Abstract: A window cover system includes an extendible window cover that has a pair of lift cords. A lift cord pulley shaft is coupled to a pair of spaced apart lift pulleys. A spring drive unit is constructed of a beveled gear system with a first gear that is spring biased to resist rotation of the first gear in one direction of rotation, and a second gear meshed with the first gear. The lift cord pulley shaft is operably coupled to the second gear and is configured to rotate therewith. The spring drive unit has a single output and no input, and the single output is coupled to the first gear.

Abstract: A method for operating a window cover utilizes an extendible window cover having a first rail, a second rail and a pair of lift cords. The first and second rails of the window cover are movable relative to each other. According to the method, at least one of the first rail and the second rail is moved in a first direction to cause the lift cords to unwind from the lift cord pulleys, thereby rotating a lift cord pulley shaft and a set of gears. Further, at least one of the first rail and the second rail is moved in a second direction to cause the lift cords to wind on the lift cord pulleys, with the lift cord pulley shaft rotating in an opposite direction.

Abstract: A method for operating a window cover utilizes an extendible window cover having a first rail, a second rail and a pair of lift cords. The first and second rails of the window cover are movable relative to each other. According to the method, at least one of the first rail and the second rail is moved in a first direction to cause the lift cords to unwind from the lift cord pulleys, thereby rotating a lift cord pulley shaft and a set of gears. Further, at least one of the first rail and the second rail is moved in a second direction to cause the lift cords to wind on the lift cord pulleys, with the lift cord pulley shaft rotating in an opposite direction.

Abstract: A window cover system includes an extendible window cover with a pair of lift cords. A lift cord pulley shaft is coupled to a pair of spaced apart lift cord pulleys. A spring drive unit has a beveled gear system with a first gear that is spring biased to resist rotation of first gear in one direction of rotation, and a second gear meshed with the first gear. The lift cord pulley shaft extends through the second gear and is configured to rotate therewith.