Patent ID: 7303232

Claim:
A backrest adjusting device for office chairs, comprising: a) a seat portion having a seat cushion and a stand for supporting the seat cushion; b) a back having a frame, a back cushion fixed on the surface of the frame, a connecting member for connecting the bottom of the back to a rear side of the seat portion, a hollow containing space formed at the middle section of the back, and an n-shaped member being disposed in the containing space and extended backward; and c) a first attaching device installed on the n-shaped member of the containing space, thereby achieving the adjustment of the three-dimensional space of position, longitudinal buffer and angular rotation, wherein the first attaching device includes: i) at least two parallel pipe bodies fixed on an internal side of the n-shaped member with an opening facing upward; ii) at least two springs sheathed into each pipe body; iii) at least two pivots, each including a first pivot and a second pivot pivotally connected with each other, wherein the first pivot has at least one portion sheathed into the pipe body and fixed by a bolt installed from a rear side of the pipe body for fixing the spring, and the second pivot is protruded and exposed from the front of the pipe body and includes a longitudinal penetrating hole, and a transversal positioning member is perpendicular to the longitudinal penetrating hole, and an end of an internal side of the transversal positioning member includes a small dome slightly protruded from a hole wall of the longitudinal penetrating hole; iv) at least two parallel rod bodies separately passing through a longitudinal penetrating hole of each second pivot and having a plurality of aligned slots corresponding to a side of the transversal positioning member, such that one of the slots is selected for embedding and positioning a small dome; and v) an attaching body being an ergonomic design with a curved shape and fixed onto upper and lower ends of two parallel rod bodies, and its surface having an external wrapped surface.