A filter cassette

Abstract

A releasably engaged filter cassette 5 comprising opposed first and second particle collecting surfaces 39 and 41, between which is an airflow channel and movable wipers 25, which moves from first to

Description

B ACKGROUND Some appliances that are configured to generate airflows include means for removing particles from air that is drawn into and / or that is discharged from the appliance. An example of such an appliance is an air purifier. One way of removing particles from an airflow is to direct the airflow between surfaces that are configured to capture particles entrained in the airflow. One example of such an arrangement is an electrostatic filter in which the surfaces are configured to attract charged particles from the airflow (such particles being charged upstream of the surfaces). SUMMARY In a first aspect, there is disclosed a filter cassette configured for releasable engagement with an appliance, the cassette comprising: opposed first and second surfaces spaced from one another so as to define an airflow channel therebetween, the surfaces being configured such that, in use, particles carried by an airflow in the airflow channel are able to collect on the first and / or second surfaces; and a wiper provided between the first and second surfaces, the wiper movable along the first and second surfaces from a first position to a second position to dislodge particles that have collected on the first and / or second surfaces. Particles collected on a surface may decrease the effectiveness of the surface at collecting further particles. Likewise, collection of a significant volume of particles on a surface may inhibit airflow along the airflow channel. Provision of a wiper that is moveable along the surfaces allows a user to remove collected particles from the surfaces to avoid (or at least reduce) these issues. The provision of the surfaces as part of a cassette that can be releasably mounted to an appliance means that such wiping can be performed remote from the appliance. For example, a user can perform the wiping in a location that facilitates disposal of such particles. Moreover, the ability to remove the cassette (and thus the surfaces) from the appliance can also allow a more thorough cleaning of the surfaces. For example, a user may be able to submerge the cassette (and thus the surfaces) in water to remove substances that may not otherwise be removable by wiping. Optional features of the first aspect will now be set out. These are applicable singly or in any combination with any aspect. In the second position, the wiper may protrude beyond an edge of at least one of the first and second surfaces. This may ensure that particles dislodged by the wiper from the surfaces are fully discharged (i.e., removed or expelled) from the airflow channel. As may be appreciated, as the wiper is moved to the second position, an accumulation of particles may form on (or ahead of) the wiper. Moving the wiper beyond the edge may ensure that this accumulation of particles does not remain on the surfaces (and thus within the airflow channel). Movement of the wiper from the first position to the second position may be in a direction towards a discharge opening of the cassette through which dislodged particles are able to be discharged (i.e., removed or expelled) from the cassette. In such arrangements, a user can direct the discharge opening towards a receptacle (such as a bin) and can move the wipers to discharge particles through the discharge opening and into the receptacle for disposal. The filter cassette may comprise a handle. The handle may be at an opposite end of the cassette to the discharge opening. This may allow a user to grip the filter away from the point of discharge of particles from the filter cassette. The handle may be in fixed relation with the first and / or second surface. That is, the handle may be rigidly connected (directly or indirectly) to the first and / or second surface. This may aid in moving the wiper relative to the first and / or second surface. The filter cassette may comprise a funnel connected between the discharge opening and the airflow channel. The funnel may comprise an internal cavity that tapers (i.e., narrows) in a direction away from the airflow channel. The funnel may define the discharge opening. The provision of a funnel may aid in directing particles discharged from the discharge opening, for example, into a receptacle for disposal. The airflow channel may comprise an airflow inlet. The airflow inlet may be for receipt of air into the airflow channel (e.g., external air drawn into the appliance). The airflow inlet may be defined between upstream edges of the first and second surfaces. For the avoidance of doubt, the terms “upstream” and “downstream” are used herein with reference to the direction of airflow along the airflow channel in normal use. The airflow channel may comprise an airflow outlet. The airflow outlet may be downstream of the airflow inlet. The airflow outlet may be for discharge of filtered air (i.e., in which at least some particles are removed from the air) from the airflow channel. The airflow outlet may be defined between downstream edges of the first and second surfaces. The airflow channel may have a width (i.e., the distance between the first and second surfaces) of between 2 mm and 15 mm, or, e.g., between 4 mm and 10 mm. The wiper may be moveable between the first and second positions in a direction that is transverse to an axis extending from the airflow inlet to the airflow outlet. Thus, the wiper may be moveable between the first and second positions in a direction that is transverse to the direction of airflow along the airflow channel in use. The wiper may be moveable in a direction that is perpendicular to the axis extending from the airflow inlet to the airflow inlet (or perpendicular to the direction of airflow along the airflow channel in use). Wiping across the airflow direction may allow the wipers to be positioned (e.g., in the first or second position), when not in use, in a manner that does not impede airflow through the airflow channel. Each of the first and second surfaces may comprise spaced opposite first and second lateral edges connecting the upstream and downstream edges of the respective surface. The wiper may be moveable between the first and second positions in a direction that extends between the first and second lateral edges. The wiper may be moveable from the first lateral edges (of the first and second surfaces) to the second lateral edges (of the first and second surfaces). Movement of the wiper may be restricted to a linear (i.e., substantially straight) path. The filter cassette may comprise means (e.g., a guide structure) for guiding the wiper along the linear path. The wiper may be formed of a non-electrically conductive material (i.e., an electrically insulative material). The wiper may, for example, comprise rubber and / or a rigid polymer (e.g., ABS plastic). The wiper may comprise a first wiping portion having an edge in contact with the first surface. The edge of the first wiping portion may be a leading edge of the first wiping portion when the wiper is moved from the first position to the second position. The term “leading” is used herein to refer to a portion that leads in movement when the wiper is moved from the first position to the second position. The first wiping portion may be elastic. For example, the first wiping portion may be more elastic than the first surface. Thus, the first wiping portion may be configured to flex when in contact with the first surface. The first wiping portion may comprise rubber. The first wiping portion may be configured to be deformed (i.e., flexed and / or compressed) from a natural position of the first wiping portion while in contact with the first surface. The first wiping portion may be configured so as to be biased against the first surface (e.g., at least in the first position). This may aid in ensuring that contact between the first wiping portion and the first surface is maintained as the first wiping portion is moved along the first surface. Likewise, in examples in which the wiper protrudes beyond an edge of the first surface in the second position, the first wiping portion (as it moves beyond the first surface) may spring back to a natural shape / position. This may provide rapid movement of the first wiping portion, which may aid in removal of particles from the first wiping portion (i.e., by flicking of the particles from the first wiping portion). The first wiping portion may have a profile that has an elongate shape. Such a profile may promote flexing of the first wiping portion. The profile may be taken on a reference plane that is parallel to a direction of movement of the wiper and that is perpendicular to the first and second surfaces. The first wiping portion may have a thickness (i.e., perpendicular to a direction of elongation) that is between 0.50 and 1.5 mm. The first wiping portion may be inclined with respect to the first surface. The filter cassette (e.g., the wiper) may comprise a second wiping portion having an edge in contact with the second surface. The second wiping portion may be as described above with respect to the first wiping portion, except that references to the first surface should be replaced with references to the second surface. The first and second wiping portions may be symmetrical (e.g., about a plane that is parallel to the first and / or second surface). Alternatively, the first and second wiping portions may be asymmetric. The first and second wiping portions may be formed of the same material. In other embodiments, the first and second wiping portions may be formed of different materials. One of the wiping portions may, for example, have greater elasticity than another of the wiping portions. The first and second surfaces may be formed of different materials and / or may comprise different surface textures. Providing first and second wiping portions of different shape and / or material may allow each of the first and second wiping portions to be suited to surfaces of different material and / or surface texture (e.g., having different coefficients of friction). The first and second wiping portions may diverge from one another in a forward direction with respect to movement of the wiper from the first to the second position. Together, the first and second wiping portions may form a V-shaped profile (i.e., in a plane that is perpendicular to the first / second surfaces). The wiper may be elongate in a width direction of the first and / or second surface (i.e., the width direction being perpendicular to the direction of movement of the wiper). The wiper may extend for substantially an entire width of at least one of the first and second surfaces. The wiper may extend for, e.g., at least 80%, or, e.g., at least 90% of the width of at least one of the first and second surfaces. In other words, the wiper may extend substantially fully across at least one of the first and second surfaces, so as to be capable of removing particles across the full width of the first / second surface. One or both wiping portions may be in the form of a strip or blade (e.g., a solid, continuous strip of material), or in some embodiments may comprise bristles (e g., so as to be in the form of a brush). The filter cassette may comprise a user input portion for receipt of a user input. The user input portion may be operatively connected to the wiper to cause movement of the wiper from the first position to the second position in response to user input. The user input portion may comprise a grip portion connected to the wiper. The grip portion may be arranged to be moved by a user to move the wiper between the first and second positions. Thus, for example, a user may grip the grip portion with one hand and grip the handle with the other, and in this way may move the wiper relative to the first and second surfaces. In other embodiments, the user input portion may provide for automatic movement of the wiper. For example, the filter cassette may comprise an actuator operatively connected to the user input portion (which may comprise, e.g., a button, touchscreen, etc.) and which may be configured to drive movement of the wiper in response to a user input received by the user input portion. In some examples, the actuator may comprise an electro-mechanical device (e.g., a motor). In some examples, the actuator may comprise a biasing member (e.g., a spring), which may be configured so as to be released from a deformed (e.g., compress or flexed) state upon receipt of a user input by the user input portion. The first and second surfaces may be planar. Alternatively, the first and second surfaces may be non-planar. For example, the first and second surfaces may be concentrically arranged or, for example, the first and second surfaces may each extend along a helical path. The first and second surfaces may be substantially parallel. Thus, the spacing between the first and second surfaces may be substantially uniform (at least in a direction of movement of the wiper). Each of the first and second surfaces may form a surface of a respective plate. Each of the first and second plates may be a unitary piece. Each plate may have a thickness (i.e., taken between opposite major surfaces of the plate) of between 0.10 mm and 2 mm. Each plate may be substantially planar. Each of the first and second plates may be substantially rectangular. Each plate may alternatively be curved. For example, the plates may be concentrically arranged. Each plate may be annular (i.e., may have an annular profile in a plane taken perpendicular to the direction of airflow along the airflow channel). Each plate may extend along a helical path (i.e., may have a helical profile taken in a plane that is perpendicular to the direction of airflow along the channel). The filter cassette may comprise a stack of spaced plates. The stack of spaced plates may comprise more than two plates, e.g., more than four plates, e g., more than six plates. The stack of plates may define a plurality of airflow channels therebetween. Each airflow channel may be provided with a respective wiper disposed therein for movement along first and second surfaces defining the respective airflow channel. Accordingly, the filter cassette may comprise a plurality of pairs of first and second surfaces, each being as described above. In such embodiments, the wipers may be connected to a slideably mounted (i.e., with respect to the surfaces) support structure. In this way the wipers may be moveable in unison by movement of the support structure. The grip portion may form part of, or be connected to, the support structure. For example, the grip portion may project from the support structure. The support structure may comprise a plurality of wiper support members that extend across the airflow channels defined between the plates. Each wiper may be mounted to a respective wiper support member. Each wiper support member may be connected by one or more frame members that are external to the airflow channels. Each wiper support member may be formed of a non-electrically conductive material (i.e., an electrically insulative material). The filter cassette may comprise a first stop member for limiting movement of the wiper(s) beyond the first position (i.e., in a direction away from the second position). The filter cassette may comprise a second stop member for limiting movement of the wiper(s) beyond the second position (i.e., in a direction away from the first position). One or both of the first and second surfaces may be a collector surface configured for collection of particles thereon. One or both of the first and second surfaces may be configured for attraction of charged particles. In this respect, the filter cassette may be an electrostatic filter cassette. One or both of the first and second surfaces may be formed of an electrically conductive material (e.g., steel or aluminium). In a second aspect, there is disclosed an air treatment system comprising: an air treatment appliance comprising a housing defining an airflow path; and the filter cassette according to the first aspect, the filter cassette configured for mounting to the air treatment appliance so that the airflow path of the air treatment appliance is in fluid communication with the airflow channel(s) of the filter cassette. Optional features of the second aspect will now be set out. These are applicable singly or in any combination with any aspect. The air treatment system may further comprise an ionizer upstream of the airflow channel(s) for ionizing particles carried by an airflow passing into the airflow channel(s). The air treatment appliance may comprise an air mover (e.g., fan, compressor or blower) for moving air through the filter cassette. The air treatment appliance may be an air purifier. In some examples, the air treatment appliance may be an air conditioner, a humidifier, a dehumidifier, or a heater. BRIEF DESCRIPTION OF THE DRAWINGS Figure lisa perspective view of an appliance. Figure 2A is a perspective cutaway view of part of an air treatment system. Figure 2B is a schematic section view of part of the air treatment system of Figure 2A. Figure 3 is a perspective view of a filter cassette of the air treatment system of Figure 2. Figure 4 is a section view of part of the filter cassette of Figure 3 when in a first position. Figure 5 is a section view of part of the filter cassette of Figure 3 when in a second position. Figure 6 is a schematic view showing a variation of the filter cassette of Figure 3. Figure 7 is a schematic view showing a variation of the filter cassette of Figure 3. Figure 8 is a side view showing a variation of the filter cassette of Figure 3. DETAILED DESCRIPTION Figure 1 shows an appliance 10 in the form of an air purifier for discharging treated air into a space. The appliance 10 includes an inlet 11 provided on a body 12 of the appliance 10, and an outlet 13 provided as part of a nozzle 14 of the appliance 10. The inlet 11 and outlet 13 are connected by an internal airflow path 47 (part of which is shown in Figure 2B). The internal airflow path 47 passes through a portion of the body 12, shown in Figures 2 A and 2B, that contains two filter cassettes 15 that are configured for releasable engagement within the body 12 of the appliance 10. Together, the filter cassettes 15 and appliance 10 provide an air treatment system 18. The filter cassettes 15 are located in cuboid recesses 16 formed in the body 12, which are separated by an internal wall 27 of the body 12. The recesses 16 are open on upper and lower sides to allow airflow 47 into the filter cassettes 15 from the inlet 11 of the appliance 10, and to flow from the filter cassettes 15 to the outlet 13 of the appliance 10. The recesses 16 are also open laterally at an external wall 17 of the body 12, which allows for insertion and removal of the filter cassettes 15 in the body 12. This opening in the external wall 17 may be covered by a removable cover. Although not shown, the filter cassettes 15 may be releasably retained in the recesses 16 by way of, e g., a snap engagement mechanism, magnetic coupling, latching arrangement, etc. A pre- filter 48 is provided upstream of filter cassettes 15, which comprises a porous media 49 supported by a frame 50. The frame 50 includes a handle 51, which facilitates removal and insertion of the pre-filter 48 in the body 12 (by way of sliding). As is apparent from Figure 2B, the appliance 10 is provided with an ionizer 46 formed of a plurality of carbon brushes positioned upstream of the filter cassettes 15 (and downstream of the pre-filter 48). The ionizer 46 is configured for ionizing any particles carried by the airflow 47 passing through the air treatment system 18. As will be described below, this allows the filter cassettes 15 to remove particles from the airflow 47. One of the filter cassettes 15 of the air treatment system 18 is shown in Figures 3, 4 and 5 (it should be appreciated that both cassettes in Figure 2A are identical). The filter cassette 15 includes a stack of spaced apart parallel planar plates 19, which define airflow channels 20 therebetween for flow of air to be treated. Each airflow channel 20 includes an inlet 21 defined between upstream edges 22 of the plates 19 (which are lower edges in use), and an opposite outlet 23 defined between downstream edges 24 of the plates 19 (which are upper edges in use). Accordingly, air flows into the filter cassette 15 through the inlets 21 and is discharged (i.e., removed or expelled) from the filter cassette 15 through the outlets 23. The plates 19 are formed of a conductive material (in particular, aluminium) such that when the charged particles (generated by the ionizer 47) pass between the plates 19 along the airflow channels 20 they are attracted to the plates 19 so to be removed from the airflow 47. As particles collect on the plates 19 the accumulation of particles can reduce the effectiveness of the plates 19 at collecting further particles, and can also be detrimental to airflow through the filter cassette 15. To dislodge collected particles from the plates 19, the filter cassette 15 further includes a plurality of wipers 25 (only some of which are labelled in Figures 4 and 5 for clarity). Each wiper 25 is provided in a respective airflow channel 20 between two adjacent plates 19 and extends substantially entirely across a width dimension W of the plates 19. The wipers 25 are mounted to a support structure 26, which includes a plurality of elongate wiper support members 28 that extend across the airflow channels 20 between adjacent plates 19. The wiper support members 28, which are formed of an electrically insulative material, are connected to one another by a rectangular frame 29 (formed of four frame members 30) that extends around a periphery of the stack of plates 19. The wiper support members 28 span the gap between two of the frame members 30 of the frame 29 (i.e., the gap between upper and lower frame member 30 of the frame 29). In this way, the support structure 26, and thus the wipers 25 are slidably mounted (i.e., interlocked) with respect to the plates 19. In particular, the support structure 26 (and thus the wipers 25) is moveable in a direction that is transverse to the direction of the airflow 47 along the airflow channels 20 between the inlets 21 and the outlets 23. The wipers 25 are moveable from a first position (shown in Figure 4) to a second position (shown in Figure 5) to dislodge particles from the plates 19. In the first position, the wipers 25 are located proximate to first lateral edges 31 of the plates 19, and in the second position the wipers are located proximate to second, opposite lateral edges 32 of the plates 19 (the lateral edges 31, 32 being edges of the plates 19 that are perpendicular to the upstream 22 and downstream 24 edges). To facilitate such movement, a grip portion 33 in the form of a tab protrudes from the support structure 26. Likewise, a handle 34 is provided on an end cap 35 of the filter cassette 15, which is fixedly mounted to the plates 19. Accordingly, a user is able to grip the handle 34 with one hand and the grip portion 33 with another and move the support structure 26 away from the end cap 35 (i.e., so as to move the wipers 25 along the plates 19 from the first position to the second position). The handle 34, as should be apparent from Figure 2, also aids in removal of the filter cassette 15 from the recesses 16 of the body 12 of the appliance 10. To limit movement of the wipers 25 beyond the second position, and also to support the plates 19 in their spaced arrangement, two elongate stop members 36 are provided at an end of the filter cassette 15 that is opposite to the cap 35. In the second position, the support structure 26 abuts against these two stop members 36, preventing the support structure 26 from travelling beyond the second lateral edges 32 of the plates 19. The end of the filter cassette 15 at which the stop members 36 are provided is open so as to provide a discharge opening 37, through which particles dislodged from plates 19 by the wipers 25 can be discharged (i.e., removed or expelled) from the filter cassette 15 (for example, into a receptacle such as a bin). As noted above, Figure 4 illustrates the wipers 25 in the first position. As is apparent from this figure, each wiper 25 includes a first wiping portion 38 that is in contact with a first surface 39 (of a respective plate 19) and a second wiping portion 40 that is in contact with a second surface 41 (of a respective plate 19). Each wiping portion 38, 40 has an elongate profile (in a plane perpendicular to the plates 19) and each wiper 25 is a unitary piece formed of an elastic material such as rubber. As a result, the wiping portions 38, 40 are able to flex and, when positioned in the airflow channels 20 (as per Figure 4) are biased against the respective first 39 and second 41 surfaces. This ensures that a leading edge 42 of each wiping portion 38, 40 remains in contact with the respective first 39 or second 41 surface as the wiper 25 is moved. The wiping portions 38, 40 of each wiper 25 diverge from one another in a forward direction (i.e., in the direction of movement from the first position to the second position), so as to form a V-shape profile. Each wiper 25 also includes a mounting portion 43 that extends rearwardly from a join between the first 38 and second 40 wiping portions (providing each wiper 25 with a Y-shaped profile). The mounting portion 43 of each wiper 25 mounts the wiper 25 to a respective wiper support member 28 of the support structure 26. The second position of the wipers 25 is shown in Figure 5. As should be apparent, in this second position, the wipers 25 (in particular, the wiping portions 38, 40 of the wipers 25) protrude beyond the second lateral edges 32 of the plates 19. This ensures that particles that are dislodged by the wipers 25 are moved off the surfaces 39, 41 of the plates 19 so as to be discharged (i.e., removed or expelled) through the discharge opening 37 of the filter cassette 15. Moreover, because the wiping portions 38, 40 are biased against the plates 19 (i.e., when in contact with the surfaces 39, 41 of the plates 19), as they are moved to the second position and protrude beyond the plates 19, they are caused to spring back to their natural positions (i.e., by flexing outwardly away from one another). This movement of the wiping portions 38, 40 can aid in dislodging any particles that remain on the wipers 25. Figures 6 and 7 schematically illustrate alternative arrangements of plates 19 for a filter cassette 15 of the type described above. In Figure 6, each plate 19 has a tubular shape and the plates 19 are arranged concentrically. The wipers 25 are arranged to move along a circular path in the airflow channels 20 between the plates 19. To achieve this movement, the wipers 25 are mounted to a support structure 26 that pivots (e.g., moved by a grip portion 33) about a pivot point 44 that is centrally positioned with respect to the tubular plates 19. In Figure 7, two plates 19 are provided (one shown in dashed lines for clarity), both of which have a spiral-shaped profile. In this example, two wipers 25 are arranged to move, each along a spiral path within a respective airflow channel 20 of two airflow channels 20 defined between the plates 19. This movement is provided by a support structure 26 that is again arranged to pivot about a central pivot point 44. However, in this example, the wipers 25 are moveable along the support structure 26 (in a radial direction) allowing the wipers 25 to follow the spiral paths as the support structure 26 is pivoted. Figure 8 depicts a variation of the filter cassette 15 shown in Figure 3. In this variation, a funnel 45 is provided at an end of the plates 19 (i.e., adjacent to the second lateral edges 32 of the plates 19). The funnel 45 has an internal cavity that is open at a first end adjacent to the plates 19 and that tapers in a direction away from the plates 19 to a further opening that provides the discharge opening 37 in this example. Accordingly, when the wipers (not shown) are moved from the first position to the second position dislodged particles are pushed into the funnel 45 and the tapered shape of the funnel 45 concentrates the dislodged particles into a smaller cross-sectional area which facilitates disposal. The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof. While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

Claims

1. A filter cassette configured for releasable engagement with an appliance, the cassette comprising:opposed first and second surfaces spaced from one another so as to define an airflow channel therebetween, the surfaces being configured such that, in use, particles carried by an airflow in the airflow channel are able to collect on the first and / or second surfaces; anda wiper provided between the first and second surfaces, the wiper movable along the first and second surfaces from a first position to a second position to dislodge particles that have collected on the first and / or second surfaces.

2. The filter cassette according to claim 1, wherein in the second position the wiper protrudes beyond an edge of at least one of the first and second surfaces.

3. The filter cassette according to claim 1 or 2, wherein movement of the wiper from the first position to the second position is in a direction towards a discharge opening of the cassette through which dislodged particles are able to be discharged from the cassette.

4. The filter cassette according to claim 3, comprising a handle at an opposite end of the cassette to the discharge opening.

5. The filter cassette according to claim 4, wherein the handle is in fixed relation with the first and / or second surface.

6. The filter cassette according to any one of claims 3 to 5, comprising a funnel connected between the discharge opening and the airflow channel.

7. The filter cassette according to any one of the preceding claims, wherein the airflow channel comprises an airflow inlet and an airflow outlet, and wherein the wiper ismoveable between the first and second positions in a direction that is transverse to an axis extending from the airflow inlet to the airflow outlet.

8. The filter cassette according to any one of the preceding claims, wherein movement of the wiper is restricted to a linear path.

9. The filter cassette according to any one of the preceding claims, wherein the wiper comprises a first wiping portion having an edge in contact with the first surface.

10. The filter cassette according to claim 9, wherein the edge of the first wiping portion is a leading edge of the first wiping portion when the wiper is moved from the first position to the second position.

11. The filter cassette according to claim 9 or 10, wherein the first wiping portion is elastic.

12. The filter cassette according to claim 11, wherein the first wiping portion is configured so as to be biased against the first surface.

13. The filter cassette according to any one of claims 9 to 12, wherein the first wiping portion is inclined with respect to the first surface.

14. The filter cassette according to any one of claims 9 to 13, comprising a second wiping portion having an edge in contact with the second surface.

15. The filter cassette according to claim 14, wherein the first and second wiping portions diverge from one another in a forward direction with respect to movement of the wiper from the first to the second position.

16. The filter cassette according to any one of the preceding claims, wherein the wiper extends for substantially a full width of at least one of the first and second surfaces.

17. The filter cassette according to any one of the preceding claims, further comprising a user input portion for receipt of a user input, the user input portion operatively connected to the wiper to cause movement of the wiper from the first position to the second position in response to user input.

18. The filter cassette according to claim 17, wherein the user input portion comprises a grip portion connected to the wiper, the grip portion arranged to be moved by a user to move the wiper between the first and second positions.

19. The filter cassette according to any one of the preceding claims, wherein the first and second surfaces are planar.

20. The filter cassette according to any one of the preceding claims, wherein each of the first and second surfaces forms a surface of a respective plate.

21. The filter cassette according to claim 20, comprising a stack of spaced plates, the stack of plates defining a plurality of airflow channels therebetween, and wherein each airflow channel is provided with a respective wiper disposed therein for movement along first and second surfaces defining the respective airflow channel.

22. The filter cassette according to claim 21, wherein the wipers are connected to a slideably mounted support structure, such that the wipers are moveable in unison by movement of the support structure.

23. The filter cassette according to any one of the preceding claims, wherein the first and / or second surfaces are formed of an electrically conductive material.

24. An air treatment system comprising:an air treatment appliance comprising a housing defining an airflow path; andthe filter cassette according to any one of the preceding claims, the filter cassette configured for mounting to the air treatment appliance so that the airflow path of the airtreatment appliance is in fluid communication with the airflow channel(s) of the filter cassette.

25. The air treatment system according to claim 24, wherein the air treatment system 5 further comprises an ionizer upstream of the airflow channel(s) for ionizing particles carried by an airflow passing into the airflow channel(s).

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