US Patent 7819473 Chair

A chair is provided that is designed so that the angle of the seat surface portion and the angle of the back surface portion are independent of each other and change, and a user can always take the optimum seated posture. The chair includes a base portion, a first link fixed to a seat and rotatably connected to the base portion, and a second link fixed to a seat back rest and rotatably connected to the first link. The chair also includes a first torque-generating mechanism that generates torque in accordance with the angle of the first link relative to the base portion; and a second torque-generating mechanism that generates torque in accordance with the angle of the second link relative to the first link.