A POINT-SYNCHRONIZED ADJUSTMENT DEVICE FOR OFFICE CHAIRS

Abstract: A point-synchronized adjustment device for office chairs, seating furniture or the like is proposed in which a fixed functional relation is effected between the inclina­ tion of the back part (3) and that of the seat part (2) by means of a support bearing which is attached at the seat shell (7) and through which, in the manner of a connecting link guide, the back stay or stay bar (11) slides.

Description: The invention relates to a reclining chair comprising a seat provided with a rigid supporting shell, a back rest displaceable in orientation relative to said seat, a rigid seat support means including means defining at a forward end of the seat a stationary pivot axis where said rigid supporting shell is attached to said rigid seat where and about which pivot axis said seat can pivot rearwardly into a reclining position, at least one backstay member one end of said backstay member being fixed at a pivot axis positioned rearwardly of the first mentioned pivot axis, and an opposing end of said backstay bar being connected to said back rest. Such a reclining chair is disclosed in DE-A-3520188. Several office chair constructions are known in which adjustment of the inclination of the back results also in an adjustment of the inclination of the seating surface. Due to the increase in the angle as the inclination of the back increases a linear extension occurs between the seating surface and the back part between the seat contact point and the point of contact with the back. Since, in such chairs, the inclination of the back can be subject to constant variation, there is a constant displacement between the seat contact point and the point of contact with the back, with the result that the clothing of the seated person is constantly displaced. This is known as the "shirt pull-out effect". By the chair construction according to DE-A-3520188 this disadvantage is avoided. The adjustment in the angle between the back part and the seating surface takes place in such a manner that the arc through which the back of the person moves is identical to the arc described by the back rest as its inclination is adjusted. During this procedure, the adjustment of the back rest causes an almost concentric rotation about an imaginary transverse axis through the hip region of the seated person. By this means it is possible to prevent the troublesome lengthwise displacement between the seating surface and the point of contact with the back. To achieve this, the mechanism must be constructed such that the downward movement of the seat plate and the simultaneous increase in the inclination of the back rest creates a virtually rigid connection without any alteration in the lengthwise distance between the seat and the back rest, so that the point at which the back of the seated person contacts the chair performs the same rotational movement as the chair itself. The required positive interlink between the inclination of the seat and the inclination of the back must be chosen to be such that the amount by which the seat is lowered is less than the corresponding amount by which the back is lowered, i.e. the inclination of the seating surface is altered less than the inclination of the back. As a rough rule of thumb for this, the angle of inclination of the seat is assumed to be half that of the inclination of the back. When the angle of the back rest is adjusted backwards by about 20% out of the normal position, the inclination and hence the lowering of the seating surface near the back must accordingly be about 10°. The point of the support for the back in this example executes a downward movement of about 7 cm. The chair known from DE-A-3520188 has the disadvantage of a relatively complicated mechanical design: a large number of articulation points are necessary in order to bring about the desired movement of the backrest and/or the seat shell. The object of the invention is to avoid this disadvantage and to provide a reclining chair in accordance with the preamble having an extremely simple mechanism to bring about the desired effect, that is to say that an inclination of the seating surface is altered less than the inclination of the back. According to the invention said seat shell includes a slide bearing means, a portion of said backstay member being slidably supported on said slide bearing means, said slide bearing means providing positive guidance between the seat shell and the backstay member such that when said seat shell reclines over an angle β the back rest inclines over an angle α which is substantially greater than angle β. As a consequence of the fact that a portion of the backstay member is slidably supported on the slide bearing means providing positive guidance between the seat shell and the backstay member, the desired effect of the seat shell reclining angle being larger than the back rest reclining angle, is brought about by very simple means. Preferably the back stay member is substantially S-shaped and one end of the back stay member extends upwardly into the back rest and the opposing end extends along and through the supporting shell and is attached to the rigid support means. DE-U-8515221 discloses a chair comprising a seat provided with a supporting shell, a back rest, a rigid seat support means including means defining at a forward end of the seat a stationary pivot axis where said supporting shell is attached to said rigid seat support means and about which pivot axis said seat can pivot rearwardly into a reclining position, at least one lever to which the back rest is fixed, said lever being connected to the support means at the pivot space from the first mentioned pivot axis. A back stay member is connected to the back rest and to the seat at a pivot spaced from the pivot connection between the lever and the seat. The lever and the back stay are pivotably connected and either the pivot connection between the back stay member and the seat or the pivot connection between the back stay member and the lever comprises a connecting element which enables a relative movement between lever and back stay or between back stay and its connecting point to the seat. Since the back stay member in this known construction is not slidably supported on slide bearing means providing positive guidance between the seat shell and the back stay member, this construction has a lot of pivot points and is very complicate. An advantageous and expedient exemplary embodiment of the invention is illustrated in the drawing and explained in more detail in the description which follows. The chair 1 shown in the figure comprises a seat part 2 and a back part 3. An adjustment (arrow 4) in the inclination of the back rest 5 is associated with a simultaneous downward movement (arrow 6). The adjustment of the back part is normally by about α₁ = 5° forwards and about α₂ = 15-20° backwards. The inclination at which the seat is lowered is designated β = 8-10°. In the front region, the seat shell 7 is attached to the seat bracket 9 at the articulation point 8. The articulation point is designed as a pivot bearing 8. In so far as the seat part in the region of the articulation point is designed as a flexible bending zone, the articulation point 8 can be made rigid. In the region between the lower seat shell and the back part 3, the seat, which is composed of the seat part 2 and the back part 3 has a bending zone 10. This bending zone is necessary in order to achieve a differential inclination as between the seat part 2 or seat shell 7 and the back part 3. However the seat part 2 and the back part 3 can also take the form of separate parts. S-shaped back stay members 11 are connected between the seat bracket 9 and the back part 3. The back stay members 11 are articulated at the seat bracket 9 by means of a fixed pivot bearing 12 and curve initially in the form of an arc (region 13), then almost parallel to the seat shell 7 or at an acute angle τ to the latter into the seat part 2 (region 14), before again curving in an arc shape (region 15) into the back part 3. The vertex 21 of the angle τ begins approximately in the region of the articulation point 8. In the back part 3, the back stay members 11 are fixed by means of a fixed bearing 16 or pivot bearing. If a fixed bearing 16 is chosen, a continuous seat shell 7, which continues in the seat part and the back part 3 and has a seat shell back part 22 is used, utilizing its intrinsic flexibility. The bearing 16 is located at the height h₁ approximately in the region of the imaginary transverse axis through the hip region of a seated person. The pivot bearing 12 is located at an approximately central point between the longitudinal axis 17 of the chair pedestal 18 and the vertical axis 19 through the articulation point 8. According to the invention slide bearings 20 are provided between the seat shell 7 and the back stay members 11. The downward movement of the back stay members 11 act directly on the seat shell 7 via the slide bearings 20 which are designed in the form of a passage through the lower region of the seat shell 7. The figure shows the adjustment in inclination from a starting position (position A) to an inclined position (position B). In this case the slide bearings 20 travel into the region 20', i.e. as the back stay elements 11 move downward, the slide bearings 20, which are fixed to the seat shell 7, slide towards the pivot bearing 12, in the process sliding along the arc-shaped region 13 of the back stay element 11. The backward movement of the seat part 2 (arrow 6) which occurs during this movement is indicated in the figure by h₂ over the chosen point 23 or 23'. The shape of the back stay members 11 and hence the movement the back stay members in the slide bearings 20, which are fixed to the seat shell 7, can be varied in order to achieve the desired functional relation in the synchronized mechanism. Of decisive importance is the connecting link guide between the back stay members 11 and the seat shell 7, in particular in the form of the arc-shaped movement (region 13) caused by the sliding movement of the slide bearings 20 on the back stay elements 11. Several modifications and additions are possible within the scope of the present invention. Inside the seat bracket 9 a coil spring mechanism may be mounted to offer an adjustable resistance against a backwards tilting of the back part. To enable a person to select the desired sitting height, the chair could be provided with a gas spring mechanism known per sé. Obviously a locking mechanism could be added to lock a selected inclination position of the back part 3. This mechanism could have a setting indicator to indicate the inclination in degrees. The front portion of the seat part may be tiltable downwards in two or more positions to adapt the length of the seat part to persons with shorter or longer upper legs.

Claims: A reclining chair comprising a seat (2) provided with a rigid supporting shell (7), a back rest (3) displaceable in orientation relative to said seat (2), a rigid seat support means (18, 9) including means defining at a forward end of the seat a stationary pivot axis (8) where said rigid supporting shell (7) is attached to said rigid seat support means (18, 9) and about which pivot axis (8) said seat (2) can pivot rearwardly into a reclining position, at least one backstay member (11) one end of said backstay member being fixed at a pivot axis (12) positioned rearwardly of the first mentioned pivot axis (8), and an opposing end (16) of said backstay bar being connected to said back rest (3), characterized in that said seat shell (7) includes a slide bearing means (20), a portion of said backstay member (11) being slidably supported on said slide bearing means (20), said slide bearing means providing positive guidance between the seat shell and the backstay member such that when said seat shell reclines over an angle β the back rest reclines over an angle α which is substantially greater than angle β. Reclining chair according to claim 1, characterized in that said backstay member (11) is substantially S-shaped and that one end of said backstay member extends upwardly into said back rest (3) and the opposing end extends along an through said supporting shell (7) and is attached to said rigid support means (18, 9).

Inventors: HANSEN, ECKHARD
Applicants: AHREND-CIRKEL B.V.
Application year: 1987
Main classification: A47C1
IPC codes: A47C1, A47C3