Note: Descriptions are shown in the official language in which they were submitted.
PIPE HANDLER
Technical Field
This invention pertains generally to material or article handling, and more
particularly to a pipe handler such as might commonly be used in the oil
drilling and
rigging industry to assist with the handling of very large and heavy pipes
that are
regularly raised to and lowered from an elevated drilling platform.
Background Art
In the oil drilling and rigging industry, drilling platforms commonly referred
to
as derricks are assembled above the earth. These derricks facilitate the
drilling and
installation of wells. The platform or work floor typically may be elevated
many feet
above the ground.
Drill strings of very large and heavy pipes are assembled or disassembled on
the
derrick. For exemplary and non-limiting purposes, these pipes may be stored
horizontally on or near the ground adjacent to the derrick. This means that
these very
large and heavy pipes must be reoriented from horizontal to more nearly
vertical
orientation, and raised from near ground level to several tens of feet into
the air.
Consequently, the handling of these large and heavy pipes is not suited to
manual labor,
and instead requires mechanical assistance.
Pipe handlers are commonly be used to assist with the handling of these very
large and heavy pipes that are regularly raised and lowered from an elevated
drilling
platform. A large number of patents are exemplary of this technology, and
provide the
background for the basic features, while also contrasting with the novel
features of the
present invention. These U.S. patents include: 2,643,006 by King, entitled
"Automatic
pipe handler," that illustrates an early automatic pipe handler, and describes
a bumper or
stop having a resilient portion in the form of a rubber or spring against
which the drill
pipe may abut, that prevents a pipe section from sliding down the dolly. U.S.
patents
3,792,783, entitled "Pipe Handling System" and 3,916,500 entitled "Pipe
handling
apparatus", each by Cicero C. Brown, describe another early automatic pipe
handler
having an endless cable or chain driving a lug to elevate a pipe in a trough
to push the
pipe toward the derrick. This same lug is also used to control the rate of
descent of the
pipe. U.S. patents 4,386,883 by Hogan et al, entitled "Materials lifting
apparatus" and
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4,494,899 by Hoang et al, entitled "Pipe trough for transporting pipe between
upper and
lower positions", each describe automatic pipe handlers with kickers to assist
with the
loading and unloading of pipes. Hogan refers to these kickers as pipe ejecting
assemblies that eject the pipe from the carriage using an arm and a ram, and
Hoang et al
refers to these as unloading arms for ejecting the pipe from the trough. Hoang
et al also
describe pipe loading arms to assist with loading pipe into the trough. U.S.
patents
4,235,566 by Beeman et al, entitled "Pipe-conveying catwalk" and 4,439,091 by
Frias,
entitled "Pipe feeding system", each illustrate carriages that move along a
trough. The
teachings and content of U.S. patent 3,559,821 by James, entitled "Drill Pipe
Handling
Apparatus" and which illustrates another drill pipe handling apparatus.
Additional U.S. patents illustrating various kicker constructions, include:
4,140,227 by Beck, entitled "Cable way apparatus for transporting pipe"; and
4,403,898
by Thompson, entitled "Pipe pick-up and laydown machine". Additional patents
showing rigid pipe handler structures, include: 2,880,881 by Robishaw,
entitled
"Unitized pipe rack"; 2,958,430 by Robishaw, entitled "Pipe rack and lay-down
trough";
4,684,314 by Luth, entitled "Pipe handling apparatus"; 6,079,925 by Morgan et
al,
entitled "Method and apparatus for lifting oilfield goods to a derrick floor";
7,635,249
by Guidroz, entitled "Pipe pick-up and laydown apparatus"; 7,665,944 by
Guidroz,
entitled "Pipe pick-up and laydown apparatus and method"; 7,992,646 by Wright
et al,
entitled "Horizontal offline stand building system"; and 8,052,368 by
Liftlewood et al,
entitled "Catwalk for a drilling rig". Other relevant patents and published
applications,
include: 6,899,510 by Morelli et al, entitled "Pipe handling system for
presenting
sections of pipe to a derrick work floor having a pipe ejection assembly";
7,021,880 by
Morelli et al, entitled "Pipe handling apparatus for presenting sections of
pipe to a
derrick work floor having a high-speed carriage assembly"; 7,163,367 by
Handley,
entitled "Multi-position height adjustment system for a pipe handling
apparatus"; and
2008/0263990 by Morelli et al, entitled "Skidding system for a catwalk". The
Handley
patent illustrates one technique for adjusting the height of the boom on an
automatic
pipe handler. In Handley, a plurality of boom ports and arm ports are
provided, and one
boom port is linked to one arm port through a hinge pin. Thee particular
selection made
by the hinge pin determines the height of the boom.
From these foregoing patents, the basic structure of a pipe handler and the
function thereof will be well understood. In addition to the foregoing
patents, Webster's
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New Universal Unabridged Dictionary, Second Edition copyright 1983, sets forth
definitions of words and terms used herein.
Disclosure of Invention
The present invention provides a novel height adjustment assembly to set the
maximum height that the skidway or trough, also sometimes referred to as the
boom,
will reach when the hydraulic lift cylinder is fully extended.
In a first manifestation, the invention is a pipe handler having a height
adjustment assembly to set an adjustable maximum height that a skidway will
reach
above a deck when a hydraulic lift cylinder is extended. A supporting carriage
supports
at least a first end of the skidway. A lift arm is pivo tally coupled to the
supporting
carriage adjacent a first terminus and is pivotal with respect to the
supporting carriage
about an axis transverse to a longitudinal axis of the skidway. An internal
rack is fixed
within the lift arm. An adjustment block couples the internal rack to the
skidway. A
locking block is coupled to the adjustment block and is operative to rigidly
engage with
the internal rack when the skidway is displaced from the deck, and thereby
prevent
relative movement of the adjustment block relative to the internal rack. A
drive is
operative to reposition the adjustment block longitudinally along the skidway
and
thereby alter the maximum height that the skidway will reach when the
hydraulic lift
cylinder is extended.
Brief Description of the Drawings
The objects, advantages, and novel features of the present invention can be
understood and appreciated by reference to the following detailed description
of the
invention, taken in conjunction with the accompanying drawings, in which:
FIG. 1 illustrates a preferred embodiment pipe handler designed in accord with
the teachings of the present invention from a projected view;
FIG. 2 illustrates the preferred skidway and lift arms incorporated in the
preferred embodiment pipe handler of Figure 1 from an enlarged, projected view
with
extraneous components hidden from view;
FIG. 3 illustrates selected interior components incorporated in the preferred
skidway and
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lift arms of Figure 2 from a similar enlarged, projected view;
FIG. 4 illustrates selected interior components incorporated in the preferred
skidway and
lift arms of Figure 2 from a rotated, enlarged, projected view better
illustrating the internal racks;
FIG. 5 illustrates a preferred plate and slide coupling the prefened skidway
and lift arms
of Figure 2 from underneath, by enlarged and projected view;
FIG. 6 illustrates an alternative embodiment pipe handler with the exterior
components
of the skidway and lift arms removed from view to illustrate the internal
components therein,
taken from a perspective view approximately midway on and slightly elevated
above the trailer
and viewing from the passenger side thereof;
FIG. 7 illustrates the alternative embodiment pipe handler of Figure 6 from a
slightly
more enlarged view and rotated about a vertical axis by approximately 180
degrees with respect
to the view of Figure 6, viewing from the driver's side and rear of the
trailer, elevated
substantially above the trailer; and
FIG. 8 illustrates the alternative embodiment pipe handler of Figure 6 from an
enlarged
perspective view, viewing from the driver's side and center of the trailer,
elevated substantially
above the trailer and looking upwards under the adjustment block and towards
the passenger side
rear of the trailer.
FIG. 9 illustrates the preferred embodiment pipe handler of Figure 1
illustrating the
hydraulic lift cylinder and secondary hydraulic boom unlock cylinder in
association with a lift
arm, by a vertical and longitudinal section view taken along section line 9'
of Figure 1.
FIG. 10 illustrates a preferred lift arm used in the preferred embodiment pipe
handler of
Figure 1 with a cam lock in a locked position, by a section view taken
adjacent to a locking block
along section line 10' of Figure 5.
Best Mode for Carrying Out the Invention
Manifested in the preferred embodiment, the present invention provides a pipe
handler
trailer 100 for use in the oil drilling and rigging industry and other
appropriate industries to assist
with the handling of very large and heavy pipes that are regularly raised to
and lowered from an
elevated surface such as a drilling platform. While a trailer is not critical
to the operation of the
invention, and so the pipe handler apparatus could conceivably be provided on
a self-propelled
vehicle such as a truck, or alternatively provided on a fixed structure
without wheels, the
provision of various trailer components such as a tongue assembly 110 with
hitch 112, wheels
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114, support legs 116, and trailer undercarriage 118 illustrated in Figure 1
allow the preferred
embodiment pipe handler trailer 100 to be transported conveniently to more
than one drilling
derrick. If a self-propelled vehicle such as truck were used, then the capital
investment in the
drive train and cab is tied up in the apparatus, and, since the pipe handler
may be left at a single
platform for extended periods, the drive train and cab are unavailable for
use. Instead, the
preferred embodiment pipe handler trailer 100 may be quickly anchored by
dropping support legs
116, which will preferably be independently adjustable to accommodate uneven
surfaces, and
then quickly disconnecting hitch 112 from a towing vehicle. The towing vehicle
is then free for
other productive use.
Trailer top 120 includes a deck 122 which in the preferred embodiment may be
provided
with one or more small gaps within which are provided pick-up and indexing
arms 124 that
facilitate the loading of pipes onto deck 122. A motor, hydraulic pump and
associated controls
and components may be provided in power box 126, though any suitable source of
energy and
motive power may be provided within the constraints of the present invention.
In accord with the teachings of the present invention, a novel height
adjustment assembly
is used to set the maximum height that the skidway or trough 130, also
sometimes referred to as
the boom, will reach when a hydraulic lift cylinder 143 is fully extended.
When stored, such as
during periods of non-use or during transport, skidway 130 will preferably
nest within deck 122.
Likewise, when a pipe is being loaded from deck 122 into trough 131, skidway
130 will also be
lowered and nested within deck 122.
In the preferred embodiment pipe handler trailer 100 illustrated in Figures 1-
5, the
elevation of the skidway, whether nested within deck 122 or angled upward and
rearward
therefrom, is controlled by boom lift 140. Boom lift 140 incorporates a pair
of lift arms 141, 142
that are pivotally mounted onto the trailer undercarriage 118 adjacent the
back end or rear of pipe
handler trailer 100. Lift arms 141, 142 pivot about an axis transverse to the
longitudinal axis of
the trailer, and the amount of pivot is controlled by hydraulic lift cylinder
143. As lift arms 141,
142 raise in a clockwise direction as seen in Figures 1 and 2 from a stored or
lowermost position
parallel to the trailer longitudinal axis, they carry skidway 130 both
rearwardly along the trailer
longitudinal axis, and also raise the rearward most point of skidway 130
significantly above deck
122. Note that the forward most point of skidway 130 stays much closer to deck
122, regardless
of the pivotal orientation of lift arms 141, 142.
Skidway 130 includes a trough 131 for receiving and holding a pipe during
conveyance.
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This trough may be sized for a single pipe diameter, but will more typically
be dimensioned to
support the largest pipe for which the pipe handler trailer 100 is designed to
accommodate.
Various apparatus known in the art may optionally be provided to better
secure, retain or hold
pipes, whether the maximum size or smaller, safely in the trough, including
various hoops,
covers or the like.
In preferred embodiment pipe handler trailer 100, and most visible in Figure
2, located
intermediate along skidway 130 are a plurality of flippers or kickers 132-135
that are operative
to kick a pipe out of trough 131. Kickers may preferably be provided in pairs,
such as 132, 133.
In such case, kicker 132 may preferably be used to flip the pipe to a first
side of the trailer herein
identified as the passenger side, which corresponds to the side of the towing
vehicle a passenger
in the front seat would be seated. In this case, kicker 133 for exemplary
purposes will flip the
pipe to the opposite or driver's side of the trailer. While the exact number
and placement of
kickers is not critical to the invention, providing at least two pairs of
kickers at distal locations
along trough 131 helps to ensure smooth discharge of pipes from the trough.
Adjacent to the forward end of the trailer and positioned to roll along the
top surface of
trough 131 is skate 136. Skate 136 may preferably be provided with a cradle
137 which holds
one end of a pipe, and also with a backstop 138 which preferably rises above
cradle 137 to
engage the end of a pipe along a transverse plane. This allows skate 136 to
cradle and move a
pipe along trough 131, to raise or lower the pipe relative to trailer deck
122.
Skate 136 is driven longitudinally along trough 131 by a drive 150, which in
the preferred
embodiment pipe handler trailer 100 is an endless chain 153 wrapping at distal
ends of trough
131 about sprockets 151, 152. At least one of sprockets 151, 152 will be
connected to a source
of motive power, such as through a hydraulic coupling back to power box 126,
though once
again, any suitable source of motive power may be used. Furthermore, other
methods and
apparatus may be used to move skate 136 longitudinally along trough 131.
Figure 3 illustrates selected interior components incorporated in the
preferred skidway
and lift arms of Figure 2, with the size and viewing angle maintained to be
similar to Figure 2
to allow inspection and comparison there between. Skate underbody 139 is
illustrated therein,
to give perspective on component location. Further towards lift arms 141, 142
is a single kicker
133, once again to maintain perspective. Surrounding kicker 133 is structure
which operates
through a plunging motion to activate kickers 132-135, though the structure
used for such
activation is not important to the present invention, and prior art methods
and apparatus
6
may also be used.
Located within lift arms 141, 142 are toothed racks 144, 145, respectively.
The
arrangement of lift arm 141 within rack 144 is visible in Figure 5, with it
understood that each
rack will be rigidly fastened or affixed to the associated lift aim. This may
be through removable
or permanent fastening techniques, as will be determined by one skilled in the
art of fabrication.
Coupling skidway 131 to lift arms 141, 142 through racks 144, 145 is
adjustment block
160. Again as best illustrated in Figure 5, plate 164 and slide 162 sandwich
about slide members
163, 165 that are supported and affixed within skidway 130. This arrangement
ensures that
adjustment -block 160 tracks and follows slide members 163, 165. Plate 164 and
slide 162 are
rigidly coupled to a shaft 166 as best illustrated in Figure 4. Shaft 166
pivotally passes through
toothed locking blocks 168 that have teeth 169 complementary to the teeth on
toothed racks 144,
145. Shaft 166 then terminates through rigid coupling with cam lock 167.
Because of the rigid couplings to shaft 166, cam locks 167 are also rigidly
coupled with
plate 164 and slide 162. This means that as lift arms 141, 142 rotate relative
to skidway 130, the
surface of cam locks 167 most nearly adjacent to lift arms 141, 142 changes.
By shaping the
outer perimeter geometry of cam locks 167 to vary in radial distance from
shaft 166, and thereby
define a cam surface which changes in radial distance with angular rotation,
cam locks 167 will
vary from finn contact with the inner wall of lift arms 141, 142 to having a
gap there between,
depending upon the angular orientation of skidway 130 relative to racks 144,
145. Figure 10
illustrates a sectional view of lift arm 142 adjacent to locking block 168,
with cam lock 167
protruding above locking block 168 (in the orientation of the drawing figure)
and thereby
engaging the inner wall of lift arm 142. This contact in turn forces locking
block 168 downward
(again, in the orientation of the drawing figure), which then drives
complementary teeth 169 into
secure engagement with the teeth of rack 145. Consequently, when in firm
contact with the inner
wall of lift arms 141, 142, this also means that locking blocks 168 will be
forced into locking
engagement with racks 144, 145, ensuring that the locking blocks 168 are
rigidly coupled to the
respective racks 144, 145 by the complementary teeth 169, and can support
great strength without
inducing relative motion there between. Most preferably, cam locks 167 will be
shaped such that
at some relatively small angular difference between skidway 130 and racks 144,
145, cam locks
167 will securely engage the inner wall of lift arms 141, 142 and will also
lock racks 144, 145
together to locking blocks 168. However, when skidway 130 and racks 144, 145
are parallel,
most preferably there will be a gap between cam locks 167 and the inner wall
of lift arms 141,
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142.
The relative position of locking blocks 168 along racks 144, 145 is adjusted
in preferred
embodiment pipe handler trailer 100 only when skidway 130 is fully lowered
into deck 122,
which results in skidway 130 and racks 144, 145 being parallel. Once lowered,
then it will be
apparent that locking blocks 168 are positioned directly vertically above
racks 144, 145. In this
position, cam locks 167 are spaced from the inner wall of lift arms 141, 142,
allowing locking
blocks 168 to be moved vertically away from racks 144, 145. This vertical
movement of locking
blocks 168 relative to racks 144. 145 is achieved through a secondary unlock
actuator 180,
visible in Figure 9. Secondary unlock actuator 180 may as in the preferred
embodiment include
hydraulic boom unlock cylinder 182 as a source of motive power. and may be
located adjacent
to lift cylinder 143. A pivotal coupling 186 couples undercarriage 118 to a
lifter arm 184 located
underneath but in contact with skidway 130 when skidway 130 is fully lowered.
Skidway 130
will only be lifted slightly by actuation of hydraulic boom unlock cylinder
182, but sufficiently
to lift complementary teeth 169 on adjustment block 160 away and fully
separated from racks
144, 145. Next, hydraulic height adjustment cylinder 170, which couples on a
first end to
skidway 130 and on a second end distal thereto to slide 162 as visible in
Figure 4, may be
activated to move adjustment block 160 longitudinally along racks 144, 145 to
a new position.
When cylinder 170, located within skidway 130 and visible in Figure 4, is
fully retracted, this
positions adjustment block 160 closest to the tops of racks 144, 145 in Figure
4, meaning
skidway 130 will be raised to the greatest elevation using boom lift 140.
Alternatively, when
cylinder 170 is fully extended, this will drive adjustment block 160 towards
the bottom of racks
144, 145, which will then result in a lower maximum elevation. Optionally,
marks or other
appropriate structure corresponding to various platform heights may be
provided along one or
more of lift arms 141, 142 and skidway 130, so an operator can determine even
when skidway
130 and boom lift 140 are fully lowered where to position adjustment block 160
relative to lift
arms 141, 142.
In an alternative embodiment to preferred embodiment pipe handler trailer 100
contemplated herein, hydraulically controlled locking blocks such as blocks
268 described herein
below are used instead of locking blocks 168. To change the height that
skidway 130 reaches,
or in other words to adjust pipe handler trailer 100 to a particular derrick
platform elevation, lift
arms 141, 142 and skidway 130 are fully lowered. This will then trigger a
safety switch, detector
or the like. When the safety switch is triggered, this in turn allows an
operator to release locking
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blocks 168 from racks 144, 145 through hydraulic or other control Once locking
blocks 168 are
released, the operator may then activate hydraulic height adjustment cylinder
170 to move
adjustment block 160 longitudinally along lift arms 141, 142, simply by
retracting or extending
hydraulic height adjustment cylinder 170.
Retracting the cylinder will cause adjustment block 160 to be drawn to the end
of travel
on lift arms 141, 142 and racks 144, 145. When in this position, and when lift
arms 141, 142 are
subsequently raised by action of hydraulic lift cylinder 143, skidway 130 will
reach to the
maximum height. To set pipe handler trailer 100 to raise skidway 130 to the
minimum height,
the operator will lower lift arms 141, 142 and skidway 130, if they are not
already lowered, which
triggers the safety switch. Then the operator will release locking blocks 168,
and next extend
hydraulic height adjustment cylinder 170.
The limits of travel of adjustment block 160 along lift arms 141, 142 may be
set by travel
limit detectors, switches or the like. In addition to, or alternatively, the
limits may be set by
limits built or incorporated into hydraulic height adjustment cylinder 143.
An alternative embodiment pipe handler trailer 200 is illustrated in Figures 6-
8 that has
very similar construction to the preferred embodiment pipe handler trailer 100
illustrated in
Figures 1-5, performs the same function, and includes the same basic
structures, such as a wheel
set 214, deck 222, supporting framework, skidway 230, and lift arms 241, 242
with racks 244,
245. The two different embodiment pipe handler trailers 100, 200 are
distinguished by the
hundreds digit, and various components within each embodiment pipe handler are
designated by
the ones and tens digits. However, many of the components are alike or similar
between the two
illustrated pipe handler embodiments, so numbering of the ones and tens digits
have been
maintained wherever possible, such that identical, like or similar components
and functions will
share the same tens and ones digits between the embodiments, and may more
readily be
identified and recognized between the embodiments. If not otherwise expressed,
those skilled
in the art will readily recognize the similarities and understand that in many
cases like numbered
ones and tens digit components may be substituted from one embodiment to
another in accord
with the present teachings, except where such substitution would otherwise
destroy operation of
the embodiment. Consequently, those skilled in the art will readily determine
the function and
operation of many of the components illustrated herein without unnecessary
additional
description. Furthermore, where a component is referenced by a particular
reference numeral in
one embodiment but not explicitly illustrated, it will be understood herein
that the reference
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numeral of the corresponding other embodiment is being referenced. So, for
exemplary
purposes, since the exterior view of Figure 1 showing preferred embodiment
pipe handler trailer
100 illustrates wheel set 114, and since there is no reference numeral 214
explicitly shown, it will
be understood that wheel set 214 is referring to a wheel set identical to
wheel set 114, but found
on the alternative embodiment pipe handler trailer 200 rather than on the
preferred embodiment
pipe handler trailer 100.
While many components are identical, as illustrated in Figures 6 - 8 screw
adjustment 270
in alternative embodiment pipe handler 200 uses acme screws 271, 272 that are
rotated through
a hydraulic motor 273 and reversing gear 274 to counter-rotate the screws and
thereby to move
adjustment block 260, instead of using hydraulic height adjustment cylinder
170. In this
alternative embodiment, the acme screws 271, 272 are rotated to extend or
retract adjustment
block 260 when skidway 230 is fully lowered, similar to but instead of
hydraulic cylinder 170
found in preferred embodiment pipe handler 100 of Figures 1-5.
Adjustment block 260 has internal threads where acme screws 271, 272 pass
through.
These internal threads mate with threads on the acme screws 271, 272, and the
ends of acme
screws 271, 272 are fixed within and relative to skidway 230. Since internal
racks 244, 245 are
fixed within lift arms 241. 242, rotation of acme screws 271, 272 will apply
forces that will cause
adjustment block 260 to move relative to the racks.
Before the lift arms 241, 242 are rotated by the hydraulic lift cylinder 243,
and while they
are fully lowered to a location nearly or fully parallel with deck 222, a
switch or the like is
triggered that then, and only then, will allow motor 273 coupled to the end of
the acme screws
271, 272 to turn. In this embodiment, motor 273 is a hydraulic motor, but
other types of motors
will be understood to reasonably be substituted therefore. Additional safety
and strength in the
adjustment assembly may be provided by a pinion gear within locking blocks 268
that rolls on
associated racks 244, 245. Locking blocks 268 may also preferably include
locking cylinders 267
that otherwise prevent relative movement between adjustment block 260 and
internal racks 244,
245. In this alternative embodiment pipe handler trailer 200, locking
cylinders 267 perform the
function of cam lock 167, but instead of being a cam activated by rotary
motion, cylinders may
be provided that are hydraulically or otherwise actuated to engage with arms
241, 242, creating
the same pressure from that engagement that is generated by cam lock 167. The
locking
cylinders, for exemplary purpose only and not limiting thereto, may comprise
features 269 such
as complementary teeth that engage with the teeth on the internal racks 244,
245. These features
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269 are ordinarily biased such as through spring, hydraulic, magnetic,
gravitational or other force
to engage securely with internal racks 244, 245 and prevent relative motion
between features 269
and the racks. Only when motive forces are applied or removed to neutralize
locking cylinders
267, such as through a hydraulic cylinder, electrical solenoid or other
suitable motive power
source will the locking cylinders 267 release features 269 from the rack
teeth. When the switch
is triggered, signifying that skidway 230 has been lowered, then these locking
cylinders 267 may
also be released to permit this relative movement.
While Figure 6 solely illustrates locking cylinders 267 in association with
locking blocks
268, Figure 7 and 8 illustrate a further alternative embodiment comprising
both locking cylinders
267 and cam locks 367, either or both which may be utilized to lock locking
blocks 268 to racks
244, 245.
When acme screws 271, 272 are rotated, the point at which skidway 230 couples
to lift
arms 241, 242 through adjustment block 260 will change, and may preferably be
adjustable from
a lowermost point on the lift arms that is relatively close to deck 222 to a
highest point on the lift
arms relatively distal to deck 222. The length of the internal racks 244, 245
and the length of
acme screws 271, 272 will limit the extent of adjustment available. Since this
relative movement
changes the height of the skidway 230 end adjacent the rear of the trailer
when lift arms 241, 242
are raised, rotating acme screws 271, 272 will adjust the height to a desired
target height. Since
the height of the drilling platform will vary between different drilling rigs,
this permits both the
maximum height (perpendicular to the trailer longitudinal axis) that skidway
230 can reach, and
the stroke that skidway 230 travels parallel to the trailer 200 longitudinal
axis as it is raised and
lowered, to be changed through a very large number of positions and settings.
By incorporating
adequate locking cylinders and safety switches, these height and stroke
settings can only be
changed when skidway 230 is fully lowered, so that there is no risk of the
skidway suddenly
dropping during use. Where desired, markings may be provided on skidway 230
that correlate
a relative position between the skidway and lift arms 241, 242 to a
predetermined maximum
height.
While the foregoing details what is felt to be the preferred and alternative
embodiments
of the invention, no material limitations to the scope of the claimed
invention are intended.
Further, features and design alternatives that would be obvious to one of
ordinary skill in the art
are considered to be incorporated herein. The scope of the invention is set
forth and particularly
described in the claims hereinbelow.
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