Chair with oscillating back

Abstract

 The chair consists of a base structure (2) bearing a back (4) and a seat (6), both jointed to the base structure (2) around respective, parallel axes. The back (4) bears a thrust mechanism (14) that acts on the rear of the seat (6) and causes it to lift up when the back (4) is pushed towards its backward reclining position. The thrust mechanism (14) is jointed to the chair back (4) and slides in a guided manner along the seat (6) in a longitudinal direction.

Description

Detailed Description of the Invention

[0001] This invention regards a chair comprising:

• a base structure
• a back whose frame is jointed to the base structure and which moves between an upright and a reclining position,
• a seat whose front section is jointed to the base structure around an axis parallel to the axis of articulation of the back, and whose rear section moves between a lowered and a raised position, corresponding to the upright and reclining position of the back respectively, and
• a thrust mechanism connected to the back which acts on the said rear section of the seat, causing it to move between its lowered and raised position.

[0002] A chair of the type described above is known under French patent no. 2.045.120. In the chair illustrated in this document, the thrust mechanism consists of a rounded body rigidly fixed to one end of the frame of the back. This body rests against the bottom surface of the seat and raises the rear of the seat when the occupant rests his weight against the back, causing it to move into a reclining position. This kinematic arrangement generates a reaction on the back of the occupant which is proportional to the said occupant's weight. However, the solution illustrated in the French document no. 2.045.120 is not suitable for application on chairs of modern design since a considerable amount of space must be provided beneath the rear of the seat to allow the thrust mechanism to oscillate.

[0003] In order to overcome the problems mentioned above this invention concerns a seat of the type described above, characterized by the fact that the above-mentioned thrust mechanism is jointed to the frame of the back and is fitted so that it slides in a guided manner along the seat in a longitudinal direction, the said thrust mechanism moving between a forward and a backward position corresponding to the reclining and upright position of the back respectively.

[0004] Thanks to these characteristics, the mechanism linking the reaction force to the weight of the occupant can be incorporated in the structure of the seat and it is therefore possible to make a simple, compact chair of modern design.

[0005] Further characteristics and advantages of this invention will be apparent from the detailed description that follows, reference being made to the annexed drawings, provided purely by way of example and without being in any way limiting.

• Figure 1 is a schematic side view of a chair according to this invention,
• Figure 2 is a longitudinal section on a larger scale of the part indicated by the arrow II in figure 1, and
• Figure 3 is a sectional scrap view according to the arrow III in figures 1 and 2.

[0006] With reference to figure 1, the number 1 indicates a chair including a base structure 2, consisting of shaped tubular metal elements, bearing a back 4 and a seat 6. The back 4 is fitted with a frame 8 consisting of a tubular element which runs along the edge of the back 4. The frame 8 is jointed to the support structure 2 around a horizontal axis A.

[0007] As can be seen in greater detail in figures 2 and 3, the seat 6 includes a pair of tubular elements 10 (only one of which can be seen in the figures) with an oblong profile cross-section which are arranged along the sides of the seat 6. The front section of the tubular elements 10 is jointed to the base structure 2 by means of pins 12 which extend parallel to the articulation axis A of the back 4. Housed inside each tubular element 10 is a thrust mechanism 14 including a fork element 18 which is connected by means of a transverse pin 16 to the lower end 20 of the frame 8. The fork element 18 bears a pair of horizontal pins 22 on which are fitted rotating wheels 24 which roll on the inside wall of the tubular element 10. The said wheels may be replaced by a runner or by any other kind of sliding device. Also mounted on the pins 22 are bushings 26 in elastic material which engage a stop element 28 consisting of the bent end-section of a plate 30 which is attached to the tubular element 10 by means of a rivet 32. The fork element 18 also bears a rod 34, one end of which extends through a hole 36 made in a counter element 38 secured to the tubular element 10. The rod 34 acts as a support for a spiral spring under compression 40 placed between the counter element 38 and the fork element 18.

[0008] In figure 2 the rest position of the chair 1 is shown by the broken line. In this configuration the back 4 is basically upright while the rear section of the seat 6 is in its lowered position. The spiral spring 40 pushes the fork element 18 in the direction indicated by the arrow B towards a position corresponding to this rest configuration.

[0009] The unbroken line in figure 2 shows the configuration for maximum backward recline of the chair back 4. In this configuration the frame 8 has oscillated around the axis A in relation to the rest position. The lower end 20 of the frame 8 causes the rear part of the seat 6 to lift up, the said seat oscillating around the front axis 12.

[0010] As a result of the oscillation of the frame 8 around the axis A the thrust mechanism 14 slides inside the tubular element 10 in the direction indicated by the arrow C, compressing the spiral spring 40. The limit positions of the thrust element 14 inside the tubular element 10 are determined by the contact of the bushings 26 with the stop piece 28. The force that the occupant exerts on the back 4 to cause it to oscillate towards its rear reclining position also generates a slight elastic deformation in the support structure 2 whose rigidity has been determined in order to accommodate this give. The articulation axis A of the back 4 thus moves to the extent shown by the letter D in figure 2.

[0011] It is apparent from the foregoing description that the chair back 4 exerts a force on the back of the occupant which depends on the load of the spring 40 and on the occupant's weight; accordingly, the oscillation rigidity of the back 4 adapts automatically to the occupant's requirements. The mechanism connecting the seat 6 to the back 4 is entirely contained inside the tubular elements 10 and the chair is therefore very compact and can even be stacked with other chairs of the same kind.

Claims

1. - Chair comprising:

- a base structure (2),

- a back (4), with a frame (8) jointed to the base structure (2), which moves between an upright position and a backward reclining position,

- a seat (6) with a front section jointed to the base structure (2) around an axis (12) parallel to the articulation axis (A) of the back (4), and with a rear section moving between a lowered and a raised position, corresponding to the upright and reclining position of the back respectively, and

- a thrust mechanism (4) supported by the frame (8) of the back (4) which engages with the said rear section of the seat (6) and thus causes it to move between the lowered and raised position,

   characterized by the fact that the said thrust mechanism (14) is jointed to the frame (8) of the back (4) and is fitted so as to slide in a guided manner along the seat (6) in a longitudinal direction, the said thrust mechanism (14) moving between a forward and back position corresponding to the reclining and upright positions of the back (4) respectively.

2. - Chair as described in claim 1, characterized by the fact that it includes elastic elements under compression (40) placed between the seat (6) and the said thrust mechanism (14).

3. - Chair as described in claim 1, characterized by the fact that the chair (6) includes a tubular element (10) inside which the said thrust mechanism (14) slides.

4. - Chair as described in claim 3, characterized by the fact that the said thrust mechanism (14) includes a fork element (18) bearing a pair of wheels (24) running on the inside wall of the said tubular element (10).

5. - Chair as described in claim 4, characterized by the fact that the said fork element (18) carries a transverse pin (16) to which the bottom end (20) of the frame (8) of the back (4) is attached.

6. - Chair as described in claim 4, characterized by the fact that the said fork element (18) bears a rod (34), one end of which extends through a hole (36) made in a counter element (38) fixed to the inside of the said tubular element (10).

7. - Chair as described in claims 2 and 6, characterized by the fact that the said elastic devices include a spiral spring (40), arranged co-axially to the above-mentioned rod (34), the ends of which engage the counter element (38) and the fork element (18) respectively.

8. - Chair as described in claim 3, characterized by the fact that the said fork element (18) bears a pair of bushings (26) in elastic material whose purpose is to engage a fixed stop element (28) carried by the tubular element (10).

9. - Chair as described in claim 3, characterized by the fact that the seat (6) includes a pair of tubular elements (10) parallel to each other and arranged along the sides of the seat (6), inside which extend respective thrust mechanisms (14) jointed to the ends (20) of a shaped tubular element (8) comprising the above-mentioned frame of the back (4).

Drawing