Stuhl mit schwenkbaren Sitz und relativ dazu schwenkbarer Rueckenlehne

The chair has, as usual, a back (7) and a seat (5) pivoting about a fixed axle (4). The back comprises a plate (70) which is mounted sliding on guiding rails (72). Said guiding rails may pivot more than the seat, when the latter is inclined backwards, by means of a guiding element (8) connected to the rod of a piston (10) of a pneumatic spring (11). The motion of the guiding element (8) drives rotatingly about a fixed axle (15) a pair of reduction levers (13) connected to said guiding element. A driving band (14) hinged to the pair of levers (13) is connected to the plate (70) of the back. Since the pivot (16) between the pair of levers (13) and the driving band (14) travels a distance (b) substantially longer than the connection point (6) between the seat and the guiding element, respectively the guiding rails (72), the plate (70) of the back is pulled downwardly along said guiding rails. Such adjusting mechanism (13, 14) allows the back to have the same motion (E - E'') as the motion of the back of a human body during the inclination of the chair.