Field of the Invention

The present invention concerns an impact absorbing device. More particularly, but not exclusively, this invention concerns an impact absorbing device and a method of producing an impact absorbing device. The invention also concerns an impact absorbing device produced to conform to a strict set of parameters.

Background of the Invention Impact absorbing devices are often made of cellular materials such as honeycombs, which may be produced using a variety of conventional techniques. Impact absorbing devices may be used for a variety of purposes, for example for personal protection, packaging, and crash protection for vehicles. Techniques of producing impact absorbing devices include production of corrugated cardboard, where an extruded two dimensional honeycomb is sandwiched between two panels.

Other techniques include the use of expandable polystyrene foams which may make up at least part of an impact absorbing device. Foams may be produced as open cell structures or closed cell structures. Open cell structures typically comprise a plurality of struts which deform to absorb impacts, and under deformation air will be pushed out of the open cell structure, with the resistance of the flow of air out of the open cell structure also adding to the impact absorption effect. Closed cell structures include struts and walls,

capturing a gas within the wall and strut structure. Under deformation, cell struts and walls are compressed, as is the gas trapped within the closed cells. The additional compression of the trapped gas may provide a closed cell foam that is capable of absorbing a much greater impact than an open cell foam made of

substantially the same material.

Modern three dimensional printing machines, using sintering of powder (laser sintering) or

photopolymerisaton of resin ( stereolithography) have been used to create three dimensional, open cell structures which may be specifically designed to meet a particular set of circumstances, for example the size and shape of the impact absorbing device, and the impact absorption characteristics required. However, these production techniques rely on powder or resin which is not sintered or cured during the production of the impact absorbing device being able to be removed from the device once production is complete. This may typically involve the impact absorbing device being shaken and/or exposed to compressed air or chemicals to remove the unwanted powder or uncured resin. As identified in "The design of impact absorbing structures for additive manufacturing" (Journal of Physics: Conference Series 382 (2012) 012042) "As closed-cell structures cannot be manufactured, the bending of cell walls and compression of trapped air that contribute to energy absorption in closed-cell foams cannot be replicated... this leaves cell strut bending as the only remaining mechanism for energy absorption in an AM (additive manufacturing) lattice structure.".

The present invention seeks to mitigate the above- mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved impact absorbing device and method of producing an impact absorbing device. Summary of the Invention

The present invention provides, according to a first aspect, an impact absorbing device comprising:

one or more closed cell structures, each closed cell structure being substantially hollow, wherein each closed cell structure comprises a plurality of layers of a first material, wherein each of the plurality of layers of material is fused to an adjacent layer of material, and each closed cell structure surrounds a second, different, material .

The second material may be a fluid, for example a liquid or a gas. The second material may be a solid material. The second material may be chosen to provide specific impact absorption characteristics.

The first material may be deposited by a first nozzle, and the second material may be deposited by a second, different, nozzle.

A liquid may be deposited within the closed cell structure during the manufacturing process by using a second, temperature controlled, nozzle. The temperature controlled nozzle may be used to ensure that the second material is deposited when at a temperature below the melting point of that material, or when at a temperature below the boiling point of that material. The second material may be deposited during the layer by layer build of the closed cell structure. Alternatively, the second material may be injected into the closed cell structure after the layer by layer build of the closed cell

structure .

Alternatively, the closed cell structure may be built in a gas chamber flooded with a gas comprising the second material, such that the gas is inevitably encapsulated within the closed cell structure.

Alternatively, a gas may be injected into a closed cell structure .

The closed cell structures may surround a second and third material. The second and third materials may be different to each other, and the first material. For example a second, solid, material may surround a third, liquid, material. Combination of a second and third material in the closed cell structure may allow further tuning of the impact absorption characteristics of the impact protection device.

Each of the closed cell structures may be the same shape and size, or vary in shape and size. The closed cell structures may be any or all of the following shapes: sphere, cube, cuboid, cylinder, hexagonal prism, cone, pyramid, and triangular prism. The skilled person will appreciate that these are example shapes only, and the closed cell structures may be any three dimensional shape with closed surfaces.

The one or more closed cell structures may comprise a single closed cell structure, the single closed cell structure comprising a plurality of chambers and channels between the chambers. The channels may be configured to allow the flow of fluid from one chamber to an

interconnected chamber. The shape and size of the plurality of chambers and channels may be configured to provide specific impact absorption characteristics.

The one or more closed cell structures may comprise a removable plug, such that removing the removable plug from the one or more closed cell structures provides an opening in the cell structure. Such an arrangement may allow the impact absorbing device to be collapsed or reduced in size, by removing the removable plug and compressing the impact absorbing device. As the impact absorbing device is compressed, the second material, may be pushed out of the impact protection device, with the resulting reduction in volume of the device. This may be advantageous when providing personal protective

equipment, such as cycle helmets. The removable plug may be reinserted to the impact absorption device once compressed to maintain the device in the compressed state. Removing the removable plug again may allow the impact absorption device to return to the uncompressed state, whereby the removable plug is reinserted into the impact absorption device.

The plurality of layers of the first material may comprise layers of materials produced by fused deposition modelling (FDM) . Fused deposition modelling comprises a technique of precise filament, layer by layer,

fabrication of a three dimensional article. Typically, fused deposition modelling comprises a small, temperature controlled, extruder forcing out a thermoplastic filament material, and depositing the thermoplastic filament material onto a platform in a layer by layer process. Fused deposition modelling has the advantage of being able to process polymers, such as production grade thermoplastics, including ABS, PC, PPSU, and Nylon.

Alternative materials may be low melting point alloys, such as zinc alloys, or Gallium alloys. Other

alternative materials may be composite materials, such as carbon fibre, glass fibre, powder-filled materials, or ceramic filled materials. Other alternative materials may be shape memory materials and/or foams. The second material may also be deposited using the FDM technique. Therefore, fused deposition modelling provides a method of producing impact absorbing devices which are

functional and stable over time. The impact absorption device may comprise a plurality of materials. According to a second aspect, the invention provides a method of producing an impact absorbing device, the method

comprising the steps of:

depositing a first layer of filament material, depositing a second layer of filament material on the first layer of filament material,

depositing one of more layers of a second material, the second material being different to the filament material ,

depositing further layers of filament material on top of previously laid layers of filament material, such that one or more closed cell structures are created surrounding the second material.

The second material may, for example, be a fluid material located in the closed cell structures. The fluid may be chosen to optimise the impact absorbing characteristics of the impact absorbing device.

Alternatively, the second material may, for example, be a solid material.

A liquid may be deposited within the closed cell structure during the manufacturing process by using a second, temperature controlled, nozzle. The temperature controlled nozzle may be used to ensure that the second material is deposited when at a temperature below the melting point of that material, or when at a temperature below the boiling point of that material. The second material may be deposited during the layer by layer build of the closed cell structure. Alternatively, the second material may be injected into the closed cell structure after the layer by layer build of the closed cell structure .

Alternatively, the closed cell structure may be built in a gas chamber flooded with a gas comprising the second material, such that the gas is inevitably encapsulated within the closed cell structure.

Alternatively, a gas may be injected into a closed cell structure . The inventor has realised that applying the fused deposition modelling technique to a method of producing impact absorbing devices allows impact protection devices to be produced, with closed cell structures, and all of the advantages provided by provision of closed cell structures, together with the advantage of being able to tune the impact absorption characteristics of the impact protection device with the choice of the second material, which is surrounded by the closed cell structure.

The impact absorbing device may be an automotive component. For example, the impact absorbing device may be an impact absorbing panel in a vehicle.

The impact absorbing device may be an aerospace component. For example, the impact absorbing device may be an impact absorbing panel in an aircraft.

The impact absorbing device may be a personal protection device. For example, the impact absorbing device may be a sports protection device, such as a shin pad or shoulder pad, a helmet, or similar protection devices .

An advantage of producing an impact absorbing device using fused deposition modelling is that one-off pieces may be produced relatively economically. For example, a personal protection device, for example a shin pad or shoulder pad, may be produced to specifically conform to a particular athlete. Production techniques such as foam extrusion, are less easily adapted for one-off

production .

The method may comprise the step of creating a three dimensional computer model of the impact absorbing device. The method may comprise the step of depositing layers of filament material using a computer controlled extruder. The computer controlled extruder may be associated with a computer control unit. The method may comprise the step of loading the three dimensional computer model of the impact absorbing device into the computer control unit. In an alternative embodiment, the method may comprise the step of creating the three dimensional model using the computer control unit. The computer control unit may analyse the three dimensional model in order to create a series of instructions for the computer controlled extruder. In alternative embodiments of the invention, the three dimensional model of the impact absorbing device may be converted into a series of extruder instructions by a separate computer, and loaded onto the computer control unit of the extruder as a separate step.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa .

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

Figure 1 shows an impact absorbing device according to a first embodiment of the invention; Figure 2 shows a series of method steps according to a second embodiment of the invention;

Figure 3 shows a system for producing impact absorbing devices according to a third embodiment of the invention;

Figure 4 shows an impact absorbing device according to a fourth embodiment of the invention; and Figure 5 shows a system for producing impact protection devices according to a fifth embodiment of the invention.

Detailed Description

Figure 1 shows a section of an impact absorbing device 10 according to a first embodiment of the

invention. The impact absorbing device 10 comprises a plurality of hollow spheres 12 which have been formed using fused deposition modelling. Loads applied to the impact absorbing device 10 will deform the cell walls of the hollow spheres 12 and also compress the gas which is trapped within the spheres 12, thereby at least partially absorbing the energy of the impact.

Figure 2 is a flowchart showing a method of creating an impact absorbing device according to a second

embodiment of the invention. The method comprises the initial step 20 of creating a three dimensional computer model of the desired impact absorbing device. This step may, for example, include performing a three dimensional scan or analysis of the object to which the impact absorbing device is to be applied. For a sports

protection device, this may comprise taking measurements of the body of an athlete so that the sports protection device fits them with high level of accuracy. This step of creating a three dimensional computer model may also comprise the step of analysing the impact absorbing properties that the impact absorbing device is required to have. This may determine the size and arrangement of the closed cell structures which make up the impact absorbing device, and/or the materials which are used to make the impact absorbing device.

The next step 22 comprises converting the three dimensional model into a series of instructions to be transmitted to computer controlled filament extruders. This step may be carried out by a conversion engine on a computer separate to the computer controlling the

filament extruders, or the computer controlling the filament extruders may also provide this function. If done on a separate computer, the instructions are then transmitted to the computer controlling the filament extruders at step 24, or if the computer used to convert the three dimensional model into a series of instructions is the same as controlling the filament extruders, this step is unnecessary.

The computer controlled filament extruders are then controlled, as indicated by step 26, according to the series of instructions such that a plurality of filament layers are extruded, one on top of another, such that a plurality of closed cell structures are created according to the design of the impact absorbing device, with the closed cell structures surrounding a second, different material .

Figure 3 shows an example of a fused deposition modelling manufacturing set up for producing impact absorbing devices according to an embodiment of the invention. A computer controlled extrusion device 34 is arranged to extrude, and deposit in layers, a

thermoplastic filament. As described above, a three dimensional computer model of the desired impact absorbing device is created, in this case by the

modelling unit 30. The modelling unit 30 sends the three dimensional model to a control computer unit 32, which translates the three dimensional computer model into a series of commands for the computer controlled extrusion device 34, such that the model may be made up of a series of layers of filament laid on top of each other. The computer controlled extrusion device 34 is located within a frame 36, with mechanical arrangements (not shown to improve clarity) configured to move the computer

controlled extrusion device 34, such that the

instructions from the control computer unit 32 are carried out, and an impact absorbing device 38 is

created. The closed cell structures of the impact absorbing device 38 may be filled with a second material, for example a liquid or gas, by injection through the layers of the extruded thermoplastic material.

Alternatively, the closed cell structures may be filled with a second material, for example a solid material, by extruding the second material in conjunction with the extrusion of the first material.

Figure 4 shows cut away view of an impact absorption device 40 comprising a single closed cell, the single closed cell comprising a plurality of chambers 42, wherein each chamber 42 is in fluid communication with one or more other chambers via a plurality of channels 44. When the impact absorption device 40 is compressed, fluid may flow between the chambers 42 via the channels 44. The size and shape of the chambers 42 and the channels 44 may be configured to provide the desired impact absorption characteristics. Such characteristics may include controlling the shape of the impact

absorption device as it deforms, for example to direct an impact in a particular way. Alternatively or additionally, the impact absorbing device may be

configured to tune the rate at which energy is dissipated under impact.

Figure 5 shows an impact protection device 50, which comprises a plurality of closed cells 52, each of the closed cells 52 made of a first material. Each of the closed cells 52 is also filled with a second, fluid, material 54. The first material is extruded by a

extruder head 56, and the second material is extruded, or deposited, by a second extruder head 58. The first material may be a standard filament material used in fused deposition modelling. The second material may be a non-Newtonian, shear thickening, fluid. Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be

appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

The present invention has been described with a single filament material being used to create the impact absorbing device. The fused deposition material

technique is equally applicable to the provision of two or more computer controlled extruders, each extruder extruding a different filament material. Therefore, impact absorbing devices comprising two or more different filament materials may be created, further increasing the possibility of creating highly specific impact absorption properties though the use of the different material characteristics.

The closed cell structures of the impact protection device may surround a gas material chosen to have

specific characteristics. The gas material may be incorporated within the closed cell structures by completing the method of filament laying within a gas chamber filled with the desired gas. Alternatively, materials may be deposited within the closed cell

structures by the use of temperature controlled nozzles, the temperature controlled to keep the second material below the melting, or boiling point of that material as required .

Example embodiments of the impact absorbing devices have included personal protection devices, automotive, and aerospace applications. However, many other types of device may be created providing the same advantages as detailed above. For example, the method may be used to produce impact absorbing devices for protection against ballistics, where improved impact absorption

characteristics may allow a lighter, more wearable, or more discrete, impact absorbing devices to be produced. Additionally, the invention may be applicable in the field of microfluidics . An alternative sport related embodiment of the invention may comprise a sole of a shoe.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable,

advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.