At the end of a production line there are three spots for containers?one is empty, one is being filled, and the other space is open and waiting for the next container type.
Wire-guided AGVs get their payloads, in this case injection molded preforms, to their destination with an error rate of virtually zero. Vehicle control software is tied into plant production software.
Forklift traffic in the preform injection molding area of Southeastern Container?s Enka, NC facility was not a problem in 1985 when the company had only two preform production lines and one forklift. However, the business of injection molding of preforms and subsequent blowmolding of those preforms into bottles has grown dramatically since 1985.
Today, Southeastern has 24 preform production lines and would need five or six forklifts to handle the input and output of these 24 lines. At this point the benefits of continued use of forklifts are no longer worth the risks. Detailed below, Southeastern Container?s experience in addressing this situation may be useful to other companies as well.
Instead of adding more forklifts, Southeastern initiated an automated guided vehicle (AGV) program that effectively replaced the forklifts. The six AGVs are supplied by AGV Products Inc. (Charlotte, NC).
The current plant has an 11-ft aisle for vehicles to use in turning around. Forklift drivers can?t do that consistently and safely. Pedestrians in the aisles were at risk of being hit. With AGVs, turns are made along the same path every time, making it easier for workers to keep out of harm?s way.
Making Bottles Keeps AGVs Busy
Southeastern Container is one of the largest blowmolders of PET bottles in the country and keeps busy producing bottles for Coca-Cola. Southeastern has seven plants that supply bottles to Coca-Cola bottlers on the east coast. Most of the Coca-Cola products bottled in the east will go into a bottle produced by Southeastern Container.
The Enka facility produces many pallet loads of PET bottles ranging from ½ liter to 3 liters. The preforms are placed in two types of containers depending on their final destination. Approximately 35% are placed in all-plastic containers and stay in-house for blowmolding. The remaining preforms are placed in corrugated containers sitting on plastic pallets and shipped to other Southeastern Container facilities for final production.
All preform containers are 48 inches long, 40 inches wide, and 48 inches tall. A full container/pallet may weigh between 675 and 1000 lb, depending on the size of the preform. Production lines change preform size frequently to respond to demands from the other Southeastern facilities. Certain lines always run in-house preforms and some always run ?export? preforms, but all lines must be capable of doing changeovers quickly and efficiently. Changeovers may require a different pallet type and the AGVs are directed to make the change with a simple point-and-click menu.
At the end of each preform production line there are three spots for containers. One container is empty, one is being filled and the other space is open, awaiting the next container type. This arrangement allows molding machines to work without interruption. The AGVs are constantly moving throughout the plant, either delivering empty containers or moving full container loads of preforms to the warehouse area.
The plant?s six AGVs work 24 hours a day, seven days a week. The plant is so busy that the AGVs are necessary to keep things running smoothly. The production process depends on the accurate deployment of preforms and the AGVs are instrumental to this operation. The AGV control system is directly tied into plant production software so that each vehicle is kept busy and there are no wasted movements throughout the plant. Navigation of every turn is reliable and safe as the wire-guided vehicles follow their designated path.
Vehicle Design and Controls
Each AGV has a mechanical bumper system that alerts the vehicle to obstructions in the vehicle path. When an obstruction is detected, the vehicle stops and notifies the host of a problem. Once the obstruction is removed, the vehicle continues on its intended path.
Overall, the AGVs navigate 60 stations in the plant, including two at each production line, three empty container pick up areas, two full container drop-off areas, one designated scrap area, and six recharging stations.
The AGVs used at the Southeastern Container facility are of the custom differential drive type, a rugged industrial version. Each vehicle has a load capacity of 1500 lb. A 48V battery powers each vehicle.
The vehicles have microprocessor-based control boards that monitor all AGV functions. The control incorporates digital and analog inputs and outputs for load handling, safety features, and steer-and-drive functions that permit bi-directional travel and automatic load handling. The control board incorporates functions such as low battery detection, low power mode (sleep mode), and navigation.
Microprocessor-based control boards monitor all AGV functions such as load handling, steer-and-drive functions, bidirectional travel, and automatic load handling.The control incorporates both digital and analog inputs and outputs.
Southeastern chose specific equipment to meet its particular needs, but many other custom and standard variations are available using laser, wire, and inertial guidance technologies.
Trace system control software coordinates all movements of the AGVs within the entire material handling system. Trace features PC hardware, a Windows NT operating system, and networking options. The system?s user interface displays AGV, load, and stationary equipment status and movement, in real-time.
Southeastern chose specific equipment to meet its particular needs, , using wire guidance, where a low-voltage, low-frequency signal is sent to in-floor wires along the AGV guidepath. This simple method of communication between the vehicles and the guidewire is ideal for applications where it is anticipated that guidepath changes will not be needed.
However, many other variations are available. AGV Products Inc. provides AGV systems with standard and custom-built vehicles, software, and control packages. They support not only wire but laser and inertial guidance technologies as well.
Laser guidance uses a rotating on-board laser that scans reflectors mounted throughout the facility, calculating the exact position of the vehicle. These reflectors are thin strips of highly reflective tape that are located in strategically determined places in the operating area.
As the AGV moves, its position is constantly updated within the system. Laser guidance offers flexibility and convenient guidance changes that can be made in AutoCAD. Inertial guidance uses an on-board solid-state gyro to measure vehicle heading while an independent encoder mounted on the wheels of the vehicle monitors the distance travelled. The vehicle?s position is updated each time that it travels over a magnet embedded in the floor along the vehicle?s travel path.
Southeastern Container Corp.
AGV Products Inc., Charlotte, NC
(704) 845-1110; www.agvp.com