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CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application is a divisional of U.S. patent application Ser. No. 13/681,918, filed Nov. 20, 2012, the content of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     There are robotic cleaning vehicles which traverse the bottom of swimming pools and other large liquid containers submerged in the contained liquid. The robotic cleaning vehicle draws in liquid from ports in their bottom and passing the liquid through filters in the body of the vehicle and expels the filtered liquid back into the large container, typically a swimming pool. These vehicles typically travel on wheels which suspend the body of the vehicle above the bottom of the container. In some cases these wheels are mounted on axles and one of the axles is held at angle other than perpendicular to the general direction of movement of the vehicle so that as the vehicle moves forward and back on its wheels it follows a path that covers a significant portion of the container. 
     SUMMARY 
     A self directed pool cleaning vehicle comprising a body includes a water inlet port and a water outlet port with the inlet port being located on the bottom of the body and containing a filter. A drive mechanism mounted to the body propels the vehicle in two generally opposed directions. A first axle and a second axle, with each axle carrying two wheels at either end, support the body and control its direction of movement in response to the drive mechanism. The axles are mounted to the body such that they can be generally perpendicular to the directions in which the drive mechanism propels the vehicle. The first axle is mounted to the body via a first slot and a second slot, with each slot extending generally in the direction in which the drive mechanism propels the vehicle such that the first axle can move toward either end of the slots. A steering structure is provided having a flexible member with at least a first portion which moves to close a portion of the first slot to limit the movement of the first axle in the first slot, the movement of the first portion changing the angle of the first axle to other than perpendicular to the directions in which the drive mechanism propels the vehicle when the first axle is used as the trailing axle. The steering structure has a locking mechanism which interacts with the body to hold the first portion in a position closing a portion of its slot. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a self directed cleaning vehicle which is an embodiment of the present invention with its remote power supply. 
         FIG. 2  is a perspective view of the rear axle and associated elements of the vehicle of  FIG. 1 . 
         FIG. 3  is a side elevation of one of the mounting slots of the rear axle with the steering ribbon unengaged. 
         FIG. 4  is a side elevation of one of the mounting slots of the rear axle with the steering ribbon engaged. 
         FIG. 5  is a perspective view of the steering ribbon and the wheel well cap that carries an axle mounting slot with the steering ribbon unengaged. 
         FIG. 6  is a perspective view of the steering ribbon and the wheel well cap that carries an axle mounting slot with the steering ribbon engaged. 
         FIG. 7  is a perspective view of entire the steering ribbon assembly including both axle mounting slots and the locking mechanism. 
         FIG. 8  is a perspective view of the bottom of the vehicle of  FIG. 1 . 
         FIG. 9  is a perspective view of the inside of the vehicle of  FIG. 1  with its filters illustrated. 
         FIG. 10  is a perspective view of the filter assembly of the vehicle of  FIG. 1 . 
         FIG. 11  is a perspective view of the mounting of the filter handle to the vehicle. 
         FIG. 12  is a perspective view of the inside of the vehicle showing the inlet ports. 
         FIG. 13  is a perspective view of one of the filter handles of the vehicle of  FIG. 1 . 
         FIG. 14  is a perspective view of the filter assembly of the vehicle of  FIG. 1  with its hinges shown. 
         FIG. 15  is a perspective view of the bottom of the vehicle of  FIG. 1  with its passive brushes illustrated. 
         FIG. 16  is a cross section along line  16 - 16  of  FIG. 6 . 
         FIG. 17  is a perspective view of the filter assembly of the vehicle of  FIG. 1  partially withdrawn from the vehicle. 
         FIG. 18  is a perspective view of a flexible ribbon with slots. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1  a self directed vehicle  10  has a body with a top bridge  11  to which is mounted an electric motor  12  with a shaft  13  projecting out of each end of motor  12 . In an alternative embodiment shaft  13  is two separate shafts, with each separate shaft extending from an opposing end of motor  12 . Attached to each end of the shaft  13  is a propeller  14  which faces an outlet port  15 . Each outlet port is covered with a flap valve  16  hinged to allow the expulsion of water from the vehicle but to prevent its ingress. The electric motor  12  has an external source of power  18  which includes a timing mechanism to reverse the direction of the rotation of the motor  12 . The vehicle  10  also has a chassis or bottom body  20  which is supported by and travels on front wheels  30  and rear wheels  40 . The rear wheels  40  are associated with a steering structure including a steering ribbon or flexible member  50  which is operated by a slide knob  52 . The front wheels  30  are carried by an axle (not shown) which is fixed in its orientation to the chassis  20 . 
     The rear wheels  40  are carried by an axle  80  (Shown in  FIGS. 2, 7 and 16 ) which is able to slide in slots  90  (Shown in  FIGS. 2-4, 6-7 and 16 ). A steering ribbon  50  is adjusted to partially block one of these slots from its rear edge. Thus when the axle  80  is the trailing axle (That is the vehicle moving away the ribbon  50 ), one end of the axle  80  cannot move to the rear of its slot and the axle  80  assumes a skewed configuration (Shown in  FIG. 16 ). 
       FIG. 2  shows details of how the wheel wells  60  of the vehicle carry the wheel well caps  70  which in turn carry the slots  90  in which is mounted the rear axle  80 . It also shows the steering ribbon  50  with its slide knob  52  being guided and supported by the wells  60  and the caps  70 . 
       FIG. 3  shows a wheel well cap  70  with its slot  90  unobscured by the steering ribbon  50  while  FIG. 4  shows a similar view in which this slot has been obscured by the steering ribbon  50 .  FIG. 6  provides another view of a slot  90  being partially obscured by the steering ribbon  50 . The steering ribbon slide knob  52 , by which the position of the steering ribbon can be adjusted, is shown as well as the steering ribbon locking protrusion which interacts with other portions of the vehicle to hold the steering ribbon  50  in a given position. Slide knob  52  may be accessed from outside the body of the vehicle. Below the protrusion  54  is a slit  56  which allows the steering ribbon  50  to flex as the protrusion is moved from one locking position to another. Slit  56  provides a springing effect to locate protrusion  54  within locking slots  102  (Shown in  FIG. 7 ).  FIG. 5  provides a view similar to that of  FIG. 6  in which the steering ribbon  50  is in a non-obscuring position. 
       FIG. 7  shows how the steering ribbon  50  interacts with other parts of the vehicle  10  to cause the back axle to become tilted when it is the trailing axle, i.e. when the vehicle is moving in a direction away from the steering ribbon. The right and left ends of the back axle  80  are each mounted in a slot  90 . The right end is free to traverse the length of its slot  90  but the steering ribbon  50  has been positioned to hold the left end at the forward end of its slot  90 . The chassis  20  of the vehicle  10  carries a steering ribbon locking bracket which in turn carries locking slots  102 . These interact with the steering ribbon protrusion  54  shown in  FIGS. 5 &amp; 6  to lock the steering ribbon  50  in various positions. In this case the ribbon has been locked in a position such that it occludes most of the left slot  90 . This occlusion can also be seen in  FIG. 6 . The slide knob  52  is used to move the steering ribbon  50  between the lock positions established by the steering ribbon locking slots  102  and the steering ribbon slit  56  and the steering ribbon protrusion  54  (Both shown in  FIGS. 5 &amp; 6 ) work together to allow the shift between locking positions. The slit  56  allows the protrusion  54  to move downward out of a locking slot  102  as the steering ribbon  50  is moved to the left or right by exerting pressure on the slide knob  52 , which is itself readily accessible from the exterior of the vehicle as can be seen in  FIG. 1 . The movement of the steering ribbon  50  is constrained by the ribbon guide track  58  which can be seen in  FIG. 16 . The flexible nature of steering ribbon  50  permits at least the end portions of steering ribbon  50  to flex to be maintained within the non linear portions of guide track  58  as the ribbon  50  is moved within the track. 
     The vehicle  10  is propelled forward and backwards on its front wheels  30  and back wheels  40  by the operation of the electric motor  12  and its associated propellers  14  expelling water out of one of its outlet ports  15 . The direction of rotation of the electric motor  12  is reversed by its remote power source  18  causing the direction of water expulsion and the direction of travel of the vehicle to be reversed. The power source  18  is conveniently equipped with a timer which causes the reversal and the timer is conveniently set to the time it takes the vehicle to traverse a length or width of the surface being cleaned. Thus as the vehicle reaches an end of this surface, the timer of the power source  18  acts to reverse its general direction of travel. When the steering ribbon  50  is locked in a position such that it occludes a portion of one of the slots  90 , it causes the back axle  80  to become tilted when the vehicle moves forward and this alters the direction of travel of the vehicle. In this way the vehicle traces a pattern that covers the entire surface to be cleaned rather than moving back and forth over the same path. 
     Referring to  FIG. 8  the bottom of the chassis  20  of the vehicle  10  is provided with inlet ports  22  which have side walls  24  and back walls  26 , as well as flap valves  28 . In one embodiment side walls  24  and back walls  26  extend from the bottom of the chassis  20  in a direction inwardly into the center of the vehicle  10 . In an alternative embodiment, flap valves are attached directly to filter frame  110 . Chassis  20  is provided with drainage slits  23  each of which has a flap valve  25 . In operation the vehicle  10  is submerged beneath the surface of a liquid such as water which covers the surface which the vehicle is to clean such as the floor of a swimming pool. The interior of the vehicle is filled with this liquid as it is submerged. The propellers  14  shown in  FIG. 1  then draw fluid in through the inlet ports  22  and expel it out of one of the outlet ports  15  shown in  FIG. 1 . 
     When the vehicle  10  has completed its cleaning operation it is raised out of the reservoir of liquid covering the surface being cleaned and the liquid contained within the vehicle is permitted to drain out through the drainage slits  23 . The inlet port flap valves  28  allow liquid to be drawn into the interior of the vehicle  10  by the action of the propellers  14  but not to allow it to drain out. On the other hand, the drainage slit flap valves  25  allow the liquid to drain out of the interior of the vehicle  10  when it is raised out of the reservoir but prevents the entrance of the fluid into the interior through the drainage slits  23  when the vehicle is submerged and the propellers  14  are in operation. 
     Referring to  FIG. 9  each of the inlet ports  22  opens into the interior of a filter frame  110  which is covered by a fine mesh material which serves to filter particulate impurities such as debris and bacteria out of the fluid which passes out of the interior of the filter frame  110 . The inlet port flap valves  28  ensure that when the propellers  14  are not active fluid which has not yet passed through the fine mesh of the filter frame  110  does not drain back out of the vehicle  110 . On the other hand, the drainage slits  23  are positioned outside the filter frame  110  and so only have access to fluid which has passed through the fine mesh of the filter frame  110 . 
     The placement of the inlet ports  22  is to accommodate the filter system which in turn is configured to facilitate easy removal of the filter frame  110 . The two inlet ports  22  are each placed on the opposite side of the centerline of the chassis  20  so that each can feed a separate filter frame  110  and yet the two together can cover the entire width of the chassis  20 . The filter frames  110  are configured to be parallel to this center line so that they can be removed without interference with the electric motor  12  and its associated propellers  14 . 
     Referring to  FIG. 10  the filter system includes filter frame  110  which carries a fine mesh material and has a top  112 , a window  114  and a handle  116 . The window  114  may be transparent which allows the operator of the vehicle  10  to easily see what larger materials have accumulated in the filter frame  110  beneath that window  114  during the cleaning operation of the vehicle  110 . 
     The handle  116  provides for the removal of the filter frame  110  for cleaning but also provides a locking function for holding the filter frame  110  in place during the cleaning operation of the vehicle  10 . This locking function is provided by the interaction of the protrusions  122  carried by the filter handle  120  as can be seen in  FIG. 12  with the front wall  117  of the filter handle  116  which can be seen in  FIG. 13 . The filter handle  116  is constructed as a downward facing u channel with a back wall  119  as well as the front wall  117 . The protrusions  122  fit between these walls in frictional engagement with the front wall  117  to lock the filter frame  110  in place during the cleaning operation of the vehicle  110 . The handle  116  also carries a depression  121  which facilitates grasping the handle  110  and raising it out of a locked position. This depression  121  mates with a depression  124  in the filter trim  120  shown in  FIG. 12  to allow easy grasping access to the locked in position filter handle  116 . The handle  116  also carries a shaped boss  118  which mates with a shaped hole  113  in the filter frame top  112  as seen in  FIG. 11  such that the upward rotation of the handle is restrained once it reaches the appropriate angle for withdrawal of the filter frame  110  from the chassis  20 . A partial withdrawal at this appropriate angle up and to the side of the centerline of the chassis  20  is shown in  FIG. 17 . 
     The filter frame  110  is also provided with a door  111  which opens on hinges  115  as can be seen in  FIG. 14 . This allows access to the interior of the filter frame  110  for the removal of debris which has accumulated during the cleaning operation of the vehicle  10 . This provides for an easy method for cleaning the filtering system. 
     The bottom of the chassis has been provided with passive brushes  130  which can be seen in  FIGS. 1 &amp; 15 . As shown each brush extends across the full width of the chassis  20 . However, if the inlet ports  22  were moved closer to the leading and trailing ends of the chassis  20  each passive brush could be shortened such that it just extended across a portion of the width. But in one such embodiment the passive brushes  130  would be mounted such that they jointly covered the entire width of the chassis. Each passive brush  130  is constructed of scrubbing elements which reach to the surface to be cleaned when the chassis  20  is supported on this surface by its front wheels  30  and its rear wheels  40 . In one embodiment the scrubbing elements are stiff bristles. 
     In another embodiment, shown in  FIG. 18 , steering member or flexible ribbon  50  includes a connecting member  140  that operatively engages axle  80 . In one implementation connecting member  140  includes a first slot  142  and a second slot  144 . Axle  80  extends through first slot  142  and second slot  144 . First slot  142  includes a first end  146  and a second end  148 , the second end  148  being closer to center section  150  than first end  146 . Similarly, second slot  144  includes a first end  152  and a second end  154 , where second end  154  is closer to center section  150  than first end  152 . Note that first slot  142  and second slot  144  have a longitudinal axis defined between first and second ends of each slot. First slot  142  and second slot  144  are in a non linear alignment with center portion  150 . Since ribbon  50  is flexible, the shape of the region of the ribbon adjacent the slots  142 ,  144  may vary as ribbon  50  is moved from one position to another position to adjust the axle angle relative to the body as described above. 
     In a center setting where knob  52  is positioned midway or equidistant between the wheels  40  attached to axle  80 , axle  80  will be perpendicular to the movement of the vehicle when the vehicle moves in a direction toward slide knob  52  as shown by vector  156 . When the vehicle is moving in the direction of vector  156  axle  80  will be pushed by and adjacent to first ends  146  and  152  of first and second slots  142  and  144  respectively. Similarly, when the vehicle moves rearward in a direction opposite vector  156 , axle  80  remains perpendicular to vector  156  with axle  80  being pushed by and adjacent to second ends  148  and  154  of first and second slots  142  and  144  respectively. 
     When a user moves slide knob  52  to a rightward position in vector direction  158 , first end  146  of first slot  142  will pull axle  80  proximate slot  142  in vector direction  156 . However, the portion of axle  80  proximate second slot  144  will be free to travel between first end  152  and second end  154  of second slot  144 . In this configuration, when the vehicle is moving in vector direction  156 , the axle  80  proximate first slot  142  will be in a fixed/restrained mode while the axle  80  proximate second slot  144  will have freedom to move toward the body opposite vector  156  such that axle  80  proximate second slot  144  will be adjacent first end  152  of second slot  144 . As a result, the axle and wheels will be at a non-perpendicular angle relative to vector  156 . This will result in the vehicle being steered or directed in a leftward motion with respect to vector  156 . For purposes of clarity, the vector direction that the vehicle will move in this mode will be between vectors  156  and  158 . 
     In this rightward mode when the vehicle is moved in a direction opposite to vector  156  axle  80  proximate first slot  142  will remain fixed relative to first end  146  of first slot  142  while the axle will be pushed to second end  154  of second slot  144 . Hence making the axle perpendicular to vector  156 . As a result the motion of the vehicle in the direction opposite to vector  156  will be straight, while the motion of the vehicle in the general direction of vector  156  will veer in a left ward direction between vectors  156  and  158  as noted above. 
     When a user moves slide knob  52  to a leftward position opposite to vector direction  158 , first end  152  of second slot  144  will pull axle  80  proximate slot  144  in vector direction  156 . However, the portion of axle  80  proximate first slot  142  will be free to travel between first end  146  and second end  148  of first slot  142 . In this configuration, when the vehicle is moving in vector direction  156 , the axle  80  proximate second slot  144  will be in a fixed/restrained mode while the axle  80  proximate first slot  142  will have freedom to move toward the body opposite vector  156  such that axle  80  proximate first slot  144  will be adjacent first end  146  of first slot  142 . As a result, the axle and wheels will be at a non-perpendicular angle relative to vector  156 . This will result in the vehicle being steered or directed in a rightward motion with respect to vector  156 . For purposes of clarity, the vector direction that the vehicle will move in this mode will be between vectors  156  and  160 . 
     In this leftward mode when the vehicle is moved in a direction opposite to vector  156  axle  80  proximate second slot  144  will remain fixed relative to first end  152  of second slot  144  while the axle  80  proximate first slot  142  will be pushed to second end  148  of first slot  142 . Hence making the axle  80  perpendicular to vector  156 . As a result the motion of the vehicle in the direction opposite to vector  156  will be straight, while the motion of the vehicle in the general direction of vector  156  will veer in a right ward direction between vectors  156  and  160  as noted above. 
     While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. It is noted that the construction and arrangement of the pool cleaning vehicle with mechanism for skewing an axle as described herein is illustrative only. Although only a few embodiments of the present invention have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g. variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. For example, elements shown as integrally formed may be constructed of multiple parts or elements and vice versa, the position of elements may be reversed or otherwise varied, and the nature of number of discrete elements or positions may be altered or varied. Additionally, the mechanism for skewing the axle may also be applied to other pool cleaning vehicles including vehicles with wheels driven by a mechanical linkage to a motor, or to vehicles employing a single propeller. Accordingly, all such modifications are intended to be included within the scope of the present invention to be included within the scope of the present invention as defined in the appended claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present inventions as expressed in the appended claims.

Summary:
A self directed pool cleaning vehicle comprising a body carrying water inlet and outlet ports with the inlet port being located on the bottom of the body with the body containing a filter is described. A drive mechanism propels the vehicle in two generally opposed directions. Two axles which each carry two wheels support the body and control its direction of movement. One axle is mounted to the body via slots that extend in the directions of motion such that this axle can move toward either end of the slots. A steering structure is provided with a portion that moves to close a portion of one of the slots and can be locked in a position that prevents one end of an axle from traversing its slot. Thus when this axle is the trialing axle it is held at other than a right angle to the two generally opposed directions.