Chair with oscillating backrest

Abstract

A chair with backrest that can be inclined backwards has a seat carried by a support ( 2 b ), connected by means of an articulated-parallelogram system ( 11, 12 ) to the fixed supporting structure ( 4, 10 ) of the chair. The support ( 17 ) of the backrest is articulated to the support ( 2 b ) of the seat and is operatively connected to said articulated-parallelogram system so that any reclining backwards of the backrest causes a raising and a slight inclination backwards of the seat. The support of the backrest ( 17 ) is moreover connected by means of an articulated arm ( 23 ) to a sliding support ( 2 a ), on which the seat is mounted ( 2 ), and is in turn mounted so that it can slide in a longitudinal direction (A) on seat support ( 2 b ).

1 . A chair ( 1 ) comprising:
 a supporting structure ( 4 );   a seat ( 2 ), having a seat support ( 2   b ), 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 ( 2   b ) 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 ( 2   b ) 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 ( 2   a ) mounted so that it can slide on the support of the seat ( 2   b ) in a longitudinal direction and in that said sliding support ( 2   a ) 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 ( 2   a ), on which the seat is mounted ( 2 ) with respect to the seat support ( 2   b ), connected by means of the articulated-parallelogram system to the fixed supporting structure ( 10 ).   
   
   
       2 . The chair according to  claim 1 , characterized in that said first articulated arm ( 11 ) is prolonged behind its articulation shaft ( 14 ) above the fixed supporting structure ( 10 ) and terminates with a rear end, connected in an articulated way around a transverse shaft ( 19 ,  20 ) to the backrest support ( 17 ), the latter being moreover connected in an articulated way around a transverse shaft ( 15 ) to the aforesaid seat support ( 2   b ). 
   
   
       3 . The chair according to  claim 2 , characterized in that the part of the aforesaid first articulated arm ( 11 ) that is prolonged further, beyond its articulation shaft ( 14 ) above the fixed supporting structure ( 10 ), carries a transverse pin ( 21 ), which is guided in a slot ( 22 ) in the fixed supporting structure ( 10 ), and presses on a return spring ( 26 ) set between said transverse pin ( 21 ) and the aforesaid fixed supporting structure ( 10 ). 
   
   
       4 . The chair according to  claim 2 , characterized in that the backrest support ( 17 ) is moreover connected to the aforesaid sliding support ( 2   a ) by means of an articulated arm ( 23 ). 
   
   
       5 . The chair according to  claim 2 , characterized in that the rear end of the aforesaid first articulated arm ( 11 ) is articulated around a transverse shaft ( 20 ) to a shackle element ( 18 ), the opposite end of which is articulated around a transverse shaft ( 19 ) above the backrest support ( 17 ). 
   
   
       6 . The chair according to  claim 3 , characterized in that the rear end of the aforesaid first articulated arm ( 11 ) is articulated around a transverse shaft ( 20 ) to a shackle element ( 18 ), the opposite end of which is articulated around a transverse shaft ( 19 ) above the backrest support ( 17 ) and in that the aforesaid articulated arm ( 23 ) that connects the backrest support ( 17 ) to the sliding support ( 2   a ) is connected in an articulated way around the aforesaid transverse shaft ( 20 ) on the aforesaid shackle element ( 18 ). 
   
   
       7 . The chair according to  claim 1 , characterized in that the aforesaid first and second articulated arms ( 11 ,  12 ) are shaped and arranged so that a rotation thereof upwards causes a slight inclination backwards of the seat ( 2 ). 
   
   
       8 . The chair according to  claim 1 , characterized in that the part of the fixed supporting structure, to which the first and second articulated arms ( 11 , 12 ) are articulated, is in the form of a box, made in which is at least one guide slot ( 22 ) for the aforesaid transverse pin ( 21 ), carried by the aforesaid first articulated arm ( 11 ), said box containing the aforesaid spring ( 26 ) set between the fixed structure and the aforesaid transverse pin ( 21 ). 
   
   
       9 . The chair according to  claim 8 , characterized in that there are provided two first articulated arms ( 11 ,  12 ), mounted articulated to the two sides of the aforesaid supporting box ( 10 ) and connected by the aforesaid transverse pin ( 21 ), which engages two guide slots ( 22 ) made in the two sides of said box ( 10 ). 
   
   
       10 . The chair according to  claim 1 , characterized in that the backrest support ( 17 ) is constituted by an arm having one end connected to the backrest ( 3 ) and the opposite end that branches into two arms ( 17   a ), the ends of which are articulated, around a common transverse shaft ( 15 ), to the aforesaid seat support ( 2   b ). 
   
   
       11 . The chair according to  claim 1 , characterized in that associated to the fixed supporting structure ( 10 ) is an auxiliary assembly ( 28 ) that can be located selectively in a first position, for the normal positioning of the chair, or in a second position, in which it prevents the inclination backwards of the backrest, or in a third position, in which auxiliary elastic means ( 33 ) forming part of said auxiliary assembly ( 28 ) determine an additional force of reaction that opposes the movement of reclining backwards of the backrest. 
   
   
       12 . The chair according to  claim 11 , characterized in that said auxiliary assembly is mounted so that it can rotate around the axis of a transverse pin ( 21 ), rigidly connected to said first articulated arm, that causes deformation of first elastic means ( 26 ) associated to the fixed supporting structure of the chair following upon a reclining backwards of the backrest. 
   
   
       13 . The chair according to  claim 12 , characterized in that said auxiliary assembly ( 28 ) has different operative positions around the axis of said transverse pin ( 21 ) and in that the operative position of the auxiliary assembly ( 28 ) is selectable by means of a selector member ( 35 ) mounted so that it can rotate around a transverse shaft ( 36 ) on the fixed supporting structure of the chair. 
   
   
       14 . The chair according to  claim 1 , characterized in that the aforesaid auxiliary elastic means are constituted by a helical spring ( 33 ), which is orientable together with said auxiliary assembly ( 28 ) around the axis of said transverse pin ( 21 ) and in that in one of said operative positions said spring ( 33 ) is set between the fixed supporting structure of the chair and the aforesaid transverse pin ( 21 ) so as to react to a movement of inclination backwards of the backrest.