A Vertical Lift Module is an advanced concept/design that came from the Vertical Carousel.
The carousel system uses a chain system that move carriers along the chain in a vertical motion. Since it is the first storage and retrieval system developed, user will need to consider an overloading situation since everything hangs from a chain (so you always have to consider what is on the other side). Think of it as a ferris wheel, in which the gondolas have to be of a same height, weight in order to maintain a balance, you sometimes have to let several empty gondolas pass before one climbs in.
A Vertical Lift Module (VLM), on the other hand, doesn’t carry such burdens. In a warehouse environment, you need to be flexible in the process of retrieving and storage of articles. You can futureproof the storage space by increasing the height of the VLM or by reducing the height of the goods.