CA2304816A1

CA2304816A1 - Synchrotilt chair with adjustable seat, back and energy mechanism

Info

Publication number: CA2304816A1
Application number: CA002304816A
Authority: CA
Inventors: Kurt R. Heidmann; Larry Dekraker; Robert J. Battey; Glenn A. Knoblock; Michelle R. Johnson; Robert M. Scheper; Arnold B. Dammermann; Kevin A. Ekdahl; Gardner J. Ii Klaasen; James A. Perkins; Gordon J. Peterson; Edward H. Punches; Charles P. Roossien; David S. Teppo; Michael J. Yancharas
Original assignee: Individual
Current assignee: Steelcase Inc
Priority date: 1997-10-24
Filing date: 1998-10-19
Publication date: 1999-05-06
Anticipated expiration: 2018-10-19
Also published as: ATE371393T1; TW483741B; US7427105B2; US6394545B2; US6991291B2; US6394546B1; DE69836596T2; EP1405583B1; US6318800B1; DE69738088D1; EP1405584A2; US6086153A; US20090001793A1; JP5080288B2; DE69836596D1; US6367877B1; CN1144555C; EP1405584A3; ATE297672T1; JP4104286B2

Abstract

A chair (20) is provided having a base assembly (21) including a base frame, a back frame (30) pivoted to the base frame for movement between upright and reclined positions, and a seat (24) slidably supported on the base frame and pivoted to the back frame so that the seat moves forwardly and its rear moves forwardly and downwardly with the back frame upon recline. A flexible back is connected to the back frame at top and bottom locations and is provided with lumbar adjustment for improved lumbar force/support and shape. A seat is provided with seat depth adjustment and with active and passive thigh flex support. A novel energy mechanism (27) is provided that includes a transverse spring (28), a lever (54), and a moment arm shift adjuster (29) for adjusting the spring tension on the back frame. The moment arm shift adjuster is readily adjustable and includes an overtorque device to prevent damage to components of the energy mechanism.

Claims

1. A chair comprising:
a base assembly including a control housing having opposing side flanges and a side pivot located proximate one of the side flanges;
a back pivoted to the base assembly for movement between upright and reclined positions;
a seat operably supported on the base assembly and connected to the back for coordinated synchronous movement with the back;
an energy mechanism for biasing the back toward the upright position, the energy mechanism including an extendable/compressible spring positioned transversely in the control housing with one end supported on one of the side flanges, and further including a lever pivoted to the side pivot, the lever having a spring-engaging portion engaging a free end of the spring and also having a seat-biasing portion operably connected to the seat; and the side pivot, the spring-engaging portion, and the seat-biasing portion being spaced from each other and arranged so that the spring biases the lever about a fulcrum located generally at the side pivot to bias the back toward the upright position, wherein the side pivot includes an adjustable pivot member constructed to change a location of the fulcrum on the lever when the pivot member is adjusted.

2. Cancelled.

3. The chair defined in claim 1 wherein the pivot member and the lever include interfacing surfaces, at least one of the interfacing surfaces being curvilinear.

4. The chair defined in claimed 3 wherein the interfacing surfaces include intermeshing teeth.

5. The chair defined in claim 4 wherein the lever comprises an L-shaped bell crank, and the fulcrum is located generally along an intermediate portion of one leg of the L-shaped bell crank.

6. The chair defined in claim 1 wherein the lever and the pivot member are pivoted about vertical axes and are movable in a common horizontal plane that provides compact positioning within the control housing.

7. The chair defined in claim 1 wherein the spring is supported by the control housing and engaged by the lever in a configuration that causes the free end of the spring to simultaneously move toward the one supported end and also move along a fore/aft direction during recline of the back.

8. A chair comprising:
a base assembly including a control housing having opposing side flanges and a side pivot located proximate one of the side flanges;
a back pivoted to the base assembly for movement between upright and reclined positions;
a seat operably supported on the base assembly and connected to the back for coordinated synchronous movement with the back;
an energy mechanism for biasing the back toward the upright position, the energy mechanism including an extendable/compressible spring positioned transversely in the control housing with one end supported on one of the side flanges, and further including a lever pivoted to the side pivot, the lever having a spring-engaging portion engaging a free end of the spring and also having a seat-biasing portion operably connected to the seat;
the side pivot, the spring-engaging portion, and the seat-biasing portion being spaced from each other and arranged so that the spring biases the lever about a fulcrum located generally at the side pivot to bias the back toward the upright position;
the spring being supported by the control housing and engaged by the lever in a configuration that causes the free end of the spring to simultaneously move toward the one supported end and also move along a fore/aft direction during recline of the back; and the lever both longitudinally compressing the spring and causing the spring to bend laterally in a non-linear manner during recline of the back.

9. In a chair having a control housing including a pivot member, a reclineable back operably connected to the control housing for movement between upright and reclined positions, and an energy source in the control housing for biasing the back toward the upright position, the improvement of an adjustable back tension control comprising:

the pivot member being adjustable; and a lever engaging the energy source and the pivot member, the lever being operably connected to the back for biasing the back toward the upright position, the lever and the pivot member having non-slip interfacing surfaces, at least one of which is curvilinear, so that the interfacing surfaces engage to define a shifting fulcrum as the lever is rotated during recline of the back, and further so that the fulcrum changes location as the pivot member is adjusted to change a moment arm over which the energy source operates.

10. The chair defined in claim 9 wherein the lever comprises a bell crank having a leg that is pivotally engaged at an intermediate location by the pivot member to define the fulcrum.

11. The chair defined in claim 10 wherein the lever pivots in a horizontal plane about a generally vertical axis to provide for compact positioning in the control housing.

12. The chair defined in claim 11 including a link and a seat-engaging bracket operably connected to the lever by the link so that the lever biases the seat-engaging bracket and the seat in a rearward direction.

13. The chair defined in claim 10 wherein the pivot member is pivoted to the control housing at a pivot location spaced from the interfacing surface of the pivot member, the interfacing surface of the pivot member being arcuately shaped and defining a constant radius from the pivot location.

14. The chair defined in claim 13 wherein the interfacing surfaces have teeth that engage.

15. The chair defined in claim 14 wherein the interfacing surface of the lever also has a curvilinear shape.

16. The chair defined in claim 9 including an adjustment mechanism for angularly adjusting the pivot member to change a length of the moment arm.

17. The chair defined in claim 16 wherein the adjustment mechanism includes an overtorque device to prevent overtorquing by a user when adjusting the pivot member.

18. The chair defined in claim 9 wherein the chair includes a seat operably positioned on the control housing and interconnected between the lever and the back.

19. The chair defined in claim 9 wherein the interfacing surfaces have teeth that engage.

20. A chair comprising:
a base assembly;
a component comprising one of a reclineable back and a movable seat pivoted to the base assembly for movement between first and second positions; and a spring with one end supported on the base assembly and another end operably connected to the component, the spring having a length and, when the component is moved from the first position to the second position, being simultaneously longitudinally compressed along the length and also laterally bent in a direction transverse to the length.

21. The chair defined in claim 20 including a lever having a first end contacting the another end of the spring and a second end linked to the component.

22. The chair defined in claim 21 wherein the lever is pivoted to the base assembly.

23. The chair defined in claim 22 wherein the component comprises the movable seat.

24. The chair defined in claim 23 including a back frame operably connected to the seat for simultaneous movement therewith.

25. A chair comprising:
a base assembly including a control housing;
a seat slidingly supported on the control housing;
a back frame pivoted to the base assembly for movement between upright and reclined positions and operably attached to the seat so that pivotal movement of the back frame and sliding movement of the seat are synchronized; and an energy mechanism including a spring having a length and an L-shaped torque member with a first leg engaging an end of the spring and a second leg extending generally parallel the length of the spring, the first leg pivotally engaging the control housing at a location spaced from the end of the spring, and the second leg being operably connected to one of the seat and the back frame so that the spring biases the torque member in a manner biasing the back frame toward the upright position.

26. The chair defined in claim 25 wherein the first leg includes a curvilinear surface that both rollingly and pivotally engages structure on the control housing as the back frame moves between upright and reclined positions.

27. The chair defined in claim 26 wherein the structure on the control housing including a pivot member with an interface surface that engages the curvilinear surface on the first leg, the surfaces being configured to positively engage to prevent undesired slippage.

28. A chair comprising:
a base assembly including a control housing;
a seat slidingly supported on the control housing;
a back frame pivoted to the base assembly for movement between upright and reclined positions and operably attached to the seat so that pivotal movement of the back frame and sliding movement of the seat are synchronized;
the control housing defining a relatively thin, horizontally extending compartment under the seat; and an adjustable energy mechanism operably positioned in the compartment, the adjustable energy mechanism including an extensible energy source, a lever operably connected between the energy source and the seat, and an adjustment member adjustably pivotally supporting the lever for adjustably controlling force transmitted from the energy source through the lever to the seat, the energy source, the lever, and the adjustment member being movable in horizontal directions only so as to operate within the relatively thin, horizontally extending compartment.

29. The chair defined in claim 28 wherein the adjustment member includes a pivot member operably attached to the control housing for shifting the lever to adjust a fulcrum of the lever.

30. Cancelled.

31. Cancelled.

32. Cancelled.

33. Cancelled.

34. Cancelled.

35. The chair defined in claim 1 wherein the base assembly includes a base frame that incorporates the housing.

36. The chair defined in claim 20 wherein the base assembly includes a base frame that incorporates the housing.

37. The chair defined in claim 25 wherein the base assembly includes a base frame that incorporates the housing.

38. The chair defined in claim 28 wherein the base assembly includes a base frame that incorporates the housing.

39. Cancelled.

40. Cancelled.

41. A chair comprising:
a base assembly including a control housing;
a single stored energy source positioned in the control housing providing a compressive force;
a back support operably interconnected with said single energy source for movement between upright and reclined positions, said single stored energy source both exerting pretension to bias the back support toward the upright position and providing resistance to tilting of the back support when reclining; and a controller for regulating the pretension of the stored energy source and tilt rate of the back support, the controller including a lever defining an adjustable fulcrum point that can be adjusted without overcoming the compressive force of the said single stored energy source.

42. The chair defined in claim 41 including a seat engaging and interconnecting the back support to the energy source.

43. Cancelled.

44. Cancelled.

45. Cancelled.

46. A chair comprising:
a base assembly;
a seat supported on the base assembly;
a back frame pivoted to the base assembly for movement between upright and reclined working positions;
a compliant back connected to the back frame in at least one top connection and to the chair at bottom connections vertically spaced from the at least one top connection, the bottom connections being located proximate a rear of the seat and in front of a bottom of the compliant back so that the bottom connections define an axis that is adapted to be generally aligned with an area associated with a seated user's hip bone and lower spine, the compliant back being flexible so that the compliant back undergoes controlled flexure between the top and bottom connections upon flexure of a seated adult user's back; and the seat having a front portion slidably supported on the base assembly and a rear portion pivotably connected to the back frame so that the seat moves forwardly in a synchronized motion with the back frame during recline of the back frame.

47. The chair defined in claim 46 wherein the compliant back includes upper and lower sections operably connected together for counter-rotational movement, the upper section being pivoted to the back frame at the top connection and the lower section including forwardly extending flanges pivoted to the back frame at the bottom connections, a rearward distance from the bottom connections to a lower front surface of the lower section being about equal to a predetermined distance calculated from an average seated adult user's hip joint to the average seated adult user's rear/lower spine bones, so that the compliant back is adapted to flex and simultaneously provide comfortable postural support upon flexure of the seated adult user's lower back.

48. The chair defined in claim 46 wherein the compliant back includes a back shell having upper and lower stiff sections connected by a flexible zone located generally in a lumbar area of a seated adult user.

49. The chair defined in claim 48 wherein the flexible zone includes a plurality of horizontal slits extending generally across the compliant back but terminating to leave an uninterrupted band of material at opposite side edges of the lumbar area.

50. The chair defined in claim 49 including a torsional lumbar support mechanism operably attached to the back shell, the torsional lumbar support mechanism biasing the shell toward a forwardly protruding convex shape for optimal lumbar support.

51. The chair defined in claim 50 including a vertically adjustable lumbar support attached to the compliant back for vertical adjustment to change a shape of a front surface of the compliant back in the lumbar area of the seated user.

52. The chair defined in claim 51 wherein the vertically adjustable lumbar support includes laterally extending handles constructed to engage and track with a perimeter edge of the compliant back and constructed to slidably engage the vertically adjustable lumbar support to permit the handles to adjust in and out to follow the perimeter edge.

53. The chair defined in claim 46 including a torsional lumbar support mechanism attached to one of the bottom connections for biasing the compliant back toward a forwardly protruding convex shape.

54. The chair defined in claim 46 including a vertically adjustable lumbar support operably attached to a front surface of the compliant back, the vertically adjustable lumbar support being configured to change a force of support at the front surface of the compliant back in a lumbar area of a seated user.

55. The chair defined in claim 54 including at least one handle that slidably engages the vertically adjustable lumbar support in a generally horizontal direction, the handle being configured to follow along a perimeter edge of the compliant back for vertically adjusting the vertically adjustable lumbar support.

56. The chair defined in claim 46 wherein the top connection includes a top pivot connection.

57. The chair defined in claim 56 wherein the top pivot connection includes a protruding T-shaped connector on the back frame and a mating recess in the compliant back, the recess being configured to receive and frictionally engage the T-shaped protruding connector to attach the compliant back to the back frame.

58. The chair defined in claim 46 wherein the compliant back includes a belt bracket attached along a bottom edge of the compliant back, the belt bracket including flanges defining a part of the bottom connectors.

59. The chair defined in claim 58 including an adjustable torsional lumbar support mechanism attached to one of the bottom connectors.

60. The chair defined in claim 46 wherein the back frame defines an inverted curvilinear arch.

61. The chair defined in claim 46 wherein the back frame includes an internal metal reinforcement and an exterior polymeric covering that covers all sides of an intermediate section of the internal metal reinforcement.

62. The chair defined in claim 46 wherein the back frame includes configured ends positioned on opposing sides of the rear portion of the seat, the configured ends defining first pivots for pivotal connection to the back frame and second pivots for pivotal connection to the seat.

63. A chair comprising:
a base assembly;
a back frame pivoted to the base assembly for movement between upright and reclined working positions; and a compliant back operably attached to the back frame at a top connection and operably attached to the chair at bottom connections, the compliant back including a forwardly extending flange generally located along its lower edge forming an axis of rotation at the bottom connections, the axis being located proximate a rear section of the seat and in front of the compliant back, the compliant back including a thoracic portion, a pelvic portion, and a flexible lumbar portion constructed so that when a seated user flexes their lower back rearwardly, a pelvic portion of the compliant back moves pivotally downwardly and rearwardly about the axis, the lumbar portion of the compliant back flexibly moves generally rearwardly to form a more planar arrangement with the pelvic portion, and a thoracic portion of the back pivots about the top connection, whereby the compliant back, in combination with the back frame and base assembly, is adapted to provide postural support for a seated user's back that is flexing and moving of the seated user's torso and spine.

64. The chair defined in claim 63 including an adjustable torsional lumbar support spring mechanism for torsionally biasing the compliant back to a forwardly protruding convex shape for optimal lumbar support for the seated user.

65. The chair defined in claim 64 wherein the compliant back includes a molded shell having a resilient lumbar section.

66. The chair defined in claim 65 including a belt bracket attached to a bottom edge of the molded shell.

67. The chair defined in claim 66 including a vertically adjustable lumbar support operably attached to a front of the compliant back.

68. The chair defined in claim 63 wherein the top connection includes a protrusion on the base frame and a mating recess on the compliant back, the recess being configured to receive and frictionally engage the protrusion.

69. The chair defined in claim 63 including a vertically adjustable lumbar support attached to the compliant back in a lumbar area of the seated user, for changing a shape of a front surface of the compliant back in the lumbar area.

70. The chair defined in claim 69 including handles operably engaging the vertically adjustable lumbar support and configured to follow a perimeter edge of the compliant back during vertical adjustment of the vertically adjustable lumbar support.

71. The chair defined in claim 63 wherein the back frame has configured ends positioned on opposite sides of the compliant back, the configured ends defining a back-tilt axis, a seat-tilt axis, and a back-shell bottom-tilt axis that is located rearwardly of the back-tilt axis and the seat-tilt axis, the back-shell bottom-tilt axis being located generally at the adjustable torsional lumbar support spring mechanism.

72. The chair defined in claim 63 wherein the compliant back includes a covering sheet, at least a stretchable portion of which is stretchable material for maintaining the covering sheet in tension on the compliant back during flexure of the compliant back.

73. The chair defined in claim 72 wherein the stretchable portion includes a strip of stretch fabric sewn to a lower edge of the covering sheet.

74. The chair defined in claim 73 wherein the compliant back includes a back shell, and includes an extrusion attached to the strip of stretch fabric, the extrusion being secured to a lower edge of the back shell.

75. The chair defined in claim 74 wherein the extrusion includes a notch for receiving an edge of the strip of stretch fabric and is sewn to the strip of stretch fabric along the notch.

76. In a chair having a base, a seat, a back frame rotatably attached to the base, and a first energy mechanism for biasing the back frame toward an upright position, the improvement comprising:
a compliant back that is flexibly bendable to define different curvilinear shapes for sympathetically supporting a seated user's back, and a belt bracket with forwardly extending flanges pivotally connecting the compliant back to the back frame at a first connection, said compliant back including a second connection pivotally connecting the compliant back to the back frame at a second location spaced vertically from the first connection, such that the compliant back is constrained to move over a range limited by the first and second connections;
and a second energy mechanism including a force generating mechanism located generally at one of the first and second connections and constructed to bias the bracket and so as to bias a lumbar portion of the compliant back forward with respect to the chair.

77. The chair defined in claim 76 wherein the belt bracken includes side flanges positioning the first connection generally at a rear of the chair's seat at a location where the first connection is adapted to be generally aligned with a pelvic bone of a typical seated adult user so that, when the seated adult user flexes his/her lower back rearwardly, a pelvic portion of the back moves downwardly and rearwardly, a lumbar portion of the back moves generally flexibly rearwardly to form a more planar arrangement with the pelvic portion, and a thoracic portion of the back pivots about the second connection, the pelvic portion and the thoracic portion being flexibly interconnected by the lumbar portion and adapted to move in a manner highly sympathetic to movements of the seated adult user's back.

78. A chair construction comprising:
a base assembly;
a seat;
a back frame pivoted to the base assembly for movement between upright and reclined positions; and a compliant back pivoted to the back frame at a fixed top connection and including forwardly extending flanges pivoted to one of the back frame, the seat, and the base assembly at bottom connections, the bottom connections being spaced laterally from a lower front central surface of the compliant back whereby, upon flexure of a seated adult user's spine and lower back, the compliant back is adapted to flex sympathetically and follow flexure of the seated adult user's back and spine.

79. The chair construction defined in claim 78 wherein the bottom connections connect the flanges of the compliant back to the back frame.

80. The chair construction defined in claim 79 wherein the compliant back comprises relatively stiff upper and lower sections interconnected by a flexible section.

81. Cancelled.

82. Cancelled.

83. A chair comprising:
a base assembly;

a seat;
an inverted U-shaped back frame having an intermediate top section and a pair of configured end sections pivoted to the base assembly, a T-shaped top connector protruding from the top section and a pair of bottom connectors in the configured end sections;
a compliant back including a top recess configured to receive and frictionally engage the top connector, and further including a belt bracket along a lower edge with opposing flanges that extend forwardly a distance for connection to the bottom connectors; and a connecting mechanism pivotally connecting the opposing flanges to the bottom connectors at a location proximate a rear of the seat.

84. The chair defined in claim 83 wherein the compliant back includes a flexible lumbar section, and wherein the distance that the flanges extend forwardly is a few inches so that the distance is calculated to be about equal to a distance from a hip joint of a seated adult user to a lower spine bone of the average seated adult user, such that the compliant back, when flexed, flexes in a sympathetic manner that provides continuous and comfortable support to a seated adult user's spine.

85. A back construction for a chair comprising:
a back frame;
a highly compliant back having a forwardly protruding lumbar support section that is characteristically very flexible and bendable, such that the compliant back can be flexed to a plurality of different convex shapes;
top and bottom connections pivotally connecting the compliant back to the back frame;
and an adjustable force-generating mechanism operably attached to at least one of the compliant back and the back frame, the force-generating mechanism being constructed to provide an adjustable biasing force that adjustably biases the lumbar support section forwardly for optimal lumbar support for a seated adult user's back, but the force-generating mechanism characteristically providing the biasing force without forcing a shape change in the compliant back.

86. A back construction for a chair comprising:
a back frame;

a highly compliant back having a forwardly protruding lumbar support section that is flexibly movable to a plurality of different convex shapes, with each shape being adapted to provide postural and comfortable support to a back of a seated adult user;
top and bottom connections pivotally connecting the compliant back to the back frame;
and an adjustable torsional force-generating mechanism operably attached to one or both of the compliant back and the back frame to bias the lumbar section forwardly for optimal lumbar support for the seated user's back, the torsional force-generating mechanism being operably mounted at the bottom connection to the back frame and the compliant back.

87. The back construction defined in claim 86 wherein the compliant back includes a relatively stiff thoracic support section and a relatively stiff pelvic support section, which are interconnected by the lumbar support section.

88. The back construction defined in claim 87 wherein the lumbar support section comprises a flexible sheet of material.

89. The back construction defined in claim 86 wherein torsional force-generating mechanism includes a spring and a handle, the handle being rotatable to wind and unwind to adjust a tension of the spring, the spring being operably connected between the compliant back and the back frame to bias the lumbar support section of the compliant back toward a forwardly convex shape.

90. The back construction defined in claim 89 wherein the torsional force-generating mechanism includes a lever to provide mechanical advantage when adjusting the tension of the spring.

91. A chair comprising:
a base assembly including a control housing having an energy source therein;
a seat on the base assembly;
a back support operably interconnected to the energy source for movement between an upright position and a reclined position, said back support including a back frame and a back shell, said back shell comprising a resiliently flexible polymeric sheet shaped to and adapted to support a back of a seated adult user, with a semi-rigid lower area disposed generally in a pelvic area on the chair, a flexible central area disposed above said lower area and generally in a lumbar area on the chair, and a semi-rigid upper area disposed above said central area in a thoracic area on the chair;
said back frame having a first attachment coupling said upper area of said back shell to the back frame, and a plurality of pivotal second attachments for pivotally coupling said lower area of the said back shell to the back frame, the second attachments constraining movement of the lower area to force flexure to occur in a controlled sympathetic manner in the lumbar area in order to adapt the back support to assure continuous and comfortable support of the seated adult user's spine in the lumbar area during flexure of the seated adult user's spine while seated, said central area of said back shell comprising a plurality of vertically spaced-apart slots in said sheet extending generally horizontally across a portion of the central area of said back support, said slots terminating prior to the perimeter edge of said sheet, whereby the said slots define a plurality of elongated horizontal resilient straps in said central area, each of said straps being dimensioned and adapted to provide resilient support for the seated adult user when sitting on the chair; and the lower area of the back shell including a reinforcement having forward extending flanges pivotally coupled to the second attachments of the back frame, said reinforcement and pivotal attachment being adapted to provide movable firm support for at least a portion of the pelvic area of the seated user.

92. The chair defined in claim 91 wherein the back frame includes a first pivot and the back frame is pivotally attached to the base assembly for movement of the back support between the upright and reclined positions, with the first pivot approximately coinciding with an axis located at a rear of the seat so that the axis is adapted to be located generally at a hip joint of the seated adult user.

93. Cancelled.

94. Cancelled.

95. A chair comprising:
a base assembly including a control housing having an energy source therein;
a seat on the base assembly;

a back support operably interconnected to the energy source for movement between an upright position and a reclined position, said back support including a back frame and a back shell, said back shell comprising a resiliently flexible polymeric sheet shaped to and adapted to support a back of a seated adult user, with a semi-rigid lower area disposed generally in a pelvic area on the chair, a flexible central area disposed above said lower area and generally in a lumbar area on the chair, and a semi-rigid upper area disposed above said central area in a thoracic area on the chair; and said back frame having a first attachment coupling said upper area of said back shell to the back frame, and a plurality of pivotal second attachments for pivotally coupling said lower area of the said back shell to the back frame, the second attachments constraining movement of the lower area to force flexure to occur in a controlled sympathetic manner in the lumbar area in order to adapt the back support to assure continuous and comfortable support of the seated adult user's spine in the lumbar area during flexure of the seated adult user's spine while seated, the pivotal second attachments for pivotally coupling said lower area of the said back shell to the back frame including a biasing device that biases the central area of the back shell in a forward direction.

96. The chair defined in claim 95 wherein the said lower area of the said back shell includes forward extending flanges pivotally coupled to the second attachments of the back frame and said biasing device includes a torsion spring operably interconnected to said forward extending flanges.

97. The chair defined in claim 96 wherein the said biasing device includes means for adjusting the pretension on the torsion spring.

98. A chair comprising:
a base assembly including a control housing having an energy source therein;
a seat on the base assembly;
a back support operably interconnected to the energy source for movement between an upright position and a reclined position, said back support including a back frame and a back shell, said back shell comprising a resiliently flexible polymeric sheet shaped to and adapted to support a back of a seated adult user, with a semi-rigid lower area disposed generally in a pelvic area on the chair, a flexible central area disposed above said lower area and generally in a lumbar area on the chair, and a semi-rigid upper area disposed above said central area and in a thoracic area on the chair; and said back frame having a first attachment coupling said upper area of said back shell to the back frame, and a plurality of pivotal second attachments for pivotally coupling said lower area of the said back shell to the back frame, the second attachments constraining movement of the lower area to force flexure to occur in a controlled sympathetic manner in the lumbar area in order to adapt the back support to assure continuous and comfortable support of the seated adult user's spine in the lumbar area during flexure of the seated adult user's spine while seated, the lower area of the back shell including forward extending flanges forming an axis of rotation at the pivotal second attachments of the back frame, said axis of rotation being located at or rearward of a rear of the seat so that the axis is generally adapted for location proximate a seated adult user's pelvic bone so that when the seated adult user flexes their lower back rearwardly, the lower portion of the back shell moves downwardly and rearwardly, and the central portion of the back shell flexes generally rearwardly to form a more planar arrangement with the lower portion.

99. A chair comprising:
a base assembly including a control housing having an energy source therein;
a seat on the base assembly;
a back support operably interconnected to the energy source for movement between an upright position and a reclined position, said back support including a back frame and a back shell, said back shell comprising a resiliently flexible polymeric sheet shaped to and adapted to support a back of a seated adult user, with a semi-rigid lower area disposed generally in a pelvic area on the chair, a flexible central area disposed above said lower area and generally in a lumbar area on the chair, and a semi-rigid upper area disposed above said central area and generally in a thoracic area on the chair; and said back frame having a first attachment coupling said upper area of said back shell to the back frame, and a plurality of pivotal second attachments for pivotally coupling said lower area of the said back shell to the back frame, the second attachments constraining movement of the lower area to force flexure to occur in a controlled sympathetic manner in the lumbar area in order to adapt the back support to assure continuous and comfortable support of the seated adult user's spine in the lumbar area during flexure of the seated adult user's spine while seated, said back frame defining a curvilinear arch.

100. The chair defined in claim 91 wherein the said back frame comprises an internal metal reinforcement encased in a resilient polymeric covering.

101. The chair defined in claim 91 including a seat operably mounted on the base assembly, the seat forming a link interconnecting the back support to the energy source.

102. A chair comprising:
a base assembly including a control housing having an energy source therein;
and a back assembly movably supported on the back assembly and including a back support operably interconnected to the energy source, said back support including a back frame and a back shell connected to the back frame by at least one connection, said back shell comprising a resiliently flexible polymeric sheet adapted to support a back of a seated adult user, the sheet including a lower area disposed generally in a pelvic area on a chair, a central area disposed above said lower area and generally in a lumbar area on the chair, and an upper area disposed above said central area and generally in a thoracic area on a chair; a cushion on a forward face of the back shell; and a vertically adjustable lumbar support located in front of the back shell, the lumbar support being movably supported on the back support and configured for vertical adjustment to change a shape of a front surface of the back in the lumbar area, said vertically adjustable lumbar support including laterally extending handles constructed to engage and follow configured non-parallel opposing perimeter edges of the back shell and constructed to slidably engage the vertically adjustable lumbar support to permit the handles to adjust laterally in and out to follow the perimeter edges.

103. A chair comprising:
a base assembly including a control housing having opposing flanges with upper edges and lubricous caps attached to the upper edges of the control housing, the lubricous caps including upper surfaces defining tracks for slidably engaging a slide member;
a back frame pivoted to the base assembly at a back pivot for movement between upright and reclined positions; and seat support structure operably supported on the base assembly and the back frame including a slide member slidably engaging the control housing for generally horizontal sliding movement and including a seat carrier pivoted to the slide member at a front seat pivot and also pivoted to the back frame at a rear seat pivot.

104. The chair defined in claim 103 including a seat shell attached to the seat support structure, the seat shell including a rear section configured to comfortably support thighs of a typical seated adult user, a front section configured to support buttocks of the seated adult user and to comfortably support a majority of the weight of the seated adult user, and a flexible zone connecting the rear section and the front section.

105. The chair defined in claim 104 including a gas spring extending between the seat support structure and the front section, the gas spring being a releasable self locking type device.

106. The chair defined in claim 105 including a bent rod axle pivoted to the seat support structure and the front section and operably connected to the gas spring.

107. The chair defined in claim 104 including a leaf spring operably supporting the front section on the seat support structure.

108. The chair defined in claim 103 including a spring mechanism positioned in the control housing, the spring mechanism being operably connected to the slide member.

109. The chair defined in claim 108 wherein the spring mechanism includes a spring positioned transversely in the control housing, and further includes a lever operably pivoted to the control housing, the lever having one end operably engaging the spring and another end operably engaging the seat support structure.

110. A chair comprising:
a base assembly including a control housing;
a back frame pivoted to the base assembly at a back pivot for movement between upright and reclined positions;
seat support structure operably supported on the base assembly and the back frame including a slide member slidably engaging the control housing for generally horizontal sliding movement and including a seat carrier pivoted to the slide member at a front seat pivot and also pivoted to the back frame at a rear seat pivot;
a spring mechanism position in the control housing, the spring mechanism being operably connected to the slide member and including a spring positioned transversely in the control housing, and further including a lever operably pivoted to the control housing, the lever having one end operably engaging the spring and another end operably engaging the seat support structure; and a pivot member, the pivot member and the lever having interfacing surfaces, at least one of which is curvilinear so that the arrangement operates like a rack-and-pinion, the pivot member being adjustable to vary a fulcrum point on the lever to adjust a length of a moment arm over which the spring acts to.

111. The chair defined in claim 110 including a back stop positioned in the control housing, the back stop being configured to engage the seat support structure to limit recline of the back frame.

112. The chair defined in claim 111 wherein the back stop includes a cam pivoted to the control housing for rotation about a vertical axis, the cam including a plurality of steps that can be selectively positioned to engage the seat support structure.

113. A chair comprising:
a base assembly including a control housing;
a back frame pivoted to the base assembly at a back pivot for movement between upright and reclined positions;
seat support structure operably supported on the base assembly and the back frame including a slide member slidably engaging the control housing for generally horizontal sliding movement and including a seat carrier pivoted to the slide member at a front seat pivot and also pivoted to the back frame at a rear seat pivot; and a seat shell slidably supported on the seat support structure for selective depth adjustment, whereby a depth of the seat shell can be selectively adjusted relative to the back frame.

114. A chair comprising:
a base assembly including a control housing with sidewalls defining a track;
a seat having a front portion with bearings slidably engaging the track and having a rear portion, the seat including a seat shell having a flexibly supported front portion;
a back pivoted to the base assembly and separately pivoted to the seat for movement between an upright position and a reclined position, the rear portion of the seat being pivoted to the back so that the seat moves forwardly and the seat rear portion moves forwardly and downwardly with a synchronous motion as the back is reclined;
a spring mechanism positioned in the central housing and operably connected to the seat for biasing the seat rearwardly, the spring mechanism including an extendable/compressible spring positioned in the control housing and a lever pivoted to the control housing and defining a moment arm with the spring for transmitting energy from the spring to the seat to bias the back to the upright position; and a gas spring operably connected between the front portion of the shell and a remaining portion of the seat adapted to carry the weight of a typical seated adult user, the gas spring being operable to adjust a position of the front portion relative to the remaining portion of the seat.

115. The chair defined in claim 114 wherein the gas spring is self-locking and releasable.

116. The chair defined in claim 115 including a control connected to the seat and including a link operably connected to the gas spring for releasing the gas spring for adjustment.

117. A chair comprising:
a base assembly including a control housing with sidewalls defining a track;
a seat having a front portion with bearings slidably engaging the track and having a rear portion, the seat including a seat shell having a flexibly supported front portion;
a back pivoted to the base assembly and separately pivoted to the seat for movement between an upright position and a reclined position, the rear portion of the seat being pivoted to the back so that the seat moves forwardly and the seat rear portion moves forwardly and downwardly with a synchronous motion as the back is reclined;
a spring mechanism positioned in the central housing and operably connected to the seat for biasing the seat rearwardly, the spring mechanism including an extendable/compressible spring positioned in the control housing and a lever pivoted to the control housing and defining a moment arm with the spring for transmitting energy from the spring to the seat to bias the back to the upright position; and a leaf spring positioned between and resiliently supporting the front section and a remaining portion of the seat.

118. A chair comprising:
a base assembly including a control housing with sidewalls defining a track;
a seat having a front portion with bearings slidably engaging the track and having a rear portion, the seat including a seat shell and a depth-adjustment structure for adjusting a depth of the seat shell relative to the back;
a back pivoted to the base assembly and separately pivoted to the seat for movement between an upright position and a reclined position, the rear portion of the seat being pivoted to the back so that the seat moves forwardly and the seat rear portion moves forwardly and downwardly with a synchronous motion as the back is reclined; and a spring mechanism positioned in the central housing and operably connected to the seat for biasing the seat rearwardly, the spring mechanism including an extendable/compressible spring positioned in the control housing and a lever pivoted to the control housing and defining a moment arm with the spring for transmitting energy from the spring to the seat to bias the back to the upright position.

119. The chair defined in claim 118 wherein the seat includes a seat Garner for supporting the seat shell and linear bearings for slidably engaging the shell on the seat carrier.

120. The chair defined in claim 119 including a latch operably extending between the seat carrier and the shell for holding the shell in a selected depth position.

121. The chair defined in claim 120 including a control connected to the seat for operating the latch.

122. A chair comprising:
a base assembly including a control housing;
a reclineable back frame pivoted to the base assembly for movement between upright and fully reclined positions;
a seat slidably supported on the control housing and pivotally supported on the back frame; and a variable backstop mechanism operably supported on the base assembly for engaging the seat to stop the seat and concurrently stop recline of the back at selected positions prior to reaching the fully reclined position, the variable backstop mechanism including a seat-engaging member and an actuator lever for adjustably moving the seat-engaging member, the seat-engaging member and the lever including intermeshing teeth for providing slip-free engagement.

123. The chair defined in claim 122 wherein the seat-engaging member includes a movable cam with steps shaped to selectively engage the seat.

124. The chair defined in claim 123 wherein the variable backstop mechanism includes a spring detent for holding the cam in a selected stopping position where a particular one of the steps is positioned to engage the seat.

125. The chair defined in claim 124 including an actuator connected to the cam for rotating the cam to select the particular one step.

126. A chair comprising:
a base assembly including a control housing;
a reclineable back frame pivoted to the base assembly for movement between upright and fully reclined positions;
a seat slidably supported on the control housing and pivotally supported on the back frame;
a variable backstop mechanism operably supported on the base assembly for engaging the seat to stop the seat and concurrently stop recline of the back at selected positions prior to reaching the fully reclined position;
the variable backstop mechanism including a movable cam with steps shaped to selectively engage the seat, and further including a spring detent for holding the cam in a selected stopping position where a particular one of the steps is positioned to engage the seat;
and an actuator connected to the cam for rotating the cam to select the particular one step, the actuator including a lever pivoted to the control housing, the lever and the cam including intermeshing teeth.

127. The chair defined in claim 126 wherein the actuator includes a rotatable handle operably connected to the lever.

128. The chair defined in claim 127 wherein the actuator includes a rod connecting the handle to the lever.

129. The chair defined in claim 127 wherein the handle includes a radially extending protrusion, and is connected to the lever by a pivot/slide joint that permits the handle to rotate about a first axis and permits the lever to rotate about a second axis that is skewed and non-parallel the first axis, with the handle driving rotation of the lever without binding.

130. A chair comprising:
a base assembly including a control housing;
a reclineable back frame pivoted to the base assembly for movement between upright and fully reclined positions;
a seat slidably supported on the control housing and pivotally supported on the back frame; and a variable backstop mechanism operably supported on the base assembly for engaging the seat to stop the seat and concurrently stop recline of the back at selected positions prior to reaching the fully reclined position, the variable backstop mechanism including a movable cam with steps shaped to selectively engage the seat; the cam further including an undulated surface adapted to engage a detent for selectively holding the steps in position to engage the seat, and still further including teeth adapted to engage mating teeth on an actuator for operating the cam.

131. A seat construction for a chair comprising:
a resiliently flexible seat shell including a front section configured to comfortably support thighs of a typical seated adult user, a rear section configured to comfortably support buttocks of a seated adult user and to comfortably support a majority of the weight of the seated adult user, and a flexible intermediate section connecting the front and rear sections, the front section being located about midway or forward therefrom on the seat shell and generally forward of the expected location of a seated adult user's hip joint so that the seated adult user's weight is substantially carried by the rear section for most adult users;
a seat cushion supported on the seat shell;
a pan-shaped seat carrier supporting the rear section of the shell, the seat carrier including a forwardly extending section extending under the flexible intermediate section and that is characteristically spaced below and not connected to the flexible intermediate section;
and an adjustable thigh-flex support mechanism operably supporting the front section of the seat shell on the forwardly extending section of the seat carrier, so that the front section is adjustable relative to the rear section to provide optimal thigh pressure and support to the seated adult user, the adjustable thigh-flex support mechanism including a pretensioned, transverse leaf spring.

132. A seat construction for a chair comprising:
a resiliently flexible seat shell including a front section configured to comfortably support thighs of a typical seated adult user, a rear section configured to comfortably support buttocks of a seated adult user and to comfortably support a majority of the weight of the seated adult user, and a flexible intermediate section connecting the front and rear sections, the front section being located about midway or forward therefrom on the seat shell and generally forward of the expected location of a seated adult user's hip joint so that the seated adult user's weight is substantially carried by the rear section for most adult users;
a seat cushion supported on the seat shell;
a pan-shaped seat carrier supporting the rear section of the shell, the seat carrier including a forwardly extending section extending under the flexible intermediate section and that is characteristically spaced below and not connected to the flexible intermediate section;
and an adjustable thigh-flex support mechanism operably supporting the front section of the seat shell on the forwardly extending section of the seat corner, so that the front section is adjustable relative to the rear section to provide optimal thigh pressure and support to the seated adult user, the adjustable thigh-flex support mechanism including a bent rod axle and a releasable, lockable gas spring for rotating the bent rod axle and thereafter holding the bent rod axle in a selected orientation.

133. A seat construction comprising:
a flexible seat shell including a front section configured to support thighs of a typical seated adult user, a rear section configured to comfortably support thighs of the seated adult user and to comfortably support a majority of the weight of the seated adult user, and a flexible intermediate section;
a T-shaped seat support pan having a bottom panel defining a full-width rear section and a partial-width front section that has a width less than the full-width rear section and that extends forwardly from a center of the rear section, the full-width rear section being configured to support the rear section of the shell with the partial-width front section extending under and spaced below the front section; and an adjustable thigh-support mechanism adjustably connecting and supporting the front section on the partial-width front section.

134. The seat construction defined in claim 133 wherein the adjustable thigh-support mechanism includes a pretensioned transverse leaf spring.

135. The seat construction defined in claim 134 wherein the adjustable thigh-support mechanism includes a bent rod axle and a releasable lockable gas spring for rotating the bent rod axle and thereafter holding the bent rod axle in a selected orientation.

136. In a chair having a reclineable back and a movable seat operably supported for synchronous movement with the back, an improvement comprising:
a seat earner having a T-shaped body including front and rear sections and including a linear bearing positioned on each side of the front section and each side of the rear section;
the seat carrier including pivots adapted to pivotally mount the seat carrier to a support for movably supporting the movable seat relative to the reclineable back;
a pan-shaped seat frame constructed to support a seat cushion and a seated user, the seat frame including a bottom panel with flat surfaces slidably engaging associated ones of the linear bearings, whereby the seat frame is depth-adjustable on the seat earner.

137. The chair defined in claim 136 wherein one of the seat carrier and the seat frame including a series of notches extending in a fore/aft direction, and the other one of the seat carrier and the seat frame include a latch for selectively engaging the notches.

138. The chair defined in claim 137 wherein seat carrier includes upwardly formed stop tabs, and including a top-mounted stop limiter attached to the seat frame, the stop limiter having a protrusion that extends downwardly through the seat frame and that is shaped to engage the stop tabs to define a maximum depth position and a minimum depth position of the seat frame on the seat carrier.

139. The chair defined in claim 136 wherein the seat frame includes flanges capturing at least two of the bearings to prevent the seat frame from being lifted vertically off of the seat carver.

140. A chair comprising:
a base assembly including a control housing having at least one up flange and a lubricous bearing supported atop each up flange;
a back frame pivoted to the base assembly at a back pivot for movement between upright and reclined positions; and seat support structure operably supported on the base assembly and the back frame including a slide member slidably engaging the lubricous bearing of each up flange for generally horizontal sliding movement and including a seat carrier pivoted to the slide member at a front seat pivot and also pivoted to the back frame at a rear seat pivot.

141. The chair defined in claim 140 wherein the at least one up flange includes two parallel side flanges on the control housing.

142. The chair defined in claim 141 wherein the lubricious bearings each comprises polymeric members attached to a top edge of the side flanges.

143. The chair defined in claim 140 wherein the base assembly includes a base frame that includes the housing, and further includes side arms that support the back frame at the back pivot.

144. The chair defined in claim 103 where in the base assembly includes a base frame that includes the housing, and further includes side arms that support the back frame at the back pivot.

145. The chair defined in claim 110 wherein the base assembly includes a base frame that includes the housing, and further includes side arms that support the back frame at the back pivot.

146. The chair defined in claim 113 wherein the base assembly includes a base frame that includes the housing, and further includes side arms that support the back frame at the back pivot.

147. Cancelled.

148. Cancelled.

149. Cancelled.

150. Cancelled.

151. Cancelled.

152. Cancelled.

153. Cancelled.

154. Cancelled.

155. Cancelled.

156. Cancelled.

157. Cancelled.

158. Cancelled.

159. Cancelled.

160. Cancelled.

161. Cancelled.

162. Cancelled.

163. A method of assembling a chair comprising steps of:
providing a chair component with laterally extending oppositely facing protrusions;
providing a back frame with end sections having recesses therein;
flexing the end sections of the back frame and simultaneously positioning the recesses of the end sections on the protrusions; and releasing the back frame so that the back frame resiliently returns to an original shape which holds the back frame in place and pivotally connects the back frame to the chair component.

164. The method defined in claim 163 wherein the chair component comprises a seat, and including providing a base assembly with side arms, and further including flexing the end sections to position the end sections between side portions of the seat and the side arms of the base assembly.

165. The method defined in claim 164 wherein the side arms include oppositely facing second protrusions, and wherein the end sections include second recesses, and including positioning the second recesses on the second protrusions.

166. The method defined in claim 165 wherein the first mentioned protrusions and the second protrusions on each respective side of the chair face in opposite directions.

167. Cancelled.

168. Cancelled.

169. The method defined in claim 164 wherein the base assembly includes a base frame comprising a housing, with the opposing side arms extending laterally and upwardly from the housing, and including positioning the configured end sections inside an upper end of the side arms but generally outside and above the housing.

170. A chair comprising:
a base assembly for supporting the chair on a floor surface while a seated user is performing tasks;
a back frame pivoted to the base assembly at a back pivot for movement between a plurality of working positions including upright and reclined working positions;
a seat pivoted to the back frame at a seat pivot spaced rearwardly and below the back pivot, the seat being slidably supported at a front portion of the base assembly for horizontal movement, the back pivot and the seat pivot being interconnected and arranged to move the seat generally forwardly and also move a rear portion of the seat downwardly with a synchronous pivoting motion as the back frame is reclined, whereby a seated user is comfortably supported in the upright and reclined working positions, and whereby the seated user is able to continue working while moving between the upright and reclined working positions without constantly having to move and adjust the base assembly back and forth relative to a stationary worksurface;
the base assembly including a control housing with an energy mechanism positioned therein that operably engages one of the back frame and the seat for biasing the back frame to the upright position; and the seat including a seat slide member that slidably engages the control housing, and further including a seat support carrier pivotally engaging the seat slide at first pivots and pivotally engaging the back frame at second pivots.

171. Cancelled.

172. The chair defined in claim 170 wherein the base assembly includes side arms that extend upwardly generally adjacent the seat for supporting the back frame and a portion of the seat.

173. The chair defined in claim 172 wherein the back frame is pivoted to the side arms.

174. The chair defined in claim 173 wherein the seat is pivoted to the back frame in a location generally proximate the side arms.

175. A chair comprising:
a base assembly for supporting the chair on a floor surface while a seated user is performing tasks;
a back frame pivoted to the base assembly at a back pivot for movement between a plurality of working positions including upright and reclined working positions;
a seat pivoted to the back frame at a seat pivot spaced rearwardly and below the back pivot, the seat being slidably supported at a front portion of the base assembly for horizontal movement, the back pivot and the seat pivot being interconnected and arranged to move the seat generally forwardly and also move a rear portion of the seat downwardly with a synchronous pivoting motion as the back frame is reclined, whereby a seated user is comfortably supported in the upright and reclined working positions, and whereby the seated user is able to continue working while moving between the upright and reclined working positions without constantly having to move and adjust the base assembly back and forth relative to a stationary worksurface;
the base assembly including a control housing with an energy mechanism positioned therein that operably engages one of the back frame and the seat for biasing the back frame to the upright position;
the base assembly including side arms that extend upwardly generally adjacent the seat for supporting the back frame and a portion of the seat;
the back frame being pivoted to the side arms;
the seat being pivoted to the back frame in a location generally proximate the side arms; and the energy mechanism including a spring positioned transversely in the control housing, and including a lever operably connecting the spring to the one of the seat and the back frame.

176. The chair defined in claim 175 including an adjustment mechanism for adjusting the lever to vary a biasing force transmitted from the spring to the seat, the adjustment mechanism including the lever and defining an adjustable moment arm on the lever for adjustably biasing the back frame toward the upright position.

177. The chair defined in claim 170 wherein the energy mechanism includes a spring positioned transversely within the control housing, and further including a lever operably connecting the spring to one of the seat and the back frame.

178. A chair comprising:
a base assembly for supporting the chair on a floor surface while a seated user is performing tasks;
a back frame pivoted to the base assembly at a back pivot for movement between a plurality of working positions including upright and reclined working positions;
a seat pivoted to the back frame at a seat pivot spaced rearwardly and below the back pivot, the seat being slidably supported at a front portion of the base assembly for horizontal movement, the back pivot and the seat pivot being interconnected and arranged to move the seat generally forwardly and also move a rear portion of the seat downwardly with a synchronous pivoting motion as the back frame is reclined, whereby a seated user is comfortably supported in the upright and reclined working positions, and whereby the seated user is able to continue working while moving between the upright and reclined working positions without constantly having to move and adjust the base assembly back and forth relative to a stationary worksurface;
the base assembly including a control housing with an energy mechanism positioned therein that operably engages one of the back frame and the seat for biasing the back frame to the upright position;
wherein the energy mechanism includes a spring positioned transversely within the control housing; and a lever operably connecting the spring to one of the seat and the back frame, the lever being pivotable about a vertical axis with a first end engaging the spring and a second end operably connected to the seat for biasing the seat rearwardly and in turn for biasing the back frame to the upright position.

179. The chair defined in claim 170 wherein the control housing includes opposing side flanges, and the seat includes bearings slidably engaging the side flanges.

180. Cancelled.

181. The chair defined in claim 170 wherein the seat includes a flexible seat shell having a rear section adapted to support buttocks of a seated adult user, and further includes a front section adapted to support thighs of the seated adult user and that is flexibly connected to the rear section, the rear section being carried and supported by the seat support carrier.

182. The chair defined in claim 170 wherein the seat includes a seat support carrier slidably connected to the base assembly and pivotally connected to the back frame, and further includes a seat shell slidably supported on the seat support carrier for manually adjustable depth adjustment.

183. A chair comprising:
a base assembly for supporting the chair on a floor surface while a seated user is performing tasks;
a back frame pivoted to the base assembly at a back pivot for movement between a plurality of working positions including upright and reclined working positions;
a seat pivoted to the back frame at a seat pivot spaced rearwardly and below the back pivot, the seat being slidably supported at a front portion of the base assembly for horizontal movement, the back pivot and the seat pivot being interconnected and arranged to move the seat generally forwardly and also move a rear portion of the seat downwardly with a synchronous pivoting motion as the back frame is reclined, whereby a seated user is comfortably supported in the upright and reclined working positions, and whereby the seated user is able to continue working while moving between the upright and reclined working positions without constantly having to move and adjust the base assembly back and forth relative to a stationary worksurface;
the base assembly including a control housing with an energy mechanism positioned therein that operably engages one of the back frame and the seat for biasing the back frame to the upright position; and a backstop mechanism attached to the control housing and configured to selectively engage the seat to limit forward movement of the seat and accordingly selectively limit recline of the back frame.

184. The chair defined in claim 170 including a compliant back assembly attached to the back frame in at least two vertically spaced locations, the compliant back assembly being constructed to flex between the at least two vertically spaced locations to provide optimal lumbar support.

185. The chair defined in claim 184 wherein the compliant back assembly includes a resiliently flexible, one piece shell.

186. The chair defined in claim 184 wherein the compliant back assembly includes a multi-piece assembly of components, each having a surface for supporting a portion of a human's back.

187. A chair comprising:
a mobile base assembly including a control housing;
a back pivoted to the base assembly for movement between upright and reclined positions;
a seat operably supported on the base assembly and connected to the back for movement between a substantially rearward working position and a forward working position;
the seat including a front portion that is slidably connected to the base assembly to move horizontally forwardly upon recline of the back so that a seated user's legs are not undesirably lifted from a floor surface during recline;
the seat further including a rear portion flexibly connected to the front portion and that is operably connected to the back to move downwardly and forwardly upon recline so that the seated user is comfortably and posturally supported during recline with an angular synchronous movement of the seat and the back, and so that a maximum forward movement of the seat and maximum angular movement of the back are limited to strokes that keep the hands of a seated user relatively constant during recline, whereby the seated user can easily and comfortably continue to work in all seated positions;
a spring mechanism positioned transversely in the control housing, and further including a lever pivotally engaging the spring mechanism and operably connected to the seat for biasing the seat toward the rearward working position and simultaneously biasing the back toward the upright position; and the control housing including side arms, and wherein the seat includes bearings that slidably engage the side arms.

188. Cancelled.

189. The chair defined in claim 187 wherein the side arms pivotally support the back at a location at a rear of the seat where the axis is adapted to be generally aligned with a hip joint of the seated user.

190. Cancelled.

191. The chair defined in claim 187 wherein the spring mechanism includes a spring resiliently supporting the front section of the seat for flexural movement to provide increased comfort for the seated user.

192. The chair defined in claim 191 wherein the seat further includes a releasable lockable gas spring operably adjustably supporting the front section for adjustable movement to provide adjustable comfort to the seated user.

193. Cancelled.

194. The chair defined in claim 189 wherein the rear portion is configured and adapted to support the buttocks of an adult seated user and a majority of the adult seated user's weight, and the front portion is configured and adapted to flexibly and comfortably support the thighs of the adult seated user without lifting the legs of the adult seated user during recline of the back.

195. The chair defined in claim 189 wherein the seat includes a seat support carrier slidably supported on the base assembly and pivotally engaging the back, and further includes a seat shell that is manually depth adjustable on the seat support carrier.

196. A chair comprising:
a base assembly including side arms;
a back frame pivoted to the base assembly at back pivots for movement between a plurality of working positions including upright and reclined working positions; and a seat pivoted to the back frame at seat pivots and slidably supported at a front portion of the base assembly, the back frame including right and left configured end sections positioned on opposite sides of the seat and between the sides of the seat and associated ones of the side arms, the configured end sections supporting first pivot bearings at the seat pivots and second pivot bearings at the back pivots, whereby the seated user is able to continue working while moving between the upright and reclined working positions.

197. A chair comprising:
a mobile spider-legged base assembly including a control housing and upwardly extending side arms;

an inverted U-shaped back frame having configured end sections positioned adjacent associated ones of the side arms and pivoted thereto at back pivots, the back pivots each comprising a first stud and a rotatable first bearing engaging the first stud;
a seat slidably supported on the control housing, the seat including a seat carrier pivoted to the configured end sections at seat pivots, the seat pivots each comprising a second stud and a rotatable second bearing engaging the second stud, the seat pivots and back pivots being spaced apart; and an adjustable energy mechanism including a transverse spring, a lever operably engaging the spring and the seat for biasing the seat toward a rearward position and in turn biasing the back frame toward an upright position, and an adjustment pivot member adjustably engaging the lever to define a fulcrum that moves during recline and that is manually adjustably changeable to relocate the fulcrum for adjustably controlling a force of the spring on the seat.

198. Cancelled.

199. Cancelled.

200. The chair defined in claim 181 wherein the seat further includes a spring resiliently supporting right and left sides of the front section for independent flexural movement to provide increased comfort for the seated user.

201. The chair defined in claim 181 wherein the seat further includes a releasable lockable gas spring operably adjustably supporting the front section for adjustable movement to provide adjustable comfort to the seated user.

202. A chair comprising:
a base assembly including a control housing;
an energy source located within the control housing;
a seat operably supported on the base assembly for generally horizontal movement between forward and rearward positions, with the seat operably interconnected to said energy source;
a back support including a back shell and a back frame supporting the back shell, wherein the back frame includes a first pivot wherein the back frame is pivotally coupled to the base assembly for movement of the back support between upright and reclined positions, and a second pivot wherein the back frame is pivotally coupled to the seat;
wherein the energy source biases the back support into an upright position by urging the seat rearward, said rearward movement of the seat inducing the back support to rotate to a generally upright position at the first pivot; and a variable backstop mechanism supported on the base assembly and operably engaging the seat, the variable backstop mechanism being configured to concurrently stop the seat and stop recline of the back support at a plurality of selectable positions between the upright and reclined position.

203. The chair defined in claim 202 wherein the first pivot axis is located at a rear of the seat where the first pivot axis is adapted to be generally aligned with a hip joint of a seated adult user.

204. The chair defined in claim 202 wherein the seat comprises a seat front slide adapted to slide forward and rearward on the control housing, a seat carrier pivotally interconnected to said control housing and said front slide, a seat frame in sliding engagement with said seat carrier, and a seat shell adapted to support buttocks and thighs of a seated adult user.

205. The chair defined in claim 204 wherein the seat shell includes a rear section configured to support the buttocks of the seated adult user and to support a majority of the seated adult user's weight, and further includes a front section adapted to support the thighs of a seated adult user, and still further includes a flexible zone connecting the rear section and the front section, and including an adjustment device connected to the front section and configured to angularly adjust the front section of the seat shell relative to the rear section, wherein the adjustment device is attached to an underside of the front section of the seat shell.

206. Cancelled.

207. A chair comprising:
a base assembly including a control housing;
an energy source located within the control housing;
a seat operably supported on the base assembly for generally horizontal movement between forward and rearward positions, with the seat being operably interconnected to said energy source, the seat including a seat shell having a rear section adapted to support buttocks of a seated adult user and a front section adapted to support thighs of the seated adult user; and a back support including a back shell and a back frame supporting the back shell, the back frame including a first pivot wherein the back frame is pivotally coupled to the base assembly, and a second pivot point wherein the back frame is pivotally coupled to the seat.