Note: Descriptions are shown in the official language in which they were submitted.
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SCAFFOLDING
Field of the Invention
The present invention relates to scaffolding, especially to height adjustable
scaffolding and post assemblies therefor for lifting heavy materials, for
example
masonry or stone products.
Background of the Invention
External walls of a building structure are often faced with a stone or masonry
product (e.g. brick, block, stone tile, slate, etc.) for reasons of enhanced
aesthetics
and/or structural strength. Facing a wall with stone or masonry product
requires
people with specialized skills and a way of lifting the heavy product to
higher
elevations so that a workman can face upper levels of the wall.
Typically, scaffolding systems are erected to provide platforms at the
necessary
height to face the wall. However, lifting the product to the height of the
platform is
difficult and scaffolding systems currently available in the are generally
capable of
supporting only limited weight. Consequently, a workman wastes much time and
energy climbing up and down the scaffolding system to both supply more product
to
the platform and raise and lower the platform to the desired height. This is
not only a
waste of valuable time, it is a safety hazard as well since most accidents on
a site
occur while setting up the scaffold system or transporting the product.
One solution to the problem has been to provide more workmen to do some of
the jobs thereby freeing the person with the specialized skills to do more of
the facing
work. While somewhat effective, more workmen results in increased costs and
does
not solve the problem of having to constantly climb off the scaffold to raise
and lower
the platform.
To solve the latter problem, many height adjustable scaffolding systems have
been developed employing a variety of mechanisms to raise and lower the
platforms.
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However, such systems are typically plagued with one or more problems, for
example,
an inability to raise and lower the platform evenly on both ends, inability to
support the
great weight required for stone and masonry products, inability to easily
expand the
system to cover walls of greater length and/or height, inability to provide
convenient
access to stone or masonry product on the scaffolding system, and inability to
conveniently adjust the height of the platforms over an incrementally smaller
distance.
There remains a need in the art to provide a convenient and safe height
adjustable scaffolding system, particularly for working with heavy material.
Summary of the Invention
There is provided post assembly for a height adjustable scaffolding system for
lifting heavy materials comprising: a free-standing upright comprising an
elongated
strut having a top end and a bottom end; a wall mount assembly engaged with
the
upright proximal the top end of the elongated strut for mounting the upright
to a
building structure; a plattorm support assembly for supporting two or more
plattorms
between two or more post assemblies, the platform support assembly comprising
a
slide tube movably engaged with the upright to permit vertical movement of the
slide
tube between the top and bottom ends of the elongated strut, two or more
platform
support arms mounted to the slide tube for supporting two or more platforms,
first
locking means for engagement with the elongated strut for preventing downward
movement of the platform support assembly; a cylinder mounting bracket movably
engaged with the upright to permit vertical movement of the cylinder mounting
bracket,
the cylinder mounting bracket comprising second locking means for engagement
with
the elongated strut for preventing downward movement of the cylinder mounting
bracket; and, a hydraulic cylinder having a first end and a second end, the
first end
mounted to the slide tube, the second end mounted to the cylinder mounting
bracket,
the hydraulic cylinder actuable to produce relative vertical movement between
the
slide tube and the cylinder mounting bracket by moving the slide tube or the
cylinder
mounting bracket.
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There is also provided a height adjustable scaffolding system comprising: two
or more post assemblies of the present invention, the upright of each post
assembly
spaced-apart from and mounted to the building structure; two or more platforms
extending between adjacent post assemblies supported on the platform support
arms
of the adjacent post assemblies; a power source for powering the hydraulic
cylinder of
each post assembly; and, control means for providing simultaneous control of
power to
all of the hydraulic cylinders.
The elongated strut of the upright may be of any suitable length and diameter.
Two or more elongated struts may be linked together by a connector to provide
additional length to the post assembly and additional height to the
scaffolding system.
Preferably, the elongated strut comprises a square tube. Preferably, the
elongated
strut has a foot at the bottom end for resting on the ground or other
relatively flat
surface. The foot may comprise a flat plate to distribute load on the strut
over a larger
surface area. The upright may comprise a brace mount located near the top of
the
elongated strut to permit securing of the top of the post assembly to the
ground by
means of a brace attached to the brace mount and the ground. The brace may
comprise guy wires, rods or like means.
The elongated strut is preferably housed within the slide tube. The elongated
strut is also preferably housed within the cylinder mounting bracket. The
slide tube
and cylinder mounting bracket are movably engaged with the upright to permit
vertical
movement of the slide tube and cylinder mounting bracket on the upright. In
one
embodiment, the slide tube and/or cylinder support bracket are square tubes
having
diameters that permit the elongated strut to slide therein. The slide tube
and/or
cylinder mounting bracket may comprise means to reduce the possibility of
binding to
the elongated strut during vertical movement, for example, bearings or low
friction
inserts or coatings. In a preferred embodiment, one or more bearings may be
used to
reduce binding between the elongated strut and the slide tube and/or cylinder
mounting bracket. Where the slide tube and cylinder mounting bracket are
square
tubes, it is advantageous to provide bearings on all four faces of the square
tubes.
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The slide tube and cylinder mounting bracket each have locking means that can
engage the elongated strut to prevent downward movement of the slide tube and
cylinder mounting bracket. The elongated strut may comprise means for
cooperating
with the locking means to ensure more secure locking. Locking means may
comprise,
for example, a pin or a sprocket or a combination of means that engages the
elongated strut. The elongated strut may comprise apertures or protrusions
that
cooperate with the pin or sprocket for more secure engagement of the locking
means.
In a preferred embodiment, the locking means comprises a pin for engagement
with a plurality of vertically spaced apertures on the elongated strut. The
pin may be
biased, for example by a spring, for engagement with the apertures. The pin
may
comprise means for selective disengagement of the pin from an aperture.
Mounted to the slide tube are two or more, preferably two, platform support
arms. When two or more post assemblies are used in spaced-apart configuration,
the
platform support arms support a platform between the two or more post
assemblies.
Preferably, there are two platform support arms mounted to the slide tube, a
lower one
for supporting a walker platform in front of the post assembly and an upper
one for
supporting a loader platform in back of the post assembly (i.e. on the side
opposite the
lower platform support arm) and above the loader platform.
One or more hydraulic cylinders are mounted between the slide tube and the
cylinder support bracket for producing relative movement between the slide
tube and
the cylinder support bracket. It is this relative movement that permits height
adjustment of the scaffold. So that the slide tube and cylinder support
bracket may
each be raised and lowered independently, it is preferable to use a double-
acting
hydraulic cylinder or a pair of single-acting hydraulic cylinders mounted in
reverse
orientation. Control and power of hydraulic cylinders may be accomplished by
methods generally known in the art.
Preferably at least one of the platform support arms is positioned between the
first and second ends of the hydraulic cylinder. Such an arrangement provides
a more
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compact and efficient post assembly that has more useful working range for a
given
length of the elongated strut.
In a scaffolding system of the present invention, the upright is spaced-apart
from the building structure to provide space between the structure and the
upright for a
5 platform. For masonry and stone work, this space is preferably about 27 to
30 inches
top provide sufficient space to work while being as close to the building
structure as
possible. In operation, the upright is free standing. In order to prevent the
upright
from falling over, the wall mount assembly permits securing the upright to the
building
structure to provide stability to the post assembly. The wall mount assembly
is
preferably movably engaged with the upright to permit vertical movement of the
upright
when the wall mount assembly is fixedly mounted to the building structure.
This
permits the building and/or upright to move in response to ground movement or
other
causes without placing a strain on the mounting connection of the wall mount
to the
building structure. Preferably, the wall mount assembly comprises a square
tube in a
manner similar to the slide tube and cylinder support bracket. Preferably, the
wall
mount assembly also comprises means for reducing the possibility of binding on
the
elongated strut, for example one or more bearings or low friction inserts or
coatings.
The scaffolding system of the present invention comprises two or more post
assemblies. For ease of operation, it is preferable to provide a means for
simultaneous selective disengagement of the first locking means on all post
assemblies. It is also preferable to provide a means for simultaneous
selective
disengagement of the second locking means on all post assemblies. Such means
may comprise a mechanism (e.g. a lever, cable, pulley, etc. or a combination
thereof)
connected to all of the first locking means or all of the second locking
means.
Connection of the lever to the locking means may be accomplished, for example,
by
cables, rods, bars, etc. or a combination thereof.
The scaffolding system may comprise a back-up support system, for example
security bolts or a winch and cable system, as a redundant security measure
and/or to
be able to effect more rapid lowering of support platforms. The post assembly
may be
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equipped with dumb waiters in the slide tube and cylinder mounting bracket to
prevent
crashing of the platforms if both are unlocked at the same time.
When used to lift stone or masonry products, the post assembly of the present
invention must support considerable weight. Therefore, in such applications,
the post
assembly should be constructed of strong, durable material, for example a
metal or
metal composite, for example iron, steel, etc.
The post assembly of the present invention advantageously permits adjusting
the height of a scaffold over the entire length of the uprights from foot to
wall mount
assembly. This provides for a greater range of heights and more increments of
heights over a given length of uprights than prior art scaffolding systems.
Further, height adjustment of the scaffold can be accomplished without having
to move planks of the platform. Therefore, height adjustment of the scaffold
may be
accomplished with loaded platforms. If desired, height adjustment may be
advantageously accomplished by a single workman from the walker platform. The
workman need not leave the walker platform to adjust the height of the
scaffold.
Masonry or stone product is conveniently located at hip height to the workman
at all
times. Such advantages provide great savings in time and effort and enhance
safety
at the job site.
Furthermore, the scaffolding system of the present invention can support
heavier loads than prior art systems. Each post assembly of the present
invention can
support up to 3000 Ibs., as opposed to 700 Ibs. for most prior art systems.
Additionally, the scaffolding system is close to the wall (within 3 feet) for
greater
convenience for the workman.
Further features of the invention will be described or will become apparent in
the course of the following detailed description.
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Brief Description of the Drawings
In order that the invention may be more clearly understood, embodiments
thereof will now be described in detail by way of example, with reference to
the
accompanying drawings, in which:
Fig. 1 is a perspective view of a post assembly of the present invention;
Fig. 2A depicts the slide tube of the post assembly of Fig. 1 as viewed from
the
side of the post assembly;
Fig. 2B depicts the slide tube of Fig. 2A as viewed from the front of the post
assembly;
Fig. 2C depicts the slide tube of Fig. 2A as viewed from the top end of the
post
assembly;
Fig. 3A is a perspective view of the cylinder mounting bracket of the post
assembly of Fig. 1;
Fig. 3B depicts the cylinder mounting bracket of Fig. 3A as viewed from the
side
of the post assembly;
Fig. 3C depicts the cylinder mounting bracket of Fig. 3A as viewed from the
front of the post assembly;
Fig. 3D depicts the cylinder mounting bracket of Fig. 3A as viewed from the
top
end of the post assembly;
Fig. 4A is a perspective view of a locking pin on the post assembly of Fig. 1;
Fig. 4B depicts the locking pin of Fig. 4A as viewed from the side of the post
assembly;
Fig. 4C depicts the locking pin of Fig. 4A as viewed from the front of the
post
assembly;
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Fig. 4D depicts the locking pin of Fig. 4A as viewed from the top end of the
post
assembly;
Fig. 5A is a perspective view of the wall mount assembly of the post assembly
of Fig. 1;
Fig. 5B depicts the wall mount assembly of Fig. 5A as viewed from the side of
the post assembly;
Fig. 5C depicts the wall mount assembly of Fig. 5A as viewed from the front of
the post assembly;
Fig. 5D depicts the wall mount assembly of Fig. 5A as viewed from the top end
of the post assembly; and,
Fig. 6 depicts a scaffolding system of the present invention having three post
assemblies arranged in a row.
Description of Preferred Embodiments
Referring to Figs. 1 to 5, a post assembly of the present invention comprises
an
upright comprising a 12 foot long 3" square steel tube 10 having a plurality
of
apertures 11 vertically spaced at regular intervals along the front face of
the 3" tube.
The bottom end of 3" tube 10 is attached to foot 12 for supporting the post
assembly
on the ground or other relatively flat surface. Foot 12 comprises a flat plate
perpendicular to 3" tube 10 for distributing weight over a larger surface area
to provide
better stability and to help prevent the post assembly from sinking into then
ground.
The top end of 3" tube 10 is attached to brace mount 13 which is a 3.5" square
steel
tube fitted over 3" tube 10. Brace mount 13 comprises a pair of sideways
extending
flanges 14 to which a brace may be connected for stabilizing the post assembly
when
it is the end post of a scaffolding system as described in relation to Fig. 6
below.
A 4 foot long 4" square steel slide tube 20 having 3" tube 10 encircled
therein is
vertically movable along the length of the 3" tube. Connected to slide tube 20
are
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upper platform support arm 21 and lower platform support arm 22. The upper and
lower platform support arms are connected to the slide tube by arm support
brackets
23 within which the platform support arms are slidably engaged and secured
with a
bolt or pin. Upper arm 21 extends perpendicularly from the rear face of slide
tube 20
and lower arm 22 extends perpendicularly from the front face of the slide
tube. Upper
arm 21 is used to support a loader platform of a scaffolding system while
lower arm 22
is used is used to support a walker platform. To help prevent slide tube 20
from
binding on 3" tube 10 during vertical movement of the slide tube, eight
bearings 24 are
mounted in upper and lower sets on each face of the slide tube. Bearings 24
extend
through the wall of slide tube 20 to engage the faces of 3" tube 10. Bearings
24 can
rotate as slide tube 20 moves vertically, either up or down. Security bolts
78,79 on
each side of the 4" tube may be screwed in, if desired, to engage the sides of
the 3"
tube as an added safety measure to prevent the 4" tube from accidentally
moving. If
the security bolts are engaged, they will need to be disengaged by screwing
them out
before height adjustment of slide tube 20 can be effected.
At a desired height, slide tube 20 is locked into place on 3" tube 10 by
engagement of spring-loaded locking pin 25 in one of the apertures 11 in 3"
tube 10.
Spring-loaded locking pin 25 is mounted on the front face of slide tube 20 and
is
biased toward the front face of 3" tube 10. As best seen in Fig. 4B, tip 31 of
pin 25 is
sloped on its upper surface to permit automatic disengagement of the pin from
the
aperture in response to upward movement of slide tube 20. Pin 25 will
automatically
bias into place in the next aperture up as slide tube 20 moves upwardly. Tip
31 of pin
is horizontal on its bottom surface to ensure that slide tube 20 cannot move
downwardly without actively disengaging the pin from the aperture.
25 When downward movement of the slide tube is desired, pin 25 may be
disengaged from aperture 11 by pulling the pin out of the aperture. This may
be
conveniently accomplished by action of swivel link 26. Referring particularly
to Fig. 4,
swivel link 26 comprises a set of steel bars pivotally linked on pins 34. In
particular,
one leg of L-shaped bar 36 is pivotally linked to one end of pin pulling bar
37 and the
corner of L-shaped bar 36 is pivotally linked to one end of fixed pin bar 38.
The other
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end of pin pulling bar 37 is pivotally linked to tail end 32 of pin 25 and the
other end of
fixed pin bar 38 is fixedly attached to housing 33 of pin 25. The other leg of
L-shaped
bar 36 may be pivotally connected to hook 27 such that an appropriate force on
the leg
of L-shaped bar 36 connected to the hook causes pin 25 to be pulled out of the
5 aperture by pin pulling bar 37. A workman standing on the walker platform
may thus
use hook 27 to pull pin 25 from aperture 11.
Once the pin is pulled from the aperture, slide tube 20 is movable downward on
3" tube 10. Especially where a large number of post assemblies are used to
construct
a scaffolding system, hook 27 on each post assembly may be conveniently
replaced
10 by a rod or tube extending between and connected to swivel links 26 of all
post
assemblies and the rod or tube connected to a single lever mounted near the
walker
platform so that action on the lever will release pins 25 on all post
assemblies
simultaneously.
Proximal the top of slide tube 20 under arm 21 but above the upper set of
bearings 24, bracket flanges 28 extend perpendicularly from the rear face.
Bracket
flanges 28 are connected to the top end of double-acting hydraulic cylinder 35
by
means of draw pin 29. Draw pin 29 may be secured by a cotter pin (not shown).
A cylinder mounting bracket comprises 6" long 4" square steel cylinder
mounting tube 40 separate from and located below slide tube 20. Cylinder
mounting
tube 40 is vertically movable along the length of 3" tube 10 in a manner
similar to that
of slide tube 20. Thus, bearings 44 help prevent binding of cylinder mounting
tube 40
and spring-loaded pin 45 locks the cylinder mounting tube at a desired height
by
engagement of the pin 45 in an aperture 11 in 3" tube 10. The action of pin 45
is the
same as that described for pin 25 above. Releasing pin 45 from aperture 11 is
accomplished by action on swivel link 46 in the same manner as described above
in
connection with swivel link 26. In the same manner as described above, pins 45
on a
plurality of post assemblies may be released individually or simultaneously.
Bracket flanges 48 extend perpendicularly from the rear face of cylinder
mounting tube 40 and are connected to the bottom end of double-acting
hydraulic
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cylinder 35 by means of draw pin 49. Draw pin 49 may be secured by a cotter
pin (not
shown). Hydraulic cylinder 35 has a lift height of 30 inches
The bottom end of hydraulic cylinder 35 is connected to cylinder mounting tube
40 as close as possible to the ground. The top end of hydraulic cylinder 35 is
connected to slide tube 20 as close as possible to the top of the slide tube
while
remaining below the upper platform support arm 21. As a result, upper platform
support arm 21 and lower platform support arm 22 are as close to the ground as
possible when slide tube 20 and cylinder mounting tube 40 are in the lowermost
position on 3" tube 10. This is particularly beneficial when working with
heavy
materials. In such an arrangement, lower platform support arm 22 is always
positioned between the top and bottom ends of the hydraulic cylinder providing
a more
compact and efficient post assembly that has more useful working range for a
given
length of the 3" tube.
A wall mount assembly is located below brace mount 13 proximal the top of 3"
tube 10 and extends perpendicularly from the front face of 3" tube 10. The
wall mount
assembly comprises 8" long 4" square steel wall mount assembly tube 50
separate
from and located above slide tube 20. Wall mount assembly tube 50 is
vertically
movable along the length of 3" tube 10 in a manner similar to that of slide
tube 20.
Thus, bearings 54 help prevent binding of wall mount assembly tube 50 to 3"
tube 10.
Wall mount assembly tube 50 is allowed to ride freely along 3" tube 10 to
accommodate settling and heaving of the post assembly due to ground surface
and/or
building movement effects. Extending perpendicularly from the from face of
wall
mount assembly tube 50 is connector post 51, which connects the wall mount
assembly tube 50 to mounting plate 52. Mounting plate 52 may be secured to a
wall
of a building structure by any convenient means, e.g. screws, bolts, etc., to
stabilize
the post assembly.
Referring to Fig. 6, a height adjustable scaffolding system of the present
invention comprises three post assemblies 5a,5b,5c similar to the one
described in
relation to Figs. 1-5 lined up in a row. For safety and stability, the post
assemblies are
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secured to a wall of a building (not shown) by fastening wall mount assemblies
50a,50b,50c to the building. Upper platform support arms 21a,21b,21c support
loader
platform 61 on which bricks may be stacked. Lower platform support arms
22a,22b,22c support walker platform 62 from which a workman may do work.
Walker
platform 62 is located below and closer to the wall than loader platform 61 so
that the
stack of bricks is conveniently at hip height to the workman and on the
opposite side of
the post assemblies, which is both more convenient and safer for the workman.
The scaffolding system is further stabilized by securing end post assemblies
5a,5c to the ground using braces 66,67. Braces 66,67 are steel rods connected
to
post assemblies 5a,5c at brace mounts 13a,13c by a pin passing through
apertures in
the rods and in the pair of sideways extending flanges of the brace mounts.
Braces
66,67 comprise ground plates 68,69 respectively, which are secured to the
ground, for
example by spikes.
Upper connecting rod 71 extends between and is connected to swivel links
26a,26b,26c on the slide tube of each post assembly. The upper connecting rod
is
connected to a single lever (not shown) at the worker platform so that the
spring-
loaded pins of each slide tube may be released simultaneously by a single
workman
when the workman desires to adjust the height of the slide tubes on the post
assemblies.
Lower connecting rod 72 extends between and is connected to swivel links
46a,46b,46c on the cylinder mounting brackets of each post assembly. The lower
connecting rod is connected to a single lever (not shown) at the worker
platform so
that the spring-loaded pins of each cylinder mounting bracket may be released
simultaneously by a single workman when the workman desires to adjust the
height of
the cylinder mounting brackets on the post assemblies.
Using an upper connecting rod permits a single workman to simultaneously
adjust the height of all of the slide tubes on the post assemblies. Using a
lower
connecting rod permits a single workman to simultaneously adjust the height of
all of
the cylinder mounting tubes on the post assemblies. If both upper and lower
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connecting rods are used, a single workman can conveniently adjust the height
of the
walker and loader platforms without having to leave the walker platform.
Double-acting hydraulic cylinders 35a,35b,35c are connected by hydraulic
supply lines to a common controller and power source (not shown).
Referring generally to the Figures, the way in which the height of the
scaffolding
system is adjusted will now be described in relation to a single post
assembly. It will
be understood that each post assembly in the scaffolding system operates
similarly
and that the operation of all post assemblies may accomplished simultaneously
as
previously described.
Starting with slide tube ZO and cylinder mounting bracket 40 in their lowest
possible positions on post assembly 10, and starting with double-acting
hydraulic
cylinder 35 fully retracted, spring-loaded pins 25 and 45 will each be engaged
within
apertures 11 in the post assembly. In order to raise the walker and loader
platforms, it
is necessary to raise slide tube 20. The hydraulic power source is switched on
and
hydraulic fluid flow to hydraulic cylinder 35 is set to drive the cylinder's
rod up and
spring-loaded pin 25 is released from its aperture thereby allowing hydraulic
cylinder
35 to extend, pushing slide tube 20 upward. When pin 25 is aligned with the
next
highest aperture in post assembly 10, spring-loaded pin 25 will automatically
engage
the next highest aperture thereby arresting upward movement of the slide tube.
If
cylinder 35 extends far enough and if apertures 11 are sufficiently close
together, it
may be possible to allow pin 25, and therefore slide tube 20, to pass by the
next
highest aperture to an aperture yet higher by maintaining action on swivel
link 26 to
keep spring-loaded pin 25 from engaging the next highest aperture.
Once hydraulic cylinder 35 is fully extended, it is necessary to raise
cylinder
mounting bracket 40 before the walker and loader platforms can be raised
further. To
raise cylinder mounting bracket 40, hydraulic fluid flow to double-acting
hydraulic
cylinder is reversed. Reversing hydraulic fluid flow may be accomplished from
a
controller mounted on the walker platform so that the workman does not need to
leave
the scaffolding system. Spring-loaded pin 45 is released from its aperture
permitting
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14
hydraulic cylinder 35 to retract since pin 25 on slide tube 20 remains engaged
within
its aperture. Fluid pressure in double-acting hydraulic cylinder drives the
cylinder's rod
down thereby pulling the cylinder's body up. Retraction of hydraulic cylinder
35 brings
cylinder mounting bracket 40 up until pin 45 engages the next highest
aperture. By
maintaining action on swivel link 46 it is possible to keep pin 45 from
engaging the
next highest aperture thereby permitting the cylinder mounting bracket to be
brought
up as high as possible.
To again raise slide tube 20, hydraulic fluid flow to double-acting cylinder
35 is
again reversed to drive the cylinder's rod up and the foregoing raising
process
repeated. The entire raising process may be repeated until slide tube 20 can
be
raised no higher on post assembly 10 due to the presence of wall mount
assembly 50
and brace mount 13.
With slide tube 20 and cylinder mounting bracket 40 in their highest possible
positions on post assembly 10, and with double-acting hydraulic cylinder 35
fully
retracted, spring-loaded pins 25 and 45 will each be engaged within apertures
11 in
the post assembly. In order to lower the walker and loader platforms, it is
necessary to
lower cylinder mounting bracket 40. Hydraulic fluid flow to hydraulic cylinder
35 is set
to drive the cylinder's rod up and spring-loaded pin 45 is released from its
aperture
thereby allowing hydraulic cylinder 35 to extend, pushing cylinder mounting
bracket 40
downward. When pin 45 is aligned with the next lowest aperture in post
assembly 10,
spring-loaded pin 45 will automatically engage the next lowest aperture
thereby
arresting downward movement of the cylinder mounting bracket. If cylinder 35
extends far enough and if apertures 11 are sufficiently close together, it may
be
possible to allow pin 45, and therefore cylinder mounting bracket 40, to pass
by the
next lowest aperture to an aperture yet lower by maintaining action on swivel
link 46 to
keep spring-loaded pin 45 from engaging the next lowest aperture.
Once cylinder mounting bracket 40 is lowered, it is necessary to lower slide
tube 20 in order to lower the walker and loader platforms. To lower slide tube
20,
hydraulic fluid flow to double-acting hydraulic cylinder is reversed and
spring-loaded
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pin 25 is released from its aperture permitting hydraulic cylinder 35 to
retract since pin
45 on cylinder mounting bracket 40 remains engaged within its aperture. Fluid
pressure in double-acting hydraulic cylinder drives the cylinder's rod down
thereby
retracting hydraulic cylinder 35. Retraction of hydraulic cylinder 35 pulls
slide tube 20
5 down until pin 25 engages the next lowest aperture. By maintaining action on
swivel
link 26 it is possible to keep pin 25 from engaging the next lowest aperture
thereby
permitting the slide tube to be pulled down as low as possible.
To again lower cylinder mounting bracket 40, hydraulic fluid flow to double-
acting cylinder 35 is again reversed to drive the cylinder's rod up and the
foregoing
10 lowering process repeated. The entire lowering process may be repeated
until
cylinder mounting bracket 40 can be lowered no lower on post assembly 10 due
to the
presence of foot 12 or the lowest aperture.
It is not advisable to release both pins 25 and 45 at the same time as this
will
permit both the slide tube and the cylinder mounting bracket to lower
simultaneously
15 causing the platforms to crash to the ground rapidly. One skilled in the
art will
understand that two single-acting hydraulic cylinders may be used in place of
one
double-acting hydraulic cylinder.
Other advantages which are inherent to the structure are obvious to one
skilled
in the art. The embodiments are described herein illustratively and are not
meant to
limit the scope of the invention as claimed. Variations of the foregoing
embodiments
will be evident to a person of ordinary skill and are intended by the inventor
to be
encompassed by the following claims.
