Patent attributes
A roller shade including a flexible sheet member having opposite parallel first and second edges, and a roller shaft rotatable in each of two opposite directions of rotation. The flexible sheet member being attached along its first edge to the roller shaft, while the second edge of the flexible sheet member is freely depending from the roller shaft. The roller shade further comprises a counterbalancing device for balancing a portion of the flexible sheet member that is unwound from the roller shaft. This counterbalancing device has means for storing a variable torque that is complementary to a variable weight of the portion of flexible sheet member that is depending from the roller shaft. The means for storing variable torque includes a helically wound tension spring operatively interposed between a stationary central rod and the roller shaft.
