Chair with conforming seat

[0002] This application claims the benefit under Title 35, U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 60/340,570, entitled CHAIR WITH CONFORMING SEAT, filed on Dec. 14, 2001.

[0003] 1. Field of the Invention

[0004] The present invention relates to chairs, and in particular, to a task chair for supporting a seated user thereon in an ergonomic manner.

[0005] 2. Description of the Related Art

[0006] Task chairs are commonly used by persons while working in a seated position in an office or other occupational environment. Typically, such chairs include a caster wheel assembly for rolling movement over a floor surface, as well as a number of manual adjustment features to allow the user to adjust the shape or movement characteristics of the chair to a desired configuration.

[0007] Many task chairs include a rigid seat pan and a rigid backrest pan, the seat pan and backrest pan including a layer of foam padding thereon which is covered by a decorative upholstery material. Although the foam padding provides some cushioning support for a seated user, the rigid and noncompliant seat pan and backrest pan may become uncomfortable to the user, especially if the user is seated at the chair for an extended period of time. In this connection, if the layer of foam padding is too thin, the user's ischium or tail bone may abut the rigid seat pan to cause discomfort, and, if the layer of foam padding is too thick, the seat may not provide a firm overall support for the user.

[0008] Other known task chairs include seats having a relatively rigid outer frame supporting a mesh or webbing material thereacross which is flexible to conform to the seated user. However, such mesh or web material may catch, wear, or snag a user's clothing when the user shifts positions in the chair or stands up from the chair. Also, such mesh or webbing material is somewhat frictionless, such that when a user uses the forward tilt mechanism of the chair, the user experiences the sensation of falling forwardly or sliding out of the chair. Similarly, when the user moves to a reclined posture in such chairs, the user tends to slide forwardly out of the chair, and the lumbar region of the user's back disengages from the lower portion of the backrest.

[0009] What is needed is a task chair which conformingly and comfortably supports a seated user, and which is an improvement over the foregoing.

[0010] The present invention provides a task chair including a seat support structure, and a seat supported by the seat support structure having a seating surface which may ergonomically conform to a seated user. The seating surface includes rigid and flexible portions connected to one another, the flexible portions allowing resilient flexing of the seating surface to create conformance zones which dynamically support a seated user in an ergonomic manner.

[0011] The rigid portions of the seat may be formed of wood, metal, or a rigid plastic, for example, and the flexible portions may be formed of a pliable urethane or a silicone material, for example. The rigid and flexible portions may be connected to one another by insert molding the flexible portions to the rigid portions, or by mechanically or adhesively joining the flexible portions to the rigid portions. The particular shape, size, and relative configurations of the rigid portions and the flexible portions may be selectively varied to provide seating surfaces having desired conformance and support characteristics for the seated user.

[0012] The seat support structure may include a seat flex lockout mechanism movable between a first position and a second position, wherein flexing of the seating surface is prevented in the first position and is allowed in the second position. Additionally, the seat support structure may include a mechanism which allows the seat to be moved between high, middle, and low positions.

[0013] Advantageously, the present task chair includes a seating surface having rigid portions which provide a relatively firm support to a seated user, and flexible portions which facilitate movement of the flexible and rigid portions of the seating surface, and which provide support to the seated user in selected zones of the seating surface. Additionally, the flexible portions permit the seating surface to resiliently flex from a relatively planar shape to a saddle or saddle-like shape which conforms to the seated user. Further, the saddle-like shape supports the seated user, preventing the user from experiencing the sensation of falling or sliding out of the chair.

[0014] In one form thereof, the present invention provides a chair, including seat support structure; and a seat supported by the seat support structure, the seat including a flexible portion and at least one rigid portion, the seat resiliently movable between a first position in which the seat has a substantially flattened shape, and a second position in which opposite sides of a front portion of the seat are flexed downwardly about a central portion of the seat to form a saddle-like shape.

[0015] In another form thereof, the present invention provides a chair, including seat support structure; and a seat supported by the seat support structure, the seat formed of a flexible material having at least one rigid member embedded therein, the seat resiliently movable between an unflexed position and a flexed position in which opposite sides of a front portion of the seat are flexed downwardly about a central portion of the seat to provide a saddle-like shape.

[0016] In a further form thereof, the present invention provides a chair, including seat support structure including a rigid support member; and a seat supported by the seat support structure, the seat including a flexible portion disposed centrally within the seat, the flexible portion supported by the rigid support member; a rigid portion disposed along each side portion of the seat opposite the flexible portion, the seat resiliently movable between an unflexed position and a flexed position in which the side portions of the seat flex downwardly about opposite sides of the flexible portion to form a saddle-like shape.

[0017] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

[0018] FIG. 1 is a side elevational view of a task chair in accordance with the present invention;

[0019] FIG. 2 is an additional side elevational view of the task chair of FIG. 1, schematically showing a user seated therein;

[0020] FIG. 3 is a rear elevational view of the task chair of FIG. 1;

[0021] FIG. 4 is a perspective view of one embodiment of a seat for the task chair of FIG. 1, showing the rigid and flexible portions of the seating surface, and further showing the flexing of the seating surface between a first position shown in solid lies and a second position shown in dashed lines;

[0022] FIG. 5 is a side perspective view of a first embodiment of a seat support structure, showing the seat support structure in a high or upright position with the seat in a non-flexed shape;

[0023] FIG. 6 is side perspective view of the seat support structure of FIG. 5, showing the seat support structure in a high or upright position with the seat flexed in a saddle-like shape;

[0024] FIG. 7 is side perspective view of the seat support structure of FIGS. 5 and 6, showing the seat support structure in a low or reclined position, with the seat flexed in a saddle-like shape;

[0025] FIG. 8 is side perspective view of the seat support structure of FIG. 5, further showing a flex lockout mechanism disposed in a disengaged position, such that flexing of the seat allowed;

[0026] FIG. 9 is side perspective view of the seat support structure of FIG. 8, showing the flex lockout mechanism disposed in an engaged position, such that flexing of the seat is prevented;

[0027] FIG. 10 is a side perspective view of a second embodiment of a seat support structure, showing the seat support structure in a high or raised position with the seat flexed into a saddle-like shape;

[0028] FIG. 11 is a side perspective view of the seat support structure of FIG. 10, showing the seat support structure in a middle position with the seat in a non-flexed shape;

[0029] FIG. 12 is a side perspective view of the seat support structure of FIGS. 10 and 11, showing the seat support structure in a low or reclined position with the seat flexed into a saddle-like shape;

[0030] FIG. 13 is a side perspective view of the seat support structure of FIGS. 10-12, showing each of the individual positions of FIGS. 10-12 with respect to one another;

[0031] FIG. 14 is a partial perspective view of a second embodiment of a seat, showing the rigid and flexible portions of the seating surface, and further showing the flexing of the seating surface between a first position shown in solid lies and a second position shown in dashed lines;

[0032] FIG. 15 is a is a partial perspective view of a third embodiment of a seat, showing the rigid and flexible portions of the seating surface, and further showing the flexing of the seating surface between a first position shown in solid lies and a second position shown in dashed lines;

[0033] FIG. 16 is a is a partial perspective view of a fourth embodiment of a seat, showing the rigid and flexible portions of the seating surface, and further showing the flexing of the seating surface between a first position shown in solid lies and a second position shown in dashed lines;

[0034] FIG. 17A is a is a partial perspective view of a fifth embodiment of a seat, showing the rigid and flexible portions of the seating surface, and further showing the flexing of the seating surface between a first position shown in solid lies and a second position shown in dashed lines; and

[0035] FIG. 17B is a front elevational view of the seat of FIG. 17A, showing the seating surface in a saddle-like shape.

[0036] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

[0037] Task chair 20 is shown in FIGS. 1-3, and generally includes seat portion 22, backrest portion 24, and seat support structure 26. Seat support structure 26 includes caster wheel assembly 32 having a plurality of arms 34 projecting radially outwardly of central hub 36, the terminal ends of arms 34 having caster wheels 38 pivotally mounted thereon. Supported within central hub 36 of caster wheel assembly 32 is a height-adjustable pneumatic cylinder 40. Cylinder 40 includes piston 42 slidably disposed therein, an upper end of which is attached to chair support beam 44 by a press fit or in another suitable manner.

[0038] A plurality of links 46 (only two of which are shown in FIGS. 1 and 2 for clarity) each include first ends 48 pivotally attached to chair support beam 44 and second ends 50 pivotally attached to seat support member 52. Referring to FIG. 3, seat support member 52 is connected to U-shaped arm support 54 having upper ends 56 to which a pair of adjustable or fixed armrests 58 are connected. Armrests 58 may include moveable armrest pads 60, which may be adjusted as desired by a user. Also attached to upper ends 56 of U-shaped arm support 54 are a pair of L-shaped brackets 62 including lower ends 64 supporting chair seat 70, and upper ends 66 pivotally attached to U-shaped arm support 54. Backrest frame 68 extends between and is moveably mounted to upper ends 66 of the two L-shaped brackets 62 and arm support 54. Backrest frame 68 is connected to and supports backrest 72 in a manner such as that described in U.S. Provisional Patent Application Serial No. 60/340,673, entitled CHAIR WITH LUMBAR SUPPORT AND CONFORMING BACK, filed Dec. 14, 2001, assigned to the assignee of the present invention, the disclosure of which is incorporated herein by reference. Backrest 72 may further include one or more features such as those described in the above-incorporated U.S. Provisional Patent Application Serial No. 60/340,673.

[0039] Referring to FIG. 4, a first embodiment of seat 70 is shown. Seat 70aincludes seating surface 76adefined by a rigid portion and a flexible portion, which are designated as 80aand 90a, respectively, in the embodiment of FIG. 4. Rigid portion 80ais generally U-shaped, with base section 82aand a pair of arm sections 84aextending therefrom toward the front of seat 70a. Flexible portion 90ais disposed around the periphery of rigid portion 80aand between arm sections 84athereof. Control knobs 88 may be integrated into the profile of seat 70afor adjusting various adjustment features of chair 20.

[0040] The rigid portion of seat 70 may be made from any suitable substantially rigid material, such as wood, metal, or a stiff plastic material, for example. Suitable wood materials for the rigid portion include, for example, a 9-ply, gumwood, upholstery grade plywood or a rotary cut maple veneer shell.

[0041] The flexible portion of seat 70 may be made from an elastomeric material, such as a urethane or a silicone material, for example. Such material may have one or more of a shore hardness ranging from 37±7A to 82±7A, a tensile strength ranging from 505 PSI to 2200 PSI as determined by ASTM D-412, and an elongation of 320% to 340% as determined by ASTM D-368. Suitable urethane materials for the flexible portion include Vantico brand polyurethanes, available from Ciba Specialty Chemicals, such as RP6400-1, RP6401-1, RP 6402-1, and RP 6410-1 polyurethanes. The thickness of the flexible portion may be uniform throughout the seat, or alternatively, the thickness of the flexible portion may be varied as desired. The flexibility of the flexible portion generally decreases with increasing material thickness. Conversely, the flexibility of the flexible portion generally increases with decreasing material thickness.

[0042] In each of the embodiments of the seats disclosed herein, the flexible portion of the seat is resiliently flexible, such that the flexible portion may flex or bend to change shape in response to a force or load exerted thereon, followed by return of the flexible portion to its original shape or position when the force or load is removed. The material of the flexible portion may also exhibit elasticity, wherein the material may stretch as necessary responsive to forces exerted thereon, followed by return to its original shape and position. Further, the flexible portion may optionally include a series of perforations, a series of ridges and valleys, scoring, or other features therein which facilitate flexing movement in designated areas of the flexible portion.

[0043] The flexible portion of seat 70 is attached to one or more rigid portions thereof by insert molding, wherein the rigid portion is placed in a mold, and the flexible portion is molded therearound such that, upon curing, the flexible portion surrounds the periphery of the rigid portion and is securely adhered to the rigid portion. For example, if the rigid portion is made of wood or another porous or semi-porous material having roughened surfaces, the flexible portion may penetrate within the interstices of the rigid portion and, upon curing, form a tight bond with same.

[0044] Another molding process which may be used to form seat 70 is performed according to a two-step molding procedure, sometimes referred to in the art as a “two-shot” molding process. First, the rigid portions are formed from a first plastic material which is substantially rigid upon curing. The first material is injected into one or more molds which correspond to the shape of the rigid portions of the seat. Then, before the material of the rigid portions is fully cured, the flexible material is injected around the rigid portions into a mold which corresponds to the shape of the seat. The flexible material forms a chemical bond with the partially cured rigid material to provide a very strong connection between the rigid and flexible portions of the seat. After the flexible and rigid materials cure, the mold is removed to provide the seat.

[0045] The rigid portion is at least partially embedded within the flexible portion such that the flexible portion surrounds the outer periphery of the rigid portion. The top and bottom surfaces of the rigid portion may be exposed, or alternatively, the rigid portion may be completely embedded or encapsulated within the flexible portion such that the flexible portion encompasses all sides of the rigid portion.

[0046] Further, as shown in FIG. 4, the rigid portion 80amay include cavities (not shown) which communicate with holes 78 therein into which flexible portion 90afills during molding to further anchor flexible portion 90ato rigid portion 80a. Alternatively, the flexible portion may be pre-molded, wherein after curing thereof, the flexible portion is mechanically joined to the rigid portion by a suitable adhesive or by suitable fasteners, for example.

[0047] Seating surface 76ais shown in FIG. 4 in a first position in solid lines. In this first position, seating surface 76ais generally flattened or planar in overall shape, but may have some inherent contour therein based upon the shapes of rigid portion 80aand/or flexible portion 90a. For example, seating surface 76amay be slightly curved upwardly at the opposite side edges thereof, the front edge of seating surface 76amay be slightly curved downwardly, or the rear edge of seating surface 76amay be slightly curved upwardly.

[0048] Seating surface 76ais shown in FIG. 4 in a second position in solid lines, in which seating surface 76ais flexed or elastically moved into a saddle or saddle-like shape. In this position, the central area of seating surface 76a, toward the front of seat 70, is supported by seat support member 52. Additionally, the rear side portions of seating surface 76aare supported in a suitable manner, such as by L-shaped seat support brackets 62 (FIG. 3). Therefore, seating surface 76ais more firmly supported in the forward central portion of the seat and on the sides in the rear of the seat to provide a relatively firm support for the buttocks of a seated user. However, the front side portions 91aof seating surface 76a, when same are not supported by seat support structure 26, may flex downwardly about each side of seat support member 52 under the weight of the thighs of a seated user, such that the central front portion of seating surface 76a, which is supported by seat support member 52, forms a protuberance 93awhich is disposed between front side portions 91aof seating surface 76a. Flexible portion 90amay stretch as necessary in the area of seat support member 52 to accommodate downward movement of front side portions 91a.

[0049] When a seated user leans rearwardly in the chair, the weight of the user is distributed to a greater extent through the user's buttocks to the rear portion of seating surface 76athan through the user's thighs to the front portion of seating surface 76a, and therefore, front side portions 91aflex downwardly about seat support member 52 to a limited extent, or not at all. However, when the user leans forwardly in the chair, the weight of the user is distributed to a greater extent through the user's thighs to the front portion of seating surface 76athan through the user's buttocks to the rear portion of seating surface 76a, and therefore, front side portions 91amay flex further downwardly about seat support member 52.

[0050] The saddle-like shape of seating surface 76aprovides a flexible, conforming, ergonomic support for the seated user. The protuberance 93aformed in the front, central portion of seating surface 76aby the flexing of front side portions 91adownwardly about seat support member 52 is disposed between the thighs of the seated user, and prevents the seated user from experiencing the sensation of failing or sliding forwardly out of the chair. In addition, seating surface 76asupports the seated user when the chair is disposed in either an upright or reclined position, as described further below. Notably, seating surfaces 76b(FIG. 14), 76c(FIG. 15), 76d(FIG. 16), and 76e(FIGS. 17A and 17B) are also resiliently moveable into a saddle-like shape to support a seated user as described above with respect to seating surface 76a.

[0051] A first embodiment of seat support structure 26 is shown in FIGS. 5-7. Seat support structure 26aincludes lower housing 100, which is mounted to the upper end of piston 42 of pneumatic cylinder 40 (FIGS. 1-3). Upper housing 102 is pivotally attached to lower housing 100 at central pivot 104. Rear end 108 of seat support member 52 and the rigid portion of seat 70 are each pivotally attached to upper housing 102 at rear pivot 106. Forward end 110 of seat support member 52 supports the flexible portion 90 of seat 70 thereon. Seat support member 52 further includes recess 112 in abutment with stop pin 114 secured to lower housing 100.

[0052] In FIG. 5, seat 70 is shown in a position in which seat 70 is either unoccupied by a user, or in which seat 70 is occupied by a user with the flexing of seat 70 prevented or “locked out” by a flex lockout mechanism, which is described below. In the position shown in FIG. 5, seat 70 is disposed in a relatively planar orientation in which seat 70 is not ergonomically flexed into a saddle-like shape.

[0053] Seat 70 is shown in a saddle-like shape in FIG. 6. In this position, the flex lockout mechanism is disengaged such that flexing of seat 70 from the substantially planar position shown in FIG. 5 to the saddle-shaped position is permitted. Specifically, when a user sits in seat 70, the user's thighs shift downwardly, causing the rigid portion of seat 70 to pivot about rear pivot 106 and the flexible portion 90 of seat 70 to flex downwardly about seat support member 52. The saddle-like shape of seat 70 supports the user in a conforming, ergonomic manner, preventing the user from experiencing the sensation of falling forwardly or sliding out of the chair, as described above.

[0054] In each of the positions shown in FIGS. 5 and 6, a spring (not shown) operably connected between lower housing 100 and upper housing 102 biases the rear portion of upper housing 102 upwardly from lower housing 100 about central pivot 104 such that stop catch 116 of upper housing 102 abuts upper edge 118 of lower housing 100. The respective abutments between stop catch 116 of upper housing 102 and upper edge 116 of lower housing 100, and between recess 112 of seat support member 52 and stop pin 114 of lower housing 100, prevent upper housing 102 and seat support member 52 from tilting forwardly from the position shown in FIGS. 5 and 6.

[0055] Seat support structure 26ais shown in a reclined or low position in FIG. 7, in which the weight of a user leaning backwardly in seat 70 overcomes the bias force of the spring between lower housing 100 and upper housing 102, and upper housing 102 pivots rearwardly and downwardly about central pivot 104 with respect to lower housing 100. As seat 70 is so reclined, stop catch 116 of upper housing 102 moves out of engagement with upper edge 118 of lower housing 100, and seat support member 52 slides with respect to lower housing 102 such that recess 112 of seat support member 52 moves out of abutment with stop pin 114 of lower housing 100.

[0056] Further, in the position shown in FIG. 7, the flex lockout mechanism is disengaged, such that flexing of seat 70 is allowed, helping to prevent slide-out of the seated user, as described above.

[0057] Also, support structure 26amay be reclined by the user from the position shown in FIG. 5 even when the flexing of seat 70 is prevented by engagement of the flex lockout mechanism. Specifically, during the operation of seat support structure 26aas shown in FIGS. 5-7, the flexing of seat 70 is either prevented or allowed by the flex lockout mechanism regardless of whether seat support structure 26ais in an upright or in a reclined position. Conversely, the reclining of seat support structure 26ais determined by the positioning of the weight of the user, and is not dependent upon whether seat 70 is in a substantially planar or in a flexed position. Thus, the flexing of seat 70 and the upright/reclined positioning of seat support structure 26aoperate independently of one another.

[0058] One suitable flex lockout mechanism 120 for seat support structure 26ais shown in FIGS. 8 and 9, and may include an actuation member such as adjustment knob 92 (FIG. 3), for example, attached to rod 94 for moving flex lockout mechanism 120 between the disengaged position shown in FIG. 8 and the engaged position shown in FIG. 9. Seat support cams 122 are attached to rod 94, and contact the undersides of a suitable portion of seat 70, such as arm sections 84aof the rigid portion 80aof seat 70a, for example. In the disengaged position shown in FIG. 8, seat support cams 122 are shifted away from the underside of seat 70, thereby permitting the flexible portion of seat 70 to flex about seat support member 52. The actuation member, such as adjustment knob 92, may be turned to rotate rod 94 and seat support cams 122 to the engaged position shown in FIG. 9, in which seat support cams 122 are disposed beneath and contact the underside of seat 70, preventing the flexible portion 90 of seat 70 from flexing about seat support member 52.

[0059] A second embodiment of seat support structure 26 is shown in FIGS. 10-13. Seat support structure 26bincludes chair support beam 44 mounted to the upper end of piston 42 (FIGS. 1-3) of pneumatic cylinder 40. A plurality of links 46a, 46b(only two of which are visible in FIGS. 10-13) each include first ends 48 pivotally attached to chair support beam 44 and second ends 50 pivotally attached to seat support member 52. Second end 50 of link 46ais attached to axle 123, which is slidably received within slot 124 of seat support member 52. Seat support member 52, links 46a, 46b, and chair support beam 44 together may form a four bar pivot structure, as described in further detail below.

[0060] Upper ends 56 of U-shaped arm support 54 and upper ends 66 of L-shaped brackets 62 (FIG. 3) are pivotally attached to one another at main pivot 128. Specifically, upper ends 66 of L-shaped brackets 62 are pivotally mounted to upper ends 56 of arm support 54 at main pivot 128, and arm support 54 extends transversely under seat 70, as shown in FIG. 3, and is rigidly connected to seat support member 52. Upper ends 66 of L-shaped brackets 62 are pivotally mounted at main pivot 128, and lower ends 64 of L-shaped brackets 62 support seat 70. Tension element 74, shown as a tension spring, for example, is attached between chair support beam 44 and chair support member 52. Alternatively, tension element 74 may be a tension band, as shown in FIGS. 1 and 2, which is made from a heavy, yet stretchable, rubber material.

[0061] Tension element 74 biases seat support structure 26bupwardly to the high position shown in FIG. 10 when a user is not seated within chair 20. When a user is seated in chair 20, tension element 74 begins to stretch, lowering seat support structure 26bto the middle position shown in FIG. 11, or to any intermediate position between the positions shown in FIGS. 10 and 12, depending upon the such factors as the weight of the user, the position of the user's center of gravity, the angle of the backrest, and the resistance to stretching of tension element 74.

[0062] FIG. 10 shows seat 70 in a saddle-like shape which is attained when the user releases the flex lockout mechanism of seat 70, such as that shown in FIGS. 8 and 9. Specifically, the weight of the user's legs shifts the user's thighs downwardly and causes seat 70 and upper ends 66 of L-shaped brackets 62 to pivot about main pivot 128 to a forward tilt position, and flexible portion of seat 70 to flex downwardly about seat support member 52.

[0063] When a position lock (not shown) is released, links 46a, 46band upper ends 66 of L-shaped brackets 62 pivot such that seat support member 52 is raised from the middle position shown in FIG. 11 to the position shown in FIG. 10. In FIG. 10, the flex lockout mechanism is disengaged, such that flexing of seat 70 from the substantially planar position shown in FIG. 11 to the saddle-shaped position is permitted. As described above, the saddle-like shape of seat 70 supports the user in a conforming, ergonomic manner, preventing the user from experiencing the sensation of falling forwardly or sliding out of the chair 20.

[0064] In FIG. 11, seat support structure 26bis shown in a middle position, in which seat 70 is occupied by a user with the flexing of seat 70 prevented or “locked out” by the flex lockout mechanism. Thus, in the position shown in FIG. 11, seat 70 is disposed in a relatively planar orientation in which seat 70 is not ergonomically flexed into a saddle-like shape.

[0065] Seat support structure 26bis shown in a low or reclined position in FIG. 12, in which the weight of a user leaning backwardly in seat 70 shifts the user's torso weight still further rearward to further overcome the bias force of tension element 74. U-shaped arm support 54 and seat support member 52 shift downwardly, and upper ends 66 of L-shaped brackets 62 pivot about main pivot 128. Additionally, as may be seen most clearly in FIG. 13, block 125 on the underside of seat support member 52 contacts link 46awhen seat support structure 26bis in a middle position. When seat support structure 26bis moved from the middle position to the low/reclined position, block 125 pushes against link 46a, causing slot 124 of seat support member 52 to slide relative to (or around) axle 123, permitting seat support member 52 to recline.

[0066] Further, in the low position shown in FIG. 12, the flex lockout mechanism is disengaged, such that flexing of seat 70 is allowed even when seat support structure 26bis in a low/reclined position, preventing the user from sliding forward in seat 70 and from disengaging his/her lumbar region from the backrest of chair 20.

[0067] The above-described high, middle, and low positions of seat support structure 26bare each shown in FIG. 13 in relation to one another, wherein tension element 74 has been omitted for clarity.

[0068] Also, seat support structure 26bmay be raised or lowered by the user from the position shown in FIG. 11 even when the flexing of seat 70 is prevented by engagement of the flex lockout mechanism. In this connection, during the operation of seat support structure 26bas shown in FIGS. 10-13, the flexing of seat 70 is either prevented or allowed by the flex lockout mechanism regardless of whether seat 70 is in a high (FIG. 10), middle (FIG. 11) or low (FIG. 12) position. Conversely, the high position and low position of seat support structure 26bis determined by the positioning of the weight of the user, and is not dependent upon whether seat 70 is in a substantially planar or in a flexed position. Thus, the flexing of seat 70 and the raising or lowering of seat support structure 26boperate independently of one another.

[0069] In each of the embodiments disclosed herein, at least a portion of the seat support member 52 of seat support structure 26 supports the front central region of seat 70. Seat support member 52, or a portion thereof, may be pivotally attached to the remainder of seat support structure 26 to enable seat support member 52 to remain in supporting contact with the underside of seat 70 throughout movement of seat support structure 26 between high and low positions.

[0070] As discussed below, and regardless of the type of seat support structure 26 which is employed in chair 20, the shapes and relative configurations of the rigid portions and the flexible portions of seat 70 may be varied substantially in order to selectively modify the nature of the support provided by the rigid portions and the flexible portions, as well as the dynamics of the flexing of the seating surface of seat 70. The embodiments of FIGS. 14-17B illustrate some possible shapes and relative configurations of the rigid portions and the flexible portions, although one of ordinary skill in the art may develop others based upon the teachings herein.

[0071] A first additional embodiment of seat 70 is shown in FIG. 14. Seat 70bincludes seating surface 76bformed by rigid portion 80band flexible portion 90b. Rigid portion 80bis generally U-shaped, and includes base section 82band arm sections 84bextending therefrom. Rigid portion 80balso includes a substantially oval-shaped cutout portion 96. Flexible portion 90bis disposed around the outer periphery of rigid portion 80b, between arm sections 84b, and within cutout portion 96. The area of flexible portion 90bwithin cutout portion 96 provides a relief area 98 which is disposed beneath the ischium of a seated user to provide flexible, cushioning support thereto. Seating surface 76bof 70bmay flex about seat support member 52 in a manner similar to that of seat 70abetween a generally planar shape (shown in solid lines) and a saddle-like shape (shown in dashed lines) in which front side portions 91bflex downwardly about seat support member 52 to form protuberance 93b. Flexible portion 90bmay stretch as necessary in the area of seat support member 52 to accommodate downward movement of front side portions 91b. When seating surface 76bis flexed to the saddle-like shape, arm sections 84bof rigid portion 80band flexible portion 90bprovide a flexible support for a seated user's thighs, while base section 82bof rigid portion 80bprovides a more rigid support.

[0072] In FIG. 15, another embodiment of seat 70 is shown. Chair seat 70cincludes seating surface 76cformed by rigid portion 80cand flexible portion 90c. Rigid portion 80cincludes base section 82cand a central, single forwardly projecting arm 84cabout which flexible portion 90cmay flex between a generally planar position (shown in solid lines) and a saddle-like-shaped position (shown in dashed lines) in which front side portions 91cflex downwardly about seat support member 52 to form protuberance 93c. Flexible portion 90cmay stretch as necessary in the area of seat support member 52 to accommodate downward movement of front side portions 91c. Thus, in the embodiment shown in FIG. 15, a flexible support is provided for the thighs of a seated user by flexible portion 90c, and a more rigid support is provided by rigid portion 80c.

[0073] A further embodiment of seat 70 shown in FIG. 16. Chair seat 70dincludes seating surface 76dformed by rigid portion 80dand flexible portion 90d. Rigid portion 80dis disposed in the rear portion of seat 70d, and flexible portion 90dis disposed in the front portion of seat 70dand around the periphery of rigid portion 80d. Flexible portion 90dmay flex about seat support member 52 between a generally planar position (shown in solid lines) and a saddle-like-shaped position (shown in dashed lines) in which front side portions 91dflex downwardly about seat support member 52 to form protuberance 93d. Flexible portion 90dmay stretch as necessary in the area of seat support member 52 to accommodate downward movement of front side portions 91d. Thus, in the embodiment shown in FIG. 16, a flexible support is provided for the thighs of a seated user by flexible portion 90d, and a more rigid support is provided by rigid portion 80d.

[0074] A further embodiment of seat 70 shown in FIGS. 17A and 17B. Chair seat 70eincludes seating surface 76eformed by rigid portions 80eand flexible portion 90e. Rigid portions 80eare disposed along the sides of seat 70d, and flexible portion 90eis disposed between rigid portions 80eand around the outer peripheries of rigid portions 80e. In a first position, shown in solid lines in FIG. 17A, seating surface 76ehas a generally flattened or planar overall shape, but may include some inherent contour therein, such as downward curvature at the front edge of seating surface 76e, for example.

[0075] Seating surface 76eis elastically movable to a second, saddle-shaped form, which is shown in dashed lines in FIG. 17A and is further shown in FIG. 17B. In this position, flexible portion 90eflexes about seat support member 52, with front side portions 91eof seating surface flexing downwardly under the weight of the thighs of a seated user. Flexible portion 90emay stretch as necessary in the area of seat support member 52 to accommodate downward movement of front side portions 91e. Front side portions 91ewill generally flex downwardly about seat support member 52 to a lesser extent (or not at all), when the seated user leans backwardly against backrest 72 and shifts more weight to the user's buttocks, which weight is transferred to the chair through the rear portion of seating surface 76ewhich is supported by L-shaped seat support brackets (FIG. 17B). Conversely, front side portions 91eof seat support surface 76ewill generally flex downwardly about seat support member 52 to a greater extent when the seated user leans forwardly away from backrest 72 and shifts more weight to the front portion of seating surface 76e, which weight is transferred to the chair through the user's thighs. In this position, the front portion of seat support member 52 supports flexible portion 90eof seating surface 76ebetween front side portions 91e, and forms a protuberance 93e(FIG. 17B) between front side portions 91eat the front of seat support surface 76e. This protuberance 93eis disposed between the thighs of a seated user and prevents the user from experiencing the sensation of sliding forwardly out of the chair.

[0076] Notably, in the embodiment of FIGS. 17A and 17B, as well as in each of the other embodiments disclosed herein, front side portions 91a-eof seat support surfaces 76a-emay flex downwardly about seat support member 52 under the weight of a user's thighs either concurrently, or independently of one another. For example, if a user leans forwardly and evenly upon a seat support surface 76a-e, transferring the user's weight to the seat support surface 76a-eevenly through each of the user's thighs, both of the front side portions 91a-eof the seat support surface 76a-ewill flex downwardly about seat support member 52 to the same extent. However, if a user leans forwardly and to one side upon the seat support surface 76a-e, transferring the user's weight to the seat support surface 76a-emore through one of the user's thighs than the other, one side portion 91a-ewill flex downwardly to a greater extent than the other side portion 91a-e. In this manner, side portions 91a-eof seat support surfaces 76a-emay flex downwardly about seat support member 52 together, independently of one another, or to mutually varying extents with respect to one another, depending upon the distribution of the user's weight on the seat support surface 76a-e.

[0077] Additionally, a further embodiment (not shown) of seat 70 may include a rigid portion shaped similarly to rigid portions 80a-eof seats 70a-eshown in FIGS. 4 and 14-17B, respectively, for example. The rigid portion is fully encapsulated in a flexible portion which is molded around the rigid portion to provide a desired seat shape, wherein such seat may exhibit flexing and conformance characteristics similar to seats 70a-eshown in FIGS. 4 and 14-7B.

[0078] While this invention has been described as having preferred designs, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.