Abstract:
The present invention provides a vacuum cleaner having an inlet ( 26 ) for dirty air, an outlet ( 24 ) for clean air, and a filter ( 44 ) located in fluid communication between the inlet and the outlet. A motor drives a fan for moving air into the inlet and through the filter to the outlet. A filter cleaning mechanism for removing dirt from the filter is provided and is operatively associated with an on/off switch for the fan motor or alternatively a separate user-operated switch, whereby operation of the switch results in operation of the filler cleaning mechanism.

Description:
FIELD OF THE INVENTION 
     The present invention relates to vacuum cleaners, and in particular to mechanisms for cleaning the filters of vacuum cleaners and vacuum cleaners comprising such mechanisms. Vacuum cleaners generally come in two main varieties, namely bagged and bagless vacuum cleaners, according to the technique they use to separate out dust and dirt from air which is drawn into the vacuum cleaner during operation. As the name implies, bagged vacuum cleaners comprise a porous bag. This is positioned with its mouth across an airflow pathway between a dirty air inlet of the vacuum cleaner and a clean air outlet therefrom, in order to capture dust and dirt entrained with the air as the air passes through the bag. Bagless vacuum cleaners on the other hand do not include a bag to intercept dust and dirt in this way, but instead use a technique for separating out dust and dirt from the incoming air which relies on inertial separation of the dust and dirt from the air, typically by applying a centrifugal force to the dust and dirt, such as in a cyclone. However, both the bagged and bagless varieties of vacuum cleaner very usually also include a filter, which operates in addition to these two main separation techniques, in order to increase the level of dust and dirt separation provided by the main separation technique alone. One or more such filters may be placed upstream or downstream of the main separation process, or in both upstream and downstream locations. The present invention is therefore equally applicable to both bagged and bagless varieties of vacuum cleaner. It is also equally applicable to larger floor-running vacuum cleaners of the cylinder and upright types, and to smaller hand-holdable vacuum cleaners, such as the present applicant&#39;s range of Dustbuster® hand-holdable vacuum cleaners. 
     BACKGROUND OF THE INVENTION 
     Regardless of the type of vacuum cleaner involved, however, any vacuum cleaner which includes a filter presents the problem that the filter will become progressively blocked with dust and dirt as the vacuum cleaner is used. This has the disadvantage of lowering the rate of air movement (i.e. volume of air moved per unit time) through the vacuum cleaner by obstructing the airflow during operation of the vacuum cleaner, thereby also reducing the overall cleaning efficiency of the vacuum cleaner. Accordingly, in order to ensure the continuing efficient operation of the vacuum cleaner, it is necessary for a user to clean the filter from time to time. In its most basic form, this means that the user manually removes the filter from the vacuum cleaner, washes or otherwise cleans it, and then replaces it back in the vacuum cleaner. However, this has the disadvantage that it requires the user to handle the dirty filter in order to clean it. A filter cleaning mechanism which, avoids this problem is therefore preferred to such manual cleaning. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, several vacuum cleaner filter cleaning techniques which avoid the need for a user to handle a dirty filter are already known in the prior art. A first example is provided by the Electrolux® range of bagless cylinder vacuum cleaners with model numbers Z8220, Z8230 and Z8240, each of which permits a filter cleaning technique working as follows. As shown schematically in  FIG. 1A , these vacuum cleaners comprise a motor  10  and a fan  12  driven by the motor  10  to move air through the vacuum cleaner from a dirty air inlet  26  via a main dirt separation device  14  (which in this case is a cyclone chamber) to a clean air outlet  24 . However, these vacuum cleaners also comprise a pair of identical, mutually interchangeable filters  16 ,  18 , which are mounted on a single, symmetrical assembly  20  within the body  22  of the vacuum cleaner. When this assembly  20  is in place, a first one  16  of the two filters is positioned across the flow of air through the vacuum cleaner between the main dirt separation device  14  and the clean air outlet  24 . The second  18  of the two filters is also in fluid communication with the main dirt separation device  14 , but not directly with the clean air outlet  24 , so that air exiting the main dirt separation device  14  passes through the first filter  16  to the clean air outlet  24  in preference to passing through the second filter  18 , as represented in  FIG. 1A  by the arrows. However, when the first filter  16  becomes blocked due to an excessive accumulation of dust and dirt thereon, a sensor also included in the vacuum cleaner detects a drop in the rate of air movement through the vacuum cleaner from the dirty air inlet  26  to the clean air outlet  24 . This in turn illuminates a light mounted on the exterior of the vacuum cleaner body, which alerts the user to the fact that the first filter  16  needs cleaning. Without needing to touch the dirt-bearing parts of the dirty filter  16 , the user can then swap the dirty filter  16  with the second, clean filter  18  by opening the body  22  of the vacuum cleaner, removing the symmetrical filter assembly  20 , turning it through 180 degrees, and reinserting it into the vacuum cleaner with the second filter  18  now in the previous location of the first, dirty filter  16  and vice versa, as shown schematically in  FIG. 1B . Thus the second filter  18 , which at this stage is clean, will be introduced into the airflow pathway of dirty air through the vacuum cleaner to the clean air outlet  24  during normal operation thereof. Opening the body  22  of the vacuum cleaner to carry out this operation also has the effect of closing off the usual inlet  26  for dirty air to the main dirt separation device  14 . Next, the user rotates the dirty first filter  16  by 360 degrees about its own axis. This activates a microswitch which operates the motor  10  to drive the air-moving fan  12 . However, since at this stage, the body  22  of the vacuum cleaner remains open and the usual inlet  26  for dirty air to the vacuum cleaner&#39;s main dirt separation chamber  14  remains closed, air is drawn from the atmosphere backwards through the dirty filter  16  by the fan  12  into the main dirt separation chamber  14 , as represented by the arrows shown in  FIG. 1B , where the dirt from the dirty filter  16  is deposited. Once the dirty filter  16  has been rotated by a full 360 degrees, the microswitch is deactivated and the motor  10  shuts down. The filter cleaning operation being complete, the user may then close the body  22  of the vacuum cleaner once more, thereby re-opening the usual inlet  26  for dirty air to the vacuum cleaner&#39;s main dirt separation chamber  14 , and the vacuum cleaner is once again ready for use. 
     Although this filter cleaning technique avoids the need for a user to handle the dirty filter in order to clean it, it has the disadvantage that the user must nonetheless open the vacuum cleaner and carry out a relatively complex sequence of operations, including removal and reinsertion of the filter assembly  20  into the body of the vacuum cleaner. The use of a pair of identical, interchangeable filters in this way instead of a single filter also increases the cost and complexity of manufacture. Moreover, the user can ignore the light mounted on the exterior of the vacuum cleaner which alerts the user to the fact that a filter cleaning operation should be carried out, which would result in insufficient filter cleaning, or carry out a filter cleaning operation when not required. Thus the frequency of filter cleaning is left entirely within the control of the user. 
     A second example of a known filter cleaning technique is disclosed in EP 1 523 916 A, also in the name of Black &amp; Decker Inc. This document describes a hand-holdable vacuum cleaner having a dirt cup housing a two-stage filter, comprising a first, course filter for filtering courser dirt and contained within the course filter, a second, fine filter for filtering finer dust. The second, fine filter is provided with a plurality of tabs arranged in a ring, which interengage with a corresponding plurality of drive tabs mounted in a ring on a filter cleaning wheel. The filter cleaning wheel comprises a gripping portion which is partially exposed through an exterior housing of the vacuum cleaner. Thus when a user takes hold of the gripping portion and uses it to rotate the filter cleaning wheel, the drive tabs mounted thereon engage with the corresponding tabs of the fine filter and cause it to rotate within the course filter. The fine filter is pleated and the course filter is provided with a plurality of ribs formed on the inner surface thereof. Thus as the fine filter rotates within the course filter, the ribs formed on the inner surface of the course filter successively contact the pleats of the fine filter. This agitates the fine filter, causing any accumulated dust adhering to the fine filter to be shaken off, through the holes of the course filter and into the dirt cup, which may then be emptied. This filter cleaning technique has the advantage that unlike the Electrolux filter cleaning technique described above, the user does not need to carry out a whole sequence of operations in order to clean the fine filter or remove the filter from the vacuum cleaner in order to do so. However, since the filter cleaning wheel is manually operated, when to clean the filter is again left entirely at the user&#39;s discretion. There is therefore a risk that the user will either neglect to clean the fine filter so that dust continues to accumulate thereon, thereby diminishing the vacuum cleaner&#39;s efficiency, or will rotate the filter cleaning wheel more often than is necessary in order to clean the filter, thereby diminishing the lifetime of the fine filter by increasing the amount of wear on the pleats of the fine filter caused by the ribs formed on the inner surface of the course filter. 
     Finally, a third example of a known filter cleaning technique is described in EP 1 231 856 A in the name of TechTronic Industries Co., Ltd. This document discloses a vacuum cleaner having a dirt collection chamber which houses a filter element provided with a top plate having a protrusion formed thereon. A leaf spring positioned above the protrusion is maintained in a bent condition away from the protrusion by being compressed between two shoulders of a rectangular recess formed in the top wall of the dirt collection chamber. The underside of the leaf spring faces but does not contact the protrusion on the top plate of the filter element, which is exposed to the leaf spring through a central opening formed in the rectangular recess of the top wall. The upper surface of the leaf spring instead contacts an actuation member in the form of a hinged lever having an upwardly directed finger-piece and a downwardly directed nose. Thus when a user presses on the finger-piece, the nose of the actuation member pushes the leaf spring through an over-centre condition and the central region of the leaf spring moves sharply downwards into a convex configuration in which it impacts on the protrusion carried by the top plate of the filter element. This results in the filter element being shaken briefly to dislodge accumulated dust adhering to the filter element therefrom, and the dislodged dust falls into the dirt collection chamber, which can then be emptied. This filter cleaning technique also has the advantage that it does a user does not need to open the vacuum cleaner in order to clean the filter element, and that the user need only press a button to carry out the filter cleaning operation. However, since the leaf spring only comes into contact with the top plate of the filter element once when the finger-piece of the actuation member is depressed, the filter element is also only shaken once, and there remains a risk that much dust will remain adhered to the filter. Moreover, once again, since when to clean the filter element is left entirely at the user&#39;s discretion, there also remains a risk that the user will forget to clean the filter element as often as is required, so that dust continues to accumulate thereon, thereby diminishing the vacuum cleaner&#39;s efficiency. 
     As may be seen, therefore, all of the prior art filter cleaning techniques described above have at least the disadvantage that they all leave the timing of when to perform a filter cleaning operation entirely within the control of the user of the vacuum cleaner. This presents the risk that the user will either forget to clean the filter often enough, resulting in reduced efficiency of the vacuum cleaner, or will clean the filter more often than is required, resulting in increased wear on the filter elements. Accordingly, it is an object of the present invention to provide a vacuum cleaner filter cleaning technique which avoids this problem in order to result in effective cleaning of the filter at regular intervals over the operational lifetime of the filter, but which also avoids the need for a user to handle a dirty filter in order to clean it and which obviates the need for a user to open the vacuum cleaner in order to clean the filter or to carry out a complex sequence of operations in order to do so. 
     In one aspect, the present invention aims to achieve this object by providing a vacuum cleaner comprising an inlet for dirty air; an outlet for clean air; a filter located in fluid communication between the inlet and the outlet; a motor; a fan driven by the motor for moving air from the inlet through the filter to the outlet; an electrical power supply for supplying power to the motor; an on/off switch for placing the motor in powered electrical connection with the fan and having a first state wherein the motor drives the fan and a second state wherein the motor does not drive the fan; and a filter cleaning mechanism for removing dirt from the filter; wherein activation of the filter cleaning mechanism is operatively associated with the on/off switch, whereby operation of the on/off switch results in operation of the filter cleaning mechanism. 
     Thus the filter is only cleaned when the vacuum cleaner&#39;s on/off switch is operated. This means that the frequency of filter cleaning is related directly to the amount of usage of the vacuum cleaner, so that the filter is cleaned neither too often nor too infrequently, but just often enough. 
     The vacuum cleaner may further comprise a timing device, wherein operation of the on/off switch from the first state to the second state activates the filter cleaning mechanism and the timing device, and the timing device subsequently deactivates the filter cleaning mechanism. Thus each time the vacuum cleaner is switched off after having been used, the filter cleaning mechanism is activated for a short time until deactivated again by the timing device, thereby cleaning the filter ready for use next time. 
     Alternatively, the vacuum cleaner may further comprise a timing device, wherein operation of the on/off switch from the second state to the first state activates the filter cleaning mechanism and the timing device, whereupon the timing device delays the motor from driving the fan, and the timing device subsequently deactivates the filter cleaning mechanism and ends the delay of the motor driving the fan. Thus each time the vacuum cleaner is switched on for use, the filter cleaning mechanism is activated for a short time until deactivated again by the timing device before the motor starts to drive the fan, thereby cleaning the filter before it is used. 
     In a third possible embodiment, the on/off switch has a third state wherein the motor does not drive the fan, operation of the on/off switch from the first state to the second state activates the filter cleaning mechanism and operation of the on/off switch from the second state to the third state deactivates the filter cleaning mechanism. Thus each time the vacuum cleaner is switched off after having been used, the filter cleaning mechanism is activated for a short time until deactivated again by the user operating the switch into its third state, thereby cleaning the filter ready for use next time. 
     Finally, in a fourth possible alternative embodiment of the first aspect of the invention, the on/off switch has a third state wherein said motor does not drive said fan, operation of said on/off switch from the second state to the third state activates said filter cleaning mechanism and operation of said on/off switch from the third state to the first state deactivates said filter cleaning mechanism. Thus each time the vacuum cleaner is switched on for use, the filter cleaning mechanism is activated for a short time until deactivated again by the user operating the switch into its first state wherein the motor starts to drive the fan, thereby cleaning the filter before it is used. 
     In a second aspect, the present invention also provides a vacuum cleaner comprising an inlet for dirty air; an outlet for clean air; a filter located in fluid communication between the inlet and the outlet; a motor; a fan driven by the motor for moving air from the inlet through the filter to the outlet; an electrical power supply for supplying power to the motor; and a filter cleaning mechanism for removing dirt from the filter; wherein the filter cleaning mechanism is electrically powered; and the vacuum cleaner further comprises a user-operated switch for activating the filter cleaning mechanism, whereby operation of the switch results in operation of the filter cleaning mechanism. 
     Thus a user of the vacuum cleaner may clean the filter merely by operating the switch without the need to carry out a complex sequence of operations, or remove the filter from the vacuum cleaner in order to do so. 
     In one possible embodiment of the second aspect of the invention, the switch has a first state in which the filter cleaning mechanism is activated and a second state in which the filter cleaning mechanism is de-activated, and the switch latches in the first and second states thereof unless operated. Thus a user may switch the filter cleaning mechanism on and off by operating the switch each time. 
     In a second possible alternative embodiment of the second aspect of the invention, the switch has a first state in which the filter cleaning mechanism is activated and a second state in which the filter cleaning mechanism is de-activated, and the switch is monostable in the second state thereof, but must be held by a user in the first state thereof. Thus in order to operate the filter cleaning mechanism, the user must hold the switch in the second state and the filter cleaning mechanism will only continue to operate for as long as the switch is held in this fashion. 
     Finally, in a third possible alternative embodiment of the second aspect of the invention, the vacuum cleaner may further comprise a timing device, wherein operation of the switch activates the filter cleaning mechanism and the timing device, and the timing device subsequently deactivates the filter cleaning mechanism. Thus in order to operate the filter cleaning mechanism, the user need only operate the switch once, which will activate the filter cleaning mechanism for a short time until it is deactivated again by the timing device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the present invention will become apparent from the following detailed description, which is given by way of example and in association with the accompanying drawings, in which: 
         FIG. 1A  schematically shows a prior art filter cleaning mechanism in a first mode of operation thereof; 
         FIG. 1B  schematically shows the prior art filter cleaning mechanism of  FIG. 1A  in a second mode of operation thereof; 
         FIG. 2  is a perspective view of a vacuum cleaner with a removable dust collection chamber having a filter cleaning mechanism according to a first embodiment of the present invention; 
         FIG. 3  is a cross-sectional view through the removable dust collection chamber of the vacuum cleaner shown in  FIG. 2 ; 
         FIG. 4  is a partially cut-away perspective view of the dust collection chamber shown in  FIG. 3 , illustrating certain aspects of the filter cleaning mechanism; 
         FIG. 5  is a perspective view of the dust collection chamber shown in  FIG. 3 , illustrating other aspects of the filter cleaning mechanism; 
         FIG. 6  is a perspective view of a removable dust collection chamber of a vacuum cleaner comprising a filter cleaning mechanism according to a second embodiment of the present invention; 
         FIG. 7  is a close-up view of a part of the dust collection chamber of either the first or second embodiment, showing a bowl release mechanism; 
         FIG. 8  is a similar view to  FIG. 7  with some of the components of the bowl release mechanism removed for the purposes of illustration and explanation; 
         FIG. 9A  is a partial cross-sectional view of the bowl release mechanism of  FIG. 7  in a first position thereof; and 
         FIG. 9B  is a partial cross-sectional view of the bowl release mechanism of  FIG. 7  in a second position thereof. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring firstly to  FIG. 2 , there is shown the body  22  of a vacuum cleaner comprising a removable dust collection chamber  28 . The removable dust collection chamber  28  includes a dirt separation device which will be described in greater detail below. Dirty air enters the vacuum cleaner via a dirty air inlet  26 , passes through the dirt separation device and exits the vacuum cleaner via a pair of clean air outlets  24  provided on opposite sides of the body  22  of the vacuum cleaner, in the manner illustrated by the arrows labelled A and B in  FIG. 2 . Because of the orientation of the vacuum cleaner body as shown in  FIG. 2 , only one of the clean air outlets  24  can be seen in this drawing. A hose and floor-cleaning head (or other similar accessory, such as an upholstery brush or crevice tool), which would normally be attached to the dirty air inlet  26 , have also been omitted from  FIG. 2  for the purposes of greater clarity in the illustration. The vacuum cleaner is switched on and off by a user depressing an on/off switch  30  mounted on the top of the body  22 . Mains electrical power is supplied to the vacuum cleaner by a cable (not shown) which enters the body  22  via an access point on the rear of the body. The cable is wound onto a spring-loaded and ratcheted drum within the body  22 , and may be retracted back into body by a user depressing a cable-rewind button  32 , which disengages the ratchet, allowing the cable to return into the body under the action of the spring. A pivoting handle  34  allows the user to pick up body  22 , which is also provided with wheels (only one of which can be seen in  FIG. 2 ) for moving the vacuum cleaner across a floor. A further handle  38  provided on the dust collection chamber  28  allows a user to remove the dust collection chamber  28  from body  22  for emptying dust and dirt therefrom, but in order to do so, the user must firstly release the dust collection chamber from body  22  by squeezing a pair of spring-loaded levers  40  in the directions indicated in  FIG. 2  by the arrows labelled C and C′. This action disengages the ends of levers  40  from beneath a pair of overhanging tabs  43  provided on body  22  and allows the dust collection chamber  28  then to be lifted out of body  22  using handle  38  in a direction towards the viewer. 
     Turning now to  FIG. 3 , there is shown a cross-sectional view through the dust collection chamber  28 . The dust collection chamber includes a dirt separation device comprising a course filter  42  and a pleated fine filter  44 . The course filter  42  is made of a rigid plastics material and includes a large number of small holes  46 . The pleated fine filter  44  is made of a porous woven material and may also be provided with a non-stick coating on the outer surface thereof. During operation of the vacuum cleaner, dirty air enters the dust collection chamber from the dirty air inlet  26  via an aperture  48  formed in a side wall of the dust collection chamber  28  in the direction indicated by the arrow labelled D in  FIG. 3 . The dirty air then swirls around the outside of course filter  42 , with dust and dirt being thrown outwardly under the action of centrifugal force and air being drawn inwardly through the large number of small holes  46  formed in the course filter  42 , which prevent the passage of any remaining large dirt particles therethrough. The partially filtered air then passes through the pleated fine filter  44 , which captures remaining fine particles of dust, and clean air exits the dust collection chamber  28  in the direction indicated by the arrow labelled E in  FIG. 3 . Handle  38  incorporates a hollow passage  50  placing the dust collection chamber  28  in fluid communication with the main body  22  of the vacuum cleaner. Filtered air therefore passes along hollow passage  50  from the dust collection chamber  28  to body  22 . The body  22  houses a motor and a fan driven by the motor, which during operation of the vacuum cleaner, generates the movement of air through the dust collection chamber  28  into the body  22  just described. Meanwhile, dust and dirt separated out from the air collect in the bottom of the dust collection chamber  28  under the action of gravity, in the region indicated in  FIG. 3  by reference numeral  52 . A series of baffles  54  formed in the bottom of the dust collection chamber  28  help to trap the dust and dirt. The bottom of the dust collection chamber  28  is also provided with a trap-door  56  which can be opened by a user in order to empty the dust collection chamber, in a manner to be described in greater detail below. 
     Whereas large particles of dirt which are caught by the course filter  42  are heavy enough to fall to the bottom of the dust collection chamber  28  under their own weight, fine particles of dust which are caught by the pleated fine filter  44  adhere thereto and must therefore be dislodged in order to prevent the pleated fine filter from becoming blocked. This is achieved in the following fashion. The inner surface of the course filter  42  is provided with a plurality of ribs  58  which interengage with the pleats of the fine filter  44 . The fine filter  44  is free to rotate within the dust collection chamber  28  relative to the course filter  42 , and may be caused to do so in a manner which will be described shortly in relation to  FIG. 4 . Thus as the fine filter  44  rotates within the course filter  42 , the ribs  58  formed on the inner surface of the course filter successively contact the pleats of the fine filter  44 . This agitates the fine filter, causing any accumulated dust adhering to the fine filter to be shaken off and to fall to the bottom of the dust collection chamber. The non-stick coating formed on the outer surface of the fine filter aids in this process. The dislodged dust then collects in the region indicated in  FIG. 3  by reference numeral  60 , and can be emptied from the dust collection chamber by a user opening trap-door  56 . 
     Turning now to  FIG. 4 , the filter cleaning mechanism which allows fine filter  44  to be cleaned in this manner will now be described. The pleats of the fine filter  44  are mounted in a frame comprising a bottom portion  62  and a top portion  64  connected to each other by pillars  66 . Top portion  64  of this frame is fixed to a rotatable hub  68  in a ring, the cross-section of this ring being indicated in  FIG. 4  by reference numeral  70 . The rotatable hub  68  is free to rotate about its own axis within the lid of the dust collection chamber  28 . The lid of the dust collection chamber is itself hollow and comprises a lower surface (labelled  72  in  FIG. 4 ) and an upper surface, which has been removed in  FIG. 4  in order to reveal a train of gears  76  contained within the hollow space of the lid. Rotatable hub  68  is also provided with a plurality of gear teeth on its outer surface, which are not visible in  FIG. 4 , but which may instead be seen in  FIG. 5 , where they are labelled by reference numeral  80 . These gear teeth  80  successively contact a first wheel of the train of gears  76  at the point indicated in  FIG. 4  by reference numeral  74 . The train of gears  76  is in turn driven by a motor  78 , which is a second motor of the vacuum cleaner, additional to the motor mounted in the body  22  which drives the fan for drawing air through the vacuum cleaner during operation thereof. Instead, the second motor  78  is dedicated to operating the filter cleaning mechanism by causing hub  68  to rotate, thereby also indirectly rotating the fine filter  44  and causing the pleats thereof to successively contact the ribs  58  formed on the inner surface of the course filter  42 . 
     In the alternative embodiment shown in  FIG. 6 , in place of the train of gears  76 , the gear teeth  80  formed around the outside of rotatable hub  68  may instead engage with teeth provided on the inside of a rubber drive belt  82  for transmitting rotary motion from the second motor  78  to the hub  68 . In either embodiment, however, second motor  78  is permanently mounted to the exterior of dust collection chamber  28 , so that when the dust collection chamber is removed from the body  22  of the vacuum cleaner by a user in order to allow it to be emptied, the motor and drive train for transmitting rotary motion from the motor to the hub remain undisturbed. 
     The source of power for motor  78  may be the same as the source of power for the main motor of the vacuum cleaner which drives the fan for moving air through the vacuum cleaner from the dirty air inlet to the clean air outlet. Alternatively, the second motor  78  may have its own separate source of power. Motor  78  may also be battery powered or mains powered. In the event that it is battery powered, the battery may be permanently in electrical connection with the motor and also mounted to the exterior of dust collection chamber  28 . Alternatively, however, the battery may instead be housed within the body  22  of the vacuum cleaner and electrically connected to the motor via electrical contact points only when dust collection chamber  28  is docked into body  22 . A similar arrangement by which electrical power is supplied to motor  78  via electrical contacts can also be used in the event that motor  78  is mains powered. In a further alternative embodiment, the filter cleaning mechanism may be driven by the main motor of the vacuum cleaner which drives the fan for moving air through the vacuum cleaner from the dirty air inlet to the clean air outlet, without the need for second motor  78 . In such a case, the power output from the main motor must be moderated by suitable gearing and/or control circuitry to ensure that the lower power demands of the filter cleaning mechanism and the higher power demands of the fan may both be met by the same motor. 
     How the trap-door  56  on the bottom of dust collection chamber  28  is opened by a user, in order to allow the dust collection chamber to be emptied, will now be described with reference to  FIGS. 7 and 8 . Mounted on the side of dust collection chamber  28  is a plunger  84 , which slides on a guide rail  86 . At the top end of plunger  84  is a push-button  88 , which allows the user to depress the plunger in the direction indicated in  FIG. 7  by arrow F, against the force of a first compression spring  90  (shown in  FIG. 8 ) which is mounted on a spring buffer  92  and is held in place by engagement with a retaining pip  85 . When the plunger  84  is depressed in this manner, the bottom end of plunger  84  pushes against a latch  94  held in a hinge mounting  96 , the plunger  84  coming into contact with the latch  94  at a point of contact indicated in  FIGS. 9A and 9B  by reference numeral  95 . The hinge mounting  96  provides an axis of rotation  97  (as shown in  FIG. 8 ), about which the latch  94  is able to pivot. The pressure applied to latch  94  by the bottom end of plunger  84  therefore causes latch  94  to rotate about the axis  97  against the force of a second compression spring  98  mounted on the side of dust collection bowl  28 . The end of latch  94  remote from axis  97  is also provided with a retaining lip  100 , which is able to engage with a catch  102  formed on trap-door  56 . On the opposite side of trap-door  56  from catch  102 , the trap-door  56  is mounted to dust collection chamber  28  via a spring-loaded hinge  104 , which may be seen in both  FIGS. 5 and 6 . Thus when latch  94  rotates about axis  97  against the force of the second compression spring  98 , retaining lip  100  is disengaged from catch  102  and trap-door  56  swings open under the spring force of hinge  104 , thereby emptying accumulated dust and dirt from within the dust collection chamber  28 . 
     The trap-door  56  may also be opened by a user pushing directly on latch  94 , which is also provided with a push-button for that purpose, without the need for the user to depress plunger  84  in order to do so. However, when the user releases the pressure placed on latch  94  either by releasing the pressure applied to it directly or by releasing the pressure previously applied to push-button  88 , plunger  84  and latch  94  return to their starting positions under the action of the two compression springs  90  and  98 . The user is then able to close trap-door  56  again by swinging it shut against the spring force of hinge  104 , until catch  102  re-engages with the retaining lip  100  of latch  94 . The relaxed and compressed states of compression springs  90  and  98  are respectively shown in  FIGS. 9A and 9B .