Patent Publication Number: US-9427123-B2

Title: Autonomous surface treating appliance

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of United Kingdom Application No. 1115608.0, filed Sep. 9, 2011, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     This invention relates in general to an autonomous floor treating appliance and particularly, though not exclusively, to an autonomous vacuum cleaner. 
     BACKGROUND OF THE INVENTION 
     Mobile robots are becoming increasingly commonplace and are used in such diverse fields as space exploration, lawn mowing and floor cleaning. The last decade has seen particularly rapid advancement in the field of robotic floor cleaning devices, especially vacuum cleaners, the primary objective of which is to navigate a user&#39;s home autonomously and unobtrusively whilst cleaning the floor. 
     In performing this task, a robotic vacuum cleaner has to navigate the area which it is required to clean and to avoid colliding with obstacles whilst doing so. A requirement for a robotic vacuum cleaner when exploring a room is to clean as close as possible up to the edges of a room. One approach to this is shown in U.S. Pat. No. 6,883,201 which equips a circular-bodied robotic floor cleaner with spinning side brushes on each of its forward flanks in order to brush debris into the path of a horizontally mounted brush bar exposed on the underside of the device and between its wheels. Such a system of opposed spinning brushes can result in debris being flicked away from the front of the device which reduces the effectiveness of this approach for cleaning the edges of a room. 
     SUMMARY OF THE INVENTION 
     It is against this background that the invention has been made. To this end, the invention provides an autonomous floor treating appliance comprising a main body defining an outer plan profile, and having a drive arrangement mounted inboard of the outer plan profile of the main body and configured to propel the appliance in a direction of movement across a surface to be cleaned, a surface treating assembly associated with the main body and carried transversely to the direction of movement, the surface treating assembly being generally elongate in form and having side edges extending parallel to the direction of movement and at a tangent to respective circular portions of the outer plan profile of the main body. 
     The invention in principle applies to any autonomous appliance directed to treating a floor surface which includes a surface treating assembly extending transversely to the direction of movement of the appliance, for example a floor sweeper, polisher or washer, or even a robotic lawnmower. However, the invention has particular utility for robotic vacuum cleaners, and so the invention will hereafter be described in this context. Thus, in one embodiment, the appliance is an autonomous vacuum cleaner and so further comprises a power source operatively connected to a suction generator operable to draw air from a dirty air inlet of the treating head into a removable dirt and dust separating apparatus. 
     Since the surface treating assembly or ‘head’ extends transversely across the main body of the appliance, such that side edges or faces extend parallel to the direction of movement and at a tangent to respective circular portions of the outer plan profile of the main body, the appliance has a configuration which allows it to clean right up to the edges of a room. Furthermore, since the plan profile of the appliance is at least partly circular, it has a beneficial shape for on-the-spot turning so it is more able to maneuver out of confined spaces and corners. Preferably, the main body is substantially circular in plan view. 
     In the exemplary embodiment, the treating head may extend transversely across a rear portion of the main body, and behind the supporting wheel arrangement. The treating assembly is therefore able to clean over the path covered by the support wheels, and so can pick up grit or dirt which may be deposited on the floor surface by the wheels. 
     In one embodiment, the main body includes a chassis and the treating head is provided on the chassis, and may be integral with the chassis. In this way, the chassis may define an elongate sole plate extending forward of the treating head along a longitudinal axis and in the movement direction. 
     The chassis may also include first and second recesses located on its opposite sides within which respective traction units of the drive arrangement are receivable. Therefore, the traction units are mountable on the chassis inboard of the outer periphery of the appliance and forward of the treating head. Beneficially, the treating assembly extends beyond the width of the traction units and so can clean the floor surface of dust and grit which the traction units may leave in their trail. 
     In order to accommodate the removable dirt separating apparatus, the main body may include a front portion defining an open platform within the dirt separating apparatus is received. Preferably, the dirt separating apparatus is substantially cylindrical and is received in the platform in an upright orientation such that its longitudinal axis extends substantially vertically, that is to say normal to the longitudinal and transverse axes of the main body. 
     Although the dirt separating apparatus can take other forms, in the exemplary embodiment it is a cyclonic separating apparatus which provides the vacuum cleaner with a particularly effective cleaning facility. 
     The dirt separating apparatus may be configured so that it forms part of the outer plan profile of the appliance, its shape therefore complementing the substantially circular profile of the appliance. Furthermore, a portion of the dirt separating apparatus may protrude beyond a front portion of the main body in the direction of movement and, in this way, the dirt separating apparatus provides the appliance with a resilient protective bumper in the event of a collision. 
     The main body structure may also include a body portion that is mounted on the chassis and movable relative thereto. This provides the appliance with the facility to detect collisions as the body will be cause to move relative to the chassis, such movement being detectable by a suitable sensing mechanism. Notably, the power source, the suction generator, the dirt separating apparatus receiving platform are provided on the body, all of which is movable with respect to the chassis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the invention may be more readily understood, reference will now be made, by way of example only, to the accompanying drawings in which: 
         FIG. 1  is a front perspective view of a mobile robot in accordance with an embodiment of the invention; 
         FIG. 2  is a view from beneath of the mobile robot in  FIG. 1 ; 
         FIG. 3  is a plan view from above of the mobile robot in  FIG. 1 ; 
         FIG. 4  is an exploded perspective view of the mobile robot of the invention showing its main assemblies; 
         FIG. 5  is a front perspective view of the chassis of the mobile robot; 
         FIGS. 6 a  and 6 b    are perspective views from either side of a traction unit of the mobile robot; 
         FIG. 7  is a side view of the traction unit in  FIGS. 6 a  and 6 b    and shows its orientation relative to a surface on which it rides; 
         FIG. 8  is a section view of the traction unit in  FIG. 7  along the line A-A; 
         FIG. 9  is an exploded perspective view of the traction unit in  FIGS. 6 a , 6 b    and  7 ; 
         FIG. 10  is a side view of the traction unit in  FIG. 7 , but shown in three swing arm positions; 
         FIG. 11  is a front view of the chassis of the mobile robot; 
         FIG. 12  is a view from underneath of the main body of the mobile robot; 
         FIG. 13  is a rear view of the chassis of the mobile robot; 
         FIGS. 14 a , 14 b , 14 c  and 14 d    are schematic views of the robot in various ‘bump’ conditions; and 
         FIG. 15  is a schematic systems view of the mobile robot. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIGS. 1, 2, 3, 4 and 5  of the drawings, an autonomous surface treating appliance in the form of a robotic vacuum cleaner  2  (hereinafter ‘robot’) comprises has a main body having four principal assemblies: a chassis (or sole plate)  4 , a body  6  which is carried on the chassis  4 , a generally circular outer cover  8  which is mountable on the chassis  4  and provides the robot  2  with a generally circular profile, and a separating apparatus  10  that is carried on a forward part of the body  6  and which protrudes through a complementary shaped cut-out  12  of the outer cover  8 . 
     For the purposes of this specification, the terms ‘front’ and ‘rear’ in the context of the robot will be used in the sense of its forward and reverse directions during operation, with the separating apparatus  10  being positioned at the front of the robot. Similarly, the terms ‘left’ and ‘right’ will be used with reference to the direction of forward movement of the robot. As will be appreciated from  FIG. 1 , the main body of the robot  2  has the general form of a relatively short circular cylinder, largely for maneuverability reasons, and so has a cylindrical major axis ‘C’ that extends substantially vertically relative to the surface on which the robot travels. Accordingly, the cylindrical axis C extends substantially normal to a longitudinal axis of the robot ‘L’ that is oriented in the fore-aft direction of the robot  2  and so passes through the centre of the separating apparatus  10 . The diameter of the main body is preferably between 200 mm and 300 mm, and more preferably between 220 mm and 250 mm. Most preferably, the main body has a diameter of 230 mm which has been found to be a particularly effective compromise between maneuverability and cleaning efficiency. 
     The chassis  4  supports several components of the robot  2  and is preferably manufactured from a high-strength injection moulded plastics material, such as ABS (Acrylonitrile Butadiene Styrene), although it could also be made from appropriate metals such as aluminium or steel, or composite materials such a carbon fibre composite. As will be explained, the primary function of the chassis  4  is as a drive platform and to carry cleaning apparatus for cleaning the surface over which the robot travels. 
     With particular reference to  FIGS. 4 and 5 , a front portion  14  of the chassis  4  is relatively flat and tray-like in form and defines a curved prow  15  that forms the front of the robot  2 . A drive arrangement is provided by first and second traction units  20  which are mounted in respective recesses  16 ,  18  in each flank of the front portion of the chassis  4 . Note that  FIG. 4  shows the chassis  4  with the traction units  20  attached and  FIG. 5  shows the chassis  4  without the traction units  20  attached. 
     The pair of traction units  20  are located on opposite sides of the chassis  4  and are operable independently to enable the robot to be driven in forward and reverse directions, to follow a curved path towards the left or right, or to turn on the spot in either direction, depending on the speed and direction of rotation of the traction units  20 . Such an arrangement is sometimes known as a differential drive, and detail of the traction units  20  will be described more fully later in the specification. 
     The relatively narrow front portion  14  of the chassis  4  widens into rear portion  22  which includes a surface treating assembly  24  or ‘cleaner head’ having a generally cylindrical form and which extends transversely across the entire width of the chassis  4  relative to the longitudinal axis ‘L’ and is positioned behind the traction units  20  with respect to the forward direction of travel. 
     With reference also to  FIG. 2 , which shows the underside of the robot  2 , the cleaner head  24  defines a rectangular suction opening  26  that faces the supporting surface and into which dirt and debris is drawn into when the robot  2  is operating. An elongate brush bar  28  is contained within the cleaner head  24  and is driven by an electric motor  30  via a reduction gear and drive belt arrangement  32  in a conventional manner, although other drive configurations such as a solely geared transmission are also envisaged. 
     The underside of the chassis  4  features an elongate sole plate section  25  extending forward of the suction opening  26  which includes a plurality of channels  33  (only two of which are labeled for brevity) which provide pathways for dirty air being drawn towards the suction opening  26 . The underside of the chassis  4  also carries a plurality (four in the illustrated embodiment) of passive wheel or rollers  31  which provide further bearing points for the chassis  4  when it is at rest on or moving over a floor surface. It should be noted that the rollers  31  support the chassis such that the underside thereof is in a parallel orientation relative to a floor surface. Furthermore, although wheels or rollers are preferred, they could also be embodied as hard bearing points such as skids or runners. 
     In this embodiment, the cleaner head  24  and the chassis  4  are a single plastics moulding, thus the cleaner head  24  is integral with the chassis  4 . Such a configuration is efficient to manufacture since the sole plate  25  and the cleaner head are provided by the same moulded component. However, this need not be the case and the two components could be separate, the cleaner head  24  being suitably affixed to the chassis  4  as by screws or an appropriate bonding technique as would be clear to the skilled person. 
     The cleaner head  24  has first and second end faces  27 ,  29  that extend to the edge of the chassis  4  behind the traction units  20  and which are in line with the cover  8  of the robot. Considered in horizontal or plan profile as in  FIGS. 2 and 3 , it can be seen that the end faces  27 ,  29  of the cleaner head  24  are flat and extend at a tangent (labeled as ‘T’) to the cover  8  at substantially diametrically opposed points along the lateral axis ‘X’ of the robot  2 . The benefit of this is that the cleaner head  24  is able to run extremely close to the walls of a room as the robot traverses in a ‘wall following’ mode therefore being able to clean right up to the wall. Moreover, since the end faces  27 ,  29  of the cleaner head  24  extend tangentially to both sides of the robot  2 , it is able to clean right up to a wall whether the wall is on the right side or the left side of the robot  2 . It should be noted, also, that the beneficial edge cleaning ability is enhanced by the traction units  20  being located inboard of the cover  8  meaning that the robot can maneuver in such a way that the cover  8  and therefore also the end faces  27 ,  29  of the cleaner head  24  are almost in contact with the wall during a wall following operation. Furthermore, since the cleaner head extends transversely across substantially the entire width of the chassis  4  and is positioned behind the traction units  20 , this means that the cleaner head  24  can clean the floor surface of dust and grit which the traction units may leave in their trail as the robot moves about. The cleaner head  24  is located behind the traction units  20  and as close to them as possible so that the cleaner head  24  can extend across the whole width of the robot whilst minimizing the ‘projections’ from the main circular form of the machine which could otherwise interfere with its ability to maneuver. 
     Dirt drawn into the suction opening  26  during a cleaning operation exits the cleaner head  24  via a conduit  34  which extends upwardly from the cleaner head  24  and curves towards the front of the chassis  4  through approximately 90° of arc until it faces in the forwards direction. The conduit  34  terminates in a rectangular mouth  36  having a flexible bellows arrangement  38  shaped to engage with a complementary shaped duct  42  provided on the body  6 . 
     The duct  42  is provided on a front portion  46  of the body  6 , and opens into a forward facing generally semi-cylindrical recess  50  having a generally circular base platform  48 . The recess  50  and the platform  48  provide a docking portion into which the separating apparatus  10  is mounted, in use, and from which it can be disengaged for emptying purposes. 
     It should be noted that in this embodiment the separating apparatus  10  consists of a cyclonic separator such as disclosed in WO2008/009886, the contents of which are incorporated herein by reference. The configuration of such separating apparatus is well known and will not be described any further here, save to say that the separating apparatus  10  may be removably attached to the body  6  by a suitable mechanism such as a quick-release fastening means to allow the apparatus  10  to be emptied when it becomes full. The nature of the separating apparatus  10  is not central to the invention and the cyclonic separating apparatus may instead separate dirt from the airflow by other means that are known in the art for example a filter-membrane, a porous box filter or some other form of separating apparatus. For embodiments of the apparatus which are not vacuum cleaners, the body  6  can house equipment which is appropriate to the task performed by the machine. For example, for a floor polishing machine the main body can house a tank for storing liquid polishing fluid. 
     When the separating apparatus  10  is engaged in the docking portion  50 , a dirty air inlet  52  of the separating apparatus  10  is received by the duct  42  and the other end of the duct  42  is connectable to the mouth  36  of the brush bar conduit  34 , such that the duct  42  transfers the dirty air from the cleaner head  24  to the separating apparatus  10 . The bellows  38  provide the mouth  36  of the duct  34  with a degree of resilience so that it can mate sealingly with the dirty air inlet  52  of the separating apparatus  10  despite some angular misalignment. Although described here as bellows, the duct  34  could also be provided with an alternative resilient seal, such as a flexible rubber cuff seal, to engage the dirty air inlet  52 . 
     Dirty air is drawn through the separating apparatus  10  by an airflow generator which, in this embodiment, is an electrically powered motor and fan unit (not shown), that is located in a motor housing  60  located on the left hand side of the body  6 . The motor housing  60  includes a curved inlet mouth  62  that opens at the cylindrical shaped wall of docking portion  50  thereby to match the cylindrical curvature of the separating apparatus  10 . Although not seen in  FIG. 4 , the separating apparatus  10  includes a clean air outlet which registers with the inlet mouth  62  when the separating apparatus  10  is engaged in the docking portion  50 . In use, the suction motor is operable to create low pressure in the region of the motor inlet mouth  62 , thereby drawing dirty air along an airflow path from the suction opening  26  of the cleaner head  24 , through the conduit  34  and duct  42  and through the separating apparatus  10  from dirty air inlet  52  to the clean air outlet. Clean air then passes through the motor housing  60  and is exhausted from the rear of the robot  2  through a filtered clean air outlet  61 . 
     The cover  8  is shown separated from the body  6  in  FIG. 4  and, since the chassis  4  and body  6  carry the majority of the functional components of the robot  2 , the cover  8  provides an outer skin that serves largely as a protective shell and to carry a user control interface  70 . 
     The cover  8  comprises a generally cylindrical side wall  71  and a flat upper surface  72  which provides a substantially circular profile corresponding to the plan profile of the body  6 , save for the part-circular cut-out  12  shaped to complement the shape of the docking portion  50 , and the cylindrical separating apparatus  10 . Furthermore, it can be seen that the flat upper surface  72  of the cover  8  is co-planar with an upper surface  10   a  of the separating apparatus  10 , which therefore sits flush with the cover  8  when it is mounted on the main body. 
     As can be seen particularly clearly in  FIG. 2 , the part-circular cut-out  12  of the cover  8  and the semi-cylindrical recess  50  in the body  6  provides the docking portion a horseshoe shaped bay defining two projecting lobes or arms  73   a  which flank either side of the separating apparatus  10  and leave between approximately 5% and 40%, and preferably 20%, of the apparatus  10  protruding from the front of the docking portion  50 . Therefore, a portion of the separating apparatus  10  remains exposed even when the cover  8  is in place on the main body of the robot  2 , which enables a user ready access to the separating apparatus  10  for emptying purposes. The flanking lobes are particularly suited to housing sensor modules, identified here at  82 , which the robot may use to map its environment and/or to detect obstacles. In this case, the material of the projecting lobes  73  should be a suitable sensor-transparent material. The sensor modules may be any sensors suitable for robot navigation, such as laser range finders, ultrasonic transducers, position sensitive devices (PSDs) or optical sensors. 
     Opposite portions of the side wall  71  include an arched recess  74  (only one shown in  FIG. 3 ) that fits over a respective end  27 ,  29  of the cleaner head  24  when the cover  8  is connected to the body  6 . As can be seen in  FIG. 1 , a clearance exists between the ends of the cleaner head  24  and the respective arches  74  order to allow for relative movement therebetween in the event of a collision with an object. 
     As has been mentioned, the separating apparatus  10  in the exemplary embodiment is a cylindrical bin that sits within the docking bay portion  50  of the robot and protrudes from the cover  8  so as to define a front of the robot  2 . Note that the bin  10  has an upright orientation such that a longitudinal axis thereof is normal to both the longitudinal and lateral axes L, X of the robot  2  and, therefore, parallel to its cylindrical/vertical axis C. Having a portion of the separating apparatus  10  exposed at the front of the robot  2  in this way allows a user to gain easy access to the separating apparatus in order to remove it from the robot  2  when it needs to be emptied. 
     Therefore, a user does not need to manipulate doors, hatches or panels in order to gain access to the separating apparatus  10 . Furthermore, the separating apparatus may be transparent so that a user can see how full the separating apparatus is, thus avoiding the need for mechanical or electronic bin-full indicators. Furthermore, a separating apparatus, particularly a cyclonic separating apparatus is lighter than electronic components such as motors and batteries so the configuration of the separating apparatus on the front of the robot further assists the robot to climb up surfaces. In prior art machines, however, the heavier components tend to be positioned at the front whilst the dust containers are positioned at the rear or towards the centre of the machine. 
     A further advantage is that the separating apparatus  10  acts as a bumper for the robot  2  since being the forward most part of the robot means that it will be the first part of the robot to contact an obstacle during a collision. Preferably the bin is made from a plastics material of suitable mechanical properties to provide a degree of resilience in the event of the robot colliding with an obstacle. One example is transparent ABS (Acrylonitrile Butadiene Styrene) manufactured in a suitable thickness (for example between about 0.5 and 2 mm) to provide the bin  10  with a suitable degree of resilience. Therefore, the bin  10  provides a degree of protection for the main body of the robot  2  from hard and or sharp objects which may otherwise damage the cover  8 . Similarly, the resilience of the bin provides a degree of protection for obstacles during collisions which may be vulnerable to damage. 
     On the upper edge of the side wall  71 , the cover  8  includes a semi-circular carrying handle  76  which is pivotable about two diametrically opposite bosses  78  between a first, stowed position, in which the handle  76  fits into a complementary shaped recess  80  on upper peripheral edge of the cover  8 , and a deployed position in which it extends upwardly, (shown ghosted in  FIG. 1 ). In the stowed position, the handle maintains the ‘clean’ circular profile of the cover  8  and is unobtrusive to the use during normal operation of the robot  2 . Also, in this position the handle  76  serves to lock a rear filter door (not shown) of the robot into a closed position which prevents accidental removal of the filter door when the robot  2  is operating. 
     In operation, the robot  2  is capable of propelling itself about its environment autonomously, powered by a rechargeable battery pack (not shown) housed within the body  6 . To achieve this, the robot  2  carries an appropriate control means which is interfaced to the battery pack, the traction units  20  and appropriate sensor modules  82  comprising for example infrared and ultrasonic transmitters and receivers on the front left and right side of the body  6 . The sensor suite  82  provides the control means with information representative of the distance of the robot from various features in an environment and the size and shape of the features. Additionally the control means is interfaced to the suction fan motor and the brush bar motor in order to drive and control these components appropriately. The control means is therefore operable to control the traction units  20  in order to navigate the robot  2  around the room which is to be cleaned. It should be noted that the particular method of operating and navigating the robotic vacuum cleaner is not material to the invention and that several such control methods are known in the art. For example, one particular operating method is described in more detail in WO00/38025 in which navigation system a light detection apparatus is used. This permits the cleaner to locate itself in a room by identifying when the light levels detected by the light detector apparatus is the same or substantially the same as the light levels previously detected by the light detector apparatus. 
     Having described the chassis  4 , body  6  and cover  8 , the traction units  20  will now be described in further detail with reference to  FIGS. 6 to 10  which show various perspective, sectional, and exploded views of a single traction unit  20  for clarity. 
     In overview, the traction unit  20  comprises a transmission case  90 , a linkage member  92  or ‘swing arm’, first and second pulley wheels  94 ,  96 , and track or continuous belt  98  that is constrained around the pulley wheels  94 ,  96 . 
     The transmission case  90  houses a gear system which extends between an input motor drive module  100  mounted on an inboard side of one end of the transmission case  90 , and an output drive shaft  102  that protrudes from the drive side of the transmission case  90 , that is to say from the other side of the transmission case  90  to which the motor module  100  is mounted. The motor module  100  in this embodiment is a brushless DC motor since such a motor is reliable and efficient, although this does not preclude other types of motors from being used, for example brushed DC motors, stepper motors or even hydraulic drives. As has been mentioned, the motor module  100  is interfaced with the control means to receive power and control signals and is provided with an integral electrical connector  104  for this purpose. The gear system in this embodiment is a gear wheel arrangement which gears down the speed of the motor module  100  whilst increasing available torque, since such a system is reliable, compact and lightweight. However, other gearing arrangements are envisaged within the context of the invention such as a belt or hydraulic transmission arrangement. 
     The traction unit  20  therefore brings together the drive, gearing and floor engaging functions into a self-contained and independently driven unit and is readily mounted to the chassis  4  by way of a plurality of fasteners  91  (four fasteners in this embodiment), for example screws or bolts, that are received into corresponding mounting lugs  93  defined around the recess of the chassis  4 . 
     The traction unit  20  is mountable to the chassis so that the first pulley wheel  94  is in a leading position when the robot  2  is traveling forwards. In this embodiment, the lead wheel  94  is the driven wheel and includes a centre bore  104  which is receivable onto the drive shaft  102  by way of a press fit. Alternative ways of securing the pulley wheel to the shaft are also envisaged, such as a part-circular clip (‘circlip’) attached to the shaft  102 . The leading wheel  94  may also be considered a sprocket since it is the driven wheel in the pair. In order to improve the transfer of drive force from the drive shaft  102  to the lead wheel  94 , the centre bore  104  of the pulley wheel may be internally keyed to mate with a corresponding external key on the drive shaft. 
     The swing arm  92  includes a leading end that is mounted to the transmission case  90  between it and the lead wheel  94  and is mounted so as to pivot about the drive shaft  102 . A bush  106  located in a mounting aperture  108  of the swing arm  92  is received on an outwardly projecting spigot  110  of the transmission case  90  through which the drive shaft  102  protrudes. The bush  106  therefore provides a bearing surface intermediate the spigot  110  and the swing arm  92  to allow the swing arm  92  to pivot smoothly and to prevent splaying relative to the transmission case  90 . The bush  106  is made preferably from a suitable engineering plastics such as polyamide which provides the required low friction surface yet high strength. However, the bush  106  may also be made out of metal such as aluminum, steel, or alloys thereof, which would also provide the necessary frictional and strength characteristics. 
     As shown in the assembled views, the swing arm  92  is mounted on the spigot  110  and the lead wheel  94  is mounted to the drive shaft  102  outboard of the leading end of the swing arm  92 . A stub axle  112  is press fit into a bore located on the opposite or ‘trailing’ end of the swing arm  92  and defines a mounting shaft for the rear pulley wheel  96 , or ‘trailing wheel’ along a rotational axis parallel to the axis of the drive shaft  102 . The trailing wheel  96  includes a centre bore  113  in which a bearing bush  114  is received in a press fit. The bush  114  is received over the axle  112  in a sliding fit so that the bush, and therefore also the trailing wheel  96 , are rotatable relative to the swing arm  92 . A circlip  116  secures the trailing wheel to the axle  112 . 
     The continuous belt or track  98  provides the interface between the robot  2  and the floor surface and, in this embodiment, is a tough rubberized material that provides the robot with high grip as the robot travels over the surface and negotiates changes in the surface texture and contours. Although not shown in the figures, the belt  98  may be provided with a tread pattern in order to increase traction over textured or rough terrain. 
     Similarly, although not shown in the figures, the inner surface  98   a  of the belt  98  is serrated or toothed so as to engage with a complementary tooth formation  94   a  provided on the circumferential surface of the leading wheel  94  which reduces the likelihood of the belt  98  slipping on the wheel  94 . In this embodiment, the trailing wheel  96  does not carry a complementary tooth formation, although this could be provided if desired. To guard against the belt  98  slipping off the trailing wheel  96 , circumferential lips  96   a ,  96   b  are provided on its inner and outer rims. As for the leading wheel  94 , a circumferential lip  94   b  is provided on only its outer rim since the belt  98  cannot slip off the inner rim due to the adjacent portion of the swing arm  92 . 
     As will be appreciated, the swing arm  92  fixes the leading and trailing wheels  94 ,  96  in a spaced relationship and permits the trailing wheel  96  to swing angularly about the leading wheel  94 . The maximum and minimum limits of angular travel of the swing arm  92  are defined by opposed arch-shaped upper and lower stops  122   a ,  122   b  that protrude from the drive side of the transmission case  90 . A stub or pin  124  extending from the in-board side of the swing arm  92  is engagable with the stops  122   a ,  122   b  to delimit the travel of the swing arm  92 . 
     The traction unit  20  also comprises swing arm biasing means in the form of a coil spring  118  that is mounted in tension between a mounting bracket  126  extending upwardly from the leading portion of the swing arm  92  and a pin  128  projecting from the trailing portion of the transmission case  90 . The spring  118  acts to bias the trailing wheel  96  into engagement with the floor surface, in use, and so improves traction when the robot  2  is negotiating an uneven surface such as a thick-pile carpet or climbing over obstacles such as electrical cables.  FIG. 10  shows three exemplary positions of the traction unit  20  throughout the range of movement of the swing arm  92 . 
       FIG. 7  shows the relative position of the wheels  94 ,  96  with respect to the floor surface F when the robot  2  is at rest, and in which position the swing arm  92  is at its minimum limit of travel, the pin  124  being engaged with the upper stop  122   a . In this position, a portion of the track  98  around the trailing wheel  96  defines a contact patch  130  with the floor surface whereas a portion of the track  98  forward of the contact patch and extending to the leading wheel is inclined relative to the floor surface F due to the larger radius of the trailing wheel  96  compared to the leading wheel  94 . This provides the traction unit  20  with a ramped climbing surface which improves the ability of the robot  2  to climb over imperfections in the floor surface, as well as over raised obstacles such as electrical cables/flexes or edges of rugs for example. As an alternative, it should be appreciated that the wheels  94 ,  96  may also be similarly sized, or even equally sized, and mounted at different heights, either on the swing arm  92  or alternatively in fixed positions relative to the chassis  4  in order to provide a forward-facing ramped climbing surface in the direction of movement. 
     In addition to the improvement in climbing ability of the inclined track  98  compared to a simple wheel, the traction unit  20  maintains a small contact patch  130  by virtue of its single trailing wheel  96  which provides a maneuvering benefit since it does not suffer the extent of slippage that would be experienced if a significant portion of the track  98  was in contact with the floor surface. 
     A further traction enhancement is provided by the outer lip  96   b  of the trailing wheel  96  which extends radially outwards further than the lip  96   a  on the inboard side of the wheel  96 . As shown clearly in  FIG. 8 , the outer lip  96   b  extends almost to the same radius as the outer surface of the track  98  and its edge is provided with a toothed or serrated formation. A benefit of this is that, in circumstances in which the robot is travelling over a soft surface such as a rug or carpet, the track  98  will tend to sink into the pile of the carpet whereby the serrated edge of the outer lip  96   b  will engage the carpet and provide the robot with increased traction. However, on hard surfaces, only the track  98  will contact the floor surface which will benefit the maneuvering ability of the robot. 
     A still further benefit is that the track arrangement provides the climbing ability of a much larger single wheel, but without the large dimension which allows the brush bar to be positioned very near to the lateral axis of the robot which is important in providing full width cleaning. As seen in this embodiment, the rotational axis of the trailing wheel  96  is substantially in line with the lateral axis of the robot which benefits maneuverability. The cleaner head is able to be positioned very close to the traction units  20 , and in this embodiment the axis of the cleaner head is spaced approximately 48 mm from the lateral axis of the robot, although it is envisaged that a spacing of up to 60 mm would be acceptable in order to minimise the amount that the cleaner head projects from the outer envelope of the main body. 
     In an alternative embodiment (not shown), the depth and the thickness of the outer lip  96   b  is increased such that the surface of the lip  96   b  lies side by side with the outer surface of the track  98  surrounding the trailing wheel  96 , in effect providing a transverse extension of the surface of the track  98 . This increases the area of the contact patch  130  also on hard surfaces which may be desirable in some circumstances. In this embodiment, it should be appreciated that the climbing ability is also retained by the inclined track surface without increasing the contact patch in the longitudinal direction of the track  98 . 
     As has been explained, the traction units  20  of the robot  2  provide an improved ability to travel over deep pile rugs and carpets, and also to negotiate obstacles such as electrical cables on the floor and also small steps between floor surfaces. However, ‘caterpillar’ type drive units can be vulnerable to ingress of debris in the nip between the wheels and the belt. To guard against this, the swing arm  92  further includes a raised block-like portion  132  that extends outwardly from the swing arm  92  in the space bounded by the opposing parts of the leading and trailing wheels  94 ,  96  and the inner surface of the track  98 . Side surfaces  132   a ,  132   b ,  132   c ,  132   d  of the debris guard block  132  are shaped to sit closely next to the adjacent surfaces of the wheels  94 ,  96  and the belt  98  whilst an outboard surface  134  of the block  132  terminates approximately in line with the outer faces of the wheels  94 ,  96 . The block  132  is therefore shaped to accommodate substantially all of the volume between the wheels  94 ,  96  and so prevents debris such as grit or stones from fouling the drive arrangement. Although the block  132  could be solid, in this embodiment the block  132  includes openings  136  which reduce the weight of the spring arm  92  and also its cost. Although the block  132  preferably is integral with the swing arm  92 , it could also be a separate component fixed appropriately to the swing arm  92 , for example by clips, screws or adhesive. 
     Referring now to  FIGS. 11, 12 and 13 , these illustrate how the body  6  is attached to the chassis  4  to enable relative sliding movement between one another and how this relative moment is interpreted by the robot  2  to gather information about collisions with objects in its path. 
     To enable relative sliding movement between the chassis  4  and the body  6 , front and rear engagement means fix the chassis  4  and the body  6  together so that they cannot be separated in the vertical direction, in a direction normal to the lateral and longitudinal axes X, L of the robot  2 , but are permitted to slide with respect to one another by a small amount. 
     Turning firstly to the front portion of the main body, as best illustrated in  FIG. 12 , a front engagement means includes a slot-like opening  140  which is generally oval in form like a racetrack/stadium or a para-truncated circle that is defined in the front portion of the body  6 , specifically in a central position in the platform  48 . A slidable pivoting member in the form of a gudgeon pin  142  is received through the opening  140  and includes a sleeve section  142   a  that extends a short way below the opening  140  and which defines an upper flange  142   b  which bears against the sides of the opening and so prevents the gudgeon pin  142  passing through it. 
     The engagement means also includes a complementary structure on the forward portion of the chassis  4  in the form of a walled-recess  144 , which is also racetrack shaped to correspond to the shape of the opening  140  in the platform  48 . The body  6  is mountable on the chassis  4  so that the opening  140  on the platform  140  body  6  overlies the recess  144  in the chassis  4 . The gudgeon pin  142  is then secured to the floor of the recess  144  by a suitable mechanical fastener such as a screw; the gudgeon pin  142  is shown ghosted in its position in the recess  144  in  FIG. 11 . The body  6  is therefore joined to the chassis  4  against vertical separation. However, since the gudgeon pin  142  is fixed immovably to the chassis  4  whilst being held slidably in the opening  140 , the body  6  can slide relative to the gudgeon pin  142  and can pivot angularly about it due to its rounded shape. 
     The forward portion of the chassis  4  also includes two channels  145 , one located on either side of the recess  144 , which serve as a supporting surface for respective rollers  147  provided on the underside of the body  6  and, more specifically, on the platform  48  either side of the opening  140 . The rollers  147  provide support for the body  6  on the chassis  4  and promote smooth sliding movement between the two parts and are shown in ghosted form in  FIG. 11 . 
     The rear engagement means constrains movement of a rear portion  150  of the body  6  relative to the chassis  4 . From a comparison between  FIG. 12  and  FIG. 13 , it can be seen that a rear portion  146  of the chassis  4  behind the cleaner head  24  includes a bump detection means  148  which also serves as a secure mounting by which means the rear portion  150  of the body  6  is connected to the chassis  4 . 
     Each side of the bump detection means includes a body support means; both body support means are identical and so only one will be described in detail for brevity. The body support means comprises a sleeve-like tubular supporting member  152  that sits in a dished recess  154  defined in the chassis  154 . In this embodiment, the dished recess  154  is provided in a removable chassis portion in the form of a plate member  155  that is fixed across the rear portion  146  of the chassis  4 . However, the recesses  154  could equally be an integral part of the chassis  4 . 
     A spring  156  is connected to the chassis  154  at its lower end and extends through the sleeve member  152 , wherein the end of the spring terminates in an eyelet  158 . The sleeve  152  and the spring  156  engage with a complementary socket  160  on the underside of the body  6 , which socket  160  includes a raised wall  160   a  with which the upper end of the sleeve  152  locates when the body  6  is mounted onto the chassis  4 . When mounted in this way, the spring  156  extends into a central opening  162  in the socket  160  and the eyelet  158  is secured to a securing pin within the body  6 . Note that the securing pin is not shown in the figures, but may be any pin or suitable securing point to which the spring  156  can attach. 
     Since the supporting sleeve members  152  are movably mounted between the chassis  4  and the body  6 , the sleeve members  152  can tilt in any direction which enables the body  6  to ‘rock’ linearly along the longitudinal axis ‘L’ of the robot, but also for the rear portion of the body  6  to swing angularly, pivoting about the gudgeon pin  142  by approximately 10 degrees as constrained by the rear engagement means as will now be explained further. In this embodiment, the springs  156  provide a self-centering force to the supporting sleeve members  152  which urge the sleeves members  152  into an upright position, this action also providing a resetting force for the bump detection system. In an alternative embodiment (not shown), the supporting sleeve members  152  could be solid, and a force to ‘reset’ the position of the body relative to the chassis could be provided by an alternative biasing mechanism. 
     Although the sleeve members  152  allow the body  6  to ‘ride’ on the chassis  4  with a certain amount of lateral movement, they do not securely connect the rear portion  150  of the body  6  to the chassis  4  against vertical separation. For this purpose, the bump detection means  148  includes first and second guiding members in the form of posts or rods  160 ,  162  provided on the body  6  which engage with respective pins  164 ,  166  provided on the chassis  4 . As can be seen in  FIG. 13 , the pins  164 ,  166  extend through respective windows  168 ,  170  defined in the plate member  155  and are retained there by a respective washer  172 ,  174 . In order to mount the rear portion  150  of the body  6  onto the rear portion  146  of the chassis  4 , the guiding members  160 ,  162  are push fit onto the pins  164 ,  166  until they contact their respective washer  172 ,  174 . The movement of the rear portion  150  of the body  6  is therefore constrained to conform to the shape of the windows  168 ,  170  such that the windows serves as a guiding track. In this embodiment, the windows  168 ,  170  are generally triangular in shape and so this will permit the body  6  to slide linearly with respect to the gudgeon pin  142  but also to swing angularly about it within the travel limits set by the windows  168 ,  170 . However, it should be noted that the permitted movement of the body  6  can be altered by appropriate re-shaping of the windows  168 ,  170 . 
     The bump detection means  148  also includes a switching means  180  to detect movement of the body  6  relative to the chassis  4 . The switching means  180  includes first and second miniature snap-action switches  180   a ,  180   b  (also commonly known as ‘micro switches’) provided on the underside of the rear portion  150  of the body  6  that, when the body  6  is mounted to the chassis  4 , are located either side of an actuator  182  provided in a central part of the rear portion  146  of the chassis  4 . In this embodiment, the actuator  182  takes the form of a wedge-shape having angled leading edges for activating the switches  180   a ,  180   b . Although not shown in the Figures, the switches  180   a ,  180   b  are interfaced with the control means of the robot. The location of the switches  180   a ,  180   b  relative to the wedge-shaped actuator  182  is shown in  FIG. 13 ; note that the switches  180   a ,  180   b  are shown in dotted lines. As can be seen, the switches  180   a ,  180   b  are positioned such that their activating arms  183  are positioned directly adjacent and either side of the angled forward edges of the wedge-shaped actuator  182 . 
     The switches  180   a ,  180   b  are activated in circumstances where the robot  2  collides with an obstacle when the robot is navigating around a room on cleaning task. Such a bump detection facility is desirable for an autonomous vacuum cleaner since sensing and mapping systems of such robots can be fallible and sometimes an obstacle will not be detected in time. Other robotic vacuum cleaners operate on a ‘random bounce’ methodology in which a means to detect a collision is essential. Therefore, a bump detection facility is needed to detect collisions so that a robot can take evasive action. For example the control means may determine simply to reverse the robot and then to resume forward movement in a different direction or, alternatively to stop forward movement, to turn 90° or 180° and then to resume forward movement once again. 
     Activation of the switches  180   a ,  180   b  will now be explained with reference to  FIGS. 14 a , 14 b , 14 c  and 14 d   , which show a schematic representation of the chassis  4 , body,  6  and bump detection means in different bump situations. In the following figures, the parts common with the previous figures are referred to with the same reference numerals. 
       FIG. 14 a    shows the relative positions of the body  6 , the chassis  4 , the gudgeon pin  142 , the body pivot opening  140 , the switches  180   a ,  180   b  and the wedge-shaped actuator  182  in a non-collision position. As can be seen, neither switch  180   a ,  180   b  has been activated as indicated by the reference ‘X’. 
       FIG. 14 b    shows the robot  2  in a collision with an obstacle in the ‘dead ahead’ position, as indicated by the arrow C. The body  6  is caused to move backward linearly, that is to say along its longitudinal axis L and, accordingly, the two switches  180   a ,  180   b  are moved backwards with respect to the wedge-shaped actuator  182  thereby triggering the switches  180   a ,  180   b  substantially at the same time as indicated by the check marks. 
     Alternatively, if the robot  2  collides with an obstacle on its right hand side, as indicated by the arrow C in  FIG. 14 c   , the body  6  will be caused to swing about the gudgeon pin  142  to the left and, in these circumstances, the switches  180   a ,  180   b  will move to the left with respect to the actuator  182  with the result that the right hand switch  180   b  is activated before activation of the left hand switch  180   a  as indicated by the check mark for switch  180   b.    
     Conversely, if the robot  2  collides with an obstacle on its left hand side, as indicated by the arrow C in  FIG. 14 d   , the body  6  will be caused to swing to the right, in which case the switches  180   a ,  180   b  will move to the right with respect to the actuator  182 , which therefore triggers the left hand switch  180   a  before the right hand switch  180   b  as indicated by the check mark for switch  180   a.    
     Although in the oblique angle collisions shown in  FIGS. 14 c  and 14 d    only one of the switches  180   a ,  180   b  is shown as activated, it should be appreciated that such a collision may also activate the other one of the switches, albeit at a later time than the first activated switch. 
     Since the switches  180   a ,  180   b  are interfaced to the control means of the robot, the control means can discern the direction of impact by monitoring the triggering of the switches  180   a ,  180   b , and the relative timing between triggering events of the switches. 
     Since the robot  2  is able to detect collisions by sensing relative linear and angular movement between the body  6  and the chassis  4 , the invention avoids the need to mount a bump shell onto the front of the robot as is common with known robotic vacuum cleaners. Bump shells can be fragile and bulky so the invention increases the robustness of the robot and also makes possible a reduction in size and complexity. 
     Turning now to  FIG. 15 , this shows schematically the control means of the robot and its interfaces with the components described above. Control means in the form of a controller  200  includes appropriate control circuitry and processing functionality to process signals received from its various sensors and to drive the robot  2  in a suitable manner. The controller  200  is interfaced into the sensor suite  82  of the robot  2  by which means the robot gathers information about its immediate environment in order to map its environment and plan an optimum route for cleaning. A memory module  201  is provided for the controller to carry outs its processing functionality and it should be appreciated that the memory module  201  could alternatively be integrated into the controller  200  instead of being a separate component as shown here. 
     The controller  200  also has suitable inputs from the user interface  70 , the bump detection means  206  and suitable rotational sensing means  208  such as rotary encoders provided on the traction units  20 . Power and control inputs are provided to the traction units  20  from the controller  200  and also to the suction motor  210  and the brush bar motor  212 . 
     Finally, a power input is provided to the controller  200  from the battery pack  214  and a charger interface  216  is provided by which means the controller  200  can carry out charging of the battery pack  214  when the battery supply voltage has dropped below a suitable threshold. 
     Many variations are possible without departing from the inventive concept. For example, although the traction units  20  have been described as having a continuous rubberized belt or track, the invention could also be performed with a track that comprises numerous discrete track or tread sections linked together to form a chain. 
     In the embodiment above, the body  6  has been described as being able to move linearly as well as angularly about the chassis. However, it should be appreciated that this is such that collisions can be detected from a wide range of angles and that the invention resides also in a bump detection system in which the body moves linearly or angularly to the chassis instead of a combination of such movement. 
     The sensing means has been described as comprising snap-action switches disposed either side of a wedge-shaped actuator and that such an arrangement conveniently enables the switches to be activated when the body moves linearly (both switches activated simultaneously) or angularly (one switch activated before the other). However, the skilled person will appreciate that other switch mechanisms are possible, for example contactless switches such as a light-gate switch, or a magnetic/Hall effect switch.