Patent Description:
Common adjustments for chairs, in particular office-type chairs, include a height adjustment of the chair seat, an adjustment of an inclination of the chair seat and the chair back as well as an arrangement of the chair seat with respect to the chair back. These chair adjustments allow users to change their sitting position in the chair as desired, such that fatigue may be minimized during long sitting periods.

Chair configurations may implement a feature which allows a chair back and a chair seat to move simultaneously during a tilting or rearward inclining motion of the chair back. The chair seat may also tilt in this motion or may be displaced otherwise relative to the chair base or chair back. The combined movement of the chair back and the chair seat may simplify chair adjustment. Tilt mechanisms for chairs are known for example from <CIT> or <CIT>.

For example, when the user leans back against the chair back and tilts the chair back and the chair seat rearward, a spring mechanism may be tensioned to urge the chair back and the chair seat forwardly in the initial position. The force with which the spring mechanism urges the chair back and the chair seat in the forward direction may be adjustable, e.g. to take into account the users weight. Adjusting this force may be burdensome, in particular when the mechanism for adjusting this force varies a bias of the spring mechanism which may be very high. For example, a screw based rotating mechanism may be used that moves one end of a spring of the spring mechanism in the longitudinal direction of the spring, i.e. in the direction of the spring force. Due to the large spring force, a large number of turns may be required to cover the full range of adjustment, for example <NUM> or more turns may be required, and still a large torque may be required for turning.

Furthermore, it has been found that tilting the chair seat in the forward direction, i.e. in a position where a rear section of the seat is higher than a front section of the seat with respect to ground, may be advantageous to minimize fatigue during long sitting periods. However, an easy and reliable way of resetting the chair seat in the initial horizontal position may be required in any situation.

Finally, a compact, reliable and cost-effective design of the mechanics providing the above discussed features may be required.

There is a need in the art for a chair tilt mechanism and a chair which address some of the above requirements. In particular, there is a need in the art for a chair tilt mechanism which is a simple and reliable construction and which provides easy adaption to different chair requirements.

According to the present invention, these needs are met by a tilt mechanism for a chair and a corresponding chair as defined in the independent claims. The dependent claims define embodiments.

According to an embodiment, a tilt mechanism for a chair is provided. The tilt mechanism is configured to affect a coordinated movement of a chair seat and chair back. The tilt mechanism comprises a base, a back support, a seat support, a first link element, a second link element, a spring element and a forward sitting adjustment element. The base may be considered as a frame for supporting the remaining components. The base may be coupled to a chair base assembly which includes a pedestal column and a number of support legs for placing the chair on the ground. The back support is configured to support the chair back and is pivotably coupled to the base. The seat support is configured to support the chair seat and is pivotably coupled to the back support. The pivot axis with which the back support is coupled to the base may be different from the pivot axis coupling the seat support and the back support. As a result, the chair seat may be tilted with respect to the chair back in a coordinated manner. The first link element, the second link element and the spring element constitute a mechanism to provide an adjustable restoring force that acts on the back support and thus indirectly on the seat support. For this, a first end of the first link element is pivotably coupled to the base, and a first end of the second link element is pivotably coupled to the back support. A second end of the second link element is coupled to a second end of the first link element. A first end of the spring element is mounted at the base and a second end of the spring element is mounted at the first link element so that the spring element urges against the first link element at an adjustable position between the first end and the second end of the first link element. As a result, upon tilting the back support, the second link element may pivot the first link element, which urges against the spring element. As the position of contact between the spring element and the first link element is adjustable, a length of a lever arm acting on the spring element is adjustable such that the restoring force varies. For repositioning the second end of the spring element along the first link element between the first and second ends of the first link element, a relatively small force is required, so that adjusting the restoring force can be performed with a small amount of force, i.e. easily and quickly by a user.

Furthermore, the tilt mechanism comprises a forward sitting adjustment element which is movable between a first position and a second position. When the forward sitting adjustment element is in the first position, a distance piece of the forward sitting adjustment element is arranged between a stop surface of the second end of the second link element and a stop surface of the base thus keeping a predefined minimum distance between the stop surface of the second end of the second link element and the stop surface of the base. When the forward sitting adjustment element is in the second position, the distance piece of the forward sitting adjustment element is not arranged between the stop surface of the second end of the second link element and the stop surface of the base thus allowing the stop surface of the second end of the second link element to move into contact with the stop surface of the base. By varying the stop position of the second link element with respect to the base, a forward tilting of the seat support can be easily and quickly enabled or disabled. Changing the seating position between a substantially horizontal arrangement of the chair seat and a forward tilted arrangement of the chair seat can be ergonomically advantageous. As this forward tilting functionality uses the second link element, additional efforts with regard to cost and space requirements may be low. Furthermore, as the second link element is pre-tensioned via the first link element by the spring element, a restoring force is provided in both positions, the forward tilted position and the not forward tilted position, i.e. the initial horizontal position.

According to various examples, the tilt mechanism may be configured as follows. When the back support is moved from a first position, in which the chair back is in an essentially upright position, to a second position, in which the chair back is in a rearward inclined position, the seat support is tilted in a rearward inclined position also. This coordinated movement may be provided by the coupling between the seat support and the back support. The first and second link elements effect that the spring element is compressed when moving from the first position to the second position. Thus a restoring force is generated that urges the back support into the first position.

The position at which the second end of the spring element urges against the first link element is adjustable. For example, adjusting this position may vary the active length of the first link element acting on the spring element when the back support is moved between the first position and the second position. Thus, the restoring force urging the back support into the first position may be varied. As a result, the restoring force can be adapted without varying the preload of the spring element. Varying the preload of the spring element usually requires a large amount of force or work by the user. This may be avoided by merely repositioning the second end of the spring element with respect to the first link element.

In further examples, the tilt mechanism may be configured such that, in the essentially upright position of the chair back, a length of the spring element depends on the adjustable position at which the second end of the spring element is urging against the first link element. For example, when the second end of the spring element is closer to the second end of the first link element, the length of the spring element may be longer than the length of the spring element when the second end of the spring element is closer to the first end of the first link element. As a result, adjustment in one direction, for example from the first end to the second end of the the first link element, may require less force or torque exerted by the user than adjustment in the opposite direction, for example from the second end to the first end the first link element. A feedback to the user whether the restoring force is enlarged or lowered, may be provided. However, the preload of the spring element is changed only slightly while the active length of the first connecting element is varied, so the force or torque required for adjustment can be moderate compared to simply varying the preload of the spring element.

For example, a section of the base, a section of the first link element and the spring element may be arranged in a triangle. Vertices of this triangle may be defined by a first pivot axis where the first end of the first link element is pivotably coupled to the base, a mounting point where the first end of the spring element is mounted at the base, and an urging point which is the adjustable position where the second end of the spring element is urging against the first link element. A geometry of this triangle depends on the adjustable position. The tension adjustment thus changes the geometry and also the preload on the spring.

According to an embodiment, for adjusting the position of coupling between the spring element and the first link element, the tilt mechanism may comprise a threaded bolt engaged with a screw nut. The screw nut is fixed to the second end of the spring element. The threaded bolt may be mounted at the first link element. Upon rotating the threaded bolt, the position between the first end and the second end of the first link element, at which the second end of the spring element urges against the first link element, is adjusted. For example, the threaded bolt may be driven by a user handle via a bevel gear arrangement. The threaded bolt and the bevel gear arrangement may be configured such that the screw nut is moved from the first end to the second end of the first link element or vice versa with a few turns of the user handle, for example with <NUM> to <NUM> turns. The restoring force of the chair back can be adjusted quickly and precisely with little effort.

Furthermore, the tilt mechanism may comprise a detent wheel coupled to the threaded bolt such that the detent wheel rotates together with the threaded bolt. The detent wheel is provided with a plurality of detent forms. The tilt mechanism may comprise at least one detent member that mates with the detent forms. The detent member is in engagement with the detent wheel. The detent member may be attached to the first link element. The detent member may resiliently engage a detent form of the detent wheel so that the detent wheel is held in detent steps without blocking rotation of the detent wheel. The detent wheel in combination with the detent member may provide feedback to the user while adjusting the restoring force and may further contribute to avoid an inadvertent adjustment due to the restoring force of the spring element. A plurality of detent members may be provided, for example two detent members arranged at opposite positions with respect to a circumference of the detent wheel. The two or more detent members arranged at equally spaced positions around the circumference of the detent wheel may contribute to align, hold and center the detent wheel.

According to various examples, the tilt mechanism may be configured such that, when the forward sitting adjustment element is in the first position and the stop surface of the second end of the second link element contacts the distance piece of the forward sitting adjustment element, the back support and the seat support are arranged in a first arrangement. When the forward sitting adjustment element is in the second position and the stop surface of the second end of the second link element contacts the stop surface of the base, the back support and the seat support are arranged in a second arrangement. In the second arrangement the seat support is inclined or tilted in the forward direction with respect to the second arrangement. In the first arrangement, the seat support is arranged essentially in a non-inclined arrangement, e.g. in an essentially horizontal position. In the second arrangement, the seat support is arranged in a forward-inclined arrangement, for example tilted at least <NUM> or <NUM> degrees in the forward direction with respect to the first arrangement. Inclining the seat support in the forward direction means that the front section of the seat support is lower than the rear section of the seat support. As merely the stop position of the second link element is varied when the forward sitting is activated or deactivated, the adjustment of the restoring force for the back support is essentially not affected.

For example, in the first position of the forward sitting adjustment element, the spring element may urge, via the first link element, the stop surface of the second end of the second link element into contact with the distance piece of the forward sitting adjustment element. The forward sitting is deactivated. In the second position of the forward sitting adjustment element, the spring element may urge, via the first link element, the stop surface of the second end of the second link element into contact with the stop surface of the base. The forward sitting is activated. In both situations, when the forward sitting is activated or deactivated, the seat support takes a defined position when the chair and thus the tilt mechanism is unloaded, either the forward tilted position or the not forward tilted essentially horizontal position. However, although the spring element causes the seat support to take a defined position, the adjustment of the restoring force for the back support is not affected and therefore adjustable independent from the activation or deactivation of the forward sitting.

According to another aspect of the present invention, a chair is provided. The chair comprises a chair base assembly, a chair seat, a chair back, and a tilt mechanism as described above. The base of the tilt mechanism is attached to the chair base assembly, the chair seat is attached to the seat support of the tilt mechanism, and the chair back is attached to the back support of the tilt mechanism.

The tilt mechanism and the chair according to embodiments may be utilized for various applications in which a coordinated tilting motion of the chair back and the chair seat is desired. For example, the chair tilt mechanism may be utilized in an office chair.

Embodiments of the invention will be described with reference to the accompanying drawings.

Exemplary embodiments of the invention will be described with reference to the drawings. While some embodiments will be described in the context of specific fields of application, such as in the context of an office type chair, the embodiments are not limited to this field of application. The features of the various embodiments may be combined with each other unless specifically noted otherwise. Same reference signs in the various drawings refer to similar or identical components.

<FIG> show a chair <NUM> which includes a tilt mechanism <NUM> of an embodiment. The chair <NUM> is illustrated to be an office-type chair having a chair base assembly <NUM> and a superstructure. The superstructure includes a chair seat <NUM>, a chair back <NUM> and components to interconnect the seat <NUM> with the chair back <NUM>. The components which will be described in more detail below, include the tilt mechanism <NUM> for effecting a coordinated motion of the chair back <NUM> and the chair seat <NUM>. The base assembly <NUM> includes a pedestal column <NUM>, a number of support legs <NUM> extending radially from the column <NUM> and a corresponding number of casters <NUM> supported on the outer ends of the support legs <NUM>. Additionally, a gas cylinder or any other lifting mechanism <NUM> may be supported by the column <NUM> to enable the height of the seat <NUM>, and thus of the chair superstructure, to be adjusted by a user.

It is to be understood that the terms "front", "rear", "left", "right", "top" and "bottom", as used herein, each have a particular meaning that is defined in relation to a flat support surface beneath the chair, for example in relation to a floor on which the chair rests and in relation to a user sitting in a usual seated position on the chair. For example, the term "front" refers to a side of the chair seat at which the knees of the user are arranged and the legs are suspending, whereas the term "rear" refers to a side of the chair seat where the back of the user and the chair back are arranged. The term "left" refers to the left hand side of the chair seat as seen from the user sitting on the chair, and the term "right" refers to the right hand side of the chair seat as seen from the user sitting on the chair. The term "bottom" refers to the side facing to the flat support surface beneath the chair, and the term "top" refers to the side facing away from the flat support surface beneath the chair. It may be assumed that the resulting directions front-rear, left-right and top-bottom represent the axes of a three dimensional Cartesian coordinate system, usually named X-axis, Y-axis and Z-axis, respectively, which are orthogonal to each other. The front-rear and the left-right directions may extend in the plane of the flat support surface and the top-bottom direction may extend in a direction perpendicular to the flat support surface.

It is to be understood that the terms "forward", "rearward" and "lateral(ly)" as used herein, also each have a particular meaning that is defined in relation to a flat support surface beneath the chair and in relation to a user of the chair. For example, the term "forward" refers to a direction moving away from the chair back and in front of a chair user along an axis which extends parallel to such a flat support surface, while the term "rearward" refers to a direction opposite to the forward direction. The term "lateral" refers to a generally horizontal direction perpendicular to both the forward and rearward direction and extending parallel to the aforementioned flat support surface. For example, terms like "to the left" and "to the right" are lateral directions as seen from a user sitting on the chair.

Tilting or inclining in the forward direction, for example tilting the chair seat such that the front side of the chair seat moves down and/or the rear side of the chair seat moves up may be considered as a rotation around an axis of rotation which extends in the left-right direction. Tilting or inclining in the rearward direction may be considered as an opposite motion to the tilting or inclining in the forward direction. For example tilting the chair back such in the rearward direction may mean that an upper part of the chair back moves to the rear with respect to the lower part of the chair back.

Furthermore, it is to be understood that the chair seat, in particular when being tilted, does not extend exactly and only in the front-rear and left-right directions. However, it is clear to a person skilled in the art, that also in this tilted condition, the chair seat essentially extends in the front-rear and the left-right directions. Likewise, it is to be understood that the chair back does not extend exactly and only in the left-right and up-down directions, in particular when being tilted or inclined, but essentially extends in these directions.

The chair <NUM> includes the tilt mechanism <NUM>, and generally the tilt mechanism <NUM> is operated to cause coordinated movement of the chair seat <NUM> and the chair back <NUM> when the chair back <NUM> is tilted. <FIG> shows the chair <NUM> in a non-tilted home position, in which the chair seat <NUM> is oriented substantially horizontally, in particular, in the front-rear direction. For example, the chair <NUM> may automatically assume this position when it is unloaded, i.e., when no user is sitting on the chair. <FIG> shows a rearward tilted position of the chair <NUM>. This position may be assumed, for example, when a user sits on the chair and leans rearward, causing the chair back <NUM> to tilt rearward. Because of the tilt mechanism <NUM>, there is a coordinated movement between the chair back <NUM> and the chair seat <NUM>. As a result, the seat surface of the chair seat <NUM> is also tilted rearward, i.e., the rear side of the seat surface is lower than the front side. A spring mechanism, which will be described in detail below, is tensioned by the reclining action so that the chair <NUM> can automatically return to the home position shown in <FIG> when the user stops pushing the chair back <NUM> rearward. Any intermediate positions between the home position shown in <FIG> and the rearward tilted position shown in <FIG> may be assumed. Also, a locking mechanism may be provided which enables a locking in any position between the home position and the rearward tilted position thus holding the chair <NUM> in a corresponding intermediate position even when the user is no longer applying a load to the chair back <NUM>. However, when the locking mechanism is unlocked, the chair <NUM> may assume the home position again.

The tilt mechanism <NUM> includes a further device, which will be referred to hereinafter as a forward sitting device, FSD. The FSD allows the chair <NUM> to be adjusted to a further home position, namely a forward tilted position. This position is shown in <FIG>. In this forward tilted position, the seat surface of the chair seat <NUM> is tilted forward, i.e., the front portion of the seat surface is lower than the rear portion of the seat surface. Due to the coordinated movement between the chair back <NUM> and the chair seat <NUM>, the chair back <NUM> assumes a steeper position compared to the home position shown in <FIG>. For example, as shown in <FIG>, the chair back <NUM> is nearly vertical. An adjustment of the FSD via, for example via a control element or handle, allows the chair <NUM> to selectively assume the non-tilted position shown in <FIG> or the forward tilted position shown in <FIG> as home position which is automatically assumed when the user no longer pushes the chair back <NUM> rearward.

As in particular illustrated in <FIG>, the tilt mechanism <NUM> includes a base <NUM>. In the installed state of the tilt mechanism <NUM> in which the tilt mechanism <NUM> is incorporated into the chair <NUM>, the base <NUM> is coupled to the pedestal column <NUM> via the lifting mechanism <NUM>. The tilt mechanism <NUM> includes a seat support <NUM> which, in the installed state of the tilt mechanism <NUM>, is coupled to the chair seat <NUM> and supports the chair seat <NUM> at a lower side thereof. The seat support <NUM> is connected to the base <NUM>. The seat support <NUM> may be mounted to the base <NUM> such that it is displaceable with respect to the base <NUM> in a front-rear direction and/or pivot-mounted around a lateral axis. The chair seat <NUM> may be fixedly coupled to the seat support <NUM>, such that a translational or rotational motion of the seat support <NUM> causes the seat <NUM> to move jointly with the seat support <NUM> in a translational or rotational manner. The tilt mechanism <NUM> includes a back support <NUM> which, in the installed state of the tilt mechanism <NUM>, is coupled to the chair back <NUM>. The chair back <NUM> may be attached to the back support <NUM> using a suitable connecting member <NUM>, such as a bar or bridge fixed to the back support <NUM>. The connecting member <NUM> may be directly and rigidly attached to the back support <NUM>.

The tilt mechanism <NUM> is configured such that the back support <NUM> is pivotably coupled to the base <NUM>, allowing the back support <NUM> to pivot relatively to the base <NUM>. As can be seen for example in <FIG>, <FIG> and <FIG>, the back support <NUM> may be coupled to the base <NUM> via a pivot <NUM>. The seat support <NUM> is pivotably coupled to the back support <NUM>. As illustrated for example in <FIG>, the seat support <NUM> may be coupled to the base <NUM> via a slidable pivot <NUM>.

As illustrated for example in <FIG> and <FIG>, a first link element <NUM> and a second link element <NUM> are provided for tensioning a spring element <NUM>. Furthermore, the second link element <NUM> defines a stop for the home position of the chair <NUM> as will be described below in connection with the FSD.

A first end <NUM> of the first link element <NUM> is pivotably coupled to the base <NUM>, for example via pivot <NUM>. A first end <NUM> of the second link element is pivotably coupled to the back support <NUM>, for example via the pivot <NUM>. The second link element <NUM> may have a U-shape with the legs extending in the front-rear direction and the base extending in the lateral direction. In the <FIG>, only one leg of the U-shape is visible and the base of the U-shape forms a second end <NUM> of the second link element <NUM>. The second end <NUM> of the second link element <NUM> is coupled to a second end <NUM> of the first link element <NUM>. As illustrated in <FIG> and <FIG>, the second end <NUM> of the second link element <NUM> may be coupled to the second end <NUM> of the first link element <NUM> via a curved contact and glide surface <NUM>. Upon tilting the back support <NUM> in the rearward direction with respect to the base <NUM>, the second link <NUM> element is essentially moved in the rear direction with respect to the base <NUM> and the first end <NUM> of the second link element <NUM> urges the second end <NUM> of the first link element <NUM> such that the first link element <NUM> is turned around pivot <NUM>. For example and as illustrated in <FIG>, the second link element <NUM> may extend from the first end <NUM> to the second end <NUM> in essentially the front-rear direction, whereas the first link element <NUM> may extend from the first end <NUM> to the second end <NUM> in essentially the up-down direction. In other words, the angled arrangement of the first link element <NUM> with respect to the second link element <NUM> causes a translational movement of the second link element <NUM> to be translated into a rotational movement of the first link element <NUM>.

The tilt mechanism comprises a tension mechanism comprising a spring element <NUM>. The spring element <NUM> may comprise for example one or more spiral springs. A first end <NUM> of the spring element <NUM> is mounted at the base <NUM> and a second end <NUM> of the spring element <NUM> is urging against the first link element <NUM> at an adjustable position between the first end <NUM> and the second end <NUM> of the first link element <NUM>. A mechanism for adjusting the position where the spring element <NUM> urges against the first link element <NUM> will be described in more detail in connection with <FIG>.

As mentioned above, the tilting mechanism comprises the FSD. As will be described in more detail in connection with <FIG>, the FSD comprises a forward sitting adjustment element <NUM> which is movable between a first position as shown in <FIG> and a second position as shown in <FIG>. The forward sitting adjustment element <NUM> comprises one or more distance pieces. In the illustrated example, the forward sitting adjustment element <NUM> comprises two distance pieces <NUM> and <NUM>. When the forward sitting adjustment element <NUM> is in the first position, the distance pieces <NUM> and <NUM> are arranged between a stop surface <NUM> of the second end <NUM> of the second link element <NUM> and a stop surface <NUM> of the base <NUM> thus keeping a predefined minimum distance between the stop surface <NUM> of the second end <NUM> of the second link element <NUM> and the stop surface <NUM> of the base <NUM>. When the forward sitting adjustment element <NUM> is in the second position, the distance pieces <NUM>, <NUM> of the forward sitting adjustment element <NUM> are not arranged between the stop surface <NUM> of the second end <NUM> of the second link element <NUM> and the stop surface <NUM> of the base <NUM> thus allowing the stop surface <NUM> to contact the stop surface <NUM>.

As a result, when the chair <NUM> is in an unloaded state, i.e. for example no one is sitting on the chair, the spring element <NUM> urges the chair back <NUM> in an upright position via the first link element <NUM>, the second link element <NUM> and the back support <NUM>. Due to the coupling between the chair seat <NUM> to the chair back <NUM>, the chair seat <NUM> is urged in an essentially horizontal or "neutral" home position. However, depending on the position of the forward sitting adjustment element <NUM>, the front stop of the second link element <NUM> and thus the chair seat <NUM> may be varied. In the first position of the forward sitting adjustment element <NUM>, the chair seat <NUM> may be actually in an essentially horizontal position, and in the second position of the forward sitting adjustment element <NUM>, the chair seat <NUM> may be slightly inclined in the forward direction, for example by a few degrees, such as <NUM>° or <NUM>° or <NUM>°, with respect to the essentially horizontal position when the forward sitting adjustment element <NUM> is in the first position. When the chair back <NUM> is tilted in the rearward direction, for example by a user sitting on the chair <NUM>, the spring element <NUM> is compressed (tensioned) by the movement of the first and second link elements <NUM>, <NUM>. As the position where the spring element <NUM> urges against the first link element <NUM> is adjustable, an active length of lever arm provided by the first link element <NUM> is varied such that the restoring force exerted by the spring element <NUM> can be adjusted to meet the needs of the user.

In detail, <FIG> show a schematic cross-sectional side view of the tilt mechanism <NUM> in an essentially horizontal non-tilted home position (<FIG>), in a rearward tilted position (<FIG>) and a forward tilted home position (<FIG>). When a user is a sitting on the chair <NUM> and leans back against the chair back <NUM>, the back support <NUM> is pivoted around pivot <NUM> in the rearward direction (<FIG> and <FIG>). The seat support <NUM> this coupled to the back support <NUM> via pivot <NUM>. When the back support <NUM> is pivoted in the rearward direction, the pivot <NUM> moves rear and down which causes the seat support <NUM> to tilt in the rearward direction. The slidable pivot <NUM> (see <FIG>) enables this tilting and sliding motion of the seat support <NUM>.

The tension mechanism of tilt mechanism <NUM> acts as follows. When the back support <NUM> is pivoted in the rearward direction, for example by a user leaning back against the chair back <NUM>, the second link element <NUM> is pulled in the rearward direction due to the coupling via pivot <NUM> (see <FIG>). The second end <NUM> of the second link element <NUM> pushes against the second end <NUM> of the first link element <NUM> and thus pivots the first link element <NUM> around pivot <NUM> in the rearward direction. As a result, the spring element <NUM> is compressed and urges the chair back <NUM> in the forward direction, see <FIG>. The chair seat <NUM> moves in a coordinated manner together with the chair back <NUM>.

When the user releases the chair back <NUM>, the chair back <NUM> moves in the forward direction and the chair seat <NUM> is moved back in the horizontal position, see <FIG>. Depending on the position of the forward sitting adjustment element <NUM>, the distance pieces <NUM>, <NUM> are either present between the stop surface <NUM> of the second end <NUM> of the second link element <NUM> and the stop surface <NUM> of the base <NUM> or not. In <FIG> the distance pieces <NUM>, <NUM> are present and keep the distance <NUM> between the stop surface <NUM> and the stop surface <NUM> such that the seat support <NUM> is in an essentially horizontal position. In <FIG> the distance pieces <NUM>, <NUM> are not present and the stop surface <NUM> abuts the stop surface <NUM> such that the seat support <NUM> is in a forward tilted position. It is to be noted that the spring element <NUM> is preloaded so that even in the forward tilted position shown in <FIG>, there is a force pressing the stop surface <NUM> against the stop surface <NUM>.

Referring to <FIG> and <FIG>, the coupling of the spring element <NUM> to the first link element <NUM> will be described in more detail. Along the length of the first link element <NUM>, a threaded bolt <NUM> is provided which extends from the first end <NUM> to the second end <NUM>. The threaded bolt <NUM> may be rotatable coupled to the first link element <NUM>. A screw nut <NUM> is mounted at the second end <NUM> of the spring element <NUM> and in engagement with the threaded bolt <NUM>. Upon rotating the threaded bolt <NUM> the position of the screw nut <NUM> may be varied between the first end <NUM> and second end <NUM> of the first link element <NUM>. As an example, the screw nut <NUM> may be positioned near the first end <NUM> as shown in <FIG>. As another example, the screw nut <NUM> may be positioned near the second end <NUM> as shown in <FIG>. In general, the screw nut <NUM> may be positioned at any position between the first end <NUM> and the second end <NUM>. By changing the position of the screw nut <NUM> along the first link element <NUM>, the position at which the second end <NUM> of the spring element <NUM> urges against the first link element <NUM> is adjusted. In this arrangement, the first link element <NUM> may be considered as a lever arm which compresses the spring element <NUM> upon rotation around pivot <NUM>. By adjusting the position at which the second end <NUM> of the spring element <NUM> urges against the first link element <NUM>, the active length of the lever arm of the first link element <NUM> is adjusted. Thus, the restoring force urging the chair back <NUM> in the forward direction is varied. For example, when the screw nut <NUM> is closer to the first end <NUM> of the first link element <NUM>, the restoring force is lower than in the case the screw nut <NUM> is it closer to the second end <NUM> of the first link element <NUM> as the spring becomes more compressed in the latter position when the chair back <NUM> is moved from the non-tilted position to the rearward tilted position.

As can be seen for example from <FIG> and <FIG> in connection with <FIG>, a "triangle" is formed by the spring element <NUM>, a part of the base <NUM>, and the active length of the first link element <NUM>. The vertices of this triangle are defined by the pivot <NUM> where the first end <NUM> of the first link element <NUM> is pivotably coupled to the base <NUM>, a mounting point where the first end <NUM> of the spring element <NUM> is mounted at the base <NUM>, and a point where the second end <NUM> of the spring element <NUM> urges against the first link element <NUM>. A geometry of this triangle depends on the adjustable position at which the second end <NUM> of the spring element <NUM> urges against the first link element <NUM>. A change of the geometry of this a triangle modifies the characteristics of the restoring force when the chair back <NUM> and chair seat <NUM> position is varied between the rearward tilted, the non-tilted and the forward tilted positions.

It is to be noticed that the length of the spring element <NUM> is not significantly changed when the position of the screw nut <NUM> is adjusted such that adjusting the position of the screw nut <NUM> does not require significant force. This enables an easy and fast adjustment of the restoring force.

As for example shown in <FIG>, the threaded bolt <NUM> may be driven by bevel gear <NUM>. A first bevel wheel <NUM> is coupled to a handle <NUM> and engages a second bevel wheel <NUM> which is coupled to the threaded bolt <NUM> near the first end <NUM> of the first link element <NUM>. When the user is turning the handle <NUM>, the threaded bolt <NUM> is driven. The bevel gear <NUM> allows that the longitudinal axis of the threaded bolt <NUM> is inclined while maintaining the engagement between the first and second bevel wheels <NUM>, <NUM>. As no significant force is required for moving the screw nut <NUM>, a gear ratio of the bevel gear <NUM> and a gear ratio of the threaded bolt <NUM> in connection with the screw nut <NUM> can be selected such that the full range of adjustment, i.e. moving the screw nut <NUM> between the first and second ends <NUM>, <NUM> of the first link element <NUM>, is covered by a few turns at the handle <NUM>, for example by four to six turns at the handle <NUM>.

As shown in <FIG>, a detent mechanism may be provided comprising a detent wheel <NUM> coupled to the threaded bolt <NUM>, for example near the second end <NUM> of the first link element <NUM>. The detent wheel <NUM> rotates together with the threaded bolt <NUM>. The detent wheel <NUM> is provided with a plurality of detent forms, for example alternating projections and recesses. The detent mechanism comprises two detent members <NUM>, <NUM> that are provided at opposite positions with respect to the circumference of the detent wheel <NUM>. The detent members <NUM>, <NUM> match the detent forms and are in engagement with the detent wheel <NUM>. The detent members <NUM>, <NUM> may be elastically displaceable in the radial direction of the detent wheel <NUM>. The detent mechanism may provide a feedback to the user turning the handle <NUM> and may inhibit an inadvertent adjustment of the screw nut <NUM>.

As discussed above, the forward sitting device (FSD) is provided for setting the home position of the chair <NUM> in either the essentially horizontal position as shown in <FIG> or in the forwarded tilted position as shown in <FIG>. In the following, the FSD is designated to be in an "inactive" state, when the forward sitting adjustment element <NUM> is in the first position in which the distance piece <NUM> is arranged between the stop surface <NUM> of the second end <NUM> of the second link element <NUM> and the stop surface <NUM> of the base <NUM> thus keeping the predefined minimum distance <NUM> between the stop surface <NUM> and the stop surface <NUM>, see <FIG>. In this inactive state, in the home position of the chair <NUM>, the back support <NUM> and the seat support <NUM> are arranged in a first arrangement as shown in <FIG>. The FSD is designated to be in an "active" state, when the forward sitting adjustment element <NUM> is in the second position in which the distance piece <NUM> does not keep the distance <NUM> between the stop surface <NUM> and the stop surface <NUM> such that the stop surface <NUM> can abut against the stop surface <NUM>, see <FIG>. In this active state, in the home position of the chair <NUM>, the back support <NUM> and the seat support <NUM> are arranged in a second arrangement as shown in <FIG>.

<FIG> shows the tilt mechanism <NUM> in the home position with the FSD in the inactive state. In the inactive state, the upper surface of the seat support <NUM> may be oriented substantially horizontally. <FIG> shows the tilt mechanism <NUM> in the home position with the FSD in the active state. As can be seen, in the active state of the FSD, the seat support <NUM> is inclined in the forwarded direction compared to the arrangement of the seat support <NUM> in the inactive state of the FSD. Likewise, in the active state of the FSD, the back support <NUM> is inclined in the forwarded direction compared to the arrangement of the back support <NUM> in the inactive state of the FSD.

As a result, in the active state of the FSD, the chair seat <NUM> is tilted a few degrees in the forward direction with respect to the arrangement of the chair seat <NUM> in the inactive state of the FSD. For example, the chair seat <NUM> may be tilted in the forward direction about <NUM>°, <NUM>° or <NUM>°.

<FIG> and <FIG> show further details of the FSD. The FSD comprises the forward sitting adjustment element <NUM>. The forward sitting adjustment element <NUM> may be actuated by a user via a handle <NUM>. The forward sitting adjustment element <NUM> may be moved laterally in the left-right direction. In <FIG>, the forward sitting adjustment element <NUM> is moved to the right (as seen from a user sitting on the chair <NUM>, i.e. to the left in <FIG>) and in <FIG>, the forward sitting adjustment element <NUM> is moved to the left (as seen from a user sitting on the chair <NUM>, i.e. to the right in <FIG>). At the forward sitting adjustment element <NUM> two distance pieces <NUM> and <NUM> are provided which move together with the forward sitting adjustment element <NUM> in the lateral left-right direction.

In the right position (<FIG>, inactive FSD), the distance pieces <NUM> and <NUM> are arranged between the stop surface <NUM> of the second end <NUM> of the second link element <NUM> and the stop surface <NUM> (not visible in <FIG>) of the base <NUM>. In this right position, the distance pieces <NUM> and <NUM> prevent that the stop surface <NUM> contacts and abuts the base at <NUM> at the stop surface <NUM>.

At the second end <NUM> of the second link element <NUM>, two recesses <NUM>, <NUM> are provided in the stop surface <NUM>. In the left position (<FIG>, active FSD), the distance pieces <NUM> and <NUM> are arranged opposed to the recesses <NUM>, <NUM>. In detail, distance piece <NUM> is arranged opposed to recess <NUM> and distance piece <NUM> is arranged opposed to recess <NUM>. The recesses <NUM>, <NUM> are dimensioned such that the distance pieces <NUM>, <NUM> can be inserted completely in the corresponding recess without protruding from the stop surface <NUM>. Therefore, in this left position, the distance pieces <NUM> and <NUM> do not prevent that the stop surface <NUM> of the link element <NUM> contacts and abuts the base at <NUM> at the stop surface <NUM>. As a result, in the left position of the forward sitting adjustment element <NUM> the second link element <NUM> can be moved further in the forwarded direction than in the right position.

<FIG> and <FIG> illustrate details of the FSD in sectional views. In <FIG>, the FSD is in the inactive state. The distance pieces <NUM>, <NUM> are not arranged opposed to the corresponding recesses <NUM>, <NUM> such that the stop surface <NUM> at the second end <NUM> of the second link element <NUM> contacts the distance pieces <NUM>, <NUM> at one side and the opposing other side of the distance pieces <NUM>, <NUM> contact the stop surface <NUM> of the base <NUM>. The distance pieces <NUM>, <NUM> keep the distance between the stop surface <NUM> and the stop surface <NUM> and inhibit a forward tilting of the seat support <NUM>. In <FIG>, the FSD is in the active state. The distance pieces <NUM>, <NUM> are arranged opposed to the corresponding recesses <NUM>, <NUM> such that the distance pieces <NUM>, <NUM> do not block the space between the stop surface <NUM> and the stop surface <NUM>. The stop surface <NUM> can directly contact the stop surface <NUM>. As a result, the seat support <NUM> can tilt forward.

<FIG> and <FIG> shown further details of the operation of the distance pieces <NUM>, <NUM> in the inactive state (<FIG>) and the active state (<FIG>) of the FSD. In the inactive state (<FIG>) the distance pieces <NUM>, <NUM> are opposed to the stop surface <NUM> such that the stop surface <NUM> cannot move in the forward direction to contact the stop surface <NUM> at the base <NUM>. In the active state (<FIG>) the distance pieces <NUM>, <NUM> are arranged opposed to the recesses <NUM>, <NUM> and can be completely inserted in the recesses <NUM>, <NUM> such that the stop surface <NUM> gets into contact with the stop surface <NUM> at the base <NUM>.

Claim 1:
A tilt mechanism for a chair, configured to affect a coordinated movement of a chair seat (<NUM>) and chair back (<NUM>), the tilt mechanism (<NUM>) comprising:
- a base (<NUM>),
- a back support (<NUM>) configured to support the chair back (<NUM>) and pivotably coupled to the base (<NUM>),
- a seat support (<NUM>) configured to support the chair seat (<NUM>) and pivotably coupled to the back support (<NUM>),
- a first link element (<NUM>), wherein a first end (<NUM>) of the first link element (<NUM>) is pivotably coupled to the base (<NUM>),
- a second link element (<NUM>), wherein a first end (<NUM>) of the second link element (<NUM>) is pivotably coupled to the back support (<NUM>) and a second end (<NUM>) of the second link element (<NUM>) is coupled to a second end (<NUM>) of the first link element (<NUM>),
- a spring element (<NUM>), wherein a first end (<NUM>) of the spring element (<NUM>) is mounted at the base (<NUM>) and a second end (<NUM>) of the spring element (<NUM>) is urging against the first link element (<NUM>) at an adjustable position between the first end (<NUM>) and the second end (<NUM>) of the first link element (<NUM>);
- a forward sitting adjustment element (<NUM>) movable between a first position and a second position,
wherein, when the forward sitting adjustment element (<NUM>) is in the first position, a distance piece (<NUM>, <NUM>) of the forward sitting adjustment element (<NUM>) is arranged between a stop surface (<NUM>) of the second end (<NUM>) of the second link element (<NUM>) and a stop surface (<NUM>) of the base (<NUM>) thus keeping a predefined minimum distance (<NUM>) between the stop surface (<NUM>) of the second end (<NUM>) of the second link element (<NUM>) and the stop surface (<NUM>) of the base (<NUM>), and,
wherein, when the forward sitting adjustment element (<NUM>) is in the second position, the distance piece (<NUM>, <NUM>) of the forward sitting adjustment element (<NUM>) is not arranged between the stop surface (<NUM>) of the second end (<NUM>) of the second link element (<NUM>) and the stop surface (<NUM>) of the base (<NUM>) thus allowing the stop surface (<NUM>) of the second end (<NUM>) of the second link element (<NUM>) to contact the stop surface (<NUM>) of the base (<NUM>).