Adjustable ergonomic chair

Abstract

An office-type chair includes a base, a height-adjustable pedestal extending upward from the base, a seat assembly including a rear seat part and a front seat part, and a linkage system connecting the pedestal to the seat assembly. The linkage system is adapted to pivot the seat assembly between a lowered position to serve as a task chair and an elevated position to serve as an elevated sitting support. A backrest arrangement may extend from the seat assembly. In the lowered position, the front and rear seat parts are both generally horizontally oriented. In the elevated position, the rear seat part may have a slight forward tilt and be positioned higher than in the lowered position, and the front seat part may extend at a downward angle relative to the rear seat part.

Claims

1. An office-type chair comprising; a base, wherein the base includes multiple support arms with casters for enabling the chair to roll along a ground surface; a height-adjustable and swiveling pedestal extending upward from the base; a seat assembly including a rear seat part pivotally connected to a front seat part at a laterally extending axis and a seat pan comprising a rear portion supporting the rear seat part and a front portion supporting the front seat part, wherein the seat assembly defines a depth direction extending through the rear seat part and the front seat part and perpendicular to the laterally extending axis, the rear seat part having a depth extending in the depth direction and the front seat part having a depth extending in the depth direction, the depth of the rear seat part being at least about twice the depth of the front seat part; a linkage system connecting the pedestal to the seat assembly, wherein the linkage system is adapted to pivot the seat assembly between a first generally planar position of the front and rear seat parts to serve as a task chair and a second more upward and forwardly non-planar angled position of the front and rear seat parts to serve as an elevated sitting support, wherein in the first position the front and rear seat parts are both generally oriented such that they are in line with each other at approximately 3.5 degrees rearward tilt, wherein in the second, elevated position the rear seat part is elevated and tilted at least about 5 degrees forward with respect to and the ground surface, wherein in the second, elevated position the front seat part extends at a downward angle with respect to the rear seat part, and wherein in the second, elevated position, the rear seat part is generally aligned above the pedestal to align a user's center of gravity above the center of the base to keep the chair stable upon the casters, and a backrest arrangement including a recline mechanism and backrest support, the backrest support extending upwardly from the seat assembly for supporting the back of a user in the first and second positions, wherein the recline mechanism is connected directly to a rear edge of the rear seat part of the seat assembly and the backrest support rotates with respect to the recline mechanism about a backrest recline axis, the recline mechanism travelling with the rear seat part as the seat assembly is pivoted between the first and second positions; wherein the linkage system includes a first link arm extending from the pedestal to the rear seat part, the first link arm having a forward end connected to the pedestal and a rear end connected to the rear seat part, the first link arm pivoting with respect to the rear seat part about a rear pivot axis and pivoting with respect to the pedestal about a forward pivot axis when the linkage system pivots the seat assembly between the first and second positions, wherein during the pivoting of the first link arm, the rear end of the first link arm moves in a continuous arcuate motion that drives the seat assembly between the first and second positions; wherein the backrest recline axis is adjacent to the rear pivot axis of the first link arm, and the backrest support is capable of rotating about the backrest recline axis in both the first and second positions of the seat assembly.

2. The chair according to claim 1 wherein the casters on the base are non-locking casters.

3. The chair according to claim 1 wherein the linkage system includes a second link arm that is connected between the pedestal and the front seat part, wherein both the first and second link arms form a four-bar linkage and articulate in a continuous motion path between a first normally seated posture position and a second more elevated sitting posture position.

4. The chair according to claim 3 wherein in the second position the front seat part is at an approximate 40 degree angle relative to the rear seat part.

5. The chair according to claim 3 wherein in the second position at least a portion of the rear seat part is approximately 5 inches higher than in the first position.

6. The chair according to claim 3 wherein the rear seat part includes a concave portion forming an ischial tuberosity pocket that acts to retain and support the user, and wherein in the second position the ischial tuberosity pocket is approximately vertically in line with the center of the height adjustable pedestal to provide stability to a user sitting on the rear seat part.

7. The chair according to claim 6 wherein the support arms each having upper ends that move in an arcuate motion between the first and second positions.

8. The chair according to claim 1 wherein the laterally extending axis between the front seat part and the rear seat part is positioned a distance adapted to be approximately 6″ forward of an occupant's ischial tuberosity bones.

9. An office-type chair for supporting a user, comprising: a base that engages a ground surface; a height adjustable and rotatable pedestal extending upwardly from the base; a seat assembly supported on the pedestal, the seat assembly including a forward seat portion and a rearward seat portion, the forward seat portion being pivotally connected to the rearward seat portion at a laterally extending axis, the rearward seat portion having a rear edge, the forward seat portion having a front edge, wherein the seat assembly defines a depth direction extending through the rearward seat portion and the forward seat portion and perpendicular to the laterally extending axis, the rearward seat portion having a depth extending in the depth direction and the forward seat portion having a depth extending in the depth direction, the depth of the rearward seat portion being at least about twice the depth of the forward seat portion; and a linkage assembly supporting the seat assembly, the linkage assembly including a rear portion connected to the rear seat portion, a forward portion connected to the forward seat portion, and an assist portion, the linkage assembly movable between a lowered position and an elevated position, wherein in the lowered position the forward seat portion and the rearward seat portion are generally aligned in a seating plane at approximately 3.5 degrees rearward tilt, and wherein in the elevated position the rearward seat portion is elevated above and tilted at least about 5 degrees forward with respect to the ground surface and the forward seat portion is pivoted at an angle with respect to the rearward seat portion, the forward seat portion extending at a downward angle from the rearward seat portion to reduce stress on the thigh of a user, wherein the assist portion can be actuated by the user to assist the movement of the seat assembly to the elevated position; wherein the rearward seat portion is adapted to retain and support the user even as the rearward seat portion is tilted forwardly when the seat assembly is in the elevated position, whereby the rearward seat portion defines a concave portion forming an ischial tuberosity pocket and the laterally extending axis is positioned nearer to the front edge than the rear edge; wherein the linkage system includes a first link arm extending from the pedestal to the rearward seat portion, the first link arm having a forward end connected to the pedestal and a rear end connected to the rear edge of the rearward seat portion, the first link arm pivoting with respect to the rearward seat portion about a rear pivot axis and pivoting with respect to the pedestal about a forward pivot axis when the linkage system pivots the seat assembly between the lowered and elevated positions, wherein during the pivoting of the first link arm, the rear end of the first link arm moves in a continuous arcuate motion that drives the linkage assembly between the lowered and elevated positions; the office type chair including a backrest arrangement including backrest support, the backrest support extending upwardly from the rear edge of the rearward seat portion of the seat assembly for supporting the back of a user in the lowered and elevated positions, wherein the backrest arrangement includes a recline mechanism such that the backrest support is rotatable about a backrest recline axis at the rear edge of the rearward seat portion and adjacent to the rear pivot axis of the first link arm, the recline mechanism travelling with the rearward seat portion as the seat assembly is pivoted between the lowered and elevated positions, and the backrest support is capable of rotating about the backrest recline axis in both the lowered and elevated positions.

10. The chair according to claim 9 wherein in the elevated position the front seat surface is at an approximate 40 degree angle relative to the rear seat surface.

11. The chair according to claim 9 wherein the backrest support extends at a backrest angle from the seat assembly, and where the movement of the seat assembly from the lowered position neither increases nor decreases the backrest angle.

12. The chair according to claim 9 wherein the change in angle of the rear seat portion from the lowered position to the elevated position is between approximately 8-10 degrees.

13. An office-type chair for supporting a user, comprising: a base including a plurality of casters for engaging and rolling along a ground surface; a height adjustable and rotatable pedestal extending upwardly from the base; a seat assembly supported on the pedestal, the seat assembly including a forward seat portion having a forward seat surface and a rearward seat portion having a rearward seat surface, the forward seat surface being pivotally connected to the rearward seat surface at a laterally extending axis, wherein the seat assembly defines a depth direction extending through the rearward seat surface and the forward seat surface and perpendicular to the laterally extending axis, the rearward seat surface having a depth extending in the depth direction and the forward seat surface having a depth extending in the depth direction, the depth of the rearward seat surface being at least about twice the depth of the forward seat surface, wherein the seat assembly is movable between a lowered position and an elevated position, wherein in the lowered position the forward seat surface and the rearward seat surface are generally aligned in a seating plane at approximately 3.5 degrees rearward tilt, and wherein in the elevated position the rearward seat surface is elevated above and tilted at least about 5 degrees forwardly with respect to the ground surface, and wherein in the elevated position the forward seat surface is pivoted at a downward angle with respect to the rearward seat surface; and a backrest arrangement connected to the rearward seat portion, the backrest arrangement including a back support extending upwardly from the seat assembly and a recline mechanism connected directly to a rear edge of the rearward seat portion, the backrest arrangement moving with the rearward seat surface between the lowered position and the elevated position, the back support pivoting about the recline mechanism with respect to the rearward seat surface about a backrest recline axis; wherein the linkage system includes a first link arm extending from the pedestal to the rearward seat portion, the first link arm having a forward end connected to the pedestal and a rear end connected to the rearward seat portion, the first link arm pivoting with respect to the rearward seat portion and the rearward seat surface about a rear pivot axis and pivoting with respect to the pedestal about a forward pivot axis when the linkage system pivots the seat assembly between the lowered and elevated positions, wherein during the pivoting of the first link arm, the rear end of the first link arm moves in a continuous arcuate motion that drives the seat assembly between the lowered and elevated positions; wherein the backrest recline axis is adjacent to the rear pivot axis of the first link arm, and the back support is capable of rotating about the backrest recline axis in both the lowered and elevated positions of the seat assembly.

14. The chair according to claim 13 wherein the change in angle of the rear seat surface from the lowered position to the elevated position is between about 8-10 degrees and the change in angle of the front seat surface with respect to the rear seat surface is about 40 degrees thereby adapted to promote a neutral posture of the user such that the user's thigh to torso angle is between about 121 and 135 degrees and the user's posterior superior iliac spine (PSIS) is located higher than the user's anterior superior iliac spine (ASIS).

15. The chair according to claim 14 wherein the rear seat surface defines a concave pocket aligned above the pedestal to support the user on the rear seat surface when the chair is in the elevated position with the front seat surface pivoted downward from the rear seat surface to relieve stress on the user's thighs.

16. The chair according to claim 15 wherein the laterally extending axis between the front seat surface and rear seat surface is positioned a distance adapted to be approximately 6″ forward of the concave pocket.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a front perspective view of a chair according to one embodiment of the present invention.

(2) FIG. 2 is a front perspective view of the chair in an elevated ergonomic position.

(3) FIG. 3 is a side view of the chair according to one embodiment.

(4) FIG. 4 is a side view of the chair in the elevated ergonomic position.

(5) FIG. 5 is a front view of the chair according to one embodiment.

(6) FIG. 6 is a front view of the chair in the elevated ergonomic position.

(7) FIG. 7 is a rear perspective view of the chair according to one embodiment.

(8) FIG. 8 is a rear perspective view of the chair in the elevated ergonomic position.

(9) FIG. 9 is a rear view of the chair according to one embodiment.

(10) FIG. 10 is a rear view of the chair in the elevated ergonomic position.

(11) FIG. 11 is a front perspective view of the chair according to one embodiment with the seat upholstery removed.

(12) FIG. 12 is a front perspective view thereof with the chair in the elevated ergonomic position.

(13) FIG. 13 is a side view of the chair according to one embodiment with a back support shown in upright and reclined positions.

(14) FIG. 14 is a schematic side view of a user's lumbar spine and pelvis.

DETAILED DESCRIPTION OF THE CURRENT EMBODIMENT

(15) Referring to the Figures, an office-type chair is shown in accordance with one embodiment of the present invention and generally designated 10. The chair 10 includes a base 12, a pedestal 14 extending upwardly from the base 12, a seat assembly 16 supported on the pedestal 14, and a backrest 18 extending upwardly from the seat assembly 16. A linkage mechanism 20 operatively connects the seat assembly 16 to the pedestal 14 or the base 12 and enables movement of the seat assembly 16 from a lowered, generally horizontal position to an elevated ergonomic position that is described in more detail below.

(16) The base 12 forms the ground engaging surface for the office-type chair 10. In one embodiment, the base 12 includes a cylindrical hub 22 and a series of five support arms 24 extending radially outwardly from the hub 22 (although other types and a different amount of supports are also possible). The support arms 24 may each include a caster 26, which in one embodiment may be non-locking casters 26. Non-locking casters may include standard non-locking casters and casters which limit the speed or amount of roll and may help prevent inadvertent repositioning or rolling away of the chair 10, for example, when a user sits on the chair in either the lowered or the elevated posture positions. In another embodiment, not shown, the casters 26 may be selectively lockable such that the user can lock the casters to prevent them from rolling and thus prevent movement of the chair 10 along the ground surface.

(17) The pedestal 14 extends upwardly from the base 12. In the illustrated embodiment, the pedestal 14 includes a lower portion 28 and an upper portion 30 fixed to the lower portion 28. The lower portion 28 is generally cylindrical, and is sized to fit within the hub 22 of the base 12. The hub 22 may include a generally conventional height adjustment mechanism that can be actuated by the user to raise and lower the pedestal 14, and thus raise and lower the height of the seat assembly 16 with respect to the ground surface, by sliding the lower portion 28 of the pedestal 14 within the hub 22. In one embodiment, an activation lever 27 is connected to the height adjustment mechanism such that a user can activate the height adjustment mechanism by pulling the lever 27. The lower portion 28 may also be capable of rotating within the hub 22 to enable swiveling rotation of the seat assembly 16. In the illustrated embodiment, the upper portion 30 of the pedestal 14 is fixed to the lower portion 28 but extends at an angle from the upper end 32 of the lower portion 28. More particularly, in the illustrated embodiment, the upper portion 30 extends upwardly at about a 30 degree angle from the generally vertical lower portion 28, and the upper portion 30 extends forwardly toward the forward edge of the seat assembly, as described in more detail below. The upper portion 30 thus acts as a support for the seat assembly 16 and linkage mechanism 20. In the illustrated embodiment, the upper portion 30 is Y-shaped, extending from a narrow first end 31 and widening to a second end 33 that forms a yolk having first 35 and second 37 arms.

(18) The seat assembly 16 is supported above the pedestal 14 and can be moved between a lowered, generally horizontal position as shown in FIG. 3 and an elevated ergonomic position as shown in FIG. 4. In one embodiment, the seat assembly 16 includes a front portion 34 and a rear portion 36. The seat assembly 16 includes a cushioned upholstery 35 extending continuously over both the front 34 and rear 36 portions. The upholstery 35 on the front 34 includes an upper surface 38 and the upholstery 35 on the rear portion 36 includes an upper surface 40. The front 34 and rear 36 portions are capable of pivoting with respect to one another, and as shown in the illustrated embodiment, the front portion 34 is capable of pivoting downwardly with respect to the rear portion 36. As described in more detail below, the front portion 34 pivots downward with respect to the rear portion when the seat assembly 16 is raised to the upper elevated position as shown in FIGS. 2, 4, 6, 8, 20 and 12. In the lowered position, such as that shown in FIGS. 1, 3, 5, 7, 9, and 11, the upper surfaces 38, 40 of the front 34 and rear 36 portions are generally aligned in a common plane. As shown in FIG. 3, this plane may be tilted slightly rearwardly from horizontal, such as about 3.5 degrees rearward of horizontal, with a rear edge 42 of the rear portion 36 thus slightly lower than a front edge 44 of the front portion 36. In another embodiment, the tilt angle of the seat assembly may be different, such as slightly greater or less than 3.5 degrees rearward tilt, or even true horizontal or a slightly forward tilt.

(19) Referring now to FIGS. 2, 4, 6, 8 and 10, when the seat assembly 16 is in the ergonomic elevated position, both portions of the seat assembly 16 may be raised from their lowered positions, and the front portion 34 is tilted downwardly with respect to the rear portion 36. In one embodiment, the rear portion 36 is raised between about 4 and 8 inches from its lowered position, and in a more particular embodiment the rear portion is raised about 5 inches from its lowered position and generally aligned above the lower portion 28 of the pedestal 14. Additionally, the rear portion 36 tilts forward with respect to its lowered position. In one embodiment, the rear portion of the seat experiences about an 8.5 degree change in its tilt angle when it is moved from the lowered to the elevated position. In one embodiment, the rear portion 36 is tilted about 5 degrees forward with respect to horizontal when the seat assembly is in the elevated position, such that the rear portion 36 experiences about an 8.5 degree change in tilt angle from the lowered position in which it is slightly rearwardly tilted at about 3.5 degrees to the elevated position in which it is tilted about 5 degrees forward.

(20) The movement of the front portion 34 is different from that of the rear portion 36 when moving to the elevated position in a manner that is predetermined to promote a neutral posture. In one embodiment, when the seat assembly 16 is moved to the elevated position, the motion of the front portion 34 is such that it generally pivots about an axis 48 extending laterally through the front edge 44 of the front portion 34. A rear edge 50 of the front portion is raised from its lowered position. As such, in the elevated position, the front portion 34 is angled downwardly from the rear portion 36. In one embodiment, this angle between front 34 and rear 36 portions is set at about 40 degrees such that the front portion 34 drops off from the rear portion 36 to relieve stress on the user's thigh and promote an ergonomic posture by enabling opening of the user's thigh-torso angle.

(21) Referring now to FIGS. 11-12, the seat assembly 16 is shown with the cushioned upholstery removed, exposing a seat pan 52. In the illustrated embodiment, the seat pan 52 is designed for use with the chair 10 in both the lowered and the elevated positions. The seat pan 52 includes a front portion 54 associated with the front portion 34 of the seat assembly and a rear portion 56 associated with the rear portion 36 of the seat assembly 16. The front portion 54 is configured to pivot or flex with respect to the rear portion 56 to enable the front portion 34 of the seat assembly 16 to pivot with respect to the rear portion 36 as noted above. In one embodiment, the front portion 54 and rear portion 56 of the seat pan pivot about a lateral axis 58 between the front 54 and rear 56 portions (and likewise the front 34 and rear 36 portions of the seat assembly 16 pivot about the lateral axis 58, which is generally aligned with pivot point 92. The location of the lateral pivot axis 58 may be selected to promote flexing of the seat assembly 16 at a desired location, such as a desired distance between the user's thighs and ischial tuberosities. In one embodiment, the lateral axis 58 is positioned about six inches forward of the pocket 60 such that the lateral pivot axis 58 is positioned about 6 inches forward of the user's ischial tuberosities, creating a comfortable experience for the majority of users.

(22) As shown in FIGS. 11 and 12, at least a portion of the rear portion 56 of the seat pan may be concave, forming a recess or “pocket” 60 for receiving the ischial tuberosities of the user. In one embodiment, the pocket 60 may be provided with a series of slots 62 extending through the seat pan 52 to provide the seat pan 52 with increased flexibility in the area of the pocket 60. In another embodiment, also shown in FIGS. 11 and 12, the seat pan 52 includes a series of slots 53 in the front portion 54 of the seat pan 52 which increase flexibility of the seat pan in the locations of the slots and thus act to relieve stress on the rear of the user's thighs. The size and locations of these slots 53 may be predetermined to relieve stress in desired locations. In the illustrated embodiment, the slots 53 include a central group 55, a left side group 57 and a right side group 59.

(23) Although various methods may be used for creating the pivot or flexing of the seat pan 52, the illustrated embodiment shows one such method that enables flexing while reducing stress on the user. As shown in FIGS. 11 and 12, in this embodiment, the front 54 and rear 56 portions of the seat pan 52 cooperate to form a bridge 64 therebetween. In particular, the rear edge 66 of the front portion 54 includes a series of spaced apart flexible fingers 68 extending outwardly therefrom. Similarly, the forward edge 70 of the rear portion 56 includes a separate series of spaced apart flexible fingers 72. The fingers 68, 72 interlock with each other, with the fingers 68 extending into the gaps between the fingers 72 and underneath the forward edge 70 of the rear portion, and with the fingers 72 extending into the gaps between the fingers 68 and underneath the rear edge 66 of the front portion 54. As shown in FIG. 12, each of the fingers 68, 72 flexes and slides with respect to the opposite adjacent finger 68, 72 as the seat assembly 16 is moved to the elevated position, providing the bridge 64 with a smoothly rounded surface at the location of the lateral axis 58. In one embodiment, the bridge 64 includes hinges 74 at the lateral edges 76, 78 of the seat pan 52 interconnecting the front 54 and rear 56 portions of the seat pan 52. The characteristics of the bridge, such as the amount of curvature of the bridge 64 and the degree of flexibility of the bridge 64 can be controlled by varying the characteristics of the fingers 68, 72.

(24) The chair 10 includes a mechanism for connecting the pedestal 14 (or, in another embodiment, the base 12) to the seat assembly 16 in order to enable the movement of the seat assembly 16 between the lowered position and the elevated ergonomic position. In the illustrated embodiment, this mechanism is a linkage mechanism 20 connected between the pedestal 14 and the seat assembly 16. As shown, the linkage mechanism 20 includes a pair of first link arms 80, a pair of second link arms 82 and an assist device 83. The first 80 and second 82 pairs of link arms collectively form a four-bar linkage. The first pair of link arms 80 extend from a central portion of the upper pedestal 30 to the rear edge 42 of the rear portion 36 of the seat assembly 16. The forward ends 84 of the link arms 80 pivot with respect to the pedestal 14 and the rear ends 86 of the link arms 80 pivot with respect to the seat assembly 16. The second pair of link arms 82 extend between the forward edge 33 of the upper pedestal 30 and the front edge 44 of the front portion 34. The second link arms 82 each include a forward end 90 pivotally connected to the pedestal 14 (and aligned with the pivot axis 48) and a rear end 92 pivotally connected to the seat assembly 16. In the illustrated embodiment, these second link arms 82 are integrated with the lateral sides 76, 78 of the seat pan 52, but they may alternatively be separate from the seat assembly 16. In one embodiment, the second link arms 82 are shorter than the first link arms 80. The arms 80, 82 can collectively be pivoted between a first position, in which they are generally horizontal, to a second position, in which they are angled upwardly. During pivoting of the link arms, the rear ends 86, 92 of the link arms move in a continuous arcuate motion that drives the seat assembly 16 from the lower position to the elevated ergonomic position. The lengths and locations of the link arms 80, 82 are thus predetermined to provide the seat assembly with the desired positioning for both positions. For reference, FIGS. 3 and 4 symbolically illustrate (with crosshairs) the locations of the front end 90 of the link arm 82, the rear end 92 of the link arm 82, the front end 84 of the link arm 80 and the rear end 86 of the link arm 80. These four crosshair locations form the pivot points for the four bar linkage 20. Once embodiment of the relative movement of the pivot points 86 and 92 between the two chair posture positions can thus be seen in FIGS. 3 and 4.

(25) The assist device 83 is mounted between a portion of the chair 10 and the seat assembly 16 and can be actuated to assist movement of the link arms 80, 82 and the seat assembly 16 to the elevated ergonomic position. In one embodiment, the assist device 83 is a gas assist cylinder 94 that is mounted between the upper pedestal 30 and the front portion 34 of the seat assembly 16. The cylinder 94 includes a piston 95 that can be actuated to extend and drive the seat assembly 16 to the elevated position. An activation lever 96 is connected to the cylinder 94, and can be pulled by the user to actuate the piston 95. In one embodiment, the assist device 83 is provided with sufficient force to move an unoccupied chair 10 from the lowered position to the elevated position, but insufficient to move an occupied chair 10. As a result, a user must change from a static posture to a dynamic posture when activating the chair 10 to move it to the elevated position. In an alternative embodiment, the assist device 83 may be a hydraulic cylinder, electric drive, or another mechanism for assisting movement of the seat assembly 16.

(26) Referring now to FIG. 13, the backrest 18 extends upwardly from the seat assembly 16. As shown, the backrest 18 is connected to the rear edge 42 of the rear portion 36 of the seat assembly 16. As a result, the backrest 18 moves with the rear portion 36 as the rear portion is moved between the lowered position and the elevated ergonomic position. In one embodiment, the backrest 18 includes a recline mechanism and is capable of reclining as shown in FIG. 13 from an upright position shown in broken lines to a reclined position shown in solid lines. The recline mechanism may be operable by the user in both the lowered position of the seat assembly and in the elevated position.

(27) FIGS. 3 and 4 show a schematic version of an occupant 99 sitting in the chair 10 in order to illustrate the posture of the user, and the change in posture of the user, between the lowered position of the chair 10 shown in FIG. 3 and the elevated ergonomic position of the chair 10 shown in FIG. 4. The position of the seat assembly 16 in the elevated ergonomic position is predetermined to position the occupant or user 99 in a neutral posture. In particular, the forward tilt of the upper surface 40 of the rear portion 36, and the angle between the upper surfaces 38, 40 of the front 34 and rear 36 portions of the seat assembly 16 are predetermined to promote a neutral posture. The relative angles and positions of the front 34 and rear 36 portions promote a neutral posture for the occupant 99. FIGS. 3 and 4 show a body centered vertical reference line 98 taken along the lateral midline of the torso using the center of the shoulder joint as reference. A midline of the thigh 100 is also shown, which is aligned with the lateral midline of the femur, using the center of the knee joint as reference. The angle 102 between these two lines is a thigh-torso angle, and as noted above is an important measure of neutral posture. As shown in FIG. 3, in the lowered position of the chair 10 (the general position of a standard task chair), the thigh-torso angle 102 is approximately between 90-100 degrees. As shown in FIG. 4, when the chair 10 has been moved to the elevated ergonomic position, the thigh-torso angle 102 is increased to about 128 degrees, within the accepted range for a neutral posture and thus providing the associated advantages for the user. This is generally attributed to the combination of the forward tilt of the upper surface 40 of the rear portion 36, and the downward angle of the front seat assembly portion 34 with respect to the rear portion 36. The forward tilt of the rear portion 36 acts to rotate the pelvis forward to keep the user's posterior superior iliac spine (PSIS) higher than the user's anterior superior iliac spine (ASIS). The downward angle of the front seat assembly portion 34, acts to relieve stress on the user's thigh and enables opening up of the thigh-torso angle 102. Importantly, the elevated ergonomic position promotes a neutral posture without pulling the user away from the worksurface. In addition, the upper surface 40 of the rear seat assembly 36—and the ischial pocket 60—support the primary weight of the user even with the chair 10 in the elevated position, reducing stress and fatigue caused by standing. Finally, in the elevated ergonomic position, the rear portion 36 of the seat assembly 16 is generally aligned above the lower portion 28 of the pedestal, aligning the user's center of gravity above the center of the base to keep the chair stable in the elevated position.

(28) Operation of the chair 10 according to one embodiment includes one or more of the steps of: (a) rolling the chair 10 to a desired position using the casters 26 (in an office environment, the desired position will generally be adjacent a worksurface); (b) sitting in the chair 10 with the chair in the lowered position, wherein the upper surfaces 38, 40 of the front 34 and rear 36 portions of the seat assembly 16 are generally aligned to form a planar seating surface; (c) adjusting the height of the seat assembly 16 to a desired position by pulling the lever 27 to actuate the height adjustment mechanism; and (d) moving the seat assembly 16 from the lowered position to the elevated ergonomic position by pulling the activation lever 96 to activate the assist cylinder 94 while the user stands slightly to enable the chair to move to the elevated ergonomic position, thereby changing the user from a static posture to a dynamic posture. When in the elevated ergonomic position, the user may release the lever 96 to lock the seat assembly 16 in the elevated position such that the user may sit on the upper surface 40 of the rear portion 36 of the seat assembly 16. In one embodiment, the seat assembly 16 locks in only the lowered position and the predetermined elevated ergonomic position in order to promote the neutral posture of the elevated ergonomic position and prevent the user from positioning the chair in a less ergonomic position. However, in an alternative embodiment the chair 10 may be configured such that the user may release the level to also lock the chair 10 in any position between the lowered position and the elevated position.

(29) The above description is that of current embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. This disclosure is presented for illustrative purposes and should not be interpreted as an exhaustive description of all embodiments of the invention or to limit the scope of the claims to the specific elements illustrated or described in connection with these embodiments. For example, and without limitation, any individual element(s) of the described invention may be replaced by alternative elements that provide substantially similar functionality or otherwise provide adequate operation. This includes, for example, presently known alternative elements, such as those that might be currently known to one skilled in the art, and alternative elements that may be developed in the future, such as those that one skilled in the art might, upon development, recognize as an alternative. Further, the disclosed embodiments include a plurality of features that are described in concert and that might cooperatively provide a collection of benefits. The present invention is not limited to only those embodiments that include all of these features or that provide all of the stated benefits, except to the extent otherwise expressly set forth in the issued claims. Features of various embodiments may be used in combination with features from other embodiments. Directional terms, such as “vertical,” “horizontal,” “top,” “bottom,” “front,” “rear,” “upper,” “lower,” “inner,” “inwardly,” “outer,” “outwardly,” “forward,” and “rearward” are used to assist in describing the invention based on the orientation of the embodiments shown in the illustrations. The use of directional terms should not be interpreted to limit the invention to any specific orientation(s). Any reference to claim elements in the singular, for example, using the articles “a,” “an,” “the” or “said,” is not to be construed as limiting the element to the singular.