Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
FIE~D OF THE INVENTION
The present invention relates to a process for
producing an insole for footwear.
The human foot is a biomechanically complex
structure evolved over millenia to accommodate human
beings walking in an upright posture on natural surfaces.
In general, natural surfaces are soft and yielding, and
confo~m to the contours of the sole of the foot, providing
uniform support for the foot in a biomechanically correct
position. However, modern conditions require the foot
to accommodate walking and running on hard, unyielding
surfaces, with the mobility of the foot restricted by
footwear. The foot has not yet evolved to accommodate
these modern conditions, and as a result foot ailments
ranging from fatigue, callouses, corns, and blisters to
serious tendon damage, muscle strain and stress fractures
are common. Overuse ailments due to poor biomechanical
function are especially common among joggers, runners and
athletes.
Insoles pre-formed to a supporting shape are well
known (see for examples, U.S.Patents 32667~ and 3161970)
but such mass-produced insoles are designed to suit only
the 'average' foot and not to promote a scientifically
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desirable relationship between the foot and leg of the
individual wearer.
Ideally, an insole should be custom-built to fit a
particular foot in a particular shoe, and should give to
that foot a support which approximates to the support
given by soft ground to the bare foot; i.e. uniform,
stable, slightly resilient support over the whole of the
lower surfaces of the foot. This type of support can be
provided by a custom-made orthopaedic insole shaped to
fit an individual foot by a doctor or podiatric specialist.
However, such custom-made insoles (called 'orthotics') are
expensive and time-consuming to produce and require expert
fitting.
Description of the Prior ~rt
The prior art discloses a number of insoles designed
to be 'customised' to an individual foot:-
U.S.Patent No.3407406 discloses a shoe padfilled withmicrospheres which deforms to fit a foot; and U.S.Patents
Nos.2794270 and 3903621 disclose a shoe lining containing
a semi-liquid mouldable material. However, these devices
cannot provide adequate support for a foot since they
continue to change shape under the pressures exerted by the
wearer's foot in use.
U.S.Patent 35~1412 discloses aboot liner into which a
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liquid resin is injected and allowed to set while the
wearerls foot is in position in the boot. This should,
in theory, give ideal support, but in practice such a
liner is restricting rather than supportive and fails to
allow for normal flexing of the foot in use. Also, the
set resin breaks down relatively rapidly in use.
U.S.Patent 396~577 discloses a casting unit in a shoe
sole, the unit being filled with a mouldable material
which is formed by a wearer's foot pressure and then
cured to retain that shape permanently. However, the
casting unit is bulky and requires a special shoe con-
struction.
U.S.Patents 4237626, 36416~ and 3244177 all disclose
partial or complete insoles which are designed to be
custom-fitted by heating the insole, placing the wearer's
foot in contact with the heated insole, and allowing the
insole to cool and set to shape while being moulded by the
wearer's foot pressure. However, although such insoles
are comfortable and reasonably supportive in use, it has
been found that they do not provide the equivalent of a
custom-made orthopaedic insole, because basically, all
these insoles can do is take an impression of the wearer's
foot, without offering correct biomechanical support for
that foot.
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Brief Summar~ of the Invention
An object of the present invention is the provision
of an inexpensive easily-fitted customized insole which is
comfortable and issupportive in terms of biomechanical
principles:- it supports and acts on the undersurface of
the foot to promote an anatomically desirable relationship
between the various parts of the body in movement and at
rest e.g. as when walking on a 'natural' surface in bare
feet. To achieve this object, the present invention
provides an insole blank comprising a sheet of thermo-
plastic material, said material having a softening-point
temperature above ambient temperature but at which the
material safely may be brought into proximity to human
skin, and said material having a thickness and a density
such that it is mouldable by normal foot pressure at the
softening-point temperature but not below the softening-
point temperature; said insole blank having the general
shape of a shoe last bottom and providing a forefoot
portion, a heel portion and an arch flare: said forefoot
portion tapering in thickness from a thickness equal to
that of the heel portion along the arch line to a thickness
of 12~-75~o of the thickness of the heel portion at the
front edge of the forefoot portion; the edge of the
insole blank being bevelled to an angle in the range
25 - 50 at least around the arch flare and the heel
portion, such that the lower surface of the insole blank
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is smaller than the upper surface and said lower surface
is approximately equal in size to the size of the last
bottom shape of the wearer's shoe; and the arch flare
corresponding in position to the medial arch of the foot
and having a width at the widest point thereof of between
20~o-~O~o greater than the ~t bottom shape of the wearer's
shoe.
Preferably
part of said heel portion is thinned to provide
a teardrop-shaped depression having its least thickness
at a point corresponding to the centre of the wearer's
heel and oriented with the rounded part thereof corres-
ponding to the wearer's heel and the attenuated part
thereof extending along the lateral side of the insole and
terminating opposite the arch flare.
The invention further provides a process for forming
an insole comprising the steps of:
(a) providing an insole blank as described above;
(b) heating said blank to or above the softening-point
. temperature of said material;
(c) with the insole blank in place in the shoe in which
it is to be worn, placing the wearer's foot in said
shoe, such that the insole blank is sandwiched
between the wearer's foot and the inside of the shoe;
(d) standing so that normal foot pressure is exerted on
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the insole blank, thereby moulding the insole blank
into the shape of a supportivë insole; and
(e) allowing the moulded insole to cool to ambient
temperature.
The insole of the present invention is designed to
be used with any ordinary shoe or boot having a conventional
upper, of the size normally worn by the wearer.
Brief Descri~tion of the Drawin~
By way of example only, a preferred embodiment of
the present invention will be described in detail, with
reference to the accompanying drawings, in which:-
Figs. 1 & 2 are side and bottom plan views respec-
tively of an insole blank in accordance with the present
invention;
Fig.3 is a side view of the completed insole;
Figs. 4 ~ 5 are side views of the medial and lateral
sides respectively of a skeletal foot in a shoe fitted with
the insole of the present invention, with the side of the
shoe broken away;
Figs. 6, 7 & ~ are sections on lines A, B & C
respectively of Figs. 4 & 5.
In Figures 4-~, the insole is shaded for clarity.
The skeletal structure depicted assumes that the foot and
lower leg are in neutral position i.e. the optimal
functional position.
D_tailed Descri~ion of the Preferred Embodiments
An insole 2 in accordance with the present invention
is formed from a sheet of any suitable material.
suitable material is a material which is thermoplastic,
with a softening-point temperature above ambient tempera-
ture but at which the material safely may be brought into
contact with or proximlty to human skin and to which foot-
wear materials may be heated without damage. Generally,
a softening-point temperature in the range 50 -~0 C is
satisfactory. The material must be of a density such
that it is mouldable by normal foot pressure above the
softening-point temperature, but remains stable and un-
affected by normal foot pressure in use. The material
must be durable:- the insole should have a service life
of at least 6-12 months. 3elow the softening-point, the
material must be resilient yet firm, and stable in shape,
so that the insole is not significantly altered by the
compressive forces exerted by the foot in use. Also, the
material must be sufficiently inert and hypoallergenic to
be useable for long per~ds in contact with or proximity to
human skin without causing skin problems. The material
may be solid sheet or open -or closed-cell foamed sheet,
and may be continuous or perforated.
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One suitable material is medium-denisity closed-cell
foamed polyethylene having Shore Hardness 35.
An insole blank 4 provides a heel portion 5, a fore-
foot portion 6 and an arch flare 7 and is cut from a sheet
of material which tapers in thickness from a thickness X
at the heel end of the blank to a thickness Y at the toe
end of the blank. The taper is not uniform along the
length of the blank:- the greater thickness X extends
from the heel to the arch line g; from the arch line g
to the toe, the thicknessgradually tapers to Y. The arch
line g-is a known characteristic of the human foot and is
the line connecting the apices of the medial and longi-
tudinal arches of the foot. From a large number of
measurements made on different human feet, it is known
that the arch line is always inclined at an angle a in
the range 55 - gO (more commonly 65 - 75) to the
longitudinal line 9 of the foot which extends between the
mid-points of the toe and of the heel.
The inclination of the line g means that the taper
in the thickness of the insole begins closer to the heel
on the lateral side 10 than on the medial side 11:-
this corresponds to the relationship between the apices
of the medial and lateral longitudinal arches of the
foot.
t is necessary for the forefoot portion 6 of the
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insole to be tapered in thickness, to provide correct
support for the metatarsal bones of the foot along their
entire length (see Figs. 4 & 5). The forefoot portion 6
provides cushioning for the metatarsal heads 12a-e (see
Fig.~)and also assists in positioning the insole correctly
in the shoe, and in preventing movement of the insole in
the shoe when in use.
The thickness X is in the range ~ mm and the
thickness Y is in the range 2-~ mm, Y being 12% - 75~o of
the thickness X.
In plan, the insole blank 4 is of conventional last
bottom shape, except for the arch flare 7 along the medial
side 11 of the insole. The arch flare 7 is 20 - ~0~0
(preferably 50~o) wider than the last bottom shape width
Z, so that when the insole blank 4 is formed to shape, the
arch flare 7 is bent upwards to provide an arch-supporting
portion, the edge 13 of which rests against the medial
side of the shoe upper, rather than on the bottom of the
shoe. Conventional arch supports generally are thickened
portions of the insole which rest on the bottom of the
shoe, and so provide a non-variable support which suits
only one~eight of arch. In contrast, the arch flare 7 can
be formed during fitting to the correct height and shape
to support correctly any height of arch, and integrate the
shoe upper, insole and sole into an efficient functional
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supporting unit for the individual foot.
The rearfoot or heel portion 5 of the insole 4
includes a teardrop-shaped portion 14 which is of reduced
thickness compared to the remainder of the heel portion
5. The thinnest part 15 of said portion 14 corresponds
to the position of the centre of a wearer's heel, and
is equal to, or 2-4 mm thicker than, the thickness y of
the forefoot portion. From said thinnest part 15, the
thickness of the portion 14 gradually increases, so that
the edges of said portion 14 join smoothly with the
remainder of the heel portion 5. The teardrop shape is
positioned such that the attenuated portion 16 of said
shape extends along the lateral side 10 of the insole
and terminates opposite the arch flare 7.
The portion 14 may be formed by grinding and may
be formed on either the upper or the lower surface of the
insole. Preferably, however, said portion is formed on
the lower surface of the insole, to allow the upper
surface to present a completely smooth surface to a
wearer's foot.
The outer periphery of the insole is bevelled to
an angle b of 25 - 50, preferably 35 - 42 (see Figs.
1 & 2). The bevel 17 may extend around the whole perimeter
of the insole, as shown, but must extend from the ball of
the foot around the heel portion of the insole. The
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bevel 17 assists the correct forming and positioning of
the arch flare 7 and also, when the insole is moulded to
shape, causes the edge of the insole to wrap up around
the side of the shoe.
In use, this wrap-up helps
to position the foot and prevents it from sliding about.
The bevel'l7 also assists in the formation of a heel cup
19 from the teardrop-shaped portion 14 when the insole is
shaped to the wearer. The heel cup 19 conforms to the
shape of the wearer's he~l, without unduly flattening the
fat pad of the heel, and allows the foot to lie correctly,
with the lateral side of the foot slightly lower than the
medial side and the heel located securely (see Figs. 6 &
7). The heel cup 19 also provides sufficient resilient
material under the lateral border of the foot to allow
efficient shock absorption as the foot strikes the ground~
Ideally, the heel cup 19 should provide a shape similar to
that formed by the foot on a 'natural'walking surface
such as soft earth.
The heel cup 19 may extend to the edge of the insole
or a flat margin (not shown) of width O - g mm may lie
between the heel cup 19 and the edge of the insole. The
width of the margin depends upon the design of the shoe
with which the insole is to be used.
The above-described insole blank is custom-fitted
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to a wearer's foot as follows:- the blank is heated to
a temperature equal to or greater than the softening-
point temperature, preferably with said blank in position
in the wearer's shoeO However, the blank may be heated
alone, and inserted in the wearer's shoe when at the
desired temperature; in this case, it is advantageous to
have a cardboard stiffener of the same shape as the bottom
forefoot portion secured to the lower surface of the fore-
foot portion, to make it easier to manoeuvre the floppy
heated insole blank into the shoe.
Next, the wearer puts an the shoe or shoes in his
ordinary shoe size (preferably, both insoles of a pair are
fltted simul~neously) and stands evenly on both feet, with
a stance such that the middle of each kneecap is aligned
with the third and fourth toes of the corresponding foot.
To assist the wearer to achieve the correct stance, a
fitting aid may be used, consisting of a horizontal base
plate with a vertical rod secured at one end:- the wearer
stands on the base plate with one end of the rod aligned
between the third and fourth toes, and the other end of
the rod touching the centre of the kneecap. In this
stance, the shape of the insole guides the foot into the
optimum position.
This stance is maintained for several minutes (e.g.
3-5 min) sufficiently to allow the insole material to cool
684~
enough to retain the desired shape. Preferably, the
wearer then walks about for a further 2-3 minutes with his
weight on his heels and on the outer sides of his feet.
Once the insoles have cooled9 they retain the
shape to which they have been moulded by the wearer's foot
pressure, and are permanently formed to that shape, unless
re-heated above the softening-point. The finished insoles
are firm, slightly resilient and flexible in the forefoot
region, and constitute what is commonly known as a semi-
rigid orthotic insole.
If the shoes are given to another wearer, or the
existing wearer's feet change due to injury, ~he insoles
can be remoulded to the desired new shape simply by
repeating the heating and moulding steps described above.
Similarly, the insoles may be re-moulded to suit another
pair of shoes.
The type of support required by a foot varys a great
deal with the type of shoe worn~ and an insole made in
accordance with the present invention is in general more
satisfactory than known custom-made insoles, because the
insole is moulded to the exact shape of the shoe in which
it is to be worn, so that it supports the wearer's foot
correctly in that particular shoe; i.e. the moulding
process forms the insole to both the foot and the inner
contours of the shoe in a functional position.
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If a wearer has particularly serious foot problems,
the moulding process may be carried out under the super-
visi~n of a medical practitioner or podiatric specialist.
The insert blank, with or without shoe, may be
heated to the desired ternperature by any suitable means
e.g. hot-air blowers or radiant or infra-red ovens. A
hot-air blower such as a commercial hair blow-dryer is
especially useful for heating insoles in position in boots:-
the blower simply is pointed down the boot~
The insole blank may have a heat-sensitive dye
incorporated in it or applied to it:- the dye changes
colour when the blank reaches the correct temperature.
For insoles made of medium-density closed cell
polyethylene, with the thickest part of the heel portion
10 mm thick, the following heating programme gives satis-
factory results:- the insoles are placed in the running
shoes in which they are to be worn; a domestic oven is
pre-heated to 100C and then turned off. The shoes
containing the insoles are placed in the oven for 15
minutes, the ovem temperature being approximately 70¢.
The shoes are then removed and fitted to the wearer as
described above.
To improve the eye-appeal of the insole blanks to
customers, and to make the blanks easier to insert into
the footwear, the blanks may be partly pre-forrned to
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shape by thermoforming techniques before being fitted to
the wearer. However, this preforming does not alter the
essential shape of the blank because the blank reverts to
its original Iflat' shape as soon as it is heated above the
softening-point prior to fitting.
The insole blanks may have a fabric liner laminated
to the upper surface thereof. The for~ed lnsole can be
removed from the shoe for washing if desired.
Figs.4-g show the way in which the insole of the
present invention supports a wearer's foot in use:- the
calcaneus 20 is held comfortably and securely in place by
the heel cup 19, as described above the arch flare 7
supports the medial arch of the foot, with the bevelled
edge 13 of the arch flare 7 resting against the side 24
of the shoe upper as shown in Fig.7. The bevel 17 causes
the edge of the insole blank to wrap up against the inside
edges 24 of the shoe as shown in Figs.6-~. This wrap-up
supports the edges of the foot and helps to position and
stabilize the foot correctly in the shoe, and also supports
and stabilizes the lateral arch of the foot. The insole
also cushions the whole sole of the foot.
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