Synchronous mechanism, office or conference seating furniture, method for adjusting the backrest force of an office or conference seating furniture with a synchronous mechanism

Abstract

The present invention relates to a synchronous mechanism and an office or conference chair with such a synchronous mechanism. Furthermore, the present invention relates to a method for adjusting the backrest force of an office or conference chair with a synchronous mechanism.

Description

AREA OF INVENTION

[0001] The present invention relates to a synchronous mechanism and an office or conference chair with such a synchronous mechanism. Furthermore, the present invention relates to a method for adjusting the backrest force of an office or conference chair with a synchronous mechanism. TECHNICAL BACKGROUND

[0002] DE 20 2007 001 395 U1 describes an example of a synchronous mechanism for office chairs. In the office chair described therein, a backrest (backrest support) is connected to a seat base that can be raised and lowered via a swivel mechanism consisting of two linkages.

[0003] Furthermore, EP 2 769 642 A1 describes a synchronous mechanism for office chairs with a restoring force of the backrest support coupled to the user's center of gravity, in which the backrest support generates a lifting and lowering movement of a seat support plate loaded by the user's weight via a swivel mechanism consisting of several links, and the seat support plate is designed to be elastically spring-loaded and, when swiveling backwards, the weight-bearing force of the user is increased and the seat support plate is deformed upwards by applying an elastic restoring force against the weight force of the user.

[0004] German patent DE 10 2017 107 636 A1 describes a synchronous mechanism for an office chair in which the point of force application relative to the point of connection of the coupling element with the backrest support can be changed depending on the angular position of the backrest support. In other words, the position of the longitudinal axis of the coupling element, defined by these two connection points, is changed by the pivoting movement of the backrest support.

[0005] To change the tilt resistance of the backrest, known synchronous mechanisms provide either a variable angle of attack for the skin spring or an increase in the preload of the main spring, for example, using a threaded spindle with a knob. However, changing the spring preload usually requires a relatively high amount of work. If the required increase in spring preload is set directly on the spring, a relatively high force is required. Similarly, known synchronous mechanisms can exhibit a constant or degressive curve for the backrest force. For example, in some prior art synchronous mechanisms, the main spring is preloaded so tightly that there is little or no progressive behavior when the backrest is tilted. SUMMARY OF THE INVENTION

[0006] Against this background, the present invention aims to provide an alternative synchronous mechanism with an improved adjustment mechanism for changing a backrest force or a swivel resistance.

[0007] According to the invention, this problem is solved by a synchronous mechanism with the features of claim 1, by an office or conference chair with the features of claim 8 and / or by a method with the features of claim 9.

[0008] Accordingly, the following is planned: - A synchronous mechanism for an office or conference chair with a seat support plate which is pivotably supported in its front area by a front seat link relative to a seat support and which is pivotably supported in its rear area by a rear seat link relative to the seat support, wherein the rear seat link has a first pivot axis and a second pivot axis arranged parallel to the first pivot axis, with a force transmission unit for transmitting a backrest force to the rear seat link, wherein the force transmission unit is coupled to the first and the second pivot axes such that when a backrest is tilted by the force transmission unit, a pressure force can be transmitted to the first pivot axis or to the second pivot axis, and with an actuable locking element for adjusting the backrest force,wherein the locking element is movable relative to the force transmission unit between a locking position and a release position, wherein the pressure force from the force transmission unit can be transmitted to the first pivot axis in the release position of the locking element and to the second pivot axis in the locking position of the locking element. - An office or conference chair, with a backrest, and with a synchronous mechanism according to the invention, wherein the backrest is coupled to the power transmission unit and supported by it. - A method for adjusting the backrest force of an office or conference chair with a synchronous mechanism, in particular a synchronous mechanism according to the invention, comprising the steps of: moving a locking element between a locking position and a release position; and changing a force path of a compressive force by moving the locking element, wherein the compressive force is transmitted from a force transmission unit of the synchronous mechanism to a first pivot axis in the release position of the locking element and to a second pivot axis in the locking position of the locking element, wherein the first pivot axis and the second pivot axis are part of a rear seat link of the synchronous mechanism and are arranged parallel to each other.

[0009] The underlying idea of ​​the present invention is to change the backrest force characteristic between a softer and a firmer setting, in particular to shift it parallel to itself. The backrest force or pivot resistance can be adjusted with minimal effort and travel by means of the locking element. The locking element is designed to change the force path depending on its position, so that the backrest force received by the force transmission unit can be introduced into the rear seat linkage via two different force paths. In the locked position, the force path via the second pivot axis results in greater resistance to the backrest force than in the unlocked position, where the force path is transmitted to the rear seat linkage via the first pivot axis. This allows for increased user comfort when adjusting the backrest force.

[0010] The first and second pivot axes should not be confused with the pivoting connections to the seat support plate or the seat support, but rather form separate components of the rear seat linkage.

[0011] For the purposes of this application, the term "office or conference seating furniture" includes in particular membrane chairs, meeting, seminar and conference chairs, and lounge furniture.

[0012] The term "synchronous mechanism" refers to components in the seat base of an office or conference chair that enable a coordinated kinematic movement between the seat and backrest. The seat, typically upholstered, is mounted on the seat support. The backrest support, which usually extends backward from the actual synchronous mechanism, carries the backrest of the office or conference chair via an upward-pointing arm. The seat support and backrest support are typically linked by a pivoting mechanism such that a backward swiveling movement of the backrest—such as that caused by the user leaning against it—induces a downward lowering movement of the rear edge of the seat.

[0013] Advantageous embodiments and further developments are described in the subclaims and in the description with reference to the figures of the drawing.

[0014] According to one embodiment of the synchronous mechanism, the locking element is rotatably mounted. The locking element can be designed such that, in the locked position, it is at least partially positioned between the power transmission unit and the second pivot axis and transmits the compressive force. For example, the locking element can be rotatably mounted within the power transmission unit. In this case, the locking element can be designed as a rocker arm, one end of which can be moved between the power transmission unit and the second pivot axis by rotating the locking element. Unlike in the locked position, the locking element does not transmit the compressive force in the released position.

[0015] According to another embodiment of the synchronous mechanism, the power transmission unit is rotatably mounted on the first pivot axis and has a gap relative to the second pivot axis. The locking element is located outside the gap in the release position and at least partially inside the gap in the locking position, so that rotation of the power transmission unit relative to the first pivot axis is blocked in the locking position. In this way, rotation of the power transmission unit relative to the first pivot axis is possible in the release position. The compressive force of the power transmission unit is transmitted to the first pivot axis in the release position of the locking element at every deflected position of the rear seat link. The second pivot axis can be moved into the gap.In the locked position of the locking link, the compressive force of the force transmission unit is transferred to the second pivot axis in every deflected position of the rear seat linkage. Both the first and second pivot axes can be made of steel.

[0016] According to a further embodiment, the synchronous mechanism also includes an actuating lever for actuating the locking element, wherein the actuating lever is mechanically operatively connected to the locking element and the locking element can be moved by tilting the actuating lever. For example, the locking element can be moved into the locked position by tilting the actuating lever in a first rotational direction, and into the released position by tilting the actuating lever in a second rotational direction. The actuating lever can, for example, have a C-shaped bracket mounted on the power transmission unit. A lever arm can project from the C-shaped bracket, the distal end of which, or the free end, is connected to the locking element. The C-shaped bracket can also be connected to a handle by means of which the actuating lever can be manually tilted by a user.

[0017] According to a further development of the synchronous mechanism, the actuating lever contacts the power transmission unit section by section, with the power transmission unit and the actuating lever interlocking in both the locked and unlocked positions. Thus, the respective position of the locking element can be fixed, meaning that the position can be secured by the detent force of the locking mechanism. Furthermore, the user receives tactile feedback regarding the correct position of the actuating lever through this locking action.

[0018] The power transmission unit can have at least two detent grooves into which a detent lug of the actuating lever can engage. Preferably, the actuating lever comprises two detent lugs. In particular, the C-shaped clip contacts the power transmission unit and can be rotated relative to it. The C-shaped clip can have one of the two detent lugs at an upper end and the other at a lower end.

[0019] According to a further embodiment of the synchronous mechanism, the first pivot axis is arranged closer to the pivotable connection with the seat support plate than to the pivotable connection with the seat frame, while the second pivot axis is arranged closer to the pivotable connection with the seat frame than to the pivotable connection with the seat support plate. Thus, a backrest in the locked position of the locking element can exert more resistance than in the unlocked position of the locking element, since the pressure force or backrest force has a reduced leverage effect via the second pivot axis. For example, the first pivot axis can have a leverage ratio of 31.5 / 28.4 with respect to the pivotable support or pivot point on the seat frame. Alternatively or additionally, the second pivot axis can have a leverage ratio of 23.4 / 36.5 with respect to the pivotable support or pivot point on the seat frame.The pivoting connection to the seat support plate and the pivoting connection to the seat frame can have a distance of 59.9 mm at the rear seat linkage. This means that the distance between the pivot point on the seat frame and the pivot point on the seat support plate can be 59.9 mm.

[0020] According to a further embodiment, the synchronous mechanism also includes a force storage device which is supported on the seat support and is designed and arranged to apply a restoring force to the front seat linkage, the restoring force of the force storage device being progressive within its effective range. For example, the force storage device can be designed as a compression spring, in particular as a helical compression spring or as a gas spring. The compression spring can be slightly compressed or pre-tensioned when the backrest is unloaded.

[0021] For example, the energy storage device can exhibit the same progressive behavior in both the locked and unlocked positions of the locking mechanism. Actuating the locking mechanism does not alter the progressive behavior of the energy storage device within its operating range. This operating range corresponds to the working path of the energy storage device between the maximum and minimum backrest tilt positions.

[0022] According to one embodiment of the method, the locking element is moved by tilting an actuating lever to actuate the locking element, the actuating lever being mechanically connected to the locking element.

[0023] The above embodiments and further developments can be combined with one another as appropriate. In particular, all features of the synchronous mechanism can be transferred to the method for adjusting the backrest force of an office or conference chair with such a synchronous mechanism, and vice versa.

[0024] Further possible embodiments, developments, and implementations of the invention also include combinations of features of the invention described previously or subsequently with regard to exemplary embodiments, even if not explicitly mentioned. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention. CONTENT OF THE DRAWING

[0025] The present invention will be explained in more detail below with reference to the exemplary embodiments shown in the schematic figures of the drawings. These show: Fig. 1A, Fig. 1B a schematic side view of a synchronous mechanism according to an exemplary embodiment, wherein the Fig. 1A the synchronous mechanism in the forward backrest position and the Fig. 1B represents the synchronous mechanism in the rear backrest position in a locked position; Fig. 2A, Fig. 2B a schematic side view of the synchronous mechanism Fig. 1A and Fig. 1B, wherein the Fig. 2A the synchronous mechanism in the forward backrest position and the Fig. 2B represents the synchronous mechanism in the rear seat position when in a release position; Fig. 3 a schematic side view of the rear seat link in the rear backrest position with the locking element in a release position; Fig. 4 a schematic perspective view of the synchronous mechanism from Fig. 1A; Fig. 5 an enlarged detail view of the actuating lever of the synchronous mechanism Fig. 4; Fig. 6 a schematic perspective view of the rear seat handlebar in the forward reclining position; Fig. 7 a schematic exploded view of the synchronous mechanism; Fig. 8 a flowchart of a method for adjusting the backrest force of an office or conference chair according to a further embodiment.

[0026] The accompanying drawings are intended to provide a further understanding of the embodiments of the invention. They illustrate embodiments and, in conjunction with the description, serve to explain the principles and concepts of the invention. Other embodiments and many of the advantages mentioned will become apparent with reference to the drawings. The elements of the drawings are not necessarily shown to scale.

[0027] In the figures of the drawing, identical, functionally equivalent and similarly acting elements, features and components - unless otherwise stated - are each provided with the same reference symbols. DESCRIPTION OF EXAMPLES OF EXECUTION

[0028] The Fig. 1A and Fig. Figure 1B shows a schematic side view of a synchronous mechanism 1 according to an exemplary embodiment, wherein the Fig. 1A the synchronous mechanism 1 in the forward backrest position and the Fig. 1B represents the synchronous mechanism 1 in the rear seatback position in a locked position. In Fig. Figure 7 shows a schematic exploded view of the synchronous mechanism 1.

[0029] The synchronous mechanism 1 is designed here for an office swivel chair and includes, for example, a seat support plate 2, a front seat link 3, a seat support 4, a rear seat link 5, a power transmission unit 8, an actuable locking element 9, an actuating lever 10 and a power storage unit 16.

[0030] The seat support plate 2 is pivotally supported at its front by the front seat link 3 relative to the seat support 4. Furthermore, the seat support plate 2 is pivotally supported at its rear by the rear seat link 5 relative to the seat support 4. The rear seat link 5 has a first pivot axis 6 and a second pivot axis 7 arranged parallel to the first pivot axis 6.

[0031] The force transmission unit 8 is designed to transmit a backrest force to the rear seat link 5. The force transmission unit 8 is coupled to the first and second pivot axes 6, 7 such that when the backrest is tilted by the force transmission unit 8, a pressure force F8 can be transmitted to the first pivot axis 6 or to the second pivot axis 7.

[0032] The locking element 9 is suitable for adjusting the backrest force and is movable relative to the force transmission unit 8 between a locking position and a release position. Fig. 1A and Fig. Figure 1B shows the blocking position of the blocking element 9, in which the pressure force F8 can be transferred from the force transmission unit 8 to the second pivot axis 7.

[0033] As in the Fig. 1A and Fig. As illustrated in Figure 1B, the power transmission unit 8 can be rotatably mounted on the first pivot axis 6 and have a gap G to the second pivot axis 7. In the locked position, the locking element 9 can be located at least partially within the gap G, so that rotation of the power transmission unit 8 relative to the first pivot axis 6 is blocked in the locked position. In the locked position of the locking element 9, the compressive force F8 of the power transmission unit 8 is transmitted to the second pivot axis 7 in every deflected position of the rear seat link 5. The first pivot axis 6 and the second pivot axis 7 can each be made of steel.

[0034] The actuating lever 10 is designed to actuate the locking element 9. The actuating lever 10 can be mechanically operatively connected to the locking element 9, and the locking element 9 can be moved by tilting the actuating lever 10. For example, the locking element 9 can be moved into the locking position by tilting the actuating lever 10 in a first rotational direction, and the locking element 9 can be moved into the release position by tilting the actuating lever 10 in a second rotational direction.

[0035] The energy storage unit 16 is supported here on the seat support 4 and is designed and arranged to apply a restoring force to the front seat link 3.

[0036] Optionally, the restoring force of the energy storage device 16 can be progressive within its operating range. In the illustrated embodiment, the energy storage device 16 is designed as a helical compression spring. In other embodiments, the energy storage device 16 can alternatively be designed as a gas spring or similar. The helical compression spring 16 can be slightly compressed or pre-tensioned when the backrest is unloaded. For example, the helical compression spring 16 can exhibit the same progressive behavior in both the locked and released positions of the locking element 9. Actuating the locking element 9 does not change the progressive behavior of the helical compression spring 16 within its operating range. The operating range corresponds to a working stroke of the helical compression spring 16 between the maximum inclination of the backrest, as shown in Fig. 1B illustrates, and the minimum inclination of the backrest, as shown in Fig. 1A illustrated.

[0037] The forward backrest position corresponds to the basic position of a backrest with the minimum incline. The rear backrest position corresponds to a position of the backrest with maximum incline. Due to a forced coupling, the seat support plate 2 and the backrest, and thus also the coupled force transmission unit 8, can only move together.

[0038] Fig. 2A, Fig. Figure 2B shows a schematic side view of the synchronous mechanism 1. Fig. 1A and Fig. 1B, wherein the Fig. 2A the synchronous mechanism 1 in the forward backrest position and the Fig. 2B represents the synchronous mechanism 1 in the rear backrest position in a release position.

[0039] The synchronous mechanism 1 according to the embodiment shown below Fig. 2A, Fig. 2B essentially corresponds to the synchronous mechanism 1 according to the embodiment shown in Fig. 1A, Fig. 1B. In Fig. 2A and Fig. Figure 2B shows the release position of the locking element 9, in which the pressure force F8 can be transferred from the force transmission unit 8 to the first pivot axis 6.

[0040] As in the Fig. 2A and Fig. As illustrated by example in Figure 2B, the locking element 9 is positioned outside the gap G in the release position. This allows the force transmission unit 8 to rotate relative to the first pivot axis 6 in the release position. The compressive force F8 of the force transmission unit 8 is transmitted to the first pivot axis 6 in the release position of the locking element 9 in every deflected position of the rear seat link 5. In the forward reclining position, the force transmission unit 8, or the pivoting element, is not pivoted inwards relative to the second pivot axis 7. When reclining backwards, the force transmission unit 8 pivots relative to the two pivot axes 6 and 7, so that the second pivot axis 7 pivots inwards relative to the force transmission unit 8, as shown in Figure 2B. Fig. Figure 2B shows that the gap G between the power transmission unit 8 and the second pivot axis 7 can thus become continuously smaller when leaning backwards.

[0041] Fig. Figure 3 shows a schematic side view of the rear seat link 5 in the rear backrest position with the locking element 9 in a release position.

[0042] The first pivot axis 6 can, for example, be arranged closer to the pivotable connection 5A with the seat support plate 2 than to the pivotable connection 5B with the seat support 4. Furthermore, the second pivot axis 7 can be arranged closer to the pivotable connection 5B with the seat support 4 than to the pivotable connection 5A with the seat support plate 2.

[0043] Thus, a backrest in the locked position of the locking element 9 can exert more resistance than in the released position of the locking element 9, since the pressure force or backrest force F8 via the second pivot axis 7 has a reduced leverage effect with respect to the pivotable connection 5B with the seat support 4.

[0044] For example, the first pivot axis 6 can have a lever ratio of 31.5 / 28.4 with respect to the pivot support or the pivot point of the pivot connection 5B on the seat support 4. Alternatively or additionally, the second pivot axis 7 can have a lever ratio of 23.4 / 36.5 with respect to the pivot support or the pivot point of the pivot connection 5B on the seat support 4. The pivot connection 5A with the seat support plate 2 and the pivot connection 5B with the seat support 4 can have a distance of 59.9 mm at the rear seat link 5. This means that the distance between the pivot point of the pivot connection 5B on the seat support 4 and the pivot point of the pivot connection 5A on the seat support plate 2 can be 59.9 mm.

[0045] Fig. Figure 4 shows a schematic perspective view of the synchronous mechanism 1. Fig. 1A. In particular, the Fig. 4 the interior of the synchronous mechanism 1 without the seat support plate 2.

[0046] The locking element 9 is rotatably mounted here. The locking element 9 can be designed such that, in the locked position, it is at least partially located between the power transmission unit 8 and the second pivot axis 7 and transmits the compressive force F8. For example, the locking element 9 can be rotatably mounted in the power transmission unit 8. As in Fig. As illustrated in Figure 4, the locking element 9 can be designed as a rocker, one end of which can be moved between the power transmission unit 8 and the second pivot axis 7 by rotating the locking element 9.

[0047] The actuating lever 10 can, for example, have a C-shaped bracket 11 mounted on the power transmission unit 8. A lever arm 12 can extend from the C-shaped bracket 11, the distal end of which, or the free end, is connected to the locking element 9. The C-shaped bracket 11 can also be connected to a handle 13, by means of which the actuating lever 10 can be manually tilted by a user. The construction of the actuating lever 10 is shown in the following. Fig. 5 is presented and described in even more detail.

[0048] Fig. Figure 5 shows an enlarged detail view of the actuating lever 10 of the synchronous mechanism 1. Fig. 4.

[0049] For example, the actuating lever 10 can contact the power transmission unit 8 in sections, with the power transmission unit 8 and the actuating lever 10 locking together in both the locked and unlocked positions. Thus, the respective position of the locking element 9 can be fixed, meaning that the respective position can be secured by the detent force of the locking mechanism. Furthermore, the locking action provides the user with tactile feedback regarding the correct position of the actuating lever 10.

[0050] The power transmission unit 8 can have at least two detent grooves 14 into which a detent lug 15 of the actuating lever 10 can engage, as shown in Fig. Figure 5 is shown as an example. Preferably, the actuating lever 10 comprises two locking lugs 15. In particular, the C-shaped clip 11 contacts the force transmission unit 8 and can be rotated relative to it. The C-shaped clip 11 can have one of the two locking lugs 15 at an upper end of the C-shaped clip 11 and the other of the two locking lugs 15 at a lower end of the C-shaped clip 11.

[0051] Fig. Figure 6 shows a schematic perspective view of the rear seat control arm 5 in the forward reclining position.

[0052] In addition to the Fig. Figure 4 shows the seat support plate 2 and a side panel of the rear seat arm 5. However, in Fig. 6 behind the side panel of the rear seat handlebar 5 the power transmission unit 8 can be seen, which is coupled to the first pivot axis 6.

[0053] A primary movement sequence of the synchronous mechanism, starting with a tilting of the backrest, can be described as follows. By adjusting the actuating lever 10 between the hard and soft settings, the rotary movement of the actuating lever 10 can be transmitted to the C-shaped clip 11. The C-shaped clip 11, with its two detent lugs 15, engages in the detent grooves 14 on the force transmission unit 8. This ensures that the two settings, hard or soft, are engaged by the detent force. The C-shaped clip 11 can then transmit the rotary movement to the rocker-type locking element 9. A cam on the C-shaped clip 11, which engages in a slot in the locking element 9, causes a tilting movement of the locking element 9. In the hard setting, the locking element 9 can block a component 17; in the soft setting, it releases the component 17 for the required pivoting movement.In the hard setting, the second pivot axis 7 can transmit the force to the rear seat link 5. In the soft setting, the first pivot axis 6 can transmit the force to the rear seat link 5. The rear seat link transmits the force to the pivoting connection 5A with the seat support plate 2. The pivoting connection 5A then transmits the force to the head plate or seat support plate 2, to the front seat link 3, and via a front axle to the energy storage device 16 or the main compression spring.

[0054] Fig. Figure 8 shows a flowchart of a method M for adjusting the backrest force of an office or conference chair according to a further embodiment. In particular, it concerns the adjustment of the backrest force of an office or conference chair with a synchronous mechanism 1 according to an embodiment according to [reference to relevant figure]. Fig. 1A-7.

[0055] The procedure includes, firstly, the step Moving M1 of a blocking element 9 and, secondly, the step Changing M2 of a force path.

[0056] In the movement step M1, the locking element 9 is moved between a locking position and a release position. For example, the locking element 9 can be moved by tilting an actuating lever 10 to actuate the locking element 9. The actuating lever 10 can be mechanically connected to the locking element 9.

[0057] In the step "Change M2", the force path of a compressive force F8 is changed by moving the locking element 9, whereby the compressive force F8 is transmitted from a force transmission unit 8 of the synchronous mechanism to a first pivot axis 6 in the release position of the locking element 9 and to a second pivot axis 7 in the locking position of the locking element 9. The first pivot axis 6 and the second pivot axis 7 are part of a rear seat link 5 of the synchronous mechanism and are arranged parallel to each other, as shown in particular in Fig. 3 is illustrated.

[0058] Although the present invention has been fully described above with reference to preferred embodiments, it is not limited to these embodiments but can be modified in many ways. For example, various features have been summarized in one or more examples in the preceding detailed description to improve the clarity of the presentation. However, it should be clear that the above description is merely illustrative and in no way limiting. It serves to cover all alternatives, modifications, and equivalents of the various features and embodiments. Many other examples will be immediately and directly clear to the person skilled in the art based on their technical knowledge, given the above description. Reference symbol list 1 Synchronous mechanism 2 Seat support plate 3 front seat handlebar 4 seat carriers 5 rear seat handlebar 5A swivel connection with the seat mounting plate 5B swivel connection with the seat support 6 first pivot axis 7 second pivot axis 8 Power transmission unit 9 Blocking element 10 operating levers 11 C-shaped clasp 12 Lever arm 13 Handle 14 Locking groove 15 Rastnase 16 energy storage units 17 Component F8 Pressure force of the power transmission unit G gap M Method for adjusting the backrest force of an office or conference chair M1 Moving a blocking link M2 Changing a force path

Claims

Synchronous mechanism (1) for an office or conference chair, comprising a seat support plate (2) which is pivotably supported in its front area by a front seat link (3) relative to a seat support (4) and which is pivotably supported in its rear area by a rear seat link (5) relative to the seat support (4), wherein the rear seat link (5) has a first pivot axis (6) and a second pivot axis (7) arranged parallel to the first pivot axis (6), comprising a force transmission unit (8) for transmitting a backrest force to the rear seat link (5), wherein the force transmission unit (8) is coupled to the first and the second pivot axes (6, 7) such that when a backrest is tilted by the force transmission unit (8) a pressure force (F8) can be transmitted to the first pivot axis (6) or to the second pivot axis (7), and comprising an actuable locking element (9) for adjusting the backrest force.wherein the locking element (9) is movable relative to the force transmission unit (8) between a locking position and a release position, wherein the pressure force (F8) can be transmitted from the force transmission unit (8) to the first pivot axis (6) in the release position of the locking element (9) and to the second pivot axis (7) in the locking position of the locking element (9). Synchronous mechanism (1) according to claim 1, characterized in that the locking element (9) is rotatably mounted. Synchronous mechanism (1) according to one of the preceding claims, characterized in that the power transmission unit (8) is rotatably attached to the first pivot axis (6) and has a gap (G) to the second pivot axis (7), wherein the locking element (9) is arranged outside the gap (G) in the release position and at least partially inside the gap (G) in the locking position, so that in the locking position a rotation of the power transmission unit (8) relative to the first pivot axis (6) is blocked. Synchronous mechanism (1) according to one of the preceding claims, further comprising an actuating lever (10) for actuating the locking element (9), wherein the actuating lever (10) is mechanically connected to the locking element (9) and the locking element (9) is movable by tilting the actuating lever (10). Synchronous mechanism (1) according to claim 4, characterized in that the actuating lever (10) contacts the power transmission unit (8) section by section, wherein the power transmission unit (8) and the actuating lever (10) lock together in the locking position and in the release position. Synchronous mechanism (1) according to one of the preceding claims, characterized in that the first pivot axis (6) is arranged closer to the pivotable connection (5A) with the seat support plate (2) than to the pivotable connection (5B) with the seat support (4), wherein the second pivot axis (7) is arranged closer to the pivotable connection (5B) with the seat support (4) than to the pivotable connection (5A) with the seat support plate (2). Synchronous mechanism (1) according to one of the preceding claims, further comprising a force storage device (16) which is supported on the seat support (4) and is designed and arranged to apply a restoring force to the front seat link (3), wherein the restoring force of the force storage device (16) is progressive in its effective range. Office or conference seating furniture, with a backrest and with a synchronous mechanism (1) according to one of claims 1 to 7, wherein the backrest is coupled to and supported by the power transmission unit (8) of the synchronous mechanism (1). Method (M) for adjusting a backrest force of an office or conference chair with a synchronous mechanism, comprising the steps: moving (M1) a locking element (9) between a locking position and a release position; and changing (M2) a force path of a compressive force (F8) by moving the locking element (9), wherein the compressive force (F8) is transmitted from a force transmission unit (8) of the synchronous mechanism to a first pivot axis (6) in the release position of the locking element (9) and to a second pivot axis (7) in the locking position of the locking element (9), wherein the first pivot axis (6) and the second pivot axis (7) are part of a rear seat link (5) of the synchronous mechanism and are arranged parallel to each other. Method (M) according to claim 9, characterized in that the locking element (9) is moved (M1) by tilting an actuating lever (10) to actuate the locking element (9), wherein the actuating lever (10) is mechanically operatively connected to the locking element (9).

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