Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
LOAD SUPPORTING PANEL HAVING IMPACT ABSORBING STRUCTURE
BACKGROUND OF THE INVENTION
[0001] This invention relates in general to impact absorbing underlayment
panels.
In particular, this invention relates to underlayment panels having deformable
elements that compress in a plurality of stages such that a load absorbing
gradient is
provided in response to an applied force.
[0002] Surfaces such as playgrounds and athletic mats, for example, are
scrutinized
for their effect on impact forces that cause related injuries to users.
Attempts have
been made to minimize the force or energy transferred to a user's body in the
event of
a fall. Various surface designs that rely on ground materials or layered
fabric
materials may help reduce the transfer of impact forces. These surface
designs,
however, are limited by the ability of the materials to spread the impact load
over a
large area. Thus, it would be desirable to provide a surface having improved
impact
force absorption and dissipation characteristics.
SUMMARY OF THE INVENTION
[0003] This invention relates to an impact absorption panel having a top side
and a
bottom side. The top side includes a plurality of drainage channels that are
in fluid
communication with a plurality of drain holes. The plurality of drain holes
connect
the top side drainage channels with a plurality of bottom side channels. The
bottom
side channels are defined by sides of adjacent projections that are disposed
across the
bottom side.
[0004] This invention also relates to an impact absorption panel having a top
side
and a bottom side where the bottom side has a plurality of projections
disposed across
at least a portion of the bottom surface. The projections have a first spring
rate
characteristic and a second spring rate characteristic. The first spring rate
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characteristic provides for more deflection under load than the second spring
rate
characteristic.
[0005] In one embodiment, an impact absorption panel comprises a top surface
and
a bottom surface. The top surface has a three dimensional textured surface and
a
plurality of intersecting drainage channels. The bottom surface is spaced
apart from
the top surface and defines a panel section therebetween. A plurality of
projections is
disposed across at least a portion of the bottom surface. The projections have
a first
stage that defines a first spring rate characteristic and a second stage
defining a second
spring rate characteristic. The first spring rate characteristic provides for
more
deflection under load than the second spring rate characteristic. The
plurality of
projections also cooperate during deflection under load such that the adjacent
projections provide a load absorption gradient over a larger area than the
area directly
loaded. In another embodiment, the first stage has a smaller volume of
material than
the second stage. Additionally, the adjacent projections define a bottom
surface
channel to form a plurality of intersecting bottom surface channels and a
plurality of
drain holes connect the top surface drainage channels with the plurality of
bottom
surface channels at the drainage channel intersections.
[0006] In another embodiment, an impact absorption panel includes a top
surface
and a bottom surface that define a panel section. A plurality of projections
are
supported from the bottom surface, where the projections include a first stage
having a
first spring rate and a second stage having a second spring rate. The first
stage is
configured to collapse initially when subjected to an impact load, the second
stage is
configured to provide greater resistance to the impact load than the first
stage, and the
panel section is configured to provide greater resistance to the impact load
than the
first and second stages. The first stage is also configured to compress and
telescopically deflect, at least partially, into the second stage. A portion
of the bottom
surface is generally coplanar with the truncated ends of adjacent projections
such that
the coplanar bottom surface portion is configured to provide a substantial
resistance to
deflection under load compared with the first and second stages. This coplanar
configuration of the bottom surface provides a structural panel section having
a
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thickness that is generally equal to the thickness of the panel section plus
the length of
the projections.
[0007] In yet another embodiment, an impact absorption panel system comprises
a
first panel and at least a second panel. The first panel has a top surface, a
bottom
surface, a first edge having a flange that is offset from the top surface and
a second
edge having a flange that is offset from the bottom surface. A plurality of
projections
are disposed across the bottom surface. The projections have a first spring
rate
characteristic and a second spring rate characteristic. The second panel has a
top
surface, a bottom surface, a first edge having a flange that is offset from
the top
surface and a second edge having a flange that is offset from the bottom
surface. A
plurality of projections are disposed across the bottom surface of the second
panel and
have a first spring rate characteristic and a second spring rate
characteristic. One of
the second panel first edge flange and the second edge flange engages one of
first
panel second edge flange and the first panel first edge flange to form a
generally
continuously flat top surface across both panels.
[0008] In one embodiment, the impact absorption panel is a playground base
layer
panel.
[0009] Various aspects of this invention will become apparent to those skilled
in
the art from the following detailed description of the preferred embodiment,
when
read in light of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Fig. lA is an elevational view of a top side of an embodiment of an
impact
absorption panel suitable as a playground base;
[0011] Fig. 1B is an enlarged elevational top view of an edge of the impact
absorption panel of Fig. 1A;
[0012] Fig. 1C is an enlarged elevational top view of a corner of the impact
absorption panel of Fig. 1A;
[0013] Fig. 2A is an elevational view of a bottom side of an embodiment of an
impact absorption panel;
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[0014] Fig. 2B is an enlarged elevational bottom view of a corner of the
impact
absorption panel of Fig. 2A;
[0015] Fig. 3 is a perspective view of an embodiment of a panel interlocking
feature of an impact absorption panel;
[0016] Fig. 4 is a perspective view of a panel interlocking feature configured
to
mate with the panel locking feature of Fig. 3;
[0017] Fig. 5 is an elevational view, in cross section, of the assembled panel
interlocking features of Figs. 3 and 4.
[0018] Fig. 6 is an enlarged elevational view of an embodiment of a shock
absorbing projection of an impact absorption panel;
[0019] Fig. 7 is a perspective view of the bottom side of the impact
absorption
panel of Fig. 6;
[0020] Fig. 8A is an enlarged elevational view of an embodiment of a deformed
projection reacting to an impact load; and
[0021] Fig. 8B is an enlarged elevational view of another embodiment of a
deformed projection reacting to an impact load.
[0022] Fig. 9 is an enlarged elevational view of another embodiment of a
deformed
projection reacting to an impact load.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] Referring now to the drawings, there is illustrated in Figs. 1A, 1B,
and 1C a
load supporting panel having an impact absorbing structure configured to
underlie a
playground area. The various embodiments of the impact absorbing panel
described
herein may also be used in indoor and outdoor impact environments other than
playgrounds and with other types of equipment such as, for example, wrestling
mats,
gymnastic floor pads, carpeting, paving elements, loose infill material, and
other
covering materials. In certain embodiments, the panel is described as a single
panel
and is also configured to cooperate with other similar panels to form a base
or impact
absorbing panel system that is structured as an assemblage of panels. The
panel,
shown generally at 10, has a top surface 12 that is illustrated having a grid
of drainage
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channels 14. Though shown as a grid of intersecting drainage channels 14, the
drainage channels may be provided in a non-intersecting orientation, such as
generally
parallel drainage channels. In the illustrated embodiment, a drain hole 16 is
formed
through the panel 10 at the intersection points of the drainage channels 14.
However,
not every intersection point is required to include a drain hole 16. The drain
holes 16
may extend through all or only a portion of the intersecting drainage channels
14 as
may be needed to provide for adequate water dispersion. Though illustrated as
a
square grid pattern, the grid of drainage channels 14 may be any shape, such
as, for
example, rectangular, triangular, and hexagon.
[0024] A first edge flange 18 extends along one side of the panel 10 and is
offset
from the top surface 12 of the panel 10. A second edge flange 20 extends along
an
adjacent side of the panel 10 and is also offset from the top surface 12. A
third edge
flange 22 and a fourth edge flange 24 are illustrated as being oriented across
from the
flanges 18 and 20, respectively. The third and fourth flanges 22 and 24 extend
from
the top surface 12 and are offset from a bottom surface 26 of the base 12, as
shown in
Fig. 2A. The first and second flanges 18 and 20 are configured to mate with
corresponding flanges, similar to third and fourth flanges 22 and 24 that are
part of
another cooperating panel. Thus, the third and fourth flanges 22 and 24 are
configured to overlap flanges similar to first and second flanges 18 and 20 to
produce
a generally continuous surface of top surfaces 12 of adjoining panels 10. A
panel
section 27, as shown in Fig. 5, is defined by the thickness of the panel
between the top
surface 12 and the bottom surface 26.
[0025] In an alternative embodiment, the panel 10 may be configured without
the
first through fourth flanges 18, 20, 22, and 24. In such a configuration, the
resulting
edges of the panel 10 may be generally flat and straight edges. In another
embodiment, the generally straight edge may include projections (not shown) to
create
a gap between adjoining panels, as will be explained below. In yet another
embodiment, the edges may be formed with an interlocking geometric shape
similar to
a jigsaw puzzle.
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Referring now to Figs. 2A and 2B, there is illustrated the bottom surface 26
of the
panel 10. The illustrated bottom surface 26 includes a plurality of projecting
shock
absorbing structures 28 disposed across the bottom surface 26. Only some of
the
projections 28 are shown on the bottom surface 26 so that the drain holes 16
may be
clearly visible. Thus, in one embodiment, the projections 28 extend across the
entire
bottom surface 26. In another embodiment, the projections 28 may be arranged
in a
pattern where portions of the bottom surface have no projections 28. The
portion
having no projections 28 may have the same overall dimension as the thickness
of the
panel 10 including the projections 28. Such a section may be configured to
support a
structure, such as a table and chairs. This portion of the bottom surface 26
is
configured to provide a structural support surface having a substantial
resistance to
deflection under load compared with the first and second stages 40 and 42.
[0026] Referring now to Figs. 3, 4, and 5, the flange 24 is shown to include a
locking aperture 30 as part of an interlocking connection to secure adjacent
panels 10
together. A flange 20' of an adjacent panel 10' includes a locking projection
32. As
shown in Fig. 5, the locking projection 32 is disposed within the locking
aperture 30.
The diameter of the locking projection is shown as "P", which is smaller than
the
diameter of the locking aperture, "A". This size difference permits slight
relative
movement between adjoining panels 10 and 10' to allow, for example, 1) panel
shifting during installation, 2) thermal expansion and contraction, and 3)
manufacturing tolerance allowance. In the illustrated embodiment, flange 18
does not
include a locking projection or aperture 30, 32. However, in some embodiments
all
flanges 18, 20, 22, and 24 may include locking apertures and/or projections.
In other
embodiments, none of the flanges may have locking apertures and projections.
[0027] Some of the flanges include a standout spacer 34, such as are shown in
Figs.
4 and 5 as part of flanges 20, and 20'. The standout spacer 34 is positioned
along
portions of the transition between the flange 20' and at least one of the top
surface 12
and the bottom surface 26. The standout spacer 34 establishes a gap 36 between
adjacent panels to permit water to flow from the top surface 12 and exit the
panel 10.
The standout spacer 34 and the resulting gap also permit thermal expansion and
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contraction between adjacent panels while maintaining a consistent top surface
plane.
Alternatively, any or all flanges may include standout spacers 34 disposed
along the
adjoining edges of panels 10 and 10', if desired. The flanges may have
standout
spacers 34 positioned at transition areas along the offset between any of the
flanges
and the top or bottom surfaces 12 and 26.
[0028] Referring now to Figs. 6 and 7 there is illustrated an enlarged view of
the
projections 28, configured as shock absorbing projections. The sides of
adjacent
projections 28 define a bottom channel 38. The bottom channels 38 are
connected to
the top drainage channels 14 by the drain holes 16. The bottom channels 38
permit
water to flow from the top surface 12 through the drain holes 16 and into the
ground
or other substrate below the panel 10. In one embodiment, the bottom channels
38
may also store water, such as at least 25mm of water, for a controlled release
into the
supporting substrate below. This slower water release prevents erosion and
potential
sink holes and depressions from an over-saturated support substrate. The
channels 38
also provide room for the projections to deflect and absorb impact energy, as
will be
explained below. Additionally, the bottom channels 38 also provide an
insulating
effect from the trapped air to inhibit or minimize frost penetration under
certain
ambient conditions.
[0029] The shock absorbing projections 28 are illustrated as having
trapezoidal
sides and generally square cross sections. However, any geometric cross
sectional
shape may be used, such as round, oval, triangular, rectangular, and
hexagonal.
Additionally, the sides may be tapered in any manner, such as a frusto-conical
shape,
and to any degree suitable to provide a proper resilient characteristic for
impact
absorption. The projections 28 are shown having two absorption stages or zones
40
and 42. A first stage 40 includes a truncated surface 44 that is configured to
support
the panel 10 on the substrate or ground. The end of the first stage 40 may
alternatively be rounded rather than a flat, truncated surface. In another
alternative
embodiment, the end of the first stage 40 may be pointed in order to be
partially
embedded in the substrate layer. A second stage or zone 42 is disposed between
the
bottom side 26 and the first stage 40. The second stage 42 is larger in cross
section
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and volume than the first stage 40. Thus, the second stage 42 has a stiffer
spring rate
and response characteristic than that of the first stage 40. This is due to
the larger area
over which the applied load is spread. In another embodiment, the first stage
40 may
be formed with an internal void, a dispersed porosity, or a reduced density
(not
shown) to provide a softer spring rate characteristic. In yet another
embodiment, the
first stage 40 may be formed from a different material having a different
spring rate
characteristic by virtue of the different material properties. The first stage
40 may be
bonded, integrally molded, or otherwise attached to the second stage 42.
Though the
first and second stages 40 and 42 are illustrated as two distinct zones where
the first
stage 40 is located on a larger area side of the second stage 42, such is not
required.
The first and second stages 40 and 42 may be two zones having constant or
smooth
wall sides where the two zones are defined by a volume difference that
establishes the
differing spring rates. Alternatively, the projections 28 may have a general
spring rate
gradient over the entire projection length between the truncated end 44 and
the bottom
surface 26.
[0030] Referring to Figs. 8A and 8B, the deflection reaction of the projection
28 is
illustrated schematically. As shown in Fig. 8A, a load "f' is applied onto the
top
surface 12 representing a lightly applied impact load. The first stage 40 is
compressed
by an amount L1 under the load f and deflects outwardly into the channel 38,
as
shown by a deflected first stage schematic 40'. The second stage 42 may
deflect
somewhat under the load f but such a deflection would be substantially less
than the
first stage deflection 40'. As shown in Fig. 8B, a larger impact load "F" is
applied to
the top surface 12. The first and second stages 40 and 42 are compressed by an
amount L2 under the load F, where the first stage 40 is compressed more than
the
second stage 42. The first stage 40 deflects outwardly to a deflected shape
40". The
second stage 42 is also deflected outwardly to a deflected shape 42". Thus,
the first
and second stages 40 and 42 progressively deflect as springs in series that
exhibit
different relative spring rates. These deflected shapes 40', 40", and 42" are
generally
the shapes exhibited when an axial compressive load is applied to the top
surface. The
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first and second stages 40 and 42 may also bend by different amounts in
response to a
glancing blow or shearing force applied at an angle relative to the top
surface 12.
[0031] The projections 28 are also arranged and configured to distribute the
impact
load over a larger surface area of the panel 10. As the panel 10 is subjected
to an
impact load, either from the small load f or the larger load F, the
projections deflect in
a gradient over a larger area than the area over which the load is applied.
For
example, as the panel reacts to the large impact load F, the projections
immediately
under the applied load may behave as shown in Fig. 8B. As the distance
increases
away from the applied load F, the projections 28 will exhibit deflections
resembling
those of Fig. 8A. Thus, the projections 28 form a deflection gradient over a
larger
area than the area of the applied load. This larger area includes areas having
deflections of both first and second stages 40 and 42 and areas having
deflections of
substantially only the first stage 40. Thus, under a severe impact, for
example, in
addition to the compression of the material in the area of the load, the first
stage 40
(i.e., the smaller portions) of the projections compress over a wider area
than the are
of the point of impact. This load distribution creates an area elastic system
capable of
distributing energy absorption over a wide area. This produces significant
critical fall
heights, as explained below. This mechanical behavior of the projections 28
may also
occur with tapered projections of other geometries that are wider at the top
than at the
bottom (i.e., upside down cones).
[0032] Referring now to Fig. 9 there is illustrated another embodiment of a
panel
100 having projections 128 that exhibit a telescopic deflection
characteristic. A first
stage 140 of the projection 128 is deflected linearly into the second stage
142. During
an initial portion of an impact load, the first stage 140 compresses such that
the
material density increases from an original state to a compressed state. A
dense zone
140a may progress from a portion of the first stage 140 to the entire first
stage. As the
impact load increases, the first stage pushes against and collapses into the
second
stage 142. The second stage 142 compresses and permits the first stage to
linearly
compress into the second stage 142 similarly to the action of a piston within
a
cylinder. A second stage dense zone 142a may likewise progress from a portion
of the
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second stage to the entire second stage. Alternatively, the dense zones 140a
and 142a
may compress proportionally across the entire projection 128.
[0033] The softness for impact absorption of the panel 100 to protect the
users,
such as children, during falls or other impacts is a design consideration.
Impact
energy absorption for fall mitigation structures, for example children's
playground
surfaces, is measured using HIC (head injury criterion). The head injury
criterion
(HIC) is used internationally and provides a relatively comparable numerical
indicator
based on testing. HIC test result scores of 1000 or less are generally
considered to be
in a safe range. The value of critical fall height, expressed in meters, is a
test drop
height that generates an HIC value of 1000. For example, to be within the safe
zone,
playground equipment heights should kept at or lower than the critical fall
height of
the base surface composition. The requirement for critical fall height based
on HIC
test values in playground applications may be different from the requirement
for
critical fall heights in athletic fields and similar facilities. Also, the
HIC/critical fall
height will vary based on the supporting substrate characteristics. In one
embodiment,
the panel 10 or the panel 100 may be configured to provide a 2.5m critical
fall height
over concrete, when tested as a component of a playground surface, and a 2.7m
critical fall height over concrete in combination with a low pile (22mm)
artificial turf
partially filled with sand. In another embodiment, the panel 10 or the panel
100 may
provide a 3.0m critical fall height over a compacted sand base in combination
with a
low pile (22mm) artificial turf partially filled with sand. By comparison,
conventional
athletic field underlayment layers are configured to provide only half of
these critical
fall height values.
[0034] These HIC/critical fall height characteristic and figures are provided
for
comparison purposes only. The panel 10 or the panel 100 may be configured to
absorb more or less energy depending on the application, such as swings,
monkey
bars, parallel bars, vertical and horizontal ladders, along with the ages of
the intended
users. In one embodiment, the projections 28 or 128 may have a first stage
height
range of 10-15mm and a second stage height range of 15-25mm. In another
embodiment, the projections 28 or 128 may be configured to be in a range of
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approximately 12-13mm in height for the first stage and 19-20mm in height for
the
second stage in order to achieve the above referenced HIC figures. The panel
10 or
the panel 100 may be made of any suitable material, such as for example, a
polymer
material. In one embodiment, the panel 10 or 100 is a molded polypropylene
panel.
However, the panel may be formed from other polyolefin materials.
[0035] The panels 10 or 100 may be assembled and covered with any suitable
covering, such as for example, artificial turf, rubber or polymer mats, short
pile
carpeting, particulate infill, or chips such as wood chips or ground rubber
chips.
[0036] The principle and mode of operation of this invention have been
explained
and illustrated in its preferred embodiment. However, it must be understood
that this
invention may be practiced otherwise than as specifically explained and
illustrated
without departing from its scope.
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