Stacking panel shutter doors

A stacking panel shutter door, comprising a torsion spring counter balancing mechanism including at least one torsion spring, wherein

• a) one end of the at least one torsion spring is fixed to a drive transmission shaft of the stacking panel shutter door, the drive transmission shaft being adapted to raise and lower at least one shutter of the stacking panel shutter door;
• and
• b) a second end of the at least one torsion spring is fixed to a separate rotatable member of the stacking panel shutter door, the separate rotatable member surrounding a substantial portion of each of the at least one torsion spring and the drive transmission shaft;
• and,
• whereby the mechanism is provided with means for enabling both of the drive transmission shaft to rotate in a first direction and the separate rotatable member to rotate in tandem in the first direction, during opening and closing of the stacking panel shutter door, in such a manner to cause respective ends of the at least one torsion spring to travel at different speeds during an opening and closing sequence, the means comprising:
• a first sprocket operatively connected to the drive transmission shaft;
• and
• a second sprocket operatively connected to the separate rotatable member;
• and,
• the first and second sprockets being in a spaced apart, planar parallel non contiguous relationship and operatively linked in a sequence or train;
• wherein the drive transmission shaft and the separate rotatable member rotate at different rates during the opening and closing of the stacking panel shutter door.