Abstract:
A self-cleaning litter apparatus that separates and extracts clumped litter waste material from litter material contained therein during use includes a chamber adapted to contain a quantity of litter material. The chamber is rotatable about a centrally disposed axis. A rake is disposed within the chamber. The rake is rotatable about an axis which is spaced apart from the chamber axis. A drive assembly is provided for simultaneously rotating the chamber about the chamber axis and for rotating the rake about the rake axis. The rake sweeps through the litter material while clumped litter waste material is directed toward the rake by rotation of the chamber to thereby separate clumped litter waste material from the litter material in the chamber, collect the separated clumped litter material in the rake and extract the separated clumped litter material from the chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Divisional of U.S. patent application Ser. No. 10/967,613 filed Oct. 18, 2004 now U.S. Pat. No. 7,017,519 and entitled “Self-Cleaning Pet Litter Apparatus and Related Method.” 
    
    
     TECHNICAL FIELD 
     The present invention pertains to litter boxes for use by animals, typically cats. More particularly, this invention is directed toward apparatus which operates in a self-cleaning fashion, either automatically or manually, to remove waste materials deposited in the litter, thereby obviating the need for frequent and periodic service by the animal&#39;s owner. 
     BACKGROUND OF THE INVENTION 
     Domestic pets, particularly cats, typically utilize a litter box for their waste needs. Such litter boxes fall into two categories, the totally manual pan or container which carries a quantity of litter and the automatic or self-cleaning variety, which also carries a quantity of litter. The present invention pertains to the latter category and the patent literature does include a variety of such devices. U.S. Pat. No. 6,568,348, for instance, is directed to a circular litter device that extracts waste from litter material by rotating a rake or the chamber. Due to rotation of the rake or chamber, solid waste is extracted from the litter material using tines, and such waste is pushed to the outer perimeter of the chamber. The curvature of the rake allows the rake to cooperate with a scoop, which simultaneously removes solid waste from the rake and retracts into a tunnel, as the rake passes thereby. 
     U.S. Pat. Nos. 6,401,661 and 6,234,112 are both directed to a self cleaning pet litter box. The pet litter container is rotatably mounted on a base member, and rotates to move the pet litter over a sieve. The sieve is ramped shaped and therefore, clumped portions of the pet litter that are not sifted through its openings are forced upwardly toward a conveyer. The conveyer serves to carry the clumped portions of pet litter away from the pet litter container. 
     U.S. Pat. No. 6,286,459 is directed to a litter container with a rotary movement sieve. The sieve is attached to a rotatable ring around the upper portion of a container. As the sieve rotates, clumped portions of solid waste are captured thereon. Since the sieve is removable, the sieve, and the clumped portions of solid waste can be removed from the container. 
     U.S. Pat. Nos. 6,082,302 and 5,447,812, are both directed to a rectangular litter device that extracts waste from litter material using a comb that traverses the pan lengthwise, eventually conveying waste clumps into a receptacle at the front of the device. 
     U.S. Pat. No. 4,574,735 is directed to a circular litter device that extracts waste from litter material using a rake which sweeps through a circular chamber. In this device, the waste material is deposited into a container which is rotated to sanitize and deodorize the contents. 
     The foregoing automatic litter devices have provided a variety of styles and mechanisms to facilitate periodic cleaning of the litter. Nonetheless, the apparatus of the present invention provides a novel approach to the design and operation of such devices by providing a single drive mechanism for the operation of all moving elements as well as other features not present in combination in a single device heretofore. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a self-cleaning litter apparatus that separates and extracts clumped litter waste material from litter material contained therein during use is provided. The litter apparatus includes a chamber adapted to contain a quantity of litter material. The chamber is rotatable about a centrally disposed axis. A rake is disposed within the chamber. The rake includes a plurality of tines for receiving clumped litter waste material from the litter material and for extracting the clumped litter waste material from the chamber. The rake is rotatable about an axis which is spaced apart from the chamber axis. A drive assembly is provided for simultaneously rotating the chamber about the chamber axis and for rotating the rake about the rake axis. The rake sweeps through the litter material while clumped litter waste material is directed toward the rake by rotation of the chamber to thereby separate clumped litter waste material from the litter material in the chamber, collect the separated clumped litter material in the rake and extract the separated clumped litter material from the chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view depicting the self-cleaning litter apparatus of the present invention; 
         FIG. 2  is an exploded isometric view of the self-cleaning litter apparatus of the present invention; 
         FIG. 3  is an isometric view depicting the underside of the self-cleaning litter apparatus of the present invention; 
         FIG. 4  is an isometric view depicting the underside of the litter pan; 
         FIG. 5  is a partial isometric view depicting the turntable of the self-cleaning litter apparatus; 
         FIG. 6  is an isometric view depicting the underside of the turntable; 
         FIG. 7  is a partial isometric view depicting the base of the self-cleaning litter apparatus and related components for driving the turntable; 
         FIG. 8  is a side elevation of a weight sensor, depicted over the contact rails carried in the base; 
         FIG. 9  is an isometric view of a weight sensor, depicted over the contact rails carried in the base; 
         FIG. 10  is another isometric view depicting the underside of the turntable and the drive mechanism, with portions of the apparatus removed for clarity; 
         FIG. 11  is a cross-sectional view of the apparatus, depicting the base, turntable, litter pan and rake assembly; 
         FIG. 11A  is an enlarged cross-section of the area  11 A, depicted in  FIG. 11 ; 
         FIG. 11B  is an enlarged cross-section of the area  11 B, depicted in  FIG. 11 ; 
         FIG. 11C  is an enlarged cross-section of the area  11 C, depicted in  FIG. 11 ; 
         FIGS. 12–16  are isometric views of the litter apparatus of the present invention, depicting the rake sequentially moving from rest, through the litter pan, out of the litter pan and depositing waste litter material into the receptacle; 
         FIG. 17  is a partial isometric view, depicting the rake assembly; 
         FIG. 18  is a partial isometric view, looking from the front of the apparatus, depicting the rake assembly in relation to the cam member for rotation of the rake; 
         FIG. 19  is a partial isometric view, looking down and from the rear side of the apparatus, depicting the rake assembly in relation to the cam members for rotation of the rake and lifting the cover on the receptacle; 
         FIG. 20  is a partial isometric view, similar to  FIG. 18 , with components removed to reveal the drive mechanism and the rake assembly; 
         FIG. 21  is a side elevation of the rake assembly, separately from the apparatus and the drive mechanism positioned beneath the base; 
         FIG. 22  is a partial isometric view, looking down and from the rear side of the apparatus, depicting the rake assembly and the rake at rest; 
         FIG. 23  is a partial isometric view, looking down and from the rear side of the apparatus, depicting the rake assembly and the rake at rest; 
         FIG. 24  is a partial isometric view, looking from the rear side of the apparatus, depicting the rake assembly and rake at rest with the receptacle cover closed; 
         FIG. 25  is a partial isometric view, similar to  FIG. 24 , with the receptacle cover opening for receipt of litter waste; 
         FIG. 26  is a block diagram of the control and sensors for the litter apparatus; and 
         FIG. 27  is a block diagram of the weight sensing mechanism. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIGS. 1 and 2 , a self-cleaning litter apparatus according to the present invention, is depicted generally by the numeral  30 . It includes a main base, generally  31 , which carries a turntable, generally  32 , a litter pan, generally  33 , received onto the turntable, a shield  34 , a hood  35 , a rake assembly, indicated generally by the numeral  36 , a waste receptacle  37 , a housing  38  for the drive mechanism, which will be described subsequently and a ramp  39 , which may optionally provide a mat  40 , for the purpose of cleaning litter from the pet upon exiting the apparatus. Of these components, the hood  35  and the ramp  39  are both optional, as the self-cleaning features of the apparatus do not require the presence of either component. In order to aid in manufacturing, while providing strength and reasonable cost, the various components are manufactured from a conventional thermoplastic, such as ABS or a polyolefin, such as polyethylene or polypropylene. Other components, such as the internal gears can be manufactured from nylon. 
     The hood  35  provides a domed top  41  which terminates in an outwardly extending annular flange  42 . A recess  43  is provided in the top  41  for receipt of an air filter element  44 , which is removable from the underside of the hood. A handle  45 , is molded into the top over the recess. The front of the hood  35  provides an opening  46 , through which the cat, or other domestic pet, enters and leaves the litter apparatus. 
     The shield  34  is removable, lifting off of the litter pan  33 , when the latter is to be cleaned. It comprises a truncated annular flange, the outer wall  47  of which frictionally engages the inner wall  48  of the hood  35 . The outer wall  47  is recessed, to provide an opening  49 , extending across less than one-half of the front of shield  35 , to allow for movement of the rake assembly  36 , as will be described later. 
     The litter pan  33  includes a body  50  having a circular base  51 , a continuous upwardly extending sidewall  52 , terminating in an outwardly extending annular flange  53 . In  FIG. 7 , the bottom of pan of  33  is depicted, showing the underside  54  of base  51 . Underside  54  provides a several projections at various positions. A coupling, generally  55 , is centrally located and includes a ring  56  encompassing a recess  58 , for receipt of a hub-spindle assembly, generally  59 , carried centrally of the turntable  32 . Radiating outwardly from the ring  56  are a plurality of fins  60 , which mate with the spindle, as will be described in greater detail below, so that as the turntable  32  is rotated, the litter pan  33  is likewise rotated. 
     Radially outwardly of the coupling  55  are a plurality of feet  61 , which are received in foot wells  62 , provided in the floor  63  of the turntable  32  ( FIG. 5 ). Radially outwardly of the feet  61  are a plurality of buttons  65 , which engage weight sensors, generally  66 , which are carried by the turntable  32 . 
     The turntable  32  is depicted in  FIGS. 5 ,  6 , and  10  to which reference should be made next. Beginning with  FIGS. 5 and 6 , the turntable is generally dish shaped and has a raised central floor  63  which extends over a major portion of the diameter. It terminates with downward sidewall, which forms the inner wall  70  of an annular trough  71 , beneath the floor. The trough continues to an outer wall  72 , which extends upwardly to join an outer rim  73 , slightly lower than the floor  63 . An outer ring wall  74  extends upwardly from the rim  73 , terminating in an upper face  75  and upstanding peripheral rim  76 . On the outside of outer ring wall  74 , a ring gear  78  is formed, which allows the turntable to be rotated. 
     In  FIG. 6 , the turntable is viewed from its underside, where it can be seen that the trough  71  has a plurality of discontinuities, each extending partially upwardly within the trough providing platforms  80 , each carrying a weight sensor  66 . As depicted in the drawing, six such platforms  80  are shown, although the turntable could be modified to provide more or less than six so long as a sufficient number are present to sense the weight of an animal in the litter pan, which will be explained hereinbelow. Returning to  FIG. 5  and the upper side of turntable  32 , the foot wells  62  in central floor  63  are coplanar with the trough  71  and are bounded by leading and trailing ramps,  81 ,  82 , which help orient the placement of the litter pan  33  and engagement of the feet  61  in the wells  62 . 
     At the center of the turntable, is the hub-spindle assembly  59 , comprising a hub  85  and a spindle  86 . The hub  85  is a small diameter cup which extends from and below the turntable floor  63  and terminates in a raised shelf  88 , also beneath the plane of the floor  63 . The spindle  86 , depicted in  FIG. 11B , provides two intersecting semi-elliptical members  89  which terminate in a rounded end upon which the recess  58  in the coupling member  55  of litter pan  33  rests, so as to be tiltably rotatable thereon. The members  89  are carried by a platform  90  and extending downwardly therefrom are four fingers  91  disposed at 90° angles from each other. The spindle fingers  91  are snapped into an open base hub  92 , formed in the floor  93  of main base  31  (see  FIG. 3 ). 
     The fingers  91  have outwardly extending flanges  94 , which lock against the bottom edge  95  of base hub  92 . As also shown in  FIG. 11B , a screw  96 , carrying a spacer  98  is driven into the central body  99  of spindle  86 , which urges the fingers  91  into engagement with the base hub  92 . In this manner the turntable  32  is fastened to the base and can likewise be disassembled by first removing the screw  96 . To aid rotation of the turntable  32  over the base hub  92  of the base  31 , a washer  100  is interposed. 
     The floor  93  of main base  31  is partially depicted in  FIG. 7  and in cross-section in  FIG. 11 , to which reference should be made next. Generally, the floor  93  is molded to allow for the turntable  32  to rotate freely therein, the latter having been mounted therein as previously described. In addition, the base also provides two other mechanisms—one to assist rotation of the turntable and one that works as part of the weight sensing mechanism, which will be described subsequently. The base has an exterior wall  103 , for appearance and enclosing the drive mechanism. 
     As clearly depicted in  FIGS. 7 and 11A , the floor  93  of main base  31  carries an annular trough  104 , near its periphery. Radially outwardly from the trough  104  is a raised shelf  105 , which extends to the inner wall  106  of base  31 . A plurality of wheels  108  are fit into recesses  109  in shelf  105 , each said wheel being rotatably mounted about an axle  110 , pressed into a mating well  111  carried in the underside of shelf  105 . The wheels  108  protrude outwardly from the shelf  105 , as depicted in  FIG. 7 , where they will periodically engage the outer edge  112  of annular trough  71  (see the underside of turntable  32 ) to keep it centered and supported about the spindle  86 . The number of wheels is not crucial to the operation of the apparatus, so long as they are equally spaced about the circumference. Typically, four wheels are adequate. 
     A like plurality of rollers  113  are carried in semi-cylindrical recesses  114 , in the shelf  105 . The rollers reduce friction between the turntable  32  and main base  31  as the turntable is rotated therein. The combined support and centering can be seen schematically in  FIG. 10 , where the main base has been removed from view, leaving the rollers  113  and wheels  108  in place against the underside of turntable  32 . Again, the number of rollers  113  is not crucial to the operation of the apparatus, so long as they are equally spaced about the circumference. Typically, eight rollers are adequate. Together, the rollers and wheels provide a supporting and centering mechanism, indicated generally by the numeral  115 , for the turntable  32 . 
     The weight sensing mechanism is indicated generally by the numeral  120  and it includes the weight sensors  66  and a track assembly, generally  121 . Referring to  FIG. 7 , the track assembly comprises a pair of electrically conductive outer and inner rails  122 ,  123 , respectively. The rails are mounted in the annular trough  104 , which is formed into a raised shelf  125 , and extends upwardly from the floor  93  of the base  31 . Spacers  126 , made from plastic or other non-conductive material, are located periodically around the shelf  125  in a number sufficient to maintain the rails parallel to each other. The spacers are suitably fastened within the trough  104  by screws, not shown, passing though apertures  128  and their width forces the opposed rails against the walls of the trough so as to remain immovable therein. An end of the outer rail  122  is bent and passes through an aperture  130  in the base to the underside and is connected electrically to a power source (not shown). The opposite end of rail  122  is brought around the trough  104  and into contact with the beginning end. In similar fashion, an end of the inner rail  123  is bent and passes to a shield  131 , where a wire (not shown) is connected, fed around tab  132  and through aperture  133  in the base to the underside for connection to the power source. The opposite end of rail  123  is brought around the trough  104  and into contact with the beginning end. 
     The weight sensors  66  are depicted in  FIGS. 8 and 9 . Each sensor comprises a body  135 , an opposed set of conductive spring feet  136 ,  138  and a compression spring  139 . The body, in turn, is formed of two pieces, a head  140 , having a square shaft  141 , extending downwardly therefrom, and a T-shaped base  142 , also square and which terminates in a cross-wise foot  143  (see  FIG. 11A ). The T-shaped base  142  is assembled from beneath the turntable  32 , though a square aperture  144  ( FIG. 6 ) and the head  140  is positioned from above the turntable after first installing the compression spring  139  about the shaft  141 . The shaft  141  is fit within an accommodating passage formed in the base  142 . Finally, the spring feet  136 ,  138  are connected by way of a flat shoe  145 , of plastic or similar material, with a screw  146  which joins the shoe  145  to the base  142  and finally to the shaft  141 . The shoe  145  is wider than the aperture  144  and prevents the sensor  66  from being removed from the turntable  32 . 
     Two installed sensors  66  are depicted in  FIG. 5 , each being positioned on a platform  148  raised up within the trough  71 . With reference to  FIGS. 11C and 11A , the turntable  32  is presented, in cross-section, resting upon the rollers  113  and centered among the wheels  108 . The buttons  65 , carried on the underside of the litter pan  33  are depicted in contact with the head  140  from a sensor  66 . In the positions shown the two make contact, however, the head has not been forced down, which would result in the spring feet  136 ,  138  contacting the rails  122 ,  123 . When the apparatus  30  is not occupied by an animal, this is the normal or operational condition. The pan is balanced on the spindle  86 , as previously described and is either stationary, or rotating during self-cleaning. Typically, a cleaning cycle is activated automatically after the expiration of a pre-set time, for instance, 30 minutes following the last activity in the apparatus. This ensures first that the pet has not decided to return and second, that the self-clumping litter has adequate time to solidify liquid waste, so that it can be readily removed from the litter as a solid mass. 
     At such time, the drive mechanism will be activated to clean the litter, as will be described hereinbelow. In operation, the weight of the animal in the pan is sufficient to cause it to tilt slightly about the spindle  86 , e.g., approximately 2°, which causes one of the buttons  65  to engage an opposed head from sensor  66 . If the buttons  65  are not employed on the pan  33 , the pan may be required to tilt a little more until the underside of the pan is brought into contact with the head of a sensor  66 . Contact with the head  140  causes the feet to make contact with the rails which sends a signal to a controller. 
     With reference to  FIG. 7 , the inner wall  106  of base  31  is shown, as is a port  150 , through which a drive gear  151  partially extends, sufficient to engage ring gear  78  from the turntable  32  and thereby cause rotation of the turntable and litter pan  33 , carried thereon. The drive mechanism will be described subsequently but at this point it is sufficient to note that when gear  151  is rotated counter clockwise, when viewed from above, the turntable will rotate in a clockwise direction, which begins and continues during a self-cleaning cycle. Concurrent with such rotation of the litter pan  33 , the rake assembly  36  is driven in a clockwise direction through the litter in the rotating pan and eventually to deposit waste material into the waste receptacle of the apparatus, indicated generally by the numeral  37 . The receptacle provides a separate container  153 , having a floor  154  and a hinged door  155 , which is automatically opened during a self-cleaning cycle. 
     With reference next to FIGS.  1  and  12 – 16 , the operation of the apparatus during a self-cleaning cycle will be discussed. For the sake of clarity no litter has been depicted in the litter pan  33 . As is common in self-cleaning litter apparatus, a self-clumping litter is recommended and it operates by clumping liquid waste, e.g., urine, into a single mass, which can then be scooped away, much the same as solid waste. In  FIGS. 1 and 12 , the apparatus  30  is at rest. In this position, the tines from the rake  160  are almost contacting the bottom  51  of litter pan  33 , where they are submerged in the litter to scoop beneath any clumps of waste material. 
     As the apparatus is cycled, which can either be controlled to operate automatically within a pre-set time of non-activity by the pet or, upon activation manually by the pet owner, the pan  33  is moving in its clockwise rotation and the rake assembly  36  is also moving in a clockwise fashion, arcuately across and through the pan. The assembly  36  moves from a rest or parked position, against the inner wall  161  of the shield  34 , near the opening  48 , proceeding in a countercurrent fashion through the litter, as depicted in  FIG. 13 . In  FIGS. 12–16 , the door  155  has been removed for clarity and a door pusher  162  is shown. Its movement will be described subsequently. In  FIGS. 12 and 13 , the door pusher has not begun to move and thus, the door  155  remains closed. In  FIG. 14 , as the rake assembly  36  continues its sweep through the litter, the door pusher  162  has begun upward movement, that is, it rotates from the entrance side  163  of the container, adjacent the shield  34 , toward the opposite, hinged side  164  of the container. As this occurs, the door  155  (not shown) which rests on the pusher is likewise beginning to lift, opening the receptacle. 
     In  FIG. 15 , the rake  160  has lifted out of the litter pan  33  and has rotated upon its axis to hold waste clumps within the rake  160  and door pusher  162  has moved further upwardly. Finally, in  FIG. 16 , the rake has first moved directly over the receptacle  37  and then rotated all the way upon its axis, allowing gravity to free the waste and waste clumps from the tines and fall into the open container  153 . The door pusher  162  is in its highest position and the door  155  will be completely open. At the end of this forward or first part of the cycle, the motor driving the mechanism is reversed, causing the retraction of the rake back into the litter pan, beneath the litter to its original resting position. While this reversal of the rake proceeds, the turntable is also reversed, to rotate counter-clockwise as the rake  160  moves downwardly through the litter and the door  155  is allowed to close. 
     While the foregoing explanation has referred to rotations in clockwise and counter-clockwise directions, such orientations are only applicable to the apparatus as shown in the drawings. Accordingly, it is to be understood that the specific directions of rotation do not constitute limitations on the practice of the present invention, as it will be appreciated that an apparatus manufactured as a mirror image of the apparatus  30 , would operate in the opposite directions, as the pan and rake moved first from the parked position and later returned to the parked position. 
     In order to ensure that waste and waste clumps are driven toward the tines, several stationary tines  165  are provided from an extension  166  provided radially inwardly from the opening  148  in the shield. As the pan  33  rotates, any clumps that were deposited or formed near the inner wall  168  of the pan will, upon rotation in clockwise fashion, be driven radially inwardly upon contacting the stationary tines  165 , where they will be in a path to be scooped away by the rake assembly  36 . As will become apparent subsequently, the turntable and pan rotate at a significantly higher rpm than the counter rotation of the rake assembly. In this manner, essentially all of the waste material is driven into the path of the oncoming rake assembly before it actually makes its complete pass through the litter. Generally, it is preferred to have the pan rotate at approximately three and one-half times the arcuate rotation of the rake assembly  36 , although ratios greater than or less than 3.5:1 are not necessarily precluded. What is important is that the ratio be high enough so that all or most of the waste material meets with the rake for removal from the pan. 
     Next, the rake assembly shall be described with specific reference to  FIG. 21 , which depicts a skeletonized structure of the rake assembly  36 , which resides on the upper side of the apparatus  30  and the drive mechanism, indicated generally by the numeral  170 , which is housed in the main base, more particularly, in the drive housing, indicated by the numeral  38 . To protect the pet as well as the owner, the moving parts of the drive mechanism are located in the lower, inside portion of the main base, as depicted in  FIG. 20 , where the various components of the apparatus have been removed to reveal the relationship between the assembly  36  and mechanism  170 . 
     The rake assembly  36  provides a central steel shaft  172 , hexagonal in cross-section for the various components it carries. Beginning at the left end, as viewed in  FIG. 21 , the rake holder  173  is attached, which carries the rake  160 , discussed hereinabove. The rake holder is semi-arcuate, of a lesser diameter than the shield  34 , in order to fit closely to the inside wall  161  when the rake holder is in its parked or rest position. The tines of rake  160  are affixed to the underside of the holder and project straight down to almost the face  51  of litter pan  33  where they are then bent forward, parallel to the pan to form a flat scoop  174  (see  FIG. 25 ). Several lateral tines  175  are affixed to the outermost end tine, to prevent waste materials from falling off the end of the scoop. The rake holder  173  is firmly joined to the shaft  172 , with the rake lock  176 . The rake holder can provide a bayonette-type of fitting to the shaft so that twisting the rake lock one-half turn will release the rake holder from the shaft for cleaning purposes as well as disassembly of the basic components of the apparatus. 
     The next component on the shaft is a small wheel  178 , which is held in place with an e-ring  179 . Adjacent the wheel is a small cam  180 , followed next by the upper main driving shaft  181 . A torsion spring  182  encircles the shaft  172  next and its two legs (not shown) are connected, one into the back of upper main driving shaft  181  and the other into a hole in shaft  172 , biasing the shaft to rotate in clockwise fashion, as viewed in  FIG. 21 . Immediately adjacent the spring  182  is another e-ring  183 , which holds a large wheel  184  in place on the shaft and at the far end of the shaft, is a key cam wheel  185 . 
     The upper main driving shaft  181  has a circular plate  190  at its midsection and a cylindrical base  191 , into which a vertical, hexagonally-shaped steel shaft  192  is located. The base member  191  passes through an aperture in rake assembly base  193 , as depicted in  FIG. 19 , the circular plate  190  providing a bearing surface for the rotation of upper main drive shaft  181  and related components upon the rake assembly base. The rake assembly base, in turn, is fastened to the upper floor  194  in drive housing  38  (see  FIG. 22 ) and is accessible when the cover  195  ( FIG. 1 ) is unfastened from housing  38 . Beneath the rake assembly base and the floor  194 , the lower main driving shaft  196  is attached to the steel shaft  192 , which is visible in  FIG. 23 , where the floor  194  has been removed. 
     Returning to  FIG. 21 , the drive mechanism  170  provides a series of intermeshing gears as follows. Gear  151 , at the far left of the drawing is the gear that drives ring gear  78  beneath the turntable  32 . Meshing with it are gears  200  and  201 , journalled to the same shaft  202 . Gear  201  meshes with upper drive gear  203 , which is driven by a motor  204 , which is affixed to a mount  205 , provided on upper gear housing  206 , depicted in  FIG. 25 . A suitable motor is of the type usually found in cordless screw drivers, which are 12 volt, and run at approximately 10,000 to 12,000 rpm. A current source of such motors is Mabuchi or Gold Effort. Of course, other motors can be employed and may require a different ratio of gears. The motor is powered by a conventional 12 volt transformer and a power output jack can be plugged into a suitable receptacle, provided on the exterior of the main base  31 , as at  199  (see  FIGS. 22 and 25 ). As such means are well understood in the art, the transformer and related wiring necessary to operate the apparatus  30  have neither been depicted nor, described herein. Of course, the apparatus  30  could be provided with a battery compartment and battery, as an alternative source of power. Such devices are well known in the art and have not been depicted herein. 
     Beneath upper drive gear  203  is lower drive gear  207  and beneath gear  207  is a bushing  208 . Lower drive gear  207  meshes with gear  209 , journalled on shaft  210  and carrying gear  211 . Gear  211  meshes with gear  212 . Immediately above gear  212  is a small gear  213 , then a large gear  214 , and another small gear  215  all four being journalled on shaft  216 . Large gear  214  meshes with gear  218 , which drives the shaft  192  to rotate the rake assembly  36 . Gear  213 , in turn, meshes with gear  219 , behind it and another small gear  220  is located above  219 , both being journalled on a shaft  221 , visible in  FIG. 20 . As will become apparent, the apparatus  30  operates from a single motor, as part of the drive mechanism  170 , which concurrently rotates the pan  33 , rotates the rake assembly and opens the cover  155  of waste receptacle  37 . As viewed in  FIG. 20 , the various gears are mounted on a lower gear housing  222 , itself mounted to the floor  223  of a lower compartment  224 , which is housed within the main base  31 , next to the waste receptacle  37 . 
     In  FIG. 17 , the inboard and outboard side walls  228 ,  229 , extending up from the drive housing  38  and surrounding around the floor  193 , define an upper compartment, generally  230 . Two removable gate guilders,  231  and  232  are provided at the front of the compartment  230 . The guilder  232  is shown in  FIG. 17  and provides a slot  234 , to accommodate the small wheel  178  of assembly  36 . A curvilinear front wall  235  of compartment  230 , slightly lower than side walls  228 ,  229 , provides an upper edge  236  along which the wheel  178  rolls. Inside of the front wall  235  are a series of vertical tabs  238  which follow the curvilinear contour of the wall, leaving a narrow channel  239 , as depicted in  FIG. 18 , into which a flexible shield member  240  is positioned (see  FIG. 22 ). 
     The shield  240  can be a length of clear plastic material and is provided with a hole  241  of sufficient diameter to receive the wheel  178  of rake assembly  36 . Although not shown in the drawings, the cover  195  also provides a continuous sidewall which mates with the sidewalls  228 ,  229 . The front portion of the sidewall of cover  195  is also curvilinear and the cover provides another series of tabs, similar to the tabs  238 , and another channel is formed. When fully assembled, the shield member  240  is positioned between the two channels and slides therein as the rake assembly traverses from the parked position in the litter pan to the dumping position over the waste receptacle. Its purpose is to minimize the entrance of dust or litter grains from the litter pan into the compartment  230 . 
     Referring now to  FIGS. 17 and 22 , adjacent the rake assembly base  193 , a arcuate platform  245  is provided on the floor  194  of compartment  230 . The arc traversed is approximately 90° and the platform is raised sufficiently to contact the large wheel  184  of rake assembly  36  in order to provide support for the rake holder  173  as it traverses the litter, carrying waste material. Behind platform  245  a second platform  246  is provided, higher than platform  245 . Unlike the former, which has only a flat upper surface, the platform  246  has a generally flat upper surface, transitioning to a downward ramp  248  which curves toward and joins the floor  194 . A third platform  249  is provided on the rake assembly base  193 , in front of the first platform  245 . Platform  249  has a ramped upper surface which begins at the rake assembly base and rises to approximately the height of the first platform  245 . It is, however, considerably shorter in length than the first two platforms. 
     The key cam wheel  185  at the opposite end of rake holder  173  has a rounded top and flat underside  250  which rides along the surface of the second platform  246 . Extending downwardly from the underside  250  is a cam  251 , which is engageable with a step  252 , along side of and integral with the second platform  246 . As the rake holder  173  begins its sweep across the litter pan, an edge of the underside  250  from cam wheel  185  is passed along the horizontal surface of platform  246 , moving from the rest position, depicted in  FIG. 12 . Just prior to the position depicted in  FIG. 13 , the cam  251  begins to contact the step  252 , which starts an upward rotation of the rake holder  173 , into a waste holding position. At this point, a minor rotation of the main driving shaft  181  occurs so that the opposite edge of the underside  250  from cam wheel  185  contacts the horizontal surface of platform  246 . With the rotation of the rake holder  173 , it is elevated out of the pan  33 , to clear the shield  34  and eventually empty its contents into the waste receptacle  37 , as depicted in  FIGS. 14–16 . Along the way, the cam wheel  185  is freed from the platform  246 . Toward the end of the forward cycle, the small cam  180  makes contact with the third platform  249 . As the cam  180  follows the ramp on platform  249 , it is rotated which, in turn, rotates the rake holder  173  in a counter-clockwise direction, as viewed from the distal end, so that the contents carried by the scoop  175  are emptied into the waste receptacle  37 , as depicted schematically in  FIG. 16 . 
     For the return cycle, the drive mechanism  170  is reversed, causing the rake holder  173  to move out of the waste receptacle toward a position of rest in the litter pan. Initial movement rotates the rake holder  173  sufficiently to clear the receptacle as the cam  180  retraces its movement over the third platform  249 . Continued rotation of the upper main driving shaft  181  causes the cam  251  to engage the second platform  246 , whereby the rake holder  173  is again returned to its leveled, or scooping position in the litter contained in the pan  33 . The torsion spring  182  assists here, biasing the rake holder  173  counter-clockwise so that the flat scoop  174  is driven into the litter. Thereafter, the driving shaft  181  concludes its rotation until the rake holder  173  is parked in its initial rest position. 
     The floor  194  and sidewall  229  of drive housing  38  are removable as a unit and together house a lower compartment, generally  256 , of the base  31 . Behind the second platform  246  is a small compartment  258 , which receives a controller  259  for operation of the apparatus  30 . The compartment  258  extends into the lower compartment and provides a slot holder  260 , housed within the base  31 . A control button  261  is provided for manual operation of the apparatus. One embodiment of apparatus is fully self-cleaning, by which is meant that the cleaning cycle being described occurs without intervention by the pet owner. Nonetheless, should the pet owner wish to initiate a cycle, the power button  261  can be activated. The apparatus  30  can also be manufactured as a manual duty device, in which instance, the circuit board is not programmed to initiate a self-cleaning cycle automatically but rather the pet owner can do so upon demand. It is to be understood that while a button is depicted, the apparatus could also be provided with a foot control switch or a remote switch. Other means of automatic activation could be initiated from a micro-chip, embedded in the collar worn by the pet. None of the foregoing devices are depicted or described, as they are well known in the art. 
     With reference to  FIG. 19 , the lower compartment  256  is exposed and reference should be made to the lower main driving shaft  196 . It is to be appreciated that several upper components have been removed to reveal elements in the lower compartment  256  and in so doing, several of the remaining elements depicted appear to be floating. At the lower end of base  196 , an inwardly directed link arm  264  extends radially out and an outwardly directed cam  265  extends radially out, approximately 165° from the link arm. The cam  265  is engage able with opposed inboard and outboard limit switches,  266  and  268 , respectively. Both switches are mounted to struts, not shown, that are provided in the underside of the floor  194 , which has been removed. The inboard switch  266  functions to reverse the cleaning of the pan ( FIG. 16 ) so that the rake assembly  36  returns to its parked position ( FIG. 12 ). The outboard switch  268  signals the apparatus to stop movement, until the next cleaning cycle is to be activated. 
     With reference next to  FIGS. 10 and 24 , the mechanism for opening the waste receptacle, which is indicated generally by the numeral  270 , will be described. It includes a link arm  271 , a lever  272 , and the door pusher  162 , described previously. These work in conjunction with the inwardly directed link arm  264 . One end of the link arm  271  is pivotally connected to the inwardly directed link arm  264 , at  273 . The other end is connected to the lever  272  at  274 , and the lever  272  is itself pivotally connected at  275  to the underside of the floor  194 . 
     As the inwardly directed link arm  264  is rotated during the forward movement (cleaning) of an operation cycle, the link arm  271  urges the lever  272  to move rearwardly, as viewed in  FIG. 25 . A cam  276 , provided by the lever  272  engages the underside of door pusher  162 , which begins to rise. The pusher  162  is pivotally mounted to a wall  278  of the waste receptacle  37  at  279 . In  FIG. 25 , the engagement of the door pusher  162  with the waste receptacle cover  155 , as it is being lifted, is depicted. The various stages of upward movement of the door pusher  162  are also apparent in the sequential views,  FIGS. 12–16 , described hereinabove, where the cover had been removed for clarity. 
     General Operation 
     Having described the components of the apparatus  30 , a general discussion of the self-cleaning cycle follows. Normally, the apparatus is at rest, which occurs whenever the apparatus has been filled with litter, turned on and is awaiting use by the pet. When the pet enters the apparatus, beginning at the ramp  39  and entering into the litter pan  33 , the weight of the animal depresses the turntable  32 , so that one of the weight sensors  66  makes contact with the rails  122 ,  123 . In other words, the weight sensing mechanism  120 ; which comprises the weight sensors and the track assembly  121 , is provided for the actuation of a petinitiated cleaning cycle. The controller is preferably programmed to signal the timer after the weight of the animal has engaged a weight sensor with the rails for a minimum of 3 to 5 seconds. In other words, a brief contact between the sensor and rails will not cause a cycle to be initiated, because the pet would not have used the litter box. After the animal concludes its business and exits the apparatus, the turntable is again fully righted upon the spindle  86  and a signal is generated to the controller  259  to begin activation of a cleaning cycle, within a pre-determined time. Recognizing that the pet may return, a sufficient period is usually 30 minutes. Additionally, the apparatus employs self-clumping litter, which requires several minutes to absorb liquid waste and form a solid having sufficient integrity to be moved. Once begun, a cycle is completed in approximately two minutes and during this period, the sensors are no longer active. 
     The controller  259  is a micro-processor based device that includes the necessary hardware, timer, software and memory for executing and performing the various functions of the apparatus  30 . As will be described, the controller receives a number of electrical inputs from certain components and, depending upon the sequence of their receipt, generates electrical output signals to those components from which input signals were received and other components. The controller  259  receives electrical power from the power source  199  which may be either from an AC residential power supply, DC batteries or the like. The controller  259  may receive a cycle input from a switch  261 . Once energized, the controller is able to receive input from the weight sensing mechanism  120 , as well as an inboard limit switch  266  and an outboard limit switch  268 . And the controller  259  is then able to control operation of a motor  204  which in turn operates the turntable as previously described. The motor  204  also receives power from the power source  199 . It will be appreciated that the motor  199  may receive power from a separate power source that is of a different value or different format, than received by the controller. Or the controller  259  may directly supply power to the motor that is stepped-up or stepped-down an appropriate amount. 
     Returning now to the operation of the apparatus, the controller  259  includes an internal timer that is actuated upon exiting of the animal. Once this time has passed, the motor is energized and as a result three movements are commenced by the controller  259 —the litter pan  33  is rotated clockwise and counter-clockwise, the rake assembly  36  begins a slower rotation through the litter and litter pan  33 , and the cover of the waste receptacle  37  is raised. 
     Following one-half completion of the cycle, where the scoop  174  has deposited litter clumps and solid waste matter into the receptacle  37 , the inboard limit switch  266  is activated by the inwardly directed link arm  264 , from lower main driving shaft  196 , which sends another signal to the controller to reverse rotation of the motor. As this occurs, the rake assembly withdraws from the receptacle  37 , the cover is closed and the assembly moves down into the litter as it simultaneously rotates back (counter-clockwise, as shown) to its parked position, with the scoop  174  submerged in the litter. Concurrently, the litter pan and turntable are also rotating in a clockwise direction, as shown. When the outwardly directed cam  265  from the upper main driving shaft  181  contacts outboard limit switch  266 , a signal is sent to the controller. While the rake has almost returned to its parked position, the forward motion of a new cycle is commenced and run for approximately 2 seconds. The effect of this action is that the backlash is taken up from the gears of the drive mechanism and as a result, the rake is actually moved rearwardly the last remaining increment to its fully parked position against or very near to the wall inner wall  161  of dust shield  42 . Once the cycle is complete, all further movement ceases until either another cycle is initiated by the pet or, the owner elects to cycle the apparatus manually by activating the switch  261  or similar control switch. 
     Another feature of the apparatus, which is programmed into the controller, is a motor overload circuit. During a cycle, should the rake encounter an obstruction that the motor cannot overcome, the amperage to the motor will increase until an overload switch signals the controller to reverse the drive mechanism. Such switches, or overload protectors, are known in the art and do not constitute a limitation of the apparatus. Typically, a clump of solidified waste may have adhered to the surface of the pan, perhaps due to low litter volume and the clump may have a mass that cannot be immediately moved by the rake. By design and programming, the rake will return to its parked position and in several seconds a new cycle will commence. Generally, a second pass at the large clump or other obstruction is sufficient to remove or move it and the cycle continues. If not, a third park and re-initiation is programmed and if that attempt is still unsuccessful, the rake returns to rest or park and the apparatus is shut-down. A red LED or similar indicator is activated by the controller to provide a visual signal to the pet owner that the apparatus is unable to operate a cleaning cycle. The owner can then determine the nature of the problem and correct it so that the cycle can then be performed. In this instance, it is likely the owner would then initiate a cycle manually, to view operation and confirm that the previous problem no longer exists. 
     As noted hereinabove, an embodiment of the apparatus  30  is also within the scope of the invention which does not self-clean automatically, that is, when the pet leaves the apparatus. To initiate self-cleaning, the pet owner decides when by pushing the button  261  or similar switch and the apparatus proceeds to follow the cycle just described. Such apparatus would not employ the sensing mechanism  120  and, because a tiltable litter pan would not be required, the turntable could also be eliminated, in which instance the pan would be driven directly. 
     Thus, it should be evident that the apparatus and method of the present invention are effective for self-cleaning of litter devices, employing rotatable litter pans. Although the foregoing explanation has been directed to the apparatus depicted in the drawings, it will be appreciated by those skilled in the art, that certain components could be varied or modified to obtain the same operation. One such modification envisioned is the combination of the turntable and litter pan into a single component, rather than two separate components. Another modification is in the sensing mechanism  120 . As described in the drawings, sensors are provided in the turntable and rails in the base, so that contact can be made. However, the location could be reversed, by placing the rails or similar elements in the turntable which would be engageable with sensors from beneath. So long as the tilting of the pan provides a signal to the controller to activate the drive mechanism, the relative position of the necessary components can be varied to suit manufacturing as well as consumer preferences. 
     Based upon the foregoing disclosure, it should now be apparent that the use of the litter apparatus described herein will carry out the objects set forth hereinabove. It is, therefore, to be understood that any variations evident fall within the scope of the claimed invention and thus, the selection of specific component elements can be determined without departing from the spirit of the invention herein disclosed and described. Thus, the scope of the invention shall include all modifications and variations that may fall within the scope of the attached claims.