Chair with seat and backrest with synchronised movement

Abstract

Chair comprising a support base, a seat including a support structure that is movable relative to the support base between a lowered position and a raised position, and a backrest having a support structure articulated to the support base around a transverse axis and oscillating around said axis between a position of maximum forward inclination and a position of maximum backward inclination, in which the seat and the backrest are mutually connected in such a way that when the backrest is in the position of maximum forward inclination the seat is in the lowered position and when the backrest is in the position of maximum backward inclination the seat is in the raised position. The support structure of the seat is connected to the support base by means of at least one rocking lever articulated to the support base and to the support structure of the backrest around two mutually parallel transverse axes. The support structure of the backrest comprises two lateral sections each of which has a connecting portion that extends beyond the axis of articulation of the backrest to the support base, the connecting portions being articulated to the support structure of the seat around a transverse axis displaced forward relative to the axis of articulation of the backrest.

1 . Chair comprising: 
 a support base,    a seat including a support structure that is movable relative to the support base between a lowered position and a raised position, and    a backrest having support structure articulated to the support base around a transverse axis and oscillating around said axis between a position of maximum forward inclination and a position of maximum backward inclination,    in which the seat and the backrest are mutually connected in such a way that when the backrest is in the position of maximum forward inclination the seat is in the lowered position and when the backrest is in the position of maximum backward inclination the seat is in the raised position,    wherein:    the support structure of the seat is connected to the support base by means of at least one rocking lever articulated to the support base and to the support structure of the backrest around two mutually parallel transverse axes,    the support structure of the backrest comprises two lateral sections each of which has a connecting portion that extends beyond the axis of articulation of the backrest to the support base, the connecting portions being articulated to the support structure of the seat around a transverse axis displaced forward relative to the axis of articulation of the backrest.    
   
   
       2 . Chair as claimed in  claim 1 , wherein it comprises an elastic device tending to thrust the backrest towards its position of maximum forward inclination and the seat towards the lowered position, the elastic device comprising a transverse flexing bar having a central portion that is fixed relative to the support base and two ends connected to said connecting portions of the backrest.  
   
   
       3 . Chair as claimed in  claim 2 , wherein the flexing bar is connected to the connecting portions of the backrest by means of two vertical levers.  
   
   
       4 . Chair as claimed in  claim 2 , wherein it comprises a device for adjusting the stiffness of the flexing bar including two movable pivot pins having respective transverse holes, mutually aligned, through which the flexing bar extends.  
   
   
       5 . Chair as claimed in  claim 4 , wherein the adjustment device comprises two rods fastened to the respective movable pivot pins and provided with respective racks meshing with a same gearwheel.  
   
   
       6 . Chair as claimed in  claim 1 , wherein the support base comprises two lateral flanges extending upward whereto are articulated said lateral sections of the support structure of the backrest.  
   
   
       7 . Chair as claimed in  claim 6 , wherein the support structure of the backrest comprises a transverse element provided with two lateral vertical arms whose top ends are articulated to said connecting portions of the backrest.