Helmet Structures and Methods

This application claims the benefit of priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 63/573,156, filed on Apr. 2, 2024, the contents of which are incorporated herein by reference as if explicitly set forth.

This application relates to structures and methods for use in protective equipment, including but not limited to helmets for use in recreational activities.

Designers of protective equipment are often faced with many conflicting requirements and challenges. For example, helmets for sporting use are expected to be lightweight, able to withstand and absorb significant impacts of different types and directions, capable of providing air flow to the wearer's head in use, as well as a comfortable and conformable fit that can accommodate variations in the size or shape of a user's head within each specific helmet size. Considerations of style, and the limitations of existing molding techniques in Expanded Polystyrene (EPS) molding, are also relevant.

Honeycomb (hexagonal) sandwich panels are commonly used for lightweight mechanical structures. In such panels, hexagonal interior walls are enclosed by parallel sheets to form a plate-like assembly. Honeycomb sandwich panels are used where a high ratio of strength to mass is needed, and are typically available in paper, aluminum, fiberglass and advanced composite materials.

The desirable properties of sandwich panels extend to products produced by additive manufacturing. For example, total weight and specific strength are key concerns for the manufacture of custom 3D-printed sport safety helmets. For some products, holes through the structure are necessary, such as in a bicycle helmet where user comfort depends on adequate airflow. Unfortunately, any holes in a sandwich panel greatly reduces its mechanical properties by allowing crumpling in-plane.

For an additive manufactured helmet there are other problems with removing all or part of the outer panels: knife-like walls oriented perpendicular to the inside that may pose a safety risk, difficulty in some additive manufacturing processes to print walls consistently when there is no peripheral support, and a tendency to propagate cracks where inner and outer walls meet at ninety degrees. Simply making holes in the outer surfaces that are smaller than the hexagons defined by the walls of a honeycomb structure retain many of these mechanical problems.

Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims.

is a view of an underside of a helmet shellaccording to some examples. The helmet shellhas been additively manufactured to include exterior walls (not shown in) and interior walls, between which are provided a honeycomb structure as will be described in more detail below.

Ventilation holesare provided in the walls. The holescorrespond to the walls of the honeycomb structure, allowing air flow to the user's head from the outside. The holesthus form a honeycomb pattern corresponding to the interior honeycomb structure. The openings of the holes at the interior and exterior walls are reinforced by cylindrical or tubular end capsformed at the upper and lower ends of the hexagons formed by the interior honeycomb structure. The transition from the walls of the honeycomb structure to the end capsmay be filleted to discourage crack propagation between the honeycomb structure and the end caps.

The reinforcement to the otherwise exposed hexagonal edges of the interior honeycomb structure provided by the end capsimproves printability and structural integrity without greatly hindering airflow from the exterior of the helmet shell to the user's head. The end capsmay have a circular, elliptical or some other cross-sectional shape.

In some examples, Fused Deposition Modelling (FDM) is used to make the helmet shell. Circular or elliptical shapes are advantageous to FDM because imprecision of starting and stopping filament precisely (retraction) does not weaken the end cap. Circular or elliptical end caps are tougher than planar endcaps and present rounded edges to the exterior surface instead of sharp edges. In some examples, the helmet shellcomprises a number of pieces that are made separately using additive manufacturing, which are then assembled into the final helmet shell. Additional components such as pads, straps and so forth are then added to the helmet shell to make up the final helmet.

is an external view of part of the helmet shellin an area above a user's forehead. The exterior of the helmet shellincludes an exterior wall, which has an aperture defined therein. The underlying honeycomb structure is exposed by the aperture defined in the exterior wall, with end capsproviding reinforcement of the honeycomb structure. The holesdefined by the end capsare coupled to the holesshown inby the hexagonal tubes forming the honeycomb structure.

As can be seen, the aperture defined by an edgeof the exterior walldoes not follow the end capsas for the interior wall. This is typically done for aesthetic or other design purposes. The end capsmay, but typically do not continue underneath the exterior wall, since reinforcement of the interior honeycomb structure in that area is then provided by the exterior wall.

Also shown inis the planeof a print bed, and a directionin which 3D printing proceeds as discussed below with reference to.

is a perspective view of an internal honeycomb structureof the helmet shell, according to some examples.shows the part of the helmet shellshown infrom another direction and with the exterior wallremoved. The normally hidden honeycomb wallsare visible, with end capsprovided on both top and bottom edges of the honeycomb wallsin areas that have ventilation through the helmet. The honeycomb wallsdefine a number of hexagonal tubes through which ventilation can be facilitated by the use of end caps.

shows the orientation of a finished componentof the helmet shellrelative to a print bedin some examples. As can be seen, the additive manufacturing of the componentis arranged so that two of the six honeycomb walls are, as far as possible, vertical to the print bed. This orientation minimizes the worst-case overhang of the honeycomb, in which walls of the honeycomb are horizontal to the print bed. This orientation is also illustrated inby the print directionand planeof the print bed.

,,andshow four different cross-sections of a component of the helmet shell, such as the front section shown inand, as the cross sections being printed advance during the additive manufacturing in direction. The cross sections shown are parallel to the planeof the print bed and advance in the direction.

is a cross section that cuts across honeycomb wallsthat are vertical in. In, continuing upwards, the vertical honeycomb wallshave each diverged into two angled honeycomb wallson the interior of the helmet shellbut not the exterior. This is because the honeycomb orientation is somewhat angled relative to the planeof the print bed. The end capson the interior of the helmet shellare now elliptical in cross section, they are on the end of a honeycomb wall that is angled to the planeof the print bed and are thus also angled, and the cross section of an angled circular cylinder or tube is an ellipse.

Incontinuing upwards in direction, the end capson the interior surface are merging as two angled honeycomb wallscome together, until they have merged and transitioned to vertical end capson a vertical honeycomb wallsas shown in.

shows the reinforcement of a honeycomb structure, in which the intersections between adjacent wallshave been reinforced. In, exterior and interior end caps,have been omitted for purposes of clarity. As shown, the intersections between adjacent wallshave been reinforced by cylindrical, conical or frustoconical columns. Cylindrical or conical reinforcement may also be used where interior walls meet the exterior.

Providing columnsat the intersections of wallsin a honeycomb structurecan improve the specific energy absorption of a sandwich panel including the honeycomb structure, or of the honeycomb structureitself. Such integrated reinforcements are harder to produce by traditional sandwich panel construction, but are well suited to additive manufacturing. Such reinforcement is aesthetically and structurally well suited for combination with end capsparallel to the head surface, and may be sized to be visually hidden by the end caps.

In the case of frustoconical columns, the diameter of a column adjacent to the inner surface of the helmet shelland the diameter of the columnadjacent to the outer surface of the helmet shellcan be varied from one column to another column around the helmet shell, or for different sections of the helmet shell, to optimize desired energy absorption and density. The end capsmay also be of variable diameter or not present everywhere. The diameters of end capsat an exterior surface of the helmet shellmay but need not match the diameter of end capsat the interior surface of the helmet shell. As before, the transition between end capsand columnsmay be filleted to reduce crack propagation.

In some examples of a bicycle helmet using a carbon-fiber reinforced polymer, the end capsparallel to the scalp of a user and near the skin, and end capsat the exterior surface of the helmet shell, have outer diameters of 2.2-3 mm and 4 mm respectively. This geometry is interpolated to form columnsperpendicular to the head where three or more walls come together. The surfaces may be constructed to smoothly vary between the diameters.

shows the reinforcement of part of a helmet shell, in which the intersections between adjacent wallshave been reinforced, in some examples.shows a part of the helmet shellnear the helmet exterior as seen from inside, with internal material removed to show detail. The left side ofis ventilated, with holesto the outside, and the right side is unventilated, with the exterior wallcovering the internal honeycomb structure. End capsare present on the top of the wallsin the ventilated area, but not where the exterior wallis present and the wallsmeet the exterior wall. Columnsof slightly smaller diameter than the end capscan be observed wherever three wallsof the hexagonal structure meet.

In an FDM printer, material must be extruded on top of already extruded material to have something to which to attach. Having no material below the nozzle (called “overhang”) leads to gross defects with material being placed away from where it is intended. Some of the postshave a flattened sideto enable FDM printing with less overhang. A cylinder having a nearly horizontal axis can create such a situation, where the bottom of the cylinder is too much “printing on air”. As shown in the image, the postshave been adjusted to be flatter in ways that reduce overhangs. Such adjustments permit easier manufacture of the device using additive manufacturing. The alternative is to print extra material that has to be manually removed later, which adds cost and complexity.

While the flattened sides, which are nearly horizontal during 3D printing, are at risk for print defects, this is less so than a round column would be. That is because, for the flattened side, the filament is extruded along a shorter path between stable endpoints (the ends of two walls), whereas the extrusion for a cylindrical column having no supporting structure has to follow a relatively long elliptical cross-section far away from support.

Infor example, in which the print bed is located below the figure, it can be seen that the sides of the poststhat have flattened sidesare the columns that have angled wallsintersecting with the postsfrom below. The columnsthat do not have flattened sides have vertical wallsbelow the column, which provides support for material deposition.

is a partial cross-sectional view of a helmetaccording to some examples. The helmethas been manufactured using one or more of the techniques described above, and includes an energy management layerformed from a honeycomb structure. As before, the honeycomb structureincludes honeycomb wallsterminating in end capsat the respective inner and outer sides of the energy management layer. In some examples, the honeycomb structureis selectively closed on the interior and/or exterior of the energy management layerby surface walls, to provide airflow and ventilation management or mounting points for accessories (e.g. straps, padding or rear adjuster mechanisms).

In the example illustrated in, the end capscomprise hollow tubes. The end. capsserve to stiffen the exterior and interior of the energy management layerand to spread impact loads across the honeycomb structure. The end capsare hollow to compress and absorb impact energy.

As before, columns(or trabecula) are located at the intersections of the honeycomb wallsto strengthen the interface between adjacent honeycomb walls, to provide additional rigidity, and to improve impact and overall performance for a certain helmet weight, specifically to provide a better energy absorption per weight ratio. Upper portions of the honeycomb wallsadjacent to the exterior surface of the energy management layerare formed from two separate walls, to provide double walls. This feature reinforces the exterior of the energy management layerand works with the external end capsto spread loads and impacts across the honeycomb structure. It also provides more efficient material usage by placing material where it is needed, saving weight by eliminating the double walls towards the interior of the hex structure where it is not needed.

The energy management layerprovides efficient crumpling in linear impacts and shears to absorb oblique impacts.

is a partial cross-sectional view of a helmetaccording to some examples. The helmethas been manufactured using one or more of the techniques described above, and includes an energy management layerformed from two honeycomb structures formed as an inner layerand an outer layerare separated by a slip plane.

The inner layerincludes inner layer honeycomb wallsthat terminate in internal end capsat the inner side of the energy management layer. The inner layer honeycomb wallshave a bead of material formed thereon along the edges where the wallsterminate at the slip plane. The outer layerincludes outer layer honeycomb wallsthat terminate in external end capsat the outer side of the energy management layer. The outer layer honeycomb wallsalso have a bead of material formed thereon along the edges where the wallsterminate at the slip plane. Except where joined as described in, a small gap is provided between the inner layerand outer layerat the slip plane.

The beads formed along the edges of the honeycomb wallsand honeycomb wallsat the slip planefacilitate relative movement between the inner layerand outer layeronce the two layers have broken away from each other as described in more detail below. Otherwise, sharp or jagged edges of the honeycomb walls,that might remain from a fabrication process such as additive manufacturing, could dig into each other or otherwise interact to provide unintended resistance to movement between the inner layerand outer layerafter breakaway.

In some examples, the honeycomb wallsof the outer layer are formed as two separate layers. The honeycomb wallsare thus double-layered or double-walled. This feature reinforces the outer layerof the energy management layerand works with the external end capsto spread loads and impacts across the energy management layer. It also provides more efficient material usage by placing material where it is needed and saving weight by eliminating the double walls in the inner layerwhere it is not needed.

In the example illustrated in, the external end capscomprise hollow tubes. The external end capsserve to stiffen the outer layerof the energy management layerand to spread impact loads across the energy management layer. The external end capsare hollow to compress and absorb impact energy. In some examples the internal end capsare also formed as hollow tubes. In some examples, the external end capsare larger than the internal end capsto provide additional rigidity to the external end capsand thus to the outer layer.

As before, columns (or trabecula) are located at the intersections of the honeycomb wallsand at the intersections of the honeycomb wallsto strengthen the interface between adjacent honeycomb walls,, to provide additional rigidity, and to improve impact and overall performance for a certain helmet weight. Columnsbetween the honeycomb wallsof the outer layerare larger than columnsbetween the honeycomb wallsof the inner layer, in some examples.

The more rigid outer layeraddresses high-velocity impacts or impacts with a blunt object (as opposed to a flat surface), and the less rigid inner layercrumples more to absorb low-velocity impacts.

As can be seen in, the slip planeis generally located at the midpoint of the energy management layer, although this can be adjusted based on design preferences. In some examples, the inner layeris tapered more aggressively than the outer layeras the two layers meet at the peripheryof the helmet. The thickness of the outer layeris thus maintained for longer than the thickness of the inner layeras the two layers meet at the peripheryof the helmet.

The outer layerand the inner layerare coupled together where they meet at the slip planeby a series of connecting shear structures that are designed and configured to give way at a certain shear force between the outer layerand inner layeras described in more detail below. The connecting shear structures are tested so that they absorb the optimal energy for oblique impacts to the helmet and then break away when subject to a shear force greater than a predetermined magnitude, allowing the outer layerand inner outer layerthen to move independently of one another.

This arrangement has benefits over the known MIPS (Multi-directional Impact Protection System), which consists of a low-friction layer inside a helmet against the user's head, which allows the rest of the helmet to slide relative to the head. Firstly, the slip planeplane, and thus its behavior, is built into the helmet, distinct from and separate from the direct interface between the helmetand the user's head. This permits the outer layerof the energy management layerto move relative to the inner layereven when the inner layerstops or is prevented from rotating. Also, the MIPS system provides very little initial resistance to rotation of the helmet on the user's head. The connecting shear structures, on the other hand, provide initial resistance to rotation of the outer layerrelative to the inner layer, providing initial absorption of shear forces before and during breakaway of the connecting shear structures, unlike the MIPS system which tends to provide little resistance to initial rotation. The amount of energy required to activate (shear) the slip plane can be adjusted by varying how well the slip planes are bonded to each other (i.e., more or less material). The functioning of the slip planealso compliments the natural movement of a helmet on a user's head that occurs due to the presence of hair, sweat, and so forth. This natural movement is similar to the movement provided by the MIPS system, and the energy management layerthus provides complimentary movement to this natural head movement.

In some examples, the energy management layeris additively manufactured/3D printed from a single material as a monolithic structure, which also has advantages over the prior MIPS system, which is assembled from several parts of disparate materials. In other examples, sections of an energy management layer comprising both an upper and a lower layer with a slip plane therebetween, are additively manufactured/3D printed from a single material as monolithic structures, which sections can then be assembled into a helmet.

is a plan view of part of a slip planebetween inner layerand outer layerof a helmetif the helmet were flattened (i.e., the curvature of the helmet was ignored), according to some examples. A layer, which could either be the inner layeror the outer layeris seen to comprise a honeycomb structure formed of wallsas before. The open ends of the honeycomb structure comprise a beadthat is formed along the edges of the wallsadjacent to the slip plane, to facilitate movement between the inner layerand outer layerafter breakaway as discussed above.

The inner layeris coupled to the outer layerat the intersections of their respective honeycomb walls,by means of connecting shear structuresthat are designed and configured to give way at a certain shear force between the outer layerand inner layer. In some examples, the connecting shear structuresare formed as flat discs aligned with the slip planeand coupled to both the inner layerand outer layer at the intersections of the honeycomb walls. In some examples, the connecting shear structuresare discs or posts formed during additive manufacturing of the energy management layer, having a diameter of approximately 1 mm and a height of approximately 0.6 mm. The diameter of such discs will vary with the density of the hexagonal structures forming the inner layerand outer layer, with a larger disc diameter if the hexagonal structure is less dense and a smaller disc diameter if the hexagonal structure is denser, to account for the number of interconnections between the inner layerand outer layeralso varying with the density of the hexagonal structure.

Various alternatives are possible for the connecting shear structures. In some examples, the connecting shear structuresare formed as a transition between the columnsof the inner layerand the columnsof the outer layer, with an appropriate taper between the inner layerand outer layer, and optionally an increase or decrease in diameter at the taper or transition between the inner layerand the outer layer, depending on the density of the hexagonal structure, to provide the intended and required breakaway resistance. In other examples, shear pins or other supplementary structures may be provided to join the outer layerto the inner layer.

is a perspective cross-sectional view through an outer layerof the helmet, according to some examples.illustrates that the hexagonal structures in the outer layerare formed from two walls, to provide the double walled structure described above. Also visible inare the columnsformed where the wallsof adjacent hexagonal structures meet. As can be seen, the columnsare not exactly cylindrical but provide a radiused fillet between adjacent hexagonal structures as illustrated in. Also visible is the slip planeand connecting shear structures.

is a transverse cross-sectional view through one of the columnsof the outer layerof the helmetofand, according to some examples. As can be seen, columnis defined by the meeting of three walls, which together form a double wall between adjacent hexagonal structures in the outer layer. Rather than abrupt transitions where the walls meet, minimum-radius filletsare provided. In some examples, the columnsare hollow, while in other examples they are filled with material to provide additional structural rigidity.

is a perspective cross-sectional view of an energy management structureof a helmet, according to some examples. In this example, a slip plane is provided between an upper layer and a lower layer of the energy management structureby providing gapsor voids between the layers along the intersectionof the wallsforming the honeycomb structures.

The upper layer and lower layer are thus interconnected by portions of the wallsof the honeycomb structures between the gapsand not by a column or post at the intersections of the wallsalong the slip plane. The wallscan thus give way under shear loads without support at the intersectionsof the walls at the slip plane. Providing gaps or holes in the wallsin this manner provides lines of weakness along/around the walls of each hexagonal structure. In the illustrated embodiment, the gapsare elliptical in shape, although it will be appreciated that other shapes, configurations, sizes and locations of gaps can be provided in the wallsalong the slip plane to provide appropriate shear behavior.

In some examples, the end capsformed at the outer side of the energy management structurehave additional structures defined therein or formed thereon to engage the outer walls. As seen in, these can comprise groovesthat are arranged to receive an inward-facing lip formed on an outer shell or wall. As seen in, these structures can also comprise outwardly-extending pinsto engage corresponding holes in an outer shell or wallto facilitate coupling and mounting of the wallto the energy management structure. The groovesin adjacent end capsare aligned with each other as appropriate to jointly define a groove corresponding to the lip of the wall.