Adjustment device for the back of a chair

An adjustment device for a back of a chair, comprising:

• (a) a fixed member, said fixed member being coupled to a bottom of a seat of said chair from a front portion thereof;
• said fixed member having a toothed portion on a rear part thereof,
• (b) a frame member fixed to said chair back, said frame member being pivoted to said rear part of said fixed member;
• said frame member having a cog fitted on a rod, said cog being rotatably disposed on said toothed portion of said fixed member;
• said frame member being biased toward said seat by a first spring connecting both said fixed member and said frame member;
• (c) an engaging member movably connected to said frame member;
• a second spring being connected to both said engaging member and said frame member for forcing said engaging member to engage said cog;
• said engaging member having stopping teeth capable of engaging said cog for preventing said cog from rotating when said engaging member is biased to connect said cog by said second spring;
• (d) a controlling rod member, said controlling member being movably connected to said frame member;
• a steel rope being connected to said engaging member and said controlling member such that said controlling member can be moved to force said engaging member to separate from said cog for said stopping teeth of said engaging member to disengage from said cog;
• said chair back and said frame member being capable of being pivoted relative to said chair seat when said stopping teeth disengage from said cog.