US20240164466A1

US20240164466A1 - Headgear and device for headgear

Info

Publication number: US20240164466A1
Application number: US18/282,932
Authority: US
Inventors: Peter Halldin; Xiaogai LI
Original assignee: Mips AB
Current assignee: Mips AB
Priority date: 2021-03-24
Filing date: 2022-03-22
Publication date: 2024-05-23
Also published as: WO2022200336A1; EP4312643A1; CN117677316A; CA3213405A1; GB202104112D0

Abstract

A cap for use with protective headgear, comprising: a stiff shell forming a layer that covers the internal surface area defined by the cap and formed from one or more sections; an adjustment mechanism, configured to adjust the form of the stiff shell to conform to an individual wearer's head, in a first operation mode, and configured to fix the form of the shell, in a second operation mode; and wherein the cap is configured such that the stiff shell substantially retains the fixed form during normal use and when subject to forces imparted to the cap during an impact.

Description

TECHNICAL FIELD The present invention relates to a device for protective headgear and protective headgear comprising said device.

BACKGROUND ART

Impact protection apparatuses generally aim to reduce the energy transferred to an object, such as a person to be protected, by an impact. This may be achieved by energy absorbing means, energy redirecting means, or a combination thereof. Energy absorbing means may include energy absorbing materials, such as a foam materials, or structures configured to deform elastically and/or plastically in response to an impact. Energy redirecting means may include structures configured to slide, shear or otherwise move in response to an impact.
Impact protection apparatuses include protective apparel for protecting a wearer of the apparel. Protective apparel comprising energy absorbing means and/or energy redirecting means is known. For example, such means are implemented extensively in protective headgear, such as helmets.
Examples of helmets comprising energy absorbing means and energy redirecting means include WO 2001/045526 and WO 2011/139224 (the entirety of which are herein incorporated by reference). Specifically, these helmets include at least one layer formed from an energy absorbing material and at least one layer that can move relative to the head of the wearer of the helmet under an impact.
Helmet construction is generally the same whether intended to be worn by an adult or a child. However, there are differences between adults and children, and children of different ages that might influence the effect of an impact.
In particular, the bones of the skull of children under the age of about 3 years, have not yet fully fused, but remain separate. The areas of separation are known as cranial sutures. The presence of cranial sutures in young children results in different behaviour of the skull during an impact to the head. This can be simulated, among other ways, using a finite element model of a child's skull. FIG. 9 schematically shows the development of a child's skull and closing of the sutures from new born to 3 years of age.
Simulations were performed using a validated Finite Element (FE) model of a child's head. The model consists of the skull, brain, membranes and cerebrospinal fluid and a validated FE model of a helmet. The FE simulations mimicked a drop of the head and helmet similar to the test method used in the current European Test standard for Child Bike helmets (EN1078). The helmet and head is dropped at 5.4 m/s to the crown part of the helmet.
FIG. 10 shows a heat map of the 1.5 year old and 18 year old skulls illustrating skull stress from the impact. It can be seen that the stress in the skull bone is larger for an 18 month old child compared to an 18 year old (adult). The stress is concentrated around the cranial sutures. This suggests that a young child is more susceptible to cranial fractures, and other serious injuries, as a result of the cranial sutures.
It is the aim of the present invention to at least partially addresses some of the problems discussed above.

SUMMARY OF THE INVENTION

According to a first aspect the invention there is provided a cap for use with protective headgear, comprising: a stiff shell forming a layer that covers the internal surface area defined by the cap and formed from one or more sections; an adjustment mechanism, configured to adjust the form of the stiff shell to conform to an individual wearer's head, in a first operation mode, and configured to fix the form of the shell, in a second operation mode; and wherein the cap is configured such that the stiff shell substantially retains the fixed form during normal use and when subject to forces imparted to the cap during an impact.
Optionally, the stiff shell forms an internal surface of the cap arranged to face the wearer's head in normal use, and is configured to directly contact the wearer's head.
Optionally, the cap is devoid of compressible material more inward than the stiff shell, relative to the wearer's head, in normal use.
Optionally, the adjustment mechanism is configured to be able to adjust the form of the stiff shell such that an average gap size between the stiff shell and a standard head form is no more than 2 mm, across a circumferential part of the stiff shell or the entire stiff shell. Optionally, the adjustment mechanism is configured to be able to adjust the form of the stiff shell such that the average gap size is no more than 1 mm.
Optionally, the stiffness of a system formed by the stiff shell, the adjustment mechanism, in the second mode, and a standard head form, is such that, during an impact, the average gap size between the stiff shell and the standard head form increases by no more than 2 mm, across a circumferential part of the stiff shell or the entire stiff shell. Optionally, the average gap size, during an impact, increases by no more than 1.5 mm.
Optionally, the stiffness of a system formed by the stiff shell, the adjustment mechanism, in the second mode, and a standard head form, is such that, during an impact, an average displacement between opposing surfaces of the stiff shell facing the standard head form, is no more than 2 mm, across a circumferential part of the stiff shell or the entire stiff shell.
Optionally, the average displacement, during an impact, increases by no more than 1.5 mm.
Optionally, the adjustment mechanism is configured to be able to adjust the form of the stiff shell such that a maximum gap size between the stiff shell and a standard head form is no more than 2 mm, across a circumferential part of the stiff shell or the entire stiff shell. Optionally, the adjustment mechanism is configured to be able to adjust the form of the stiff shell such that the maximum gap size is no more than 1 mm.
Optionally, the stiffness of a system formed by the stiff shell, the adjustment mechanism, in the second mode, and a standard head form, is such that, during an impact, the maximum gap size between the stiff shell and the standard head form increases by no more than 2 mm, across a circumferential part of the stiff shell or the entire stiff shell. Optionally, the maximum gap size, during an impact, increases by no more than 1.5 mm.
Optionally, the stiffness of a system formed by the stiff shell, the adjustment mechanism, in the second mode, and a standard head form, is such that, during an impact, a maximum displacement between opposing surfaces of the stiff shell facing the wearer's head, is no more than 2 mm, across a circumferential part of the stiff shell or the entire stiff shell.
Optionally, the maximum displacement, during an impact, increases by no more than 1.5 mm.
Optionally, the material forming the sections of the stiff shell has a Young's Modulus of at least 1 GPa.
Optionally, the sections forming the stiff shell are formed from polycarbonate.
Optionally, the stiff shell is at least 1 mm thick.
Optionally, a surface of the cap arranged to face away from the wearer's head, in normal use, is a low friction surface. Optionally, the low friction surface is provided by the material properties of the one or more sections forming the stiff shell.
Optionally, the stiff shell is arranged to at least cover a part of the forehead, the top of the head, a part of the back of the head and a part of each side of the head of the wearer, in normal use.
According to a second aspect of the invention, there is provided a protective headgear comprising: the cap of any preceding claim; and at least one protective layer covering the cap.
Optionally, the cap is configured to rotate relative to the at least one protective layer under an oblique impact to the protective layer.
Optionally, the headgear further comprises at least one connector configured to connect the cap and the at least one protective layer while permitting the relative rotation.
Optionally, a sliding interface is provided between the cap and the at least one protective layer.
Optionally, a shearing interface is provided between the cap and the at least one protective layer.
Optionally, the at least one protective layer comprises an energy absorbing layer.
Optionally, the at least one protective layer comprises a hard outer stiff shell.
According to a third aspect of the invention there is provided a method of protecting a wearer of protective headgear from head injury, comprising: encasing the head of the wearer in a cap, the cap comprising: a stiff shell forming a layer that covers the internal surface area defined by the cap and formed from one or more sections; an adjustment mechanism, for adjusting the form of the stiff shell, in a first operation mode, and configured to fix the form of the stiff shell, in a second operation mode; and wherein the cap is configured such that the stiff shell substantially retains the fixed form, during normal use and subject to forces imparted to the cap during an impact; the method comprising adjusting the form of the stiff shell to conform with the wearer's head and fixing said form.
Optionally, the form of the stiff shell is adjusted such that an average gap size between the stiff shell and the wearer's head, in normal use, is no more than 2 mm. Optionally, the form of the stiff shell is adjusted such that the average gap size is no more than 1 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail below, with reference to the accompanying figures, in which:

FIG. 1 schematically shows a cross-section through a first example helmet;

FIG. 2 schematically shows a cross-section through a second example helmet;

FIG. 3 schematically shows a cross-section through a third example helmet;

FIG. 4 schematically shows a cross-section through a fourth example helmet;

FIG. 5 schematically shows a cross-section through a fifth example helmet;

FIG. 6 schematically shows a cross-section through a sixth example helmet;

FIG. 7 schematically shows a cross-section through a seventh example helmet;

FIG. 8 shows an eighth example helmet;

FIG. 9 schematically shows the development of a child's skull and closing of the sutures from new born to 3 years of age;

FIG. 10 shows a heat map of the 1.5 year old and 18 year old skulls illustrating skull stress from an impact;

FIG. 11 shows a first example cap in a first configuration;

FIG. 12 shows a first example cap in a second configuration;

FIG. 13 shows a second example cap in a first configuration;

FIG. 14 shows a third example cap in a first configuration;

FIG. 15 shows a fourth example cap in a first configuration;

FIG. 16 shows a gap between cap and head form.

DETAILED DESCRIPTION

It should be noted that the Figures are schematic, the proportions of the thicknesses of the various layers, and/or of any gaps between layers, depicted in the Figures have been exaggerated for the sake of clarity and can of course be adapted according to needs and requirements.
General features of example helmets are described below with reference to FIGS. 1 to 7 .
FIGS. 1 to 7 show example helmets 1 comprising an energy absorbing layer 3. The purpose of the energy absorbing layer 3 is to absorb and dissipate energy from an impact in order to reduce the energy transmitted to the wearer of the helmet. Within the helmet 1, the energy absorbing layer may be the primary energy absorbing element. Although other elements of the helmet 1 may absorb that energy to a more limited extent, this is not their primary purpose.
The energy absorbing layer 3 may absorb energy from a radial component of an impact more efficiently than a tangential component of an impact. The term “radial” generally refers to a direction substantially toward the centre of the wearers head, e.g. substantially perpendicular to an outer surface of the helmet 1. The term “tangential” may refer to a direction substantially perpendicular to the radial direction, in a plane comprising the radial direction and the impact direction.
The energy absorbing layer may be formed from an energy absorbing material, such as a foam material. Preferable such materials include expanded polystyrene (EPS), expanded polypropylene (EPP), expanded polyurethane (EPU), vinyl nitrile foam; or strain rate sensitive foams such as those marketed under the brand-names Poron™ and D3O™.
Alternatively, or additionally, the energy absorbing layer may have a structure that provides energy absorbing characteristics. For example, the energy absorbing layer may comprise deformable elements, such as cells or finger-like projections, that deform upon impact to absorb and dissipate the energy of an impact.
As illustrated in FIG. 6 , the energy absorbing layer 3 of the helmet 1 is divided into outer and inner parts 3A, 3B.
The energy absorbing layer is not limited to one specific arrangement or material. The energy absorbing layer 3 may be provided by multiple layers having different arrangements, i.e. formed from different materials or having different structures. The energy absorbing layer 3 may be a relatively thick layer. For example, it may be thickest layer of the helmet 1.
FIGS. 1 to 7 show example helmets 1 comprising an outer layer 2. The purpose of the outer layer 2 may be to provide rigidity to the helmet. This may help spread the impact energy over a larger area of the helmet 1. The outer layer 2 may also provide protection against objects that might pierce the helmet 1. Accordingly, the outer shell may be a relatively strong and/or rigid layer, e.g. compared to an energy absorbing layer 3. The outer layer 2 may be a relatively thin layer, e.g. compared to an energy absorbing layer 3.
The outer layer 2 may be formed from a relatively strong and/or rigid material. Preferable such materials include a polymer material such as polycarbonate (PC), polyvinylchloride (PVC) or acrylonitrile butadiene styrene (ABS) for example. Advantageously, the polymer material may be fibre-reinforced, using materials such as glass-fibre, Aramid, Twaron, carbon-fibre and/or Kevlar.
As shown in FIG. 7 , one or more outer plates 7 may be mounted to the outer layer 2 of the helmet 1. The outer plates 7 may be formed from a relatively strong and/or rigid material, for example from the same types of materials as from which the outer layer 2 may be formed. The selection of material used to form the outer plates 7 may be the same as, or different from, the material used to form the outer layer 2.
In some example helmets, the outer layer 2 and/or the energy absorbing layer 3 may be adjustable in size in order to provide a customised fit. For example the outer layer 2 may be provided in separate front and back parts. The relative position of the front and back parts may be adjusted to change the size of the outer layer 2. In order to avoid gaps in the outer layer 2, the front and back parts may overlap. The energy absorbing layer 3 may also be provided in separate front and back parts. These may be arranged such that the relative position of the front and back parts may be adjusted to change the size of the energy absorbing layer 3. In order to avoid gaps in the energy absorbing layer 3, the front and back parts may overlap.
FIGS. 1 to 4 shows example helmets 1 comprising an interface layer 4. Although not shown in FIGS. 5 to 7 , these example helmets may also comprise an interface layer 4. The purpose of interface layer 4 may be to provide an interface between the helmet and the wearer. In some arrangements, this may improve the comfort of the wearer. The interface layer 4 may be provided to mount the helmet on the head of a wearer. The interface layer 4 may be provided as a single part or in multiple sections.
The interface layer 4 may be configured to at least partially conform to the head of the wearer. For example, the interface layer 4 may be elasticated and/or may comprise an adjustment mechanism for adjusting the size of the interface layer 4. In an arrangement, the interface layer may engage with the top of a wearer's head. Alternatively or additionally, the interface layer 4 may comprise an adjustable band configured to encircle the wearer's head.
The interface layer 4 may comprise comfort padding 4A. Multiple sections of comfort padding 4A may be provided. The comfort padding 4A may be provided on a substrate 4B for mounting the comfort padding to the rest of the helmet 1.
The purpose of the comfort padding 4A is to improve comfort of wearing the helmet and/or to provide a better fit. The comfort padding may be formed from a relatively soft material, e.g. compared to the energy absorbing layer 3 and/or the outer layer 2. The comfort padding 4A may be formed from a foam material. However, the foam material may be of lower density and/or thinner than foam materials used for the energy absorbing layer 3. Accordingly, the comfort padding 4A will not absorb a meaningful amount of energy during an impact, i.e. for the purposes of reducing the harm to the wearer of the helmet. Comfort padding is well recognised in the art as being distinct from energy absorbing layers, even if they may be constructed from somewhat similar materials.
The interface layer 4, and/or comfort padding 4A that may be part of it, may be removable. This may enable the interface layer 4 and/or comfort passing 4A to be cleaned and/or may enable the provision of an interface layer and/or comfort padding 4A that is configured to fit a specific wearer.
Straps, e.g. chin straps, may be provided to secure the helmet 1 to the head of the wearer.
The helmets of FIGS. 1 to 4 are configured such that the interface layer 4 is able to move, for example slide, in a tangential direction relative to the energy absorbing layer 3 in response to an impact. As shown in FIGS. 1 to 4 , the helmet may also comprise connectors 5 between the energy absorbing layer 3 and the interface layer 4 that allow relative movement between the energy absorbing layer 3 and the interface layer 4 while connecting the elements of the helmet together.
The helmet of FIG. 5 is configured such that the outer layer 2 is able to move, for example slide, in a tangential direction relative to the energy absorbing layer 3 in response to an impact. As shown in FIG. 5 , the helmet 1 may also comprise connectors 5 between the energy absorbing layer 3 and the outer layer 2 that allow relative movement between the energy absorbing layer 3 and the outer layer 2 while connecting the elements of the helmet together.
The helmet of FIG. 6 is configured such that the outer part 3A of the energy absorbing layer 3 is able to move, for example slide, in a tangential direction relative to the inner part 3B of the energy absorbing layer 3 in response to an impact. As shown in FIG. 6 , the helmet 1 may also comprise connectors 5 between the outer part 3A of the energy absorbing layer 3 and the inner part 3B of the energy absorbing layer 3, that allow relative movement between the outer part 3A of the energy absorbing layer 3 and the inner part 3B of the energy absorbing layer 3, while connecting the elements of the helmet together.
The helmet of FIG. 7 is configured such that the outer plates 8 are able to move, for example slide, in a tangential direction relative to the outer layer 2 in response to an impact. As shown in FIG. 7 , the helmet may also comprise connectors 5 between the outer plates 8 and the outer layer 2 that allow relative movement between the outer plates 7 and the outer layer 2, while connecting the elements of the helmet together.
The purpose of helmet layers that move or slide relative to each other may be to redirect energy of an impact that would otherwise be transferred to the head the wearer. This may improve the protection afforded to the wearer against a tangential component of the impact energy. A tangential component of the impact energy would normally result in rotational acceleration of the head of the wearer. It is well know that such rotation can cause brain injury. It has been shown that helmets with layers that move relative to each other can reduce the rotational acceleration of the head of the wearer. A typical reduction may be roughly 25% but reductions as high as 90% may be possible in some instances.
Preferably, relative movement between helmet layers results in a total shift amount of at least 0.5 cm between an outermost helmet layer and an inner most helmet layer, more preferably at least 1 cm, more preferably still at least 1.5 cm. Preferably the relative movement can occur in any direction, e.g. in a circumferential direction around the helmet, left to right, front to back and any direction in between.
Regardless of how helmet layers are configured to move relative to each other, it is preferable that the relative movement, such as sliding, is able to occur under forces typical of an impact for which the helmet is designed (for example an impact that is expected to be survivable for the wearer). Such forces are significantly higher than forces that a helmet may be subject to during normal use. Impact forces tend to compress layers of the helmet together, increasing the reaction force between components and thus increasing frictional forces. Where helmets are configured to have layers sliding relative to each other the interface between them may need to be configured to enable sliding even under the effect of the high reaction forces experienced between them under an impact.
As shown in FIGS. 1 to 7 , a sliding interface may be provided between the layers of the helmet 1 that are configured to slide relative to each other. At the sliding interface, surfaces slide against each other to enable relative sliding between the layers of the helmet 1. The sliding interface may be a low friction interface. Accordingly, friction reducing means may be provided at the sliding interface. Example sliding interfaces are described further below, in relation to each of the example helmets 1 shown in FIGS. 1 to 7 .
The friction reducing means may be a low friction material or lubricating material. These may be provided as a continuous layer, or multiple discrete patches, or portions of material, for example. Possible low friction materials for the friction reducing means include waxy polymers such as PC, PTFE, ABS, PVC, Nylon, PFA, EEP, PE and UHMWPE, Teflon™, a woven fabric such as Tamarack™, a non-woven fabric, such a felt.
Such low friction materials may have a thickness of roughly 0.1-5 mm, but other thicknesses can also be used, depending on the material selected and the performance desired. Possible lubricating materials include oils, polymers, microspheres, or powders. Combinations of the above may be used.
In one example the low friction material or lubricating material may be a polysiloxane-containing material. In particular the material may comprise (i) an organic polymer, a polysiloxane and a surfactant; (i) an organic polymer and a copolymer based on a polysiloxane and an organic polymer; or (iii) a non-elastomeric cross-linked polymer obtained or obtainable by subjecting a polysiloxane and an organic polymer to a cross-linking reaction. Preferred options for such materials are described in WO2017148958.
In one example the low friction material or lubricating material may comprise a mixture of (i) an olefin polymer, (ii) a lubricant, and optionally one or more further agents. Preferred options for such materials are described in WO2020115063.
In one example the low friction material or lubricating material may comprise an ultra high molecular weight (UHMW) polymer having a density of ≤960 kg/m³, which UHMW polymer is preferably an olefin polymer. Preferred options for such materials are described in WO2020115063.
In one example the low friction material or lubricating material may comprise a polyketone. Preferred options for such materials are described in WO 2020/260185.
In some arrangements, it may be desirable to configure the low friction interface such that the static and/or dynamic coefficient of friction between materials forming sliding surfaces at the sliding interface is between 0.001 and 0.3 and/or below 0.15. The coefficient of friction can be tested by standard means, such as standard test method ASTM D1894.
The friction reducing means may be provided on or be an integral part of one or both of the layers of the helmet 1 that are configured to slide relative to each other. In some examples, helmet layers may have a dual function, including functioning as a friction reducing means. Alternatively, or additionally, the friction reducing means may be a separate from the layers of the helmet 1 that are configured to slide relative to each other, but provided between the layers.
Instead of the sliding interface, in some examples, a shearing interface may be provided between the layers of the helmet 1 that are configured to move relative to each other. At the shearing interface, a shearing layer shears to enable relative movement between the layers of the helmet 1. The shearing layer may comprise a gel or liquid, which may be retained within a flexible envelope. Alternatively, the shearing layer may comprise two opposing layers connected by deformable elements that deform to enable shearing between the two opposing layers.
A single shearing layer may be provided that substantially fills the volume between two layers of a helmet. Alternatively, one or more shearing layers may be provided that fill only a portion of the volume between two layers of a helmet, e.g. leaving substantial space around the shearing layers. The space may comprise a sliding interface, as described above. As such, helmets may have a combination of shearing and sliding interfaces. Such shearing layers may act as connectors 5, which are described further below.
FIGS. 1 to 7 schematically show connectors 5 . The connectors 5 are configured to connect two layers of the helmet while enabling relative movement, e.g. sliding or shearing, between the layers. Different numbers of connectors 5 may be provided than as shown in FIGS. 1 to 7 . The connectors 5 may be located at different positions than as shown in FIGS. 1 to 7 , for example at a peripheral edge of the helmet 1 instead of a central portion.
Typically, a connector 5 comprises first and second attachment parts respectively configured to attach to first and second parts of the helmet and a deformable part between the first and second attachment parts that enables the first and second attachment parts to move relative to each other to enable movement between the first and second parts of the helmet of the helmet. Connectors 5 may absorb some impact energy by deforming.
The specific arrangements of each of the example helmets shown in FIGS. 1 to 7 are described below.
FIG. 1 shows a helmet comprising an outer layer 2, an energy absorbing layer 3 and an interface layer 4. The interface layer 4 is provided as a single layer and comprises comfort padding.
The helmet of FIG. 1 is configured such that the interface layer 4 is able to slide relative to the energy absorbing layer 3 in response to an impact. A sliding interface is provided between the interface layer 4 and the energy absorbing layer 3.
A sliding layer 7 is provided on a surface of the energy absorbing layer 3 facing the sliding interface. The sliding layer 7 may be moulded to the energy absorbing layer 3 or otherwise attached thereto. The sliding layer 7 may be formed from a relatively hard material, e.g.
relative to the energy absorbing layer 3. The sliding layer 7 is configured to provide friction reducing means to reduce the friction at the sliding interface. This may be achieved by forming the sliding layer 7 from a low friction material, such as PC, PTFE, ABS, PVC, Nylon, PFA, EEP, PE and UHMWPE. Alternatively, or additionally, this may be achieved by applying a low friction coating to the sliding layer 7, and/or applying a lubricant to the sliding layer 7.
Alternatively or additionally, friction reducing means, to reduce the friction at the sliding interface, may be provided by forming the energy absorbing layer 3 from a low friction material, by applying a low friction coating to the energy absorbing layer 3 and/or applying a lubricant to the energy absorbing layer 3.
The helmet 1 shown in FIG. 1 also comprises connectors 5 attached to the interface layer 4. The connectors are also connected to the sliding layer 7 to allow relative sliding between the energy absorbing layer 3 and the interface layer 4. Alternatively, or additionally, one or more of the connectors 5 may be connected to another part of the remainder of the helmet 1, such as the energy absorbing layer 3 or the outer shell 2. The connectors 5 may also be connected to two or more parts of the remainder of the helmet 1.
It should be understood that such an arrangement of the energy absorbing layer 3 and the interface layer 4 may be added to any helmet described herein.
FIG. 2 shows a helmet comprising an outer layer 2, an energy absorbing layer 3 and an interface layer 4. The interface layer 4 is provided as a plurality of independent sections each comprising comfort padding.
The helmet of FIG. 2 is configured such that the section of the interface layer 4 are able to slide relative to the energy absorbing layer 3 in response to an impact. A sliding interface is provided between the sections of the interface layer 4 and the energy absorbing layer 3.
An sliding layer 7 is provided on a surface of the energy absorbing layer 3 facing the sliding interface. The sliding layer 7 may be moulded to the energy absorbing layer 3 or otherwise attached thereto. The sliding layer 7 may be formed from a relatively hard material, e.g. relative to the energy absorbing layer 3. The sliding layer 7 is configured to provide friction reducing means to reduce the friction at the sliding interface. This may be achieved by forming the sliding layer 7 from a low friction material, such as PC, PTFE, ABS, PVC, Nylon, PFA, EEP, PE and UHMWPE. Alternatively, or additionally, this may be achieved by applying a low friction coating to the sliding layer 7, and/or applying a lubricant to the sliding layer 7.
Alternatively or additionally, friction reducing means, to reduce the friction at the sliding interface, may be provided by forming the energy absorbing layer 3 from a low friction material, by applying a low friction coating to the energy absorbing layer 3 and/or applying a lubricant to the energy absorbing layer 3.
The helmet 1 shown in FIG. 2 also comprises connectors 5 attached to each independent section of the interface layer 4. The connectors 5 are also attached to the sliding layer 7 to allow relative sliding between the energy absorbing layer 3 and the sections of the interface layer 4. Alternatively or additionally, one or more of the connectors 5 may be connected to another part of the remainder of the helmet 1, such as the energy absorbing layer 3 or the outer shell 2. The connectors 5 may also be connected to two or more parts of the remainder of the helmet 1.
It should be understood that such an arrangement of the energy absorbing layer 3 and the interface layer 4 may be added to any helmet described herein.
FIG. 3 shows a helmet comprising an outer layer 2, an energy absorbing layer 3 and an interface layer 4. The interface layer 4 is provided as a single layer and comprises comfort padding 4A attached to a substrate 4B. The substrate 4B may be bonded to the outer side of the comfort padding 4A. Such bonding could be through any means, such as by adhesive or by high frequency welding or stitching.
The helmet of FIG. 3 is configured such that the interface layer 4 is able to slide relative to the energy absorbing layer 3 in response to an impact. A sliding interface is provided between the interface layer 4 and the energy absorbing layer 3.
The substrate 4B of the interface layer 4 faces the sliding interface. The substrate 4B may be formed from a relatively hard material, e.g. relative to the energy absorbing layer 3 and/or the comfort padding 4A. The substrate 4B is configured to provide friction reducing means to reduce the friction at the sliding interface. This may be achieved by forming the substrate 4B from a low friction material, such as PC, PTFE, ABS, PVC, Nylon, PFA, EEP, PE and UHMWPE. Alternatively, or additionally, this may be achieved by applying a low friction coating to the substrate 4B, and/or applying a lubricant to the substrate 4B. In alternative example, the substrate 4B may be formed from a fabric material, optionally coated with a low friction material.
Alternatively or additionally, friction reducing means, to reduce the friction at the sliding interface, may be provided by forming the energy absorbing layer 3 from a low friction material, by applying a low friction coating to the energy absorbing layer 3 and/or applying a lubricant to the energy absorbing layer 3.
The helmet 1 shown in FIG. 3 also comprises connectors 5 attached to the interface layer 4. The connectors are also connected to the energy absorbing layer to allow relative sliding between the energy absorbing layer 3 and the interface layer 4. Alternatively, or additionally, one or more of the connectors 5 may be connected to another part of the remainder of the helmet 1, such as the outer shell 2. The connectors 5 may also be connected to two or more parts of the remainder of the helmet 1
It should be understood that such an arrangement of the energy absorbing layer 3 and the interface layer 4 may be added to any helmet described herein.
FIG. 4 shows a helmet comprising an outer layer 2, an energy absorbing layer 3 and an interface layer 4. The interface layer 4 is provided as a plurality of independent sections each comprising comfort padding 4A attached to a substrate 4B. The substrate 4B may be bonded to the outer side of the comfort padding 4A. Such bonding could be through any means, such as by adhesive or by high frequency welding or stitching.
The helmet of FIG. 4 is configured such that the interface layer 4 is able to slide relative to the energy absorbing layer 3 in response to an impact. A sliding interface is provided between the interface layer 4 and the energy absorbing layer 3.
The substrate 4B of the sections of the interface layer 4 faces the sliding interface. The substrate 4B may be formed from a relatively hard material, e.g. relative to the energy absorbing layer 3 and/or the comfort padding 4A. The substrate 4B is configured to provide friction reducing means to reduce the friction at the sliding interface. This may be achieved by forming the substrate 4B from a low friction material, such as PC, PTFE, ABS, PVC, Nylon, PFA, EEP, PE and UHMWPE. Alternatively, or additionally, this may be achieved by applying a low friction coating to the substrate 4B, and/or applying a lubricant to the substrate 4B. In alternative example, the substrate 4B may be formed from a fabric material, optionally coated with a low friction material.
Alternatively or additionally, friction reducing means, to reduce the friction at the sliding interface, may be provided by forming the energy absorbing layer 3 from a low friction material, by applying a low friction coating to the energy absorbing layer 3 and/or applying a lubricant to the energy absorbing layer 3.
The helmet 1 shown in FIG. 4 also comprises connectors 5 attached to the sections of the interface layer 4. The connectors 5 are also connected to the energy absorbing layer 3 to allow relative sliding between the energy absorbing layer 3 and the interface layer 4. Alternatively, or additionally, one or more of the connectors 5 may be connected to another part of the remainder of the helmet 1, such as the outer shell 2. The connectors 5 may also be connected to two or more parts of the remainder of the helmet 1
It should be understood that such an arrangement of the energy absorbing layer 3 and the interface layer 4 may be added to any helmet described herein.
FIG. 5 shows a helmet comprising an outer layer 2 and an energy absorbing layer 3. Although not shown, an interface layer may additionally be provided.
The helmet of FIG. 5 is configured such that the outer layer 2 is able to slide relative to the energy absorbing layer 3 in response to an impact. A sliding interface may be provided between the outer layer 2 and the energy absorbing layer 3
Although not shown, an additional layer may be provided on a surface of the energy absorbing layer 3 facing the sliding interface. The additional layer may be moulded to the energy absorbing layer 3 or otherwise attached thereto. The additional layer may be formed from a relatively hard material, e.g. relative to the energy absorbing layer 3. The additional layer may be configured to provide friction reducing means to reduce the friction at the sliding interface. This may be achieved by forming the additional layer from a low friction material, such as PC, PTFE, ABS, PVC, Nylon, PFA, EEP, PE and UHMWPE. Alternatively, or additionally, this may be achieved by applying a low friction coating to the additional layer and/or applying a lubricant to the additional layer.
Alternatively or additionally, friction reducing means, to reduce the friction at the sliding interface, may be provided by forming the outer layer 2 from a low friction material, providing an additional low friction layer on a surface of the outer layer 2 facing the sliding interface, by applying a low friction coating to the outer layer 2 and/or applying a lubricant to the outer layer 2.
The helmet 1 shown in FIG. 5 also comprises connectors 5 attached to the outer layer 2. The connectors 5 are also attached to the energy absorbing layer 3 (or additional layer) to allow relative sliding between the energy absorbing layer 3 and the sections of the interface layer 4. Alternatively or additionally, one or more of the connectors 5 may be connected to another part of the remainder of the helmet 1, such as an interface layer. The connectors 5 may also be connected to two or more parts of the remainder of the helmet 1.
It should be understood that such an arrangement of the outer shell 2 and the energy absorbing layer 3 may be added to any helmet described herein.
FIG. 6 shows a helmet comprising an outer layer 2 and an energy absorbing layer 3. As illustrated, the energy absorbing layer 3 of the helmet shown in FIG. 6 is divided into outer and inner parts 3A, 3B. Although not shown, an interface layer may additionally be provided.
The helmet of FIG. 6 is configured such that the outer part 3A of the energy absorbing layer 3 is able to slide relative to the inner part 3B of the energy absorbing layer 3 in response to an impact. A sliding interface may be provided between the outer part 3A of the energy absorbing layer 3 and the inner part 3B of the energy absorbing layer 3.
Although not shown, an additional layer may be provided on a surface of one or both of the inner and outer parts 3A, 3B of the energy absorbing layer 3 facing the sliding interface. The additional layer may be moulded to the inner or outer parts 3A, 3B of the energy absorbing layer 3 or otherwise attached thereto. The additional layer may be formed from a relatively hard material, e.g. relative to the energy absorbing layer 3. The additional layer may be configured to provide friction reducing means to reduce the friction at the sliding interface. This may be achieved by forming the additional layer from a low friction material, such as PC, PTFE, ABS, PVC, Nylon, PFA, EEP, PE and UHMWPE. Alternatively, or additionally, this may be achieved by applying a low friction coating to the additional layer and/or applying a lubricant to the additional layer.
Alternatively or additionally, friction reducing means, to reduce the friction at the sliding interface, may be provided by forming one or both of the inner and outer parts 3A, 3B of the energy absorbing layer 3 from a low friction material, providing an additional low friction layer on a surface of the inner and outer parts 3A, 3B of the energy absorbing layer 3 facing the sliding interface, by applying a low friction coating to the inner and outer parts 3A, 3B of the energy absorbing layer 3 and/or applying a lubricant to the inner and outer parts 3A, 3B of the energy absorbing layer 3.
The helmet 1 shown in FIG. 6 also comprises connectors 5 attached to the outer layer 2. The connectors 5 are also attached to the energy absorbing layer 3 (or additional layer) to allow relative sliding between the energy absorbing layer 3 and the sections of the interface layer 4. Alternatively or additionally, one or more of the connectors 5 may be connected to another part of the remainder of the helmet 1, such as an interface layer. The connectors 5 may also be connected to two or more parts of the remainder of the helmet 1.
It should be understood that such an arrangement of inner and outer parts 3A 3B of the energy absorbing layer 3 may be added to any helmet described herein.
FIG. 7 shows a helmet comprising an outer layer 2 and an energy absorbing layer 3. As shown in FIG. 7 , one or more outer plates 7 are mounted to the outer layer 2 of the helmet 1. The outer plates 7 may be formed from a relatively strong and/or rigid material, for example from the same types of materials as from which the outer layer 2 may be formed. Although not shown, an interface layer may additionally be provided.
The helmet of FIG. 7 is configured such that the outer plates 8 are able to slide relative to the outer layer 2 in response to an impact. A sliding interface may be provided between the outer plates 8 and the outer layer 2.
Friction reducing means, to reduce the friction at the sliding interface, may be provided by forming the outer layer 2 and/or the outer plates 8 from a low friction material, providing an additional low friction layer on a surface of the outer layer 2 and/or the outer plates 8 facing the sliding interface, by applying a low friction coating to the outer layer 2 and/or the outer plates 8, and/or applying a lubricant to the outer layer 2 and/or the outer plates 8.
The helmet 1 shown in FIG. 7 also comprises connectors 5 attached to the outer plates 7 The connectors 5 are also attached to the outer layer 2 to allow relative sliding between the plates 7 and the outer layer 2. Alternatively or additionally, one or more of the connectors 5 may be connected to another part of the remainder of the helmet 1, such as the energy absorbing layer 3. The connectors 5 may also be connected to two or more parts of the remainder of the helmet 1.
In such an arrangement, in the event of an impact on the helmet 1, it can be expected that the impact would be incident on one or a limited number of the outer plates 17. Therefore, by configuring the helmet such that the one or more outer plates 7 can move relative to the outer layer 2 and any outer plates 7 that have not been subject to an impact, the surface receiving the impact, namely one or a limited number of outer plates 7, can move relative to the remainder of the helmet 1. In the case of an impact, this may reduce the rotational acceleration of the head of a wearer.
It should be understood that such an arrangement of outer plates 7 may be added to any helmet described herein, namely an arrangement having a sliding interface between at least two of the layers of the helmet 1.
Some helmets, such as those shown in FIGS. 1 to 6 , are configured to cover a top portion of the head and the above described helmet structures are appropriately located in the helmet to cover a top portion of the head. For example, a helmet may be provided to substantially cover the forehead, top of the head, back of the head and/or temples of the wearer. The helmet may substantially cover the cranium of the wearer.
Some helmets may be configured to cover other parts of the head, alternatively or additionally to a top portion. For example, helmets such as the helmet shown in FIG. 8 may cover the cheeks and/or chin of the wearer. Such helmets may be configured to substantially cover the jaw of the wearer. Helmets of the type shown in FIG. 8 , are often referred to as full-face helmets. As shown in FIG. 8 , cheek pads 30 may be provided on either side of the helmet 1 (i.e. left and right sides). The cheek pads 30 may be arranged within an outer shell 2 of the helmet 1 to protect the side of the face of the wearer from an impact.
The cheek pads 30 may have the same layered structure as the example helmets described above. For example, the cheek pads 30 may comprise one or more energy absorbing layers as described above, and/or an interface layer as described above, and/or layers that move relative to each other as described above, optionally, layers may be connected by connectors as described above. Alternatively or additionally, the cheek pads 30 themselves may be configured to move relative to the outer shell 2 and, optionally be connected to the outer shell by connectors as described above.
Helmets as described above may be used in various activities. For example, protective helmets may be used in ice hockey, cycling, skiing, snow-boarding, skating, skateboarding, equestrian activities, American football, baseball, rugby, soccer, cricket, lacrosse, climbing, golf, airsoft, and roller derby.
Examples of injuries that may be prevented or mitigated by the helmets described above include Mild Traumatic Brain Injuries (MTBI) such as concussion, and Severe Traumatic Brain Injuries (STBI) such as subdural haematomas (SDH), bleeding as a consequence of blood vessels rapturing, and diffuse axonal injuries (DAI), which can be summarized as nerve fibres being over stretched as a consequence of high shear deformations in the brain tissue.
Depending on the characteristics of the rotational component of an impact, such as the duration, amplitude and rate of increase, either concussion, SDH, DAI or a combination of these injuries can be suffered. Generally speaking, SDH occur in the case of accelerations of short duration and great amplitude, while DAI occur in the case of longer and more widespread acceleration loads.
FIG. 11 shows a first example of a device according to the present disclosure for use with protective headgear. In particular, the device may be used with any one of the helmets described above, or variations thereof.
The device shown in FIG. 11 is a cap 40 comprising a stiff shell 41. As shown, the stiff shell 41 may be a main component of the cap 40. For example, it is common for headgear to have a layered structure and the stiff shell 41 may be the only layer within the cap 40. However, that may not be the case in other examples. In general, the stiff shell 41 forms a layer that covers the internal surface area defined by the cap 40. The stiff shell 41 may form an internal surface of the cap 40 arranged to face the wearer's head in normal use, and may be configured to directly contact the wearer's head. Additional layers may be provided externally to the stiff shell 41, i.e. further from the wearer's head.
The stiff shell 41 covers at least a portion of the skull of the wearer. The stiff shell 41 may cover at least the circumference of the head of a wearer. The stiff shell 41 may cover a part of the forehead, the top of the head, a part of the back of the head and a part of each side of the head of the wearer. Accordingly, the stiff shell 41, may have a substantially hemispheric shape.
The stiff shell 41 may be substantially inelastic in tension. The stiff shell 41 may be rigid or may be bendable.
The cap 40 may be of a size suitable to be worn by a child under 5 years of age, preferably under 4 years of age. The cap may be of a size suitable to be worn by a child with a head circumference of less than 53 cm, preferably less than 52 cm, preferably less than 51 cm. The cap 40 may be configured to fit a standard head form with such a head circumference.
The standard head form may be the European Standard EN 960:2006 head form of a suitable size.
A shown in FIG. 11 , The cap 40 further comprises an adjustment mechanism 50. The adjustment mechanism 50 is configured to adjust the form of the stiff shell 41 to conform to an individual wearer's head, in a first operation mode. The adjustment mechanism 50 is configured to fix the form of the shell 41, in a second operation mode.
As shown in FIG. 11 , the stiff shell 41 may be formed as one section. To enable adjustability, the stiff shell 41 may comprise an opening 42. The opening 42 may extend from an edge to a crown portion of the stiff shell 41. The opening 42 may be configured such that portions of the stiff shell 41 on opposite sides of the opening 42 area able to move relative to each other to close or widen the opening 42. Thus the form of the stiff shell 41 may be adjusted to fit a wearer.
As shown in FIG. 11 , the adjustment mechanism 50 may comprise a strap 51. The strap 51 may be connected on one side of the opening to the stiff shell 41, e.g. by a fixed connector 52, and configured to span the opening 42. The strap 51 may be connected to the stiff shell 41 at the other side of the opening 42 by an adjustable connector 53. The adjustable connector 53 may connect to the strap 51 at a plurality of locations (discretely or continuously) along the length of the strap 41. The adjustable connector 53 may be operable in two modes, namely a first mode where in the connection to the strap 51 can be adjusted and a second mode that fixes the connection.
In the example shown in FIG. 11 , the strap 41 may comprise one or more slots configured to engage with a protrusion in the adjustable connector 53. The protrusion may be selectively engaged with the slots to allow adjustment or to fix the connection. This arrangement may be similar to that of a zip-tie.
FIG. 12 shows the cap 40 of FIG. 11 adjusted to fit a smaller head circumference.
FIG. 13 shows an example cap 40 with an alternative adjustment mechanism 50. As shown, the adjustment mechanism may comprise a strap 54 that is integral with the stiff shell 41 on one side of the opening 42. The strap may comprise a slot 55 along its length. This slot may be configured to engage with an adjustable connector 56. The slot 55 may slide over the adjustable connector 56, which may selectively fix the strap 54 in position.
FIG. 14 shows an example cap 40 with a further alternative adjustment mechanism 50. As shown, the adjustment mechanism may comprise a wire 57 that is threaded (e.g. a plurality of times) across the opening 42, via retainers 58. The wire 57 is connected to an adjuster 59, which can be adjusted to tighten or loosen the wire to close or widen the opening 42.
FIG. 15 shows an example cap 40 in which the stiff shell 41 is provided in a plurality of sections, with openings provided between 42 each section. As shown, the cap 40 may comprise an adjustment mechanism similar to that shown in FIG. 14 . The adjustment mechanism may comprise a wire 57 that is threaded across the openings 42, via retainers 58. The wire 57 is connected to an adjuster 59, which can be adjusted to tighten or loosen the wire to close or widen the opening 42.
In each of the above examples, the cap 40 is configured such that the stiff shell 41 substantially retains the fixed form (during normal use) and when subject to forces imparted to the cap 40 during an impact. If the cap 40 forms part of an item of protective headgear, this may be an impact to the headgear.
In this context, fixing the form may mean that that the system formed by the stiff shell 41 and the adjustment mechanism 50, behaves as though the system was not adjustable, for example as though the adjustment mechanism 50 was replaced by sections of stiff shell homogenous with the rest of the stiff shell.
In each of the above examples, the adjustment mechanism 50 may be configured to be able to adjust the form of the stiff shell 41 such that an average gap size between the stiff shell 41 and a standard head form is no more than 2 mm, across a circumferential part of the stiff shell 41, or across the entire stiff shell 41. This is more easily measurable for a standard head form than a real head, but translates to the same for a real head. FIG. 16 shows the gap 70 between the stiff shell 41 and an outer surface of a head form 60. The adjustment mechanism 50 may be configured to be able to adjust the form of the stiff shell 41 such that the average gap size is no more than 1 mm.
The adjustment mechanism 50 may be configured to be able to adjust the form of the stiff shell 41 such that a maximum gap size between the stiff shell 41 and a standard head form 60 is no more than 2 mm, across a circumferential part of the stiff shell 41, or across the entire stiff shell 41. The adjustment mechanism 50 may be configured to be able to adjust the form of the stiff shell 41 such that the maximum gap size is no more than 1.5 mm.
The gap size may be calculated based on a direction normal to a surface of the head form at a given location. Average gap size may be calculated as the mean gap size for a plurality of locations around the head form.
Simulations have shown that providing a small gap 70 may reduce the stress to the skull resulting from an impact to a child's head.
In each of the above examples, the stiffness of the system formed by the stiff shell 41 and the adjustment mechanism 50, in the second mode, may be such that, during an impact, the average gap size between the stiff shell 41 and the standard head form increases by no more than 2 mm, across the circumferential part of the stiff shell 41, or across the entire stiff shell 41. The configuration may be such that the average gap size, during an impact, increases by no more than 1.5 mm.
The stiffness of the system formed by the stiff shell 41 and the adjustment mechanism 50, in the second mode, may be such that, during an impact, an average displacement between opposing surfaces of the stiff shell 41 facing the standard head form, is no more than 2 mm, across the circumferential part of the stiff shell 41, or across the entire stiff shell 41. The configuration may be such that the average displacement, during an impact, increases by no more than 1.5 mm.
The stiffness of the system formed by the stiff shell 41 and the adjustment mechanism 50, in the second mode, may be such that, during an impact, the maximum gap size between the stiff shell 41 and the standard head form increases by no more than 2 mm, across the circumferential part of the stiff shell 41, or across the entire stiff shell 41. The configuration may be such that the maximum gap size, during an impact, increases by no more than 1.5 mm.
The stiffness of the system formed by the stiff shell 41 and the adjustment mechanism 50, in the second mode, may be such that, during an impact, a maximum displacement between opposing surfaces of the stiff shell 41 facing the wearer's head, is no more than 2 mm, across the circumferential part of the stiff shell 41, or across the entire stiff shell 41. The configuration may be such that the maximum displacement, during an impact, increases by no more than 1.5 mm.
The impact may be that experienced during a standard drop test, e.g. shock absorption test according to European standard EN1080, which drops a standard head form onto a flat anvil from 1.5 m to have an impact velocity of 5.4 m/s.
Simulations have shown that skull stress can be reduced with a system having a stiffness that ensures the maintenance of a small gap size between the stiff shell 41 and the wearer.
The material forming the sections of the stiff shell 41 has a Young's Modulus of at least 1 GPa, preferably at least 2 GPa.
The material forming the stiff shell 41 may be Polycarbonate. The material may have a thickness of more than 0.5 mm and no thicker than 3 mm, preferably between 1 mm and 2 mm, e.g. 1.5 mm. The strap 51 may be formed from the same material or a different material.
The stiffness of the system formed by the stiff shell 41 and the adjustment mechanism 50, in the second mode, may at least equal to the stiffness of a complete, nonadjustable stiff shell formed from a material having Young's Modulus of at least 1 GPa, preferably at least 2 GPa.
In some examples, the stiffness of the stiff shell 41 may be different in different potions of the stiff shell.
It is common for headgear to comprise soft, comfort padding at an interface with the head to make the headgear more comfortable to wear. However, the cap 40 may be devoid of compressible material, such as comfort padding, more inward than the stiff shell 41, relative to the wearer's head, particularly around the circumference portion of the stiff shell 41, for example.
As described above, the cap 40 may form part of a protective headgear. For example, the cap 40 may be an additional layer to the example helmets described above or replace an interface layer 4 of the helmet. For example the cap 40 may be used as an interface layer as described above in relation to the example helmets.
According to some examples, the cap 40 may be configured to rotate relative to the at least one protective layer (e.g. an energy absorbing layer and/or a hard outer shell) under an oblique impact to the protective layer. The headgear may further comprise at least one connector configured to connect the cap 40 and the at least one protective layer while permitting the relative rotation.
A sliding interface may be provided between the cap 40 and the at least one protective layer. A surface of the cap 40 arranged to face away from the wearer's head, in normal use, may be a low friction surface. The low friction surface may be provided by the material properties of the one or more sections forming the stiff shell 41.
Alternatively, a shearing interface may alternatively be provided between the cap 40 and the at least one protective layer.
Variations of the above described examples are possible in light of the above teachings. It is to be understood that the invention may be practiced otherwise and specifically described herein without departing from the spirit and scope of the invention.

Claims

1. A cap for use with protective headgear, comprising:

a stiff shell forming a layer that covers the internal surface area defined by the cap and formed from one or more sections;

an adjustment mechanism, configured to adjust the form of the stiff shell to conform to an individual wearer's head, in a first operation mode, and configured to fix the form of the shell, in a second operation mode; and wherein

the cap is configured such that the stiff shell substantially retains the fixed form during normal use and when subject to forces imparted to the cap during an impact.

2. The cap of claim 1, wherein the stiff shell forms an internal surface of the cap arranged to face the wearer's head in normal use, and is configured to directly contact the wearer's head.

3. The cap of claim 1 any preceding claim, wherein the cap is devoid of compressible material more inward than the stiff shell, relative to the wearer's head, in normal use.

4. The cap of claim 1, wherein the adjustment mechanism is configured to be able to adjust the form of the stiff shell such that an average gap size between the stiff shell and a standard head form is no more than 2 mm, across a circumferential part of the stiff shell or the entire stiff shell; wherein, optionally, the adjustment mechanism is configured to be able to adjust the form of the stiff shell such that the average gap size is no more than 1 mm.

5. (canceled)

6. The cap of claim 1, wherein the stiffness of a system formed by the stiff shell, the adjustment mechanism, in the second mode, and a standard head form, is such that, during an impact, the average gap size between the stiff shell and the standard head form increases by no more than 2 mm, across a circumferential part of the stiff shell or the entire stiff shell; wherein, optionally, the average gap size, during an impact, increases by no more than 1.5 mm.

7. (canceled)

8. The cap of claim 1, wherein the stiffness of a system formed by the stiff shell, the adjustment mechanism, in the second mode, and a standard head form, is such that, during an impact, an average displacement between opposing surfaces of the stiff shell facing the standard head form, is no more than 2 mm, across a circumferential part of the stiff shell or the entire stiff shell; wherein, optionally, the average displacement, during an impact, increases by no more than 1.5 mm.

9. (canceled)

10. The cap of claim 1, wherein the adjustment mechanism is configured to be able to adjust the form of the stiff shell such that a maximum gap size between the stiff shell and a standard head form is no more than 2 mm, across a circumferential part of the stiff shell or the entire stiff shell; wherein, optionally, the adjustment mechanism is configured to be able to adjust the form of the stiff shell such that the maximum gap size is no more than 1 mm.

11. (canceled)

12. The cap of claim 1, wherein the stiffness of a system formed by the stiff shell, the adjustment mechanism, in the second mode, and a standard head form, is such that, during an impact, the maximum gap size between the stiff shell and the standard head form increases by no more than 2 mm, across a circumferential part of the stiff shell or the entire stiff shell; wherein, optionally, the maximum gap size, during an impact, increases by no more than 1.5 mm.

13. (canceled)

14. The cap of claim 1, wherein the stiffness of a system formed by the stiff shell, the adjustment mechanism, in the second mode, and a standard head form, is such that, during an impact, a maximum displacement between opposing surfaces of the stiff shell facing the wearer's head, is no more than 2 mm, across a circumferential part of the stiff shell or the entire stiff shell; wherein, optionally, the maximum displacement, during an impact, increases by no more than 1.5 mm.

15. (canceled)

16. The cap of claim 1, wherein the material forming the sections of the stiff shell has a Young's Modulus of at least 1 GPa.

17. The cap of claim 1, wherein the sections forming the stiff shell are formed from polycarbonate.

18. The cap of claim 1 wherein the stiff shell is at least 1 mm thick.

19. The cap of claim 1, wherein a surface of the cap arranged to face away from the wearer's head, in normal use, is a low friction surface wherein, optionally, the low friction surface is provided by the material properties of the one or more sections forming the stiff shell.

20. (canceled)

21. The cap of claim 1, wherein the stiff shell is arranged to at least cover a part of the forehead, the top of the head, a part of the back of the head and a part of each side of the head of the wearer, in normal use.

22. Protective headgear comprising:

the cap of claim 1; and

at least one protective layer covering the cap.

23. The headgear of claim 22, wherein the cap is configured to rotate relative to the at least one protective layer under an oblique impact to the protective layer wherein, optionally, the headgear further comprises at least one connector configured to connect the cap and the at least one protective layer while permitting the relative rotation.

24. (canceled)

25. The headgear of claim 23, wherein:

a sliding interface is provided between the cap and the at least one protective layer or a shearing interface is provided between the cap and the at least one protective layer.

26. (canceled)

27. The headgear of claim 22, wherein:

the at least one protective layer comprises an energy absorbing layer; or the at least one protective layer comprises a hard outer stiff shell.

28. (canceled)

29. A method of protecting a wearer of protective headgear from head injury, comprising:

encasing the head of the wearer in a cap, the cap comprising:

an adjustment mechanism, for adjusting the form of the stiff shell, in a first operation mode, and configured to fix the form of the stiff shell, in a second operation mode; and wherein

the cap is configured such that the stiff shell substantially retains the fixed form, during normal use and subject to forces imparted to the cap during an impact;

the method comprising adjusting the form of the stiff shell to conform with the wearer's head and fixing said form.

30. The method of claim 29, wherein the form of the stiff shell is adjusted such that an average gap size between the stiff shell and the wearer's head, in normal use, is no more than 2 mm; wherein, optionally, the form of the stiff shell is adjusted such that the average gap size is no more than 1 mm.

31. (canceled)