While the VLMs and vertical carousels offer many of the same benefits, and the term VLM is often used to both, they differ in how they operate.
Vertical Lift Modules (VLMs)
VLMs store columns of trays against the front and back walls inside the machine. Between these two columns, in the middle of the machine, is space for the mechanical inserter/extractor or crane to travel up and down to access the trays. Trays are retrieved from their storage location and delivered to the operator access area where items can be picked or replenished as needed. VLMs can reach heights up to 98 feet.
In carousels, shelves connected in a loop rotate along the track until the desired shelf reaches the operator. A vertical carousel is a series of bins mounted to a vertical oval track inside a large cabinet. The motion is similar to a Ferris wheel. The carousel bins rotate to bring the required items to the operator. Because carriers are connected in a fixed order, the entire carousel will rotate in whichever direction provides the fastest access to the desired carrier. Vertical carousels can reach heights up to 32 feet.