EP2410890B1

EP2410890B1 - Seat backrest

Info

Publication number: EP2410890B1
Application number: EP10756428.8A
Authority: EP
Inventors: Erik Malm
Original assignee: Malmstolen AB
Current assignee: MALMSTOLEN PRODUKTION AB
Priority date: 2009-03-25
Filing date: 2010-03-25
Publication date: 2013-12-18
Anticipated expiration: 2030-03-25
Also published as: EP2410890A1; WO2010110732A1; EP2410890B8; EP2410890A4

Abstract

The invention relates to a seat backrest comprising a rigid frame (25) supporting a contourable portion constituted by a covering upholstery layer (26) and at least one elastomeric layer (27) interposed between the covering upholstery layer (26) and the frame; and resilient means (24) between the frame (25) and the elastomeric layer (27) to impart a curvature to the covering upholstery layer (26) and the elastomeric layer (27) to produce a desired contour at least in the lumbar region. The resilient means (24) is located in a cavity (24) in a portion of the elastomeric layer (27) facing the frame, and that the resilient means (24) comprises at least one pocketed spring assembly (30), each spring assembly comprising at least one continuous coiled spring member, each said continuous spring member being enclosed in a covering material (31, 32) and extending between opposing sides of the cavity (24).

Description

TECHNICAL FIELD

The invention relates to the technical field of backrests for chairs, in particular ergonomic backrests forming part of a chair or a seat.

BACKGROUND ART

There are a wide variety of individual ergonomic chairs and seats providing a variety of adjustable options and configurations to provide support for the users back and to suit the user's need to change the posture of his body whilst seated.
Typically, such seats are configured to offer a varying degree of fit to the user's anatomy or change of posture. Such seats' adjustability options can include seat height adjustability from floor level, seat depth adjustability from front seat edge to base of back rest, backrest angle adjustability in relation to the seating surface, height of lumbar support from seating surface, and backrest height adjustability in relation to seating surface. In ergonomic chairs and seats the support in at least the lumbar region is of interest for providing proper support for the users back.
Conventional chairs and seat backrests are often filled with foam, which is a simple way of achieving a predetermined shape for the backrest. A problem with conventional foam cushions is that they may not accommodate for different users' body shapes and body weights. Generally a foam cushion is really only suitable for a fairly narrow range of body weights and shapes.
An alternative solution may be to provide the lumbar region with an inflatable portion that may be adjusted in size to accommodate the shape of the back for the individual user. A problem with such solutions is that the inflatable portion can be relatively soft when not inflated and relatively hard when inflated. In addition, an inflatable portion may not provide an ergonomically suitable lateral support when the user changes posture.
JP 57 122810 discloses another alternative construction. Individual coiled springs are introduced and fitted into separate recesses in the foam material of the backrest of a chair.
The object of the invention is to provide an improved ergonomic backrest for chairs or seats by providing a backrest that can accommodate for different users' body shapes and body weights, as well as providing an ergonomic lateral support in at least the lumbar region of the backrest.

DISCLOSURE OF INVENTION

The above problems are solved by a backrest according to the appended claims.
The invention relates to a backrest, in particular a seat backrest, for various types of chairs, such as office chairs. The backrest may be an integrated part of a chair or to be detachable and/or portable. A portable backrest may be attached to and used in other applications, such as vehicle seats, wheel chairs or other types of chairs.
The backrest according to the invention comprises a rigid frame supporting a contoured portion with a covering upholstery layer and at least one elastomeric layer interposed between the covering upholstery layer and the frame. A resilient means is arranged between the frame and the elastomeric layer to impart a curvature to the covering upholstery layer and the elastomeric layer to produce a desired contour at least in the lumbar region. This curvature may be determined by the shape or contour of the surface of the rigid frame facing the at least one elastomeric layer and the resilient means. The resilient means is located in a corresponding cavity in a portion of the elastomeric layer facing the frame and comprises at least two parallel pocketed spring assemblies. The at least one elastomeric layer may comprise single layer of a single elastomeric material, or two or more layers of the same or different elastomeric materials each having different elastic properties.
Preferably, the outer dimensions of the resilient means is substantially the same as the dimensions of the cavity. The resilient means is preferably, but not necessarily, arranged to fill the cavity in the vertical and transverse extension of the backrest. Similarly, the thickness of the resilient means, measured at substantially right angles to the frame, is at least the same as the depth of the cavity in the surface of the at least one elastomeric layer facing the frame. In order to ensure that the desired curvature is imparted to the covering upholstery layer the thickness of the resilient means, in its unloaded state, may exceed the depth of said cavity.
The resilient means may comprise one or more, single or parallel pocketed spring assemblies, depending on the coil diameter and/or wire diameter used for each spring assembly. Hence, the resilient means may comprise a single pocketed spring assembly, for example extending along a centre section in the vertical extension of the backrest. The resilient means may also comprise multiple parallel spring assemblies extending along the entire height and/or width of the backrest. In this context the term "spring assembly" is defined as a coiled spring member enclosed by a pocket. Each coiled spring member may comprise at least one continuous coiled metal spring member formed by coiling a spring metal wire. Alternatively, the spring assembly may comprise a pair of continuous coiled metal spring members, arranged in parallel and interconnected, said spring members formed by coiling a spring metal wire. Also, each said continuous coiled spring member is enclosed in a covering and extending between opposing sides of the cavity. The covering may comprise a fabric or other suitable material.
Each pocketed spring assembly may comprise a pair of facing fabric sheets joined to each other, said fabric sheets being divided into a plurality of pockets by spaced lines of attachment, each pocket containing a single coiled spring member, each of said pockets being of a length equal to a corresponding spring assembly. In order to form suitable pockets, a first sheet may be kept flat, while a second sheet is given an undulating shape and is attached to the first sheet along, for instance, the upper portion of each undulation. In this case, the lines of attachment will be located in an outer surface of the resilient means, facing either the frame of the cavity in the elastomeric layer. Alternatively, both the first and the second sheets are given an undulating shape, with the same number of undulations. Each pair of contacting upper and lower portions of the respective sheets are then attached along adjacent lines of attachment. In this case, the lines of attachment will be located between the outer surfaces of the resilient means, for instance half-way between the outer surfaces in material sheets of equal size are used. In both the above examples, the pockets formed between adjacent lines of attachment are sufficiently large to allow a coiled spring member to be introduced into each pocket. Each coiled spring member may be attached to one or both material sheets at one or more locations in order to hold the coiled spring member in place.
Each spring assembly may comprise at least one continuous coiled metal spring member formed from a single length of wire formed into a row of single or parallel coil springs. In the latter case, the continuous coiled metal spring member comprises a row formed by a pair of coil springs arranged interconnected and side-by-side along the extension of the spring assembly. Each of said coil springs having an upper end turn, a lower end turn and a plurality of central convolutions between said end turns. The said central convolutions may define an axis of said coil spring, said coil springs of said continuous spring member being arranged in a row and interconnected by interconnecting segments of wire located alternatively in top and bottom portions of the continuous spring member. The height of spring assemblies is equal to or greater than the depth of the cavity between the frame and the elastomeric layer.
According to one example, the at least one pocketed spring assembly may extend between opposing surfaces in the cavity in the vertical extension of the backrest. In the case of multiple spring assemblies, the length of the parallel spring assemblies, measured along the frame of the backrest, may be equal in the direction of the vertical extension of the backrest. However, one or more spring assemblies along opposite outer side edges of the resilient means may have a reduced length.
According to an alternative example, the at least one pocketed spring assembly may extend between opposing surfaces in the cavity in the transverse extension of the backrest. The at least one pocketed spring assembly is located substantially at right angles to an axis defining a central vertical axis of the backrest. Half the length of each spring assembly extends in the said transverse extension on either side of the central vertical axis. In this case, the length of multiple parallel spring assemblies may be equal in the transverse direction. However, one or more spring assemblies along the upper or lower side edges of the resilient means may have a reduced length.
According to the above examples, the cavity containing the at least one pocketed spring assembly can be arranged in the lower part of the backrest, that is, in correspondence with the lumbar region of the user's vertebral column. Alternatively, the cavity containing the pocketed spring assemblies can be arranged in the lower and intermediate part of the backrest, that is, in correspondence with the lumbar and thoracic regions of the user's vertebral column.
As stated above, the length of the single or parallel spring assemblies may be varied. For example, spring assemblies located adjacent a central vertical axis of the frame may be greater than spring assemblies located remote from said central vertical axis. For instance, a resilient means comprising four parallel spring assemblies may have two central spring assemblies extending over the lumbar and the thoracic regions and two outer spring assemblies extending over the lumbar region only. For the case where the spring assemblies are arranged in a transverse direction across the backrest, the length of the spring assemblies may, for instance, vary with the width of the backrest along its vertical extension, or have a greater length in the lumbar or thoracic regions.
In the examples given above, the cavity containing the pocketed spring assemblies is arranged to extend to match the height, the transverse width and the vertical height of the resilient means. Also, the thickness of the elastomeric layer may vary in transverse and vertical directions of the backrest, and will preferably but not necessarily have its greatest thickness in the lumbar region of the backrest. The thickness of the elastic layer between the inner surface of the cavity and the surface facing a user may have a minimum desired value, depending on the material used. The thickness may for instance be selected so that individual coils in the underlying spring assembly can not be felt through the elastic layer. The thickness of the elastic layer covering the resilient means is preferably, but not necessarily constant over the area of the cavity.
The resilient means comprising ,multiple parallel pocketed spring assemblies may be made up of spring assemblies having different sizes. The parallel spring assemblies making up the resilient means may for instance vary in spring height, coil diameter and wire diameter. Depending on the location in the seat backrest, the pocketed spring assemblies may comprise coiled springs of different heights. The height of a coiled spring member in a spring assembly may, for example, be selected between 30-60 mm. Suitable steps for varying heights between adjacent spring assemblies may in this case be 30, 40, 50 or 60 mm.
The properties of each spring assembly may be controlled by selecting coiled springs having different wire diameters. For instance, if one or more spring assemblies require a relatively higher spring stiffness than one or more adjacent spring assemblies, then a coiled spring with a greater wire diameter is selected. Examples of suitable spring wire diameters may be 1-1,5 mm, which wire diameters may be varied in steps of, for instance, 0,1 mm.
The size and resilient properties of the pocketed spring assemblies may also be varied by selecting coiled spring members having different coil diameters.
Hence, it is possible to adapt the physical dimensions of the resilient means by varying the length and/or height, as well as the number of adjacent spring assemblies making up the resilient means. The desired resilient properties of each spring assembly may be modified by selecting a suitable height, coil diameter and/or wire diameter for each coiled spring member. A further factor to consider is the available thickness of the elastic material comprising the cavity into which the resilient means is placed during assembly of the seat backrest. If the thickness of the elastic layer between the inner surface of the cavity and the surface facing a user has a minimum desired value, then a spring with a lesser height may be required for part of the length of the resilient means. This may be the case where the thickness of the elastic layer is gradually reduced between the lumbar region and the upper region of the backrest. A reduction in thickness where parallel spring assemblies are arranged to extend in the vertical extension of the backrest may be achieved by combing individual spring assemblies with different heights end-to-end.
The rigid frame may preferably, but not necessarily, comprise a rigid shell delimiting the outer peripheral contour of the backrest and having a vertical extension substantially conforming to the shape of a spinal column. This shape may be imparted through the resilient means and the at least one elastomeric layer to the upholstery layer facing a user. The frame may comprise a suitable moulded resin material, for example an ABS-plastic material. A frame of this type may be reinforced by an injection or coating of polyurethane and/or by metal inserts. Reinforcing ribs in the surface of the frame itself may also be used.
During the manufacture of the backrest, the resilient means may be placed in its intended position on the frame and the elastomeric is located onto the frame where the resilient means is slotted into the cavity. The elastomeric layer may be attached to the frame by any suitable means, such as an adhesive. The upholstery layer is then placed over the surface facing the user and is mounted to the frame. The upholstery layer may either be attached around the outer peripheral edge thereof, or stretched around the rear surface of the frame to partially or completely cover the rear surface of the backrest.
The ergonomic chair according to the invention is primarily intended to provide an improved support for at least the lumbar region of the back, but may also be extended to the thoracic region located above the lumbar region.
In this context, the lumbar region is defined as the region of or pertaining to the abdominal segment of the torso, between the diaphragm and the pelvis. The five vertebrae in the lumbar region of the back are the largest and strongest in the movable part of the spinal column, and can be distinguished by the absence of a foramen in the transverse process, and by the absence of facets on the sides of the body. In most mammals, the lumbar region of the spine curves outward forming a curvature that is concave posteriorily. The actual spinal cord terminates between vertebrae one and two of this series, called L1 and L2. The nervous tissue that extends below this point are individual strands that collectively form the cauda equina. In between each lumbar vertebra a nerve root exits, and these nerve roots come together again to form the largest single nerve in the human body, the sciatic nerve. The sciatic nerve runs through the back of each leg and into the feet. This is why a disorder of the low back that affects a nerve root, such as a spinal disc herniation, can cause pain that radiates along the sciatic nerve down into the foot. There are several muscles in the low back that assist with rotation, flexibility and strength. These muscles are susceptible to injury, especially while lifting heavy objects, or lifting while twisting. The lumbar portion of the spine bears the most body weight and also provides the most flexibility, a combination that makes it susceptible to injury and wear and tear over time. This is why low back pain is so prevalent.
The thoracic region is located immediately above the lumbar region. The thoracic vertebrae extend from the seventh cervical vertebra down to the first lumbar vertebra. The transverse processes or the thoracic vertebrae have surfaces that articulate with the ribs. Some rotation can occur between the thoracic vertebrae, but their connection with the rib cage prevents much flexion or other excursion.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described in detail with reference to the attached figures. It is to be understood that the drawings are designed solely for the purpose of illustration and are not intended as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to schematically illustrate the structures and procedures described herein.

Figure 1: schematically illustrates a perspective view of a chair provided with a backrest according to the invention;
Figure 2: shows a front view of the chair in Figure 1;
Figure 3: shows a cross-sectional view taken in a vertical plane through the backrest of the chair in Figure 2;
Figure 4: shows a cross-sectional view taken in a horizontal plane through the backrest of the chair in Figure 2; and
Figure 5: shows an exploded view of the internal structure of the backrest.

EMBODIMENTS OF THE INVENTION

Figure 1 schematically illustrates a perspective view of a chair provided with a backrest according to the invention. The chair described in this example is an office type chair. With reference to Figures 1 and 2, a chair 10 according to the shown example comprises a central column 11 with adjustable height which column 11 is attached to a base 12. The base 12 is provided with a number of wheels 13 upon which the chair 10 can be moved around. In this example five wheels are used. At its upper end the central column 11 supports a seat support structure 14, on which a seat 15 is fastened. The chair further comprises a pair of armrests 16 attached to two arms 17 which extend laterally and from opposite sides of the chair relative to the seat support structure 14.
The chair 10 comprises a backrest 20 attached to a backrest support structure 21. A lower portion of the backrest support structure 21 is attached to the seat support structure 14 and an upper portion of the backrest support structure 21 is attached to a lower portion of the backrest 20. A headrest 22 is attached to a headrest support structure 23 at an upper portion of the backrest 20.
The chair 10 is also provided with a number of control levers for releasing, adjusting and locking the relative positions of the seat 15, the backrest 20 and the headrest 22. The control levers can be conventional devices for adjusting the vertical, longitudinal or angular position of the seat; the vertical or angular position of the backrest; or the vertical position of the headrest. These control levers are not part of the current invention and will not be described in further detail here.
Figure 2 shows a front view of the chair in Figure 1. The backrest 20 shown in this figure is provided with a lumbar support structure in the form of a resilient means 24. The resilient means 24 is arranged internally in the backrest 20 and is schematically indicated in dashed lines in Figure 2.
Figure 3 shows a cross-sectional view taken in a central vertical plane III-III at right angles to and in the vertical extension of the backrest 20 of the chair shown in Figure 2.
The backrest 20 comprises a rigid frame 25 supporting a contourable portion including a covering upholstery layer 26 and an elastomeric layer 27 interposed between the covering upholstery layer 26 and the frame 25. The resilient means 24 is arranged between the frame 25 and the elastomeric layer 27 to impart a curvature to the covering upholstery layer 26 and the elastomeric layer 27 to produce a desired contour at least in the lumbar region L. This curvature is mainly determined by the shape or contour of the surface of the rigid frame 25 facing the elastomeric layer 27 and the resilient means 24. The resilient means 24 is located in a corresponding cavity 28 in a portion of the elastomeric layer 27 facing the frame 25 and comprises a number of parallel pocketed spring assemblies 30. Figure 3 shows the resilient means located in the lumbar region L. However, as indicated by dash-dotted lines in Figures 2 and 3, a further resilient means 24' can extend from the lumbar region and at least up to the thoracic region T. Depending on the desired application, the resilient means can extend over a limited area, as indicated by the resilient means 24 in the lumbar region, or over a larger area, as indicated by the further resilient means 24' in the lumbar and thoracic regions. In fact, the vertical and transverse extension of the resilient means can cover the entire area 24" of the backrest facing the user.
Figure 4 shows a cross-sectional view taken in a horizontal plane IV-IV in a transverse direction through the backrest 20 of the chair 10 in Figure 2.
As indicated in Figure 4, the outer dimensions of the resilient means 24 is substantially the same as the dimensions of the cavity 28. The resilient means 24 is arranged to fill the cavity in the vertical and transverse extension of the backrest 20. Similarly, the thickness of the resilient means 24 in its unloaded state, measured at substantially right angles to the frame 25, is substantially the same as the depth of the cavity 28 into the surface of the elastomeric layer 27 facing the frame 25.
In the example shown in Figure 4, the resilient means 24 comprises three parallel pocketed spring assemblies 30. The number of spring assemblies can be varied, depending on the coil diameter and/or wire diameter used for each spring assembly, depending on the desired properties in each section of the backrest. Each spring assembly 30 comprises one pocketed continuous coiled metal spring member formed by coiling a spring metal wire. Each said continuous spring member is enclosed in a fabric covering 31 and extends between opposing sides of the cavity 28. The continuous coiled spring members are only schematically indicated in Figures 3 and 4. For instance, in Figure 4, the continuous coiled spring members can be formed from a single length of wire formed into a row of single or parallel coil springs. In the latter case, the continuous coiled metal spring member comprises a row formed by a pair of coil springs arranged interconnected and side-by-side along the extension of the spring assembly.
The pocketed spring assemblies 30 are enclosed by a pair of facing fabric sheets 31, 32 which are joined to each other and divided into a plurality of pockets by spaced lines 33 of attachment. This is indicated in Figure 5, which shows an exploded view of the internal structure of the backrest. Each pocket contains a single coiled spring member and each of said pockets has a length equal to the spring assembly 30. In order to form suitable pockets, a first sheet 31 is kept flat, while a second sheet 32 is given an undulating shape and is attached to the first sheet along the upper portion of each undulation. In the example shown in Figure 4, the lines 33 of attachment will be located in an outer surface of the resilient means 24, facing the frame 25. The pockets formed between adjacent lines of attachment are sufficiently large to allow a coiled spring member to be introduced into each pocket. Each coiled spring member can be attached to one or both material sheets at one or more locations in order to hold the coiled spring member in place within its pocket.
Each continuous spring member is formed from a single length of wire formed into a plurality of parallel coil springs, each of said coil springs having an upper end turn, a lower end turn and a plurality of central convolutions between said end turns. The said central convolutions may define an axis of said coil spring, said coil springs of said continuous spring member being arranged in a row and interconnected by interconnecting segments of wire located alternatively in top and bottom faces of the continuous spring member. In this example, the height of the spring assemblies 30 is equal to the depth of the cavity 28 between the frame 25 and the elastomeric layer 27.
According to the example shown in Figure 3 and 5, the parallel pocketed spring assemblies 30 extend between opposing surfaces in the cavity 28 in the vertical extension of the backrest 20. In this case, the length of all the parallel spring assemblies 30 is equal in the direction of the vertical extension of the backrest 20. However, a resilient means as described above can comprise one or more spring assemblies along opposite outer side edges of the resilient means having a reduced length, or two or more central spring assemblies having an increased length.
According to the above examples, the cavity containing the pocketed spring assemblies can be arranged in the lower part of the backrest, that is, in an area correspondence with the lumbar region of the user's vertebral column. Alternatively, the cavity containing the pocketed spring assemblies can be arranged in the lower and intermediate part of the backrest, that is, in correspondence with the lumbar region L and the thoracic region T of the user's vertebral column. The approximate location of these regions are indicated in Figure 3.
In the above examples, relating to Figures 1-5, the cavity 28 containing the pocketed spring assemblies 30 is arranged to extend at least between 1/3 and 3/4 of the transverse width of the backrest 20 in the lumbar region L thereof. Also, the transverse thickness of the elastomeric layer 27 varies in both the vertical and the transverse direction along the frame 25, and has its greatest thickness in the lumbar region L of the backrest 20.
The rigid frame comprises a rigid shell delimiting the outer peripheral contour of the backrest and having a vertical extension substantially conforming to the shape of a spinal column. This shape may be imparted through the resilient means and the at least one elastomeric layer to the upholstery layer facing a user. The frame may comprise a suitable moulded resin material, in this case a polyurethane reinforced ABS-plastic material. As indicated in Figures 3 and 4, the covering upholstery layer 26 extends not only over the entire elastomeric layer 27 facing the user, but also the rear surface of the frame 25.
The invention is not limited to the embodiments described above. For instance, in the embodiment shown in the figures the resilient means is shown to extend over a limited area of the backrest. However, the resilient means may, if desired, extend over the entire area of the backrest facing a user. Also, according to an alternative example, the parallel pocketed spring assemblies can extend between opposing surfaces in the cavity in the transverse extension of the backrest. The pocketed spring assemblies arranged in this way may be located in an area correspondence with the lumbar region of the user's vertebral column, or in correspondence with the lumbar and thoracic regions of the user's vertebral column.
In addition, the backrest may also be a detachable and/or portable unit. A portable backrest may be attached to and used in other applications, such as vehicle seats, wheel chairs or other types of chairs. For this purpose the outer periphery or the rear portion of the backrest may be provided with suitable attachment means compatible with a seat belt, a strap or a system of straps for releasable attachment of the backrest.

Claims

A seat backrest (20) comprising a rigid frame (25) supporting a contoured portion constituted by a covering upholstery layer (26) and at least one elastomeric layer (27) interposed between the covering upholstery layer (26) and the frame (25); and resilient means (24) between the frame (25) and the elastomeric layer (27) to impart a curvature to the covering upholstery layer (26) and the elastomeric layer (27) to produce a desired contour at least in the lumbar region, wherein the resilient means (24) is located in a cavity (28) in a portion of the elastomeric layer (27) facing the frame (25) characterized in that the resilient means (24) comprises at least one pocketed spring assembly (30), said pocketed spring assembly (30) comprising at least one continuous coiled spring member formed into a row of coil springs, each said continuous coiled spring member being enclosed in a covering material (31, 32) and extending between opposing sides of the cavity (28).
A seat backrest according to claim 1, characterized in that each pocketed spring assembly (30) comprises a covering material (31, 32) including a pair of facing fabric sheets (31, 32) joined to each other, said fabric sheets (31, 32) being divided into a plurality of pockets by spaced transverse lines (33) of attachment, each pocket containing a single coiled spring member, each of said pockets being of a length equal to a pocketed spring assembly (30).
A seat backrest according to claim 1 or 2, characterized in that said continuous coiled spring member being formed from a single length of wire formed into a plurality of parallel coil springs, each of said coil springs having an upper end turn, a lower end turn and a plurality of central convolutions between said end turns, said central convolutions defining an axis of said coil springs, said coil springs of said continuous coiled spring member being arranged in a row and interconnected by interconnecting segments of wire located alternatively in top and bottom portions of the continuous coiled spring member.
A seat backrest according to any one of claims 1-3, characterized in that the height of the at least one pocketed spring assembly (30) is equal to or greater than the depth of the cavity (28) between the frame (25) and the elastomeric layer (27).
A seat backrest according to any one of claims 1-4, characterized in that the at least one pocketed spring assembly (30) extends between opposing surfaces in the cavity (28) in the vertical extension of the backrest (20).
A seat backrest according to any one of claims 1-4, characterized in that the at least one pocketed spring assembly (30) extends between opposing surfaces in the cavity (28) in the transverse extension of the backrest (20)_.
A seat backrest according to any one of claims 1-6, characterized in that the cavity (28) containing the at least one pocketed spring assembly (30) is arranged at least in a lower part of the backrest (20), that is, in correspondence with the lumbar region of the user's vertebral column.
A seat backrest according to any one of claims 1-6, characterized in that the cavity (28) containing the at least one pocketed spring assembly (30) is arranged at least in a lower and intermediate part of the backrest (20), that is, in correspondence with the lumbar and thoracic regions of the user's vertebral column.
A seat backrest according to any one of claims 1-8, characterized in that the resilient means (24) comprises pocketed spring assemblies (30) of different lengths.
A seat backrest according to any one of claims 1-9, characterized in that the cavity (28) containing the pocketed spring assemblies (30) is arranged to match the size of the resilient means (24).
A seat backrest according to any one of claims 1-10, characterized in that the resilient means (24) comprises pocketed spring assemblies (30) of different sizes.
A seat backrest according to claim 11, characterized in that the pocketed spring assemblies (30) comprises coil springs of different heights.
A seat backrest according to claim 11 or 12, characterized in that the pocketed spring assemblies (30) comprises coil springs having different wire diameters.
A seat backrest according to any one of claims 11-13, characterized in that the pocketed spring assemblies (30) comprises coil springs having different coil diameters.
A seat backrest according to any one of claims 1-14, characterized in that the frame (25) comprises a rigid shell delimiting the outer peripheral contour of the backrest (20) and having a vertical extension conforming to the shape of a spinal column.
A seat backrest according to any one of claims 1-15, characterized in that the frame (25) comprises a moulded resin material.