A wearable air purifier

Abstract

A wearable air purifier 101 comprising headgear 102 for wearing on a wearer’s head, a fan assembly 103, 104, operable to generate a filtered airflow and a nozzle 105 attachable to the fan assembly to

Description

Background of the Disclosure Exposure to air pollution such as pollutant gases or airborne particulates presents a risk of harm to human health. An approach to reducing a person’s exposure to air pollution is to use a wearable air purifier to discharge filtered air towards a wearer’s face. Summary of the Disclosure The invention is defined according to the claims. A first aspect of the present disclosure provides a wearable air purifier, comprising: headgear for wearing on a wearer’s head, a fan assembly operable to generate filtered airflow, a nozzle attachable to the fan assembly to receive airflow generated by the fan assembly and discharge the airflow towards the wearer’s face, wherein the fan assembly is releasably attachable to the headgear. 20 25 In other words, the fan assembly is reversibly attachable and detachable by the wearer from the headgear. Thus the wearer may attach the fan assembly to the headgear when the provision of filtered airflow by the fan assembly is desired, and detach the fan assembly from the headgear when the airflow is not desired. The headgear may thus be used without the fan assembly attached, and thus without the additional mass and bulk of the fan assembly. This may be useful where the headgear has functionality independent of the fan assembly, for example, where the headgear comprises a headband, hat, helmet or headphones. In such applications, the wearer may desire to wear the headgear, e g., the headphones, without the fan assembly in scenarios where the filtered airflow is not desired, such as in environments with low levels of air pollution. Whereas in environments with high levels of air pollution the wearer may desire to also receive the filtered airflow to reduce their exposure to the air pollution. The headgear and components thereof may thus have dual functionality, which may desirably reduce a perceived need for the wearer to have separate air purifying and non-air purifying headgears, for example, separate air purifying and non-air purifying headphones. 10 15 20 25 In particular, because the nozzle attaches to the fan assembly, the fan assembly and the nozzle may be attached to and detached from the headgear as an assembly, which may allow convenient attachment and detachment of the fan assembly and nozzle with respect to the headgear. In comparison, if the nozzle were to attach to the headgear, instead of directly to the fan assembly, the wearer may be required to separately attach and detach both the nozzle and the fan assembly from the headgear, which may be relatively inconvenient for the wearer. Additionally, because the nozzle attaches and directly to the fan assembly, rather than indirectly via the headgear, the fan assembly may be fluidly coupled directly to the nozzle to pass filtered airflow to the nozzle, and is not required to releasably fluidly couple to the headgear to allow airflow to flow to the nozzle. And indeed, the direct coupling of the nozzle to the fan assembly, means that the nozzle is not required to fluidly couple to the headgear to receive the airflow. Thus a risk of airflow leakage between the fan assembly and the nozzle may be reduced. The nozzle functions to carry airflow from the fan assembly closer to the wearer’s face, e.g., closer to the nose / mouth region of the wearer’s face. Thus, the fan assembly may be attached to the headgear at a location relatively remote from the wearer’s face, for example, at the side, top, or rear of the wearer’s head, thereby avoiding obstructing the wearer’s face, e.g., obstructing the wearer’s vision. Whereas, notwithstanding that the fan assembly may be relatively remote from the wearer’s face, the filtered airflow may still be provided relatively directly to the wearer’s nose and / or mouth via the nozzle, thereby reducing dilution of the filtered airflow by unfiltered ambient air prior to inhalation. The nozzle may, for example, be arranged to extend from the fan assembly in front of the wearer’s face, to thereby duct airflow from the fan assembly to the front of the wearer’s face, e.g., to the wearer’s lower nasal and mouth region. The wearable air purifier may comprise a battery and a conductor assembly to conduct electrical power from the battery to the fan assembly, wherein the battery is mounted to 30 the headgear, and the conductor assembly comprises a releasable conductive coupler to facilitate releasable conductive coupling of the fan assembly to the battery. In other words, the battery for powering the fan assembly may be mounted directly to the headgear instead of being integrated with the fan assembly, and a breakable electrical coupling is provided to the fan assembly, the breakable coupling allowing the releasable 5 attachment of the fan assembly to the headgear. Mounting the battery to the headgear, instead of to the fan assembly, may desirably result in the mass of the battery being brought closer to a centre of gravity of the wearer’s head. Thereby wearer comfort may be improved. Whereas, the releasable conductive coupler accommodates the releasable attachment of the fan assembly to the headgear. The conductor assembly could directly 10 conductively couple the battery to the fan assembly, or could conductively couple the battery indirectly to the fan assembly, for example, via a fan controller mounted to the headgear. LD 20 The releasable conductive coupler may be configured to couple and decouple by attachment and detachment respectively of the fan assembly to the headgear. In other words, the breakable electrical coupling may be made and broken in result of the fan assembly being attached to and detached from the headgear. This may be desirably convenient to the wearer. In comparison, it may be less convenient if the wearer were required to manually make or break the electrical coupling separately to attaching or detaching the fan assembly to or from the headgear, for example, by the wearer separately manually coupling an electrical plug and socket. The releasable conductive coupler may comprise conductive contacts that are spring-25 biased towards a coupled position. The sprung contacts may thus provide a more resilient electrical coupling by the spring action accommodating movement of the fan assembly relative to the headgear when the fan assembly is attached to the headgear. The fan assembly may be releasably attachable to the headgear without relative rotation 30 between the fan assembly and the headgear. In other words, the fan assembly could attach to and detach from the headgear in a rotationally static motion. This may be desirably convenient to a wearer, as the user is not required to rotationally manipulate the fan assembly to attach or detach. In particular, this arrangement may be desirable where the fan assembly, or a part thereof, is configured to 5 be rotatable relative to the headgear, in which case rotational manipulation of the fan assembly may be accommodated by the rotation mechanism, and may not result in attachment or detachment of the fan assembly. The fan assembly may comprise a base that is releasably attachable to the headgear and 10 a fan housing in which a fan for generating the airflow is located and to which the nozzle is attachable to receive the airflow, wherein the fan housing is rotatably attached to the base to facilitate rotation of the nozzle relative to the headgear. 15 In other words, the fan housing, and so the nozzle attached thereto, may be rotatable relative to the headgear. Rotation of the nozzle relative to the headgear may be desirable as it allows the position of the nozzle relative to the wearer’s face to be varied, and so adjustment of the trajectory of airflow discharged by the fan assembly, for example, to accommodate for different sizes of different wearer’s heads. In particular, rotation of the fan housing complete with the nozzle allows rotation of the nozzle relative to the headgear 20 without rotation relative to the fan housing, thereby avoiding a requirement for a rotatable fluid coupling between the fan housing and the nozzle. However, rotation of the fan assembly relative to the headgear is complicated by the fan assembly being releasably attachable to the headgear, as a releasable rotation mechanism 25 may be difficult to implement. In particular, where conductors extend between electrical components on the headgear, such as a battery mounted to the headgear, and electrical components on the fan assembly, rotatable and releasable conductive couplers may be difficult to implement. By this feature however the desired rotation of the nozzle is accommodated within the fan assembly itself, negating the need for either a flexible fluid 30 coupling between the nozzle and the fan housing or a releasable and rotatable coupling, and in particular a releasable and rotatable conductive coupler, between the headgear and the fan assembly. Instead, by this feature, the base may attach to the headgear in a releasable yet rotationally-static manner. Thus, both mechanical and electrical couplings between the base and the headgear may be simplified, which may be less expensive to manufacture and more reliable in use. Indeed, the releasable conductive coupler may releasably conductively couple the base to the headgear, and a rotatable conductive coupler may rotatably conductively couple the base to the fan. 10 Thus, the releasable conductive coupler between the headgear and the base may be rotationally static, whilst still allowing rotation of the fan housing and so the nozzle relative to the headgear. The wearable air purifier may comprise a speaker attached to the headgear for supporting by the headgear over a wearer’s ear, wherein the fan assembly is releasably attachable to the headgear to be supported by the headgear on an opposite side of a median plane of the wearer to the speaker. 20 In other words, the headgear could embody headphones, with a speaker for audio playback, etc. By locating the speaker on an opposite side of the wearer’s median plane to the side on which the fan assembly is located, the mass of the speaker may balance out the mass of the fan assembly, thereby the centre of gravity of the wearable air purifier may be closer to a centre of gravity of the wearer’s head. Thus, wearer comfort may be improved. 25 The wearable air purifier may comprise a further conductor assembly to conduct electrical power from the battery to the speaker. In other words, the speaker may also be supplied with electrical power by the same battery as supplies the fan assembly. As a result, a need for a dedicated battery to supply the speaker is avoided, and accordingly cost and mass may be reduced. Where the battery is shared between the fan assembly and the speaker, via the conductor assembly and the further conductor assembly respectively, the battery may be mounted to the headgear, in preference, for example, to mounting the battery to the fan assembly. In this arrangement, the further conductor assembly is thus not required to be releasable 5 to permit attachment / detachment of the fan assembly to the headgear. As a result the further conductor assembly may provide a more reliable electrical coupling between the speaker and the battery than may be provided if the further conductor assembly were required to be releasable. This thus ensures a continuous power supply to the speaker, and thus reliable operation of the speaker. 10 The nozzle may be releasably attachable to the fan assembly. In other words, the nozzle could be reversibly detachable by the wearer from the fan assembly. Thus the wearer may detach the nozzle from the fan assembly, which may desirably facilitate ex-situ cleaning LO of the nozzle, or user replacement of the nozzle. In other examples, the nozzle could be 15 non-releasably attachable to the fan assembly. For example, the nozzle could be permanently attached to the fan assembly, or even formed integrally with the fan assembly. CM The wearable air purifier may comprise an alert system for generating an alert, the alert 20 system comprising a fan assembly sensor to sense if the fan assembly is attached to the headgear and an environmental condition sensor to sense an environmental condition, wherein the alert system is configured to sense an environmental condition sensor using the environmental condition sensor, determine whether the sensed environmental condition meets a threshold, sense if the fan assembly is attached to the headgear using 25 the fan assembly sensor, and generate an alert signal in the event that the sensed environmental condition meets the threshold and the fan assembly is not sensed to be attached to the headgear. In other words, the wearable purifier may sense an environmental condition and 30 subsequently generate an alert if the sensed environmental condition meets, e.g., matches or exceeds, the threshold and the fan assembly is not currently attached to the headgear. Thus, in a scenario where the wearer is wearing the headgear without the fan assembly attached to the headgear, but the environmental condition is determined to meet the predefined threshold, the wearer can be alerted to the environmental condition to thereby prompt the wearer to attach the fan assembly to the headgear, to thereby counter the 5 environmental condition. The environmental condition sensed could, for example, be one or more pollutant gases in the ambient air, such as, nitrogen dioxide or another pollutant gas in ambient air, or particulate matter, such as PM2.5 sized particulates. In these examples, the threshold 10 could be a concentration of the sensed gas or particulate pollutant, such that pollutant concentrations meeting the threshold concentration, i.e., pollutant concentrations equal to or greater than the threshold, result in generation of the alert signal. 15 The wearable air purifier could comprise a device for converting the alert signal into a wearer-perceptible alert, such as visible, audible or haptic alert. For example, the wearable air purifier could comprise a light located on a visible surface that is controlled to illuminate in response to the alert signal. Alternatively, the wearable air purifier could comprise a communication device, such as a radio transmitter, for communicating the alert signal to an external device, such as a mobile telephone, whereby the external device 20 may generate the wearer-perceptible alert. The alert system may be in communication with the speaker and configured to communicate the alert signal to the speaker. 25 In other words, the alert system may use the onboard speaker to generate an audible alert to the wearer when the environmental condition threshold is met and the fan assembly is not attached. Such an audible alert may be particularly useful for the head-worn format, as the apparatus may be outside of the wearer’s field of view, and thus providing a visible alert may be suboptimal. The alert system may be mounted to the headgear. In other words, the alert system may be mounted to the headgear separately of the fan assembly, rather than being incorporated into the fan assembly. Consequently, the alert system may continue to function effectively even if the fan assembly is detached from the headgear. For example, with the alert system 5 being mounted to the headgear, the environmental condition sensor continues to be exposed to the same environmental conditions as the wearer of the headgear, even if the fan assembly is detached and stowed in a remote location, e.g., stowed in the wearer’s pocket or backpack. In particular, in an example where the fan assembly is suppled with electrical power by a battery mounted to the headgear, rather than a battery incorporated 10 in the fan assembly, the alert system may share the same battery even when the fan assembly is detached. Additionally, by mounting the alert system to the headgear, the alert system is not required to also be releasably attachable to the headgear to facilitate 15 the releasable attachment of the fan assembly. The wearable air purifier may comprise a fan controller for controlling an airflow rate of the fan assembly, wherein the fan controller is in communication with the environmental condition sensor, and the fan controller controls the airflow rate of the fan assembly based on a signal from the environmental condition sensor. 20 In other words, the fan controller may control the airflow rate of the fan assembly based on the sensed environmental condition. Thus, the airflow rate may be varied to counter the environmental condition. For example, the sensed environmental condition could be a concentration of pollutant gases, such as nitrogen dioxide, in the air. Thus, where the concentration of the pollutant gas in the air is relatively high, the controller may control 25 the fan assembly to generate airflow at a relatively high rate, to thereby best exclude polluted ambient air from the wearer’s nose / mouth region. Because the fan controller shares the environmental condition sensor from the alert system, the fan controller does not require a dedicated environmental condition sensor. Thus, cost and complexity of the fan controller is reduced. The wearable air purifier may comprise a further fan assembly operable to generate a further airflow, wherein the nozzle is attachable to the further fan assembly to receive the further airflow and discharge the further airflow towards the wearer’s face, the further fan assembly is releasably attachable to the headgear to be supported by the headgear on an 5 opposite side of a median plane of the wearer to the fan assembly, and the nozzle is flexible to permit relative movement of the fan assembly and the further fan assembly when the fan assembly and the further fan assembly are attached to the nozzle. 10 15 20 25 In other words, the wearable air purifier may comprise a further fan assembly, and the nozzle may collect airflows from both the fan assembly and the further fan assembly and direct both airflows towards the wearer’s face. By using two fan assemblies, the wearable air purifier may be capable of supplying relatively high rates of filtered airflow to the wearer. By locating the further fan assembly on the opposite side of the median plane to the fan assembly, the torque exerted on the wearer’s head about the median plane by the mass of the fan assembly may be countered by the mass of the further fan assembly. Thus, the centre of gravity of the wearable air purifier may be brought closer to the median plane, i.e., the centre of the wearer’s head, thereby improving wearer comfort. Thus, this dual-fan assembly configuration has various advantages. However, a complication with using dual-fan assemblies in this configuration is that the nozzle mechanically connects the two fan assemblies, which may restrict relative movement of the fan assembly and the further fan assembly, which may complicate attachment and detachment of the fan assemblies to the headgear. The flexibility of the present nozzle however may desirably permit relative movement of the fan assemblies, which may thereby aid attachment and detachment of the fan assemblies from the headgear, as the wearer may more easily manipulate the relative positions and / or orientations of the fan assemblies during attachment / detachment. The fan assembly and the further fan assembly may comprise respective male or female locating features for cooperating with male or female locating features of the headgear to 30 locate the fan assembly and the further fan assembly relative to the headgear, wherein the nozzle is flexible to permit relative movement of the fan assembly and the further fan assembly when the fan assembly and the further fan assembly are attached to the nozzle such that the locating features of the fan assembly and the further fan assembly may clear and engage with the respective locating feature of the headgear mutually simultaneously during attachment of the fan assembly and the further fan assembly to the headgear. 5 The cooperating locating features of the headgear and the fan assemblies may assist with correct location of the fan assemblies to the headgear during attachment by the wearer, and may further improve the attachment of the fan assemblies to the headgear, thereby desirably reducing a risk of the fan assemblies inadvertently detaching from the headgear 10 in use. For example, the headgear may comprise male locating features configured to be received in respective female locating features of the fan assembly and the further fan assembly, to thereby locate the fan assembly and the further fan assembly. LD 20 However, engaging and disengaging the male and female locating features, during attachment and detachment respectively of the fan assemblies may require relative movement of the fan assemblies, to thereby enable the locating features of the fan assemblies to clear and engage / disengage the corresponding locating feature of the headgear during attachment and detachment respectively of the fan assemblies. This relative movement between the fan assemblies may be prevented if the nozzle were rigid. The flexibility of the nozzle is this example however permits the relative movement between the fan assemblies, such that the fan assemblies may be simultaneously attached / detached from the headgear whilst connected to the nozzle. According to a second aspect of the present disclosure, there is provided a wearable air 25 purifier, comprising: headgear for wearing on a wearer’s head, a fan assembly operable to generate filtered airflow and comprising an outlet to discharge the filtered airflow from the wearable air purifier for inhalation by the wearer, wherein the fan assembly is releasably attachable to the headgear. 30 In other words, the fan assembly is reversibly attachable and detachable by the wearer from the headgear. Thus the wearer may attach the fan assembly to the headgear when the provision of filtered airflow by the fan assembly is desired, and detach the fan assembly from the headgear when the airflow is not desired. The headgear may thus be used without the fan assembly attached, and thus without the additional mass and bulk of the fan assembly. This may be useful where the headgear has functionality independent 5 of the fan assembly, for example, where the headgear comprises a headband, hat, helmet or headphones. In such applications, the wearer may desire to wear the headgear, e.g., the headphones, without the fan assembly in scenarios where the filtered airflow is not desired, such as in environments with low levels of air pollution. Whereas in environments with high levels of air pollution the wearer may desire to also receive the 10 filtered airflow to reduce their exposure to the air pollution. The headgear and components thereof may thus have dual functionality, which may desirably reduce a perceived need for the wearer to have separate air purifying and non-air purifying headgears, for example, separate air purifying and non-air purifying headphones. 15 Put another way, the fan assembly comprises an outlet for discharging the filtered airflow directly out of the wearable air purifier for inhalation by the wearer. The filtered airflow directly discharged from the fan assembly may be directed towards the wearer’s face, past the wearer’s face and / or generally towards the vicinity of the wearer's face. 20 Thus, the fan assembly does not fluidly couple with the headgear in order to discharge the filtered airflow. In other words, there is no fluid coupling downstream of the fan assembly, i.e., there is no fluid coupling along the filtered air flow path after the outlet of the fan assembly. 25 Accordingly, the wearable air purifier may be used by the wearer with the fan assemblies, but without the nozzle described above, in order to receive the filtered airflow. The outlet may extend at least partially around a perimeter of the fan assembly. In other words, the outlet may be elongate in a direction about the perimeter of the fan assembly, 30 thereby shaping the discharged filtered airflow into a column of flowing air. In contrast to a point outlet, the discharged fdtered airflow may maintain its shape for longer after being discharged. The fan assembly may comprise a protrusion and the outlet may be provided within the 5 protrusion. In other words, the outlet may be provided within a protrusion of the fan assembly, which may for example shape and / or direct the discharged filtered airflow according to the shape of the protrusion. Accordingly, by providing the outlet within a protrusion, the discharged filtered airflow may be more accurately shaped and directed for inhalation by the user. 10 The fan assembly may comprise a fan assembly mating surface arranged to contact a headgear mating surface when the fan assembly is attached to the headgear, wherein the outlet is provided in a fan assembly surface other than the fan assembly mating surface. 15 In other words, the outlet is provided on a surface of the fan assembly that does not contact the headgear. In this way, the filtered airflow may be discharged directly from the fan assembly, and the wearable air purifier, without requiring a fluid coupling between the fan assembly and the headgear. 20 When the fan assembly is attached to the headgear, the outlet may be proud of the headgear. In other words, the outlet may be offset, for example in an axial direction and / or a radial direction, from the headgear such that no part of the outlet overlaps with, or is covered or obscured by, the headgear. Put another way, the outlet may be positioned on the fan assembly such that a portion of the fan assembly, for example a portion of the 25 body or casing of the fan assembly, is provided between the outlet and the headgear, for example in the axial direction. The fan assembly may be attachable to the headgear by way of a rotatable coupling for varying a position of the outlet relative to the headgear. In other words, the fan assembly, 30 and so the outlet, may be rotatable relative to the headgear. Rotation of the outlet relative to the headgear may be desirable as it allows the position of the outlet relative to the wearer’s face to be varied, and so adjustment of the trajectory of airflow discharged by the fan assembly, for example, to accommodate for different sizes of different wearer’s heads. In particular, rotation of the fan housing complete with the outlet allows rotation of the outlet relative to the headgear without rotation relative to the fan housing, thereby 5 avoiding a requirement for a rotatable fluid coupling. The rotatable coupling may comprise a magnet coupling. The wearable air purifier may comprise a battery and a conductor assembly to conduct electrical power from the battery to the fan assembly, wherein the battery is mounted to 10 the headgear, and the conductor assembly comprises a releasable conductive coupler to facilitate releasable conductive coupling of the fan assembly to the battery. 20 25 In other words, the battery for powering the fan assembly may be mounted directly to the headgear instead of being integrated with the fan assembly, and a breakable electrical coupling is provided to the fan assembly, the breakable coupling allowing the releasable attachment of the fan assembly to the headgear. Mounting the battery to the headgear, instead of to the fan assembly, may desirably result in the mass of the battery being brought closer to a centre of gravity of the wearer’s head. Thereby wearer comfort may be improved. Whereas, the releasable conductive coupler accommodates the releasable attachment of the fan assembly to the headgear. The conductor assembly could directly conductively couple the battery to the fan assembly, or could conductively couple the battery indirectly to the fan assembly, for example, via a fan controller mounted to the headgear. The releasable conductive coupler may be configured to couple and decouple by attachment and detachment respectively of the fan assembly to the headgear. In other words, the breakable electrical coupling may be made and broken in result of the fan assembly being attached to and detached from the headgear. This may be desirably convenient to the wearer. In comparison, it may be less convenient if the wearer were required to manually make or break the electrical coupling separately to attaching or detaching the fan assembly to or from the headgear, for example, by the wearer separately manually coupling an electrical plug and socket. The releasable conductive coupler may comprise conductive contacts that are spring-5 biased towards a coupled position. The sprung contacts may thus provide a more resilient electrical coupling by the spring action accommodating movement of the fan assembly relative to the headgear when the fan assembly is attached to the headgear. The fan assembly may be releasably attachable to the headgear without relative rotation 10 between the fan assembly and the headgear. In other words, the fan assembly could attach to and detach from the headgear in a 15 rotationally static motion. This may be desirably convenient to a wearer, as the user is not required to rotationally manipulate the fan assembly to attach or detach. In particular, this arrangement may be desirable where the fan assembly, or a part thereof, is configured to be rotatable relative to the headgear, in which case rotational manipulation of the fan assembly may be accommodated by the rotation mechanism, and may not result in attachment or detachment of the fan assembly. 20 The fan assembly may comprise a base that is releasably attachable to the headgear and a fan housing in which a fan for generating the airflow is located, and the fan housing is rotatably attached to the base to facilitate rotation of the outlet relative to the headgear. In other words, the fan housing, and so the outlet, may be rotatable relative to the 25 headgear. Rotation of the outlet relative to the headgear may be desirable as it allows the position of the outlet relative to the wearer’s face to be varied, and so adjustment of the trajectory of airflow discharged by the fan assembly, for example, to accommodate for different sizes of different wearer’s heads. In particular, rotation of the fan housing complete with the outlet allows rotation of the outlet relative to the headgear without 30 rotation relative to the fan housing, thereby avoiding a requirement for a rotatable fluid coupling. However, rotation of the fan assembly relative to the headgear is complicated by the fan assembly being releasably attachable to the headgear, as a releasable rotation mechanism may be difficult to implement. In particular, where conductors extend between electrical 5 components on the headgear, such as a battery mounted to the headgear, and electrical components on the fan assembly, rotatable and releasable conductive couplers may be difficult to implement. By this feature however the desired rotation of the outlet is accommodated within the fan assembly itself, negating the need for either a flexible fluid coupling or a releasable and rotatable coupling, and in particular a releasable and rotatable 10 conductive coupler, between the headgear and the fan assembly. Instead, by this feature, the base may attach to the headgear in a releasable yet rotationally-static manner. Thus, both mechanical and electrical couplings between the base and the headgear may be 15 simplified, which may be less expensive to manufacture and more reliable in use. Indeed, the releasable conductive coupler may releasably conductively couple the base to the headgear, and a rotatable conductive coupler may rotatably conductively couple the base to the fan. Thus, the releasable conductive coupler between the headgear and the base may be 20 rotationally static, whilst still allowing rotation of the fan housing and so the outlet relative to the headgear. The wearable air purifier may comprise a speaker attached to the headgear for supporting by the headgear over a wearer’s ear, wherein the fan assembly is releasably attachable to 25 the headgear to be supported by the headgear on an opposite side of a median plane of the wearer to the speaker. In other words, the headgear could embody headphones, with a speaker for audio playback, etc. By locating the speaker on an opposite side of the wearer’s median plane 30 to the side on which the fan assembly is located, the mass of the speaker may balance out the mass of the fan assembly, thereby the centre of gravity of the wearable air purifier may be closer to a centre of gravity of the wearer’s head. Thus, wearer comfort may be improved. The wearable air purifier may comprise a further conductor assembly to conduct electrical 5 power from the battery to the speaker. In other words, the speaker may also be supplied with electrical power by the same battery as supplies the fan assembly. As a result, a need for a dedicated battery to supply the speaker is avoided, and accordingly cost and mass may be reduced. 10 Where the battery is shared between the fan assembly and the speaker, via the conductor assembly and the further conductor assembly respectively, the battery may be mounted to the headgear, in preference, for example, to mounting the battery to the fan assembly. In this arrangement, the further conductor assembly is thus not required to be releasable to permit attachment / detachment of the fan assembly to the headgear. As a result the 15 further conductor assembly may provide a more reliable electrical coupling between the speaker and the battery than may be provided if the further conductor assembly were required to be releasable. This thus ensures a continuous power supply to the speaker, and thus reliable operation of the speaker. 20 The wearable air purifier may comprise an alert system for generating an alert, the alert system comprising a fan assembly sensor to sense if the fan assembly is attached to the headgear and an environmental condition sensor to sense an environmental condition, wherein the alert system is configured to sense an environmental condition sensor using the environmental condition sensor, determine whether the sensed environmental 25 condition meets a threshold, sense if the fan assembly is attached to the headgear using the fan assembly sensor, and generate an alert signal in the event that the sensed environmental condition meets the threshold and the fan assembly is not sensed to be attached to the headgear. 30 In other words, the wearable purifier may sense an environmental condition and subsequently generate an alert if the sensed environmental condition meets, e.g., matches or exceeds, the threshold and the fan assembly is not currently attached to the headgear. Thus, in a scenario where the wearer is wearing the headgear without the fan assembly attached to the headgear, but the environmental condition is determined to meet the predefined threshold, the wearer can be alerted to the environmental condition to thereby 5 prompt the wearer to attach the fan assembly to the headgear, to thereby counter the environmental condition. The environmental condition sensed could, for example, be one or more pollutant gases in the ambient air, such as, nitrogen dioxide or another pollutant gas in ambient air, or 10 particulate matter, such as PM2.5 sized particulates. In these examples, the threshold could be a concentration of the sensed gas or particulate pollutant, such that pollutant concentrations meeting the threshold concentration, i.e., pollutant concentrations equal to or greater than the threshold, result in generation of the alert signal. 15 The wearable air purifier could comprise a device for converting the alert signal into a wearer-perceptible alert, such as visible, audible or haptic alert. For example, the wearable air purifier could comprise a light located on a visible surface that is controlled to illuminate in response to the alert signal. Alternatively, the wearable air purifier could comprise a communication device, such as a radio transmitter, for communicating the 20 alert signal to an external device, such as a mobile computing device (e.g. a smart phone and / or smart watch), whereby the external device may generate the wearer-perceptible alert. The alert system is in communication with the speaker and configured to communicate 25 the alert signal to the speaker. In other words, the alert system may use the onboard speaker to generate an audible alert to the wearer when the environmental condition threshold is met and the fan assembly is not attached. Such an audible alert may be particularly useful for the head-worn format, 30 as the apparatus may be outside of the wearer’s field of view, and thus providing a visible alert may be suboptimal. The alert system may be mounted to the headgear. In other words, the alert system may be mounted to the headgear separately of the fan assembly, rather than being incorporated into the fan assembly. Consequently, the alert system may continue to function effectively even if the fan assembly is detached from the headgear. For example, with the alert system being mounted to the headgear, the environmental condition sensor continues to be exposed to the same environmental conditions as the wearer of the headgear, even if the fan assembly is detached and stowed in a remote location, e.g., stowed in the wearer’s pocket or backpack. In particular, in an example where the fan assembly is supplied with electrical power by a battery mounted to the headgear, rather than a battery incorporated in the fan assembly, the alert system may share the same battery even when the fan assembly is detached. Additionally, by mounting the alert system to the headgear, the alert system is not required to also be releasably attachable to the headgear to facilitate the releasable attachment of the fan assembly. The wearable air purifier may comprise a fan controller for controlling an airflow rate of the fan assembly, wherein the fan controller is in communication with the environmental condition sensor, and the fan controller controls the airflow rate of the fan assembly based on a signal from the environmental condition sensor. 20 In other words, the fan controller may control the airflow rate of the fan assembly based on the sensed environmental condition. Thus, the airflow rate may be varied to counter the environmental condition. For example, the sensed environmental condition could be a concentration of pollutant gases, such as nitrogen dioxide, in the air. Thus, where the 25 concentration of the pollutant gas in the air is relatively high, the controller may control the fan assembly to generate airflow at a relatively high rate, to thereby best exclude polluted ambient air from the wearer’s nose / mouth region. Because the fan controller shares the environmental condition sensor from the alert system, the fan controller does not require a dedicated environmental condition sensor. Thus, cost and complexity of the 30 fan controller is reduced. The wearable air purifier may comprise a further fan assembly operable to generate a further filtered airflow, wherein the further fan assembly comprises a further air outlet for discharging the further filtered airflow from the wearable air purifier for inhalation by the wearer, wherein the further fan assembly is releasably attachable to the headgear to be 5 supported by the headgear on an opposite side of a sagittal plane of the wearer to the fan assembly. In other words, the wearable air purifier may comprise a further fan assembly, and the outlet may collect airflows from both the fan assembly and the further fan assembly and 10 direct both airflows towards the wearer’s face. By using two fan assemblies, the wearable air purifier may be capable of supplying relatively high rates of filtered airflow to the wearer. By locating the further fan assembly on the opposite side of the median plane to the fan assembly, the torque exerted on the wearer’s head about the median plane by the LO mass of the fan assembly may be countered by the mass of the further fan assembly. Thus, 15 the centre of gravity of the wearable air purifier may be brought closer to the median plane, i.e., the centre of the wearer’s head, thereby improving wearer comfort. Thus, this dual-fan assembly configuration has various advantages. CM The wearable air purifier may further comprise a nozzle attachable to the fan assembly to 20 receive airflow generated by the fan assembly via the outlet and discharge the airflow towards the wearer’s face. The nozzle may function to carry airflow from the fan assembly closer to the wearer’s face, e.g., closer to the nose / mouth region of the wearer’s face. Thus, the fan assembly 25 may be attached to the headgear at a location relatively remote from the wearer’s face, for example, at the side, top, or rear of the wearer’s head, thereby avoiding obstructing the wearer’s face, e.g., obstructing the wearer’s vision. Whereas, notwithstanding that the fan assembly may be relatively remote from the wearer’s face, the filtered airflow may still be guided to the wearer’s nose and / or mouth via the nozzle, thereby reducing dilution 30 of the filtered airflow by unfiltered ambient air prior to inhalation. The nozzle may, for example, be arranged to extend from the fan assembly in front of the wearer’s face, to thereby duct airflow from the fan assembly to the front of the wearer’s face, e.g., to the wearer’s lower nasal and mouth region, to be discharged from an outlet of the nozzle. When the nozzle is attached to the fan assembly, the outlet of the nozzle may be the outlet of the wearable air purifier for discharging the filtered airflow for inhalation by the user. 5 The nozzle may be releasably attachable to the fan assembly. In other words, the nozzle could be reversibly detachable by the wearer from the fan assembly. Thus the wearer may detach the nozzle from the fan assembly, which may desirably facilitate ex-situ cleaning of the nozzle, or user replacement of the nozzle. In other examples, the nozzle could be 10 non-releasably attachable to the fan assembly. For example, the nozzle could be permanently attached to the fan assembly, or even formed integrally with the fan assembly. The wearable air purifier may comprise: a nozzle attachable to the fan assembly to receive 15 airflow generated by the fan assembly via the outlet and discharge the airflow towards the wearer’s face; and a further fan assembly operable to generate a further airflow, wherein the nozzle is attachable to the further fan assembly to receive the further airflow and discharge the further airflow towards the wearer’s face, the further fan assembly is releasably attachable to the headgear to be supported by the headgear on an opposite side 20 of a median plane of the wearer to the fan assembly, and the nozzle is flexible to permit relative movement of the fan assembly and the further fan assembly when the fan assembly and the further fan assembly are attached to the nozzle. The fan assembly and the further fan assembly may comprise respective male or female 25 locating features for cooperating with male or female locating features of the headgear to locate the fan assembly and the further fan assembly relative to the headgear, wherein the nozzle is flexible to permit relative movement of the fan assembly and the further fan assembly when the fan assembly and the further fan assembly are attached to the nozzle such that the locating features of the fan assembly and the further fan assembly may clear 30 and engage with the respective locating feature of the headgear mutually simultaneously during attachment of the fan assembly and the further fan assembly to the headgear. The cooperating locating features of the headgear and the fan assemblies may assist with correct location of the fan assemblies to the headgear during attachment by the wearer, and may further improve the attachment of the fan assemblies to the headgear, thereby 5 desirably reducing a risk of the fan assemblies inadvertently detaching from the headgear in use. For example, the headgear may comprise male locating features configured to be received in respective female locating features of the fan assembly and the further fan assembly, to thereby locate the fan assembly and the further fan assembly. LD However, engaging and disengaging the male and female locating features, during attachment and detachment respectively of the fan assemblies may require relative movement of the fan assemblies, to thereby enable the locating features of the fan assemblies to clear and engage / disengage the corresponding locating feature of the headgear during attachment and detachment respectively of the fan assemblies. This relative movement between the fan assemblies may be prevented if the nozzle were rigid. The flexibility of the nozzle in this example however permits the relative movement between the fan assemblies, such that the fan assemblies may be simultaneously attached / detached from the headgear whilst connected to the nozzle. 20 According to a third aspect of the present disclosure, there is provided a wearable air purifier, comprising: headgear for wearing on a wearer’s head, a fan assembly operable to generate filtered airflow, a nozzle attachable to the fan assembly to receive airflow generated by the fan assembly and discharge the airflow towards the wearer’s face. The fan assembly may be releasably attachable to the headgear. 25 Any feature of any one aspect may be incorporated in any other aspect. For example, the fan assembly of the third aspect may not fluidly couple with the headgear in order to discharge the filtered airflow. In other words, there may be no fluid coupling downstream of the fan assembly, i.e., there may be no fluid coupling along the filtered air flow path 30 after the outlet of the fan assembly. Additionally, or alternatively, the fan assembly pf the third aspect may comprise an outlet for discharging the filtered airflow directly out of the wearable air purifier for inhalation by the wearer. The filtered airflow directly discharged from the fan assembly may be directed towards the wearer’s face, past the wearer’s face and / or generally towards the vicinity of the wearer's face. 5 Brief Description of the Drawings In order that the present disclosure may be more readily understood, embodiments of the disclosure will now be described, by way of example, with reference to the accompanying drawings, in which: 10 Figure 1 is a schematic perspective view of a wearable air purifier embodying the present disclosure; Figure 2 is a schematic front elevation view of the wearable purifier; 15 Figure 3 is a schematic partially exploded perspective view of the wearable air purifier; Figure 4 is a schematic partially exploded front elevation view of the wearable air purifier; Figure 5 is a schematic front cross-sectional view of the wearable air purifier, 20 Figure 6 is a schematic partially exploded front cross-sectional view of the wearable air purifier; Figure 7 is a schematic side elevation view of the wearable air purifier; 25 Figure 8 is a further schematic side elevation view of the wearable air purifier; Figure 9 is a schematic depiction of an alert system of the wearable air purifier; 30 Figure 10 is a flow diagram depicting an example alert generation process performed by the alert system. Figure 11 is a schematic perspective view of the wearable air purifier according to an aspect of the present disclosure. 5 Figure 12 is a schematic perspective view of the wearable air purifier according to an aspect of the present disclosure. Figure 13 is a schematic cross-sectional view of an earcup of the wearable air purifier. 10 Detailed Description of the Disclosure A wearable air purifier 101, embodying aspects of the present disclosure, is shown schematically in Figures 1 and 2. As will be described in further detail herein, the wearable air purifier 101 is configured to be worn on a wearer’s head and deliver a filtered airflow towards a lower nasal and mouth region of a wearer’s face. Consequently, the 15 wearer’s exposure to ambient air pollution may desirably be reduced. The wearable air purifier 101 comprises headgear 102 for mounting on a wearer’s head, a pair of fan assemblies 103, 104, for generating filtered airflows, and a nozzle 105 for directing the airflows from the fan assemblies 103,104 towards the lower nasal and mouth 20 region of the wearer’s face. The headgear 102 has the form of over-the-ear headphones, and comprises a headband 106 and left and right ear cups 107, 108 connected to respective ends of the headband 106. The headband 106 is arcuate, and is configured to overlie a top and sides of the 25 wearer’s head in use, to thereby support the earcups 107, 108 over the wearer’s left and right ears respectively. The headband 106 is formed to resiliently hold the earcups 107, 108 against opposite sides, i.e., left and right sides respectively, of the wearer’s head, to thereby firmly retain the headgear 102 mounted on the wearer’s head. The headband 106 is resiliently flexible to accommodate differing distances between the ear cups, and so 30 differing head widths. The earcups 107, 108 are pivotally mounted to the ends of headband 106, to facilitate pivoting of the ear cups 107, 108 to accommodate different head shapes. The left and right earcups 107, 108 comprise respective speaker housings for housing components, such as respective speakers, as will be described in further detail with particular reference to Figure 5. The speakers in the earcups 107, 108 may thus be supported by the headgear 102 over the wearer’s ears, e.g., to facilitate use of the headgear 102 as headphones. The earcups 107, 108 comprise respective annular cushions 109, 110 for cushioning against the wearer’s head. The fan assemblies 103, 104 are releasably attachable to a respective one of the earcups 107, 108, such that the headgear 102 may releasably support the fan assemblies 103, 104 at left and right sides respectively of the wearer’s head. The releasable attachment of the fan assemblies 103, 104 to the ear cups 107, 108 will be described in further detail with reference to later Figures. 20 25 30 The nozzle 105 is attachable at left and right ends 111, 112 to a respective one of the fan assemblies 103, 104 of the headgear 102. The nozzle 105 defines air inlets at the left and right ends 111, 112, to mate with respective air outlets of the fan assemblies 103, 104, to thereby receive filtered airflow from the fan assemblies 103, 104 when so attached. The nozzle 105 is configured to extend from the left and right ends 111, 112 width-wise across the wearer’s face. The nozzle 105 comprises an air outlet at a central region approximately mid-way between the left and right ends 111,112, to be positioned approximately directly in front of and facing the wearer’s lower nasal and mouth region, in use. The nozzle 105 thus functions to duct filtered airflows from the fan assemblies 103, 104, supported at the sides of the wearer’s head, to the central outlet of the nozzle 105, and for discharging the airflows therefrom towards the lower nasal and mouth region of the wearer’s face. In use, when the fan assemblies 103, 104 are attached to the earcups 107, 108 respectively, the headgear 102 thereby supports the nozzle 105 in front of the wearer’s face. In particular, in result of the nozzle 105 being attached to the headgear 102, via the fan assemblies 103, 104, on opposite, left and right, sides of the wearer’s head, the nozzle 105 is well supported and less prone to unintended movement, e.g., vibration of the nozzle 105 in use. In comparison, coupling of the nozzle 105 to the headgear 102 at only one side of the wearer’s head, for example, at the left end 111 only, may result in a torque 5 being exerted on the single coupling by the mass of the nozzle, and may result in excessive undesired movement of the nozzle in use. LD 20 Like the headband 102, the nozzle 105 is configured to be flexible in a width dimension, i. e., parallel to the width dimension of the wearer’s head, so as to allow a distance between the point of coupling of the nozzle 105 to the headgear 102 to be varied. This flexibility advantageously allows the nozzle 105 also to accommodate differing distances between the fan assemblies 103, 104. This may advantageously accommodate differing distances between the ear cups 107, 108, and thus differing widths of wearers’ heads. Additionally, the flexibility of the nozzle 105 may desirably aid attachment and detachment of the fan assemblies 103, 104 to the ear cups 107, 108 respectively, as will be described in further detail with reference to later Figures. In examples, the nozzle 105 is configured to not contact the wearer’s face, such that it is supported by the headgear 102 a short distance in front of the wearer’s face. This noncontact configuration may advantageously improve wearer comfort, inasmuch that the potential for skin irritation or other discomfort caused by contact of the nozzle 105 with the wearer’s face is reduced. Referring next in particular to Figures 3 and 4, because the fan assemblies 103, 104 are 25 releasably attachable to a respective one of the earcups 107, 108 of the headgear 102, the fan assemblies 103, 104, and the nozzle 105 attached thereto, may be releasably attached and detached from the headgear 102 by the wearer. In examples, the fan assemblies 103, 104 and the nozzle 105 are configured to be attachable to and detachable from the headgear as an assembly, in which the nozzle 105 remains attached to the fan assemblies 30 103, 104 during attachment / detachment of the fan assemblies 103, 104 to / from the headgear 102. 10 15 20 25 Thus the wearer may attach the fan assemblies 103, 104 to the headgear 102 when the wearer desires the provision of filtered airflow, such as when the wearer is in an environment with relatively high levels of environmental air pollution, and the wearer may detach the fan assemblies 103, 104 from the headgear 102 when the filtered airflow is not desired, such as when the wearer is in an environment with relatively low levels of environmental air pollution. The headgear 102 may thus be used in the latter scenario without the fan assemblies 103, 104 attached, and thus without the additional mass and bulk of the fan assemblies 103,104. For example, the headgear may be used by the wearer simply as headphones for audio playback. The headgear 102 and components thereof, to be described in further detail with reference to later figures, may thus have dual functionality, which may desirably reduce a perceived need for the wearer to have separate air purifying and non-air purifying headphones. Because the nozzle 105 attaches directly to the fan assemblies 103, 104, the fan assemblies 103, 104 and the nozzle 105 may be attached to and detached from the headgear 102 as an assembly, which may allow convenient attachment and detachment of the fan assemblies 103, 104 and nozzle 105 with respect to the headgear 102. In comparison, if the nozzle 105 were to attach to the headgear 102, for example to the earcups 107, 108, instead of directly to the fan assemblies 103, 104, the wearer may be required to separately attach and detach both the nozzle 105 and the fan assemblies 103, 104 from the headgear 102, which may be relatively inconvenient for the wearer. Additionally, because the nozzle 105 attaches directly to the fan assemblies 103, 104, rather than, for example, attaching to the ear cups 107, 108 or the headgear 102 more generally, the fan assemblies 103, 104 are not required to releasably fluidly couple to the ear cups 107, 108 or the headgear 102 more generally to deliver filtered airflow to flow to the nozzle 105. Indeed, in this configuration, the nozzle 105 is not required to fluidly couple to the headgear 102 to receive the filtered airflows, and thus a risk of airflow leakage between the fan assembles 103, 104 and the nozzle 105 may be reduced. 30 The nozzle 105 could be releasably attached to the fan assemblies 103, 104, for example, by magnet couplings, clips, or releasable catches. Thus, the nozzle 105 may be detachable by the wearer from the fan assemblies 103, 104, for example, to facilitate ex-situ cleaning of the nozzle 105. In other examples, nozzle 105 could be non-releasably attached to the fan assemblies 103, 104. For example, the nozzle 105 could be structurally integral with housings of the fan assemblies 103, 104. LD 20 To assist the wearer with the releasable attachment of the fan assemblies 103, 104 to the ear cups 107, 108 respectively, each of the ear cups 103, 104 is provided with a male locating feature, in the form of a protruding portion 301, and each of the ear cups is provided with a corresponding female locating feature, in the form of intruding portion 302. The protruding portion 301 of each earcup 107, 108 cooperates with the intruding portion 302 of the respective fan assembly 103, 104 to function as a locating feature. This may desirably aid correct positioning of the fan assembly 103,104 relative to the headgear 102 during attachment of the fan assemblies 103, 104 by the wearer. Each of the ear cups 107, 108 defines a mating surface 304, that is flat and generally annular and extends around the circumference of the protruding portion 301. The fan assemblies 103, 104 each similarly define a flat and generally annular mating surface 303 extending around the circumference of the intruding portion x. The mating surfaces 303, 304 of the fan assemblies 103, 104 and the ear cups 107, 108 are arranged to contact when the fan assemblies 103, 104 are attached to the respective ear cups 107, 108, to thereby stably support the fan assemblies 103, 104 relative to the headgear 102. Referring next in particular to Figures 5 and 6, in examples the fan assemblies 103, 104 are substantially like, as are the earcups 107, 108, and also the mechanism of attachment of the fan assemblies 103, 104 to the earcups 107, 108. Thus, for brevity, only fan 25 assembly 104 and right ear cup 108 will be described in detail herein, on the understanding that substantially the same teachings apply to fan assembly 103 and left ear cup 107. Nozzle 105 is omitted from Figures 5 and 6 to avoid obscuring the described features. Conductors are depicted by dashed lines. 30 Headgear 102 comprises batteries 501, 502 located in cushions of the headband 106, and conductor assembly 503 for electrically coupling the batteries 501, 502 and for electrically coupling the batteries 501, 502 to components of the ear cup 104 and the fan assembly 108. The ear cup 104 comprises speaker housing 504 attached to an end of the headband 106. 5 The speaker housing 504 is substantially hollow, and defines the protruding portion 302 and the mating surface 303. The protruding portion 301 is generally frustoconical in shape, and narrows progressively in area in the direction of protrusion. The mating surface 303 is flat and generally annular, and extends around the circumference of the protruding portion 301. A speaker 505 is located in the speaker housing 504, and is supplied with 10 electrical power by the batteries 501, 502 via the conductor assembly 503. A rear part of the speaker 505 is located within the part of the volume of the speaker housing 504 defined by the protruding portion 301. LD 20 The fan assembly 104 comprises fan housing 506 and base 507. The fan housing 506 is rotatably mechanically coupled to the base 507. Thus, the fan housing 506 may be rotated relative to the base 507. The fan housing 506 and base 507 together define intruding portion 302. The intruding portion 302 defines a generally frustoconical intrusion into the fan assembly 104, that narrows in area progressively in the direction of intrusion. Base 507 defines the mating surface 303 that is flat and generally annular, and extends around the circumference of the intruding portion 302. The fan housing 506 is hollow, and a motor driven fan 508, fan controller 509, and an air filter 510 are located therein. The motor driven fan 508 is supplied with electrical power by the batteries 501, 502 via the conductor assembly 503 and the fan controller 509. The fan housing 506 comprises inlet aperture(s) 511 and outlet aperture 512. The outlet aperture 512 is arranged to fluidly 25 couple with an inlet at the right end 112 of the nozzle 105 when the nozzle 105 is attached to the fan housing 506. The base 507 of the fan assembly 108 comprises mechanical attachment features 601 for releasably mechanically coupling to a cooperating mechanical attachment feature 602 30 mounted to the speaker housing 504, to thereby releasably mechanically couple the fan assembly 104 to the ear cup 108. The mechanical attachment features 601,602 are located on the mating surfaces 303, 304 of the base 507 of the fan assembly 104 and the speaker housing 504 respectively. The mechanical attachment features 601, 602 are selected to couple to adequately attach the fan assembly 104, and nozzle 105, to the earcup 108 in use, yet allow the wearer to releasably make and break the coupling to allow the wearer 5 to releasably attach and detach the fan assembly 104 to and from the ear cup 108. The mechanical attachment features 601, 604 could, for example, be magnet couplings, clips, releasable catches, or any other suitable releasable fastener. LD The mechanical attachment features 601, 602 may be configured to allow the fan assembly 104 to attach to the earcup 108 in a rotationally static motion, i.e., such that the fan assembly 104 is not required to be rotated, in a screw action, to attach the fan assembly 104 to the ear cup 108. Thus, the wearer may attach / detach the fan assemblies 103, 104, and so the nozzle 105, to the ear cups 107, 108, without rotating the fan assemblies 103, 104, and thereby avoiding rotation of the nozzle relative to the headgear. Consequently, a risk of the nozzle 105 fouling the wearer’s face, or articles such as spectacles on the wearer’s face, may be reduced. The conductor assembly 503 comprises a releasable conductive coupling for releasably conductively coupling the fan assembly 104 to the ear cup 108. The releasable conductive 20 coupling is formed by cooperating conductive contacts 603, 604 located on mating surfaces 303, 304 of the base 507 of the fan assembly 108 and the speaker housing 504 respectively. In examples, the conductive contact 603 of the fan assembly 104 forms a socket and the conductive contact 604 of the ear cup 108 forms a pin to be received in the socket to make the conductive coupling. The pin may be spring-loaded to maintain the 25 conductive coupling between the ear cup 108 and fan assembly 104 notwithstanding a small degree of relative movement between the ear cup 108 and fan assembly 104. Where more than one conductive line is required, the releasable conductive coupling may comprise the appropriate number of pairs of conductive contacts. 30 The conductor assembly 503 further comprises a rotatable conductive coupler 513, for rotatably conductive coupling the conductive contact 603 mounted to the base 507 with the fan controller 509 mounted to the fan housing 506. The rotatable conductive coupler 513 thus conductively couples the fan controller 509 to the conductive contact 603 in a way that permits relative relation between the fan housing 506 and the base 507, whilst maintaining an electrical connection between the fan controller 509 and the batteries 501, 5 502. The rotatable conductor assembly 513 could, for example, comprise one or more ribbon cables, or slip rings. Fan 508 is thus controllable by fan controller 509 to draw air in through inlets 511, via filter 510, and discharge the filtered airflow via the outlet 512 to the nozzle 105, as 10 described previously with reference to earlier Figures. Referring in particular to Figure 5, when the fan assembly 104 is attached to the ear cup 15 108, the protruding portion 301 of the ear cup 108 is accommodated in the intruding portion 302 of the fan assembly 104, such that the protruding portion 301 fills substantially the whole volume of the intruding portion 302, and the surface of the protruding portion 301 contacts the surface of the intruding portion 302. In this attached condition, the mating surface 303 of the fan assembly 104 is in contact with the mating surface 304 of the ear cup 108. 20 The rotation of the fan housing 506 relative to the base 507 rotation may desirably allow the wearer to rotate the nozzle 105 relative to the headgear 102 when the fan assemblies 103, 104 are attached to the ear cups 107, 108, as will be described in further detail with reference to later Figures. In particular, because the fan housing 506 is rotatable relative to the base 507, this rotation of the nozzle 105 relative to the headgear 102 may be 25 achieved despite the base 507 being rotationally static relative to the earcup 108. Consequently, the mechanical fastening features 601, 602 and the conductive coupling contacts 603, 604, are not required to accommodate rotation of the base 507 relative to the ear cup 108. Rather, the mechanical fastening features 601, 602, and the conductive coupling parts 603, 604 need only accommodate static releasable attachment of the fan 30 assembly 104 to the earcup 108. Thus, the mechanical fastening features 601, 602, and the conductive coupling parts 603, 604 may be simplified. Ear cup 108 further comprises an alert system 514 located in the speaker housing 504. Alert system 514 is provided to monitor an environment condition and alert the wearer if the fan assembly 104 is detached from the earcup 108 and the monitored environmental 5 condition is unacceptable. Thus, the wearer may be prompted to attach the fan assembly 104 to the headgear 102, so that the wearer may receive the filtered airflow to counter the unacceptable environmental condition. Alert system 514 comprises fan assembly sensor 515, environmental condition sensor 10 516, and controller 517. The fan assembly sensor 516 is to sense if the fan assembly 104 is attached to the ear cup 15 108. The fan assembly sensor 516 is located on the mating surface 304 of the speaker housing 504, and is arranged to interact with the mating surface 303 of the fan assembly 104 when the fan assembly 104 is attached to the ear cup 108. Thus, the fan assembly sensor 515 can be interrogated by the controller 517 to determine if the fan assembly 104 is attached to the ear cup 108. For example, the fan assembly sensor 515 could comprise a momentary switch arranged to be depressed by the fan assembly 104 when the fan assembly 104 is attached to the speaker housing 108. 20 The environmental condition sensor 516 is to sense an environmental condition. The environmental condition sensor is exposed to ambient air via apertures in the speaker housing 504. The environmental condition sensor could, for example, be sensitive to one or more pollutant gases in the ambient air, such as, nitrogen dioxide or another pollutant 25 gas in ambient air, or to particulate matter, such as PM2.5 sized particulates. The controller 517 is configured to interrogate the fan assembly sensor 515 to sense if the fan assembly 104 is attached to the ear cup 108, interrogate the environmental condition sensor 516 to sense the particular environmental condition of interest, and then selectively 30 generate a wearer-perceptible alert to the wearer if the fan assembly 104 is not attached to the ear cup 108 and the sensed environmental condition meets a particular criteria. For example, the controller 517 could comprise one or more predefined threshold values representing threshold environmental condition levels considered to be unacceptable to the wearer, for example, threshold pollutant gas concentration levels. In this case, if the sensed environmental condition meets, e.g., equals or exceeds the threshold value, and 5 the fan assembly 104 is not attached to the ear cup 108, the alert system may generate a wearer-perceptible alert, to thereby prompt the wearer to attach the fan assembly 104 to the earcup 108. Thus, in a scenario where the wearer is wearing the headgear 102 without the fan assembly 104 attached to the headgear 102, but the environmental condition is determined to meet the predefined threshold, the wearer can be alerted to the environmental condition to thereby prompt the wearer to attach the fan assembly 104 to the headgear 102, to receive filtered airflow to thereby counter the environmental condition. 20 25 Referring next in particular to Figures 7 and 8, because of the previously described rotation of the fan housing 506 relative to the base 507 of the fan assemblies 103, 104, the nozzle 105 may be rotated relative to the headgear 102 in use. This may desirably enable the nozzle position to be adjusted relative to the headgear to suit different head sizes. Further, referring in particular to the configured depicted in Figure 8, this rotation may allow the nozzle to be rotated by the wearer away from the lower nasal / mouth region to a lowered position. This lowered position may usefully allow the wearer to move the nozzle away from their mouth, which may, for example, be desirable when the wearer is conversing with another person, eating or drinking. Referring next to Figure 9, in examples, the controller 517 of alert system 514 comprises input / output device 901, memory 902, processor 903, and system bus 904. The controller 517 of the alert system 514 is configured to generate the wearer-perceptible alert in dependence on whether the fan assembly 104 is attached to the headgear 102, sensed by fan assembly sensor 515, and on whether an environmental condition, sensed by environmental condition sensor 516, meets a threshold. The alert system 514 could, for example, utilise the speaker 505 to generate an audible alert to the wearer. The alert system could, for example, further send a signal to the fan controller 509 to vary the rate of airflow generated by the fan 508 in dependence on the sensed environmental condition. Thus, the airflow rate generated by the fan 508 may be varied to counter the 5 environmental conditions. Input / output interface 901 is provided for connection of the fan assembly sensor 515, the environmental condition sensor 516, the batteries 501, 502, the speaker 505, and the fan controller 509. Memory 902 stores a computer program, comprising machine-readable 10 instructions, for interrogating the fan assembly sensor 515 and the environmental condition sensor 516, and for generating an alert signal and / or a signal to the fan controller 509. Memory 902 further stores one or more predefined environmental condition threshold values, representing environmental conditions considered unacceptable to the wearer. Processor 903 is configured for receiving and processing signals from the fan 15 assembly sensor 515 and the environmental condition sensor 516, sense if the fan assembly 104 is attached to the headgear, based on a signal from the fan assembly sensor 515, sense the environmental condition using the environmental condition sensor 516, determine if the sensed environmental condition meets the threshold value stored in memory 902, and subsequently generate an alert signal if the sensed environmental 20 condition is determined to meet the threshold. The components 901 to 903 of the controller are in communication via system bus 904. Referring finally to Figure 10, in examples the computer program for generating the alert and controlling the airflow rate of the fan 508, based on the signals from the fan assembly 25 sensor 515 and / or the environmental condition sensor 516 comprises five stages. At stage 1001, the computer program causes the processor 903 to initiate the alerting procedure. The initiation stage could be triggered, for example, by a wearer’s input, such as wearer pressing an ‘ON’ button connected to the input / output interface 901 of the 30 controller 517, or by a wearer beginning to use the headgear for audio playback and thus energising the speaker 505. At stage 1002, the computer program causes the processor 903 to interrogate the fan assembly sensor 515 to determine if the fan assembly 104 is attached to the ear cup 108. If the determination is that the fan assembly is attached to the ear cup 108, the process 5 may cease, and stage 1001 may subsequently be repeated periodically. If the determination is that the fan assembly is not attached to the ear up 108, the process may proceed to stage 1003. At stage 1003, the computer program causes the processor 903 to interrogate the 10 environmental condition sensor 516 to sense the environmental condition. At stage 1004, the computer program causes the processor 903 to retrieve the threshold 15 environmental condition threshold value from memory 902, compare the environmental condition sensed at stage 1003 to the threshold value retrieved from memory 902, and determine if the sensed environmental condition meets the threshold value. If the determination is that the sensed environmental condition does not meet the threshold, e.g., is less than the threshold, the process may cease, and stage 1001 may subsequently be repeated periodically. If the determination is that the environmental condition does meet the threshold, e.g., is equal to or greater than the threshold, the process may proceed to 20 stage 1005. At stage 1005 the computer program causes the processor 903 to generate an alert signal and / or a fan speed signal. Stage 1005 could, for example, involve the processor 903 outputting an alert signal to the speaker 505, via input / output device 901, to thereby cause 25 the speaker 505 to generate an acoustic noise to alert the wearer. Stage 1005 could, for example, further involve the processor 903 outputting a fan speed signal to the fan controller 509, via input / output interface 901, to thereby cause the fan controller 509 to set the airflow rate of the fan 508 to a relatively high rate, to thereby counter the environmental condition. The operations of stages 1002 to 1004 could be performed in various alternative orders. For example, the operations of stage 1002 could be performed after the operations of stages 1003 and 1004, and / or the operations of stage 1004 could be performed before the operations of stage 1003, etc. Stage 1005 could involve generating one or both of the fan 5 alert signal and the fan speed signal. Wearable air purifiers 1100, 1101 embodying aspects of the present disclosures, are shown schematically in Figures 11 and 12. The wearable air purifiers 1100, 1101 shown in Figures 11 and 12 share many features in common with the wearable air purifiers 10 shown in Figures 1 to 10 and reference numerals in common have been maintained where appropriate. 15 Indeed, the only difference between the examples in Figures 11 and 12 and the examples described in relation to Figures 1 to 10 is the absence of the nozzle 105. Otherwise, the wearable air purifiers function as described above. In the example shown in Figure 11, the fan assemblies 103, 104 are attached to the headgear without the nozzle 105, such that the filtered airflow is discharged from the wearable air purifier from the outlets 512a, 512b. 20 The filtered airflow is discharged directly from the fan assemblies 103, 104 by way of the outlets 512a, 512b without any fluid coupling, i.e., without any airflow coupling or without an airflow path, between the fan assemblies and the headgear. The outlets are provided about a perimeter of the fan assemblies and sit proud, i.e., are radially offset, 25 from the headgear. The outlets are positioned such that the outlets are facing externally to the entire wearable purifier, such that airflow is sent to the wearer for inhalation without communicating with a nozzle. The fan assemblies 103, 104 may comprise a filter for filtering the airflow generated by 30 the fan. The filters may be C-shaped filters, such that the ducts connecting the fans to the 21 03 25 outlets 512a, 512b may travel through a thickness of the filter, i.e., through the gap in the filter defined by the C-shape. In the example shown in Figure 12, the fan assemblies 103, 104 are attached to the 5 headgear without the nozzle 105, such that the filtered airflow is discharged from the wearable air purifier from outlets provided within the protrusions 1102, 1103. The filtered airflow is discharged directly from the fan assemblies 103, 104 by way of the outlets within protrusions 1102, 1103 without any fluid coupling between the fan 10 assemblies and the headgear. The protrusions are provided about a perimeter of the fan assemblies and sit proud, i.e., are radially offset, from the headgear. Figure 13 shows a cross-section of an earcup 108 with a fan assembly 104 attached. In particular, Figure 13 illustrates the airflow path, depicted by arrows, from the inlet 15 apertures 511 to the outlet 512a via the fan 508. As shown in Figure 13, no airflow passes through the earcup 108 portion of the headgear due to the lack of fluid coupling between the fan assembly 104 and the headgear.

Claims

1. A wearable air purifier, comprising:5 headgear for wearing on a wearer’s head, the headgear comprising a headbandand an ear cup connected to an end of the headband,a fan assembly operable to generate filtered airflow and comprising an outlet to discharge the filtered airflow from the wearable air purifier for inhalation by the wearer, wherein the fan assembly is releasably attachable to the headgear via the ear cup.

102. The wearable air purifier of claim 1, wherein the outlet extends at least partially around a perimeter of the fan assembly.I14 / 3. The wearable air purifier of any preceding claim, wherein the fan assembly15 comprises a protrusion, and wherein the outlet is provided within the protrusion.

4. The wearable air purifier of any preceding claim, wherein the fan assembly comprises a fan assembly mating surface arranged to contact a headgear mating surface when the fan assembly is attached to the headgear, wherein the outlet is provided in a fan 20 assembly surface other than the fan assembly mating surface.

5. The wearable air purifier of claim 4, wherein, when the fan assembly is attached to the headgear, the outlet is proud of the headgear.25 6. The wearable air purifier of any preceding claim, wherein the fan assembly isattachable to the headgear by way of a rotatable coupling for varying a position of the outlet relative to the headgear.

7. The wearable air purifier of claim 6, wherein the rotatable coupling comprises a 30 magnet coupling.

8. The wearable air purifier of any preceding claim, comprising a battery and a conductor assembly to conduct electrical power from the battery to the fan assembly, wherein the battery is mounted to the headgear, and the conductor assembly comprises a releasable conductive coupler to facilitate releasable conductive coupling of the fan 5 assembly to the battery.

9. The wearable air purifier of claim 8, wherein the releasable conductive coupler is configured to couple and decouple by attachment and detachment respectively of the fan assembly to the headgear.

10. The wearable air purifier of claim 9, wherein the releasable conductive coupler comprises conductive contacts that are spring-biased towards a coupled position.1511. The wearable air purifier of any one of the preceding claims, wherein the fan assembly is releasably attachable to the headgear without relative rotation between the fan assembly and the headgear.

12. The wearable air purifier of any one of claims 8 to 11, wherein the fan assembly comprises a base that is releasably attachable to the headgear and a fan housing in which 20 a fan for generating the airflow is located, and the fan housing is rotatably attached to the base to facilitate rotation of the outlet relative to the headgear.

13. The wearable air purifier of claim 12, wherein the releasable conductive coupler releasably conductively couples the base to the headgear, and a rotatable conductive 25 coupler rotatably conductively couples the base to the fan.

14. The wearable air purifier of any one of the preceding claims, comprising a speakerattached to the headgear for supporting by the headgear over a wearer’s ear, wherein the fan assembly is releasably attachable to the headgear to be supported by the headgear on 30 an opposite side of a median plane of the wearer to the speaker.

15. The wearable air purifier of claim 14, comprises a further conductor assembly to conduct electrical power from the battery to the speaker.

16. The wearable air purifier of any one of the preceding claims, comprising an alert 5 system for generating an alert, the alert system comprising a fan assembly sensor to sense if the fan assembly is attached to the headgear and an environmental condition sensor to sense an environmental condition, wherein the alert system is configured to sense an environmental condition sensor using the environmental condition sensor, determine whether the sensed environmental condition meets a threshold, sense if the fan assembly 10 is attached to the headgear using the fan assembly sensor, and generate an alert signal in the event that the sensed environmental condition meets the threshold and the fan assembly is not sensed to be attached to the headgear.1517. The wearable air purifier of claim 16, wherein the alert system is in communication with the speaker and configured to communicate the alert signal to the speaker.

18. The wearable air purifier of claim 16 or claim 17, wherein the alert system is mounted to the headgear.2019. The wearable air purifier of any one of claims 16 to 18, further comprising a fan controller for controlling an airflow rate of the fan assembly, wherein the fan controller is in communication with the environmental condition sensor, and the fan controller controls the airflow rate of the fan assembly based on a signal from the environmental 25 condition sensor.

20. The wearable air purifier of any one of the preceding claims, comprising a further fan assembly operable to generate a further filtered airflow, wherein the further fan assembly comprises a further air outlet for discharging the further filtered airflow from 30 the wearable air purifier for inhalation by the wearer, wherein the further fan assembly isreleasably attachable to the headgear to be supported by the headgear on an opposite side of a sagittal plane of the wearer to the fan assembly.

21. The wearable air purifier of any one of the preceding claims, wherein the wearable5 air purifier further comprises a nozzle attachable to the fan assembly to receive airflow generated by the fan assembly via the outlet and discharge the airflow towards the wearer’s face.

22. The wearable air purifier of claim 21, wherein the nozzle is releasably attachable10 to the fan assembly.LD2023. The wearable air purifier of any one of claims 1 to 19, wherein the wearable air purifier further comprises:a nozzle attachable to the fan assembly to receive airflow generated by the fan assembly via the outlet and discharge the airflow towards the wearer’s face; anda further fan assembly operable to generate a further airflow,wherein the nozzle is attachable to the further fan assembly to receive the further airflow and discharge the further airflow towards the wearer’s face, the further fan assembly is releasably attachable to the headgear to be supported by the headgear on an opposite side of a median plane of the wearer to the fan assembly, and the nozzle is flexible to permit relative movement of the fan assembly and the further fan assembly when the fan assembly and the further fan assembly are attached to the nozzle.

24. The wearable air purifier of claim 23, wherein the fan assembly and the further 25 fan assembly comprise respective male or female locating features for cooperating with male or female locating features of the headgear to locate the fan assembly and the further fan assembly relative to the headgear, wherein the nozzle is flexible to permit relative movement of the fan assembly and the further fan assembly when the fan assembly and the further fan assembly are attached to the nozzle such that the locating features of the 30 fan assembly and the further fan assembly may clear and engage with the respectivelocating feature of the headgear mutually simultaneously during attachment of the fan assembly and the further fan assembly to the headgear.21 03 25

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