Patent ID: 8381793

Claim:
A lift mechanism for a Venetian blind comprising: a drive shaft, lift cords for raising and lowering slats of the Venetian blind, at least one tubular member mounted for rotation always with, and for an axial displacement over, the drive shaft, an associated guide for maintaining the lift cords in a proper axial position and for directing the lift cords to an outer circumferential surface portion of said tubular member, whereby the lift cords upon rotation and axial displacement of said tubular member are helically wound on or off the outer circumferential surface portion of the tubular member resulting in the slats of the Venetian blind being raised or lowered as the tubular member rotates, and wherein the axial displacement of the tubular member over the drive shaft is controlled in synchronism with the rotation of said drive shaft thereby controlling the pitch of the helical winding of the cords on the outer circumferential surface portion of the tubular member, wherein the axial displacement over the drive shaft is controlled by a linear worm gear of a rack rail and pinion system, where a circumferentially threaded pinion is rigidly connected to the tubular member and rotationally coupled to the drive shaft and the threads of the threaded pinion are in engagement with a stationary rack rail, said threaded pinion operating as an axial driving mechanism for the tubular member in synchronization with the drive shaft and thereby controlling the pitch of the helical winding of the lift cords onto the tubular member.