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A chair control includes a flexible truss having tandem springs interconnected in spaced relation so that they interact to provide a unique torque versus displacement profile during flexing, with a portion of one of the springs moving longitudinally relative to a portion of the other spring as they

A chair control includes a flexible truss having tandem springs interconnected in spaced relation so that they interact to provide a unique torque versus displacement profile during flexing, with a portion of one of the springs moving longitudinally relative to a portion of the other spring as they are flexed. A stop on the springs limits the longitudinal movement, thereby limiting the angle of tilt both in the upright and rearward chair back positions. In one form, the springs are pairs of leaf springs connected in tandem and operably attached to a chair back and bottom formed by a corrugated member. In another form, one of the springs is a flexible shell forming a chair with the other spring attached thereto in a nested arrangement. In yet another form, the flexible truss is a separate module installable in furniture as a self-contained energy absorber.

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1. A chair, comprising: a chair seat; a chair back operably interconnected to said chair seat for relative rearward movement; and a flexible truss operably connected to and interconnecting said chair back and seat for supporting said chair back during said rearward movement, comprising: a firs

1. A chair, comprising: a chair seat; a chair back operably interconnected to said chair seat for relative rearward movement; and a flexible truss operably connected to and interconnecting said chair back and seat for supporting said chair back during said rearward movement, comprising: a first elongate spring means for absorbing energy having a length and shape that extends from said chair seat to said chair back, said first elongate spring means being attached to said chair seat and chair back and controlling the rearward movement of said chair back, said first spring means being resiliently flexible and defining a first torque versus displacement profile; a second elongate spring means for absorbing energy having a length and shape corresponding to said first elongate spring means so that said second elongate spring means also extends from said chair seat to said chair back, said second spring means being resiliently flexible and defining a second torque versus displacement profile, said second spring means being spaced a distance from said first spring means such that at least a part of said first and second spring means slidingly move longitudinally with respect to each other during flexing; and means for operably interconnecting said first and second spring means along said lengths including locations proximate the ends of said spring means in an interactive arrangement so that said first and second profiles combine to define a desired torque versus displacement profile, said first and second spring means being fixed to each other at one location, but being relatively movable at other locations so as to define the desired torque versus displacement profile as said chair back is moved relative to said chair seat. 2. An apparatus as set forth in claim 1 including at least one spacer that spaces said first and second spring means apart, but which permits relative longitudinal movement between said spring means as said spring means are flexed. 3. An apparatus as set forth in claim 1 wherein at least one of said elongate spring means includes leaf springs. 4. An apparatus as set forth in claim 3 wherein said first and second spring means are arranged in a tandem arrangement in pairs. 5. An apparatus as set forth in claim 1 including a sheet folded to form a corrugated member that is operably connected to said flexible truss, said corrugated member having a plurality of first walls oriented generally normally to said flexible truss, and a plurality of second walls connected to said first walls and defining a support surface thereon adapted to support a seated person, said support surface including portions defining said chair seat and other portions defining said chair back. 6. An apparatus as set forth in claim 5 wherein said first walls include apertures for receiving at least one of said elongate spring means, said corrugated member being adapted to flex with said at least one elongate spring means. 7. An apparatus as set forth in claim 1 including stop means for limiting the longitudinal movement between said first and second spring means as said spring means are flexed. 8. An apparatus as set forth in claim 7 including spacers located at said locations for spacing said first and second spring means a predetermined distance apart along the lengths of said spring means. 9. An apparatus as set forth in claim 7 wherein said stop means pretensions said first and second spring means so that said flexible truss only begins to bend upon overcoming the pretension in said flexible truss. 10. An apparatus as set forth in claim 1 wherein said flexible truss acts to control the movement of said chair back as said chair back moves between upright and tilted positions. 11. An apparatus as set forth in claim 2 including stop means operably attached to said first and second spring means for limiting the longitudinal movement between said first and second spring means as said spring means are flexed, said stop means controlling the position of said chair back when in one of said upright and tilted positions. 12. An apparatus as set forth in claim 3 wherein said stop means is adjustable to vary the location of said upright and tilted positions. 13. A modular flexible truss for use on a chair including a chair seat and a chair back, comprising: first and second elongate springs each having a comparable length and shape, said springs being arranged in a nested arrangement so that at least a part of said springs slide relative to each other as they are flexed, said first elongate spring including an end connected to said chair seat and another end connected to said chair back so that said first spring controls the rearward movement of said chair back; and means for operably interconnecting said first and second springs along said lengths in an interactive arrangement wherein portions of said first and second springs are displaced with respect to each other and exhibit a desired torque versus displacement profile during flexing, said means for operably interconnecting including spacers that space said first and second springs apart and permit relative movement between portions of said first and second springs as said springs are flexed, so that a unique torque versus displacement profile different from the individual characteristics of said springs is obtained as said flexible truss is flexed. 14. An apparatus as set forth in claim 13 wherein said elongate springs include leaf springs. 15. An apparatus as set forth in claim 13 including stop means for limiting the longitudinal movement between said first and second spring as said springs are flexed. 16. An apparatus as set forth in claim 15 wherein said stop means includes a first stop to stop said first and second springs in a first position, said flexible truss being pretensioned when in said first position so that said flexible truss only can be flexed upon overcoming the pretension in said flexible truss. 17. A flexible truss for use on furniture, comprising: first and second elongate springs having a length and shape, said springs being arranged in a nested arrangement so that at least a part of said springs slide relative to each other as they are flexed; means for operably interconnecting said first and second springs along said lengths in an interactive arrangement wherein portions of said first and second springs are displaced with respect to each other and exhibit a desired torque versus displacement profile during flexing, said means for operably interconnecting including spacers that space said first and second springs apart and permit relative movement between portions of said first and second springs as said springs are flexed, so that a unique torque versus displacement profile different from the individual characteristics of said springs is obtained as said flexible truss is flexed; and stop means for limiting the longitudinal movement between said first and second springs as said springs are flexed, said stop means including a first stop adapted to restrain said first and second springs in a first position, said flexible truss being pretensioned when in said first position so that said flexible truss only can be flexed upon overcoming the pretension in said flexible truss, said stop means including a slot in one of said springs and a peg in the other of said springs, said peg slideably positioned in said slot of said one spring and engaging the ends of said slot to limit the longitudinal movement between said springs. 18. An apparatus as set forth in claim 17 wherein said elongate springs include leaf springs. 19. A chair comprising: a chair seat; a chair back located at an angle to said chair seat and movable between a tilted position and an upright position with respect to said chair seat; a flexible truss operably interconnecting said chair seat and chair back, said flexible truss controlling the path of movement of said chair back and the force required for said movement, comprising: first and second elongate springs having a length and shape, said springs being arranged in tandem in a nested arrangement so that portions of said springs move relative to each other as they are flexed; means for interconnecting said first and second springs along said lengths in an interactive arrangement, said means for interconnecting including at least one spacer that spaces said first and second springs apart so that a unique torque versus displacement profile can be obtained as said first and second springs are flexed; and stop means interconnecting said first and second springs for limiting the longitudinal movement between said first and second springs as said springs are flexed to thereby control the location of said chair back when in said upright position, said stop means pretensioning said first and second springs when in said upright position so that said chair back only begins to tilt rearwardly upon overcoming the pretension in said springs. 20. A chair as defined in claim 19 wherein said at least one spacer includes a plurality of spacers. 21. A chair comprising: a shell including a back and seat and an intermediate portion connecting said back and seat, said shell being resiliently flexible about said intermediate portions so as to permit said back to tilt rearwardly relative to said seat; at least one elongate spring having a length operably connected to said shell at multiple locations along said length in an interactive arrangement wherein said spring and said intermediate portion are in tension against each other during flexing, said shell being configured to slideably engage said at least one elongate spring at several locations, said spring being slideably attached to said shell at said several locations so that said shell and spring combine to form a tandem spring arrangement, said spring including a portion that moves longitudinally with respect to said shell as the spring and shell are simultaneously flexed; and stop means for limiting the longitudinal movement of said spring relative to said shell, said stop means engaging said spring and abuttingly engaging said shell at one of said locations to hold said spring and shell in pretension so that said back only begins to move rearwardly upon overcoming said pretension. 22. A flexible truss for use on a chair including a seat and a back, the back being movable in a rearward direction and a forward direction, comprising: an elongated spring associated with the back for biasing the back in the forward direction to an upright position relative to the seat, said elongated spring having first and second ends; an elongated member including a third end fixed relative to said spring first end, and including a fourth end; spacers for spacing at least a portion of said elongated member a distance from said elongated spring so that said fourth end moves longitudinally relative to said second end of said elongated spring when said elongated spring is flexed; and a stop operably connecting said fourth end of said elongated member to said second end of said elongated spring for limiting the relative movement of said second end with respect to said fourth end in at least one direction when said elongated spring is flexed and thus limiting the overall movement of said back as said back is moved in one of said forward direction and said rearward direction. 23. A flexible truss as defined in claim 22 wherein said elongated member includes a second elongated spring. 24. A flexible truss as defined in claim 22 wherein said elongated spring includes a one-piece shell. 25. A flexible truss as defined in claim 22 wherein said elongated member limits the movement of the back in the forward direction. 26. A flexible truss as defined in claim 22 including a flexible sheet forming said seat and back. 27. A flexible truss as defined in claim 26 wherein said sheet includes multiple folds to thus form a corrugated member. 28. A flexible truss as defined in claim 22 wherein said elongated member limits the movement of the back in the rearward direction. 29. A flexible truss as defined in claim 28 wherein said elongated member limits the movement of the back in the forward direction.