Patent ID: 6866080

Claim:
A method of opening and closing an opening in a structure with a bi-fold door having first and second panels, each panel having a top portion and a bottom portion, means movably mounting the first panel on the structure, hinges connecting the first panel to the second panel to allow the first and second panels to be moved from generally vertically aligned positions closing the opening to side-by-side folded positions opening the opening, and door lift devices having rotatable members having a common axis of rotation operable to selectively open and close the bi-fold door, and means mounting the door lift devices on the bottom portion of the second panel comprising: connecting elongated flexible webs to the rotatable members, training each web over a roller connected to a top portion of the first panel, anchoring each web to the bottom portion of the first panel, aligning each web normal to the axis of rotation of a rotatable member, maintaining the alignment of the web with the rotatable member to ensure an overlapping relationship of the web around the rotatable member, simultaneously rotating the rotatable members in one direction with a power unit at a constant rate of speed to wind the webs in overlapping relation around the rotatable members, maintaining the alignment of the webs with the rotatable members during rotation of the rotatable members in the one direction to wind the webs around the rotatable members to ensure overlapping relationship of the webs around the rotatable members to move the first and second panels at an increasing rate of speed from a closed position to an open position, rotating the rotatable members in a direction opposite the one direction at a constant rate of speed to unwind the webs from overlapping relationship around the rotatable members, and maintaining the alignment of the webs with the rotatable members during rotation of the rotatable members in the direction opposite the one direction to unwind the webs from the rotatable members to maintain the overlapping relationship of the webs on the rotatable members during unwinding of the webs from the rotatable members to move the first and second panels at a deceasing rate of speed from an open position to a closed position.