present invention has an advantage in that when any one of the agv port is disabled the mgv port complements the disabled agv port thereby smoothly operating the production line although the system as described has two agv input ports two agv output ports a convertible mgv input output port and two agv lines it will be readily apparent to one of ordinary skill that other combinations of agv and mgv ports are possible and within the scope of the invention it will also be apparent that the systems as described may be expanded in a modular fashion to be suited for manufacturing facilities of different sizes further although the systems as described pertain to the manufacture of lcds it will be apparent that the present invention may be applied to the manufacture of other products in which the manufacturing process involves multiple steps and partially completed items need to be temporarily stored although the present invention has been explained by the embodiments shown in the drawings described above it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments but rather that various changes or modifications thereof are possible without departing from the spirit of the invention accordingly the scope of the invention shall be determined only by the appended claims and their equivalents fig5 illustrates a flow chart for a mgv port according to the present invention as illustrated in fig5 a method for driving the stocker is operated by the cassette transfer command of the stocker master controller detecting an event occurrence s 1 when the event occur sending an automatic operation signal to the manual guided vehicle port in response to the event s 2 converting the manual guided vehicle port to the automatic.