grounds these eccentric assembly 100 is usually have an outer eccentric member 104 inner eccentric member 102 a mechanical stopper 106 journals 108 coupling the outer eccentric member 104 and the inner eccentric member 102 together at the end of the outer eccentric member 104 and a bearing 110 at the outer ends of the journals 108 the outer eccentric member 104 is a rigid cylinder having added thickness around the lower part of it the added thickness works as a mass so it can have eccentric mass that is lighter at one part and heavier at the other part the shape of the added thickness can be varied but in this prior art it is a half cylinder located partially on the lower part of the outer eccentric member 104 at the upper part of the outer eccentric member 104 there is a stopper 106 to mechanically stop the rotation of the inner eccentric member 102 in the prior art the stopper 106 is quarter arc shaped bar protruded toward inside of the outer eccentric member 104 with a small thickness so that it can prevent the movement of the inner eccentric member 102 however the weight of the stopper 106 is not substantial enough to prevent the outer eccentric member 104 from working as eccentric member since the additional mass of the outer eccentric member 104 is much larger than that of the stopper 106 the inner eccentric member 102 is rotatably connected to the axis of the rotation in this prior art.