Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2023574
~ ARTICULATING 8TAIRWAY
Field of the Invention
This application pertains to an articulating stairway
having stair treads which remain level as one end of the stairway
articulates through a range of positions above, below or level
with the other end of the stairway.
Background of the Invention
There are a variety of situations in which it is
desirable to extend a stairway between two levels which are
vertically displaced by an unknown distance, or by a distance
which changes over time. Consider, for example, a tidal water
ship berthed adjacent a dock. The vertical displacement between
the deck of the ship and the dock changes over time as the tides
ebb and flow. The vertical displacement between the deck of the
ship and the dock also changes over time as the ship is loaded
and/or unloaded, whether the ship is in tidal water or not. If
the ship is in tidal water its deck may be displaced through a
vertical range of 50 or more feet by the combined effects the
tide and the ship's load. That is, the deck of a fully loaded
ship riding at low tide may be 50 feet or more lower than the
deck of the same ship riding unloaded at high tide. It will thus
be understood that large vertical displacements must be accommo-
dated by stairways (gangways) which extend between a dock and atidal water ship berthed adjacent the dock.
The prior art has evolved a variety of stairway
structures having treads which remain level while one end of the
stairway is raised or lowered relative to the other end. For
example, United States Patent No. 298,212 issued 6 May, 1884 for
an invention of T. I. Knight entitled "Gangway For Ships"
provides a gangway in which a plurality of treads are pivotally
connected between inner and outer pairs of parallel rails which
swing past one another as one end of the gangway is raised or
lowered relative to the other end. The structure is somewhat
complex and therefore relatively expensive to construct.
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United States Patent No. 1,167,893 issued 11 January,
1916 for an invention of P. J. Fickinger entitled "Compensating
Stairway" p~ovides a stairway having a somewhat complicated
system of gears and chains for maintaining the treads level as
one end of the stairway is raised or lowered relative to the
other end. United States Patent No. 1,215,827 issued 13
February, 1917 for an invention of E. R. Lord entitled "Landing
Steps" provides another stairway whose treads are kept level by
lo a rather complex gear drive mechanism as one end of the stairway
is raised or lowered relative to the other end. The mechanical
complexity of the Fickinger and Lord structures increases their
capital cost and also increases the risk of mechanical failure.
United States Patent No. 4,013,140 issued 22 March,
1977 for an invention of Jacques Pradon entitled "Safety
Equipment" provides a stairway whose treads are pivotally
connected between a single pair of lower, parallel "strings" such
that the treads remain level as one end of the stairway is raised
or lowered relative to the other end. The treads are fixed to
uprights which are in turn pivotally connected to a pair of
upper, parallel rails surmounted by a handrail. The "strings"
are pivotally connected at one end to a fixed support, but the
ends of the upper rails are not fixed. The upper rails may
therefore be displaced along their longitudinal axes. Such
displacement would alter the plane of the treads, by tilting them
away from the horizontal.
United States Patent No. 4,168,764 issued 25 September,
1979 for an invention of Tom Walters entitled "Level Step Stair
Walkway" is similar to the Knight structure, in that the stair
- treads are pivotally connected between inner and outer pairs of
parallel rails which swing past one another as one end of the
gangway is raised or lowered relative to the other end. The
structure is relatively complex and expensive.
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The present invention provides an mechanically simple,
inexpensive, articulating stairway whose treads remain level as
one end of the stairway articulates through a large vertical
displacement range relative to the other end of the stairway.
Summary of the Invention
In accordance with the preferred embodiment, the
invention provides an articulating stairway, having a first pair
of horizontally spaced, parallel rails and a second pair of
horizontally spaced, parallel rails aligned above the first pair
of rails. A plurality of treads are provided, with each tread
being pivotally connected between the first and second pairs of
rails on two vertically aligned, parallel, horizontal axes.
First and second pivot pins extend from the opposed
ends of each tread to form one of the axes aforesaid. First and
second risers project from the opposed ends of each tread. Third
and fourth pivot pins extend from each of the risers to form the
other axis.
The preferred embodiment of the invention may be
alternatively characterized as providing an articulating stairway
having a first pair of horizontally spaced, parallel rails and
a second pair of horizontally spaced, parallel rails aligned
above the first pair of rails, with a plurality of treads
extending horizontally between the rails. A pair of risers
project from the opposed ends of each tread. Each riser is
pivotally connected between vertically aligned pairs of points
on the first and second pairs of rails. The vertically aligned
pairs of points remain vertically aligned as one end of the
stairway pivots above or below the other end of the stairway.
The first and second pairs of rails are positioned
such that vertical separation between the upper surfaces of the
first pair of rails and the lower surfaces of the second pair
of rails is a maximum when both ends of the stairway are level
with one another; decreases as one end of the stairway pivots
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above or below the other end of the stairway; and, decreases to
zero as one end of the stairway pivots to the maximum possible
extent above or below the other end of the stairway.
First, second, third and fourth brackets are provided.
The respective brackets are pivotally connected between verti-
cally opposed ends of one rail of the first pair of rails and one
rail of the second pair of rails on two vertically aligned,
parallel, horizontal axes.
Brief Description of the Drawinqs
Figure 1 is an oblique pictorial illustration of an
articulating stairway constructed in accordance with the
preferred embodiment of the invention.
Figure 2 is a side elevation view of the articulating
stairway of Figure 1 (viewed from the rear side of Figure 1).
In Figure 2, phantom lines are used to show the maximum extent
to which the left end of the stairway may pivot above or below
the right end of the stairway.
Figure 3 is an enlarged cross-sectional illustration
taken with respect to line 3-3 of Figure 1 to provide details of
the stair treads and the brackets which pivotally connect the
vertically opposed rail ends together.
Figure 4 is an enlarged cross-sectional illustration
taken with respect to line 4-4 of Figure 2 to provide further
details of the stair treads.
Detailed Description of the Preferred Embodiment
The drawings illustrate an articulating stairway 10
having a first pair of horizontally spaced, parallel rails 12,
14 and a second pair of horizontally spaced, parallel rails 16,
18 aligned above rails 12, 14 respectively. A plurality of stair
treads 20, 22, 24, etc. are provided. As hereinafter described
in greater detail, each tread is pivotally connected between the
`. 2023574
first and second pairs of rails on two vertically aligned,
parallel, horizontal axes such as axes 26, 28 illustrated in
Figure 3 for tread 30. A handrail (shown in phantom outline in
Figure 1) may be provided as a safety feature, and also to
improve the structural integrity of stairway 10 (for example, by
fixing a plurality of bracing struts between the handrail and
the upper surfaces of rails 16, 18 as illustrated in Figure 2).
As best seen in Figure 4, a first pivot pin 32 extends
from one end of stair tread 30 to pivotally engage within a
reinforced aperture 34 in rail 14. A second pivot pin 36 extends
from the horizontally opposed end of stair tread 30 to pivotally
engage within reinforced aperture 38 in the horizontally opposed
rail 12. Horizontally aligned pivot pins 32, 36 form horizontal
axis 26. A first riser 40 projects upwardly at the end of tread
30 from which first pivot pin 32 extends. A second, identical
riser 42 projects upwardly at the end of tread 30 from which
second pivot pin 36 extends. A third pivot pin 44 extends from
the upper end of riser 40 to pivotally engage within reinforced
aperture 46 in rail 18. A fourth pivot pin 48 extends from the
upper, horizontally opposed end of riser 42 to pivotally engage
within reinforced aperture 50 in the horizontally opposed rail
16. Horizontally aligned pivot pins 44, 48 form horizontal axis
28. All of the stair treads are similarly pivotally connected
between the first and second pairs of rails. The horizontal axes
which intersect the first pair of rails 12, 14 lie in one plane;
and, the horizontal axes which intersect the second pair of rails
16, 18 lie in another plane parallel to the first plane.
As best seen in Figure 3, a bracket 52 is pivotally
connected between the vertically opposed ends 54, 56 of rails 14,
18 on two vertically aligned, parallel, horizontal axes 58, 60.
Axis 58 lies in the same plane as the aforesaid horizontal axes
which intersect the first pair of rails 12, 14; and, axis 60 lies
in the same plane as the horizontal axes which intersect the
second pair of rails 16, 18.
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~ As best seen in Figure 2, the first and second pairs
of rails are positioned such that the vertical separation between
the upper surfaces 62 of the first pair of rails 12, 14 and the
lower surfaces 64 of the second pair of rails 16, 18 is a maximum
"a" when both ends of stairway 10 are level with one another.
The vertical separation decreases, as shown at "b", as one end
of stairway 10 pivots above or below the other end of stairway
10. The vertical separation decreases to zero (i.e. the upper
surfaces 62 of the first pair of rails 12, 14 contact the lower
surfaces 64 of the second pair of rails 16, 18 as shown at "c")
as one end of stairway 10 pivots to the maximum possible extent
above or below the other end of stairway 10.
In operation, stairway 10 may, for example, be mounted
on a suitable support structure atop a dock (not shown). If a
ship (not shown) is berthed at the dock then one end of stairway
10 is extended, with the aid of a crane, and placed on the deck
of the ship. The other end of stairway 10 remains on the dock,
with provision being made for the dock end of the stairway to
slide back and forth along the longitudinal axis of stairway 10
as stairway lo articulates in the following manner.
As the tides ebb and flow (assuming the ship to be in
tidal water) and/or as the ship is loaded and unloaded, the
vertical displacement between the dock and the ship's deck
changes. Suppose for example that the ship is initially unloaded
and riding at high tide. In this case the ship end of stairway
10 will likely be displaced vertically above the dock end of
stairway 10 by a significant amount. Now, suppose that the same
ship is fully loaded and riding at low tide beside the same dock.
In this case the ship end of stairway 10 will likely be displaced
vertically below the dock end of stairway 10 by a significant
amount. In between the two extremes aforesaid the ship end of
stairway 10 is displaced vertically through a wide range of
positions, relative to the dock end of stairway 10, with the dock
end of stairway 10 sliding back and forth along the longitudinal
axis of stairway 10. At all times the treads of stairway 10 are
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202357~
kept level because they are supported, as aforesaid, by risers
which are pivotally connected between vertically aligned pairs
of axes intersecting the first and second pairs of rails, such
that each vertically aligned pair of axes remains vertically
aligned as one end of stairway 10 pivots above or below the other
end of stairway 10.
As will be apparent to those skilled in the art in the
light of the foregoing disclosure, many alterations and modifica-
tions are possible in the practice of this invention withoutdeparting from the spirit or scope thereof. For example, instead
of focusing on a horizontal "neutral" position, as heretofore
assumed, one could instead focus upon a vertical neutral
position. This could be accomplished by mounting the stair
treads at positions rotated 90 with respect to the positions
shown in the drawings, and by supporting one end of stairway 10
on a horizontal surface, so that the structure extended verti-
cally upward from that surface. The upper end of the stairway
could then be allowed to pivot off the vertical, to either side.
The stair treads would remain level because, in this orientation
of the stairway, the risers are pivotally connected between
horizontally aligned pairs of axes intersecting the first and
second pairs of rails, such that each horizontal aligned pair
of axes remains horizontally aligned as the upper end of the
stairway pivoted to one side or the other relative of the lower
end of the stairway. Accordingly, the scope of the invention
is to be construed in accordance with the substance defined by
the following claims by interchanging the terms vertical and
horizontal as circumstances may require.
