The invention relates to a chair frame for a swivel chair, for example for a reclining chair. The invention also relates to a chair comprising such a chair frame.

Swivel chairs are commonly known, for example as office chairs. An example of such an office chair is disclosed in the German patent: DE 42 02 067 C1. This office chair comprises a frame and a seat, wherein the seat is attached to the frame by means of a leg. The seat is, relative to the stationary leg, rotatable around a substantially vertical axis.

In DE 42 02 067 C1 , a curved, non-vertical ly extending leg is disclosed, which stretches between a middle part of the seat and a side of the frame. The lack of a vertical chair leg creates a storage space under the seat.

Reclining chairs, which typically feature a movable backrest and footrest, in order to provide a pleasant supine position, are equipped with rotating legs. An example of this is disclosed in US 2014/292052 A1 , in which also a sloping to the back standing leg is disclosed, in order to create space under the seat for the collapse of the foot rest.

A disadvantage of the well-known chairs with non-vertical legs is that they are not only load at a normal pressure, like vertical gradient legs are under the influence of gravity, but that they are also subjected to bending. Particularly disadvantageous are the changes in the direction in which the bending moment is applied, as a result of a rotation of the seat relative to the leg.

The object of the invention is to provide a chair frame which lacks the above disadvantage, or at least to provide an alternative chair frame.

The invention provides a chair frame that is configured to support the seat of a chair. The frame is a connection between a ground plane, in particular a ground plane surface, and the seat which is made to receive a person.

The frame comprises a base which is configured to rest on a ground plane. The ground plane is defined as a plane that runs parallel to a first horizontal direction and a second horizontal direction. A most stable position of the frame is obtained when the ground plane is flat, so free from relative altitude differences. Perpendicular to the first horizontal direction and the second horizontal direction is a vertical direction that is perpendicular to the ground plane.

The frame is suitable for placement on somewhat sloping ground surfaces; meaning that at least one of the vectors on the ground plane is not parallel to a horizontal direction.

The frame has been designed to provide a sufficiently wide and stable support on the ground, so that the center of gravity of the chair, including that of the seat with a person on it, is within the maximum length of the base, over which the chair would tilt. If the center of gravity would fall outside though, there would be a resulting tilting moment, which would cause the chair to tilt around the extreme length of the base frame.

The frame comprises a stand that is, through a connection, connected to the base with a proximal end, wherein the stand extends in diagonally upward direction with respect to the frame. The proximal end is defined as the end of the stand that is, in a mounted or use condition, arranged against the base.

The stand substantially extends along a longitudinal axis, where, seen along the longitudinal axis, at a side that is opposite to the proximal end a distal end is provided. The longitudinal axis substantially extends between the proximal end of the stand and the distal end of the stand.

The angled upward direction along which the stand extends is defined in a way, that the longitudinal axis of the stand stands under a non-right angle in relation to the vertical direction and also stands under a non-right angle in relation to the first horizontal

direction. The distal end of the display stand is located diagonally above the proximal end, when the frame is in use. That is to say that the distal end, seen along the vertical direction, above the proximal end, and seen along the first horizontal direction, is at distance from the proximal end.

The frame comprises a holder, which is formed at the distal end of the stand and configured to receive the seat. The holder comprises a rotating bearing that has been designed to create a lower relative rotation round a rotating axis, which mainly runs parallel to the vertical direction, between the seat and the stand. Through this rotating bearing the seat can be rotated around the rotating axis relative to the mount. The rotating bearing blocks a relative movement in the horizontal directions of the seat relative to the base, so that the seat is stationary relative to the base.

The stand is elongated and has a longitudinal axis. The stand is formed like a profile substantially extending along the longitudinal axis. Such a profile is featured as a central section, that is made in a middle area of a cross section of the profile, and an outer part, which is at distance from the middle.

Compared to a solid stand, a profile has the advantage that it is lighter and, relative to a sleeve or tube-shaped cross section, the stand has the advantage that it can better accommodate shear, and therefore capable of withstanding larger shear forces. The profile shaped stand has an additional advantage, it can be loaded on torque, which is particularly advantageous when the seat of the chair is rotated sideways from a neutral, forward position.

The stand comprises an upper flange plate and a lower flange plate. The upper flange plates extends above the lower flange plate, wherein the upper flange plate, seen along the vertical direction, is placed at a distance from the lower flange plate.

Because of the diagonally upwards stand, there are larger bending moments than the bending moments that, for example, occur in vertical stands, like those known from conventional office chairs or recliners. The bending moments on this stand result in larger normal stresses around a neutral, stress-free axis, when compared with the normal stresses that occur in the well-known vertical stands.

By creating a stand with two flange plates, at distance from each other, the occurring of normal stresses are lower, because the flange plates are at a greater distance from the neutral tension-free axis. In an embodiment the stand comprises a body plate that stretches between the upper flange and the lower flange plate. The body plate forms a connection between the upper flange plate and the lower flange plate.

The body plate, which mutually connects the flange plates in an embodiment, runs through the neutral tension-free axis, and therefore has a relatively small share in absorbing the applied bending moments.

The advantage of the stand according to the invention is that, at similar applied bending moments, it can be provided lighter than the known upright tubular stands. This is because there is more material on places where the normal stresses are greater, like the flange plates, and that there is relatively little material on places where the normal stresses are lower, such as the body plate. When no body plate would be provided, there is no material provided on the places where the normal stresses are low.

In an embodiment of the chair frame, the upper flange plate and the lower flange plate are parallel to the second horizontal direction. The two flange plates extend

substantially two-dimensional and are spanned by two vectors. In this embodiment of the frame, one of the vectors of the flange plates is parallel to the second horizontal

direction. The body plate also extends substantially two-dimensional, in which one of the two vectors, which span the body plate, extends parallel to the vertical direction.

In an embodiment, the stand has an I-shaped cross section in a plane perpendicular to the longitudinal axis. The upper horizontal part of the I-shape is formed by the upper flange plate, while the lower horizontal section of the I-shape is formed by the lower flange plate. The vertical portion of the I-shape is formed by the body plate, which is located along the vertical direction and is connected with central located parts of the flange plates.

In an embodiment the stand comprises two body plates that extend parallel to each other, in the vertical direction. The two body plates are, seen along the second horizontal direction, placed at a distance of each other. In a further embodiment, the body plates are placed at the extreme sides from the flange plates, seen along the second horizontal direction, so that a tube shaped profile is formed. The diameter of the stand, in a plane perpendicular to the longitudinal axis, has a rectangular shape.

In an embodiment the flange plates are along at least a portion of their length, seen along the longitudinal axis, connected to the body plate by means of a weld. Such a weld is relatively easy to apply, but provides sufficient strength for the stand.

In an alternative embodiment, the stand is formed as a whole, for example by means of extrusion. The flange plates are thereby integrally connected with the body plate. In a further alternative embodiment, releasable connections, such as nuts and bolts, are fitted to the flange plates to connect to the body plate.

In an embodiment of the frame, the height of the body plate of the stand is tapered along the longitudinal axis. The height of the body plate near the proximal end of the stand is larger than the height of the body plate near the distal end. The upper flange plate and lower flange plate converge there towards each other, seen from the proximal end of the stand to the distal end. Because the bending moments are greater near the proximal end than near the distal end, the flange plates at the proximal end may be further from each other than at the distal end, wherein the height of the body plate is larger at the proximal end. The smaller height of the plate near the distal end provides that less material is used, compared to than when the height of the body plate over the entire length of the stand would be equal to that at the proximal end.

In an embodiment, the base has at least three chair legs, with free ends that are configured to rest on the ground plane. The opposite ends of the chair legs are joined together in a common point. The free ends of the legs extend radially outward, from the common point.

The base comprises at least three legs, because it defines the six degrees of freedom, displacements in three perpendicular directions and rotations to three perpendicular axes, ensuring that the base is set firmly on the ground plane.

In an embodiment, the legs extend are diagonally up from their free ends towards to the common point. The relatively low standing free ends are, when being in use, in contact with the ground plane, while the common point is above the ground plane.

In the common point, the chair legs are preferably releasably connected, so that the base can be transported unassembled and can be mounted later, so that the space that the base occupies during transport is relatively small. In an alternative embodiment, the chair legs may be mounted to each other in the common point with a non-releasable connection, for example with a welded seam.

In a further embodiment, the base comprises two front legs and two rear legs as chair legs that diverge from the common point. The front legs and rear legs stretch out radially from the common point, relative to each other, and are rotated around an axis parallel to the vertical direction. The two front legs are placed on one side of the common point

substantially next to each other and the two rear legs are also placed next to each other, substantially at an opposite side of the common point.

The front legs are, measured between their free ends and the common point, longer than the rear legs. The common point, where the front legs and rear legs are connected to each other, stands thereby behind the center of gravity of the four free ends of the front legs and rear legs.

In an embodiment, the base is symmetric with respect to a symmetry-plane spanned through the vertical direction and the first horizontal direction. On either side of the longitudinal symmetric-plane, which stretches through the common point, a front leg and a rear leg is arranged.

In an embodiment of the frame, the connection between the stand and the base is arranged at the common point of the base. The tilted up stand stretches, seen along the first horizontal direction seen, between the two front legs. The holder at the distal end of the stand, which is configured to receive the seat of the chair, is, seen along the first horizontal direction, between the front legs. Preferably, the axis of rotation of the holder stretches through the center of gravity of the free ends of the legs. This ensures that, regardless of a rotational position of the seat relative to the base, the force that each leg applies on the ground plane stays the same.

Furthermore, because the proximal part of the stand itself is further to the back, it provides an additional space under the holder. For example, when the seat comprises a fold- out footrest, this additional space can be used to house the seat in collapsed state.

Relative to the known chair bases with, for example, vertical ranging stands, the additional space under the holder has the ability to attach a larger and extra-long footrest to the seat. Because according to the invention, in a collapsed state, the frame can place the long footrest, under the holder. The space for the footrest under the holder increases relative to the well-known chair frames.

In an alternative embodiment the base is H-shaped. The base has, instead of the three or more chair legs, two beams and a bridge element. The beams are configured to rest on the ground plane and extend parallel to each other. The beams are at distance from each other and are connected by the bridge element that is in a perpendicular direction between the beams.

The beams extend substantially parallel to the first horizontal direction and the bridge element extends substantially parallel to the second horizontal direction, perpendicular to the first horizontal direction.

The bridge element is on top of the beams. The beams are in contact with the ground plane, while the bridge element is above it and separated from the ground plane.

In a further embodiment, the connection between the stand and the base is in a middle part of the bridge element. The connection is provided on the bridge element, and on the part of it that is in between the beams. Preferably, the stand is arranged in the middle of the bridge element, between the beams, wherein the stand extends forward from the bridge element, seen along the first horizontal direction, between the beams.

The invention further provides a chair that is made to accommodate one or more persons. The chair comprises a seat and a chair frame according to the invention. The seat is, relative to the chair frame, rotatable around a vertical axis of rotation, so that the person in the chair can rotate around a vertical axis, without requiring a rotation of the chair base.

In an embodiment, the seat is rotatable between a neutral position, in which the seat is aligned parallel to the first horizontal direction, and a rotated position, in which the seat is rotated relative to the neutral position.

When the seat is in the neutral position, there will occur a bending moment in the stand around the second horizontal direction, wherein the upper flange plate and the lower flange plate will be respectively subjected to a tensile stress and a compressive stress.

When the seat is in a rotated position, for example when it has rotated 90° around the axis of rotation, the stand will further be exposed to a torsion moment around the first horizontal direction.

Because the stand is formed as a profile, comprising the flange plates and the body plate, both the bending moments and the torque moments of the seat are passed onto the ground plane, while the stand remains sufficiently stiff, providing a sturdy chair. In a further embodiment, the chair is a reclining chair. The chair seat comprises a seat plane and a footrest. The footrest is movable between a pull-out position, in which it is essentially parallel to the seat plane, and a folded position, in which it is folded under the seat plane.

In the pull-out position, the footrest forms, in line with the seat plane, a support for the legs and feet of the person in the chair. In the folded position, however, the footrest may not disturb the person, for example when getting in or out of the chair.

The tilted up stand of the frame provides, at least in the neutral position of the chair, an additional space under the seat plane, where the footrest may stay in its folded position.

Compared to the well-known reclining chairs with, for example, vertical ranging stands, the additional space under the seat offers the possibility of a larger, extra-long footrest. With the seat according to the invention, the footrest may, in its folded position, also be placed under the holder and the axis of rotation, such that the space for the footrest under the seat plane is thus enlarged compared to the well-known reclining chairs.

In an embodiment the armrests at the sides of the chair stretch to the ground plane. This offers the advantage that the rotatable chair according to the invention, or in particular the rotatable reclining chair, may have the appearance of a normal chair with a fixed frame.

With the well-known reclining chairs, the stand and the holder are visible, making one see that the chair is a reclining chair. The appearance of a normal armchair is reached by the tilted up stand, which allows that, at least from the front of the chair, the stand and the holder are placed out of sight, because the stand is downward and backwards. As a result, this chair fits within a larger variety of interiors, particularly when there are multiple seats, with a different appearance, placed on the same mount.

The invention will be explained on the basis of a further embodiment of the invention, with reference to the attached figures, in which:

Figure 1 shows the detailed shape of the chair frame in perspective;

Figure 2 shows a top view on the embodiment of Figure 1 ,

Figure 3 shows a side view on the embodiment of Figure 1 ,

Figure 4 shows a cross-section of a stand of the embodiment of Figure 1 ,

Figure 5 shows a top view on an alternative embodiment of the chair frame according to the invention, and

Figure 6 shows a side view of an embodiment of a chair according to the invention.

Figure 1 indicates an embodiment of a chair frame according to the invention, referred to with reference numeral 1. Chair frame 1 is created to support the seat of a chair, which in Figure 1 for the benefit of clarity is not fully displayed. Figure 6 shows a chair, using reference number 100, comprising the chair frame 1 and a seat 101.

Chair frame 1 comprises a base 10 with four legs, which are created to rest on a ground plane. The ground plane is not displayed in the attached figures, but is mainly spanned by a first horizontal direction H' and a second horizontal direction H", which are perpendicular to each other. A vertical direction (V) is defined perpendicular to the ground plane, and so under a straight angle with the first horizontal direction (Η') and the second horizontal direction (H").

Chair frame 1 is further configured to provide support to a seat, while the base 10 rests on a non-horizontal ground plane. Preferably there is a flat and evenly ground plane, so that all the legs of the frame 1 are in contact with the ground plane, and that the chair is set firmly on the ground plane.

The four legs of the base 10 comprise two front legs 1 1 and two rear legs 12. The front legs 11 and rear legs 12, turned around the vertical axis (V), are placed at an angle with respect to each other. The legs are placed mirrored relative to a mirror plane passing through the first horizontal direction (Η') and the vertical direction (V). On either side of the mirror plane a front leg 11 and a rear leg 12 of the base 10 is arranged.

The legs 1 1 , 12 diverge from a common point 13 of the base 10, where they connect with their proximal ends. The opposite ends of the legs 1 1 , 12 are free ends 1 1', 12', that radially extends from the common point 13. The free ends 11 ', 12' of the legs are configured to rest on the ground plane, so that they support the seat frame 1 and, depending on the flatness of the ground plane, form a solid support for the chair.

The front legs 11 of the base 10 are, radially measured from the common point 13, longer than the rear legs 12. The tipping point of the frame 1 , around which the chair would tilt if its center of gravity there would exceed it, is moved forward along the first horizontal direction (Η'). As a result, the center of gravity of the chair, compared to chair bases with legs of equal length, can be moved further forward, without the seat tilting. This provides an advantage when getting in the chair, or when getting up from the chair, because it stays more stable despite moving the weight of the person further forward.

The frame 1 comprises a stand 20, which is, with its proximal end 22, connected to the common point 13 of base 10. The stand is 20 through connection 21 connected to the base 10. In the embodiment of the chair frame 1 according to the invention the connection 21 is a detachable connection. This offers an additional advantage that the frame 1 can be assembled on location, so that the space required for transport is reduced. In an alternative embodiment, the stand and the base can be non-detachable, or even integral connected.

The stand 20 stretches, starting from its proximal end 22, in a sloping upward direction along a longitudinal axis (L), as displayed in more detail in Figure 3. The stand 20 comprises a distal end 23, that is, along the longitudinal axis (L), opposite to the proximal end 22.

The distal end 23 is, compared to the proximal end 22, further forward and up, past the first horizontal direction (H ') and the vertical direction (V). The longitudinal axis (L) of the stand 20, located between the proximal end 22 and distal end 23, is put under a non-straight angle (a) with the vertical direction (V) and under a non-straight angle (β) with the first horizontal direction (Η').

At the distal end 23 of the stand 20 is a holder 24. The holder 24 is configured to hold the chair seat, in such a way that the seat, relative to the frame 1 , is rotatable around a rotation axis, which runs parallel to the vertical direction (V). The holder 24 comprises a slide bearing with a cylindrical opening 25 as rotation bearing, in which the longitudinal direction of the cylindrical opening 25 extends parallel to the vertical direction (V) and the axis of rotation. The cylindrical opening 25 is created to concentrically accommodate the cylindrical pen of a seat. As a result, a rotatable connection is created between the frame 1 and the seat, which is configured to allow a relative rotation around the axis of rotation and to prevent a relative displacement between the frame 1 and seat.

As a result of the upward direction in stand 20, the holder 24 is in between the front legs 11 , instead of above the common point 13, as would be the case in a vertical direction stand. Because the rear legs 12 are longer than the front legs 11 , the holder 24 is, seen in a horizontal plane, arranged above a central area of the base 10. The point where the seat applies a vertically oriented force on the frame 1 , is located in a central area between the free ends 11 ', 12' of the front legs 11 and rear legs 12.

The stand 20 is shaped as a I-shaped profile, which is located along the longitudinal axis (L). This means that the stand 20 has an I-shaped cross section in a cross section IV - IV perpendicular to the longitudinal axis (L). In Figure 4 the cross section IV - IV is displayed in further detail.

The stand 20 comprises an upper flange plate 26 and a lower flange plate 27. Both the upper flange plate 26 and the lower flange plate 27 extend between the proximal end 22 and distal end 23 of the stand 20. The stand 20 comprises a body plate 28 located along the longitudinal axis (L) between the upper flange plate 26 and the lower flange plate 27.

The flange plates 26, 27 are aligned in such a way, that a component of the plane by which they are spanned, is parallel to the second horizontal direction (H"). The body plate 28 is arranged perpendicular to the upper flange plate 26 and arranged perpendicular to the lower flange plate 27, and is the body plate 28 is arranged parallel to the vertical direction (V).

In the present embodiment, the body plate 28 with the upper flange plate 26 and the lower flange plate 27 are connected by means of welded connections 29. These welded connections 29 extend along the flange plates 26, 27 and the body plate 28 between the proximal end 22 and distal end 23 of the stand 20.

The welded connections 29 provide a connection between the flange plates 26, 27 and the body plate 28 that is strong enough to be used in a chair frame and lateral forces in the stand 20 are evenly distributed, because the welded connections 29 are mainly along the longitudinal axis (L) of the stand 20.

In an alternative embodiment, the stand is formed by an extruded profile with a I- shaped cross section, in which the flange plates and the body plate are formed from a block and integrally connected.

The I-shaped stand 20, compared to existing sleeve-or tube-shaped stands, offers the advantage that this has a large bending stiffness and that a relatively small amount of material used. Because the two flange plates 26, 27 are on relatively large distance from each other and from a neutral (bend) axis, they can handle larger bending moments than if they are placed close to each other. The body plate 28, that is close to the (bend) axis, will contribute very little to the bending stiffness. By providing a single body plate 28, relative to for example vertical sides at a tube profile, a relatively light profile is ensured, that at the same time, ensures sufficient bending stiffness to the chassis 1.

The biggest bending moments in the stand 20 occur near the proximal end 22, because this section is on the largest distance from the holder 24, and so the biggest moment for the downward force. The height (h) of the body plate 28 of the display stand 20 is tapered along the longitudinal axis (L). Near the proximal end 22 of the stand 20, the height (h) of the body plate 28 is relatively the largest, placing the flange plates 26, 27 at a relatively large distance from each other, and with it the relatively largest bending moment. Near the distal end 23 of the stand 20 the height (h) of the body plate 28 is relatively small, because the bending moments acting on there also are relatively small.

Between the proximal end 22 and distal end 23 of the stand 20 the height (h) of the body plate 28 runs tapered, from the relatively large height (h) near the proximal end 22 to the relatively small height (h) near the distal end 23.

Figure 5 shows a top view on an alternative embodiment of the chair frame T according to the invention. The frame T comprises, as well as the frame 1 that is displayed in figures 1 - 4, a stand 20' and a holder 24', in which stand 20' is formed by two flange plates and a body plate, which extends in the vertical direction between the flange plates. The stand 20' is also located in tilted upward direction, wherein the holder 24' is, relative to a proximal portion of the stand 20', placed along the first horizontal direction (Η').

The frame 1 ' further comprises an H-shaped base 10', which is configured to support the stand 20'. The base 10' comprises two beams 30', which extends parallel to the first horizontal direction (Η'). The beams 30' are configured to rest on the ground plane and, in order to have a good stability of the frame 1 ', they are set at a distance from each other along the second horizontal direction (H").

Between the beams 30' of the base 10', along the second horizontal direction (H"), a bridge element 40' stretches. The bridge element 40' is arranged on the beams 30' and positioned above the ground plane. At a central area 41 ' of the bridge element 40', the stand 20' is connected to the base 10', by means of a connection.

The bridge element 40' is connected to the beams 30' and to a rear part 31 ' of the beams 30'. A front part 32' of the beams 30' has a greater length (i) than the length (£) of a rear part 33' of the beams 30'. This ensures that the position of the holder 24' is centrally between the beams 30' and ensures, despite the tilted stand 20', a stable chair frame 1 '.

Figure 6 is an embodiment of the chair 100 according to the invention, referred to by reference numeral 100. The seat 100 comprises the frame 1 that is displayed in figures 1 - 4. The seat 101 of the chair 100 is arranged on the frame 1 and is, compared to the frame 1 , rotatable around an axis of rotation (R) that extends parallel to the vertical direction (V). In Figure 6, the chair 100 is displayed in a neutral position, in which a sitting direction of a person in the chair 100 is parallel to the first mainly horizontal direction (Η').

The seat 101 comprises a frame element 102 that is, through a cylindrical pin 103, attached to the holder 24 of the frame 1. The cylindrical pin 103 is concentrically arranged in the through opening 25 in the holder 24, such that the seat 101 is rotatable around the axis of rotation (R), relative to the frame 1.

The seat 100 in Figure 6 is a reclining chair. To this end, the seat 101 comprises a backrest 104 that is rotatable connected to the frame element 102 and can be moved between an upright position, as is displayed in Figure 6, and a backward position, in which the backrest 104 is, relative to the upright position in Figure 6, rotated counterclockwise.

The seat 101 further comprises a footrest 105 that is rotatably attached to the frame element 102 and can be moved between a folded position and a pull-out position. In Figure 6, the footrest 105 is displayed in the folded position, folded under the frame element 102. In the pull-out position, the footrest 105 is, compared to the folding position in Figure 6, rotated counterclockwise, so that the footrest 105 substantially extends parallel to the seat plane 106 of the seat 101.

Reference list:

I chair frame

10 base

I I front leg

11 ' free end

12 rear leg

12' free end

13 common point

20 stand

21 connection

22 proximal end

23 distal end

24 holder

25 rotation bearing

26 upper flange plate

27 down flange plate

28 body plate

29 weldment

100 chair

101 seat

102 frame element

104 backrest

105 footrest

106 seat plane

V vertical direction

H' first horizontal direction

H" second horizontal direction

L longitudinal axis

R axis of rotation