Mechanics for a piece of seating furniture, especially for an office chair

Abstract

The invention relates to a mechanism for a piece of seating furniture. In order to provide a structurally particularly simple solution for adjusting the kinematics of a piece of seating furniture, a mechanism is proposed comprising a base support (2) that can be placed on a chair column (3), a seat support (4), a backrest support (5) that can be pivoted backwards, and a main spring arrangement (11) for acting on the mechanism (1) against the movement of the backrest support (5), wherein the base support (2), the seat support (4) and / or the backrest support (5) are connected to each other via pivot axes (13, 16, 19), characterized in that the relative position of at least one of the pivot axes (16) to the other pivot axes (13, 19) can be changed independently of a pivoting movement of the backrest support (5).

Description

[0001] The invention relates to a mechanism for a piece of seating furniture, in particular for an office chair, especially for an office chair with a backrest support that can be swivelled backwards.

[0002] Such a mechanism, as used as a component in the seat base of office chairs in particular, provides a kinematic system that results in a specific relative movement of chair components to each other. For example, a defined relative movement of the seat and backrest can produce a correlated seat-backrest movement, in which case it is referred to as a synchronous mechanism.

[0003] Various solutions for adjusting the kinematics of seating furniture are known in the art. In office chairs, this usually involves adjusting the swivel of the backrest, particularly its swivel resistance. This often requires complex adjustment mechanisms that typically occupy a considerable portion of the available installation space, thus placing relatively narrow limits on the free design of the office chair. Furthermore, the adjustment of the backrest swivel must always be made manually by the user, for example, by operating an adjustment element or with the aid of an external drive, such as an electric motor. In addition, it is a disadvantage that the adjustment is always made "by feel," without necessarily being based on ergonomic considerations.

[0004] One object of the present invention is to provide a structurally particularly simple solution for adjusting the kinematics of a piece of seating furniture.

[0005] This problem is solved by the mechanism specified in claim 1 or by the seating furniture specified in claim 10. According to this invention, the mechanism comprises a base support that can be placed on a chair column, a seat support, and a backrest support that can be pivoted backwards, wherein the base support, the seat support, and / or the backrest support are connected to one another via pivot axes. Furthermore, the mechanism is provided with a main spring assembly for acting on the mechanism in the opposite direction to the movement of the backrest support. According to the invention, the mechanism is characterized in that the relative position of at least one of the pivot axes to the other pivot axes can be changed independently of a pivoting movement of the backrest support.

[0006] The kinematics of a seating mechanism, particularly an office chair, are regularly determined by, or influenced by, the arrangement of real or virtual pivot axes between the mechanism's components. Typically, this arrangement of pivot axes is not modifiable when the mechanism is at rest (i.e., when none of the components connected via pivot axes are performing any relative movement, and the mechanism is therefore in its static state). In other words, there is no way to change the arrangement of the pivot axes, especially their distances from one another.

[0007] A key concept of the invention is to provide, in the mechanism of a piece of seating furniture, particularly an office chair, for a change in the relative position of at least one of the pivot axes to the other pivot axes, whereby this change in the axis position occurs independently of any pivoting movement of the backrest support. In other words, the position of at least one of the pivot axes relative to the position of at least one of the other pivot axes can be changed while the mechanism is in its unpivoted (rest) state. In this way, the movement behavior of the pivot mechanism can be adjusted in a particularly simple manner from a design perspective.

[0008] How the adjusted position of the pivot axis differs from its initial position, i.e., what change the relative position of at least one pivot axis undergoes, can be determined as needed by suitable design and / or functional configuration of the mechanics or the adjustment mechanism for changing the axis position. The inventive concept of a pivot axis whose position can be changed in the rest state of the pivoting mechanism can be applied to a wide variety of mechanical systems.

[0009] Advantageous embodiments of the invention are specified in the dependent claims.

[0010] According to a preferred embodiment of the invention, the seat support can be pivoted backwards synchronously with the backrest support, and the main spring arrangement is designed to act on the mechanism against this synchronous movement of the seat and backrest support.

[0011] According to a preferred embodiment of the invention, the position-adjustable pivot axis is the pivot axis of the mechanism that connects the seat support to the rearward-pivoting backrest support. This is preferably the pivot axis of the mechanism that, when the backrest support pivots, moves along a path of motion relative to a position-fixed pivot axis whose pivoting movement of the backrest support is not traceable, wherein this position-fixed pivot axis is particularly the main pivot axis of the mechanism. In this way, by changing the position of the position-adjustable pivot axis in the rest state of the mechanism, the distance between the position-adjustable pivot axis on the one hand and the (when the mechanism pivots)The main pivot axis of the mechanism (the position-fixed axis of the backrest support) can be changed, thus altering the length of the effective lever arm during a synchronous movement of the seat support induced by pivoting the backrest support. In particular, the mechanism can be designed such that the distance between the position-adjustable pivot axis and the main pivot axis of the mechanism in the adjustment position of the position-adjustable pivot axis is greater than the distance between the position-adjustable pivot axis and the main pivot axis of the mechanism in the initial position of the position-adjustable pivot axis.

[0012] According to a preferred embodiment of the invention, changing the position of at least one pivot axis does not cause any significant change to the main spring assembly. In particular, the position of the spring elements of the main spring assembly and the positions of the spring ends of these spring elements remain essentially the same. In other words, changing the position of the at least one pivot axis occurs while the overall position of the main spring assembly remains essentially unchanged. The adjustment of the kinematics of the mechanism is achieved in such a way that neither the preload nor the spring rate of the spring elements of the spring assembly changes. In this way, it is possible to dispense with structurally complex adjustment mechanisms for the spring elements of the spring assembly that actuates the mechanism against the movement of the backrest support.The kinematics are adjusted without manipulating the main spring arrangement of the mechanism.

[0013] According to a preferred embodiment of the invention, the seat support and a movement component of the base support form a movement unit that is movable relative to the chair column, the distance traveled by the movement unit depending on the weight of a user placing weight on the seat support. The change in the relative position of at least one of the pivot axes to the other pivot axes, as proposed in the invention, is effected by such movement of the movement unit, i.e., movement dependent on the weight of the user.In other words, a movement of the motion unit from an unloaded initial state to a user-weight-dependent sinking state (adjustment movement) caused by a user sitting on the seat results in a change in the relative position of at least one of the pivot axes to the other pivot axes, which allows the kinematics of the mechanism and, as a result, in particular the synchronous movement of the mechanism to be adjusted, especially the pivoting resistance of the backrest during such a synchronous movement.

[0014] By implementing a single motion unit, a particularly simple adjustment mechanism and a simple and robust mode of operation can be achieved, along with a simple mechanical design. The specific type of movement performed by the motion unit is initially irrelevant for the realization of the invention. Preferably, however, the movement is in the vertical direction, i.e., in the direction in which the user sits on the chair. In this way, a direct and particularly simple transmission of the weight force to act on the kinematics is possible.

[0015] The kinematics are therefore preferably adjusted automatically, meaning that the office chair user does not have to perform any additional steps, either manually or with the aid of an external drive. Instead, the kinematics are adjusted simply by the user sitting down in the office chair. The mechanism thus adjusts itself automatically, preferably without any change to the main spring assembly, depending on the user's weight. It is therefore particularly easy to design the mechanism in such a way that its kinematics result in optimal swivel characteristics from an ergonomic perspective.

[0016] For a user of high weight, the adjustment is preferably such that a large resistance is encountered when swiveling the backrest of the office chair, while swiveling the backrest is significantly easier for a user of low weight in comparison.

[0017] A structurally simple solution and a compact design are achieved according to a particularly preferred embodiment of the invention, especially when the seat support and the movement component of the base support are arranged such that they do not change their relative positions during a user-weight-dependent relative movement of the movement unit. In other words, the seat support and the movement component of the base support move directly and immediately together relative to the chair column. The seat support and the movement component of the base support move along a single, common path.

[0018] According to a preferred embodiment of the invention, in addition to the main spring arrangement for acting on the mechanism against the movement of the backrest support, a secondary spring arrangement is provided, which influences the distance traveled by the movement unit depending on the user's weight. The resistance to compression of the movement unit can be determined by selecting the spring elements of this arrangement. In other words, the stiffness of the spring elements of the secondary spring arrangement determines the compression depth of the movement unit. It is particularly advantageous if the secondary spring arrangement also serves to return the movement unit to its initial state as soon as the user no longer bears weight on the seat support.

[0019] One embodiment of the invention has proven to be particularly advantageous from a design perspective, in which this secondary spring arrangement acts between the movement unit, in particular the movement component of the base support, on the one hand, and a fixed component of the base support, which can be placed on the chair column and is fixed relative to the chair column, on the other hand. In other words, a two-part base support is provided, wherein the fixed component of the base support is not part of the movement unit. The movement component of the base support, and thus the entire movement unit, is movably connected to the fixed component, in particular via a linkage arrangement.

[0020] Since a rearward pivoting backrest support is also provided, several, partly interdependent, partly independent relative movements of mechanical components are possible, whereby, with the exception of the fixed component of the base support, all other parts of the mechanism are movable relative to the fixed component.In addition to the user-weight-dependent relative movement of the movement unit caused by the user sitting on the seat, which adjustment movement causes a change in the relative position of at least one of the pivot axes of the mechanism and thus a change in the kinematics of the mechanism, and which regularly also includes the backrest support, a pivoting movement of the backrest support can be caused by the user leaning against the backrest, by which movement, according to a preferred embodiment of the invention, the seat support can be pivoted backwards synchronously with the backrest support and the main spring arrangement is designed to actuate the mechanism against this synchronous movement of the seat and backrest support.

[0021] According to a preferred embodiment of the invention, the at least one position-changeable pivot axis is driven by a transmission means interacting with the motion unit during a weight-dependent relative movement of the motion unit. This transmission means can be, in particular, a tension element, a lever, a belt, a wedge, a spindle, a cam, or a plurality of these interacting means. It has proven particularly advantageous if a cam provided on the fixed component of the base support serves as a driver, since this allows direct and immediate actuation of the position-changeable pivot axis by the fixed component without additional force transmission means. Preferably, this cam is designed such that it drives the pivot axis in all directions relevant to the change in position when the motion unit moves, i.e.,both from an unadjusted starting position of the swivel axis to a weight-dependent adjustment position and from this adjustment position back to the starting position.

[0022] According to a preferred embodiment of the invention, a guide is provided for the at least one position-adjustable pivot axis. The position-adjustable pivot axis is guided in this guide when the seat is loaded or unloaded by the user. In this way, a particularly precise and defined change in the position of the pivot axis is possible with simple design means. This guide, which is preferably designed as a linear guide, is provided by the base support, the seat support, and / or the backrest support.

[0023] According to a preferred embodiment of the invention, a safety device is provided which prevents unintentional adjustment of the position of the at least one position-adjustable pivot axis, which is set by the user's weight, when the backrest support is pivoted, and / or prevents unintentional pivoting of the backrest support when the position of the at least one position-adjustable pivot axis is adjusted in a manner dependent on the user's weight. It has proven particularly advantageous if a guide for the position-adjustable pivot axis formed jointly by several mechanical components contributes to the realization of this safety device.

[0024] The invention is not limited to synchronous mechanisms in which a specific relative movement of the seat and backrest occurs. It can also be used in other mechanical systems, for example, in mechanisms where the pivoting of the backrest occurs independently of the seat or when the seat is stationary (asynchronous mechanisms), or together with the seat as a single unit of movement (rocking mechanisms). Likewise, the invention is not limited to office chairs but can also be applied to other seating furniture.

[0025] An embodiment of the invention is explained in more detail below with reference to the drawings. These show: Fig. 1. A front view of a synchronous mechanism in an unloaded, unrotated state, Fig. 2 a side view of a synchronous mechanism in an unloaded, non-rotating state, Fig. 3 a cutaway side view of a synchronous mechanism in an unloaded, unrotated state along line AA in Fig. 1, Fig. 4 A side view of a synchronous mechanism in an unloaded, pivoted state, Fig. 5 a side view of a synchronous mechanism in a maximally loaded, pivoted state, Fig. 6 A cutaway side view of a synchronous mechanism in a maximally loaded, pivoted state, Fig. 7 A side view of a synchronous mechanism in a maximally loaded, pivoted state, Fig. 8 a sectional view along line BB in Fig. 2, Fig. 9 a section view along line CC in Fig. 5, Fig. 10 another sectional view according to Fig. 4, with partially removed backrest support, Fig. 11 the view of a position-changeable pivot axis with gears and sliding blocks (these are shown only on one of the two sides).

[0026] All figures depict the invention only schematically and with its essential components.

[0027] The synchronous mechanism 1 has a base support 2, which is connected to the upper end of a (in Fig. The base support 2 is connected to the chair column 3 (indicated in the figures). The base support 2 is divided into two parts and comprises a movement component 21 on the one hand and a fixed component 22 on the other, which can be placed on the chair column 3 and is fixed relative to the chair column 3, as explained in more detail below.

[0028] The mechanism 1 further comprises a substantially frame-shaped seat support 4. A seat (not shown) with a padded seat surface is mounted on the seat support 4.

[0029] The mechanism 1 further comprises a backrest support 5, which has two rearward-extending side struts 6 that connect to the actual backrest (not shown). The backrest, which is height-adjustable in modern office chairs, can also be integrally connected to the backrest support 5.

[0030] The entire synchronous mechanism 1 is mirror-symmetrical with respect to the central longitudinal plane, as far as the actual kinematics are concerned. Therefore, the following description always assumes that the actual pivoting mechanism consists of paired structural elements on both sides.

[0031] The backrest support 5 is directly and pivotally connected to the base support 2 via the lower end 14 of a cheek 7 attached to the side strut 6, by being articulated to the movement component 21 of the base support 2 at a transverse pivot axis 13, which forms the main pivot axis of the mechanism. This allows the backrest support 5 to pivot about the pivot axis 13 in the pivot direction 20, see [reference]. Fig. 4.

[0032] Secondly, the backrest support 5 is directly and pivotally connected to the seat support 4 by its cheek 7 being articulated via a transverse second pivot axis 16 to a mounting cheek 15 attached to the rear end 17 of the seat support 4. Thus, pivoting the backrest support also moves the seat support 4 in the pivot direction 20.

[0033] Furthermore, the seat support 4 is connected at its front end 18 to the movement component 21 of the base support 2 via a rotary-sliding joint. This joint is formed by a third transverse pivot axis 19, which is mounted in a further mounting flange 25 of the seat support 4 and engages in a guide 8 of the movement component 21 of the base support 2. In this way, when the backrest is loaded, the backrest support 5 pivots in the direction 20 to the rear and downwards, with the seat support 4 simultaneously being moved and pivoted backwards by this pivoting movement. In other words, the seat support 4 and the backrest support 5 move synchronously to the rear. Instead of the rotary-sliding joint, another suitable articulated connection of the seat support 4 to the base support 2 can also be provided.

[0034] Furthermore, the mechanism 1 comprises a main spring assembly 11 for acting upon the mechanism in the opposite direction to the movement of the backrest support 5. The mechanism 1 is pre-tensioned by the main spring assembly 11 in the opposite direction of pivoting 20 – i.e., towards the home position of the synchronous mechanism. This main spring assembly 11, designed to actuate the mechanism from its unpivoted home position to a pivoted position, has two compression springs 9 arranged parallel to each other on either side of the central longitudinal plane in a common horizontal plane, which are hereinafter also referred to as synchronous springs. Each of the two compression springs 9 is supported with its front end 23 (movable during a synchronous movement) in the seat's longitudinal direction 30 against the third pivot axis 19, while the rear end 24 (fixed during a synchronous movement) in the seat's longitudinal direction 30 is supported against the movement component 21 of the base support 2.

[0035] The seat support 4, together with the backrest support 5 and the movement component 21 of the base support 2, forms a movement unit that is movable relative to the fixed component 22 of the base support 2 and the chair column 3, without the relative positions of the components of the movement unit 21, 4, 5 changing during such relative movement. In other words, there is a direct and immediate joint movement of the seat support 4 and the movement component 21 of the base support 2 relative to the chair column 3. The seat support 4 and the movement component 21 of the base support 2 move along a single, common path of motion.

[0036] The fixed component 22 of the base support 2 includes a receptacle 10 for the upper end of the chair column 3. The chair column 3 can be height-adjustable. However, when the movement unit 21, 4, 5 is lowered, the fixed component 22 of the base support 2 is stationary. The movement component 21 of the base support 2 is movably connected to the fixed component 22 via a linkage 26. The linkage 26 comprises two parallel links 27, 28 of equal length, each articulated to the fixed component 22 and the movement component 21 of the base support 2, respectively, and adjustable in the form of a parallelogram. With the aid of this parallelogram linkage 26, the movement component 21, and thus the movement unit 21, 4, 5, i.e., the entire remaining mechanical assembly, can be moved relative to the fixed component 22 of the base support 2. To influence this movement in a defined manner, a secondary spring arrangement 12 is provided.The centrally arranged spring element 19 of the secondary spring assembly 12, which will also be referred to as the adjusting spring, acts between the moving component 21 on the one hand and the fixed component 22 on the other. The adjusting spring 19, designed as a compression spring, is supported with one end 33 at the pivot point 35 of the upper link 27, located at the front of the moving component 21 of the base support 2 (as viewed in the longitudinal direction 30 of the seat), while its other end 34 is supported at the pivot point 36 of the lower link 28, located at the rear of the fixed component 22 of the base support 2 (as viewed in the longitudinal direction 30 of the seat).

[0037] The fixed component 22 of the base carrier 2 is not part of the movement unit 21, 4, 5. When a user sits on the seat, the movement unit moves relative to the fixed component 22 of the base carrier 2 in a lowering direction 31 defined by the handlebar arrangement 26, typically linearly and vertically downwards, see Fig. 5. Starting from an initial state, the movement unit 21, 4, 5 moves into a user-weight-dependent sinking state. The distance traveled by the movement unit 21, 4, 5 depends on the weight of a user placing a load on the seat support 4.

[0038] During such a lowering movement of the motion unit 21, 4, 5, the second pivot axis 16, whose relative position can be changed in the unpivoted rest state of the mechanism, is moved from its initial position by a central driver 40 of the fixed component 22 of the base support 2, as shown in the Fig. 2, Fig. 3 shown, pressed upwards into a weight-dependent adjustment position, as shown in the Fig. 5, Fig. Figure 6 shows that the driver 40 is designed as a closed cam guide in which the pivot axis 16 is located. The pivot axis 16 is then pressed upwards by a lower stop surface 41 of the driver cam 40 at its central section 50, the diameter of which is adapted to the width of the cam guide.

[0039] Such a change in the axis position alters the distance 32 between the second pivot axis 16 on the one hand and the first pivot axis 13 on the other, and thus the length of the effective lever arm during a synchronous movement of the seat support 4 induced by pivoting the backrest support 5. This results in a changed movement characteristic of the mechanism; in other words, the kinematics of the mechanism are changed.

[0040] A change in the position of the second pivot axis 16 does not cause any or any significant change in the main spring assembly 11, in particular no change in the preload and no change in the spring rate of the spring elements 9 of the main spring assembly 11.

[0041] In addition to the user's weight, the stiffness of the spring elements 19 of the secondary spring assembly 12 determines the compression depth of the movement unit 21, 4, 5 and thus the distance by which the position-variable pivot axis 16 is adjusted when the user sits down on the seat against the spring force of these spring elements 19. When the user stands up from the seat, the secondary spring assembly 12 acting on the movement unit 21, 4, 5 causes the movement unit to return to its unloaded initial state, thereby returning the pivot axis 16, again driven by the drive cam 40, to its initial position. For this purpose, an upper stop surface 42 of the drive cam 40 engages the pivot axis 16 and presses it downwards.

[0042] Both the lower stop surface 41 and the upper stop surface 42 of the drive cam 40 are designed as circular tracks so that the pivot axis 16 does not lose simultaneous contact with both stop surfaces 41, 42 on its central piece 50 when the axis position is adjusted and is safely guided by the stop surfaces 41, 42 during the entire adjustment movement.

[0043] The secondary spring assembly 12 is pre-tensioned. For particularly light users, the movement unit 21, 4, 5 does not move in the lowering direction 31. The position of the pivot axis 16 does not change when such a user sits on the seat. If a user's weight exceeds a certain value, which can be determined by the spring characteristics of the secondary spring assembly 12, the movement unit 21, 4, 5 lowers to a greater or lesser degree, and consequently, the pivot axis 16 changes position to a different adjustment position from its initial position. The distance 32 of the secondary pivot axis 16 to the main pivot axis 13 of the mechanism 1, and thus the lever arm, is greater in the adjustment position of the pivot axis 16. Fig. 5) as the distance 32 of the second pivot axis 16 to the main pivot axis 13 in the starting position of the pivot axis 16 ( Fig. 2) Since the pivot axis 16 can continuously and steplessly assume its weight-dependent positions, a large number of different adjustment positions of the pivot axis 16 are possible.

[0044] The resulting adjustment positions cause a greater rearward movement of the seat support 4 during a subsequent synchronous movement of the mechanism 1. This results in the front spring end 23 of the spring element 9 of the main spring assembly 11 being driven further rearward, consequently compressing this spring element 9 more strongly. As a result, the pivoting resistance of the backrest support 5 increases the greater the user's weight and the further the weight-dependent adjustment position of the second pivot axis 16 is from its initial position.

[0045] For adjusting the position of the second pivot axis 16, an axis guide 37 designed as a linear guide is provided. The axis guide 37 has stops at its ends to limit the adjustment movement of the pivot axis 16.

[0046] The axis guide 37 is formed by a first guide element 38 provided by the seat support 4 and a second guide element 39 provided by the backrest support 5. Both guide elements 38, 39 are designed as elongated slots with a straight opening contour. The second pivot axis 16 rests simultaneously in both elongated slots 38, 39. The elongated slots 38, 39 change their relative positions according to the different pivoting movements of the backrest support 5 and the seat support 4 during synchronous movement. For example, in the maximum pivoted state, the backrest support elongated slot 39 is slightly inclined backwards when viewed in the longitudinal direction 30 of the seat, see [reference]. Fig. 4, while the seat support slot 38 is still slightly inclined forward in this pivoted state, see Fig. 10.

[0047] In order to prevent the pivot axis 16 from sliding downwards in the axis guide 37 during a synchronous movement of the mechanism 1, i.e. a pivoting of the backrest support 5 in the pivot direction 20 to the rear with simultaneous engagement of the seat support 4, the proposed constructive solution makes use of several approaches.

[0048] Sliding blocks 43, 44 are provided at both ends of the position-changeable pivot axis 16, which are rotatably mounted on the pivot axis 16 independently of each other, see Fig. 11. Via these sliding blocks 43, 44, the pivot axis 16 is guided simultaneously on sliding surfaces 45, 46 of both elongated holes 38, 39 and thus simultaneously on both the seat support 4 and the backrest support 5, see Fig. 8, Fig. 9.

[0049] Furthermore, a gear 47 is attached to the pivot axis 16 at each end of the axis between the pairs of sliding blocks, see Fig. 11. The gear 47 meshes simultaneously with racks 48, 49, which are provided adjacent to the sliding surfaces 45, 46 in the elongated holes 38, 39, so that the pivot axis 16 engages via the teeth of the gear 47 simultaneously with a rack 48 of the seat support 4 and a rack 49 of the backrest support 5, see Fig. 8, in which the starting position of the pivot axis 16 is shown, and Fig. 9, which shows the largest possible adjustment position of the swivel axis 16.

[0050] The sliding blocks 43, 44 also serve as spacers and prevent the gears 47 from jamming in the racks 48, 49 when forces act on the pivot axis 16, as is the case during an adjustment movement, i.e. a lowering movement of the motion unit 21, 4, 5, or during a synchronous movement of the mechanism.

[0051] During synchronous movement, the pivot axis 16 is held in position in the seat support slot 38 by the inhibiting effect of the synchronizing spring 9. While the effect of the synchronizing spring 9 does not directly extend to holding the position of the pivot axis 16 in the backrest support slot 39, since the pivot axis 16 is guided in both slots 38 and 39 simultaneously, the inhibiting effect caused by the synchronizing spring 9 also serves to inhibit the movement of the pivot axis 16 in the backrest support slot 39.

[0052] When the gears 47 mesh with the racks 48, 49, rotation of the pivot axis 16 is prevented. Since, during synchronous movement, the seat support 4 pivots by a smaller angle (e.g., 10°) than the backrest support 5 (e.g., 20°), a torque is simultaneously generated between the gears 47 and the racks 48, 49, causing the gears 47 to push the pivot axis 16 radially. This, in turn, exerts a force on the sliding surfaces 45, 46 of the elongated holes 38, 39 via the sliding blocks 43, 44, which also inhibits the movement of the pivot axis 16.

[0053] The meshing of the gears 47 in the racks 48, 49 simultaneously prevents an unwanted translational movement of the pivot axis 16 in the elongated holes 38, 39, so that, for example, a displacement of the seat support 4 relative to the backrest support 5 along the axis guide 37 is avoided.

[0054] In this way, the axis guide 37, with its design, simultaneously constitutes a safety device, which ensures, in particular, that the position of the second pivot axis 16 in the axis guide 37 does not change during the synchronous movement, and thus that there is no change in the length of the effective lever arm. This not only prevents unintentional adjustment of the position of the pivot axis 16 when the backrest support 5 is pivoted, and unintentional pivoting of the backrest support 5 when the position of the pivot axis 16 is adjusted, but also ensures that the components 4 and 5 of the mechanism do not move unintentionally relative to each other during an adjustment movement or a synchronous movement.

[0055] All features described in the text, the following claims, and the drawings can be essential to the invention, both individually and in any combination. These features or combinations of features can each constitute an independent invention, the right to claim which is expressly reserved.

[0056] When specifying a combination of features defining an invention, individual features from the description of an embodiment do not necessarily have to be combined with one or more or all other features specified in the description of that embodiment; in this respect, any subcombination of features of one or more embodiments is expressly disclosed.

[0057] Furthermore, tangible features of the device can be reformulated and used as process features, and vice versa. Features reformulated in this way are implicitly disclosed. Reference symbol list 1 Mechanics, synchronous mechanics 2 base carriers 3 Chair column 4 seat carriers 5 backrest supports 6 Side strut of the backrest support 7 Cheek 8 Backstage tour 9 Synchronous spring 10 Mounting points for chair column 11 Main spring arrangement (synchronous spring arrangement) 12 Auxiliary spring arrangement (adjusting spring arrangement) 13 first pivot axis, main pivot axis 14 lower end of the cheek of the backrest support 15 rear mounting side of the seat carrier 16 position-adjustable, second swivel axis 17 rear end of the seat carrier 18 front end of the seat carrier 19 third pivot axis 20 Swivel direction of the backrest support 21 Movement component of the base carrier 22 Fixed component of the base support 23 front spring end of the synchronizing spring 24 rear end of the synchronizing spring 25 front mounting side of the seat carrier 26 Handlebar arrangement 27 first, upper handlebar 28 second, lower handlebar 29 Adjustment spring 30 Seat lengthwise 31 Lowering direction 32 axle spacing, lever arm 33 front spring end of the adjusting spring 34 Rear end of the adjusting spring 35 first pivot point 36 second pivot point 37 axis guidance 38 first guide element, seat support elongated hole 39 second guide element, backrest support slot 40 participants, guided tour 41 lower stop surface of the driver 42 upper stop surface of the driver 43 first sliding block (seat support) 44 second sliding block (backrest support) 45 first sliding surface (seat support) 46 second sliding surface (backrest support) 47 gear 48 Seat support rack 49 Backrest support rack 50 center piece

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