US Patent 7396079 Seating with shape-changing back support frame

A back includes an integrated articulating back frame and a back support. The back frame has a lower segment pivoted to a chair control, an upper segment for thoracic support, and links forming a four-bar linkage with the upper and lower segments, with a joint being formed at the lumbar region. The back support is stretchable in limited directions to accommodate shape change in the articulating back frame but to provide adequate support to a seated user. Upon receiving a rearward pressure on the lumbar joint, the back frame itself changes shape. The pivot locations in the four bar linkage create a mechanism that simultaneously controls rotational and translational movement of the upper segment during flexure of the lumbar. The back frame is close to the back support to provide significant design flexibility, but permit substantial lumbar flexure. Various back supports are contemplated that accommodate articulation of the back frame.