Wearable air purifier

Abstract

A wearable air purifier comprises headgear for wearing on a wearer’s head, a driver assembly supported by the headgear and a fan assembly releasably mounted to the driver assembly. The driver assembly

Description

B ACKGROUND 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 In a first aspect, there is provided a wearable air purifier comprising: headgear for wearing on a wearer’s head; a driver assembly supported by the headgear, the driver assembly comprising a driver configured to generate a rotating magnetic field; and a fan assembly releasably mountable to the driver assembly, the fan assembly comprising an impeller configured to be driven by the rotating magnetic field and rotate about a rotational axis. Providing a fan assembly that is releasably mountable to the driver assembly allows a user to remove the fan assembly when not in use. Removing the fan assembly in this way can provide for more convenient storage of the wearable air purifier. Such removal can also allow a user to wear the headgear without the additional weight and volume of the fan assembly. Further, providing an arrangement in which the fan assembly is driven by a rotating magnetic field can reduce the complexity of the fan assembly. For example, such an arrangement may mean that the fan assembly does not require an onboard power source (e.g. a battery) to drive the impeller. Likewise, the fan assembly can be free of any connectors (e.g. sockets) that would otherwise be necessary for the transfer of power and / or control signals and that can be susceptible to fouling. Optional features of the first aspect will now be set out. These are applicable singly or in any combination with any aspect. The impeller may comprise a central hub and a plurality of blades extending (e.g. radially) from the hub. The impeller (e.g. the hub of the impeller) may be rotatably mounted within the fan assembly for rotation about the rotational axis. For example, the impeller (e.g. the hub) may be rotatably mounted by way of a bearing. The impeller may be a radial impeller configured to discharge airflow in a direction that is perpendicular to the rotational axis (i.e. an axial direction). The impeller may be configured to receive an airflow in a direction parallel to the rotational axis (i.e. a radial direction). The impeller may form part of a fan of the fan assembly. The fan may comprise a fan housing within which the impeller is mounted. The fan housing may comprise a fan inlet and a fan outlet. The fan may be a radial fan. The fan assembly may comprise a fan assembly inlet for airflow into the fan assembly and a fan assembly outlet for discharge of an airflow from the fan assembly. The fan assembly may comprise a fan assembly housing within which the impeller is mounted. The fan assembly inlet and / or the fan assembly outlet may be formed in the fan assembly housing. The fan assembly outlet may be configured to deliver an airflow towards a lower nasal and mouth region of the wearer’s face. The fan assembly inlet may extend circumferentially about the rotational axis. The fan assembly inlet may comprise a plurality of apertures (e.g. an array of apertures extending circumferentially around the rotational axis). At least in use, the releasably mounting of the fan assembly to the driver assembly may at least partly be provided by the rotating magnetic field (i.e. the rotating magnetic field may aid in retaining the fan assembly on the driver assembly). In some embodiments, the releasably mounting may alternatively or additionally be provided by releasable coupling means in the form of a mechanical connector (e.g. bayonet connection, snap fit connection, threaded connection, etc) or a further magnetic connection (i.e. beyond that provided by the rotating magnetic field). The fan assembly and / or driver assembly may comprise a locating feature for locating the fan assembly on the driver assembly when mounted thereto (e.g. to provide accurate alignment of the rotating magnetic field with the impeller in use). One of the fan assembly and the driver assembly may comprise a protruding portion and the other of the fan assembly and the driver assembly may comprise an intruding portion for receipt of the protruding portion when the fan assembly is mounted to the driver assembly. The protruding portion may be complementary in shape to the intruding portion. The protruding portion and / or intruding portion may be configured to guide the fan assembly onto the driver assembly. For example, one or both of the protruding portion and intruding portion may comprise one or more sloped surfaces for guiding the fan assembly onto the driver assembly. One or both of the protruding portion and intruding portion may taper (e.g. may be substantially frustoconical in shape). Such an arrangement may aid in accurately aligning the fan assembly with the driver assembly, and thus the rotating magnetic field with the impeller (in use). When the driver assembly comprises a protruding portion, the driver may be at least partly received in an interior of the protruding portion. Such an arrangement may provide an efficient use of space within the driver assembly. The driver assembly may comprise a first wall and the fan assembly may comprise a second wall. The first wall may form part of a driver assembly housing for housing the driver. The second wall may form part of the fan assembly housing. The first and second walls may be in contact when the fan assembly is mounted to the driver assembly. External surfaces of the first and second walls may face one another when the fan assembly is mounted to the driver assembly. The external surface of the first wall may face outwardly in use (i.e. away from a wearer’s head when the wearable air purifier is worn). The external surface of the second wall may face inwardly in use (i.e. towards a wearer’s head when the wearable air purifier is worn). The protruding and intruding portions may each be provided on a respective one of the first and second walls. In some embodiments, the rotating magnetic field may be provided by a rotating magnetic coupling. For example, the driver may comprise a motor having a rotatable portion that is driven to rotate about the rotational axis. The magnetic coupling may be provided to magnetically couple the rotatable portion to the impeller when the fan assembly is releasably mounted to the driver assembly. In this way, the magnetic coupling may be configured to transmit torque from the rotatable portion to the impeller such that rotation of the rotatable portion causes the impeller to rotate in response to the transmitted torque. Accordingly, rotation of the impeller may be provided without requiring a power source (or, indeed, any electronics) to be provided as part of the fan assembly. The motor may comprise a rotor and a stator. The rotatable portion may be integral with the rotor (i.e. may form part of the rotor) or may be mounted to the rotor. The stator may comprise windings arranged to drive the rotor to rotate about the rotational axis (i.e. when current is passed through the windings in a sequence that generates a rotating magnetic field). The motor may be an electric motor. The motor may be, for example, a brushless DC motor, permanent magnet synchronous motor (PMSM), induction motor, stepper motor, etc. The magnetic coupling may comprise a first coupling portion provided on and / or in the impeller or the rotatable portion. The magnetic coupling may comprise a second coupling portion provided on and / or in the other of the impeller and the rotatable portion. The first coupling portion may comprise a magnetic material and the second coupling portion may comprise a magnetic material or a ferromagnetic material (e.g. alloys comprising iron, cobalt, nickel, etc.). In other words, at least one of the first and second coupling portions may comprise a magnetic material and the other of the first and second coupling portions may comprise a material that is magnetically attracted to magnetic material. The magnetic material of the first coupling portion may comprise one or more permanent magnets. The first coupling portion may comprise a plurality of permanent magnets (which may be referred to as “first permanent magnets”). The plurality of first permanent magnets may be uniformly distributed about the rotational axis. The plurality of first permanent magnets may be evenly spaced in a circumferential direction around the rotational axis. The first coupling portion may comprise between six and fifteen permanent magnets, or e.g. between nine and twelve permanent magnets. The first permanent magnets may alternate in polarity around the rotational axis. That is, each first permanent magnet of the first coupling portion may neighbour two further first permanent magnets of opposite polarity. Such an arrangement may increase the amount of torque that can be applied between the first and second coupling portions. As above, the magnetic material of the second coupling portion may comprise ferromagnetic material. For example the magnetic material may comprise a plate of ferromagnetic material. In some embodiments the magnetic material may comprise radially extending portions forming poles that magnetically interact with the rotating magnetic field generated by rotation the first coupling portion. Alternatively or additionally, the magnetic material of the second coupling portion may comprise one or more permanent magnets. The magnetic material of the second coupling portion may comprise a plurality of permanent magnets (which may be referred to as “second permanent magnets”). The plurality of second permanent magnets may be uniformly distributed about the rotational axis. The plurality of second permanent magnets may be evenly spaced in a circumferential direction around the rotational axis. The magnetic material of the second coupling portion may comprise between six and fifteen permanent magnets, or e.g. between nine and twelve permanent magnets. The plurality of second permanent magnets may alternate in polarity around the rotational axis. That is, each second permanent magnet may neighbour two further second permanent magnets of opposite polarity. Each first permanent magnet of the first coupling portion may be alignable (e.g. dependent on the rotational position of the rotor / impeller) with a respective second permanent magnet of the second coupling portion. Such alignment may be along an axis that is parallel or perpendicular to the rotational axis. Each first permanent magnet may be alignable with a respective second permanent magnet of opposite polarity. The first and second coupling portions may be arranged to provide a face-to-face magnetic coupling. Thus, the first and second coupling portions may be axially spaced from one another (i.e. when the fan assembly is mounted to the driver) and the magnetic coupling extends between the first and second coupling portions in the axial direction (i.e. parallel to the axis of rotation). Alternatively or additionally, the first and second coupling portions may be arranged to provide a coaxial magnetic coupling. Thus, the first and second coupling portions may be concentrically arranged (i.e. when the fan assembly is mounted to the driver assembly). That is, one of the first and second coupling portions may circumferentially surround the other of the first and second coupling portions (e.g. one of the first and second coupling portions may comprise a protrusion for receipt in a recess of the other of the first and second coupling portions). In such embodiments, the magnetic coupling extends between the first and second coupling portions in the radial direction. The first coupling portion may be provided on and / or in the rotatable portion and the second coupling portion may be provided on and / or in the impeller. When the second coupling portion comprises a plurality of permanent magnets, the permanent magnets may be mounted to the hub the impeller. The one or more permanent magnets may be enclosed within one or more respective cavities formed in the hub of the impeller. The one or more permanent magnets may be fully embedded (e.g. over-moulded) within the hub of the impeller. The one or more permanent magnets may be retained in (e.g. may be push-fit into) one or more blind holes formed in the hub. Each blind hole may be oriented such that a closed end of the blind hole is closer than an opposite open end of the blind hole to the first coupling portion of the rotatable portion. Accordingly, each blind hole may be arranged such that a magnet received in the blind hole is urged towards the closed end of the hole by the magnetic attraction of the magnet in a direction towards the first coupling portion (on the rotatable portion). This may aid in retaining the permanent magnets within the hub of the impeller (especially in use when the impeller is rotated by the rotating magnetic field). The driver may be adjacent to the first wall of the driver assembly. The first coupling portion may be adjacent to the first wall of the driver assembly. The second coupling portion may be adjacent to the second wall of the fan assembly. In this way, the first and second coupling portions may be separated only by the first and second walls. Such close proximity of the first and second coupling portions may aid in maximising the transfer of torque from the first coupling portion to the second coupling portion. Above, the rotating magnetic field is described as being provided by a rotating magnetic coupling. In other embodiments, the rotating magnetic field may instead be generated by a stator configured to generate such a rotating magnetic field. That is, the driver may comprise a stator configured to generate the rotating magnetic field and the impeller may comprise a rotor configured to be driven to rotate about the rotational axis by the rotating magnetic field when the fan assembly is mounted to the driver assembly. For example, the stator may comprise windings arranged such that, when current is passed through the windings in a particular sequence, a rotating magnetic field is generated. The driver may comprise a controller configured to control the supply of current to the windings of the stator to generate a rotating magnetic field. In this respect, the rotor and stator may effectively function as an electric motor. The rotor may comprise one or more magnetic or ferromagnetic portions. For example, the rotor may comprise an array of permanent magnets to be rotated by the rotating magnetic field. The array of permanent magnets may be uniformly distributed around the rotational axis. The plurality of permanent magnets of the rotor may be evenly spaced in a circumferential direction around the rotational axis. The rotor may be radially outward of the stator when the fan assembly is mounted to the driver assembly. The rotor may circumferentially surround the stator (the rotor and stator may be concentrically arranged) when the fan assembly is mounted to the driver assembly. For a given power, such a rotor (sometimes referred to as an outer rotor) may have a lower length (i.e. taken along the rotational axis) to diameter ratio, which can make such arrangements compact and flat. This may be particularly desirable when the fan assembly is to be positioned on the side of a wearer’s head. The stator may be annular so as to define an internal recess. The bearing of the impeller may be received within the internal recess of the annular stator when the fan assembly is mounted to the driver assembly. The rotor may form part of the impeller or may be mounted to the impeller. The rotor may form part of, or be mounted to, the hub of the impeller. The hub of the impeller may comprise a central portion received within the internal recess of the stator. The hub of the impeller may comprise an outboard portion that is radially outward of, and circumferentially surrounds, the central portion. The central portion and the outboard portion may be connected by a radially extending portion (e.g. a flange and / or radially extending arms). The rotor may form part of the outboard portion or may be mounted to the outboard portion. In some embodiments, the rotor and stator may be configured to operate as an induction motor when the fan assembly is mounted to the driver assembly. In such embodiments, the rotor may comprise an electrically conductive material. Likewise, in such embodiments, the rotor may be located within the recess of the stator. The stator may comprise windings arranged to induce an electrical current in the rotor in a manner. Embodiments in which the rotor and stator are configured to operate as an induction motor may avoid the need to include permanent magnets within the fan assembly. This may be beneficial for minimising the weight of the fan assembly. Likewise, in some cases permanent magnets may attract debris (i.e. formed of ferromagnetic material), which may collect on an external surface of the fan assembly. The stator may be housed within an annular stator housing. The stator housing may be provided by an annular protrusion in the driver assembly housing. The fan assembly may comprise an annular stator-receiving recess arranged for receipt of the stator housing (and thus the stator). The stator-receiving recess may be formed in the fan assembly housing. The stator housing may be configured for close (i.e. snug) fit within the stator-receiving recess. This may ensure accurate alignment between the stator and the rotor. In any embodiment described above, the impeller may be directly driven by the rotating magnetic field. This means that rotation of the impeller is effectively controlled by the driver. Thus, it may not be necessary for the fan assembly to include a controller (or e.g. any electrical circuitry) for controlling movement of the impeller. This may simplify construction of the fan assembly. The wearable air purifier may comprise a power source operatively connected to the driver to supply power to the driver. The power source may be a battery (e.g. a rechargeable battery). The power source may form part of the driver assembly. The wearable air purifier may comprise speaker assembly supported by the headgear so as to locate over an ear of a wearer when worn. The speaker assembly and driver assembly may share a common housing. The speaker assembly may comprise a speaker (which may be operatively connected to the power source). Accordingly, the wearable air purifier may be in the form of a pair of headphones. The headgear may be in the form of a headband for extending over the top of a wearer’s head when worn. The wearable air purifier may comprise first and second ear cups mounted to opposite ends of the headgear (e.g. headband) so as to locate over a wearer’s ears when the headgear is worn. Each of the first and second ear cups may comprise a respective driver assembly and fan assembly as described above. Each ear cup may comprise a respective speaker assembly as described above. The wearable air purifier may comprise a nozzle. The nozzle may be configured to deliver airflow from each fan assembly to the wearer (e.g. to a lower nasal and mouth region of the wearer). The nozzle may be attachable at left and right ends thereof to a respective one of the ear cups. The nozzle may be attachable at left and right ends thereof to a respective one of the fan assemblies. In some embodiments the nozzle may be fixed to the fan assemblies, and removal of the nozzle from the headgear may be provided by release of the fan assemblies from the driver assemblies. The nozzle may be configured to be contactless to the wearer’s face (for example, spaced apart from the wearer’s mouth and / or nasal area when the head wearable air purifier is worn with the nozzle attached). The nozzle may be configured to be face-contacting (for example, the nozzle may be configured to contact the wearer’s mouth and / or nasal area when the head wearable air purifier is worn with the nozzle attached). The nozzle may define air inlets at the left and right ends that communicate with the air outlets of the fan assembly (i.e. to receive purified airflow from the fan assemblies). The nozzle may be configured to extend from the left and right ends width-wise across the wearer’s face, and may comprise an air outlet at a central region approximately mid-way between the left and right ends to be positioned approximately directly in front of and facing the wearer’s lower nasal and mouth region, in use. In this way, the nozzle may function to duct filtered airflow from each of the fan assemblies (which may be supported at the sides of the wearer’s head), to the central outlet of the nozzle, so as to discharge the airflow from each fan assembly towards the lower nasal and mouth region of the wearer’s face. In a second aspect, there is provided a head support assembly of a wearable air purifier, the head support assembly comprising: headgear for wearing on a wearer’s head; and a driver assembly supported by the headgear, the driver assembly comprising a driver configured to generate a rotating magnetic field; the driver assembly configured for releasably mounting a fan assembly to the driver assembly, the fan assembly comprising an impeller configured to be driven by the rotating magnetic field and rotate about a rotational axis. The headgear and driver assembly of the second aspect may be as described above with respect to the first aspect (e.g. may include one or more of the optional features of the first aspect). In a third aspect, there is provided a fan assembly releasably mountable to a driver assembly supported by headgear for wearing of on a wearer’s head to form a wearable air purifier, the fan assembly comprising an impeller configured to be driven by a rotating magnetic field generated by a driver of the driver assembly and rotate about a rotational axis. The fan assembly of the third aspect may be as described above with respect to the first aspect (e.g. may include one or more optional features of the first aspect). Thus, for example, the fan assembly of the third aspect may comprise a first coupling portion provided on and / or in the impeller to magnetically couple with a second coupling portion provided on and / or in the rotatable portion. The first coupling portion may comprise a magnetic material and the second coupling portion may comprise a magnetic or ferromagnetic material. When the fan assembly is releasably mounted to the driver assembly, the magnetic coupling of the first and second coupling portions may be configured to transmit torque from a rotatable portion, driven to rotate about a rotational axis by the driver assembly, to the impeller such that rotation of the rotatable portion causes the impeller to rotate in response to the torque transmitted. BRIEF DESCRIPTION OF THE DRAWINGS Figure lisa perspective view of a wearable air purifier. Figures 2A and 2B are section views of an ear cup of a wearable air purifier respectively in a released position and a mounted position. Figure 3 is a section view of a driver and an impeller of a wearable air purifier according to a first embodiment. Figures 4 and 5 are section views of variations of the first embodiment of Figure 3. Figure 6 is a section view of a driver and an impeller of a wearable air purifier according to a second embodiment. DETAILED DESCRIPTION Figure 1 illustrates a wearable air purifier 10 comprising headgear 11 for wearing on a wearer’s head. In the illustrated embodiment the headgear 11 is in the form of a headband (i.e. to extend over the top of a wearer’s head), but in other embodiments alternative headgear may be provided. The wearable air purifier 10 includes first 12 and second 13 ear cups mounted at opposite ends of the headgear 11 so as to locate over a wearer’s ears when the headgear 11 is worn. Each ear cup 12, 13 includes a driver assembly 14 supported by the headgear 11, and a fan assembly 15 that is releasably mountable to the driver assembly 14. The fan assembly 15 of each ear cup 12, 13 is configured to be driven by the driver assembly 14 when mounted thereto to draw an airflow into a circumferential fan assembly air inlet 16 of the fan assembly 15 and to discharge the airflow through a fan assembly outlet 17 of the fan assembly 15 for delivery to a user. In particular, the airflow is delivered towards a lower nasal and mouth region of the wearer’s face. In the illustrated embodiment, the delivery of the airflow to this region of a wearer’s face is provided by a nozzle 18. The nozzle 18 is attachable at left 19 and right 20 ends thereof to a respective one of the ear cups 12, 13 (as is indicated by dash-dotted arrows 70, 71). The nozzle 18 defines nozzle air inlets 21 at the left 19 and right 20 ends (of the nozzle 18) that communicate with the fan assembly outlets 17 of the fan assemblies 15 (i.e. to receive purified airflow from the fan assemblies 15). The nozzle 18 is configured to extend from the left 19 and right 20 ends width-wise across the wearer’s face, and comprises a nozzle air outlet 22 at a central region approximately mid-way between the left 19 and right 20 ends to be positioned approximately directly in front of and facing the wearer’s lower nasal and mouth region, in use. The nozzle 18 thus functions to duct filtered airflow from each of the fan assemblies 15 supported at the sides of the wearer’s head, to the central nozzle outlet 22 of the nozzle 18, so as to discharge the airflow from each fan assembly 15 towards the lower nasal and mouth region of the wearer’s face. Each ear cup 12, 13 also includes a speaker assembly 23, which shares a common housing 24 with the driver assembly 14. Each speaker assembly 23 includes a speaker 25 directed towards a wearer’s ear when the wearable air purifier 10 is worn, allowing the wearable air purifier 10 to function as a pair of headphones. An annular cushion 26 is also provided on an inner side (facing the wearer’s head) of each speaker assembly 23 so as to seat against the side of a wearer’s head (for comfort) when the wearable air purifier 10 is worn. The annular cushion 26 surrounds the speaker 25 to define a space into which sounds is directed by the speaker 25. It should be appreciated that both ear cups 12, 13 are the substantially the same, except that one ear cup 12, 13 is a mirror image of the other. The internal components of the second ear cup 13 are shown schematically in Figure 2A (in which the fan assembly 15 is separated from the driver assembly 14) and Figure 2B (in which the fan assembly 15 is mounted to the driver assembly 14). It should be appreciated that the below description is also equally applicable to the first ear cup 12. As apparent from Figures 2A and 2B, the fan assembly 15 comprises a radial fan 27 including a fan housing 28 and an impeller 29 housed within the housing 28. The housing 28 includes a central inlet 30 and a radial outlet 31 for airflow into and out of the fan 27. The impeller 29 includes a central hub 32 and a plurality of blades 33 extending radially outwardly from the hub 32. The impeller 29 is rotatably mounted within the fan housing 28 so as to be rotatable about a rotational axis 34 (see Figure 2A). The orientation of the impeller 29 is such that when the ear cup 13 is worn, the rotational axis 34 of the impeller 29 is substantially normal to the side of a wearer’s head (i.e. it extends laterally in a direction away from / towards the wearer’s ear). The impeller 29 is a radial impeller such that it is configured to draw air into the fan 27 in an axial direction along the rotational axis 34 and discharge air in a radial direction with respect to the rotational axis 34. The impeller 29 is driven to rotate by a rotating magnetic field, which is generated by a driver 35 of the driver assembly 14. When rotated in this manner, the impeller 29 draws an airflow 73 into the fan assembly 15 via the fan assembly inlet 16. The fan assembly 15 comprises a filter 36 that is directly downstream of the fan assembly inlet 16 so that the airflow 73 passes into the fan assembly inlet 16 and through the filter 36. This helps to remove unwanted particles from the airflow 73 (i.e. the filter 36 purifies the airflow). The purified air is subsequently discharged as an airflow 74 by the impeller 29 through the fan assembly outlet 17 (and may be directed to the wearer’s lower nasal and mouth region by the nozzle 18 when attached). As is particularly apparent from Figure 2A, to facilitate mounting of the fan assembly 15 to the driver assembly 14 (as indicated by dash-dotted arrow 72), the fan assembly 15 includes an intruding portion 37 and the driver assembly 14 includes a complementary protruding portion 38. The protruding portion 38 is provided on a first wall 40 forming part of the driver assembly 14 and the intruding portion 37 is provided on a second wall 39 that forms part of the fan assembly 15. The first wall 40 faces outwardly, in a direction away from a wearer’s head when the ear cup 13 is worn. The second wall 39 faces inwardly in a direction towards the wearer’s head when the ear cup 13 is worn. When the fan assembly 15 is mounted to the driver assembly 14, the first 40 and second 39 walls are brought into abutment with one another. The fan assembly 15 may be retained on the driver assembly 14 by the rotating magnetic field generated by the driver 35. In some embodiments, the fan assembly 15 and driver assembly 14 may alternatively or additionally be retained together by e.g. a bayonet connection, screw connection, further magnetic connection, etc. The protruding 38 and intruding 37 portions include sloped side surfaces 41 (i.e. so as to be tapered), which aid in guiding the fan assembly 15 onto the driver assembly 14. The intruding 37 and protruding 38 portions also help to ensure that the fan assembly 15 and driver assembly 14 are correctly aligned, which facilitates accurate alignment of the rotating magnetic field (generated by the driver 35) and the impeller 29. The driver 35 of the driver assembly 14 is located partly within an interior of the protruding portion 38 of the driver assembly 14. As illustrated, the driver 35 is positioned against the first wall 40 of the driver assembly 14 and the fan 27 is positioned against the second wall 39 of the fan assembly 15. This ensures that there is minimal distance between the driver 35 and the impeller 29 when the fan assembly 15 is mounted to the driver assembly 14 (which helps to establish a strong magnetic coupling between the impeller 29 and the driver 35). The speaker assembly 23 is located inwardly of the driver assembly 14, so as to be between the driver assembly 14 and a wearer’s head when the wearable air purifier 10 is worn. The speaker 25 is arranged to direct sound (when active) into the space defined within the annular cushion 26, and towards a wearer’s ear (when the wearable air purifier 10 is worn). As may be appreciated, by driving the impeller 29 via a rotating magnetic field, it is not necessary to incorporate a power source into the (releasably mounted) fan assembly 15. Instead a power source 42 (in the form of a rechargeable battery) is provided within the common housing 24 of the driver assembly 14 and speaker assembly 23 and may be operatively connected to each of the driver 35 and the speaker 25 for supply of power to the driver 35 and speaker 25. This simplifies the construction of the ear cup 13 and minimises the number of connectors that may need to be provided. This is beneficial as such connectors may be susceptible to fouling, and could otherwise reduce the durability of the wearable air purifier 10. For example, the fan assembly 15 can be free of connectors for e.g. charging a power source (because the fan assembly 15 does not require a power source) and / or free of connectors for e.g. transfer of power from the driver assembly 14 (because the impeller 29 is instead driven by the rotating magnetic field). The power source 42 is operatively connected to the driver 35 and the speaker 25 by way of a controller 64, which can control the speaker and the driver 35. As may be appreciated, alternatively, separate controllers may be provided to control the speaker 25 and driver 35. Figure 3 illustrates one way in which the driver 35 may generate the rotating magnetic field. In this embodiment, the driver 35 comprises a rotatable portion 43 that forms part of a rotor of a motor (e.g. a brushless DC motor). In other embodiments the rotatable portion 43 may instead be mounted to the rotor. The rotatable portion 43 is configured to be driven by the motor to rotate about the rotational axis 34. The rotatable portion 43 comprises a first coupling portion 44 comprising an array of first permanent magnets 45 embedded in an outwardly facing surface 46 of the rotatable portion that faces the impeller 29 (i.e. in use, when the wearable air purifier 10 is worn, this outwardly facing surface 46 faces away from the wearer’s head). The first permanent magnets 45 are spaced evenly from one another in a circumferential direction about the rotational axis 34 (so as to be uniformly distributed about the rotational axis 34). The first permanent magnets 45 are also arranged so as to alternate in polarity in the circumferential direction. As may be appreciated, when the rotatable portion 43 is rotated about the rotational axis 34 (as per arrow 77) by the motor, the array of first permanent magnets 45 (i.e. the first coupling portion 44) is rotated so as to generate magnetic field that also rotates. As will be described below, it is this rotating magnetic field that drives rotation of the impeller 29. The impeller 29 comprises a second coupling portion 47, which comprises an array of second permanent magnets 48 (only two of which are shown). In other embodiments, the second permanent magnets 48 may be replaced by a ferromagnetic material. Together, the first 44 and second 47 coupling portions provides a magnetic coupling that couples the impeller 29 (magnetically) to the rotatable portion 43, so as to provide transfer of torque from the first coupling portion 44 to the second coupling portion 47. The second permanent magnets 48 of the impeller 29 are embedded in the hub 32 of the impeller 29, and (although not apparent from the figures) are spaced evenly in a circumferential direction about the rotational axis 34. The circumferential spacing of the second permanent magnets 48 of the impeller 29 is the same as that of the first permanent magnets 45 of the rotatable portion 43. In this way, each second permanent magnet 48 of the impeller 29 is alignable (along an axis parallel to the rotational axis) with a respective permanent magnet 45 of the rotatable portion 43. The second permanent magnets 48 of the impeller 29 also alternate in polarity in the circumferential direction. Thus, each second permanent magnet 48 of the impeller 29 is alignable with a respective first permanent magnet 45 of the rotatable portion 43 that is of opposite polarity. This alignment of the first permanent magnets 45 and second permanent magnets 48 is indicated by the dashed lines 75 in Figure 3. In use, when the impeller 29 and rotatable portion 43 are brought into close proximity (i.e. when the fan assembly 15 is mounted to the driver assembly 14), each first permanent magnet 45 (on the rotatable portion 43) magnetically couples with a respective second permanent magnet 48 (on the impeller 29). Thus, when the rotatable portion 43 is subsequently rotated, the second permanent magnets 48 of the impeller 29 are driven to rotate by the first permanent magnets 45 of the rotatable portion 43. In this way, the impeller 29 is driven to rotate about the rotational axis 34 to move air through the fan assembly 15 as already described above. Such rotation of the impeller 29 is facilitated by the mounting of the impeller 29 to a portion of the second wall 39 of the fan assembly 15. Figure 4 schematically illustrates a variation of the embodiment of Figure 3, with the only difference being the manner in which the second permanent magnets 48 are mounted to the hub 32 of the impeller 29. In the present embodiment, the hub 32 of the impeller 29 is provided with blind holes 49 extending into an outwardly facing surface 50 of the hub 32 that is distal from the rotatable portion 43. Thus, each blind hole 49 opens in a direction opposite to the rotatable portion 43. The second permanent magnets 48 are received in the blind holes 49, such that attraction of the second permanent magnets 48 of the impeller 29 towards the first permanent magnets 45 urges the second permanent magnets 48 further into the blind holes 49 (i.e. further securing the second permanent magnets 48 within the impeller 29). Figure 5 illustrates a further variation, which differs from that shown in Figures 3 and 4 in that the direction of the magnetic coupling between the rotatable portion 43 and the impeller 29. In Figures 3 and 4 the magnetic coupling is in an axial direction, substantially parallel to the rotational axis 34. In the embodiment of Figure 5, the magnetic coupling is in a radial direction (with respect to the rotational axis 34). In Figure 5, the hub 32 of the impeller 29 defines a central recess 51 in which a protrusion 52 of the rotatable portion 43 is received. The protrusion 52 of the rotatable portion 43 comprises a first circumferential surface 53, and the recess 51 of the impeller hub 32 is defined by a complementary second circumferential surface 54 spaced outwardly from the first circumferential surface 53. The second permanent magnets 48 of the impeller 29 are embedded in the second circumferential surface 54 and the first permanent magnets 45 of the rotatable portion 43 are embedded in the first circumferential surface 53. In Figures 3, 4 and 5, the rotating magnetic field is provided by a rotating magnetic coupling between the impeller 29 and the driver 35. Figure 6 illustrates a further way in which the impeller 29 can be driven by the driver 35 of the driver assembly 14. In particular, in the embodiment of Figure 6, a rotatable magnetic field is generated by controlling current through windings 56 of a stator 55 of the driver 35. In the illustrated embodiment, the stator 55 is annular and is housed within an annular stator housing 57 that projects from the first wall 40 of the driver assembly 14 (i.e. projects outwardly away from a wearer’s face when the wearable air purifier 10 is worn). The stator 55 comprises a plurality of windings 56 that are arranged such that pairs of windings 56 can have current passed therethrough in sequence to generate a rotating magnetic field. In other words, the stator is configured to function in the manner of a stator 56 of a brushless DC motor. The hub 32 of the impeller 29 comprises a central portion 58 comprising a bearing 59 that rotatably mounts the impeller 29 to the second wall 39 of the fan assembly 15. When the fan assembly 15 is mounted to the driver assembly 14, the bearing 59 is received within a central recess 60 of the annular stator 55. The hub 32 of the impeller 29 further comprises an outboard portion 61 that is radially outward of the central portion 58 of the hub 32, and that is connected to the central portion 58 by radially extending arms 62. The blades 33 of the impeller 29 extend radially outwardly from this outboard portion 61 of the hub 32. The central portion 58 of the hub 32, outboard portion 61, and arms 62 define a space that accommodates an annular stator-receiving recess 63 formed in the second wall 39. As should be appreciated from the figure, when the fan assembly 15 is mounted to the driver assembly 14, the stator housing 57 is received snugly within the stator-receiving recess 63. Such mounting is performed by relative movement of the fan assembly 15 and the driver assembly 14 as indicated by the dash-dotted arrows 76 provided in Figure 6. A plurality of permanent magnets 64 are mounted to the outboard portion 61 of the impeller hub 32 so as to be evenly spaced circumferentially from one another around the rotational axis 34. In particular, the permanent magnets 64 are mounted a surface of the outboard portion 61 that faces inwardly towards the central portion 58 of the hub 32. Thus, when the fan assembly 15 is mounted to the driver assembly 14 (and the stator 55 is received within the stator-receiving space 63), the permanent magnets 64 are radially aligned with the windings 56 of the stator 55. In operation (i.e. when the driver 35 is activated), current is supplied to the windings 56 of the stator 55 in a manner that generates a rotating magnetic field (that rotates about the rotational axis 34). This rotating magnetic field drives the permanent magnets 64 to rotate about the stator 55 (and about the rotational axis 34). This, in turn, causes rotation of the impeller 29 (and thus the blades 33 of the impeller 29) to move air through the fan assembly 15 as previously described above. As may be appreciated, in such an arrangement it can be desirable to ensure accurate alignment between the windings 56 of the stator 55 and the permanent magnets 64 of the impeller 29. To facilitate this, the impeller 29 may be hard mounted within the fan assembly 15 (i.e. to substantially restrict movement of the impeller 29 to rotational movement about the rotational axis 34).

Claims

1. A wearable air purifier comprising:headgear for wearing on a wearer’s head;a driver assembly supported by the headgear, the driver assembly comprising a driver configured to generate a rotating magnetic field; anda fan assembly releasably mountable to the driver assembly, the fan assembly comprising an impeller configured to be driven by the rotating magnetic field and rotate about a rotational axis.

2. The wearable air purifier according to claim 1, wherein the driver assembly comprises:a motor having a rotatable portion that is driven to rotate about the rotational axis; andwherein a magnetic coupling is provided to magnetically couple the rotatable portion to the impeller when the fan assembly is releasably mounted to the driver assembly, the magnetic coupling configured to transmit torque from the rotatable portion to the impeller such that rotation of the rotatable portion causes the impeller to rotate in response to the torque transmitted.

3. The wearable air purifier according to claim 2, wherein the magnetic coupling comprises:a first coupling portion provided on and / or in the impeller or the rotatable portion; anda second coupling portion provided on and / or in the other of the impeller and the rotatable portion; andwherein the first coupling portion comprises a magnetic material and the second coupling portion comprises a magnetic or ferromagnetic material.

4. The wearable air purifier according to claim 3, wherein the magnetic material of the first coupling portion comprises one or more permanent magnets.

5. The wearable air purifier according to claim 4, comprising a plurality of permanent magnets uniformly distributed about the rotational axis.

6. The wearable air purifier according to claim 5, wherein the plurality of permanent magnets alternate in polarity around the rotational axis.

7. The wearable air purifier according to any one of claims 3 to 6, wherein the first coupling portion is provided on and / or in the rotatable portion and the second coupling portion is provided on and / or in the impeller.

8. The wearable air purifier according to claim 7, wherein the magnetic material of the second coupling portion comprises one or more permanent magnets mounted to a hub of the impeller.

9. The wearable air purifier according to claim 8, wherein a plurality of permanent magnets are mounted to the hub so as to be uniformly distributed about the rotational axis.

10. The wearable air purifier according to claim 8 or 9, wherein the plurality of permanent magnets alternate in polarity around the rotational axis.

11. The wearable air purifier according to any one of claims 8 to 10, wherein the one or more permanent magnets are enclosed within one or more respective cavities formed in the hub.

12. The wearable air purifier according to any one of claims 8 to 10, wherein the one or more permanent magnets are retained in one or more blind holes formed in the hub, andwherein each blind hole is oriented such that a closed end of the blind hole is closer than an opposite open end of the blind hole to the first coupling portion on the rotatable portion.

13. The wearable air purifier according to claim 1, wherein:the driver comprises a stator configured to generate the rotating magnetic field; andthe impeller comprises a rotor configured to be driven to rotate about the rotational axis by the rotating magnetic field when the fan assembly is mounted to the driver assembly.

14. The wearable air purifier according to claim 13, wherein the rotor comprises one or more magnetic or ferromagnetic portions.

15. The wearable air purifier according to claim 14, wherein the rotor comprises an array of permanent magnets to be rotated by the rotating magnetic field.

16. The wearable air purifier according to any one of claims 14 to 15, wherein the rotor is radially outward of the stator.

17. The wearable air purifier according to claim 16, wherein the stator is annular so as to define an internal recess into which a bearing of the impeller is received when the fan assembly is mounted to the driver assembly.

18. The wearable air purifier according to claim 13 or 14, wherein the rotor and stator are configured to operate as an induction motor when the fan assembly is mounted to the driver assembly.

19. The wearable air purifier according to any one of the preceding claims, wherein: the driver assembly comprises a protruding portion; andthe fan assembly comprises an intruding portion to accommodate the protruding portion of the driver assembly when the fan assembly is mounted to the driver assembly.

20. The wearable air purifier according to any one of the preceding claims, wherein the impeller is a radial impeller configured to receive an airflow in a direction parallel to the rotational axis and to discharge the airflow in a direction that is perpendicular to the rotational axis.

21. The wearable air purifier according to any one of the preceding claims, comprising a battery operatively connected to the driver to supply power to the driver.

22. The wearable air purifier according to any one of the preceding claims, comprising a speaker assembly supported by the headgear so as to locate over an ear of a wearer when worn, the speaker assembly comprising a speaker.

23. A head support assembly of a wearable air purifier, the head support assembly comprising:headgear for wearing on a wearer’s head; anda driver assembly supported by the headgear, the driver assembly comprising a driver configured to generate a rotating magnetic field;the driver assembly configured for releasably mounting a fan assembly to the driver assembly, the fan assembly comprising an impeller configured to be driven by the rotating magnetic field and rotate about a rotational axis.

24. A fan assembly releasably mountable to a driver assembly supported by headgear for wearing of on a wearer’s head to form a wearable air purifier, the fan assembly comprising an impeller configured to be driven by a rotating magnetic field generated by a driver of the driver assembly and rotate about a rotational axis.

25. The fan assembly according to claim 24, comprising:a first coupling portion provided on and / or in the impeller to magnetically couple with a second coupling portion provided on and / or in the rotatable portion;wherein the first coupling portion comprises a magnetic material and the second coupling portion comprises a magnetic or ferromagnetic material;5 wherein, when the fan assembly is releasably mounted to the driver assembly, themagnetic coupling of the first and second coupling portions is configured to transmit torque from a rotatable portion, driven to rotate about a rotational axis by the driver assembly, to the impeller such that rotation of the rotatable portion causes the impeller to rotate in response to the torque transmitted.10

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