WO2018173085A1 - Articulation machanism for chairs - Google Patents

Abstract

Articulation mechanism (1) for chairs comprising a frame (2), a support (4) for a seat-backrest body (5) and a first (6) and a second (7) articulation system configured in such a manner that the articulation mechanism takes on an at-rest configuration and a maximum tilting configuration, where the second articulation system (7) comprises a first slot (8) afforded in one between the support (4) and the frame (2) and a first pin (9) firmly constrained to the other between the support (4) and the frame (2), where the first pin (9) slidably engages the first slot (8) and where a first angle (10) formed between a tangent (11) to the first slot (8) in an instant contact point (12) and a horizontal line (13), above the horizontal line (13), faces rearward.

Description

DESCRIPTION

"ARTICULATION MECHANISM FOR CHAIRS"

Technical field of the invention

The present invention relates to an articulation mechanism for chairs, in particular of the type in which the seat and the backrest are mutually rigidly connected, typically in a single body.

State of the art

There are known chairs (in the jargon called 'tilting'), in particular for office, which comprise an articulation mechanism comprising a frame constrained to a supporting base for resting the chair on the ground and a support for a single seat-backrest body of the chair, the support being mounted on the frame by means of a pivot hinge, fixed with respect to the frame, so as to be able to tilt around the fixed pivot between an at-rest position and a maximum tilting position (typically for a maximum tilting amplitude of 15°-20°).

When the support is tilted under the action of a user's stress (typically exerted on the backrest), the mechanism opposes an elastic reaction which tends to set the support back into the at-rest configuration (i.e. without stress). This reaction is typically obtained by the contribution of an elastic element, for example at least one spring interposed between the frame and the support. Typically, in order to adapt the response of the mechanism to the weight and/or to the preferences of the user, the reaction of the mechanism to a given tilting is adjustable, for example thanks to a user-operated adjustment system to vary the degree of preloading of the elastic element. In the case, for example, of a spring operating in compression during the tilting, it is provided a system for adjusting the degree of compression of the spring in a given configuration (i.e. that of at-rest).

The more the spring is compressed, the higher is the reaction of the mechanism to a given tilting.

Summary of the invention

The Applicant has found that the known articulation mechanisms for chairs have some drawbacks and/or can be improved in some aspects.

For example, the Applicant has observed that in the known articulation mechanisms the difference in height of the front edge of the seat between the maximum tilting configuration and the at-rest configuration (in the jargon called 'legs lifting') may be excessive.

Furthermore, the Applicant has observed that in the known mechanisms, in order to obtain a sufficient reaction, it is necessary to size the spring considerably, with consequent increase in the overall dimensions and/or weight and/or construction costs.

Furthermore, the Applicant has observed that in the known mechanisms the adjustment system of the spring to vary the reaction of the latter, besides complicating the use of the chair by the user (who must know how to operate the adjustment), produces an increase in the overall dimensions and/or weight and/or construction costs.

An object of the present invention is to provide for an articulation mechanism for chairs which solves one or more of the problems described above. This object is achieved by an articulation mechanism for chairs in accordance with the attached claims and/or having the following characteristics.

According to an aspect the invention relates to an articulation mechanism for chairs, comprising:

- a frame (preferably rigid) designed to be associated with a base for a chair;

- a (preferably rigid) support for a (preferably rigid) seat-backrest body;

- a first and a second articulation system arranged in a rear and front portion of said frame, respectively, and configured to secure said support to said frame in an articulated manner,

wherein said articulation mechanism does not have a backrest support element distinct from said support for the seat-backrest body,

wherein said first and second articulation system are configured in such a manner that said articulation mechanism takes on an at-rest configuration, in the absence of tilting forces acting upon the support, and a maximum tilting configuration in which said support is roto-translated with respect to the at-rest configuration, wherein said second articulation system comprises, for each side of said articulation mechanism, a first slot afforded in either one of said support and said frame and a first pin firmly constrained to the other of said support and said frame, wherein the first pin engages said first slot in such a manner that said first pin slides in said first slot during the transition of the tilting mechanism from the at-rest configuration to the maximum tilting configuration and vice versa,

wherein, in a reference plane perpendicular to said first pin, a first angle, defined as an acute angle formed between a tangent to the first slot in an instant contact point between the first slot and first pin and a horizontal line, and above the horizontal line, faces rearward.

According to a further aspect, the present invention relates to a chair comprising the articulation mechanism in accordance with the present invention and said rigid seat-backrest body rigidly mounted on said support. The terms vertical, horizontal, upper, lower and the like refer to the vertical direction of gravity in a condition of normal use of a chair comprising the articulation mechanism of the present invention.

The terms front and rear refer to a normal use of a chair comprising the present invention, wherein the user's legs are located at the front portion of the mechanism.

Without limiting to any theory, the aforesaid characteristics allow that, as the user weight varies, the reaction of the mechanism to a given tilting is more intense the heavier is the user (in the jargon this effect is called 'weighing-people'), all this regardless of the presence or absence of a 'hardness' adjustment (e.g. the preload of the reaction spring or the position of its anchoring ends).

In fact, in use, the support is subject to the weight force of the user, which generates a substantially vertical weight force acting on the slot or on the pin (depending on which of the two is firmly constrained to the support). This weight force can be instantaneously decomposed into a component tangential to the slot in the instant contact point and in a component perpendicular to it (which is cancelled by the constraining reaction which has an application point in the instant contact point between pin and slot). The tangential component of the weight force tends to push down the support in opposition to the tilting motion and this component must be overcome to effect and maintain the tilting. Therefore, the aforesaid characteristics of the first angle cause, as the user weight varies, the reaction of the mechanism to a tilting to be more intense the heavier is the user, even in the absence of adjustments of the mechanism.

Moreover, the pin-slot coupling involves a sliding friction (static and dynamic) between the pin and slot surfaces in mutual sliding. This friction, having an application point in the instant contact point, is generally proportional to the overall constraining reaction perpendicular to the contact surface, which tends to push the pin and the slot against each other. This overall constraining reaction comprises the aforesaid component of the weight force perpendicular to the tangential component (and possibly the perpendicular component of the action force, better described further below). Therefore, as the user weight varies, the sliding friction force is greater the greater is the weight of the user and this effect contributes to the variation of the reaction of the mechanism according to the user weight.

In a comparative solution in which the second articulation system consists of a connecting rod directly hinged to the frame and to the support, the Applicant has found that the reaction of the mechanism is, given the same spring, generally lower than the reaction of the present invention, which uses slots and pins. According to the Applicant, this may be due to the sliding friction that develops between the pin and the slot and which, on the contrary, is negligible in the case of a connecting rod.

The present invention in one or more of the aforesaid aspects may have one or more of the following preferred characteristics. Where appropriate, the aforesaid reference plane perpendicular to the pin is taken as reference. Preferably, said first and second articulation system are configured so that in the maximum tilting configuration a front portion of said support is higher and more rearward than in the at-rest configuration. In this way, the legs lifting is limited.

Preferably, said first angle in said at-rest configuration is less than or equal to said first angle in said maximum tilting configuration. In this way, the 'weighing people' effect increases as the tilting increases.

Preferably, said first slot comprises at least one rectilinear section, more preferably it is entirely rectilinear (for example, said first angle remains constant during at least one portion of the, most preferably during the whole, movement of the tilting mechanism from the at-rest configuration to the maximum tilting configuration). In this way the mechanism, while being 'weighing-people', provides a regular reaction during the tilting (for example, the tilting force applied at one point of the backrest is substantially linear with the resulting tilting angle).

Preferably, said first angle gradually increases (more preferably monotonically) during at least one part of the, more preferably during the whole, movement of the tilting mechanism from the at-rest configuration to the maximum tilting configuration. Preferably, said first slot comprises at least one curvilinear section, more preferably it is entirely curvilinear. In this way the 'weighing-people' effect is amplified as the amplitude of the tilting increases.

In fact, when the seat support is stressed by tilting (for example by exerting a tilting force on the backrest which is firmly constrained to the seat), the tilting force generates an action force on the pin or on the slot (depending on which of the two is firmly constrained to the seat support) that produces the relative motion between pin and slot and therefore the tilting of the seat. The action force can be decomposed into its two components: the one tangential to the slot in the reaction point and the one perpendicular to the first. The perpendicular component is cancelled by the constraining reaction of the slot-pin coupling (which has an application point in the point of instant contact between pin and slot, where the perpendicular component of the action force and the constraining reaction push the pin against the slot), while the tangential component is the one that produces the relative motion between pin and slot. In accordance with the invention, as the tilting angle increases, the tangential component of the action force is progressively reduced in favour of an increase in the perpendicular component.

Moreover, as the tilting angle increases, the tangential component of the weight force increases progressively to the detriment of a decrease in the perpendicular component of the weight force.

As the tilting angle increases, the tilting force necessary for the tilting must overcome, in addition to any elastic spring reaction force (which typically increases substantially linearly with the tilting angle), also the aforesaid tangential component of the weight force, which increases progressively and the more the greater is the user's weight, provided that the tangential component of the action force decreases. The result of these effects is a gradual hardening of the reaction as the tilting increases, additional to that of the spring's elastic return force, and proportional to the user weight.

Finally, the Applicant observes that as the tilting angle increases, the contribution to the sliding friction force provided by the weight force decreases, while the contribution to the sliding friction force provided by the action force increases, thereby ensuring that the friction is always present.

Preferably, said first slot comprises at least one circular arc section, more preferably the entire first slot has circular arc extension.

The present invention also provides for solutions wherein said first angle is equal to zero in at least one tilting configuration, for example in the at-rest configuration. For example, at least a section of the first slot may be rectilinear and horizontal.

Preferably, said first angle in said at-rest configuration is greater than or equal to 10°, more preferably greater than or equal to 15°, and/or less than or equal to 50°, more preferably less than or equal to 40°.

Preferably, said first angle in said maximum tilting configuration is greater than or equal to 40°, more preferably greater than or equal to 50°, still more preferably greater than or equal to 60°.

The Applicant has verified that these conformations and/or values give the mechanism good ergonomic and/or 'weighing-people' characteristics.

In an embodiment, said first slot is afforded in said frame, preferably in a respective side wall of the frame, and said first pin is firmly constrained to said support.

In an alternative embodiment, said first slot is afforded in said support, preferably in a respective side wall of the support, and said first pin is firmly constrained to said frame, more preferably it is integral (that is, in a single piece) with said frame.

The Applicant has verified that both the aforesaid solutions have proved to be functional. According to the Applicant, the solution with the first pin integral to the frame reduces the production costs, since the pin can be moulded together with the frame and therefore does not require production and assembly as a separate element. Preferably in the embodiment wherein the first slot is afforded in the frame, said first slot has (at least a section of) curvilinear extension with the concavity facing frontward and upward. More preferably, said first slot has (at least a section of) circular arc extension with centre arranged in a front-upper quadrant with respect to the first slot.

Preferably, in the embodiment with the first slot afforded in the support, said first slot has (at least a section of) curvilinear extension with the concavity facing rearward and downward. More preferably, said first slot has circular arc extension with centre arranged in a rear-lower quadrant with respect to the first slot.

Preferably, said circular arc has a radius greater than or equal to 50 mm, more preferably greater than or equal to 60 mm, and/or less than or equal to 200mm, more preferably less than or equal to 150mm.

In this way, during the entire tilting, it is achieved a configuration of the tangents in the instant contact point of the slot-pin coupling which gives good ergonomic and/or 'weighing-people' properties, for example in terms of response to the tilting perceived by the user along the entire tilting amplitude.

Preferably, said first articulation system comprises, more preferably for each side of said articulation mechanism, a connection element (directly) hinged to said frame in a rotation point and (directly) hinged to said support in a hinge point.

Preferably, in said at-rest configuration, the hinge point is located, with reference to said reference plane, in back of a vertical line passing through said axis of rotation and/or above a horizontal line passing through said axis of rotation. In this way the legs lifting is limited, as the rear portion of the support tends to lower during the tilting.

Preferably, said first articulation system comprises, for each side of said articulation mechanism, a second slot afforded in either one of said support or said frame and a second pin firmly constrained to the other of said support or said frame, wherein the second pin engages said second slot in such a manner that said second pin slides in said second slot during the transition of the tilting mechanism from the at-rest configuration to the maximum tilting configuration and vice versa. The applicant considers that the pin-slot coupling, with respect to the connection element, produces greater friction forces as explained above, which can be advantageously exploited to reduce the size of the elastic reaction element.

In said reference plane, a second angle is defined as an acute angle formed between a tangent to the second slot in a respective instant contact point between the second slot and second pin and a horizontal line, above the horizontal line.

Preferably, said second angle in said at-rest configuration is less than or equal to said second angle in said maximum tilting configuration, said second angle facing frontward. In this way it is given good ergonomics to the seat.

Preferably, the second slot comprises at least one rectilinear section, more preferably it has entirely rectilinear extension (for example said second angle remains constant during at least a portion of the, more preferably during the whole, movement of the tilting mechanism from the at-rest configuration to the maximum tilting configuration).

Preferably, said second angle gradually increases (more preferably monotonically) during at least one part of the, more preferably during the whole, movement of the tilting mechanism from the at-rest configuration to the maximum tilting configuration. Preferably, the second slot comprises at least one curvilinear section, more preferably it has entirely curvilinear extension.

Preferably, said second slot comprises at least one circular arc section, more preferably the entire second slot has a circular arc extension.

Preferably, said second angle in said at-rest configuration is greater than or equal to 20°, more preferably greater than or equal to 30°, and/or less than or equal to 80°, more preferably less than or equal to 70°. Preferably, said second angle in said maximum tilting configuration is greater than or equal to 40°, more preferably greater than or equal to 50°, even more preferably greater than or equal to 60°.

In an embodiment, said second slot is afforded in said frame and said second pin is firmly constrained to said support. Preferably, said second slot has a curvilinear extension with concavity facing frontward and downward. More preferably, said second slot has circular arc extension with centre arranged in a front-lower quadrant with respect to the second slot.

In an alternative embodiment, said second slot is afforded in said support and said second pin is firmly constrained to said frame, more preferably it is integral (that is, in a single piece) with said frame. Preferably, said second slot has a curvilinear extension with concavity facing frontward and downward. More preferably, said second slot has circular arc extension with centre arranged in a front-lower quadrant with respect to the second slot.

See the discussion about the second articulation system.

Preferably, the articulation mechanism comprises at least one elastic element (e.g. a spring) operatively interposed between said frame and said support. In this way, advantageously, the elastic reaction force exerted by the elastic element counteracts the tilting of the support with respect to an at-rest condition, all the greater the wider is the tilting.

Preferably, said elastic element is configured to operate in extension. Preferably in the at-rest configuration, said elastic element exerts a residual elastic return force between support and frame ('preload').

Preferably, said elastic element is (directly) abutted, at a first end thereof, to the frame and, at a second end thereof, to the first articulation system or to the support for the seat. In this way the mechanism is structurally simple, rational and effective. Preferably the first end of the elastic element is abutted to a pin firmly constrained to said frame and arranged in a front-lower portion of the frame. Preferably, the second end of the elastic element is abutted to a pin firmly constrained to said support and interposed, in said reference plane, between said first and second articulation system. The Applicant has verified that, with respect to a solution in which the second end of the elastic element is abutted to the first articulation system (for example on the hinge pin between the connecting element and support or on the coupling pin between the support and the frame of the first hinge system), the above solution allows a greater and more linear elongation of the elastic element during the entire tilting, and at the same time provides a return torque of the elastic element having a greater arm during the entire movement of the mechanism. This results in a good progressivity of the reaction of the mechanism also in the last portion of the entire tilting.

In an embodiment the articulation mechanism comprises an adjustment system structured for moving a first and/or a second end of said elastic element with respect to the frame and/or the support, and/or for varying the elastic constant of the elastic element (for example by varying the number of active turns of the spring). In this way the user can adjust the 'hardness' of the response for a given tilting.

Preferably, the chair comprises a supporting base for resting it on the ground and a stem mounted on the supporting base, said frame being rigidly mounted at an upper end of said stem.

Brief description of the drawings

The characteristics 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 mechanism according to a first embodiment of the present invention in a configuration of at-rest and maximum tilting respectively;

figures 3 and 4 show a schematic side view of a mechanism according to a second embodiment of the present invention in a configuration of at-rest and maximum tilting respectively;

figures 5 and 6 show a schematic side view of a mechanism according to a third embodiment of the present invention in a configuration of at-rest and maximum tilting respectively;

figures 7 and 8 show a schematic side view of a mechanism according to a fourth embodiment of the present invention in a configuration of at-rest and maximum tilting respectively;

figures 9A, 9B and 10A, 10B schematically show an example of decomposition of the forces according to the present invention.

Detailed description of some embodiments of the invention

The figures show an articulation mechanism 1 for chairs according to the present invention. For the purposes of exposition conciseness, the same reference numbers will be used for corresponding elements in the various embodiments.

The articulation mechanism 1 comprises a rigid frame 2, which is for example designed to be rigidly mounted at an upper end of a stem 3 mounted on a supporting base (not shown) for resting a chair on the ground. The articulation mechanism 1 comprises a support 4 (preferably but not necessarily rigid) on which, in use, a rigid seat-backrest body 5 is rigidly mounted. The stem 3 and the seat-backrest body 5 are schematically shown in dashed lines only in the fig. 1 as they are known in themselves.

The support 4 is mounted on the frame 2 in an articulated manner by means of a first 6 and a second 7 articulation system arranged respectively in the rear and front position of the frame.

Consistent with the fact that the backrest (or at least one portion thereof) and the seat (or at least one portion) are rigidly connected, the articulation mechanism is devoid of a dedicated element for supporting the backrest, distinct from the support 4 for the seat-backrest body.

The first and second articulation system 6, 7 allow the articulation mechanism 1 to take on an at-rest configuration (shown in figures 1 , 3, 5, 7, 9A and 10A), in the absence of tilting forces acting on the support (or for tilting forces lower than the possible preload of the spring), and a maximum tilting configuration (shown in figures 2, 4, 6, 8, 9B and 10B) in which a front portion of the support is higher and more rearward compared to the at-rest configuration.

The second articulation system 7 comprises, for each side of the articulation mechanism, a first slot 8 afforded in either one of the support and the frame and a first pin 9 firmly constrained to the other of the support and the frame, wherein the first pin slides in the first slot during the transition of the tilting mechanism from the at-rest configuration to the maximum tilting configuration and vice versa.

In a reference plane perpendicular to the first pin (for example the lying plane of the figures or a plane parallel to it), a first angle 10 is defined as an acute angle formed between a tangent 11 to the first slot 8 in an instant contact point 12 between the first slot and first pin and a horizontal line 13, the first angle being above the horizontal line.

It is observed that figures 1 -8 show a view of one side of the mechanism 1 , the side being defined with respect to the axes of the cinematic pins. In other words, by the sides of the mechanism it is meant the two opposite portions of the mechanism with respect to a median plane of the mechanism perpendicular to the axes of the cinematic pins (i.e. the pins 9, 31 , 32, 41). Typically, the first and/or the second articulation system are specular with respect to the median plane of mechanism 1. Therefore, for example, the shown elements are reproduced symmetrically also on the side of the mechanism opposite to that shown.

Preferably, the articulation mechanism 1 comprises an elastic element 20 (e.g. a spring, only schematically illustrated in the figures) operatively interposed between the frame and the support to counteract the tilting of the support with respect to the at-rest configuration, all the greater the wider it is the tilting.

Preferably, as shown in the figures, the elastic element 20 is directly abutted, at a first end thereof, to a pin 21 firmly constrained to the frame and placed in a front-lower portion of the frame, and at a second end opposite to the first end of the elastic element, to a pin 22 firmly constrained to the support for the seat and interposed, in the reference plane, between the first and the second articulation system. Advantageously, the mechanism of the present invention is able to react with a suitable reaction, even in the presence of a single elastic element placed on one side only. The elastic element therefore makes exception to the above described symmetry of the two sides.

In the exemplary embodiments of figures 1-4, the first slot 8 is afforded in the respective side wall of the frame and the first pin 9 is firmly constrained to the support.

The mechanism 1 in the shown examples comprises a distinct and separate pin 9 for each side of the mechanism, each pin engaging a respective first slot 8. In this way it is possible to guarantee the necessary space for the elastic element, which is interposed between the two pins. However, the present invention also provides for the mechanism comprising a single pin 9 passing through the entire frame 2 and engaging both the first slots.

In the examples shown in figs. 1-4, the first slot 8 has circular arc extension with centre 15 arranged in a front- upper quadrant with respect to the first slot.

In the exemplary embodiments of figures 5-8, the first slot 8 is afforded in the respective side wall of the support and the first pin 9 is integral with the respective wall of the frame.

Exemplarily, the first slot has circular arc extension with centre 16 arranged in a rear-lower quadrant with respect to the first slot.

Exemplarily, the first angle 10, which faces rearward, is equal to 27° in the at-rest configuration, and it is equal to 88° in the maximum tilting configuration.

In the exemplary embodiments of figures 1 , 2, 5 and 6, the first articulation system 6 comprises, for each side of the articulation mechanism, a connection element 30 directly hinged to the frame in a rotation point 31 and directly hinged to the support 4 in a hinge point 32.

Preferably, in the at-rest configuration the hinge point 32 is located in back of a vertical line 33 passing through the axis of rotation and above a horizontal line 13 passing through the axis of rotation.

In the exemplary embodiments of figures 3, 4, 7 and 8 the first articulation system 6 comprises, for each side of the articulation mechanism, a second slot 40 alternatively afforded in the respective wall of the frame (figs 3 and 4) or in the respective wall of the support (figs 7 and 8) and a second pin 41 respectively firmly constrained to the respective wall of the support (figs 3 and 4), or to the respective wall of the frame (figs 7 and 8).

In the reference plane, a second angle 42 is defined as the acute angle formed between a tangent to the second slot in a respective instant contact point between the second slot and the second pin and a horizontal line, the second angle being above the horizontal line.

In the examples shown in figures 3, 4, 7 and 8, the second slot 40 has circular arc extension with centre arranged in a front-lower quadrant with respect to the second slot.

In this way, the second acute angle 42 increases monotonically during the entire movement of the tilting mechanism from the at-rest configuration to the maximum tilting configuration.

Figures 9A and 9B show schematically and for illustrative purposes only the slot-pin coupling in the case in which the slot is afforded in the frame, respectively in the configuration of at-rest and maximum tilting.

Figures 10A and 10B show schematically and for illustrative purposes only the slot-pin coupling in the case in which the slot is afforded in the support, respectively in the configuration of at-rest and maximum tilting.

The number 50 indicates the weight force and the number 51 indicates the action force, these forces acting on the pin 9 of the support, in the case of figures 9A and 9B, or on the slot 8 of the support, in the case of figures 10A and 10B.

The ratio between the magnitudes of the weight force and the action force is chosen in a totally arbitrary way, for illustrative purposes only.

For the sake of descriptive clarity, the application point of these forces is assumed to be the instant contact point 12 between the slot and the pin.

The numbers 50 'and 51' indicate the respective component of the forces along the tangent 11 to the slot at the contact point 12 and the numbers 50 "and 51" indicate the respective component of the forces along the direction perpendicular to the tangent 11.

The vector 52 indicates the constraining reaction between pin and slot, direct perpendicularly to the tangent 11, having magnitude equal to the sum of the components 50 "and 51". The components 50 "and 51" and the reaction 52 push the pin and the slot against each other and are responsible for the sliding friction.

Although in the shown examples the side walls of the support are externally with respect to the frame, the present invention also provides for solutions (not shown) in which the side walls of the support are internally with respect to the frame. In this case, when the first pin is integral with the respective wall of the frame, it protrudes towards the inside, instead of towards the outside, as in the shown examples. The present invention also provides for solutions (not shown) in which the first and/or second slots are rectilinear, or are obtained by combining at least one rectilinear section and at least one curvilinear section.

Furthermore, the present invention also provides for solutions (not shown) in which the first articulation system has the slots afforded in the frame and the second articulation system has the slots afforded in the support, and vice versa. Still the present invention also includes solutions in which a system for adjusting the hardness of the spring is provided, for example a system for moving at least one anchoring end of the spring with respect to the frame or the support.

Claims

1 CLAIMS

1. An articulation mechanism (1) for chairs, comprising:

- a frame (2) designed to be associated with a base for a chair;

- a support (4) for a seat-backrest body (5);

- a first (6) and a second (7) articulation system arranged in a rear and front portion of said frame, respectively, and configured to secure said support (4) to said frame (2) in an articulated manner,

wherein said articulation mechanism (1) does not have a backrest support element distinct from said support for the seat-backrest body,

wherein said first (6) and second (7) articulation system are configured in such a manner that said articulation mechanism takes on an at-rest configuration, in the absence of tilting forces acting upon the support, and a maximum tilting configuration in which said support is roto-translated with respect to the at-rest configuration, wherein said second articulation system (7) comprises, for each side of said articulation mechanism, a first slot (8) afforded in either one of said support (4) and said frame (2) and a first pin (9) firmly constrained to the other of said support (4) and said frame (2), wherein the first pin (9) engages said first slot (8) in such a manner that said first pin (9) slides in said first slot (8) during the transition of the tilting mechanism from the at-rest configuration to the maximum tilting configuration and vice versa,

wherein, in a reference plane perpendicular to said first pin, a first angle (10), defined as an acute angle formed between a tangent (11) to the first slot (8) in an instant contact point (12) between the first slot and first pin and a horizontal line (13), and above the horizontal line, faces rearward.

2. The articulation mechanism according to claim 1, wherein said first slot (8) comprises at least one rectilinear section.

3. The articulation mechanism according to claim 1 or 2, wherein said first slot (8) comprises at least one curvilinear section and wherein said first angle (10) gradually increases during at least one part of the movement of the tilting mechanism from the at-rest configuration to the maximum tilting configuration.

4. The articulation mechanism according to any one of the preceding claims, wherein said first angle in said at-rest configuration is greater than or equal to 10° and/or less than or equal to 50°, and/or wherein said first angle in said maximum tilting configuration is greater than or equal to 40°.

5. The articulation mechanism according to any one of the preceding claims, wherein said first slot (8) is afforded in said frame and said first pin (9) is firmly constrained to said support, and wherein said first slot has curvilinear extension with the concavity facing frontward and upward.

6. The articulation mechanism according to any one of claims 1 to 4, wherein said first slot (8) is afforded in said support and said first pin (9) is solidly constrained to said frame, and wherein said first slot is curvilinear in extension with the concavity facing rearward and downward.

7. The articulation mechanism according to any one of the preceding claims, wherein said first articulation 2

system (6) comprises, for each side of said articulation mechanism, a connection element (30) hinged to said frame (2) in a rotation point (31) and hinged to said support (4) in a hinge point (32) and wherein, in said at- rest configuration, the hinge point (32) is located, with reference to said reference plane, in back of a vertical line (33) passing through said axis of rotation (31) and above a horizontal line (13) passing through said axis of rotation.

8. The articulation mechanism according to any one of claims 1 to 7, wherein said first articulation system (6) comprises, for each side of said articulation mechanism, a second slot (40) afforded in either one of said support (4) or said frame (2) and a second pin (41) firmly constrained to the other of said support (4) or said frame (2), wherein the second pin (41) engages said second slot (40) in such a manner that said second pin slides in said second slot during the transition of the tilting mechanism from the at-rest configuration to the maximum tilting configuration and vice versa, wherein, in said reference plane, a second angle (42), defined as an acute angle formed between a tangent to the second slot in a respective instant contact point (12) between the second slot and second pin and a horizontal line, above the horizontal line, gradually increases during at least one part of the movement of the tilting mechanism from the at-rest configuration to the maximum tilting configuration

9. The articulation mechanism according to any one of the preceding claims, further comprising an elastic element (20) operatively interposed between said frame and said support, wherein said elastic element abuts, at a first end thereof, against the frame (2) in a lower front portion of the frame, and at a second end thereof, against a pin (22) solidly constrained to said support and interposed, in said reference plane, between said first and second articulation system.

10. A chair comprising a supporting base for resting it on the ground, a stem (3) mounted on the supporting base, the articulation mechanism (1) according to any one of the preceding claims, and said seat-backrest body rigidly mounted on said support, wherein said frame (2) is rigidly mounted on said stem.