A collapsible structure has a base panel that includes separate first and second sides, a foldable frame member having a folded and an unfolded orientation, and a fabric material covering portions of the frame member to form the base panel when the frame member is in the unfolded orientation. The structure...http://www.google.com.hk/patents/US6289910?utm_source=gb-gplus-share專利 US6289910 - Collapsible structures
