Patent ID: 7410216

Claim:
A tension adjustment mechanism for controlling tilting resistance of a seat-back assembly in a chair, said tension adjustment mechanism comprising: a control body; a pivot member pivotally connected to said control body so as to pivot during tilting of said seat-back assembly; a biasing member acting on said pivot member to resist pivoting of said pivot member and resist tilting of said seat-back assembly, said biasing member including at least one movable biasing element which is displaceable about a pivot axis in opposite first and second directions extending along a first adjustment path to progressively vary the tilting resistance generated by said biasing member, said biasing member having a cam surface associated therewith to effect displacement of said biasing element along said first adjustment path; a cam member supported on said control body adjacent said biasing element which said cam member has a respective cam surface which supports said biasing element thereon, said cam member being actuatable along opposite third and fourth directions extending along a second adjustment path to displace said biasing element and progressively vary the tilting resistance, said second adjustment path being oriented transverse to said first adjustment path, and said cam member including said cam surface which is non-uniformly tapered in a sideward direction extending parallel to said second adjustment path to define a non-uniform contour along said cam surface which non-linearly varies the amount of displacement of said biasing element along said first adjustment path during movement of said cam member along said second adjustment path, said cam surface of said cam member further being sloped in a facing direction transverse to said second adjustment path so as to face toward said biasing element and maintain contact between said cam surfaces during movement of said cam member along said second adjustment path; and a drive arrangement having a rotatable adjustment shaft which extends sidewardly within said control body and is manually rotatable, said drive arrangement effecting displacement of said cam member along said second adjustment path by rotation of said adjustment shaft so that said cam member is sidewardly movable toward or away from said biasing element through said third and fourth directions depending upon the direction of rotation of said adjustment shaft, wherein movement of said cam member in said third direction toward said biasing element effects displacement of said biasing element in said second direction to counteract said biasing element, and movement of said cam member in said fourth direction away from said biasing element permits displacement of said biasing member in said first direction.