Patent Publication Number: US-6981538-B2

Title: Positional control device for sectional doors

Description:
RELATED APPLICATION 
   This application replaces Provisional Application No. 60/315,932 filed on Aug. 31, 2001 and entitled POSITIONAL CONTROL DEVICE FOR SECTIONAL DOORS. 

   FIELD OF THE INVENTION 
   The present invention relates to a mechanism for temporarily holding a sectional overhead door at any desired position between its fully opened and fully closed positions. 
   BACKGROUND OF THE INVENTION 
   Vertically movable sectional doors, such as those used in warehouses and other industrial settings typically employ spring, pulley and cable assemblies to counterbalance the weight of the overhead door in its motion along roller tracks. 
   Any imbalance which arises, e.g. through aging of the component springs of the door mechanism can result in an undesired and unpredictable tendency of the overhead door to “coast” or “drift”. This can have costly and dangerous consequences, for example, in the event of a downward drifting of an opened sectional door as a forklift truck is backing up through the opening. 
   A number of systems have been devised to eliminate door drift, typically making use locking devices that are mechanically or electrically switchable between on and off positions. Examples are afforded by the drop-catch mechanism for vertically movable doors disclosed in U.S. Pat. No. 6,042,158 (Horn) and the locking system for sectional doors disclosed in U.S. Pat. No. 6,145,570 (Mullet et al). 
   None of these systems, however, allows one to manually raise or lower the door in the usual way to a selected position and then leave the door there, with confidence that it will not drift up or down from that selected position. 
   SUMMARY OF THE INVENTION 
   It is a principal object of the present invention to provide a mechanism to prevent undesirable drifting of an overhead door upward or downward from fully opened, partly opened or fully closed positions, yet allowing the door to be manually moved to a different position without the need for any separate operation to release the door from its starting position. 
   With a view to achieving this object, I have designed a mechanism which couples the upward and downward motion of the door to the rotation of a sprocket wheel. When the sprocket wheel is at rest, any tendency of the door to drift is resisted by a spring-loaded ratchet arm engaging the teeth of the sprocket. By proper setting of the loading spring, the force exerted by the ratchet mechanism to hold the door in its given position is readily overcome by manually raising or lowering the door to a different position, thereby rotating the sprocket wheel to a new position in which the ratchet arm again exerts sufficient engagement force with the sprocket to prevent drifting of the door. 

   
     Other objects, features and advantages of the present invention will become apparent on reading the detailed description which follows of a preferred embodiment of the invention in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a schematic vertical sectional view of the mechanism according to the invention, seen in the direction facing the plane of a door on which the device is installed; 
       FIG. 2  is a perspective part-sectional view of the device seen in a direction generally perpendicular to the plane of the door; 
       FIG. 2A  is a schematic detail illustration of the interaction between the compression spring means and the pendulum arm/ratchet locking means in operation of the invention; and 
       FIG. 3  is an isolated schematic drawing of the pendulum ratchet arm of the device according to the illustrated embodiment of the invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
   Referring to the drawing figures, the housing  10  for the apparatus is fixedly mounted in position to a wall adjacent to the parallel roller tracks of the overhead door by mounting clip  10   a.    
   Apparatus according to the present invention may be used in association with any of a number of different kinds of torsion spring counterbalance systems for sectional doors. A typical such counterbalance system is exemplified in U.S. Pat. No. 5,419,010 (Mullet), incorporated herein by reference for its teaching on counterbalancing systems for sectional doors. The positional control device of the present invention is mechanically coupled to the sectional door counterbalance system at the system&#39;s horizontal spring shaft (drive tube) which rotates about its horizontal axis clockwise/counterclockwise with the raising/lowering of the door. 
   Vertical motion of the door along its tracks is accompanied by the rotational motion of the roller chain sprocket  14  having a central drive shaft  14   a  which is linearly coupled to the existing conventional door spring shaft  16  by a collar  18  and set screw  18   a . A bearing or bushing  14   b  holds drive shaft  14   a  in secure alignment with sprocket wheel  14 . 
   A pendulum ratchet arm  20  having a specially shaped, bifurcated head  20   a , best seen in  FIG. 3 , is pivotally mounted at its tail end  20   b  to spring tensioning means comprising a compression spring  22  interposed between a pendulum ram  22   a  and vertically adjustable spring block  22   b  coupled to adjusting screw  23 . Slide channel  24  holds spring  22  against the top end of pendulum arm  22   a  and restricts the arm  22   a  to linear motion within the channel. 
   As best seen with reference to  FIGS. 2A and 3 , raising the door manually will rotate sprocket wheel  14  in one rotational direction, here illustrated by arrow A, so that the engagement of one projection from the bifurcation of the head  20   a  of the sprocket requires arm  20  to be pivoted about a pivot point  20   b  in its tail end, compressing spring  22  between pendulum arm  22   a  and spring block  22   b  through a central position of maximum spring compression, then turning the ratchet arm  20  to its other extreme orientation illustrated at  20 A. 
   At orientation  20 A, a projection formed by the bifurcation of the head of the ratchet arm engages sufficiently with one of the sprocket teeth  14   b , to hold the door at its position under a preset tension of compression spring  22 , selected to be great enough to resist the torque applied to sprocket wheel  14  by the reason of weight of the door, but can be easily overcome by manual force applied to the door to raise or lower it to another position. 
   Similarly, lowering the door manually will rotate sprocket wheel  14  in the other rotational direction, illustrated by arrow B, from position A, through a central compressive position, to a final orientation  20 B. With the door released at that point, the second projection formed by the bifurcation of the head of ratchet arm  20  engages with sprocket wheel  14  to resist drifting of the door by opposing the torque which the free weight of the door applies to sprocket wheel  14 . 
   From this description it will be seen that the positional control device of the present invention prevents accidental drifting of an overhead door upwardly or downwardly from any position along its full path of travel. It allows the door to be manually moved to a different elevation without the need to “unlock” the door from its original position, since the added force applied by the person raising or lowering the door suffices to overcome the spring-biased engagement of the ratchet head with the sprocket teeth. 
   The invention has been described with reference to a particular preferred embodiment, but will be understood by those of ordinary skill in the art that modifications may be made to the structure disclosed herein without departing from the spirit and scope of the invention, defined by the attached claims.