Note: Descriptions are shown in the official language in which they were submitted.
113530~
Summary of the Invention
This invention relates to agricultural irri-
gation systems. While such systems are well known, practical
utilization of them in the past has been limited on the
whole to the so-called center pivot units. Such units
have a sprinkling pipe mounted on mobile towers which travel
in circles about a pivot point where the water is also
supplied. Motion is obtained by independently driving
the outermost tower and then moving inside towers as needed
to maintain a generally straight-line relationship among
the pipe segments. It can be seen then that a center pivot
unit need only propagate alignment signals from the outside
in. An inherent disadvantage of the center pivot system
is that most agricultural fields are rectangular or square
and the center pivot system does not irrigate the corners
of such a field. The missed area amounts to approximately
twenty-two percent of the area of a square circumscribed
about the circle irrigated by a center pivot system.
An irrigation unit which moves in a straight
line across a field, lateral to the pipe, obviates this
problem of missing portions of the field. However, such
linear-motion systems have been difficult to control because
the entire system moves and there is no reference point
or fixed end for maintaining proper position of the system.
More particularly the one-way alignment signal propagation
used in center pivot units is inadequate for controlling
a laterally moving system.
Therefore, a primary object of this invention
is a linear motion irrigation system which is fully controllable
to assure that the unit will stay on its path.
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" 113530~
:
Another object is a movable irrigation system
that gives 100 percent coverage of the field.
Another object is a system of the above
type with an improved application rate.
Another object is a system of the above
type that has uniformity of its application rate.
Another object is an irrigation system that
has reduced friction losses.
Another object is a system with a direct
linear relationship of its application rate.
Another object is a system of the above
type which has a uniform application of herbicides and
insecticides.
Another object is a unit of the above type
in which the evaporation rate will be improved.
Another object is a unit of the above type
which is less complex than center pivot units which have
an arrangement for watering the corners.
Another object is a unit of the above type
which is more compatible with harvesting equipment in that
the ruts created are parallel and not circular and harvesting
equipment can move parallel to the ruts.
Another object is a unit of the above type
which has less hydraulic loss.
Another object is a movable irrigation system
which is much more compatible with other farming practices.
Another object is a unit of the above type
which is much more efficient in labor required, water used,
and fuel consumed.
1135301
Another object is a two-way signal propagation
; means which allows the unit to be steered in either direction
should it deviate from its desired path.
Another object is a linear motion irrigation
unit in which most of the control hardware may be the same
as that used in center pivot systems.
Another object is a steering system for
a linear motion irrigation unit which does not require
speed controlling means for the towers other than
the independently driven towers.
Another object is a steering control system
which senses the return to the normal path and disengages
the path-correcting signal so as to prevent overcorrection.
Another object is a linear-motion irrigation
unit which carries a self-contained power unit including
an engine-generator set and a water pump.
Accordingly, the invention is directed to
a mobile irrigation unit of the type having a pipe string
supplied with water under pressure with sprinkler units
thereon for irrigating an agricultural field. The pipe
is supported at intervals by wheeled towers which have
motors for propelling the towers across the area to be
irrigated in a generally straight line, perpendicular to
the pipe string. Means are provided for detecting mis-
alignment between segments in the pipe string and for
activating the tower motors in response to such misalignment.
The improved method of steering the irrigation unit comprises
the steps of:
Il) independently driving the towers at
the two ends of the pipe string,
~ 2) activating inboard tower motors in
response to misalignment created by motion of adjacent
towers,
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113530~
(3) sensing the overall location of the unit
with reference to a designated path,
(4) generating a correction signal when the
unit deviates from the path,
(S) utilizing the correction signal to stop
or slow down the independent motion at the end tower, in
which direction a path correction is required. In this
operational mode the unit motion is primarily governed
by the advancement of the tower at the opposite end which
causes the entire unit to pivot about a point at or beyond
the other end. This brings the unit back toward the desired
path. The correction signal is released as the unit begins
to return to the desired path so as to avoid overcorrection.
Brief Description of the Drawinqs
Figure 1 is a schematic plan view of a linear
motion irrigation system in accordance with the present
invention;
Figure 2 is a schematic side view of the irrigation
unit;
Figure 3 is a schematic plan view of the irrigation
unit and its tower-motion alignment signal propagation
means;
Figure 4 is a side view of the path sensor;
Figure 5 and 6 are perspectives of portions of
the path sensor, partially exploded;
Figures 7 and 8 are perspective views of the
motor-activating means and the tower-motion alignment signal
propagatlon means;
Figures 9 and 10 are perspective views of another
embodiment of the motor-activating means and tower-motion
signal propagation means;
` ` ~13S3()1
Figure 11 is a perspective view of the power
unit sling support;
Figure 12 is a perspective of a variant
form of power unit; and
Figure 13 is a schematic similar to Figure 3.
Description of the Preferred Embodiment
Figure 1 is a schematic of a mobile agricultural
irrigation system 10. The system may be considered to
be made up of a series of joined pipe segments or spans
12 supported by wheeled towers 14 and a truss structure
16. The pipe segments 12 are jointed by flexible couplings
at joints 18. The system is designed to move laterally
across a field, powered by motors either electric, hydraulic,
or otherwise, on the individual towers, following a path
defined by a path-defining means or reference line or guidance
reference 20, which may typically be a wire supported on
or near the ground by stakes but, in certain situations
or installations, could be a pipe or track or signalling
system built on or in the ground, possibly below the surface.
A power unit 22 in the nature of a power
pack is suspended from the pipe string 12, as disclosed
hereinafter. This unit may include an engine for driving
one or more main water pumps. In the preferred embodiment,
the engine also drives a generator which provides electric
power for the tower motors, but it might be the generator
for a hydraulic system. The details of the power pack
or power unit and its support will be explained hereinafter.
Figure 2 shows the irrigation system as
it might be arrayed or disposed across a field including
a guide arrangement or sensing unit 24 whose function will
be described in detail below. A water supply unit, which,
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~ 1~353(~1
in this case, is shown as an open ditch 26, is constructed
or arranged more or less in a straight line, although it
might be otherwise. The ditch provides a source of water
to be picked up for distribution by the system. It will
be understood that the particular number of towers, shown
in Figures 1 and 2, is not critical and could be different
from the actual number shown. An equal number of spans
and/or towers on each side of the ditch is not required.
Generally each pipe segment is supported
by and rigidly connected to a tower. Moreover, the tower
span connection is made at one end of the span, in this
case shown as the one nearest one end or the other of the
machine or unit 10. For purposes of identification, the
end with the tower connection will be referred to as the
tower end or outboard end of the span, with the opposite
end being referred to as the free or inboard end. It will
be understood that the free or inboard end is joined by
a flexible joint or coupler to the tower end of the next
inside pipe segment. For purposes of description, each
tower and pipe segment has a letter designation and, in
general, the letters are common to corresponding tower
and span pairs.
The foregoing description is not applicable
at selected intermediate points of the pipeline. The spans
at these points are rigidly connected to towers at both
ends of the span. Thus, spans 12D and 12G have no free
end. Together with towers 14D, 14E, 14F and 14G, respectively,
they form two more or less rigid four-wheel vehicles.
Two flexible joints 18M and 18N are located between the
four-wheel vehicle to provide pipeline flexibility and
steering control~
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Figures 7 and 8 show the components of a
typical pipe connection and the associated controls which
activate the tower motor. Referring to both Figures, the
free end 28 of a pipe section is coupled to the tower end
30 of the next inboard section. A flexible split coupler
32, such as shown in U.S. Patent No. 3,994,514, seals the
two pipe ends relative to each other so that water does
not leak. The coupler positions the pipe extremities in
spaced relation so as to allow certain angulation of one
pipe relative to the other throughout the full 360 of
its circumference. The coupler is primarily a sealing
device and is not intended to be the structural member
responsible for holding the pipe string together. That
task is performed by a universal joint indicated generally
at 34.
One type of universal joint is the do~ble
clevis arrangement shown in Figure 8, which allows for
both vertical and horizontal angulation of one pipe section
relative to another but does not permit longitudinal pipe
movements. The joint comprises a horizontal yoke 36, a
vertical yoke 38, both pivotally connected to a gimbal
ring 40 by capscrews or the like 42. A horizontal yoke
36 is fixedly attached to the free end of a pipe span.
A vertical yoke 38 is fixedly attached to the tower end
of a pipe span. As noted above, the spans 12D and 12G
have no free ends so those spans carry only vertical yokes.
Also, the center spans 12E-12F, which are rigidly connected
together by a T-joint, have no tower ends so they carry
only horizontal yokes. These correspond with vertical
yokes on the inboard ends of spans 12D and 12G to form
joints 18M and 18N (Fig.3). The gimbal ring 40 is free
to rotate about a vertical axis Y or horizontal axis X
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~135391
1 according to the angulation between pipe segments. As will be
pointed out below, rotation of the gimbal ring about the vertical
axis Y is one of the inputs utilized to activate the tower motors.
The motor activating means comprises the universal joint,
a motor switch arm coupled to the motor switch, a control arm
and control wires. A switch arm and switch 44 are mounted on
the control box 46 which is enclosed by a cover. A bracket 48
extends from the gimbal ring 40 to support the control box 46
conveniently near the tower 14, providing good service access.
Actuation of the switch and arm 44 causes power to be supplied
to the tower motor. The switch arm is connected by linkage 50
to a control rod 52. The rod, in turn, is attached to a control
arm 54 which is mounted on a pivot 56 which in turn rests on the
top of the gimbal ring 40. The control rod 54 is free to pivot
about vertical axis Y on pivot 56 but is normally restrained to
a fixed position, transverse to the pipe string, by control rods
or wires 58. These wires are fixed to the outer ends of the con-
trol arm and extend inboard toward the free end of the pipe
section where they are anchored to a spreader bar 60, shown in
Figure 7, which is rigidly attached to the free end of the pipe.
The purpose of the spreader bar is to prevent entanglement of
the control wires in the support truss 16.
The guide or sensing unit 2~ is shown in Figures 4-6
and includes path sensing means and heading correction signal
generating means, or the like. The guide means is mounted to
a suitable base plate or member 62 and is enclosed by a housing.
The base and housing are suspended somewhere along the pipe string,
preferably in the middle of the string, although it need not be so.
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The path-sensing means comprises a pair of quills 64 and
64a. As can be seen in Figures 4-6, the quills 64 and
64a are each mounted or otherwise connected to a shaft
66. Each such shaft is supported in a bearing 68 which
is welded or otherwise rigidly fastened to the outside
surface of the base plate 62. Return springs 70 are connected
between the top of the quills and the brackets 72. The
quills extend to a point where they are disposed on each
side of the path-defining means, shown in this case as
a wire 20. Thus the quills may be considered to enclose
the path-defining means, be it a wire, cable, or otherwise.
The correction signal generating means
associated with each quill includes an arm 74, switch 76,
a friction drive 78, a one-way clutch 80, and a timing
device 82. The arms of switch 76 are spring-biased to
the neutral or open condition. The one-way clutch 80
includes a housing 84 enclosing a clutch element 86 and
bearings 88. The clutch 80 is mounted on shaft 66 which
extends through the base plate 62. The clutch housing
84 has a projection 90 for supporting the arm 74. The
friction drive 78 includes a stub shaft 92 pinned to
projection 90, a coil spring 94, and washers 96 which are
held on the stub shaft by a lock nut 98, or the like.
Stops 100 and lOOa are affixed to the base plate 62 on
either side of arm 74. It will be understood that while
a double quill arrangement has been described and shown,
any path-sensing means could be used. For example, a
single quill with forked end enclosing a path-defining
means would be acceptable and would function quite
efficiently. Indeed, mechanical sensing means in certain
situations or installations is not a necessity as electro-
optical devices could be used in certain applications to
sense a deviation from the path and the start of a correction
back toward the path.
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-" 11353~1
The operation of the irrigation unit is
as follows:
The normal lateral movement of the system
is obtained by independently driving two master towers
according to a pre-chosen program. All of the remaining
are slave towers and move in response to the master towers,
moving at such times as are ~ecessary to maintain the pipe
string in alignment. The master tower can be controlled
by an adjustable primary timer which may call for the cont
inuous forward motion of the outside towers or for a stepwise
progression where the towers are driven for selected intervals
and then turned off for an interval. The particular program
chosen will depend on the amount o~ irrigation desired
for a particular field. It has been found preferable to
make the towers at the two ends of the unit or system,
the master towers with all intermediate or inboard towers
being slave towers. While this arrangement is preferred
and will be used in this description, it is not absolutely
essential. The master towers could be elsewhere than at
the ends.
The forward motion of the master towers
14A and 14J moves the tower end of the outermost pipe seg-
ments 12A and 12J forward. This in turn causes a horizontal
angulation between pipe segments 12A-12B and 12J-12I~
This angulation is reflected at the free ends of spans
12A and 12J by motion of the horizontal yoke 36 or 102
which causes the gimbal ring 40 to rotate about vertical
axis Y, in Figures 8 and 10. The mounting of control box
46 reguires the box to rotate with the gimbal ring. How-
ever, since the control arm 54 is pivoted about the vertical
axis Y, it does not rotate as it is fixed by control wires
58. Thus, there will be a relative movement between the
control box 46 and the control arm. This movement actuates
switch arm 44 through control rod 52 and linkage 50.
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This activates the motors on the slave towers 14B and 14I,
thus setting those towers in motion.
As towers 14B and 14I move forward, the
horizontal yoke at the free end of pipe segments 12B and
12I rotates the gimbal ring at the next universal joint,
again about vertical axis Y. This in turn trips the switch
in the towers 14C and 14H control boxes and the process
starts for the next pipe segment. This misalignment signal
propagates from both end towers 14A and 14J toward the
middle of the pipe string. At some intermediate point
the two signals will meet and be cancelled. If the machine
is symmetrical, as in Figures 1 and 2, and if both sides
of the unit are progressing signals will meet and be cancelled
at the middle segment 12E and 12F.
The alignment signal propagation across
the four-wheeled vehicles that spans 12D and 12G is somewhat
different. These spans have no free end available to cause
gimbal ring rotation. So control wires 58 are used instead
to rotate control arm 54. For example, looking at Figure
3, when tower 14D moves ahead of tower 14E the control
wires 58X, fastened to spread bar 60X, cause rotation of
control arm 54X. This in turn trips switch arm 44 at joint
18M and starts the tower motor on tower 14E. Conversely,
if tower 14E moves ahead of tower 14D, control wires 58Y
fastened to spreader bar 60Y cause rotation of control
arm 54Y. This trips the switch and starts the motor on
tower 14D. A similar arrangement is provided across span
12G.
It will be understood that during normal
operation alignment signals will be propagated in both
directions, from time to time, at any point along the machine.
1~3S301
While the primary impetus activating the slave towers is
the master tower motion, with its resulting outside-in
alignment signal, there will be a need to propagate signals
in the opposite direction also. For example, suppose spans
12A and 12B are aligned but 12B and 12C are not. The tower
14C will be activated, carrying the free end of span 12B
forward. This will negate the prior alignment between
spans 12A and 12B. Thus, tower 14B will require the capability
of responding to slave tower 14C's motion, as well as that
of master tower 14A. The present invention accomplishes
this as explained hereinafter.
When the irrigation unit 10 is following
the desired path, quill 64 and 64A are on either side of
the cable or wire 20 but do not necessarily touch it.
In this situation each quill and arm are in their neutral
or home position, which is indicated as position 1 in FIgure
4. In this neutral or home position they may be considered
to be at a certain angle to each other, which will be referred
to as the home angle. If the irrigation unit strays from
its desired path, which it will, one quill or the other
say for examlpe the quill 64, will contact the wire or
cable 20 which will cause rotation of the shaft 66 away
from its home position 1 in Figure 4 toward position 2.
When this happens, the clutch element 86 engages housing
84 causing it to rotate with shaft 66. The friction drive
78 connects the housing 84 and arm 74 so that they rotate
together, thereby maintaining their home angle relationship
between the arm 74 and quill 64. This motion of arm 74
actuates switch 76 which in turn actuates the timing device
82, by a circuit not shown but which may be conventional,
which generates a path-correction signal whose function
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11 353Q~
will be explained below. Once the switch 76 has been actuated,
arm 74 will then engage the stop 100 to prevent further
motion which could damage or decrease the sensitivity of
the switch. Should the machine continue its off route
or wayward path, causing the quill 64 to be moved out toward
position 3, the friction drive permits the arm to slip
on projection 90, thus allowing the housing 84 to continue
rotation with the shaft 66 even though the arm 74 is held
fixed by stop 100. The arm and quill will now form an
angle less than the home angle.
When the unit begins to correct its heading,
the quill moves back toward position 2. Since at this
position the quill and arm form less than the home angle,
some relative rotation is desirable to return both elements
to their neutral position. Upon the initial return motion
the quill 64, shaft 66, clutch 80 and arm 74 all rotate
together toward the home or neutral position. Since the
arm's initial rotation was limited by stop 100, it has
only a short arc to move to regain its home position.
This is accomplished with the accompanying release of switch
76, under the urging of the spring-loaded switch arm.
Also, during the return rotation the clutch element 86
disengages housing 84. When that disengagement occurs,
the quill 64 is disconnected from the clutch housing 84
and also from arm 74 which allows the quill to regain its
home position under the force or urging of the return spring
70.
If the one-way clutch 80 was not provided,
the arm would continue its return rotation until abutting
stopped 100a. The spring 70 would have to overcome the
friction between arm 74 and housing 84 to yet quill 64
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113S301
While this could be done, it would require a much stronger
return sprinq. This would greatly reduce the sensitivity
of the device.
When the machine strays from the desired
patb, the g~idance means will act to correct the heading
of the unit to bring it back to the proper path. If, for
example, the machine strays to the left, quill 64 will
contact guide cable 20 which will cause the cable to move
toward position 3 shown in Figure 4. This activates the
secondary timer 82 which interrupts the normal control
of the primary timer over the master towers. The secondary
timer alters the rate of one master. Preferably, it will
cause the master tower 14J to reduce its forward speed,
thus causing the machine to establish a new, corrected
heading in the following manner.
The left-hand end tower 14A continues to
move forward at its normal rate. This in turn moves the
left side slave towers forward as they respond to misalignment
caused by motion of the master tower. When the misalignment
signal gets to the intermediate towers, it is no longer
cancelled by a corresponding signal coming from the right
hand side of the machine because the right hand master
tower has been shut down or slowed by the guidance means.
In Figure 3, it can be seen that as slave tower 14F moves
forward, the control wires 58 will rotate the control arm
54 on the tower 14G. As that tower 14G moves forward,
its control wires 58 will cause the control arm of the
next outboard tower 14~ to pivot, tripping the motor switch,
thus activating that tower. This signal propagation continues
in the same manner all the way to the right hand end tower.
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~ 1~35301
The effect of this will be to cause the entire machine
to pivot about a point beyond the right hand end tower,
thereby establishing a corrected heading which will bring
the machine back from the position to which it has strayed.
As soon as the machine starts to correct its position,
quill 64 will move from position 3 toward position 1.
Immediately upon the start of the quill's return motion
the one-way clutch 80 disengages. This in turn releases
the rotational bias on arm 74, allowing the spring-loaded
switch 76 to open. When the switch 76 opens the secondary
timer 82 shuts off, thus returning the right master tower
14J to its primary rate. This action locks in the new
heading as soon as the machine has started to return to
the position from which it strayed. If the heading correction
were to be continued until ~he machine had returned to
its initial position, too much correction would result,
thereby causing unacceptable hunting or lunging toward
the guidance wire or cable with increasing amplitudes and
frequencies which would eventually require the shutdown
of the machine. If the machine were to stray to the right,
qill 64a and its associated components will perform the
same function as just described for quill 64.
To appreciate the desirability of two-way
signal propagation, resort may be had to Figures 3 and
7. As explained above, normal inward signal propagation
occurs upon rotation of the gimbal ring about the vertical
axis. This rotation is caused by joint angulation created
by motion of the free end 28 of a pipe segment. Thus if
the tower shown in Figure 7 is considered to be tower 14C,
inward si~nal propagation occurs when tower 14B moves ahead
of 14C, causing the horizontal yoke at the free end 28
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of pipe segment 14B to rotate gimbal ring 40 about vertical
axis Y. This moves the control box 46, tripping the switch
to start the motor on tower 14C. So the pipe 12B itself
transmits the inward signal. In contrast, pipe 12C cannot
readily transmit an outward signal to tower 14C because
the tower end 30 of pipe 12C is held fixed by the tower
structure.
Outward signal propagation is needed when
an inboard tower, such as 14D, moves ahead of an outboard
unit, such as 14C. When this occurs the pipe segment 12B
does not move so the free end of 12B cannot trip the switch
through gimbal ring rotation as it does for inward propagation.
Further, the tower end 30 of segment 12C cannot move to
create a switch-tripping action because the tower end's
position is held fixed by the tower 14C. Thus, without
two-way signal propagation means, tower 14C would not "know~
that tower 14D had moved ahead~ Severe misalignment will
result, forcing the shutdown of the unit. The present
arrangement averts this breakdown by including tower motion
signal propagation means in the form of control wires 58
and pivoted control arm 54. Since the control wires 58
are fixed to a spreader bar 60 near the free end of segment
12C, they will move forwardly with tower 14D. This motion
of the wires causes a rotational motion of the control
arm 54 at tower 14C. The free end 28 of pipe 12B, gimbal
ring 40 and control box 46 all are stationary at this time,
so there is relative motion between the arm and the control
box. This trips the switch and activates the motor on
tower 14C. So the control wires 58 transmit the outward
signal. At the four-wheel vehicles the control wires transmit
both inward and outward signals.
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" ~3S301
It will be noted that without the control
wires, outward signal propagation would not take place
even if there was joint angulation at tower 14C upon advance-
ment of tower 14D~ Such angulation would require the pipe
12C to impart torque to tower 14C sufficient to pivot it,
overcoming the resistance of the tires on the ground.
Even if such a scrubbing or skidding pivot were achieved,
the results would only be a pivoting of vertical yoke 38
about vertical axis Y, in Figure 8. There would be neither
gimbal ring rotation nor control arm rotation to trip the
switch and, hence, the motor on 14C would not start. Under-
standably, it is far superior not to force a scrubbing
pivot of a support tower. The unit capable of doing that
would be extremely expensive, as only short spans of very
strong pipe could be used, a greater number of towers would
be needed, and coupling the pipe segments would be a problem.
Use of control wires eliminates the need for using the
pipe to transmit alignment signals outwardly.
Thus it can be seen that two-way signals
propagation is desirable and that the universal joint,
control wires and control arm of the present arrangement
or equivalent means makes possible such two-way signal
propagation utilizing the basis control box and tower motors
of a normal center pivot system.
Figures 9 and 10 show an alternate embodiment
of the motor-activating means which utilizes a torsion
flexible joint 102 such as that shown in U.S. Patent 3,983,898
which is similar to the universal joint 34 except that
the horizontal yoke 102 and 104 is elongated and affixed
to a pipe-hugging box 10~. The control box is mounted
directly on the horizontal yoke and moves with that portion
of the joint. The spreader bar is shown as having been
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~1353(~1
deleted so that the control wires are attached to the pivot
56 of the control arm. Other parts may be the same as
in Figures 7 and 8 and the same reference numberals have
been applied, where appropriate.
In Figure 11 a self-contained power pack has
been shown which incorporates various features which may
be used or included with the present invention. A sling
support 108 carries the power unit and has a rectangular
frame 110 suspended from the main irrigation pipe 12 by
rods or cables 112. The power unit rests on the frame
110 and may include an engine driving an irrigation water
pump, not shown in this form. The pump picks up water
from a source, such as the ditch 26, and supplies it under
pressure to the pipe string through a T-joint or connection
114. If the tower motors are electric, the engine may
also drive a generator to provide electric power. Or it
may be a hydraulic setup.
The weight of the power unit dictates or makes
it desirable that the length of the spans 12E and 12F
supporting it be less than the regular span length. For
example, a t~pical wheel-to-wheel distance between towers
14E and 14F may be 30 feet as compared to something on
the order of 150 feet for the other spans. The shorter
span length necessitates placement of joints 18M and 18N
between towers 14E and 14F so that sufficient flexibility
is provided to prevent loss of steering control. This
joint placement leads to creation of the four-wheeled vehicle
mentioned above, which is acceptable because the span length
of 12D and 12G is sufficient to permit use of control wires
in both directions across the pipe segments. The joint at
18M is a torsionally flexible joint, such as described in
U.S. Patent 3,983,898 and shown in Figures 9 and 10, for
example.
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1135301
While it is preferable to locate the support
sling 108 and the associated foreshortened span at the
middle of the machine~ such a location is not required.
The sling could be anywhere along the pipe string to accomodate
the source of the water location or the ditch, or whatever
it is. Likewise, while a symmetric machine has been shown
and is preferred to cancel extraneous forces lon~itudinal
to the pipe, a symmetric arrangement is not an absolute
necessity and may not be desired in certain installations.
In Figures 12 and 13 a variant form has been
shown in which the middle pipe segment 116 does not have
a free end as the middle towers 118 and 120 support both
ends of the segment. The control rods 122 and 124 are
both mounted on the gimbal ring's vertical axis or pivot,
being axis Y, much like Figures 7 and 8, and the control
wires thereto, at 126 and 128, are crossed so that as tower
118 moves forward the control wires 126 and 128 will rotate
the control arm 124 on the other middle tower 120 and vice
versa. This in turn actuates the switch in the control
box which starts movement of the other middle tower 120.
As tower 120 moves forward, its control wires, to the right
in Figure 13, will cause the control arm of the next outboard
tower to pivot, tripping the motor switch, etc. This signal
propagation continues in the same manner as set forth herein-
before. Towers 118 and 120 are rigidly coupled to each
end of the center span 116 so that, in a sense, the composite
makes up a four wheel rigid frame or drive which, to turn
slightly one way or the other, requires a slip or skid
motion.
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11353(~1
A self-contained power unit 130 is shown in Figure
12 as including a suitable engine 132 which may drive both
a pump 134 and a generator 136. The generator may supply
electric power to the various tower motors. The pump picks
up water from a water source, which may be an open ditch
138, through a suitable intake pipe 140. If the water
source is a ditch, the position of the intake pipe to the
ditch may be controlled by a cable or any other suitable
means, as indicated at 142, connected thereto or a float
attached to the intake pipe (not shown). Water is fed
under pressure from the pump through a suitable riser 14
and through a T-joint to the main irrigation pipe 116.
The engine may have a suitable gasoline or diesel fuel
tank 146, possibly one on each tower. The engine, generator
and pump may be mounted on a suitable platform or frame
148 which is suspended above the water source by a sling
arrangement 150 which may include four straps 152 which
rise to a rectangular carrier 154 or the like which is
attached by angles 158 to the main irrigation pipe or center
span 116. Guide wires or rods 160 may be appropriately
disposed to prevent the sling from swaying excessively.
As shown, four such rods are used, but there might be more
or less. While the power unit or power pack is shown supported
from the middle pipe segment 116, it should be understood
that it could hang or be located at any position where
the pipe is sufficiently rigid. The details of the power
pack in Figure 12 could be used in the Figure 11 form.
While the preferred form and several variations
have been shown and/or described, numerous additional modi-
fications, substitutions, alterations and additions may
be made without departing from the inventive theme.
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