Abstract:
A seat adjustment mechanism for a chair includes a first handle which controls the height of the seat above a surface supporting the chair. A second handle allows the user to selectively lock the seat at a user selected angle relative to the supporting surface. As the seat is tilted into a desired position, the seat adjustment mechanism provides limited horizontal and vertical movement of the seat to maintain the chair in an ergonomically correct position. The mechanism includes a housing or enclosure adapted for connection to a pedestal, and a seat bracket for mounting to the underside of the seat. An intermediate bracket is pivotably mounted to the lower enclosure. One end of the seat mounting bracket is pivotably connected to an end of the intermediate bracket, and the other end of the seat bracket is interconnected with the lower enclosure via a link arrangement. A selectively operable locking mechanism is interconnected between the lower enclosure and the intermediate bracket, for selectively preventing and allowing angular movement of the intermediate bracket relative to the lower enclosure, to lock the seat in a predetermined angular position or to enable the seat to pivot relative to the pedestal.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to chairs, and in particular, to an adjustment mechanism for controlling the height and the tilt of a seat for a chair, as well as the angle of the chair backrest relative to the seat. 
     It is well known in the art to incorporate mechanisms into a chair to permit the tilting of the chair back and/or seat in order to enhance the comfort of a user. In order to control the positioning of the seat and backrest, complicated mechanisms are often required. These mechanisms are actuated by a plurality of handles, buttons, levers and the like in order to control the various movements of the seat. The plurality of handles not only detract from the aesthetic properties of the chair, but also render adjustment of the seat and backrest difficult for a user who is unfamiliar with the operation and function of each actuator. 
     Further, prior art adjustment mechanisms tend to be complicated in that they require many parts. For example, in Miotto, U.S. Pat. No. 5,348,371, a chair is provided which incorporates a mechanical device to effectuate the synchronous movement of the seat and backrest. In order to selectively lock the seat in a user selected stationary position, a plurality of friction discs are provided. By rotation of a handle under the seat of the chair, the discs are compressed so as to prevent movement of the seat by friction. The large number of parts involved in this type of locking arrangement adds to the overall cost and complexity of the mechanism. 
     Therefore, it is a primary object and feature of the present invention to provide a chair control mechanism which is simple to operate and inexpensive to manufacture. 
     It is a further object and feature of the present invention to provide a chair control mechanism for a chair wherein a user may adjust the vertical height of the seat with one lever and the seat and backrest angle with another lever. 
     It is a further object and feature of the present invention to provide a chair control mechanism wherein the angle of the seat with respect to the supporting surface of the chair, and the angle of the backrest relative to the seat, may be easily manipulated and selectively locked into position with a single handle. 
     In accordance with the present invention, a device for adjusting the position of a seat of a chair is adapted for use with a pedestal including a central vertical column. The central column includes a gas piston assembly for varying the length thereof. An enclosure is connectable about an upper end of the central column. An actuator element is pivotably mounted to the enclosure and movable between a first actuating position wherein the actuator element actuates the gas piston assembly thereby allowing the length of the central column to be adjusted to a user selected length, and a second non-actuating position wherein the central column is maintained by the gas piston assembly at the user selected length. A handle extends from the enclosure and is pivotably movable between a first position wherein the handle urges the actuator element into the first, actuating position, and a second position. Means are provided for urging the actuator element toward the non-actuating position. 
     It is also contemplated to provide a plunger housing extending laterally from the enclosure and a plunger element slidably supported therein. The plunger element has a first end engaging the actuator element and a second end engaging the handle wherein movement of the handle between the first and second positions causes the plunger element to slide axially within the plunger housing. The handle is pivotably mounted to the plunger housing such that a first end of the handle extends into the plunger housing and a second end of the handle extends outwardly therefrom. 
     The device also includes a seat bracket interconnected to the seat and a link element pivotably mounted to the seat bracket and to the enclosure, for interconnecting the seat bracket to the enclosure. The link element allows for limited horizontal and vertical movement of the seat bracket with respect to the enclosure. An intermediate bracket is pivotably mounted to the enclosure and to the seat bracket at a location spaced from the link element, and pivotable movement of the seat bracket with respect to the enclosure results in a corresponding pivotable movement of the intermediate bracket with respect to the enclosure over a predetermined range. The intermediate bracket may be locked at a user selected position for selectively fixing the position of the seat bracket to the enclosure, and thereby the position at the seat relative to the pedestal. A back support member is connected to the intermediate bracket, such that movement of the intermediate bracket results in adjustment in the angular position of the back relative to the seat. In this manner, the angle of the back is adjusted synchronously with adjustment of the seat angle. 
     In accordance with another aspect of the invention, a seat adjustment mechanism is provided for controlling movement of a seat of a chair. The seat adjustment mechanism includes a bracket assembly operatively connected to the seat for allowing horizontal and vertical movement of the seat over a predetermined range. A locking element is provided for locking the seat at a user selected position within the predetermined range. 
     In accordance with yet another aspect of the invention, a device is provided for interconnecting a seat to a central support. The device includes an enclosure operatively connected to the support. A seat connection bracket is operatively connected to the seat and a link element interconnects the enclosure and the seat connection bracket. An intermediate bracket is pivotably mounted to the enclosure and to the seat connection bracket wherein a predetermined pivotable movement of the intermediate bracket with respect to the enclosure translates into a corresponding predetermined movement of the seat connection bracket with respect to the enclosure. A locking member is provided for maintaining the intermediate bracket in one of a plurality of predetermined positions with respect to the enclosure. 
     Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings furnished herewith illustrate a preferred construction of the present invention in which the above advantages and features are clearly disclosed as well as others which will be readily understood from the following description of the illustrated embodiment. 
     In the drawings: 
     FIG. 1 is a side elevational view of a chair incorporating the chair control mechanism of the present invention; 
     FIG. 2 is a cross-sectional view taken along line  2 — 2  of FIG. 1 showing a bottom plan view of the mechanism of the present invention; 
     FIG. 3 is a cross-sectional view taken along line  3 — 3  of FIG. 2; 
     FIG. 4 is a cross-sectional view taken along line  4 — 4  of FIG. 2 showing a seat height control assembly of the chair control mechanism in a non-actuating position; 
     FIG. 5 is a cross-sectional view, similar to FIG. 4, showing the seat height control assembly in an actuating position; 
     FIG. 6 is a cross-sectional view taken along line  6 — 6  of FIG. 2; 
     FIG. 7 is a cross-sectional view, similar to FIG. 6, showing multiple positions of the chair control mechanism in phantom; 
     FIG. 8 is a cross-sectional view taken along line  8 — 8  of FIG. 6 showing a seat angle locking assembly of the chair control mechanism; 
     FIG. 9 is an enlarged, cross-sectional view showing a portion of the seat angle locking assembly of FIG. 8 in a locked position; 
     FIG. 10 is a cross-sectional view, similar to FIG. 9, showing the seat angle locking assembly in an unlocked position; 
     FIG. 11 is a cross-sectional view taken along line  11 — 11  of FIG. 6; 
     FIG. 12 is a cross-sectional view taken along line  12 — 12  of FIG. 6; 
     FIG. 13 is a cross-sectional view taken along line  13 — 13  of FIG. 6; 
     FIG. 14 is an enlarged, sectional view showing an alternate seat angle locking assembly for the chair control mechanism of the present invention; and 
     FIG. 15 is a cross-sectional view of the alternate seat angle locking assembly taken along line  15 — 15  of FIG.  14 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a chair  10  is provided incorporating a chair control mechanism generally designated by the reference  12 . Chair  10  includes a seat  13  and a backrest  14  mounted to a back support member  15 , commonly known as a “J-bar”, which includes a back mounting portion  16  and seat mounting portion  17  interconnected with chair control mechanism  12 . 
     Pedestal  18  includes a plurality of legs  20  diverging from a central hub  22 . Each leg  20  terminates at a caster  24  to facilitate the rolling of chair  10  across a supporting surface  25 . Each caster  24  includes a forked wheel supporting bracket  26  depending from a leg mounting portion  28 . Each bracket  26  defines a wheel receiving cavity for receiving wheel  30  between forks  26   a  and  26   b . Each wheel  30  is interconnected to its corresponding bracket  26  by an axle  32  extending between each fork  26   a  and  26   b  of the bracket  26  so as to allow for rotation of wheel  30  about the axle. 
     A cylindrical housing  32  extends vertically from hub  22  to support chair control mechanism  12 . Cylindrical housing  32  includes a first support member  33  which is mounted to hub  22 , and a second support member  34  is telescopically mounted to first support member  33 , in accordance with conventional technology. A gas piston assembly is interconnected with first and second support members  33 ,  34 , respectively, in a manner as is known. As best seen in FIGS. 3-5, the gas piston assembly  32  includes a conical mounting portion  36  which is mounted to chair control mechanism  12  for controlling the vertical position of seat  13 , as hereinafter described. 
     Chair control mechanism  12  includes a fixed position support member in the form of a first lower housing or enclosure  40 . Lower enclosure  40  includes a generally flat lower plate  42  having first  44  and second  46  walls extending vertically from opposite sides thereof. A front wall  43  interconnects first and second walls  44  and  46 , respectively, and lower plate  42 . Lower plate  42  includes a centrally positioned aperture  48  therein for receiving a tapered sleeve  50 , which is mounted to lower plate  42  such as by welding. Conical mounting portion  36  of the gas piston assembly engages the internal wall of tapered sleeve  50 , to rigidly and stationarily mount lower enclosure  40  to cylindrical housing assembly  32 . 
     Lower enclosure  40  further includes an upper plate  54  also having an opening  56  therein for receiving sleeve  50  therethrough, and sleeve  50  is secured to upper plate  54  such as by welding. Upper plate  54  is vertically spaced from lower plate  42  and is interconnected to first and second walls  44  and  46 , respectively, and front wall  43 . Upper plate  54  includes a channel member  57  (FIGS. 3-5) for pivotably supporting a gas piston actuating element  60 . Gas piston actuating element  60  includes a horizontal first end  62  which abuts a gas piston stem  64 , and a vertical second end  66 . 
     A generally cylindrical plunger housing  68  extends laterally from vertical wall  46  of lower enclosure  40 . Plunger housing  68  includes a generally cylindrical inner surface  70  which defines a plunger receipt cavity  72 . A generally cylindrical slider element  74  is positioned within plunger cavity  72  and includes an outer cylindrical surface  76  which forms a slidable interface with inner surface  70  of plunger housing  68 . 
     A plunger element  80  is supported partially within a cavity  82  in slider element  74  and projects from an inner end  84  thereof. Plunger element  80  extends through an opening  88  in vertical wall  46  of lower enclosure  40  and into contact with vertical end  66  of gas piston actuating element  60 . 
     A handle  96  is pivotally mounted via a pivot pin  100  to plunger housing  68 . Handle  96  includes a spherical head  97  and a nose-like inner end  98  which extends into the plunger receipt cavity  72  defined by plunger housing  68 . Inner end  98  of handle  96  terminates at an angled slider engaging surface  104  which abuts an outer end  106  of slider element  74  having a complementary engagement surface. A portion of head  97  is flattened and coplanar with slider engagement surface  104 . Handle  96  also includes an outer end  101  extending outwardly from head  97 , terminating in a finger engagement area  102  for engagement by a user. 
     In operation, handle  96  is pivotable about pivot pin  100  between a first, non-actuating position, FIG. 4, and a second, actuating position, FIG.  5 . Movement of handle  96  to its actuating position of FIG. 5 engages end  98  with the angled engagement surface defined by outer end  106  of slider element  74 , to move slider element  74  axially to the left in FIG. 5 so as to cause plunger element  80  to urge actuator element  60  counterclockwise. As actuator element  60  is urged counterclockwise, end  62  thereof engages and depresses gas piston stem  64 , FIG. 5, thereby allowing vertical adjustment of second support member  34  relative to first support member  33 , to position seat  13  at a user selected height. In order to maintain the user selected height, handle  96  is pivoted about pivot pin  100  to the first, non-actuating position, FIG. 4, thereby allowing gas piston stem  64  to return to its at-rest position, which functions to move actuator element  60  clockwise about channel member  57  from its FIG. 5 position to its FIG. 4 position. 
     Referring to FIGS. 6-7 and  12 , a generally U-shaped intermediate bracket  110  is pivotably mounted to lower enclosure  40  by a centrally located pivot pin  112 . Intermediate bracket  110  includes a generally flat base portion  114  and walls  116  and  118  depending from opposite sides thereof. Walls  116  and  118  include corresponding axially aligned openings  120  and  122 , respectively. Similarly, vertical walls  44  and  46  of lower enclosure  40  include openings  124  and  126 , respectively, in axial alignment with openings  120  and  122  in walls  116  and  118 , respectively. 
     As shown in FIGS. 2,  3 ,  6  and  7 , seat mounting portion  17  of back support member  15  is mounted to intermediate bracket base portion  114  by means of a series of bolts  129 . 
     As best seen in FIG. 12, end  128  of pivot pin  112  extends through opening  120  in wall  116  and opening  124  in wall  44 , while end  130  extends through opening  122  in wall  118  and through opening  126  in wall  46 . Pivot pin  112  is fixed to walls  116 ,  118  adjacent openings  120 ,  122 , such as by welding. As best seen in FIG. 7, intermediate bracket  110  may pivot with respect to lower enclosure  40  about pivot pin  112  throughout a range of angular positions between a forwardly tilted position shown in solid lines and a rearwardly tilted position shown in phantom. 
     Lower enclosure  40  is also interconnected to an upper seat bracket  140  by forwardly located first and second links  142  and  144 , respectively, FIG.  13 . Upper seat bracket  140  is generally U-shaped and includes a generally flat upper plate  146  having first,  148  and second  150  walls depending therefrom. Walls  148  and  150  include corresponding openings  152  and  154 , respectively, which are in axial alignment with each other. A first end  156  of a pivot pin  158  extends through opening  152  in wall  148  and a second end  160  of pivot pin  158  extends through opening  154  in wall  150 . Heads  162  and  164  are placed on corresponding ends  156  and  160 , respectively, of pivot pin  158  in order to maintain pivot pin  158  in position. Pivot pin  158  passes through an opening in the upper end of each of links  142 ,  144 . 
     Links  142  and  144  interconnect pivot pin  158  with a pivot pin  166  mounted to lower enclosure  40 . Pivot pin  166  includes a first end  168  which extends through an opening  170  in vertical wall  44  of enclosure  40 , and a second end  172  which extends through an opening  174  in vertical wall  46  of enclosure  40 . Walls  150 ,  152  of upper seat bracket  140  overlap the ends of pivot pin  166 , to prevent lateral movement of pivot pin  166  and maintain pin  166  in positive relative to upper seat bracket  140  and enclosure  40 . Pivot pin  166  passes through an opening formed in the lower end of each of links  142 ,  144 . 
     Referring to FIG. 11, intermediate bracket  110  and upper seat bracket  140  are interconnected by a rearwardly located pivot pin  180 . Pivot pin  180  includes a first end  182  which extends through an opening  184  in wall  116  of intermediate bracket  110  and through an opening  186  in wall  148  of upper seat bracket  140 . A second end  190  of pivot pin  180  extends through an opening  192  in wall  118  of intermediate bracket  110  and through an opening  194  in wall  150  of upper seat bracket  140 . Heads  196  and  198  are mounted to corresponding ends  182  and  190 , respectively, of pivot pin  180  to maintain pivot pin  180  in position. 
     As best seen in FIG. 2, upper seat bracket  140  includes first  204  and second  206  forward flanges extending laterally from walls  148  and  150 , respectively, of upper seat bracket  140 . In addition, rearward flanges  208  and  210  extend laterally from walls  148  and  150 , respectively, of upper seat bracket  140 . Flanges  204 ,  206 ,  208  and  210  include a corresponding aperture therethrough in order to interconnect upper seat bracket  140  to the underside of seat  13 , such as a seat board or other rigid member, by means of screws  212  or the like. 
     Referring to FIG. 7, the tilting or pivoting movement of seat  13  is controlled by links  142  and  144  which interconnect upper seat bracket  140  with lower enclosure  40 , and by pivot pin  180  which interconnects upper seat bracket  140  with intermediate bracket  110 . When seat  13  is tilted forwardly and downwardly, from right to left in FIG. 7 as shown in solid lines, the forward end of upper seat bracket  140  pivots counterclockwise about pivot pin  166  through links  142 ,  144 , while intermediate bracket  110  pivots counterclockwise about pivot pin  112 . When seat  13  is tilted rearwardly and upwardly, from right to left in FIG. 7 as shown in phantom, upper seat bracket  140  pivots clockwise about pivot pin  166  through links  142 ,  144 , while intermediate bracket  110  pivots clockwise about pivot pin  112 . As described, movement of seat  13  translates into a corresponding movement of intermediate bracket  110  about pivot pin  112  over a predetermined range. In addition, movement of seat  13  translates into a corresponding movement of upper seat bracket  140  about pivot pin  166  through links  142 ,  144  relative to lower enclosure  40  and about pivot pin  180  relative to intermediate bracket  110 . As shown in FIG. 7, seat bracket  140  moves in a front-rear direction during movement of seat  13  by pivoting action between links  142 ,  144  and upper and lower pivot pins  158 ,  166 , respectively. That is, clockwise movement of intermediate bracket  110  about pivot pin  112 , caused by the user reclining in seat  13  to exert a downward force on the rear end of intermediate bracket  110  through seat bracket  140  and pivot pin  180 , causes the forward end of seat bracket  140  to pivot clockwise about pivot pin  166  through links  142 ,  144 . Simultaneously, seat bracket  140  pivots counterclockwise relative to links  142 ,  144  about pivot pin  158 . Conversely, counterclockwise movement of intermediate bracket  110  about pivot pin  112 , caused by the user leaning forwardly in seat  13  to exert an upward force on the rear end of intermediate bracket  110  through seat bracket  140  and pivot pin  180 , causes the forward end of seat bracket  140  to pivot counterclockwise about pivot pin  166  through links  142 ,  144 . Simultaneously, seat bracket  140  pivots clockwise relative to links  142 ,  144  about pivot pin  158 . 
     During angular movement of seat  13 , which results in pivoting movement of intermediate bracket  110  about pivot pin  112 , the angle of back  14  is simultaneously and synchronously adjusted along with the angle of seat  13  by the pivoting movement of intermediate bracket  110 . As can be seen in FIG. 7, back mounting member  15  pivots about pivot pin  180  during pivoting movement of intermediate bracket  10  about pivot pin  112 . When intermediate bracket  110  is in its rearwardmost tilted position shown in phantom in FIG. 7, seat mounting portion  17  of back support member  15  is substantially parallel with the underside of seat  13  and upper wall  146  of seat bracket  140 . When seat  13  is pivoted to its forwardmost position as shown in solid lines in FIG. 7, seat mounting portion  17  of back support member  15  is pivoted forwardly relative to upper wall  146  of seat bracket  140 , to move backrest  14  forwardly relative to seat  13 . 
     As best seen in FIGS. 6-10, in order to maintain intermediate bracket  110  in a user selected position, a locking assembly  218  is provided. Locking assembly  218  includes a generally cylindrical lock member housing  220  extending laterally from vertical wall  44  of lower enclosure  40  in a direction opposite that of plunger housing  68 . Lock member housing  220  includes a generally cylindrical inner surface  222  which defines a lock member receipt cavity  224 . A generally cylindrical slider element  226  is positioned within lock member receipt cavity  224  and includes an outer cylindrical surface  228  which forms a slidable interface with inner surface  222  of lock member housing  220 . A locking pin or element  230  is supported within a passage  232  in slider element  226  and projects from an inner end  234  thereof. A recess  227  is provided in inner end  234  of slider element  226  in order to accommodate a spring  238  positioned about locking element  230 . As shown in FIG. 9, spring  238  has a first end  240  embedded in a groove  242  in locking element  230  and a second end  244  abutting the outer surface  246  of lower enclosure wall  44  so as to bias locking element  230 , and hence slider element  226 , away from wall  44 . A spring  247  bears between the inner end of passage  232 , shown at  248 , and the inner end of locking element  230 . Spring  247  functions to bias locking element  230  outwardly relative to slider element  226  and toward wall  44 . 
     A handle  250  is pivotally mounted via a pivot pin  252  to lock member housing  220 . Handle  250  is constructed similarly to handle  96 , and includes a spherical head which extends into the lock member receipt cavity  224 . Head  254  of handle  250  defines an angled slider engaging surface  256  which abuts an outer end  258  of slider element  226  having a complementary engagement surface. Head  254  of handle  256  also includes a nose-like inner end or locking tip  260  dimensioned for receipt in a corresponding recess  262  in the outer end  258  of slider element  226 . Handle  250  also includes an outer end  266  extending outwardly from head  254 , terminating in a finger engagement area  268  for engagement by a user. 
     In operation, handle  250  is pivotable about pivot pin  252  between a first, non-actuating position, FIG. 10, and a second, actuating position, FIG.  9 . In the non-actuating position, spring  238  overcomes the bias of spring  247  and forces slider element  226  to the left in FIG. 10 so as to disengage locking element  230  from intermediate bracket  110 . In order to lock intermediate bracket  110  in a predetermined position, handle  250  is pivoted clockwise such that slider element  226  is urged to the right in FIG.  9 . As slider element  226  is urged to the right in FIG. 9, springs  247  and  238  are compressed and an inner end  280  of locking element  230  extends into one of a series of openings  216   a - 216   c  formed in wall  116  of intermediate bracket  110 . Each opening  216   a - 216   c  in wall  116  of intermediate bracket  110  corresponds to a predetermined angular position of intermediate bracket  110  related to lower enclosure  40 . By inserting locking element  230  into a corresponding opening  216   a - 216   c  in wall  116  of intermediate bracket  110 , intermediate bracket  110  cannot pivot with, respect to lower enclosure  40  on pivot pin  112 . This, in turn, prevents movement of upper seat bracket  140  and, consequently, of seat  13 . 
     In order to maintain locking element  230  in its selected opening  216   a - 216   c  in wall  116  of intermediate bracket  110 , locking tip  260  of handle  250  is positioned within corresponding recess  262  in slider element  226 . With locking tip  260  of handle  250  received within recess  262  in slider element  226 , locking element  230  is retained in the selected one of openings  216   a - 216   c  in intermediate bracket  110  against the bias of spring  238 . As best seen in FIG. 7, intermediate bracket  110  may also be locked in position by extending inner end  280  of locking element  230  over intermediate bracket side wall  116  such that locking member  230  engages base portion  114  of intermediate bracket  110  to lock seat  13  in its forwardmost tilted position. In addition, locking element  230  may be positioned to engage the lower end of intermediate bracket side wall  116  to lock seat  13  in its rearwardmost tilted position and to fix the position of backrest  14 . In this manner, intermediate bracket  116  with its three openings  216   a - 216   c , in combination with locking member  230 , provides five locking positions for intermediate bracket  110 , and thereby for seat  13 . 
     With handle  250  in the non-actuating position, intermediate bracket  110  is free to pivot on pivot pin  112 . This allows seat  13  to be moved freely relative to pedestal  18  throughout its entire range of motion, as illustrated in FIG.  7 . 
     Referring to FIG. 3, a spring assembly  282  is provided for urging intermediate bracket  110  toward a home position wherein seat  13  assumes a predetermined angle, which may be generally horizontal. Spring assembly  282  includes a conventional coil spring  284  which defines an upper end in engagement with upper plate  54  of lower enclosure  40  at a recess  286  formed therein. Coil spring  284  extends downwardly from recess  286 , and defines a lower end which is received in a tension adjustment cap  288 . It is contemplated to enclose spring  284  within a bellows  289 , FIG. 1, so as to prevent user contact with spring  284  and to enhance the overall aesthetic appearance of mechanism  12 . 
     Tension adjustment cap  288  is threaded onto a first end  290  of a rod  292 . A second end  294  of rod  292  extends through an opening formed in base portion  114  of intermediate bracket  110 . A pin  296  interconnects end  294  of rod  292  to base portion  114  of intermediate bracket  110 . 
     In operation, the rearward tilting or reclining of seat  13  of chair  12  causes counterclockwise rotation of intermediate bracket  110  about pivot pin  112 . This movement causes tension adjustment cap  288  to be drawn upwardly through rod  292  toward lower enclosure  40 , which is resisted by the compression force of spring  284  which bears against tension adjustment cap  288 . As the forces causing the counterclockwise rotation of intermediate bracket  110  about pivot pin  112  are relaxed, spring  284  urges intermediate bracket  110  to its home position, FIG.  3 . 
     A thrust bearing  298  is mounted between a spring washer  300 , which engages the lower end of coil spring  284 , and the inner surface of tension adjustment cap  288  in order to facilitate rotation of cap  288 . A user may adjust the force exerted by spring  284  by rotating the tension adjustment cap  288  relative to rod  292 . This provides an adjustment in the amount of force required to tilt seat  13 , and also in the home position of intermediate bracket  110 . 
     Referring to FIGS. 14 and 15, an alternate locking assembly  304  in accordance with the present invention is shown. With the exception of the locking assembly, the chair disclosed in FIGS. 14-15 is identical to that previously described, and hence, the previous description of the chair  10  will be understood to apply to the chair shown in FIGS. 14-15, with common reference characters being used. 
     Locking assembly  304  includes a generally cylindrical lock member housing  306  which extends laterally from vertical wall  44  of lower enclosure  40 . Lock member housing  306  includes a generally cylindrical inner surface  308  which defines a lock member receipt cavity  310 . A generally cylindrical slider element  312  is positioned within lock member receipt cavity  310  and includes an outer cylindrical surface  314  which forms a slidable interface with the inner surface  308  of lock member housing  306 . 
     Locking assembly  304  further includes first  316  and second  318  locking elements supported by slider element  312 . Locking elements  316  and  318  have first ends  324  and  326 , respectively, received within corresponding passages  330  and  332 , respectively, in slider element  312 . Coil springs  334  and  336  are positioned within passages  330  and  332 , respectively, in slider element  312 . As best seen in FIG. 15, coil springs  334  and  336  urge corresponding locking elements  316  and  318 , respectively, toward wall  116  of intermediate. bracket  110 . 
     Locking elements  316  and  318  also include corresponding springs  348  and  350 , respectively. Springs  348  and  350  define first ends  352  and  354 , respectively, embedded in corresponding grooves  356  and  358 , respectively, in locking elements  316  aid  318 , respectively. Second ends  360  and  362  of springs  348  and  350 , respectively, abut the outer surface  246  of wall  44  of lower enclosure  40  so as to bias locking elements  316  and  318 , respectively, and thereby slider element  312 , away from wall  44 . 
     In the embodiment of FIGS. 14 and 15, a pair of offset, staggered rows of openings are formed in side wall  116  of intermediate bracket  110 , in place of openings  216   a - 216   c  (FIGS.  6 - 8 ). As shown in FIG. 14, a first row of openings  364   a ,  364   b  and  364   c  is formed in intermediate bracket side wall  116 , in alignment with locking element  318 . A, second row of openings  364   d ,  364   e  is offset from first row  364   a - 364   c , in alignment with locking element  316 . Openings  364   d ,  364   e  are staggered in location relative to openings  364   a - 364   c , such that opening  364   d  is located between openings  364   a  and  364   b , and opening  364   e  is located between openings  364   b  and  364   c.    
     In operation, as previously described, handle  250  is pivotable about pivot pin  252  between a first, non-actuating position, and a second, actuating position. In the non-actuating position, springs  348  and  350  bias slider element  312  to the left in FIG. 15, through engagement of locking elements  316 ,  318  with slider element  312  through springs  334 ,  336 , respectively, so as to disengage corresponding locking elements  316  and  318 , respectively, from openings  364   a - 364   e  in intermediate bracket  110 . In order to lock intermediate bracket  110  in a predetermined position, handle  250  is pivoted clockwise such that slider element  312  is urged to the right in FIG.  15 . As slider element  312  is urged to the right in FIG. 15, the inner end of each locking element  316 ,  318  is moved toward and into engagement with intermediate bracket side wall  116 . If one of locking elements  316 ,  318  is in alignment with one of openings  364   a - 364   e , the inner end of the locking element extends into the aligned one of openings  364   a - 364   e  under the influence of the outer spring, such as  334 ,  336 . As shown in FIG. 15, locking element  318  is shown with its inner end extending through opening  364   c , with the inward biasing force provided by its outer spring  336  functioning to overcome the outward biasing force provided by its inner spring  350 . Locking element  316  is shown with its inner end in engagement with intermediate bracket side wall  116  under the influence of the inward bias provided by its outer spring  334 , which overcomes the outward bias provided by its inner spring  348 . 
     Each opening  364   a - 364   e  in wall  116  of intermediate bracket  110  corresponds to a predetermined position for intermediate bracket  110  relative to lower enclosure  40 . By inserting one of the locking elements  316  and  318  into a corresponding one of openings  364   a - 364   e  in wall  116  of intermediate bracket  110 , intermediate bracket  110  cannot pivot with respect to lower enclosure  40  on pivot pin  112 . This, in turn, prevents movement of upper seat bracket  140  and, consequently, of seat  13 , to thereby lock seat  13  in a desired user-selected position. In addition, as in the prior embodiment, locking element  318  is engageable with either the upper or lower edge of intermediate bracket side wall  116  to maintain intermediate bracket  110  in its forwardmost and rearwardmost tilted positions, respectively. In this manner, intermediate bracket  110  and the five openings  364   a - 364   e  formed in side wall  116  provide seven locking positions for intermediate bracket  110 , and thereby for seat  13 . 
     As previously described, with handle  250  in the non-actuating position, intermediate bracket  110  is free to pivot on pivot pin  112 . Spring assembly  282  urges intermediate bracket  110  to the home position wherein seat  13  may be oriented generally horizontal. 
     In either embodiment of the locking assembly, the locking elements, such as  230 ,  316  and  318 , are retained in their locking position within an opening in intermediate bracket side wall  116  when handle  250  is first moved to its non-actuating position of FIG. 10, due to friction exerted on the locking member by lower enclosure wall  44  and intermediate bracket side wall  116 . When the user tilts seat  13  so as to relieve this frictional force on the locking member such as  230 ,  316  and  318 , the spring, such as  238 ,  348  and  350 , respectively, functions to draw the respective locking member outwardly from the opening in intermediate bracket side wall  116  within which the respective locking member was received. In the release operation, the user must have his or her body in contact with back  14  in order to tilt seat  13 . This avoids the possibility of back  14  hitting the user while releasing locking assembly  218  when sitting on seat  13  and not in contact with back  14 , as was the case with prior art mechanisms of this type. This provides an “anti-shock” feature for chair control mechanism  12 . In addition, when handle  250  is first moved to its actuating position of FIG. 9, the locking member such as  230 ,  316  and  318  may not be in exact alignment with one of the openings in intermediate bracket side wall  116 , and will thus initially engage the outer surface of intermediate bracket side wall  116 . Subsequent forward or rearward tilting movement of seat  13  by the user will cause angular displacement of intermediate bracket  116  as described previously, and movement of one of the openings in intermediate bracket side wall  116  into alignment with the respective locking element  230 ,  316  and  318  to enable the locking element to pass into the aligned opening. 
     As can be appreciated, mechanism  12  is relatively simple in its construction and components, and yet provides a wide range of pivoting movement of seat  13  with a large number of user-selectable locking positions for maintaining seat  13  in a desired angular position. Mechanism  12  eliminates the complexity and cost associated with a friction disk-type locking assembly while nonetheless providing a relatively large number of locking positions. In addition, mechanism  12  provides ergonomically advantageous operation by simultaneously translating the seat in a frontward-rearward direction upon pivoting movement of the seat, due to the operation of links  142 ,  144 . 
     Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.