Vertical Carousels were sold for many years prior to the introduction of the first Vertical Lift Modules. While there are still applications for which a Vertical Carousel is the best solution, a Vertical Lift Module provides a number of inherent advantages over the Vertical Carousel:

A Vertical Carousel has a series of carriers that rotate vertically in a closed loop. The entire inventory stored in a Vertical Carousel is moved when parts are retrieved, compared to stationary rack inventory with a Vertical Lift Module (VLM).
Since the entire inventory moves with a Vertical Carousel, the weight must be carefully distributed to prevent high loading on the drive.
Drive components and motor horsepower required for a Vertical Carousel are typically much larger than in a VLM.
As inventory moves around the top and bottom of the enclosed loop of a Vertical Carousel, the shelves must rotate to keep level and prevent spillage of inventory. This requires a special cam follower mechanism not required on a VLM.
Vertical Carousels have a practical limit on height that is significantly lower than a VLM.
Maintenance requirements for Vertical Carousels far exceed those required for Vertical Lift Modules due to the complexity and configuration of mechanical components.

As a result of the above items, the overall cost per unit of storage space is significantly higher on a Vertical Carousel compared to a Vertical Lift Module. Therefore, the Vertical Lift Module (VLM) is the preferred method for storage.

VSR Horizontal Carousels

Horizontal Carousels operate similarly to Vertical Carousels, except that the carriers rotate horizontally. Horizontal Carousels are used when automated storage is desired but vertical space is not available. Due to the arrangement of shelves on the carriers in Horizontal Carousels, the picking height varies significantly. This does not allow for comfortable, ergonomic picking of product. Both Vertical Lift Modules and Vertical Carousels present parts to the operator ergonomically.