Roller shade with a counterbalancing device

A roller shade comprising:

• a flexible sheet member;
• a roller shaft rotatable in each of two opposite directions of rotation, the flexible sheet member having a first end coupled to the roller shaft and a second end freely depending from the roller shaft, so as to define a raised position of the roller shade in which the flexible sheet member is wound about the roller shaft and a lowered position in which the flexible sheet member is unwound from the roller shaft;
• a counterbalancing device for balancing a portion of the flexible sheet member that is unwound from the roller shaft, the counterbalancing device including:
• a stationary central rod;
• a helically wound tension spring for storing a variable torque complementary to a variable weight of the portion of the flexible sheet member that is depending from the roller shaft, one end of the helically wound tension spring being coupled to a spring holder and an opposite end of the helically wound tension spring being coupled to a spring winder;
• a screw threaded shaft provided in operative association with the spring winder;
• and
• a rod adjuster that is selectively rotatable to rotate the stationary central rod relative to the screw threaded shaft so as to increase or decrease the tension of the helically wound tension spring by relative rotation of the spring holder;
• and
• a bottom bar coupled to the second end of the flexible sheet member;
• wherein:
• the variable torque stored in the helically wound tension spring prevents rotation of the roller shaft due to the variable weight of the portion of the flexible sheet member depending from the roller shaft in any position between the fully wound and the fully unwound position and increases as the second end of the flexible sheet member is lowered;
• and
• the rod adjuster is engageable to adjust the tension in the helically wound tension spring when the roller shaft is mounted in position on mounting brackets.