Patent ID: 7503370
Filing Date: 2009-03-17
Classification: E06B,F03G

Abstract:
1. A window covering of the type including a headrail, a bottom rail and window covering material located therebetween, the bottom rail being movable between a fully raised and a fully lowered position with respect to the headrail and being movable to intermediate positions therebetween, the window covering further including cord means coupled to the bottom rail and extending to the headrail for causing the bottom rail to be moved toward and away from the headrail, the improvement comprising: a spring motor including a cord spool; the cord means coupling the bottom rail to the cord spool; the spring of the spring motor being coupled to the cord spool to exert spring forces upon the spool as cord is wound therefrom and wound thereon, the spring being an elongate spring which moves from a first to a second spring storage drum and which is selected to have sufficient spring force to essentially balance the bottom rail against movement when the bottom rail is in any position; and a cord drag mechanism comprising: the covering material being movable by an operator to a selected desired position by the operator urging the bottom rail upwards or downwards to a desired position, and the arrangement being such that the bottom rail remains in the selected desired position, and in which there is sufficient friction in the movable parts of the window covering that the effect of friction compensate for any imbalance between (i) the weight of the bottom rail and as much of the window covering material that is supported by the bottom rail at any particular extension of the window covering and (ii) the upwards force applied by the spring motor to the bottom rail at said particular extension, which upwards force (ii) essentially balances the weight (i) with the bottom rail in any position, but with friction completing the balance to avoid free-fall of the bottom rail or self-raising of the bottom rail.