US Patent 7293833 Chair and support mechanism unit thereof

A chair is provided with a base 6 fixed at an upper end of a leg pillar 5, a back support unit 13 attached to the base 6 so as to tilt backward, a backrest 3 attached to the back support unit 13, and a spring unit 14 supporting the backward tilt of the back support unit 13. The spring unit 14 is to expand and contract in a back and forth direction when viewed from above and arranged further behind than a tilt supporting point 16a of the back support unit 13. The back support unit 13, the spring unit 14, and the base 6 constitute a kind of link mechanism and the spring unit 14 will expand and contract mainly at the front end, while tilting backward.