Patent ID: 8272693

Claim:
A weight-responsive chair comprising: a chair frame; a seat pivotally supported on said chair frame at a front portion by a front pivot link; and having a rear portion overlying said chair frame; a back comprising a back upright pivotally connected to said chair frame at pivot points on opposite sides of the chair frame and having a connector link that extends forwardly from each said pivot point of said back which connects to said rear portion of the seat, a combination of the front pivot link, the chair frame, the seat and the connector links of the back upright defining a four-bar linkage wherein rearward tilting of the back upright effects lifting of the rear portion of the seat and causes the connector links to pivot upwardly and thereby lift the seat against the weight of the user; and a tension mechanism connected between the chair frame and the back upright to provide a relatively low level of resistance to tilting of the back upright, said tension mechanism including a biasing arrangement which serves to restore the seat and back to an upright position, said chair frame including sidewardly directed mounting posts adjacent said pivot points and a stationary plate, and said tension mechanism further including a sub-assembly mounted to each said mounting post, said sub-assembly comprising a rotation bearing as well as a biasing spring and a rotatable plate which are supported on said bearing, which bearing in turn mounts to said mounting posts so that said spring cooperates with said stationary and rotatable plates and said rotatable plate is rotatable about an axis of said bearing, said rotatable plate being connected to said back upright so as to rotate therewith and generate said low level of resistance to tilting.