主权项 |
1. Roller shade including a flexible sheet member having opposite parallel first and second edges, 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 in a longitudinal direction thereof, the second edge of the flexible sheet member being freely depending from the roller shaft, so as to define a raised position of the roller shade in which the flexible sheet member is fully wound about the roller shaft and a lowered position in which the flexible sheet member is fully unwound from the roller shaft, the roller shade further comprising a counterbalancing device for balancing a portion of the flexible sheet member that is unwound from the roller shaft, the counterbalancing device having means for storing a variable torque complementary to a variable weight of the portion of flexible sheet member that is depending from the roller shaft, wherein the variable torque stored in the means for storing variable torque prevents rotation of the roller shaft due to the variable weight of the portion of flexible sheet member depending from the roller shaft in any position between the fully wound and the fully unwound position and increasing as the second edge of the flexible sheet member is lowered, and wherein the means for storing variable torque includes a helically wound tension spring. |