Automatic waistrest adjusting device for office chairs

Abstract

An automatic waistrest adjusting device for office chairs includes a waistrest combined with the bottom of a backrest, and the waistrest comes with a design of connecting a curved flexible metal plate and making use of whose flexibility to suspend the bottom of the waistrest that can be turned flexibly with a user's waist to achieve an ergonomic stepless angular adjustment to allow the user's waist to lean at the most comfortable position. The waistrest adjusting device combines the waistrest and the backrest by simple components and assembling method, and achieves the effects of preventing poor performance and quality caused by an elastic fatigue and extending the use life.

1 . An automatic waistrest adjusting device for office chairs, comprising:
 a) a seat, having a chair leg disposed at the bottom of the seat;   b) a stand, with the bottom pivotally coupled to a rear side of the seat;   c) a backrest, disposed at the front of the stand, and having a framework and an external cover installed onto the framework; and   d) a waistrest, disposed at the bottom of the framework of the backrest,   
       wherein one or more upper installation notches are formed at the bottom of the backrest framework, and one or more upper positioning holes are formed in a vertical direction from a surface of the framework to the upper installation notch; 
       wherein the waistrest includes an external frame and an external cover installed onto the external frame, and a lower installation notch and a corresponding lower positioning hole are formed at the top of the external frame and opposite to the upper installation notch; and 
       wherein at least one curved flexible metal plate, coupled between the backrest framework and the waistrest external frame, and having an upper fixing surface formed at an upper end portion and opposite to the upper installation notch of the framework, and an upper locking hole formed on the upper fixing surface and at a position opposite to the upper positioning hole and fixed by an upper bolt, and a lower fixing surface is formed at a lower end portion and opposite to the lower installation notch, and a lower locking hole is formed on the lower fixing surface and at a position opposite to the lower positioning hole and fixed by a lower bolt, and an n-shaped curved body is formed between the upper and lower fixing surfaces, such that after the n-shaped curved body is locked to the upper and lower installation notches by the upper and lower fixing surfaces respectively, the n-shaped curved body is situated at a gap formed between the bottom of the backrest framework and the top of the waistrest external frame, and whose elasticity makes the top side of the waistrest as a rotational connecting end to suspend the bottom in the air to achieve an ergonomic stepless angular adjustment. 
     
     
         2 . The automatic waistrest adjusting device for office chairs as recited in  claim 1 , wherein the curved flexible metal plate is a steel plate. 
     
     
         3 . The automatic waistrest adjusting device for office chairs as recited in  claim 2 , wherein the gap S between the upper and the lower of the n-shaped curved body of the curved flexible metal plate is smaller than 3 cm, and the depths D between the front and the rear is greater than the gap S. 
     
     
         4 . The automatic waistrest adjusting device for office chairs as recited in  claim 3 , wherein the gap S is between 0.5 cm to 1.5 cm. 
     
     
         5 . The automatic waistrest adjusting device for office chairs as recited in  claim 1 , wherein the framework of the backrest comprises a front framework, a rear framework, a transverse bar installed at the rear side of the framework, and two parallel longitudinal slide sleeves installed on the transverse bar and displaceable to be up and down on the positioning portion of the stand for adjusting the height of the backrest. 
     
     
         6 . The automatic waistrest adjusting device for office chairs as recited in  claim 5 , wherein the cross-section of the rear framework is substantially a U-shaped groove, and the front framework is embedded into the U-shaped groove and latched and fixed by using concave and convex combining members at a joint of the front framework and the U-shaped groove. 
     
     
         7 . The automatic waistrest adjusting device for office chairs as recited in  claim 5 , wherein the external frame of the waistrest is comprised of a front frame and a rear frame, and the waistrest is displaced with the backrest up and down on the stand. 
     
     
         8 . The automatic waistrest adjusting device for office chairs as recited in  claim 7 , wherein the cross-section of the rear frame is a substantially U-shaped groove while the front frame are embedded in the U-shaped groove, and concave and convex connecting members are used for combining the rear frame and the front frame.