Counterweight system

• US 4,351,245 A
• Filed: 09/04/1980
• Issued: 09/28/1982
• Est. Priority Date: 09/04/1980
• Status: Expired due to Term

• Current Assignee: Les Industries Elifer Incorporated
• Original Assignee: Joseph L. Laporte
• Inventors: Laporte, Joseph L.
• Primary Examiner(s): Zugel, Francis K.
• Application Number:
  US06/184,039
• Time in Patent Office: 754 Days
• Field of Search: 108/136, 108/2, 108/4, 108/144, 248/364, 248/572, 248/571
• US Class Current: 108/136
• CPC Class Codes: A47B 27/06 balancing by means of springs

Abstract

A counterweight system is disclosed, which is advantageously used for counterbalancing the table top of a vertically-adjustable drafting table. Obviously, the counterweight system could be used for other applications. When used in a drafting table of the type including a frame and a table top provided with vertical legs guided for up-and-down movement within the frame, cables are attached to the lower end of the two legs and are trained over a common pulley and attached to said pulley, which is freely rotatably mounted within the frame. A spiral-shape cam member is fixed to one side of the pulley and an additional cable which is attached to the pulley is trained over the cam member and attached at its other end to one end of tension springs, the other end of which is attached to the frame. The varying force exerted by the springs, with the change of their elongation, is compensated by the variable lever arm of the application of said force on the rotational axis of the cam member and pulley, so that the torque exerted by the springs on the pulley is substantially constant over all of the rotated positions of the cam member and pulley. Therefore, the load or table top is substantially counterbalanced by the springs at anyone of its adjusted positions.

Claims

1. A drafting table comprising a frame of inverted U-shaped hollow construction having a top transverse bight member and two upright sides downwardly depending from the ends of said bight member;

a leg assembly including first and second legs vertically displaceable within the respective sides of said U-shaped frame and upwardly protruding through said bight member;

a table top mounted on the upper ends of said first and second legs and overlying said bight member;

a horizontal pivot shaft extending transversely through said bight member and mounted therein adjacent said first leg;

a first pulley having a cylindrical peripheral wall close to said first leg and a pair of spaced side walls mounted on said shaft;

a cam member secured to one of said side walls of said pulley;

said cam member having a spiral shaped cam surface progressively distant from the rotational axis of said pivot shaft;

first and second flexible ties trained in the same direction around said pulley and each having one end portion extending through said peripheral wall and within said pulley and attached to the latter by a common removable tie pin extending through said side walls of said first pulley, the peripheral wall of said first pulley guiding said first flexible tie alongside said first leg, the other end of said first flexible tie being secured to the lower end of said first leg;

said second flexible tie having its other end secured to the lower end of said second leg;

said second flexible tie being trained around a second pulley rotatively and transversely mounted within said bight member, spaced from said pivot shaft and located adjacent said second leg;

said second pulley guiding said second flexible tie alongside said second leg, said second flexible tie extending directly from said second pulley to said first pulley within said bight member;

the points of tangential contact of said first and second flexible ties with the peripheral wall of said first pulley being angularly spaced from each other around said first pulley;

a third flexible tie having one end trained around said cam surface and secured to said first pulley by said common tie pin;

the other end of said third flexible tie being fastened to at least one tension coil spring which in turn is secured to said frame within said bight member at the opposite end of said tension spring, whereby the increasing force exerted by said tension spring on said member as it stretches is compensated by the decreasing lever arm of the point of tangential contact of said third flexible tie on said cam surface as said cam member rotates between two limit positions so as to counterbalance said table top and legs at any adjusted position of said table top; and

tension adjustment means for said tension spring, said inverted U-shaped hollow frame defining a space between said upright sides which is completely free of any obstruction.