Vacuum cleaner

Abstract

Disclosed is a vacuum cleaner comprising a suction generator configured to generate airflow along an airflow path of the vacuum cleaner, a filter disposed in the airflow path such that the airflow passes through the filter; and an actuator configured, in use of the suction generator, to move the filter, to filter dirt from the airflow.

Description

[0001] VACUUM CLEANER

[0002] BACKGROUND

[0003] Debris-laden airflow that is drawn into a vacuum cleaner must be filtered to remove debris and dust from the airflow before the airflow is expelled from vacuum cleaner. There is a general desire to reduce the size of vacuum cleaners, without compromising performance.

[0004] SUMMARY

[0005] A first aspect of the invention provides a vacuum cleaner comprising a suction generator configured to generate airflow along an airflow path of the vacuum cleaner, a filter disposed in the airflow path such that the airflow passes through the filter; and an actuator configured, in use of the suction generator, to move the filter, to filter dirt from the airflow.

[0006] A vacuum cleaner according to the first aspect may provide enhanced air filtration through the filter compared to a vacuum cleaner in which the filter is not moved to filter dirt from the airflow. Moving the filter may alter a position of apertures of the filter such that dirt that would have passed through an aperture, had the filter not been moved, may instead impact the filter and be inhibited from passing through the filter, whilst permitting filtered airflow to pass through the filter. Moving a filter, to filter dirt from airflow, may provide one or more of the following advantages compared to other arrangements capable of filtering dirt from an airflow with comparable filtration efficiency: a more compact arrangement, lower pressure loss across the filter, and lower power consumption.

[0007] The vacuum cleaner may comprise a control system configured to cause the actuator to vary a speed of movement of the filter on the basis of a rate of the airflow generated by the suction generator. The rate of airflow generated by the suction generator may have a direct influence on a speed at which the airflow is travelling when the airflow reaches the filter. It has been found that an increased speed of movement of the filter may be required to maintain filtration efficiency for an increased speed of airflow at the filter.

[0008] The actuator may be configured to oscillate or reciprocate the filter. This may permit use of a relatively simple and space-efficient arrangement to move the filter compared to other types of movement. This may also provide a relatively repeatable and reliable movement of the filter compared to other types of movement.

[0009] The actuator may be configured to oscillate or reciprocate the filter at an ultrasonic frequency, for example above 20kHz. This may reduce acoustic emissions within human hearing range from the vacuum cleaner in use, compared to frequencies below ultrasonic frequencies. This may also provide improved filtration of dirt from the airflow compared to lower frequencies.

[0010] The actuator may be configured to oscillate or reciprocate the filter at a frequency of at least 30kHz. This may provide improved filtration of dirt from the airflow compared to lower frequencies.

[0011] The actuator may be configured to oscillate or reciprocate the filter with an amplitude that is at least equal to a minimum diameter of apertures of the filter. Accordingly, each aperture of the filter may be temporarily blocked by material of the filter that is adjacent to the aperture during an oscillation or reciprocation of the filter, to help prevent dirt from passing through the aperture.

[0012] The actuator may comprise a piezoelectric device, which may provide rapid response times, smooth movement of the filter, and relatively low power consumption compared to some other types of actuators.

[0013] The actuator may be rigidly fixed to the filter. This may provide improved transfer of force from the actuator to the filter compared to a non-rigid connection between the actuator and the filter.

[0014] Apertures of the filter may have a first diameter at an upstream face of the filter and a second diameter, less than the first diameter, at a downstream face of the filter. Accordingly, each aperture may be defined by funnel-shaped surface between the upstream and downstream faces of the filter. This may provide better filtration efficiency compared to the apertures having a cylindrical-shaped surface between the upstream and downstream faces of the filter. The apertures may each comprise a convex surface between the upstream face and the downstream face of the filter. This has been found to provide better filtration efficiency compared to the funnel-shaped surface being linear or concave. Filters comprising such apertures may also be more easily manufactured compared to other shapes.

[0015] The convex surface may have a constant radius between the upstream face and the downstream face of the filter. This has been found to provide better filtration efficiency compared to a non-constant radius.

[0016] The second diameter may be in the region from 0.1 mm to 0.3 mm. This may be suitable to filter dirt, for example dust particles, of a size typically entrained in airflow of vacuum cleaners, for example particles that are less than 10pm, less than 6pm, less than 3 pm or less than 1pm.

[0017] The actuator may be configured to move the filter by a distance that is at least equal to the second diameter. Accordingly, each aperture may be temporarily entirely blocked by material of the filter that surrounds, is adjacent to, or defines, the apertures, such that dirt contacts the material of the filter rather than passes through the apertures.

[0018] The actuator may be configured to move the filter in a direction perpendicular to a direction in which apertures of the filter extend through the filter. This may provide improved filtration efficiency compared to other directions.

[0019] The actuator may be configured to move the filter in a direction parallel to a major face of the filter. This may provide improved filtration efficiency and space-efficiency compared to other directions.

[0020] The filter may be disposed at an oblique angle relative to the airflow path. The filter may be disposed at an oblique angle relative to a direction of a bulk of airflow along the airflow path immediately upstream of the filter. This may provide improved filtration efficiency compared to the filter being disposed normal to the airflow path and / or normal to the direction of the bulk of airflow. The oblique angle may be less than 45 degrees, less than 30 degrees, less than 20 degrees, or less than 10 degrees. A smaller angle may increase filtration efficiency.

[0021] Each aperture in the filter may be of the same size as each other aperture in the filter. This may provide more uniform filtration across the filter compared to a filter with apertures of different sizes.

[0022] The filter may be omni-symmetric across an area of the filter that is disposed in the airflow path. This may provide more uniform filtration across the filter compared to a non-omni- symmetric filter.

[0023] The filter may comprise, or may be, a perforated screen having a regular arrangement or array of perforations. Such a regular arrangement or array of perforations may provide uniform filtration across the perforated screen.

[0024] The filter may comprise, or may be, a mesh, such as an electroformed mesh. An electroformed mesh may exhibit relatively high consistency of aperture size across the mesh, compared to other filters of similar filtration efficiency. An electroformed mesh may be formed relatively quickly, simply and repeatably. An electroformed mesh may be formed from a metallic material suitable for holding its shape during movement by the actuator.

[0025] The filter may have a thickness in the region from 0.05 mm to 0.1 mm. This may provide a stiffer filter compared to smaller thicknesses, whilst reduce weight and space-consumption of the filter compared to greater thicknesses.

[0026] The vacuum may comprise a resiliently deformable seal around a periphery of the filter. This may inhibit dirt-laden airflow from by-passing the filter. This may also inhibit tribological wear between the filter and surrounding surfaces of the vacuum cleaner. The seal may extend around a complete periphery of the filter. The vacuum cleaner may comprise a dirt collection chamber upstream of the filter. This may help to direct dirt away from the filter, to help maintain filtration performance of the filter. Ducting from the airflow path to the dirt collection chamber may be disposed to an edge of the airflow path. This may help to inhibit dirt filtered from the airflow by the filter from being re-entrained in the airflow.

[0027] The vacuum cleaner may comprise a free space immediately upstream of the filter. The free space may allow dirt that has been prevented from passing through the filter to travel away from the filter, for example towards the dirt collection chamber.

[0028] The free space may have a volume that is at least 5 times greater than a volume occupied by the mesh. This may help to better prevent dirt from bouncing back into the filter compared to a smaller free space.

[0029] The vacuum cleaner may comprise a further filter disposed in the airflow path such that the airflow passes through the further filter. This may increase filtration efficiency of the vacuum cleaner.

[0030] Apertures of the further filter may have a different cross-sectional area to apertures of the filter, and may thus filter different sizes of dirt compared to the filter.

[0031] The further filter may be upstream of the filter, and the apertures of the further filter have a greater cross-sectional area than the apertures of the filter. The further filter may thus provide a primary airflow filtration stage, and the filter may provide a secondary airflow filtration stage. The filter and the further filter may thus be tailored to filter different dirt sizes and dirt types. For example, the further filter may be more robust than the filter, as the further filter would be required to withstand impacts from larger debris than the filter.

[0032] The vacuum cleaner may comprise a further actuator configured, in use of the suction generator, to move the further filter, to filter dirt from the airflow. As with the filter, this may provide one or more of the following advantages compared to other arrangements that could be used as the first filter, capable of filtering dirt from an airflow with comparable filtration efficiency: a more compact arrangement, lower pressure loss across the filter, and lower power consumption.

[0033] The further actuator may have any of the features of the actuator discussed above.

[0034] The further actuator may be configured to move the further filter by a different amount to an amount by which the actuator is configured to move the filter. The further actuator may be configured to move the further filter at a different speed to a speed by which the actuator is configured to move the filter. Accordingly, movement of each of the filter and the further filter may be tailored to improve filtration efficiency, for example based on an aperture size of the filter and further filter and / or a speed of airflow at the filter and further filter.

[0035] The vacuum cleaner may comprise a chamber having an airflow inlet, an airflow outlet and a wall configured to separate the airflow inlet and the airflow outlet. The further filter may be disposed in a portion of the wall and be arranged to allow an airflow through the wall from the airflow inlet to the airflow outlet to provide a filtered airflow through the wall. The filter may be disposed between the wall and the airflow outlet and be arranged to allow the filtered airflow to pass through the filter to the airflow outlet to provide a further filtered airflow to the airflow outlet. This may provide a particularly space-efficient and filtrationefficient arrangement.

[0036] The wall may have a generally U-shaped cross-sectional shape. The filter may have a generally U-shaped cross-sectional shape and substantially surround a downstream face of the wall. This may provide a particularly space-efficient and filtration-efficient arrangement.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure l is a diagram of a vacuum cleaner according to an example;

[0039] Figure 2 is a diagram of a main unit of the vacuum cleaner of Figure 1, according to an example; Figure 3 is a schematic diagram of a slice view of a dirt separation system of the main unit of Figure 2, according to an example;

[0040] Figure 4 is a schematic diagram of a cross-sectional view of the dirt separation system of Figure 3, according to an example;

[0041] Figure 5 is a schematic diagram of a cross-sectional view of part of a filter of the filtration system of Figure 3, according to an example, shown in a first position and a second position;

[0042] Figure 6 is a schematic diagram of an actuator of the dirt separation system of Figure 2, according to an example;

[0043] Figures 7a-c are schematic diagrams of airflow through the part of the filter of Figure 5, with the part of the filter either stationary, moving at a first speed, and moving at a second speed, respectively;

[0044] Figures 8a-b are schematic diagrams of airflow through the part of the filter of Figure 5, with the airflow at different flow rates;

[0045] Figure 9 is a schematic diagram of a slice view of a dirt separation system of the main unit of Figure 2, according to another example;

[0046] Figure 10 is a schematic diagram of a cross-sectional view of the dirt separation system of Figure 9, according to an example;

[0047] Figure 11 is a schematic diagram of a slice view of a dirt separation system of the main unit of Figure 2, according to another example; and

[0048] Figures 12 and 13 are schematic diagrams of different configurations of a part of the dirt separation system of Figure 11, according to examples. DETAILED DESCRIPTION

[0049] A vacuum cleaner 10 according to an example is illustrated in Figure 1. The vacuum cleaner 10 comprises a main unit 12, a wand 14, and a cleaner head 16. The vacuum cleaner 10 is a so-called “handheld” vacuum cleaner, with a user able and intended to support the main unit 12 in their hand in use, and is battery powered. The main unit 12 is selectively detachable from the wand 14.

[0050] A side view of the main unit 12 is illustrated in isolation in Figure 2. The main unit 12 comprises a main inlet 20, a housing portion 22, a handle portion 24, a battery assembly 26 and a main outlet 28. The main inlet 20 is positioned at a front end 30 of the main unit 12, and the main outlet 28 is positioned towards a rear end 32 of the main unit 12 in a side wall of the housing portion 22. The housing portion 22 has a longitudinal axis 34 extending from the front end 30 to the rear end 32.

[0051] A suction generator 36 (shown with dashed lines to denote that the suction generator 36 is contained within the housing portion 22) is disposed between the main inlet 20 and the main outlet 28. The suction generator 36 comprises, for example, an electric motor and impeller arrangement within a motor housing (not shown) mounted within the housing portion 22. The suction generator 36 is powered by the battery assembly 26.

[0052] A control system 38 (shown with dashed lines to denote that the control system 38 is contained within the housing portion 22) is disposed towards the rear end 32 of the main unit 12 and is in electrical communication with the suction generator 36. The control system 38 comprises a user interface (not shown) accessible by a user at the rear end 32.

[0053] A dirt separation system 100 is contained within the housing portion 22 and is shown schematically in cross-sectional view in a direction along the longitudinal axis 34 in Figure 3, and normal to the longitudinal axis 34 along the line A-A in Figure 4. Figure 4 is looking towards the front end 30 of the main unit 12. The dirt separation system 100 is disposed between the main inlet 20 and the suction generator 36, is generally cylindrical, and defines a dirt separation chamber 102. A front wall 103 of the dirt separation system 100 is towards the front end 30 of the main unit 12 and defines a chamber inlet 104. A rear wall 105 of the dirt separation system 100 is further from the front end 30 of the main unit 12 than the chamber inlet 104 and defines a chamber outlet 106 (shown in dashed lines in Figure 4 by way of explanation only). The chamber inlet 104 is in fluid communication with the main inlet 20. The chamber outlet 106 is in fluid communication with the main outlet 28.

[0054] A longitudinal core 109 separates the chamber inlet 104 from the chamber outlet 106. The longitudinal core 109 has a generally horseshoe-shaped cross-section about the longitudinal axis 34, as best shown in Figure 4. The horseshoe-shaped cross-section is generally constant between the front and rear walls 103, 105. The longitudinal core 109 has a generally hollow interior and divides the dirt separation chamber 102 into a pre-filter chamber portion 112 that generally surrounds the longitudinal core 110, and a filtered chamber portion 114 within the longitudinal core 109.

[0055] A U-shaped wall 110 of the longitudinal core 109 extends parallel to the longitudinal axis 34 and is disposed at an inner portion of the generally horseshoe-shaped cross-section. A primary filter in the form of a shroud 116 is recessed within the U-shaped wall 110 and extends along a rounded part of the U-shaped wall 110. The shroud 116 is metallic and comprises a plurality of apertures 118 extending therethrough. The apertures 118 are shown by way of example in Figure 3, and are not shown to scale. The apertures 118 are each generally cylindrical, have a diameter of around 200 pm and are uniformly distributed across the shroud 116. It will be appreciated that in other examples the shroud may be formed from a different material and / or may have apertures of a different size, such as in the region from 100 pm to 150 pm.

[0056] A partition wall 119 is disposed within the filtered chamber portion 114 and extends parallel to the longitudinal axis 34. The partition wall 119 separates the shroud 116 from the chamber outlet 106. A secondary filter 120 in the form of an electroformed mesh 120 is recessed within the partition wall 119. The electroformed mesh 120 is generally planar, and is separated from the shroud 116 by a free space 122.

[0057] The electroformed mesh 120 comprises a plurality of apertures 126 extending therethrough. The apertures 126 are arranged omni-symmetrically across the electroformed mesh 120. The apertures 126 are shown by way of example in Figure 3, and are not shown to scale. A crosssection of portion of the electroformed mesh 120 is shown in more detail in Figure 5.

[0058] The electroformed mesh 120 is formed from nickel sulphate and has a thickness T of around 0.08 mm. The electroformed mesh 120 has an upstream face 128, which faces towards the U-shaped wall 110, and a downstream face 130 opposite the upstream face 128. Each aperture 126 is generally circular, and is defined by an annular convex surface 132 with a constant radius between the upstream and downstream faces 128, 130. The annular convex surface 132 has a first diameter DI of around 0.3 mm at the upstream face 128, and a second diameter D2 of around 0.12 mm at the downstream face 130.

[0059] A primary dirt collection chamber 123 is disposed within the pre-filtered chamber portion at the front wall 103, and a secondary dirt collection chamber 124 is disposed within the free space 122 at the front wall 103.

[0060] A seal 138 extends around a complete periphery of the electroformed mesh 120, between the electroformed mesh 120 and the partition wall 119. The seal 138 is resiliently deformable.

[0061] An actuator 140 is recessed in the partition wall 119 and is clamped to the electroformed mesh 120. The actuator 140 is powered by the battery assembly 26. The actuator 140 is an ultrasonic oscillator, and is shown schematically in more detail in Figure 6. The actuator 140 comprises a transducer 142, in this example a Langevin transducer 142 and an amplifier 146. The transducer 142 comprises a piezoelectric device 144 connected to the amplifier 146. The amplifier 146 is clamped to the electroformed mesh 120 at an opposite end of the amplifier 146 to the piezoelectric device 144. In use of the actuator 140, the actuator 140 receives electrical power from the battery assembly 26, which is converted into mechanical vibrations by the transducer 142. The amplifier 146 amplifies mechanical vibrations generated by the transducer 142 and, being clamped to the electroformed mesh 120, transfers the vibrations to the electroformed mesh 120 to oscillate the electroformed mesh 120. The actuator 140 is arranged to oscillate the electroformed mesh 120 in a direction parallel to the upstream and downstream faces 128, 130 of the electroformed mesh 120, as denoted by the arrows M in Figures 3, 6 and 7. The direction is also parallel to the longitudinal axis 34 of the main unit 12.

[0062] The actuator 140 is operable in different modes of operation. In some modes of operation, each oscillation of the electroformed mesh 120 has an amplitude that is equal to or greater than the second diameter D2 of the apertures 126 of the electroformed mesh 120, in this example around 0.15 mm. During each oscillation, the electroformed mesh 120 is moved from a first position, as shown in Figure 5 in solid lines, to a second position, as shown in Figure 5 in dashed lines, and then back to the first position. This ensures that an opening of each of the apertures 126 at the downstream face 130 of the electroformed mesh 130 is entirely covered during each oscillation. In other modes of operation, each oscillation has an amplitude that is less than the second diameter D2 of the apertures 126 of the electroformed mesh 120, for example less than the second diameter D2 by an amount that is insufficient to allow dirt, such as dust particles, of a predetermined size to pass through. A frequency of oscillation is controlled by the control system 38, as described hereinafter.

[0063] The seal 138 is arranged to maintain a seal between the electroformed mesh 120 and the partition wall 119 during oscillation of the electroformed mesh 120, without inhibiting the oscillation.

[0064] In response to a user input, provided at the user interface, to power on the vacuum cleaner 10, the control system 38 is configured to supply power from the battery assembly 26 to the suction generator 36 and the actuator 140. In use, the suction generator 36 generates an airflow from the cleaner head 16, along the wand 14 to the main inlet 20, and through the main unit 12, via the dirt separation system 100, to the main outlet 28. Airflow drawn through the cleaner head 16 is generally dirt laden. The dirt separation system 100 is arranged to separate dirt from the dirt-laden airflow as the airflow passes through the dirt separation system 100, such that airflow that is expelled from the main outlet 28 is cleaner than airflow that enters the main inlet 26.

[0065] After entering the main unit 12 via the main inlet 20, the dirt-laden airflow is drawn into the pre-filtered chamber portion 112 of the dirt separation chamber 102 via the chamber inlet 104. A first portion of the dirt-laden airflow is drawn through the U-shaped wall 110 via the shroud 116. Larger dirt and debris that is entrained in the dirt-laden airflow is separated from the dirt-laden airflow as the dirt-laden airflow passes through the apertures 118 of the shroud 116. Accordingly, a pre-filtered airflow passes into the free space 122 between the shroud 116 and the electroformed mesh 120.

[0066] A second portion of the dirt-laden airflow circulates around the longitudinal core 109 and recirculates around the pre-filtered chamber portion 112, mixing with dirt-laden airflow entering the pre-filtered chamber portion 112 via the chamber inlet 104. Dirt that is separated from the dirt-laden airflow settles under gravity in the primary dirt collection chamber 123.

[0067] A first portion of the pre-filtered airflow is then drawn through the partition wall 119 via the electroformed mesh 120, while the electroformed mesh 120 is being oscillated by the actuator 140. Dirt, in particular particulates such as dust particles, entrained in the prefiltered airflow is separated from the pre-filtered airflow as the pre-filtered airflow passes through the apertures 126 of the electroformed mesh 120. The oscillation of the actuator 140 helps to inhibit pieces of dirt entrained in the pre-filtered airflow that have a smaller diameter than the second diameter D2 of the apertures 126 of the electroformed mesh 120 from passing through the partition wall 119. Accordingly, a filtered airflow, which is more filtered than the pre-filtered airflow, is drawn from the dirt separation chamber 102 to the chamber outlet 106.

[0068] A second portion of the pre-filtered airflow re-circulates around the free space 122, mixing with pre-filtered airflow entering the free space 122 via the shroud 116. Dirt that is separated from the pre-filtered airflow settles under gravity in the secondary dirt collection chamber The primary and secondary dirt collection chambers 123, 124 are generally outside of an airflow path of a bulk of the respective dirt-laden and pre-filtered airflows, which helps to inhibit re-entrainment of the pieces of dirt.

[0069] The front wall 103 is movable relative to a remainder of the dirt separation system 100 when the suction generator 36 is not in use. Moving the front wall 103, in this example by rotating the front wall 103 about a hinge (not shown) to a side of the dirt separation chamber 102, allows dirt in the primary and secondary dirt collection chambers 123, 124 to be expelled from the dirt separation chamber 102.

[0070] An example passage of the first portion of the dirt-laden airflow and first portion of the prefiltered airflow through the dirt separation system 100 is denoted by arrow Fl in Figure 3. An example passage of the second portion of the dirt-laden airflow and second portion of the pre-filtered airflow through the dirt separation system 100 is denoted by arrow F2 in Figure 3. It will be appreciated that the arrangement of the dirt separation system 100 will also encourage airflow to travel circumferentially through the dirt separation chamber 102. The dirt separation system 100 is arranged such that a bulk of the pre-filtered airflow generally travels towards the electroformed mesh 120 at oblique angles because the prefiltered airflow generally travels both radially and circumferentially around the free space 122. The recirculating of the second portion of the pre-filtered airflow causes the pre-filtered airflow to travel towards the electroformed mesh 120 along different airflow paths, a majority of which are non-perpendicular to the electroformed mesh 120 rather than directly from the shroud 116 to the electroformed mesh 120 in a radial direction. Filtration efficiency has been found to increase at smaller angles between the pre-filtered airflow and the electroformed mesh 120.

[0071] By oscillating the electroformed mesh 120, filtration efficiency of the dirt separation system 100 is increased compared to the electroformed mesh 120 remaining stationary, as shown schematically in Figures 7a-8c. This may negate a need for a further filtration stage downstream of the chamber outlet 106. Oscillating the electroformed mesh 120 has also been found to reduce pressure loss across the dirt separation system 100 compared to other filtration arrangements of comparable filtration efficiency. An oscillating electroformed mesh 120 may also be more space-efficient that other filtration arrangements, which may reduce an overall size of the main unit 12.

[0072] The shape of the apertures 126 of the electroformed mesh 120 helps to increase filtration efficiency compared to other shapes, because dirt that contacts the convex surface 132 is deflected back towards the free space 122 and away from the aperture 126.

[0073] In Figures 7a-c, dirt particles that have a diameter of at least 1 pm and less than the diameter of the apertures 126 are depicted by the dotted arrows. In each of Figures 7a-c, the suction generator 36 is in operation and generating airflow at a predetermined flow rate. Figure 7a shows the electroformed mesh 120 when stationary. A majority of the dirt particles ultimately pass through the electroformed mesh 120. Figure 7b shows the electroformed mesh 120 when oscillating between the first position (shown in solid lines) and the second position (shown in dashed lines) at a frequency of around 20 kHz and with an amplitude of D2. A first portion of the dirt particles are inhibited from passing through the electroformed mesh 120, and rebound off the electroformed mesh 120. Some of the dirt portion of dirt particles recirculate around the free space 122 whilst others settle in the dirt collection chambers under gravity. A second portion of the dirt particles passes through the electroformed mesh 120. Figure 7c shows the electroformed mesh 120 when oscillating between the first position (shown in solid lines) and the second position (shown in dashed lines) at a frequency of around 35 kHz and with an amplitude of D2. Substantially all of the dirt particles are inhibited from passing through the electroformed mesh 120 and rebound off the electroformed mesh 120. The dirt particles recirculate around the free space 122 and ultimately settle in the dirt collection chambers under gravity. In this example, oscillating the electroformed mesh 120 at frequencies above 35 kHz may offer a diminishing return in improved filtration efficiency compared to power consumption.

[0074] The control system 38 is operable to cause a change in speed of operation of the motor of the suction generator 36 to change a flow rate of airflow drawn into the cleaner head 16, for example based on a surface type over which the cleaner head 16 is moved or a mode of operation selected by the user. The control system 38 causes a change in a frequency of oscillation of the electroformed mesh 120 on the basis of the speed of the motor. A higher speed of the motor is associated with a higher frequency of oscillation of the electroformed mesh 120. At higher flow rates of airflow, dirt entrained in the pre-filtered airflow generally travels towards the electroformed mesh 120 at a higher speed than at lower flow rates of airflow, and may therefore have a higher chance of passing through the electroformed mesh 120 at lower frequencies because each aperture 126 is uncovered for longer at lower frequencies. In this example, a minimum frequency of oscillation is 20 kHz, and a maximum frequency of oscillation is 40 kHz.

[0075] In Figures 8a and 8b, dirt particles that have a diameter of at least 1 pm and less than the diameter of the apertures 126 are depicted by the dotted arrows. In each of Figures 8a and 8b, the suction generator 36 is in operation and the actuator 140 is oscillating the electroformed mesh 120 between the first position (shown in solid lines) and the second position (shown in dashed lines) at a frequency of around 30 kHz and with an amplitude of D2. In Figure 8a, the suction generator 36 is generating airflow at a higher flow rate than in Figure 8b. It can be seen that filtration efficiency is lower for the higher flow rate depicted in Figure 8a; more dirt particles pass through the electroformed mesh 120.

[0076] This is because an interception ratio of the electroformed mesh 120 is higher in the scenario depicted in Figure 8b than in Figure 8a. The interception ratio (IR) is defined as a time taken for a particle to pass through the electroformed mesh 120 (Particle time, Pt) divided by a time taken for the electroformed mesh 120 to move a distance equal to the second diameter D2 (Moving time, Mt):

[0077] IR = Pt / Mt

[0078] The Particle time Pt is calculated by dividing the thickness of the electroformed mesh 120 by a particle velocity of a particle in the pre-filtered airflow. For a particle at Stokes Number ~1 the flow velocity is equal to the particle velocity. Through a filter, such as the electroformed mesh 120, this is the normal velocity through the hole. As particle diameter increases, particle velocity reduces, therefore increasing the Particle time Pt. As air flow rate increases the particle velocity increases, therefore reducing the Particle time Pt. The Moving time Mt is calculated by dividing the second diameter D2 of the apertures 126 of the electroformed mesh 120 by a mesh velocity. The mesh velocity is directly a function of the frequency of oscillation of the electroformed mesh 120. A higher frequency equates to a higher mesh velocity. Therefore, higher frequencies result in a lower moving time Mt and thus a higher interception ratio IR.

[0079] A higher interception ratio IR is associated with higher interception of dirt particles, and thus higher filtration efficiency, than a lower interception ratio IR. In this example, the control system 38 is configured to maintain the interception ratio IR at 1 or higher regardless of a speed of operation of the suction motor 36. Accordingly, at higher speeds of operation of the suction motor 36, the control system 38 causes the actuator to operate at higher frequencies.

[0080] An alternative example dirt separation system 200 is shown schematically in cross-sectional view in a direction along the longitudinal axis 34 in Figure 9, and normal to the longitudinal axis 34 along the line A-A in Figure 10. Figure 10 is looking towards the front end 30 of the main unit 12. The dirt separation system 200 may replace the dirt separation system 100 in the main unit 12 of the vacuum cleaner 1. The dirt separation system 200 has a number of common features to the dirt separation system 100 described above, and common features have the same reference number but increased by 100.

[0081] The dirt separation system 200 shown in Figures 9 and 10 comprises a dirt separation chamber 202, a chamber inlet 204 and a chamber outlet 206. The longitudinal core 109 of the dirt separation system 100 described above is omitted. Instead, the chamber inlet 204 is separated from the chamber outlet 206 by a first partition wall 250 and a second partition wall 252. The first and second partition walls 250, 252 each extend between the front wall 203 and the rear wall 205 parallel to the longitudinal axis 34 and are generally planar. The first partition wall 250 divides the dirt separation chamber 202 into a pre-filtered chamber portion 212 and a filtered chamber portion 214. The second partition wall 252 separates the first partition wall 250 from the chamber outlet 206. The first and second partition walls 250, 252 are separated from one another by a free space 222. A shroud 216 is recessed in the first partition wall 250, and has the same properties as the shroud 116 described with reference to Figures 3 and 4, except that the shroud 216 of this example is planar rather than curved. An electroformed mesh 220 is recessed in the second partition wall 252, and has the same properties as the electroformed mesh 120 described with reference to Figures 3 and 4. An actuator 240 is clamped to the electroformed mesh 120 and is arranged to oscillate the electroformed mesh 220 as described above with reference to Figures 3-6. The dirt separation system 200 may be simpler to manufacture than the dirt separation system 100.

[0082] Primary and secondary dirt collection chambers 223, 224 are disposed adjacent to the front wall 203.

[0083] The dirt separation system 200 is operable in the same manner as the dirt separation system 100 described above, and will not be described again, for brevity. Example airflow routes through the dirt separation chamber 102 are depicted by the arrows Fl, F2 of Figure 9.

[0084] Another alternative example dirt separation system 300 is shown schematically in cross- sectional view in a direction along the longitudinal axis 34 in Figure 11. The dirt separation system 300 is similar to the dirt separation system 200 described with reference to Figures 9 and 10 and common features have the same reference number, but increased by 100.

[0085] The dirt separation system 300 comprises a dirt separation chamber 302 having a chamber inlet 304 and a chamber outlet 306. A separating wall 360 extends normal to the longitudinal axis 34 and divides the dirt separation chamber 302 into a forward chamber 362 and a rear chamber 364. An aperture 366 extends through the separating wall 360.

[0086] A first partition wall 350 extends between the front wall 303 and the separating wall 360 parallel to the longitudinal axis 34 and is generally planar. The first partition wall 350 divides the forward chamber 362 into a pre-filtered chamber portion 312 and a filtered chamber portion 314. The first partition wall 350 separates the chamber inlet 304 from the aperture 366. A shroud 316 is recessed in the first partition wall 350, and has the same properties as the shroud 116 described with reference to Figures 3 and 4, except that the shroud 316 of this example is planar rather than curved.

[0087] A second partition wall 352 within the rear chamber 364 extends normal to the longitudinal axis 34 and parallel to the separating wall 360. The second partition wall 352 is positioned between the separating wall 360 and the rear wall 305, and is separated from the separating wall 360 by a free space 322. The second partition wall 352 separates the aperture 366 from the chamber outlet 306. An electroformed mesh 320 is recessed in the second partition wall 352, and has the same properties as the electroformed mesh 120 described with reference to Figures 3 and 4. An actuator 340 is clamped to the electroformed mesh 120 and is arranged to oscillate the electroformed mesh 320 as described above with reference to Figures 3-6, except that the oscillations are in a direction normal to the longitudinal axis 34.

[0088] Primary and secondary dirt collection chambers 323, 324 are disposed adjacent to the front wall 203. The dirt separation system 300 also comprises a duct (not shown) that defines a channel from the free space 322 to the primary dirt collection chamber 323, through which dirt separated from airflow may pass in use.

[0089] The dirt separation system 300 is operable in the same manner as the dirt separation system 100 described above, and will not be described again, for brevity. Example airflow routes through the dirt separation chamber 302 are depicted by the arrows Fl, F2 of Figure 11. The dirt separation system 300 may provide improved filtration efficiency compared to the dirt separation systems 100, 200 described above.

[0090] Alternative example configurations of the rear chamber 364 are shown in Figures 12 and 13. In Figure 12, the second partition wall 352 and the electroformed mesh 320 are disposed at an angle A to the separating wall 360. In this example, the angle A is around 30 degrees. Placing the electroformed mesh 320 at such an angle causes a bulk of airflow, generated in operation of the suction generator 36, to travel towards the electroformed mesh 320 at a smaller angle than in the configuration shown in Figure 11, which may increase filtration efficiency of the dirt separation system 300 compared to the configuration shown in Figure 11. It will be appreciated that other angles may be employed in other examples. In Figure 13, a third partition wall 354 within the rear chamber 364 extends normal to the longitudinal axis 34 and parallel to the separating wall 360 and the second partition wall 352. The third partition wall 352 is positioned between the second partition wall 352 and the rear wall 305, and is separated from the second partition wall 352 by a second free space 356. A second electroformed mesh 370 is recessed in the third partition wall 354, and has the same properties as the electroformed mesh 120 described with reference to Figures 3 and 4, except that the first and second diameters DI, D2 of the second electroformed mesh 370 are smaller than the respective first and second diameters DI, D2 of the electroformed mesh 320. A second actuator 372 is clamped to the second electroformed mesh 370 and is arranged to oscillate the second electroformed mesh 370 as described above with reference to Figures 3- 6, except that the oscillations have a smaller amplitude to an amplitude of oscillation of the electroformed mesh 320. This arrangement provides plural (in this example two) stages of filtration using an oscillating filter, in this example electroformed meshes. In other examples, more than two such stages may be provided. In addition, or alternatively, given two more such stages, the oscillations of each respective filter may be in different directions, in order to further improve filtration performance.

[0091] It will be appreciated that other arrangements fall within the scope of the claims, and that the vacuum cleaner 10 described with reference to Figures 1 to 13 is shows by way of example only. Variations are envisaged, as described, by way of example only, below.

[0092] Any suitable type of actuator may be employed to move the electroformed mesh to filter dirt from the airflow.

[0093] The actuator may be configured to move the electroformed mesh non-linearly, for example may be configured to rotate the electroformed mesh about a pivot, or to move the electroformed mesh in a sinusoidal fashion.

[0094] Any suitable type of filter may be employed in place of the electroformed mesh and / or the shroud.

Claims

CLAIMS1. A vacuum cleaner comprising a suction generator configured to generate airflow along an airflow path of the vacuum cleaner, a filter disposed in the airflow path such that the airflow passes through the filter; and an actuator configured, in use of the suction generator, to move the filter, to filter dirt from the airflow.

2. The vacuum cleaner according to claim 1, comprising a control system configured to cause the actuator to vary a speed of movement of the filter on the basis of a rate of the airflow generated by the suction generator.

3. The vacuum cleaner according to claim 1 or claim 2, wherein the actuator is configured to oscillate the filter.

4. The vacuum cleaner according to claim 3, wherein the actuator is configured to oscillate the filter at an ultrasonic frequency.

5. The vacuum cleaner according to claim 4, wherein the actuator is configured to oscillate the filter at a frequency of at least 30kHz.

6. The vacuum cleaner according to any one of claims 3 to 5, wherein the actuator is configured to oscillate the filter with an amplitude that is at least equal to a minimum diameter of apertures of the filter.

7. The vacuum cleaner according to any one of the preceding claims, wherein apertures of the filter have a first diameter at an upstream face of the filter and a second diameter, less than the first diameter, at a downstream face of the filter.

8. The vacuum cleaner according to claim 7, wherein the apertures each comprise a convex surface between the upstream face and the downstream face of the filter.

9. The vacuum cleaner according to claim 8, wherein the convex surface has a constant radius between the upstream face and the downstream face of the filter.

10. The vacuum cleaner according to any one of claims 7 to 9, wherein the second diameter is in the region from 0.1 mm to 0.3 mm.

11. The vacuum cleaner according to any one of claims 7 to 10, wherein the actuator is configured to move the filter by a distance that is at least equal to the second diameter.

12. The vacuum cleaner according to any one of the preceding claims, wherein the actuator is configured to move the filter in a direction perpendicular to a direction in which apertures of the filter extend through the filter.

13. The vacuum cleaner according to any one of the preceding claims, wherein the actuator is configured to move the filter in a direction parallel to a major face of the filter.

14. The vacuum cleaner according to any one of the preceding claims, wherein the filter is omni-symmetric across an area of the filter that is disposed in the airflow path.

15. The vacuum cleaner according to any one of the preceding claims, wherein the filter is an electroformed mesh.

16. The vacuum cleaner according to any one of the preceding claims, wherein the filter has a thickness in the region from 0.05 mm to 0.1 mm.

17. The vacuum cleaner according to any one of the preceding claims, comprising a resiliently deformable seal around a periphery of the filter.

18. The vacuum cleaner according to any one of the preceding claims, wherein the filter is disposed at an oblique angle relative to the airflow path.

19. The vacuum cleaner according to claim 18, wherein the oblique angle is less than 45 degrees.

20. The vacuum cleaner according to any one of the preceding claims, comprising a further filter disposed in the airflow path such that the airflow passes through the further filter, wherein apertures of the further filter have a different cross-sectional area to apertures of the filter.

21. The vacuum cleaner according to claim 20, wherein the further filter is upstream of the filter and the apertures of the further filter have a greater cross-sectional area than the apertures of the filter.

22. The vacuum cleaner according to claim 20 or claim 21, comprising a further actuator configured, in use of the suction generator, to move the further filter, to filter dirt from the airflow.

23. The vacuum cleaner according to claim 21 , or according to claim 22 when dependent on claim 21, comprising a chamber having an airflow inlet, an airflow outlet and a wall configured to separate the airflow inlet and the airflow outlet, wherein: the further filter is disposed in a portion of the wall and is arranged to allow an airflow through the wall from the airflow inlet to the airflow outlet to provide a filtered airflow through the wall, and the filter is disposed between the wall and the airflow outlet and is arranged to allow the filtered airflow to pass through the filter to the airflow outlet to provide a further filtered airflow to the airflow outlet.

24. The vacuum cleaner of claim 23, wherein the wall has a generally U-shaped cross- sectional shape.

25. The vacuum cleaner of claim 24, wherein the filter has a generally U-shaped cross- sectional shape and substantially surrounds a downstream face of the wall.

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