Patent ID: 8573281

Claim:
A top down/bottom up covering for an architectural opening comprising in combination: a headrail; at least two horizontally disposed vertically movable rails supporting at least one panel of collapsible shade material; at least two flexible lift cords affixed to each rail; a control system component associated with each rail, each component including an elongated drive shaft, a system for reciprocally and reversibly rotating said drive shaft about its longitudinal axis, a wrap spool rotatable with said drive shaft and connected to a lift cord such that said lift cord can be wrapped about or unwrapped from said wrap spool, vertical movement of said rails being effected by wrapping and unwrapping of said lift cords about said spools, and a cord tension control system for preventing said lift cords from becoming entangled at said wrap spools, said cord tension control system including a threaded shaft associated with and rotatable in unison with each drive shaft, a nut threaded on each of said threaded shafts for translating movement along an associated shaft, the nuts on said threaded shafts overlapping in their path of travel along an associated threaded shaft whereby upon engagement of said nuts with an adjacent nut the drive shafts will be prohibited from rotating in a predetermined direction thereby prohibiting the wrap spools on said drive shafts from rotating; said cord tension control system further including a housing in which said threaded shafts are rotatably mounted, fixed abutments in said housing in engagement with said threaded shafts to prevent a predetermined amount of axial movement of said shafts in a predetermined direction and resilient members in said housing biasing each of said shafts against said fixed abutments.