US Patent 6862845 Drop-catch mechanism for an overhead door

A drop-catch mechanism for preventing the door leaf of an overhead door from rapidly closing upon breakage of the balancing spring thereof. The drop-catch mechanism having an input member for coupling with the balancing spring of the overhead door, a ratchet wheel for coupling with a winding axle carrying the door leaf of the overhead door, a pawl, and a positive mechanical drive for moving the pawl from a free position that allows rotation of the ratchet wheel to a catching position that blocks rotation of the ratchet wheel, the positive mechanical drive being configured such that, in use, breakage of the balancing spring coupled to the input member causes the pawl to move from the free position to the catching position.