Patent ID: 8251636

Claim:
A lid closing method used for closing a closed container comprising a container body having an opening on one lateral side thereof, a lid for closing the opening, and an engagement means for fixedly attaching the lid to the opening of the container body by an operation from outside one of the lid and the closed container, by using a lid opening/closing system that comprises: a mini-environment having an opening portion; a door that is movable between a position at which the door nearly closes the opening portion and a position at which the door leaves the opening portion open, and comprises a lid holding means for holding the lid; a docking plate on which the closed container is allowed to be placed in such a way that the opening is opposed to the opening portion, the docking plate being movable toward and away from the opening portion together with the closed container to arrange, when located at a position close to the opening portion, the closed container at a first position at which the lid is to be detached, and to arrange, when located at a position away from the opening portion, the closed container at a second position at which loading and unloading of the closed container is to be performed; and a docking plate driving means for causing the docking plate to move toward and away from the opening portion, the lid closing method comprising the steps of: moving the lid to the position at which the door nearly closes the opening portion; determining, before the operation from outside is performed, presence of the door at the position at which the door nearly closes the opening portion and presence of the docking plate at the first position; fixedly attaching the lid to the closed container by the engagement means; and after the operation from outside is performed, again determining the presence of the door at the position at which the door nearly closes the opening portion and the presence of the docking plate at the first position.