Auto-returning height-control assembly for a chair

An auto-returning height control assembly in which an outer cylinder and a spindle are included and the spindle is projected outwards inside the outer cylinder comprises;

• a sleeve member which covers and fixes an outer cylindrical surface of the spindle and in which more than one projection is formed along the direction of its axis;
• a first cam member which allows the sleeve member in which the grooves are formed to rotate about its logitudinal axis and in which an side is in slope and combined to an inside cylindrical surface of an outer cylinder;
• a second cam member in which a projection is formed inside the inner cylindrical surface and the projection is inserted into the groove of the sleeve member so that up and down movement against the sleeve member is done and rotates simultaneously with the sleeve member along the rotation direction of the sleeve member and in which a slope side corresponding to the slope side of the first cam member is formed;
• and
• an elastic member which pushes the second cam member inside the outer cylinder and makes the slope side of the first cam member and the second cam member contact one another.