Telescopic positioning mechanism for chair backrest

Claim 1

A telescopic positioning mechanism mounted on a chair for releasably locking a backrest of said chair in one of a plurality of vertical positions relative to a support affixed to a seat of said chair, comprising: a channel on said backrest including a notched member consisting of a plurality of notches, a top ramp at a top end of said notched member, and a bottom ramp at a bottom end of said notched member; a guide on said support including a center section, a plurality of horizontal and vertical flanges, a plurality of grooves defined by said flanges, a recess adjacent said groove, a stud, and a torsion spring on said stud; and a latch member biased by said torsion spring to engage with one of said notches in a locked position, said latch member including a ratchet bar and a projection, wherein said backrest is moved in a first direction to cause said locked latch member to disengage from said notch, said latch member is biased in a second direction to move into engagement with a next adjacent one of said notches by virtue of said torsion spring, in a highest position said ratchet bar passes over a lowest one of said notches to cause said latch member to move along said bottom ramp of said lowest one of said notches to a free position in which said projection is engaged with said recess, and in a lowest position said ratchet bar passes over a highest one of said notches such that said latch member moves along said top ramp of said highest one of said notches to a position in which said projection is out of engagement with said recess.