Counterweight system

Claim 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.