Note: Descriptions are shown in the official language in which they were submitted.
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SCREW SCISSOR LIFT
This application claims priority to US provisional application serial no.
60/642267 filed
January 7, 2005.
Field of The Invention
The field of the invention is scissor lifts.
Background of The Invention
Scissor lifts have been widely used across many applications for many years.
Among
other things, such lifts have been used to raise automobiles and other heavy
equipment, people,
building components, supplies, structural components, and to provide
scaffolding, work stands,
patient beds and so forth. Operation of the scissor must be operated in some
manner, and in
some instances the scissor is operated using a screw drive. Examples in the
patent literature
include US6719282 to Frank (Apr 2004); US6684443 to Thomas et al. (Feb 2004);
US20040005961 to lund et al. (Jan 2004); US6655875 to Pignato (Dec 2003);
US5996961 to
Johnson (Dec 1999); and US5593137 to Johnson (Jan 1997); US5105915 to Gary
(Apr 1992);
and US3817346 to Wehmeyer (Jun 1974). This and all other referenced patents
and applications
are incorporated herein by reference in their entirety. Where a definition, or
use of a term in a
reference incorporated by reference, is inconsistent or contrary to the
definition of that term
provided herein, the definition of that term provided herein applies and the
definition of that term
in the reference does not apply.
Despite these varied uses, and the considerable experience of decades of use,
there are
still problems associated with screw-type scissor lifts. One problem is that
the screw mechanism
tends to bind. Another problem is that there is a very significant mechanical
disadvantage
working against extension of the scissor mechanism in a compressed position.
In prior art
scissors, the retraction must usually provide at least a 10 angle between the
screw drive and the
lowest arm of the scissors. That problem can be resolved by limiting the
extent to which the
scissor mechanism can retract, but then the mechanism is not so compact as one
might prefer.
Thus, there still remains a need for improvements in screw-type scissor lifts.
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Summary of the Invention
The present invention provides apparatus, systems and methods in which a
scissor lift for
lifting a payload, comprises a first pair of scissored arms disposed to lift
the payload and an
energy storage device disposed to store energy as the payload is lowered, and
provide further lift
to the payload as the payload is raised.
At a fully retracted position, the scissored arms define a support angle of at
least 150 ,
more preferably at least 165 , still more preferably at least 175 , and most
preferably 180 . At
the extreme of 180 , this corresponds to an angle of 0 between the screw
drive and the lowest
arm of the scissors, which means that such scissor lifts can be considerably
more compact than
prior art lifts.
In another aspect of preferred embodiments, a bearing is used at a pivot
joining the first
and second arms, with hardened washers on either sides of the bearing. These
features help
reduce side to side sway of the scissor mechanism, and therefore of the
payload. In especially
preferred embodiments the bearing is sufficiently stiff to restrict side to
side movement of the
payload such that movement of the payload under operation of the lift is
substantially planar.
In still another aspect of preferred embodiments, a screw, piston, cable,
chain, rack and
pinion or other actuator is mechanically coupled to one of the scissor arms to
provide motive
force to the lift. In especially preferred embodiments the actuator drives
both arms of the lowest
(or only) pair of scissor arms.
There must be some source of motive force that drives the actuator, and in
preferred
embodiments that source comprises an electric motor.
The energy storage device is preferably a helical wire spring, but can
alternatively be any
suitable spring, whether helical or non-helical, having thin or thick wires,
and whether
constructed of metals, non-metals, or a combination. In still other
embodiments the energy
storage device could be a flat spring, a gas piston, or even a piece of rubber
or other elastomeric
mass.
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Contemplated lifts can comprise more than one pair of scissored arms, either
laterally
adjacent to one another, or more likely stacked on top of one another. At the
lower end of the
lift, the bottom (or only) pair of scissors is preferably coupled to a
substantially immovable base
at spaced apart first and second pivots, and a connector that transmits motive
force to the scissors
is restricted by a guide to movement substantially within a single plane. At
the upper end of the
lift, the top (or only) pair of scissors is preferably coupled to a movable
platform at spaced apart
third and fourth pivots. The moveable platform directly or indirectly supports
the payload.
Various objects, features, aspects and advantages of the present invention
will become
more apparent from the following detailed description of preferred embodiments
of the
invention, along with the accompanying drawings in which like numerals
represent like
components.
Brief Description of The Drawings
Figures lA, 1B are partial cutaway perspective views of a cabinet containing a
scissor lift
that can be used in conjunction with a plasma television or other screen.
Fig 2 is a perspective view of the lift of Figures 1 A, 1 B, in an extended
configuration.
Fig. 3 is a perspective view of the base assembly of the lift of Figures lA,
1B.
Fig. 4 is a perspective view of the bogie of the lift of Figures 1A, 1B.
Fig. 5 is a perspective view of the scissor arm bearings of the lift of
Figures 1A, 1B.
Fig. 6 is a perspective view of the upper platform assembly of the lift of
Figures 1A, 1B.
Fig. 7 is a perspective view of the safety cap assembly of the lift of Figures
1 A, 1 B.
Fig. 8 is a perspective view of the lift of Figures 1 A, 1 B, with a
controller assembly.
Fig. 9 is a perspective side view of the lift of Figures 1A, 1B, to clearly
depict the support
angle.
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Detailed Description
Figures 1A and 1B generally depict a lift 100 supporting a plasma screen 200
and a
cabinet 300. In Fig. 1A the screen is fully extended to a viewing position
outside the cabinet
300, and in Fig. 1B the fully retracted screen is descended into the main
cavity of cabinet 300.
The lift 100 generally includes a base assembly 110, counter balance spring
111, a thrust bearing
frame 112, a thrust bearing 113, a thrust bearing race 114, a shaft bearing
115, a drive screw 116,
a drive nut assembly 117, and a base frame 118.
In Figure 2 the lift 100 is shown supporting a superstructure comprising a
platform
assembly 140, which is coupled to a cap frame 150. Details of the
superstructure are better
visualized in Figures 6 and 7, which show the upper platform assembly 140 as
including a upper
platform frame 141 and screen brackets 142A, 142B. The cap frame 150 generally
includes a
cap 151, a machine screw 152, springs 153, washers 154, and nuts 155. The
springs 153 permit
self-leveling or other accommodation of the cap along the horizontal surface
of a table or other
structure in which the cabinet 300 is mounted. The cap 151 can advantageously
fit into the top
of a table or other structure using a beveled groove and key arrangement.
In Figures 3- 5 the base assembly 110 supports a bogie 120, which generally
includes a
drive nut 121, a bogie frame 122, and a wheel 123 (cam follower). The bearing
joint 130
generally includes a thrust bearing race 131, a thrust bearing 132, a shoulder
bolt 133, a shoulder
bolt nut 134, and a scissor frame 135.
The binding problem alluded to above is resolved by using a thrust bearing on
one end,
but not on the other. The mechanical disadvantage problem is resolved by using
a spring, gas
cylinder, fluid spring, or other biasing element that adds additional force
when the scissors is in a
highly retracted configuration. The biasing element can be positioned as shown
in the figures, or
in many other configurations that provide a similar function. The spring can
even, for example,
be disposed about the screw. In preferred embodiments the biasing element
provides and
additional force up to 10 times that provided by the screw, and allows screw
drive / scissors
angles of 5 or even less. Currently preferred springs provide force of 50
pounds per inch, and
are between 3" and 12" long. In some embodiments springs or different force
profiles can be
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interchanged, and can be color coded or marked in some other manner to
accommodate different
desired lift characteristics.
Figure 8 additionally depicts a control assembly 160, which generally includes
a digital
controller 161, a stop limit switch 162, and a slow limit switch 163. Reducing
the speed as the
lift retracts at low angles (creep mode) allows much greater accuracy in
positioning, and greatly
improves the safety profile. It also helps prevent overload on the
screw/motor. The controller
preferably controls a high torque electric motor. Capacity of contemplated
embodiments is 200
# or more of load.
The lift is in communication with a drive controller 161. The drive controller
161 can be
used to control and/or provide power to the drive mechanism (not shown) of the
lift 410. A
preferred drive controller has a transceiver or receiver in order to receive
signals from a remote
control device. It is further contemplated that a lift can be incorporated
into a home appliance
center and control of the lift can therefore be accomplished using a computer
or other device
programmed to control home appliances. Such control can also be accomplished
remotely from
a distal location, if necessary. It may be desirable for a parent to monitor a
child's "T.V. time",
and as such, enhancements can be built into the controller that can prevent
the lift and or the
projector from operation without authority.
Figure 9 generally depicts a lift supporting a payload which special emphasis
on the
support angle a. The lift base frame 110 supports the scissors arms 135, the
helical wire spring
111, the electric motor 121, and the actuator screw. The scissor arms 135, are
driven by the
actuator screw 120. The scissor arms 135, supports the upper platform assembly
140, which
supports the payload.
Thus, specific embodiments and applications of a screw scissor lift have been
disclosed.
It should be apparent, however, to those skilled in the art that many more
modifications besides
those already described are possible without departing from the inventive
concepts herein. The
inventive subject matter, therefore, is not to be restricted except in the
spirit of the appended
claims. Moreover, in interpreting both the disclosure, all terms should be
interpreted in the
broadest possible manner consistent with the context. In particular, the terms
"comprises" and
"comprising" should be interpreted as referring to elements, components, or
steps in a non-
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exclusive manner, indicating that the referenced elements, components, or
steps may be present,
or utilized, or combined with other elements, components, or steps that are
not expressly
referenced.
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