Backrest with lumbar depth adjustment

Abstract

The disclosure relates to a backrest for a seating furniture, comprising: a base part; a backrest part comprising: a flexible backrest section ; and an inflexible support section (1); wherein the inflexible support section is attached to the base part at a lower section thereof; wherein the flexible backrest section is attached via a pivot axis to the inflexible support section between an upper section and the lower section of the inflexible support section; an adjustment mechanism situated between a lower section of the flexible backrest section and the base part; wherein the adjustment mechanism comprises: a frame part slidably supported on the base part; a guide slit in the frame part, the guide slit (11) having an inclined alignment in relation to a direction of sliding movement of the frame part; and a peg attached to and protruding from the lower section (of the flexible backrest section, the peg extending into the guide slit; wherein sliding movement of the frame part causes the peg to move along the guide slit, thereby adjusting a shape of the flexible backrest section. The disclosure further relates to a method of adjusting a backrest shape.

Description

Background:

[0001] The comfort and ergonomic support provided by chairs, and especially task or office chairs are critical factors for users who spend extended periods sitting. In particular, lumbar support adjustment plays a key role in ensuring proper spinal alignment and reducing lower back strain. Various solutions have been developed to allow for the adjustment of lumbar depth in office chairs, providing users with the ability to customize the level of support according to their individual needs.

[0002] One such solution is disclosed in European Patent EP2689692B1, which describes a system for adjusting the backrest shape of an office chair. However, while this system achieves its primary objective of adjustable shape of the back support, it presents certain limitations. A significant drawback of the disclosed mechanism is that the adjustment of the lumbar support is mechanically linked to the adjustment of the headrest. This dual adjustment may not be desirable for all users, as it does not allow for independent control of these two crucial ergonomic features. Moreover, the adjustment process requires multiple turns of the adjustment mechanism, often involving significant force, making it cumbersome and impractical for some users, particularly those who require quick and simple adjustments. Documents CN 1448090 A, EP 2689692 B1, US 7874619 B2 and EP 2100539 A1 discloses known solutions.

[0003] In contrast, there is a growing demand for lumbar adjustment systems that offer ease of use with minimal effort. The ability to adjust the lumbar depth with a single, simple movement is of great importance in modern office chairs. Such a feature would allow users to make adjustments quickly and intuitively, ensuring that the chair can adapt to a range of postures and preferences throughout the day. The ideal system should not only enable independent lumbar adjustment but also facilitate effortless operation, ensuring that users of all physical capabilities can adjust their chairs without unnecessary strain or delay.Summary:

[0004] It is an object of the present disclosure to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages in the prior art and solve at least the above-mentioned problem. The present invention addresses these issues by providing a lumbar depth adjustment mechanism that offers smooth and simple operation across the full range of adjustment, without affecting other ergonomic features such as the headrest. This improved system seeks to enhance user comfort and convenience, promoting better ergonomics and overall well-being in the workplace.

[0005] According to a first aspect there is provided a backrest for a seating furniture, comprising: a base part ; a backrest part comprising: a flexible backrest section ; and an inflexible support section ; wherein the inflexible support section is attached to the base part at a lower section thereof; wherein the flexible backrest section is attached via a pivot axis to the inflexible support section between an upper section and the lower section of the inflexible support section ; an adjustment mechanism situated between a lower section of the flexible backrest section and the base part ; wherein the adjustment mechanism comprises: a frame part slidably supported on the base part ; a guide slit in the frame part, the guide slit having an inclined alignment in relation to a direction of sliding movement of the frame part ; and a peg attached to and protruding from the lower section of the flexible backrest section, the peg extending into the guide slit ; wherein sliding movement of the frame part causes the peg to move along the guide slit, thereby adjusting a shape of the flexible backrest section.

[0006] According to some embodiments, the adjustment mechanism further comprises an adjustment lever connected to the frame part and operable by a user.

[0007] According to some embodiments, the frame part is movable on, or along, a path defined by gliding means on the base part or frame part.

[0008] According to some embodiments, the gliding means comprises a gliding path on the base part and a corresponding gliding support on a bottom of the frame part.

[0009] According to some embodiments, the adjustment mechanism further the backrest comprises a connector portion extending from the lower section of the flexible backrest section, wherein the peg protrudes from the connector portion.

[0010] According to some embodiments, the connector portion is rotationally attached at one end to the base part via a pivot axis.

[0011] According to some embodiments, the guide slit comprises one or more grooves spaced along orifices of the slit for the peg to rest in and be stationarily supported.

[0012] According to some embodiments, movement of the frame part in a first direction displaces the lower section of the flexible backrest section in a second direction substantially perpendicular to the first direction.

[0013] According to some embodiments, the backrest comprises a cover supported by the flexible backrest section and the inflexible support section.

[0014] According to some embodiments, adjustment of the shape of the flexible backrest section causes a corresponding adjustment to a shape of the cover. 10. A seating furniture the backrest comprises the backrest of any preceding.

[0015] According to some embodiments, the seating furniture is an office chair.

[0016] According to a second aspect there is provided a method of adjusting a backrest shape, the method comprising: providing a backrest according to any of the first aspect; sliding the frame part of the adjustment mechanism; causing, by the sliding of the frame part, movement of the peg along the inclined guide slit ; and adjusting, by the movement of the peg, a shape of the flexible backrest section.

[0017] Effects and features of the second aspect are to a large extent analogous to those described above in connection with the first aspect. Embodiments mentioned in relation to the first aspect are largely compatible with the second aspect.

[0018] The present disclosure will become apparent from the detailed description given below. The detailed description and specific examples disclose preferred embodiments of the disclosure by way of illustration only. Those skilled in the art understand from guidance in the detailed description that changes and modifications may be made within the scope of the disclosure.

[0019] Hence, it is to be understood that the herein disclosed disclosure is not limited to the particular component parts of the device described or steps of the methods described since such device and method may vary. It is also to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting. It should be noted that, as used in the specification and the appended claim, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements unless the context explicitly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several devices, and the like. Furthermore, the words "comprising", "including", "containing" and similar wordings does not exclude other elements or steps.Brief descriptions of the drawings

[0020] The above objects, as well as additional objects, features and advantages of the present disclosure, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of example embodiments of the present disclosure, when taken in conjunction with the accompanying drawings. Fig. 1 illustrates an adjustable backrest as seen slanted from a back view according to an embodiment of the present disclosure. Fig. 2 illustrates upper support end of the backrest according to an embodiment of the present disclosure. Fig. 3 illustrates the lower support end of the backrest according to an embodiment of the present disclosure. Fig. 4 illustrates the underside of the base part according to an embodiment of the present disclosure. Fig. 5 illustrates lower support end of the backrest and base part, seen from the backside, according to an embodiment of the present disclosure. Fig. 6 illustrates a side view of a backrest and base part according to an embodiment of the present disclosure. Fig. 7 illustrates a close up of the adjustment mechanism situated between the base part and connector portion according to an embodiment of the present disclosure. Fig. 8 illustrates a close up of the adjustment mechanism situated between the base part and connector portion according to an embodiment of the present disclosure. Fig. 9 illustrates a close up of the adjustment mechanism situated between the base part 5 and connector portion according to an embodiment of the present disclosure. Fig. 10a and 10b illustrates a close up of the flexible section, the base part and connector portion according to an embodiment of the present disclosure. Fig. 11a and 11b illustrates a close up of the flexible section, inflexible section and lever according to an embodiment of the present disclosure. Detailed description:

[0021] The present disclosure will now be described with reference to the accompanying drawings, in which preferred example embodiments of the disclosure are shown. The disclosure may, however, be embodied in other forms and should not be construed as limited to the herein disclosed embodiments. The disclosed embodiments are provided to fully convey the scope of the disclosure to the skilled person.

[0022] Fig. 1a and 1b illustrates an adjustable backrest that normally forms part of a seating furniture (not shown), such as a chair, the adjustable backrest comprising a base part 5 and a backrest part 8. The base part 5 is adapted to attached to a seat, undercarriage, chassis or a base. Fig. 1a shows the backrest from a side, wherein the backrest part 8 has a lower support end 8b facing the base part 5 and an upper support end 8a facing away from the base part 5.

[0023] The first aspect of this disclosure shows a backrest for a seating furniture 1, comprising: a base part 5; a backrest part 8 comprising: a flexible backrest section 2; and an inflexible support section 1; wherein the inflexible support section 1 is attached to the base part 5 at a lower section 1b thereof; wherein the flexible backrest section 2 is attached via a pivot axis 9 to the inflexible support section 1 between an upper section 1a and the lower section 1b of the inflexible support section 1; an adjustment mechanism situated between a lower section 2b of the flexible backrest section 2 and the base part 5; wherein the adjustment mechanism comprises: a frame part 10 slidably supported on the base part 5; a guide slit 11 in the frame part 10, the guide slit 11 having an inclined alignment in relation to a direction of sliding movement of the frame part 10; and a peg 12 attached to and protruding from the lower section 2b of the flexible backrest section 2, the peg 12 extending into the guide slit 11; wherein sliding movement of the frame part 10 causes the peg 12 to move along the guide slit 11, thereby adjusting a shape of the flexible backrest section 2.

[0024] Fig. 1b illustrates the adjustable backrest as seen slanted from a back view, wherein the backrest comprising a flexible backrest section 2 and an inflexible support section 1. Said two backrest sections 1, 2 are in the illustration adjacent situated frames with a curvature that aligns. The inflexible support section 1 comprises an upper section 1a and a lower section 1b and is attached to the base part 5 at the lower section 1b. The flexible backrest section 2 and an inflexible support section 1 supports and suspends a fabric or cover 3, wherein the cover 3 is formed by the shape of the flexible backrest section 2 and an upper part 1a of inflexible support section 1. In a non-illustrated example, the cover 3 can be two separate sections for the flexible backrest section 2 and an upper part 1a.

[0025] In the context of this disclosure, the term "flexible" should be understood to refer to a material or structural element that is capable of bending, yielding, or deforming in response to applied force, preferably an expected force during normal use, without breaking or suffering permanent deformation. This flexibility allows the backrest to adapt to the movements or pressure exerted by the user, enhancing comfort or ergonomic function.

[0026] In particular, "flexible" does not imply that the part is freely movable in all directions; instead, it may be limited to specific directions or ranges of motion, depending on the material properties or the design constraints. The flexibility can arise from the inherent characteristics of the material (e.g., rubber, plastic, or certain metals) or through specific structural design features, such as joints, hinges, or a segmented construction.

[0027] Thus, in the herein disclosed context, "flexible" should be understood as referring to the ability of the backrest component to provide controlled, non-rigid movement to improve user interaction or comfort, without compromising its structural integrity.

[0028] In the context of this disclosure, the term "inflexible" should be understood to refer to a material or structural element that is rigid and does not significantly bend, deform, or yield under normal forces applied during use. This part is designed to maintain its shape and structural integrity, resisting movement or deformation when subjected to pressure or load.

[0029] Specifically, "inflexible" implies that the part is constructed from materials or is designed in a way that ensures stability and firmness, providing consistent support to the user. The rigidity of this part can be essential for ensuring the overall structural support of the furniture, particularly in maintaining the posture of the user or enhancing durability. The inflexibility may arise from the nature of the material itself (e.g., wood, metal, or hard plastics) or from a combination of materials and design features that prioritize stability.

[0030] Thus, in the herein disclosed context, "inflexible" should be understood as referring to the backrest component that remains fixed and unyielding during typical use, contributing to the structural strength and supportive function of the furniture.

[0031] Fig. 2 illustrates upper support end 8a of the backrest part 8, wherein the flexible backrest section 2 comprises an upper section 2a and a lower section 2b.The the flexible backrest section 2 is in the top end of upper section 2a attached via a pivot axis 9 to the inflexible support section 1 between the upper section 1a and a lower section 1b of the inflexible support section 1. As seen in the figure, the cover 3 covers the area defined by the frames 1, 2. The pivot axis 9 may be a troughing hinge extending through the width of the backrest part 8 or two separate mirrored hinges on either lateral side of the backrest part 8.

[0032] Fig. 3 illustrates the lower support end 8b of the backrest part 8, wherein the lower section 2b of the flexible backrest section 2 ends at, and is supported by, an adjustment mechanism , or parts thereof, such that the flexible backrest section 2 extends between a pivot axis 9 (or first hinge 9) and the adjustment mechanism. It should be understood that a hinge comprises an axis and that terms such as hinge, pivot, axis, pivot axis etc. can be used to describe one, two, or more members pivoting, or rotating, around an axis.

[0033] Fig. 4 illustrates the underside of the base part 5, wherein the base part 5 is illustrated with a hinged connection through the second pivot axis 16.

[0034] Fig. 5 illustrates lower support end 8b of the backrest part 8 and base part 5 as seen from the backside, with the adjustment mechanism situated between the lower section 2b of the flexible backrest section 2, or a connector portion 7, and the base part 5.

[0035] The adjustment mechanism comprises a frame part 10, the frame part 10 being slidably supported on the base part 5 and comprises a guide slit 11 with an inclined or slanted alignment in relation to a first direction of sliding movement of the frame part 10.

[0036] The adjustment mechanism comprises further a peg 12 attached to, and protruding from, the lower section 2b of the flexible backrest section 2, or a connector portion 7. As seen in the figure, the connector portion 7 extends from the bottom of the lower section 2b of the flexible backrest section 2. The connector portion 7 can also be rotationally attached in one end to the base part 5 via a second pivot axis 16. The peg 12 protrudes out from the lower section 2b of the flexible backrest section 2, or the connector portion 7, and into the guide slit 11 of the frame part 10. Such that when the frame part 10 is slidably manipulated in a direction, the peg 12 slides or moves in the guide slit 11 of the frame part 10. An adjustment lever 4 is connected to the frame part 10 and is operable by a user, such that when the lever 4 is moved in a first direction R1, the frame part 10 moves in the same direction, and the inclined guide slit 11 forces the peg 12 in a second direction R2 perpendicular, or close to, to the first direction R1.

[0037] The frame part 10 is movable on a path defined by rolling or gliding means 13 on the base part 5 or the frame part 10. The gliding means 13 may comprise a gliding path 14 on the base part 5, or the frame part 10, and corresponding gliding support 15 on the other of frame part 10 and the base part 5, for instance on the bottom of the frame part, such that the frame part 10 can traverse relative to the base part 5. The gliding path 14 can be perpendicular to the direction of lift R2 of the lower section 2b, which will make the movement easier to induce by a user. This is also aided by the gliding path 14, and hence the movement R1 of the lever, being longitudinal along the direction of both the first and second pivot axis 9, 16. The inclination of the guide slit 11 thus acts as a wedge forcing the peg 12 close to perpendicular to the movement of the lever 4 and frame 10. The path defined by the gliding path 14 and gliding means 13 can be straight or curved, as illustrated in the figures.

[0038] The frame part 10 is connected or in contact with the lower section 2b of the flexible backrest section 2 by the peg 12. Said peg 12 comprises an protrusion or extensions through the slit 11, and is attached to, and protruding from, a lower section 2b of the flexible backrest section 2 by a connector portion 7 situated between the a peg 12 and the lower section 2b of the flexible backrest section 2.

[0039] When lever 4 is adjusted to the left direction in the figure (first direction R1), the slope or inclination of the guide slit 11 pushes the peg 12 upwards (in the figure). This movement of the peg 12 forces the lower section 2b to move upwards as well,, as it follows the peg 12, this results in rotary movement of the connector portion 7 around the second pivot axis 16.

[0040] Fig. 6 illustrates a side view of a backrest part 8 and base part 5 with the movements the first and second pivot axis 9, 16 (or first and second hinge 9, 16) and the corresponding movement or change in shape, of the flexible backrest section 2. Since the flexible backrest section 2 and the connector portion 7 is connected together, rotary movement of connector portion 7 forces the lower section 2b (of flexible backrest section 2) in a forward and upward direction. Since the upper section 2a of the flexible backrest section 2 is rotatable attached via pivot axis 9, the upwards movement R1 of the lower section 2b causes the flexible backrest section 2 to alter shape which cause geometry change (stippled line in fig. 6). The alteration of the shape of flexible backrest section 2 causes the fabric or cover 3 to conform to said change, and it deforms to achieve lumbar depth adjustment for a user.

[0041] Thus, traversing / moving the frame 10 in the first direction R1, displaces the bottom portion of the lower section 2b of the flexible backrest section 2 in a direction perpendicular, or close to perpendicular, to the first direction R1, thereby pivoting the flexible support section 2 around the first pivot axis 9 and second pivot axis16, or first hinge and second hinge. Thus, the mechanism 10 can be used to influence the backrest an order to change the backrest shape or design of the backrest part 8 and the shape of the cover 3, in particular its curvature extending in the sagittal plane in the region of the flexible backrest section 2.

[0042] Fig. 7 illustrates a close up of the adjustment mechanism situated between the base part 5 and connector portion 7. As can be seen in the figure, the peg 12 is to the left far end of the guide slit 11. In the figure, the guide slit 11 has it lowest portion in the first end (left in figure) and its highest portion in the second end (right in the figure). Furthermore, the slit 11 may comprise groves 17, 17', 17", 17‴, 17ʺʺ or resting cut outs spaced along the orifices of the slit 11 for the peg 12 to come at rest and be stationary supported. In fig. 7, the peg 12 is situated close to / or in the lowest part of the slit 11 and thus, the lower section 2b of the flexible backrest section 2 is situated at its lowest position.

[0043] Fig. 8 illustrates the same mechanism and parts as in fig. 7, however, the lever 4 is moved along the first direction R1 compared to the position of fig. 7. Since the peg 12 is stationary with regards to movement in the first direction, the inclination of the slit 11 forces the peg 12 in the second direction R2 (illustrated in figs. 5 and 6). As the peg 12 is connected to the connector portion 7, and the connector portion is connected to the lower section 2b of the flexible backrest section 2, the lower section 2b is also moved in the second direction R2, thus compressing the flexible section 2 between the pivot axis 9 and connector portion 7, resulting in a more arched shape of the flexible section 2 than prior to movement of the lever 4.. This only affects the flexible section 2, and the upper part 1a of inflexible support section 1 remains unchanged, for the seated user's comfort. As seen in the figure, the peg 12 is at rest in groove 17" in the slit 11.

[0044] Fig. 9 illustrates the same mechanism and parts as in fig. 7 and 8, however, the lever 4 is moved further along the first direction R1 compared to the position of fig. 7 and 8. Since the peg 12 is stationary with regards to movement in the first direction, the inclination of the slit 11 forces the peg 12 further in the second direction R2. As the peg 12 is connected to the connector portion 7, and the connector portion is connected to the lower section 2b of the flexible backrest section 2, the lower section 2b is also moved further in the second direction R2, thus compressing the flexible section 2 between the pivot axis 9 and connector portion 7, resulting in an even more arched shape of the flexible section 2, providing additional lumbar support. This only affects the flexible section 2, and the upper part 1a of inflexible support section 1 remains unchanged, for the seated user's comfort. As seen in the figure, the peg 12 is at rest in groove 17ʺʺ in the slit 11.

[0045] Fig. 10a and 10b illustrates a close up of the flexible section 2, the base part 5 and connector portion 7. In both fig. 10a and 10b, the base part 5 is stationary, whilst the connector portion 7 and flexible section 2 is in two different positions between the figures. In fig. 10a, the lever of the adjustment mechanism will be in a first position, corresponding to the position as illustrated in fig. 7. In said position, the peg 12, and thus the lower section 2b of the flexible backrest section 2, will be in the lowermost position, and an angle between the connector portion 7 and the base part 5, going through the second pivot axis 16, will be at its smallest angle A1.

[0046] In fig. 10b, the lever of the adjustment mechanism will be in a second position, corresponding to the position as illustrated in fig. 9. In said position, the peg 12, and thus the lower section 2b of the flexible backrest section 2, will be in the uppermost position, and an angle between the connector portion 7 and the base part 5, going through the second pivot axis 16, will be at its largest angle A2, wherein A2 is greater than A1.

[0047] Fig. 11a and 11b illustrates a close up of the flexible section 2, inflexible section 1 and lever 4. In both fig. 11a and 11b, the inflexible section 1 is stationary, whilst the flexible section 2 is in two different positions between the figures. The position of the lever 4 in fig.11a and 11b corresponds to the positions of the lever in fig. 10a and 10b, respectively. In fig. 10a, the lever of the adjustment mechanism will be in a first position, corresponding to the position as illustrated in fig. 7 and 10a. In said position, the peg 12, and thus the lower section 2b of the flexible backrest section 2, will be in the lowermost position, and an angle between the connector portion 7 and the base part 5, going through the second pivot axis 16, will be at its smallest angle A1. In this position, the difference in the arch or shape between the flexible section 2 and inflexible section 1 will be at it's minimum, represented by a distance D1, which corresponds to the minimum arch of the shape of the cover 3.

[0048] In fig. 11b, the lever of the adjustment mechanism will be in a second position, corresponding to the position as illustrated in fig. 9 and 10b. In said position, the peg 12, and thus the lower section 2b of the flexible backrest section 2, will be in the uppermost position, and an angle between the connector portion 7 and the base part 5, going through the second pivot axis 16, will be at its largest angle A2, wherein A2 is greater than A1. In this position, the difference in the arch or shape between the flexible section 2 and inflexible section 1 will be at it's maximum, represented by a distance D2, which corresponds to the maximum arch of the shape of the cover 3, wherein D2 is greater than D1.

[0049] The second aspect of this disclosure relates to a method of adjusting the shape of a backrest, the method comprising: providing a backrest the first aspect according to any of the first aspect; sliding the frame part 10 of the adjustment mechanism; causing, by the sliding of the frame part 10, movement of the peg 12 along the inclined guide slit 11; and adjusting, by the movement of the peg 12, a shape of the flexible backrest section 2.

[0050] The person skilled in the art realizes that the present disclosure is not limited to the preferred embodiments described above. The person skilled in the art further realizes that modifications and variations are possible within the scope of the appended claims. Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed disclosure, from a study of the drawings, the disclosure, and the appended claims.

Claims

1. A backrest for a seating furniture (1), comprising: a base part (5); a backrest part (8) comprising: a flexible backrest section (2); and an inflexible support section (1), wherein the inflexible support section (1) is attached to the base part (5) at a lower section (1b) thereof; wherein the flexible backrest section (2) being attached via a pivot axis (9) to the inflexible support section (1) between an upper section (1a) and the lower section (1b) of the inflexible support section (1); an adjustment mechanism situated between a lower section (2b) of the flexible backrest section (2) and the base part (5); wherein the adjustment mechanism comprises: a frame part (10) slidably supported on the base part (5); a guide slit (11) in the frame part (10), the guide slit (11) having an inclined alignment in relation to a direction of sliding movement of the frame part (10); and a peg (12) attached to and protruding from the lower section (2b) of the flexible backrest section (2), the peg (12) extending into the guide slit (11); wherein sliding movement of the frame part (10) causes the peg (12) to move along the guide slit (11), thereby adjusting a shape of the flexible backrest section (2).

2. The backrest of claim 1, wherein the adjustment mechanism further comprises an adjustment lever (4) connected to the frame part (10) and operable by a user.

3. The backrest of claim 1 or 2, wherein the frame part (10) is movable on, or along, a path defined by gliding means (13) on the base part (5) or frame part (10).

4. The backrest of claim 3, wherein the gliding means (13) comprises a gliding path (14) on the base part (5) and a corresponding gliding support (15) on a bottom of the frame part (10).

5. The backrest of any preceding claim, wherein the adjustment mechanism further comprising a connector portion (7) extending from the lower section (2b) of the flexible backrest section (2), wherein the peg (12) protrudes from the connector portion (7).

6. The backrest of claim 5, wherein the connector portion (7) is rotationally attached at one end to the base part (5) via a second hinge (16).

7. The backrest of any preceding claim, wherein the guide slit (11) comprises one or more grooves (17, 17', 17") spaced along orifices of the slit (11) for the peg (12) to rest in and be stationarily supported.

8. The backrest of any preceding claim, wherein movement of the frame part (10) in a first direction (R1) displaces the lower section (2b) of the flexible backrest section (2) in a second direction (R2) substantially perpendicular to the first direction (R1).

9. The backrest of any preceding claim, further comprising a cover (3) supported by the flexible backrest section (2) and the inflexible support section (1).

10. The backrest of claim 9, wherein adjustment of the shape of the flexible backrest section (2) causes a corresponding adjustment to a shape of the cover (3).

11. A seating furniture comprising the backrest of any preceding claim.

12. The seating furniture of claim 11, wherein the seating furniture is an office chair.

13. A method of adjusting a backrest shape, the method comprising: providing a backrest according to any of claims 1-10; sliding the frame part (10) of the adjustment mechanism; causing, by the sliding of the frame part (10), movement of the peg (12) along the inclined guide slit (11); and adjusting, by the movement of the peg (12), a shape of the flexible backrest section (2).

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