Chair adjusting device

Abstract

A chair adjusting device includes a seat support board, a base, a backrest linking base, two elastic sets, and a backrest. The two elastic sets may provide an auxiliary elastic force to the backrest linking base. The seat support board has a rear side slidably mounted on the two side plates of the backrest linking base by two pivot knobs, so that the seat support board may be moved in concert with the backrest linking base. A primary urging spring is mounted on the support rod, and has a top edge urged on a bottom face of the seat support board.

What is claimed is:  
     
         1 . A chair adjusting device, comprising: a seat support board, a base, a backrest linking base, two elastic sets, and a backrest, wherein: 
 the seat support board has a front side provided with two oblique support racks, the front side of the seat support board is formed with a shaft hole, and a first shaft is extended through the shaft hole, so that the front side of the seat support board is pivotally mounted on the base, the seat support board has a rear side slidably mounted on two side plates of the backrest linking base by two pivot knobs, so that the seat support board may be moved in concert with the backrest linking base;    the base has two side plates for passage of a second shaft, so that the backrest linking base may be pivotally mounted on the two side plates of the base by the second shaft, a support rod is screwed and positioned between the two side plates of the base, a primary urging spring is mounted on the support rod, and has a top edge urged on a bottom face of the seat support board;    the backrest linking base is pivotally mounted on the base by the second shaft, and front ends of the two side plates of the backrest linking base are symmetrically pivoted with two elastic sets respectively; and    each of the two elastic sets includes two pivot bases, a slide rod, and an auxiliary spring, a first one of the two pivot bases of each of the two elastic sets is positioned between the two side plates of the base by a third shaft, and a second one of the two pivot bases of each of the two elastic sets is pivoted and positioned on the front end of each of the two side plates of the backrest linking base, so that the backrest linking base is constantly subjected to an auxiliary elastic force by the two elastic sets.    
     
     
         2 . The chair adjusting device in accordance with  claim 1 , wherein the base is secured on a foot post.  
     
     
         3 . The chair adjusting device in accordance with  claim 1 , further comprising a hook rod extended through a bottom face of the base, wherein the hook rod has a top end hooked on a side edge of the primary urging spring, and a bottom end screwed into a locking sleeve.  
     
     
         4 . The chair adjusting device in accordance with  claim 1 , wherein the backrest is L-shaped, and is threadedly secured on a rear side of the backrest linking base.  
     
     
         5 . The chair adjusting device in accordance with  claim 1 , wherein the auxiliary spring is mounted on the slide rod which is slidably pivoted between the two pivot bases.