Note: Descriptions are shown in the official language in which they were submitted.
il2~6929
Description
LIFT
Technical Field
The present invention relates to a portable,
multistage lift which incorporates a reeving system for at
least part of the elevating system to cause the lift stages
to move relative to one another.
Background Art
-- More specifically, the present invention is an
improvement over my prior~Pà~ent ~o~ 4,015,686, issued April
5, 1977. As noted in my prior patent, for construction and
repair service work, it is often necessary that personnel or
relatively heavy materials or equipment be raised to an
elevated position on a work platform or load-carrying forks.
If the lift has a single mast and the load is supported so
that its center of gravity is offset from the lift axis,
there is created a moment tending to tip over the lift. If
the lift is to be of lightweight construction for ease of
transport and it is to have the ability to raise to eleva-
tions in the range of 30-40 feet, it is difficult to main-
tain stability even if outriggers are provided for the baseof the unit. Stability is, of course, particularly impor-
tant if the lift is being used to raise personnel to an
elevated working level. With such a lift, it is also desir-
able to not have to use outriggers on the base which extend
laterally because this limits how close the lift can be
located with respect to the wall of a building or other
structure.
It is also preferred to have such a lift operate
in a manner whereby the work platform moves to the top of
the upper mast section before the various mast sections move
relative to one another. Otherwise, the upper stage of the
lift may come in contact with the overhead structure before
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the working platform has reached the desired height. It is
also preferred that the elevation of the working platform,
after it has been elevated to substantially the desired
height, be able to be adjusted.
Disclosure of Invention
The present invention utilizes a mast structure
similar to that shown in my prior patent, 4,015,686, but
incorporates an improved reeving system and use of a coun-
terbalance arm which projects from the top of one of themovable mast sections in a direction opposite that occupied
by a load-carrying unit. Load is transferred through the
reeving system from the working platform to the outer end of
the arm, and this creates a counterbalancing moment to off-
set that created by the load. The system depends upon thelowest of the movable mast sections being powered upwardly
independently of the reeving system by a suitable elevating
means such as a hydraulic or pneumatic cylinder, a jack, or
a lifting cable operated by a stationary winch. A recharge-
able battery pack may be provided on the base of the lift topower the elevating means.
Several embodiments of the invention are disclosed.
In the preferred embodiment, the counterbalance arm is
mounted on the lowermost movable mast section and the reev-
ing system incorporates a single cable for transferring a
downward counterbalancing force to the arm and for causing
the movable mast section(sJ above the lowermost movable mast
section to raise responsive to raising of the lowermost
movable mast section by an independent elevating means.
In other embodiments, the counterbalance arm is
mounted on the top mast section and the reeving system
incorporates more than one cable, namely, the same number of
cables as movable mast sections. One of the cables trans-
fers the downward counterbalancing force to the arm. The
other cable(s) is(are) used to cause the movable mast sec-
tion(s) to move upwardly to the desired extent responsive to
raising of the lowermost movable mast section by an indepen-
dent elevating means.
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Brief Description of the Drawings
In the accompanying drawings:
Fig. 1 is a front perspective view of a lift
embodying the present invention:
Fig. 2 is a side elevational view of the lift
shown with the load-carrying unit at the ground level;
Fig. 3 is a side elevational view of the lift in
partly raised position, namely, at the level at which the
load-carrying unit has reached its upper limit of travel
relative to the top section of the mast;
Fig. 4 is a side elevational view of the lift at
its maximum raised elevation;
Fig. 5 is a detailed transverse sectional view of
the mast when in lowered position;
Figs. 6 and 7 are detailed sectional views taken
as indicated in line 6-6 of Fig. 5 and showing the manner in
which the top mast section is retarded against movement
relative to the next mast section while the load-carrying
unit is being raised relative to the top mast section;
Fig. 8 is another detailed view taken as indicated
in line 8-8 of Fig. 5 and shows the location of the stops
for limiting upward movement of the various mast sections
relative to one another;
Pig. 9 is an elevational view of a modified system
with the counterbalance arm on the top mast section;
Fig. 10 is a side elevational view of a modified
system like that in Fig. 9, but with an additional mast
stage;
Fig. 11 is a side elevational view illustrating a
unit of the type shown in Fig. 1, but with an additional
intermediate mast section; and
Fig. 12 is a side elevational view illustrating a
unit of the type shown in Fig. 1, but modified to replace
the lift cylinder with another lifting means and with the
; 35 reeving system modified to speed raising and lowering of the
working platform relative to the top stage of the lift.
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Best Mode for Carrying Out the Invention
For purposes of example, the invention is
disclosed in Figs. 1-7 of the drawings as applied to a lift
having three telescopic mast stages or sections, namely, a
stationary base stage 20 mounted on a base 18, an inter-
mediate stage 21, and a top stage 22. A load support unit
23 is slide mounted at the rear of the top stage 22 and is
interconnected by a cable 24 on a reeving system with a
forwardly projecting counterbalance arm 26 mounted at the
top of the intermediate stage 21. The intermediate stage is
extended and retracted by action of a double-acting hydrau-
lic cylinder unit 28 or other suitable elevating means. The
unit 28 has its cylinder seated on the base assembly 18 and
housed in the base stage 20, and has its piston rod 28a con-
nected at its upper end to a cross-shaft 30 (Fig. 5) mounted
at the upper end of the intermediate stage. As will be
explained in detail later, raising of the intermediate stage
by the unit 28 responsively causes raising of the load
support unit 23 to the upper end of the top stage 22 and
raising of the top stage relative to the intermediate stage
by way of a reeving system.
The load support unit 23 has a pair of forks 23a
projecting forwardly from a cross-member at the lower end of
a slide section 23b. This slide section and the three mast
sections 20-22 may be aluminum extrusions having basically
the same cross-section as shown in Fig. 5. The extrusion
has reversed symmetrical portions at both lateral sides
which are connected by a rear web 30 and a center web 31.
In the case of the intermediate mast section 21, the center
web is formed with a central forwardly arched portion 31a to
accommodate the front of the hydraulic cylinder 28. The
side portions of the extrusion each have an outwardly pro-
jecting rear track flange 32 continuing from the rear web
30, a closure portion 33 forming a box with the webs 30-31,
and a front inwardly facing channel formed by a rearwardly
facing central flange 34, an outer flange 35, and a front
track flange 36. To guide the intermediate stage 21, the
base stage 20 is provided with a pair of aligned rollers 38
journaled on stub shafts 40 extending through the outer
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flanges 35 of the base stage 20 to a position between the
rear track flanges 32 of the intermediate stage 21 and the
front track flanges of the base stage 20. Nuts 42 secure
the shafts 40 in position. In like manner, a pair of
aligned rollers 44 is mounted on the intermediate stage 21
for engagement by the rear track flanges 32 of the top stage
22, and a pair of aligned rollers 46 is mounted on the top
stage 22 for engagement by the rear track flanges of the
load support unit 23. To further assist in guiding the load
support unit 23 along the top stage 22, an additional set of
rollers 48 is provided. This set is mounted by shafts 50
projecting outwardly from the closure portions 33 of the
slide section 23b near the lower end thereof so as to engage
the front face of the central flanges 34 of the top stage 22
through cutouts in the bottom of the rear track flanges 32
of the slide section 23b. The lower end portions of the top
stage 22 and intermediate stage 21 are also preferably
fitted with a second set of guide rollers in the same manner
as the lower rollers 48 on the load-carrying unit 23.
The cable 24 in the reeving system is dead-ended
at its rear end at 52 on the arm 26 and at its front end at
54 on the load-carrying unit 23. As best seen in Fig. 4,
the cable 24 extends downwardly from its forward end around
a diagonal sheave 54 at the lower end of the slide section
23b, upwardly over a sheave 56 at the upper end of the top
stage 22, downwardly around a diagonal sheave 58 at the
lower end of the top stage 22, upwardly over a sheave 60 at
the top of the intermediate stage 21, downwardly around
sheaves 62 and 64, and upwardly to the arm 26. The sheaves
62 and 64 are journaled near the bottom of a lower strut
assembly 66 extending rearwardly from the back of the bottom
stage 20. This strut assembly 66 serves as a cable guard
and helps support a pair of rearwardly projecting struts 68
for an axle 70. Transport wheels 72 are mounted on the axle
3~ 70, and outwardly of the wheels 72 the axle 70 has a pair of
handles 74. Another set of transport wheels 76 is mounted
slightly above ground level on an axle 78 aft of the rear of
the base assembly 1~.
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The base assembly 18 has a pair of front reches 80
latched in position and having casters 82 at their forward
ends to complement rear casters 83 provided with locks.
These reaches 80 are adapted to be unlatched and swung
upwardly at 84 for compact storage. When the forks 23a are
in their lowered position, they are situated between the
reaches 80, as shown in Fig. 1. The forks 23a may be made
to have an alternate position located at the top of the
slide section 23b, as disclosed in my prior United States
Patent 3,876,039,~so t~atPa re~a~ively short load resting on
the forks will always extend above the top of the mast when
the load-carrying unit 23 is at its upper limit of travel
relative to the top stage of the mast.
With the described arrangement, the entire lift
assembly can be rocked back onto the wheels 76 while grip-
ping the handles 74 and easily wheeled about a jobsite.
Both sets of wheels 72, 76 can be used to support and roll
the lift unit on a truck bed, for example, being used to
move the unit to another jobsite.
A pair of stop shoes 88 is mounted on the outside
faces of the portions 33 near the top of the three mast sec-
tions 20-22 for engagement by stops 89 mounted, respective-
ly, near the lower ends of section 23b of the load-carrying
unit, the top mast section 22 and the intermediate mast
section 21. These stops 88, 90 preferably have cooperating
bevel faces 80a, ~Oa (Fig. 8) to assist in rigidifying the
mast when fully extended. Directing attention to Figs. 6-7,
it will be noted that the stops 88 are spaced forwardly of
the rear track flange 32 of the next forward section. It
will also be noted that the flanges 32 have been cut back at
their upper end approximately the diameter of the rollers 44
to provide a cam 32a. This is done so that top mast section
22 can rock forward slightly under load to the position
shown in Fig. 6 while the mast section 22 is at the same
height as the intermediate section 21. When in such posi-
tion, the forward top section 22 cannot move upwardly rela-
tive to the intermediate section 21 without the cam 32a of
the top section 22 coming into engagement with the underside
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of the top roller 44 of the intermediate mast section 21.
As will be further discussed, when the cam 32a does engage
the underside of the roller 44, relative motion between the
top and intermediate mast sections is retarded and cannot
continue until the top mast section swings rearwardly suffi-
ciently to permit the cam 32a to ride over the back of the
roller 44, as shown in Fig. 7. This retarding action makes
certain that the load-carrying unit 23 will move to the top
of the top mast section 22 before the latter moves upwardly
relative to the intermediate mast section 21.
Attention is now directed to Figs. 2-4, showing
the various stages of the load-carrying units and mast
sections. Starting with load-carrying unit 23 at its
lowermost position, as shown in Fig. 2, when the hydraulic
cylinder 20 is activated, thereby causing the intermediate
mast section to move upwardly relative to the base section
20, the portion of the cable 24 between the load-carrying
unit 23 and the top of the intermediate mast section 21 is
shortened an amount equal to twice the extension of the
hydraulic cylinder. This means that the load-carrying unit
23 will initially move upwardly relative to the base section
20 a distance equal to three times the amount of extension
of the hydraulic cylinder. Hence, when the mast section has
moved upwardly one-third of its total possible extension,
the load-carrying unit will have reached the top of the top
mast section 22. In this regard, a load on the load-carry-
ing unit will have caused the top mast section 22 to rock
slightly forward relative to the intermediate mast section
21, as previously discussed with respect to Figs. 6-7,
thereby preventing the top mast section 22 from moving
upwardly relative to the intermediate mast section 21 while
the load-carrying unit 23 is moving upwardly relative to the
top mast section 22. Accordingly, the mast sections and the
load-carrying unit should be in the position shown in Fig. 3
when the load-carrying unit 23 has reached the top of the
top mast section 22. Further extension of the cylinder 28,
and the resulting shortening of the cable portion between
the mast sections 22 and 21, cause the top section 22 to
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move upwardly relative to the base section 20 at a rate
three times the cylinder extension, and this results in the
upper mast section 22 becoming fully extended relative to
the intermediate mast section 21 when the latter has moved
upwardly two-thirds of its potential movement relative to
the base section 20. Further extension of the hydraulic
cylinder 28 then completes the full extension of the mast
section shown in Fig. 4 as the intermediate section 21 is
moved to the top of the base section 20.
Directing attention to Fig. 12, there is illus-
trated a modified reeving system in which the cable 24 has
an additional pass 24' between the arm 26 and strut 66 about
a sheave 64' on the arm and dead-ends at 52' on the strut
66. The result of this modification is that the load-carry-
ing unit 23 moves upwardly responsive to extension of the
cylinder unit 28 acting on the intermediate mast section 22,
at a faster rate, and namely, ~our times the extension of
the cylinder unit 28 rather than three times. Similarly,
the top stage 22 then moves upwardly relative to the inter-
mediate stage at four times the amount of further extensionof the cylinder unit. As a result, the load-carrying unit
is at the upper end of the top mast section 22 when the
cylinder unit 28 has one-fourth of its total extension, and
the top section 22 reaches its upper limit of travel rela-
tive to the intermediate section 21 when the cylinder unit28 has one-half of its total extension. Fig. 12 also illus-
trates an alternative elevating means to the cylinder unit
28, and namely, a winch 90 operating on a cable 91 extending
over a sheave 92 at the upper end of the base stage 20 and
downwardly to a connection 93 to the lower end of the
intermediate mast section 21.
Directing attention to Fig. 11, there is illus-
trated a mast with an additional intermediate section 21a.
This section 21a has the same retarding arrangement (Figs.
6-7) with the top mast section 22 as previously described.
The reeving system has been expanded to include sheaves 58a,
60a at the lower end and upper end, respectively, of the
additional intermediate mast section 21a. It will also be
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noted that the reeving system also has been modified as in
Fig. 12 to add another pass 24' between the arm 26 and strut
66 and thereby give three p~sses. This is the minimum num-
ber of passes for three movable mast stages (one pass per
movable mast stage), just as at least two passes were neces-
sary for two movable mast sections, as shown in Figs. 2-4,
to achieve the desired total result of the present inven-
tion.
In the embodiment of Fig. 11, when the cylinder
unit 28 extends one-fourth of its total extension, the load
carrying unit 23 reaches the top of the top mast section 22,
at which point all three of the mast sections 21, 21a and 22
are at the same extended height of one-fourth of the total
extension of the cylinder unit 28. The top mast section 22
then begins to move upwardly relative to the upper inter-
mediate mast section 21a at a rate of four times the addi-
tional extension of the cylinder unit, so that it reaches
the upper end of its travel relative to the upper intermedi-
ate section 21a when the cylinder unit is halfway extended.
Similarly, the upper intermediate section 21a then reaches
the upper end of its travel relative to the lower inter-
mediate section 21 when the cylinder unit 28 has extended
three-fourths of its total extension.
Figs. 9 and 10 show two further embodiments in
which the counterbalance arm is moved to the top mast sec-
tion 22 and designated 26'. In the Fig. 9 embodiment, the
reeving system involves a cable 28a extending from a winch
90' on its strut 66 upwardly to the arm 26' and includes a
second cable 28b extending from the upper end of the base
stage 20 over a sheave 60a at the top of the intermediate
stage 21 and then downwardly to a connection at the lower
end of the top stage 22. It will be apparent that the
second cable 28b causes the top stage 22 to move upwardly
relative to the intermediate stage 21 responsive to exten-
sion of the cylinder unit 28 and at the same rate. Return-
ing to the other cable 28a, it passes around a sheave 100 at
the outer end of the arm 26', travels forwardly over a
sheave 101 at the upper end of the top stage 22, goes
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downwardly around a sheave 102 on the load-carrying unit 23,
and then passes upwardly to an anchor point 103 at the upper
end of the top stage 22. When the cylinder unit is in its
fully retracted position and the load-carrying unit 23 is at
the bottom of the mast with the winch 90' locked, extension
of the cylinder unit results in upward movement of the load-
carrying unit 23 relative to the top stage 22 as well as
upward movement of the top stage 22 relative to the inter-
mediate stage 21. AS the length of cable between the arm
26' and winch 90' increases responsive to upward travel of
the top stage 22, the two passes of the cable from the
sheave 101 and dead-end 103 to the sheave 102 on the load-
carrying unit 23 cause the latter to move upwardly relative
to the top stage the same distance as the extension of the
cylinder unit 28. Hence, under these conditions, the load-
carrying unit 23 will reach the top of the mast at the same
time as the mast becomes fully extended. However, when the
mast is not fully extended, the winch 90' can be operated at
will to move the load-carrying unit to its upper limit of
travel relative to the top mast stage 22 or to otherwise
adjust the position of the load-carrying unit.
The Fig. 10 embodiment, like that of Fig. 11, has
an additional intermediate mast section 21a. The reeving
system includes a third cable 28c passing upwardly from the
upper end of the lower intermediate section 21 over a sheave
60b at the top of the upper intermediate section 21a and
then downwardly to a connection at the lower end of the top
stage 22. This third cable 28c causes the top stage 22 to
move upwardly relative to the upper intermediate section 21a
at the same rate as the cable 28b causes the upper inter-
mediate section 21a to move upwardly relative to the lower
intermediate section 21 responsive to extension of the cyl-
inder unit 28. It will be noted that an additional sheave
104 has been added at the upper end of the top stage 22 for
the cable 28a and that the dead-end at the forward end of
this cable has been moved to 103' on the load-carrying unit
23. The result is to increase the number of passes of the
cable 28a between the top stage 22 and the load-carrying
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unit 23 from two (as in the Fig. 9 embodiment) to three in
correspondence with the number of movable mast stages so
that the load-carrying unit will move from base level to the
upper end of the mast at the same time as the mast becomes
fully extended responsive to extension of the cylinder unit
28 or other elevating means. A winch can also be provided
on the strut 66 for the cable 28a for adjustment of the
load-carrying unit 23 as previously described with respect
to the embodiment of Fig. 9.
In all of the described embodiments, a downward
force is exerted on a counterbalance arm by a cable connect-
ed to the load-carrying unit. This force acts rearwardly of
the mast on a sufficient moment arm to counterbalance the
moment created at the front of the mast by the load. Hence,
the mast is greatly stabilized.
The described embodiments of this invention may
have further variations which will be apparent to those
skilled in the art. Accordingly, this invention is not
limited to the specific embodiments described unless
required by the nature of the prior art or the appended
claims.
