Tension adjustment mechanism for a chair

A tension adjustment mechanism for controlling resistance to tilting of a seat-back assembly of a chair, said tension adjustment mechanism comprising:

• a mechanism body;
• a pivot member pivotally attached to said mechanism body which said pivot member pivots about a horizontal pivot axis in response to tilting of said seat-back assembly;
• a biasing member acting on said pivot member so as to resist said tilting of said seat back assembly wherein said biasing member includes a biasing element which is displaceable in opposite directions to vary the tilting resistance;
• a cam member having a first portion supporting said biasing element wherein said biasing element applies a biasing force against said cam member, said cam member further including a first arcuate cam surface, and being pivotally supported by said mechanism body so as to pivot about a horizontal pivot axis;
• and
• a drive arrangement comprising a drive member having second arcuate cam surface disposed in opposing relation with and in sliding contact with said first arcuate cam surface on said cam member, said drive member being displaceable sidewardly in a sideward direction by a manual actuator to effect displacement of said cam member about said pivot axis to vary the relative position of said biasing element and vary the tilt resistance, one of said first and second arcuate cam surfaces having a three-dimensional contour which is tapered in said sideward direction and sloped in a front-to-back direction transverse to said sideward direction to maintain continuous contact across a width of the other of said first and second arcuate cam surfaces during changes in the orientation of said first arcuate cam surface on said cam member during pivoting of said cam member by said drive member.

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 primary biasing member acting on said pivot member to resist pivoting of said pivot member, said biasing member including movable elements which are displaceable to vary the tilting resistance generated by said biasing member;
• a cam member which is movable to displace said biasing elements wherein said cam member includes a tapered cam surface and said biasing elements apply an element biasing force to said cam member;
• and
• a drive arrangement having a rotatable adjustment shaft which extends sidewardly within said control body and is manually rotatable, said drive arrangement further including drive members mounted on said adjustment shaft so as to be movable toward each other or away from each depending upon the direction of rotation of said adjustment shaft, said drive members including tapered cam surfaces which cooperate with opposite sides of said tapered cam surface on said cam member wherein movement of said drive members toward each other effects displacement of said cam member in a first direction counteracting said biasing elements and movement of said drive members away from each other permits movement of said cam member in a second direction corresponding to the direction which said biasing members act on said cam member, said element biasing force acting on said tapered surfaces of said drive members such that said element biasing force has an axially directed force component;
• said drive arrangement further including secondary biasing members acting between said control body and said drive members which each apply a counter-biasing force to said drive members along said shaft axis which said counter-biasing force counteracts the element biasing force applied to said drive members, wherein said counter-biasing force counteracts said axially directed force component to facilitate manual rotation of said adjustment shaft and the resultant movement of said drive members.