Patent Publication Number: US-2020281157-A1

Title: Pet Animal Housing Unit With Safe Access To Grass On A Lawn

Description:
FIELD OF THE INVENTION 
     The invention relates generally to improvements in animal housing units, and more particularly to animal enclosure construction that may be adjusted to provide an access point for caged pets to graze outdoors safely without leaving the safety of the housing unit. 
     DESCRIPTION OF THE RELATED ART 
     Various types of animal housing units have been developed to house indoor pets. For example, rabbits, hamsters and guinea pigs are frequently confined in cages indoors. The cages come in various sizes, shapes and configurations. 
     U.S. Pat. No. 3,195,505 issued to F. C. Hauth et al. is an example of a small animal cage, the entire content of which is incorporated herein. The cage in Hauth comprises three main parts: an upper wire lattice portion forming the main enclosure, a grated or pervious floor portion, and a lower base portion. The grated or pervious floor portion is suspended above the floor of the lower base portion and serves to keep the animals away from its urine and droppings, which pass through the grated or pervious floor portion and land on the floor of lower base portion. 
     Hauth&#39;s three-part design is primarily tailored for the needs of laboratories. Cages designed for raising indoor pets typically do not contain a grated or pervious floor portion. Instead, the pet lives directly on the floor of the lower base portion. A layer of bedding is provided within the lower base portion to absorb the pet&#39;s urine and keep its droppings from contacting the lower base portion. The bedding is typically made of highly absorbent material, such as paper, wood shavings, etc. and may further contain chemical substances for absorbing, neutralizing or masking undesirable odors from the pet. 
     The three-part or two-part (without the grated or pervious floor portion) designs continue to be the mainstream designs more than fifty years after Hauth was issued. Of course, many changes have been implemented without departing from the overall design. For example, advancements in material sciences have led to the development of cheaper and more processable materials for manufacturing parts of a cage. Plastic is frequently used in place of metal for making the cage. Additionally, cages with more than one level of platform have been developed, such as those described in U.S. Pat. No. 5,964,189 to Northrop et al., and U.S. Pat. No. 6,318,295 to Wade, which are incorporated in their entirety herein. 
     While all of the above-referenced patents provide for useful cages, they do not permit the pet inhabitant to graze on fresh grass outdoors. Instead, the caged pets are typically fed indoors. At feeding time, the pet caretaker would bring food into the cage and place it within the food container. The food is often purchased, such as dried grass cuttings (hay), cucumbers, carrots and blueberries, which adds cost to the pet caretaker. 
     Feeding pets with fresh grass that is grown on a lawn or a meadow is an appealing concept for many pet caretakers for several reasons. First, fresh grass is often readily available for several seasons in a year. Many households, especially those located in rural or suburban areas, have lawns where fresh grass is grown during certain seasons each year. Second, using the fresh grass as a substitute for, or supplement to, purchased food reduces the cost of raising the pet. Third, many pets prefer to eat fresh grass from a lawn over purchased hay. 
     Despite the appeals of fresh grass, many pet caretakers have chosen not to use it as a substitute or supplement, at least not on a regular basis. This is because there have not been any convenient and safe methods for doing it. Taking the pet outside its cage and leaving it on the lawn often incur unacceptable level of risks. For example, eagles or hawks may circle the sky in certain rural areas, looking for prey. The pets may also escape from the lawn and venture into the wild or worse, traffic on the road. In light of these risks, some pet caretakers have chosen to collect fresh grass from outside, and then bring the grass indoors to feed the pets. In collecting the fresh grass, the pet caretakers frequently hold the tips of the grass with fingers of one hand and cut the grass with a pair of scissors or a knife held in the other hand. This process is both cumbersome and dangerous, and the pet caretakers risk cutting the fingers that hold the tips of the grass. 
     Known cage designs, including those described in the above patents, do not allow indoor pets to graze outdoors. Indoor pets living in these cages do not have access to grass even if the cages are brought outside and placed on the lawn. Therefore, there exists a need for a pet cage that can allow pets to safely reach fresh grass on a lawn or a meadow. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In a first embodiment of this invention, the pet cage comprises an upper cage member forming the main enclosure and a lower base member. The lower base member has a bottom and several sidewalls connected sequentially to enclose the bottom. An opening is created along the lower edge of a first sidewall and extends along the bottom toward the sidewall that opposes the first sidewall. Guides are provided along the edges of the opening for receiving and supporting an exchangeable plate. Exchangeable plates with different designs are provided, such as plates without any access points (e.g., through-holes), and plates with one or more access points. An exchangeable plate without any access point is used when access to grass is not desired, such as when the pet is housed indoors. A plate with one or more access points is used when access to grass is desired. 
     The second embodiment of the invention differs from the first embodiment in that guides are provided along the edges of the opening for receiving and supporting an exchangeable tray. Each exchangeable tray comprises two opposing sidewalls, a front plate, a bottom plate and preferably, a backplate. The exchangeable tray may be supported on the guides in different ways. For example, the bottom plate of an exchangeable tray may contact with and rest upon horizontally extending edges of the guides when the exchangeable tray is inserted into the opening. Alternatively, the top of the opposing sidewalls of the exchangeable tray may have horizontally extending lips or edges that may be perched on top the guides when the exchangeable tray is inserted into the opening. One or more exchangeable trays are provided with different bottom plate designs, such as a bottom plate without any access points or a bottom plate with one or more access points. An exchangeable tray with a bottom plate without any access points is used when access to grass is not desired, such as when the pet is housed indoors. An exchangeable tray with a bottom plate having one or more access points is used when access to grass is desired. 
     The third embodiment of the invention differs from the first embodiment in that guides are provided along the edges of the opening for receiving and supporting two or more exchangeable plates. When inserted into the opening, the exchangeable plates are placed substantially on top of each other and suspended at different heights from the bottom of the lower base member. Different exchangeable plates can be inserted as needed. For example, an exchangeable plate without any access points can be used above an exchangeable plate with one or more access points, when access to grass is not desired, such as when the pet is housed indoors. The top exchangeable plate can be removed when access is desired. 
     The fourth embodiment of the invention differs from the first embodiment in that the edge portions of the exchangeable plate have channels defined therein for receiving the corresponding edge portions of the opening in the bottom of the lower base member. In this design, no guides are needed along the edges of the opening of the lower base member. Exchangeable plates with different designs are provided, such as plates without any access points (e.g., through-holes), and plates with one or more access points. An exchangeable plate without any access point is used when access to grass is not desired, such as when the pet is housed indoors. An exchangeable plate with one or more openings is used when access to grass is desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be understood more readily from the following detailed description of the invention, when taken in conjunction with the accompanying drawings. 
         FIG. 1  is a view in elevation and partially in section of a pet cage in accordance with a first embodiment of the invention, wherein the pet cage is in a fully assembled state. 
         FIG. 2  is a perspective view of a pet cage in accordance with the first embodiment of the invention, wherein the pet cage is in an expanded state. 
         FIG. 3  is a greatly enlarged view in elevation and in section showing a portion of the upper grille section of the pet cage of  FIG. 1 . 
         FIG. 4  is a greatly enlarged view of the parts in  FIG. 1  that are surrounded by  4 - 4 . 
         FIG. 4A  is a greatly enlarged view in perspective showing in detail a connecting hook member  30  in accordance with the first embodiment of the invention. 
         FIG. 5  is a greatly enlarged cross-sectional view of a portion of the lower base member surrounded by  5 - 5  in  FIG. 1 , and indicated by  5 - 5  in  FIG. 2 . 
         FIG. 5A  is a top view of the parts shown in  FIG. 5 , as indicated by  5 A- 5 A. 
         FIG. 5B  is a first alternative design for the guide  50 A as shown in  FIG. 5 . 
         FIG. 5C  is a second alternative design for the guide  50 A as shown in  FIG. 5 . 
         FIG. 6A  is a top view of the body portion of an exchangeable plate without any access point in accordance with the first embodiment of the invention. 
         FIG. 6B  is a top view of the body portion of an exchangeable plate having multiple small circular access points in accordance with the first embodiment of the invention. 
         FIG. 6C  is a top view of the body portion of an exchangeable plate having two large circular access points in accordance with the first embodiment of the invention. 
         FIG. 6D  is a top view of the body portion of an exchangeable plate having a rectangular access point in accordance with the first embodiment of the invention. 
         FIG. 7  is a perspective view of an exchangeable tray in accordance with a second embodiment of the invention. 
         FIG. 8  is a cross-sectional view of the exchangeable tray in  FIG. 7  that is cut along the line  8 - 8  as the exchangeable tray engages with the lower base member. 
         FIG. 9  is a cross-sectional view of an exchangeable tray as the tray engages with the lower base member in accordance with an alternative design of the second embodiment of the invention. 
         FIG. 10  is a cross-sectional view of a portion of the lower base member in accordance with a third embodiment of the invention. 
         FIG. 11  is a cross-sectional view of a portion of the lower base member in accordance with a fourth embodiment of the invention. 
         FIG. 12  is a perspective view of a pet cage having a lower base member, a sidewall enclosure, and a lid with a trapezoidal cross section. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is explained in connection with the following exemplary embodiments. They are provided as examples to facilitate the description of the invention and should not be regarded as exclusive embodiments. As discussed below, multiple variations can be made to the design of the cage without departing from the spirit or scope of the invention. 
     The first embodiment of the invention is illustrated in  FIGS. 1 through 6D .  FIG. 1  shows a pet cage  10  as it appears when fully assembled and in use indoors. The cage  10  comprises two major components, namely, an upper cage member  11  and a lower base member  13 , which are shown in a detached state in  FIG. 2 . Both components preferably have a frusto-pyramidal configuration, although other configurations, such as a cube, rectangular prism, or another geometric shape may also be used without departing from the spirit or scope of this invention. 
     As shown in  FIGS. 1 and 2 , the upper cage member  11  of the cage  10  is preferably made from a plurality of rigid wire members which are preformed and joined together to form a mesh enclosure of the desired size. The mesh enclosure enables the following: air exchange between the pet cage and the environment, ambient light to reach the pet, the caretaker to see inside the cage and observe the pet, and the pet to see outside the cage. A central portion of the upper cage member  11  is formed by a series of inverted generally U-shaped and spaced apart wire members  14 . The wire members  14  form opposite side members  15  and  16  and a roof portion  17 . A series of spaced apart horizontal wires  18  are provided on the side members  15  and  17  and the roof portion  17 . The wires  18  extend across and are joined to the wire members  14  (preferably at a 90 degree angle) to form the mesh pattern of this central section. The other sides of the upper cage member  11  are formed by separate upright side members  19  and  20 , which are formed from a series of vertical wire members  21  and horizontal wire members  22 . The side member  19  is fixed to the central portion of the upper cage member  11  between the sides  15  and  16  by clips or bands  23  that extend around the edge wire members of both the central member and the side member  19 . The other side member  20  is hinged to a horizontal frame member  24 , which is connected to the opposite sides  15  and  16  near the bottom edge of the upper cage portion  11 , by a series of clips or bands  25  so that it can pivot thereon and provide a door  25 A for the cage. 
     As shown in  FIGS. 1 and 2 , the lower base member  13  is where the pet, such as our guinea pig, Cinnamon, as depicted in  FIG. 1 , resides. The lower base member  13  is made from a sheet material and has a generally rectangular bottom  33  and a frusto-pyramidal shape formed by upwardly divergent sidewalls  34 A,  34 B,  34 C and  34 D. The bottom  33  can also be shaped other than a rectangle or a square, in which case, multiple sidewalls are provided to fully enclose the bottom  33 . Instead of extending in an upwardly divergent manner, the sidewalls can also extend upwardly with a straight angle relative to the bottom  33 . In either case, the sidewalls are connected in serial, i.e., one after another along shared edges (e.g.,  34 A to  34 B,  34 B to  34 C,  34 C to  34 D,  34 D to  34 A), to form an enclosure. The enclosure has a top perimeter and a bottom perimeter. Around the top perimeter is a horizontally extending edge flange portion  32  of uniform width. The horizontally extending edge flange portion  32  is connected at its outer edge to an upwardly extending edge portion  35  (see  FIG. 4 ). The top perimeter is adapted to receive the upper cage member  11  as discussed below. The bottom perimeter meets with the perimeter of the bottom  33  so that the enclosure and the bottom  33  are of an integral construction or separately formed but joined to each other. 
       FIG. 3  illustrates a portion of the upper cage member  11  that is designed for regulating the door  25 A. The door  25 A is controlled by a latch  26  and a catch member  29 . The latch  26  is provided on the side member  20  and comprises a resilient sheet member with a bent end flange  27 . The catch member  29  is fixed to the roof portion  17  and comprises an end hook  28 . The latch  26  is adapted to interact with the end hook  28 , and when it fits behind the end hook  28 , the interaction will keep the door  25 A in a closed state. When the door  25 A moves from an open position toward a closed position, the bent end flange  27  first touches the front (left) side of the end hook  28 . Further movement of the door  25 A will deform latch  26  and the bent end flange  27 , effectively causing the bent end flange  27  to move downward, and at the same time, the end hook  28  deforms and moves upward. When the bent end flange  27  moves past the end hook  28  and comes into contact with its back (right) side, the latch  26 , the bent end flange  27  and the end hook  28  will return to their undeformed state with the bent end flange  27  securely resting on the back side of the end hook  28  to keep the door  25 A in the closed position. To open the door  25 A, the end hook  28  is pushed upward, and/or the latch  26  and the bent end flange  27  are pushed downward. At this time, the end hook  28  and the bent end flange  27  will disengage, allowing the door  25 A to be opened. 
       FIGS. 4 and 4A  provide detailed views of the connecting hook member  30  and the top perimeter of the enclosure formed by the sidewalls of the lower base member, as shown in  FIGS. 1 and 2 . The connecting hook member  30  is provided on one or more sides of the cage for releasably connecting the upper cage member  11  and the lower base member  13 . The connecting hook member  30  is formed from resilient sheet material. At its upper end, the connecting hook member  30  is adapted to releasably connect to some vertical and/or horizontal wire members in the upper cage member  11 . The upper end can be designed as shown in  FIG. 4A , or can be a simple tab (such as the lower lip portion  31 ) that engages a horizontal wire member in the upper cage member  11 . At its lower end, the connecting hook member  30  is adapted to releasably connect to the lower base member  13 . This is achieved by incorporating an inwardly and upwardly extending lower lip portion  31  that is adapted to fit around and under the horizontally extending edge flange portion  32  on the lower base member  13 . 
     When the upper cage member  11  and the lower base member  13  are connected by one or more connecting hook members  30 , the horizontally extending edge flange portion  32  directly supports the weight of the upper cage member  11  and passes the weight downward into the sidewalls, and the upwardly extending edge portion  35  forms an enclosure around the lower edge of the upper cage member  11  to prevent the upper cage member  11  from moving laterally in relation to the lower base member  13 . When all hook members  30  are removed, the upper cage member  11  and the lower base member  13  can be separated. 
     As shown in  FIGS. 1 and 2 , the lower base member  13  is partially cut out in at least one sidewall as well as in the bottom to permit the pet to access grass when needed. The sidewall  34 A of the lower base member is partially cut out, creating a side opening  46 A at a location where the sidewall  34 A meets the bottom  33 . 
       FIG. 5  is a cross-sectional view of a portion of the bottom of the lower base member  11 , where access points are provided (as indicated by  5 - 5  in  FIGS. 1 and 2 ). As shown in  FIG. 5 , the bottom  33  of the lower base member  13  is partially removed, creating a bottom opening  48  that is defined by the gap between two opposing edges  48 A and  48 B on the bottom  33 . The edges  48 A and  48 B preferably run parallel to each other. The bottom opening  48  has a first end and a second end. On the first end, the bottom opening  48  connects with the side opening  46 A. In the direction of the second end, the bottom opening  48  runs through the interior of the bottom  33  away from the sidewall  34 A, preferably in a direction that is perpendicular to the sidewall  34 A. The bottom opening  48  may extend partially or the entire distance to the sidewall  34 C, which is directly or substantially opposite to the sidewall  34 A. If the bottom opening  48  reaches the sidewall  34 C, it may terminate as it reaches the sidewall  34 C, leaving the sidewall  34 C intact. Alternatively, the bottom opening  48  may terminate as a side opening  46 B on the sidewall  34 C, which mirrors the side opening  46 A on the sidewall  34 A. 
     A guide  50 A is provided adjacent and along the edge  48 A of the bottom opening  48 . Similarly, a guide  50 B is provided adjacent and along the edge  48 B of the bottom opening  48 . Each guide runs the entire length of the bottom opening  48  (i.e., from the first end to the second end of the bottom opening  48 ), and has bottom, side and top portions identified as  52 ,  54 , and  56 , respectively. The portions  52 ,  54  and  56  are preferably formed as a unitary structure. They also can be formed as separate elements and then assembled using any conventional means, such as using a glue or a fastener (screws, bolts/nuts, etc.). The bottom portion  52  can merge into the bottom  33  adjacent to the edges  48 A and  48 B (as shown in  FIG. 5 ), or can be a separate element placed on top and attached to the bottom (as shown in  FIG. 5B ). In the latter case, the bottom portion  52  can be attached to the bottom by any conventional means, for example, by forming them as a unitary structure using a mould or forming them as separate elements that are connected using a glue or a fastener (screws, bolts/nuts etc.). The middle portion  54  projects away from the bottom  33  in the direction of the upper cage member  11 . The top portion  56  is placed on top and connected to the middle portion  54 , and runs substantially parallel to the bottom  33 . 
     The bottom, middle and top portion ( 52 ,  54  and  56 ) along each edge ( 48 A or  48 B) cooperate to define a recessed space ( 60 A or  60 B) for engaging an exchangeable plate  70 . The recessed space ( 60 A or  60 B) has a length, a height  61 , and a depth  62 . The length of the recessed space is the same as the length of the guide, and the length of the bottom opening  48 . The guides are preferably dimensioned such that at its highest point, the distance  63  from the bottom  33  is similar to or more than the depth of bedding that is typically used for the pet cage. For example, the distance  63  can be about 1 to 3 inches, and preferably about 2 inches. If necessary, the top portion  56  may possess an element  57  that extends away from the bottom  33  so as to create the desired distance  63  (see  FIG. 5C ). 
     As shown in  FIGS. 5 and 5A , an exchangeable plate  70  is provided to regulate the pet&#39;s access to grass. The exchangeable plate  70  has two edge portions ( 70 A and  70 B) for engaging with the corresponding recessed space ( 60 A or  60 B), and a body portion  70 C. The surfaces of the edge portions  70 A and  70 B and the matching surfaces of the recessed space  60 A and  60 B can be smooth surfaces. Alternatively, these surfaces can modified to enhance friction when the edge portions  70 A and  70 B and the surface of the recessed space  60 A and  60 B are engaged with each other. The surfaces can be modified (e.g., roughened) using any conventional means, such as those disclosed in U.S. 2008/0038453 to Atsushi Yusa et al., DE19729891A1 to Hartmut Sauer, U.S. Pat. No. 5,826,586 to Ajit K. Mishra et al., and EP0875360A2 to Herbert Horn, et al, which are incorporated herein. As a further alternative, the edge portions  70 A and  70 B may be adapted to releasably engage with the recessed space  60 A and  60 B using the locking pin and detent hole combination as taught in U.S. Pat. No. 4,966,020 to Scott M. Fotheringham et al. (see e.g., column 5, lines 34-46, FIGS. 5-7), which is incorporated herein. In this design, one or more locking pins will be placed in each of the edge portions  70 A and  70 B, and detent holes are created in matching locations in the top portion  56  of the guides  50 A and  50 B. 
     The length of the exchangeable plate  70  is substantially the same as the length of the bottom opening  48  from the latter&#39;s first end to the second end. The width of the body portion  70 C of the exchangeable plate  70  is substantially the same as the width of the bottom opening  48 , i.e., the gap between  48 A and  48 B. The width of the edge portions  70 A and  70 B is substantially the same as the depth  62  of the recessed space  60 A and  60 B. The thickness of the edge portions  70 A and  70 B of the exchangeable plate  70  is substantially the same as the height  61  of the recessed space  60 A or  60 B. The body portion  70 C may have the same or a different thickness as that of the edge portions  70 A and  70 B. 
     The body portion  70 C of the exchangeable plate  70  can be designed in multiple formats for use under different situations. For example, in a first design ( FIG. 6A ), the plate does not have any access points, which is used when access to grass is not desired. In other designs ( FIGS. 6B, 6C and 6D ), the plate can have one or more access points (e.g., through-holes  80 ). When the pet cage is placed on the lawn, the pet can access the grass through the through-holes  80 . The holes can be in any suitable size and geometric shapes, including circular , oval-shaped, star-shaped, rectangular, square, etc. 
     The exchangeable plate  70  can be readily installed on or removed from the lower base member  13 . To install an exchangeable plate, the caretaker would insert a first end ( 52 A, see  FIG. 5B ) of the exchangeable plate  70  into the side opening  46 A on the lower base member  13 , with the edges  70 A and  70 B inserted into the corresponding recessed space  60 A and  60 B. The caretaker would then continue pushing the plate into the interior of the bottom  33  until the exchangeable plate  70  is fully inserted, at which point  70 C substantially covers up the entire bottom opening  48 . As fully inserted, the second end  52 B of the exchangeable plate  70  abuts the side opening  46 A. The first end  52 A of the exchangeable plate  70  abuts the inside of the opposing sidewall  34 C or, if a side opening  46 B is provided on the side wall  34 C, the side opening  46 B. To remove a plate, the caretaker would pull the plate toward either the side opening  46 A or  46 B until the plate is completely disengaged from the lower base member  13 . 
     Gripping means are provided on the exchangeable plate  70  to facilitate the insertion or removal by hand. The gripping means can be depressions or small through-holes formed into the underside of the exchange plate  70  for receiving fingers. The gripping means can also be loops, rings, handles, knobs, bars and/or lips formed into or attached to the ends  52 A and/or  52 B. 
     The second embodiment, illustrated in  FIGS. 7 and 8 , is identical with the first embodiment except that the exchangeable plate is replaced with an exchangeable tray with necessary modifications made to the guides so that they can effectively engage with the tray. 
       FIG. 7  is a perspective view of an exchangeable tray in accordance with this embodiment. The exchangeable tray  170  has two opposing sidewalls  171  and  172 , a front plate  175 , and a bottom plate  178 . The exchangeable tray preferably further has a backplate  179 . The sidewalls and plates  171 ,  172 ,  175 ,  178  and  179  share commons edges where they meet and together, they define an interior space  181  that is substantially a rectangular prism. Attached to the front plate  175  is a means  184  for pulling the tray  170  out of the lower base member when needed. Such means can be any of the conventional designs, such as one or more finger-receiving recesses, loops, rings, handles, knobs, bars and/or lips. 
     Similar to  FIG. 5  in the first embodiment,  FIG. 8  is a cross-sectional view showing an opening  148  in a part of the bottom  133  of the lower base member, and the exchangeable tray  170  that is adapted to engage with the opening  148  (see cut line  8 - 8  in  FIG. 7 ). The opening  148  extends in a width direction between two opposing edges  148 A and  148 B, and extends in a length direction from a side opening on a first sidewall to the interior of the bottom  133 , preferably reaching a second sidewall that is opposed to the first sidewall, and optionally terminating at a side opening on the second sidewall. Guides  150 A and  150 B are provided adjacent to each of the edges  148 A and  148 B to engage with the exchangeable tray  170 . The guides  150 A and  150 B extend in a length direction that is substantially along the length direction of the edges  148 A and  148 B. Each guide has substantially an “L” shaped cross section, comprising a horizontal portion  152  and a vertical portion  154 . The horizontal portion  152  can merge into the bottom  133  adjacent to the edges  148 A and  148 B (as shown in  FIG. 8 ), or it can be a separate element placed on top and attached to the part of the bottom  133  immediately adjacent to the edges (similar to how  52  is separate from and joined to  33  in  FIG. 5B ). The vertical portion  154  extends from the bottom  133  of the lower base member for a distance  163  that is similar to or more than the depth of the bedding that is typically used for the pet cage. Similar to what is described above, the distance  163  is about 1 to 3 inches, and preferably about 2 inches. 
     When the exchangeable tray  170  is placed into the side opening  146 A in a sidewall and further into the opening  148  in the bottom  133  of the lower base member, the undersides of the exchangeable tray that are located directly under the sidewalls  171  and  172  come into contact with and rest on top of the horizontal portion  152 . 
     The exchangeable trays can also be designed to engage with the bottom of the lower base member in a different manner. Similar to  FIG. 8 ,  FIG. 9  is a cross-sectional view showing an opening  248  of the bottom  233  of the lower base member, and an exchangeable tray  270  that is adapted to engage with the opening  248 . The opening  248  extends in a width direction between two opposing edges  248 A and  248 B, and extends in a length direction from a side opening on a first sidewall to the interior of the bottom  233 , preferably reaching a second sidewall that is opposed to the first sidewall, and optionally terminating at a side opening on the second sidewall. Guides  254 A and  254 B are provided adjacent to the edges  248 A and  248 B. The guides  254 A and  254 B extend in a length direction that is substantially along the length direction of the edges  248 A and  248 B. The guides  254 A and  254 B extend in a height direction for a distance  263  from the inner surface of the bottom  233 . The distance  263  is similar to or more than the depth of the bedding that is typically used for the pet cage. Similar to what is described above, the distance  263  is about 1 to 3 inches, and preferably about 2 inches. 
     The exchangeable tray  270  has two opposing sidewalls  271  and  272 , a front plate  275 , and a bottom plate  278 , and preferably further has a backplate  279 . The exchangeable tray  270  has a lip  281  on top of the sidewalls  271  and  272 . The lip  281  extends from the sidewalls  271  and  272  horizontally and outwardly in relation to the interior space of the exchangeable tray  270 . When the exchangeable tray  270  is inserted into the opening  248 , the underside of the lip  281  comes into contact with the top surface of the guides  254 A and  254 B, thereby supporting the weight of the exchangeable tray  270  on the bottom  233  of the lower base member. 
     Similar to the body portion  70 C in the first embodiment, the bottom plate  178 / 278  can have various designs, including those with or without access points (similar to what are shown in  FIGS. 6A through 6D ). When the cage is kept indoors, an exchangeable tray without any access points (e.g., through-holes) is placed inside the lower base member. When the cage is moved outdoors for access to fresh grass, an exchangeable tray with one or more access points is placed inside the lower base member. 
     The third embodiment, illustrated in  FIG. 10 , is substantially identical with the first embodiment except that the guides are modified to accommodate two or more exchangeable plates. Similar to  FIG. 5  in the first embodiment,  FIG. 10  is a cross-sectional view showing an opening  348  in a part of the bottom  333  of the lower base member, and two exchangeable plates  378  and  379  that are adapted to engage with the opening  348 . The opening  348  extends in a width direction between two opposing edges  348 A and  348 B, and extends in a length direction from a side opening on a first sidewall to the interior of the bottom  333 , preferably reaching a second sidewall that is opposed to the first sidewall, and optionally terminating at a side opening on the second sidewall. Two “F”-shaped guides  350 A and  350 B are provided adjacent edges  348 A and  348 B. The guides  350 A and  350 B extend in a length direction that is substantially along the length direction of the edges  348 A and  348 B. The guides  350 A and  350 B extend in a height direction for a distance  363  from the inner surface of the bottom  333 . The distance  363  is similar to or more than the bedding that is typically used for the pet cage. Similar to what is described above, the distance  263  is about 1 to 3 inches, and preferably about 2 inches. 
     The body portion of the exchangeable plates  378  and  379  can be designed according to the first embodiment. See  FIGS. 6A through 6D . For example, the exchangeable plate  378  (the lower plate) may be a plate with one or more access points (e.g., through-holes) in its body portion, and the exchangeable plate  379  (the upper plate) may be a plate with no access points in its body portion. When the cage is indoors, both exchangeable plates can be inserted inside the cage as shown in  FIG. 10 . The exchangeable plate  379  presents an uninterrupted upper surface that can hold the bedding material or otherwise be available to the pet as a walking surface. When the cage is outdoors and access to fresh grass is desired, the exchangeable plate  379  is removed, exposing the exchangeable plate  378  to the pet. The pet can access fresh grass through the holes in the exchangeable plate  378 . Once grass feeding is completed, the exchangeable plate  379  can be replaced, recreating the uninterrupted surface. 
     The fourth embodiment, illustrated in  FIG. 11 , is substantially identical with the first embodiment except that the exchangeable plate has two edge portions, each of which has a channel defined therein for engaging with an edge portion of the bottom of the lower base member adjacent to the opening. Similar to  FIG. 5  in the first embodiment,  FIG. 11  is a cross-sectional view showing an opening  448  in a part of the bottom  433  of the lower base member, and an exchangeable plate  470  with two edge portions  470 A and  470 B having channels  442 A and  442 B defined therein. The opening  448  extends in a width direction between two opposing edges  448 A and  448 B, and extends in a length direction from a side opening on a first sidewall to the interior of the bottom  433 , preferably reaching a second sidewall that is opposed to the first sidewall, and optionally terminating at a side opening on the second sidewall. The opposing edges  448 A and  448 B are the side edges of edge portions  444 A and  444 B of the bottom  433 . The edge portions  470 A and  470 B of the exchangeable plate, and the channels  442 A and  442 B extend in a length direction that is substantially along the length direction of the edges  444 A and  444 B. Barrier members  454  are provided on the bottom  433  adjacent to the edge portions  444 A and  444 B, and extend in a length direction that is parallel to the edge portions  444 A and  444 B. The barrier members extend in a height direction for a distance  463  from the inner surface of the bottom  333 . The distance  463  is similar to or more than the bedding that is typically used for the pet cage. Similar to what is described above, the distance  463  is about 1 to 3 inches, and preferably about 2 inches. 
     The body portion  470 C of the exchangeable plate  470  can be designed according to the first embodiment. See  FIGS. 6A through 6D . For example, the body portion  470 C may have access points, such as through-holes  480 . 
     The exchangeable plate  470  can be readily installed on or removed from the lower base member. To install an exchangeable plate, the caretaker would insert a first end  452 A of the exchangeable plate  470  into the side opening  446 A on the lower base member, with the edges  444 A and  444 B of the bottom  433  inserted into the corresponding channels  442 A and  442 B of the exchangeable plate. The caretaker would then continue pushing the plate into the interior of the bottom  433  until the exchangeable plate  470  is fully inserted, at which point  470 C substantially covers up the entire bottom opening  448 . As fully inserted, the second end  452 B of the exchangeable plate  470  abuts the side opening  446 A. The first end  452 A of the exchangeable plate  470  abuts the inside of the opposing sidewall  434 C or, if a side opening  446 B is provided on the side wall  434 C, the side opening  446 B. To remove an exchangeable plate, the caretaker would pull the plate toward either the side opening  446 A or  446 B until the exchangeable plate is completely disengaged from the lower base member. 
     In all the preceding embodiments, all parts of the cage can be made of any suitable materials, such as a metal, a plastic, or a metal coated with plastic. Examples of suitable metal materials include aluminum, copper, brass, steel, and stainless steel, and the metal parts may be further galvanized. Suitable plastics for making these parts or coating metal parts are well known in the art, and examples include polyolefins, acrylics, epoxies, polyimide-imides, polyesters, polyesterim ides, polyam ides, polyimides, polysulfones and polyurethanes and co-polymers thereof, such as those described U.S. Pat. Nos. 3,617,364, 3,829,545, 3,893,642, 4,521,363, 4,541,980, U.S. Patent Application Publication No. 20080193755, which are incorporated herein by reference. Particularly preferred polymer materials include polyethylene, polypropylene, polycarbonates, polyethylene terephthalate, polyacrylates (e.g., poly(methyl methacrylate)), acrylonitrile butadiene styrene (ABS) and polyvinyl chloride. The wires are preferably metal coated with a plastic. The lower base member, the exchangeable plates, and the exchangeable trays are preferably formed entirely of a plastic. 
     The invention focuses on the modifications made to the bottom and sidewalls of the lower base member. As a result, the upper cage member can be in any known shape or form. For example, the pet cage in accordance with the present invention may have a more modern design  500  shown in  FIG. 12 , which Cinnamon lives in. In this design, the cage has an upper cage member  511  comprising a plurality of sidewalls forming an enclosure  512  and a lid  512 A. The lid  512 A has a generally trapezoidal or semi-circular cross section and is rotatably attached to the upper perimeter of a sidewall by hinges. The cage further has a lower base member  513  showing a side opening  546 A immediately adjacent to the bottom of the lower base member. 
     The invention also contemplates a design where the use of an exchangeable plate with access points, or an exchangeable tray with a bottom plate having access points, is entirely avoided. In this case, an exchangeable plate without any access point or an exchangeable tray with a bottom plate having no access points are used when the pet is indoors, and are removed without replacement when the pet is placed outdoors for grass feeding. In this design, the opening  48 ,  148 ,  248 ,  348 , or  448  are the access points. However, this design is disfavored due to the absence of structural support provided by an exchangeable plate or exchangeable tray, and the risk of the pet falling out of or escaping from the opening during transport. 
     Although the invention has been described in conjunction with preferred forms thereof, it will be appreciated by those skilled in the art, that additions, modifications, substitutions, and deletions may be made without departing from the spirit or scope of the invention as defined in the appended claims.