Worm gear drive mechanism for a covering for architectural openings

Abstract

A drive module for a covering for architectural openings includes a driver worm and a driven worm with axes of rotation substantially parallel to each other.

1 . An arrangement for covering an architectural opening, comprising: 
 a movable covering for architectural openings defining a longitudinal direction;    an elongated rod extending in said longitudinal direction and operatively connected to said covering;    a first worm gear defining a first axis of rotation oriented in said longitudinal direction and defining a first lead angle;    a second worm gear meshing with and driven by said first worm gear; said second worm gear defining a second axis of rotation and a second lead angle, wherein said first and second axes of rotation are substantially parallel to each other, and said second lead angle is larger than said first lead angle, said second worm gear being coaxial with and operatively connected to said elongated rod; and    a housing supporting said first and second worm gears for rotation.    
     
     
         2 . An arrangement as recited in  claim 1 , wherein said covering includes a plurality of lift cords, and wherein said elongated rod is operatively connected to said lift cords.  
     
     
         3 . An arrangement as recited in  claim 1 , wherein said covering is a blind including a plurality of slats supported on a plurality of ladder tapes, and wherein said elongated rod is operatively connected to said ladder tapes for tilting said slats open and closed.  
     
     
         4 . An arrangement as recited in  claim 1 , and further comprising: 
 a pulley defining a cord-receiving surface, said pulley being operatively connected to said first worm gear; and    first and second counter-wrapped actuating cord segments secured to said pulley, wherein pulling on said first cord segment rotates said first worm gear in a first direction, and pulling on said second cord segment rotates said first worm gear in the opposite direction.    
     
     
         5 . An arrangement as recited in  claim 4 , wherein said cord-receiving surface is substantially cylindrical and includes at least one annular flange separating said counter-wrapped cord segments.  
     
     
         6 . An arrangement as recited in  claim 4 , wherein said cord-receiving surface includes at least one frustroconical portion.  
     
     
         7 . An arrangement as recited in  claim 6 , wherein said cord-receiving surface is threaded.  
     
     
         8 . An arrangement as recited in  claim 1 , wherein the lead angles of said first and second worm gears are in the 3 to 7 degree range, and the difference between the lead angle of the first worm gear and the lead angle of the second worm gear is less than 4 degrees.  
     
     
         9 . An arrangement as recited in  claim 8 , wherein the difference in the lead angles between said first and second worm gears is in the 1 to 3 degree range, and said axes of rotation of said first and second worm gears are offset from being truly parallel to each other by said difference in the lead angles.  
     
     
         10 . An arrangement as recited in  claim 9 , wherein said housing includes a first housing portion and a second housing portion, which, when assembled, substantially enclose and secure said first and second worm gears, preventing axial movement of said first and second worm gears and defining bearing support surfaces which rotationally support said first and second worm gears and maintain said offset between said first and second worm gears.  
     
     
         11 . An arrangement as recited in  claim 1 , wherein said first worm gear further defines an interrupted thread portion, and said housing further defines a bearing support portion which is received by said interrupted thread portion and supports said first worm gear.  
     
     
         12 . An arrangement for a covering for an architectural opening, comprising: 
 a movable covering having an extended position and a retracted position;    at least one cord operatively connected to said movable covering for extending and retracting said movable covering;    a driver operatively connected to said cord, said driver including 
 a first worm gear defining a first axis of rotation and a first lead angle;  
 a second worm gear meshing with and driven by said first worm gear; said second worm gear defining a second axis of rotation and a second lead angle, wherein said first and second axes of rotation are substantially parallel to each other, and said second lead angle is larger than said first lead angle; and  
 a housing supporting said first and second worm gears for rotation.  
   
     
     
         13 . An arrangement as recited in  claim 12 , wherein said covering is a horizontal blind and said cord is a lift cord.  
     
     
         14 . An arrangement as recited in  claim 13 , and further comprising a lift rod driven by said second worm gear and a plurality of lift spools mounted on said lift rod, said cord being wrapped onto one of said lift spools.  
     
     
         15 . An arrangement as recited in  claim 14 , and further comprising a drive spool drivingly connected to said first worm gear.