CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 10/372,489, filed Feb. 21, 2003 and entitled “Self-Cleaning Litter Box” which claims the benefit of U.S. Provisional Application Ser. No. 60/373,435, filed Apr. 18, 2002 and entitled “Self-Cleaning Litter Pan”. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention relates to a litter box, and more particularly, to a self-cleaning litter box for cats. 
     BACKGROUND OF THE INVENTION 
     Most domesticated cats are trained to use litter boxes to eliminate solid and liquid wastes. These litter boxes are sized to hold particulate litter that absorbs moisture and suppresses odors from the cat waste. After multiple uses of the litter box by the cat, the pet owner can manually dump the waste and litter particulate from the litter box for disposal. 
     Because of the unsanitary environment inside the litter box, some pet owners are reluctant to regularly service these litter boxes. In addition, pet owners who frequently travel cannot service these litter boxes on a regular bases. Therefore, various forms of self-cleaning cat litter boxes have been devised for automatically cleaning litter boxes. Many of these devices incorporate a motor driven rake that sifts through the litter pan to carry or push the litter clumps into a separate waste container. Unfortunately, many of these automatic litter boxes remain difficult to clean and oftentimes require more maintenance than traditional (non-automated) litter boxes. For example, over time litter and waste clumps can attach to the rake tines. If litter clumps remain attached to the rake, the litter will harden and decrease the effectiveness of the rake. Further, the additional clumps attached to the rake tines will increase the weight of the rake thereby increasing the load on the motor. As a result, the motor can be damaged. If the motor is battery operated, battery life can be substantially decreased. In addition, because litter clumps remain attached to the rake, undesirable odors will likely result. In order to thoroughly clean the rake, the rake should be detached from the litter box. This usually requires the use of tools, is dirty and requires considerable amounts of time to disassemble and then reassemble. 
     In addition, many self-cleaning litter boxes can hold only limited amounts of litter. This is especially true of litter boxes incorporating a motor driven rake that sifts through the litter pan. If the litter level inside the pan is too deep, the rake may be unable to sift through the pan and additional power may be required. As a result, if the motor is battery operated, battery life can be considerably decreased and/or a larger motor may be required. In most instances, providing a larger motor is not an option due to space and cost considerations. Furthermore, many present rake configurations are not effectively able to handle deep litter levels because the rake tines lack sufficient strength. Thus, larger tines have been devised to provide additional strength. However, larger tines result in larger surface areas that contact the caustic litter pan environment. This contact can substantially reduce the usable life of the rake. Because cats desire to dig and bury their waste inside the litter, there is a need to overcome the above-mentioned disadvantages in order to provide a deep litter level inside the litter pan. 
     Finally, many litter boxes, both non-automated and automated, are ineffective in containing litter particulate inside the litter box. When cats enter or exit the litter box, litter particulate is often scattered around the litter box. As a result, the pet owner must manually clean the area around with litter box. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a litter box for cats. The liter box is self-cleaning so as to automatically remove waste clumps that form from cat excretions. The self-cleaning litter box comprises a litter pan for holding a predetermined amount of cat litter, a rake for sifting through the cat litter to remove any waste clumps located therein, a drive assembly for moving the rake through the cat litter, and a base member to support the litter pan and contain the drive assembly. A waste box is located adjacent the front wall to store clumps of litter carried by the rake. The litter pan is sized to accommodate multiple cats at one time while also allowing a deep layer of litter to be stored therein. This allows the cats to dig or scratch the litter. A waste box is located adjacent the front wall to store clumps of litter carried by the rake. 
     During operation, the rake travels through the litter pan to collect waste clumps and to deposit the collected clumps inside the waste box. The rake includes a cross support member to support a plurality spaced apart tines. Each tine is mounted on the support bar at a slight angle and are generally parallel with respect to each other. A pair of rake support arms are located on the ends of the cross member 
     The rake tines are preferably coated with either a chrome, TEFLON® or nylon coating in order to reduce or eliminate pitting and other damage to tines. Further, the coating prevents residue from clumping and remaining attached to the rake after the sweeping cycle. The rake is lightweight so that a greater volume of litter can be stored inside the upper pan without damaging the motor. 
     A stabilizer bar, mounted in the base, is used to support and transport a rake support structure. The rake support structure is used to support the rake during the sweeping cycle. The rake is easily removed from the litter box in a simple manner and without the use of tools in order to clean or replace as necessary. 
     The rake is moved across the litter pan by a drive assembly that is preferably contained inside the base and below the litter pan. The drive assembly includes a DC motor that is mounted stationary to the base. The DC motor drives a pair of belts that connect to the stabilizer bar. Thus, when the belts are moved, the stabilizer bar will also move. 
     Upon activation of the drive assembly, the rake will sift through the litter to collect and push litter clumps toward the waste box. As the rake pushes the clumps toward the waste box, the rake tines push the clumps upward along an inclined ramp. As the rake approaches the waste box, the waste box lid opens so as to receive the waste clumps. After the litter clumps have been deposited inside the waste box, the motor stops and reverses directions so as to return the rake to the rear wall in the same fashion. 
     The waste receptacle can optionally be fitted with a removable tray and/or a disposable liner so that the waste receptacle can be emptied in an easy manner. In addition, a litter pan liner can be provided to fit inside and to protect the interior of the litter pan. Both liners are provided to add additional protection from the corrosive environment of the waste box and litter pan. 
     An upper hood and a lower hood are also provided. The lower hood attaches to the base so as to protect the base and drive assembly from litter scatter, cat hair, cat spray, etc. 
     The upper hood portion attaches to the lower hood portion to provide a cover above the litter pan. The upper hood portion contains a storage compartment located on the top surface to store pet supplies or litter box components such as waste box liners, for example. Additionally, the upper hood portion contains a chamber for housing a filter. A visor portion extends over the waste box to direct odors that are released from the waste box into the upper hood when the waste box is opened. The visor can be detached or retracted when access to the interior is necessary for servicing the litter pan or waste box. After servicing the interior, the visor can be re-attached or expanded so as to be mounted above the waste box. 
     Rake movement is controlled by sensors that detect the presence of a cat or foreign object in the box. In operation, once the user actuates the present litter box by actuating the on/off switch, a power up sweeping cycle occurs after a preset time delay. The rake moves from the “home” position, adjacent to the rear wall of the litter pan toward the waste box. When the rake approaches the waste box, clumps fall off the rake and into the waste box. The motor and belt drive system reverse directions to return the rake to the home position. 
     Once the rake is in the “home” position, sensors located in the litter chamber detect the presence of a cat. Once it is determined that the cat has exited the litter chamber, a delay mechanism delays the sweeping cycle until after a sufficient amount of time has passed to permit the litter clumps to harden. If, after rake movement begins, a cat or foreign object enters the litter box, the sensors will detect the presence and the raking action will stop. In addition, if the rake encounters a clump or pile of litter that is too large for the rake to move through the litter box, the rake will return to the home position until the pet owner manually removes the clump. 
     The delay mechanism provides for setting the cycle delay time after the cat exits the litter chamber. Thus, the pet owner will be able to select the length of the delay time before the sweeping cycle commences in order to allow sufficient time to permit the litter clumps to harden. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front perspective view of the present invention with the hood covering the litter pan; 
         FIGS. 2   a  and  2   b  are an exploded perspective view illustrating the present invention; 
         FIG. 3  is a front perspective view of the litter box illustrating the rake in the storage position with the lower and upper hoods omitted; 
         FIG. 4  is a front elevation view of the rake; 
         FIG. 5  is a front perspective view of the litter box illustrating the rake disposed in the litter pan between the front and rear walls; 
         FIG. 6  is a perspective view of the litter box illustrating the rake on the front wall ramp illustrating the waste box lid opening; 
         FIG. 7  is a front perspective view illustrating the base pan and drive assembly; 
         FIG. 8  is a top plan view of the litter pan illustrating the sensor placement; 
         FIG. 9  is a side view of the rake disposed inside the litter pan showing the angled rake tines; 
         FIG. 10  is a front perspective view illustrating the pan and lower hood spray proof rim; 
         FIG. 11  is a perspective view of the waste box liner; 
         FIG. 12  is an exploded perspective view of the ramp and ramp rug; 
         FIG. 13  is a section view of the ramp and rug of  FIG. 12  taken along the line  13 — 13 . 
         FIG. 14  is an enlarged view of the rug of FIG.  13 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1-3  illustrate self-cleaning litter box  20 . In a preferred embodiment, litter box  20  includes a base  22 , a litter pan  24  for holding a supply of litter, a lower hood  26  and an upper hood  28 . Litter box  20  further includes a rake  30  disposed in litter pan  24 , a rake support assembly  32  to support rake  30 , a drive assembly  34  ( FIG. 7 ) to move the rake while installed in the litter pan, and a waste box  36  to receive waste clumps from litter pan  24 . 
     Referring to  FIGS. 3 and 4 , litter pan  20  is illustrated connected to base  22  with lower and upper hoods  26  and  28  removed. Referring specifically to rake  30 , rake  30  includes a plurality of tines  38  attached to a cross support bar  40 . Cross support bar  40  includes a first end  42  having an offset portion  44  and a second end  46  having an offset portion  48  ( FIG. 4 ) to engage litter pan  24 . Cross support bar first and second ends  42  and  46  each contain a rake arm  50  and  52  to support bar  40  when connected to litter box  20 . Rake  30  is preferably fabricated from a metal material such as stainless steel. It should be realized by one of ordinary skill that tines  38  can be fabricated from any other material, such as plastic, so long as tines  38  have a sufficient strength to rake through litter pan  24  without being deflected or destroyed. Rake  30  is lightweight in order to reduce the load on the motor (described in detail below). This permits a greater volume of litter to be stored inside litter pan  24  without having to increase to size of the motor. Since cats enjoy scratching and digging the litter, a deep litter level is desirable. 
     A protective coating may be used to protect tines  38  in order to reduce or eliminate pitting or other damage to tines  38 . The coating may include, for example, chrome, nylon, or TEFLON®. Furthermore, the coating acts as a barrier to prevent residue from attaching to the rake during operation. Residue collected on rake tines  38  can increase the weight of the rake, which oftentimes can damage the drive motor or even require additional power to move the rake through litter pan  24 . Residue collected on rake tines  38  also prevents the tines from effectively sifting through the litter, causing excess litter to be removed from litter pan  24 . In addition, litter will spread unevenly inside pan  24 . By having a material that contains a high strength to weight ratio, rake tines  38  can be fabricated smaller to reduce the tine surface area contacting the litter. In a preferred embodiment, tines  38  contain a circular cross section; however, it should be realized by one of ordinary skill that any cross sectional shape can be used including square, oval, teardrop, rectangular, triangular, etc. 
     Referring specifically to  FIG. 3 , a rake support  32  supports rake  30  when installed on litter box  20 . Rake support assembly  32  includes posts  54  and  56 , and post supports  58  and  60 . Posts  54  and  56  include end openings  62  and  64  defining entranceways to hollow interiors  66  and  68 . Each post  54  and  56  includes a slot  70  and  72 , respectively, extending longitudinally along the length of each post to receive cross support bar  40 . Rake arms  50  and  52  ( FIG. 4 ) are sufficiently sized so as to slideably engage hollow interiors  66  and  68  respectively. When rake  30  is connected to posts  54  and  56 , gravity acts on the rake to keep the rake mounted inside hollow interiors  66  and  68 . Rake  30  can be removed from rake support  32  in a simple manner and without the use of tools in order to clean or replace the rake as necessary. To remove rake  30 , the rake is lifted so that arms  50  and  52  are removed from posts  54  and  56 . Likewise, to install rake  30 , rake arms  50  and  52  are aligned with openings  62  and  64  and are inserted therein. 
     As seen in  FIGS. 3 and 6 , litter pan  24  includes a bottom wall  74  and spaced apart first and second sidewalls  76  and  78 , an inclined front wall  80  ( FIG. 6 ) and a rear wall  82 , defining a litter chamber  84 . Litter pan  24  has an open top to allow cats to enter and exit chamber  84  and is sized to accommodate multiple cats at one time. Each sidewall  76  and  78  contains a planar surface  86  and  88  extending along the top of the sidewalls to support rake cross support member  40  at offset portions  44  and  48  (FIG.  4 ). As rake  30  sweeps between front and rear walls  80  and  82 , the rake is supported by surfaces  86  and  88 . Planar surfaces  86  and  88  contain elevated sections  222 - 228  to raise rake  30  as it travels between front wall  80  and rear wall  82 . 
     Litter pan bottom wall  74  includes strengthening members  90  extending between litter pan front wall  80  and rear wall  82  to provide additional strength to bottom wall  74 . Members  90  are preferably ribs integrally molded into bottom wall  74  to prevent warping or sagging. In addition, a shoulder  92  extends along sidewalls  76  and  78 . Shoulders  92  are positioned above bottom wall  74  to indicate the litter fill level. Thus, litter can be filled inside chamber  84  until the litter level reaches a height adjacent shoulders  92 . 
     As illustrated in  FIG. 2   b , a pan liner  94  is provided to fit inside and to protect walls  74 - 82  of litter chamber  84 . The liner contains walls  96 - 104  and is preferably vacuum molded with a poly vinyl chloride (PVC) material. However, other materials may be used including those having biodegradable polylactide. Typical prior art litter pan liners are fabricated from a polyethylene bag. These bags are typically attached loosely to the litter boxes and, if used in conjunction with a raking system, the bag can become tangled with the rake tines. A molded liner provides advantages over polyethylene liners because molded liners will not tangle with rake tines  38 . In addition, as cats scratch and dig, the polyethylene liner may become rearranged. By using liner  94 , the pet owner can keep the litter box clean without having to expose litter box  20  to soap, water or other moisture that might damage the electrical components. Also, the vacuum formed liner  94  for litter pan  24  prevents walls  74 - 82  from being scratched and worn from the constant movement of the abrasive litter materials. If walls  74 - 82  become scratched, the walls will tend to hold odor and waste. 
     Referring to  FIGS. 2   b  and  6 , waste box  36  can be seen. Waste box  36  is located adjacent litter pan front wall  80  and contains a bottom wall  106 , a rear wall  108 , a front wall  110 , a pair of sidewalls  112  and  114  and a lid  116  pivotably mounted to hinge  118 . As seen in  FIG. 2   b , waste box  36  and litter pan  24  are illustrated as being integrally molded as one piece; however, it should be realized by one of ordinary skill that waste box  36  can be a separate component attachable to litter pan  24 . As will be explained in greater detail below, as rake  30  travels upward along inclined wall  80  (FIG.  6 ), lid  116  pivotably opens so that litter clumps (not shown) collected by rake  30  during the raking cycle can be deposited inside waste box  36 . Once the litter clumps are deposited inside waste box  36 , the rake returns to rear wall  82  and lid  116  closes to seal any odors from the surrounding area. 
     As illustrated in  FIG. 2   b , waste box  36  can optionally include an inner tray  120  that is removable when cleaning or servicing the waste box. Inner tray  120  includes sidewalls  122  and  124 , end walls  126  and  128  and a bottom wall  130 . Inner tray  120  is configured to be inserted inside waste box  36 . 
     A disposable waste box liner  132 , as illustrated in  FIG. 11 , can be optionally used to protect inner tray  120 , or, if waste box  36  is being used without tray  120 , liner  132  can be used to protect waste box walls  106 - 114 . Disposable liner  132  contains pleated sidewall portions  134  and  136  and end walls  138  and  140  to form a pocket  144  to receive and hold waste clumps. End walls  138  and  140  each contain a strap or handle  146  and  148 . A top wall or flap portion  150  is also included and is sized to connect and to protect the underside of waste box lid  116  from dirt and waste. Flap portion  150  is substantially the same dimension as lid  116  and contains a pocket  152  along the length of the bag to attach to lid edge  116 ′. 
     During installation of waste box liner  132 , handles  146  and  148  allow the user to open the bag so that pleated sidewalls  134  and  136  can open to conform to the width of inner tray  120 , or waste box  36 , if tray  120  is not being used. Sidewalls  134  and  136  and handles  146  and  148  are designed to tuck in and around inner tray  120  after waste box liner  132  is installed. 
     When removing liner  132  from waste box  36 , waste box lid  116  is opened using a handle  154  (best seen in FIG.  6 ). Flap  150  is then disconnected from lid  116  and flap  150  is used to cover pocket  144 . As discussed in further detail below, any litter particulate that may exist between lid  116  and flap  150  will act to hold down the flap over pocket  144  to contain odors inside the pocket. Disposable liner  132  can be removed from waste box  36  by handles  146  and  148 . Upon removal, handles  146  and  148  can then be used to further seal pocket portion  144  by tying the handles together. The liner is a plastic bag, preferably fabricated from polyethylene or a polypropylene material. 
     When closed, waste box lid  116  serves as a step or platform to allow the cat to enter litter chamber  84 . After the cat exits waste box  20 , any litter particulate that is attached to the cat&#39;s paws may eventually collect on waste box lid  116 . To prevent litter particulate from sliding off lid  116  and onto the surrounding floor when lid  116  pivotally opens, waste box lid  116  contains openings  156  to receive the litter particulate. Thus, as lid  116  opens during the raking cycle (FIG.  6 ), any litter particulate that has settled on lid  116  will slide toward openings  156  and into waste box  36 , instead of scattering on the surrounding floor. 
     Referring to  FIG. 7 , base  22  and drive assembly  34  can be seen. Base  22  includes a front wall  158 , a rear wall  160 , and a pair of sidewalls  162  and  164  to house drive assembly  34 . In a preferred embodiment, litter pan  24  rests above and is supported by base  22 . Litter pan  24  covers and encloses drive assembly  34  to insulate operational noises during the raking cycle which also preventing injury to animals or pet owners. In addition, the litter inside litter chamber  84  insulates the noise produced during the raking cycle. 
     Drive assembly  34  includes an electric motor  166 , a first shaft  168  connected to a second shaft  170  by belts  172  and  174 . A belt and pulley system includes belts  172  and  174  that are supported by pulleys  176  located on opposed ends of shafts  172  and  174 . While only pulleys  176  are illustrated attached to belt  172 , it should be realized by those of ordinary skill that the identical configuration can be seen in mirror image on belt  174 . A stabilizer bar  178  attaches to belts  172  and  174  so as to be moved by the belts between walls  158  and  160 . In this configuration, both ends of stabilizer bar  178  travel at exactly the same rate. Stabilizer bar  178  connects to rake post supports  58  and  60  and is operable to move between base front wall  158  and rear wall  160 . In operation, motor  166  drives first shaft  168  that in turn rotates pulleys  176  to move belts  172  and  174 . Motor  166  is a standard DC motor that can be powered by batteries or by standard household electricity. 
     Base  22  includes a groove  180  having groove endwalls  182  and  184  and groove sidewalls  186  and  188 . Groove  180  extends parallel to base sidewalls  162  and  164  and between base front and rear walls  158  and  160 . Groove  180  is sufficiently sized to receive an offset portion  178 ′ of stabilizer bar  178  so that as stabilizer bar  178  travels between front wall  158  and rear wall  160 , offset portion  178 ′ travels inside groove  180 . Groove sidewalls  186  and  188  prevent stabilizer bar  178  from movement in the lateral direction between base sidewalls  162  and  164 . 
     The ends of stabilizer bar  178  extend through slots  198  and  200  and are adapted to connect to rake post supports  58  and  60 . Thus, when rake supports  58  and  60  are connected to stabilizer bar  178 , the stabilizer bar moves rake  30  (when installed) between litter pan front wall  80  and litter pan rear wall  82 . 
     During the raking cycle, stabilizer bar  178  is transported from base rear wall  158  toward forward wall  160  until stabilizer bar triggers a relay  202 . Once relay  202  is triggered, a signal is sent to a microprocessor (not shown) which in turn sends a signal to motor  166  to reverse the direction of stabilizer bar  178  in the direction of base rear wall  158 . If however, relay  202  fails, offset portion  178 ′ will contact groove end wall  182  to prevent the stabilizer bar from traveling further and potentially damaging other components, such as shaft  168  Likewise, as stabilizer bar nears base rear wall  158 , stabilizer bar  178  will trigger relay  204  to send a signal to shut off motor  166 . If relay  204  fails, offset portion  178 ′ will contact groove end  184  so as to prevent further movement of stabilizer bar  178 . 
     Referring to  FIGS. 3 ,  4  and  8 , rake movement is partially controlled by sensors  206  and  208  that detect the presence of a cat or foreign object in the box. Sensors  206  and  208  preferably include infrared photocell detectors that detect when a beam has been disturbed or broken. Sensors  206  and  208  each include a transmitter designated by the letter “T” and a detector or receiver, designated by the letter “R”. As illustrated in  FIG. 8 , transmitter  206 T and receiver  208 R are disposed along litter pan sidewall  76 . A receiver  206 R is also disposed along litter pan sidewall  78  and is aligned with transmitter  206 T. Transmitter  208 T is disposed on sidewall  78  opposite receiver  208 R. Receivers  206 R and  208 R, which detect signals generated by transmitters  206 T and  208 T, operate to detect the presence of a cat or a foreign object within the litter chamber  84 . It should be realized by one of ordinary skill that a greater or fewer number of photo cell detectors can be used if litter chamber  24  is larger or smaller. 
     Transmitters  206 T and  208 T are disposed on opposite sidewalls  76  and  78  to prevent transmitter  206 T from interfering with receiver  208 R and to prevent transmitter  208 T from interfering with receiver  206 R. In this configuration, transmitter  206 T is independent of transmitter  208 T; therefore, when rake  30  enters the beam spread area  206 B for transmitter  206 T, transmitter  208 R will remain operable to detect cats or other obstructions. The same is true when rake  30  enters beam spread area  208 B. In order to permit the litter pan sensors to detect objects in the widest area inside litter chamber  84 , transmitters  206 T and  208 T are spaced apart so that beam spread areas  206 B and  208 B are adjacent each other or have minimal overlap, as seen in FIG.  8 . 
     In operation, the user supplies power to litter box  20  by actuating an on/off switch (not shown). An initial “power up” rake sweep cycle begins after a set time delay. Rake  30  begins the sweep cycle by moving from the “home position,” located adjacent litter pan rear wall  82  (FIGS.  3  and  9 ), and continuing through the middle portion of litter chamber  84  ( FIGS. 5 and 9 ) toward inclined front wall  80 . During this time, any litter clumps (not shown) present in litter chamber  84  are pushed toward inclined front wall  80 . Once rake  30  reaches inclined front wall  80 , rake  30  pushes the litter clumps (not shown) upward along inclined front wall  80 , as best seen in FIG.  6 . As rake  30  travels upward along inclined wall  80 , lid ramps  210  and  212  engages rollers  214  and  216 , located on ear ears  218  and  220 . Ears  218  and  220  are attached to waste box lid  116  so that as rollers  214  and  216  travel upward along lid ramps  210  and  212 , lid  116  will pivotably open. During this time, cross member  40  is pushed upward by planar surface ramps  222  and  224  so that rake arms  50  and  52  ( FIG. 4 ) raise inside and slideably engaged hollow interiors  66  and  68 . As rake  30  travels to the uppermost portion of inclined wall  80  and planar surface ramps  222  and  224 , the litter clumps will fall off rake  30  into the waste box  36 . Movement of rake  30  is terminated at the top end of inclined front wall  80  when the position of stabilizer bar  178  is detected by relay  204  (FIG.  7 ). When relay  204  is triggered, a signal is sent to a microcontroller which in turn sends a signal to motor  166  to reverse directions to move rake  30  to the “home” position (FIG.  3 ). Upon approaching litter pan rear wall  82 , movement of rake  30  is terminated when the stabilizer bar position is detected by relay  202  (FIG.  7 ). 
     As seen specifically in  FIG. 9 , tines  38  are angularly disposed with respect to rake arms  50  and  52 . This angled configuration permits the waste clumps to gravitally fall from rake  30  into waste box  36 . 
     Referring back to  FIG. 3 , sidewall planar surfaces  86  and  88  include ramps  226  and  228  which are inclined to lift rake  30  upward as the rake approaches litter pan rear wall  82 . In addition, litter pan bottom wall  74  includes a ramp  230 . This configuration ensures that rake  30  can continue to travel to and from the home position to overcome the natural buildup of litter that occurs adjacent rear wall  82 . Litter buildup occurs as a result of rake  30  traveling to the “home” position. In addition, at the commencement of the raking cycle, the inclined planar surface ramps  226  and  228  and bottom wall ramp  230  enable rake  30  to gradually dig “down” into the litter as rake  30  travels toward inclined front wall  80  along ramp  230 . Ramps  226  and  228  are sufficiently sized to raise rake  30 ; however, tines  38  still remain below the top surface of the litter level. 
     After the initial power up sweep, as described above, litter box  20  is ready for use. When the cat enters litter chamber  84 , sensors  206  and/or  208  detect the presence of the cat. Once sensors  206  and/or  208  detect that the cat has exited litter chamber  84 , a signal is sent to a timer to delay the commencement of the sweeping cycle after a predetermined delay period. A switch  232  ( FIG. 7 ) can be optionally provided to allow the pet owner to determine the predetermined length of the delay period before commencing the sweeping cycle. In a preferred embodiment, switch  232  is a three position switch that allows the pet owner to set the delay period for either ten, fifteen or twenty minutes as some litter clumps require different time lengths to sufficiently harden before being swept by rake  30 . In the alternative, a remote control  280  ( FIG. 1 ) can include a switch  232  to permit the pet owner to select the predetermined delay period. When the delay period expires, sensors  206  and  208  confirm that no cat or foreign object is present in litter chamber  84 . If a cat or foreign object is detected, raking operation will not start. If no cat or foreign object is detected, rake moves forward until reaching waste box  36 . Upon reaching waste box  36 , rake  30  stops to permit the litter clumps to fall inside waste box  36 . After a short period of time elapses, rake  30  then reverses directions, as previously described, and returns to the “home” position (FIG.  3 ). During the raking cycle, sensors  206  and  208  continue to detect whether a cat or foreign object has entered litter chamber  84 . If, during the raking cycle, a cat or foreign object is detected, the raking sequence stops until the cat or foreign object is no longer in litter chamber  84 . 
     A motor load sensor (not shown) will detect if rake  30  encounters a waste clump or pile of litter that is too great to be moved by the rake. Motor load sensor operates by monitoring the load on motor  166  such that when the load across the motor reaches a predetermined value, a signal will be sent to the microcontroller which in turn sends a signal to reverse the direction of motor  166  to return rake  30  to either litter pan front wall  80  or litter pan rear wall  82 , whichever is in the reverse direction of the path. Rake  30  will then reverse direction and travel toward the waste clump in an additional attempt to move the clump. If after multiple attempts the clump cannot be moved, the pet owner will be alerted that litter box  20  requires maintenance. 
     As can be best seen in  FIG. 9  rake tines  38  extend downward and are located adjacent bottom wall  74 . A slight gap G extends between tines  38  and bottom wall  74  to prevent rake from scratching floor  74 . However, gap G should be a minimal distance so as to prevent litter clumps from remaining inside the bottom of litter chamber  84 . 
     As seen in  FIG. 10 , lower hood  26  is installed to surround litter pan  24 . Hood  26  includes a forward wall  234 , a pair of sidewalls  236  and  238 , and a rear wall  240  to surround and protect litter pan  24  and base  22 . Lower hood  26  is mounted on hood supports  242  and  244  and is locked to base  22  with latch  246  (additional hood supports  242  and  244  and latch  246  are also located in mirror image along sidewall  236 ). 
     As can be seen, lower hood sidewalls  236  and  238  conceal rake supports  58  and  60 , posts  54  and  56 , and lid ramps  210  and  212 . By concealing these moving elements, the litter box  20  is maintained clean and better protected from litter, cat hair, spray, etc. 
     Interior sidewalls  248  and  250  and rear wall  252  are a sufficient height above litter pan  24  to protect the areas surrounding the litter pan from litter scatter and cat spray. In addition, a rim  254  extending along interior walls  248  and  250  cover cross member offset portions  44  and  48  (offset portions best seen in FIG.  4 ). A rim  256  also extends along rear wall  252 . Rims  254  and  256  reduce spray and litter scatter that may damage the moving elements described above. 
     In addition to reducing litter scatter and spray, rims  254  prevent rake  30  from rising above and separating from planar surface  86  and  88 . During the raking cycle, rake  30  tends to rise up as it moves through the litter. Thus, the shape of rims  254  correspond to the shape of planar surfaces  86  and  88  and are sufficiently spaced apart such that cross support bar offset portions  44  and  48  can be placed between rims  254  and planar surfaces  86  and  88 . This prevents rake  30  from rising above planar surfaces  86  and  88  during the raking cycle. Latches  246  are used to secure lower hood  26  to base  22  to prevent rake  30  from pushing hood  26  upward. 
     When it is desired to remove rake  30  from litter box  20 , lower hood  26  is detached from base  22  by unlocking latches  246 . Once unlocked, lower hood  26  is lifted away from base  22  thereby exposing rake offset portions  44  and  48  being connected to rake supports  32 . As previously explained, rake  30  is lifted so that arms  50  and  52  are removed from posts  54  and  56 . To install rake  30  in litter box  20 , rake arms  50  and  52  are aligned with openings  62  and  64  and inserted therein. Hood  26  is then re-attached to base  22  and locked by latches  246 . 
     As seen in  FIGS. 1 and 12 , an entrance ramp  258  can be attached to litter box  20  to allow a cat to easily enter and exit litter chamber  84 . Ramp  258  is removable such that litter box  20  can be used with or without the ramp. A rug  260  can be used to overlay ramp  250  to catch any litter that is spread when the cat exits litter chamber  84 . 
     Referring to  FIGS. 13 and 14 , rug  260  includes a backing layer  262  and a twisted fabric loop material  264  attached the backing layer. Twisted fabric loop material  264  is preferably a twisted cotton loop that is approximately 1-1.25 inches in length. Twisted loops  264  are spaced apart such that litter can be trapped between each fabric loop material  264 . This prevents litter from scattering on the surrounding floor area. Alternatively, twisted fabric loop material  264  may be substituted for twisted, but non-looped material, if desired. 
     Rug backing  262  contains a plurality of elastic loops  266  ( FIG. 12 ) attached to backing  262  so that rug  260  can be easily attached to hooks  268  on ramp  258 . In addition to being attachable to ramp  258 , rug  260  can be sufficiently sized overlay the floor area surrounding or adjacent to litter box  20 . Multiple sections can be attachable together, using a hook and pile fastener for example, to protect the surrounding areas. 
     Referring back to  FIGS. 1 and 2   a , upper hood  28  is used to cover litter pan  20 . It should be realized by one of ordinary skill that litter box  20  can be used without upper hood  28  if it is desired to operate as a “non-hooded” or an “open” litter box. Hood  28  includes a removable visor portion  270  located above waste box  36 . Visor portion  270  extends over waste box  36  so that as waste box lid  116  opens, odors will be directed by visor portion  270  into hood  28 . A filter  272  is mounted to hood  28  toward the rear portion of litter box  20 . Thus, odors that rise from litter chamber  84  or those that are released from waste box  36 , when open, can be filtered by filter  272 . The filter is most preferably a polyester substrate with charcoal and zeolite particles stored in a polyethylene bag. 
     Visor portion  270  can be completely detached from hood  28  (as seen in  FIG. 2   a ) to allow access to waste box  36  without detaching hood  28  entirely from litter box  20 . In the alternative, visor portion  270  can be pivotably mounted to hood  28  so that it remains attached at all times; thus when it is desired to access waste box  36 , visor portion  270  can be pivotably opened. Visor portion  270  is preferably fabricated from a translucent or transparent, but slightly tinted material, so that the consumer can view litter chamber  84  while also providing the cat sufficient privacy. 
     In addition, hood  28  includes a storage compartment  274  that is sized to receive and store pet supplies such as replacement waste box liners. Storage compartment  274  contains a lid  276  that can be opened for easy access inside storage compartment  274 . The pet owner can remove lid  276  to gain access inside interior  274  by using finger grips  277  to completely lift lid  276  away from hood  28 . Hood  28  also can optionally include a storage compartment or receiving area  278  for holding remote control  280  ( FIG. 1 ) to operate litter box  20 . 
     Other alterations and modifications of the invention will likewise become apparent to those of ordinary skill in the art upon reading the present disclosure, and it is intended that the scope of the invention disclosed herein be limited only by the broadest interpretation of the appended claims to which the inventors are legally entitled.
A rake for a litter box for collecting pet excrements, the litter box containing a bottom surface, a front wall, a rear wall, a first and second sidewall to define a litter chamber for holding a supply of litter, the rake includes a bar having first and second ends and extends from the first sidewall to the second sidewall and is movable between the front and rear walls. The bar includes a plurality of tines. A rake support is attached to the bar for supporting the first and second ends of the bar for slideable movement between the front and rear walls. A rake arm is connected to the first and second ends of the bar for slideably engaging the rake supports, such that said bar is selectively connectable to the rake supports without using fasteners.