Abstract:
A chair seat that is movable between an upright and a forward position includes a spring mechanism that biases the seat toward the upright position. The spring mechanism includes camming structures that utilize both compressional and torsional forces from the spring to bias the seat toward the upright position. The compression of the spring exerts a positive force that must be overcome before the seat can be moved out of its upright position. The chair seat is constructed from a number of discrete components that are secured together without the use of welding or separate fasteners, such as via snap-fits. The discrete components include positioning tabs, special shapes, and other features that prevent them from being improperly assembled. The components of the chair seat may all be constructed out of suitable durable plastics, such as polypropylene, polyethylene, polycarbonate, and glass filled thermoplastics.

Description:
[0001]    This application is a divisional of commonly assigned application Ser. No. 09/653,401 filed Sep. 1, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates generally to chair seats, and in particular to chair seats that are rotatable between a forward position in which a user can sit on the chair and an upright position in which the chair seat is positioned out of the way of a user walking by the chair.  
           [0003]    In general, chairs include the following four structures: (1) a seat upon which the user sits, (2) a chair back against which the user leans his or her back, (3) arm rests for supporting the user&#39;s arms, and (4) a support structure for supporting the three previously mentioned structures on the ground. In one particular type of chair, generally referred to as a theater-style chair, the seat is rotatable between a forward position and an upright position. In the forward position, the seat is generally horizontal and allows a person to sit on the seat. In the upright position, the seat is nearly vertical, which allows the space which the chair occupies to be decreased and thereby provide more room for the person to walk by the seat. Stadium style chairs are generally found in sports arenas, stadiums, theaters, and similar types of venues. The seats are generally arranged in continuous rows in which a person has to walk between the rows in order to arrive at their chosen chairs. The chair seats are constructed such that they remain in an upright position until a person sits on them. This allows sufficient room for people to walk between the rows in order to arrive at their seats. This generally allows the rows of seats to be positioned closer together than they otherwise would be able to while still comfortably accommodating the chair users.  
           [0004]    In order to provide a chair seat that returns to the upright position after a person has exited the chair, it has been necessary in the past to provide some sort of biasing mechanism to return the chair to this upright position. These biasing mechanisms have often involved springs which undergo torsion when a person sits on the chair seat. When the person exits the chair seat, the torsional force of the spring returns the chair to an upright position. Often times this spring would act against metallic components of the chair and thereby cause undesirable squeaking when the chair seat rotated. Furthermore, the upright position at which the seat came to rest was often determined by the precise angle at which the spring was no longer undergoing any torsional forces. This made it difficult to ensure that the upright position of a succession of chairs aligned in a row was the same. Without such uniformity, the aesthetic appearance of the chairs is diminished.  
           [0005]    Past chair seats have also suffered from other disadvantages. As one example, prior chair seats have often required the use of welding and other mechanical fasteners such as screws. The use of both welding and separate mechanical fasteners increases the time and labor necessary to manufacture a seat. Providing additional fasteners also increases the material costs for the chair seat. Another disadvantage of prior chair seats is their predominant use of metallic parts. For those metallic parts which are visible to a user it is often necessary to paint the exterior surfaces of the metal in order to provide an aesthetically satisfactory appearance. This painting step, of course, increases the overall cost for manufacturing the chair. Additionally, when metallic parts are used, they often come in contact with each other. This can lead to undesirable squeaking when the chair seat is rotated or otherwise moved due to the motion of the seat occupant. These and other disadvantages have led to the desire for an improved chair seat that substantially overcomes these problems.  
         SUMMARY OF THE INVENTION  
         [0006]    Accordingly, the present invention provides a chair seat whose manufacture requires no welding and no separate fasteners for securing the component parts together. The chair seat is also primarily made out of plastic, which eliminates the possibility of metal-metal squeaking, along with the necessity of painting any exterior surfaces. The chair seat of the present invention also overcomes prior difficulties associated with the spring mechanism and the uniform alignment of the chair seat in its upright position.  
           [0007]    A chair seat according to one embodiment of the present invention comprises a bucket and at least one bearing about which the bucket can rotate between a rest position and a forward position. The bearing includes at least one flexible tab that is flexible between a locking and an unlocking position. The chair seat further includes a spring assembly positioned in the bucket which biases the bucket toward the rest position. A bearing block is attached to the bucket and includes an aperture through which the bearing and the flexible tab is inserted. The flexible tab moves to an unlocking position while being inserted through the aperture and returns to the locking position after it has been inserted completely through the aperture. The flexible tab thereby secures the bearing block to the bearing.  
           [0008]    A chair seat according to another embodiment of the present invention includes a right and a left bracket which are adapted to be attached to at least one base. A right bearing is attached to the right bracket and a left bearing is attached to the left bracket. The right and left bearings are both made out of plastic. A plastic seat bucket is also provided which includes a right and left aperture for receiving the right and left bearings respectively. The plastic seat bucket is rotatable about the right and left bearings from an upright position to a forward position. The seat bucket further includes right and left seat stops which are integrally molded into the seat bucket. The right and left brackets each include bracket stops which are integrally molded onto the right and left brackets. The bracket stops contact the seat stops and stop the seat bucket when the seat bucket is rotated to a forward position. The chair seat further includes a spring mechanism which resists rotation of the seat bucket to the forward position such that the seat bucket will rotate out of the forward position when a user exits the chair.  
           [0009]    According to another embodiment of the present invention, a chair seat includes a bucket and a substrate positioned on top of the bucket. One of the bucket and the substrate contains at least one flexible tab and the other of the bucket and the substrate contains a recess dimensioned to receive the flexible tab. The flexible tab and recess secure the bucket and substrate together without the use of welding or separate fasteners. The chair seat further includes a spring mechanism that biases the bucket and substrate toward an upright position. The spring mechanism is attached to the bucket without the use of welding or any separate fasteners.  
           [0010]    According to yet another aspect of the present invention, a spring assembly for a chair seat that is rotatable between a seated position and an upright position is provided. The spring assembly includes a static cam which is attached to the chair seat and maintains the same position with respect to the chair seat when the chair seat is rotated from the upright position to the seated position. The spring assembly further includes a dynamic cam which is positioned adjacent the static cam. The dynamic cam rotates and moves linearly with respect to the chair seat when the chair seat is rotated from the upright position to the seated position. A spring is positioned adjacent the dynamic cam and is compressed by the dynamic cam when the chair seat is rotated from the upright position to the seated position. The spring also undergoes torsion when the chair seat is rotated from the upright position to the seated position. Both the compression and torsion forces experienced by the spring cause the spring to resist rotation of the chair seat to the seated position.  
           [0011]    According to yet another aspect of the invention, a method is provided for controlling the movement of a chair seat that is rotatable from a rest position to a forward position. The method comprises providing a spring, a cam member, and a stop on the cam member. The stop on the cam member corresponds to the rest position of the chair seat. The spring is positioned in the chair seat such that the spring undergoes substantially no torsion when the chair seat is in the rest position. The spring is compressed in the chair seat against the cam member when the spring is in the stop position such that the spring exerts a camming force on the chair seat to retain the chair seat in the rest position. 
       
    
    
       [0012]    The chair seat of the present invention reduces the costs of manufacturing chair seats significantly. The reduction in cost is the result of a number of factors. First, the manufacturing process does not involve any welding or use of separate fasteners. Second, the chair seat does not need to have any exterior surfaces painted. Third, the bulk of the chair seat is manufactured from durable, plastic materials which cost less than prior materials. Fourth, the number of components which go into the completed seat has been reduced. And fifth, the chair seat may include alignment features that prevent the component parts from being improperly assembled, thereby reducing assembly costs. In addition to the cost savings, the chair seat provides significant benefits, such as the elimination for the potential of squeaking noises in the chair. The materials of the chair are also highly wear resistant and durable. Further, the chair seats return to a uniform position after a user exits the seat. These and other benefits, results, and objects of the present invention will be apparent to one skilled in the art, in light of the following specification when read in conjunction with the accompanying drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is an exploded, perspective view of a chair that includes one embodiment of the chair seat of the present invention;  
         [0014]    [0014]FIG. 2 is a perspective view of a pair of chairs, one of which has a chair seat in a seated or forward position and another of which has a chair seat in an upright position;  
         [0015]    [0015]FIG. 3 is an exploded, perspective view of a bucket assembly and a spring substrate according to one embodiment of the present invention;  
         [0016]    [0016]FIG. 4 is an exploded, perspective view of a bucket assembly and an ergonomic substrate according to another embodiment of the present invention;  
         [0017]    [0017]FIG. 5 is a plan view of the ergonomic substrate of FIG. 4;  
         [0018]    [0018]FIG. 6 is a sectional view of the substrate of FIG. 5 taken along the line VI-VI;  
         [0019]    [0019]FIG. 7 is an elevational view of the ergonomic substrate;  
         [0020]    [0020]FIG. 8 is a plan view of the spring substrate of FIG. 3;  
         [0021]    [0021]FIG. 9 is a sectional view of the spring substrate of FIG. 8 taken along the line IX-IX;  
         [0022]    [0022]FIG. 10 is a sectional view taken along the line X-X of FIG. 8;  
         [0023]    [0023]FIG. 11 is an enlargement of the circled area in FIG. 10;  
         [0024]    [0024]FIG. 12 is a plan view of a bucket;  
         [0025]    [0025]FIG. 13 is an elevational view of the bucket of FIG. 12;  
         [0026]    [0026]FIG. 14 is a sectional view taken along the line XIV-XIV of FIG. 12;  
         [0027]    [0027]FIG. 15 is a sectional view taken along the line XV-XV of FIG. 12;  
         [0028]    [0028]FIG. 16 is a sectional view taken along the line XVI-XVI of FIG. 12;  
         [0029]    [0029]FIG. 17 is an exploded, plan view of the bucket assembly;  
         [0030]    [0030]FIG. 18 is an unexploded, sectional view taken along the lines XVIII-XVIII of FIG. 17;  
         [0031]    [0031]FIG. 19 is an enlarged view of the circled area of FIG. 18 labeled XIX;  
         [0032]    [0032]FIG. 20 is a perspective view of a right hand bracket;  
         [0033]    [0033]FIG. 21 is a side, elevational view of the bracket of FIG. 20;  
         [0034]    [0034]FIG. 22 is a front, elevational view of the bracket of FIG. 20;  
         [0035]    [0035]FIG. 23 is a fragmentary view of a recess on the underside of the bracket of FIG. 22;  
         [0036]    [0036]FIG. 24 is a sectional view taken along the line XXIV-XXIV of FIG. 23;  
         [0037]    [0037]FIG. 25 is a perspective view of a right hand bracket with a shaft attached;  
         [0038]    [0038]FIG. 26 is a front, elevational view of a left hand bracket;  
         [0039]    [0039]FIG. 27 is a perspective view of a left hand bracket and bearing;  
         [0040]    [0040]FIG. 28 is a plan view of the bracket and bearing of FIG. 27 illustrated separated from each other;  
         [0041]    [0041]FIG. 29 is a perspective view of the shaft;  
         [0042]    [0042]FIG. 30 is a side, elevational view of the shaft of FIG. 29;  
         [0043]    [0043]FIG. 31 is an end, elevational view of the shaft of FIG. 29;  
         [0044]    [0044]FIG. 32 is an end, elevational view of the shaft of FIG. 29, illustrating an end opposite that of FIG. 31;  
         [0045]    [0045]FIG. 33 is a sectional view taken along the line XXXIII-XXXIII of FIG. 32;  
         [0046]    [0046]FIG. 34 is a sectional view taken along the line XXXIV-XXXIV of FIG. 30;  
         [0047]    [0047]FIG. 35 is an elevational view of a first end of the bearing of FIG. 27;  
         [0048]    [0048]FIG. 36 is an elevational view of a second end of the bearing of FIG. 27;  
         [0049]    [0049]FIG. 37 is a side, elevational view of a bearing block;  
         [0050]    [0050]FIG. 38 is a front, elevational view of the bearing block of FIG. 37;  
         [0051]    [0051]FIG. 39 is a sectional view taken along the line XXXIX-XXXIX of FIG. 38;  
         [0052]    [0052]FIG. 40 is a plan view of the bearing block of FIG. 38;  
         [0053]    [0053]FIG. 41 is a bottom view of the bearing block of FIG. 38;  
         [0054]    [0054]FIG. 42 a  is an exploded, elevational view of the spring assembly;  
         [0055]    [0055]FIG. 42 b  is an enlarged plan view of the spring assembly of FIG. 42 a  shown assembled;  
         [0056]    [0056]FIG. 43 is a perspective view of a static cam;  
         [0057]    [0057]FIG. 44 is a side, elevational view of the static cam of FIG. 43;  
         [0058]    [0058]FIG. 45 is an elevational view of the back of the static cam;  
         [0059]    [0059]FIG. 46 is a sectional view taken along the line XLVI-XLVI of FIG. 44;  
         [0060]    [0060]FIG. 47 is a sectional view taken along the line XLVII-XLVII of FIG. 45;  
         [0061]    [0061]FIG. 48 is an enlargement of the circled area of FIG. 45 labeled XLVIII;  
         [0062]    [0062]FIG. 49 is a side, elevational view of a dynamic cam;  
         [0063]    [0063]FIG. 50 is a sectional view taken along the line L-L of FIG. 49;  
         [0064]    [0064]FIG. 51 is an elevational view of one end of the dynamic cam of FIG. 49;  
         [0065]    [0065]FIG. 52 is a sectional view taken along the line LII-LII of FIG. 51;  
         [0066]    [0066]FIG. 53 is an elevational view of a second embodiment of a dynamic cam;  
         [0067]    [0067]FIG. 54 is a perspective view of a spring sleeve;  
         [0068]    [0068]FIG. 55 is a plan view of the spring sleeve of FIG. 54;  
         [0069]    [0069]FIG. 56 is an end, elevational view of the spring sleeve;  
         [0070]    [0070]FIG. 57 is an elevational view of the spring;  
         [0071]    [0071]FIG. 58 is a perspective view of a foam cover;  
         [0072]    [0072]FIG. 59 is an end elevational view of a bracket cover; and  
         [0073]    [0073]FIG. 60 is a side, elevational view of a bracket cover. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0074]    The present invention will now be described with reference to the accompanying drawings wherein like reference numerals correspond to like elements in the several drawings. The general components of a theater-style chair are illustrated in FIG. I, and include a chair back  62 , a right and left base  64   a, b,  and a chair seat  66 . Chair seat  66  includes a pair of brackets  68  which support chair seat  66  on right and left bases  64   a  and  b.  Each base  64  includes a seat support  70  having a flat top surface in which an aperture is defined. The aperture receives a fastener, such as a screw or bolt, which is also inserted through a corresponding aperture in each of the seat brackets. Chair seat  66  is thereby secured to bases  64 .  
         [0075]    For purposes of illustration only, chair back  62  is depicted in FIG. 1 as being secured to bases  64  via a pair of wings  72 . Each wing  72  includes a plurality of fastener holes which are used to secure chair back  62  to bases  64  via fasteners inserted through these holes and into corresponding holes in bases  64 . The particular manner in which chair back  62  is secured to the bases forms no part of the present invention, and it will be understood that a variety of different techniques can be used to secure chair back  62  to the bases. It will further be understood that chair bases  64  are depicted in FIGS. 1 and 2 as illustrative examples only. Chair bases  64  can take on any of a variety of different forms, so long as support is provided to chair seat  66 .  
         [0076]    Chair seat  66  is rotatable between a forward position and an upright position. As generally illustrated in FIG. 2, the chair on the left of FIG. 2 has its chair seat  66  positioned in a forward position, which is the position the chair seat would be in when a person sits on the chair. The chair on the right in FIG. 2 is depicted with chair seat  66  in an upright position, which is the position the chair automatically assumes when no person is actually sitting on the chair. The forward position is generally horizontal, although it may be angled upward as much as 10° or more to provide the desired level of comfort to the chair user. The upright position may or may not be completely vertical. In some instances, the upright position is approximately 70°, while in other situations it may be desirable to have the upright position completely vertical, i.e., 90°. In many situations, the chair seat rotates upwardly to a rest position which is somewhere between the horizontal and vertical position, such as 70°. This rest position is the position the chair assumes when no forces are applied to the chair seat. The chair seat, however, can further rotate up to 90° when a person pushes on the underside of the chair seat. Thus, when a person walks by the chair, his or her leg may push against the chair seat and cause it to further rotate toward a truly vertical position. For those chair seats that have their rest position defined at 90°, they do not generally allow the chair seat to be further rotated when a person pushes on the under side of the chair seat. Chair seat  66  of the present invention includes a novel spring mechanism which automatically returns chair seat  66  to a desired, preset position after a user exits the chair. Chair seat  66  further includes a simplified design structure which allows it to be manufactured more efficiently than prior art chair seats. The details of the construction of chair seat  66  follow.  
         [0077]    Chair seat  66  is generally made up of a bucket assembly  74 , a substrate  76 , and upholstery  78  which is attached to a top side of substrate  76 . Bucket assembly  74  and substrate  76  are depicted in FIG. 3, while one example of upholstery  78  is depicted in FIG. 58. Substrate  76  depicted in FIG. 3 is adapted to receive a plurality of serpentine springs (not shown in FIG. 3) which flexibly support a person sitting on chair seat  66 . Spring substrate  76  is one of a plurality of types of substrates which may be attached to bucket assembly  74 . As depicted in FIG. 4, an ergonomic substrate  76  can be attached to bucket assembly  74 . Ergonomic substrate  76  includes a generally flat surface  80  to which foam or other cushioning may be applied. Ergonomic substrate  76  does not use any serpentine springs, and provides a different feel for the user than spring substrate  76 .  
         [0078]    Ergonomic Substrate  76   
         [0079]    Ergonomic substrate  76  is generally depicted in FIGS.  4 - 7 . Ergonomic substrate  76  includes a plurality of apertures  82  defined in main surface  80 . Apertures  82  in the illustrated embodiment are circular and there are five of them. Apertures  82  serve two purposes. First, certain types of foam require an air outlet when they are compressed, such as when a user sits on the foam. If such foam is attached to the top side of main surface  80 , apertures  82  provide air outlets when the foam is compressed by a user sitting on it. Second, apertures  82  allow foam to be attached directly to ergonomic substrate  76  during the molding process. During such a molding process, the foam travels from the top side of substrate  76 , through apertures  82 , and expands somewhat on the back surface of ergonomic substrate  76 . The foam thus mushrooms through apertures  82  and prevents removal of the foam from substrate  76 . Such a molding process, however, does not need to be used. The foam can be secured to main surface  80  of substrate  76  via adhesive, if desired. The advantage of molding the foam directly onto substrate  76  is the avoidance of the additional step of applying adhesive in attaching the foam.  
         [0080]    Ergonomic substrate  76  further includes four corner indentations  84  which are defined adjacent each of the four corners of substrate  76 . Corner indentations  84  accommodate overlapping fabric which is secured to substrate  76 . In other words, when fabric is attached to substrate  76 , it is drawn over the top, the bottom, and both of the sides of substrate  76 . At each of the corners, the fabric is twice as thick as elsewhere due to the overlap of fabric from adjacent sides of substrate  76 . In order to have the fabric to the underside of substrate  76  at a generally uniform level across the entire backside of substrate  76 , it is necessary to provide corner indentations  84  to accommodate the overlapping thickness at each corner. When fabric is secured the underside to ergonomic substrate  76 , it may be secured thereto via staples, or by another suitable fastening technique.  
         [0081]    Ergonomic substrate  76  further includes a pair of supports  86  which extend downward from the top side of substrate  76 . Supports  86  contact a bottom surface  88  of bucket  90  when substrate  76  is secured thereto. Supports  86  thereby help support ergonomic substrate  76  on bucket  90 . Ergonomic substrate  76  further includes a pair of rear fastening tabs  92  and forward fastening tabs  94 . Each of these fastening tabs are used to secure substrate  76  to bucket  90  without the use of any welding or separate fasteners. Fastening tabs  92  and  94  are generally flexible and fit into corresponding recesses defined in bucket  90 . Specifically, rear fastening tabs  92  fit into rear apertures  96  defined in a back wall  98  of bucket  90  (FIG. 12). Forward fastening tabs  94  fit into a single aperture  100  and a double aperture  102  defined in an internal rib  104  of bucket  90 . Double aperture  102  includes a center pane  106  which fits into a corresponding notch  108  defined in one of forward fastening tabs  94 . In the illustrative embodiment of FIGS. 5 and 7, notch  108  is defined in the lower one of the two forward fastening tabs  94 . The receipt of center pane  106  in notch  108  helps insure proper side to side alignment of substrate  76  with bucket  90 . Each of rear and forward fastening tabs  92  and  94  includes a shaft portion  110  and a hook portion  112  disposed at the lower end of shaft portion  110  (FIG. 6). As discussed more thoroughly herein, ergonomic substrate  76  is molded out of plastic and shaft portion  110  is slightly flexible. In addition, bucket  90  is molded out of plastic and back wall  98  and internal rib  104  are also slightly flexible. Because of this flexibility, substrate  76  can be pushed downward onto bucket  90 , which will cause fastening tabs  92  and  94  to flex against back wall  98  and internal rib  104  of bucket  90 , respectively. As substrate  76  is pushed further down on top of bucket  90 , rear fastening tab  92  and forward fastening tabs  94  eventually reach rear apertures  96 , along with single aperture  100  and double aperture  102 . When rear and forward fastening tabs  92  and  94  reach these apertures, they return to their unflexed position. Because the hook portions  112  fit through the corresponding apertures, they prevent substrate  76  from being removed from bucket  90 . Bucket  90  and substrate  76  are thereby secured together via a snap fit which does not require any separate fasteners or welding.  
         [0082]    Ergonomic substrate  76  further includes an alignment notch  114  defined on the underside of substrate  76 . Alignment notch  114  includes a V-shaped portion  116  and a rectangular portion  118  (FIG. 7). Alignment notch  114  is oriented generally in a direction extending from one side of substrate  76  to another. Rectangular portion  118  has a width generally the same as the width of a center wall  120  defined in the interior of bucket  90  (FIG. 4). Another alignment notch  122  is defined along the top of center wall  120 . Alignment notch  122  includes a V-shaped portion  124  and a rectangular portion  126 . Rectangular portion  126  has a width corresponding to the thickness of alignment notch  114  of substrate  76 . Alignment notch  122  is generally defined in a front to back direction along bucket  90 . Alignment notches  114  and  122  fit snugly together when substrate  76  is attached to bucket  90 . V-shaped portions  116  and  124  provide camming action which facilitates the alignment of substrate  76  with respect to bucket  90 . When substrate  76  and bucket  90  are secured together, center wall  120  is received into rectangular portion  118  and the wall defining alignment notch  114  is received into rectangular portion  126 . Because alignment notch  114  is oriented generally in a side to side direction, while alignment notch  122  is oriented in a front to back direction, the interaction of these two notches helps align substrate  76  with respect to bucket  90  in both forward to back and side to side directions.  
         [0083]    Spring Substrate  76   
         [0084]    Spring substrate  76  is an alternative substrate that can incorporated into chair seat  66  of the present invention. Spring substrate  76  is depicted in FIGS. 3 and 8- 11 . Spring substrate  76  includes a hump  128  generally defined around the perimeter of spring substrate  76 . A staple wall  130  is also defined around the perimeter of spring substrate  76  and is positioned inwardly from hump  128 . Staple wall  130  provides a generally flat surface into which staples can be inserted in order to secure fabric over the top of spring substrate  76 . Like ergonomic substrate  76 , spring substrate  76  includes four corner indentations  84  defined in staple wall  130 . Corner indentations  132  provide recessed areas for accommodating overlapping fabric at the corners of spring substrate  76  (FIG. 8). A plurality of spring supports  134  are defined in hump  128  along opposite sides of spring substrate  76 . Spring supports  134  secure springs, such as serpentine spring  136 , to spring substrate  76 . In the embodiment illustrated in the drawings, there are five pairs of spring supports  134 . These five pairs of spring supports  134  accommodate five serpentine springs  136 , although only one such spring is illustrated in FIG. 8. Serpentine springs  136  are flexible and provide spring cushioning to chair seat  66 . In the illustrated embodiment, serpentine springs  136  are oriented to extend from one side to another side of substrate  76 . This orientation has been found to provide better comfort to a user sitting on chair seat  66 , although it will be understood that serpentine springs can alternatively be oriented to extend from the front to the back of spring substrate  76 . Serpentine springs  136  are attached to spring substrate  76  without the use of any separate fasteners or welding. Specifically, each end of each serpentine spring  136  is attached one of spring supports  134 . As illustrated in FIG. 11, each spring support  134  is generally shaped like an inverted “J.” The inverted J-shape provides a spring recess  138  into which the end of the spring  136  fits. A lip  140  is defined at the end of spring support  134  and helps retain springs  136  and each of the spring supports  134 . The ends  142  of springs  136  (FIG. 8) are also curved inwardly to prevent springs  136  from detaching from spring supports  134 . In order to attach one of springs  136  to spring substrate  76 , the spring  136  is stretched around to oppositely disposed spring supports  134 . When the stretching force applied to the spring ceases, the length of the spring contracts, which causes the spring to securely hold itself in spring recesses  138 .  
         [0085]    Spring substrate  76  includes rear fastening tabs  92  and forward fastening tabs  94  which are the same as the rear and forward fastening tabs of ergonomic substrate  76 . They are inserted into the same apertures defined in bucket  90  and allow spring substrate  76  to be snap fit onto bucket  90  without the use of welding or other fasteners. One of the forward fastening tabs  94  includes a notch  108  which receives center pane  106  on bucket  90  and thereby helps to align spring substrate  76  in a side to side manner with respect to bucket  90 . Spring substrate  76  further includes an alignment notch  114  that is identical to the alignment notch of ergonomic substrate  76 . Alignment notch  114  of spring substrate  76  performs the same function and serves the same purpose as the alignment notch of ergonomic substrate  76 , which was described above and need not be repeated here.  
         [0086]    Bucket  90   
         [0087]    Bucket  90  is depicted in FIGS.  3 - 4  and  12 - 16 . Bucket  90  includes a perimeter wall  144  that extends around the perimeter of bucket  90 . Perimeter wall  144  can be divided into a front wall  146 , a first side wall  148 , a back wall  98 , and a second side wall  150 . Adjacent front wall  146  is an internal rib or wall  104  in which single aperture  100  and double aperture  102  are defined, as discussed previously. A pair of front reinforcement walls  152  extend between front wall  146  and internal wall  104 . Front reinforcement walls  152  add structural strength to bucket  90  and assist in keeping front wall  146  straight during the molding process. Bucket  90  further includes two internal sidewalls  154  that extend from front wall  146  to back wall  98 . Internal sidewalls  154  are oriented generally parallel to first and second sidewalls  148  and  150 . Internal sidewalls  154  help provide further strength to bucket  90 . A front crosswall  156  and a rear crosswall  158  extend across bucket  90  between internal sidewalls  154 . Front and rear crosswalls  156  and  158  are located generally around the axis about which chair seat  66  rotates. The spring mechanism and bearing structures which allow chair seat  66  to rotate are partially housed between front and rear crosswalls  156  and  158 , as will be discussed in more detail herein. As illustrated in FIG. 15, crosswalls  156  and  158  do not have a uniform height. Instead, the height of both of these walls is reduced generally in the center of seat bucket  90 . This reduction in height creates additional space between the serpentine springs and the bucket for user comfort. Bucket  90  further includes a right enclosure  160  and a left enclosure  162 . Right and left enclosures  160  and  162  receive and partially house brackets  68 . Right and left enclosures  160  and  162  each include a top wall  164  that extends between perimeter wall  144  and internal side walls  154 . Right and left enclosures  160  and  162  further include front and rear walls  166  and  168 , which also extend between perimeter wall  144  and internal walls  154 . A front and back stop  170  and  172  are further defined in right and left enclosures  160  and  162  (see FIGS.  13 - 14 ). When seat bucket  90  is rotated to its forward position, front and back stops  170  and  172  contact corresponding surfaces on brackets  68 . Front and back stops  170  and  172  thereby stop seat bucket  90  in its forward position and prevent it from rotating further forward. A pair of recesses  174  are defined adjacent front and back stops  170  and  172 . Recesses  174  are defined for molding considerations. Specifically, recesses  174  are molded into seat bucket  90  to avoid molding a completely solid block which would likely lead to internal cracking during the cooling of the molded part.  
         [0088]    A bearing aperture  176  is defined in right and left enclosures  160  and  162 . Each bearing aperture  176  receives a bearing block which, in turn, receives the bearing about which chair seat  76  rotates, as will be described more fully below. A pair of upper ribs  178  are defined above bearing aperture  176  on an exterior side of internal side walls  154  (FIG. 13). A seat  180  is defined between upper ribs  178 . Seat  180  receives an upper positioning tab  182  defined on the aforementioned bearing blocks. Upper positioning tabs  182  help align and secure the bearing blocks to bucket  90 . A pair of lower ribs  184  is defined along the interior side of internal side walls  154  and located just underneath bearing aperture  176  (FIG. 12). Lower ribs  194  define a lower seat  186  in between them, which receives a lower positioning tab  188  from the bearing block. Lower positioning tab  188  helps to further align and position the bearing block with respect to bucket  90 .  
         [0089]    Bucket  90  further includes a plurality of generally triangular walls  190  which intersect perimeter wall  144  at right angles. Triangular walls  190  are molded into seat bucket  90  to provide additional strength and help maintain the proper shape for seat bucket  90 . An additional pair of triangular walls  190  are defined to intersect front and rear cross walls  156  and  158 .  
         [0090]    As illustrated in FIG. 16, bottom surface  88  of bucket  90  is shaped to define a veneer recess  192  defined on the underside of bucket  90 . Veneer recess  192  is defined to optionally receive a wooden veneer positioned on the underside of seat bucket  90 . The wooden veneer can be secured to seat bucket  90  by an adhesive, separate fasteners, or any other suitable technique.  
         [0091]    Overview of Rotational Assembly  
         [0092]    As illustrated in FIG. 17, a number of components are attached to seat bucket  90  in order to support seat bucket  90  and allow it to rotate between a forward and an upright position. These components include a right hand bracket  68 A, a right hand shaft or bearing  194 A, a spring assembly  196 , a left hand bearing block  198 , a left hand shaft or bearing  194 B, and a left hand bracket  68 B. Ideally, all of these components are aligned along the horizontal axis about which chair seat  66  rotates, however, due to floor imperfections or lack of alignment between respective bases  64 , the right hand components may not be perfectly aligned with the left hand components. A certain amount of misalignment, however, can be accommodated without any problems.  
         [0093]    Right and left brackets  68 A and  68 B each include a fastening aperture  200  which receives a fastener, such as a screw or bolt, used to secure each of the brackets to bases  64 . After being secured to bases  64 , right and left brackets  68 A and  68 B are completely stationary during the rotation of chair seat  66 . Right hand bearing  194 A is attached to right hand bracket  68 A and likewise does not move or rotate during the rotation of chair seat  66 . Right hand bearing  194 A provides a bearing about which certain components of spring assembly  196  rotate. Left hand bearing  194 B is attached to the left hand bracket  68 B and also does not rotate or move during the rotation of chair seat  66 . Left hand bearing block  198  fits over a left hand bearing  194  and rotates about bearing  194 . Left hand bearing block  198  therefore remains stationary with respect to bucket  90 , but rotates with respect to left hand bearing  194 B. Spring assembly  196  functions to return bucket  90  to an upright position after a user has exited chair seat  66 . Spring assembly  196  includes four components: (1) a static cam  202 , (2) a dynamic cam  204 , (3) a spring  206 , and (4) a spring sleeve  208 . Static cam  202  is static with respect to bucket  90 . In other words, static cam  202  does not move or rotate with respect to seat bucket  90 . However, static cam  202  does rotate with respect to right hand bracket  68 A. Specifically, static cam  202  rotates about right hand bearing  194 A. Dynamic cam  204  does not rotate with respect to right hand bracket  68 A, and therefore does rotate with respect to seat bucket  90 . Dynamic cam  204  also moves in a linear direction along right hand bearing  194 A. This linear motion causes a compression and decompression of spring  206 , as will be discussed more below. Spring sleeve  208  is attached static cam  202  and therefore has the same rotational motion as does static cam  202 . A more detailed construction and interaction of these components follows.  
         [0094]    Brackets  68   
         [0095]    Right hand bracket  68 A is illustrated in FIGS.  20 - 25 . As shown in FIG. 21, right hand bracket  68 A is made up of a hemispherical portion  210 , a circular mid-section  212 , a stop section  214 , and a shaft support  216 . Hemispherical portion  210  is interrupted by fastening aperture  200 . A pair of vertical grooves  218  are defined in hemispherical portion  210 , adjacent fastening aperture  200 . Grooves  218  are designed to receive corresponding structure from a cap  444  (FIGS.  58 - 59 ) which fits over fastening aperture  200 . The cap  444  generally has the same curvature as hemispherical portion  210  and helps prevent food items from collecting on top of fastening aperture  200 . Cap  444  includes an end wall  446  having a pair of ridges  448  which fit into grooves  218 . A pair of recesses  450  provide gripping areas for removing cap  444  from bracket  68 . A semicircular recess  452  allows access to be gained to the fastener holding bracket  68  to the base while the cap is in place. Circular mid-section  212  of bracket  68  is positioned so as to be generally aligned with perimeter wall  144  of bucket  90 , as is more clearly illustrated in FIGS. 18 and 19. Stop section  214  of right hand bracket  68 A includes a forward stopping surface  220  and a back stopping surface  222  (FIG. 22). Forward and back stopping surfaces  220  and  222  contact front and back stops  170  and  172  defined in bucket  90  when bucket  90  has rotated to the forward position. Shaft support  216  has a generally hexagonal shape when viewed from its end, such as depicted in FIG. 22. Shaft support  216  is inserted into a hexagonally shaped bore defined in right hand bearing  194 A. Because of the hexagonal shape of this bore, right hand bearing  194 A is prevented from rotating about shaft support  216 . As illustrated in FIGS. 18 and 19, right hand bracket  194 A includes a cylindrical bore  224  that extends through shaft support  216  and stop section  214 . Cylindrical bore  224  both reduces the amount of plastic necessary to mold right hand bracket  68 A, and also reduces the potential for separation of the plastic during cooling due to areas of relatively large thickness.  
         [0096]    Right hand bracket  68 A further includes a tab recess  226  defined on the underside of right hand bracket  68 A, generally in stop section  214 . Tab recess  226  is depicted in FIGS. 23 and 24. Tab recess  226  is designed to receive a correspondingly shaped tab from right hand bearing  194 A which there by secures right hand bearing  194  A to right hand bracket  68 A, as illustrated in FIG. 25. In this manner, right hand bearing  194 A is secured to right hand bracket  68 A without welding or the use of separate fasteners. Right hand bearing  194 A is illustrated generally in FIGS.  25 , and  29 - 34 .  
         [0097]    Bearings  194   
         [0098]    Right hand bearing  194 A is generally tubular shaped and includes an interior bore  228 . Bore  228  is hexagonally shaped toward an attachment end  230  of right hand bearing  194 A and generally circularly shaped toward a free end  232  of right hand bearing  194 A. Right hand bearing  194 A further includes a flexible fastening tab  234  which extends outwardly along the longitudinal axis of right hand bearing  194 A from attachment end  230 . Fastening tab  234  is generally flexible, but resiliently returns to the orientation depicted in FIG. 29. When right hand bearing  194 A is inserted over shaft support  216  of right bracket  68 A, fastening tab  234  flexes outwardly until it snaps into place in tab recess  226 . In this manner, right hand bearing  194 A is secured to shaft support  216  without the use of any welding or separate fasteners.  
         [0099]    Right hand bearing  194 A further includes a top longitudinal groove  236  and a bottom longitudinal groove  238 . As can be seen in FIG. 32, bottom longitudinal groove  238  has a greater width than top longitudinal groove  236 . Longitudinal grooves  236  and  238  receive correspondingly shaped longitudinal ribs defined on dynamic cam  204 . Because of the different width between top and bottom longitudinal grooves  236  and  238 , there is only one orientation in which dynamic cam  204  can be slid onto right hand bearing  194 A. This helps insure that the persons assembling chair seat  66  do so in a correct manner. Longitudinal grooves  236  and  238  provide a track along which dynamic cam  204  slides when seat  66  is rotated.  
         [0100]    Right hand bearing  194 A further includes a side fastening tab  240  that is inwardly flexible, but resiliently returns to the position depicted in FIG. 29. Side fastening tab  240  is used to secure static cam  202  on right hand bearing  194 A. During assembly, static cam  202  is slid over right hand bearing  194 A starting at free end  232  and moving toward attachment end  230 . As static cam  202  moves in this direction, it eventually contacts side fastening tab  240 . As static cam  202  is moved further, it pushes side fastening tab  240  inward. After static cam  202  is moved completely past side fastening tab  240 , side fastening tab  240  snaps back to its unflexed position. In this unflexed position, side fastening tab  240  prevents static cam  202  from being removed from right hand bearing  194 A. When static cam  202  is attached to right hand bearing  194 A, it is positioned over a bearing surface  242 , defined on right hand bearing  194 A. Static cam  202  rotates about bearing surface  242  when chair seat  66  is rotated between its upright and forward position.  
         [0101]    Left hand bearing  194 B is depicted in FIGS.  27 - 28  and  35 - 36 . Left hand bearing  194 B is shorter than right hand bearing  194 A because left hand bearing  194 B does not need to provide any support for a spring assembly. Left hand bearing  194   b  includes a smooth, cylindrical, external bearing surface  244  about which bearing lock  198  rotates when chair seat  66  rotates. Left hand bearing  194 B includes an attachment end  246  and a free end  248 . A fastening aperture  250  is defined adjacent attachment end  246 . Fastening aperture  250  receives a snap ridge  354  defined on left hand bracket  68 B. Snap ridge  354  extends vertically a slight distance such that bearing  194 B must flex to extend over ridge  354 . This flexing is facilitated by an adjacent ramp  356 . After left hand bearing  194 B extends over ridge  354 , a snap portion  358  returns to its original, unflexed position. Due to ridge  354 , left hand bearing  194 B is prevented from being removed from left hand bracket  68 B.  194 B further includes a pair of flexible tabs  252  which extend outward from free end  248 . Flexible tabs  252  are disposed on opposite sides of each other and resiliently returned to the unflexed position depicted in FIGS.  27 - 28 . Flexible tabs  252  include a camming surface  254  and a ridge  256 . Flexible tabs  252  are used to secure bearing block  198  in a snap fitting manner without the use of welding or any separate fasteners. When bearing block  198  is to be inserted onto left hand bearing  194 B, it is slid over left hand bearing  194 B starting at free end  248 . Bearing block  198  is moved in a direction toward attachment end  246 . As it moves in this direction, it contacts camming surfaces  254  which force flexible tabs  252  to flex inwardly. After bearing block  198  has been completely pushed onto left hand bearing  194 B, it is no longer in contact with camming surfaces  254 . Consequently, flexible tabs  252  snap back to their unflexed position. Ridges  256  prevent bearing block  198  from being retracted off of left hand bearing  194 B. A flange  258  disposed generally around the circumference of left hand bearing  194 B prevents bearing block  198  from sliding off attachment end  246 . A groove  360  in left hand bearing block  198  receives a tab  362  on left hand bearing  194 B to thereby ensure that bearing block  198  can only be attached in one orientation. This prevents improper assembly.  
         [0102]    As illustrated in FIG. 36, left hand bearing  194 B includes a cylindrical, internal bore  260  into which shaft support  216  of left hand bracket  68 B is inserted. Unlike right hand bracket  68 A, left hand bracket  68 B has a shaft support  216  that is circular in cross section, rather than hexagonal. This helps insure that left hand bearing  194 B is not inadvertently attached to right hand bracket  68 A, or that right hand bearing  194 A is not inadvertently attached to left hand bracket  68 B. Left hand bearing  194 B further includes an internal, longitudinal rib  262 . Longitudinal rib  262  slides into a correspondingly longitudinal groove  264  defined in left hand bracket  68 B (see FIG. 26). Longitudinal rib  262  helps insure that left hand bearing  194 B remains stationary with respect to left hand bracket  68 B. Longitudinal rib  262  also insures that left hand bearing  194 B can only be attached to the left hand bracket  68 B in one orientation, i.e., it cannot be attached upside down or otherwise.  
         [0103]    Left hand bearing block  198  is depicted in detail in FIGS.  37 - 41 . Left hand bearing block  198  includes an internal bore  266  that is generally cylindrical, as is illustrated in FIG. 38. Bore  266  receives left hand bearing  194 B. The diameter of bore  266  is slightly larger than bearing  194 B in order to allow bearing block  198  to rotate about left hand bearing  194 B. As discussed earlier, left hand bearing block  194 B includes an upper positioning tab  182  and a lower positioning tab  188 . These positioning tabs are used to properly position and secure bearing block  198  to bucket  90 . Upper positioning tab  182  fits into upper seat  180  defined on bucket  90 . Lower positioning tab  188  fits into lower seat  186  defined on bucket  90 . Upper and lower seats  180  and  186  are defined along internal sidewall  154 . Thus, when bearing block  198  is secured to seat bucket  90 , a front surface  268  of upper positioning tab  192  contacts internal sidewall  154 . Further, a rear surface  270  of lower positioning tab  188  contacts internal sidewall  154 . Bearing block  198  further includes an end section  272  that has an external surface which is generally square shaped. This square shaped external surface fits into the correspondingly shaped bearing aperture  176  defined in seat bucket  90 . The square shape of end section  272  and bearing aperture  176  help to stabilize bearing block  198  with respect to seat bucket  90 .  
         [0104]    Spring Assembly  196   
         [0105]    Spring assembly  196  is depicted in an exploded view in FIG. 42. Spring assembly  196  according to one embodiment of the present invention includes static cam  202 , dynamic cam  204 , spring  206  and spring sleeve  208 . Static cam  202  is depicted in detail in FIGS.  43 - 48 . Static cam  202  functions both as a bearing block and to provide a camming action that will be described in more detail below. Static cam  202  includes an upper positioning tab  274  and a lower positioning tab  276 . Upper and lower positioning tabs  274  and  276  function in the same manner as upper and lower positioning tabs  182  and  188  of left hand bearing block  198 . Specifically, upper positioning tab  274  fits into upper seat  180  defined on the right hand side of seat bucket  90 . Lower positioning tab  276  fits into lower seat  186  defined on the right hand side of seat bucket  90 . The placement of upper and lower positioning tabs  274  and  276  and upper and lower seats  180  and  186  helps position and immobilize static cam  202  with respect to bucket  90 . Upper positioning tab  274  includes a front surface  278  which contacts internal sidewall  154  when static cam  202  is positioned inside of bucket  90 . Lower positioning tab  276  includes a back surface  280  which contacts internal sidewall  154  when static cam  202  is positioned inside of bucket  90 .  
         [0106]    Static cam  202  further includes an end section  282  that has an external surface which is generally square shaped. End section  282  fits into bearing aperture  176  on the right side of seat bucket  90 . The square shape of end section  282  and bearing aperture  176  helps insure that static cam  202  remains stationary with respect to bucket  90 . The top surface of upper positioning tab  274  may include the word “top” molded into it. This helps the person assembling chair seat  66  position static cam  202  correctly in bucket  90 . Static cam  202  further includes a pair of dovetail recesses  284  defined on opposite sides of static cam  202 . Dovetail recesses  284  are dimensioned to receive dovetail tabs defined on spring sleeve  208 , as will be further described when discussing spring sleeve  208  below. Static cam  202  includes a cylindrical bore  286  which receives right hand bearing  194 A. As illustrated in FIG. 46, static cam  202  further includes a cylindrical surface  288  which contacts side fastening tab  240  of right hand bearing  194 A when static cam  202  is inserted onto right hand bearing  194 A. Cylindrical surface  288  prevents static cam  202  from being retracted off of right hand bearing  194 A.  
         [0107]    Static cam  202  includes three cam ramps  290 , generally arranged in a cylindrical orientation. Each cam ramp  290  includes a camming surface  292 . Camming surfaces ramp outwardly from static cam  202  and terminate at a tip  294 . A stop surface  296  extends from tip  294  back toward the main body of static cam  202 . Adjacent each stop surface  296  is a short, flat surface  298  that is oriented perpendicularly to stop surface  296 . Flat surface  298  extends from stop surface  296  to the next adjacent camming surface  292 . Camming surfaces  292  interact with corresponding camming surfaces defined on dynamic cam  204 .  
         [0108]    Dynamic Cam  204   
         [0109]    A first embodiment of dynamic cam  204  is depicted in FIGS.  49 - 52 . As shown in FIG. 51, dynamic cam  204  includes a central, longitudinal aperture  300  which is generally cylindrically shaped but for the interruption of an upper longitudinal rib  302  and a lower longitudinal rib  304 . Upper and lower longitudinal ribs  302  and  304  fit into top and bottom longitudinal grooves  236  and  238  defined on right hand bearing  194 A. Upper longitudinal rib  302  has a narrower thickness than lower longitudinal rib  304 . This difference in thickness prevents dynamic cam  204  from being attached to right hand bearing  194 A upside down. The interaction of upper and lower longitudinal ribs  302  and  304  with upper and lower longitudinal grooves  236  and  238  also provides a track system in which dynamic cam  204  can slide linearly toward and away from static cam  202  as chair seat  66  rotates. Dynamic cam  204  includes a plurality of cam ramps  306  of which, in the illustrated embodiment, there are three. Each cam ramp  306  includes a forward camming surface  308 , a stop surface  310 , a rearward camming surface  312 , and a rest surface or apex  314 . Cam ramps  306  are arranged in a generally cylindrical shaped orientation which has the same cross sectional diameter as static cam  202 . As illustrated in FIGS. 50 and 52, dynamic cam  204  includes a spring recess  316  defined on an end of dynamic cam  204  opposite cam ramps  306 . Spring recess  316  is generally a circular groove into which spring  206  seats itself. A spring opening  318  interrupts spring recess  316  and provides a seat for a non-torsional end  320  of spring  206 .  
         [0110]    Spring Sleeve  208   
         [0111]    Spring sleeve  208  is depicted in FIGS.  54 - 56 . Spring sleeve  208  includes two generally parallel sidewalls  322  which terminate at an end wall  324 . Sidewalls  322  are further connected by a bottom wall  326 . Sidewalls  322 , end wall  324  and bottom wall  326  all enclose spring  206 . A pair of dovetail inserts  328  are defined on the ends of sidewalls  322  opposite end wall  324 . Dovetail inserts  328  are used to secure spring sleeve  208  to static cam  202  without the use of welding or any separate fasteners. In particular, dovetail inserts  328  each fit into dovetail recesses  284  defined on static cam  202 . After dovetail inserts  328  are inserted into dovetail recesses  284 , they are prevented from being removed by spring  206 . Spring  206  undergoes compression when dovetail inserts  328  are inserted into dovetail recesses  284 . This compression force exerts a force on spring sleeve  208  which pushes it away from static cam  202 . However, because of dovetail inserts  328  being inserted into dovetail recesses  284 , spring sleeve  208  and static cam  202  are firmly held in contact with each other. In other words, because of the shape of dovetail inserts  328 , spring sleeve  208  can only detach from static cam  202  if spring sleeve  208  is first moved toward static cam  202 . Spring  206  prevents such movement.  
         [0112]    Sidewall  322  of spring sleeve  208  contact front and rear crosswalls  156  and  158  of seat bucket  90  when spring sleeve  208  is inserted into seat bucket  90  a ridge  330  disposed generally around the periphery of end wall  324  also contacts front and rear cross walls  156  and  158  when spring sleeve  208  is inserted in 6 o seat bucket  90 . A bottom extension  332  (see FIG. 56) contacts bottom surface  88  of seat bucket  90  and helps align and stabilize spring sleeve  208  in seat bucket  90 . Because of spring sleeve  208 &#39;s contact with seat bucket  90 , along with its attachment to static cam  202 , spring sleeve  208  will rotate will rotate with bucket  90  when it rotates. When spring sleeve  208  rotates, it forces spring  206  to partially rotate, thereby exerting a torsional force on spring  206 . Spring  206  includes a torsional end  334  which seats itself in a spring recess  336  defined adjacent end wall  324 . Spring sleeve  208  further includes an upper and lower hemisphere  338  and  340 . Upper and lower hemisphere  338  and  340  extend into spring sleeve  208  from end wall  324 . Upper an lower hemispheres  338  and  340  have a diameter which corresponds generally to the interior diameter of spring  206 . Spring  206  thereby fits around upper and lower hemispheres  338  and  340 . These hemispheres help to maintain spring  206  in the correct position and orientation during the rotation of seat bucket  90 .  
         [0113]    Operation of Spring Mechanism  
         [0114]    As noted previously, right hand bracket  68 A and right hand bearing  194 A remain stationary during the rotation of chair seat  66 . Dynamic cam  204  does not rotate at all during this motion, but does slide linearly back and forth toward and away from static cam  202 . Static cam  202  undergoes no linear movement, but rather rotates around right hand bearing  194 A as chair seat  66  rotates. In other words, static cam  202  remains stationary with respect to seat bucket  90 , but rotates with respect to right hand bracket  68 A. Spring sleeve  208  is affixed to static cam  202  and therefore also rotates with respect to right hand bearing  194 A. With respect to spring  206 , its non-torsional end  320  remains seated against dynamic cam  204  during the rotation of seat bucket  90 . Non-torsional end  320  does not rotate and thus does not have a torsional force exerted on it. Torsional end  334  of spring  206 , however, is seated against spring sleeve  208 , which does rotate with seat bucket  90 . Torsional end  334  therefore rotates as seat bucket  90  rotates. As torsional end  334  rotates, spring  206  experiences a torsional force, which spring  206  resiliently opposes. The counter acting torsional force exerted by spring  206  helps return chair seat  66  to its rest position when a user has exited the chair. When chair seat  66  remains in the rest position, spring  206  is partially compressed. As chair seat  66  rotates to either a forward position, or to a more upright position, spring  206  undergoes further compression. The counteracting force exerted by spring  206  against this compression helps maintain chair seat  66  in its rest position, as will be described more below.  
         [0115]    When chair seat  66  is in rest position, spring  206  is undergoing compression which causes spring  206  to exert a counteracting force which pushes dynamic cam  204  toward static cam  202 . In this rest position, the three tips  294  of static cam  202  seat themselves in the three apexes  314  in dynamic cam  204 . Further, the three forward camming surfaces  308  of dynamic cam  204  are in contact with the three camming surfaces  292  of static cam  202 . A gap  342  also exists in this rest position between stop surface  310  of dynamic cam  204  and stop surface  296  of static cam  202 . This gap allows chair seat  66  to be rotated upwardly past its rest position. In the embodiment illustrated in FIG. 42, the rest position of chair seat  66  is approximately 70° from the horizontal position. Gap  342  allows chair seat  66  to be rotated from the 70° position up to a completely upright, 90° position. This would typically occur when a person is walking by the chair and brushes against chair seat  66 , or is otherwise standing in front of chair seat  66  and leaning against the chair seat while it is in its upright position. When chair seat  66  begins rotating toward its forward position, static cam  202  rotates with chair seat  66 . The rotation of static cam  202  forces camming surfaces  292  of static cam  202  into forward camming surfaces  308  of dynamic cam  204 . Camming surfaces  292  and forward camming surfaces  308  thereby cause dynamic cam  204  to slide linearly away from static cam  202  as chair seat  66  rotates forward. This linear sliding of dynamic cam  204  further compresses spring  206 . Additionally, the forward movement of chair seat  66  causes spring sleeve  208  to rotate torsional end  334  of spring  206 . Thus, when chair seat  66  is rotated to a forward position, spring  206  undergoes both compressional and torsional forces. Spring  206  resiliently resists both of these forces, but these forces are overcome by a person sitting on chair seat  66 . When the user exits chair seat  66 , spring  206  pushes dynamic cam  204  back toward static cam  202 . The movement of dynamic cam  204  toward static cam  202  causes static cam  202  to rotate due to the interaction of forward camming surfaces  308  with camming surfaces  292 . The rotation of static cam  202  causes seat bucket  90  to rotate. The rotation of static cam  202  terminates when spring  206  has pushed dynamic cam  204  toward static cam  202  to as great of an extent as possible. In this closely packed position, tips  294  of static cam  202  are seated in apexes  314  of dynamic cam  204 . This is the chair seats rest position.  
         [0116]    After a person exits the chair seat, the torsional forces of spring  206  also help return chair seat  66  to its rest position. Spring  206  exerts a torsional force against spring sleeve  208 , which, in turn, transfers the force to static cam  202 . This torsional force further helps return chair seat  66  to its upright position.  
         [0117]    One of the advantages of having spring  206  undergo both torsional and compressional forces is the soft return of chair seat  66  to its rest position. As chair seat  66  returns to its rest position, the torsional forces exerted by spring  206  rapidly diminish to zero in the rest position. The fact that there is no torsional force exerted on the spring when chair seat  66  is in its rest position helps avoid the loud clanking or thumping noise typically associated with various prior art chairs when the chair seat returns to its rest position. Another advantage of using both compressional and torsional forces is the creation of a positive force that acts to retain chair seat  66  in its rest position. When chair seat  66  is in its rest position, spring  206  is partially compressed. This partial compression urges dynamic cam  204  towards static cam  202 , thereby resisting any rotational movement of chair seat  66 . In order to begin rotation of chair seat  66 , it is necessary to first overcome the compressional forces exerted by spring  206  on the static and dynamic cams. Thus chair seat  66  does not begin rotating until a certain minimal rotational force greater than zero is applied. The compressional force of spring  206  positively seats tips  294  in apexes  314 , which thereby helps insure a uniform alignment of chair seats when they are in their rest position.  
         [0118]    As mentioned previously, the spring assembly depicted in FIGS. 42A and B allows chair seat  66  to rotate from its rest position upwardly towards a more upright position. When a user pushes against the under side of chair seat  66 , this causes an upward rotational force to be exerted on chair seat  66 . When chair seat  66  rotates further upward, tips  294  of static cam  202  move along rearward camming surfaces  312  of dynamic cam  204 . This movement forces dynamic cam  204  to travel linearly away from static cam  202 . This reverse rotation of static cam  292  continues until stop surface  310  of the dynamic cam contacts stop surface  296  of the static cam. At this point, further upward rotation is not possible. When a user stops upward rotational forces, both the torsional and compressional forces exerted on spring  206  cause chair seat  66  to return to its rest position.  
         [0119]    If it is desired to have a chair seat in which its rest position is the vertical most position allowable, this can be accomplished by substantially removing rearward camming surfaces  312  from dynamic cam  204 . An example of such a modified dynamic cam  204 ′ is depicted in FIG. 53. Dynamic cam  204 ′ has no rearward camming surface  312 . Rearward rotation beyond the chair&#39;s rest position is therefore not possible when using the dynamic cam  204 ′ depicted in FIG. 53.  
         [0120]    In the currently preferred embodiment, all of the components of chair seat  66  are made of plastic with the exception of spring  206 , serpentine springs  136  and the upholstery attached to substrate  76 . While other materials can be used within the scope of the invention, the following materials have been selected for use in the current embodiment. Right and left bracket  68 A and B are molded from 33% glass filled nylon. Spring sleeve  208  is molded from polycarbonate. Right and left hand bearings  194 A and B are both molded from acetyl. Left hand bearing block  198  and static cam  202  are both molded from nylon. Dynamic cam  204  is molded from nylon  66 . Seat bucket  90  is molded from 20% glass filled polypropylene. Ergonomic substrate  76  is molded from polyethylene, while spring substrate  76  is molded from 10% talc filled polypropylene. Cap  444  is molded from polypropylene.  
         [0121]    While the present invention has been described in terms of the preferred embodiments depicted in the drawings and discussed in the above specification, it will be understood by one skilled in the art that the present invention is not limited to these particular preferred embodiments but includes any and all such modifications that are within the spirit and scope of the present invention as defined in the appended claims.