Abstract:
A backrest for use with a chair includes a support structure. The support structure has a rigid outer rim and flexible inner back support section. The support section consist of a number of generally parallel slats (vertically extending members) which seperately support parallel longitudinal sections of the person&#39;s back. Each slat produces a force against the person&#39;s back responsive to the weight placed on the slat by the person&#39;s back. As the person shifts positions, each slat moves to dynamically provide an increased or decreased force against the person&#39;s back, depending on whether the person is applying an increased or decreased force against the slat.

Description:
FIELD OF THE INVENTION 
     This invention relates to backrests for chairs. More particularly, the invention relates to a backrest that provides adjustable support to the lumbar region of the back of a user seated on a chair. 
     BACKGROUND OF THE INVENTION 
     Backrests that provide lumbar support are known. The majority of these backrests have a non-adjustable lumbar support. The lumbar support is built into the back rest and is therefore configured to provide adequate support for a typical person. In practice, such backrests provide inadequate support for people who are larger or smaller than average. Adjustable lumbar supports are also known, however, these devices tend to have complex adjustment mechanisms that are both heavy and costly. 
     For example, Kemmann describes an adjustable backrest in U.S. Pat. No. 4,810,033. This backrest has an outer frame that holds a deformable plate that provides lumbar support. The top portion of the plate (i.e. the region of the plate nearer the upper back of a user) is formed into a series of longitudinal slats, running from the top of the lumbar support to its centre. The lower portion of the lumbar support plate (i.e. the portion which actually supports the user&#39;s back) does not have any openings and is less flexible. A control knob is drivingly connected to the plate through a complex mechanism and is rotatably mounted to change the position of the lower portion of the plate to force the plate outwardly to whereby the plate provides lumbar support. 
     One disadvantage of lumbar adjustment mechanisms is that they utilize complex and costly adjustment mechanisms. Therefore, they tend to be provided on more expensive chairs. Thus they may be provided on chairs for executives and professionals but not an secretarial chairs who would also benefit from a more ergonomic chair. Further, due to the complexity of the mechanism, the mechanism is prone to breaking. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the instant invention, there is provided a backrest for supporting a person&#39;s back having a front surface and a rear surface, the backrest comprising a flexible support section having a fixed end which is mounted to a support structure and a free end which is displaceable vertically with respect to the fixed end, the support section is configured to be compressed and displaced forwardly when the free end is moved towards the fixed end; an adjustment member drivingly connected to the free end; and a detent member for selectively receiving the adjustment member in one of a plurality of positions, the support member biasing the adjustment member into retaining engagement with the detent member due to the compression of the flexible support member by the displacement of the free end towards the fixed end. This provides a simple, reliable mechanical adjustment member for a back rest of a chair and, preferably for the lumbar support member of a back rest. 
     In one embodiment, the support structure comprises a frame and a shell mounted on the frame and the support section is provided as part of the shell. 
     In another embodiment, the frame has an opening sized to receive therein the support section. 
     In another embodiment, the support member comprises a plurality of slats extending vertically between the fixed end and the free end of the support section. 
     In another embodiment, the slats extend from a position adjacent the fixed end to a position adjacent the free end. 
     In another embodiment, the shell comprises a perimeter section surrounding a central section in which the support structure is provided and, when mounted on a chair, the support structure has a vertical extent sufficient to support at least the lumbar region of the person when seated in the chair. 
     In another embodiment, the shell has first engagement members and the frame has second engagement members configured to engage the first engagement members whereby the engagement of the first and second engagement members retains the shell on the frame. 
     In another embodiment, one of the first engagement members and the second engagement members comprise a plurality of openings and the other of the first and second engagement members comprises projecting members that are locking received in the openings. 
     In another embodiment, the fixed end comprises the upper end and the free end comprises the lower end and the detent member comprise a plurality of vertically spaced apart members each of which has a downwardly extending recess and the adjustment member is sized to be received in each recess. 
     In another embodiment, the detent member comprises a plurality of vertically spaced apart members each of which has a recess to receive therein the adjustment member and support member biases the adjustment member into engagement with the recesses. 
     In another embodiment, the frame has a front face and a vertically extending opening adjacent the free end, the shell is mounted on the front face, the adjustment member is mounted at the free end of the support structure and has a handle which extends through the vertically extending opening whereby the support structure may be actuated from the rear of the backrest. 
     In accordance with another aspect of the instant invention, there is provided a backrest for supporting a user&#39;s back having a front surface and a rear surface, the backrest comprising a frame; a shell mounted on the frame, the shell having a flexible support section; and first engagement members provided an the shell and second engagement members provided on the frame, the second engagement members are configured to engage the first engagement members whereby the engagement of the first and second engagement members retains the shell on the frame. This construction provides a simple and easily manufacturable flexible back rest for a chair. 
     In accordance with another aspect of the instant invention, there is provided a backrest a backrest for supporting a user&#39;s back having a front surface and a rear surface, the backrest comprising a shell having a perimeter section surrounding a central section and a plurality of slats extending vertically between the perimeter to occupy the central section and, when mounted on a chair, the slats have a vertical extent sufficient to support at least the lumbar and mid back regions of the person when seated in the chair; a frame having an opening sized to receive therein the slats; and mounting members to mount the shell on the frame. This construction provides a simple and easily manufacturable flexible back rest for a chair. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be explained, by way of example only, with reference to the drawings in which: 
     FIG. 1 is a front perspective view of a first embodiment of a backrest according to the present invention; 
     FIG. 2 is a rear perspective view of the backrest of FIG. 1; 
     FIG. 3 is a front perspective view of the frame of the backrest of FIG. 1 without the lumbar support shell; 
     FIG. 4 is a front perspective view of a lumbar support shell of the backrest of FIG. 1; 
     FIG. 5 is an enlarged exploded view of the lever and a handle of the backrest of FIG. 1; 
     FIG. 6 is a sectional view along the line  6 ′— 6 ′ of the backrest of FIG. 1 in a first position; 
     FIG. 7 is a sectional view along the line  6 ′— 6 ′ of the backrest of FIG. 1 in a second position; 
     FIG. 8 is a perspective view of the backrest of FIG. 1 when in use by a person; 
     FIG. 9 is a sectional view along the line  9 — 9  of the backrest of FIG. 1 illustrating the flexing of the lumbar support shell when a person is seated upright in the chair; 
     FIG. 10 is a sectional view along the line  9 — 9  of the backrest of FIG. 1 illustrating the flexing of the lumbar support shell when the person using it turns to one side; 
     FIG. 11 is a front perspective view of a second embodiment of a backrest according to the present invention; and, 
     FIG. 12 is a rear perspective view of the backrest of FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference is first made to, FIGS. 1 and 2, which show an exemplary backrest  20  made according to the present invention. Backrest  20  is comprised of a frame  22  (see FIG. 3) a support shell  24  (see FIG.  4 ), a lever  25  (see FIG. 5) and is adapted to be mounted to a chair having a seat. 
     Frame  22  may be of any particular shape that provides a mount for receiving support shell  24 . As shown in FIGS. 1,  2 , and  3 , frame  22  has a top  40 , a bottom  42 , and opposed front and rear sides  54  and  56 . Top  40  and bottom  42  define a longitudinal or vertical axis  44  and the outer perimeter of frame  22 . Preferably, backrest  20  is covered with padding (eg. foam) and a covering (eg. cloth or leather). As such, except for the added dimension contributed by the padding, the outer perimeter of backrest  20  is substantially the same as that of frame  22 . 
     Frame  22  may be mounted to the chair by any means known in the art. Thus backrest  20  may be mounted to the seat support of the chair or to the seat itself. In the embodiment shown in FIGS. 1,  2  and  3 , frame  22  has a mounting section  26  at its bottom which may be mounted either to a seat support of a chair or to a seat itself. Base section  28  extends between mounting section  26  at top  40 . Mounting section  26  and base section  28  meet at corner  34 . Mounting section  26  has a number of mounting holes  30  that may be used to mount frame  22  onto a seat or base of a chair (not shown). Optionally, mounting section  26  has a U-shaped reinforcing ridge  27  extending from its bottom. Reinforcing ridge  27  increases the rigidity of mounting section  26  so that it will not substantially flex during use. Mounting section  26  and base section  28  are preferably connected by a number of ribs  32 . Ribs  32  provide increased strength at corner  34  so as to ensure that mounting section  26  and base section  28  are not easily pulled apart at corner  34 . 
     In one preferred embodiment, support shell  24  is adapted to be mounted on frame  22  and to provide a mount for flexible support section  66 . Accordingly, support shell  24  may be of any particular shape which is sized to be received on frame  22 . As shown in FIG. 4, support shell  24  has a top  80 , a bottom  81 , a front side  60 , a rear side  62 , left side  76  and a right side  78 . Top  80  and bottom  81  define a longitudinal axis  83 , which is parallel to the longitudinal axis  44  of frame  22 , when support shell  24  is mounted on frame  22 . 
     Flexible support section  66  may be of any configuration which will bow outwardly when compressed to provide variable support to a person seated in a chair to which backrest  20  is affixed. When at least one of the upper and lower ends of flexible support section  66  is displaced towards the other, flexible support section  66  is compressed and bows outwardly (frontwardly) to provide support (or an additional amount of support) to a person seated in the chair. To permit the discrete adjustments of the amount of support provided by flexible support section  66 , frame  22  is provided with at least one detent member (eg. support rib  48 ) for releasably receiving at least one abutment member which is drivingly connected to flexible support section  66  to compress flexible support section  66 . Preferably, detent members have an upper surface for receiving therein the abutment member. Flexible support section may be positioned so that when backrest  20  is mounted on a chair, it provides lumbar support to a person seated in the chair. However, this arrangement may be used to provide flexible support to other portions of the back of a person and in one embodiment, provides support to the lumbar and mid back of a person. 
     In one aspect of this invention there is provided a flexible support section  66  which is not adjustable to vary the amount of support provided. In such a case, flexible support structure extends vertically from one opposed side of perimeter  64  to the other opposed side of perimeter  64 . In such an embodiment, the advantages of the simplified construction of the flexible back rest this design is still obtained. 
     In another aspect of this invention, flexible support structure advantageously utilizes the simple adjustment mechanism of this design to allow the amount of support to be varied. In this embodiment, flexible support section  66  has a fixed end  70  and a free end  72 . Fixed end  70  is joined to rim  64 , while free end  72  is independently moved longitudinally toward or away from fixed end  70 . In such an embodiment, it will be appreciated that support shell  24  and frame  22  may be integrally moulded as a unit. In such a case the integral unit comprises a support structure for the flexible support section. Regardless of the mechanism used, frame  22  and shell  24  define a one piece assembly and provide a support for slats  84  so that free end  72  of slats  84  may be moved along axis  83  whereby the compression of slats  84  biases the adjustment member (eg. rod  90 ) into the detent member (eg. notch or recesses  49 ,  50 ,  51 ). 
     In the preferred embodiment shown in FIGS. 1,  3  and  4 , a two piece construction is used and support shell  24  may be mounted to frame  22  by any means known in the art. Accordingly, support shell  24  and frame  22  may be releasably mounted together by releasable male and female engagement members. Alternately, support shell  24  and frame  22  may be permanently connected together by mechanical means (eg. screws or rivets) or by chemical means (eg. an adhesive of spot welding) or by the non-releasable interengagement of elements. 
     In the embodiment of FIG. 3, shell  24  and frame  22  are assembled together by first and second engagement members that are preferably male and female engagement members  36  and  74 . Male engagement members  36  comprise a plurality of mounting tabs spaced around the periphery of an opening  38  (see FIG.  3 ). Each mounting tab  36  has a hook  37 . Female engagement members  74  comprises a plurality of mounting slots which are positioned to receivably engage mounting tabs  36 . 
     As shown in FIG. 4, rim  64  has a plurality of mounting slots  74  which are aligned with mounting tabs  36  of frame  22 . Support shell  24  is mounted on frame  22  by inserting mounting tabs  36  through mounting slots  74 . The hook  37  of each mounting tab  36  catches one side of the corresponding mounting slot  74  and thereby holds support shell  24  fixedly on the front surface of frame  22 . 
     Support shell  24  is preferably sized such that rim  64  extends slightly outwardly of the edge of frame  22  along its left side  76 , its right side  78  and its top  80 . A lip  82  is formed along left side  76 , right side  78  and top  80  of support shell  24 . A lip  82  which extends rearwardly from the surface of support shell  24  is preferably provided to add rigidity to rim  64 . 
     Flexible support section  66  may be a thin plastic plate. In either embodiment, flexible support section  66  is preferably divided into a plurality of slats  84  by longitudinal slots  86 . In the preferred embodiment shown in the Figures, there are three slots  86  providing four slats  84  however, more or less slats may be provided. If flexible support member is not adjustable, then slats  84  preferably extend from the top of shell  24  to the bottom of shell  24 . If flexible support member is adjustable, then slats  84  preferably extend from the top of shell  24  towards the bottom of shell  24 . For example, support shell  24  may have an outer rim or perimeter  64  and a flexible support section  66  is provided centrally therein and is are separated by a generally U-shaped slot  68 . U-shaped slot  68  may be shaped to conform with reinforcing wall  58  of frame  22 , so that when support shell  24  is mounted on frame  22 , reinforcing wall  58  extends through slot  68 . 
     The amount of support provided by flexible support member  66  is preferably varied by an adjustment member which is drivingly connected to free end  72  and a detent member for selectively receiving the adjustment member in one of a plurality of positions, flexible support member  66  biasing the adjustment member into retaining engagement with the detent member due to the compression of flexible support member  66  by the displacement of the free end  72  towards the fixed end  70 . Preferably, the detent member comprise a plurality of vertically spaced apart members each of which has a downwardly extending recess and the adjustment member is sized to be received in each recess. Preferably, the detent member comprises a plurality of support ribs  48  on the front side of web  46 . Each support rib  48  has a lower notch  49  a middle notch  50  and an upper notch  51 , which are vertically spaced apart. The lower notches  49  of all the support ribs  48  are aligned. Similarly, the middle notches  50  are aligned and the upper notches  51  are aligned. At the bottom centre of free end  72 , a cavity  88  is provided. Cavity  88  is aligned with support ribs  48  when support shell  24  is mounted on frame  22  and is made wide enough to allow all of the support ribs  48  to pass through it. 
     In the preferred embodiment of backrest  20 , base section  28  has four support ribs  48  each of which has three notches  49 ,  50  and  51 . In a different embodiment of a backrest according to the present invention, a different number of support ribs, having a different number of notches, may be provided. Web  46  has a longitudinal slot  52  centred between the two central support ribs  48 . Slot  52  extends below the lower notch  49  and above the upper notch  51  in each of support ribs  48 . Optionally a reinforcing wall  58  surrounds opening  38  and web  46  on the front side of frame  22 . Reinforcing wall  58  provides rigid support to frame  22  to reduce its flexibility when backrest  20  is in use. 
     FIG. 5 which shows the adjustment member  25  positioned adjacent the free end  72  of flexible support section  66  from rear side  62 . Adjustment member  25  utilizes a rod which is removably receivable into downwardly extending notches  49 ,  50  and  51 . Notches need not be sized to lockingly receive rod  90  since due to the compression of flexible support section  66 , rod  90  is biased downwardly into the notch with which it is aligned. 
     Preferably, rod  90  is removably mounted to free end  72  by engagement members. Accordingly, adjustment member  25  may also comprise an arm  92  and a pair of hooks  94  (male engagement members). Flexible support section  66  has a pair of mounting clamps  96  a pair of opposed mounting tabs  98  on each side of cavity  88 . Mounting clamps  96  cooperate with rod  90  and mounting tabs  98  (female engagement members) cooperate with hooks  94  to hold adjustment member  25  in a fixed position at the bottom rear side of flexible support section  66 . Hooks  94  are inserted into tabs  98  and rod  90  is inserted into clamps  96 . Tabs  98  and hooks  94  cooperate to prevent adjustment member  25  from being pulled from flexible support section  66  by a rearward force. Clamps  96  and rod  90  prevent adjustment member  25  from twisting upward or downward when adjustment member  25  is moved during the use of backrest  20 . Arm  92  extends rearwardly from the centre of rod  90 . As shown in FIG. 2, arm  92  extends through slot  52  in frame  22 . A handle  100  is affixed to the end of arm  92 . 
     Frame  22  and support shell  24  may be manufactured from plastic or another material. Preferably, frame  22  is substantially rigid so that it will not flex when backrest  20  is in use. Reinforcing wall  58  optionally provides rigidity to frame  22 . Similarly, optional rim  64  of support shell  24  is preferably substantially rigid and lip  82  provides rigidity for rim  64 . As noted above, optional reinforcing ridge  27  provides rigidity to mounting section  26 . Flexible support section  66 , however, is preferably flexible so that when free end  72  is moved closer to or further away from fixed end  70 , flexible support section  66  flexes to become more or less convex, as viewed from the front side  60  of support shell  24  (FIGS.  6  and  7 ). 
     The adjustment of back rest  20  to provide differing levels of lumber support will now be explained with reference to FIGS. 6 and 7. FIG. 6 shows backrest  20  configured to provide a relatively low level of lumbar support. FIG. 7 shows backrest  20  configured to provide an increased level of lumbar support. Referring to FIG. 6, rod  90  of adjustment member  25  (which is fixedly attached to the bottom rear side of flexible support section  66 ) is positioned in notch  49 . Rod  90  of adjustment member  25  is positioned in notch  49 . The distance between the top of fixed end  70  and the bottom of free end  72  of flexible support section  66  is distance  102 . Flexible support section  66  appears convex when viewed from the front of backrest  20 . 
     To increase the degree of lumbar support provided by backrest  20 , and more particularly by flexible support section  66 , a user may grasp handle  100  and lift adjustment member  25  from notch  49  and place it in notch  50  or notch  51 . In order to do this, the user must first simultaneously move adjustment member  25  forward and upward, then lift adjustment member  25  to the appropriate height depending on the notch  50  or  51  in which arm  90  is to be inserted and then pull adjustment member  25  back to seat arm  90  in the selected notch. Since adjustment member  25  is fixedly attached to the bottom rear side of flexible support section  66 , moving adjustment member  25  from notch  49  to notch  50  or notch  51  will decrease the distance between fixed end  70  and free end  72  of flexible support section  66 . 
     FIG. 7 shows arm  90  of adjustment member  25  positioned in notch  51 . The distance between the top of fixed end  70  and the bottom of free end  72  is distance  104 . Distance  104  is substantially less than distance  102 . As a result, the convexity of flexible support section  66  when viewed from the front of backrest  20  has been increased. A user seated on the chair to which backrest  20  has been attached will receive greater lumbar support from flexible support section  66 , when it is configured as shown in FIG. 7 than when it is configured as shown in FIG.  6 . 
     A user may return backrest  20  to the configuration of FIG. 6 by grasping handle  100  and moving adjustment member  25  such that arm  90  is released from notch  51  and then lowering adjustment member  25  and then positioning arm  90  in notch  49 . Alternatively, the user may position arm  90  in notch  50  which will cause flexible support section  66  to have a degree of convexity intermediate that shown in FIGS. 6 and 7 and will provide an intermediate level of lumbar support. 
     In this way, backrest  20  provides a simple mechanism for adjusting the degree of lumbar support provided by backrest  20 . Flexible support section  66  is configured such that it will bias its free end  72  downward at all times. Accordingly, when arm  90  of adjustment member  25  is inserted into any one of notches  49 ,  50  or  51 , flexible support section  66  will apply a downward force to hold arm  90  in the selected notch. 
     In use, the front side of backrest  20  is normally be covered by a padding material and a fabric cover (not shown). A user, therefore, does not normally lean directly against backrest  20  or flexible support section  66 , but does so through the cover and the padding material. 
     Reference is next made to FIG. 8 which illustrates the operation of backrest  20  when in use by a person  106 . When a person  106  leans against backrest  120  and particularly against flexible support section  66 , slats  84  of flexible support section  66  will be deformed in rearwardly. Each slat  84  independently supports a different longitudinal portion of the user&#39;s back in general. As a result, a user with a wider back will cause outer slats  108  and  114  to be deformed more than would a user with a narrower back. A user with a narrower back will receive a greater proportion of lumbar support from the inner slats  110  and  112 . Since slats  84  flex independently of one another, flexible support section  66  conforms to the actual shape of a particular user&#39;s back and conforms to different users who may use backrest  20  at different times, without requiring adjustment. 
     Reference is made to FIG.  9 . The position of slats  108 ,  110 ,  112  and  114  when backrest  20  is not in use is shown at  108   a ,  110   a ,  112   a  and  114   a , respectively, in dotted outline. The position of slats  108 ,  110 ,  112 , and  114  when a typical person is leaning against backrest  20  is shown at  108   b ,  110   b ,  112   b  and  114   b , respectively, in solid outline. When person  106  leans against backrest  20 , slats  108 ,  110 ,  112  and  114  are deformed from positions  108   a ,  110   a ,  112   a  and  114   a  to positions  108   b ,  110   b ,  112   b  and  114   b . The deformation of each slat  108 ,  110 ,  112 , and  114  will depend on the weight applied by person  106  to that particular slat. 
     Reference is next made to FIG.  10 . The positions  108   b ,  110   b ,  112   b  and  114   b  of slats  108 ,  110 ,  112  and  114 , respectively, when person  106  is leaning against backrest  20 , as in FIG. 9, is shown in dotted outline. When person  106  turns to one side, slate  108 ,  110 ,  112  and  114  move to positions  108   c ,  110   c ,  112   c  and  114   c , shown in solid outline. Slats  112  and  114  have deformed further backwards while allowing slat  110  to move somewhat forward and allowing slat  108  to return entirely to its unused position  108   a.    
     FIGS. 8,  9  and  10  illustrate how the independent flexibility of slats  108 ,  110 ,  112  and  114  allows flexible support section  66  to reactively provide differing degrees of support to differing longitudinal portions of a user&#39;s back, depending not only on the size and shape of the user&#39;s back but also on the position in which the user is seated at any particular time. Accordingly, by using a flexible support section  66  comprising a plurality of independently movable slats  84  a back rest support is provided that will not only conform to the shape of the back of a user but will also conform to the position of the back of a user as the user moves in the chair. 
     Reference is next made to FIGS. 11 and 12, which illustrate a second exemplary backrest  220  made according to the present invention. Backrest  220  comprises of a frame  222 , a support shell  224  and an adjustment member  25 . Backrest  220  is similar to backrest  20  in structure and operation, except that back rest  220  is designed for portable use with different chairs, rather than for mounting on a single chair. Components of backrest  220  which are identical to corresponding components of backrest  20  are identified by the same reference numerals. 
     Frame  222  has a base section  228 , but does not have a mounting section. Instead, backrest  220  has a pair of mounting straps  226  affixed to the rear side  256  of frame  222 . Straps  226  may be provided with buckles  227  and may be used to attach backrest  222  in front of the backrest of a typical chair (not shown), thereby adding the functionality of backrest  222  to the chair. 
     Rim  264  of support shell  224  extends beyond the perimeter of base section  228  on all sides. A lip  282  is formed around the perimeter of rim  264  to provide rigidity to rim  264 . 
     Backrest  220  is adjusted to provide differing levels of lumbar support in exactly the same manner as described above for backrest  20 . Depending on the construction of the chair (not shown) to which backrest  220  is attached, it may be necessary to adjust backrest  220  by positioning rod  90  in the appropriate notch  49 ,  50  or  51  (notches  50  and  51  not shown in FIGS. 11 and 12) prior to affixing backrest  220  on the chair (i.e. if the backrest of the chair would obstruct handle  100 ). 
     Backrest  20  and backrest  220  have been described as providing lumbar region of a user&#39;s back. Depending on the vertical contour of the support section of the backrest, support may be provided to lumbar, medial and upper regions of the back simultaneously. Such an embodiment of a backrest according to the present invention may support both the vertically central section of the user&#39;s back (along the spine) and the lateral sides (i.e. the left and right sides) of the user&#39;s back. 
     These and other variations of a backrest according to the present invention will be within the competence of a person skilled in the art. All such variations fall within the scope of the invention, which is limited only by the following claims.