Abstract:
The present invention relates to a surface treating appliance for separating particles from a fluid flow. Particularly, but not exclusively, the invention relates to a domestic vacuum cleaner for separating particles, such as dirt and dust particles, from a dust laden airflow. The surface treating appliance includes a first cyclonic cleaning stage, a second cyclonic cleaning stage arranged downstream from the first cyclonic cleaning stage, and an electrostatic filter connected to a controlled high voltage power supply, the electrostatic filter being arranged separate from, but in fluid communication with, the first cyclonic cleaning stage and the second cyclonic cleaning stage.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of United Kingdom Application No. 0912932.1, filed Jul. 24, 2009, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a surface treating appliance for separating particles from a fluid flow. Particularly, but not exclusively, the invention relates to a domestic vacuum cleaner for removing dust particles, from a dust laden airstream. 
       BACKGROUND OF THE INVENTION 
       [0003]    It is known to separate particles, such as dirt and dust particles from a fluid flow using mechanical filters, such as mesh and foam filters, cyclonic separating apparatus and electrostatic separators. 
         [0004]    Known cyclonic separating apparatus include those used in vacuum cleaners. Such cyclonic separating apparatus are known to comprise a low efficiency cyclone for separating relatively large particles and a high efficiency cyclone located downstream of the low efficiency cyclone for separating the fine particles which remain entrained within the airstream (see, for example, EP 0 042 723B). 
         [0005]    Known electrostatic filters include frictional electrostatic filters and electret medium filters. Examples of such filters are described in EP0815788, U.S. Pat. No. 7,179,314 and U.S. Pat. No. 6,482,252. 
         [0006]    Such electrostatic filters are relatively cheap to produce but suffer from the disadvantage that their charge dissipates over time resulting in a reduction of their electrostatic properties. This in turn reduces the amount of dust the electrostatic filter can collect which may shorten the life of both the electrostatic filter itself and any further downstream filters. 
         [0007]    Known electrostatic filters also include filters where dust particles in an airstream are charged in some way and then passed over or around a charged collector electrode for collection. An example of such an electrostatic filter is described in JP2007296305 where dust particles in an airstream are charged as they pass a “corona discharge” wire and are then trapped on a conductive filter medium located downstream of the corona discharge wire. A disadvantage with this arrangement is that they are relatively inefficient, are made from relatively expensive materials and the collector electrodes require constant maintenance in order to keep them free of collected dust. Once the collector electrodes are coated in a layer of dust they are much less efficient. 
         [0008]    Another example of an electrostatic filter is shown in GB2418163 where the dust particles in an airstream are charged as they pass a corona discharge wire located inside a cyclone. The charged dust particles are then trapped on the walls of the cyclone which are coated in a conductive paint. While this arrangement is compact it suffers from the disadvantage that dust collects on the inside of the cyclones. Not only does this require constant and difficult maintenance removing dust from the walls of the cyclone, but also any dust trapped inside the cyclone will interfere with the cyclonic airflow decreasing the separation efficiency of the cyclone itself. 
         [0009]    It is desirable for the efficiency of an electrostatic filter to be as high as possible (i.e. to separate as high a proportion as possible of very fine dust particles from the airstream), while maintaining a reasonable working life. 
         [0010]    In certain applications, for example in domestic vacuum cleaner applications, it is also desirable for the appliance to be made as compact as possible without compromising on performance and/or filter life. An apparatus which was more efficient while also being compact enough to allow packaging into an appliance such as a vacuum cleaner would therefore also be desirable. 
       SUMMARY OF THE INVENTION 
       [0011]    Accordingly the present invention provides a surface treating appliance comprising a first cyclonic cleaning stage, a second cyclonic cleaning stage arranged downstream from the first cyclonic cleaning stage, and an electrostatic filter connected to a high voltage power supply, the electrostatic filter being arranged separate from, but in fluid communication with, the first cyclonic cleaning stage and the second cyclonic cleaning stage. 
         [0012]    Advantageously this arrangement has been found to help increase both the dust separation efficiency of the surface cleaning appliance and the life of the electrostatic filter and/or any other downstream filters. 
         [0013]    As used herein the term “high voltage power supply” shall be taken to mean that the high voltage supply is generated from solid state electronics rather than by frictional generation. 
         [0014]    In a preferred embodiment the present invention provides a surface treating appliance comprising a first cyclonic cleaning stage, a second cyclonic cleaning stage arranged downstream from the first cyclonic cleaning stage, and an electrostatic filter connected to a controlled high voltage power supply, the electrostatic filter being arranged separate from, but in fluid communication with, the first cyclonic cleaning stage and the second cyclonic cleaning stage. 
         [0015]    As used herein the term “controlled” shall be taken to mean that the voltage is maintained for a range of impedances and the current is limited below that impedance range. This may be achieved by closed loop current and voltage control of the power supply. 
         [0016]    The term “separate from” as used herein shall be taken to mean that the electrostatic filter is not located physically within the first cyclonic cleaning stage or the second cyclonic cleaning stage i.e. the electrostatic filter is not subjected to the cyclonic airflow set up inside the cyclonic cleaning stages during use. 
         [0017]    In a preferred embodiment the first cyclonic cleaning stage comprises a single cylindrical cyclone and a dust collecting bin. The dust collecting bin may be formed from a lower section of the cylindrical cyclone itself or it may be in the form of a separate dust collecting bin removably attached to the base of the cylindrical cyclone. The second cyclonic cleaning stage may comprise a plurality of secondary cyclones arranged in parallel and a dust collecting bin, which is preferably arranged below the secondary cyclones. 
         [0018]    The electrostatic filter may be located upstream of the first cyclonic cleaning stage, between the first and the second cyclonic cleaning stages or downstream from the second cyclonic cleaning stage. These arrangements have been found to be advantageous because dust particles collected by the electrostatic filter do not get trapped inside the cyclones of the first and second cyclonic cleaning stages. When dust particles get trapped inside a cyclone they can interfere with the cyclonic airflow resulting in decreased separation efficiency. Having the electrostatic filter separate from the cyclonic cleaning stages is therefore advantageous. 
         [0019]    In a particularly preferred embodiment the electrostatic filter may be located downstream of the second cyclonic cleaning stage. This arrangement is particularly advantageous because electrostatic filters have been found to be more efficient when challenged with small dust particles, for example dust particles smaller than 1 micron. Placing the electrostatic filter downstream of the second cyclonic cleaning stage therefore ensures that the electrostatic filter is only challenged with the very small particles which have managed to pass through the first and second cyclonic cleaning stages. In addition as dust particles pass through the first and second cyclonic cleaning stages during use, they become charged due to friction with the walls of the cyclonic cleaning stages. This pre charging of the dust particles also helps to improve the dust collecting efficiency of the electrostatic filter. 
         [0020]    In a particular embodiment the surface treating appliance may further comprise one or more further cyclonic cleaning stages arranged downstream of the second cyclonic cleaning stage and upstream of the electrostatic filter. 
         [0021]    In a particular embodiment the secondary cyclones of the second cyclonic cleaning stage are arranged above the first cyclonic cleaning stage, preferably in a ring formation about a central axis of the first cyclonic cleaning stage. The dust collecting bin of the second cyclonic cleaning stage may be annular in shape. 
         [0022]    In a preferred embodiment the first cyclonic cleaning stage may be arranged to at least partially, and preferably totally surround the dust collection bin of the second cyclonic cleaning stage. In such an embodiment the first cyclonic cleaning stage may be also be annular in shape. This arrangement may be advantageous as it provides for a compact structure. 
         [0023]    In a preferred embodiment at least a portion of the second cyclonic cleaning stage may be arranged to at least partially surround the electrostatic filter. In a preferred embodiment the electrostatic filter may be surrounded by the dust collection bin and/or the secondary cyclones of the second cyclonic cleaning stage. In a most preferred embodiment the dust collection bin of the second cyclonic cleaning stage surrounds a lower portion of the electrostatic filter and the secondary cyclones surround an upper portion of the electrostatic filter. 
         [0024]    The first and second cyclonic cleaning stages, the electrostatic filter and the high voltage generator preferably form at least part of a separating apparatus which is removably mounted on a main body of the surface treating appliance. In a particular embodiment the electrostatic filter may be arranged longitudinally through the separating apparatus, for example such that the electrostatic filter is centred about a longitudinal axis of the separating apparatus. In an alternative embodiment the high voltage generator may be located on the main body of the surface treating appliance. 
         [0025]    The electrostatic filter preferably comprises a filter medium located between a first and a second electrode each at a different voltage during use such that a potential difference is formed across the filter medium. The first and second electrodes preferably form at least a portion of an air pathway in which the filter medium is located, such than in use air flows through the filter medium. 
         [0026]    Preferably the first and second electrodes are substantially non-porous. Preferably the filter medium has a length and the first and second electrodes are non-porous along the length of the filter medium. In a most preferred embodiment the first and second electrodes are non-porous along their entire length. 
         [0027]    As used herein the term “non-porous” shall be taken to mean that the first and second electrodes have continuous solid surfaces without perforations, apertures or gaps. In a preferred embodiment the first and second electrodes are non-porous such that during use an airflow travels along the length of the electrodes through the filter medium. Ideally the airflow does not pass through the first or second electrodes. 
         [0028]    Such an arrangement where the air does not have to flow through the electrodes during use may be advantageous because it may reduce the pressure drop across the electrostatic filter. In addition because the electrodes are non-porous they have a larger surface area than they would if the electrodes were porous. This may improve the overall performance of the electrostatic filter. 
         [0029]    In a preferred embodiment the filter medium may be an electrically resistive filter medium. As used herein the term “electrically resistive filter medium” shall be taken to mean that the filter medium has a resistivity of from 1×10 7  to 1×10 13  ohm-meters at 22° C. In a most preferred embodiment the filter medium may have a resistivity of from 2×10 9  to 2×10 11  ohm-meters at 22° C. The electrical resistivity of the filter medium may vary along the length of the filter medium. In a particular embodiment the electrical resistivity may decrease in a downstream direction. 
         [0030]    This electrostatic filter uses the potential difference formed across the filter medium to collect dust in the filter medium itself rather than on collector electrodes. This arrangement is advantageous over previous electrostatic filters because there are no collector electrodes to clean. This may reduce the need for maintenance and increase the life of the filter due to the dust retention capacity of the filter medium. 
         [0031]    The potential difference occurs because the electrically resistive filter medium provides a load and therefore only a small current flows through it. However the electric field will disturb the distribution of any positive and negative charges, in the fibers of the electrically resistive filter medium, causing them to align with their respective electrode. This process causes the dust to bond to or settle on the fibers of the filter medium because dust particles in an airstream passing through the filter will be attracted to respective positive and negative ends of the filter medium. This may help to cause the dust particles to be trapped in the filter medium itself without requiring the dust particles to be captured on a charged electrode. 
         [0032]    The electrostatic filter may also further comprise at least one corona discharge means, the filter medium being arranged downstream of the corona discharge means. Adding a corona discharge means advantageously may increase the efficiency of the electrostatic filter. This is because the corona discharge means helps to charge any dust particles in the airstream before they pass through the filter medium thus helping to increase dust particle attraction to the filter medium. 
         [0033]    In a preferred embodiment the corona discharge means may comprise at least one corona discharge electrode of high curvature and at least one electrode of low curvature. This arrangement may be advantageous as it may generate a large source of ions for charging any dust particles in the airstream. These charged dust particles are then more likely to be filtered out by the filter medium which has the potential difference across it during use. 
         [0034]    The electrode of low curvature may be a flat or a curved surface. The corona discharge electrode may be in any suitable form as long as it is of a higher curvature than the electrode of low curvature. In other words the corona discharge electrode is preferably of a shape which causes the electric filed at its surface to be greater than the electric field at the surface of the electrode of low curvature. Examples of suitable arrangements would be where the corona discharge electrode is one or more wires, points, needles or serrations and the electrode of low curvature is a tube which surrounds them. Alternatively the electrode of low curvature may be a flat plate. 
         [0035]    In a particular embodiment the corona discharge electrode may be formed from a portion of the first or second electrode. In a preferred embodiment the corona discharge electrode is in the form of one or more points formed from or on a lower or upper edge of the first or second electrode. Ideally the lower or upper edge of the second electrode is serrated to form the corona discharge electrode. 
         [0036]    The electrode of low curvature may also be formed from a portion of the first or second electrode. In a particular embodiment the upper or lower edge of the second electrode is serrated to form the corona discharge electrode and a corresponding upper or lower portion of the first electrode forms the electrode of low curvature. The position of the electrode of low curvature and/or the corona discharge electrode depends on the orientation of the electrostatic filter and the direction in which air enters it during use. For example, if the electrostatic filter is arranged such that air enters from an upper end then the electrode of low curvature and the corona discharge electrode are preferably located on an upper portion of the first and second electrode. Alternatively, if the electrostatic filter is arranged such that air enters from a lower end then the electrode of low curvature and the corona discharge electrode are preferably located on a lower portion of the first and second electrode 
         [0037]    This arrangement is advantageous as there is no requirement for separate components forming the corona discharge electrode or the electrode of low curvature. 
         [0038]    In a preferred embodiment the electrode of low curvature projects both upstream and downstream from a lower or upper surface of the corona discharge electrode. This may help to maximize the volume over which the ionizing field is generated thus maximizing the opportunity for charging dust particles as they pass through the ionizing field. 
         [0039]    In an alternative embodiment the corona discharge electrode may be remote from the first and second electrodes. In such an embodiment the corona discharge electrode may be in the form of one or more wires, needles, points or serrations. In such an embodiment the electrode of low curvature may still be formed from a portion of the first or second electrode. In a particular embodiment a portion of the second electrode may form the electrode of low curvature. In a preferred embodiment the electrode of low curvature and the corona discharge electrode are arranged to maximize the volume over which the ionizing field is generated to maximize the opportunity for charging dust particles as they pass through the ionizing field. 
         [0040]    In another alternative embodiment the corona discharge means i.e. both the corona discharge electrode and the electrode of low curvature may be located remotely from the first and second electrodes. 
         [0041]    The first and second electrodes may be of any suitable shape, for example they may be planar and the filter medium may be sandwiched between the layers. Such planar layers may be of any suitable shape for example square, rectangular, circular or triangular. In a particular embodiment the separating apparatus may comprise a plurality of first and second electrodes arranged in parallel. In such an embodiment filter medium is preferably located between adjacent electrodes and the adjacent electrodes are at a different voltage during use such that a potential difference is formed across the filter medium. The first and second electrodes may be arranged inside a tubular passageway which forms an outer surface of the electrostatic filter. In such an embodiment the electrodes are preferably arranged longitudinally down the tubular passageway. Such an arrangement provides a plurality of parallel air passages running longitudinally through the electrostatic filter. Preferably the tubular passageway is non-electrically conductive, for example it may be formed form a plastics material. 
         [0042]    In such an embodiment the first electrodes and the second electrodes are preferably at different voltages during use. All of the first electrodes are preferably at the same voltage and all of the second electrodes are preferably at the same voltage. The first electrodes may have either a higher or a lower voltage than the second electrodes. In a particularly preferred embodiment the first electrodes may be at 0 Volts or +/−2 kV and the second electrodes may be at from +/−2, or 4, or 5, or 6, or 7, or 8, or 9, or 10 to 11, or 12, or 13, or 14, or 15 kV. In a most preferred embodiment the second electrodes may be at from −2 or −4 to −10 kV. The electrodes may be regularly spaced apart inside the tubular passageway, for example the first and second electrodes may be arranged from 1 mm, or 3 mm, or 5 mm, or 7 mm to 9 mm, or 10 mm, or 12 mm, or 15 mm, or 20 mm apart. 
         [0043]    In an alternative embodiment the first and/or the second electrodes may be tubular, for example they may be cylindrical with the filter medium located between the electrode tubes. In a preferred embodiment the first and second electrodes may be located concentrically with the filter medium located concentrically between them. Preferably the second electrode is located concentrically inside the first electrode and therefore has a smaller diameter than the first electrode. 
         [0044]    The electrostatic filter may also further comprise a third electrode. In such an embodiment the second electrode may be located between the first and the third electrodes. The third electrode may also be of any suitable shape but is preferably cylindrical and in such an embodiment the second electrode may preferably be concentrically located between the first electrode and the third electrode. In such an embodiment a further filter medium may be located between the second electrode and the third electrode. Preferably the further filter medium comprises an electrically resistive filter medium as described above. Preferably the third electrode is located concentrically inside the second electrode and therefore has a smaller diameter than the second electrode. Again this arrangement is advantageous as it allows for a very compact structure. 
         [0045]    Such an arrangement provides a plurality of annular air passages running longitudinally through the electrostatic filter. 
         [0046]    Again the second electrode and the third electrode are preferably each at a different voltage during use such that a potential difference is formed across the further filter medium. 
         [0047]    In such an embodiment the first electrode and the third electrode may be at the same voltage during use. The second electrode may be either positively or negatively charged. Ideally the second electrode is negatively charged. The first electrode and the third electrode may have either a higher or a lower voltage than the second electrode. In a preferred embodiment the first electrode and the third electrode may have a higher voltage than the second electrode. In a particularly preferred embodiment the first electrode and the third electrode may be at 0 Volts or +/−2 kV and the second electrode may be at from +/−2, or 4, or 5, or 6, or 7, or 8, or 9, or 10 to 11, or 12, or 13, or 14, or 15 kV. In a most preferred embodiment the second electrode may be at from −2 or −4 to −10 kV. The electrodes may be regularly spaced apart for example the first, second and third electrodes may be arranged from 1 mm, or 3 mm, or 5 mm, or 7 mm to 9 mm, or 10 mm, or 12 mm, or 15 mm, or 20 mm, or 40 mm apart. 
         [0048]    The electrodes described above in relation to all of the embodiments may be formed from any suitable conductive material. Preferably, the first and/or second and/or third electrodes are formed from a conductive metal sheet, foil or coating of from 2 microns, or 10 microns, or 50 microns or 0.1 mm, or 0.25 mm, or 0.5 mm, or 1 mm, or 1.5 mm, or 2 mm to 2.5 mm, or 3 mm, or 4 mm in thickness. Additionally or alternatively the filter medium may be coated with one or more of the electrodes. For example one or more surfaces of the filter medium may be coated with a conductive material. 
         [0049]    In a preferred embodiment the surface treating appliance may further comprise an air passage a first end of which is in fluid communication with the second cyclonic cleaning stage and a second end of which is in fluid communication with the electrostatic filter wherein at least a portion of the electrostatic filter is arranged to at least partially surround the air passage. In such an embodiment the electrostatic filter may be annular in shape. 
         [0050]    The electrostatic filter may be in direct fluid communication with an exit port of the separating apparatus or it may be in fluid communication with the exit port via an exit passage located downstream of the electrostatic filter. The exit port may be located on an upper or lower end of the separating apparatus. 
         [0051]    In a particular embodiment at least a portion of the exit passage may be formed longitudinally through the separating apparatus. The air passage may surround the electrostatic filter and may be annular in shape. In such an embodiment at least a portion of the exit passage may be surrounded by the second cyclonic cleaning stage. 
         [0052]    In an alternative embodiment at least a portion of the exit passage may be formed longitudinally through the separating apparatus such that at least a portion of it is surrounded by the air passage and/or the electrostatic filter and/or the second cyclonic cleaning stage. 
         [0053]    These arrangements are particularly advantageous as they allow for a very compact structure. These concentric arrangements also help to increase the safety of the appliance since both the first cyclonic cleaning stage and the dust collecting bin of the second cyclonic cleaning stage are located between the electrostatic filter which is connected to a high voltage source and a user. 
         [0054]    In a particular embodiment the electrostatic filter may extend from a top edge of the second cyclonic cleaning stage to at or near a base of the separating apparatus. Preferably the electrostatic filter may extend along 40, or 45, or 50, or 55, or 60, or 65, or 70, or 75, to 80, or 85, or 90, or 95, or 100 percent of the distance between the top edge of the second cyclonic cleaning stage and the base of the separating apparatus. Alternatively or additionally the electrostatic filter may extend from 50, or 55, or 60, or 65, or 70, to 75, or 80, or 85, or 90, or 95, or 100 percent of the length of the separating apparatus. 
         [0055]    The filter medium may be of any suitable material for example glass, polyester, polypropylene, polyurethane or any other suitable plastics material. In a preferred embodiment the filter medium is an open cell reticulated plastics foam, for example a polyurethane foam. Reticulated foams are formed when the cell windows within the foam are removed to create a completely open cell network. This type of filter medium is particularly advantageous as the foam may hold its structure in an airflow. The polyurethane foam may be derived from either polyester or polyether. 
         [0056]    The pore size/diameter, PPI or type of filter medium may vary along the length of the filter medium. For example the pore size may decrease or increase in a downstream direction. As used herein the terms “pore size” and “pore diameter” are interchangeable. A method for measuring the average pore size/diameter and calculating the pores per inch is given in the specific description. 
         [0057]    Such a change in pore size may be a gradual change which occurs in a single filter medium or a plurality of sections of filter medium may be brought together to form a filter medium which has a varying pore size across it&#39;s length. The PPI may also decrease or increase in a downstream direction, or alternatively it may vary in another random or non-random way. 
         [0058]    The filter medium or a section of it may have 3, or 5, or 6, or, 8 or, 10, or 15, or 20, or 25, or 30 to 35, or 40, or 45, or 50, or 55, or 60 pores per inch (PPI) with an average pore diameter of from 0.4, or 0.5, or 1, or 1.5, or 2, or 2.5, or 3, or 3.5 to 4, or 4.5, or 5, or 5.5, or 6, or 6.5, or 7, or 7.5, or 8, 8.5 mm (or 400 microns to 8500 microns). In a preferred embodiment the filter medium or a section of it may have from 8 to 30 PPI with an average pore diameter of from 1.5 mm to 5 mm. In another preferred embodiment the filter medium or a section of it may have from 3 to 30 PPI with an average pore diameter of from 1.5 mm to 8 mm. Most preferably the PPI may be from 3 to 10 PPI. In a preferred embodiment an upstream portion/section of the filter medium may have a PPI of 3 PPI and a downstream portion/section may have a PPI of 6 PPI. In a preferred embodiment an upstream portion/section of the filter medium may have an average pore diameter of 7200 microns (7.2 mm) and a downstream portion/section may have an average pore diameter of 4500 microns (4.5 mm). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0059]    The invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0060]      FIG. 1  is a canister vacuum cleaner incorporating a separating apparatus according to the present invention; 
           [0061]      FIG. 2  is an upright vacuum cleaner incorporating a separating apparatus according to the present invention; 
           [0062]      FIG. 3   a  is a longitudinal section through the separating apparatus shown in  FIGS. 1 and 2 ; 
           [0063]      FIG. 3   b  is a horizontal section through the separating apparatus shown in  FIGS. 1 and 2 ; 
           [0064]      FIG. 4  is a schematic section through the electrostatic filter shown in  FIG. 3 ; 
           [0065]      FIG. 5  is a section through an alternative embodiment of a separating apparatus; 
           [0066]      FIG. 6   a  is a longitudinal section through an alternative embodiment of a separating apparatus; 
           [0067]      FIG. 6   b  is a horizontal section through the embodiment shown in  FIG. 6   a ; and 
           [0068]      FIG. 7  is a section through an alternative embodiment of a separating apparatus. 
       
    
    
       [0069]    Like reference numerals refer to like parts throughout the specification. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0070]    With reference to  FIGS. 1 and 2  a vacuum cleaner is shown and indicated generally by the reference numeral  1 . 
         [0071]    In  FIG. 1  the vacuum cleaner  1  comprises a main body  2 , wheels  4  mounted on the main body  2  for maneuvering the vacuum cleaner  1  across a surface to be cleaned, and a separating apparatus  6  removably mounted on the main body  2 . A hose  8  communicates with the separating apparatus  6  and a motor and fan unit (not shown) is housed within the main body  2  for drawing dust laden air into the separating apparatus  6  via the hose  8 . Commonly, a floor-engaging cleaner head (not shown) is coupled to the distal end of the hose  8  via a wand to facilitate manipulation of a dirty air inlet  10  over the surface to be cleaned. 
         [0072]    In use, dust laden air drawn into the separating apparatus  6  via the hose  8  has the dust particles separated from it in the separating apparatus  6 . The dirt and dust is collected within the separating apparatus  6  while the cleaned air is channeled past the motor for cooling purposes before being ejected from the vacuum cleaner  1 . 
         [0073]    The upright vacuum cleaner  1  shown in  FIG. 2  has a main body  2  in which a motor and fan unit (not shown) is mounted and on which wheels  4  are mounted to allow the vacuum cleaner  1  to be maneuvered across a surface to be cleaned. A cleaner head  14  is pivotably mounted on the lower end of the main body  2  and a dirty air inlet  10  is provided on the underside of the cleaner head  14  facing the surface to be cleaned. A separating apparatus  6  is removably provided on the main body  2  and ducting  16  provides communication between the dirty air inlet  10  and the separating apparatus  6 . A wand and handle assembly  18  is releasably mounted on the main body  2  behind the separating apparatus  6 . 
         [0074]    In use, the motor and fan unit draws dust laden air into the vacuum cleaner  1  via either the dirty air inlet  10  or the wand  18 . The dust laden air is carried to the separating apparatus  6  via the ducting  16  and the entrained dust particles are separated from the air and retained in the separating apparatus  6 . The cleaned air is passed across the motor for cooling purposes and then ejected from the vacuum cleaner  1 . 
         [0075]    The separating apparatus  6  forming part of each of the vacuum cleaners  1  is shown in more detail in  FIGS. 3   a ,  3   b ,  5 ,  6   a ,  6   b  and  7 . The specific overall shape of the separating apparatus  6  can be varied according to the type of vacuum cleaner  1  in which the separating apparatus  6  is to be used. For example, the overall length of the separating apparatus  6  can be increased or decreased with respect to the diameter of the separating apparatus  6 . 
         [0076]    The separating apparatus  6  comprises a first cyclonic cleaning stage  20 , a second cyclonic cleaning stage  22  and an electrostatic filter  70  located longitudinally through the separating apparatus  6 . An embodiment of the electrostatic filter can be seen in more detail in  FIG. 4 . 
         [0077]    The first cyclonic cleaning stage  20  can be seen to be the annular chamber  38  located between the outer wall  24  which is substantially cylindrical in shape and the second cylindrical wall  36  which is located radially inwardly from the outer wall  24  and spaced from it. The lower end of the first cyclonic cleaning stage  20  is closed by a base  26  which is pivotably attached to the outer wall  24  by means of a pivot  28  and held in a closed position by a catch  30 . In the closed position, the base  26  is sealed against the lower ends of the walls  24 ,  36 . Releasing the catch  30  allows the base  26  to pivot away from the outer wall  24  and the second cylindrical wall  36  for emptying the first cyclonic cleaning stage  20  and the second cyclonic cleaning stage  22   
         [0078]    In this embodiment the top portion of the annular chamber  38  forms a cylindrical cyclone  32  of the first cyclonic cleaning stage  22  and the lower portion forms a dust collecting bin  34 . The second cyclonic cleaning stage  22  comprises  12  secondary cyclones  50  which are arranged in parallel and a second dust collecting bin  64 . 
         [0079]    A dust laden air inlet  40  is provided in the outer wall  24  of the first stage cyclone  20 . The dust laden air inlet  40  is arranged tangentially to the outer wall  24  so as to ensure that incoming dust laden air is forced to follow a helical path around the annular chamber  38 . A fluid outlet from the first cyclonic cleaning stage  20  is provided in the form of a shroud  42 . The shroud  42  comprises a cylindrical wall  44  in which a large number of perforations  46  are formed. The only fluid outlet from the first cyclonic cleaning stage  20  is formed by the perforations  46  in the shroud  42 . 
         [0080]    A passageway  48  is formed downstream of the shroud  42 . The passageway  48  communicates with the second cyclonic cleaning stage  22 . The passageway  48  may be in the form of an annular chamber which leads to inlets  52  of the secondary cyclones  50  or may be in the form of a plurality of distinct air passageways each of which leads to a separate secondary cyclone  50 . 
         [0081]    A third cylindrical wall  54  extends downwardly from a vortex finder plate  56  which forms a top surface of each of the secondary cyclones  50 , towards the base  26 . The third cylindrical wall  54  is located radially inwardly of the second cylindrical wall  36  and is spaced from it so as to form a second annular chamber  58  between them. 
         [0082]    When the base  26  is in the closed position, the third cylindrical wall  54  may reach down to and be sealed against the base  26  as shown in  FIGS. 5 and 6   a . Alternatively as shown in  FIGS. 3   a  and  7  the third cylindrical wall  54  may stop short of the base  26  and may be sealed by an electrostatic filter base plate  60 . 
         [0083]    The secondary cyclones  50  are arranged in a circle substantially or totally above the first cyclonic cleaning stage  20 . A portion of the secondary cyclones  50  may project into the top of the first cyclonic cleaning stage  20 . The secondary cyclones  50  are arranged in a ring which is centred on the axis of the first cyclonic cleaning stage  20 . Each secondary cyclone  50  has an axis which is inclined downwardly and towards the axis of the first cyclonic cleaning stage  20 . 
         [0084]    Each secondary cyclone  50  is frustoconical in shape and comprises a cone opening  62  which opens into the top of the second annular chamber  58 . In use dust separated by the secondary cyclones  50  will exit through the cone openings  62  and will be collected in the second annular chamber  58 . The second annular chamber  58  thus forms the dust collecting bin  64  of the second cyclonic cleaning stage  22 . A vortex finder  66  is provided at the upper end of each secondary cyclone  50 . The vortex finders  66  may be an integral part of the vortex finder plate  56  or they may pass through the vortex finder plate  56 . In all of the embodiments shown the vortex finders fluidly connect with the electrostatic filter  70 . 
         [0085]    In the embodiments shown in  FIGS. 3   a ,  5  and  7  the vortex finders  66  lead into vortex fingers  68  which in  FIGS. 3   a  and  5  communicate with an air passage  74  which leads to the lower end of the electrostatic filter  70  and in  FIG. 7  communicates directly with the top end of the electrostatic filter  70 . It is however possible that the vortex finders  66  could communicate with a plenum or manifold  98  which in turn communicates with an air passage or directly with the electrostatic filter  70 . In  FIG. 6   a  it can be seen that the vortex finders  66  communicate with a plenum  98  which communicates directly with the top end of the electrostatic filter  70 . 
         [0086]    In  FIGS. 3   a  and  3   b  it can be seen that the air passage  74  is arranged longitudinally down the centre of the separating apparatus  6 . The electrostatic filter  70  is arranged around the air passage  74  such that the air passage  74  is partially or totally surrounded by the electrostatic filter  70 . An upper end of the electrostatic filter  70  is fluidly connected to the exit port  96  of the separating apparatus  6  via the exhaust manifold  94 . The exhaust manifold  94  at least partially surrounds the vortex fingers  68  to form an exhaust manifold containing two fluidly distinct air passages, the first being the exhaust manifold  94  itself and the second being the vortex fingers  68 . 
         [0087]    In  FIG. 5  it can be seen that the air passage  74  is annular in shape and is at least partially surrounded by the electrostatic filter  70 . The air passage  74  is arranged to provide a fluid passageway, or individual fluid passageways to the lower end of the electrostatic filter  70 . An exhaust passage  100  provides a fluid passageway between the upper end of the electrostatic filter  70  and the exit port  96  which is located on a lower end of the separating apparatus  6 . The exhaust passage  100  is arranged longitudinally down the centre of the separating apparatus  6 . The air passage  74  is arranged around the exhaust passage  100  such that the exhaust passage  100  is partially or totally surrounded by the air passage  74 . 
         [0088]    In  FIG. 6   a  it can be seen that the plenum  98  fluidly connects the vortex finders  66  and the electrostatic filter  70 . A lower end of the electrostatic filter  70  is fluidly connected to the exit port  96  of the separating apparatus  6  which is located at a lower end of the separating apparatus  6 . In this embodiment there is no air passage or exhaust passage. 
         [0089]    In  FIG. 7  it can seen that the vortex fingers  68  lead directly to the electrostatic filter  70 . An annular exhaust passage  100  is arranged around the electrostatic filter  70  such that the electrostatic filter  70  is arranged longitudinally down the centre of the separating apparatus  6  and is partially or totally surrounded by the annular exhaust passage  100 . An upper end of the annular exhaust passage  100  is fluidly connected to the exit port  96  of the separating apparatus  6  via the exhaust manifold  94  located at an upper end of the separating apparatus  6 . Again the exhaust manifold  94  at least partially surrounds the vortex fingers  68  to form an exhaust manifold  94  containing two fluidly distinct air passages, the first being the exhaust manifold  94  itself and the second being the vortex fingers  68 . 
         [0090]    In the embodiments described above the electrostatic filter  70  is arranged longitudinally down the separating apparatus  6  such that the secondary cyclones  50  and at least a portion of the dust collecting bin  64  surround the electrostatic filter  70 . It can be seen that the secondary cyclones  50  surround a top portion of the electrostatic filter  70  and the dust collecting bin  64  surrounds a lower portion of the electrostatic filter  70 . It can also be seen that the electrostatic filter  70  extends from the vortex finder plate  56  to near the base  26 . 
         [0091]    In the embodiment shown in  FIGS. 3   a ,  3   b ,  4  and  5  the electrostatic filter  70  comprises concentrically arranged cylindrical first, second and third electrodes  76 ,  78 ,  80 . A filter medium  82  is located between both the first and second electrodes  76 ,  78  and the second and third electrodes  78 ,  80 . 
         [0092]    The electrostatic filter  70  also comprises a corona discharge means in the form of a corona discharge electrode  84  and two electrodes of low curvature  86 . The electrostatic filter  70  would however function without the corona discharge means. 
         [0093]    The first electrode of low curvature  86  is an extension of the first electrode  76  below a lower surface  88  of the filter medium  82  and the second electrode of low curvature  86  is an extension of the third electrode  80  below the lower surface  88  of the filter medium  82 . 
         [0094]    The corona discharge electrode  84  is in the form of a serrated lower edge  90  of the second electrode  78  which extends below the lower surface  88  of the filter medium  82 . The electrodes of low curvature  86  can be seen to project both upstream and downstream of the serrated lower edge  90  of the corona discharge electrode  84 . 
         [0095]    The first and third electrodes  76 ,  80  are at 0 Volts and the second electrode  78  is at from −4 to −10 kV. The electrodes  76 ,  78 ,  80  are connected to a high voltage power supply. The high voltage power supply is generated by a PCB  93  which is preferably located in an exhaust manifold  94 . 
         [0096]    The electrodes  76 ,  78 ,  80  may be formed from any suitable conductive material, for example aluminium. 
         [0097]    In the embodiment shown in  FIGS. 6   a  and  6   b  the electrostatic filter  70  comprises a plurality of first and second flat plate electrodes  76 ,  78  which are arranged in parallel. Filter media  82  is located between each adjacent first and second electrodes  76 ,  78  to form a layered electrostatic filter  70 . The electrostatic filter  70  may be any shape in cross section but is preferably cylindrical. The first and second electrodes  76 ,  78  are arranged inside the third cylindrical wall  54  which provides a tubular passageway which forms an outer surface of the electrostatic filter  70 . The first and second electrodes  76 ,  78  are arranged longitudinally to provide a plurality of parallel air passages which run longitudinally through the electrostatic filter  70 . 
         [0098]    The electrostatic filter  70  also comprises a corona discharge means in the form of corona discharge electrodes  84  and electrodes of low curvature  86 . The electrostatic filter  70  would however function without the corona discharge means. Each electrode of low curvature  86  is an extension of a first electrode  76  above the upper surface  102  of the filter media  82 . The corona discharge electrodes  84  are in the form of serrated upper edges  91  of the second electrodes  78  which extend above the upper surfaces  102  of the filter medium  82 . The electrodes of low curvature  86  can be seen to project both upstream and downstream of the serrated upper edges  91  of the corona discharge electrodes  84 . 
         [0099]    The first electrodes  76  are at 0 Volts and the second electrodes  78  are at from −4 to −10 kV. The electrodes  76 ,  78  are connected to a high voltage power supply. 
         [0100]    In  FIG. 7  it can be seen that the electrostatic filter  70  described above has been replaced with an alternative type of electrostatic filter  70 . In this embodiment the electrostatic filter  70  may be a frictional electrostatic filter or an electret medium electrostatic filter  70 . 
         [0101]    This electrostatic filter  70  could of course be replaced by an electrostatic filter  70  as described in relation to  FIGS. 3   a ,  3   b ,  4 , 5,  6   a  and  6   b . Equally the electrostatic filter  70  described in  FIGS. 3   a ,  3   b ,  4 , 5,  6   a  and  6   b  could be replaced with a different type of electrostatic filter  70 , for example a frictional electrostatic filter or an electret medium filter. 
         [0102]    During use of the embodiments described above dust laden air enters the separating apparatus  6  via the dust laden air inlet  40  and, because of the tangential arrangement of the inlet  40 , the dust laden air follows a helical path around the outer wall  24 . Larger dirt and dust particles are deposited by cyclonic action in the annular chamber  38  and collected in the dust collecting bin  34 . The partially-cleaned dust laden air exits the annular chamber  38  via the perforations  46  in the shroud  42  and enters the passageway  48 . The partially-cleaned dust laden air then passes into tangential inlets  52  of the secondary cyclones  50 . Cyclonic separation is set up inside the secondary cyclones  50  so that separation of some of the dust particles which are still entrained within the airflow occurs. The dust particles which are separated from the airflow in the secondary cyclones  50  are deposited in the second annular chamber  58  which forms at least part of the dust collecting bin  64  of the second cyclonic cleaning stage  22 . The further cleaned dust laden air then exits the secondary cyclones  50  via the vortex finders  66 . The further cleaned dust laden air then passes into the electrostatic filter  70 . 
         [0103]    In the embodiment shown in  FIGS. 3   a  and  3   b , the further cleaned dust laden air passes out of the vortex finders  66 , along the vortex fingers  68  and down the air passage  74  towards the lower end of the electrostatic filter  70 . The air then travels past the corona discharge means formed from the corona discharge electrode  84  and the electrodes of low curvature  86  such that any dust particles remaining in the further cleaned dust laden air become charged. The further cleaned dust laden air containing the charged dust then travels upwardly through the filter medium  82 . A potential difference is generated across the filter medium  82  causing the charged dust particles to be attracted to respective positive and negative ends of the filter medium  82 , thus trapping them within the filter medium  82 . 
         [0104]    The cleaned air then leaves the top of the electrostatic filter  70  via apertures  92  in the vortex finder plate  56  and enters the exhaust manifold  94 . The cleaned air then exhausts the separating apparatus  6  via the exit port  96 . 
         [0105]    In the embodiment shown in  FIG. 5 , the further cleaned dust laden air passes out of the vortex finders  66 , along the vortex fingers  68  and down the air passage  74  towards the bottom end of the electrostatic filter  70 . The air then travels past the corona discharge means formed from the corona discharge electrode  84  and the electrodes of low curvature  86  such that any dust particles remaining in the further cleaned dust laden air become charged. The further cleaned dust laden air containing the charged dust then travels upwardly through the filter medium  82 . A potential difference is generated across the filter medium  82  causing the charged dust particles to be attracted to respective positive and negative ends of the filter medium  82 , thus trapping them within the filter medium  82 . 
         [0106]    The cleaned air then leaves the top of the electrostatic filter  70  and enters the exhaust passage  100  which directs air downwardly through the centre of the separating apparatus  6  to the exit port  96  which is located on the lower end of the separating apparatus  6 . 
         [0107]    In the embodiment shown in  FIGS. 6   a  and  6   b , the further cleaned dust laden air passes out of the vortex finders  66  and enters the plenum  98 . The air passes through the plenum  98  and enters the top of the electrostatic filter  70 . The air then travels past the corona discharge means formed from the corona discharge electrode  84  and the electrodes of low curvature  86  such that any dust particles remaining in the further cleaned dust laden air become charged. The further cleaned dust laden air containing the charged dust then travels downwardly through the filter medium  82 . A potential difference is generated across the filter medium  82  causing the charged dust particles to be attracted to respective positive and negative ends of the filter medium  82 , thus trapping them within the filter medium  82 . 
         [0108]    The cleaned air then leaves the lower end of the electrostatic filter  70  and exhausts the separating apparatus  6  via the exit port  96  located on the lower end of the separating apparatus  6 . 
         [0109]    In the embodiment shown in  FIG. 7 , the further cleaned dust laden air passes out of the vortex finders  66 , along the vortex fingers  68  and into the electrostatic filter  70 . The further cleaned dust laden air travels downwardly through electrostatic filter  70 . 
         [0110]    The cleaned air then leaves the lower end of the electrostatic filter  70  and travels up the exhaust passage  100  to exit the separating apparatus  6  via the exit port  96  located on the upper end of the separating apparatus  6 . 
         [0111]    It will be appreciated from the description that the separating apparatus  6  includes two distinct stages of cyclonic separation and a distinct stage of electrostatic filtration. The first cyclonic cleaning stage  20  comprises a single cylindrical cyclone  32 . The relatively large diameter of the outer wall  24  of which means that comparatively large particles of dirt and debris will be separated from the air because the centrifugal forces applied to the dirt and debris are relatively small. Some fine dust will be separated as well. A large proportion of the larger debris will reliably be deposited in the dust collecting bin  34 . 
         [0112]    There are  12  secondary cyclones  50 , each of which has a smaller diameter than the cylindrical cyclone  32  and so is capable of separating finer dirt and dust particles than the cylindrical cyclone  32 . They also have the added advantage of being challenged with air which has already been cleaned by the cylindrical cyclone  32  and so the quantity and average size of entrained dust particles is smaller than would otherwise have been the case. The separation efficiency of the secondary cyclones  50  is considerably higher than that of the cylindrical cyclone  32  however some small particles will still pass through the secondary cyclones  50  to the electrostatic filter  70 . 
         [0113]    In the embodiments described above the filter medium  82  may be formed from any suitable material for example an open cell reticulated polyurethane foam derived from a polyester. 
         [0114]    The filter medium  82  has a PPI in the range of 3 to 12 PPI, preferably 8 to 10 PPI and most preferably 3 to 6 PPI. The pore size and PPI of the filter medium  82  shown in  FIG. 3   a  varies along its length because it is formed from two sections each having a different pore size and PPI. In the embodiment shown in  FIG. 3   a  the upstream portion has a 3 or 8 PPI and the downstream portion has 6 or 10 PPI. 
         [0115]    The pore size/diameter may be measured using the following method.
   1) Microscopic pictures of the foam structure should be taken through horizontal sections insuring pore consistency.   2) Five individual pores should be selected.   3) The diameter of each pore should be measured to an accuracy of no less than 100 micron and an average should be taken over the 5 pores.   4) This average pore size (pore diameter) is measured in microns or mm.   
 
         [0120]    The pores per inch is calculated by dividing 25400 (1 inch=25400 microns) by the pore diameter in microns. 
         [0121]    In the embodiments shown it is preferable that all of the electrodes are non-porous. However, as long as the first and second electrodes are non-porous it is possible that any other electrodes present could be porous if desired.