An eccentric assembly controlled by a rotational speed thereof. The eccentric assembly includes: a housing driven and rotated by a motor; an eccentric shaft installed in the housing to have a changeable angular position by rotating relative to the housing; a locking device adopted to lock the eccentric shaft by engaging with one side of the eccentric shaft and to unlock the eccentric shaft when a rotational speed of the housing is greater than a locking critical speed; a clamping device adopted to clamp an opposite side of the one side of the eccentric shaft that engages with the locking device and to release clamping to the eccentric when a rotational speed of the housing is greater than a clamping critical speed; and a stopper installed in the housing so as to limit a rotation angle of the eccentric shaft generated when locking and clamping to the eccentric shaft are released.