Abstract: A foldable cover of simple structure and light weight is provided. The cover consists of multiple cover sections which are connected by hinges so that they may be folded together. Each of the cover sections has a hole in its surface through which a cable extends, such that when the cable is pulled, the cover sections are folded together at one side of the opening. The cable is initially pulled from a height above the cover sections so that the first pair of cover sections are caused to buckle upwards and then fold together. Further pulling on the cable causes the remaining pairs of cover sections to buckle and fold one pair at a time. When the cover is being extended, a tension is maintained on the pulling cable so as to control the falling speed of the cover sections as they unfold. Hinges and wheels that are used on the cover and around the holes exhibit a low rotational friction, so that the cover may be opened and closed easily.

Abstract: A drawbridge apparatus for reversibly spanning from a first pier to a second pier. The apparatus comprises first and second cantilevered beams, rack and pinion beam drive mechanisms, first and second bascular leaves, first and second hinged leaves, and rack and pinion leaf drive mechanisms. The first and second cantilevered beams are slidably coupled to the first and second piers, respectively. The beams are arranged and configured to project from the first and second bases to a location between the two where the beams make a locking interconnection when the bridge is in its down configuration. The beam drive mechanisms cause the first and second cantilevered beams to slide from and into the first and second bases, respectively. The first and second bascular leaves have first and second counterweight portions and first and second span portions, respectively. The bascular leaves are pivotally coupled to the bases at the intersections of the counterweight portions with the span portions.