US 7,343,958 B1
	Overhead door lift system
A. Anthony East, East Bend, N.C. (US); Darrin Brunk, Lawrence, Kans. (US); Yannick Funk, Drummondville (Canada); Normand Savard, Drummondville (Canada); and Mathieu Provencal, St. Dares de Brompton (Canada)
Assigned to Amarr Company, Winston-Salem, N.C. (US)
Filed on Apr. 04, 2005, as Appl. No. 11/98,187.
Int. Cl. E05F 11/04 (2006.01)

U.S. Cl. 160—191  [16/401; 242/602.1]

9 Claims

1. A counterbalance mechanism for a sectional overhead door of a type having a substantially non-linear lift-weight to lift-height ratio, wherein the mechanism comprises at least one substantially linear torsion spring and is capable of applying different counterbalancing lift forces to the door at different intermediate door positions between a fully closed position and a fully open position, wherein the difference between an intermediate lift weight of the door and a corresponding counterbalancing lift force at any intermediate door position is substantially constant, wherein the counterbalance mechanism further comprises at least one cable drum having a cable winding groove therearound having a first groove end corresponding to a first end of the drum and having a second groove end corresponding to a second end of the drum, wherein the winding groove has substantially continuously varying groove minor radii between the first and second groove ends, wherein the winding groove has a first minor radius at a first turn that is greater than a second minor radius at a second turn and is greater than a third minor radius at a third turn, and wherein the second turn is located between the first turn and the first end of the drum and the third turn is located between the first turn and the second end of the drum.