Note: Descriptions are shown in the official language in which they were submitted.
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[0001]
TITLE OF THE INVENTION
[0002] MAST LIFT AND MAST LIFT SYSTEM
BACKGROUND OF THE INVENTION
[0003] The present invention relates to a personnel lift and, more
particularly, to a portable lift machine including a work platform raised
and lowered on a mast by a lifting system. The lifting machine may be
free-standing or non free-standing, transportable and operable by a single
user.
[0004] The ladder concept is several thousand years old. Existing
ladders, however, can be cumbersome and difficult to maneuver.
Additionally, conventional ladders can be unstable particularly on uneven
ground, and a work area is limited to the user's reach.
[0005] Ladder companies are reluctant to develop powered
mechanical products. It would be desirable, however, to develop a
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personnel lift that achieves many of the advantages of a ladder, e.g., can
be set up and used by a single operator, lightweight, etc., while providing
for greater stability and a larger working area in a portable powered
machine.
[0006] Mast climbing platforms are known and typically include a
mast that can be free-standing or supported by a wall or other support
structure. However, existing mast climbers have minimum SWL loads of
1000 lbs and are not portable or operable by a single user due to their
size. Vertical mast products and aerial work platforms include a moving
platform and generally are only free-standing assemblies. These
machines are also typically too large for portability and are very far from
the many advantages provided by a ladder in terms of portability, low
cost and ease of use.
[0007] To achieve portability, a light weight, reliable lift system
mechanism is desirable to provide the functionality expected of a device
which lifts personnel.
SUMMARY OF THE INVENTION
[0008] A mast lift includes a base or mast frame, a mast on which
a carriage supporting a work platform is movable, and a power source,
which may be an on-board power pack or a user-supplied source such as
a power drill. The various components can also be utilized as part of a
modular system where modular components can be used in varying
models.
[0009] Exemplary features of the carriage and lifting system
include the use of an overload clutch in combination with an overrun
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brake to avoid the lifting mechanism such as a rope or the like from being
unwound
off a winding dram after reaching the bottom of travel or if encountering an
obstacle.
An emergency brake secures the work platform to the mast in the event of loss
of
rope tension or rope failure, engagement of which to the mast at the bottom of
travel
serves to both stop the further unwinding of the rope from the dram and also
to
provide a latch to hold the carriage in the down position during transport,
etc.
100101 An energy absorbing feature may be provided between the platform
and the carriage that reduces the peak impact load that can be exerted on the
structure. This feature provides a type of elastic bumper and/or crumple zone
in the
unlikely event of complete hoist rope failure and emergency brake deployment.
[00111 Another exemplary feature is spring-mounted stepped rollers for a
telescopic mast.
[0012] In one aspect of the present invention there is provided mast lift
comprising: a mast supported on a mast base; a work platform movably secured
to
the mast; a lift system coupled between the work platform and the mast, the
lift
system effecting raising and lowering of the work platform on the mast and
including: at least one lifting rope connected between the work platform and
the mast
via a brake frame and a hoist drum connected to the work platform, wherein the
brake frame is displaced between an engaged position and a disengaged position
based on an amount of tension on the lifting rope, a spring connected to the
brake
frame and urging the brake frame toward the engaged position, and a carriage
latch
assembly including a carriage latch hook coupled with the brake frame and a
pin
secured to the mast, wherein when the tension on the lifting rope is lost upon
the
work platform reaching a bottom of travel, the brake frame is disposed in the
engaged position, and the carriage latch hook is displaced into engagement
with the
pin, and an idler roller cooperable with the brake frame and displaceable with
the
brake frame between the engaged position and the disengaged position, wherein
the
idler roller is biased toward the engaged position, and wherein the lifting
rope is
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cooperable with the idler roller such that tension on the lifting rope
maintains the
brake frame in the disengaged position.
[0013] The lift system preferably includes a worm drive gear box operably
connected to the hoist drum, where the gear box is driven via a drive shaft
coupleable with a drive source. The lift system may include two or more
lifting
ropes. In one arrangement, the mast lift additionally includes an idler roller
cooperable with the brake frame and displaceable with the brake frame between
the
engaged position and the disengaged position, where the idler roller is biased
toward
the engaged position, and where the lifting rope is cooperable with the idler
roller
such that tension on the lifting rope maintains the brake frame in the
disengaged
position.
[0014] The drive source may be one of a power pack or a handheld power
drill. In this context, the drive shaft may be biased toward a disengaged
position such
that activation of the drive shaft requires an opposite force against the
bias.
[0015] The mast base is preferably structured such that the mast lift is
free-
standing, although the mast lift can be free standing or leaning.
[0016] In another aspect of the present invention, there is provided a
lift
system coupleable between a work platform and a mast, the lift system
effecting
raising and lowering of the work platform on the mast, wherein the lift system
comprises: at least one lifting rope connected between the work platform and
the
mast; an emergency brake cooperable with the at least one lifting rope and
movable
between an engaged position engaging the mast and a disengaged position
disengaging the mast based on an amount of tension on the lifting rope; a
carriage
latch assembly cooperable with the emergency brake, the carriage latch
assembly
automatically locking the work platform to the mast when the work platform
reaches
a lowermost position; and an idler roller coupled to and movable with the
emergency
brake between the engaged position and the disengaged position, the idler
roller
being cooperatively engaged with the at least one lifting rope such that the
tension in
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the lifting rope displaces the idler roller to maintain the emergency brake in
the
disengaged position, wherein the carriage latch assembly comprises a carriage
latch
hook coupled with the idler roller and a pin secured to the mast, wherein when
the
idler roller is disposed in the engaged position, the carriage latch hook is
engageable
with the pin.
[0017]
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] These and other aspects and advantages of the present invention
will
be described in detail with reference to the accompanying drawings, in which:
[0019] FIGURE 1 is a perspective view of the mast lift according to an
exemplary configuration;
[0020] FIGURE 2 is a front perspective view of a lifting system for the
mast
lift;
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[0021] FIGURE 3 is a rear perspective view of the lifting system;
[0022] FIGURE 4 is a side view of the lifting system;
[0023] FIGURE 5 is a side view of the lifting system on the mast;
and
[0024] FIGURE 6 shows an energy absorbing member.
DETAILED DESCRIPTION OF THE INVENTION
[0025] With reference to FIG. 1, the mast lift described herein
generally includes a base or mast frame 12 supporting a mast 14 on
which a work platform 13 is movable between a lowered position (shown
in FIG. 1) and a raised position via a carriage assembly or lift system 15.
Preferably, the components are modular, thereby enabling the machine to
be quickly and reliably assembled and disassembled for ease of transport
by one person. Component assembly typically takes the average skilled
worker less than 30 seconds. The modular system also allows various
components to be used on different types of mast and base designs,
increasing product versatility. In an alternative embodiment, the mast 14
includes telescoped sections to provide for a greater height mast that can
retract to be more compact for transport. The mast lift shown in FIG. 1 is
a free-standing mast lift, i.e., the machine is capable of independent
support and positioning. The components of the lifting structure
described below are equally applicable to a non free-standing machine,
and the invention is not necessarily meant to be limited to the illustrated
exemplary free-standing lift embodiment.
[0026] The base or mast frame 12 is provided with a one-way
retracting castor system. This ensures no sprung castor support to the
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platform when a user is on the platform. With no user on the platform, a
simple activation deploys the castor for ease of relocation of the lift.
[0027] The work platform 13 is secured to the carriage or lift
system 15 via mounting pins, a hook and a latch, all of which engage
during a simple assembly operation that takes less than ten seconds to
complete safely, and cannot readily be incorrectly assembled in an unsafe
manner. With reference to FIGS. 2-5, one or preferably two lifting ropes
1, 2 are connected at the top of the mast 14 via a tension equalizing loop
(not shown) that ensures equal tension on each rope while maintaining
independent rope terminations at the top of the mast 14. The ropes 1, 2
extend along the front of the mast 14 and into the carriage 15. Rollers 18
mount the carriage 15 onto the mast 14 and also ensure that the platform
13 does not rotate around the mast 14. The rollers 18 are preferably
stepped and spring-loaded to act on the telescopic variation.
[0028] The ropes 1, 2 preferably pass over an emergency brake
release idler roller 3 before being wrapped onto a main hoist drum 4.
Platform lift is achieved by a worm drive gear box 8 turning the hoist
drum 4 to wind the lifting ropes 1, 2. In a preferred embodiment, the
hoist drum 4 is grooved to help ensure that the ropes 1, 2 wind onto the
drum 4 in a first layer of constant diameter until the middle of the drum is
reached, after which the ropes 1, 2 may roll back onto themselves
forming a second layer.
[0029] The worm drive gear box 8 is driven via a drive shaft 10,
which may be activated by a modular power pack or alternatively via a
hand-held power drill or the like. The drive shaft 10 is provided with
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two-action operation, requiring the shaft to be pushed down to engage the
worm drive gear box 8 and rotated. Using a hand-held power drill, the
two-action activation requires that the operator push down on the shaft
and pull the trigger on the drill to move the platform 13. The operator is
protected from excessive backlash torque if he fails to activate the second
action via the overload clutch, which slips if the second action is not
properly completed. With the power pack, securing the power pack to
the drive shaft 10 fixes the drive shaft in the pushed down position for
activation. The gear box 8 preferably also has an intput on the bottom
side to allow manual descent from underneath in the event of an
incapacitated operator.
[0030] Tension on the lifting ropes 1, 2 is sensed by any suitable
device. In one construction, the lifting rope tension exerts a force
through an idler roller 3 on a bell crank 17, which operates in cooperation
with an emergency brake frame or idler roller frame 5 and its mounting
link 11 to cause brake shoes 6 to be released from the mast 14 and remain
released from the mast 14 while tension remains on the lifting ropes 1, 2.
As such, this configuration permits the carriage 15 to move freely in
normal use.
100311 The idler roller 3 may be eliminated with the use of a
swinging brake frame 5 that is disengaged by tension on the lifting ropes
1, 2 and engaged when tension is lost. That is, in the event that tension in
the ropes 1, 2 is lost, a spring 29 attached between the top front roller 18
axle and the brake frame 5 via the link 11 causes the brake shoes 6 to
come into contact with the mast 14, and due to the high friction between
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the shoes 6 and the mast 14, and the weight of the platform applied via
link 11 to the front of the emergency brake frame 5 cause cross-binding
of the emergency brake frame 5 around the mast 14 to occur, so locking
the emergency brake frame 5 to the mast 14. The load on the platform 13
is then no longer supported by tension in the ropes 1, 2, but rather is
supported by the mast 14 via the mounting link 11, the emergency brake
frame 5 and the brake shoes 6.
[0032] The system is designed so that the emergency brake
engages within a very short amount of fall following loss of tension in the
lifting ropes 1, 2, which helps to minimize the impact forces from
activation of the emergency brake. Energy from the rapid deceleration
caused by the engagement of the self-energizing emergency brake could
be damaging to the machine given the high peak forces that can be
applied in an emergency engagement of the brake. The configuration
described herein minimizes the extent of peak loading by incorporating
an energy absorbing member 20 such as energy absorbing rubber springs
mounted between the carriage 15 and the platform 13 as shown in FIG. 6.
An additional benefit of the energy absorbing rubber springs 20 when
combined with other features in the design is a crumple zone effect to
restrain the maximum G forces on the user in the event of catastrophic
failure (akin to a crumple zone in a modern car).
[0033] With continued reference to FIGS. 2-5, an overload clutch 9
operates on the drive shaft 10 to ensure that no more than a maximum
safe working load plus a small margin can be lifted by the hoist drum 4.
The overload clutch 9 transmits the drive torque into the gear box 8 via
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the drive shaft 10 in a preferred embodiment of the concept but could be
incorporated in another part of the drive chain to achieve the same
outcome. Any suitable device could be used for the overload clutch 9,
and the invention is not meant to be limited to a specific design. In one
construction, a series of interleaved spring-loaded washers or the like in
an oil bath serve as an overload clutch, wherein upon application of a
predetermined load (torque), the washers slip relative to one another.
[00341 An over-run brake 7 is also incorporated in the drive train.
The over-run brake 7 acts to stop the lifting ropes 1, 2 from being wound
off the drum 4 when the machine is fully lowered to the bottom of travel
and also in the unlikely event of the platform 13 being hung up on an
obstacle during downward travel. The over-run brake 7 senses a loss of
tension in the ropes 1, 2 via the emergency brake mechanism 5 via a pin
19 or other engaging component acting on a lever arm 7a, which is spring
loaded to engage the emergency brake frame 5. When tension is lost in
the ropes 1, 2, normally only due to reaching the bottom of travel, the
emergency brake frame 5 moves to its engaged position, which causes an
over-run brake lever 7a to lower a dog-clutch 7b onto the drive shaft 10
so that the drive shaft 10 is prevented from further rotating. Power from
the drive motor then is absorbed by the slipping overload clutch 9, which
while slipping creates a noise that should lead the operator to stop
operating the motor.
[0035] The dog-clutch 7b is preferably a one-way dog-clutch
device that allows travel in the lift up direction when it is activated, and
prevents travel in the lift down direction when it is activated, hence
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avoiding the ropes 1, 2 becoming slack, running out or winding to the end
of the drum 4. This design enables the operator to lift up from a position
in which the over-run brake 7 is engaged as this in turn creates tension on
the ropes 1, 2, which in turn releases the emergency brake (and carriage
to mast latch) and releases the over-run brake 7.
[00361 The idler roller 3 is displaceable between an emergency
brake engaged position when ropes 1, 2 are under low tension and a
disengaged position when ropes 1, 2 are supporting the weight of the
loaded platform. At the bottom of travel, the platform rests on the base
causing low tension in ropes 1, 2 so causing the idler roller mount or bell
crank 17 to rotate consistent with the emergency brake engaged position.
The bell crank 17 is utilized in this position to latch the carriage 15 to the
mast 14 when the platform is in the fully lowered position. That is, as
shown in FIGS. 3-4, when tension in ropes 1, 2 is lost, typically due to
reaching the bottom of travel, the emergency brake frame 5 is pivoted
(clockwise in FIG. 3) by action of the spring 29 preferably attached
between the top front roller 18 axle and the brake frame 5 (although the
spring could attach from anywhere on the carriage), which in turn causes
a carriage latch assembly 30, 32 (shown schematically in FIG. 3)
including a carriage latch hook 30 attached to the bell crank 17 to swing
inward toward a center of the mast 14. When the carriage is at the
bottom of travel, this movement brings the carriage latch hook 30 under a
pin or pins 32 of the assembly located on the mast 14. Thus, at the
bottom of travel, the carriage is automatically latched to the mast 14.
When the operator drives the platform 13 up the mast 14, tension in the
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ropes 1, 2 moves the emergency brake frame 5 (counterclockwise in FIG.
3) against the force of the spring 29, which in turn releases the carriage
latch hook 30. This structure provides an added benefit of ensuring that
the carriage does not move when the mast is lifted off the base holding
the carriage. It also stops the carriage from moving along the mast during
transport.
[0037] The overall result of the design is a carriage that can climb
a mast with one or more, preferably two, lift ropes plus an emergency
brake, plus control of overload, end of travel control, over-run control
and auto on/off lock down latch at the bottom of travel. The simple
mechanism includes all these features yet weighs only about 30 lbs.
[0038] As described, the configuration achieves these important
safety and operational functions without the use of any electric or
electronic devices, thereby keeping the design simple from a cost, weight
and maintenance perspective. As would be apparent to those of ordinary
skill in the art, however, use of electric or electronic devices to perform
these functions is possible, and the invention is not necessarily meant to
be limited to the described configuration.
[0039] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiments, it is to be understood that the invention is not to be limited
to the disclosed embodiments, but on the contrary, is intended to cover
various modifications and equivalent arrangements included within the
scope of the appended claims as purposively construed.
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