Patent Publication Number: US-2020281156-A1

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

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. non-provisional patent application Ser. No. 16/297,658 filed Mar. 10, 2019, entitled “Pet Animal Housing Unit With Safe Access To Grass On A Lawn.” 
    
    
     FIELD OF 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 cages have been developed to house indoor pets. For example, 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 with a preset size and shape, the entire content of which is incorporated herein by reference thereto. 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 chips, 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 changing the overall design. Advancements in material sciences have led to the development of cheaper and more processable materials for manufacturing parts of the cage. For examples, metal has been replaced by plastic materials for making many parts, including the lower base portion. 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, the entirety of their contents is incorporated herein by reference thereto. 
     Another advancement in the design of pet cages is the development of expandable or collapsible cages. A conventional cage is designed such that its size and shape are preset at the time of the installation and cannot be adjusted during use. Expandable or collapsible cages are designed such that the cages can be expanded or collapsed depending on needs. 
     While there are several examples of cages with an adjustable size, most of them are portable cages used to transport animals. For example, U.S. Pat. No. 7,228,820 to Kellogg describes an expandable and collapsible portable cage that includes a pliable cover and a semi-rigid frame that can be adjusted for size. U.S. Pat. No. 5,054,426 to Panarelli describes an expandable enclosure for animals that includes two rigid shells. The rigid shells are slidably connected to a middle portion such that sliding the two rigid portions apart expands the enclosure accordingly. U.S. Pat. No. 5,960,744 to Rutman describes an expandable closure for animals including a first and a second compartments. Each of the compartments has an open end and a closed or closeable end. The compartments are positioned in telescoping relation providing a composite volume that includes both of the open ends, and a substantially liquid-tight seal between the compartments at the bottom is included. 
     While all of above-referenced patents provide for useful cages, they do not permit the pet inhabitant to graze on fresh grass outdoors. The caged pets are typically fed indoors using foods that are either purchased from stores or online. At feeding time, the caretaker would bring food into the cage and place it within the food container. The food is often purchased, such as dried grass cuttings, which adds cost to the caretaker. 
     Feeding pets with fresh grass that is grown on a lawn is an appealing concept for many pet owners for several reasons. First, the fresh grass is often readily available for several seasons in a year. Many households, especially those located in a 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 dry grass. If the pets are allowed to graze on fresh grass, it also would significantly reduce the workload borne by the caretakers. 
     Despite the appeals of feeding pets with fresh grass, many pet owners have chosen not to do it. 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 constantly circle the sky in certain rural areas, looking for preys. The pets may also escape from the lawn and venture into the wild or worse, traffic on the road. In light of these risks, many pet owners have chosen to collect fresh grass from outside, and then bring the grass indoors to feed the pets. 
     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 when 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. 
     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. 
     A fifth embodiment, as illustrated in  FIGS. 13 through 19 , is directed to a construction that has at least two portions for its base member: a fixed portion and one or more adjustable portions that can be extended or collapsed as needed. Instead of providing access points at the bottom surface of the base member, which is essentially the fixed portion in its entirety, as described in the preceding embodiments, or in addition to such access points that are located in the fixed portion, access points are provided by one or more adjustable portions that are located adjacent, and attached to one or more sides of the fixed portion of the base member. Each of the adjustable portions can alternate between a fully extended, partially extended, and fully collapsed state. The adjustable portions have fully open or partially open bottoms that provide access. When in the partially or fully extended state, access to grass is provided at the bottoms of the adjustable portions. 
    
    
     
       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. 
         FIG. 13  is a perspective view of a pet cage in accordance with a fifth embodiment of the invention wherein the adjustable portion is substantially in a collapsed state. 
         FIG. 13A  is a perspective view of a pet cage in accordance with a fifth embodiment of the invention wherein the adjustable portion is in a partially extended state. 
         FIG. 13B  is a perspective view of a pet cage in accordance with a fifth embodiment of the invention wherein the adjustable portion is in a fully extended state. 
         FIG. 14  is a top view of the lower base member along the cut-line shown as  14 - 14  in  FIG. 13 . 
         FIG. 14A  is a top view of the lower base member along the cut-line shown as  14 A- 14 A in  FIG. 13A . 
         FIG. 14B  is a top view of the lower base member along the cut-line shown as  14 B- 14 B in  FIG. 13B . 
         FIG. 15  is a front view of the lower base member as shown by the arrow  15  in  FIG. 14 . 
         FIG. 15A  is a front view of the lower base member as shown by the arrow  15 A in  FIG. 14A . 
         FIG. 15B  is a front view of the lower base member as shown by the arrow  15 B in  FIG. 14B . 
         FIG. 16  is a cross-sectional, front view of the fixed portion of the base member along the cut line  16 - 16  as shown in  FIG. 14 . 
         FIG. 17  is a side view of the adjustable portion of the base member viewed from a cross-sectional line  17 - 17  in the fixed portion of the base member as shown in  FIG. 14 . 
         FIG. 17A  is a side view of the adjustable portion of the base member viewed from a cross-sectional line  17 A- 17 A in the fixed portion of the base member as shown in  FIG. 14A . 
         FIG. 17B  is a side view of the adjustable portion of the base member viewed from a cross-sectional line  17 B- 17 B in the fixed portion of the base member as shown in  FIG. 14B . 
         FIG. 18  is a plan view of a conventional butt hinge that can be used as a fastening means for the fifth embodiment, as indicated by the call-out box  18  in  FIGS. 15B and 19 . 
         FIG. 19  is a perspective view of a hinge and its surrounding members as shown by the arrow  19  in  FIG. 14B . 
     
    
    
     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  363  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. 
     Referring to the first to the fourth embodiments, 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. 
     In the first to the fourth embodiments, 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. 
     The fifth embodiment, as illustrated in  FIGS. 13 through 19 , is directed to a construction that has at least two portions for its base member: a fixed portion and one or more adjustable portions that can be extended or collapsed as needed. Instead of providing access points at the bottom surface of the base member, which is essentially the fixed portion in its entirety, as described in the preceding embodiments, or in addition to such access points that are located in the fixed portion, access points are provided by one or more adjustable portions that are located adjacent, and attached to, one or more sides of the fixed portion of the base member. As described below, each of the adjustable portions can alternate between a fully extended, partially extended, and fully collapsed state. The adjustable portions have fully open or partially open bottoms. When in a partially or fully extended state, access to grass is provided through the opening in the bottoms of the adjustable portions. 
     As illustrated in  FIGS. 13, 13A and 13B , which are perspective views of the pet cage in accordance with the fifth embodiment wherein the adjustable portion is in a fully collapsed state, partially collapsed state and a fully extended state, respectively, the pet cage  600  comprises (i) an upper cage member  611 , which comprises an enclosure  612  and a lid  612 A, (ii) a base member  613 B, which comprises a fixed portion  602  and one or more adjustable portions  602 A. 
       FIGS. 14, 14A, and 14B , are respectively a top view of the lower base member along (i) the cut line  14 - 14  in  FIG. 13 , (ii) the cut line  14 A- 14 A in  FIG. 13A , and (iii) the cut line  14 B- 14 B in  FIG. 13B . As best illustrated in  FIGS. 14, 14A, and 14B , the fixed portion  602  is fixed in its shape and size and comprises a bottom member  614  and multiple sidewalls arranged in serial to form an enclosed structure except for an opening  690 C on one side (or more than one side if more than one adjustable portion is desired). While the fixed portion  602  is shown to have 4 sides in  FIGS. 13 to 19 , it may have 3, 5, or more sides. 
     The fixed portion  602  serves as the permanent activity space for the pet, and is available at all times for the pet to roam around, play and feed in. Consistent with its role as the permanent activity space, bedding material can be provided on the bottom member  614 . The fixed portion  602  may further contain (i) one or more openings in the bottom member of the lower base portion, such as the ones identified by  48 ,  148 ,  248 ,  348 ,  448 , and (ii) the opening in one or two opposing sidewalls, such as the ones identified by  46 A,  46 B,  146 A,  446 A,  446 B,  546 A, as described in any of the preceding embodiment, which are arranged to accommodate one or more exchangeable plate or exchangeable tray in the same manner as described earlier. 
     At the side opening  690 C in the fixed portion  602 , a lip  690 A replaces a sidewall that would otherwise be present to form a complete enclosed structure as shown in the preceding embodiments (see e.g.  FIG. 2 ). As best seen in  FIG. 16 , which is a cross-sectional view of the fixed portion  602  along the cut line  16 - 16  in  FIG. 14 , as well as  FIG. 17 , which is a side view of the adjustable portion of the base member viewed from a cross-sectional line  17 - 17  in the fixed portion of the base member as shown in  FIG. 14 , the lip  690 A is low in height (preferably 1-3 inches arising from the bottom member  614 ) when compared to a sidewall in order to provide access for the pet to move between the fixed portion and the adjustable portion and at the same time, is high enough to keep the bedding material in the fixed portion from falling off the bottom member  614  into the adjustable portion. 
     As seen in  FIGS. 14, 14A and 14B , the lip  690 A is located between two opposing sidewalls  615  and  615 A, and is the low barrier between the fixed portion  602  and the adjustable portion  602 A. The length of the lip  690 A runs the entire gap between the opposing sidewalls  615  and  615 A. The opposing sidewalls  615  and  615 A have side edges  620  and  620 A, respectively, both of which run substantially perpendicular to the length direction of the lip  690 A. Together with the lip  690 A, the side edges  620  and  620 A define the opening  690 C. 
     As illustrated in  FIGS. 13, 13A and 13B , the adjustable portion  602 A comprises an end wall  690 , and two foldable pairs of wall segments, i.e., the pair  694 / 695  and the pair  694 A/ 695 A. As described in more detail below, the foldable pairs of wall segments may open or close to change the space contained by the adjustable portion  602 A while serving to connect the end wall  690  to the fixed portion  602 . 
     The end wall  690  has two edges  698  and  698 A, which together define the length of the end wall  690  therebetween. The length of the end wall  690  is substantially the same as the length of the lip  690 A. For example, in  FIG. 14A , the length of end wall  690  is substantially equal to the gap between the opposing walls  615  and  615 A, which, as described above, is also the length of the lip  690 A. 
     Preferably, the end wall  690  has a height that is substantially the same as the height of any other sidewalls of the base member  613 B. The end wall is preferably 5 inches in height, 0.5 inches in thickness, and substantially equal in length to the lip  690 A. 
     Regardless whether the adjustable portion is in the the extended or collapsed state, the end wall  690  serves as an end wall for the base member  613 B. In the collapsed state, the edge  698  of the end wall  690  is located adjacent, and runs parallel, to the edge  620  of the enclosure, and the edge  698 A of the end wall  690  is located adjacent, and runs parallel, to the edge  620 A of the enclosure. 
     The end wall  690  may also have a plate (not shown in any figures) extending horizontally at its bottom in the direction of the lip  690 A, creating an “L”-shaped cross section with the end wall  690  being the upright portion and the plate being the horizontal portion. This plate serves to limit the amount of opening at the bottom of the adjustable portion  602 A when the adjustable portion  602 A is in a partially or fully extended state, and also provides additional structural strength to the end wall  690 . This plate extends in a length direction the entire length of the end wall  690 , and preferably 0.5 to 3 inches in a width direction. The parts can be dimensioned such that when in a fully collapsed state, the plate is located immediately above the lip  690 A or under the bottom ( 614 ) of the fixed portion  602 . 
     The foldable pairs of wall segments are arranged between, and are the intermediary for connecting the end wall  690  and the fixed portion  602 . Each pair comprises two wall segments of substantially identical shape and size (preferably rectangular or square), which are joined to each other along a common edge and may rotate relative to each other from an open-and-apart state (i.e., 180 degrees between the pair as shown in  FIG. 14B ) to an overlapping state (i.e., substantially 0 degree between the pair as shown in  FIG. 14 ) through an infinite number of intervening states (represented by  FIG. 14A ). For example, the foldable pair of wall segments  694  and  695  are joined to each other along a common edge and may rotate relative to each other around an axis  692  that is located at the common edge. Similarly, the foldable pair of wall segments  694 A and  695 A are joined to each other along a common edge and may rotate relative to each other around an axis  692 A that is located at the common edge. Axes  692  and  692 A may be provided using any conventional means that may impart rotation, such as a hinge. 
     Preferably, the wall segments  694 ,  694 A,  695  and  695 A each have a height and width that is substantially the same as the height of any other sidewalls of the base member  613 B. The wall segments preferably have a length that is 40-49% of the length of the lip  690 A, and a preferred height of 5 inches and a preferred thickness of 0.5 inches. 
     In addition to the common edge where the pair of wall segments are connected to each other, each wall segment has a far edge that is opposite from the common edge. The far edges are for connecting the pair of wall segments to the end wall  690  on one end and the fixed portion of the base member on the other end. For example, as best seen in  FIGS. 14, 14A and 14B , the pair of wall segments  694 / 695  has two far edges, one being the far edge located on the wall segment  694  and rotatably connected to the edge  698  of the end wall  690  around an axis  691 , and the other being the far edge located on the wall segment  695  and rotatably connected to the side edge  620  of the sidewall  615  around an axis  693 . The axes  691  and  691 A, and  693  and  693 A may be provided using any conventional means that may impart rotation, such as a hinge. Similarly, as best seen in  FIGS. 14, 14A and 14B , the pair of wall segments  694 A/ 695 A has two far edges, one being the far edge located on the wall segment  694 A and rotatably connected to the edge  698 A of the end wall  690 A around an axis  691 A, and the other being the far edge located on the wall segment  695 A and rotatably connected to the side edge  620 A of the sidewall  615 A around an axis  693 A. 
     As best seen in  FIG. 14 , in a fully collapsed state, the wall segments  694  and  695  fully or substantially fully overlap on to each other, having an angle about 0 degrees therebetween at the axis  692 . Similarly, the wall segments  694 A and  695 A fully or substantially fully overlap on to each other, having an angle about 0 degrees therebetween at the axis  692 A. 
     In the corresponding front view of the lower base member, as shown in  FIG. 15 , the axes  691  and  693  (shown in the form of hinges) are located close to each other and separated only by the combined thickness of the pair of wall segments  694  and  695 . The end wall  690  is at 0° from wall segments  694  and  694 A. The angle measurement between the front wall  615  and wall segment  695 , and the angle between the front wall  615 A and wall segment  695 A, are determined by the equation [180×(n−2)]÷n, where the variable n is the number of sides of the base member  613 B. In  FIGS. 13 to 19 , where the fixed portion  602  is shown to be a 4-sided structure, the angles created by the front wall  615  and wall segment  695 , and the back wall  615 A and wall segment  695 A, are both 90°. 
     In  FIG. 17 , which is a side view of the adjustable portion of the base member viewed from a cross-sectional line  17 - 17  in the fixed portion of the base member as shown in  FIG. 14 , the wall segments  695  and  695 A and the axes  692  and  692 A combine to completely or substantially fill the opening  690 C in the enclosed structure of the fixed portion  602 . In this configuration, the axes  692  and  692 A are touching or substantially touching each other. The wall segments  694 ,  694 A,  695  and  695 A, the end wall  690 , and the lip  690 A are substantially parallel to one another in their length directions. 
     When the adjustable portion is expanded from the collapsed state toward the fully extended state, the pair of wall segments  694  and  695  rotate toward an increasingly open-and-apart state, in which the pair remains connected at their common edges around axis  692  but is increasingly farther apart between the far edges. Similarly, the pair of wall segments  694 A and  695 A rotate toward an increasingly open-and-apart state, in which the pair remains connected at their common edges around axis  692 A but is increasingly farther apart between the far edges. During this continuum from the collapsed state toward the fully extended state, because the far edges of the pair of wall segments remain connected to an edge of the end wall  690  or a side edge of the sidewall  615  (or  615 A), the opening motion of each pair of wall segments causes the axes  692  and  692 A to retract away from the center of the adjustable portion  602 A, creating an open space between  692  and  692 A. The retraction of  692  and  692 A from each other is also seen in  FIG. 17A . Simultaneously, the wall segments move away from the end wall  690  and the lip  690 A to create an open space between these members. Namely, the wall segment  694  rotates away from the end wall  690  around the axis  691  to create a space between the wall segment  694  and the end wall  690 , the wall segment  694 A rotates away from the end wall  690  around the axis  691 A to create a space between the wall segment  694 A and the end wall  690 , the wall segment  695  rotates away from the lip  690 A around the axis  693  to create a space between the wall segment  695  and the lip  690 A, and the the wall segment  695 A rotates away from the lip  690 A around the axis  693 A to create a space between the wall segment  695 A and the lip  690 A. During this continuum of motion, the end wall  690  is gradually removed from, but remains parallel to, the lip  690 A. The concerted motion by the pairs of wall segments  694 ,  695 ,  694 A,  695 A, the end wall  690  and the lip  690 A leads to the formation and enlargement of a continuous open space  690 B. Open space  690 B has a fully or partially open bottom, which provides the pet access to grass on a lawn. 
       FIG. 14A  is effectively a representative and a snapshot in the continuum from the collapsed state to the fully extended state. In  FIG. 14A , the pair of wall segments  694  and  695  rotate around the axis  692  and form an angle “Alpha” between the two segments. Similarly, the pair of wall segments  694 A and  695 A rotate around the axis  692 A and form an angle “Alpha” between the two segments. As is obvious from the use of the same notation “Alpha”, the two angles are congruent and remain congruent as they increase from 0 to 180 degrees as the adjustable portion transitions from the collapsed state to the fully extended state. In the snapshot shown in  FIG. 14A , the wall segments  694  and  694 A are at an angle of Alpha/2 from the end wall  690 . Similarly, the wall segments  695  and  695 A are at an angle of Alpha/2 from the lip  690 A. These two angles are also congruent and remain congruent during the transition of states. 
     In the front view ( FIG. 15A ) that corresponds to  FIG. 14A , the axes  691  and  693 , again shown as hinges, are further apart than in the fully collapsed state. The distance between the axes  691  and  693  is substantially defined by simple geometry, i.e., 2×length of each wall segment×sin(Alpha/2). 
     The transition from a collapsed state to an extended state can be facilitated by the inclusion of a handle  696  on the end wall  690 . When a user pulls on the handle  696  in the direction of extending the adjustable portion  602 A, the adjustable portion  602 A extends. When a user pushes on the handle  696 , or another part of the end wall  690 , in the direction of collapsing the adjustable portion  602 A, the adjustable portion  602 A collapses. 
     As best seen in  FIG. 14B , in a fully extended state, the wall segments  694  and  695  are completely or substantially fully open and apart from each other, having an angle about 180 degrees therebetween at the axis  692 . The wall segments  694  and  695  are collinear to each other. Similarly, the wall segments  694 A and  695 A are fully or substantially fully open and apart from each other, having an angle about 180 degrees therebetween at the axis  692 A. The wall segments  694 A and  695 A are collinear to each other. The axes  692  and  692 A are located far apart from each other and are separated by the full length of the lip  690 A. The wall segments  694  and  694 A are at a right angle or substantially at a right angle to the end wall  690 . The wall segments  695  and  695 A are at a right angle or substantially a right angle to the lip  690 A. 
     In the corresponding front view of the lower base member, as shown in  FIG. 15B , the axes  691  and  693  (shown in the form of hinges) are located far apart from each other and separated substantially by the combined lengths of the wall segments  694  and  695 . 
     In  FIG. 17B , which is the side view of the adjustable portion  602 A viewed from a cross-sectional line  17 B- 17 B in the fixed portion of the base member as shown in  FIG. 14B , the wall segments  694 ,  694 A,  695 , and  695 A are fully retracted and form the sides of the adjustable portion  602 A. The inner side of the end wall  690  is fully in view and serves to fill in the opening  690 C in the enclosed structure of the fixed portion of the lower base member. 
     In this fully extended state, the open space  690 B is enclosed by the end wall  690 , wall segments  694 ,  695 ,  694 A,  695 A, and the lip  690 A. The open space  690 B is at its maximum value. The open space  690 B has a fully open or partially open bottom, which provides the pet access to grass on the lawn. 
     The hinges used in this fifth embodiment can be any of the known hinges. Examples include Rockler Woodworking and Hardware Butt Hinge (item no. #44018), Everbilt hinges (model nos. 13654, 14449, 14874, 14979, 14981, 14985, 15002, 15029, 16909, 19092, 20094, 20175, 20600, 20114, 20164, 20284, 20605), Crown Bolt (model nos. 14982, 15031, 15065, 15409, 15411, 15494, 16115, 16123, 18105, 18107, 18114, 20824), Dynasty Hardware hinges (model nos. SP-40-58-US15-2PK), National Hardware hinges (model nos. N148-585, N241-190), Murphy Door hinges (model no. FMHD), SOSS hinges (model no. 218US26D), and hinges of similar designs by the above-mentioned suppliers as well as other suppliers. The hinges used in this invention can be made of brass, nickel, plastic, or other desired materials. These hinges also utilize holes in the hinge plates, to accept a fastener, which effectively connects the hinges to each of the part such as  620 ,  620 A,  690 ,  694 ,  694 A,  695  and  695 A. 
     As illustrated in  FIG. 18 , conventional butt hinges  691 ,  692 ,  693 ,  691 A,  692 A, and  693 A, can be used to provide an axis. Each hinge comprises two hinge plates, which are connected to intertwining sleeves (also known as tubular sections). A first hinge plate  700  is connected to sleeves  704 ,  704 A, and  704 B. The hinge plate  700  has holes  701 ,  702 , and  703  to accept fasteners, such as a fastener  707 . A second hinge plate  700 A is connected to sleeves  705  and  705 A, which are preferably equal in dimensions to the sleeves  704 ,  704 A, and  704 B, and fit within the gaps created amongst the three sleeves. When the pin  706  is placed through sleeves  704 ,  705 ,  704 A,  705 A, and  705 B, the sleeves are fixed in a collinear arrangement and the hinge plates  700  and  700 A can rotate relative to each other along the common longitudinal axis  706 A. The gap between the sleeves  705  and  705 A is equal in dimensions to the dimensions of the sleeve  704 A. The gap between the sleeves  704  and  704 A are equal in dimensions to the dimensions of the sleeve  705 . The gap between the sleeves  704 A and  704 B are equal in dimensions to the dimensions of the sleeve  705 A. Since the dimensions are all equal to each other, the sleeves fit together, where the bottom of the sleeve  704  touches the top of the sleeve  705 , the bottom of the sleeve  705  touches the top of the sleeve  704 A, the bottom of the sleeve  704 A touches the top of the sleeve  705 A, and the bottom of the sleeve  705 A touches the top of the sleeve  704 A. When the pin  706  is placed into the sleeves  704 ,  704 A,  704 B,  705 , and  705 A, the sleeves are all locked into one line, creating an assembly of rotating hinge plates. 
       FIG. 19  is a view of the hinge  693  and surrounding members as indicated by  19  in  FIG. 14B . As illustrated in  FIG. 19 , a hinge, such as one shown in  FIG. 18 , is used to connect wall segment  695  to front wall  615 . Hinge plate  700  is fastened to the inner side of the front wall  615  using fasteners  707 . Hinge plate  700 A is fastened to the inner side of the wall segment  695  using fasteners  707 . These two hinge plates are connected among a common axis, which is created when the pin  706  is inserted into the sleeves, or tubular sections:  704 ,  704 A,  704 B,  705 , and  705 A, when the sleeves are collinear. When the hinge is fastened in this manner, the sleeves, or tubular sections,  704 ,  704 A, and  704 B are adjacent to and touching the edge  620  of the front wall  615 , and wall segment  695  can rotate relative to the front wall  615 . 
     The hinge  691  preferably has its hinge plates attached to the insides of the end wall  690  and wall segment  694 . 
     As can be understood from the drawings, the adjustable portion  602 A preferably has at least one axis of symmetry, as shown by S-S in  FIG. 14B . The halves below and above the S-S axis are substantially identically structured, including how the hinges are attached to the wall segments, the end wall segment  690  and the opposing front walls  615  and  615 A. 
     Preferably, a net  697  is provided and connected to the top of the end wall  690  and the top of the edges  620  and  620 A, to ensure that the pet does not jump out of the enclosure of the adjustable portion when the adjustable portion  602 A is in a partially or fully extended state. 
     The net  697  is preferably a permanent installation between the top of the edges  620  and  620 A, and the top of the end wall  690 . In this configuration, the net  697  may be made of a non-stretchable or stretchable material. 
     If a non-stretchable material is used, the net  697  is made to be large enough to cover the entire top of the adjustable portion  602 A in a fully extended state. When the adjustable portion  602 A is fully or partially collapsed, the net  697  will hang loose between the end wall  690  and the top of the edges  620  and  620 A. When the adjustable portion is fully extended, the net  697  is fully extended. Materials suitable for making a non-stretchable net  697  can be any filament or fiber known in the art, such as natural yarn or a polymeric material, including but not limited to, polyolefins, acrylics, epoxies, polyamide-imides, polyesters, polyesteramides, polyamides, polyimides, polysulfones and polyurethanes and co-polymers thereof. Examples of polymer filaments are disclosed in numerous patents and patent applications, including EP0506983A1 to Masuda, EP0618985B1 to Bhoori, EP1054085B1 to Kanamori, DE19580248C5 to Horii, WO1995027818A1 to Ballard, US20090075543A1 to Zhang, the disclosure of which are incorporated herein. 
     If a stretchable material is used, the net  697  is permanently attached to the top of the end wall  690 A. When the adjustable portion  602 A moves from a fully collapsed state into a fully extended state, the net  697  stretches in sync to the adjustable portion  602 A, to keep the top closed at all times. Materials suitable for making a stretchable net  697  can be any elastic filament or fiber known in the art, such as natural rubber, plasticized polyvinyl chloride, low density polyethylene, thermoplastic rubber, ethylene-ethyl acrylate, ethylene-butylene copolymer, polybutylene and copolymers thereof, ethylene-propylene copolymers, chlorinated propylene, chlorinated polybutylene or mixtures of those, polyurethane elastomeric materials, polyester elastomeric materials, polyamide elastomeric materials, copolymers of isobutylene and isoprene, and additional materials disclosed in U.S. Pat. No. 4,425,393 to Benedyk, U.S. Pat. No. 4,874,447 to Hazelton, U.S. Pat. No. 4,657,802 to Morman, U.S. Pat. No. 4,833,012 to Makimura, U.S. Pat. No. 4,820,572 to Killian, U.S. Pat. No. 4,803,117 (Daponte), U.S. Pat. No. 4,940,464 to Van Gompel, U.S. Pat. No. 4,938,757 to Van Gompel, U.S. Pat. No. 4,938,753 to Van Gompel, and U.S. Pat. No. 6,140,442 to Knight, the disclosure of which are incorporated herein. 
     When the pet is kept indoors, the adjustable portion  602 A is in a fully collapsed state, so that the pet only lives in the fixed portion  602 , which has a bedding material. When the pet is to be fed with fresh grass on a lawn, the pet cage is moved outdoors and rested on a lawn, and the adjustable portion  602 A is transitioned into a partially or, more preferably, a fully open state, exposing the partially or fully open bottom underneath the adjustable portion  602 A. The pet then may migrate from the fixed portion  602  to the adjustable portion  602 A to access fresh grass. Once feeding is completed, the pet is directed to return to the fixed portion  602  and the adjustable portion  602 A is returned to the fully collapsed state. 
     The adjustable portion is not only limited to the use of feeding, but may also be used to conveniently clean bedding from the cage. When the cage is to be cleaned, the adjustable portion  602 A is transitioned into a partially or, more preferably, a fully open state. The pet then may migrate from the fixed portion  602  to the adjustable portion  602 A to temporarily make it more convenient to clean the bedding in the cage, without interference from the pet. Once cleaning is completed, the pet is directed to return to the fixed portion  602  and the adjustable portion  602 A is returned to the fully collapsed state. 
     While the figures described herein for the fifth embodiment are substantially based on the fourth embodiment, and represents a modern construction of pet cages, this invention is not limited to such construction. For example, the pet cage in accordance with the fifth embodiment can comprise an upper cage member and a lower base member as described in any of the preceding embodiments. One example would be the first embodiment, wherein the enclosure and lid are effectively incorporated into the upper cage member and/or the base member. 
     While only one adjustable portion is illustrated in  FIGS. 13 to 19 , the base member may have one or more additional adjustable portions of similar construction, each matching the shape and size of the sidewall of the lower member to which the additional adjustable portion is adjacent to. If desired, additional adjustable portions may be added to the fixed portion by converting one wall to a lip and connecting an adjustable portion with a construction as described above. 
     In all the preceding embodiments, all parts of the cage, including the parts of the adjustable portion  602 A, 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, polyamide-imides, polyesters, polyesteramides, polyamides, polyimides, polysulfones and polyurethanes and co-polymers thereof, such as those described U.S. Pat. No. 3,617,364 to Jarema, U.S. Pat. No. 3,829,545 to Van Vlaenderen, U.S. Pat. No. 3,893,642 to Van Vlaenderen, U.S. Pat. No. 4,521,363 to Vogel, U.S. Pat. No. 4,541,980 to Kiersarsky, U.S. Patent Application Publication No. 20080193755 to Guise, 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. 
     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.