TECHNICAL FIELD

The present invention relates to a padding component for protective headgear. The present invention also relates to a method of embedding an optical fibre in a component.

BACKGROUND

Head injury is a known risk associated with contact sports such as American football and rugby. Impacts to the head are common in such sports and can result in conditions such as concussion. It is desirable to monitor impacts to a player’s head during training and competition in contact sports. Monitoring impacts to a player’s head can be useful in developing techniques during training to minimise the severity and/or frequency of head impacts. It can also be useful in determining whether to withdraw a player during competition in order to mitigate potential long-term head injury.

In some contact sports, protective headgear is worn to mitigate head injury. For example, helmets with hard outer shells are worn in American football and scrum caps are worn in rugby. Helmets are also worn by other users, such as motorcyclists and construction workers. Helmets present an opportunity for monitoring impacts to a user’s head. It is also desirable to ensure a correct fit of a helmet.

A variety of sensors are known which can be used to measure forces. These sensors include fibre optic sensors, such as fibre Bragg grating (FBG) sensors, and inertia-based sensors such as accelerometers. It is also known to incorporate such sensors with helmets to monitor head impacts. The Riddell Head Impact Telemetry System (RTM) utilises accelerometers attached to an interior surface of padding of an American football helmet. “Fiber optic sensor embedded smart helmet for real-time impact sensing and analysis through machine learning” by Zhuang et al. discloses forming a groove in an external surface of an American football helmet, placing an FBG in the groove, and filling the groove with epoxy with the FBG in situ to hold the FBG in place.

Known helmets utilising sensors to monitor head impacts suffer from a number of limitations. Inertia-based sensors typically have a high power demand and are not as accurate as optical sensors. The location of the FBG in the helmet disclosed in Zhuang et al. is spaced far apart from a user’s head in use, meaning the actual forces at the user’s head cannot be accurately measured. In addition, the arrangement of the FBG in a groove in an external surface of the helmet held in place by epoxy provides limited adhesion between the FBG and the helmet. This affects the accuracy of measurements obtained using the FBG, discussed further below. Furthermore, the thickness of the helmet at the groove is reduced which may affect the protective properties and/or the structural integrity of the helmet.

SUMMARY

A first aspect of the invention provides a padding component for protective headgear. The padding component comprises a padding element and a fibre Bragg grating embedded in the padding element.

A fibre Bragg grating (FBG) is an optical fibre comprising a section with a periodic variation in refractive index, forming a Bragg reflector. The optical fibre comprises a core in which the Bragg reflector is located and a cladding surrounding the core. By ‘embedded’, it is meant that the section of the optical fibre comprising the Bragg reflector is fixed within and surrounded by the body of the padding element. In use, the FBG can be used as part of an FBG sensor or force monitoring system to measure forces on the padding element.

There are a number of advantages associated with using an FBG to measure forces on a padding element over known alternatives, such as an accelerometer. An FBG can be used to sample data at a very high rate, for example in the region of 250kHz. FBGs are also immune to electromagnetic interference. This is particularly advantageous in a sports setting, such as during a competitive game where there are many sources of noise such as radio waves and other broadcasting signals.

The padding element may comprise a thickness, and at least a portion of the fibre Bragg grating may be embedded in the padding element at a distance from a surface of the padding element in a range of 40-60% of the thickness. This may sufficiently protect the FBG from external conditions while not affecting the accuracy of measurements obtained using the FBG. In use, the padding element may form part of the padding of a helmet, such as an American football helmet or a motorcycle helmet, or other protective headgear such as a rugby scrum cap.

Locating the FBG within the padding element means that, in use, the FBG is arranged proximate a user’s head, allowing forces at the user’s head to be more accurately measured. For example, shear forces at the interface between the user’s head and an item of protective headgear, such as a helmet, may have the potential to incur brain injury because they have the potential to induce rotational acceleration to the user’s head. Positioning the FBG close to the interface means that the forces imparted by the helmet to the user’s head can be more accurately monitored. Embedding the FBG in the padding element ensures good adhesion between the FBG and the padding element, enhancing the accuracy of measurements obtained by the interrogator.

Adhesion between the FBG and the padding element may be characterised by slippage between the FBG and the padding element, with less slippage being a characteristic of good adhesion, and/or air gaps within the structure of the padding element, with fewer air gaps being a characteristic of good adhesion.

The padding element may be additive manufactured. The padding element may be formed using any suitable additive manufacturing method, such as fused deposition modelling or stereolithography. The padding element may comprise a porous structure (i.e. comprising voids). The padding element may comprise a rectilinear or grid infill pattern. The FBG may be embedded in the porous structure. The padding element may comprise a structure which is a result of the padding element being additive manufactured, and the FBG may be embedded in this structure.

The padding element structure may comprise voids. For example the padding element may comprise a cellular structure (comprising periodic voids), a foam like structure (with a quasi-random or random distribution of void sizes), a mesh structure (comprising mostly voids, with structural strands formed in a periodic or random pattern) or any other suitable infill structure. The voids may allow for fluid communication through the padding element. A change in length of the optical fibre of an FBG can be affected by thermal expansion of the optical fibre, as well as tension applied to the optical fibre. In order to accurately determine a force resulting from strain within the optical fibre, it is desirable to remove or compensate for the effect of thermal expansion on measurements obtained using the FBG. A further advantage of embedding the FBG in the padding element is that the FBG is thermally insulated, thereby helping to reduce the effect of variations in temperature of the FBG on the output indicative of a force on the padding element.

The padding component may comprise a reference FBG embedded in the padding element adjacent to the FBG. The optical fibres of the FBG and the reference FBG may have different sensitivities to temperature. The optical fibres of the FBG and the reference FBG may comprise cores of different materials to provide the different sensitivities to temperature. For example, one of the optical fibres may comprise a polymer core and the other optical fibre may comprise a silica core. Alternatively, or additionally, the cores of the optical fibres may comprise different dopants, such as germanium, and/or different amounts of dopants to provide the different sensitivities to temperature.

The optical fibres of the FBG and the reference FBG may be arranged in the same orientation. The optical fibres of the FBG and the reference FBG may extend in parallel. The maximum spacing between the optical fibres of the FBG and the reference FBG may be 1cm or less.

The padding component may comprise a temperature sensor embedded in the padding element. By ‘embedded’, it is meant that the temperature sensor is fixed within and surrounded by the body of the padding element. The maximum spacing between the optical fibre of the FBG and the temperature sensor may be 1cm or less.

The reference FBG and/or the temperature sensor can be used to compensate for the effects of temperature on strain measurements obtained using the FBG.

The padding element may comprise a thermoplastic. The thermoplastic may comprise a thermoplastic polyurethane. These materials are particularly well suited to use as padding for protective headgear due to their flexibility and impact-absorbing properties when cured. A second aspect of the invention provides a padding system for protective headgear. The padding system comprises: the padding component of any of the above described embodiments, wherein the padding component is a first padding component and the padding system further comprises a second padding component comprising a padding element and a fibre Bragg grating embedded in the padding element. The fibre Bragg gratings of the first and second padding components may share a common optical fibre. The second padding component may have any of the features of embodiments of the first padding component as described above. Where a single optical fibre comprises more than one FBG, each FBG of the single optical fibre may be configured with a different Bragg wavelength.

In use, the padding system may be used to monitor forces acting on different portions of a user’s head. For example, the first padding component may be adjacent a user’s right cheek and the second padding component may be adjacent a user’s right temple. It may be advantageous to monitor impact forces on different portions of a user’s head, for example, as impacts on different portions of the head may be associated with different types or severities of injuries. By providing an optical fibre comprising multiple FBGs, with each FBG embedded in the padding element of a different padding component, only a single optical fibre with a central light source and interrogator are required to monitor forces on different portions of a user’s head. This is advantageous over known accelerometer-based systems, for example, which may require complex electrical wiring extending between different padding components. The padding system may further comprise a third padding component and a fourth padding component, wherein each of the third and fourth padding components comprise a padding element and a fibre Bragg grating embedded in the padding element. The fibre Bragg gratings of the third and fourth padding components may share a common optical fibre separate to the common optical fibre of the first and second padding components. The third and fourth padding components may have any of the features of embodiments of the first padding component as described above.

In use, the padding system of the above embodiment may be used to monitor forces acting on different portions of different areas of a user’s head. For example, the first plurality of padding components may comprise a padding component configured to be positioned adjacent the user’s right cheek and a padding component configured to be positioned adjacent the user’s right temple, and the second plurality of padding components may comprise a padding component configured to be positioned adjacent the user’s left cheek and a padding component configured to be positioned adjacent the user’s left temple. The system can be used to monitor forces on either side of the user’s head, and more specifically at the user’s right or left cheek or right or left temple.

The padding system may comprise any suitable number of padding components, each padding component comprising a padding element and an FBG embedded in the padding element. The padding system may comprise an optical fibre comprising any suitable number of FBGs, with each FBG embedded in the padding element of a different padding component. Any two or more FBGs may share a common optical fibre.

The padding system may comprise a first padding component configured to be positioned adjacent the back of a user’s head, a second padding component configured to be positioned adjacent the user’s right temple, a third padding component configured to be positioned adjacent the user’s left temple, a fourth padding component configured to be positioned adjacent the front of the user’s head, and a fifth padding component configured to be positioned adjacent the top of the user’s head. The first padding component may comprise a padding element and three FBGs embedded in the padding element. One of the FBGs may be aligned with an x-axis, another of the FBGs may be aligned with a y-axis, and the other FBG may be aligned with a z-axis. The second and third padding components may each comprise an FBG aligned with the y-axis and an FBG aligned with the z-axis. The fourth and fifth padding components may comprise an FBG aligned with the x-axis and an FBG aligned with the z-axis.

In use, the x-axis may extend through the centre of gravity of a user’s head and through the centre of the back of the user’s head, the y-axis may extend through the centre of gravity of a user’s head and through the centre of the user’s temples, i.e. through the centre of the side of the user’s head, and the z-axis may extend through the centre of gravity of a user’s head and through the centre of the top of the user’s head.

The padding system may comprise any suitable number of FBGs to monitor forces acting on a user’s head. As few as six or seven FBGs, configured to be strategically positioned around a user’s head, may sufficient to obtain a full picture of the forces acting on the user’s head.

A third aspect of the invention provides a force monitoring system for protective headgear. The force monitoring system comprises: the padding component or the padding system of any of the above described embodiments; a light source configured to transmit light to the or each fibre Bragg grating; and an interrogator configured to measure a wavelength of light reflected by the or each fibre Bragg grating and produce an output indicative of a force on the padding element in which the fibre Bragg grating is embedded in dependence on the measured wavelength.

The wavelength measured by interrogator may be the shifted Bragg peak. The output indicative of a force may comprise an output indicative of a magnitude of a force. Techniques for determining a force on the padding element using a measure wavelength of light reflected by the fibre Bragg grating embedded in the padding element will be apparent to those skilled in the art.

Where the force monitoring system comprises the padding system of any of the above described embodiments, the interrogator may be configured to produce an output indicative of an identity of the padding component comprising the padding element in which the fibre Bragg grating is embedded. The padding components of the padding system may be arranged such that each padding component is located at a different portion of a user’s head in use. The output indicative of an identity of a padding component can be used to determine the location of an impact force on the user’s head, for example.

The above aspect of the invention provides a system which can be used to monitor the magnitude and location of forces on the head of a user of protective headgear. In one example, the padding system can be installed in an American football helmet worn by a player and the system can be used to monitor impacts on the head of the player during training or during a competitive game. In another example, the system can be used to measure forces of the helmet acting on the head of the player to determine a correct fit of the helmet. For example, the system can be used to determine that a fit of the helmet is too tight if forces of the helmet acting on the head of the player (indicated by the strain measured by the FBGs) exceed a predetermined threshold. The interrogator may comprise any detector configured to detect a wavelength of light reflected by the Bragg grating of the FBG. The interrogator may comprise a processor or arrangement of processors. The processor or arrangement of processors may be configured to determine a strain of the optical fibre of the FBG in dependence on the wavelength of light and optionally to determine a force on the padding element in dependence on the strain of the optical fibre using known techniques. In some embodiments, the interrogator may merely determine the wavelengths of light reflected by the Bragg grating of the FBG, and processing of this data may be performed remote from the helmet.

Where a padding component comprises a reference FBG embedded in the padding element adjacent to the FBG, the optical fibres of the FBG and the reference FBG having different sensitivities to temperature, the light source may be configured to transmit light to the reference FBG. The interrogator may be configured to measure a wavelength of light reflected by the reference FBG. The interrogator may be configured to compare a wavelength of light reflected by the FBG and a wavelength of light reflected by the reference FBG. The interrogator may be configured to determine the effect of thermal expansion on the output indicative of a force on the padding element, using the comparison of the wavelengths of light reflected by the two fibre Bragg gratings and the known sensitivities to temperature of the two optical fibres, using a known technique. As such, the force monitoring system can compensate for the effects of temperature on the output indicative of a force on the padding element.

The force monitoring system may comprise a processor configured to receive the or each output from the interrogator. The processor may be further configured to process the or each output from the interrogator and produce an output indicative of a recommended action to reduce a risk of injury in dependence on the or each output from the interrogator. In one example, the padding system may be installed in an American football helmet and the recommended action may be to remove a player wearing the helmet from a training session or competitive game. The force monitoring system may further comprise a transmitter and a receiver. The transmitter may be configured to communicate with the interrogator and the receiver. The receiver may be configured to communicate with the transmitter and the processor. The receiver may be configured to receive the or each output from the interrogator via the transmitter and deliver the or each output from the interrogator to the processor. In one example, the padding system may be installed in an American football helmet, alongside the interrogator and the transmitter. The receiver and processor may be located at a sideline of a playing field, for example as part of a computing device. During a game, the processor may produce outputs indicative of recommended actions to reduce a risk of injury to a player wearing the helmet to allow a coach, manager, or the like to monitor the recommended actions and make appropriate decisions regarding the player, such as whether or not to substitute the player.

The force monitoring system may comprise a processing unit comprising the light source, the interrogator, and the transmitter. The padding system of any of the above described embodiments may comprise the processing unit.

In other embodiments, the transmitter may be configured to communicate with the processor and the receiver. The receiver may be configured to communicate with a further processor and configured to deliver the output received from the processor to the further processor. In one example, the padding system, the processor, and the transmitter may be installed in an American football helmet, and the receiver and further processor may be located at a sideline of a playing field.

The force monitoring system may be configured to produce an output indicative of a recommended action to reduce a risk of injury in real time. By ‘real time’ it is meant that there is negligible delay between a force being applied to one or more of the padding elements, the interrogator producing the or each output indicative of a force, the processor receiving the or each output from the interrogator, and the processor producing the output indicative of a recommended action to reduce a risk of injury.

The force monitoring system may comprise a processing unit comprising the light source, the interrogator, the transmitter, and the processor. The padding system of any of the above described embodiments may comprise the processing unit. The processor may be further configured to determine a cumulative impact in dependence on the or each output from the interrogator. The processor may be configured to produce the output indicative of a recommended action to reduce a risk of injury in dependence on the cumulative impact. For example, the processor may be configured to determine a sum of forces on one or more padding elements over a period of time to provide a cumulative impact. Determining a cumulative impact (or injury risk) may alternatively or additionally comprise counting a number of times a force or combination of forces has met a pre-determined criteria. The output of the processor may be a recommendation to remove an American football player wearing a helmet comprising the padding system from a training session or game when the cumulative impact exceeds a predetermined threshold.

The processor may be further configured to receive an input indicative of an unacceptable force and produce the output indicative of a recommended action to reduce a risk of injury in dependence on a comparison between an output from the interrogator and the unacceptable force. For example, a user of the force monitoring system may provide an input to the processor based on a maximum acceptable force magnitude on the padding element, and the processor may be configured to produce the output based on a comparison between an output from the interrogator and the maximum acceptable force magnitude. Where the force monitoring system comprises the padding system of any of the above described embodiments, a user of the force monitoring system may provide an input to the processor based on an identity of one of the padding components at which any magnitude of force is unacceptable. If an output from the interrogator is indicative of a force on the padding element greater than the acceptable force magnitude, or if an output from the interrogator is indicative of a force at the padding component at which any magnitude of force is unacceptable, the recommended action may be to remove an American football player wearing a helmet utilising the force monitoring system from a training session or game.

A fourth aspect of the invention provides an item of protective headgear. The item of protective headgear comprises the padding component or the padding system of any of the above-described embodiments.

The item of protective headgear may comprise an American football helmet. The item of protective headgear may comprise a helmet comprising an outer shell with the padding component arranged inside the outer shell. In other embodiments, the protective headgear may not comprise an outer shell. For example, the protective headgear may comprise a rugby scrum cap or the like.

The item of protective headgear may comprise an internal surface at least partially defining an internal volume for receiving a user’s head. The padding component may comprise the internal surface. The FBG may be within 5 -20mm of the internal surface. The padding element may comprise the internal surface. Alternatively, the padding component may comprise additional padding or cushioning comprising the internal surface. Locating the FBG close to the user’s head may mean that forces at the user’s head can be accurately measured.

A fifth aspect of the invention provides a method of embedding an optical fibre in a component. The method comprises: forming a first portion of the component using an additive manufacturing process, the first portion of the component comprising a groove; placing the optical fibre in the groove; and forming a second portion of the component over the groove with the optical fibre in the groove using the additive manufacturing process.

The method may be used to produce the padding component of any of the above described embodiments of the invention. The method may comprise forming a first portion of the padding element using an additive manufacturing process, the first portion comprising a groove; placing the fibre Bragg grating in the groove; and forming a second portion of the padding element over the groove with the fibre Bragg grating in the groove using the additive manufacturing process.

The method provides improved adhesion between the component and the optical fibre, and improved alignment of the optical fibre with an intended orientation.

The method may comprise maintaining a temperature of the first portion of the component while placing the optical fibre in the groove. The method may comprise maintaining a temperature of the first portion of the component while forming the second portion of the component. This may help to improve adhesion between the first and second portions of the component. Maintaining a temperature of the first portion of the component may comprise maintaining the temperature of the first portion of the component immediately after, or substantially immediately after, the first portion of the component has been formed.

The method may comprise forming the first and second portions of the component within an enclosure. The method may comprise maintaining a temperature in the enclosure. Maintaining the temperature in the enclosure may comprise using a heater.

Maintaining a temperature of the first portion of the component may encompass minimising a decrease in the temperature of the first portion of the component. This may be achieved by minimising the time periods between forming the first portion of the component and placing the optical fibre in the groove, and placing the optical fibre in the groove and forming the second portion of the component.

The method may comprise: providing: a first reel, a second reel, and a build platform; fixing the first reel to the build platform at a first location; forming the first portion of the component at a first position on the build platform; fixing the first reel to the build platform at a second position on the build platform; fixing the second reel to the build platform at a third position on the build platform, wherein the first position is aligned between the second and third positions; winding a first end of the optical fibre around the first reel; and winding a second end of the optical fibre around the second reel.

The reels hold the optical fibre in place within the groove while the second portion of the component is formed over the groove. Winding the optical fibre around the reels distributes the strain in the optical fibre resulting from the tension required to hold the optical fibre within the groove. The location of the reels outside the area of the build platform where the component is formed also means that any localised strain in the optical fibre is outside the portion of the optical fibre held within the groove. The reels may be particularly advantages in embodiments in which the additive manufacturing process is SLA, and the component is formed in a downwards direction from the build platform. The reels help prevent the optical fibre from falling out of the groove under gravity.

Because the reels are mounted on the build platform, the overall footprint of the platform is not increased. This may be advantageous when used with particular additive manufacturing techniques which require the build platform to be enclosed within housing of limited volume.

The optical fibre can be wound around the reels such that the optical fibre extends between the reels at a height above the build platform. The first portion of the component can be formed such that a height of the groove above the build platform is the same as the height of the optical fibre above the build platform. As such, minimal bending of the optical fibre is required to hold the optical fibre in the groove. An alternative means of holding the optical fibre in the grove might be to anchor the optical fibre to the build platform, such that the optical fibre extends from the build platform, over an edge of the first portion of the component, and into the groove. The bending of the optical fibre over the edge of the first portion of the component and the tension in the optical fibre required to hold the optical fibre in place may be such that the optical fibre becomes damaged. In contrast, the reels of embodiments of the invention may only require the optical fibre to be bent around the arc of the reels. This may mitigate damage to the optical fibre.

The method may comprise adjusting tension in the optical fibre when the first end is wound around the first reel and the second end is wound around the second reel by rotating at least one of the first reel and the second reel relative to the build platform. At least one of the first reel and the second reel may be fixed in translation relative to the build platform and selectively rotationally fixed relative to the build platform. The method may comprise rotating at least one of the first reel and the second reel relative to the build platform when the first end is wound around the first reel and the second end is wound around the second reel to adjust tension in the optical fibre, followed by rotationally fixing the or each reel relative to the build platform to maintain the desired tension in the optical fibre. The reels therefore provide a simple means of accurately adjusting tension in the optical fibre to hold the optical fibre in the groove.

The method may comprise: providing a first support block at a fourth position on the build platform, wherein the fourth position is aligned between the first position and the second position; providing a second support block at a fifth position on the build platform, wherein the fifth position is aligned between the first position and the third position; and supporting the optical fibre across the first and second support blocks. A height of each of the support blocks above the build platform may be the same as a height of the groove above the build platform.

Due to the nature of winding the optical fibre around the reels, the optical fibre may extend from the reels at different heights. The support blocks help to ensure that the portion of the optical fibre placed within the groove extends at a height above the build platform that is the same as a height of the groove above the build platform. This minimises bending of the optical fibre at the interface between the fibre and the groove, which in turn mitigates any permanent strain in the optical fibre once the optical fibre has been embedded in the component. In the case where the optical fibre comprises an FBG used to measure strain in the component, for example, the presence of permanent strain in the fibre could affect the accuracy of measurements obtained using the FBG.

A height of at least one of the first reel, the second reel, the first support block, and the second support block above the build platform may be adjustable. This allows the height of the portion of the optical fibre placed within the groove above the build platform to be adjusted in dependence on a height of the groove above the build platform. The method may comprise adjusting a height of at least one of the first reel, the second reel, the first support block, and the second support block above the build platform.

At least one of the first and second support blocks may comprise a rounded upper surface for supporting the optical fibre. This may help to distribute strain in the optical fibre.

At least one of the first and second support blocks may comprise a groove. The method may comprise placing the fibre in the groove of the or each support blocks. The groove of the or each support block may be arranged in the rounded upper surface of the respective support block. The groove of the or each support block may help to ensure the optical fibre is appropriately aligned.

The method may comprise forming the first and second support blocks using the additive manufacturing process at the same time as forming the first portion of the component. This may help to ensure that a height of each of the first and second support blocks above the build platform is the same as a height of the grove of the first portion of the component above the build platform. The additive manufacturing process can be suitably controlled to ensure that the heights are the same.

The method may comprise forming the first portion of the component on a build platform. The additive manufacturing process may comprise depositing strands of material to form the first portion of the component. The strands of material may be deposited at an angle to an axis of the first portion of the component which is parallel to a longitudinal axis of the groove when the groove is formed. The angle may be within the range of 30-60 degrees or 40-50 degrees. The angle may be greater than or equal to 0 degrees and less than or equal to 90 degrees. This may provide a groove with an acceptably consistent width along the length of the groove.

The additive manufacturing process may comprise depositing a first plurality of strands of material in a first plane to form a first layer. Each strand of the first plurality of strands may be deposited in parallel to the other strands of the first plurality of strands. The additive manufacturing process may comprise depositing a second plurality of strands of material in a second plane over the first layer to form a second layer. Each strand of the second plurality of strands may be deposited in parallel to the other strands of the second plurality of strands. Each strand of the second plurality of strands may be deposited perpendicularly to the strands of the first plurality of strands. Each strand of the first and/or second plurality of strands may extend at an angle to an axis of the first portion of the component which is parallel to a longitudinal axis of the groove when the groove is formed. The angle may be greater than or equal to 0 degrees and less than or equal to 90 degrees. The angle may be within the range of 30-60 degrees or 40-50 degrees. This may provide the component with a grid infill pattern, the walls of the infill pattern extending at an angle to the longitudinal axis of the groove.

A maximum depth of the groove of the first portion of the component may be greater than or equal to a maximum diameter of the optical fibre. This means that the optical fibre is kept below the surface of the first portion of the component comprising the groove during forming of the second portion of the component, thereby protecting the optical fibre from high temperatures which may be present during the additive manufacturing process. This also protects the optical fibre from collisions with a forming component used in the additive manufacturing process, such as a print head or nozzle. The additive manufacturing process may comprise fused deposition modelling (FDM) or stereolithography (SLA). Any suitable additive manufacturing process may be used. FDM is typically a quick and affordable process. SLA can be used to produce grooves with smooth internal surfaces, thereby improving adhesion between the optical fibre and the component. The method according to the fifth aspect can be used to manufacture any of the first to fourth aspects.

According to a sixth aspect, there is provided an article produced using the method of the fifth aspect.

A seventh aspect of the invention provides apparatus for embedding an optical fibre in a component. The apparatus comprises a build platform for forming the component thereon using an additive manufacturing process; a first reel for winding a first end of an optical fibre therearound and fixable to the build platform at a first position on the build platform; and a second reel for winding a second end of the optical fibre therearound and fixable to the build platform at a second position on the build platform. The apparatus may additionally comprise any of the features of the build platform, reels, and support blocks as described above with reference to other embodiments of the invention.

An eighth aspect of the invention provides a method of fitting an item of protective headgear comprising the padding system according to an embodiment of the invention as described above. The item of protective headgear may comprise an adjustable sizing device. The adjustable sizing device may comprise an inflatable bladder and/or an adjustable strap adjustable to adjust a fit of the item of protective headgear. The method may comprise: fitting the item of protective headgear to a user’s head; receiving the output from the interrogator; and adjusting the adjustable sizing device in dependence on the output from the interrogator. For example, the output from the interrogator may indicate that a force exerted on the padding element by the user’s head is above a predetermined threshold, therefore indicating that a fit of the protective headgear is too tight or too loose. The adjustable sizing device can then be adjusted to loosen/tighten the fit of the protective headgear. The process of receiving the output from the interrogator and adjusting the adjustable sizing device in dependence on the output may be repeated as many times as necessary to provide a correct fit of the protective headgear.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 shows a front view of a prior art item of protective headgear;

Figure 2 shows an underside view of the item of protective headgear of Figure 1;

Figure 3 shows a close-up underside view of a padding component of the item of protective headgear of Figures 1 and 2;

Figure 4 shows a front view of the padding component of Figure 3;

Figure 5 shows a front view of a padding component for protective headgear according to an embodiment of the invention;

Figure 6 shows a further view of the padding component of Figure 5;

Figure 7 shows a rigid prototype of the padding component of Figures 5 and 6;

Figure 8 shows a schematic plan view of a padding system for protective headgear according to an embodiment of the invention;

Figure 9 shows a schematic plan view of a padding system for protective headgear according to another embodiment of the invention;

Figure 10 shows a schematic view of a force monitoring system according to an embodiment of the invention;

Figure 11 shows an underside view of an item of protective headgear according to an embodiment of the invention;

Figures 12a-f show various external views of the item of protective headgear of Figure i i ;

Figures 13a and 13b each show a further external view of the item of protective headgear of Figure 11;

Figures 14a and 14b each show a prior art padding system;

Figure 15 shows a flowchart illustrating a method of embedding an optical fibre in a component according to an aspect of the invention;

Figure 16 shows a flowchart illustrating a method of embedding an optical fibre in a component according to an embodiment of the invention;

Figure 17 shows a schematic isometric view of an apparatus for embedding an optical fibre in a component according to an aspect of the invention; Figure 18 shows a schematic isometric view of the apparatus of Figure 17 in use; Figure 19 shows a schematic side view of the apparatus of Figure 17 in use;

Figure 20 shows a schematic plan view of the apparatus of Figure 17 in use;

Figures 21 to 23 each show a schematic isometric view of the apparatus of Figure 17 in use;

Figure 24 shows a schematic cross-sectional view of a groove of a first portion of a component with an optical fibre received within the groove;

Figure 25 shows a test component with an electrical wire embedded therein;

Figure 26 shows the test component of Figure 25 with the electrical wire removed; Figure 27a shows a microscopic image of a groove in a component printed at 0 degrees orientation;

Figure 27b shows a microscopic image of a groove in a component printed at 45 degrees orientation;

Figure 27c shows a microscopic image of a groove in a component printed at 90 degrees orientation; and

Figure 28 shows reflected signals from an FBG embedded in a prototype component and a reference non-embedded FBG.

DETAILED DESCRIPTION

Figures 1 and 2 show a prior art item of protective headgear 10. The item of protective headgear is an American football helmet 10. Figure 1 shows a front view of the helmet 10. The helmet 10 comprises a hard outer shell 110 and a plurality of padding components 1 attached to the internal surface of the outer shell 110. Figure 2 shows an underside view of the helmet 10 with more of the padding components 1 being visible. The padding components 1 comprise a right cheek padding component la, a left cheek padding component lb, a forehead padding component lc, a crown padding component Id, a rear padding component le, a right temple padding component If, and a left temple padding component lg.

Figure 3 shows a close-up underside view of the right cheek padding component la of the helmet 10 of Figures 1 and 2. The padding component la comprises a padding element 11 and cushioning 12. The padding element 11 is formed of a flexible, shock absorbing material such as thermoplastic polyurethane. The cushioning 12 is attached to a surface of the padding element 11, via an adhesive for example, such that the cushioning 12 is arranged proximate the head of a user of the helmet in use. The cushioning 12 is formed of a compressive foam or the like.

Figure 4 shows a front view of the padding component la of Figure 3. The padding element 11 of the padding component la comprises a base 111, a plurality of shock absorbing protrusions 112 protruding from the base 111, and a plurality of attachment protrusions 13 protruding from the base 111. The base 111 and protrusions 112, 13 may be formed by injection moulding. Each of the attachment protrusions 13 has a fastening element, in the form of one part of a popper, attached thereto for attaching the padding component la to the internal surface of the outer shell 110 of the helmet 10.

Figure 5 shows a front view of a padding component 2 for protective headgear according to an embodiment of the invention. The padding component 2 comprises a padding element 21 and a fibre Bragg grating FBG 221 embedded in the padding element 21.

The geometry and dimensions of the padding element 21 is based on that of the prior art right-cheek padding element la of Figure 4. The padding element 21 comprises a base 211, a plurality of shock-absorbing protrusions 212 protruding from the base 211, and a plurality of attachment protrusions 213 protruding from the base 211 for attaching fastening elements thereto, as described above. The padding component 2 comprises an optical fibre 22, a portion of which is embedded in the base 211 of the padding element 21. The portion of the optical fibre 22 which is embedded in the base 211 comprises the FBG 221. The dashed line in Figure 5 indicates the portion of the optical fibre 22 which is embedded in the base 211 either side of the FBG 221. The dotted line in Figure 5 indicates the FBG 221. The optical fibre 22 extends from either end of the FBG 221 through the base 211 and out through a side wall of the base 211 to allow for connection of the optical fibre 22 to a light source, an interrogator, and/or a further optical fibre. In other embodiments, the optical fibre 22 may only extend from one end of the FBG 221 through the base 211 and out through a side wall of the base 211.

It will be appreciated that although the padding element 2a is described with reference to the prior art padding element la of Figure 4, this is merely illustrative and in other embodiments the padding element of the invention may take any suitable form. The padding element may be any suitable size or shape to provide a padding component for protective head wear. In other embodiments, the padding element may not comprise a base, protrusions, or attachment features.

In the embodiment of Figure 5, the padding element 21 is manufactured using an additive manufacturing process, such as fused deposition modelling or stereolithography, and is formed of thermoplastic polyurethane. In other embodiments, the padding element 21 may be manufactured using a different suitable technique, such as injection moulding. Embodiments of the padding element 21 may be formed of any suitable material which is able to absorb impact forces in use, to protect the head of a user of protective headgear comprising the padding element 21, and which is suitably flexible so as to conform to an internal surface of an item of protective headgear.

Figure 6 shows a further view of the padding component 2 of Figure 5, demonstrating the flexibility of the padding element 21. For clarity, not all features of the padding component 2 are labelled in Figure 6.

Figure 7 shows a prototype component 3 which is a rigid prototype of the padding component 2 of Figures 5 and 6. The prototype component 3 comprises an element 31 comprising a base 311, a plurality of protrusions 312 protruding from the base 311, and a plurality of attachment protrusions 313 protruding from the base 311. The padding element 31 is manufactured using an additive manufacturing process and is formed of a thermoplastic material which is rigid when cured. The prototype component 3 demonstrates that the geometry of the padding component 2 of Figures 5 and 6 can be achieved using an additive manufacturing process.

Figure 8 shows a schematic plan view of a padding system 20 for protective headgear according to an embodiment of the invention. In this embodiment, the padding system 20 provides the padding for an American football helmet. The padding system 20 comprises the padding component 2a of Figures 5 and 6 and a plurality of further padding components 2b-g. The padding component 2a provides a right cheek padding component 2a. The further padding components 2b-g comprise: a left cheek padding component 2b, a forehead padding component 2c, a crown padding component 2d, a rear padding component 2e, a right temple padding component 2f, and a left temple padding component 2g. Each of the further padding components 2b-g comprises a padding element comprising a base, a plurality of shock-absorbing protrusions protruding from the base, and one or more fastening elements for attaching the padding element to the internal surface of an outer shell of an American football helmet. For clarity, these features are not labelled in Figure 8. The fastening elements comprise parts of poppers, t-nuts and bolts and/or parts of Velcro (RTM). Each of the further padding components 2b-g comprises a fibre Bragg grating FBG 221b-g embedded in the base of the padding element of the padding component.

The padding system 20 comprises a first optical fibre 22a, a second optical fibre 22b, a third optical fibre 22c, and a fourth optical fibre 22d. The first optical fibre 22a comprises the FBGs 221a and 22 If embedded in the padding elements of the right cheek padding component 2a and the right temple padding component 2f respectively. The second optical fibre 22b comprises the FBGs 221b and 22 lg embedded in the padding elements of the left cheek padding component 2b and the left temple padding component 2g respectively. The third optical fibre 22c comprises the FBG 22 le embedded in the padding element of the rear padding component 2e. The fourth optical fibre 22d comprises the FBGs 221c and 22 Id embedded in the padding elements of the forehead padding component 2c and the crown padding component 2d respectively.

The padding system 20 further comprises a processing unit 501, which may form part of a force monitoring system described in further detail below. The processing unit 501 comprises a light source configured to transmit light to each of the FBGs 221a-g via the optical fibres 22a-d and an interrogator configured to measure a wavelength of light reflected by each of the FBGs 221a-g and produce an output indicative of a force on the padding element in which the FBG is embedded in dependence on the measured wavelength. Each of the optical fibres 22a-d feed into the processing unit 501 to receive light from the light source and transmit light reflected by the FBGs 221a-g to the interrogator. In other embodiments, the processing unit 501 may not be present.

The padding system 20 further comprises means for compensating for the effects of temperature on the outputs indicative of forces on the padding elements. This may comprise a reference FBG (not shown) embedded in each of the padding elements as described above, or any other suitable means. The first optical fibre 22a extends from the FBG 221a embedded in the padding element of the right cheek padding component 2a, through the padding element of the right cheek padding component 2a, out through a side wall of the padding element of the right cheek padding component 2a, across a gap between the right cheek padding component 2a and the right temple padding component 2f, in through a side wall of the padding element of the right temple padding component 2f, through the padding element of the right temple padding component 2f to the FBG 22 If embedded in the padding element of the right temple padding component 2f, through the padding element of the right temple padding component 2f and out through a side wall of the padding element of the right temple padding component 2f, across a gap between the right temple padding component 2f and the rear padding component 2e, in through a side wall of the padding element of the rear padding component 2e, through the padding element of the rear padding component 2e, and out through a side wall of the padding element of the rear padding component 2e to the processing unit 501. The other optical fibres 22b-d extend through the padding elements of the padding system 20 in a similar manner as shown in Figure 8

It will be appreciated that the padding system 20 of Figure 8 is merely illustrative of an embodiment of the invention and that the orientation and placement of the optical fibres 22a-d and FBGs 221a-g may vary between embodiments.

Figure 9 shows a schematic plan view of a padding system 30 for protective headgear according to another embodiment of the invention. The padding system 30 of Figure 9 comprises all the features of the padding system 20 of Figure 8, with like reference numerals used to refer to like features. The padding system 30 of Figure 9 comprises additional FBGs to the padding system 20 of Figure 8 including: an additional FBG 221ef embedded in the padding element of the right temple padding component 2f; additional FBGs 221e ₂ and 221e ₃ embedded in the padding element of the rear padding component 2e; an additional FBG 22 leg embedded in the padding element of the right temple padding component 2g; an additional FBG 22 ld2 embedded in the padding element of the crown padding component 2d; and additional FBG 221c ₂ embedded in the padding element of the forehead padding component 2c.

Figure 9 demonstrates that embodiments of the invention provide padding systems comprising any suitable number, placement, and orientation of FBGs. It will be appreciated that the number, placement, and orientation of FBGs will vary depending on the particular application of the padding system.

Figure 10 shows a schematic view of a force monitoring system 40 according to an embodiment of the invention. The force monitoring system 40 comprises the padding system 20 of Figure 8, including the processing unit 501, and a computing device 406. For clarity, features of the padding system 20 are not labelled. In other embodiments, the force monitoring system 40 may comprise a different padding system, such as the padding system 30 of Figure 9 or any other padding system according to an embodiment of the invention. In addition to a light source 401 and an interrogator 402, the processing unit 501 comprises a transmitter 403. The computing device 406 comprises a receiver 404, a processor 405, and a user interface 406. The computing device 406 may take the form of any suitable device, such as a laptop computer, a tablet, or a smartphone. In use, the padding system 20, including the processing unit 501, may be installed in an American football helmet and the computing device may be located at a sideline of a field of play or training area.

The interrogator 402 is configured to measure a wavelength of light reflected by each of the FBGs of the padding system 20 and produce an output indicative of a magnitude of a force on the padding element in which the FBG is embedded in dependence on the measured wavelength. The interrogator 402 is also configured to produce an output indicative of an identity of the padding component comprising the padding element in which the fibre Bragg grating is embedded. The interrogator 402 is therefore configured to provide outputs indicative of the magnitude and location of forces on the padding components of the padding system 20.

The transmitter 403 is configured to communicate with the interrogator 402 to receive outputs from the interrogator 402 indicative of forces on the padding elements of the padding system 20. The transmitter 403 is configured to wirelessly communicate with the receiver 404 of the computing device 406 to deliver outputs from the interrogator

402 to the computing device 406. Any suitable means of wireless communication between the transmitter 403 and the receiver 404 may be provided, such as Bluetooth (RTM) or WiFi (RTM). The receiver 404 is configured to communicate with the processor 405 to deliver outputs from the interrogator 402 received from the transmitter

403 to the processor 405. The processor 405 is configured to process the outputs from the interrogator 402 and produce an output indicative of a recommended action to reduce a risk of injury in dependence on the outputs from the interrogator 402. The processor 405 is communication with the user interface 407 to display information to a user of the computing device 406 which is indicative of the output from the processor 405. The processor 405 is also configured to receive an input indicative of an unacceptable force and produce the output indicative of a recommended action to reduce a risk of injury in dependence on a comparison between outputs from the interrogator and the unacceptable force.

The force monitoring system 40 is configured to produce an output indicative of a recommended action to reduce a risk of injury in real time. In an example use case, wherein the padding system 20 is implemented in an American football helmet, a coach or manager may provide inputs to the processor 405 indicative of unacceptable impact forces specific to a particular player using the helmet. The unacceptable impact forces may include forces to any area of the head with a magnitude above a predetermined threshold, and forces of any magnitude to the back of the head. During training or during a competitive game, the interrogator 402 may produce an output which is indicative of a force with a magnitude above the predetermined threshold on one of the padding elements of the padding system. The processor 405, in response, may then provide a recommended action to remove the player from the training session or game, and this recommended action may be displayed in suitable form, for example by means of a graphic or text, by the user interface 407 of the computing device 406. The interrogator 402 may produce an output which is indicative of a force on the rear padding component 2e (see Figure 8), i.e. a force on the back of the player’s head. The processor 405, in response, may then provide the same recommended action.

The processor 405 is also configured to determine a cumulative impact in dependence on outputs from the interrogator 402. In the above example use case, the coach or manager may provide inputs to the processor 405 indicative of an unacceptable cumulative impact force. The processor 405 is configured to sum the magnitudes of the impact forces determined by the interrogator 402 and determine when the sum of the impact forces reaches the unacceptable cumulative impact force. The processor 405, in response, may then provide a recommended action to remove the player from the training session or game, and this recommended action may be displayed in suitable form, for example by means of a graphic or text, by the user interface 407 of the computing device 406.

Figure 11 shows an underside view of an item of protective headgear 50 according to an embodiment of the invention. In this embodiment, the item of protective headgear takes the form of an American football helmet 50. The helmet 50 comprises the padding system 30 of Figure 9. The helmet 50 comprises a hard outer shell 510, and the padding components 2a-g are attached to the internal surface of the outer shell 510. For clarity, only the padding components 2a-g and the processing unit 501 are shown, and the processing unit 501 is shown schematically. It will be appreciated that the size, configuration, and location of the processing unit 501 may vary between embodiments of the invention. For example, in some embodiments the processing unit 501 may be attached to the internal surface of the outer shell 510, and in other embodiments the processing unit 501 may be attached to an external surface of the outer shell 510.

The padding components 2a-g are arranged such that the shock absorbing protrusions extend between the base of the padding elements and the internal surface of the outer shell 510 of the helmet 50. Each padding component 2a-g further comprises cushioning attached to the base of the padding element on an opposite side of the base to the shock absorbing protrusions, such that, in use, the cushioning sits between the head of a wearer of the helmet 50 and the padding element. The surfaces of the cushioning of the padding components 2a-g which lie adjacent a wearer’s head in use define an internal volume of the helmet 50 for receiving a wearer’s head. Each FBG is within 5-20mm of the surface of the respective cushioning defining the internal volume.

Figures 12a-f show various external views of the helmet 50 of Figure 11. Figures 12a-f show schematically the arrangement of the FBGs and optical fibres relative to the outer shell of the helmet 50. It will be appreciated that Figures 12a-f are illustrative; the FBGs and optical fibres are not actually arranged on an outer surface of the outer shell of the helmet 50.

Figures 13a and 13b each show a further external view of the helmet 50 of Figure 11, with the positions of the padding components 2a-g relative to the outer shell of the helmet 50 indicated. Figures 14a and 14b each show cushioning of padding components of a prior art padding system 60, 70 for a motorcycle helmet. The padding system 60 of Figure 14a comprises a single padding component having different portions corresponding to different portions of the human head. The padding system 70 of Figure 14a comprises: a first padding component comprising cushioning 701, the first padding component comprising a crown portion, a front portion, a rear portion, and two side portions; a right cheek padding component comprising cushioning 702; and a left cheek padding component comprising cushioning 703.

Embodiments of the invention may comprise a similar padding system to that of the prior art padding systems 60, 70, wherein one or more of the padding components comprise a padding element and an FBG embedded in the padding element. The padding element may comprise a flat, flexible sheet, comparable to the base of the padding element of Figure 4 without the shock-absorbing protrusions. The padding element may be arranged between the respective cushioning and a hard outer shell of a motorcycle helmet in use. This demonstrates that embodiments of the invention may be applicable to any suitable item of protective headgear, such as a motorcycle helmet.

Figure 15 shows a flowchart illustrating a method 100 of embedding an optical fibre in a component according to an aspect of the invention. The method comprises: forming 101 a first portion of the component using an additive manufacturing process, the first portion of the component comprising a groove; placing 102 the optical fibre in the groove; and forming 103 a second portion of the component over the groove with the optical fibre in the groove using the additive manufacturing process.

Figure 16 shows a flowchart illustrating a method 200 of embedding an optical fibre in a component according to an embodiment of the invention. The method 200 comprises: providing 201 a first reel, a second reel, and a build platform; providing 202 a first support block at a first position on the build platform; providing 203 a second support block at a second position on the build platform; forming 204 the first portion of the component at a third position on the build platform, wherein the third position is aligned between the first position and the second position; fixing 205 the first reel to the build platform at a fourth position on the build platform; fixing 206 the second reel to the build platform at a fifth position on the build platform, wherein the first, second, and third positions are aligned between the fourth and fifth positions; winding 207 a first end of the optical fibre around the first reel; supporting 208 the optical fibre across the first and second support blocks; placing 209 the optical fibre in the groove of the first portion of the component; winding 210 a second end of the optical fibre around the second reel; adjusting 211 tension in the optical fibre by rotating at least one of the first reel and the second reel relative to the build platform; and forming 212 the second portion of the component over the groove with the optical fibre in the groove.

Figure 16 illustrates an example order in which steps of a method according to an embodiment of the invention may be carried out. In other embodiments, some of the steps may be carried out simultaneously or in a different order to that illustrated in Figure 16. For example, the support blocks may be formed using the additive manufacturing process at the same time as forming the first portion of the component or the support blocks may be provided separately after the first portion of the component has been formed. Supporting the optical fibre across the first and second support blocks and placing the optical fibre in the groove of the first portion of the component may be carried out simultaneously or in the reverse order. In some embodiments, some of the steps may be omitted. For example, the support blocks may not necessarily be formed.

Figure 17 shows a schematic isometric view of an apparatus 80 for embedding an optical fibre in a component according to an aspect of the invention. The apparatus 80 comprises: a build platform 81, a first reel 82, and a second reel 83. The build platform 81 is for forming the component thereon using an additive manufacturing process. The first reel 82 is for winding a first end of an optical fibre therearound. The first reel 82 is fixable to the build platform 81 at a first position on the build platform. The second reel 83 is for winding a second end of the optical fibre therearound. The second reel 83 is fixable to the build platform 81 at a second position on the build platform. The apparatus 80 may be used in a method according to any embodiment of the invention as described above. The apparatus 80 may be used to hold the optical fibre in the groove of the first portion of the component during forming of the second portion of the component.

Figures 18 to 23 show the apparatus 80 in use in embedding an optical fibre in a component. Figure 18 shows a schematic isometric view, Figure 19 shows a schematic side view, Figure 20 shows a schematic plan view, and Figures 21 to 23 show schematic close-up views of parts of the apparatus 80. Figures 18 to 23 show a first portion of a component 4 formed on the build platform 81 between first and second support blocks 5, 6. A first end of an optical fibre 7 is wound around the first reel 82 and a second end of the optical fibre 7 is wound around the second reel 83, such that the optical fibre 7 extends between the reels 82, 83. The optical fibre 7 is supported between the reels 82, 83 across the first and second support blocks 5, 6. Figure 23 shows a close-up view of the first portion of the component 4, the first and second support blocks 5, 6, and the optical fibre 7. The first portion of the component 4 comprises a groove 41. The first and second support blocks 5, 6 each comprise a rounded upper surface, with a groove 51, 61 provided in the rounded upper surface. The optical fibre 7 is received within the grooves 41, 51, 61 of the first portion of the component 4, the first support block 5, and the second support block 6.

The first portion of the component 4 may be formed using an additive manufacturing process, for example in accordance with a method according to an embodiment of the invention. The first and second support blocks 5, 6 may be formed using the same additive manufacturing process at the same time as forming the first portion of the component 4. The additive manufacturing process can be controlled such that the grooves 41, 51, 61 of the first portion of the component 4 and the support blocks 5, 6 are provided at the same height above the build platform 81. In other embodiments, the support blocks 5, 6 may be formed separately and suitably secured to the build platform 81.

With each end of the optical fibre 7 wound around one of the reels 82, 83, it is inherent that the optical fibre 7 may extend from one of the reels 82, 83 at a different height above the build platform 81 than the other reel 82, 83, particularly if the optical fibre 7 is wound around each reel 82, 83 multiple times. The support blocks 5, 6 help to ensure that the optical fibre 7 extends towards the groove 41 of the first portion of the component 4, away from the reels 82, 83, at a controlled height above the build platform 81. This helps to ensure that the optical fibre 7 is held securely in the groove 41 of the first portion of the component 4. A second portion of the component can then be formed over the first portion of the component 4 with the optical fibre 7 held within the groove 41 of the first portion of the component 4, for example in accordance with a method according to an embodiment of the invention. Each reel 82, 83 is fixed in translation relative to the build platform 81 by means of a threaded bolt (not shown in Figures 18 to 22). Figure 23 shows a close-up view of the first reel 82 showing the bolt 821 fixing the first reel 82 in translation relative to the build platform 81. In one embodiment, a countersunk M5 bolt may be used, but any suitable threaded bolt could be used. The build platform 81 comprises a threaded bore at the first and second locations. Each threaded bore is configured to receive the threaded bolt fixing the respective reel 82, 83 in translation relative to the build platform 81. Each reel 82, 83 comprises a smooth, i.e. non-threaded bore, extending along the central axis thereof and configured to receive the respective threaded bolt. The threaded bolts extend through the non-threaded bore of the respective reel 82, 83 and into the respective threaded bore in the build platform 81.

The threaded bolts allow the reels 82, 83 to be selectively rotationally fixed to the build platform 81. Each of the reels 82, 83 can be rotated about the respective threaded bolt when the threaded bolt is received within the non-threaded bore of the reel 82, 83 and partially received in the respective threaded bore in the build platform 81. This enables one or both of the reels 82, 83 to be rotated relative to the build platform 81 when the optical fibre 7 is wound around the wheels to adjust the tension in the optical fibre 7. When the desired tension in the optical fibre 7 is obtained, the or each threaded bolt can be tightened to rotationally fix the respective reel 82, 83 relative to the build platform 81. In this configuration, the heads of the threaded bolts will exert a force on the upper surface of the respective reel 82, 83 directed towards the build platform 81 to rotationally fix the reels 82, 83.

Figure 24 shows a schematic cross-sectional view of the groove 41 of the first portion of the component 4 with the optical fibre 7 received within the groove 41. The groove 41 comprises a lower portion with a semi-cylindrical cross-section and an upper portion with a rectangular cross-section. The maximum depth of the groove is greater than the maximum radius of the optical fibre 7, such that the optical fibre 7 sits below the surface of the first portion of the component 4 when received in the groove 41. This helps to protect the optical fibre 7 during forming of the second portion of the component. In other embodiments, the groove may comprise a different cross-section, such as a completely square or rectangular cross-section. Due to the depth of the groove and the rectangular cross-section of the upper portion of the groove 41, there are parts of the groove 41 which are not occupied by the optical fibre 7 when the optical fibre 7 is received within the groove, as shown in Figure 24. Figure 25 shows a test component 251 with an electrical wire 252, 1mm in diameter, embedded therein using a method according to an embodiment of the invention. In this example, the additive manufacturing process was FDM and the material used to form the test component 251 was PLA (polylactic acid). The first portion of the test component 251 comprised a groove as show in Figure 24. Figure 26 shows the test component 251 with the electrical wire 252 removed and the resulting bore 261 through the test component 251. This demonstrates that during forming of the second portion of the test component 251, the PLA occupied the parts of the groove not occupied by the electrical wire 252 after the electrical wire 252 had been placed in the groove.

Figures 27a-c each show a microscopic image of a cross-section of a component produced using a method according to an embodiment of the invention. In this example, the additive manufacturing process was FDM. The FDM process comprised depositing strands of material from a nozzle to form layers of material forming the component. The strands of material were deposited at an angle to an intended longitudinal axis of the groove, referred to as the print orientation. Figures 27a-c each show the groove formed in the first portion of the respective component. The component of Figure 27a has been formed using a print orientation of 0 degrees. The component of Figure 27b has been formed using a print orientation of 45 degrees. The component of Figure 27c has been formed using a print orientation of 90 degrees.

Figures 27a-c show the width of the respective groove measured at three points along the length of the groove. The standard deviation of the groove width for the blocks printed at 0, 45, and 90 degrees orientation are 8.0, 2.7, and 8.2 respectively. This suggests that a print orientation of 45 degrees produces the most consistent groove width.

Figure 28 shows the amplitude of reflected light signals (line 391) from an optical fibre. A portion of the optical fibre has been embedded in a prototype component using a method according to an embodiment of the invention. The embedded portion of the optical fibre comprises a chirped FBG. In this example, the additive manufacturing process was FDM. After the optical fibre comprising the chirped FBG had been placed in the groove of the first portion of the component, the ends of the optical fibre extending out of the groove were secured directly to a build platform on which the first portion of the component had been formed. This caused bending of the optical fibre where the optical fibre extended at an angle out of the groove towards the build platform. The second portion of the component was then formed with the optical fibre secured in this manner.

Figure 28 also shows the amplitude of reflected light signals from a non-embedded reference optical fibre comprising an FBG of the same type as the embedded FBG (line 392). As shown in Figure 28, both the non-embedded reference FBG and the embedded

FBG produce square wave reflections due to the chirped FBGs.

On the left-hand side, the square wave for the reference FBG has a steeper edge than the square wave for the embedded FBG. This may be a result of the bending in the optical fibre comprising the embedded FBG described above. In some applications, modification of the square wave caused by bending of the optical fibre during forming of the component may be undesirable. The use of the reels and the support blocks described above may help to mitigate bending in the optical fibre. Methods according to embodiments of the invention may be used to embed optical fibres in a variety of different components, including padding components for protective headgear as described above. Further examples include wearable technology, such as straps for smart watches or the like.