Chair with oscillating backrest

A chair (1) comprising:

• a supporting structure (4);
• a seat (2), having a seat support (2b), connected to the supporting structure (4, 10) by means of an articulated-parallelogram connection (11, 12), including at least one first arm (11) and at least one second arm (12), each of which is articulated both to the seat support (2b) and to the supporting structure (10) so that the seat can be displaced between a lowered position and a raised position;
• a backrest (3) with a backrest support (17), mounted so that it can slide between a substantially upright position and a position reclined backwards, said backrest support (17) being operatively connected to the seat support (2b) in such a way that a displacement of the backrest (3) towards a position reclined backwards causes a displacement of the seat (2) towards a raised position, and vice versa, so that the backrest is recalled towards its upright position by a force depending at least in part upon the weight of the person sitting on the seat (2);
• and
• elastic means (26), operatively set between the supporting structure (10) and said first articulated arm (11) or said second articulated arm (12), or said backrest support (17), which tend to recall the seat (2) towards the lowered position and the backrest (3) towards the upright position,
• said chair being characterized in that said seat (2) is carried by a sliding support (2a) mounted so that it can slide on the support of the seat (2b) in a longitudinal direction and in that said sliding support (2a) is operatively connected to said backrest support (17) so that an inclination backwards of the backrest support (17) causes a recession of the sliding support (2a), on which the seat is mounted (2) with respect to the seat support (2b), connected by means of the articulated-parallelogram system to the fixed supporting structure (10).