| 摘要 |
A roller shade (1) including a flexible sheet member (9) having opposite parallel first and second edges (11, 13), and a roller shaft (3) rotatable in each of two opposite directions of rotation. The flexible sheet member (9) is attached along its first edge (11) to the roller shaft (3), while the second edge (13) of the flexible sheet member (9) is freely depending from the roller shaft (3). A raised position of the roller shade (1) is defined when the flexible sheet member (9) is fully wound about the roller shaft (3) and a lowered position is defined when the flexible sheet member (9) is fully unwound from the roller shaft (3). The roller shade (1) further comprises a counterbalancing device (23) for balancing a portion of the flexible sheet member (9) that is unwound from the roller shaft (3). This counterbalancing device has means, such as a helical spring (not shown but in use located between spring winder (55) and spring holder (57)), for storing a variable torque that is complementary to a variable weight of the portion of flexible sheet member (9) that is depending from the roller shaft (3). The variable torque thus stored prevents rotation of the roller shaft (3) due to the variable weight of the portion of flexible sheet member (9) depending from the roller shaft (3) in any position between the raised and lowered positions. The variable torque also increases as the second edge (13) of the flexible sheet member (9) is lowered. Due to the complementary torque provided by the counterbalancing means, no additional braking means is required or provided. |
