What is the working principle of a vertical lift container?

Vertical lift containers feature fixed shelves on both the front and rear sides, with a lift carriage (equivalent to a freight elevator) in the middle. Materials are stored on the shelves using trays. To retrieve items, the lift carriage ascends to the required material level, pulls the tray onto the carriage, then descends to the window, where the tray is pushed to the loading/unloading port. The reverse process is for storing materials.