US Patent 7254868 winding and anti-drop assembly for door counterbalance system

A counterbalance system (25) for a door (D) movable between a closed position and an open position having an axle (20), a cable drum (15) attached to the axle, a winding shaft (35) interconnected with the axle by a counterbalance spring (26), and a pawl (70) selectively movable between a first position for adjusting tension in the counterbalance spring and a second position for preventing rotation of the cable drum upon failure of the counterbalance spring, thereby limiting movement of the door toward the closed position.