Chair having back shell with selective stiffening

A chair comprising:

• a base;
• a seat supported on said base, said seat including a bottom shaped to support a buttock area of an adult user thereon;
• a back pivotally supported on said base;
• a control operatively connecting said base and said back, and selectively controlling rearward tilting of said back;
• a cushion assembly shaped to support the back of a user thereon;
• an inner shell construction connecting said cushion assembly with said back, said inner shell construction comprising:
• a semi-rigid, resiliently flexible sheet, having forward and rearward surfaces forming a back shaped to selectively support a back area of an adult user thereon with the cushion assembly being on the forward surface of the shell construction;
• said back having a substantially flat planar shape, a generally continuous thickness and extending substantially continuously in a plane, so that the forward surface of said sheet defines a substantially uninterrupted planar portion, with a central, area disposed directly behind a lumbar area of a seated adult user to selectively support the same, and an upper area disposed above said central area and generally behind an upper back area of a seated user to selectively support the same;
• and
• a plurality of ribs formed integrally with said sheet on the rearward side thereof, and extending generally vertically along the central area of said back to stiffen the central area of said back in a vertical plane for firm support of at least the lumbar area of the seated user, yet dimensioned to permit at least the upper portion of said back to flex in a horizontal plane for improved freedom of movement to the upper back area of the seated user.

A chair comprising:

• a base;
• a seat supported on said base;
• a back support pivotally supported on said base;
• a synchrotilt control operatively connecting said base and said back support, and selectively controlling rearward tilting of said back support;
• a cushion assembly shaped to support the back of a user thereon;
• and
• a shell construction connecting said cushion assembly with said back support, said shell construction comprising:
• a semi-rigid, resiliently flexible sheet having substantially planar forward and rearward surfaces, said sheet having a generally continuous thickness and extending substantially continuously in a plane, so that said sheet exhibits strength in all directions in the plane but is flexible in directions not in said plane and the forward surface of said sheet defines a substantially uninterrupted planar portion, said sheet shaped to selectively support a back area of the seated user thereon with the cushion assembly being on the forward surface of the shell construction;
• a plurality of spaced apart vertical ribs projecting rearwardly from said rearward surface of said sheet and extending across said sheet for selectively reinforcing said sheet, said vertical ribs being selectively positioned at predetermined locations to provide a predetermined amount of forwardly directed support in a vertical plane to the user's back area when the user urges his back rearwardly in the chair;
• and
• a plurality of angled ribs interconnected in at least one location with said vertical ribs and projecting rearwardly from said rearward surface of said sheet and further extending across at least an upper part of said sheet for selectively reinforcing said sheet, said angled ribs being selectively positioned at predetermined locations to provide a predetermined amount of torsional support to the user's back area when the user moves his upper body in a direction having a torsional component, said angled ribs defining an integrally molded T-shaped cross section with said planar sheet at an intersection formed therewith for stiffening said sheet along the intersection.

A chair comprising:

• a base;
• a seat supported on said base;
• a back support pivotally supported on said base;
• a control operatively connecting said base and said back support, and selectively controlling rearward tilting of said back support;
• a cushion assembly shaped to support the back of a user thereon;
• and
• a shell connecting the cushion assembly with the back support, said shell comprising:
• a semi-rigid, resiliently flexible sheet having substantially planar forward and rearward surfaces, said sheet having a generally continuous thickness and extending substantially continuously in a plane, so that said sheet exhibits strength in all directions in the plane but is flexible in directions not in said plane and the forward surface of said sheet defines a substantially uninterrupted planar portion, said sheet shaped to support a back area of an adult user thereon with the cushion assembly being on the forward surface of the shell;
• and
• a plurality of spaced apart first ribs projecting rearwardly from said rearward surface of said sheet for selectively reinforcing said sheet, and at least one second rib positioned at a substantially different angle to the first ribs in a non-parallel relationship.