Field of the invention

The invention relates to furniture, and a furniture constaiction set.

Background of the invention

Many systems are known to provide furniture that can be reduced in size and volume, allowing easy use, transportation and assembly. For instance, many types of collapsible chairs and tables are known. For instance for use in camping, there are many known types of collapsible chairs.

Alternatively, furniture is known that can be assembled and disassembled in an easy way.

US5667329 according to its abstract describes a quick change PVC pipe connection system which comprises a pipe having a pair of opposite spaced apertures extending through one end. A fitting has a flange with a pair of opposite spaced orifices extending through the flange. A pair of pins are provided. A facility within the pipe is for forcing each pin through one aperture in the pipe and into one orifice in the flange of the fitting, when the end of the pipe is inserted into the flange of the fitting, so as to retain the pipe to the fitting. The connection system seems to use standard PVC pipe, and in an embodiment shown in the drawings, it is used for building a chair, although the description remains very general. PVC pipe does not seem suited for building ridged furniture.

EP1256305 according to its abstract describes a connecting element for connecting at least two pipes and/or for closing at least a pipe end. Here, the connecting element is connectable via a groove-spring connection or the like with the respective tube, in which preferably the spring is provided to the connecting member and the groove is provided on the tube. Preferably, the tube is in the region of the connection with the connecting element partially hollow and the connecting element can be inserted in the tube. By joining pipes with this connection element a piece of furniture is created, especially a towel rack. US3893774 according to the abstract relates to pipe connectors for connecting square pipes in three dimensions to form show cases or article display stands, etc. In particular, according to the introduction, the documents ".. contemplates a two-piece pipe connector for connecting square pipes to form a finished structure comprising a cube-like base piece with connecting legs as well as a disk-like head and a locking sleeve having an open end and a rectangular end sized to enter a square pipe. The open end receives the disk-like head." It continues "This invention is particularly useful with connectors to be used for connecting pipes in three dimensions when displaying relatively small-sized articles for sale so that one of the principle objects of the present invention is to provide connectors capable of connecting pipes firmly and securely and which are easy to manufacture."

In that construction, pipes that have a rectangular cross section are pressed relatively loosely onto a connector end and subsequently rotated 45 degrees, resulting in a friction locking. A separate locking sleeve of elastic material is provided for that friction locking.

JPS501 1832 discloses a construction similar to US3893774. Here a pipe that has a rectangular cross section is placed on a connector end relatively easily due to an non- rectangular cross section of the connector end. The rectangular pipe is then rotated 45 degrees in order to squeeze the pipe onto the connector end. This provides a constaiction that can only hold limited, constant loads. Temperature changes may also influence the firmness of locking.

Summary of the invention

The invention provides a piece of furniture that provides easy transportation, assembling and provides a stable furniture construction.

The invention pertains to piece of seating furniture comprising a furniture frame comprising a series of tubes having a non-circular cross section and a series of coupling elements for coupling said tubes together, said series of coupling elements comprising at least one coupling element comprising at least three tube-receiving ends, said tube- receiving ends having a root and an end, said end of at least one of said tube-receiving ends further comprising a bushing, said bushing having a dimension adapted for tightly fitting at the end of said tube-receiving end and a dimension fitting said tubes, wherein said tubes and said tube-receiving ends comprise respective locking means for in a blocking position blocking longitudinal movement of a said tube and a said coupling element with respect to one another when said tube is slid onto a tube-receiving end, and in a free position allowing said tube to be removed from said tube-receiving end.

The invention further pertains to a furniture constaiction set, comprising a series of tubes and a series of coupling elements having ends allowing coupling with ends of said tubes.

The piece of furniture can be disassembled into an easily storable and transportable package. Furthennore, it allows a relatively light-weight constaiction, for instance for a chair having a weight of less than 5 kg.

Furthermore, it allows for a constaiction in which several pieces for furniture can be combined, for instance into a complete lounge set. Alternatively, it may even be considered to make other pieces of furniture, like a bed. This also requires a tight fitting of tube and coupling part for preventing for instance squeaking.

A tube can also be referred to as a hollow structural section or hollow section. This can be a metal profile with a hollow tubular cross section, but also plastic and/or fiber reinforced sections are possible. Such a hollow structural section of members can in general be circular, square, or rectangular sections, although other shapes are available, such as elliptical.

A hollow structural section may also be referred to as a tube or structural tubing. The corners may be heavily rounded, and may have a radius which is approximately twice the wall thickness. The wall thickness can be uniform around the section.

A hollow structural section in three basic shapes can also be referenced as circular hollow section, square hollow section, and rectangular hollow section.

In the current invention, in embodiments the tubes are made of metal. In embodiments, the tubes are made of aluminium, which provides a good trade-off between weight and price. As will be elucidated below, the tubes in embodiments have a substantially rectangular cross section with rounded corners. Tn embodiments, walls between the rounded corners have an outward curvature. These walls can also be labelled as slightly convex. It was found that this allows a higher flexure strength.

Coupling elements can be made from material suitable for the specific purpose.

In particular, polymer material, including reinforced polymer material, and metal are suitable. In particular, these materials are mouldable materials. In an embodiment for providing tight fitting, the material is dimensionally stable. The material in an embodiment has a compression strength of at least 80 MPa, in particular more than 100

MPa. Good fitting was possible when a strength ISO2039-1 was more than 100 MPa, in particular more than 150 MPa.

In embodiments, a coupling element is injection moulded. Other production methods are also possible, like 3D printing.

The coupling elements can be produced completely or partly from metal, like for instance aluminium. This can for instance be produced using injection moulding, or even 3D printing. Metal can be selected for combining high strength and low weight.

Alternatively or in combination, a coupling element can be produced from a polymer material, for instance an injection-mouldable polymer composition. Such a composition may comprise a reinforcement, for instance a reinforcement insert or fiber reinforcement. As an example, for the coupling elements a suitable polyamide like nylon can be used. For instance a material marketed under the name Grivory may be used. In an embodiment, PA6 (Nylon-6) with between 20 and 40 Wt % (in particular around 30% by weight) glass fiber and UV-resistant additive may be used. For the tubes, in an embodiment aluminium of the type 6063 -T66 can be used, or aluminium of the type 6063-T66, or T5 aluminium.

The bushing can be made of a metal or it can be can or comprise a polymer composition. The bushing can be injection moulded, 3D printed, or it may be produced using another, suitable method for mass production. Just like the coupling element, the bushing is from a material that is dimensionally stable. Preferably, the compression strength is also at least 80 MPa.

In particular, the current design allows a demountable or disassemblable furniture piece. In particular, it proved possible to design such a piece of furniture that also complies with any one of NPR-CEN/TR581-4, EN581 -2, NEN-EN 1022 and NEN-EN

1728:2000, or in combination.

In an embodiment, the tube-receiving ends are dimensioned for fitting in an end of said tubes, and said bushing has an inner dimension adapted for fitting around said tube-receiving end and an outer diameter for tightly fitting inside one of said tubes.

In an embodiment, a coupling element comprises a common part from which tube-receiving ends extend. The tube-receiving ends are attached to the common part at their roots. In an embodiment, the tube-receiving ends at or near said root comprise a diameter increasing part dimensioned for tightly fitting in said tube. In order to prevent clearance and provide tight fitting while maintaining easy mounting, at or near the end a tube-receiving end comprises a further diameter increasing part. The diameter increasing part may partly or completely comprise said bushing.

In an embodiment, the tube-receiving ends not provided with said bushing comprise a diameter increasing part dimensioned for tightly fitting in said tube.

In an embodiment, the piece of furniture further comprises a locking provision for blocking longitudinal movement of said tube and said coupling element with respect to one another.

In an embodiment, said tube-receiving ends comprise a tubular end. In particular, the tube-receiving end has a cross section matching a cross section of the tubes, more in particular said tube-receiving and said tubes have a production tolerance in diameter of less then 0.6%, in particular less then 0.3%.

In an embodiment, the tube-receiving ends provide tube-receiving sleeves, said tube-receiving sleeves having an opening and an end, and said bushing is an insertable bushing, said bushing having an outer dimension adapted for fitting in said opening of said tube-receiving sleeve and an inner diameter fitting around said tubes.

In an embodiment, the bushing comprise an abutment flange for extending from said outer dimension of said coupling sleeve and a abutment against said opening of said tube-receiving sleeve and a bushing end for extending in said tube-receiving sleeve.

In an embodiment, the tube has an unround cross section, and the tube-receiving end has a matching unround cross section. In embodiments, an example of such an unround cross section is provided. In particular, the cross section is substantially rectangular. In an embodiment thereof, the tubes are substantially or functionally rectangular with rounded corners.

In an embodiment, at least one tube-receiving end of a coupling part comprises a rabbet in at least one quadrant of its cross section.

In an embodiment, at least some of said tubes have a substantially rectangular outer cross section with one quadrant comprising a rabbet. In an embodiment, said rabbets of tubes coupled together by said coupling elements provide a perimetrical rabbet for holding a rectangular panel. In particular these rabbets provide a frame or cadre about the panel.

In an embodiment, said tubes have rounded corners, in particular when going from a wall part to said rounded corner, said rounded corners have a curvature which is continuous.

In an embodiment, the tubes have a functionally rectangular cross section with rounded corners and have walls connecting these rounded corners, wherein said walls have an outward curvature about a longitudinal axis of said tubes, in particular said walls are convex. It was found to provide increasing strength. Furthermore, it allows more firm hold of a tube-receiving end.

In an embodiment, the cross section of the tube-receiving end matches the cross section of tube. In particular, an outer cross section of a tube-receiving end matches an inner cross section of a tube. In an alternative embodiment, an inner cross section of a tube-receiving end matches an outer cross section of a tube. The tube-receiving end or a coupling part and a tube are designed to mutually provide a tight fit of a tube end on a tube-receiving end of a coupling part. In particular, to allow on the one hand relatively easy mounting, and on the other hand allow a tight-fitting without clearance, the tube- receiving end near its root and near its end have a modified cross section to provide a tight fit. In particular, one or more tube-receiving ends comprise a bushing for modifying this fitting, for providing this tight fit. In an embodiment, the coupling element comprises tube-receiving ends comprising tube parts that have a cross section that matches a cross section of the tubes.

In an embodiment, the tubes have a functionally rectangular cross section with rounded corners.

In an embodiment, at least some of said tubes have a substantially rectangular outer cross section with one quadrant comprising a rabbet, and said rabbets of mutually coupled tubes together providing a perimetrical rabbet for holding a rectangular panel.

In an embodiment, at least part of said coupling elements comprise two tube- receiving ends that are mutually rectangularly oriented.

In an embodiment, at least part of said coupling elements comprise three tube- receiving ends that are mutually rectangularly oriented. In an embodiment, at least part of said coupling elements comprise four tube- receiving ends that are mutually rectangularly oriented.

In an embodiment, the tube-receiving sleeves at their coupling element ends comprise an abutment against a tube end inserted in said sleeve of said coupling element, in particular said abutment is provided to hold the tube ends against displacement in a direction normal to the tube surface, more in particular said abutment comprising a series of ledges abutting an outer surface of a tube end when inserted in said sleeve at four opposite sides for holding said tube end positioned.

The invention further pertains to a piece of furniture comprising a furniture frame comprising a series of tubes having a non-circular cross section and a series of coupling elements for coupling tubes together, said series of coupling elements comprising at least two tube-receiving ends, said tube-receiving ends having a root and an end, at said root, said tube-receiving ends comprise a diameter increasing part having an outer dimension for tightly fitting in said tubes, and said tube-receiving ends further comprising a diameter increasing part near said end having a dimension for tightly fitting in said tubes. In this respect, tolerances in diameter of the tube are less than +/- 0.7%, in particular less than +/- 0.6%. for instance, at a diameter of about 3.00 cm, production tolerances are +/- 0.15 cm. Regarding the tube-receiving end, the tolerances are at least as tight as for the tube. In particular, tolerances are less than 0.3%. For instance, when the inner diameter of the tube is 3.00 cm as illustrated above, production tolerance of the diameter of the tube-receiving end are 3.00 cm -0.20cm - 0.15 cm. In this example, the tube-receiving end fits into the tube.

In an embodiment, said piece of furniture comprises at least one coupling element comprising at least three tube-receiving ends, wherein at least one of said diameter increasing parts comprise a bushing, said bushing having a dimension adapted for fitting at the end of said tube-receiving end and a dimension fitting said tubes.

In an embodiment, the bushing has an inner dimension adapted for fitting around said tube-receiving end and an outer diameter for fitting inside one of said tubes.

The invention further pertains to a piece of furniture comprising a furniture frame comprising a series of tubes having a non-circular cross section and a series of coupling elements for coupling tubes together, said series of coupling elements comprising at least one coupling element comprising at least three tube-receiving ends, said tube- receiving ends having a root and an end, and at least one of said tube-receiving ends further comprising a bushing, said bushing having a dimension adapted for fitting at the end of said tube-receiving end and a dimension fitting said tubes.

The invention further pertains to a furniture constaiction set, comprising a series of tubes and a series of coupling elements having ends allowing coupling with ends of said tubes.

In an embodiment of this furniture construction set, it further comprises a series of clamps for holding furniture elements together.

The invention further pertains to piece of furniture comprising a furniture frame comprising a series of tubes having a non-circular cross section and a series of coupling elements for coupling tubes together, said series of coupling elements comprising at least one coupling element comprising at least three tube-receiving ends, said tube- receiving ends having a root and an end. Further features of described embodiments can be combined with such coupling elements and/or tubes.

The person skilled in the art will understand the term "substantially" in this application, such as in "substantially encloses" or in "substantially extends up to". The term "substantially" may also include embodiments with "entirely", "completely", "all", etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term "substantially" may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term "comprise" includes also embodiments wherein the term "comprises" means "consists of.

Furthermore, the terms first, second, third and the like if used in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements. In the device or apparatus claims enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The invention further applies to a piece of furniture or parts thereof comprising one or more of the characterising features described in the description and/or shown in the attached drawings. The invention further pertains to a piece of furniture, or parts thereof, comprising one or more of the characterising features described in the description and/or shown in the attached drawings.

The various aspects discussed in this patent can be combined in order to provide additional advantages. Furthermore, some of the features can form the basis for one or more divisional applications.

Brief description of the drawings

Embodiments of a piece of furniture and parts thereof will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, showing an embodiment of a construction element, and showing in:

Figure 1 an embodiment a piece of furniture, in particular an example of a chair;

Figure 2 the chair of figure 1 with the upholstery removed;

Figure 3 an example of a complete lounge set comprising the chair of figure 1, and a matching table;

Figure 4 a detail of the chair of figure 2 as indicated;

Figure 5 an exploded view of a coupling element;

Figure 6 a cross section of the coupling element as indicated in figure 8;

Figure 7 a cross section of a coupling element as indicated in figure 7;

Figure 8 an exploded view of an alternative piece of furniture, here a chair, showing an alternative embodiment of the furniture coupling;

Figure 9 a cross section of a tube;

Figure 10 a cross section of a tube with a rabbet at one comer;

Figure 11 a four-way coupling element of figure 8 with coupled tubes; Figure 12 an exploded view of the coupling element of figure 1 1, including a sleeve

Figure 13 a cross section as indicated in figure 12;

Figure 14 a clamp for holding pieces of furniture of the lounge set of figure 3 together;

Figure 15 the clamp of figure 14 clamping together tubes parallel to one another; Figure 16 an exploded view of an alternative four- way coupling element including a sleeve,

Figure 17 an embodiment of a three-way coupling element in perspective view, and

Figure 18 an alternative embodiment of a three-way coupling element.

The drawings are not necessarily on scale.

Description of preferred embodiments

Figure 1 shows a piece of furniture 1, in particular person-carrying piece of furniture, like a seating furniture such as a chair. The piece of furniture has a frame 2. It comprises cushions 3 forming the upholstery of the chair. In the current embodiment, the cushions 3 are inflatable, making then easy to store. In figure 2, the cushions 3 are removed, showing upholstery supports 9. In the current embodiment, the upholstery supports 9 are panels that are fibre-reinforced, making these panels both ridged and lightweight. The panels may be hollow, or may comprise a foamed core, further reducing their weight.

In figure 3, it is shown how the pieces of furniture 1 form a complete lounge set. To that end, the various pieces of furniture are connected together. The seats are here coupled to form an L-shaped sofa or lounge set. Furthermore, a lounge set table 10 is provided. The table top is here from the same material as the upholstery support 9 discussed earlier.

The furniture frame 2 is build from tubes 4 that are connected to one another using coupling elements 5, 6, 7, 7'. In fact, there are in this chair three types of coupling elements used: elbow pieces 5, four-way coupling elements 6, and three-way coupling elements 7 and 7'. Three-way coupling element 7 does not have a rabbet, while coupling element 7' has a rabbet for receiving a cushion support plate 9 (shown in figure 2). The support plate 9 fits tightly in the rabbet, thus provided additional rigidity. Using tubes 4 coming in two lengths, and the coupling elements as defined, it is possible to construct the complete lounge set frame 2 that is shown in figure 2.

The depicted pieces of furniture are examples of possibilities. Furthermore, other designs of the elements (tube, coupling element, cushions, for instance) are possible that may provide separate design and/or copyright right aspects.

In figures 1-3, the tubes are slid into the tube-receiving ends. Thus, the tube- receiving end in fact forms a sleeve for receiving the end of a tube.

A first embodiment of the frame will be discussed in detail in figures 4-8. A further embodiment will be discussed in figures 8 and 11-13 In this embodiment, the tube-receiving ends are inserted into the tubes.

Figure 4 shows by way of example a four-way coupling element 6. This coupling element is also indicated in figures 1-3 in use. In figure 5, the coupling element is shown in exploded view (orientation changed, rotated 90° clockwise). In figure 6 a cross section is shown, and in figure 7 a further cross section as indicated in figure 6.

The coupling element 6 has in this case four coupling element tube-receiving ends 12 that each receives a tube 4. The ends of the tubes 4 are in this embodiment inserted into the coupling element tube-receiving ends 12. These tube-receiving ends this in fact provide sleeves 12 for receiving the ends of tubes 4 in them. The cross sectional shape of the tubes 4 and the specific construction of the coupling element 5, 6, 7 are designed to provide easy and swift coupling, but to also provide a ridged frame 2 that has very limited to no instability that most current tube-coupling element end frames have. In furniture that is used for supporting a person, for instance for seating, this is important for providing a relaxed sitting position. It is solid like ordinary home furniture. This can be achieved by reducing clearance between tube end and tube- receiving end as much as possible.

For locking and holding the coupling elements 5, 6, 7 and tubes 4 together to avoid a tube 4 getting removed from a tube-receiving end 12, locking means 13, 14 are provided. These locking means 13, 14 block longitudinal movement of tube 4 and coupling element with respect to one another. In this embodiment, the coupling elements are provided with holes 13, and the ends of the tubes are provided with spring-biased locking pins 14. The locking pins 14 as such are known.

For maintaining the tubes 4 firmly positioned in the coupling elements 5, 6, 7, two provisions are provided. First, the coupling element tube-receiving sleeves 12 are provided with a diameter adjustment at a root of a tube-receiving end 12. Furthermore, at the end of the tube-receiving end 12, a further diameter adjustment is provided. Furthermore, some of ends of the coupling element tube-receiving sleeves 12 are provided with bushings 16. It was found that providing the sleeves' inner surface with these bushings 16 in this way allows tight fitting of the tubes 4 at the receiving end or the sleeves 12. It was found that in some coupling elements 6, 7, one or more tube-receiving ends 12 needed to be provided with these bushings in order to allow them to be removed from a mould when the coupling elements are injection moulded.

The diameter adjustment in a sleeve 12 is provided by providing an abutment 21 against a tube end inserted in said sleeve 12 of said coupling element 5, 6, 7. The abutment 21 may be placed to abut the inner surface of the tubes 4. In the current embodiment, the abutment 21 abuts against the outer surface of the tubes 4, at their ends. In particular, the abutment is provided to hold the tube ends against displacement in a direction "normal" to the tube surface. In this way, in combination with the bushings 16, the tubes 4 are held in the sleeves 12 to provide a ridged frame 2 that shows not or minimal clearance. The tubes 4 do not move in the coupling elements. In the current embodiment, a series of ledges 21 is provided that each abuts an outer wall or outer surface of a tube 4. Thus, the tube end is abutted from four opposite sides.

In figures 9 and 10, embodiments of the tubes 4 in cross section are illustrated.

The tube of figure 9 in embodiments, as also illustrate in the drawings, is here used for vertical parts of the furniture. The tube is hollow, having in cross section a peripheral wall. The tube is substantially rectangular. It has four rounded corners connecting four wall parts. Here, the wall parts are curved. The wall parts 27 bulge outward. The wall parts 27 are curved in transverse direction of the tube. The radius of curvature here is around 180 mm. In embodiments, the tubes are about 60-90 cm long, and have a width of about 2-3 cm. The wall thickness can be between 1 and 1 .5 mm.

The tube 4 illustrated in figure 10 in cross section in embodiments is used for horizontal parts of the furniture. It also has a substantially rectangular cross section. It has rounded corners 15 connecting wall parts. Again, these wall parts have a radius of curvature. Furthermore, one of the rounded corners is modified by a rabbet 1 1. With tube sections having a cross section as illustrated in figure 10 with a rabbet 1 1, mounted into (or forming) a piece of furniture with a peripheral rabbet 11 as illustrated in the previous drawings, a receiving rabbet 1 1 is formed for holding for instance an upholstery support plate 9 that supports upholstery. The tubes 4 thus in fact frame the support plate 9. When the rabbet 1 1 is tightly about the support plate 9, this can provide additional rigidity.

In figures 8 and 11-13, as stated earlier, a second embodiment of the coupling of tubes 4 using coupling elements 5, 6, 7 is discussed. Again, these coupling elements 5, 6, 7 can, as mentioned earlier, have two, three, four, five or six tube-receiving ends. In this embodiment, instead of inserting the tubes 4 into the tube-receiving ends like in the earlier embodiment where the tube-receiving ends in fact form sleeves over the ends of the tubes 4, here an end of a tube 4 is slid over the tube-receiving end 29 of a coupling element 5, 6, 7. Thus, the tube-receiving end 29 of a coupling element 5, 6, 7 fits inside the end of a tube 4. Again, stability is an issue. Clearance between the inside or inner surface of a tube 4 and the coupling element tube-receiving end 29 is to be reduced as much as possible. Furthermore, weight will be reduced as much as possible while providing a solid piece of furniture.

In figures 1 1-13, as an example, a coupling element 6 that has four tube-receiving ends 29 is illustrated. As explained, there can be coupling elements having another number of tube-receiving ends 29. Often, the tube-receiving ends 29 are all perpendicular or substantially perpendicular with respect to one another. This is illustrated in the drawings. Other angles between tube-receiving ends may however be possible, for providing further creative construction possibilities. The embodiment using tube-receiving end that are inserted into tubes provide a more stable construction, and may be seem as more aesthetic.

In the embodiments shown in the drawings, the tubes 4 that define a horizontal plane in the piece of furniture are provided with a rabbet 1 1 in one quadrant. When assembled, all the rabbets of tubes that define one plane are all directed towards one another. Tn this way, an substantially peripheral rabbet 1 1 is provided that can receive and hold an upholstery support plate 9 that is shown in figure 2. The tubes 4 thus frame the support plate 9 or provide a cadre for the support plate 9.

In order to reduce the weight and material used for the tubes 4 as much as possible, while providing pieces of furniture that can carry a substantial load. Usually, a chair should hold a person of at least 150 kg while sitting in the piece of furniture, while letting himself drop in a seating position, and while getting up out of the chair. In embodiments, a tube 4 is selected that has is hollow and has a peripheral wall. The tube 4 a substantially rectangular cross section with rounded corners 15 and has walls 27 that are curved in cross section. This was shown in figures 9 and 10.

In particular, the piece of furniture should comply with any one of EN-EN 1728:2012, NPR-CEN/TR 581-4, NEN-EN 1022.

In embodiments depicted in the drawings, two types of hollow tubes 4 are used. The first type is shown in figure 9 in cross section. It has a substantially rectangular cross section with rounded corners 15. Walls 27 connecting the corners 15 are curved. The curvature is here continuous, increasing strength. In particular, when going from wall part 27 to rounded corner 15, the curvature is continuous. In this way, it provides a higher flexural strength. This allows a reduction in wall thickness and thus weight when compared to a rectangular cross section with straight walls for providing a defined flexural strength, or provide an increased flexural strength for a defined wall thickness.

Flexural strength, also known as modulus of rupture, bend strength, or fracture strength, is a material property, defined as the stress in a material just before it yields in a flexure test. The transverse bending test is most frequently employed, in which a specimen having either a circular or rectangular cross-section is bent until fracture or yielding using a three point flexural test technique. The flexural strength represents the highest stress experienced within the material at its moment of aipture. It is measured in terms of stress.

In figures 14 and 15, a clamp 40 for holding together pieces of furniture is illustrated. In particular, the clamp 40 can hold together tubes 4 parallel to one another. In this way, when using one or more similar clamps 40, pieces of furniture like illustrated in figure 1, can be held together to form a lounge set, like for instance the configuration illustrated in figure 3. The clamp 40 has a connecting bar 41 that is provided with extending arms 42. Arms 42 extend in transverse direction away from the connecting bar 41. Here, the arms are provided at opposite ends of the connecting bar 41. The arms 42 extend away from the connecting bar 41 in the same direction. The arms 42 are positioned to hold two tubed substantially parallel together. The ends 43 of the arms 42 are bent towards one another to hold the two tubes 4. Thus, the ends 43 extend around and beyond the rounded corners 15 of the tubes 4. To improve clamping and prevent tubes from nibbing against one another and get damaged, a nose 45 is provided in between the arms 42 and extending in the same direction as the arms 42.

Here, the clamp 40 holds together two tubes 4 of the type that have a rabbet 1 1, (tube illustrated in figure 10). A clamp can also be dimensioned to hold two tubes 4 of the type illustrated in figure 9.

The clamps 40 can for instance be applied for holding the lounge configuration of figure 3 together. For instance, a clamp 40 can be provided at the front region just behind a coupling element 7', and at the back rest.

As already mentioned, the fitting of the coupling elements 5, 6, 7 and the tubes 4 is important. If dimensional tolerances are too wide, the fitting of the tubes 4 onto the coupling elements 5, 6, 7 may become loose and the piece of furniture may appear less solid. For that reason, in particular the production tolerance of the coupling elements is relatively narrow. For the embodiment where the tube-receiving ends 29 are inserted into the tubes 4, the coupling elements thus all have diameter increasing portions 31 at the root of the tube-receiving ends 29. Furthermore, most of the tube-receiving ends 29 have diameter-increasing portions 30 at the end or tip of the tube-receiving ends 29. These diameter-increasing portions are provided around the tube-receiving ends 29, or for instance two opposite faces of substantially rectangular tube-receiving ends 29. The tube-receiving ends 29 may be slightly tapers, while the cross-section increasing parts (including the bushing(s)) cancel this tapering.

It was found that due to these narrow tolerances, a coupling part or element when produced in an injection moulding process would be difficult if not impossible to remove from a mould. For that reason amongst others, the already-mentioned bushings 16 have been introduced. In the design of figure 12, for instance, two bushings 16 were used on opposite tube-receiving ends 29. It was found that if tube-receiving ends 29 extend in three dimensions, the bushings 16 became needed. Thus, for coupling elements with three or more tube-receiving ends 29 and the tube-receiving ends 29 extending in three dimensions, a bushing on at least one tube-receiving end 29 was needed. For a coupling element 6 for four- way coupling, in the design of figure 12 it proved sufficient to provide a bushing 16 on two in opposite direction extending tube- receiving ends 29. In figure 12, the tube-receiving ends 29 of coupling elements 6 that does not have a rabbet 11. Figure 16 shows yet an alternative coupling element 6 that has four tube- receiving ends 29. It was found that a coupling element 6 with a bushing 16 on one tube-receiving end 29 would allow a sufficiently tight fitting of the tubes while still allowing the coupling element 6 to be produced using injection moulding, using the same dimensionally-stable or form-retaining material. In this embodiment, the tubes can be slid onto the tube-receiving ends 29 almost up to the central part of the coupling element 6. Yet, still indent 32 in the corner of the coupling element 6 (like in figure 11) is needed such that in combination with the rabbets 1 1 of attached (not shown) tubes 4 to provide a perimetrical rabbet.

Again, the respective dimensions of the tube-receiving ends 29 and of corresponding tubes 4 are such that the tubes fit tightly on the tube-receiving ends 29, allowing the tubes to be slid on, but without clearance that makes a chair squeak or gives an instable feeling in use.

In figure 17, an embodiment of a three-way coupling element is illustrated. In this embodiment, none of the tube-receiving ends 29 has a rabbet. To all three tube- receiving ends 29 of this coupling element, a tube with the cross-section indicated in figure 9 can be coupled.

In figure 18, an alternative embodiment of a three-way coupling element 7 is depicted. In fact, this embodiment corresponds to the embodiment shown in figure 8 in used in constructing a chair. Here, two of the tube-receiving ends 29 have a rabbet 32 that corresponds with the rabbet 1 1 of a tube 4 (cross section in figure 10), and the third tube-receiving end 29 is adapted for receiving a tube with a cross section as indicated in figure 9.

It will also be clear that the above description and drawings are included to illustrate some embodiments of the invention, and not to limit the scope of protection. Starting from this disclosure, many more embodiments will be evident to a skilled person. These embodiments are within the scope of protection and the essence of this invention and are obvious combinations of prior art techniques and the disclosure of this patent. Reference numbers

1 piece of furniture

2 furniture frame

3 upholstery

4 tube

5 coupling element, elbow

6 coupling element, four-way

7 coupling element, three-way

9 upholstery support / upholstery support plate

10 table

1 1 rabbet

12 tube-receiving end/coupling element sleeve

13 coupling element locking end

14 tube locking end

15 rounded corners of tube

16 bushing

17 bushing flange

18 bushing end

19 bushing locking lip

20 bushing locking hole

21 coupling element tube end abutment ledges

22 coupling element reinforced corner end

26 tube wall

27 tube wall part (bulging outward)

29 tube-receiving end

30 diameter increased portion at end

31 diameter increased portion at root

32 rabbet in/on coupling element

33 diameter increasing portion at root of tube-receiving end

34 bushing locking lip

35 bushing locking part on coupling element

40 clamp connecting bar amis end of arm reinforcement ri nose