A taste for automation
With 5,000 pallets about to come pouring into its new DC each day, Gordon Food Service decided there was just one thing to do: automate.
When food-service distributor Gordon Food Service (GFS) began planning for the construction of its fourth distribution center a few years back, it decided early on that the DC would be automated. GFS's other three distribution centers take considerable advantage of material handling automation. When it came to the new facility in Shepherdsville, Ky., the distributor decided to follow the same course to ensure an efficient and cost-effective operation. In GFS's eyes, automation would be critical to increasing throughput, optimizing cube utilization, and keeping close track of pallets.
The question was how to go about it. The 300,000-square-foot center, which was being built to serve customers in Kentucky and Tennessee, as well as parts of Indiana, Illinois, Arkansas, and Missouri, would be a high-throughput operation, handling up to 5,000 incoming pallets per day. Furthermore, its handling requirements would be relatively complex. As is typical of grocery distribution centers, the building would have separate sections to hold dry, chilled, and frozen products—approximately 10,000 stock-keeping units (SKUs) in all. That meant that the system would have to be set up to accommodate the flow of thousands of pallets each day into not one, but three separate storage areas (ambient, refrigerated, and freezer storage).
There were other challenges as well. For example, the automation plan for the Kentucky facility would have to provide a way to handle waves of inbound pallets quickly within the small footprint allocated to receiving. It also had to be capable of managing storage positions within the automated storage and retrieval system (AS/RS) to ensure that stock positions were not depleted. Furthermore, the system had to make provisions for the disposition of the empty pallets created as workers selected products to fill orders. On top of that, the company wanted to make sure that any automated system would be cost-effective to maintain as well as easily adaptable for future needs.
A matter of coordination
The decision to break ground on a fourth distribution center in 2004 was prompted by the company's rapid growth. Headquartered in Grand Rapids, Mich., GFS is the largest family-owned and -operated broad-line food-service distributor in North America. GFS delivers about 16,000 national brands and private-label products to more than 45,000 customers, which include restaurants, hotels, health care institutions, colleges and universities, and businesses both in the United States and Canada. Besides its wholesale distribution business, it operates more than 120 GFS Marketplace stores in Florida, Illinois, Indiana, Kentucky, Michigan, Ohio, Pennsylvania, and Tennessee.
As it set about the task of designing the new facility, GFS came up with a plan for a unique AS/RS system with its own "intelligence" to expedite the put-away of incoming products. To execute that plan, the food-service distributor turned to German company Viastore Systems GmbH. GFS contracted with Viastore to provide not only the automated storage and retrieval (AS/RS) technology, but also the material flow control (MFC) software needed to run the system.
The software Viastore developed oversees the inbound receiving operation and interfaces with the host warehouse management system (WMS). Basically, the MFC optimizes pallet movement, integrates all sub-systems, and provides command history, system status, and system diagnostics—all in real time. It also contains a special mathematical algorithm designed to minimize AS/RS moves. The complex algorithm in the MFC also requires the AS/RS machines to scan all storage positions in the DC on an hourly basis to ensure that pallet locations at the ends of the aisles are not depleted.
Before installing any automated equipment in the Kentucky center, Viastore took it for a virtual test drive by conducting a simulation. Using actual order data from one of the company's other distribution centers, it ran tests to model the system's capabilities and prove that, even in worst-case scenarios, the system could still meet throughput requirements. Simulation was also used to improve and refine the system.
Just take the shuttle
As for the tricky problem of handling waves of inbound pallets rapidly within a small space, Viastore came up with a shuttle car system that allowed GFS to quickly and efficiently transfer pallets from inbound conveyor spurs to the correct storage aisle. Forklift truck drivers off-load pallets from inbound trucks and then take them to an inbound transfer station, which feeds the conveyor spurs.
As an added feature, the shuttle cars are equipped with sophisticated controls to move loads gently, without sudden acceleration or deceleration. By eliminating the risk of a bumpy ride, the shuttle cars have effectively reduced the amount of pallet shrink-wrapping required for load stabilization before put-away. "Compared to our other facilities that utilize chain conveyors with 90-degree right transfers, the shuttle car solution provides a much more smooth and stable transition from the input conveyors to the crane pickup stations," says Kirk Mortenson, DC development manager for GFS. "This fact has enabled us to reduce the number of stretch wrappers from what we originally had planned."
The shuttle cars whisk full pallet loads to the AS/RS system, which consists of nine storage/retrieval machines equipped with double-deep pallet shuttles. The system measures approximately 98 feet high and more than 450 feet long. In the freezer and dry grocery sections of the warehouse, the system ranges between 16 and 17 levels high. In the cooler area, however, it only reaches 12 levels high. The AS/RS contains more than 60,000 unique storage locations.
GFS's warehouse management system determines whether the inbound loads are sent to reserve storage or to pick face locations. The control system on the AS/RS verifies the pallet's size, weight, and product ID and then sends it to a dedicated pick or storage location.
To expedite the picking process, the AS/RS system also features integrated pick levels where workers have access to the pick faces on the two levels closest to the ground. Workers refer to pick labels as they walk the aisles to select cases of products needed to fill orders. Once a worker picks an item, he or she applies a label to the carton and then deposits the box on the outbound conveyor system. FKI Logistex furnished the outbound conveyor system, which has the capacity to ship 185,000 cases per day. The conveyor transports the product cases to a staging area, where the items are then floor-loaded into a truck for delivery via GFS's fleet of refrigerated vehicles.
About 95 percent of GFS's outbound shipments consist of full cases. Selectors pick those cases from pallets placed into the pick location by the AS/RS machines. The remaining 5 percent of the company's outbound shipments are full pallets. When full pallets are needed to fill an order, the AS/RS itself will pull out the skids and route them to a designated shipping spur. The WMS then directs a forklift operator to go to the shipping spur and deliver the pallet to a particular loading door.
The system enhances efficiency by automatically providing for the pick bays to be replenished on a regular basis. To make that happen, Viastore put sensors on its AS/RS cranes to create a "pallet sensing" mechanism. A typical AS/RS with integrated order fulfillment uses photo-eye sensors on every pick face location to signal when product is needed from reserve storage or the inbound area. Viastore's approach, by contrast, was to create a dynamic pallet-sensing system that scans every pick location as the storage/retrieval machines travel by these locations at full speed.
Dynamic pallet sensing has allowed GFS to greatly reduce the amount of field wiring and piping required in its Kentucky warehouse. On top of that, the unique design eliminated the need for more than 10,000 sensors on pick faces, providing more cost-effective automation. "We are very pleased with the 'sensing on the fly,'" says Mortenson. "This has been much easier to troubleshoot and maintain compared to individual wired locations."
Nowadays, when a crane sensor detects an empty bay, it automatically triggers stock replenishment. Oftentimes pallets received into the system are placed right into the pick bay rather than storage. "Putting items directly into pick reduces moves on the crane by eliminating a put-away move and then later, a replenishment move," says Mortenson. "Keeping the pick bays full also [eliminates] the need for picking the product later and enables us to complete the work in a more timely [fashion]."
To accommodate the need to remove empty pallets from the gravity pick faces, the system was designed so that workers can stack empties in the empty pallet returns located periodically throughout the aisles. The storage/retrieval machines take the stacks of empty pallets back to the shuttle cars in the inbound area. To direct that task, Viastore wrote special code into the MFC logic.
In addition, trash chutes have been built into the AS/RS to collect and remove bulky waste materials like cardboard and discarded shrink-wrap. Trash tossed into the chutes is collected in bins at the floor of the high rise. For leaking or damaged product that can't be thrown down the chute, three-foot-high containers are staged on every level of the AS/RS. When these containers need to be emptied, workers can use the control system to request their removal. The containers are transported back out on the pallet conveyor to a specified spur, where the custodians can empty the refuse into a compactor or trash bin.
A unique feature of the automated system installed at the Shepherdsville DC is that its storage/retrieval machines were designed with double-deep telescopic shuttle forks with synchronized chain conveyors on the lift carriages. This innovation has cut cycle times at pickup and drop-off stations in half by eliminating the need to wait for telescopic arms to pick up or drop off full pallets. In addition, the chain-driven mechanism has resulted in a substantial space savings. In fact, the space freed up allowed GFS to add an additional storage level in the building.
As for the technical details, the Viastore solution features Windows server-based technology, the SQL Server database management system, and Wonderware software. A graphical software package, Wonderware enables visualization and system monitoring capabilities. It provides a user interface for workers to monitor AS/R movements and solve problems as they arise.
How has the automated system worked out? GFS reports that it's proved to be both reliable and accurate. To begin with, the system runs with minimal interruptions. Since the Kentucky facility opened in early 2006, the automated system has experienced 99.9 percent uptime. In addition, accuracy in replenishment and picking has been close to 100 percent.
"Automation has enabled us to improve our overall performance in the facility and to our customers," says Mortenson. "We are very pleased with the performance of the system both in terms of throughput and uptime," he adds. "The Viastore machines are very fast, and we are able to transfer loads efficiently and move on to the next move."
About the Author
James Cooke is a principal analyst with Nucleus Research in Boston, covering supply chain planning software. He was previously the editor of CSCMP’s Supply Chain Quarterly and a staff writer for DC Velocity.
More articles by James A. Cooke
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