A portable and reversible collapsible structure that contains a bottom panel and a plurality of side panels. Each of the side panels contains a fabric material attached to at least one frame with each frame foldable between an expanded position and a recoiled position. At least two side panels are hingedly connected to opposing sides of the bottom panels. At least one detachable side panel is further attached to the bottom panel and in a position that is in between the opposing side panels. The connection between the detachable side panel and the bottom panel is reversible and detachable by a user. The connection between the detachable side panel and one of the opposing side panels is also reversible according to the needs of a user.

FIELD OF INVENTION 
     The present invention is related to collapsible toy structures such as tents and playhouses. 
     BACKGROUND OF INVENTION 
     Collapsible structures that are used for playhouses are well-known in the art. They are typically collapsible into a small volume but can be easily popped up by various means, including the use of extendable frames and inflatable tubes. U.S. Pat. No. 6,305,396 described a collapsible structure that is provided with a plurality of foldable frame members each having a folded and an unfolded orientation. A fabric material is provided for covering a portion of each frame member to form a side panel therefrom. The structure may be folded and stored by folding the side panels and their corresponding frame members on top of each other about the hinge portions to have the side panels and frame members overlying each other. The overlying side panels and frame members are then collapsed by twisting and folding to form a plurality of concentric frame members to substantially reduce the size of the structure. 
     The above described structure has many advantages, but has the limitation of not being able to have substantially different sizes for the side panels. It is therefore an object to have present invention to provide improved collapsible structures. 
     SUMMARY OF INVENTION 
     Accordingly, the present invention provides a portable and reversibly collapsible structure that contains a bottom panel and a plurality of side panels. Each of the side panels contain a fabric material attached to at least one frame with each frame foldable between an expanded position and a recoiled position. At least two side panels are hingedly connected to opposing sides of the bottom panel. At least one detachable side panel is further attached to the bottom panel and in a position that is in between the opposing side panels. The connection between the detachable side panel and the bottom panel is reversible and detachable by a user. The connection between the detachable side panel and one of the opposing side panels is also reversible according to the needs of a user. 
     According to one embodiment, the bottom panel assumes a quadrilateral shape having two opposing edges interposing two opposing ends. Two side panels are connected to the opposing edges of the bottom panel (these two side panels are also referred to as the first and second connected side panels for ease of the description) while a first and second detachable side panels are provided at the two opposing ends. The first detachable side panel is provide with attachment means at the bottom for detachable attachment to one of the ends of the bottom panel. The first detachable side panel also contains an attachment means for detachable attachment to one side to the second connected side panel but is hingedly connected to one side of the first connected side panel. The second detachable side panel is detachably connected at the bottom to the other end of the bottom panel. This second detachable side panel is also provided with an attachment means for detachable attachment to one side of the first connected side panel but is hingedly attached on the other side to the second connected side panel. 
     In a second embodiment, the two detachable side panels are completely detachable from the bottom and the two connected panels. 
     In a third embodiment, the two connected side panels each contains two frames that are hingedly adjoined side by side to form a single side panel. 
     A distinct advantage of the instant invention is that the collapsible structure according to the present invention is extremely flexible in terms of size and shapes. Rectangular structures with the long side substantially longer than the short end, may be made and easily collapsible similar to the equilateral shape that was previously provided in the art. Furthermore, there is an added advantage of the second embodiment being able to interchange one or both end panels such that different shapes and functions may be substituted conveniently. The present invention thus provide a truly versatile and inter-convertible structure. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1A is a drawing of a partial structure according to one embodiment of the present invention showing the two side panels that are hingedly connected to the bottom panel. 
     FIG. 1B shows the two detachable end panels according to the same embodiment as FIG.  1 A. 
     FIG. 1C shows a portion of the same embodiment as FIGS. 1A and 1B showing a zipper as the attachment means for attaching the detachable panel onto the connected side panel and bottom panel. 
     FIG. 1D shows a perspective view of the same embodiment with the top of the structure detached. 
     FIG. 1E shows a perspective view of the same embodiment with the top structure attached. For clarify of illustration, the hidden sides of the panels are also shown. 
     FIG. 1F shows how the two connected side panels may be folded and stacked together. 
     FIG. 2A shows a second embodiment according to the present invention in which the side panels are similar to the one shown in the first embodiment but the top assume the look of a wagon. 
     FIG. 2B shows the bottom side of the wagon top. 
     FIG. 2C is a perspective view of the assembled structure according to the same embodiment as FIG.  2 A. 
     FIG. 3A shows a third embodiment in which a rooftop is provided above the side panels. 
     FIG. 3B shows a perspective view of the same embodiment as FIG. 3A with the rooftop attached thereto. 
     FIG. 3C shows the same embodiment as FIG. 3A with the detachable side panel partially detached. 
     FIG. 3D shows the partial views of the same embodiment as FIG. 3A illustrating how different detachable end panels may be provided and inter-changeable therebetween. 
     FIG. 4A shows a fourth embodiment according to the present invention in which an teepee structure is shown. 
     FIG. 4B is a diagram to show how the side panels in FIG. 4A may be detachable by unzipping therefrom. 
     FIG. 4C shows unzipped or detached side panels that are aligned with the neighbouring panel in preparation for folding the panels into the collapsed form. 
     FIG. 4D is a diagrammatic representation of the four side panels shown in FIG. 4A being superimposed and aligned one on top of another and with one comer of the side panel being twisted to illustrate how the collapsible form may be obtained. 
     FIG. 4E shows the second step of the folding process of the same example shown in FIG.  4 D. 
     FIG. 4F shows the final step of the folding process of the same embodiment in which one loop-shaped frame is folded into three concentric loops. 
    
    
     DETAILED DESCRIPTION 
     Referring first to FIGS. 1A to  1 E, one embodiment of the present invention contains two opposing side panels  22  and  24  that are connected theretogether by a rectangular shaped bottom fabric  26 . In this embodiment, panel  22  contains two loops  40   a  and  40   b  each defining a flat surface. The two loops are placed juxtaposing each other with their respective flat surfaces defining the flat surface of the side panel and with a fabric placed across the two loops and sewn together such that they form a single side panel. Side panel  24  is also similarly constructed with two loops  40   c  and  40   d  positioned juxtaposing each other and another panel sewn thereover to form a single panel. The two side panels  22  and  24  are sewn together on opposing sides of a rectangular shaped bottom panel. Since the loops are rigid, the direction of movement for the two side panels relative to the bottom panel is typically a rotational movement about an axis defined by the bottom side of each side panel in the direction as shown by the arrow and is hereinafter referred to as a hinged connection. The rotational movement allowed by the hinged connection is simply due to the flexibility of the fabric material. In the preferred embodiment, there is no requirement to install an actual hinge in the side panel or bottom panel, although such hinges are not excluded from the scope of the instant invention. The hinged connection, however, does not preclude the  2  frames of the same panel from rotating towards each other at 90 degrees from the hinged connection as shown in FIG.  1 F and explained later. In this embodiment two long half zippers  28  and  30  are provided with one half sewn on either side of side panel  24  across bottom panel  26  and all the way along the sides  22   d  and  22   b  of the side panels  22  and  24  respectively. In greater detail as shown in FIGS. 1A and 1B, the half-zipper  30  starts from a corner fabric flap  24   a  of frame  24  and extend along the side  24   b  of panel  24  down to one end  26   b  of bottom panel  26  along the side  22   b  of panel  22  and ends with attachment to a fabric flap  22   a  that extends from the corner of side panel  22 . Similarly, half-zipper  28  starts from a corner fabric flap  22   c  of frame  22  and extend along the side  22   d  of panel  22  down to the other end  26   c  of the bottom panel  26  along the side  24   d  of panel  24  and ends with attachment to a fabric flap  24   c  that extends from the comer of side panel  24 . 
     End panels  32  and  34  as shown in FIG. 1B contains the other half-zipper  32   a  and  34   a  respectively that are adapted for complementary zipping with half-zippers  28  and  30  respectively. As shown in FIG. 1C, end panel  34  contains zipper  34   a  that allows the panel to be attached to flap  24   a  and side  24   b  of side panel  24 . Further attachment is provided with end  26   b  of bottom panel  26  and across to side  22   b  of side panel  22 . The zipper  34   a  finally zip up from an extension flap  22   c  that extends from the upper top corner of side panel  22 . Once the side panels are attached, a rectangularly shaped open structure is defined as shown in FIG.  1 D. In this embodiment, a top is also provided and is attachable to the rectangular structure using Velcro™ tape  38   a  that may be attachable to the complementary Velcro™ side  38   b  that is provided on side panel  22  and  24  and also along the top edge of end panels  32  and  34 . 
     In this embodiment, side panels  22  and  24  each consists of two loop frames that are shown as  40   a  to  40   d  are shown in FIGS. 1A and 1D. The same frame is not illustrated in FIG. 1E in order not to obscure the structure are shown. The possibility of using twin frames for the side panel shows one advantage of the instant invention. The side panel can be unfolded and the two frames  40   a  and  40   b  of the same panel may be folded as shown in FIG. 1F such that they overlay each other. Each of the twin frames may also be folded along line A—A as shown in FIG. 1F such that all four frames may be unzipped and folded to aligned one above another. Since the end panel  32  and  34  are completely detachable, they may also be put on top of these stacks of frames such that all the frames may now be twisted together to from concentric loops simultaneously for ease of storage. 
     FIGS. 2A to  2 C shows a similar embodiment of the same invention except that the end panels  32  and  34  are replaced by taller end panels  42  and  44  and top  36  is replaced by wagon top  46 . Top  46  also contains three identical loops  46   a  that may be kept apart by extendible rods  46   b . The wagon top is then tied onto the frame by lengths of fabric  48  that are provided at the appropriate places. 
     FIGS. 3A to  3 D show another embodiment of the present invention in which side panels  50  and  52  each formed by a single loop are attached at the bottom by a bottom panel  51 . End panel  54  and  56  are completely detachable by unzipping zippers  58  and  60  (see FIG.  3 C). The end panels  54  and  56  have heights that are higher than side panel  50  and  54  such that a downward-sloping rooftop  62  may be supported above the end panels. The rooftop  62  may be attached to the side structure via attachment strings  64  that are provided at the appropriate places. In this example, a window  66  is provided on side panel  50  and a door  68  provided on end panel  56  such that these structures may appear like a house. The other end panel  54  contains a window with curtain  70  that may be used as a public stage or Theatre. 
     Referring to FIGS. 4A to  4 F, a fourth embodiment of the present invention contains a structure that assumes the shape of an Indian teepee tent. The tent contains four panels  80 ,  82 ,  84  and  86  that have identical shapes of a substantially triangular form with two neighbouring panels  80  and  84  hingedly connected by the side and the opposing two neighbouring panels  82  and  86  also hingedly connected at the side. A zippers is provided for attachment between panels  80  and  82 . Another zipper is provided for attachment between panels  84  and  86 . These zippers also run along the bottom of panels  80  and  84  for attachment to the bottom panel  87 . In this way, the two connected side panels  80  and  84  may be completely detached from the other side panels and also from the bottom panel  87 . Thus, bottom panel  87  is permanently connected to side panels  82  and  86  and may be folded theretogether during the storage process. After detachment, the panels are shown in FIG. 4C with panels  80  and  84  (panel  84  not shown as it is behind panel  80 ) forming one group and panels  82  and  86  forming another group (panel  82  also not shown as it is behind panel  86  in FIG.  4 C). All four panels may then be stacked together as shown in FIG.  4 D and twisted according to the steps shown in FIGS. 4D to  4 F into a recoiled position of three concentric loops to reduce the size for ease of storage. 
     While the above examples are used to illustrate various aspects of the present invention, it is clear that they are for illustration only and are not meant to limit the scope of the invention as claimed herein. Nevertheless, these examples served to illustrate the versatility of the instant invention. For example, the top illustrated in FIGS. 1D and 1E assumes the appearance of an opening vehicle while a wagon top and a rooftop are shown in subsequent examples. These tops require side panels with different heights in order to make their shape realistic and the technical solution according to the present invention is to inter-change the various side panels conveniently by providing attachment means thereto. Furthermore, it is clear that tops of many other shapes may be produced and adapted for use according to the present invention. For example, tops that are conical, dome, pyramidal or tapered in shape may also be inter-changed according to the present invention. Although zippers are used in the examples and is the preferred means for attachment of the end panels to the bottom panel and the side panels, it is clear that other means of attachment, such as simple strings and lengths of fabric may be used to tie the side panels together. In the preferred embodiment, the end panels are attached not only to the frame of the side panel, but also to the extending corner flaps such that the structures are very stable. The comer flaps provide anchoring points for improved stability of the side panels. 
     In addition to the completely detachable end panels as described above, it is also possible for the end panel to be detachable from the bottom panel and one of the side panel, while hingedly connected to the other side panel. This specific embodiment would not conveniently allow for changeability of the end panels, but would still allow the side panel to assume various lengths and shapes, since each end panel can still be folded together with the connected side panel. This can easily be done by changing to a shorter zipper and permanently sewing one side of the end panel to one side of a side panel. 
     If the end panels are completely detachable, the side panels may assume a long rectangular shape even with the use of a single frame for each side panel. Once the end panel are detached from the side panels, the side panels may be stacked together and twisted into their recoiled position.