ll

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CYZ/AQD£LR
SHUT‘QFF
VALVE
I
Fflyfidf’
l
. IWEIVWQCUPj
i . ’1
[1.5M

Fig. 5. Hydraulic circuit selected to control
the weeding head.

cylinder, then, would be used to move the weeding head in only one direc-
tion. It would overcome the spring in retracting the head and this spring
would supply the energy to extend the head back into the row again.

This arrangment of using the hydraulic cylinder only for retracting
the weeding head permitted the use of a single acting cylinder and a
simple two-way circuit (fig. 5) was selected to control it. This circuit
consisted of a pump and a shut-off valve, acting as a control valve, with
the cylinder connected by a tee between them, With the bumper free and
the valve open, oil from the pump would flow through the valve and back
to the tank. As soon as the bumper contacted a bush and the head would
have to be retracted, the bumper would close the valve, stOp the flow of
_ oil to the tank, force the oil to back up into the cylinder, and retract

the head. When the bumper moved past the bush, it would again be free,

12

 

 

 
  

PATH
A.___.C” 055 FORWARD
W yngc/Zy

M ~ BUSH
VELOC/Tr

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9

    

fir RE TRACT/0N

 

 

CR__/______T/CAL SECTION
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Fig. 6. Diagram showing how the path of the weeding
head across the ground would determine the bumper's
location and shape.
the valve would open, the oil would be released from the cylinder, and
the spring would extend the weeding head back into the row again.

Shape of the bumper. Since the movement of the weeding head would
be controlled directly by the bumper, the type of movement necessary to
.maneuver the head arounda bush determined it's location and shape. When
the weeding head was being retracted out of the row, it's path across the
ground would be the resultant of the forward motion of the tractor and the
lateral motion of retraction (fig. 6). Any point on the weeding head
"would follow this path, so if the front corner of the head was to clear
the bush, retraction had to be started soon enough so that it's path would
take it out of the row before it came abreast of the stump. This meant
that the bumper would have to be located.at an angle and in front of a

line drawn from.this front corner along the path of motion. Regardless

13

of where the bush contacted the bumper, then, retraction would start soon
enough so the front corner would clear the bush.

After retracting the head so the front corner would clear, it would
be necessary to hold the head in the retracted position until the rear
corner was past the bush. This meant that the bumper would have to extend
back to the rear corner and end somewhere in back of this point. The
bumper, then, would consist of an angular section in front of the weeding
head for retraction and a straight section parallel to the row across
the end of the weeding head to hold the head in the retracted position
until it was completely past the bush.

Qperation of the system. In operation, a weeder with this control
system would move down the row with the end of the head extended just
past the center line. With the bumper free, oil would flow fromrthe pump
through the control valve, and back to the tank. The extension spring
would hold the head in place. When the bumper came in contact with a
bush, it would close the valve, direct oil into the cylinder (fig. 5) and
retract the head. The head would continue to retract as long as the bumper
kept the valve closed. Since the bumper would be attached to the head,
however, retracting the head would tend to erase the bumper's action on
the valve by moving the head away from the bush. When the head had moved
away far enough to Open the valve, retraction would stap. This would
keep the bumper in contact with the bush and the weeding head would follow
it around a bush.

Since this circuit had only two positions for the control valve, the
head would have to alternate between retraction with the valve closed and

extension with the valve open. This would mean that the head would hunt

1A

between these two positions while following the bumper around a bush and
would come to equilibrum only when the bumper had moved past the bush and
the head moved to the fully extended position. This hunt would be most
noticeable when the bush was in contact with the straight section of the
bumper across the end of the head. During retraction, if ideal conditions
prevailed such that the bumper followed the exact line of travel and there
were point contact with the bush, the bumper would hold the valve closed
during the full time the bush was in contact with the retraction section.
After passing the corner, however, the head would move away fromLthe

bush until the bumper no longer would hold the valve closed. The head
would then start extending until it would move the bumper into the bush
and close the valve again. The system would cycle between these two
conditions until the bumper would move past the bush and the head could
extend the full distance back into the row. Since ideal conditions could
not be obtained on the retraction section, the head would follow this
pattern of cycling throughout the entire length of the bumper.

Although this cycling, or hunt, would not be desirable, it was an
outgrowth of the simple circuit and.the simple two position control valve.
fie eliminate it would have required a.more complex circuit and since there

was no way of knowing actually how detrimental this cycling would be with-
.cnfit test, it was decided to use this circuit and add refinements only if

field test indicated they were needed.

THE FIRST EXPERIMENTAL MACHINE

Preliminary Considerations

In order to field test the proposed automatic control system, it
was decided to modify Hall’s machine to incorporate the necessary elements
for adding the automatic control. This modification would be simplified
by the fact that the John Deere MT tractor with which the weeder was used
was well adapted to the proposed.type of control system. The hydraulic
pump on the tractor had a capacity of 7.0 g.p.m. at 1650 r.p.m. and was
driven directly from the engine. The ground speed in low gear was 1.75
n.p.h. at 1650 r.p.m. which was lower than most tractors. This combi-
nation of a high capacity hydraulic pump and a low ground speed was
favorable for working out the ratio of forward motion to lateral motion
without resorting to unusual features to obtain the necessary retraction
speed. Having the pump driven directly from the engine would.keep the
power available regardless of ground travel and since there would be no
control except by means of the bumper, this arrangment was considered

mandatory.

Design of the Control Elements
Mr shape and pivot point. Since the bumper had to match the
forward and lateral movement of the weeding head and would be correct
for only one set of conditions, it's shape was worked out on the basis
of operation in low gear and the use of a 1-3/1. inch diameter hydraulic

cylinder. At 900 r.p.m. the hydraulic pump would move this ram at the

16

rate of 6.2 inches per second while the tractor would move forward at the
rate of 18.3 inches per second. The use of a three to one lever arm
between the hydraulic cylinder and the weeding head would bring this ratio
into a more favorable condition so that the head would.move at the rate of
18.6 inches per second. Since the full stroke of the weeding head was

12 inches, this ratio would correspond to 12 inches of forward travel to
the 12 inches of lateral travel for full movement.

It was decided to try one bumper with exactly this ratio on the
retraction section and one bumper with the inner end moved forward to
correspond to a 15 to 12 ratio. This second bumper would start retraction
sooner all along it's length and would provide a factor of safety pro.
portional to the distance the head had to retract.

The pivot point for the bumper was set at 9 inches in from.the front
corner of the head and 6 inches in front. Assuming that the head would
Operate 3 inches beyond the center line of the row, this would provide a
minimum of a 6 inch lever arm the entire time the bush was in contact
with the bumper.

Control valygg. Since the force required to operate it had to be
kept small, the control valve was designed especially for this control
circuit. This valve consisted of a two land spool operating in a bore
lith the inlet and outlet ports entering the bore between the two lands
(fig. 7). With the valve Open, the oil would enter through one port and
leave from the other. With this arrangment, the area exposed to the oil
would be the same on both lands and the force exerted by the oil would
be the same in both directions. In closing the valve, the large land on

the spool would move across the outlet opening and close it off but the

17

 

 

 

 

 

 

 

 

 

 

 

 

iUMf rA/wr l
i J \ l
l
\
- L H.—
- _
t: a 1r " ~ ;

Fig. 7. Diagram showing pressure balance on
the control valve.
pressure load on the spool would still remain balanced on the two lands.

This valve would remain balanced at all times and could be moved with a

small force regardless of any change in pressure that might occur in the
hydraulic circuit.

Incorporation of the Control Elements
Bumper and valve. The most significant change made in Hall's machine
(fig. 8) in order to incorporate the control elements was the addition

of a hood (fig. 8,A) over the weeding head. This hood was necessary to
provide a mounting place for the bumper that would move with the weeding
head and it also provided a shield for the weeding knives.

The bumper pivot (fig. 8,8) consisted of a triangular plate with
the bumper (fig. 8,0) attached to the forward point. A link to the valve
(fig. 8,D) was attached to one rear point and a spring to hold the bumper
out and the valve Open (fig. 8,E) was attached to the other rear point.

This external Spring was the only means of holding the valve open when the

18

 

0., 0.!
.4:

q,

~
I

a
' P
§

0 A

 

-‘I
~, .7 . ‘
e ' . '
V

e,

b

. ‘A ‘

Fig. 8. Hall's weeder with the automatic control
elements incorporated.
bumper was free and was made adjustable to compensate for the inertia of
the bumper and variances in the stiffness of the bush shoots. The link
to the valve was positioned so there would be 1 inch between control
positions and the straight section of the bumper would be parallel to
the row just before the valve would close.'

QzlinderI return gprigg, and lever arm. The hydraulic cylinder
(fig. 8,F) was attached to the base frame and extended out to the lever

 

arm.(fig. 8,G). The extension spring (fig. 8,H) was.located directly
above it. The pivot point for the lever arm was also attached to the
main frame and the lever arm and links were proportioned so that when
the end of the head was 3 inches past the center line of the row the

tractor would be centered between the rows.

19

Circuit connectigggg The tractor hydraulic system was tapped at
the control valve under the seat with the pressure line running to a
tee (fig. 8,J) at the base of the cylinder. The circuit was completed
by running a line to the valve (fig. 8,K) and back to the filler con-

nection on the reservoir.

Preliminary Test
After modifying the weeder, it was given a preliminary test by
setting up stakes and driving the weeder past them.the same as it would
be driven past a blueberry bush. This preliminary test was used only
to verify that the automatic control system was functioning as planned

and was capable of retracting the head and taking it around an object.

Field Test

Conditions of the test. The machine was given a Field test Oct. 6,
1951 at the Boo-Hoot Blueberry Farm, Holland, Michigan. The weather was
clear and the soil damp from a recent rain. The bushes were about ten
years old and were set out on a four by ten spacing. The rows were
hilled from the use of a disc and grape hoe. There were few weeds.

Performance of the weeder. The field operation of the control system
paralleled very closely the projected operation set forth in planning the
system. The tractor was driven between the rows so that the end of the
weeding head was about three inches past the center line of the row (fig. 9).
The bumper retracted the head at each bush (fig. 10) and after it was
passed, the spring extended it back into the row again (fig. 11). After
'working both sides (fig. 12), the row area was almost completely worked
(fig. 13) with all maneuvering of the head being done by the automatic

control system.

 

Fig. 9. Weeder positioned between the rows.

 

Fig. 10. Path of retraction on the approach side
of a bush.

 

Fig. 11. Path of extension on the back side
of a bush.

§

9

~.‘~-g=u,i.
.‘ .,.' s. _,‘9-‘«-':-..

8"- \

Fig. 12. ‘Weeder working the second side of the
row with an overlap at the center.

 

21

 

 

Fig. 13. Row area after working both sides.

With the weeder operating in the soil, the head would make from.two
to four reversals due to the two position circuit before moving completely
past a bush.

The chief difficulty encountered during field operation was keeping
the weeding head operating at the proper depth. Since the depth regulating
shoe and the head were widely separated (fig. 9), ground irregularities
would.make the head lift out of the ground or bury itself until the bush
could not move the bumper. Only when the contour of the ground was quite
uniform.could the machine be operated for any distance without adjusting
the depth shoe.

In order to evaluate the shape requirements of the bumper both bumpers
were tested along the same row. The bumper shaped exactly to the angle of

the path of motion did not retract the head soon enough to clear the bush

23

without forcing it's way past. The other bumper was more satisfactory,
however, and only occasionally was there any evidence of forcing while

maneuvering around a bush.

Evaluation of the machine

The control system. The performance of the control system.in itself
was generally satisfactory since it was able to maneuver the head around
each bush with no assistance from the operator. The bumper proved to be
a satisfactory sensing method, the control circuit functioned as planned,
and the two worked well together.

The inherent instability of the system, although apparently not
detrimental to the Operation, was objectionable to watch. The hunt
while maneuvering around a bush seemed to make the machine erratic and
_was very noticable.

Since the head would follow the bumper around a bush, the 15 to 12
ratio bumper represented too low a retraction speed in relation to the
forward speed and left a long point of ground unweeded on the approach
side of each bush.

The small diameter on the bumper had a tendency to bark the plants
although this did not occur often.

The complete weeder. The performance of the weeder as a complete
automatic controlled unit was not as satisfactory as the performance of
the control system alone. The unit could not be considered reliable
since ground irregularities might bury the head and jam up the control
system.at any time. Constant adjustment of the depth shoe was necessary

and if the rows were hilled excessively the weeder could not be used

at all.

The 12 inch stroke of the weeding head was not adequate for automatic
control. If a bush was out of line the head could not retract far enough

to clear and this could not be detected until a collision actually occurred.

THE SECOND EXPERIMENTAL MACHINE

Preliminary Considerations

The successful working of the control system.on the first machine
indicated that automatic control of the weeding head was feasible so it
was decided to continue working with this type of control system.and
to carry the work into a second machine. Since the first experimental
machine using Hall's weeder could be used only when conditions were ideal
for depth regulation, it was also decided to build a new weeder with
which to carry on the control system testing. This new weeder would have
the depth shoe closer to the weeding head, have a greater 1ateral.movement,
and have it's own hydraulic system devoted exclusively to the control of
the weeding head.

There were two phases of the control systemrthat needed improvement.
Modifications in the circuit were needed to eliminate the hunt while the
head was being maneuvered around a bush and more retraction speed was

needed in order to reduce the long point on the approach side of the bush.

The New weeder
Frame and drizgg; The frame of the new weeder (fig. 14) was basically
a vertically pinned four bar linkage that was used to support the weeding
head and.still allow it to move laterally in and out of the row. The shaft
of the weeding head (fig. lL,A) served as one bar of the linkage with two
curved arms (fig. 14,B) running forward to an upper frame member (fig. 14,0)

that formed the fourth bar. These arms were connected to the upper frame

-25

 

Fig. 11.. New weeder used for testing the automatic
control system. Top - Front quarter view.
Bottom - Rear quarter view.

27

member by means of yokes and vertical pins (fig. lh,D) so that the head
could swing in and out but could not move vertically. This upper frame
member, then, would support the weeding head and was attached at the
inner end to a central frame section (fig. 1h,E) that was rigidly attached
to the tractor. This upper frame member was attached to the center section
by means Of a horizontal pivot (fig. lh,F) so that the outer end could
move up or down but could not swing back. Since the weeding head and
this upper frame member would move as a unit, the depth shoe (fig. 1A,G)
was positioned in front of the weeding head and was attached.to the outer
end of this upper frame member. As the shoe moved the outer end of the
frame up or down, the weeding head would.move up or down with it. This
would allow the shoe to regulate depth immediately in front of where the
head was working and still allow it to move freely in and out of the row.

An arm (fig. 14,H) was attached to this upper frame member with a
cable running to the tractor lift to swing the head up for transport.

The central frame section served as a mount for the belt drive to
the weeding head (fig. 14,J). This belt drive originated at the front
Of the engine, ran over to the frame pivot, along the outer curved arm,
and down to the weeding head.

The weegigg head. The weeding head (fig. 15) Of the new machine
remained the same with the exception of the front edge of the hood which
was raised to provide a larger Opening.

Control elements. The hydraulic pump (fig. 14,K) was mounted on the
central frame seetion and was driven from the front of the engine with
the same drive that was used for the weeding head. This central frame

section was hollow and served as the oil reservoir.

28

   

Fig. 15. weeding head of the new machine.

\.

’

e

3

 

Fig. 16. Upper section of the frame showing
the hydraulic cylinder and the springs
used to extend the head.

29

The control valve (fig. 15,A) was moved from.it's position on the
weeding head to a position between the two curved arms but it was still
Operated by a link (fig. 15,8) directly from.the bumper.

One end of the hydraulic cylinder (fig. 16,A) was attached to the
outer end of the upper frame member and the other end was attached to
the inner one Of the two curved head support arms. The extension springs
(fig. 16,B) were similarly located but were attached to the bottom.of the
upper frame member to make room for the head drive belts. Attaching the
hydraulic cylinder to the inner support arm allowed the outer arm to
carry most of the weight of the head and the inner arm.to carry the load

of retracting the head out of the row.

The New Control System

The control circuit. The new control circuit (fig. 17) was the same
basic type that was used on the first machine in that control action
would be initiated by shutting off the flow to the tank and forcing the
Oil to back up into the cylinder. In this circuit, however, the Oil
would enter the cylinder over a check valve so it could not be forced out
as soon as the pump line was Opened to tank again. This would allow the
head to be stopped and held in place rather than reversing it's motion
when the bumper moved away from a bush. When the head was to be extended,
Oil would be released through a separate line to the control valve that
could be controlled separately from the tank shut-off.

The control valve contained the regular shut-off for the pump-to-
tank line and an additional shut-Off for the cylinder-return line. Both

Of these shut-offs were balanced and were arranged so that as the valve

CVA INDéR

—_._-

 

 

 

 

 

 

 

 

CHECK
VA L V5

 

a

 

flMfl~h°

 

 

 

 

 

 

 

Fig. 17. New circuit incorporating a hold position
used to control the weeding head.
was moved from.the Open position the cylinder return shut-off would occur
first. As the valve spool continued to move, this line would remain
shut off and the tank shut-off would occur after the spool had moved
farther on it's travel.

This would give the control valve three positions. ‘With both sections
of the valve Open and the bumper free, the head would be allowed to extend
it's full length. With both sections of the valve shut off, oil would be
forced into the cylinder and would not be able to escape. This would put
the control valve in the retract position. Between these two positions
would be the third position with the pump line Open but the cylinder
return line closed. This would provide a hold position since no Oil would

be forced into the cylinder but none could escape.
In operation, with the bumper free and the valve Open, this circuit
would allow oil to flow from.the pump, through the control valve, and back

 

31

to the tank with the spring holding the head in the extended position.
When the bumper contacted a bush it would move the control valve through
the hold position and into the retract position. As the head retracted
it would carry the bumper away from the bush and move the control valve
back to the hold position. This would stOp the head movement by opening
the pump line to tank but the head would not start to extend because the
cylinder return line would still be blocked. If further retraction were
needed, the bumper would move the valve into the retract position again
and back into the hold position when the head tended to move away from
the bush.

As soon as the bumper would move completely past the bush it would
swing free and move the control valve into the extend position allowing
the oil to escape by the cylinder return line.

. This circuit would allow the head to remain stationary when the
straight section of the bumper was in contact with the bush instead of
cycling between the retract and extend conditions.

Shape Of the bumper. The same l-B/L inch diameter hydraulic cylinder
was used on the new machine and was attached to the head support arms
(fig. l6,A) so as to produce a 6:1 ratio of movement between the cylinder
and the weeding head. With a ground speed of 1.66 m.p.h. and a pump
capacity of 6.0 g.p.m. at 900 r.p.m. this arrangement produced a ratio of
10 inches of forward travel for the 18 inches of lateral travel for the
full stroke of the weeding head. By keeping the same 3 inch advance on
the inner end, the bumper was shaped to correspond to a 13 to 18 ratio.

The link was attached to the bumper support plate so there would be

1 inch between control positions and the bumper was set so the straight

32

section would be parallel to the row just before the valve would enter
the retract position.
The new bumper had a diameter of 1 inch in place of the l/2 inch

diameter one used on the first machine.

Preliminary Test on Stakes

Qifficulties encountered. After completing the machine, it was
given it's first trial by using stakes in the same manner as the first
machine. The first indication of this test was that the stability that
was supposed to be gained by the circuit change was not present and the
weeding head would hunt for position the same as the first machine.
Instead of holding when it moved away from the stake, the head would
reverse, move back into the stake, and cycle between the retract and
extend conditions. After three or four cycles the head would settle down
and hold but in regular Operation the weeding head would be past the stake
before this would occur.

Close observation while the control system.was working indicated
that the head was moving far enough after the flow of Oil to the cylinder
was stopped to carry the bumper through the hold position and into the
extend position.

‘Egploratory tests. In order to have a basis for evaluating cor-
rective measuries for this overtravel condition a marker was attached
to the outer end of the weeding head (fig. 18) and the machine was driven
past the stakes at three selected speeds. Overtravel and hunting occurred
in all cases. It was present when the tractor was Operated a A00 engine

r.p.m. (.7h m.p.h.) but it was not pronounced (fig. 19,top). At 600

 

Fig. 18. Weeding head showing marker and string
attached to the bumper.

engine r.p.m. (1.1] m.p.h.) it became quite prominent (fig. l9,cen.)
and at 900 engine r.p.m. (1.66 m.p.h.) the head was completely unstable
(fig. 19, bot.).

A string was tied to the bumper so the valve could be held in the
retract position and the weeder was driven over open ground at the same
three speeds to get a trace of the head over it's full retraction stroke.
Instead of moving across the ground in a straight line, there was a
definite bend in the trace in all three cases (fig. 20). This bend
occurred close to the outer end of the stroke at hOO r.p.m. (fig. 20,top),
farther in at 600 r.p.m. (fig. 20,cen.), and still farther in at 900
r.p.m. (fig. 20,bot.).

The shape of this trace indicated that the first energy supplied

to the cylinder was being stored somewhere in the frame due to deflections

k.$'do .0

t; sin. 8‘.
*3

tax :16 o:
I . m \

 

“6

mm

mm:
ammm.
war.
mama
t..
New.
flaw
s mm
“mm.“
mmam
“mm.
s.ma
uom
mmc

Fig. 19.

Fig. 20.
during a full retraction stroke. Tap - 1.00 r.p.m.
Center - 600 r.p.m. Bottom - 900 r.p.m.

 

Trace made by marker on the weeding head

35

in the arms, hydraulic lines, or some other place and.was being released
during the first part of the stroke so as to increase the lateral speed
during this period. This condition corresponded to having a half wave
of the natural frequency of vibration of the head and frame superimposed
on the steady state motion. Since the absolute speed of retraction was
high (23i/sec.) even at 400 r.p.m., it was quite possible to be in the
range of the natural frequency of the head support arms.

This meant that the release of this stored energy from.the frame
was contributing to the overtravel as well as the kinetic energy of the
head.that would always be present and tending to carry the head past the
point where the retracting force was shut off.

Corrective meaggges. One condition noted in those early test was
that the depth shoe would lift off the ground when the head started to
‘move and would drOp back as soon as the head was under motion. Since
the pivot for the head support linkage was above the head the inertia of
starting would move the head outward and upward. The head.would move
back downward and inward just about the same time that it would be re-
quired to step moving away from the stake. This condition was a possible
source of energy storage so the weight on the depth shoe was increased
from 25 pounds to 100 pounds and the runs on the stakes repeated.

Some improvement was shown by this move (fig. 21) but it was slight
and under these conditions the depth shoe would.bury itself in a very
short distance.

Since the lifting of the depth shoe was not contributing appreciably
to the overtravel of the head, other corrective measures were taken.

Provision was made to increase the spread between control positions at the

37

 

600 r.p.m.

Center -

pone

Trace made by marker on the weeding head
Battom "" 900 r.p.m.

with increased weight on the depth shoe.
Tap - 1.00 r

Fig. 21.

bumper from.1 to 2 inches to allow more distance for the springs to absorb
the kinetic energy of the head.without affecting the control valve and

a stronger set of extension springs was made up (fig. 16,B) in order to
absorb the kinetic energy sooner. These new springs had a load corre-
sponding to 60 pounds at the weeding head.when it was fully extended and

a load of 240 pounds when it was fully retracted. The original springs
were the same as the spring on the first machine and had a load corre-
spending to 20 pounds at the weeding head.when it was extended and 80
pounds when it was retracted. These new springs were capable of absorbing
all the kinetic energy of the head within the 2 inch spacing of the control
positions anywhere during the stroke and at any speed up to 900 r.p.m.

The control valve was modified to incorporate tspered.metering slots
on the shut~off edges of the spool lands instead of the sharp edge that
was first used. Instead-of shutting off instantly, these slots would allow
a gradual shut off of the flow and.a gradual build up of pressure so as to
produce a more gradual acceleration of the head. This would allow more
of the first energy supplied by the cylinder to go into head.movement
and less into storage within the frame. These slots were arranged so they
would become effective after the first l/h of the travel between positions,
and were of such a size that at 900 r.p.m. the pressure drop through them
would overcome the lowest load of the extension springs as soon as the
slots became effective. One spool was made up with A metering slots to
correspond to the light return springs and one spool was made up with
2.metering slots to correspond.to the heavy springs.

The weeder was driven past the stakes again using the heavy springs,

the two groove spool, and the extended bumper positions (fig. 22). At

l‘f‘h‘i‘o l .\u\/
9‘30"?” K (I

”f.“ ":1.
was" m

"l ry.\',l

 

Fig. 22. Trace made by marker on the weeding head
with increased spread on the control positions,
metering slots in the valve spool, and increased
load in the extension springs. Tap - 1.00 r.p.m.
Center - 600 r.p.m. Bottom - 900 r.p.m.

39

LO

A00 r.p.m. the control action was smooth with no sign of overtravel

(fig. 22,top). At 600 r.p.m. the control action was still (fig. 22,cen.)
smooth. At 900 r.p.m. there was some overtravel (fig. 22, hot.) on the
initial retraction but it was not far enough to move through the hold

position and the head did not cycle.

First Field.Test

Conditions of the test. The weeder was given it's first field test
on Aug. 23, 1952 at the Triangle Blueberry Farm, South Haven, Michigan.
The weather was clear and the soil was dry. The rows were moderately
hilled and were quite weedy.

Performance of the weeder. The weeder was first operated with the
light springs, the four groove spool, and the 1 inch spacing of the
control positions. Operation with the weeder working in the soil provid-
ed a damping effect on the system.and the cycling was not as severe as
it was in the test on the stakes. The spacing of the control positions
was increased to 2 inches and a noticable decrease in the cycling resulted.
If the tractor speed.was kept below 600 r.p.m. the control system would
.Iove the head around the bushes about half the time without overtraveling
enough to reverse the head.

The presence of weeds in the row during these tests gave a better
indication of the ground coverage characteristics of this weeder with the
new control circuit. The tractor was driven between the rows with the
depth shoe traveling Just beside the stumps (fig. 23). Before any weeding

was done the row was well filled with weeds (fig. 2A). Going one way
(fig. 25) cleaned out one side and the reverse pass (fig. 26) completely

cleaned out the row area.

 

Fig. 23. The new weeder being driven between
rows of bushes.

 

Fig. 21.. Row area before any weeding was done.

‘1 . ‘flgi'...

 

 

Fig. 25. Bow area after being weeded from one side.

 

Fig. %. Bow area after being fully weeded.

cyc
row
and
pro
ext
Nov:
than

A3

 

Fig. 2?. Path of the weeding head on the approach
side of a bush showing the improved ground
coverage.

With the increased retraction speed the head would move in much
closer on the approach side and leave a smaller area unweeded at the
base of the bush (fig. 27).

Not only were the light springs inadequate to keep the head from
cycling but they tended to be slow in extending the head back into the
row after the bush had been passed. Substitution of the heavy springs
and the two groove spool completely stepped the cycling of the head but
provided a more severe extension action at the same time. This severe
extension would often push the head into the bush as the end of the bumper
moved past the outermost shoots. This condition was caused by the fact
that as the bumper left the outermost shoots it would move forward as well

as outward. This would take the bumper away from the rear corner of the

hood and leave this area without a bumper to hold the head away from the
bush. As long as the extension speed was moderate or slow the head would
pass the bush without hitting it but the heavy springs would move the head

too fast to clear the bush in all cases.

Second Test on Stakes

Since the first field test indicated that one set of extension
springs was too light for proper operation of the weeding head and the
other set was too heavy, an intermediate set was made up that had a load
of 30 pounds with the head extended and a load of 120 pounds with the
head retracted. A new valve spool was also made up with the metering
slots proportioned for these springs and a new bumper was made up that
had a section turned in toward the tractor at the rear corner of the hood
to extend the point at which the bumper would swing free.

This arrangement was checked on the stakes in order to compare it to
the other arrangements (fig. 28). At 400 r.p.m. (fig. 28,top) and 600,
r.p.m. (fig. 28,cen.) the control system worked as smoothly as it had
with the heavy springs. At 900 r.p.m. (fig. 28,bot.), however, the

system was not as stable and there was some cycling.

Second Field Test
Conditions of the test. The weeder was field tested again at the
Triangle Blueberry Farm, Aug. 30, 1952 one week after the first test.
The field conditions were the same as in the previous test.
Performance of the weeps}; The weeder was first tested with the
intermediate springs and valve and the extended bumper (fig. 29). This

arrangement provided almost perfect control of the weeding head as long

 

 

28. Trace made by the marker on the weeding head
with intermediate springs and metering slots.

Top - 1.00 r.p.m. Center - 600 r.p.m.

Bottom - 900 r.p.m.

1.5

 

Fig. 29. Weeder being Operated with the extended
bumper.

as the tractor was operated below 600 r.p.m. The tractor could not be
operated above this speed, however, without the control system becoming
unstable and cycling starting to occur.

The heavy springs were tested with the extended bumper but it did

not completely keep the head from being pushed into the bushes.

Evaluation of the Machine
Control system. After the proper corrective measures had been taken,
observations indicated that the new control system with the hold position
provided much improved control. The higher retraction speed produced
better ground coverage and the control system changes were satisfactory

within the limited operating range of idle to 600 r.p.m.

1+7

The larger diameter bumper did not bark the bushes even though the
hold out spring had to be stronger because of the higher weight and
inertia.

The cgglete weeder. The weeder as a unit could only be considered
partially successful since there was a definite limit on the speed at
which it could be operated. The performance of the control system was
more responsive to speed changes than to changes in the control elements
which indicated that the source of the overtravel was tied very closely
to the weight of the weeding head and the natural frequency of the head
and frame as a wit.

The depth regulation system was very effective and no trouble could
be ascribed to this source.

The 18 inch total movement of the head proved to be adequate
especially since the depth shoe served as an indicator for keeping the

weeder properly oriented between the rows.

SUMMARY

Conclusions
Although two different weeders were used for testing them, the two
control systems were of the same basis type and evaluation of their

performance in the field leads to the following conclusions:

1. An automatic control system.can be made to satisfactorily maneuver

the weeding head around bushes without assistance from the operator.

2. Either of the control systems developed in this investigation is
adequate to maneuver the weeding head around bushes but the control
system.incorporating the hold position, although more complex, is more
satisfactory and should be used unless the application will not warrant

the additional eXpense.

3. In order to have satisfactory ground coverage, the retraction speed
of the weeding head should be equal to or greater than the forward speed

of the tractor.

A. Accurate depth control is necessary to keep the bumper out of the

dirt and the system functioning properly.

5. The sensing bumper must be provided with means for retracting the
head sooner than theoretically necessary in order to compensate for

lag in the control system.

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6. When using the control system incorporating the hold position, the
inertia of the weeding head and the flexability of the frame both contribute
to overtravel and.unstability in the system.and must be considered when

planning the application and setting limits for it's use.

Recommendations for Further Study

Since there was a limit to the speed at which the second control
system would give smooth control of the weeding head, future study should
be directed toward the requirements for raising this limit so that a
weeder using this system.could be operated at a higher speed. The weight
of the weeding head, the stiffness of the frame, and the damping effects
of the soil are factors that should be evaluated for their effect on
the control systemfls stability.
A control system.based on a double acting cylinder could provide a
more positive control of the hydraulic cylinder and should be investigated.
Different types of weeding heads and their effect on the control
system.is another area where further study should be made.

Since it did not always function properly on irregular shaped bushes,
future study is needed on the requirements of the bumper as a sensing
element. Greater length, more surface area, and other systems of mounting

are possible approaches.

BIBLIOGRAPHY

Johnston, 8. Essentials of Blueberry Culture. Michigan State College
Agricultural Experiment Station, East Lansing, Cir. Bull. 188,
2 nd. rev, 1951.

Hall, C. W. A Tractor Cultivator for Blueberries. Unpublished report,
Michigan State College, East Lansing, 1950, 29 numb. leaves.

Marks, L. 8. Mechanical Engineer's Handbook, 1. th Ed., Mc Grew-Hill
Book Co., New York, 1941.

Tractor Field Book, Farm Implement News, Chicago, 1951.

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