Picker-to-Part Storage Systems

These systems are operationally and economically best for many applications. They are particularly suitable in cases where low to moderate throughput and storage volumes are combined with a wide range of types of products to be stored.

Bin shelving is the most basic, most popular method for small-parts storage [Figure]. However, it is not an inherently space-efficient technique, because of wasted overhead space and air space in the shelves to allow reach-in. Space utilization is often less than 50%. Therefore, from the respect of less space utilization with more picker time requirement, shelves may turn out to be infeasible / non-profitable if not designed with care.

A relatively new type of shelf storage that is gaining popularity is the pick-to-light system. In this type of system, the shelves have light displays which show from which shelf to pick in what quantities. The pick rate and accuracy is better, but the cost is higher.

Here is a movie (courtesy of Rapistan Demag Co.) that shows the order picking in a light-to-pick system.

Yet another type of shelving is "movable-aisle system". In this type of system, there is a saving of aisle space, since the aisle space is created dynamically when there is a specific pick-up. This type of system is suitable in areas in which a group of movable carriers are served by a small number of lift trucks or people, or the activity rates are moderate to low.

Modular storage drawer is a chest of drawers[Figure]. It is more efficient with respect to space-utilization, accuracy, and safety, but costlier than shelves. Modular drawer storage is particularly good for very small-parts. Advantages over shelves can be listed as:

• maximized space utilization by compartmentalization
• elimination of reach-in space
• less total floor space, decreased travel distances
• increased accuracy, cleanliness and security

In a warehouse, drawers are typically aligned in a space-efficient manner

Gravity flow rack is the type of rack in which products are stored on an inclined surface, and the next product advances/rolls to front due to gravity as a pick is made from the pick surface. Flow rack is typically used for active items which are stored in fairly uniform sized and shaped cartons. Replenishments are done from the replenishment aisle in the back. The back-to-front movement assures first-in-first-out (FIFO) turnover of material.

The man-aboard automated storage and retrieval system (AS/RS) is an automated storage and retrieval system in which the picker rides aboard a storage/retrieval machine to pick locations along an aisle [Figure]. Man-aboard AS/RS offer significant reductions in order pick time and space usage, compared to shelves and racks. However, these systems are the most expensive.

For a more detailed discussion of different types of shelves and other equipment, the reader is referred to (Weiss, Cramer, 1988).