Seat for a reclining office chair

Abstract: A seat portion (14) for a seat (10) wherein the seat portion (14) comprises a panel comprising a rear portion to support the occupant. The rear portion has a longitudinal centerline and incorporates two zones (162) either side of the longitudinal centerline. Each of the zones comprises a first pattern of weakeners arranged in a series of spaced sinuous lines. Furthermore, a substantial portion of the panel, apart from the zones (162) may also be provided with a pattern of weakeners arranged in a series of spaced sinuous lines (163), interrupted by the zones (162).

Description: Field of the Invention The present invention relates to a flexible or foldable panel for a seat such as a chair or a stool. In particular, although not exclusively, the invention relates to a flexible panel for a reclinable office chair. A seat depth adjustment mechanism is also described, While the invention is described in terms of commercial office chairs, the invention may have application to any other type of seating such as public seating for theatres, aircraft or domestic seating. Background to the Invention When a person sits in a chair, there are two boney protuberances on which the person sits. These are reffered to as the ischial protuberositises. It can be uncomfortable to sit on these for a period of time and therefore seats such as chairs and stools are generally padded with one or more layers of foam for user comfort. Depending upon the quality of the foam, the user can still experience some discomfort after a period of time because once he sinks down into the foam, he still may encounter a greater resistance bearing on the ischial protuberosities, compared to other parts of his derriere. It is an object of at least an aspect of the present invention to provide a flexible seat panel which more comfortably accommodates the occupant's ischial protuberosities. In office chairs, it is desirable to have seat portions in which the forward portion is deflectable under the weight of the occupant See for example US Patents Nos. 5,050,931 and US 4,498,702. US Patent No. 5,050,931 has a generally flexible seat portion but a relatively complex spring mechanism is required in order to upwardly bias the forward portion and prevent it from unduly sagging under the occupant's weight The arrangement shown in US Patent 4,498,702 is a cumbersome arrangement in which a separate forward portion of the seat portion is connected to a rearward portion of the seat portion by leaf springs. The prior art suffers from the disadvantage that in order for the seat portion to have sufficient strength, complex spring mechanisms are required to prevent the forward portion from unduly sagging under the weight of the occupant. It is yet another object of at least an aspect of the present invention to provide a flexible or foldable seat panel which alleviates the requirement for a complex spring mechanism to resist undue sagging of the forward portion of the seat portion. As the reader will appreciate, people come in a great deal of different shapes and sizes. As the chair market stands at present, office chairs are required to cater for a large range of occupant sizes. A commonly available adjustment is seat depth adjustment as illustrated in US Patent 5,871,258. This US patent also illustrates that the forward portion of the seat portion may be deflectable under the occupant's weight thereby defining a transverse fold line. However, the fold line is disposed the same distance from the front of the seat portion, irrespective of the seat depth position which does not cater for different sizes of seat occupants. Furthermore, another disadvantage of this prior art arrangement is that a complex spring arrangement is required to upwardly bias the forward portion of the seat portion. In one embodiment, the user is required to adjust the spring force to suit his requirements and in another embodiment the spring force is non-adjustable. Further seat panels are described in US-A-5 664 835 and US-A-4 418 958. It is therefore an object of at least an aspect of the present invention to provide a means for resisting flex of the forward portion of the seat portion which offers a resistance correlating to the seat depth position. Summary of the Invention In accordance with a first aspect of the present invention there is provided a seat portion for a seat according to claim 1. Preferably the panel is of a unitary construction which is weakened in specific locations enabling the zones to form pockets which accommodate the ischial protuberosities of an occupant sitting in the seat. Preferably, a plurality of weakeners are provided to provide the zones with increased "give" in response to an occupant sitting in the seat. The weakeners may be in the form of apertures. For example, the seat panel may be perforated. However, a slotted pattern is the most preferred construction. An alternative construction is to provide weakeners, each of which is in the form of a reduction in thickness in the specific location where it is desired to increase flexibility. The seat portion may also include a forward portion integrally formed with the back portion to form a unitary shell to support the occupant. The seat panel might be provided with an overall pattern of weakeners to enhance flexibility. The zones may have an increased concentration of weakeners compared to the remainder of the seat panel. For example, a preferred overall pattern is a pattern of weakeners arranged as a series of spaced transversely extending sinuous lines. Preferably the pattern of transversely extending sinuous lines is interrupted by the two zones. The zones may be of any shape such as circular, square, although a rectangular shape is preferred which allows some flexibility as to the particular location of the seated occupant relative to the seat panel and also allows for the fact that chair occupants come in an different shapes and sizes. In a most preferred form of the invention, the zones also include a pattern of weakeners arranged in spaced longitudinally extending sinuous lines. Preferably, the weakeners in the zones are slots. Additionally, the longitudinally extending lines within the zones may be more closely spaced than the transversely extending lines in the remainder of the seat panel. Moreover, it is also preferred that the frequency of the repeating wave of the longitudinally extending lines in the zones is greater than the frequency of the transverse sinuous lines in the remainder of the seat panel. As mentioned above, the seat panel is preferably an integral one piece panel incorporating the rear portion and the forward portion. Additionally, the seat panel could be integral with the back panel incorporating an integral hinge to allow flexibility between the back panel and the scat panel. The seat panel is preferably of moulded plastics construction which is moulded in a specific shape to enhance user comfort. In particular, the rear of the seat panel may be dished. Furthermore, at approximately one third of the length of the seat panel along the longitudinal centreline, there may be provided a transverse plateau portion which is generally flat. Forwardly of the transverse plateau portion, preferably the seat portion dips downwardly. Additionally, the corners may also dip downwardly. In a most preferred form of the invention the panel essentially comprises a sheet. The sheet may incorporate stiffening webs on the underside thereof extending in either the transverse or longitudinal direction. Preferably, the stiffening webs extending in the transverse direction follow the pattern of spaced transversely extending sinuous lines. The transverse webs may be disposed in between the lines of weakeners. In accordance with a second aspect of the present invention there is provided a seat panel for a seat comprising a rear portion to support the occupant, the rear portion having a longitudinal centerline and incorporating two zones either side of the longitudinal centerline, there being surrounding portions surrounding the zones, wherein the panel is of a construction which provides enhanced flexibility in each of the zones compared to the surrounding portions and wherein a substantial portion of the panel, apart from the zones is provided with a pattern of weakeners arranged in a series of spaced sinuous lines, interrupted by the zones. The flexible panel described in the abovementioned aspect may incorporate any of the preferred features described in accordance with the first aspect of the invention as set out above. In accordance with the third aspect of the present invention there is provided a seat construction for supporting a seat occupant, the seat construction including: a seat portion which is foldable about a transverse fold under the weight of the occupant; a seat depth adjustment mechanism to adjust the position of the seat portion in and out over a range of positions between an extended position and a retracted position, wherein the seat portion incorporates a resistance to folding which increases as the seat position is adjusted towards the extended position. In a preferred form of the invention, the seat depth adjustment mechanism may include a seat guide, the seat portion being moveable relative to the seat guide with the seat portion being transversely foldable relative to a fixed portion of the seat guide such that the transverse fold shifts by an amount corresponding to the depth adjustment of the seat. Accordingly, the transverse fold may lie anywhere within a predetermined transition zone on the seat portion. The construction of the seat portion may vary over the transition zone in order to provide the corresponding adjustment of the resistance to folding. For example, the thickness of the seat portion may increase over the transition zone in the direction towards the rear of the seat portion. The transition and thickness may be a stepped increase or gradual ie tapered seat portion. In a preferred form of the invention, the seat portion incorporates longitudinally extending stiffening webs. Suitably, the longitudinal webs are provided on the underside of the seat portion. The longitudinally extending webs may increase in girth over the transition zone in the direction towards the rear of the seat. For example, the webs may increase in height or alternatively increase in thickness. In a most preferred form of the invention, the longitudinally extending webs begin at nil thickness at the beginning of the transition zone and gradually increase m height in the rearward direction, over the transition zone, the longitudinal webs being maintained of a uniform height rearwardly of the transition zone. Preferably there are four longitudinally extending stiffening webs. Preferably, the seat portion is one piece. In a most preferred form of the invention, the seat portion is an integral moulded plastic panel construction. The seat depth adjustment mechanism may be selectively operable by the seat occupant. The position of the seat portion may be adjustable in increments so that the seat portion may adopt any one of a finite number of positions between the extended and the retracted position. Preferably, the seat depth adjustment mechanism includes a lock having a locked configuration and an unlocked configuration with the seat depth adjustment mechanism being normally biased towards the locked configuration with an actuator provided to selectively move the lock to the unlocked configuration. In a preferred form of the invention, the seat depth adjustment mechanism includes a seat carriage slidably supported on the seat guide. The seat carriage may incorporate the seat portion. However, in a preferred form of the invention, the seat portion is a discrete member attached to the seat carriage. In a most preferred form of the invention the seat portion is in the form of a flexible panel fixed to the seat carriage. The panel further includes a plurality of dependent spacers disposed forwardly of the seat carriage. Preferably, the spacers bear against the seat guide when the occupant's weight is brought to bear on a forward part of the seat portion. Preferably the spacers are arranged in a longitudinally extending line and gaps may be provided between adjacent spacers such that when the sides or edges of the spacers on each side of the gaps engage, the maximum curvature of the transverse fold is defined. Most preferably, the gaps are in the form of invoked V-shaped gaps such that on maximum curvature of the transverse fold, the sides of each gap engage with each other to close the gap. Most preferably, the spacers comprise a series of blocks which extend longitudinally over the length of the transition zone. Preferably, the blocks also reduce in height towards the front of the seat portion. The top of the blocks may define a taper. In a most preferred form of the invention, the seat carriage is slidably supported on two guides arranged on opposite sides of the seat construction. Accordingly, there may be two sets of spacers, each of which bear against a respective seat guide. As has been explained in accordance with the first aspect of the invention, the seat portion may comprise a flexible panel which is moulded into a three dimensional shape to enhance comfort for the occupant. The features of three dimensional shape described above in accordance with the first aspect of the invention may be applied to the aspect of the invention defined above. Additionally, the seat panel may incorporate a pattern of weakeners to enhance the flexibility and the foldability of the seat panel as discussed in connection with the foregoing aspects of the invention. In accordance with another aspect of the present invention there is provided a seat construction for supporting a seat occupant including: a seat portion which is foldable about a transverse fold under the weight of the occupant; a seat depth adjustment mechanism to adjust the seat portion in and out over a range of positions between an extended position and a retracted position, the seat depth adjustment mechanism including a seat guide relative to which the seat portion is adjustably moveable, wherein the seat portion folds transversely about a fixed portion of me seat guide. Accordingly, a transition zone may be defined in the seat portion between the location of the transverse fold in the retracted position of the seat portion and the location of the transverse fold in to the extended position of the seat portion. Preferably, the seat portion is a one piece plastics panel provided with a patterns of weakeners, the pattern extending for at least the width of the transition zone to enhance the transverse foldability of the seat panel over the transition zone. The pattern of weakeners may incorporate any of the features described above in accordance with the first aspect of the invention. The preferred form is a series of spaced lines of discontinuous slots, the lines extending sinuously in a transverse direction with the lines curving convex forwardly across the centreline of the seat portion. Additionally, the seat portion may be carried by a seat carriage which is moveable relative to the seat guide. The seat portion may be in the form of a flexible panel which incorporates dependent spacers as described in connection with the preceding aspect of the invention. In accordance with still another aspect of the present invention there is provided a flexible seat panel for supporting a seat occupant, the seat panel being foldable about a transverse fold under the weight of the occupant wherein the panel incorporates longitudinally extending stiffening webs which, for at least a portion of their length increase in girth in the rearward direction. The longitudinal webs may be variable in either width or height or a combination of both over said portion of their length. Preferably, the webs taper in height in the rearward direction. The panel may be foldable about a transverse fold anywhere within a transition zone disposed in an intermediate location of the panel. Preferably, the webs offer increased resistance to folding as the transverse fold is moved in the rearward direction over this transition zone. The above aspect of the invention may incorporate any of the features described in connection with the foregoing aspects. In accordance with a further aspect of the present invention there is a provided a seat depth adjustment mechanism including: a seat guide; and a seat carriage slidably supported on the seat guide, the seat carriage being slidable between a retracted position and an extended position, wherein the seat guide has a guide glide surface and the seat carriage has a carriage glide surface, the guide glide surface and the carriage glide surface being in sliding engagement with each other, wherein one of the glide surfaces is formed by a liner having integral resilient projections engaging the other of the glide surfaces. Preferably the liner is in the form of a plastic liner having integrally formed projections. The plastic liner may be moulded. The resilient projections may be of any shape. In the preferred form of the invention the resilient projections are in the form of archlets. Preferably, the archlets are formed with ends which are contiguous with the remainder of the glide surface from which they project with the side edges of the archlets being spaced therefrom, thereby defining arch-shaped openings on each side. Preferably, the archlets are arranged in a staggered pattern. Preferably, the liner is incorporated into the seat guide. However, this is not essential and the liner may alternatively be incorporated into the carriage. In a preferred form of the invention, there are two seat guides on opposite sides of the carriage, slidably supporting the carriage. In this form of the invention, each of the seat guides may incorporate a liner, the two liners being a mirror image of each other. Each of the plastic liners may be supported by a metal part of the guide. Where two liners are incorporated into respective seat guides, the glide surfaces with the projections may define two facing uptight glide surfaces engaging against upright glide surfaces on opposite sides of the carriage. Preferably, each glide surface with the projections is maintained in spaced configuration from the associated metal part of the seat guide. This also provides a measure of resiliency for the glide surface with projections. Preferably, the glide surface with projections is maintained in spaced configuration front the associated scat guide by a peripheral wall extending from the seat guide to the glide surface with projections. It will be appreciated that this arrangement with two facing glide surfaces with projections is advantageous since it centres a carriage between the two seat guides. The arrangement also takes up any slack between the carriage and the adjacent seat guides, thereby reducing the risk of jamming of the seat carriage between the seat guides. The liners may also include upper glide surfaces on which the carriage is supported. These upper glide surfaces may be provided with or without resilient projections. Preferably, the liners are formed as integrally moulded plastic constructions including the upper glide surfaces and the upright glide surfaces, and being of L-shape in transverse section. The seat adjustment mechanism may be provided with a user operable lock in order to secure the seat carriage at a selected location between the retracted position and the extended position. Preferably, the lock is biased towards the locked configuration. In accordance with yet another aspect of the present invention, there is provided a seat depth adjustment mechanism including: a seat guide; and a scat carriage slidably supported on the seat guide, the seat carriage being slidable between a retracted position and an extended position, the seat guide including a supporting portion supporting a liner, the liner having a guide glide surface and the scat carriage having a carriage glide surface, the guide glide surface and the carriage glide surface being in sliding engagement with each other, wherein the guide glide surface includes integral resilient projections directed towards and engageable with the supporting portion, the remainder of the guide glide surface being spaced from the supporting portion. This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth. The invention consists in the foregoing and also envisages constructions of which the following gives examples. Brief Description of the Figures In order that the invention may be more fully understood, some embodiments will now be described by way of example with reference to the Figures in which: Figure 1 is a perspective, partially exploded view of a chair in accordance with a preferred embodiment of the chair; Figure 2a is an exploded perspective view of a back portion of the chair shown in Figure 1; Figure 2b is a perspective view of a back attach casting forming part of the back portion of the chair illustrated in Figure 2a; Figure 3 is an assembled view of a lower portion of the back portion of the chair illustrated in Figure 2; Figure 4 is a perspective view of a main transom of the chair of Figure 1; Figure 5 is a perspective view of an assembly from the underside of the main transom illustrated in Figure 4; Figure 6 is a perspective view of the assembled chair looking down upon the main transom illustrated in Figure 4; Figures 7 and 8 show an adjustable clamp not forming part of the present invention; Figure 9 is an enlarged perspective view of a portion of the main transom illustrated in Figure 4; Figure 10 to 26 show an alternative chair not forming part of the present invention; Figure 27 is a further exploded view of parts making up the back portion of the first embodiment; Figure 28 is a perspective view from the rear of the assembled parts illustrated in Figure 27; Figure 29 is a perspective view illustrating in exploded fashion, a spring carrier and a leaf spring as used in the first embodiment; Figure 30 is a perspective view of the chair of the first embodiment from the side rear, with certain parts removed for clarity; Figure 31 is a schematic view of the main elements of the recline mechanism of the chair of the first embodiment; Figure 32 is a side view of a seat guide, being one of the elements shown in Figure 31; Figure 33 is a side view of the chair of the first embodiment illustrated in Figure 1, illustrating the arrangement of the main links with occupant weight applied to the seat portion; Figure 34 is a side view as per Figure 33, except with the occupant weight removed from the seat portion. Figure 35 is a side view of the chair of Figure 1, illustrating the recline action of the chair; Figures 36 to 40 show views relating to the chair of Figures 13 to 26, not part of the present invention. Figure 41a is a perspective view of the chair according to the second embodiment from the rear, with certain parts removed for clarity; Figure 41b is a perspective view of a detail of Figure 41a; Figure 42 is a schematic view of the main elements of the recline mechanism of the chair according to the second embodiment; Figure 43 is a perspective underside view of the seat guide, one of the main elements of the recline mechanism of the chair according to the second embodiment; Figure 44 is a side view of the main parts of the recline mechanism of the chair according to the second embodiment; Figure 45 is a side view as per Figure 44, except with the seat added; Figure 46 is a perspective view of a seat panel which may be used with either the first or second embodiment of chair; Figure 47 is a perspective view of the underside of the seat panel shown in Figure 46; Figure 48 is a plan view of the underside of the seat panel illustrated in Figure 46; Figure 49 is a perspective view of a detail of the underside of the seat panel illustrated in Figure 47; Figure 50 is a schematic longitudinal sectional view through the middle of the seat panel illustrated in Figure 46; Figure 51 is a schematic view of the side edge; Figure 52 is a schematic transverse sectional view through the seat panel at approximately 150 mm forward of the rear edge; Figure 53 is a schematic transverse sectional view at approximately 120 mm from the front edge; Figure 54 is a schematic view of the front edge of the seat panel illustrated in Figure 46; Figure 55 is a perspective view of the chair according to the first embodiment with the seat panel removed to show a seat depth adjustment mechanism; Figure 56 is a perspective view showing similar detail to Figure 55; Figure 57 is a perspective view with the seat panel removed, showing the workings of the seat depth adjustment mechanism; Figure 58 is a side view of a portion of the chair with the seat panel in an extended position; Figure 59 is a side view of a portion of a chair illustrated in Figure 58 with the seat panel in a retracted position; Figure 60 is an underside perspective view of the portion of the chair illustrated in Figures 58 and 59 illustrating the seat depth adjustment mechanism; Figure 61 is a perspective view of the chair according to a second embodiment with the seat panel removed to show a seat depth adjustment mechanism; Figure 62a is a different perspective view showing a similar detail to Figure 61; Figure 62b is a perspective view of the opposite side the seat guide to that shown in Figure 43; Figure 62c is a perspective view of the seat guide as shown in Figure 62b except with a portion removed. Figure 63 is a side view of a portion of the chair with the seat panel in a retracted position; Figure 64 is a side view of the portion of the chair ofFigure 63 with the seat panel in an extended position; Figure 65 is an underside view of the portion of the chair illustrated in Figures 63 and 64 illustrating the seat depth adjustment mechanism. Figure 66 to 88 show various features not forming part of the present invention. Figure 89 is a schematic bottom view of a slightly modified form of the seat panel; and Figure 90 is a perspective, partly exploded view of a chair. Description of Preferred Embodiment First Embodiment Since the Figures illustrate the chair from various different angles as convenient to explain certain parts, an arrow marked "F" has been inserted into the drawings where appropriate. Accordingly the terms forward, rearward, left side and right side should be construed accordingly. Figure 1 illustrates an office chair 10 including a main assembly having a seat portion 14 and a back portion 16. The seat portion 14 and the back portion 16 are supported above the ground by a supporting frame including a wheeled base 18 and a central support column 20. The central support column 20 houses a pneumatic spring (not shown) for height adjustment of the seat portion 14 in conventional fashion. The pneumatic spring is connected to the main transom 22 of the chair which is illustrated in Figure 4. The main transom 22 extends transversely across the chair and is connected to the pneumatic spring by way of central spring connection ring 23. Figure 1 also illustrates two detachable arm assemblies 24. The arm assemblies 24 each include an upper armrest 26 which is padded for user comfort. Each aim assembly 24 includes an upright support structure 28. The armrest 26 is mounted to the upper end of the upright support structure 28. The lower end of the upright support structure has an elongate attachment portion 30 extending inwardly therefrom at a downwardly inclined angle relative to the upright support structure 28. The elongate attachment portion 30 is releasably engaged within one end of the main transom 22. The manner of attachment is not significant to the present invention and the reader may refer to our co-pending Patent Application US Serial No..........., the details of which are incorporated herein by reference. Back Portion The back portion 16 is defined by a peripheral frame 34 which is approximately rectangular in shape, as shown in Figure 2. In the finished chair the peripheral frame 34 has a mesh fabric stretched over. Within the opening defined by the rectangular peripheral frame 34, a lumbar support mechanism 36 is provided. Figure 2 illustrates more clearly the form of the peripheral frame 34. The peripheral frame 34 is constructed of a flexible plastics material such as injection moulded reinforced polyester. The peripheral frame 34 is of integral construction and comprises two upright members 38, a top beam 40 and a bottom beam 42. The upright members 38 are bowed with a gentle serpentine curve sweeping forwardly in the upward direction and then rearwardly beyond the lumbar region. This is a shape which is comfortable to the chair occupant. The upright members 38 include channels 44 which are open in the direction facing rearwardly as shown in Figure 28. The upright members 38 are also joined by an intermediate back beam 46. The back beam 46 supports the lumbar support mechanism 36. Rigidly connected to the lower end of the peripheral frame 34 is a back attach casting 48. The back attach casting 48 is an integrally cast component as shown in Figure 2b. The back attach casting 48 includes two pairs of sprigs 50 which engage with aligned apertures 52 provided at the bottom of the upright members 38. This enables the lower region of the peripheral frame 34 to be securely fixed to the back attach casting 48. An additional snap fitting (not shown) may be provided. The back attach casting 48 also includes 2 pairs of opposed walls 54 on opposite sides (more clearly seen in Figure 27). Each pair of spaced walls 54 defines a forwardly extending channel 64 in which a spring carrier 60 is received. Each pair of opposed walls 54 includes aligned slots 56. The spring carrier 60 (to be described more fully in connection with Figure 27) has pins 62 on opposite sides to engage with the aligned slots 56. Furthermore, the back attach casting 48 includes two forwardly extending hollow projections 66. The hollow projections 66 each define a socket 68. Two back extension arms 70 are welded within respective sockets 68 of the hollow projections 66. Referring to Figure 3 for greater clarity, each back extension arm 70 includes a forward nose portion 72 and a chin portion 74. An extension arm aperture 75 extends through the back extension arm 70 in a position rearwardly of the nose portion 72 and the chin portion 74. Reference is now made to Figure 4 which illustrates the main transom 22 which extends transversely across the chair as already explained. The main transom 22 is supported on a pneumatic spring at central spring support ring 23. The main transom is a beam-like construction of diecast aluminium with pivot features 76 formed at opposite ends. At each end, the pivot features comprise opposed supporting webs 78. The opposed supporting web 78 have rear aligned apertures 80. In the assembled chair, the extension arm aperture 75 of one of the back extension arms is aligned with the rear aligned apertures 80 on one side of the main transom to receive a main pivot pin (not shown) herethrough. Likewise the other back extension arm 70 is pivotally attached to the main transom 22 on the other side. Each back extension arm is pivotable about the associated main pivot pin and the recline axis R of the back portion 16 is thereby defined. Recline Limits As mentioned above, a nose portion 72 is defined forwardly of each back extension arm 70. The nose portion 72 has two bosses 84 extending sideways from the flanks of the nose portion 72. The bosses 84 are receivable within facing slots 86 in the opposed supporting webs 78. Each of the facing slots 86 has a base formed therein. During rotation of the back extension arm 70 about pivot R, the bosses 84 move within respective ones of the facing slots 86. In the forward most position of the back portion 16 in its pivoting action about the recline axis R, the bosses 84 will bottom out at the bases of the slots 86 thereby defining forward limits. This is referred to as the "forward active position"of the back portion 16. The chin portion 74 of each back extension arm 70 includes a first abutment surface 88 for engagement with a second abutment surface 90 (see Figure 9) provided as part of the rear wall of the main transom 22. On each side, when the first abutment surface 88 engages with the second abutment surface 90, the rearward recline limit of the back portion 16 of the chair will be thereby defined. It would not be possible for the chair portion 16 to recline back any further once the two abutment surfaces come into engagement although flexing of the peripheral frame is still possible in this position. As shown in Figure 4, the main transom 22 has a reaction surface 98 against which the first spring 94 engages. The reaction surface 98 is centrally disposed and has a depth corresponding to the depth of the first spring 94. The reaction surface 98 forms part of an integrally formed projection extending rearwardly from the main transom 22. As the back portion 16 reclines rearwardly about the recline axis R, the first recline spring 94 engages against the reaction surface 98, thereby biasing the back portion 16 against reclining action. Stiffness adjustment of Peripheral Frame Figure 27 illustrates a further exploded view of parts assembled with the peripheral frame 34. As described previously, a back attach casting 48 is fixed to the back of the peripheral frame 34. The back attach casting 48 has two upright channels 64 arranged at either end, each defined by opposed walls 54. The opposed walls 54 have aligned slots 56 arranged therein for receipt of pins 62 provided on a spring carrier 60. The specific form of the spring carrier 60 is illustrated more clearly in Figure 29. The spring carrier 60 is in the form of an elongate member which is approximately square or rectangular in cross section with the pins 62 being arranged on opposite sides. One end of the member is provided with a rebate 124. The other end of the spring carrier is forked for pivotal connection with another linkage as will subsequently be explained. The forked end has aligned apertures 126. The rebate 124 has spaced threaded bores 130 provided therein. A leaf spring 128 has a lower end 131 shaped to be received within the rebate 124. The lower end 131 has two spaced apertures 133 provided therein. These apertures 133 align with the threaded bores 130 provided on the spring carrier so that the leaf spring 128 may be securely fastened to the spring carrier 60. From the lower end 131 in the upwards direction, the leaf spring 128 gradually increases in width with a slight tapering in thickness, although overall the leaf spring 128 is of generally elongate configuration as shown. The leaf spring 128 is constructed from high tensile spring steel. As can be seen in Figure 27, there are two spring carriers provided on opposite sides of the back portion, each received within a respective one of the channels 64 and mounted for pivotal movement about an axis defined through the bases of the aligned slots 56. Figure 28 illustrates the assembled combination whereby each of the leaf springs lie against the back of the peripheral frame 34 in a respective channel 44. As already described the peripheral frame 34 has a degree of flexibility. By rotating the spring carrier about pins 62 so that the forked end 125 moves rearwardly, the leaf spring 128 will be caused to act against the lower portion of the peripheral frame thereby increasing its stiffness against rearward flexing. The two spring carriers act in unison in a manner which will be described in connection with Figures 30 to 34. The stiffness of the lower portion of the peripheral frame 34 can thereby be adjusted by adjustment of the position of the spring carrier 60. Further, the channels 64 in which each of the spring carriers 60 are received are closed rearwardly by a rear wall 135 of the back attach casting 48. The rear wall 135 defines a stop against which the forked ends 125 of the spring carriers engage, thereby defining the maximum rotation of the spring carrier 60 and thus the maximum stiffness which can be imparted by the leaf spring 128 to the peripheral frame 34. Figure 30 illustrates the main elements of the recline mechanism. The back attach casting 48 has been removed for clarity, together with the right back extension arm 70. The left back extension arm 70 is shown in position pivotally connected to the main transom 22. The forked end 125 of each spring carrier 60 is connected to a push link 139. Reverting to Figure 3, it can be seen that the lowerportion of the peripheral frame 34 has an access opening 143 to enable the push link 139 to engage with the forked end 125 of the spring carrier 60 disposed within the assembled back attach casting 48. The forward end of the push link 139 is connected to a drive link 141 (see Figure 30) which is one element of a four bar linkage which will be understood more fully from a consideration of the schematic illustration of Figure 31. Figure 31 illustrates only one four bar linkage and it will be apparent to the reader that two such four bar linkages are provided, one on each side of the chair 10. The drive link 141 extends at an inclined upwards angle from its connection with push link 139. The drive link 141 is curved along its length with the centre of the curve being disposed rearwardly and upwardly. The drive link 141 is mainly of rectangular cross section. The drive link 141 is pivotally connected at an intermediate location along its length to the main transom 22 for pivoting motion about the recline axis R. Specifically, the drive link 141 is pivotally connected to lie adjacent to the outer one of the opposed supporting webs 78 of the main transom 22. A common pivot pin (not shown) interconnects both of the opposed supporting webs 78, the back attach arm 70 through aperture 75, and the drive link 141. The main transom 22 forms another element of the four bar linkage. As has already been explained, the main transom 22 is centrally mounted to the supporting frame at the top of the central support column 20 which incorporates a height adjustable pneumatic spring 145. The height adjustment 145 is selectively operable by the chair occupant. However, the main transom 22 is normally stationary relative to the supporting frame. The seat portion 14 is slidably mounted to a seat guide 149 in a manner which will be described more fully in connection with Figures 55 to 60. The seat guide 149 thereby forms another element of the four bar linkage. The upper end of the drive link 141 is pivotally connected to the seat guide 149. Another link in the form of a front support link 151 interconnects the seat guide 149 and the main transom 22. The front support link 151 is of generally rectangular cross section and, like the drive link 141 is curved along its length with the centre of curvature disposed upwardly and rearwardly. From Figure 30 it can be seen that both ends of the drive link 141 are forked. The lower end is forked to accommodate the lower end of the push link 139. The upper end of the drive link 141 is also forked. The seat guide also has a dependent lobe 155 as shown in Figure 32. The forked upper ends of drive link 141 are disposed on each side of the lobe 155 and the inner fork is pivotally connected between the lobe 155 and the side wall of the seat guide 149. The outer fork is fanned in shape for aesthetic reasons and the pivotal connection does not extend therethrough. Likewise, the upper end of the front support link 141 is also forked with the inner fork being pivotally connected between a seat guide 149 and another lobe 157 (see Figure 32), with the outer fork being of fanned shape. The lower end of the front support link 151 is pivotally connected on the outside of the outer one of the opposed supporting webs 78 (see Figure 4) by means of a pin (not shown) extending through aligned forward apertures 153 on the forward end of the opposed supporting webs 78. It will be appreciated that the connection of the lower end of the drive link 141 and the front support link 151 are blind connections as shown for aesthetic reasons. Operation of Recline Mechanism The operation of the recline mechanism will now be explained in connection with Figure 31. Reference is only made to the four bar linkage elements on one side of the chair. The reader will appreciate that the elements are duplicated on the other side of the chair. As already stated above, the back portion 16 is reclinable about recline axis R. First and second recline springs bias the seat portion 16 into the forward active position. In the unoccupied state, the arrangement of the elements of the four bar linkage is determined by the spring tension of leaf spring 128. The natural resiliency of the leaf spring 128 will tend to straighten the leaf spring 128 thereby urging the spring carrier 60 in a clockwise direction about the pins 62. This determines the position of the push link in the unoccupied state of the chair. With no force exerted on the seat guide 149, the elements of the four bar linkage will be held in an unoccupied position on account of the natural resiliency of the spring 128 acting through push link 139. When a user bears weight W against the seat portion 14, this will be taken up by the seat guide 149 whereby the drive link 141 will be driven to rotate in an anticlockwise direction around recline axis R. This will cause the push link 139 to move generally upwardly and rearwardly thereby rotating spring carrier 60 anticlockwise about pivot pins 62. The lower portion of the peripheral frame 34 is rigidly held within back attach casting 48 which is stopped in its forward active position as already explained. With anticlockwise rotation of the spring carrier 60, the leaf spring 128 will be caused to bend with the upper part pushing against the back of the peripheral frame 34. Depending upon the flexibility of the peripheral frame 34, the occupant's weight will be taken up by a spring tension in leaf spring 128 as it flexes against the back of the peripheral frame 34. This has the effect of stiffening the back portion against rearward flexing. It will be appreciated that the tension imparted to leaf spring 128 will depend upon the weight of the user W applied to the seat portion 14. The greater the weight W, the greater the tension taken up by the leaf spring 128 and thus the greater the degree of stiffness imparted to the leaf spring 128 to resist rearward flexing of the peripheral frame 34. Accordingly, the stiffness of the peripheral frame 34 will be adjusted according to the weight W of the chair occupant. If the occupant's weigh W exceeds a predetermined level then the leaf spring 128 will be tensioned to a point where the forked end 125 of the spring carrier 60 engages against the rear wall 135 of the back attach casting 48. This provides a limit to the amount of tension imparted to the leaf spring 128. The limit is reached at about 80 kg. Figure 33 illustrates the downward motion of the seat guide 149 as the user applies weight W. When the occupant alights from the chair, the seat portion 14 will move upwardly as indicated by arrow U in Figure 34. As already mentioned, the gentle serpentine shape of the peripheral frame 34 is designed to correspond with the shape of the occupant's spine for the comfort of the occupant. With the flexing action of the back portion, the ergonomies of the chair are further enhanced because this enables the occupant to exercise his spine. The general health of a person's spine is enhanced by movement. The stiffness of the back portion in rearward flexing is adjusted according to the occupant's weight. Therefore, within a certain range, the ease of rearward flexing will correlate to the weight of the occupant. Therefore, a light person will be able to obtain full benefit from the rearward flexing action by applying a light force against the peripheral frame. Also, a heavier person will encounter a greater resistance to flexing, ensuring that the peripheral frame is not too floppy for a large person. The chair is designed so that, the occupant will be able to obtain deflection through flexing in the range of 80 mm to 120 mm. Figure 35 illustrates the reclining action of the chair 10. When the user applies their weight to the seat portion 14, the seat portion will move downwardly as already described and adopt a position just above the seat guide 149 as illustrated by the solid lines. Once a user has applied their weight to the seat portion 14, the leaf spring 128 takes up a corresponding amount of spring tension whereupon the spring carrier 60 and the push link 139 will adopt a more or less fixed position relative to the back attach casting 48. Therefore, as the user leans against the back portion 16, the back attach casting 48, spring carrier 60, push link 139 act in unison driving the drive arm 141 to rotate in a clockwise direction through push link 139. The arrangement of the four bar linkage is such that the seat guide 149 will adopt a position with a net increase in height and with an increase in rearward tilt angle compared to the occupied position of the seat guide 149 before recline. In practice, there may be some slight shifting between the leaf spring 128, the spring carrier 60 and the push link 139. Since the seat portion 14 undergoes a net increase in height with the rearward recline action, the occupant's weight W will be counteracting the recline action, together with the bias applied by the first and second recline springs 94,96. The weight of the occupant W will therefore be a variable factor in the case with which the back portion 16 reclines. If the adjustable second recline spring 96 is set at a constant level then a heavier person will encounter a greater resistance to reclining action than a lighter person. This establishes an automatic correlation between the weight of the person and the resistance to the reclining action. For a large proportion of people who fit within physical norms this automatic adjustment may be sufficient However people come in all different shapes and sizes and therefore additional adjustment is required through the use of the clamping adjustment as explained previously. For example, a very tall, light person may obtain leverage through their height which makes the back portion 16 fall back too easily against their low weight W. The net increase in height also has the advantage of raising the occupant during recline so that the eye level of the chair occupant can be maintained even though he is undergoing a reclining action. Once the chair is fully reclined (as determined by the first abutment surface 88 engaging against second abutment surface 90), the peripheral frame will still be able to flex under additional force applied by the chair occupant. As already mentioned, it is considered that the peripheral frame will be capable of undergoing deflection in the range of 80 mm to 120 mm. During the recline action, it is considered that the weight of the user against the back portion will bring about a deflection of up to 20 mm. Therefore, once the recline limit is reached, the occupant still has further deflection available through flexing of the peripheral frame in the range of 60 to 100 mm. As explained subsequently in connection with Figures 55 to 60, the seat portion 14 is only supported by the seat guide 149 at a rear portion thereof with a forward portion being unsupported. As shown in Figure 32, a transition point 161 is disposed behind the forward edge 160 of the seat guide 149. The transition point 161 marks the boundary between the planar upper surface 178 of the scat guide 149 and a forwardly inclined lead surface 285. The seat portion 149 is foldable transversely at this location. The transition point 161 hence defines the division between the rearward portion and the forward portion of the seat portion 14. Since the seat portion 14 is slidable forwardly and rearwardly for seat depth adjustment as will be explained in connection with Figures 55 to 60, the division between rearward portion and forward portion of the seat will vary as a function of seat depth. Figure 35 illustrates the changing curvature of the back portion 16 and seat portion 14 in recline. The solid lines indicate the forward active position in the occupied configuration. The dotted lines illustrate the reclined position. As the back portion 16 reclines, the seat guide 149 attains a net increase in height and an increased rearward tilt. This effectively cups the occupant's derrière, negating any inclination to slide forwardly during the recline action. The seat portion 14 is also flexible and since the occupant's derrière is undergoing a net increase in height together with increased rearward tilt, a greater amount of weight from the occupant's legs will be brought to bear against the forward portion of the seat portion 14. Accordingly, the seat portion 14, will be allowed to fold transversely at the transition point 161 on the seat guide 149. To achieve maximum benefit from the cupping action, the occupant ought to adjust the seat depth so that with his derriere abutting the back portion, transition point 161 approximately corresponds to the gluteal fold of the occupant's derriere. Therefore, during recline, the occupant's derriere will be cupped between the rear portion of the seat portion 14 and a lower region of the back portion 16 while the forward portion of the seat drops forwardly under the weight of the occupant's legs. Locating the transverse fold at the gluteal fold of the occupant ensures that undesirable pressure will not be brought to bear against the back of the occupant's legs. Seat Panel Figure 46 is a perspective view of a preferred form of the seat portion 14. The seat portion 14 is in the form of a flexible plastic panel, whose flexibility is enhanced by the arrangement of slots as indicated. The plastic panel may be injection moulded plastic such as TPR. It will be noted that while the seat panel 14 is depicted in the computer generated drawings of Figures 47-49 to be a flat panel, the seat panel is in fact dish shaped as can be seen from the schematic views illustrating the various cross-sections in Figures 50 to 54. Figure 50 is a longitudinal section through the middle of the seat panel 14 illustrating the general curved configuration with a rolled over edge. The edge drops by an amount of dimension A. Figure 51 illustrates the side edge of the seat panel 14. The side edge is flatter than the middle section. Additionally, the forward edge dips down a dimension B, where B is larger than A. Figure 52 illustrates a transverse sectional view at about 150 mm from the rear of the seat whereas the view Figure 53 depicts the transverse cross sectional view 120 mm from the front edge. This is essentially a flat shape. Therefore, the rear part of the seat behind 120 mm from the front edge is essentially dished for user comfort whereas in front of this, the seat portion inclines downwardly in the forward direction. Additionally, as can be seen in Figure 54, the front edge is also curved so as to incline downwardly toward the sides. The illustrations in Figures 50-54 are merely indicative of the moulded shape of the seat panel 14. The seat panel is also flexible to accommodate the occupant and to respond to movement of the occupant The arrangement of slots in the seat panel 14 as shown in Figure 46 is designed to enhance the flexibility of the seat panel 14. The mangement of slots in the forward half of the panel is designed to facilitate folding along the transverse fold. In particular, it can be seen that the slots are arranged in a series of spaced sinuous lines 163 extending transversely across the seat portion 14 with the central part being shaped convex forwardly with the outer parts being shaped concave forwardly. The lines of slots 163 are discontinuous. As already explained, the seat portion 14 is dished at least in a rearward part. This dishing may be accentuated by the occupant in the seat. The series of spaced sinuous lines 163 enables the seat panel 14 to fold transversely, even though the rear part is dished. Furthermore, at the front corners, the slotted pattern 164 is such as to extend diagonally across the corners following the curvature of the transverse sinuous lines 163: In this way, if the user moves a leg to one of the forward corners then the diagonal arrangement of the slots 164 will enable the forward corner to fold under the weight of the occupant's leg. In the rear half of the panel, the slots are arranged in a pattern to accommodate the ischial protuberosities of the occupant. In particular, the slotted pattern provides two spaced, approximately rectangular zones 162 whose locations correspond to the ischial protuberosities of the occupant (assuming the occupant is properly seated with an appropriate seat depth adjustment). The two zones 162 interrupt the transverse slot pattern. Each zone is comprised of slots arranged in a series of longitudinally extending, transversely spaced sinuous lines. The lines of slots are discontinuous. The longitudinal arrangement of slots in each zone 162 enables the remaining material between the longitudinal lines of slots to spread apart thereby creating pockets, one for each ischial protuberosity of the seat occupant. Figure 47 illustrates longitudinal stiffening webs 165 provided on the underside of seat panel 14. There are five stiffening webs, two disposed along the opposite side edges. A further two are disposed on each side at 60 mm from the corresponding side edge. Another is centrally disposed. The longitudinal stiffening webs are constant in height from the back edge of the seat portion until the taper start point 164 from where they progressively reduce in height until a taper finish point 166. (The central web however terminates early) The seat portion 14 accommodates a depth adjustment as will be explained in connection with Figures SS to 60. The seat portion folds transversely about the transition point 161 on the seat guide 149. It will be appreciated that if the seat panel 14 is located in a rearward position in order to suit a small person then the depth of the stiffening ribs in the region at the transition point 161 is shallow thereby offering little resistance to flexing. Generally, this suits a small, light weight person. However, for a larger person, the seat panel will be disposed further forwardly in relation to the seat guide 149. The depth of the stiffening ribs in the location of the transition point 161 will be deeper, thereby offering increased resistance to bending. This suits a larger, heavier person. The start taper point 164 is at a position which corresponds to the transition point 161 when the seat is at its full forward position to suit a large person. The taper finish point 166 is at a position corresponding to the transition point on the seat guide 149 with the seat in the rear most position to suit a small person. The taper start point 164 and the taper finish point 161 define a transition zone therebetween. The transverse fold may be disposed at a range of positions within the transition zone, dependent on seat depth adjustment. The pattern of transversely extending sinuous lines of slots extends for at least the transition zone. Figure 47 also illustrates transverse stiffening webs 168. The stiffening webs 168 follow the pattern of the transversely arranged sinuous slots 163. As already explained, the seat panel is moulded in a dished shape. However, it is desirable to limit curvature, especially about a longitudinal axis at the front part of the seat portion. Accordingly, the transverse stiffening webs 168 help to retain the shape of the front part without inhibiting the transverse folding action under the weight of the user. Additionally, a back web is provided along the back of the seat panel 14 on the underside as shown in Figure 47. Figure 49 illustrates in greater detail the arrangement of features along one side edge. Between the two longitudinal webs 465 is a series of spacer blocks 270 extending in a line between the taper start point 164 and the taper finish point 166. Between each of the spacer blocks 270 is a wedge-shaped gap 272 widening towards the top. As will be explained in connection with Figures 55 to 60, the seat panel 14 sits atop a seat carriage 167. Depending upon me position of me seat carriage 167 relative to the seat guide 149, there will normally be a forward portion of the seat guide 149 (including the lead surface 285) in front of the seat carriage 167. A rear part of the seat panel 14 is secured atop the seat carriage 167 so that forwardly of the seat caniage 167 mere will be a gap between the seat guide 149 and the seat panel 14. The spacer blocks 270 extend into this gap. As the seat panel 14 folds, the spacer blocks 270 bear against the top of the seat guide 149. It can be seen that the spacer blocks 270 also taper off in height as shown. Furthermore, the spacer blocks 270 will define the maximum curvature of the seat panel along the transverse fold since once the side walls of the wedge-shaped gaps 272 engaged with each other, further curvature will be prevented. A guard also extends alongside the spacer blocks 270 to provide a barrier against the user's fingers being trapped. Seat Depth Adjustment Mechanism Figure 55 illustrates the main elements of the seat depth adjustment mechanism. The seat guide 149 is one of the elements of the four bar linkage discussed previously. There are two seat guides 149 disposed on opposite sides of the chair. The two seat guides 149 provide a guide for a slidable seat carriage 167. A rear part of the seat panel 14 illustrated in Figures 47-54 is attached to the carriage 167. The rear half only of the seat panel 14 is attached to the seat carriage 167. The seat panel 14 may be moved forwardly and rearwardly by the sliding action of the seat carriage 167 on the seat guide 149. As shown in Figure 49, rearwardly of the spacer blocks 270 on the underside of the seat panel 14 is a longitudinally extending rib 274 and then a short tab 276 spaced rearwardly of the longitudinally extending rib 274. The rib 274 engages within a channel 278 (see Figure 55) of the seat carriage 167 and the tab 276 is a snap fit connection within the recess 280 located rearwardly on the seat carriage 167. Furthermore, four spaced retention tabs 282 engage against soffit 284 of the carriage 167. The retention tabs 282 retain the seat panel 14 engaged with the seat carriage 167 while the longitudinal rib is the main load bearing part. Figure 55 also illustrates the controls for the height adjustable pneumatic spring 145. A height adjustment control lever 169 is mounted for pivotal motion on the outside of the right hand seat guide 149. The pivotal motion of the height adjustment control lever 169 is replicated by the height adjustment control actuator 170 which is connected to one end of a control cable 172. The other end of the control cable 172 is connected to the top end of pneumatic gas spring 145. As the user lifts the height adjustment control lever 169, the control cable 172 releases the gas spring in the conventional known manner and the chair occupant adjusts the height of the seat portion 14 to suit his requirements. Figure 56 is a further detailed view of the left side of the seat carriage 167. The seat guide 149 includes a plastic seat guide liner 176. The seat guide liner is of elongate configuration with an upper glide surface 178 and an inner glide surface 180. The inner glide surface 180 is spaced from the inner side of the metal part seat guide 149 with a peripheral wall 182 maintaining the inner glide surface 180 in spaced configuration therefrom. The seat guide liner 176 is thereby hollow behind the inner glide surface 180. The upper glide surface 178 is received within a rebate in the upper surface of the metal part of the seat guide 149 in order that the upper glide surface 178 is contiguous with the upper surface of the metal part of the seat guide 149. The seat guide liner 176 provides a bearing surface for easy sliding of the seat carriage 167. As such, the seat guide liner 176 may be comprised of nylon or acetal. The reader will appreciate that a symmetrical arrangement is provided on the right hand side of the chair. The seat carriage 167 is of unitary cast aluminum construction and comprises two spaced slides, each of which engages with a respective seat guide 149. Each slide is of a generally L-shaped configuration having an upright glide surface 186 on an inner wall for sliding engagement with the inner glide surface 180 and a horizontal glide surface 187 for engaging with the upper glide surface 178. The carriage is of a symmetrical configuration about a central upright longitudinally extending plane of the chair. The two slides provided on the right and left are thereby of opposite configuration. The two slides are joined by transversely extending bearers 190. The inner glide surface 180 is moulded with a series of archlets which extend from the inner glide surface 180. The archlets 184 protrude inwardly (relative to the chair as a whole) to bear against the upright glide surface 186 of the seat carriage 167. The archlets may be arranged in any pattern but preferably they are staggered along the length of the inner glide surface 180. Both of the seat guide liners 176 have inwardly extending archlets bearing against the associated upright glide surfaces of 186 of the carriage 167. The archlets 184 thereby act against the carriage to centre the carriage 167 centrally between the two seat guides 149. Furthermore, in the event that the parts are not accurately tooled, the resilient archlets 184 will take up any slack between the upright glide surface 186 and the inner glide surface 180. This assists to prevent jamming of the carriage 167 within the seat guides 149. Figure 57 illustrates the control for seat depth adjustment. The inner wall of both slides 185 have a lower edge with a series of spaced notches 192. A seat depth adjustment bar 194 has two teeth 196, each arranged at opposite ends of the bar 194. The seat depth adjustment bar 194 is moveable between a latched position in which the teeth 196 engage in a respective one of the notches 192 and an unlatched position in which the carriage 167 is free to slide along the seat guide 149. The seat depth adjustment bar 194 is controlled by a seat depth adjustment button 200. The seat depth adjustment button 200 is moveable from the latched position against the bias of a spring (not shown) to move the seat depth adjustment bar 194 into the unlatched position whereby the teeth 196 no longer engage in the notches 192. The seat carriage 167 can then be slid to an appropriate seat depth whereupon the occupant releases the seat depth adjustment button 200 to enable the teeth 196 to engage with the closest of the notches 192. A seat depth stop 174 (Figure 55) formed as a dependent projection from the seat carriage 167 determines the forward position of the seat carriage 167 as it engages with the adjustment bar 194 or sleeves 158 receiving the ends of the adjustment bar 194. The rear limit is defined by a pin (not shown) extending inwardly from the seat guide 149 to engage within a slot of the seat carriage 167. The slot is machined to define a stop to engage with the join in the rear most position of the seat portion. Figures 58 and 59 illustrate the extended and retracted positions respectively of the seat portion 14. Seat Depth Adjustment - Second Embodiment Figure 61 and 62 illustrate a modified form of the seat carriage 167 and the seat guide 149'. The seat carriage 167' is a unitary cast aluminum construction with two spaced slides as explained with the first embodiment, each of which engage with a respective seat guide 149'. The two slides are joined by a unitary deck construction having a series of transversely extending ribs as shown. As with the previous embodiment, the seat guides 149' include seat guide liners 176' having an upper glide surface 178' and an inner glide surface 180' to slidably engage with the respective slide of the seat carriage 167'. The seat guide liners 176' will be described in greater detail in connection with Figure 62b and 62c. As shown in Figure 61, the second embodiment of the chair includes a control lever 169' on the right hand side (left hand side of the figure). This lever 169' is a dual actuator for both the seat height adjustment and seat depth adjument. The control lem 169 is mounted for pivotal motion on the outside of the right hand seat guide 149'. The control lever 169' effects the operation of a dual actuator 170' mounted on the inside of the right band seat guide 149'. The actuator 170' includes a first actuator portion 170a and a second actuator portion 170b. The first actuator portion 170a is connected to cable 172' which connects to the top end of a pneumatic gas spring 145'. As the user raises the control lever 169', the control cable 172' releases the gas spring in the conventional known manner and the chair occupant adjusts the height of the seat portion 14 to suit his requirements. The second actuator portion 170b is connected via cable 488 to a pivotable pawl 490. The pawl is engageable between any one of a plurality of teeth provided on a rack 492 formed on the underside of the seat carriage 167'. The pawl and rack arrangement 490, 492 is also duplicated on the other side of the seat carriage 167' as shown in Figure 62. The cable 488 passes from the right hand pawl 490 around to the other side of the seat carriage 167' for simultaneous operation of the two pawls 490. The user depresses the control lever 169' to operate the second actuator portion 170b to pivot the two pawls against a bias out of engagement with the teeth of the associated rack 492. The seat carriage 167' can then be slid to an appropriate seat depth where upon the occupant releases the control lever 169' to enable each of the pawls 490 to engage with the associated rack 492. Figure 61 also illustrates a forward cover 495 which is shaped in a serpentine manner for aesthetic purposes to extend in front of the main transom 22'. The cover 495 is joined to the seat guides 149' on each side through the use of integrally formed bosses 497 which can be seen in Figure 62b and Figure 62c. As already explained, the seat guide 149' illustrated in Figure 62b includes a seat guide liner 176'. The seat guide liner 176' includes an upper glide surface 178' and an inner glide surface 180'. Thus, the seat guide liner 176' is essentially L-shaped in configuration. The inner glide surface 180 is formed with a series of spaced integral resilient projections 500. The integral resilient projections 500 are directed inwardly. The seat guide liner 176' is supported on a metal supporting part of the seat guide liner as shown in Figure 62c. The inner glide surface 180 is disposed in spaced configuration from the inside of the supporting part of the seat guide 149'. Additionally, the supporting part of the seat guide 149' includes three spaced rests 502. The integral resilient projections 500 are shaped like ramps, the ends of which engage against the associated rest 502. The majority of the inner glide surface 180' is thereby resiliently held in spaced configuration from the supporting part of the seat guide 149'. It can been seen in Figure 59 of the first embodiment that a gap exists between the top surface of the seat guide 149 and the spacer blocks 270 which extend from the seat panel 14. This gap might be one in which the occupant can get their fingers caught. Accordingly, a movable comb like formation 504 is incorporated into the seat guide liner 176' as shown in Figure 62b. The comb like formation 504 has an upper surface continuous with the upper glide surface 178' and dependent prongs 506 which extend downwardly. The prongs are receivable into a series of corresponding pits 508 formed in the metal supporting part of the seat guide 149'. The movable comb like formation 504 is resiliently flexible and would normally extend to fill the gap between the leading edge 285 of the seat guide 149' and the dependent spacer blocks 270'. For instance, see Figure 63 although in Figure 63, the occupant's weight is not yet bearing on seat panel 14 and thus the seat panel 14 has not yet come to rest on top of the comb like formation 504. Additionally, the dependent spacer blocks are not visible in this view because the seat panel 14 has a peripheral guard to prevent jamming of fingers in the V-shaped gaps of the spacer blocks 270'. When the user's weight bears forwardly of the seat panel 14, the spacer blocks 270' will come to bear against the comb like formation 504 which will deflect as the seat portion 14 folds about the transverse fold. In this way, the comb like formation 504 presents an additional guard to mitigate the likelihood of user's fingers being caught between the seat panel 14 and the seat guide 149'. However, the comb like formation 504 does not interfere with the transverse folding of the seat panel 14. Figure 63 illustrates the seat panel 14 in its inward retracted position whereas Figure 64 illustrates the seat panel 14 located in its outer most extended position. Figure 89 illustrates in schematic form, the underside of the slotted seat panel 14. Mounted to the underside of the seat panel 14 is a scabbard which is curved in form. The scabbard 350 houses an instruction slide 352 which is also curved and slides in and out of the scabbard at one end. From above, the instruction slide 352 has printed indicia thereon providing user instructions to the seat occupant. The foregoing describes embodiments of the present invention and features not forming part of the present invention and modifications may be made thereto without departing from the scope of the appended claims.

Claims: A seat portion (14) for a seat wherein the seat portion comprises a panel comprising a rear portion to support the occupant and a remainder portion, the rear portion having a central section extending along a longitudinal centreline and two spaced apart, flexible zones (162), one on either side of the central section, each of the flexible zones comprising a first pattern of weakeners arranged in a series of spaced sinuous lines, and wherein the flexible zones are more flexible than the central section and at least a major part of the remainder of the panel. The seat portion as claimed in claim 1 wherein the sinuous lines extend longitudinally. The seat portion as claimed in claim 2 wherein the sinuous lines are discontinuous. The seat portion as claimed in claim 1 wherein the weakeners are in the form of apertures. The seat portion as claimed in claim 3 wherein the weakeners are in the form of slots. The seat portion as claimed in claim 1 wherein the zones are substantially rectangular. The seat portion as claimed in claim 1 wherein the seat portion further comprises a forward portion integrally formed with the rear portion. The seat portion as claimed in claim 7 wherein a substantial part of the seat portion, apart from the zones is provided with a second pattern of weakeners. The seat portion as claimed in claim 8 wherein the second pattern of weakeners is arranged as a series of spaced sinuous lines. The seat portion as claimed in claim 9 wherein the sinuous lines of the second pattern are transversely extending. The seat portion as claimed in claim 10 wherein weakeners of the second pattern are in the form of apertures. The seat portion as claimed in claim 10 wherein the weakeners of the second pattern are in the form of slots. The seat portion as claimed in claim 12 wherein the sinuous lines of the second pattern are discontinuous. The seat portion as claimed in claim 10 wherein the frequency of the sinuous lines in the first pattern is greater than the frequency of the sinuous lines in the second pattern. The seat portion as claimed in claim 10 wherein the sinuous lines in the first pattern are more closely spaced than the sinuous lines in the second pattern. The seat portion as claimed in claim 1 wherein the seat portion is a unitary plastic panel. The seat portion as claimed in claim 16 wherein the panel is moulded to form a dished shape in the rear and, at approximately one third of the length of the seat panel from the front edge along the longitudinal centreline, there is a transverse plateau portion which is generally flat with the seat portion dipping downwardly, forwardly of the transverse plateau portion. The seat portion as claimed in claim 17 wherein each of the front corners dip downwardly. The seat portion as claimed in claim 9 wherein stiffening webs are incorporated on the underside of the panel. The seat portion as claimed in claim 19 wherein the stiffening webs extend in the transverse direction and are disposed in between the lines of weakeners, following the pattern of spaced transversely extending sinuous lines.

Inventors: PENNINGTON MARK RUNDLE, PRINCE JONATHAN WILLIAM, PENNINGTON, MARK RUNDLE, PRINCE, JONATHAN WILLIAM
Applicants: FORMWAY FURNITURE LTD, FORMWAY FURNITURE LIMITED
Application year: 2001
Main classification: A47C7
IPC codes: A47C5, A47C7, A47C1, A47C3