Goods to Person Technology
Traditionally planned distribution centers utilize a person to goods order-picking strategy and work on a labor-intensive paper based framework or possibly an RF handheld scanner to direct and fulfill orders. In this type of order fulfillment model, inventory stock is received and put away in the dedicated storage location until an associate is directed to pick a piece, case or pallet of that inventory item from the storage location. Distribution centers have utilized this structure, person to goods order-picking strategy, for quite a long time. However, as the quantity of SKUs increases, energized by market transformations such as e-commerce and the growing interest for just-in-time ordering, personnel reliability and accessibility have become a major limitation in order speed and accuracy. It was once satisfactory for a picker to invest 60% of the time moving and 40% of the time picking. In many markets, that efficiency ratio does not compete anymore and new technology is required in order to stay ahead. For this reason, a significant number of companies are grasping a goods to person fulfillment strategy utilizing trend setting innovation in distribution and fulfillment centers. The goods to person concept is straightforward – associates stay in one location while the items to be picked and packed are presented to them through some type of automation. There are multiple forms of Goods to Person automation, from automated storage and retrieval systems – also referred to as ASRS or AS/RS, to horizontal and vertical carousels, vertical lift modules, or other robotic, electrical and mechanical material handling systems.
Unit Load Automated Storage & Retrieval Systems (AS/RS)
When planning a new distribution center that has a significant amount of full pallet traffic, inbound and outbound, a unit load automated storage and retrieval system should be considered. These systems utilize high bay pallet storage locations and very narrow aisles, thereby effectively utilizing the available cubic space of the warehouse. In fact, these types of AS/RS systems can be as high as 100′ and also form the structural framework of the building in which it is used. In the narrow aisles in between the rows of pallet storage are heavy duty cranes that travel the length of the aisle and raise and lower to match all pallet heights in storage. These cranes can store and retrieve pallets weighing up to 5,000 pounds from these pallet locations at a consistent and safe speed and deliver them to either a pallet conveyor at the end of the AS/RS aisle for continued transport or to an associate at the pickup and delivery (P&D) station for picking and processing.
Common applications for unit load AS/RS include:
- High volume cold storage warehouse where labor is inefficient and effective use of cubic space is critical
- Rules for inventory control is important and can be automated, such as first in, first out due to expiring product requirements
- Order profile is such that there are a significant amount of slow to medium moving SKUs that are stored and shipped in full pallet loads
- Order consolidation where multiple pallets in a single order can be accumulated until the last pallet of an order is received and ready to ship
Mini Load Automated Storage and Retrieval Systems (AS/RS)
Mini load automated storage and retrieval systems work similar to the unit-load counterpart. The main difference between the unit load and mini load is the storage medium for the SKUs. Instead of full pallets of SKUs being stored and retrieved in narrow aisle high bay pallet racking, SKUs are stored in much smaller trays, case or tote locations where the typical maximum load is 1,000 pounds. As such, mini load AS/RS systems can hold a high volume of relatively small, low to medium velocity SKUs that are ordered in low quantities per line item.
In a distribution center’s evolution from manual processes to more automated processes, the mini-load AS/RS would normally be the technology to use after graduating from a multi-level pick module, especially if the pick module utilizes a zone routing method for totes or shipper cartons to be tracked and diverted only the the areas within the pick module where the SKUs are located. Although very efficient, these pick modules require more associates to fulfill and the available cubic space is not utilized as efficiently as the mini load.
Applications where mini load AS/RS are commonly used include:
- eCommerce fulfillment where there are a high number of available SKUs, but the lines per order and quantities per line are small.
- Very controlled inventory requirements where products are high value, have expiration dates or are subject to strict accountability and regulation requirements.
- In a kitting and assembly environment where kits are put together from multiple SKUs that are stored and retrieved automatically and presented to the associate at the end of the aisle workstation for consolidation and further transportation or conveyance to assembly operations.
Vertical Lift Modules (VLM)
Vertical lift modules utilize numerous trays stored in vertically stacked slots. The trays are the same width as the VLM unit, which is typically from 8 feet to 12 feet wide. Also, the trays are usually divided and sub-divided with small storage bins. Associates stand in front of the opening of the VLM where trays are presented to them after being retrieved from their storage slots from above. When the associate picks the necessary items from the bins on the trays, the tray is pulled back inside the machine, carried up to the proper storage slot and the next tray is retrieved and presented to the associate.
Vertical Lift Modules are commonly used in multiple side by side arrangements where one associate can cover multiple adjacent VLMs. Additionally, the VLM is an efficient use of available cubic space as they can go as high as 100 feet. The amount of trays is primarily dependent on the products being stored The smaller the height of the products that are stored, the closer the storage slots can be located, which translates into more trays to be stored. The most common application for Vertical Lift Modules is in the fulfillment of many orders that have very small SKUs, such as hardware, electronics or kitted parts for assembly. Therefore, small, each picks would be the most common type of SKU stored in VLMs and they are either slow moving, single line-item picked or they are fast moving SKUs that are batch picked and have a corresponding “put wall” or “put to light” station adjacent to the VLM.
Horizontal carousels use a train of carriers that are connected in a continuous loop. Hanging from the carriers are narrow shelves, typically made of wire, that can hold cartons or individual containers for storing products. When the control system for a carousel receives an order, the drive system moves the train of carriers until the carrier that holds the proper shelf is in front of the associate. The associate picks the item from the proper shelf slot and the carousel turns the carriers until the next item to be picked is presented.
Since waiting for the carriers to turn and present the appropriate shelves to the associate is non-productive, horizontal carousels are usually operated in either a two carousel or four carousel pod where the carousels are located side by side. Therefore, when the associate is picking from a shelf on one carousel, the adjacent carousels in the pods are already rotating and getting the next item to be picked ready for the associate. Additionally, horizontal carousels can be stacked on top of each other so that available cubic space is used efficiently.
Considerations when thinking about using horizontal carousels:
- High density storage for a high number of SKUs. However, the SKUs must be able to fit inside the shelving on the carriers.
- Available room in order to create a pod of horizontal carousels. Otherwise, especially if single line item picking, the horizontal carousel might be extremely inefficient
- When using a pod of carousels coupled with a batch picking and put wall deconsolidation station adjacent to the associate, the horizontal carousel will likely be able to achieve a high amount of lines per hour throughput rate.
High Density Cube-Based Storage and Retrieval
Using small robots that travel along the top row of a grid of stacked cubes, multiple levels high, that drops an extractor down to the highest bin in the stack and pulls it up to the surface for further transport to an associate station located anywhere on the perimeter of the grid, a very efficient and automated use of available storage space is accomplished. The advantages to this type of goods to person technology include the ability to add storage capacity by expanding in all directions with more levels up or outward, the ability to add throughput capacity with the addition of more robots on top, the ability to add as many associate stations anywhere along the perimeter and the ability to dynamically slot the SKUs being stored in the most efficient manner just through the natural progression of having slower moving SKUs drop closer to the bottom of their respective stacks as faster moving SKUs get located above.