Field of the Invention

The present invention relates to a cleaner head for a vacuum cleaner and to a vacuum cleaner comprising the cleaner head. Particularly, although not exclusively, the present invention relates to a cleaner head employing an electrostatic field to facilitate entrainment of dirt particles within a suctioning airflow, and to a vacuum cleaner comprising the cleaner head.

Background

Removing dust from a carpet is one of the key performance factors for a vacuum cleaner. The ASTM F608 standard is used to measure vacuum cleaners’ efficacy and is calculated as a geometric mean of the pick-up scores achieved on four types of carpets: Shag, Multilevel, Plush and Level loop. Conventional floorcare technologies suffer from lower scores in Shag and Multilevel carpets. This can have a disproportionately negative effect on the total pick-up score. Therefore, it is desirable to improve the ability of a cleaner head and/or a vacuum cleaner to extract dust (i.e. dirt particles) from deep within a carpet to improve the cleaner head’s/vacuum cleaner’s resulting score for the geometric mean ASTM F608.

Additionally, there is a continuous drive to reduce the energy required to pick up dirt particles from a floor surface, i.e. both from carpets and hard floors. It can be helpful to agitate or move dirt particles from the surface to be cleaned using mechanisms beyond mechanical agitation and/or strong suctioning airflows, which can be energy intensive.

It is known that as particles get smaller, the balance of different physical forces acting on them changes. For example, as particle size decreases from 1 mm to 1 pm, dirt particles become increasingly less susceptible to gravity, mechanical agitation and air flow, and instead increasingly more susceptible to electrostatic, capillary and van der Waals forces. Consequently, the behaviour of super fine dust (e.g. made up of dust particles < 1 pm) is dominated by electrostatic, capillary and van der Waals forces rather than by gravity, mechanical agitation and air flow.

Due to these properties of small particles, it is possible to manipulate dirt particles up to 1 mm over distances of up to 1 cm by using an electrostatic field. Furthermore, it is known that about 99% of the mass of the dirt particle mixture used in an ASTM pick-up test is provided by particles with a size less than 425 pm (ASTM F608 A1). Thus, it is possible to augment a vacuum cleaner’s pick-up performance, specifically pick-up performance on carpets, and/or its energy efficiency by employing electrostatic agitation instead of/ in addition to mechanical agitation and/or a suctioning airflow.

The present invention has been devised in light of the above considerations. Summary of the Invention

In a first aspect, the present invention provides a cleaner head for a vacuum cleaner, the cleaner head being connectable to a suctioning airflow to clean a surface; wherein the cleaner head comprises an electrode for generating an electrostatic field between the electrode and the surface to be cleaned to apply a force to cause dirt particles to move towards the electrode and into a flow path of the airflow, thereby facilitating entrainment of the dirt particles within the airflow.

Advantageously, providing the cleaner head with an electrode for generating an electrostatic field can augment the cleaner head’s pick-up ability. That is, the electrostatic field created by the electrode causes dirt particles from the surface to be cleaned, e.g. a carpet/ hard floor, to experience a force directed towards the electrode.

Preferably, the dirt particles are electrostatically agitated in addition to mechanically agitated, e.g. with a brushbar mounted on a surface-engaging portion of the cleaner head. The electrode may extend along/around the full length of the brushbar. When the brushbar is circular, the electrode may for example extend around it to form a helicoidal electrode surface. The electrode may be exposed to air (i.e. uncovered) or may be covered, for example embedded in a portion of the vacuum cleaner, such as the brushbar, so as to benefit from electrical insulation. Alternatively, the cleaner head may be used as a solid powder aerosoliser that does not use mechanical agitation but only electrostatic agitation to generate a continuous stream of aerosolised solid particles which feeds into the suctioning airflow.

Depending on the size of the dirt particles and the type of surface to be cleaned, the dirt particles can experience different effects in the generated electrostatic field. For example, small dirt particles (e.g. <10 pm) are accelerated towards the electrode such that they are lifted from the surface to be cleaned and may become fully aerosolised. Larger dirt particles (e.g. 10 pm-500 pm) cannot be fully aerosolised but can instead be temporarily lifted from the surface to be cleaned which is sufficient to facilitate their entrainment within the suctioning airflow. Regardless of their size, most dirt particles in the generated electrostatic field experience a force which causes them to move towards the electrode and into the flow path of the suctioning airflow. Thus, the dirt particles can be more easily picked up from a hard floor or a carpet, e.g. by drawing them from within a carpet to a carpet surface. The dirt particles can then be directed into the flow path of the suctioning airflow and be entrained therewithin, thereby improving the cleaner head’s efficacy. Herein, by entrained it is meant that the dirt particles are captured within the suctioning airflow, e.g. such that they can be directed to a filter element within a vacuum cleaner comprising the cleaner head.

Optional features of the present invention are outlined below. The invention includes the combination of the aspects and optional features described except where such a combination is clearly impermissible or expressly avoided. Optionally, the electrode may be a mesh electrode comprising a conductive framework defining a plurality of openings, the plurality of openings configured to allow the dirt particles to pass therethrough to enter the airflow. Here, by conductive, it is meant electrically conductive. The plurality of openings may together form an open area of the mesh electrode, while the conductive framework may form a closed area of the mesh electrode. It may be desirable to maximise the open area of the mesh electrode such that the proportion of dirt particles which pass through the mesh electrode to enter the suctioning airflow is maximised. For example, the open area of the mesh electrode may range from at least 35% to 99%, e.g. from 35% to 95% of the total area of the mesh electrode. Generally, the open area of the mesh electrode may be maximised by realising the mesh electrode as a mono-filar electrode.

Optionally, each of the plurality of openings of the mesh electrode may have an area of at least 0.28 mm ² , or at least 0.79 mm ² . It has been found that such areas allow a sufficient proportion of the accelerated dirt particles to pass through the mesh electrode (and not contact the conductive framework which may cause the dirt particles to stick to it and/or drop back to the surface to be cleaned). Specifically, the lower limit of 0.28 mm ² corresponds to a circular opening having a diameter of 600 pm which is equal to the largest diameter of silica particles used in the ASTM F608 test. Thus, by ensuring that each of the plurality of openings of the mesh electrode has an area of at least 0.28 mm ² , it can be ensured that the mesh electrode does not act as a sieve preventing pick-up of particles smaller than 600 pm. The lower limit of 0.79 mm ² may enhance safety of operation.

Optionally, the conductive framework of the mesh electrode consists of a plurality of strands which define the openings, each of the strands having a maximum thickness of 1 mm or less. This maximum thickness may correspond to the thickness of a strand along the plane of the mesh; or the thickness of a strand of the mesh in a direction transverse to the plane of the mesh or both. The plane of the mesh herein is considered the plane along which all of the strands lie. This is typically a flat plane but may be curved. For example, the maximum thickness of each strand may be around 0.7 mm. Varying the thickness of the strands can allow the generated electrostatic field and/or closed area of the mesh electrode to be varied as required.

Optionally, each of the plurality of openings of the mesh electrode may be polygonal. Preferably, each of the plurality of openings of the mesh electrode may be hexagonal. Alternatively, if not polygonal, each of the plurality of openings may be circular.

Typically, the electrode is connectable to a power supply to create a potential difference and/or voltage gradient between the electrode and the surface to be cleaned, thereby generating the electrostatic field. The potential difference may be constant or may oscillate. In effect, the surface to be cleaned may be thought of as existing at a zero potential, and the electrode may be connected to the power supply such that it is at positive or negative non-zero potential, thereby providing the potential difference and/or voltage gradient therebetween having respectively a positive or negative polarity. Optionally, the polarity of the created potential difference may be variable over time. For example, the polarity may be periodically, e.g. cyclically, switched from positive to negative and vice versa. Additionally or alternatively, the magnitude of the potential difference may be variable over time, e.g. periodically switched. This may be done for example at regular intervals of time. Conveniently, varying the polarity and/or magnitude of the potential difference may mitigate a risk of dirt particles becoming polarised due to the electrostatic field which may hinder the cleaner head’s pick-up performance.

Optionally, the ratio of the created potential difference to the distance between the electrode and the surface to be cleaned may be 3 MV/m or less. This value corresponds to the breakdown voltage of air. Therefore, by not exceeding this value, it can be ensured that air between the electrode and the surface to be cleaned does not break down to ozone and plasma, which can hinder the pick-up performance of the cleaner head and/or pose safety hazards. Furthermore, experiments have indicated that dirt particles having sizes <425 pm are most susceptible to field strengths approaching 3 MV/m.

Optionally, the created potential difference may be within the range of 1 kV to 10 kV. Preferably, the created potential difference may be 6kV or less, 4 kV or less, 2.6 kV or less, and/or 2.5k kV or less.

Optionally, the electrode may be mounted proximal to a surface-engaging portion of the cleaner head such that, in use, the distance between the plane of the electrode and the surface to be cleaned is 5 cm or less.

For example, the created potential difference between the electrode and the surface to be cleaned may be 6 kV at a distance of 5 mm, 4 kV at a distance of 3 mm, 2.5 kV at a distance of 2 mm, and/or 1 kV at a distance of 1 mm. A suitable configuration can be chosen based on the type of surface to be cleaned (e.g. hard floor or carpet) and/or on the size of the dirt particles. Generally, it has been observed that smaller dirt particles (e.g. <10 pm) can be more easily lifted off the surface to be cleaned under the influence of an electrostatic field and more easily entrained into a suctioning airflow compared to larger dirt particles due to smaller dirt particles’ relatively lower settling velocities.

Optionally, the plane of the electrode may be angled relative to the surface to be cleaned to produce a gradient in the electrostatic field. Preferably the angle of the plane is orientated such that the region of greatest field strength is positioned closest to the flow path of the suctioning airflow. Thus, the accelerated dirt particles can be guided to a position where the suctioning airflow is the strongest to facilitate their entrainment therewithin. For example, the acute angle between the plane of the electrode and the surface to be cleaned may be within the range of 0 to 45 degrees.

Optionally, the cleaner head may have a geometric mean ASTM F608 score of 25% or more, and preferably 30% or more. In a second aspect, the present invention provides a vacuum cleaner comprising: a vacuum motor for driving a suctioning airflow; and a cleaner head according to the first aspect connected to the suctioning airflow.

Advantageously, the vacuum cleaner comprising the cleaner head of the first aspect can simultaneously have reduced energy consumption and improved pick-up efficacy compared to conventional vacuum cleaners. This is because augmenting the cleaner head with an electrode generating an electrostatic field can be a more energy-efficient way of improving pick-up efficacy compared to alternative solutions such as increasing the amount of mechanical agitation provided by the cleaner head and/or the strength of the suctioning airflow provided by the vacuum motor.

Summary of the Figures

Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

Fig. 1 schematically shows a cleaner head according to an embodiment of the present invention;

Fig. 2 schematically shows an experimental setup simulating the pick-up performance of a cleaner head according to an embodiment of the present invention;

Fig. 3A and 3B respectively show a schematic and a photographic enlarged view of a portion of the experimental setup of Fig. 2;

Fig. 4 schematically shows the mesh structure of the electrode of the experimental setup of Fig. 2;

Figs. 5A-5C show three variant configurations of the electrode of Figs. 4A and 4B relative to a surface to be cleaned containing dirt particles;

Fig. 6 shows a percentage breakdown of different types of dirt particles present in a dirt particle mixture used in an ASTM F608 pick-up test; and

Fig. 7 is a plot showing the proportion of dirt particles picked up by the experimental setup of Fig. 2 from different types of surfaces to be cleaned.

Detailed Description of the Invention

Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference. A cleaner head 100 for a vacuum cleaner according to an embodiment of the present invention is discussed with reference to Fig. 1 . The cleaner head 100 is connectable to a suctioning airflow, e.g. provided by a vacuum cleaner. The cleaner head 100 may comprise means for mechanically agitating dirt particles off the surface to be cleaned. In the example of Fig. 1 , the cleaner head comprises a rotatable brushbar 11 forming a surface-engaging portion of the cleaner head and providing mechanical agitation. The cleaner head 100 comprises an electrode 4 for generating an electrostatic field between the electrode and a surface to be cleaned 2 to apply a force to cause dirt particles 3 to move towards the electrode 4 and into a flow path of the suctioning airflow, thereby facilitating entrainment of the dirt particles within the airflow. The suctioning airflow may transport the entrained dirt particles to a filter element and/or bin of e.g. a vacuum cleaner comprising the cleaner head 100.

The electrode 4 is preferably a mesh electrode comprising a conductive framework defining a plurality of openings (see Fig. 4), the plurality of openings configured to allow the dirt particles 3 to pass therethrough to enter the suctioning airflow. The electrode 4 is preferably mounted proximal to a surface-engaging portion of the cleaner head such that, in use, the distance between the plane of the electrode and the surface to be cleaned is 5 cm or less. In the example of Fig. 1 , the surface-engaging portion is provided by the rotatable brushbar 11 and the electrode 4 is wrapped around an internal portion of the rotatable brushbar. The electrode extends around the full length of the brushbar to form a helicoidal electrode surface. Thus, the plane of the electrode 4 is curved which allows the electrode to rotate together with the rotatable brushbar 11 . Therefore, at all times during use, a portion of the surface to be cleaned 2 is opposed to a portion of the electrode along a depth direction such that the region between the electrode and the surface to be cleaned in the depth direction is always inside the generated electrostatic field. Thus, the surface to be cleaned 2 can be simultaneously subjected to electrostatic agitation provided by the electrode and to mechanical agitation provided by the rotatable brushbar. The electrode may be exposed to air (i.e. uncovered) or may be covered, for example embedded in the brushbar so as to benefit from electrical insulation.

To generate the electrostatic field, the electrode 4 is connected to a power supply (not shown) to create a potential difference (i.e. voltage) and/or voltage gradient between the electrode 4 and the surface to be cleaned 2. The potential difference may be constant or may oscillate. In effect, the surface to be cleaned is at 0 potential, and when the electrode 4 is connected to the power supply, it is either at positive or negative non-zero potential, thereby providing the potential difference and/or voltage gradient therebetween having respectively a positive or negative polarity. Preferably, the created potential difference is within the range from 1 kV to 10 kV, e.g. it may be 6kV or less, 4 kV or less, 2.6 kV or less, and/or 2.5k kV or less. For example, the created potential difference between the electrode 4 and the surface to be cleaned 2 may be 6 kV at a distance of 5 mm, 4 kV at a distance of 3 mm, 2.5 kV at a distance of 2 mm, and/or 1 kV at a distance of 1 mm. A suitable configuration can be chosen based on the type of surface to be cleaned (e.g. hard floor or carpet) and/or on the size of the dirt particles. Generally, it has been observed that smaller dirt particles (e.g. <10 pm) can be more easily lifted off the surface to be cleaned 2 under the influence of the electrostatic field and more easily entrained into the suctioning airflow compared to larger dirt particles due to smaller dirt particles’ relatively lower settling velocities.

In the example of Fig. 1 , the polarity of the created potential difference is variable overtime. This is achieved by providing the electrode 4 with two oppositely polarised portions, each forming a respective helicoidal electrode surface. That is, a first half 12a of the electrode 4 (left-hand side arc in Fig. 1) is maintained at positive potential to produce positive polarity between the electrode and the surface to be cleaned 2, and a second half 12b of the electrode (right-hand side arc in Fig. 1) is maintained at negative potential to produce negative polarity between the electrode and the surface to be cleaned. The two portions 12a, 12b of the electrode 4 are electrically insulated from one another to enable them to maintain their opposite polarities. In the example of Fig. 1 , this is achieved by a pair of electrical insulators 13a, 13b interposed between the two portions 12a, 12b of the electrode 4. As the brushbar 11 rotates (as indicated by the clock-wise arrows in Fig. 1), the two portions 12a, 12b of the electrode 4 also rotate relative to the surface to be cleaned such that the polarity of the generated potential difference is cyclically switched, e.g. at regular time intervals. Conveniently, this can mitigate the risk of dirt particles 3 becoming polarised due to the electrostatic field which may hinder the cleaner head’s pick-up performance. It is envisaged that in addition to or instead of varying the polarity, the magnitude of the potential difference may be varied overtime to achieve the same effect. For example, this may be achieved using the configuration of Fig. 1 , with the two portions 12a, 12b of the electrode 4 being maintained at potentials of different magnitudes.

Next, an experimental setup 1 simulating the pick-up performance of a cleaner head according to an embodiment of the present invention is discussed with reference to Fig. 2. In effect, the experimental setup 1 acts as a solid powder aerosoliserthat does not use mechanical agitation but only electrostatic agitation to generate a continuous stream of aerosolised solid particles which feeds into a suctioning airflow.

The experimental setup 1 comprises a surface to be cleaned 2 which is provided by a substrate. The substrate 2 is provided with dirt particles 3 deposited thereon. A mesh electrode 4 is provided above the substrate 2 such that it overlies it in a vertical direction. An extraction hose 5 containing a suctioning airflow is provided above the mesh electrode such that the mesh electrode is interposed between the substrate 2 and a suction opening 5a of the extraction hose 5. The suction opening 5a of the extraction hose 5 is spaced from the surface to be cleaned 2 such that dirt particles cannot be lifted and picked up by the suctioning airflow alone, i.e. unaided by a generated electrostatic field by the electrode 4.

A non-suction opening (not shown) of the extraction hose 5 is connected to an externally controlled pump (not shown) which provides the suctioning airflow. The flow path of the suctioning airflow is from the mesh electrode towards the slave vac and is indicated by arrows inside the extraction hose 5 in Fig. 2. The substrate 2, mesh electrode 4, and a part of the extraction hose 5 including the suction opening 5a are all enclosed within an isolation box 6 containing a safety interlock 10. The safety interlock acts to prevent the electrode 4 being switched on whilst the door (not shown) of the isolation box 6 is open, thereby ensuring safety of operation. The electrode is electrically connected to a power supply 8 such that, in use, it is at non-zero potential relative to the zero- potential substrate to create a potential difference therebetween which generates an electrostatic field. The potential difference can be monitored on an oscilloscope 7 coupled to the power supply and on a voltmeter coupled to the electrode by using a high-voltage probe. The potential difference and/or its polarity (positive/negative) can be switched using a user-operable switch 9 on the power supply 8. For example, the potential difference may be constant or may oscillate. Conveniently, the polarity of the created potential difference may be varied overtime, e.g. as discussed in relation to Fig. 1 .

Preferably, the ratio of the created potential difference to the distance between the electrode 4 and the substrate 2 is 3 MV/m or less. By not exceeding this value, it can be ensured that air between the electrode and the surface to be cleaned does not break down to ozone and plasma, which can hinder the pick-up performance of the cleaner head and/or pose safety hazards. Furthermore, experiments have indicated that dirt particles having sizes <425 pm are most susceptible to field strengths approaching 3 MV/m.

A schematic and a photographic enlarged views of a portion of the experimental setup of Fig. 2 are respectively shown in Figures 3A and 3B. The schematic view of Fig. 3A is a side view, while the photographic view of Fig. 3B is a perspective partial view from the top and the side. In both figures the substrate 2, dirt particles 3, mesh electrode 4, and the suction opening 5a of the extraction hose 5 are shown. The direction of the suctioning airflow is indicated by an arrow in Fig. 3A. The electrode 4 is mounted at a distance, d, of 5 cm or less from the substrate 2 for optimised electrostatic field generation. In this example, the created potential difference is 16 kV at a distance d=10 mm. However, in a cleaner head configuration 100 such as the one shown in Fig. 1 , it is preferable that the potential difference does not exceed 10 kV due to safety considerations.

The structure of the mesh electrode 4 is discussed in more detail with respect to Fig. 4. As discussed above, the mesh electrode 4 comprises a plurality of openings 4b provided by a conductive framework 4a. The plurality of openings 4b together form an open area of the mesh electrode 4, while the conductive framework 4a forms a closed area of the mesh electrode. It is generally desirable to maximise the open area of the mesh electrode such that the proportion of dirt particles 3 which pass through the mesh electrode to enter the suctioning airflow is maximised. For example, the open area of the mesh electrode may range from at least 35% to 99% of the total area of the mesh electrode.

The conductive framework 4a of the mesh electrode 4 consists of a plurality of strands which define the openings 4b, each of the strands having a maximum thickness of 1 mm or less. In this example, the maximum thickness of each strand is around 0.7 mm. Varying the thickness of the strands can allow the generated electrostatic field and/or closed area of the mesh electrode to be varied as required. Furthermore, in this example, the maximum thickness corresponds to both the thickness of a strand along the plane of the mesh and to the thickness of a strand of the mesh in a direction transverse to the plane of the mesh. The plane of the mesh herein is considered the plane along which all of the strands lie. In this example it is a flat plane, but it may be curved instead (as discussed with reference to Fig. 1). In this example, each of the plurality of openings 4b of the mesh electrode 4 is polygonal, specifically hexagonal. It is envisaged that the openings may not be polygonal, but e.g. circular instead. For example, the hexagons may each have a side of 5 mm or 6 mm. Thus, in a preferred embodiment, each of the plurality of openings 4b of the mesh electrode 4 has an area within the range of 65 mm ² to 115 mm ² .

The conductive framework 4a may be formed by weaving the plurality of strands, overlapping them, or integrally forming them to provide the framework. Generally, the conductive framework may be formed in any manner inasmuch it can act as an electrode and provides openings to achieve a mesh structure.

Next, three variant configurations of the electrode 4 of Fig. 4 relative to a surface to be cleaned 2 containing dirt particles 3 are discussed with respect to Figures 5A to 5C.

In a first configuration (see Fig. 5A), the plane of the electrode 4 is flat and angled relative to the surface to be cleaned 2 (a substrate with dirt particles 3 deposited thereon) to produce a voltage gradient therebetween when the electrode is connected to the power supply 8. The voltage gradient in turn creates a gradient in the generated electrostatic field. Thus, the generated electrostatic field is strongest where the distance between the electrode 4 and the surface to be cleaned 2 is smallest (i.e. in the rightmost corner of the substrate 2 in Fig. 5A). Thus, the dirt particles in the generated electrostatic field experience a force having components towards the electrode 4 and towards the right end of the substrate 2 (i.e. where the electrostatic field is strongest). The dirt particles used in this example are coarse dirt particles (i.e. their size ranges within the range 10 pm - 500 pm). Thus, under the generated electrostatic field, the dirt particles are “swept” into the right corner of the substrate in a pile which partially protrudes from the openings 4b of the mesh electrode 4. Conveniently, by varying the orientation and relative angle of the plane of the electrode with respect to the surface to be cleaned 2, the dirt particles can be swept into a region, e.g. closest to the flow path of a suctioning airflow and/or a region where the suctioning flow is strongest. Thus, entrainment of the dirt particles 3 within the suctioning airflow can be improved. Specifically, it has been found that it is beneficial to configure the electrode 4 relative to the surface to be cleaned 2 such that the acute angle, a, therebetween is within the range of 0 to 45 degrees.

Next, a second configuration is discussed with reference to Fig. 5B. In this example, the mesh electrode 4 is parallel to the surface to be cleaned 2, as shown in Figures 2 and 3. The size of the dirt particles is chosen to be small, i.e. <20 pm. Thus, under the effect of the electrostatic field generated by the electrode, the fine dirt particles are accelerated towards the electrode and fully aerosolised, as indicated by the aerosol cloud 3’ on the right-hand side of Fig. 5B. Therefore, due to their small size relative to the open area of the electrode 4, most of the dirt particles pass through the mesh. Furthermore, it has been observed that the aerosol cloud 3’ does not settle but remains suspended above the mesh electrode 4 for a relatively long time ready to be picked up by the suctioning airflow. This relatively long settling time is due to the small particles’ low settling velocities. Finally, a third configuration is discussed with reference to Fig. 5C. In this example, the electrode 4 is arranged in the same manner relative to the surface to be cleaned 2 as in Fig. 5B, i.e. parallel thereto. However, a different size of dirt particles is used. Specifically, the dirt particles in this example are dirt grains, i.e. larger than the coarse dirt particles of Fig. 5A and > 425 pm. Thus, under the effect of the electrostatic field generated by the electrode 4, the dirt grains 3 are accelerated towards the electrode 4 for a brief period of time and then lose momentum and drop back to the surface to be cleaned 2. Unlike the fine dirt particles of Fig. 5B, the dirt grains of Fig. 5C are temporarily lifted off the surface to be cleaned 2 rather than suspended above it for an unlimited period of time. However, it has been observed that this too has a beneficial effect on pickup efficacy as the particles are lifted into proximity of the suctioning airflow allowing them to be entrained within and swept away by it.

The ASTM F608 performance of the experimental setup 1 of Fig. 2 has been tested on different types of surfaces to be cleaned, each provided with a mixture of dirt particles, and the results are summarised in the plot of Fig. 7. The appropriate type of mixture of dirt particles has been determined with reference to the mass fraction breakdown of an ASTM F608 silica particle mixture shown in Fig. 6.

The plot of Fig. 6 shows a percentage breakdown of different types of dirt particles present in a dirt particle mixture used in an ASTM F608 pick-up test. The mixture is obtained by mixing silica sand of different size classes as defined in the table. It has been found the 96% of the mass of the mixture is provided by dirt particles having sizes, x, within the range from 150 pm to 425 pm, more specifically this corresponds to the central 3 bins of the ASTM F608 standard (150-212, 212-300 and 300-425um).

The experimental setup 1 of Fig. 2 has been used to simulate the performance of a cleaner head according to an embodiment of the present invention when used on different types of surfaces to be cleaned, each provided with a dirt particle mixture suitable for ASTM F608 testing. Fig. 7 is a plot showing the proportion of dirt particles picked up from each type of surface. The types of surfaces to be cleaned include acrylic, PTFE, polycarbonate, stainless steel, polyethylene, shag carpet, wilton carpet, and wood. The mixture of dirt particles includes the following types of dirt particles as categorised by size: 150 pm, 212 pm, 300 pm, dolomite with sizes of up to 500 pm, and silica flour (e.g. commercially available R10™) with sizes of 10 pm or less. The sliding scale on the right-hand side of the plot shows the colour gradient corresponding to different proportions of dirt particles picked up from the surface to be cleaned - ranging from 0 to 1 (i.e. 100%). The back regions on the plot represent values for which the performance of the experimental setup 1 has not been tested.

Overall, the performance of the experimental setup 1 indicates that providing a mesh electrode interposed between a surface to be cleaned and a suctioning airflow can enable the pick-up of large proportions of differently sized dirt particles for a variety of surfaces, unaided by mechanical agitation or by the suctioning airflow (as discussed above, in the experimental set up for proof of concept, the suctioning airflow alone cannot pick up any dirt particles off the surface). For example, it was found that found over 83% (and up to 94%) of the 212 pm and the 300 pm dirt particles are picked up from stainless steel and wood solely through electrostatic agitation, allowing them to subsequently be transported away from the surface to be cleaned by cautioning airflow. In terms of performance on carpet surfaces, such as the shag and wilton, significant pick-up is observed as well. Around 12% of the 300 pm dirt particles (which make up nearly 32% of the dirt particle mixture of Fig. 6) are picked up from the shag carpet solely through electrostatic agitation. In the case of the wilton carpet, over 53% of the dirt particles of each of the three sizes shown in Fig. 7 are picked up under the action of the electrostatic field generated by the electrode.

Thus, combining the electrostatic pickup technology of the experimental setup of Fig. 2 with means for mechanical agitation of dust particles, e.g. the brushbar 11 of Fig. 1 , can render an energy-efficient cleaner head having a substantially improved pick-up performance compared to existing floorcare technologies. For example, it is estimated that such a cleaner head may have an improved geometric mean ASTM F608 score of at least 25%, or at least 32%. In such a cleaner head, suctioning airflow alone can pick up dust from a surface but the presence of the electrode allows one to remove or reduce the suction from the surface, thereby reducing the energy consumption and augmenting pick up.

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.

For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example +/- 10%.