Note: Descriptions are shown in the official language in which they were submitted.
WO 2023/285576 1
PCT/EP2022/069697
Functional Reactive Layer Helmet
Specification
The invention relates to an impact mitigation structure, particularly a
helmet, particularly a
helmet for cycling, as well as to a method for producing such an impact
mitigation structure,
particularly helmet.
Injury to a person or damage to an object can occur when the person or object
is subjected
to an impact of sufficient magnitude. Considerable developmental effort has
been expended
to produce helmets which provide protection from potentially damaging or
injurious impacts.
Head injuries, which can be incurred as a result of participation in sports
such as cycling are
a common cause of serious brain injuries.
A brain trauma may occur as a consequence of either a focal impact upon the
head, a
sudden acceleration or deceleration within the cranium, or a combination of
both impact and
movement. Impact protection is therefore important in preventing brain
injuries as a result of
impacts to the head.
Head protection, in the form of helmets, is designed to reduce the forces
experienced by a
user's head during an impact. Generally, a helmet comprises at least one
impact absorbing
layer which is designed to absorb a portion of the forces to which the helmet
is subjected
during an impact.
However, helmets often do not provide adequate protection during an impact
against both
linear and tangential forces. As oblique impacts are common, impacts will
often include both
linear and tangential components. Particularly, an oblique impact means that
the force acting
on the outer surface of the helmet that is e.g. hitting the tarmac upon a
crash comprises a
component that extends tangentially with respect to said outer surface at the
location of the
impact.
Unfortunately, such tangential forces in particular result in the rotational
acceleration of the
brain, which has been linked to bridging vein rupture. In turn, this may be
responsible for
subdural hematomas, and diffuse axonal injuries. Tangential forces during an
impact may
also result in neck injuries.
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Based on the above, the problem to be solved by the present invention is to
provide an
improved helmet that is capable of reducing the above-mentioned injuries
related to oblique
impacts comprising a tangential force acting on the helmet / head of the
person wearing the
helmet.
This problem is solved by an impact mitigation structure, particularly helmet,
having the
features of claim 1 and a method having the features of claim 51.
Preferred embodiments of this first aspect of the present invention are stated
in the
corresponding dependent claims and are described below. Furthermore, further
aspects of
the present invention are introduced below.
According to claim 1, a helmet is disclosed, particularly a cycling helmet,
comprising:
- A first layer forming an outer surface of the helmet,
- a second layer, and
- a reactive layer sandwiched between the first layer and the second layer,
and preferably
connected to the first and second layers.
In the following, the invention is described predominantly with respect to a
helmet. However,
according to a second aspect of the present invention, an impact mitigation
structure is
disclosed. Since the underlying principle of the present invention does not
only apply to
helmets, but impact mitigation structures in general, the notion of a helmet
can be replaced in
all embodiments and aspects of the present invention by the more general
notion of an impact
mitigation structure. For example, apart from a helmet, such an impact
mitigation structure can
be car bumper, a crash barrier, a paintwork (e.g. in key locations on a
vehicle), a body part of
a vehicle (e.g. car body), protective armor.
In the following features of the first layer are described as well as its
interaction with the reactive
layer and the second layer. It should be noted however, that the helmet
preferably comprises
several such first layer that can be arranged side-by-side on the second layer
of the helmet,
with a corresponding number of reactive layers arranged between the respective
first layer and
underlying second layer. Thus, all features and embodiments described below
with reference
to one first layer also apply to embodiments where the helmet comprises a
plurality of first
layers and reactive layers (which can form membranes, see below). Furthermore,
in all
embodiments, the second layer can be formed in one piece, but can also be
formed by multiple
sheets arranged side by side (particularly on the energy absorbing layer, see
below).
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Furthermore, according to an embodiment, adjacent first layers/panels can be
shaped to have
a ramp that facilitate direction and free movement of a first layer (over the
respective ramp).
According to a preferred embodiment, the first and the second layer are stiff
layers, wherein
said stiffness is particularly due to material (modulus of elasticity) and
shape of said layers. A
material that is stiff can withstand high loads without elastic deformation.
Typically, thin sheets
of polycarbonate can be used as basis of said layers which result in
sufficiently stiff structures
when being arranged in a curved configuration adapted to the shape of a head
of a person.
According to a preferred embodiment of the helmet, the reactive layer
comprises a plurality of
rigid balls (e.g. spherical bodies), that particularly remain rigid during
normal use of the helmet
and are configured to roll at an impact threshold over an outer surface of the
second layer (so-
called B surface). This means that in case a pre-defined tangential force acts
on the first layer
due to an oblique impact (e.g. helmet and head therein hitting the ground)
exceeds a
predefined threshold force, said rolling is initiated.
In this context "rolling over" an outer surface of the second layer does not
necessarily mean
that there is a contact between the balls and the outer surface of the second
layer, since
intermediary layers can be arranged between the balls and said outer surface
of the second
layer. Therefore "rolling over" also includes rolling on such an intermediary
layer. Particularly,
as will be described further below, the balls form part of the reactive layer
that can be a
membrane comprising a substrate film to which the balls can be bonded by means
of an
adhesive, wherein the substrate film can be bonded by an adhesive layer to the
outer surface
of the second layer. Thus, here, the balls may roll on the substrate film and
said adhesive.
Furthermore, the balls do not need to be spheres and may deviate from a
perfect spherical
shape. Therefore, the notion of a ball according to the present invention
therefore includes
rollable elements and the balls may also be referred to as rollable elements.
Furthermore, the first and/or the second layer do not need to be homogenous
layers, but can
each consist of different materials and/or layers stacked on top of one
another.
In a preferred embodiment, the balls can be formed out of polycarbonate.
According to
alternative embodiments, the balls can be formed out of one of the following
materials:
polystyrene (PS), acrylonitrile butadiene styrene (ABS), polyvinyl chloride
(PVC), polyethylene
terephthalate (PET), polypropylene (PP), polyethylene (PE), poly(methyl
nnethacrylate)
(PMMA). Each of these materials can be used in conjunction with all other
embodiments of the
helmet described herein.
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Preferably, according to an embodiment, the rigid balls are formed from a
material comprising
a Young's modulus (modulus of elasticity) in the range from 0.5 to 10 GPa.
Particularly, according to a preferred embodiment, the balls comprise a
diameter in the range
from 0.5 to 5 mm, wherein particularly the diameter is 2 mm.
According to a preferred embodiment of the helmet, the balls are distributed
along an inner
surface of the first layer such that they cover an area that corresponds to
10% to 50%,
preferably 15% to 30%, preferably about 20% of the area of said inner surface.
Particularly, the lower this packing density of the balls, the better for
product weight.
Particularly 20% density (of surface area covered in balls) is close to the
lower limit where any
lower density may allow the inner surface of the first layer to be depressed
by hand between
adjacent balls. Thus, there is an inverse correlation between ball packing
density and stiffness
of the inner surface of the first layer and outer surface of the second layer.
Furthermore, according to a preferred embodiment of the helmet the balls of
the reactive layer
are bonded to a substrate film via an adhesive configured to undergo brittle
failure. The
substrate film can be formed out of a polymer, particularly PVC. According to
preferred
embodiments the adhesive is one of the following adhesives: Cyanoacrylate,
polyvinyl acetate
(PVA), epoxy.
According to an embodiment, the rigid balls in the reactive layer are bonded
to a substrate film
via a primarily brittle-failure-based adhesive.
Furthermore, according to a preferred embodiment of the helmet, the substrate
film comprises
a thickness smaller than 200 pm.
Further, according to a preferred embodiment of the helmet, the substrate film
comprises an
adhesive layer preferably consisting of a pressure sensitive adhesive arranged
on a side of
the substrate film facing away from said plurality of balls.
Furthermore, according to a preferred embodiment of the helmet, the reactive
layer is or
comprises a membrane bonded to the first and the second layer, wherein the
membrane
comprises said substrate film and the plurality of balls arranged thereon.
Particularly, the
membrane can comprise a vinyl both for wet and dry applications.
Further, preferred, the membrane or the substrate film is bonded to the outer
surface of the
second layer via said adhesive layer consisting of said pressure sensitive
adhesive of the
substrate film.
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Furthermore, in an embodiment, the membrane or the plurality of balls is
bonded to an inner
surface of the first layer (so-called A surface) via an adhesive layer,
preferably an adhesive
layer comprising (or consisting of) a thermo-softening adhesive. Particularly,
the adhesive
becomes active during high temperature moulding and therefore allows to bond
the balls of
the reactive layer to the inner surface of the first layer in a mold in which
a portion of the helmet
is formed.
Furthermore, an embodiment, the first layer comprises: a sheet (the sheet
being preferably
formed from a plastic material such as polycarbonate (PC)), a color layer
(e.g. a colored ink
layer) arranged on an inner surface of the sheet, a protective layer arranged
on the color layer,
wherein said adhesive layer that bonds the membrane to the inner surface of
the first layer is
bonded to the protective layer. A further coat such as a light bleed
preventing coat (see also
below) can be applied to the color layer before the protective layer is
arranged on the color
layer / further coat.
However, according to a further preferred embodiment of the present invention,
instead of
using a membrane, the balls can be bonded (e.g. directly) to the outer surface
of the second
layer with an adhesive, particularly an adhesive comprising PVA (poly(vinyl
alcohol)).
Particularly, in all embodiments, the outer surface of the second layer faces
outwards, i.e.,
away from a head of a person wearing the helmet, wherein the inner surface of
the first layer(s)
faces towards the head of said person wearing the helmet.
In preferred embodiment of the helmet, the protective layer is a heat
resistant ink layer.
Particularly, the heat resistant ink layer can be screen printed or UV printed
onto the color layer
(e.g. colored ink layer) or the coated color layer (see above).
According to a further embodiment of the helmet, the protective layer is a
polymer layer,
particularly a polyvinylchloride layer. Other materials such as PC can also be
used instead of
PVC.
Furthermore, preferably, the respective protective layer comprises a thickness
below 0.1 mm
and/or a yield strength larger than 20 MPa according to an embodiment of the
helmet.
Further, according to a preferred embodiment of the helmet, the protective
layer has a thermal
expansion differing less than 5 ck from a thermal expansion of a material of
the first layer.
According to yet another embodiment of the helmet, the first layer is a twin
sheet assembly
comprising an outer sheet and an inner sheet being thermoformed simultaneously
in particular,
wherein both sheets preferably consist of polycarbonate (PC).
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Preferably, in an embodiment, the inner sheet of the twin sheet assembly is
perforated,
particularly so as to allow the negative pressure of the forming to pass
through to the outer
sheet so that not only the inner sheet is pulled down onto the forming.
Furthermore, in an embodiment, a color layer (particularly a colored ink
layer) and an adhesive
layer (particularly an adhesive ink layer) are arranged between the outer and
the inner sheet,
wherein particularly the color layer is arranged on the outer sheet and the
inner sheet is bonded
to the outer layer via the adhesive ink layer and the color layer.
Further, according to a preferred embodiment of the helmet according to the
present invention,
the helmet comprises an energy absorbing layer, wherein an inner surface of
the second layer
bonded to the energy absorbing layer by an adhesive layer (e.g., acrilux).
Such an adhesive
can comprise 25% to 30% titanium dioxide in powder form containing 1% or more
of particles
with aerodynamic diameter below 10 pm (CAS 13463-67-7). Further, the adhesive
(e.g.
acrilux) can comprise 25% to 30% 4-hydroxy-4-methylpentan-2-one; diacetone
alcohol (CAS
123-42-2). Further, the adhesive (e.g. acrilux) can contain 15% to 20% 1-
methoxy-2-propanol;
monopropylene glycol methyl ether (CAS 107-98-2).
Furthermore, according to a preferred embodiment of the helmet, the second
layer comprises
recesses (e.g. at an edge of the second layer) and/or through-holes through
which portions
(e.g. through-welds) of the energy absorbing layer extends towards the first
layer, said portions
of the energy absorbing layer being bonded to the first layer (through-weld).
Particularly, the
first layer comprises said adhesive layer (e.g. thermo-softening adhesive)
arranged thereon,
wherein said portions of the energy absorbing layer can be bond to the first
layer via said
adhesive layer. Alternatively, said adhesively layer can be completely or
partially omitted and
said portions of the energy absorbing layer can be bonded to the first layer
(i.e. without said
adhesive layer as an intermediary layer).
Preferably, according to a preferred embodiment, the outer surface of the
second layer locally
bends upwards around the respective recess and/or through-hole to reduce a
separation
between the inner surface of the first layer and said outer surface of the
second layer,
particularly so as to avoid a bleeding of the energy absorbing layer into a
volume between said
inner and outer surfaces during manufacturing of the energy absorbing layer.
According to a preferred embodiment, the energy absorbing layer comprises
polystyrene,
preferably expanded polystyrene (EPS) or polyurethane, particularly expanded
polyurethane
(EPU), or polypropylene, particularly expanded polypropylene (EPP). For a
molding process,
where the energy absorbing layer is formed adjacent the first and the second
layer and the
intermediary reactive layer (e.g. membrane) using preferably an in-moulding
(see also below),
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the material for the energy absorbing layer can be provide in the cavity of
the mould as bulk
material (e.g. in the form of pellets).
Further, according to a preferred embodiment of the helmet, the reactive layer
is configured to
facilitate relative movement between the first layer and the second layer by
the rolling of balls
of said plurality of balls between the first and the second layer (i.e.
between the A surface and
the B surface), wherein said rolling of balls provides a low rolling
resistance in the range from
0.0001 to 0.2, preferably in the range from 0.02 to 0.05, preferably in the
range between 0.025
to 0.04 between the balls and an inner surface of the first layer or an inner
surface connected
to the first layer or between the balls and an outer surface of the second
layer or an outer
surface connected to the second layer, wherein particularly said range applies
to the interface
with the lower rolling resistance. A particularly preferred rolling resistance
amounts to about
0.025. Another particularly preferred rolling resistance amounts to about
0.04.
It is to be noted that the rolling resistance relates to the surface that the
balls actually contact.
Therefore, in case intermediary layers are present between the first layer and
the balls, the
latter roll on a surface connected to the first layer (i.e. a surface formed
by the respective
intermediate layer). Likewise, in case intermediary layers are present between
the second
layer and the balls, the latter roll on a surface connected to the second
layer (i.e. a surface
formed by the respective intermediate layer).
Preferably, the rolling of the balls between the A and B surfaces provides an
extremely low
resistance-to-motion (RTM) (in this context rolling resistance, could also be
friction or any other
mechanical/geometric resistance) form of movement. However, employing rolling
does not
intrinsically make the movement occur more readily, it merely lowers the lower
limit, allowing
other movement inhibiting mechanisms to become the dominant factors (i.e.
adhesives and/or
connectors initially connecting the first and second layers).
Particularly, relative movement is facilitated between the impacted surface,
e.g. the first layer
hitting tarmac) and the second layer being fixed with respect to head of a
person wearing the
helmet thus reducing risk of traumatic brain injury (TBI).
Preferably, a separation between the inner surface of the first layer (A
surface) and the outer
surface of the second layer (B surface) remains as constant as possible.
Should an impact
occur where the balls are required to roll into an area where the separation
between the said
inner surface and said outer surface is smaller - then they would wedge and
the RTM would
shoot up. Particularly, according to an embodiment, upon a typical impact said
separation
varies less then 20%, particularly less than 15%, particularly less than 10%,
preferably less
than 5%.
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According to a preferred embodiment of the present invention, the balls of the
reactive layer
are bodies (particularly round or ellipsoidal bodies) comprising a roundness
above 0.7, more
preferably a roundness above 0.8, more preferably a roundness above 0.9, more
preferably a
roundness above 0.95, more preferably a roundness above 0.97, more preferably
a roundness
above 0.99. Preferably, in an embodiment, the balls are spherical bodies.
With respect to a cross-section of a ball that extends orthogonally to an axis
of rotation of the
ball about which the ball can rotate, roundness is defined as the ratio
between the area of a
circle inscribed in the cross-section and the area of a circle circumscribing
the cross-section,
i.e., the maximum and minimum sizes for circles just sufficient to fit within
and enclose the
cross-section.
According to an embodiment, the balls preferably comprise a constant diameter
and/or volume.
According to an alternative embodiment, the balls comprise different diameters
and/or
volumes.
According to yet another embodiment, the balls can be solid bodies or hollow
bodies.
Further, as the second layer moves relative to the first layer, particularly
under the first layer,
the outer surface of the second layer and the inner surface of the first layer
preferably maintain
their congruent relationship. Therefore, according to a preferred embodiment,
the inner surface
of the first layer (A surface) and the outer surface of the second layer (B
surface) are concentric
with respect to one another.
During an impact there may be enough energy to flatten the A and/or B surfaces
enough to
affect the predetermined congruency and concentricity factors. Stiffening the
B surface (in
particular) reduces the deformation magnitude. Furthermore, as the B surface
moves under
the A surface, the B surface can become exposed as balls roll away. If this
exposed portion
can make contact with the impacting surface, then a shear force can be
transferred, increasing
the RTM drastically. This issue can be mitigated by ensuring that all
impactable locations are
protected by the reactive layer. According to a preferred embodiment, the
first layer(s) and the
reactive layer(s) therefore cover at least 50% of the outer surface of the
second layer,
preferably at least 70%, more preferably at least 80%, more preferably at
least 90%.
According to yet another preferred embodiment of the helmet according to the
present
invention, the membrane or reactive layer is congruent to the inner surface of
the first layer.
Particularly, if the force of an impact is not spread over a large enough area
then local loading
of the reactive layer can be too large which may lead to a flattening of balls
and/or ball
indentation an adjacent surface such as the inner surface of the first layer
and/or the outer
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surface of the second layer. This could lead to an increased RTM. To prevent
either from
happening, the camber and undulation of the inner surface of the first layer
and an underlying
portion of the outer surface of the second layer is preferably as low as
possible so that less
point loading can occur. Preferably, at any point, a radius of curvature of
said inner surface
and/or of said portion of the outer surface is larger than 40mm, preferably
larger than 60mm,
preferably larger than 80mm, preferably larger than 100 mm.
Particularly, as the outer surface of the second layer moves under the inner
surface of the first
layer, the inner surface of the first layer may start butting up against non-
congruent portions of
the outer surface of the second layer. In case the outer surface of the second
layer is not
ramped at these locations to encourage the inner surface of the first layer to
bend away, then
the inner surface of the first layer may lock up and the RTM will rise.
Furthermore, according to a preferred embodiment of the helmet, the second
layer forms at
least one ramp to cause the first layer to bend away from the second layer to
avoid butting up
of the first layer on a portion of the second portion. This is also denoted as
edge ramping.
Similar to edge ramping, but in the trailing direction, the inner surface of
the first layer may
hook onto details of the outer surface of the second layer causing the RTM to
rise. This is also
denoted as edge hooking. Accordingly, in an embodiment, this is prevented by
ensuring the of
the of helmet geometry has no hard or sharp trailing edges.
Particularly, according to an embodiment, the energy absorbing layer and/or
the second layer
comprises an edge portion having a chamfered or rounded edge to prevent a
trailing edge of
the first layer from becoming caught on said edge portion when moving relative
to the second
layer and/or energy absorbing layer over said edge portion.
Particularly, according to an embodiment, the reactive layer is configured to
hold the first layer
such that a tangential force required to activate rolling of balls of the
reactive layer is about
0.1kN, or or such that an energy introduced by the impact force (FT) has to
exceed a threshold
of 2.5 Joule to activate rolling of the balls.
Furthermore, in a typical scenario, the goal of reducing shear forces acting
on the brain can
be directly correlated to decreasing the RTM of the reactive layer. However,
once the RTM
gets low enough, an inverse correlation starts to emerge, where, as the RTM is
lowered, the
shear forces acting on the brain rise. This is because during an oblique
impact two moments
act on the helmet, a positive one created between the inertia of the head
twisting against the
stationary ground, and a negative one created by the center of gravity of the
twisting against
the normal force of the ground. This means that the lowest resultant moment on
the head
(which causes the lowest shear forces) happens when the positive moment equals
the
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negative moment. If the RTM gets low enough then the positive moment tends to
zero and the
negative moment becomes the major moment on the head. This leads to the
requirement of
controlling the RTM not just diminishing it as much as possible.
One such preferred example/embodiment is to add speed bumps to the outer
surface of the
second layer that inhibit rolling slightly. These speed bumps can have
variable height and
frequency to tune the RTM. Speed bumps can overlap in different orientations
to affect different
impact orientations differently. Thus, according to a further preferred
embodiment of the
helmet, the outer surface of the second layer comprises a plurality of
protrusions (particularly
integral with the second layer) forming a corrugated structure, i.e., speed
bumps, that inhibit
the rolling of balls of said plurality of balls.
Particularly, for certain impact directions the first layer may move towards
the face of a person
wearing the helmet. To address both perceived and actual danger, this may pose
with
facial/ocular lacerations, small particle hitting the eyes etc. Therefore, the
helmet preferably
comprises a corresponding peeling mechanism. This mechanism sees the front-
most part of
the first layer being bonded to the second layer causing a leading edge of the
first layer to
remain in place during an oblique impact, and the rest of the first layer to
fold over itself.
Preferably, this folding means the first layer's leading edge is curved - not
sharp. The curving
profile can also retain ejected balls and act like a shield.
Particularly, according to preferred embodiment of the helmet, the first layer
comprises a front
portion connected to the energy absorbing layer causing the front portion of
the first layer to
remain in place during an oblique impact in a first direction from a rear of
the helmet towards
the front of the helmet, while a remaining portion of the first layer being
connected to the front
portion is separated from the second layer (and particularly folds over
itself), and wherein,
during an oblique impact in a second direction from the front of the helmet
towards the rear
from the helmet, the front portion is configured to disengage from the energy
absorbing layer
or the remaining portion of the first layer is configured to tear apart from
the front portion of the
first layer.
Further, according to a preferred embodiment of the helmet, said front portion
forms a tab
comprising an opening, the tab being embedded in the energy absorbing layer
(particularly in
a front portion of the helmet/energy absorbing layer), wherein a portion of
the energy absorbing
layer extends through said opening such that said portion holds the tab in
place upon said
oblique impact in the first direction and breaks to release the tab upon said
oblique impact in
the second direction.
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Particularly, to achieve this the front part/ tab can have a thinner cross
section as the remaining
portion of the first layer and/or the first layer can comprise a predetermined
breaking point.
Another way to reduce perceived and actual danger associated with balls
ejecting during an
impact is to increase the ball adhesion as much as possible while ensuring
there is no gain in
the RIM.
According to a preferred embodiment of the helmet according to the present
invention a first
strength of the bonds between the balls and an inner surface of the first
layer or an inner
surface connected to the first layer differs from a second strength of the
bonds between the
balls and an outer surface of the second layer or an outer surface connected
to the second
layer. According to a preferred embodiment, the second strength is larger,
particularly so as to
retain more balls to the second layer. Preferably, the second strength is at
least twice as large
as the first strength, particularly at least three times as large,
particularly at least 8 to 20 times
as large.
Furthermore, edge finishes of the first layer and helmet in general are
preferably designed to
avoid snagging during everyday use. The length, angle and thickness of the
overhang can
cause more geometric locking.
Further, according to a preferred embodiment of the helmet, upon an impact
force on the first
layer, the first layer is configured to deform in shape and move relative to
the second layer.
Further, according to a preferred embodiment of the helmet, the first layer
comprises an edge
region, where particularly the first layer meets the second layer or is
coupled to the second
layer, wherein the edge region is configured to reduce a transfer of a radial
force acting on the
first layer from the first layer to the second layer.
Further, according to a preferred embodiment of the helmet, said edge region
is formed by a
portion of the first layer extending at an angle (x) with respect to a normal
of an outer surface
of the second layer, said angle (x) being in the range from 20 to 80 ,
preferably 30 to 70 ,
preferably 40 to 60 , preferably 40 to 50 . Particularly, the cosine of said
angle x (cos(x))
determines the magnitude of transmissible load (for given material
properties). If this angle is
too small, a significant portion of the impact force is transmitted directly
to the outer surface of
the second stiff layer instead of the reactive layer, particularly membrane,
creating high friction.
If the angle is too big, the majority of the force is transmitted to the
intermediary layer allowing
it to move relative to the outer surface
Further, according to a preferred embodiment of the helmet, the first layer
comprises an edge
region that is connected to the outer surface of the second stiff layer by a
compressible
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intermediary layer, particularly to reduce a transfer of a radial force acting
on the first layer
from the first layer to the second layer. For instance, the intermediary layer
can be a foam tape
or other media that yields readily.
Further, according to a preferred embodiment of the helmet, the first layer is
configured to store
and release energy as a result of an impact to the first layer to reduce
rotational motion of a
head of a person wearing the helmet
Further, according to a preferred embodiment of the helmet, the first layer is
configured to
change its shape relative to the second layer during impact, wherein
particularly the first layer
comprises an auxetic structure.
Further, according to a preferred embodiment of the helmet, the first layer is
shaped to pivot
the helmet during impact and thereby reduce rotational motion of a head of a
person wearing
the helmet.
Further, according to yet another preferred embodiment of the helmet, the
first layer is
configured to deform during an impact such that a free movement of the first
layer is inhibited
during impact, wherein particularly said deformation causes a peeling of the
adhesive bonding
the balls to the outer surface of the second layer, particularly via said
substrate film and its
adhesive layer.
Furthermore, according to a preferred embodiment of the helmet, the first
layer comprises a
buckling for supporting said pivoting. Particularly, the buckling can have a
round shape or a
wedge shape. Particularly, said buckling can be configured to snap-through
under an impact,
particularly oblique impact.
Further, according to a preferred embodiment of the helmet, upon an impact,
the buckling is
configured to flatten and increase in width resulting in a translational
movement of a boundary
region of the buckling causing the balls to roll.
This can be used to increase duration at which the reactive layer can operate.
Particularly, as
the first layer deforms it can also move relative the second layer. This
increases the time at
which the reactive layer is working, which may require less reactive layer -
less weight, or
better controlling dynamics.
Furthermore, advantageously, as the shell deforms, the width increases which
helps to reduce
the exposure between the first and the second layers. Preferably, the inner
surface of the first
layer should be hemispherical for better rolling performance. An outer surface
of the first layer,
via which surface the helmet is impacted in a crash, might not want to be
hemispherical for
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aesthetic or aerodynamic reasons, but may comprise other functional features
such as the
buckling(s) described above.
Further, according to a preferred embodiment of the helmet, the buckling is
configured to
provide a redirection of a normal force of an impact acting on the first layer
such that the normal
force comprises a distance to the center of mass of the system comprised of
the helmet and a
head of a person wearing the helmet
Furthermore, according to a preferred embodiment of the helmet, the first
layer, particularly
the buckling, is configured to deform on impact to prevent geometric locking
of the first stiff
layer due to a mechanical interaction with an adjacent structure of the
helmet, wherein
particularly deformation of the first stiff layer, particularly of the
buckling, causes an edge region
of the first stiff layer to lift up from the reactive layer so as to not
become entangled with
adjacent structures of the helmet.
Furthermore, according to a preferred embodiment of the helmet, the inner
surface of the first
stiff layer is configured to become congruent with the outer surface of the
second stiff layer
during an impact, particularly so as to increase the duration of impact and
sliding before
contact.
Furthermore, particularly, the first layer can elastically deform and/or
plastically deform and/or
fracture during impact. Furthermore, the first layer can comprise at least one
relief cut and/or
at least one structural element to permit deformation.
Further, according to a preferred embodiment of the helmet, the first layer
contacts the reactive
layer (particularly membrane) merely via a localized portion of the inner
surface of the first
layer (i.e. said portion comprising an area being smaller than the area of the
inner surface of
the first stiff layer), wherein particularly said portion is arranged at a
perimeter of the first layer.
Further, according to a preferred embodiment of the helmet, said localized
portion(s) comprise
an increased stiffness compared to an adjacent portion of the first layer,
particularly so as to
reduce the area of the reactive layer necessary for facilitating relative
movement between the
first layer and the second layer.
Preferably, the helmet is a cycling helmet. However, the technology of the
present invention
and variations thereof can be applied to other helmets. Even helmets that are
not made via
EPS in-moulding but via injection moulding. Particularly, the helmet can also
be a motorcycle
helmet. For such a helmet, higher impact speeds allow the activation force for
facilitating the
rolling of the balls of the reactive layer or membrane to be higher. This adds
to the durability
of the helmet during manufacturing and everyday use
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Particularly, in an embodiment of the invention, instead of basing the first
layer(s) on sheets
e.g. formed out of polycarbonate, the first layer(s) and the second layer can
be injection molded
first and second layers.
The helmet according to one of the preceding claims, wherein the respective
first layer is an
injection-moulded first layer and/or wherein the second layer is an injection-
moulded second
layer.
Injection moulding for a helmet such as a motorcycle helmet is afforded by the
weight
requirements of such helmets being less strict than regarding cycling helmets
and by the linear
impact.
The helmet according to one of the preceding claims, wherein a portion of an
inner surface of
the respective first layer is bonded to a portion of an outer surface of the
second layer.
Particularly, according to an embodiment, the portion of the inner surface of
the respective first
layer is bonded to the portion of the outer surface of the second layer by
means of a double-
sided adhesive tape. Preferably, said portion of the inner surface is an edge
portion of the inner
surface of the first layer. Further, preferably said portion of the outer
surface is an edge portion
of the outer surface of the second layer
The helmet according to one of the preceding claims, wherein the first layer
is connected to
the second layer by connectors, the respective connector protruding from an
inner surface of
the first layer and extending through an associated through-opening of the
second layer with
an end portion of the connector, the end portion engaging with the second
layer (wherein the
end potion preferably comprises a nose engaging behind an edge region of the
through-
opening) to connect the first layer to the second layer, wherein the
respective connector is
configured to break at said impact threshold to release the first layer from
the second layer.
Furthermore, according to a preferred embodiment of the helmet, the first
layer is a sacrificial
layer configured to smooth out a surface impacting on an outer surface of the
first layer of the
helmet to allow the balls to roll on the sacrificial layer. Preferably, the
sacrificial layer is
configured to be completely released from the helmet or partially released
from the helmet
during an oblique impact and particularly to not translate during said impact
relative to the
impacting surface (i.e. to stick to the impacting surface). Partially released
particularly means
that the helmet comprises a structure that still connects the sacrificial
layer to the helmet after
release, such as e.g. a tether.
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According to yet another preferred embodiment of the helmet according to the
present
invention, an energy necessary to release the respective ball is in the range
between 0.005
Joules and 0.5 Joule per ball.
The helmet comprises a plurality of first layers, and a reactive layer
sandwiched between each
first layer and the second layer (and connected to the first and second
layers).
Particularly, as described above the respective reactive layer comprises a
plurality of rigid
balls, that remain rigid during normal use of the helmet and are configured to
roll at an impact
threshold over an outer surface of the second layer. Furthermore, the
respective reactive layer
can be a membrane as described above, which will also be detailed further down
below.
Furthermore, preferably, the respective first layer and associated reactive
layer (or membrane)
comprise an elongated shape and are preferably arranged side by side in the
direction of the
helmet's cross axis and preferably extend along the longitudinal axis of the
helmet (i.e. from
the back to the front of the helmet), wherein the vertical axis of the helmet
is essentially normal
to the head of the person wearing the helmet.
the first layers being arranged adjacent one another. Particularly, this means
that neighboring
first stiff layers comprise edge portions contacting one another
Furthermore, each first layer of said plurality of first layers can be
configured according to the
embodiments described herein with respect to the first layer described above,
which will be
briefly reiterated further down below.
Preferably, according to an embodiment, the rigid balls are formed from a
material comprising
a Young's modulus (modulus of elasticity) in the range stated above.
Particularly, according to a preferred embodiment, the balls comprise a
diameter in the range
stated above.
Furthermore, particularly, the balls are distributed along an inner surface of
the respective first
layer such that they cover an area that corresponds to 10% to 30%, preferably
about 20% of
the area of said inner surface of the respective first layer.
Further, preferably, the rigid balls are bonded to a substrate film of the
corresponding reactive
layer via an adhesive configured to undergo brittle failure. Particularly, the
respective substrate
film comprises a thickness smaller than 200 pm.
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Particularly, the respective substrate film comprises an adhesive layer
preferably consisting of
a pressure sensitive adhesive arranged on a side of the respective substrate
film facing away
from said plurality of balls.
Furthermore, the respective reactive layer preferably is (or comprises) a
membrane bonded to
the first and the second layer, wherein the respective membrane comprises the
respective
substrate film and the respective plurality of balls arranged thereon.
Preferably, as described
above, the respective membrane or the substrate film is bonded to the outer
surface of the
second layer via said adhesive layer consisting of said pressure sensitive
adhesive of the
respective substrate film.
Furthermore, preferably, the respective membrane or its respective plurality
of balls is bonded
to the inner surface of the first layer (A surface), particularly during high
temperature moulding,
via an adhesive layer, preferably an adhesive layer comprising or consisting
of a thermo-
softening adhesive.
Particularly, as described above, the respective first layer can a sheet (the
respective sheet
being preferably formed from a plastic material such as polycarbonate (PC)), a
color layer (e.g.
a colored ink layer) arranged on an inner surface of the respective sheet, a
protective layer
arranged on the color layer, wherein said adhesive layer that bonds the
respective membrane
to the inner surface of the respective first layer is bonded to the respective
protective layer.
Particularly, in all embodiments, the inner surface of the respective first
layer faces towards
the head of said person wearing the helmet.
Furthermore, particularly, the respective protective layer can be a heat
resistant ink layer (the
heat resistant ink layer can be screen printed or UV printed onto the color
layer (e.g. colored
ink layer)). Furthermore, alternatively, the respective protective layer can
be one of the layers
mentioned above. Further, particularly, the respective protective layer can
comprise a
thickness below 0.1 mm and/or a yield strength larger than 20 MPa. Further,
particularly, the
respective protective layer can have a thermal expansion differing less than 5
% from a thermal
expansion of a material of the respective first layer.
Furthermore, alternatively, the respective first layer that can also be a twin
sheet assembly as
described above, comprising an outer sheet and an inner sheet (e.g.
thermoformed
simultaneously), wherein both sheets preferably consist of polycarbonate (PC),
wherein the
inner sheet of the respective twin sheet assembly is perforated (see also
above).
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According to yet another preferred embodiment of the present invention, the
first layer can be
formed by a fabric or comprise a fabric. Particularly, in all embodiments of a
helmet according
to the present invention, the first layer can be formed or comprise such a
fabric.
According to another preferred embodiment of the helmet according to the
present invention,
the respective first layer and the associated reactive layer (particularly in
form of the respective
membrane) form a replaceable unit. Particularly, after an oblique impact, the
respective
membrane, and if still partially connected, the respective first layer, are
configured to be
removed (e.g. manually) and replaced by a replacement unit comprised of a
first layer and a
membrane wherein the replacement unit is configured to be connected to the
outer surface of
the second layer (particularly bonded to the outer surface of the second layer
by an adhesive
layer). Therefore, a third aspect of the present invention also relates to a
replacement unit
comprising a first layer and a membrane. The first layer and the membrane can
be further
characterized as described herein in relation to the method and helmets.
Furthermore, a fourth
aspect of the present invention relates to a system comprising a helmet
according to the
present invention and at least one replacement unit according to the present
invention.
According to a fifth aspect of the present invention relating to a helmet, a
helmet is disclosed,
the helmet comprising a first layer forming an outer surface of the helmet,
and a second layer,
wherein under an oblique impact, the first layer can move relative to the
second layer, wherein
particularly the second layer can move under the first layer.
According to a preferred embodiment of the helmet according to the fifth
aspect, the first layer
comprises an angled edge portion that is arranged on a face side of the second
layer (the face
side extending in a thickness direction of the second layer) and can thus
slide along the face
side without being caught on the latter.
Furthermore, according to a preferred embodiment of the helmet according to
the fifth aspect,
the helmet comprises an energy absorbing layer, the second layer being
arranged on the
energy absorbing layer.
Furthermore, according to a preferred embodiment of the helmet according to
the fifth aspect,
the energy absorbing layer comprises a raised boundary portion that ramps up
towards a
periphery of the energy absorbing layer and provides an outer surface being
flush with an outer
surface of the angled edge portion of the first layer.
According to yet another preferred embodiment of the helmet according to the
fifth aspect, the
second layer comprises an edge portion that covers the raised boundary portion
which ramps
up towards the periphery of the energy absorbing layer, wherein preferably the
edge portion
of the second layer provides an outer surface being flush with an outer
surface of the first layer.
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Furthermore, the helmet according to the above described fifth aspect of the
present invention
can comprise a reactive layer sandwiched between the first layer and the
second layer as
described herein. Particularly, the helmet according to the fifth aspect of
the present invention
can be further characterized by the features stated in claims 1 to 58, the
corresponding
embodiments described herein, and all the other features of the helmets
described herein.
Furthermore, according to the first aspect of the present invention, a method
is disclosed,
namely a method for manufacturing a helmet, particularly a helmet for cycling,
particularly a
helmet according to the present invention as described and claimed herein,
wherein the
method comprises the steps of:
(a) Providing a first layer and an adhesive layer arranged thereon,
(b) Providing a second layer and an adhesive layer arranged thereon,
(c) Providing a membrane comprising a plurality of balls bonded to a
substrate film
of the membrane using an adhesive (the adhesive being preferably configured
to undergo brittle failure), the substrate film comprising an adhesive layer
on a
side facing away from said plurality to balls,
(d) Arranging the membrane on an outer side of the second stiff layer and
bonding
the membrane to the second layer via said adhesive layer of the substrate film
(e) Arranging the first layer, the second layer and the membrane in a
cavity of a
mould, wherein the membrane is arranged between the first and the second
layer, and
(f) Providing a material in the cavity adjacent the adhesive layer arranged
on the
second layer and forming an energy absorbing layer of the helmet, wherein the
energy absorbing layer is bonded to an inner surface of the second layer via
said adhesive layer arranged on the second layer, and bonding the plurality of
balls to the first layer via said adhesive layer arranged on the first layer.
Particularly, according to a preferred embodiment of the method, step f)
comprises providing
a heated material in the cavity adjacent the adhesive layer arranged on the
second layer and
pressurizing the cavity for forming the energy absorbing layer, wherein the
energy absorbing
layer is bonded to an inner surface of the second layer via said adhesive
layer arranged on the
second layer, and bonding the plurality of balls to the first layer via said
adhesive layer
arranged on the first layer. The heated material can be provided in an
embodiment by heating
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the material in the cavity or by injecting heated, particularly molten,
material into the cavity of
the mould.
Furthermore, in all embodiments, the second layer can be formed in one piece,
but can also
be formed by multiple sheets arranged side by side on the energy absorbing
layer.
According to a preferred embodiment of the method, the adhesive layer arranged
on the first
layer is a thermo-softening adhesive layer (step a)), and/or wherein the
adhesive layer
arranged on the second layer is a thermo-softening adhesive layer (step b)),
particularly a
binder ink such as acrilux, and/or wherein the adhesive layer of the substrate
film comprise a
pressure sensitive adhesive.
Particularly, in a preferred embodiment of the method, the material is a bulk
material,
particularly in the form of pellets, wherein particularly said material is
polystyrene (PS),
particularly expanded polystyrene (EPS).
Particularly, the material is heated in the cavity by means of super-heated
steam, particularly
at about 2bar, particularly for a time span of 4 minutes to 5 minutes, which
also softens the
thermo-softening adhesive layers for bonding the balls to the first layer and
the second layer
to the energy absorbing layer.
Furthermore, according to a preferred embodiment of the method, providing a
first layer in step
(a) comprises proving a sheet as a base structure of the first layer, applying
a color layer on
the sheet (preferably by printing, e.g. screen printing, a colored ink on the
sheet), wherein
thereafter preferably a light bleed preventing base coat is applied on the
color layer, optionally
applying a protective layer on the color layer (particularly on the light
bleed preventing base
coat), wherein particularly the protective layer is one of the layers
described above, particularly
a cross-linked polymer barrier coat, and wherein arranging said adhesive layer
on the first layer
comprises arranging said adhesive layer on the protective layer.
Particularly, according to an embodiment of the method the sheet is
thermoformed and
trimmed to achieve a desired contour of the sheet (or first layer). The sheet
can be
thermoformed and trimmed after having applied said color layer, particularly
light bleed
preventing base coat, protective layer and adhesive layer.
Particularly, the sheet of the first layer can be made out of polycarbonate
(PC).
Furthermore, according to a preferred embodiment of the method, providing the
second layer
in step (b) comprises proving a sheet (as a base structure of the second
layer), applying a
color layer on the sheet of the second layer (preferably by printing, e.g.
screen printing, a
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colored ink on the sheet), wherein thereafter preferably a light bleed
preventing base coat is
applied on the color layer, and wherein arranging said adhesive layer on the
second layer
comprises arranging said adhesive layer on the color layer, particularly on
the light bleed
preventing base coat.
Particularly, according to an embodiment of the method the sheet of the second
layer is
thermoformed and trimmed to achieve a desired contour of the sheet (or first
layer). The sheet
can be thermoformed and trimmed after having applied said color layer,
particularly light bleed
preventing base coat, protective layer and adhesive layer.
Particularly, the sheet of the second layer can be made out of polycarbonate
(PC).
As described above, the helmet can comprise a plurality of first layers. In
this case the above
described step (a) comprises providing said plurality of first layers (each
first layer can be
provided as described above with respect to the first layer).
Furthermore, according to a preferred embodiment of the method, step (c) of
providing the
membrane comprises providing the substrate film by kiss cutting a laminate
comprising a top
layer and a backing, the substrate film being kiss cut from the top layer
resulting in the substrate
film arranged on the backing and a surrounding portion of the top layer,
wherein particularly
the substrate film comprises an elongated shape being adapted to a geometry of
a
corresponding portion of the outer surface of the second layer.
According to a preferred embodiment of the method, step (c) further comprises:
- removing said surrounding portion (also denoted as negative web),
- arranging dots (preferably of a diameter of about 2mm) of said adhesive,
particularly in a repeating or desired pattern, onto the substrate film, and
- placing a ball of said plurality of balls on each dot of adhesive and
curing or letting
the adhesive cure to bond the balls to the substrate film.
According to a preferred alternative embodiment of the method, step (c)
further comprises:
- applying a layer of said adhesive onto the substrate film,
- removing said surrounding portion (also denoted as negative web) before
the
adhesive has set, and
- placing said plurality of balls in a repeating or desired pattern on the
layer of said
adhesive and curing or letting the adhesive cure to bond the balls to the
substrate
film.
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Furthermore, according to a preferred embodiment of the method, the second
layer comprises
recesses (e.g. at an edge) and/or through-holes through which portions of the
material extend
upon heating the material and pressurizing the cavity towards the first layer
to bond with the
first layer via said adhesive layer arranged on the first layer (i.e. through-
weld). In an
embodiment, the adhesive layer arranged on the first layer is partially or
completely omitted
and said portions of the material extending through the recesses and/or
through-holes bond to
the first layer (e.g. without an intermediary separate adhesive layer, see
also above). Thus, in
step a) and f) described above said adhesive layer may not be used at all or
merely for bonding
the balls to the first layer.
According to a preferred embodiment, the substrate film is formed out of a
polymer, particularly
PVC, see also above.
Once cooled, the fully formed helmet body is preferably removed from the
cavity, and can have
ancillaries added and may then be packaged.
Furthermore, in the method according to the present invention and its
embodiments described
herein, the balls can be bonded to the outer surface of the second layer
(particularly directly)
using an adhesive, particularly an adhesive comprising PVA, i.e., the
substrate film can be
omitted.
Furthermore, in the method according to the present invention and its
embodiments
described herein the balls (whether via membrane or direct) can be bonded to
the outer
surface of the second layer B before the outer surface of the second layer is
formed into
shape.
Furthermore, according to a sixth aspect, the present invention relates to a
helmet,
particularly a helmet for cycling, according to the features of claim 59.
Particularly, the sixth aspect of the present invention relates to a helmet,
particularly a helmet
comprising a motion inhibiting layer to reduce negative rotation.
In an impact of a helmet on an object, particularly of a helmet on a street or
other kind of
terrain in a bicycle accident, the normal component FN of the impact force
directed
perpendicular from the particular impact location of the object is in general
not aligned with
the center of mass of a head of a person wearing the helmet. The displacement
between the
normal force and the center of mass of the head thereby represents a first
lever arm vector
Li with the product of normal force and the first lever arm causing a first,
negative torque of
the head. In the absence of other forces, a negative rotation of the head with
a negative
direction of rotation is induced.
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However, due to friction or other resistive forces, such as rolling resistance
between the
object and an outer layer, the outer layer is subject to a tangential friction
force, FT. The
displacement between the direction of the tangential friction force and the
center of mass
represents a second lever arm vector L2 with the product of the tangential
friction force and
the second lever arm vector leading to a second, positive torque to helmet and
head. The
positive torque is directed opposite to the negative torque caused by the
normal component
of the impact force and the first lever arm vector.
Depending on the magnitude of the respective torques, upon impact, the head
will rotate
either positively (along the direction of the friction force) or negatively
(opposite to the
direction of the friction force).
In both cases, the net rotation of the head upon impact is known to cause
severe injuries for
the brain and neck of the person.
Typically, helmets in the prior art rotate positively because the resistive
forces between the
various layers forming the helmet are relatively high. However, recent helmet
developments
have now reduced resistive forces to a regime that features negative rotation
of the helmet
upon impact.
It is object of the present invention to provide a helmet with enhanced safety
features,
particularly with respect to the aforementioned problem of negative rotation
that can be
manufactured particularly cost efficient. The object is achieved by the device
having the
features of claim 59.
Advantageous embodiments are described in the corresponding dependent claims.
The invention discloses according to the sixth aspect a helmet for protecting
the head of a
person upon an impact, the helmet comprising an outer surface, the helmet
being configured
to reduce negative rotation of a head of the person wearing the helmet
resulting from an
impact force acting on the outer surface of the helmet upon said impact.
As stated above, the negative rotation of the head is directed along the
negative torque
caused by the normal component of the impact force and the first lever arm
vector
corresponding to the displacement between the normal component of the impact
force and
the center of mass. As such, the negative rotation is directed opposite of the
positive torque
created by the cross product of the tangential friction force acting on the
outer surface upon
impact and the second lever arm vector extending parallel to the normal
component of the
impact force to the center of mass. In the context of the present invention,
the term 'center of
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mass' refers to a center of mass of the helmet and a person wearing the
helmet, particularly
the center of mass of the helmet and a head of a person wearing the helmet.
While helmet in the prior art typically feature positive rotation due to the
relatively high friction
between the outer surface of the helmet and the head of the person,
application of
sufficiently low friction layers may result in negative rotation. Since any
kind of rotation is
harmful for head and neck of the person, the present invention proposes to
introduce at least
one motion inhibiting element to the helmet in order to reduce the rotation of
the helmet,
particularly the negative rotation.
According to an embodiment of the sixth aspect of the present invention, the
helmet may
further comprise an inner layer and at least one outer protective layer
wherein for reducing a
positive rotation of the head of the person wearing the helmet upon impact,
the at least one
outer protective layer may be configured to move relative to the inner layer.
Preferably, said
inner layer may comprise energy absorbing elements and/or an energy absorbing
material,
so as to form an energy absorbing layer.
In case the motion between the inner layer and the at least one outer
protective layer is
characterized by a sufficiently low friction to result in negative rotation of
the helmet, the
motion inhibiting elements may be configured to reduce a negative rotation of
the helmet.
According to another embodiment of the sixth aspect of the present invention,
the motion
inhibiting elements may be used to introduce an additional amount of friction
to the helmet,
particularly to the inner layer and the at least one outer protective layer,
so as to
advantageously reduce a negative rotation of the helmet, providing protection
for the head
and neck of the person wearing the helmet.
The motion inhibiting elements are preferably adapted such that the negative
torque
counteracts the positive torque such that upon impact, the head and helmet
experience an
angular velocity in the range from -15 rad/s to +15 rad/s, preferably -10
rad/s to +10 rad/s,
more preferably -5 rad/s to +5 rad/s.
According to an embodiment of the sixth aspect of the present invention, the
motion inhibiting
elements may be arranged between the inner layer and the at least one outer
protective
layer. In this embodiment, the inhibiting layer may advantageously interact
with both the
inner layer and the at least one outer protective layer so as to control the
amount of friction
between the inner layer and the at least one outer protective layer, thereby
reducing the
negative rotation of the helmet upon an impact force.
To this end, the motion inhibiting elements may also comprise or be a motion
inhibiting layer.
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According to another embodiment of the sixth aspect of the present invention,
the motion
inhibiting layer may be integrally formed with the inner layer and/or the at
least one outer
protective layer. Forming the motion inhibiting layer integrally with the
inner layer and/or the
at least one outer protective layer advantageously contributes to reduce
fabrication costs and
-time of the helmet.
According to another embodiment of the sixth aspect present invention, the
motion inhibiting
layer may be configured to deform upon the impact force. Particularly, the
deformation of the
motion inhibiting layer may for example be a compression or a stretching
accompanied by
corresponding compression- or shearing forces that may be used to counteract
the negative
rotation of the helmet.
According to another embodiment of the sixth aspect of the present invention,
the helmet
may additionally comprise an intermediate layer arranged between the inner
layer and the at
least one outer protective layer, said intermediate layer being configured to
promote the
relative motion between the inner layer and the at least one outer protective
layer. In
particular, the intermediate layer may be a low friction layer comprising
interfaces to the inner
layer and the at least one outer protective layer with friction coefficient,
rolling resistance
coefficients and the like that are low enough to cause a net negative rotation
of the helmet
upon impact. Depending on the choice of the intermediate layer, the motion
inhibiting layer
may be adapted to compensate the resulting net friction force between the
various layers so
as to achieve a minimum net rotation of the helmet upon impact, particularly a
minimum
negative rotation.
According to another embodiment of the sixth aspect of the present invention,
the motion
inhibiting layer comprises a flexible layer, particularly a fabric or a
webbing arranged between
the motion inhibiting layer and at least one of the following: the inner
layer, the intermediate
layer, the at least one outer protective layer. The compression or shearing
forces caused
within the flexible layer upon impact may be used to counteract the relative
motion between
the inner layer and the at least one outer protective layer and particularly
the negative
rotation of the helmet. The motion inhibiting layer may alternatively comprise
flexible
interfaces arranged between the motion inhibiting layer and at least one of
the following: the
inner layer, the intermediate layer, the at least one outer protective layer.
According to another embodiment of the sixth aspect of the present invention,
at least one of
the following may comprise a plurality of stacked sub-layers: the inner layer,
the at least one
outer protective layer, the motion inhibiting layer, the intermediate layer.
The aforementioned
layers may alternatively or additionally also comprise multiple mutually
connected shell
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segments that are arranged essentially in a respective plane extending along
the respective
layer.
According to another embodiment of the sixth aspect of the present invention,
the motion
inhibiting layer may be arranged at least partially within the intermediate
layer. As such, the
inhibiting layer introducing additional friction may directly interact with
the intermediate layer
used to reduce the friction, so as to fine tuning the resulting net friction,
particularly the net
friction between the inner layer and the at least one outer protective layer.
According to another embodiment of the sixth aspect of the present invention,
the
intermediate layer may be integrally formed with at least one of the
following: the inner layer,
the motion inhibiting layer, the at least one outer protective layer. Forming
the motion
inhibiting layer integrally with the inner layer and/or the at least one outer
protective layer
advantageously contributes to reduce fabrication costs and -time of the
helmet.
According to another embodiment of the sixth aspect of the present invention,
the
intermediate layer and/or the motion inhibiting layer may comprise rollable
elements, said
rollable elements being configured to promote the motion of the inner layer
relative to the at
least one outer protecting layer upon the impact force. Particularly, the
rollable elements may
be for example rolls, beads and the like. The rollable elements may for
example comprise a
circular diameter between 0.1 mm and 4 mm, particularly between 1 mm and 2 mm,
wherein
the circular diameter refers to a circular cross-section of the rollable
elements. The rollable
elements advantageously contribute to a substantially lower friction force and
rolling
resistance between the intermediate layer and the inner layer and/or the at
least one outer
protective layer. Depending on the choice of the rollable elements, the motion
inhibiting layer
may be adapted to compensate the resulting net friction force between the
various layers so
as to achieve a minimum net rotation of the helmet upon impact, particularly a
minimum
negative rotation.
Additionally, the intermediate layer and/or the motion inhibiting layer may
comprise breaking
elements configured to fail upon the impact force, enabling the rollable
elements to interact
with the inner layer and the at least one outer protective layer, so as to
promote the motion of
the inner layer relative to the at least one outer protecting layer.
According to another embodiment of the sixth aspect of the present invention,
together with
the inner layer and the at least one outer protective layer, the motion
inhibiting layer may
delimit at least one volume, so as to confine at least a fraction of the
rollable elements in the
at least one volume. As such, also several volumes, particularly with a
different number
and/or different geometries of rollable elements may be used to finetune the
resulting net
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friction between the various layers, particularly between the inner layer and
the at least one
outer protection layer upon impact.
According to another embodiment of the sixth aspect of the present invention,
the rollable
elements, the inner layer, the intermediate layer, the at least one outer
protective layer and
the motion inhibiting layer may comprise a lower or a larger stiffness,
wherein the stiffness of
the rollable elements is lower or larger than the stiffness of at least one of
the following: the
inner layer, the intermediate layer, the at least one outer protective layer,
the motion
inhibiting layer. By choosing different stiffnesses between the rollable
elements and the
various layers, the friction between the various layers, particularly the
rolling resistance may
be controlled, so as to achieve a minimum net rotation of the helmet upon
impact, particularly
a minimum negative rotation. For example, the rollable elements may comprise a
larger
stiffness than at least one of the various layers mentioned above.
Alternatively, the rollable
elements may also comprise a lower elasticity than at least one of the various
layers
mentioned above. The difference in elasticity thereby represents a parameter
to vary the
rolling resistance. For example, the lower elasticity may correspond to a
young's modulus of
less than 3 GPa.
For example, a rolling resistance coefficient between the intermediate layer,
particularly the
intermediate layer comprising rollable elements, and the at least one outer
protective layer
and/or the inner layer may be below 0.2.
Optionally, a coefficient of friction between the motion inhibiting layer and
the intermediate
layer, particularly the intermediate layer comprising rollable elements, or
the at least one
outer protective layer or the inner layer may differ from a coefficient of
friction between the
intermediate layer and the at least one outer protective layer or the inner
layer. As such, the
motion inhibiting layer may preferably be used to introduce an amount of
friction into the
helmet comprising the various layers mentioned above.
For example, a coefficient of friction between the intermediate layer or the
motion inhibiting
layer and the at least one outer protective layer or the inner layer may be
below 0.8.
According to another embodiment of the sixth aspect of the present invention,
the motion
inhibiting layer may comprise a viscous fluid or a gel. The viscous fluid
and/or gel may
preferably be configured to introduce a shear stress to the various layers
mentioned above,
particularly a shear stress between the inner layer and the at least one outer
protective layer.
The viscous fluid or gel may preferably be used in combination with the
intermediate layer,
particularly a low friction intermediate layer optionally comprising rollable
elements, wherein
the viscous fluid or gel may be chosen such that the interplay of the
viscosity creating
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additional shear stress and the intermediate layer reducing the friction
results in a minimum
net rotation of the helmet upon impact, particularly a minimum negative
rotation. Preferably,
the viscous fluid and/or the gel may be arranged in a leak tight volume
enclosed by at least
the inner layer and the outer protective layer so as to retain the viscous
fluid or gel.
For example, the viscous fluid or the gel may comprise a viscosity within
0.001 and 10 Pa s.
According to another embodiment of the sixth aspect of the present invention,
the motion
inhibiting layer may comprise a non-Newtonian fluid or gel. As such, the
viscosity of the fluid
or gel may depend on the shear stress, which may advantageously be used as
another
parameter to finetune the interplay of the fluid or gel creating additional
shear stress and the
intermediate layer reducing the friction, so as to achieve a minimum net
rotation of the
helmet upon impact, particularly a minimum negative rotation.
According to another embodiment of the sixth aspect of the present invention,
the motion
inhibiting layer may comprise motion inhibiting elements. The motion
inhibiting elements are
preferably configured to inhibit the relative motion between the inner layer
and the at least
one outer protective layer. The motion inhibiting elements may advantageously
be used in
combination with the intermediate layer, particularly with the intermediate
layer comprising
rollable elements, so as to achieve a minimum net rotation of the helmet upon
impact,
particularly a minimum negative rotation.
To this end, individual motion inhibiting elements forming the motion
inhibiting elements may
be configured to rupture upon the impact force. To this end, a geometrical
feature,
particularly a diameter, a width or a length of an individual inhibiting
element may be
indicative for an individual rupture force required to rupture an individual
inhibiting element,
wherein the rupture force counteracts the negative rotation of the helmet upon
the impact
force.
For example, the motion inhibiting elements may cover less than 80% of a total
lateral
surface area defined by the at least one outer protective layer.
The motion inhibiting elements may for example be formed as at least one of
the following: a
cylinder, a cone, a pyramid, a cuboid, a truncated cone.
Optionally, the motion inhibiting elements may contact the at least one outer
protective layer
and the inner layer via a lateral contact surface area, wherein a ratio of the
lateral contact
surface area and the total lateral surface area is for example within 0.05 and
0.5.
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According to another embodiment of the sixth aspect of the present invention,
the motion
inhibiting layer may comprise a connector or a plurality of connectors being
integrally formed
between at least two of the following: the inner layer, the intermediate
layer, the at least one
outer protective layer.
Said connector or connectors may be configured to deform and/or to rupture
simultaneously
and/or sequentially upon the impact force, so as to counteract the negative
rotation of the
helmet. The connectors may preferably be used in combination with the
intermediate layer,
particularly the intermediate layer comprising rollable elements, wherein the
choice of
connectors introducing friction and the intermediate layer reducing friction
may be adapted to
achieve a minimum net rotation of the helmet upon impact, particularly a
minimum negative
rotation.
To this end, individual connectors forming the plurality of connectors may
comprise individual
rupture forces, wherein the individual rupture forces take on at least two
values. As such, a
plurality of individual connectors with tailored deformation or rupturing
properties may be
used within the motion inhibiting layer to achieve a minimum net rotation of
the helmet upon
impact, particularly a minimum negative rotation.
For example, the connectors may comprise or be an adhesive, a thermoplastic,
an
elastomer, a ceramic or a metal.
Preferably, the connectors may have a different elasticity than the inner
layer and/or the at
least one outer protective layer. The difference in elasticity between the
connectors and the
inner layer and/or the at least one outer protective layer may advantageously
be used to vary
the friction and/or the rolling resistance between the connectors and the
inner layer and/or
the at least one outer protective layer.
Again, referring to the motion inhibiting layer, the motion inhibiting layer
may comprise at
least one of the following: a plastic material, an elastic material, a
polymer, a metal.
According to another embodiment of the sixth aspect of the present invention,
the motion
inhibiting layer may be configured such that the reduction of negative
rotation of the helmet
depends on a direction of the impact force. To this end, for example a
plurality of said
connectors or inhibiting elements, particularly comprising different
individual rupturing forces
may be used.
As such, the motion inhibiting layer may be configured such that the reduction
of negative
rotation upon an impact force resulting in a rotation of the helmet around a
first axis is larger
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than the reduction of negative rotation upon an impact force resulting in a
rotation of the
helmet around a second axis.
For example, the first axis may run through a coronal plane within a head of a
person
wearing the helmet and the second axis may run through a sagittal plane within
the head of
the person wearing the helmet. Since most impacts induce a stronger (negative)
rotation of
the head and helmet around an axis through the coronal plane compared to the
sagittal
plane, this choice of the first axis and the second axis may advantageously
contribute to
reduce a net rotation of the helmet, particularly a negative rotation.
Preferably, the motion inhibiting layer may be configured to limit the motion
of the inner layer
relative to the at least one outer protective layer upon the impact force to
an absolute
rotational velocity of less than 15 rad/s, wherein the rotational velocity may
be positive or
negative.
According to yet another embodiment of the sixth aspect of the present
invention, at least
two of the following may be configured to geometrically and/or mechanically
lock so as to
reduce the negative rotation upon impact: the inner layer, the intermediate
layer, the motion
inhibiting layer, the outer protective layer. To this end, the inner layer,
the intermediate layer,
the motion inhibiting layer and/or the outer protective layer may comprise
geometrical
features that promote a geometrical locking between at least two of these
layers, for example
pairwise interlocking segments of each of the at least two layers which engage
upon impact
and the like.
According to another embodiment of the sixth aspect of the present invention,
in the absence
of the motion inhibiting elements or the motion inhibiting layer, upon impact,
the helmet
would experience negative rotation, or exceed a pre-defined positive threshold
of positive
rotation.
Particularly, exemplary embodiments of aspects of the present invention are
described below
in conjunction with the Figures. The Figures are appended to the claims and
are accompanied
by text explaining individual features of the shown aspects of the present
invention and their
embodiments. Each individual feature shown in the Figures and/or mentioned in
the text of the
Figures may be incorporated (also in an isolated fashion) into a claim
relating to the device
according to the present invention. Furthermore, the features disclosed in
conjunction with a
specific aspect can be combined with embodiments of other aspects of the
present invention
in every sensible way.
In the following, exemplary embodiments as well as further features and
advantages of the
present invention are described below with reference to the Figures, wherein
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Fig. 1 shows an embodiment of the helmet according to the
present invention,
Fig. 2 shows an alternative embodiment of the detail shown in
Fig. 1,
Fig. 3 shows a cross-sectional view of an embodiment of the
helmet according to the
present invention, wherein the respective first layer comprises a front
portion
being embedded in the energy absorbing layer of the helmet,
Fig. 4 shows details of two embodiments of a helmet according to
the present
invention, wherein here a protective layer is provided for preventing an
excessive indentation of the balls of the reactive layer into the color layer
of
the first layer of the helmet, wherein (A) and (C) show the situation before
applying heat and pressure in the cavity of a mould, and (B) and (D) shows the
situation after moulding of the helmet with the balls embedded into the
adhesive layer, but prevented from further intrusion by the respective
protective layer ((A) and (B): protective layer on top of color layer; (C) and
(D):
protective layer formed by lower sheet of a twin sheet assembly),
Fig. 5 shows an embodiment of kiss cutting the substrate film for carrying
the ball of
reactive the layer/membrane,
Fig. 6 shows an embodiment of bonding the reactive
layer/membrane to the outer
surface of the second layer of the helmet,
Fig. 7 shows an embodiment of the helmet according to the
present invention,
wherein two adjacent first layers of the helmet each comprise a chamfer at the
opposing edges toward mutual locking up of said first layers went said first
layers move relative to one another,
Fig. 8 shows an embodiment of the helmet according to the
present invention,
wherein the first layer is connected to the second layer of the helmet by
means
of connectors extending from the first layer to the second layer,
Fig. 9 shows an embodiment of the helmet according to the
present invention
allowing the initiating of the reactive layer of the helmet by means of a
buckling
feature upon an impact,
Fig. 10 shows an embodiment of the helmet according to the
present invention
allowing lifting an edge portion of a first layer by means of a buckling
feature of
the first layer upon impact,
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Fig. 11 shows an embodiment of the helmet according to the
present invention
allowing pivoting of the helmet upon impact,
Fig. 12 shows an embodiment of the helmet according to the
present invention
allowing release of the first layer in a desired direction due to a
deformation of
the first layer upon impact,
Fig. 13 shows an embodiment of the helmet, wherein the first
layer is configured so as
to achieve altering the direction of normal forces on the helmet to alter the
moment caused by the center of mass of the system comprises of the helmet
and the head wearing the helmet,
Fig. 14 shows an embodiment of the helmet according to the present
invention
allowing the reduction of transmission of radial forces from the first layer
to the
second layer where the two layers meet,
Fig. 15 shows an alternative embodiment for the reduction of said
radial force, and
Fig. 16 shows an embodiment of a helmet having a chamfered or
rounded edge portion
to prevent an edge of the first layer from becoming caught on said edge
portion.
Fig. 17 shows a schematic of the relevant forces and lever arm
vectors corresponding
to positive and negative torque of a helmet upon impact on an object.
Fig. 18a-c shows various impact scenarios of a person wearing a
helmet impacting on an
object, wherein the resulting forces cause a positive rotation of the head and
helmet (scenario Fig. 18c), a negative rotation of the head and helmet
(scenario Fig. 18b) and the ideal case of zero rotation (scenario Fig. 18a).
Fig. 19a shows an embodiment of the helmet according to the sixth
aspect of the
present invention, comprising at least one outer protective layer, a motion
inhibiting layer and an inner layer.
Fig. 19b shows various motion inhibiting elements of the motion inhibiting
layer.
Fig. 20 shows an embodiment of the helmet according to the sixth
aspect of the
present invention, wherein the at least one outer protective layer is
integrally
formed with the motion inhibiting layer.
Fig. 21 shows an embodiment of the helmet according to the sixth
aspect of the
present invention, comprising a fluid or gel.
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Fig. 22 shows an embodiment of the helmet according to the sixth
aspect of the
present invention, comprising a flexible layer.
Fig. 23 shows an embodiment of the helmet according to the sixth
aspect of the
present invention, comprising at least one connector.
Fig. 1 shows an embodiment of a helmet 1 according to the present invention.
According
thereto, the helmet comprises at least one first layer 10, preferably a
plurality of first layers
forming an outer surface of the helmet 1 on which an impact, particularly
oblique impact may
occur, i.e., an impact having a force component running tangentially with
respect to said outer
surface.
The helmet 1 further comprises a second layer 30, and reactive layers 20, each
reactive layer
being sandwiched between an associated first layer 10 and the second layer 30.
In case the
helmet comprises a single first layer 10, the helmet can comprise just a
single reactive layer
underneath it. In the following, the invention will be described in the
context of multiple first
layers 10. As shown in Fig. 1 the first layers 10 preferably comprise a
longitudinal shape and
15 extend along the longitudinal axis X of the helmet 1. Furthermore,
preferably, the first layers
10 are arranged side by side in the direction of the cross axis Y of the
helmet 1. Further, the
first layers 10 are preferably configured as stiff first layers 10 which can
be achieved by
selecting an appropriate material for the first layers 10 and geometry during
the curved shape
of the first layers 10 contributes to said stiffness. Particularly the first
layers 10 can be formed
20 out of polycarbonate and can comprise a thickness in the range from 0.25
mm to 20 mm,
preferably 0.4 to 1 mm. Furthermore, the first layers 10 can each comprise a
curvature in the
direction of the longitudinal axis X as well as in the direction of the cross
axis Y. Other materials
for the first layers are also conceivable. Likewise, as the first layers 10,
the second layer 30
being arranged beneath the first layers 10 is also preferably adapted to be
stiff in the sense
described above. Furthermore, the second layer 30 is arranged on an energy
absorbing layer
40 configured to absorb energy of an impact on the helmet 1 particularly in a
normal direction
of the outer surface of the helmet (e.g. along the vertical axis of the
helmet). The energy
absorbing layer 40 can be formed out of an expanded polystyrene foam (EPS) and
can be
bonded to an inner surface 30b of the second layer by an adhesive layer (33)
(e.g. acrilux or
other suitable therm 0-softening adhesives)
The second layer 20 preferably comprise a thickness in the range from 0.25 mm
to 20 mm and
may also be formed out of polycarbonate. As shown in Fig. 1, the helmet may
comprise
through-openings 8 extending through the layers 10, 20, 40 for allowing
venting of the head of
a person wearing the helmet 1. Such through-openings 8 may by flanked by first
layers 10 on
either side of the respective through-opening.
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Preferably, the respective reactive layer 20 comprises a plurality of balls 2
(e.g. in the form of
preferably rigid spherical bodies) that remain rigid during normal use of the
helmet 1 (when no
impact occurs) and are configured to roll at an impact threshold over an outer
surface 30a of
the second layer 30 (also denoted as B surface).
The impact threshold corresponds to a pre-defined tangential force on a first
layer 10 that, if
exceeded upon an oblique impact, caused the balls 2 to roll. In a preferred
embodiment, the
balls comprise a diameter of about 2 mm. Further, the balls can comprise the
packing density
described herein. Preferably, the respective reactive layer 20 is configured
to hold the
respective first layer 10 such that a tangential force required to activate
rolling of the balls 2 of
the reactive layer is about 0.1kN (or higher).
Preferably, as indicated in Fig. 1 the respective reactive layer 20 (Fig. 1
shows only one such
reactive layer 20, but such a reactive layer 20 is present under each first
layer 10) is formed
as a membrane 20 that comprises the balls 2 and can be handled in a convenient
fashion
during production of the helmet 1.
Particularly, as indicated in the details of Fig. 1 and 2, the respective
membrane 20 comprises
a substrate film 21 and a plurality of balls 2 arranged thereon. Particularly,
the balls 2 are
bonded to the substrate film 21 via an adhesive 22 that is preferably
configured to undergo
brittle failure to allow the balls to roll on the substrate 21 / over the
second layer 30 when said
impact threshold is exceeded. Preferably, the substrate film 21 comprises a
thickness smaller
than 200 pm and can be formed out of a polymer such as PVC. Other materials
are also
conceivable. Furthermore, the substrate film 21 can comprises an adhesive
layer 23 such as
a pressure sensitive adhesive (PSA) arranged on a side of the substrate film
21 facing away
from the balls 2. This allows one to easily place the membrane on the second
layer 30 as
shown in Fig. 6 either manually or automatically (e.g. by means of a suitable
machine) and
bond the respective membrane 20 with the balls 2 therein to the second layer
30.
Furthermore, the membrane 20 can be bonded to the inner surface 10a of the
respective first
layer 10 by an adhesive layer 14 applied to the respective first layer 10 that
bonds to the balls
2 of the respective membrane 20, e.g. during forming of the energy absorbing
layer 40. For
this, the adhesive layer 14 can comprise a thermo-softening adhesive.
Furthermore, as shown in Fig. 4, the respective first layer 10 is preferably
formed in a manner
that prevents an excessive indentation of the balls 2 into the thermo-
softening adhesive layer
14 during production. For this, as shown in Fig. 4 (A) and (B), the respective
first layer 10
comprises a sheet 11 being preferably formed from a plastic material such as
polycarbonate
(PC), at least one color layer 12 (e.g. a colored ink layer) arranged on an
inner surface of the
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sheet 11, optionally a light bleed preventing base coat applied to the at
least one color layer
12, and a protective layer 13 arranged on the color layer 12 (or base coat),
wherein said
adhesive layer 14 that bonds the membrane 20/balls 2 to the inner surface 10a
of the first layer
is arranged on the protective layer 13. The protective layer 13 now achieves
that during
5 forming of the helmet 1 in a mould, the balls 2 do not intrude through
the heated soft adhesive
layer 14 into the color layer 12, but are prevented from doing so by the
protective layer 13 (cf.
Fig 13(B)). This also prevents that the balls 2 are visible from the outside
in case a transparent
material is used for the sheet 11. The protective layer 13 can e.g. be formed
out of the materials
stated above and preferably comprises a thickness below 0.1 mm and/or a yield
strength larger
10 than 20 M Pa.
Alternatively, as shown in Fig. 4 (C) and (D), the first layer 10 can be a
twin sheet assembly
comprising an outer sheet 11 and an inner sheet 110 that can be thermoformed
simultaneously, wherein both sheets 11, 110 preferably consist of
polycarbonate. Here, at least
one color layer 12 (particularly a colored ink layer) and an adhesive layer
140 (particularly an
adhesive ink layer) are arranged between the outer and the inner sheet 11,
110, the adhesive
layer 140 bonding the inner sheet 110 to the outer sheet via the at least one
color layer 12.
The penetration barrier for the balls 2 is now formed by the inner sheet 110,
i.e., in the mould
the balls 2 can indent the softened adhesive layer 14, but are prevented from
intruding further
layers by the inner sheet 110 (cf. Fig. 4 (D)) which thus forms a protection
layer of the first
layer 10.
Furthermore, as indicated in the details of Figs 1, 2 and in Fig. 7, the
helmet 1 preferably
comprises ramp features that cause the respective first layer 10 to bend away
from the second
layer 30 to avoid butting up of the first layer 10 on a portion of the helmet
1, particularly on
second layer 30 or a neighboring first layer 10 or another structure.
As shown in the detail of Fig. 1, the first layer 10 comprises an angled edge
portion 10b that is
arranged on a thin face side 30c of the second layer 30 and can thus slide
along the face side
30c without being caught by the latter. Furthermore, preferably, the energy
absorbing layer 40
comprises a raised boundary portion 40a that ramps up towards the periphery of
the energy
absorbing layer 40 and provides an outer surface 40b being flush with an outer
surface 10c of
the angled edge portion 10b of the adjacent first layer 10. The angled edge
portion 10b can
also have a round transition to an adjacent portion of the first layer 10.
In the modification of this edge termination shown in Fig. 2, the second layer
30 comprises an
edge portion 30d that covers the raised boundary portion 40a that ramps up
towards the
periphery of the energy absorbing layer 40. Here, the edge portion 30d of the
second layer 30
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provides an outer surface 30e being flush with the outer surface 10c of the
adjacent first layer
10.
Furthermore, as indicated in Fig. 7, the helmet 1 can comprise two adjacent
first layers 10,
wherein the two first layers 10 preferably comprise adjacent edges 10d,
wherein each edge
10d preferably comprises a chamfer 10e allowing an obliquely impacted first
layer 10 to move
more easily on top of a neighboring first layer 10 without becoming entangled
with the adjacent
first layer 10. Alternatively, or in addition, the second layer 30 may
comprise a ramp region 9,
e.g. in form of a recess or indentation, below the edges 10d of the adjacent
first layers 10 thus
allowing an edge 10d of an obliquely impacted first layer to be lifted upwards
and travel over
the respective adjacent first layer 10 and its edge 10d.
Furthermore, as shown in Fig. 16, the energy absorbing layer 40 and/or the
second layer 30
can comprises an edge portion 80 having a chamfered or rounded edge 80a to
prevent a
trailing edge 10g of the first layer 10 from becoming caught on said edge
portion 80 when
moving relative to the second layer and/or energy absorbing layer over said
edge portion 80
after an oblique impact that causes relative movement of the first layer in
direction D3 with
respect to the second layer 30 / energy absorbing layer 40. Fig. 16 (A) shows
the situation
before an impact, and Fig. 16 (B) shows the relative movement between first
and second layer
10, 30 after an oblique impact. Said edge 10g is also denoted as trailing edge
with respect to
direction 03. Furthermore, on an inner surface of the first layer 10, the
first layer 10 can
comprise a fillet 81 for allowing the edge 10g to smoothly travel over the
edge portion 80.
Furthermore, for certain impact directions the first layer 10 may move towards
the face of a
person wearing the helmet 1 (e.g. in the direction of the longitudinal axis X
and downwards
following the curvature of the second layer 30, cf. Fig. 1). To avoid such a
situation, the
respective first layer 10 (or at least some of the first layers 10) comprises
a front portion 101
as shown in Fig. 3 that is embedded in the energy absorbing layer 40 so that
the front portion
101 of the first layer 10 remain in place during an oblique impact in a first
direction D1 from a
rear of the helmet 1 towards the front of the helmet 1, while a remaining
portion 102 of the first
layer 10 being connected to the front portion 101 is separated from the second
layer 30 and
may fold over itself as indicated by the solid arrow. However, during an
oblique impact in a
second direction D2 from the front of the helmet 1 towards the rear from the
helmet 1, said
front portion 101 can be allowed to disengage from the energy absorbing layer
40 (and from
the helmet) so that it becomes completely separated from the helmet 1.
Alternatively, the
remaining portion 102 of the first layer 10 can be configured to tear apart
from the front portion
of the first layer 10, for instance along a predetermined breaking point.
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Particularly, front portion 102 can be a tab 102 comprising an opening 103,
the tab 102 being
embedded in a front portion of the energy absorbing layer 40, such that a
portion 400 of the
energy absorbing layer 40 extends through said opening 103 such holding the
tab 102 in place
upon said oblique impact in the first direction Dl. The portion 400 can be
configured to break
to release the tab 102 upon said oblique impact in the second direction D2.
Alternatively, the
remaining portion 102 of the first layer 10 may break away from the tab 102
(e.g. at a
predetermined breaking point, see above). Particularly, the front part / tab
101 can have a
thinner cross section as the remaining portion 102 of the first layer 10.
Furthermore, as shown in Fig. 14, the first layers 10 of the helmet preferably
comprise edge
terminations, i.e., edge regions 10b that are configured to reduce a transfer
of a radial force FR
from the first layer 10 to the second layer (30) (e.g. acting on the
respective first layer 10 upon
an impact). In other words, areas where inner and outer layers 10, 30 meet,
shall preferably
inhibit the transfer of the radial force. If an impact were to happen at this
point and load was
taken by the joint rather than the adjacent balls 2, a relative movement
between the layers
would be restricted proportionally to the magnitude of load upheld by the
joint. Therefore, the
respective edge region 10b can be an angled edge region 10b that extends at an
angle x with
respect to a normal N of an outer surface 30a of the second layer 30, wherein
said angle x is
preferably in the range from 20 to 80 , preferably 30 to 70 , preferably 40
to 60 , preferably
40 to 500. Particularly, cos(x) determines the magnitude of transmissible
load (for given
material properties). If the angle x is too small, a significant portion of
the impact force is
transmitted directly to the second layer 30 instead of the reactive layer 20,
creating high friction.
If on the other side, the angle x is too big, the majority of the force is
transmitted to the reactive
layer 20 allowing it to move relative to the second layer 30.
Alternatively, as shown in Fig. 15 the respective first layer 10 can comprises
an edge region
10b that is connected to the outer surface 30a of the second layer 30 by a
compressible
intermediary layer 4, particularly to inhibit said transfer of a radial force
FR acting on the first
layer 10 from the first layer 10 to the second layer 30. For instance, the
intermediary layer 4
can be a foam tape or other media that yields readily.
Furthermore, Fig. 9 shows an embodiment of a helmet 1 according to the present
invention,
wherein here the respective first layer 10 is configured to deform during an
impact such that a
free movement of the first layer 10 is inhibited during impact, wherein
particularly said
deformation causes a peeling of the adhesive 22 bonding the balls 2 to the
outer surface 30a
of the second layer 30 (e.g. via said substrate film 21 and its adhesive layer
23).
As shown in the sequence (A) to (D) of Fig. 9, upon an oblique impact, the
convex buckle 5 is
configured to flatten and increase in width resulting in a translational
movement of a boundary
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region 50 of the buckle causing the balls 2 to roll. This is a further form of
initiating the reactive
layer 20. As the first layer 10 deforms it initiates the reactive layer 20
because a downward
force causes a translational movement that then causes balls to roll.
Furthermore, this mechanism increases a duration at which the reactive layer
20 can operate.
As the first layer 10 deforms it can also move relative to the second layer
30. This increases
the time at which the reactive layer 20 is working. Thus, less reactive layer
20 may be needed
which means less weight. Furthermore, due to the buckle 5 exposure of the
second layer 30
can be prevented. As the first layer 10 deforms and the buckle 5 flattens, its
width increases
which helps to reduce the exposure between adjacent first layers 10.
Furthermore, Fig. 10 shows a variant of the buckle 5 of the respective first
layer 10, wherein
here the buckle 5 is configured to deform on impact to prevent geometric
locking of the
respective first layer 10 due to becoming entangled with an adjacent structure
of the helmet 1.
Therefore, the buckle 5 is adapted so as to cause an edge region 51 of the
respective first
layer 10 to lift up upon impact on the buckle 5. Due to the raised edge region
51, the risk of
butting of the edge region 51 against edges of neighboring structures is
significantly reduced.
Thus, geometric locking is prevented due to a peeling motion which differs
from the shearing
motion which may occur without buckle 5.
Particularly, the respective first layer 10 comprises at least one buckle 5
for supporting said
pivoting. Particularly The buckling 5 can have a round shape or a wedge shape
As shown in Fig. 11, a buckle 5 provided on the respective first layer 10 can
also be utilized to
pivot the helmet 1 upon impact so as to reduce a rotational motion of a head
of a person
wearing the helmet. Particularly, the buckle 5 can have a wedge shape and is
made stiff so as
to not deform on impact but initiate rotation of the helmet 1 and head about
the contact point
between the tip of the buckle and the impacting surface.
Furthermore, as indicated in Fig. 12, the buckle 5 may also be utilized to
achieve a release in
a specific direction. As the first layer stores energy e.g. by having the
buckle deformed on
impact, it may release it in a particular direction that could be beneficial
in controlling motion
to the head
Furthermore, as shown in Fig. 13, the buckle 5 can be adapted in shape so as
to achieve a
redirection of a normal force Ni of an impact acting on the first layer 10
such that the redirected
normal force Ni comprises a distance A to the center of mass C of the system
comprised of
the helmet 1 and the head of a person wearing the helmet 1 which introduces a
non-zero lever
arm A acting against rotation of the helmet upon the oblique impact on buckle
5.
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As shown in Fig. 13, without the buckle 5, the lever arm in Ni is zero as it
goes straight through
the center of mass C. With the deformable wedge-shaped buckle 5 the lever arm
in N2 is A,
which is the perpendicular distance between the center of mass C and N2.
In the embodiments described above, the respective first layer 10 is e.g.
connected to the
second layer 30 by means of adhesives. However, in addition or alternatively,
the respective
first layer 10 may also be connected to the second layer 30 by means of
connectors 6 as
shown in Fig. 8. The respective connector 6 can protrude from the inner
surface 10a of the
respective first layer 10 and extend through an associated through-opening 300
of the second
layer 30 with an end portion 60 of the connector 6, wherein the end portion 60
engaging with
the second layer 30 for connecting the first layer 10 to the second layer 20.
Particularly, the
end potion 60 can comprise a nose 61 that is configured to engage behind an
edge region 301
of the through-opening 300 to connect the first layer 10 to the second layer
30. Further, the
connector 6 is configured to break at a defined impact threshold to release
the first layer 10
from the second layer 30, and allow rolling of the balls 2 in particular.
In order to manufacture the helmet 1 as shown in Fig. 1 according to an
embodiment of the
method of the present invention, the first layers 10, second layer(s) 30 and
the intermediary
reactive layer 20 may be provide as follows.
Particularly, for providing the second layer 30, flat sheets 31 can be screen
printed on an inner
surface with a colored ink 32, a light bleed preventing base coat,
particularly a protective layer,
and a binder ink (adhesive layer) 33 designed to bond the second layer 30 to
an energy
absorbing layer 40 (e.g. out of EPS) during in-moulding. Particularly, the
flat sheets 31 are
thermoformed and trimmed (e.g. to conform to the desired shape of the helmet
1).
Similarly, for providing the first layers 10, flat sheets 11 can be screen
printed on an inner
surface with a colored ink 12, a light bleed preventing base coat, a cross-
linked polymer barrier
coat (protective layer) 13 to prevent the balls 2 from being visible from the
outside, and a
thermo-softening binder ink (adhesive layer) 14, specially formulated to bond
the first layer 10
to the balls 2. The flat sheets are thermoformed and trimmed (e.g. to conform
to the desired
shape of the helmet 1).
Furthermore, in order to provide the respective reactive layer / membrane 20,
substrate films
21 (e.g. out of PVC) are kiss cut into strips that follow the geometry of the
second layer 30 as
shown in Figs. 5 and 6.
Particularly, as shown in Fig. 5, providing the substrate films 21 comprises
kiss cutting a
laminate 7 (e.g. with a tool 3) comprising a top layer 70 and a backing 71,
the substrate films
21 being kiss cut from the top layer 70 resulting in the substrate films 21
arranged on the
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backing 71 and a surrounding portion 72 (so called negative web). This
negative web 72 is
removed and the substrate films 21 are indexed with small -2 mm dots of
adhesive 22 that are
applied to the substrate films 21 in a repeating pattern. The balls 2 are
placed in each dot of
adhesive 22. The adhesive cures/is cured, bonding the balls 2 to the substrate
films 21.
The manufactured membranes 20 are applied like a decal to the outer surface
30a of the
second layer 30, indexing it to details and edges of the surface 30a
Then both the first layers 10 and the second layer 30 are placed inside a
cavity of a mould of
an in-moulding machine. The helmet is formed via EPS backfilling, which yield
the energy
absorbing layer 40. The combination of temperature, pressure and particularly
moisture (to
better conduct heat) causes the ball binding ink 14 to bond to the balls 2 and
connect the first
layers 10 to the second layer 30 and membrane sub-assembly 20, and further
causes the EPS
binder ink 33 on the inside 30b of the second layer 30 to bond the second
layer 30 to the
energy absorbing layer 40.
Once cooled, the fully formed helmet body is removed from the in-moulding
machine, has
ancillaries added and is packaged.
Alternatively, instead of applying dots of adhesive 22, a layer of said
adhesive 22 can be
applied onto the substrate film 21. Then the negative web 72 is removed before
the adhesive
22 has set, and the balls 2 are placed in the desired pattern on the layer of
said adhesive 22.
The adhesive is then cured or allowed to cure to bond the balls 2 to the
substrate film 21.
Fig. 17 demonstrates the problem of rotational forces on a head and/or a neck
of a person
occurring upon an impact. Generally, the impact of a helmet B100 on an object,
particularly of
a helmet B100 on a street or other kinds of terrain in a bicycle crash causes
a normal
component EN of the impact force directed perpendicular from the particular
impact location of
the object. In the example shown in Fig. 17, the object is represented by an
oblique plane with
the helmet B100 impacting vertically downwards, resulting in an oblique
impact. As shown
here, the normal force is in general not aligned with a center of mass of a
head of a person
wearing the helmet B100. A non-zero displacement between the normal component
and a
center of mass B90 of an assembly of the helmet B100 and the head of a person
wearing the
helmet B100 thereby represents a first lever arm vector Li, with the product
of the normal
component and the first lever arm causing a non-zero negative torque B2 of the
head and
helmet B100. In the absence of other forces, a negative rotation of the head
with a negative
direction of rotation would be induced.
Due to friction and other resistive forces, such as a rolling resistance and
the like between
the object and an outer layer of the helmet B100, an outer surface of the
helmet B100 is
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subject to a tangential friction force, FT, as indicated in Fig. 17. A
displacement between the
center of mass B90 and the tangential friction force represents a second lever
arm vector L2
with the product of the tangential friction force and the second lever arm
vector
corresponding to a positive torque B1 to the head and helmet B100. The
positive torque B1
is directed opposite of the negative torque B2 caused by the normal component
and the first
lever arm vector.
Next to the sufficiently low friction between the outer surface of the helmet
B100 and the
head of the user required to result in negative rotation, there is a second
requirement needed
to observe negative rotation of the head and helmet B100 upon impact: The
center of mass
B90 needs to be above the normal component of the impact force in case of a
vertically
downwards impact (as the one indicated in Fig. 17), since a center of mass B90
below the
normal component of the impact force otherwise results in an additional
contribution to the
positive torque, reinforcing the positive rotation. The opposite holds in an
impact along a
vertically upward direction (as it may occur when the person wearing the
helmet collides with
an obstacle like a bridge or other objects), the center of mass B90 needs to
be below the
normal component of the impact force (not shown in Fig. 17). However, this
second
requirement is generally met due to the weight of the body of the person
wearing the helmet,
moving the center of mass B90 away from the helmet towards the body.
Ideally, the positive and negative torques Bl, B2 cancel out, such that zero
rotation occurs to
head and neck and the entire head and helmet B100 slides downwards the oblique
plane as
a whole, as sketched in the scenario of Fig. 18a.
Depending on the magnitude of the positive and negative torques B1, B2, upon
impact, the
head and helmet B100 will rotate either positively (along the direction of the
positive torque
B1 due to the friction force, scenario shown in Fig. 18c) or negatively (along
the direction of
the negative torque B2 due to the normal component, opposite to the direction
of the friction
force, scenario shown in Fig. 18b).
In both cases, the net rotation of the head upon impact is known to cause
severe injuries for
the brain and neck of the person.
Now referring to Fig. 19a, a helmet B100 according to the invention comprises
an inner layer
B11, at least one outer protective layer B12 and a motion inhibiting layer
B13, wherein upon
an impact on the at least one outer protective layer B12, the at least one
outer protective
layer B12 is configured to move relative to the inner layer B11 and wherein
the motion
inhibiting layer B13 is configured to reduce a negative rotation of the helmet
B100 resulting
upon the impact.
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Preferably, said inner layer B11 may comprise energy absorbing elements and/or
an energy
absorbing material, so as to form an energy absorbing layer.
As mentioned above, the regime of negative rotation of the helmet 3100
requires a
sufficiently low friction between the various layers, particularly a
sufficiently low friction
transmission from the at least one outer protective layer B12 to the inner
layer B11. To this
end, the helmet 9100 may additionally comprise an intermediate layer 914
configured to
lower the friction between the at least one outer protective layer 812 and the
inner layer B11.
For example, as shown in Fig. 19a, the intermediate layer B14 may comprise
rollable
elements B20 that contribute to a substantially lower friction and/or rolling
resistance by
promoting the motion between the at least one outer protective layer B12 and
the inner layer
B11 upon impact.
Said rollable elements B20 may be for example rolls, beads and the like,
particularly with a
circular diameter between 0.1 mm and 4 mm, particularly between 1 mm and 2 mm,
wherein
the circular diameter refers to a circular cross-section of the rollable
elements B20.
According to the invention, the inhibiting layer is configured to reduce a
negative rotation of
the helmet B100 resulting upon the impact. To this end, the inhibiting layer
may comprise
inhibiting elements, that in turn increase the friction between the at least
one outer protective
layer B12 and the inner layer B11, particularly in combination with the
rollable elements 820
shown in Fig. 19a. The resulting net friction between the at least one outer
protective layer
B12 and the inner layer B11 is preferably chosen such that the rotation,
particularly the
negative rotation of the helmet B100 upon impact is reduced.
According to an embodiment of the present invention, at least one of the
following may
comprise a plurality of stacked sub-layers: the inner layer B11, the at least
one outer
protective layer B12, the motion inhibiting layer B13, the intermediate layer
B14. The
aforementioned layers may alternatively or additionally also comprise multiple
mutually
connected shell segments that are arranged essentially in a respective plane
extending
along the respective layer.
As shown in the embodiment illustrated in Fig. 19a, the motion inhibiting
layer 13 or the
motion inhibiting elements B70 may be at least partially arranged within the
intermediate
layer B14 arranged between the at least one outer protective layer B12 and the
inner layer
811, which advantageously contributes to finetune an interaction of the
friction reducing
intermediate layer B14 and the friction increasing motion inhibiting layer
B13, so as to
minimize the rotation, particularly the negative rotation of the helmet 3100
upon impact.
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Still referring to Fig. 19a, together with the inner layer B11 and the at
least one outer
protective layer B12, the motion inhibiting layer B13 may delimit at least one
volume B50, so
as to confine at least a fraction of the rollable elements B20 in the at least
one volume B50.
In this embodiment, also several volumes B50, particularly with a different
number and/or
different geometries of rollable elements B20 may be used to finetune the
resulting net
friction between the various layers, particularly between the inner layer B11
and the at least
one outer protection layer upon impact.
In another embodiment of the sixth aspect of the present invention, the
rollable elements
B20, the inner layer B11, the intermediate layer B14, the at least one outer
protective layer
B12 and the motion inhibiting layer B13 comprise a lower or a larger
elasticity, wherein the
elasticity of the rollable elements B20 is lower or larger than the elasticity
of at least one of
the following: the inner layer B11, the intermediate layer B14, the at least
one outer
protective layer B12, the motion inhibiting layer B13. By finetuning the
various elasticities, a
desired net friction between the inner layer B11 and the at least one outer
protective layer
B12 can be achieved, so as to control the rotation, particularly the negative
rotation of the
helmet B100 upon impact.
For example, the lower elasticity may correspond to a young's modulus of less
than 3 GPa.
For example, a rolling resistance coefficient between the intermediate layer
B14 and the at
least one outer protective layer B12 and/or the inner layer B11 may be below
0.2.
For example, a coefficient of friction between the intermediate layer B14 or
the motion
inhibiting layer B13 and the at least one outer protective layer B12 or the
inner layer B11 may
be below 0.8.
Fig. 19b shows various motion inhibiting elements B70. For example, the motion
inhibiting
elements B70 may comprise a cylinder, a cone, a pyramid, a cuboid, a truncated
cone.
The motion inhibiting elements B70 are preferably configured to inhibit the
relative motion
between the inner layer B11 and the at least one outer protective layer B12.
The motion
inhibiting elements B70 may advantageously be used in combination with the
intermediate
layer B14, particularly with the intermediate layer B14 comprising rollable
elements B20, so
as to achieve a minimum net rotation of the helmet B100 upon impact,
particularly a
minimum negative rotation. The particular choice of geometry for the motion
inhibiting layer
B13 thereby represents a tool to control the amount of friction or rolling
resistance of
between the intermediate layer B14 and the at least one outer layer or the
inner layer B11.
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Fig. 20 presents another embodiment of the sixth aspect of the present
invention, wherein
the motion inhibiting layer B13 is integrally formed with the at least one
outer protective layer
B12. To this end, the two integrally connected layers may form an outer shell
of the helmet
B100, representing the at least one outer protective layer B12, while
additionally comprising
motion inhibiting elements B70 that inhibit the motion of the intermediate
layer B14 arranged
between the outer shell and the inner layer B11. As shown in Fig. 20, the
intermediate layer
B14 preferably comprises the rollable elements B20. Forming the motion
inhibiting layer B13
integrally with the inner layer B11 and/or the at least one outer protective
layer B12
advantageously contributes to reduce fabrication costs and -time of the helmet
B100.
However, this embodiment is not limited to an integral connection of only the
motion
inhibiting layer B13 and the at least one outer protective layer B12, but
refers to any form of
integral connection between at least two of the following: the at least one
outer protective
layer B12, the motion inhibiting layer B13, the intermediate layer B14, the
inner layer B11.
Fig. 21 shows another embodiment of the sixth aspect of the present invention,
in which the
motion inhibiting layer B13 comprises viscous a fluid or gel B60. The viscous
fluid or gel B60
may preferably be configured to introduce a shear stress to the various layers
mentioned
above, particularly a shear stress between the inner layer B11 and the at
least one outer
protective layer B12. As shown in Fig. 21, the viscous fluid or gel B60 may
preferably be
used in combination with rollable elements B20, wherein the viscous fluid or
gel B60 may be
chosen such that the interplay of the viscosity creating additional shear
stress and the
intermediate layer B14 reducing the friction results in a minimum net rotation
of the helmet
B100 upon impact, particularly a minimum negative rotation. Preferably, the
viscous fluid or
gel B60 may be arranged in a leak tight volume enclosed by at least the inner
layer B11 and
the outer protective layer B12 so as to retain the viscous fluid or gel B60.
For example, the viscous fluid or gel B60 may comprise a viscosity within
0.001 and 10 Pa s.
According to another embodiment of the sixth aspect of the invention, the
motion inhibiting
layer B13 may comprise a non-Newtonian fluid or gel B61. As such, the
viscosity of the fluid
or gel B60, B61 may depend on the shear stress, which may advantageously be
used as
another parameter to finetune the interplay of the fluid or gel B60, B61
creating additional
shear stress and the intermediate layer B14 reducing the friction, so as to
achieve a
minimum net rotation of the helmet B100 upon impact, particularly a minimum
negative
rotation.
Fig. 22 shows another embodiment of the sixth aspect of the present invention,
wherein the
motion inhibiting layer B13 comprises a flexible layer B15, particularly a
fabric or a webbing.
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The intermediate layer B14, particularly the rollable elements B20, may for
example be
embedded in the flexible layer B15. Upon impact, resulting compression- or
shearing forces
caused within the flexible layer B15 may be used to counteract the relative
motion between
the inner layer B11 and the at least one outer protective layer B12 and
particularly the
negative rotation of the helmet B100. In this way, the low friction or rolling
resistance
provided by the rollable elements B20 may be partially compensated by the
flexible layer
B15, so as to fine tune the resulting net friction between the inner layer B11
and the at least
one outer protective layer B12.
However, this embodiment is not limited to a flexible layer B15 arranged only
between the
motion inhibiting layer B13 and the intermediate layer B14, but refers to a
flexible arranged
between any of at least two of the following: the at least one outer
protective layer B12, the
motion inhibiting layer B13, the intermediate layer B14, the inner layer B11.
Fig. 23 shows another embodiment of the sixth aspect of the present invention,
wherein the
motion inhibiting comprises connectors B80 arranged between the at least one
outer
protective layer B12 and the inner layer B11.
Preferably, said connector B80 or connectors B80 may be configured to deform
and/or to
rupture simultaneously and/or sequentially upon the impact, so as to
counteract the negative
rotation of the helmet B100.
The connectors B80 may preferably be used in combination with the intermediate
layer B14,
particularly the intermediate layer B14 comprising rollable elements B20,
wherein the choice
of connectors B80 introducing friction and the intermediate layer B14 reducing
friction may
be adapted to achieve a minimum net rotation of the helmet B100 upon impact,
particularly a
minimum negative rotation.
To this end, individual connectors B80 forming the plurality of connectors B80
may comprise
individual rupture forces, wherein the individual rupture forces take on at
least two values. As
such, a plurality of individual connectors B80 with tailored deformation or
rupturing properties
may be used within the motion inhibiting layer B13 to achieve a minimum net
rotation of the
helmet B100 upon impact, particularly a minimum negative rotation.
For example, the connectors B80 may comprise or be an adhesive, a
thermoplastic, an
elastonner, a ceramic or a metal.
However, this embodiment is not limited to connectors B80 arranged only
arranged between
the at least one outer protective layer B12 and the inner layer B11, but
refers to connectors
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B80 arranged between any of at least two of the following: the at least one
outer protective
layer B12, the motion inhibiting layer B13, the intermediate layer B14, the
inner layer B11.
10
20
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