ARTICULATION SYSTEM FOR CHAIRS

The present invention relates to an articulation system for chairs, in particular of the type in which the movements of seat and backrest are synchronized with each other.

There are known chairs, in particular for office, which comprise an articulation system comprising a rigid frame bound to a ground resting base, a seat support and a backrest support of the chair. The seat support and the backrest support are distinct and separate from each other, and are both articulated with respect to the frame and furthermore, thanks to an articulation mechanism that connects them, they are mutually articulated so that a movement of one corresponds to a predetermined movement of the other. In some solutions, the articulation system that connects the two supports is adjustable so that the relationship between the two movements can be varied.

When one of the two supports moves under an user's action (typically exerted on the backrest), the system opposes itself with an elastic reaction which tends to return both supports in the at-rest configuration (i.e. without actions). This reaction is typically obtained by means of an elastic element, for example at least one spring. In some solutions, in order to adapt the system's response to the user's weight and/or preferences, the reaction of the system to a given oscillation is adjustable, for example thanks to a user- actuatable adjustment system to vary the preload degree of the elastic element or the position of at least one anchoring point of the elastic element to the frame and/or to one of the two supports.

In some embodiments of the known articulation systems, as the user's weight varies, the reaction of the system to a given oscillation is more intense the heavier is the user (in the jargon this effect is called 'weighing-people'), regardless of the presence or not of an adjustment of the reaction of the elastic element.

WO 2009/153811 A1 describes an adjustment device for chairs comprising a main body; a seat support and a backrest support mounted on the main body; and articulation means for movably engaging the backrest support and the seat support to the main body, the articulation means comprising a lever rotating with respect to the main body and hinged to the seat support and to the backrest support, to obtain a determined relationship of movement between the backrest support and the seat support.

WO 2010/097818 A1 describes a device for synchronizing the inclination of the backrest and of the seat of a chair, of the type comprising a first crank integral with the frame of the backrest and hinged to the rear part of the seat frame and to the support, and a second crank hinged to the front part of the seat frame and to the support, to form, together with the seat frame, an articulated quadrilateral.

The Applicant has found that the known articulation systems for chairs have some drawbacks and/or can be improved in some aspects. For example, the Applicant has observed that in the articulation systems of WO 2009/153811 A1 and WO 2010/097818 A1 , the front hinge point of the seat travels along an arc of a circle with centre facing the back of the system, and this implies that, given a certain relationship between vertical component and horizontal component of the translational motion of the front part of the seat in the initial stretch of the movement (close to the at-rest configuration), said relationship changes during the movement progressively becoming unbalanced towards the horizontal component at the expense of the vertical one. In particular, the raising rate of the front of the seat per oscillation unit of the backrest is progressively lower as the degree of oscillation of the backrest increases with respect to the at-rest position. This means that the effect of the user's weight on the seat, which tends to oppose to the inclination ('weighing-people'), tends to decrease as the backrest oscillates, until it is cancelled and potentially changes sign for greater oscillations.

Still according to the Applicant, this behaviour determines a response to the oscillation perceived by the user that is not always optimal along the whole oscillation range, and/or it determines limitations in the amplitude of oscillation of the backrest and/or of the seat.

An object of the present invention is to provide an articulation system for chairs which solves one or more of the problems described above.

This object is achieved by an articulation system for chairs according to the attached claims and/or having the following features.

According to a first aspect the invention relates to an articulation system for chairs, the system comprising: - a (rigid) frame to be associated with a base of the chair;

- a (rigid) seat support mounted on said frame;

- at least one articulation element, rigid and hinged to said frame to be able to rotate about an axis of rotation, wherein said seat support is hinged to said articulation element in a rear hinge point,

- a backrest support, distinct from said seat support, coupled to said articulation element;

wherein the articulation system further comprises a (rigid) rod hinged to a front portion of said frame in a first hinge point and to a front portion of the seat support in a second hinge point,

wherein said articulation element and said rod are structured so that said articulation system assumes an at-rest configuration in the absence of oscillation forces acting on the seat support and/or on the backrest support, and a maximum oscillation configuration in which said seat support is roto-translated with respect to the at-rest configuration,

and wherein in the passage from the at-rest configuration to the maximum oscillation configuration, and vice versa, said articulation element and said rod rotate respectively about said axis of rotation and said hinge point in the opposite direction. According to a further aspect, the present invention relates to a chair comprising the articulation system according to the present invention.

The chair preferably comprises a seat for a user rigidly coupled to said seat support and/or a backrest rigidly coupled to said backrest support.

The terms vertical, horizontal, upper, lower and the like refer to a condition of normal use of a chair embodying the articulation system of the present invention. For example, 'superior' refers to a higher vertical heigt, etc.

The terms front, rear, backward, advanced and the like refer to a normal use of a chair embodying the present invention, wherein the user's legs are located at the front portion of the system. For example, 'anteriorly' refers to a more advanced position towards the front end, regardless of the specific vertical height.

Geometric elements such as angles, relative positions, etc. refer to a reference plane perpendicular to said axis of rotation.

According to the Applicant, the synchronized articulation systems between backrest and seat of WO 2009/153811 A1 and WO 2010/097818 A1 , in which the rear articulation element and the front rod rotate in the same direction and in the at-rest configuration the hinge point between rod and seat is at the front and at the top of the hinge point between rod and frame, cause that, during the oscillation, the hinge point of the seat is forced to travel, on the reference plane, a trajectory shaped as an arc of a circle with a concavity facing the axis of rotation of the rear articulation element. This movement of the front hinge point can generate an upper dead point of the trajectory of the hinge point, in which the latter moves almost horizontally, and/or the above explained dynamics of variation of the relationship between vertical and horizontal component of the translational motion of the front part of the seat.

This in turn causes functional limits to the overall articulation system, for example of the type described above.

The present solution, on the other hand, thanks to the rotation in the opposite direction of the two articulation elements, allows the generation of movement dynamics of backrest and/or seat that cannot be achieved with the rotation in the same direction, and capable of providing improved ergonomic properties to the chair, as it will be better clarified from the following.

The present invention in one or more of the aforesaid aspects may have one or more of the following preferred features, some of which refer to the aforesaid reference plane.

Preferably in the at-rest configuration said second hinge point is in a lower (and more preferably rear or vertical) position with respect to the first hinge point. Preferably in the maximum oscillation configuration the second hinge point is in a position higher than the position of the second hinge point in the at-rest configuration (more preferably posteriorly to the first hinge point, even more preferably below the first hinge point).

The aforesaid positioning of the rod allows that during the oscillation the front hinge point of the seat travels, on the reference plane, a trajectory shaped as an arc of a circle with concavity turned upwardly (and preferably anteriorly) with respect to the hinge point.

This allows for example to avoid upper dead points for the front part of the seat. Furthermore, the present solution achieves a relationship between the horizontal and vertical motion components which evolves in an opposite manner with respect to the evolution obtained in the known case of a lever articulation in which the arc of a circle has the concavity turned rearwards. For example, the raising rate increases with increasing rotation of the articulation element, throughout the whole range of the rotation of the latter. The magnitude of raising depends on the specific design of the rod.

Furthermore, according to the Applicant, the aforesaid trajectory shaped as an arc of a circle gives to the system the 'weighing people' effect described above. In fact, the support, in use, is subject to the weight force of the user, which generates a substantially vertical weight force acting on the front hinge point. This weight force can be instantaneously decomposed into a component tangential to the aforesaid arc of a circle at the hinge point and into a radial component (directed like the aforesaid joining line and which is cancelled by the constraining reaction of the rod). The tangential component of the weight force tends to push down the support in opposition to the oscillation motion and this component must be overcome to set and maintain the oscillation. Therefore, as the weight of the user varies, the reaction of the system to an oscillation is more intense the heavier is the user, even in the absence of adjustments of the reaction of the elastic element.

When the seat support is acted in roto-translation (for example by acting an oscillation force on the backrest which is articulated to the seat), the oscillation force generates an action force on the rod-support hinge point which induces the rotation of the rod and therefore the roto-translation of the seat. The action force can be decomposed into its two components: the one tangential to the aforesaid arc of a circle at the hinge point and the radial one. The radial component is cancelled by the constraining reaction of the rod, while the tangential component is the one which produces the rotational torque of the rod.

With the present invention, as the oscillation increases, the 'active' component of the weight force (i.e. the tangential one) increases progressively at the expense of the radial one, while the active component of the action force decreases at the expense of the radial one. The synergistic combination between these two trends produces a progressive stiffening of the reaction with increasing oscillation, whose magnitude is a function of the user's weight.

Finally, the Applicant considers that the front articulation by rigid rod between the seat support and the backrest support is preferable to alternative coupling systems, such as for example those with a pin sliding along a slot, since the latter involves the generation of a sliding friction (static and dynamic) between the mutual sliding surfaces of pin and slot. The Applicant has verified that this friction, having an application point in the instantaneous contact point, is difficult to control in magnitude, thus creating problems in the predictability and/or reliability of the oscillation movement.

Preferably in said at-rest configuration an angle formed between a line joining said first and second hinge point and a horizontal straight line, said angle being above the horizontal line and in front of the joining line, has a first value greater than or equal to 10° and less than or equal to 90° and in said maximum oscillation configuration said angle has a second value less than the first value and greater than or equal to 0°. The applicant has verified that these values contribute to obtaining good dynamics of movement of the seat and/or of response to the oscillation.

Preferably said first value is greater than or equal to 20°, more preferably greater than or equal to 30°, even more preferably greater than or equal to 40°. In this way, the weighing-people effect in the at-rest configuration is limited.

Preferably said first value is less than or equal to 80°, more preferably less than or equal to 70°. In this way it is possible to obtain a sensitive weighing-people effect described above even close to the at-rest configuration.

Preferably said second value is less than or equal to 40°, more preferably less than or equal to 30°. In this way a high weighing-people effect can be achieved near the maximum oscillation configuration as well as a high vertical component of the seat motion.

Preferably a difference between said first and second value of the angle is greater than or equal to 10°, more preferably greater than or equal to 20°, even more preferably greater than or equal to 30°. In this way it can be obtained good dynamics of the above described effect of progressive stiffening and/or of evolution of the relationship between horizontal and vertical components of the seat motion.

Preferably a distance between said first and second hinge point is greater than or equal to 10 mm, more preferably greater than or equal to 15 mm, and/or less than or equal to 100 mm, more preferably less than or equal to 90 mm.

Preferably a distance between said rear hinge point and said axis of rotation is greater than or equal to 20 mm, more preferably greater than or equal to 30 mm, and/or less than or equal to 150 mm, more preferably less than or equal to 100 mm.

Preferably a distance between said first hinge point and said axis of rotation is greater than or equal to 80 mm, more preferably greater than or equal to 90 mm, and/or less than or equal to 200 mm, more preferably less than or equal to 150 mm. Preferably said first hinge point is above the axis of rotation, more preferably below the rear hinge point at least in the maximum oscillation configuration. Preferably in the at-rest configuration the first hinge point and the rear hinge point differ by less than 10 mm in height.

Preferably in the at-rest and/or maximum oscillation configuration the second hinge point is above the axis of rotation, and more preferably below the rear hinge point.

The Applicant has verified that the aforesaid dimensional values and/or the aforesaid relative positions give optimal ergonomic performances.

Preferably said seat support is directly hinged to said articulation element. In this way the system is structurally simple and rational.

Preferably, at least in said at-rest configuration, the rear hinge point is above said axis of rotation.

In an embodiment, in said at-rest configuration and/or and in said maximum oscillation configuration the rear hinge point is in front of the axis of rotation. In this way, since also the rear portion of the support tends to rise during the oscillation, there is a "weighing-people" effect even at the rear hinge point. This solution is particularly advantageous in the absence of a system for adjusting the reaction of the elastic element for a given oscillation of the supports.

In an embodiment, in said at-rest configuration and/or in said maximum oscillation configuration, the rear hinge point is rearwardly with respect to the axis of rotation. In this way it is limited the raising of the legs (and in general the raising of the whole seat), since the rear portion of the support tends to lower during the oscillation. This solution is particularly advantageous in combination with a system for adjusting the reaction of the elastic element for a given oscillation of the supports, which provides for the limited 'weighing-people' effect.

In an embodiment the backrest support is rigidly constrained to said articulation element. For example, the articulation element may be a whole with said backrest support, or the backrest support can be rigidly fixed to the articulation element. In this way the whole system is structurally simple, reliable and economical in its production.

In an alternative embodiment, the backrest support is connected to the articulation element in an articulated manner. In this way, further degrees of freedom are introduced between the backrest and the seat, for greater ergonomics and/or versatility and/or comfort of the chair.

For example, in the aforesaid alternative embodiment, the articulation system can comprise a further articulation element, rigid and hinged to said frame to rotate about a further axis of rotation, wherein said backrest support is hinged to said articulation element at a part of the articulation element opposite to said rear hinge point of the seat support with respect to said axis of rotation, and it is also hinged to said further articulation element. Preferably, the articulation system comprises at least one elastic element (e.g. a spring) operatively interposed between said frame and said seat support and/or between said frame and said backrest support. In this way, advantageously, the elastic reaction force developed by the elastic element opposes to the oscillation with respect to the at-rest configuration, typically the greater the more pronounced is the inclination.

Preferably, said elastic element is configured to work in extension. Preferably in the at-rest configuration, said elastic element exerts a residual elastic returning force between support and frame ('preload'). Preferably said elastic element has a first end (directly) abutting against the frame and a second end (directly) abutting against the rear hinge point and/or against the seat support.

In an embodiment, the first end of the elastic element is directly abutting against a pin integral with said frame and placed in a front-low portion of the frame. Preferably the second end of the elastic element is directly abutting against a hinge pin defining said rear hinge point.

Preferably the chair comprises a floor resting base and a stem mounted on the floor resting base, said frame being rigidly mounted on an upper end of said stem.

The features and the advantages of the present invention will be further clarified by the following detailed description of some embodiments, presented by way of non-limiting example of the present invention, with reference to the attached figures, in which:

- figures 1 and 2 show a schematic side view of a system according to the present invention respectively in an at-rest and maximum oscillation configuration, with some parts in transparency;

- figures 3A and 3B schematically show an example of decomposition of the forces according to the present invention.

The figures show in side view an articulation system 1 for chairs according to the present invention. Typically, the opposite side of the system 1 , not visible, symmetrically comprises some elements shown and described here, as better specified.

The articulation system 1 comprises a rigid frame 2, which is for example to be rigidly mounted on an upper end of a stem 3 mounted on a floor resting base (not shown) of a chair.

The articulation system 1 further comprises a rigid seat support 4, and a backrest support 5, rigid and distinct from the seat support, both mounted on the frame in an articulated manner. In the shown examples, the seat support consists of two separate and specularly identical parts, one on each side of the system, of which only one is visible in the figures.

The chair typically comprises a seat 6 rigidly coupled to the seat support 4 and a backrest 7 rigidly coupled to the backrest support 5. The stem, the seat and the backrest are schematically shown in dashed lines only in fig. 1 , as for example of a known type. The articulation system further comprises, for each side of the articulation system, an articulation element 14, rigid and hinged to the frame to rotate about an axis of rotation 15.

In the embodiments illustrated in the figures, the backrest support 5 is a whole (i.e. a single piece) with the articulation element 14 (or better with the two articulation elements, one on each side). Alternatively (not shown) the backrest support can be distinguished from the articulation element, but rigidly fixed to the latter. In both cases, during the oscillation, the backrest simply rotates about the axis of rotation 15, for example with a maximum oscillation amplitude of 18°.

In an alternative embodiment, not shown, the backrest support is connected to the articulation element in an articulated manner, similarly to the articulation of the backrest support with respect to the frame and to the seat support described in the aforesaid document WO 2009/153811 A1 , to which reference is made for details.

The seat support 4 is directly hinged to the articulation element in a rear hinge point 16. For example, the hinge can be made with a single pin passing through the whole system, or a pair of pins, one on each side, each pin being integral with the seat support 4 and the articulation element 14.

Typically, the articulation system 1 comprises at least one elastic element 20 (only schematically shown), for example a spring, operatively interposed between the frame 2 and the seat support 4, to oppose itself to the roto-translation of the seat with respect to the at-rest configuration, the greater the more pronounced is the roto-translation. For example, a first end of the elastic element 20 is directly abutting against a fixed pin 17 integral with the frame and placed in a front portion of the frame and a second end of the elastic element is directly abutting against the hinge pin which makes the rear hinge point 16.

The articulation system further comprises, for each side, a rod 9 hinged to a front portion of the frame in a first hinge point 10 and to a front portion of the seat support in a second hinge point 11.

The articulation element 14 and the rod 9 allow the articulation system to assume an at-rest configuration (shown in figure 1), in the absence of oscillation forces acting on the seat support and/or on the backrest support (or when such oscillation forces do not exceed the possible preloading force of the elastic element

20), and a maximum oscillation configuration (shown in figure 2), wherein the seat support is roto- translated with respect to its position in the at-rest configuration and the backrest support takes the maximum possible oscillation with respect to the at-rest position. During the roto-translation, the rod 9 rotates about the first hinge point 10, fixed with respect to the frame 2. Typically, in the at-rest configuration, the seat 6 is arranged horizontally and/or the backrest 7 is substantially vertical.

It is observed that the figures show a view of one side of the system 1 , the side being defined with respect to the kinematic axes. In other words, by the sides of the system there are meant the two opposite portions of the system with respect to a median plane of the system perpendicular to the kinematic axes (e.g. axes 15, 16, 10, 11 etc). Typically, the articulation system is specular with respect to the median plane, possibly with the exception of some elements such as the elastic element that can only be present on one side or may have differences between the two sides. Therefore, for example, the illustrated elements are reproduced symmetrically also on the side of the system opposite to that shown.

As exemplarily shown in figures 1-2, in a reference plane perpendicular to the axis of rotation 15 (for example the lying plane of the figures), in the transition from the at-rest configuration to the maximum oscillation configuration, and vice versa, the articulation element 14 and the rod 9 rotate in the opposite direction about the respective axes of rotation fixed with respect to the frame.

Moreover, exemplarily, in the at-rest configuration the second hinge point 11 is in a lower and more rearward position with respect to the first hinge point 10 and in the maximum oscillation configuration the second hinge point 11 is in a position higher than the position of the second hinge point 11 in the at-rest configuration (i.e. the rod 9 is rotated clockwise with reference to the side shown in the figures).

Conventionally, in the reference plane, an angle 18 is defined as the angle formed between a line 20 joining the first and second hinge point and a horizontal line 13, the angle being above the horizontal line and in front of the joining line.

Exemplarily, as in the shown example, the angle 18 in the at-rest configuration is equal to about 60° and in the maximum oscillation configuration it is equal to 17°, with a difference between the two values equal to 43°.

Exemplarily the distance between the first and second hinge point 10, 11 is equal to about 20 mm, the distance between the rear hinge point 16 and the axis of rotation 15 is equal to about 36 mm and the distance between the first hinge point 10 and the axis of rotation 15 is equal to about 114 mm.

Preferably in the at-rest and maximum oscillation configuration, the first and second hinge point 10, 11 are below the rear hinge point 16 and above the axis of rotation 15.

In the shown example, in the at-rest and maximum oscillation configuration, the rear hinge point 16 is in front of and above the axis of rotation 15. In this embodiment, in the transition from the at-rest configuration to that of maximum oscillation, the seat roto-translates in such a way that both the back and the front (the latter to a greater extent) are lifted and retreat (giving the 'weighing-people' effect). Advantageously, the relative ratio between the raising and the retraction of the front varies as a function of the oscillation, wherein in the final stretch of the movement the raising has a higher prevalence than in the beginning of the movement. This embodiment can therefore be advantageously free of a system for adjusting the reaction of the elastic element, as in the shown example.

In an alternative embodiment, not shown, in the at-rest and maximum oscillation configuration, the rear hinge point 16 is rearwardly with respect to, and above, the axis of rotation 15. In this embodiment, in the transition from the at-rest configuration to the maximum oscillation configuration, the seat roto-translates moving rearwards so that the front remains substantially at the same height (the 'weighing-people' effect at the back is therefore negligible). Therefore, this embodiment preferably comprises a system for adjusting the reaction of the elastic element. For example, in addition to the first elastic element 20, arranged on one side of the system 1 , a second elastic element (not shown) may be provided on the other side of the system, the second elastic element having a first end abutting against a pin movable with respect to the frame 2 (by means of an adjustment system actuatable by the user or automatically, and not shown in detail as, for example, of the known type) and a second end abutting against the pin of the rear hinge point 16. In an embodiment, the adjustment system is structured to move the first end or both ends of the elastic element with respect to the frame and/or to the backrest support, and/or to vary the elastic constant of the elastic element (for example, varying the number of active spring turns). In this way the user can adjust the 'stiffness' of the response to a given oscillation.

Figures 3A and 3B show schematically, and for illustrative purposes, the rod 9, respectively in the at-rest and maximum oscillation configuration.

Number 50 indicates the weight force and number 51 indicates the action force. The ratio between the lengths of the weight force and the action force is totally arbitrary, for illustrative purposes only. For the sake of descriptive clarity, the second hinge point 11 is assumed as the application point of these forces. Numbers 50' and 51 ' indicate the respective component of the forces along the tangent to the arc of circle 30 of the trajectory of the second hinge point 11 and numbers 50" and 51 " indicate the respective component of the forces along the radial direction. The radial components 50" and 51 " are cancelled by the constraining reaction (not shown) of the rod 9.

Figures 3A and 3B show how the 'active' components of the forces 50' and 51 ' follow, during the oscillation, the dynamics described above, producing a progressive stiffening of the response of the articulation system.

In an embodiment, not shown, the front rod 9 can be replaced by a rotating element mounted on the frame with an axis of rotation parallel to the axis of rotation 15 (for example a bearing mounted on a side wall of the frame) and coupled to the seat support in eccentric position with respect to the axis of rotation of the rotating element, to make the aforesaid second hinge point (for example a pin integral with one among the rotating element and the seat support engages a respective hole or slot afforded in the other among the seat support and the rotating element, wherein the pin or the slot on the rotating element is in eccentric position).

Although in the shown examples the side walls of the seat support are externally with respect to the frame, the present invention also contemplates solutions (not shown) in which such side walls are located internally.

Moreover, the rods 9, shown externally to the seat support, can be interposed between the frame and the seat support or even inside the frame.

The present invention also contemplates solutions, not shown, wherein in the at-rest configuration the second hinge point is in an upper (and preferably front) position with respect to the first hinge point and the rear hinge point is below (and preferably rearwardly with respect to) the axis of rotation.