HELMET STRUCTURES AND METHODS

FIELD OF THE INVENTION

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

BACKGROUND

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.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

FIG. 1 is a view of an underside of a helmet shell according to some examples.

FIG. 2 is an external view of part of the helmet shell of FIG. 1 in an area above a user’s forehead.

FIG. 3 is a perspective view of an internal honeycomb structure of the helmet shell of FIG. 1, according to some examples.

FIG. 4 shows the orientation of a finished component of the helmet shell of FIG. 1 relative to a print bed, in some examples.

FIGS. 5A through 5D show four different cross-sections of a component of the helmet shell of FIG. 1, as the cross sections being printed advance during the additive manufacturing.

FIG. 6 shows the reinforcement of a honeycomb structure, in which the intersections between adjacent walls have been reinforced, according to some examples.

FIG. 7 shows the reinforcement of part of a helmet shell in which the intersecti ons between adjacent walls have been reinforced, in some examples.

FIG. 8 is an exploded view of a constant-force pad to be used in protective equipment, such as helmets, according to some examples.

FIG. 9 is a chart 900 showing the relationship between pad displacement (movement due to pressure from the wearer) and force applied, in some examples.

FIG. 10A and FIG. 10B illustrate front and side views respectively of the pad of FIG. 8, in an assembled configuration and in 3D print orientation.

FIG. 11 shows a perspective view of a helmet substrate 1100 according to some examples.

FIG. 12 shows a perspective views of the helmet substrate of FIG. 11.

FIG. 13 is a perspective view of a pad 1300 in which springs used to provide the constant force deflection reside in the helmet substrate, according to some examples.

FIG. 14 shows a perspective view of a helmet substrate 1400 in which hidden detail of post holes is shown, according to some examples.

FIG. 15 shows two polymer constant-force accordion-shaped springs designed for FDM fabrication.

FIG. 16 shows a perspective view of two parts of a helmet that are to be joined together during assembly of the helmet, according to some examples.

FIG. 17 shows an end view and two perspective views of an extrinsic spline, according to some examples.

DETAILED DESCRIPTION

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.

In some examples, provided is a personal protective item such as a helmet. The personal protective item includes a hexagonal structure comprising a plurality of hexagonal tubes, each hexagon tube having a first end and a second end and being formed by a plurality of walls, the first and second ends being defined by edges of the plurality of walls, and a cylindrical end cap on at least some of the edges of the plurality of walls. At least some of the hexagonal tubes may be open adjacent to the end caps for ventilation. The end caps may be circular cylinders or circular tubes, or may be elliptical in shape.

The personal protective item may further include an end wall coupled to at least some of the edges of the walls to close the ends of at least some of the hexagonal tubes, the edges of the walls of the hexagonal tubes adjacent to the end wall not having cylindrical end caps.

In some examples, the personal protective item may also include supporting columns along the hexagonal tubes where the walls of adjacent hexagonal tubes meet. The supporting columns may taper from the first end to the second end. A side of at least one supporting column may be flat to enhance 3D printability. A diameter of the supporting columns may also vary across the personal protective item.

The personal protective item may be assembled from at least a first part and a second part, the first part having a spline defined thereon and the second part having a groove defined therein for receiving the spline.

The personal protective item may be assembled from at least a first part and a second part and an extrinsic spline, the first part having groove defined therein for receiving the spline and the second part having a groove defined therein for receiving the spline.

In some examples, the personal protective item includes a pad for providing user comfort, the pad including a plate that is deflectable relative to a substrate of the personal protective time, the pad being coupled to the substrate by one or more constant force springs. The pad may include a number of posts mounted to the plate, the posts being received by post holes defined in the substrate.

In some examples, a personal protective item such as a helmet includes an inner wall having a first aperture defined therein, an outer wall having a second aperture defined therein, a honeycomb structure located between the inner wall and the outer wall, the honeycomb structure including a plurality of hexagonal tubes having first ends and second ends, the first and second ends of a first group of the hexagonal tubes being exposed through the first aperture and the second aperture, and end caps located on the first and second ends of the first group of hexagonal tubes. The first and second ends of a second group of hexagonal tubes are coupled to the inner wall and the outer wall respectively without having end caps.

The hexagonal tubes may comprise tube walls, and the personal protective item may further include supporting columns along the hexagonal tubes where the tube walls of adjacent hexagonal tubes meet. The supporting columns may taper along the length of the hexagonal tubes, and a diameter of the supporting columns may vary across the personal protective item.

The personal may further include a pad for providing user comfort, the pad includes a plate that is deflectable relative to a substrate of the personal protective time, the pad being coupled to the substrate by one or more constant force springs.

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

FIG. 1 is a view of an underside of a helmet shell 100 according to some examples. The helmet shell 100 has been additively manufactured to include exterior walls (not shown in FIG. 1) and interior walls 102, between which are provided a honeycomb structure as will be described in more detail below.

Ventilation holes 106 are provided in the walls 102. The holes 106 correspond to the walls of the honeycomb structure, allowing air flow to the user’s head from the outside. The holes 106 thus 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 caps 104 formed 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 caps 104 may be filleted to discourage crack propagation between the honeycomb structure and the end caps 104.

The reinforcement to the otherwise exposed hexagonal edges of the interior honeycomb structure provided by the end caps 104 improves printability and structural integrity without greatly hindering airflow from the exterior of the helmet shell to the user’s head. The end caps 104 may have a circular, elliptical or some other cross-sectional shape.

In some examples, Fused Deposition Modelling (FDM) is used to make the helmet shell 100. 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 shell 100 comprises a number of pieces that are made separately using additive manufacturing, which are then assembled into the final helmet shell 100, for example as discussed below with reference to FIG. 16 and FIG. 17. Additional components such as pads, straps and so forth are then added to the helmet shell to make up the final helmet.

FIG. 2 is an external view of part of the helmet shell 100 in an area above a user’s forehead. The exterior of the helmet shell 100 includes an exterior wall 202, which has an aperture defined therein. The underlying honeycomb structure is exposed by the aperture defined in the exterior wall 202, with end caps 104 providing reinforcement of the honeycomb structure. The holes 206 defined by the end caps 104 are coupled to the holes 106 shown in FIG. 1 by the hexagonal tubes forming the honeycomb structure.

As can be seen, the aperture defined by an edge 204 of the exterior wall 202 does not follow the end caps 104 as for the interior wall 102. This is typically done for aesthetic or other design purposes. The end caps 104 may, but typically do not continue underneath the exterior wall 202, since reinforcement of the interior honeycomb structure in that area is then provided by the exterior wall 202.

Also shown in FIG. 2 is the plane 210 of a print bed, and a direction 208 in which 3D printing proceeds as discussed below with reference to FIG. 4.

FIG. 3 is a perspective view of an internal honeycomb structure 300 of the helmet shell 100, according to some examples. FIG. 3 shows the part of the helmet shell 100 shown in FIG. 2 from another direction and with the exterior wall 202 removed. The normally hidden honeycomb walls 302 are visible, with end caps 104 provided on both top and bottom edges of the honeycomb walls 302 in areas that have ventilation through the helmet. The honeycomb walls 302 define a number of hexagonal tubes through which ventilation can be facilitated by the use of end caps 104

FIG. 4 shows the orientation of a finished component 402 of the helmet shell 100 relative to a print bed 404 in some examples. As can be seen, the additive manufacturing of the component 402 is 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 404. This orientation is also illustrated in FIG. 1 by the print direction 208 and plane 210 of the print bed.

FIGS. 5A through 5D show four different cross-sections of a component of the helmet shell 100, such as the front section shown in FIG. 2 and FIG. 3, as the cross sections being printed advance during the additive manufacturing in direction 208. The cross sections shown are parallel to the plane 210 of the print bed and advance in the direction 208.

FIG. 5A is a cross section that cuts across honeycomb walls 302 that are vertical in FIG. 2. In FIG. 5B, continuing upwards, the vertical honeycomb walls 302 have each diverged into two angled honeycomb walls 504 on the interior of the helmet shell 100 but not the exterior. This is because the honeycomb orientation is somewhat angled relative to the plane 210 of the print bed. The end caps 502 on the interior of the helmet shell 100 are now elliptical in cross section, they are on the end of a honeycomb wall that is angled to the plane 210 of the print bed and are thus also angled, and the cross section of an angled circular cylinder or tube is an ellipse.

In FIG. 5C continuing upwards in direction 208, the end caps 502 on the interior surface are merging as two angled honeycomb walls 302 come together, until they have merged and transitioned to vertical end caps 502 on a vertical honeycomb walls 302 as shown in FIG. 5D.

FIG. 6 shows the reinforcement of a honeycomb structure 600, in which the intersections between adjacent walls 602 have been reinforced. In FIG. 6, exterior and interior end caps 104, 502 have been omitted for purposes of clarity. As shown, the intersections between adjacent walls 602 have been reinforced by cylindrical, conical or frustoconical columns 604. Cylindrical or conical reinforcement may also be used where interior walls meet the exterior.

Providing columns 604 at the intersections of walls 602 in a honeycomb structure 600 can improve the specific energy absorption of a sandwich panel including the honeycomb structure 600, or of the honeycomb structure 600 itself. 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 caps 104 parallel to the head surface, and may be sized to be visually hidden by the end caps 104.

In the case of frustoconical columns 604, the diameter of a column adjacent to the inner surface of the helmet shell 100 and the diameter of the column 604 adjacent to the outer surface of the helmet shell 100 can be varied from one column to another column around the helmet shell 100, or for different sections of the helmet shell 100, to optimize desired energy absorption and density. The end caps 104 may also be of variable diameter or not present everywhere. The diameters of end caps 104 at an exterior surface of the helmet shell 100 may but need not match the diameter of end caps 104 at the interior surface of the helmet shell 100. As before, the transition between end caps 104 and columns 604 may be filleted to reduce crack propagation.

In some examples of a bicycle helmet using a carbon-fiber reinforced polymer, the end caps 502 parallel to the scalp of a user and near the skin, and end caps 104 at the exterior surface of the helmet shell 100, have outer diameters of 3 mm and 4 mm respectively. This geometry is interpolated to form columns 604 perpendicular to the head where three or more walls come together. The surfaces may be constructed to smoothly vary between the diameters.

FIG. 7 shows the reinforcement of part of a helmet shell 700, in which the intersections between adjacent walls 702 have been reinforced, in some examples. FIG. 7 shows a part of the helmet shell 100 near the helmet exterior as seen from inside, with internal material removed to show detail. The left side of FIG. 7 is ventilated, with holes 206, and the right side is unventilated, with the exterior wall 202 covering the internal honeycomb structure. End caps 104 are present in the ventilated area, but not where the exterior wall 202 is present. Columns 704 of slightly smaller diameter than the end caps 104 can be observed wherever three walls 702 of 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 posts 708 have a flattened side 706 to 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 posts 708 have 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 706, which are nearly horizontal during 3D printing, is at risk for print defects, this is less so than a round column would be. That is because, for the flattened side 706, the filament is extruded along a shorter path between stable endpoints, whereas the extrusion for a cylinder has to follow a relatively long elliptical cross-section far away from support.

In FIG. 7 for example, in which the print bed is located below the figure, it can be seen that the sides of the posts 708 that have flattened sides 706 are the columns that have angled walls 702 intersecting with the posts 708 from below. The columns 704 that do not have flattened sides have vertical walls 710 below the column 704, which provides support for material deposition.

FIG. 8 is an exploded view of a constant-force pad 800 to be used in protective equipment, such as helmets, according to some examples. Pads are used in many applications to isolate a rigid surface from a human body part. For example, foam pads are commonly incorporated into sports gear, such as helmets, to provide user comfort. Pads fill the gap between the substrate and the body to allow equipment to be worn despite having an imprecise fit. Pads are commonly made of a foam. There may be additional layers to control the force-displacement curve, wick sweat, adhere to the substrate, provide an attractive appearance, and so on.

Pads are most comfortable when they provide a consistent and controlled pressure. When sports equipment has a poor fit, the pressure may be too small (or zero) such that the equipment is not held in place correctly. Alternately, pressure that is too high is uncomfortable or painful. Foam pads generally transmit more force as they get squeezed into a smaller volume. However, this limits the comfortable range of motion. While a conventional pad allows choosing a density to increase or decrease pressure, this cannot guarantee comfort as the ideal density will still differ with fit, and pressure may not be evenly distributed across the pad.

One possible approach is to use a viscoelastic material (“memory foam”) so that pressure points even out over time. A potential problem with memory foam is its reduced ability to sustain constant pressure over time.

Instead of a foam, pressure may be spread using a relatively stiffer panel that distributes load over the entire pad surface. The stiffness may be chosen to allow some curvature (e.g., across the forehead), while still distributing force at small scales. Deflection of the pad is arranged to provide a flat force-displacement curve, as described in more detail below with reference to FIG. 9.

The pad 800 shown in FIG. 8 comprises a relatively stiff and smooth plate 802 with rounded edges suitable for prolonged contact with skin, which distributes load evenly to prevent pressure points, posts 804 for coupling the pad 800 to the helmet, and a spring 806 that provides a flat force-displacement curve as described with reference to FIG. 9.

Each post 804 includes a conical base 808 for stability, which mates with a conical upper edge 1104 of a post holes 1102 in the helmet substrate as shown in FIG. 11 and FIG. 12, a body 812 that slides into the post holes 1102 in the substrate to permit the pad to deflect and retract toward the substrate under pressure, and a conical split snap feature 810 that permits insertion into but not retraction of each post 804, to hold the pad 800 in place on the helmet substrate.

The spring 806 comprises primary walls 814 that are aligned with the boundary of the pad 800 to permit movement of the plate 802 relative to the helmet substrate, as well as a secondary wall 816 that prevents inversion of the primary walls 814 where the primary walls 814 meet the substrate. In one example the components of the pad can be 3D printed simultaneously and bonded thermally by proximity.

To obtain a force-displacement curve that is flat instead of stiffening with displacement, the primary walls 814 comprise an angled first wall 820 and an angled second wall 822 that meet at a waist 818, where buckling occurs when pressure is applied to the pad 800. In contrast to a traditional pad, the material properties only affect stiffness at the point (the waist 818) where buckling occurs. The buckling mechanism described in this example is an inward bend in the pad primary walls 814, but other arrangements are possible.

The material used for construction of the pad 800 can be quite stiff relative to traditional foam, but foam, wicking fabric or aesthetic material may also be laser, knife or die-cut and adhered to the surface of the plate 802 opposite to the posts 804. A preferred material for the pad is polyether thermoplastic polyurethane (TPU) of shore 95A durometer which allows a smooth yet flexible surface and no additional material necessary.

Because the spring 806 has a flatter force-displacement curve than foam, the range of displacement can be larger than a traditional pad, without discomfort. The recess for the pad in the substrate and the depth of the holes for receiving the mounting posts can also be designed to accommodate the entire retracted pad 800 all the way to the adjacent surface of the substrate.

The secondary wall 816 prevents the primary walls 814 from turning inside-out (inversion) when the pad 800 is deeply depressed. Another solution would be to thicken the perimeter of the first wall 820 in the area that comes in contact with the recess in the substrate. Such thickening prevents undue expansion of the first wall 820 without affecting the apparent stiffness, because the compliance of the primary walls 814 is primarily at the waist 818.

FIG. 9 is a chart 900 showing the relationship between pad displacement (movement due to pressure from the wearer) and force applied, in some examples. The chart 900 shows displacement of the pad on the x-axis in response to increasing force on the y-axis. The relationship between increasing force and increasing displacement for the pad 800 and other pads contemplated herein is shown by line 902. The conventional linear spring response is shown by the line 904. As can be seen, there is a range of acceptable or preferred forces for the pad 800 as shown in the chart 900 by the upper limit 906 and lower limit 908. When the force in response to displacement of the pad is too low, the pad fails to stabilize the personal equipment (such as a helmet) relative to the body. When the force in response to displacement is too high, it is uncomfortable and chafes, for example by reducing blood flow.

An ordinary foam pad creates a linear relationship between displacement and force, as seen by the linear spring response line 904. The stiffness of the foam/spring can be arranged to match the slope of the line to available or preferred displacements. However, regardless of the stiffness, there is a narrow range of displacements within the acceptable range of force, as can be seen. In comparison, a near constant-force spring is able to maintain a comparable force as displacement increases, allowing a larger range of displacements to be acceptable to the wearer than can be achieved by a linear response.

As can be seen from FIG. 9, the constant force response illustrated by line 902 is not perfectly constant as displacement increases. In particular, there is a relatively steep initial increase in the force required to create initial displacement, followed by some variation of the generally flat line 902 within the acceptable range of force, with a rapid increase in the force required for additional displacement beyond a certain point, due to densification. “Constant force response” is thus to be understood in this context.

FIG. 10A and FIG. 10B illustrate front and side views respectively of the pad 800 of FIG. 8, in an assembled configuration and in 3D print orientation. As can be seen, the posts 804 extend above the spring 806 on the side of the pad 800 opposite to the plate 802. Also shown in FIG. 10B is the split snap feature 810 illustrating the slot 1002 formed in the posts 804 to permit the two sides of each post 804 to flex inward to permit insertion of the post 804 into the helmet substrate. The end of the post 804 is thus able to snap into place in a post hole while the undersurface of the conical split snap feature 810 prevents withdrawal by engaging a corresponding surface in the post hole.

FIG. 11 shows a perspective view of a helmet substrate 1100 according to some examples. The substrate 1100 forms part of a helmet shell 100 for example. The substrate 1100 includes three post holes 1102 sized and located to receive the posts 804 of the pad 800. The post holes 1102 are deep enough to allow each post 804 to fully extend into its post hole 1102 when the pad 800 is under pressure. Post hole upper edges 1104 are conical to facilitate post insertion and also for engagement with the conical post bases 808 when the pad is fully depressed, to provide additional lateral support to the pad 800 when fully depressed. The undersides of the split snap features 810 engage corresponding surfaces in the post holes 1102 to prevent withdrawal of the posts 804 from the post holes 1102.

Also defined in the substrate is a recess 1106 that matches the overall shape of the pad 800. In some cases, the floor of the recess 1106 does not correspond to the entire shape of the pad 800 as shown, which permits the pad 800 to overlap with other functional equipment areas, such as the strap support 1108 seen in the figure.

FIG. 12 shows a perspective view of the helmet substrate 1100 of FIG. 11, in which hidden detail of the post holes 1102 is shown. A lower region 1204 of each post hole 1102 is sufficiently wide so as to fully accommodate the split snap feature 810. An upper surface 1202 of the lower region engages the undersurface of the conical split snap feature 810 to prevent post withdrawal, while allowing each post 804 to slide in to its full depth.

The apparatus shown in FIG. 8 and FIG. 10A & B to FIG. 12 combines the pad surface, constant force spring, and the conical retention snaps into a single part. These functions may instead be separated to allow independent fabrication, different materials, alternative assembly methods, end user adjustments, or greater depth of travel. FIG. 13 to FIG. 15 together illustrate an alternate constant force pad implementation in which springs are separate parts that reside in the helmet substrate for increased range of motion.

FIG. 13 is a perspective view of a pad 1300 in which the springs used to provide the constant force deflection reside in the helmet substrate, according to some examples. The pad 1300 combines the functions of the plate 802 and posts 804 of the pad 800 of FIG. 8, excluding the spring 806. As before, the pad 1300 includes a relatively stiff and smooth plate 1302 with rounded edges suitable for prolonged contact with skin, and for distributing load evenly to prevent pressure points. The pad 1300 includes posts 1304 with partial conical bases 1306 for stability, which mate with a conical upper edge 1406 of post holes 1402 (see FIG. 14) in the helmet substrate. In some examples, the posts 1304 shown in FIG. 13 slide into post holes 1402 in the helmet substrate against springs 1502 (see FIG. 15) in the post holes 1402, to permit the pad 1300 to retract toward the substrate under pressure. The posts 1304 in FIG. 13 can however also be used with an outer spring arrangement attached to the pad 1300 as describe above with reference to FIG. 8.

The posts 1304 include four-way conical split snap features 1308 that permit insertion of a post 1304 into, but not retraction of, a post 1304 from a post hole 1402, to hold the pad 1300 in place. Arches 1310 are defined in the post walls and holes 1312 are provided in the plate 1302, for example under the posts 1304, to reduce overall weight. An upper surface 1314 of the split snap feature 1308 may have an angled outer portion to permit insertion of the posts 1304 into the post holes 1402, and a flat upper portion to engage a spring 1502.

As before, the surface of the plate 1302 on the other side from the posts 1304 may have a material bonded thereto to enhance comfort, for example in the case of prolonged skin contact.

FIG. 14 shows a perspective view of a helmet substrate 1400 in which hidden detail of post holes 1402 is shown, according to some examples. FIG. 14 shows the post holes 1402 as if seen from within the helmet substrate. The post holes 1402in FIG. 14 are functionally equivalent to the post holes 1102 in FIG. 11, and are appropriately sized (for example with a larger diameter and deeper depth) to accommodate a spring 1502 in each post hole 1402. Each post hole 1402 includes a chamfer 1408 at the bottom that encourages a spring 1502 to remain centrally aligned.

The post holes 1402 are deep enough to allow each post 1304 to fully extend into its post hole 1402 on top of a compressed spring 1502 when the pad 1300 is under pressure. Post hole upper edges 1406 are conical to facilitate post insertion of a the posts 1304 and also for engagement with the post conical bases 1306 when the pad 1300 is fully depressed, to provide additional lateral support to the pad 1300 when fully depressed. The undersides of the split snap features 1308 engage corresponding surfaces in the post holes 1402 to prevent withdrawal of the posts 1304 from the post holes 1402.

A lower region 1404 of each post hole 1402 is sufficiently wide so as to fully accommodate the split snap feature 1308 and a spring 1502, which may expand radially when compressed.

Any type of spring may be used within the post holes 1402, but preferably constant force springs are used.

FIG. 15 shows two polymer constant-force accordion-shaped springs 1502 designed for FDM fabrication. Each spring 1502 has a flat end 1504 that is contacted by the end of the post 1304 and a tapered end 1506 for contacting the chamfer 1408 at the bottom of the post hole 1402. The springs 1502 are hollow to permit the alternating spring walls (such as spring wall 1508 and spring wall 1510) to compress and expand towards and away from each other during use. The flat end 1504 of each spring 1502 also includes a hole 1514 to reduce weight and to allow users to manipulate the springs 1502 during insertion or replacement.

The spring force provided by the springs 1502 is primarily as a result of buckling occurring at the outer edges 1516 and waists 1518 between adjacent spring walls, such as spring wall 1508, 1510 and 1512. The springs 1502 may be any shape, but the octagonal radial accordion design illustrated in FIG. 15 reduces engagement with any imperfections in or on the walls of the lower region 1404 of the post hole 1402.

The spring 806 in FIG. 8 and the springs 1502 in FIG. 15 may be seen as a stack of effectively conical shells (also known as coned-disc springs, conical spring washers, or Belleville springs.) These compact springs feature a force plateau near zero at the point where the spring “turns inside out,” so the force-displacement profile can be tuned by modifying the dimensions of the spring for the desired displacement.

Any mechanism capable of plateauing force may be substituted, including but not limited to: cantilever springs, volute springs, leaf springs, torsion springs, wave springs, gas springs, main springs, or dilatant or auxetic foams and lattices.

The helmet shell 100 of FIG. 1 may be assembled from two or more separate parts. In this regard, FIG. 16 shows a perspective view of two parts of a helmet that are to be joined together during assembly of the helmet, according to some examples.

Additive manufacturing processes are typically limited to a “build volume,” for example, by the range of motion of the printer’s mechanism. There are also process-specific limitations to parts that include requiring the part to have a flat surface to make contact with a “print bed,” disallowing certain angles, limitations on the number of concurrent materials used in a part, and disallowing enclosed regions that prevent raw material from being removed.

It is common to work around these limitations by splitting parts into multiple pieces that undergo later assembly. These pieces can be combined in many ways, such as sewing, screwing, welding, solvent welding, snapping, etc. It is desired to have a robust technique that requires little skill, time and equipment for assembly.

As disclosed herein, parts may be joined with “dovetail” joints, or may require external parts, for example “biscuit” or “butterfly” joints. The word “spline” is used herein to describe any such mating part as used in specific 3d-printed processes.

Assembling rigid pieces into a composite structure requires that they slide relative to one another along some path with a cross-section invariant to rotation and translation along the path. In woodworking for practical reasons this is typically a straight line. The straight line is a special case of a circular arc, which is a special case of a most general helical path. As helical curves are the most general family of shapes, the word “helical” here may be understood to apply to straight or circular paths without loss of generality.

Splines may be partially printed directly into one part (intrinsic), or created as a separate component that holds larger pieces together (extrinsic). In the latter case, it can be useful to print the spline using the same production process. Each part may incorporate any number and type of splines for joining to neighboring parts.

Additive manufacturing makes joinery shapes possible that would not be possible in traditional processes such as lathing or injection molding. The ideal path may be optimized by software in a manner appropriate to the domain, rather than set rigidly in a Computer Aided Design (CAD) tool. For example, a 3d-printed helmet may conform to users’ heads for best possible comfort and safety. Segments of the unique helmet may be combined using helical joints defined by software while still respecting printing process constraints and mechanical performance requirements. The helical path may be placed optimally based on the contour of each customer’s head.

The construction of an optimal helical path is domain specific. However, a practical special case is constructing a circular path that follows a planar print bed in order to mate two parts formed from a reference design by an arbitrary coordinate space transformation. Three points define a unique circle, so when tolerances permit, a circular path can be constructed by observing the transform at three predefined points, from which a circular and planar path can be recovered suitable for joining. The strength of this technique is that the coordinate transform need not be linear and is bounded only by the need to keep the print beds planar.

Fused Deposition Modelling of a 3D-printed helmet is used as an example. The helmet is divided into individually printed sections, which are assembled by sliding together intrinsic splines or inserting extrinsic splines. Splines may be constructed by any convenient process, not necessarily 3d-printing. Parts may be solid, filled with a pattern, or have thin walls. The material may be different for the spline and the connecting parts. Once installed splines may be held in place in many ways including being welded, solvent welded, glued, shimmed, or friction fit.

In this regard, FIG. 16 shows a first part 1602 and a second part 1604 forming part of a helmet shell 1600. The first part 1602 has a helical groove 1606 defined therein into which an intrinsic spline 1608 on second part 1604 can be slid to mate the first part 1602 to the second part 1604. In the example first part 1602 is printed on a print bed that is parallel to the plane dividing the two parts. The geometry of the groove 1606 is thus constrained to the plane of the print bed of the first part 1602. The groove 1606 has an angled roof relative to the print bed for the first part 1602 for printability, to reduce overhang.

The second part 1604 is printed on a print bed facing the reader. Second part 1604 also has a groove 1610 constrained by the print bed into which an extrinsic spline (not shown) will be inserted for attaching another part (also not shown).

FIG. 17 shows an end view and two perspective views of an extrinsic spline 1702, according to some examples. The end view of the spline 1702, on the left, shows the print orientation of the spline 1702 relative to a horizontal print bed. The spline 1702 is butterfly-shaped with upper and lower faces that slope by at most 45 degrees to the print bed, for printability. The butterfly shape of the spline 1702 prevents separation of the two parts when the left and right sides of the spline 1702 are received in opposing grooves of the two parts that are to be assembled.

The perspective view in the middle shows a chamfer 1704 on the insertion end of the spline 1702 for easier insertion into corresponding grooves in the two parts that are to be assembled.

The perspective view on the right side shows a surface 1706 that is angled to match an exterior contour of the parts to be joined, to provide a smooth finish and to conceal the hole formed by the grooves of the joined parts.

	Number	Date	Country
	63251164	Oct 2021	US
	63324972	Mar 2022	US

HELMET STRUCTURES AND METHODS

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CPC

International Classifications

Abstract

Description

Claims

CROSS REFERENCE TO RELATED APPLICATIONS

Provisional Applications (2)