U.S. patent application number 10/855636 was filed with the patent office on 2005-12-01 for folding table.
Invention is credited to Lietuvietis, Vilis I..
Application Number | 20050263045 10/855636 |
Document ID | / |
Family ID | 34969393 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050263045 |
Kind Code |
A1 |
Lietuvietis, Vilis I. |
December 1, 2005 |
Folding table
Abstract
Folding table having a fastener to releasably hold each of one
or more legs, rigidly attatched to a rotational leg supportive
structural shaft parallel and adjacent to the underside of the
table. The legs can be fastened or unfastened into/from an erect
position by a rotational leverage force applied to the leg. The
fastener provides a manually breakable and engagable grip between
two surfaces being fastened to each other. The primary resistance
of such a table against collapse is due to the limit of the legs'
opening rotational travel, the frictional force of the floor on the
legs, and the rotational sets of table legs being configured
substantially oppositely. In a four-legged rectangular table
configuration, when using such fasteners, each pair of legs is
rigid in the opposite direction, providing overall table rigidity.
Also encompassed is a variation permitting non-releasing leg
latching, including a latch release mechanism.
Inventors: |
Lietuvietis, Vilis I.;
(Harjumaa, EE) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET
2ND FLOOR
ARLINGTON
VA
22202
US
|
Family ID: |
34969393 |
Appl. No.: |
10/855636 |
Filed: |
May 28, 2004 |
Current U.S.
Class: |
108/131 ;
108/133 |
Current CPC
Class: |
A47B 3/0809
20130101 |
Class at
Publication: |
108/131 ;
108/133 |
International
Class: |
A47B 003/00 |
Claims
1. A folding table, comprising: a table top; at least one leg, each
leg being rigidly connected to a respective cross member to form a
respective rigid leg assembly; a pivot assembly pivotally
connecting each respective leg assembly to an underside of said
table, said pivot assembly substantially spanning a length of a
respective cross member; and a means for holding each leg assembly
in a first position, wherein an axis of each said pivot assembly is
eccentric to a respective cross member, allowing the cross member a
limited range of rotation from said first position when one of said
legs is erect, to said second position, when said one of said legs
is folded against the underside of the table, when said cross
member is in said first position, a surface of a respective rigid
leg assembly contacts a surface of the underside of the table.
2. The folding table according to claim 1, wherein the means for
holding the leg assembly comprises an automatically engaging and
automatically disengaging fastener structured and arranged to join
the cross member to the table structure and preventing rotation of
the cross member with a grip sufficient for maintaining reasonable
resistance to table collapse, and permitting ready breaking of this
grip by a user applying manual lever force to an end of the leg in
order to fold the leg assembly.
3. The folding table according to claim 2, wherein the means for
holding the leg assembly is selected from the group consisting of
limited grip fasteners that are magnetic, adhesive, vacuum,
mechanical, or rubber, enabling automatic engaging of the legs in
the first position and automatic disengaging of the legs from the
first position by applying manual pressure to a leg assembly.
4. The folding table according to claim 2, wherein the means for
holding the leg assembly is a locking spring having a cross
sectional contour enabling automatic engaging of the legs in the
first position and automatic disengaging of the legs from the first
position through manual rotational pressure applied at a leg.
5. The folding table according to claim 4, wherein the cross member
is approximately square in cross section, and said pivot assembly
is a continuous hinge mounted at a longitudinal corner of the
rotational leg assembly adjacent to the table surface.
6. The folding table according to claim 5, further comprising: a
channel profile frame supporting the table top, a base plate
rigidly attached to and supported by said channel profile frame,
and a channel profile structural member rigidly combined with the
channel profile frame which together form a closed profile rigid
tube situated adjacent and parallel to a respective leg assembly
affording a mounting surface and rigid support for the locking
spring, one of said leg assemblies being mounted within a perimeter
of the frame and adjacent to said frame through said pivot assembly
to a surface of said base plate.
7. The folding table according to claim 4, wherein the locking
spring is metallic, plastic or elastic material.
8. The folding table according to claim 1, wherein the means of
holding the leg assembly in the first position are fixed to the
table.
9. The folding table according to claim 1, wherein the means of
holding the leg assembly in the first position are fixed to the
cross member.
10. The folding table according to claim 3, wherein the axis of the
pivot assembly is at a corner of the cross member allowing the
cross member to turn from the first position to the second
position, so that when said legs are in said first position, the
legs end their freedom of travel by the cross member contacting a
rigid stopping surface which is part of the underside of the
table.
11. The folding table according to claim 1, wherein said at least
one leg is connected to a respective cross member to form one of a
U-shaped, L-shaped, I-shaped and Y-shaped leg assembly.
12. The folding table according to claim 1, wherein there are at
least three rotational leg assemblies and the table top has a
non-rectangular shape.
13. The folding table as claimed in claim 1, wherein there is at
least two of said leg assemblies that are substantially opposite to
each other so that said leg assemblies open in substantially
opposing directions.
14. The folding table as claimed in claim 1, further comprising a
means for disengaging said means for holding each leg assembly in
said first position.
15. A folding table, comprising: a table top; at least one leg
pivotally connected to said table top, said at least one leg being
pivotable from a first position substantially parallel to said
table top, to a second position substantially perpendicular to said
table top; at least one cross member extending substantially
parallel to said table top, said at least one leg being rigidly
connected to a respective cross member, said respective cross
member pivoting when said at least one leg pivots; at least one
pivot assembly rigidly connected at a respective first end to said
table top and rigidly connected at a respective second end to a
respective cross member; and at least one fastener engaging a
respective cross member when a respective leg is in said second
position and being spaced apart from said respective cross member
when said respective leg is in said first position.
16. The folding table as claimed in claim 15, wherein said at least
one leg, said at least one cross members and said at least one
fastener number three and said table top is substantially
round.
17. A folding table according to claim 15, wherein the fastener is
a locking spring having a cross sectional contour that
automatically engages a respective cross member when a respective
leg is in said second position, and automatically disengages said
respective cross member when said respective leg is in said first
position, when a user manually applies rotational pressure to said
respective leg.
18. The folding table according to claim 15, wherein said at least
one cross member is substantially square in cross section and said
at least one pivot assembly is a continuous hinge.
19. The folding table according to claim 15, further comprising: a
channel profile frame supporting the table top, said at least one
leg and at least one cross members being mounted within a perimeter
of the frame and adjacent thereto, and a channel profile structural
member rigidly connected to the channel profile frame to form a
closed profile rigid enclosure situated adjacent and parallel to
the cross member, said fastener being connected to said channel
profile structure.
20. The folding table according to claim 15, wherein a pair of legs
are fixed to a respective cross member, forming a U-shape rigid
pair of two legs and the cross member.
21. The folding table as claimed in claim 15, wherein there are at
least two legs that are substantially opposite to each other so
that each of said at least two legs open in a substantially
opposing direction.
22. The folding table as claimed in claim 15, wherein said fastener
extends over a majority of said respective cross member.
23. The folding table as claimed in claim 15, further comprising a
fastener disengaging mechanism that is movable from a first
fastener disengaging position spaced apart from said fastener to a
second fastener disengaging position in contact with said fastener,
so that in said second fastener disengaging position, said fastener
disengages said respective crossmember.
24. The folding table according to claim 23, wherein the fastener
is a locking spring having a cross sectional contour that
automatically engages a respective cross member when a respective
leg is in said second position, and said fastener disengaging
mechanism includes a spring driven handle that is pivotable to
cause the mechanism to contact and disengage said locking spring
from said respective cross member so that said respective leg is
movable to said first position, when a user manually applies
rotational pressure to said respective leg.
25. The folding table according to claim 24, wherein the handle is
pivotal about a shaft and comprises a release plate that slidingly
engages the crossmember when the handle is pivoted.
26. The folding table according to claim 25, wherein the shaft
pivots within an elongate hole and an arc of motion between said
first fastener disengaging position and said second fastener
disengaging position is substantially 90.degree..
27. A foldable support structure, comprising: a substantially
planar top; a plurality of legs pivotally connected to said top,
said plural legs being pivotable from a first position
substantially parallel to said top, to a second position
substantially perpendicular to said top; a plurality of pivotable
cross members extending substantially parallel to said top, at
least one of said plural legs being rigidly connected to a
respective cross member, so that said respective cross member
pivots when said at least one plural leg pivots; a plurality of
pivot assemblies connected at a respective first end to said top
and connected at a respective second end to a respective one of
said plural cross members and spanning a length of a respective one
of said plural cross members; and a plurality of fastening members
connected to said top and releasably engaging a respective one of
said plural cross members when said plural legs are in said second
position and being spaced apart from said respective one of said
plural cross members when said plural legs are in said first
position.
28. The foldable support structure as recited in claim 27, wherein
said fastening members are selected from the group consisting of
snap-open/snap-shut resilient fasteners, magnets, releasable
adhesives, suction members, elastic or mechanical clips and locking
springs.
29. The foldable support structure as recited in claim 27, wherein
said plural pivot assemblies span substantially an entire length of
said respective one of said plural cross members.
30. The foldable support structure as claimed in claim 27, further
comprising a plurality of disengaging members connected to a
respective one of said plural cross members that disengage a
respective one of said plural fastening members from said
respective one of said plural cross members.
31. The foldable support structure as claimed in claim 30, wherein
each of the plural disengaging members comprises a handle pivotal
from a first handle position to a second handle position, said
handle disengaging a respective one of said plural fastening
members in said second handle position, and a handle stopping block
to stop said handle from pivoting beyond said second handle
position.
Description
FIELD OF THE INVENTION
[0001] This invention is related to a folding table construction,
and more specifically a table leg locking mechanism for securing at
least one table leg in an erect supportive position from a folded
position against and parallel to the underside of the table.
BACKGROUND ART
[0002] Numerous technical solutions are known in the field of
folding tables. From U.S. Pat. No. 4,064,815 is known a table leg
locking mechanism, which locks joined pairs of table legs in either
their supportive or their folded positions at their cross member.
The locking mechanism includes a pivot mount situated within a
rectangular housing attached to the underside of the table. This
locking mechanism consists of a pair of sleeves mounted on a
tubular cross member, such that one sleeve is welded, or in some
other manner securely united to its associated housing, and the
other sleeve is rigidly united to the tubular cross member. A
spring is connected to the tubular cross member whereby constant
pressure is exerted between the two sleeves, one against the other,
to insure locking of the table legs into position. The sleeves are
interlocked together by virtue of their shape, in which one of the
sleeves has wedge-shaped protrusions on its end, conforming to
matching wedge shaped notches in the adjoining end of the other
sleeve. There is one lock for each united pair of legs at each end
of the table. The resulting table construction does not achieve the
elegant slimness and light weight preferred in folding tables,
since the rotating tube locking force is concentrated at a short
wedge which requires a fairly large overall radius for the circular
locking mechanism to achieve its necessary strength, resulting in a
relatively bulky mechanism, shrouded by a bulky frame. The long
term strength of such a design is questionable, due to its complete
reliance on the table top for support of the legs and locking
mechanism, with the frame giving no direct support to the legs and
locking mechanism. The given solution is not an optimal design for
the best universal table utility, in which a leg is near each
corner of a rectangular table.
[0003] The current state of the art of folding tables is
fundamentally limited by the tradeoff achieved between strength and
rigidity, and the aesthetic execution of the locking mechanism.
Today's most popular folding tables generally continue a half
century practice of using interfering, unaesthetic, visible angled
braces for the legs. In addition, legs are paired in such a way
that it is impossible to sit between such legs at the table end.
Due to the impossibility of sitting at the table end, between the
legs of the shorter models of the most popular type of folding
table, which continues to dominate the state of the art, the only
proposed solution to enable end seating at these types of tables is
to increase leg room distance between the end of the table and the
legs, which generally requires making the table longer. In attempts
to attain these features, excessively expensive or flimsy tables
have been developed. This limits the utility of tables based on the
state of the art.
SUMMARY
[0004] An objective of the present invention is to overcome the
limitations mentioned above in a compact, light, simple and
economical, strong, rigid, safe, and mechanically and aesthetically
optimal folding table, whose execution in metal (the top may be
other than metal) is practically indistinguishable from the clean
lines of a nonfolding welded frame metal table. A further objective
of this invention is to present a solution for automatically
locking and unlocking of the hinged legs in their erect position.
In other words, the operator simply and obviously, by grasping and
pulling or pushing a leg, extends, or folds the legs, without any
separate thought or action to actually lock or unlock the legs,
which automatically "snap" into or out of their "locked" erect
position by applying force on a table leg. Another object is to
ensure table leg rigidity and security in the working, erect
position by the overall design.
[0005] This invention is applicable to a broad variety of
embodiments, depending on the choice of materials, the chosen
technologies, the aesthetic and functional executions, various
levels of quality and price. Two obviously differing embodiments
are the one of 100% plastic, and the sheet steel frame and
structure with particleboard top version, reflecting the most
popular common construction. The following overview for a preferred
embodiment of this invention approximates the most popular prior
art folding table attributes. Such a preferred embodiment consists
of a particleboard (plastic, wooden, combination, or similar) table
top supported by an open "U" profile sheet steel frame and a pair
of rotational leg assemblies, which can include a single leg or
pair of legs, achieved through a construction in which a leg (one
or more) is rigidly joined to a hinged, lockable horizontal cross
member (typically tubular), of preferably square cross section,
such that by rotating a leg, two rigidly joined legs at a time are
automatically locked into or out of the erect position. Such a
tubular cross member is rotationally attached to the table at a
pivot. The preferred embodiment of this pivot is a continuous
("piano") hinge attached to an intermediate steel plate which
rigidly unites into a self-supporting unit the entire hinged leg
assembly and table frame combination, independent of (without) the
table top. By appropriate bonding and fastening to the frame and
intermediate plate, the table top can enhance the strength and
rigidity of both the frame and intermediate plate. The intermediate
plate's resistance to deformation, through numerous means of
stiffening and strengthening well known to the art, is the
foundation of the strength and rigidity of the legs in their erect
working position.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 illustrates a front view of a preferred embodiment of
the table with legs unfolded according to the present
invention.
[0007] FIG. 2 illustrates an end view of the preferred embodiment
of the table with legs unfolded according to the present
invention.
[0008] FIG. 3a illustrates a bottom view of the preferred
embodiment of the table with legs folded according to the present
invention.
[0009] FIG. 3b illustrates a front view of the preferred embodiment
of the table with legs folded according to the present
invention.
[0010] FIG. 4 illustrates a bottom view of a preferred embodiment
of the table with legs unfolded according to the present
invention.
[0011] FIG. 5 illustrates an enlarged corner view of FIG. 4.
[0012] FIG. 6 illustrates table leg locking mechanism with legs
folded according to the present invention.
[0013] FIG. 7 illustrates the table leg locking mechanism in the
process of unfolding the legs, at the point that the crossmember
supporting the legs is pressing into the spring, forcing it against
the backing plate in order to force the end of the spring in
contact with the crossmember to ride up and over the corner of the
crossmember to establish the locked condition of FIG. 8 according
to the present invention. The two arcs in the drawing are circles
centered on the pivot of the hinge of leg assembly rotation,
showing the locus of movement of the two vital corners of the leg
cross member in relation to the cross member locking spring, which
is designed and contoured to ride up the first surface with which
it comes in contact, ride over the corner with the next surface,
and establish a firm lock or grip on the second surface, as
described in the sequence of Figures.
[0014] FIG. 8 illustrates table leg locking mechanism with legs
erect and in their fully locked condition according to the present
invention.
[0015] FIG. 9 illustrates table leg locking mechanism in the
process of folding the legs, at the point of breaking the grip of
the spring at its contact with the bottom surface of the cross
member, as the spring is stretched into a more flattened contour,
and is forced to ride over the corner of the crossmember to
establish the unlocked condition of FIG. 6 according to the present
invention.
[0016] FIG. 10 illustrates the full cycle of motion of the locking
spring by superimposing the previously illustrated different
positions of the locking spring when engaging and disengaging the
cross member according to the present invention.
[0017] FIG. 11 illustrates an alternate embodiment of the
invention.
[0018] FIG. 12 illustrates the profile of an alternate metal
locking spring, which is readily adaptable to a plastic version
executed in thicker material.
[0019] FIG. 13 shows a rotational stop reinforcing bracket in a
vertical side view with leg unfolded, shaded with hash lines,
placed (welded or brazed) at the four corners of the table frame to
provide a second rigid stop applied directly to the four legs, at
the point of greatest mechanical stress. If the tubular cross
member were perfectly rigid, this would be less necessary, but due
to torsional twisting, such reinforcements would help relieve
stress near the ends of the hinge in heavy duty applications.
[0020] FIG. 14 shows the reinforcing bracket of FIG. 13 in full
detail, in horizontal view, crosshatched, and also in the
sheetmetal layout prior to bending into the bracket
configuration.
[0021] FIG. 15 shows a horizontal table view with legs unfolded of
the reinforcing brackets at all four corners of the table.
[0022] FIG. 16 shows the table of FIG. 15 with the legs folded,
revealing an additional stiffening crossmember, which is not
necessary for common use, but for certain grades of tables, of
certain sizes and applications, may prove advantageous to add, as
an option.
[0023] FIG. 17 shows the appearance of the optional stiffening
crossmember of FIG. 16 with the legs in their working position.
[0024] FIG. 18 shows an alternative embodiment of a table, wherein
the table is modified to adapt to a magnetic strips, instead of a
spring latch.
[0025] FIG. 19 shows matched, oppositely polarized attracting
magnetic strips in use, attached to both the cross member and the
table.
[0026] FIG. 20 shows the magnetic strips attached only to the cross
member.
[0027] FIG. 21 shows an embodiment of the present invention having
an optional non-releasably engaging spring and a spring lock
disengaging device.
[0028] FIG. 22 shows a cross-sectional view of the embodiment of
FIG. 21.
[0029] FIG. 23 shows a bottom left-hand view of a table leg locking
mechanism having an optional spring lock disengaging device
according to the invention.
[0030] FIG. 24 shows a bottom right-hand view similar to
[0031] FIG. 23 (mirror image view).
[0032] FIG. 25 shows an alternate spring lock disengagement
device.
[0033] FIG. 26 shows a cross-sectional view of the embodiment of
FIG. 25.
[0034] FIG. 27 shows a bottom view of a table leg locking mechanism
having an optional spring lock disengaging device according to the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0035] The present invention is more particularly described in the
following exemplary embodiments that are intended as illustrative
only since numerous modifications and variations therein will be
apparent to those skilled in the art. The preferred embodiments are
now described with reference to the figures, in which like
reference characters indicate like parts throughout the several
views.
[0036] In FIGS. 1 and 2 is illustrated a preferred embodiment of
the folding table according to the invention. The table comprises
table top 1, table frame 2 and legs 3. The metal embodiment of the
table unfolded (the top may be other than metal) is practically
indistinguishable from the clean lines of a nonfolding welded frame
metal table.
[0037] The preferred embodiment in FIG. 3A comprises a
particleboard (or similar) table top 1 supported by a table frame 2
and legs 3, achieved through a construction in which each pair of
legs 3 are rigidly joined to a rotating lockable cross member 5
(typically tubular), of nearly square cross section, such that by
rotating a leg, two legs at a time are automatically locked into or
out of the erect position. FIG. 3b illustrates that according to
the present invention the folded rotating leg assembly and the
locking mechanism can be hidden behind an ordinary table frame 2.
Such a rotating leg assembly 3 and 5 is rotationally attached to
the table at a robust pivot 6 as illustrated in FIGS. 4 and 5. The
preferred embodiment of this pivot is a continuous ("piano") hinge
7 attached robustly to an intermediate plate 8, which rigidly
interconnects into a self-supporting unit the entire hinged leg
assembly and table frame combination, independent of (without) the
table top 1. By appropriate bonding and fastening to the frame 2
and intermediate plate 8, the table top 1 enhances the strength and
rigidity of both the frame 2 and intermediate plate 8. The
intermediate plate's 8 resistance to deformation determines the
strength and rigidity of the legs in their erect working
position.
[0038] The intermediate plate 8 is for the support, through rigid
connection with the frame and firm bonding with the table top, of
the high leverage stresses exerted by the tubular cross member and
legs combination 3 and 5 in conjunction with the hinge 7, and to a
small extent the locking forces on the locking spring 9 through
combined bracket 10 and frame 2. Therefore the intermediate plate 8
can be welded or brazed along its continuous contact with all three
sides of the frame 2, and the frame in this area, although an open
"U" profile, or channel, should be closed to form a rigid tube by
channel 10, as drawn, adjacent to the rotational legs and cross
member unit, and for highest heavy duty rigidity, closed around the
curves unto the end of the intermediate plate (not shown in the
drawings, which reflect a medium quality version). As seen by
comparing FIG. 7 with FIG. 8, a leg stopping surface 11 of FIG. 7,
prevents the leg assembly 3,5 from rotating beyond substantially 90
degrees (so that stopping surface 11 is substantially parallel to
leg assembly surface 12).
[0039] A preferred inexpensive enhancement to the basic design
discussed thus far, including the three-legged round version of
this table, is the second leg stop bracket 15 illustrated in FIGS.
13 and 14. Such an optional bracket 15 at each leg, located near
each corner of the table frame in the case of a rectangular table
frame as shown unfolded and folded in FIGS. 15 and 16, respectively
(which would fit nicely also underneath a round table having four
legs), adds a second stopping surface at each of the legs, which is
exactly the point of greatest stress on the piano hinge due to
leverage, and reduces that leverage ratio at least by a factor of
one to the square root of 2. In other words the stress on the hinge
is reduced to no more than 0.707 times what it was without this
bracket. Because the bracket 15 can contact the leg at a point
beyond the spring-engaging corner of the cross member, this stress
reduction is even greater, giving a ratio number even smaller than
0.707. FIG. 15 also shows two support blocks 20 in the center of
the table whose purpose is to support the table legs while the
table is being carried with the legs folded. A long table would of
course have four such support blocks instead of two, one for the
foot of each leg.
[0040] The leg stopping surfaces of the intermediate plate 8 and
the optional leg stopping bracket 15 can be protected from
corrosion with either suitable metal plating, or special thin
plastic films, with possible adhesive backing, instead of paint
which can crack or chip under the high stress of high-leverage
contact. The corresponding contact surfaces of the rotating
horizontal cross member can likewise be protected from possible
corrosion.
[0041] A higher quality, heavy duty table can also feature brazing
or welding some of the links in the continuous hinge located
nearest to the legs both to the intermediate plate, as well as to
the hinge plate itself, to prevent the rolled hinge from unrolling
under stress which may be somewhat more concentrated at the legs 2,
due to the imperfect rigidity of the cross member 5. On the
contrary, for a cheap table, the floor plate could be of more
deformable steel, unconnected to the frame, or entirely eliminated
(preferably compensated through the use of a hinge with a wider
leaf for greater adhesive bonding surface to the underside of the
table), and the construction less robust, with a lowering of
quality. For plastic top tables, including blow molded tables, the
top of the intermediate plate 8 would likely need to be reinforced
to be made highly rigid, which can be done as simply as bonding a
strong wooden board to this area. Or the complete metal table
structural unit, reinforced by a rigid stiffening panel on top of
intermediate plate 8, could be molded directly into a suitably
reinforced plastic table top matrix in a single molding
operation.
[0042] At each tubular cross member 5 is a one-piece locking
mechanism, a simple spring approximately as illustrated (e.g. FIG.
8), by means of which the tubular cross member 5 is firmly pressed
against its rotational limit, in practically full surface contact
with the intermediate plate 8 (and possibly also the end surfaces
of the legs 3, depending on how they are united with the cross
member 5, although a welded splice of the tubes trimmed at 45
degrees joined to form 90 degree corners would seem to produce an
optimal joint for square tubing.). The locking spring 9, which is
rigidly attached to the adjacent frame element 10 (FIGS. 6-10), can
engage the cross member 5 near the maximum distance from the cross
member pivot 6 for maximum mechanical locking advantage, or
counter-leverage (thus minimizing the strength requirement of the
locking spring).
[0043] The preferred sheet steel support, i.e. frame element 10 for
the locking spring 9, performs several functions: it closes the "U"
channel frame next to the leg bearing cross member to form a rigid
tube, adding necessary strength and rigidity for the intermediate
plate 8 to support the high locking stresses due to leg leverage;
it provides an appropriate mounting surface for attaching the
locking spring 9; it provides a backing surface to limit the
rearward yielding motion of the locking spring 9 in the direction
of the frame during locking, thereby forcing the locking spring 9
to engage and lock the cross member 5 at the optimum angular
position in the turn of the legs for locking (see FIG. 7).
[0044] The result of such a spring movement limiter, or stop, is
assured, "positive" locking action. Also, unlocking is
advantageously "delayed" in terms of rotational angle, since there
is no stop for the spring 9 in the opposite, forward, or unlocking
direction (See FIG. 9). Consequently, the legs 4 must be turned a
greater angular distance than for locking before the locking spring
9 will disengage, which is a safety advantage to avoid sudden and
unintended collapse of the table under extreme forces on the
table.
[0045] By virtue of extending the locking spring 9 up to nearly the
entire length of the rotating cross member 5 which it engages, the
use of an inexpensive light and flexible spring becomes possible
due to the unusually high pressure attainable from an unusually
wide spring. Thus, a key inventive step is the realization that
adequate locking force, without the use of the customary unsightly
and interfering diagonal leg braces, is achievable by exploiting
the long locking geometry available along the normally extensive
length of the cross member (typically the narrow, or "end", width
in the case of a rectangular table) by application along the edge
diagonally opposite from the hinged corner of this cross member the
cumulative pressure of an uncommonly wide spring. The spring needs
to be quite yielding (elastic) in order to effectively and durably
engage and disengage the cross member (see FIG. 10).
[0046] The required flexibility normally, or intuitively, suggests
weak locking force, and therefore unsuitability of such a spring
for securely holding a table erect in normal use, working against
anticipated great leg leverage at the cross member. The wide
structural span (from leg to leg in case of a leg at either end) of
the cross member is available for application along this width of
an unusually long spring whose cumulative pressure by virtue of
this width would attain the required locking force.
[0047] A corrolary insight was the recognition that to attain
secure table stability the locking force applied by the spring 9
need not be great, because the table as a whole is always held
rigidly erect by at least one of the two rigidly joined sets of
legs. In a traditional completely rigid table, both pairs of legs
do this. In this invention, one rotating set of legs is nearly
always forced against its rigid mechanical stop, or at right angles
to it, which meets with inherently rigid resistance, for any
direction of force on the table, resulting in adequate overall
table rigidity, in spite of the fact that at the opposite set of
legs the locking spring may theoretically yield at a relatively low
force applied at the foot of the table leg.
[0048] Balancing spring properties against spring length can attain
any practical total distributed spring locking force. The greater
the spring length, the gentler, more flexible, more durable, and
less exotic or expensive can be the spring material. Consequently,
the choice of spring materials advantageously grows with the spring
length, such as economy, and ability to weld, braze, form, etc.
Thus the large available span of the rotating cross member 5
enables a wide choice of materials, not excluding plastic, for an
all-plastic table, including a suitable version of the locking
spring 9.
[0049] The obvious concern regarding the limited, possibly even
weak locking force of any such locking spring is answered by the
fact that the present invention embodies a robust physical limit to
the leg rotation in the direction of extension. Because the
opposite pairs of legs 4 open in opposite directions, for any force
applied to the table, one set of legs will always be forced against
its rigid stop, and hence hold the table rigidly immobile, within
the constraints of floor friction, while the locking spring 9 of
the opposite pair of legs, which is potentially subject to
compression by such a force if the opposite pair of legs slip on
the floor, can be designed to be as rigid as necessary, using
material or dimensional properties, such as added spring thickness
or width, multiple spring layers, or support structures as needed.
In other words, great total locking force of the locking spring 9
is consequently not necessary and locking force which is
comfortably modest for snapping the rotational leg assembly (or
unit) into lock and snapping out of lock, is very acceptable.
[0050] A practical tradeoff, or optimized balance between the
property of ease of locking and unlocking of the legs, and
resistance to leg collapse under applied table force is determined
experimentally by dragging the table under various loads across
floors of various frictional resistance. Lubrication of the sliding
locking spring 9 contact with the cross member 5 may be addressed
by plating the cross member 5 with a soft metal such as copper, to
form a bearing interface with the hard metal of the spring. Many
lubrication techniques are known, and the open and accessible
structure of the lock facilitates easy conventional lubrication and
cleaning.
[0051] The preferred implementation of this invention favors
popular folding table sheet steel channel (sheetmetal bent in a "U"
shape) for the frame, as well as popular fiberboard or unreinforced
plastic table material, or the reinforced blow molded plastic table
tops coming into popularity. Fiberboard and especially unreinforced
plastic tables need supporting frames, since such a table lacking a
supporting frame can sooner or later distort or fail. Folded or
erect, the simple and simple to use, compact, lightweight, yet
robust locking mechanism pertaining to this invention is concealed
within the perimeter and shallow depth of the table frame, and when
erect, the table is scarcely distinguishable from the optimal lines
and configuration of a welded tubular steel frame table, whereby
the aesthetic objective of this invention is achieved. In addition,
safety is provided for the user, in that the table can be designed
so that nothing extends below the table frame to interfere or snag,
except the legs in their extended position. A table incorporating
the benefits of this invention permits optimal freedom of seating
at the ends of even the shortest table because the table legs are
at the corners of the table.
[0052] Many variations of this invention may be effected, without
departing from the scope of the invention. Folding table of the
invention can have table top of arbitrary size, shape, structure
and composition (see for example FIG. 11). In principle, this
invention may be readily implemented totally in plastic.
Preferably, reinforced plastic where needed. In addition, the legs
3 can be reinforced as shown in FIG. 17 using optional stiffening
crossmember 25.
[0053] In a much lighter all-plastic version, there may be no
apparent frame, and probably bulkier parts, with much internal
reinforcement, probably with fibers, and structural parts of the
metal version could be only functionally adapted into the plastic
embodiment. In other words, the plastic functional equivalent
embodiment of this invention may use parts which are very different
in appearance from the metal version, may not embody all of those
parts, and may have parts or structure which is not at all present
in the description of the popular metal frame and legs version
described in the preferred embodiment above. Similar comments apply
to other materials, and combinations of materials. Even the spring
may be plastic.
[0054] But having a different design for a plastic spring latch--a
flat vertical plastic sheet mounted in a similar position with
respect to the square cross member as in the metal version, but
having relatively small movement, and having a rigid engaging
"catch" on the end, as an angled "tooth", or "shoulder" to engage
by spring pressure the corner of the cross member at a wedging
angle, so as to yield, break its grip and slide back under
unlocking tension. This approach would also work in metal, but less
effectively than the presented version, as a simple flat spring
with a less than 90 degree bend at the end, either flat or possibly
curved round to engage by wedging action the corner of the cross
member (FIG. 12).
[0055] A variety of latch designs is readily conceivable. Instead
of the spring the means of holding the cross member in its erect
position with firm force against its stop can be a
snap-open/snap-locked resilient fastener, which can be magnetic,
adhesive, vacuum (e.g. suction cup), spring (e.g. clip), rubber
(e.g. clip), mechanical (clip), or similar, enabling automatic
engaging of the legs in their erect position, and automatic
disengaging of the legs from their fixed erect position. FIG. 18
shows a magnetic strip, instead of a latch spring. Obviously, the
magnetic strip may be attached to either surface being joined, and
work just as well. Or two strips of approximately half the
thickness (and magnetic strength) of the preceding single strip can
be applied to BOTH surfaces to be locked together, such that the
magnetic polarization of the vinyl strips are opposite, so the
strips attract. Such paired strips are commercially available,
particularly for use in latching together nonmagnetic materials
such as plastic or wood. Herein lies the application of such a
strip in an all-plastic version of my table. A metal version is
shown in FIG. 8, but the plastic version can easily be molded such
that the magnetic strip is imbedded into the cross member, so as to
present a continuous flat surface where the two surfaces come in
contact. In FIG. 18, the magnetic strip is attached to the table,
not the cross member. FIG. 19 shows matched, oppositely polarized
attracting magnetic strips in use, attached to both the cross
member 5 and the table 2. FIG. 20 shows the magnetic strips
attached only to the cross member.
[0056] An all wooden table is possible under this concept, with the
obvious exception of the spring, its engaging surface on the wooden
cross member, hinges, and similar hardware typically of metal in
wooden tables. The invention makes no suggestion of dimensions or
relative proportions, as does the ideal embodiment. The spring can
thus be long or short, in the horizontal direction parallel to the
axis of the horizontal crossmember, and can be of any shape and
relationship to the surrounding structures, segmented or
continuous, connected in any manner to the table or frame at any
suitable location, so long as it accomplishes the same function:
automatically (without operator intervention, other than turning
the legs as described) engaging and disengaging the table leg cross
member with enough force to hold the cross member securely in the
erect position. A short table would necessarily have the legs
offset in one way or another (legs folded on top of each other
(thus having half the thickness shown) or side by side, etc.)
[0057] It is also conceivable to attach the spring to the rotating
cross member, which could be, for example, an angle ("L" profile)
or channel ("U" profile) iron instead of a rectangular tube such
that the spring is located within the sides of the L or U, which
would then engage a suitable structure fastened to, or part of, the
table surface or frame (An example of such a structure is an
inverted "L" angle iron along the frame adjacent to the rotating
cross member, whose edge engages the locking spring in the cross
bar, etc.).
[0058] In other words, whereas in the preferred embodiment, the
spring was fixed to the table (frame), and the rotating cross
member which the spring is to engage was moving, these roles can be
easily reversed, by attaching the locking spring to the cross
member, to engage a structure analogous in function if not in form
to the moving cross member structure in the preferred embodiment
described above, without departing from the scope of this
invention. The preferred means of holding the legs in the folded
position may be replaced by any other means, and likewise, the leg
deformation support.
[0059] These are nonessential to the invention, and may in fact, be
entirely absent, and still meet the scope of this invention. In
addition, the described embodiment is a table, however, the concept
of the invention would be equally applicable to a chair, a bench or
any other structure that could be folded for storage or the
like.
[0060] Further, the invention has been described in connection with
three or four legs. However, the invention would work equal well
with two legs. A two legged embodiment would have broad feet to
stabilize the legs. Even a one legged embodiment is within the
scope of the invention.
[0061] In the embodiments described above, by manually applying
pressure to a respective leg to cause the fastener to break its
grip, the table legs can be moved from the erect position to the
folded position. In another embodiment, a disengagement device can
be employed. In a preferred embodiment the disengagement device is
a spring latch disengagement device.
[0062] FIG. 21 shows a partial X-Ray view of the latch mechanism in
the approximate center of the hinged leg-bearing rotational cross
member 5, showing an embodiment of a disengagement device, operator
control handle 31. Also shown is the supporting rotational pivot
shaft 32 of handle 31 and the surrounding structure. The control
handle position is displayed in its normal retracted, or "home"
position. This control handle has a spring return 34 as shown in
FIG. 22 to automatically return the control handle 31 to this home
position when the operator releases it.
[0063] The view of FIG. 21 is from the bottom of the table, or from
the floor, looking up at the mechanism against the underside of the
table, near the edge of the table. The edge of the table frame 2 is
shown. In the operation of the latch, the handle 31 is swung on its
shaft 32, 90 degrees outward from the table, crossing the table
frame 2 to where it is perpendicular to table frame 2. In this
position, the table leg locking spring 9 is forced fully away from
and disengages the leg supporting rotational crossmember 5,
permitting the legs 3 to be folded. However, the handle 31 need not
be turned 90 degrees and can be turned at different angles in order
to disengage the locking spring 9.
[0064] FIG. 21 shows edges of the lower flange of the "U" channel
table frame 2 and edges of the square tubular rotational leg
bearing cross member 5. FIG. 21 also shows the pivot hinge 7,
showing the horizontal and vertical leaves and hinge segments, the
base plate 8 supporting the folding leg structure, to which the
hinge 7 is attached and the latching spring 9, shown in its engaged
position, engaging the crossmember 5. Bend lines 10 of frame
stiffening channel to which latching spring 9 is attached are also
shown.
[0065] A cam bearing block 36 is rigidly attached to spring
disengagement plate 37. The spring disengagement plate 37, slides
in a substantially 90.degree. arc (see FIGS. 23 & 24) to
release spring 9. Control handle return stopping block 38 is
rigidly attached to disengagement plate 37. A circular cam 46 is
rigidly attached to shaft 32, closely engaging for a sliding fit
circular holes in both cam bearing block 36 and spring
disengagement plate 37.
[0066] Note that the spring disengagement plate 37 slides on the
surface of crossmember 5 (such that the motion of all points on its
surface describe a short substantially 90.degree. arc, the locus of
which is depicted in FIGS. 23 & 24) by means of intermediary
blocks 50, 51, and 52; cam bearing block 36, and its own 90.degree.
bent edge. Blocks 50 and 51 are rigidly attached to crossmember 5,
and block 52 is rigidly attached to disengagement plate 37. The
central intermediary block, via which disengagement plate 37
maintains constant sliding contact with crossmember 5, is the cam
bearing block 48, in approximately the middle of plate 37, yet
positioned (optionally and optimally--not necessary but
recommended) such that when maximum disengagement force is applied
by plate 37 to spring 9 (at the substantially 90.degree. turn of
handle 31), the spring force on plate 37 is balanced around the
pivot hole of cam 46.
[0067] If an ideal perfect balance such as just described could be
maintained and guaranteed, blocks 50 and 51 (FIGS. 23 & 24)
would not be needed. However, because of imprecision in
manufacturing, the latter three blocks at each end of plate 37
enforce perfect balance, or parallel alignment, of plate 37 with
crossmember 5 and spring 9, ensuring uniform disengagement of
spring 9. Also, when control handle 31 is released, spring 34 (FIG.
22) forces the handle 31 and spring disengagement plate 37 to
return to their normal positions. This "normal position" is
established by the motion limiting contact of blocks 51 and 52
(FIGS. 23 & 24) at both ends of plate 37. Sliding contact is
maintained between the sliding surfaces of blocks 51 and 52 by
retaining plates 53 (FIG. 23 & 24) and the retaining effect of
control handle 31 itself.
[0068] A return to rest stopping block 38 to stop the travel of the
control handle in its resting position: This stopping block 38 is
rigidly attached to the spring release plate 37 at its rear edge.
Block 38 is preferably a block of metal brazed, welded, or
similarly attached to plate 37.
[0069] FIG. 22 is a cross sectional view that is virtually
identical to the main features of the corresponding cross sectional
view shown for the releasably latched version of FIG. 7. The basic
difference being that the latching spring 9 in the releasable
version has a more sloping, releasable bend to it, whereas in this
version the bend is sharper, and grabs hold of the cross member 5
with a grip which will not let go by force applied to the table
legs. Therefore, the release mechanism 31 is added. This
demonstrates that no change in tooling will be necessary to
manufacture both versions of this table at one facility.
[0070] FIG. 22 shows the latch release operating handle 31, which
is rigidly attached to a circular cam disc 35, and both of the
former are rigidly attached to the pivot shaft 32, supported by
bearings 33A and 33B, and tensioned by latch mechanism return
spring 34 to automatically return the mechanism to its normal,
disengaged position when the control handle 31 is released by the
operator. The cam disc 35 slidingly engages identical holes in
bearing plate 36 and spring disengagement plate 37. Bearing plate
36 and disengagement plate 37 are rigidly attached to each other,
and their combination makes sliding contact with the surface of
crossmember 5, in such a manner that all points of the latter two
exhibit a motion described by the short 90.degree. arcs shown in
FIGS. 23 and 24. As the control handle is turned 90.degree., the
locus of the motion at all points on the sliding structure is this
short 90.degree. arc. Control handle return stopping block 38 is
rigidly attached to disengagement plate 37.
[0071] FIG. 23 shows a bottom left-hand view of a table leg locking
mechanism. FIG. 24 also shows a bottom view of a table locking
mechanism. The two end views are nearly identical, the differences
being due to the fact that the motion of all points on the spring
unlocking plate 37 describes a short arc of substantially
90.degree. such as depicted in FIG. 23; and in FIG. 24, the
corresponding identical motion of the opposite end of the
mechanism. The key to understanding the layout is in viewing the
position of locking spring 9: in the fully unlocking position of
control handle 31, when it is turned 90.degree. to its terminal
unlocking position, the ends of the unlocking plate 37 and the
locking spring 9 coincide, so as to produce balanced force on the
unlocking plate 37 which has its supporting cam bearing hole in its
center. Thus if the construction were perfect, motion stopping
blocks 50 on each end of plate 37 would be unnecessary. These
latter blocks are in place only to perform an insurance function to
insure that in the maximum unlocking position of the control handle
31, the spring 9 is truly pushed evenly back across the entire
length of the cross member 5, fully disengaging it. Therefore, this
embodiment is shown over engineered for purposes of illustration of
the principle involved in order to make alternate embodiments
easier for the practitioners of the art. This latter is not
necessary for this invention.
[0072] A main feature of this embodiment is the elements for the
control and restriction of the motion of locking spring
disengagement plate 37. This motion is described by the two short
arcs, drawn with arrows at the ends, describing substantially
90.degree.. Three identical stopping, or motion limiting bars are
shown: 50, 51, and 52. Bar 51 is rigidly attached to spring
disengagement plate 37; and bars 50 and 52 are rigidly attached to
the leg-bearing horizontal crossmember 5, such that bar 51 slides
between bars 50 and 52, the latter two bars limiting the motion of
bar 51.
[0073] Thus, bar 50 insures that when plate 37 is in its maximum
disengagement extension, both bars 50 at each end are in contact
with both bars 51, insuring that the locking spring 9 is forced
back uniformly and precisely to its optimal disengagement position.
This position is sensed by the operator, in that he feels the
resistance of the blocking, as well as sees the 90.degree. position
of the handle; at which point the operator knows that the locking
spring is disengaged, and he may begin to rotate the table legs to
fold them.
[0074] Bar 52 at both ends of the spring disengagement plate 37
stops the spring 34 driven motion of the entire mechanism at its
resting position, where the control handle 31 is parallel to the
horizontal crossmember 5, and the spring disengagement plate 37 is
resting in its fully retracted position.
[0075] Retaining and guide plate 53, in conjunction with its
mounting and precision spacing block 54, insure that the ends of
the spring disengagement plate 37 cannot be forced out of their
normal positions. This is not necessary to the operation of this
invention, but is a useful precaution against accident or
vandalism.
[0076] FIGS. 23 and 24 also show optional elements such as table
leg "glide", or foot 26, assuring an acceptable contact between the
table and floor surface. Pop rivets 40, or other suitable fasteners
for convenient manufacture are also shown.
[0077] As set forth above, FIG. 24 is nearly identical to FIG. 23,
and contains the same identical elements. The embodiment of FIG. 24
demonstrates fully the 90.degree. arc in which all of the points on
the spring release plate 37 move. The intention of this figure is
for the reader to compare the two ends of the mechanism, and
referring to the two 90.degree. arcs tipped with arrows, visualize
the motion of spring release plate 37, to which are rigidly
attached the intermediate stopping bars 51. One can discern the
90.degree. arc motion traversed by stopping bar 51 as it travels
from its resting contact with bar 52 (shown) to its limiting
contact with bar 50 (not shown, but indicated by the arrows).
[0078] FIG. 25 is an embodiment that is only a slight modification
of the preferred embodiment of the latch unlocking mechanism
described above with respect to FIGS. 21-24, entailing only minor
differences, wherein the numbering of the parts common or similar
to the two embodiments are exactly the same. Where there is a
unique element, it has a unique number.
[0079] A primary difference between the two embodiments (of FIGS.
21-24 and 25-27) is that the cam bearing block 36, which in FIGS.
21-24 was rigidly attached to spring disengagement plate 37, is in
the embodiment of FIGS. 25-27, free to slide in contact with the
latter. And the spring disengagement plate 37 is restrained in its
freedom of motion by elongated hole 47 within the latter, through
which control handle shaft 32 extends, having a close sliding
contact with the latter, such that the hole and the pin comprise
the guide for the freedom of motion available for plate 37.
Therefore the motion of plate 37 is restricted to motion
substantially perpendicular to the axis of crossmember 5, and
substantially parallel to its surface, which directly pushes
locking spring 9 backwards to its unlocked position. Thus, as the
control handle 31 is turned 90.degree. from its rest position, cam
bearing block 36 describes exactly the same 90.degree. arc of
motion which it did in the embodiment of FIG. 21-24, above, but
being always in contact with the two surfaces of disengagement
plate 37, as it traverses its full arc of motion, it pushes
against, and slides along, the 90.degree. flange of plate 37,
forcing that flange and plate 37 in the direction of locking spring
9. Since plate 37 is captive in its hole 47 to guide pin 32, plate
37 is thereby constrained to move directly against spring 9,
forcing it back to its unlocking position.
[0080] Similar to the embodiment of FIGS. 21-24, at the ends of
disengagement plate 37 are stopping blocks 39 and 42 to insure the
forward and rearward limits of travel of 37. In this case, there is
no intermediate block (corresponding to bar 51 in the embodiment of
FIGS. 21-24). Rather, there are cutouts in the body of plate 37
itself which provide the stopping surfaces analogous to the
function of bar 51 previously.
[0081] A return to rest stopping block 38 is used to stop the
travel of the control handle 31 in its resting position. This
stopping block 38 is rigidly attached to the spring release plate
37 at its rear edge. The stopping block 38 is preferably an angle
bracket that can be brazed or welded (or attached in any suitable
manner) to plate 37, at its rear edge. However, note that this
bracket is preferably located as near as practical to the center of
plate 37. In this central position, the spring driven handle 31
acting on the bracket 38 forces plate 37 backwards to its normal
rest position.
[0082] FIG. 27 further shows a retaining and guide plate 41 for
spring release plate 37, insuring that the latter, which is long
and easy to bend, can not be forced out of its position and
damaged. In addition, a forward stop 42, or motion limit for spring
release plate 37, ensures even and precise unlocking of the
latching spring 9. A rear stopping surface 43 for plate 37, fixes
the rest position of plate 37. Preferably, surface 43 is a notch in
plate 37. A forward stopping surface 44 for plate 37, fixes the
spring unlocking position of plate 37. Preferably surface 44 is
also a notch in plate 37.
[0083] In view of the foregoing, the invention resides in the novel
selection, arrangement and combination of parts performing clear
functional roles of novel choice and combination, as described and
claimed, producing a new and advantageous result; it being
understood that changes in the precise embodiment of the invention
herein disclosed may be made within the scope of what is claimed
without departing from the spirit of the invention.
* * * * *