Collapsible frame structure for pen and cot

A collapsible pen, comprising

• a collapsible frame which comprises:
• two pairs of first frame legs pivotally connected with each other in a cross manner to form a pivotal “X” structure;
• two pairs of second frame legs pivotally connected with each other in a cross manner to from a pivotal “X” structure, wherein said two pairs of first frame legs are perpendicularly connected with said two pairs of second frame legs respectively to form a box structure that defines an interior cavity surrounding by said first and second frame legs;
• four upper frame joints pivotally connecting four upper ends of said first frame legs with four upper ends of said second frame legs respectively;
• and
• four lower frame joints, each of which is positioned under one of said upper frame joints, pivotally connecting four lower ends of said first frame legs with four lower ends of said second frame legs respectively;
• and
• a fabric made boundary shelter supported by said collapsible frame structure,
• wherein said boundary shelter is suspended in said interior cavity by overlappingly supporting four top edge portions of said boundary shelter on said four upper frame joints respectively.