Retrofitting an Aging Control System for Automated Storage and Retrieval
Control systems sometimes need to be upgraded or replaced, especially for critical operations such as an overhead storage and delivery system in a discrete manufacturing facility that uses thousands of different parts daily.
Here’s how Matrix Technologies helped a major appliance manufacturer upgrade their automated manufacturing process with a control system retrofit that minimized downtime and streamlined startup.
Discrete manufacturing plants must know where each part is stored, and then efficiently deliver those parts where they are needed on the assembly line just in time to ensure uninterrupted production. An Automatic Storage and Retrieval system (AS/RS) is very often used for this.
The manufacturing site was using an integrated batch system that tracks parts in real time and uses a conveyor system to move them from storage to the required location whenever an operator orders them. That system included 1500 parts carriers holding 14,000 parts with 50 different part numbers.
The plant had an aging control system consisting of an Allen-Bradley PLC3 to control the conveyors, and a Digital Equipment Systems (DEC) PDP-11/08 to keep inventory of the parts and track their location.
The project presented several challenges. The client wanted to:
- Minimize downtime.
- Minimize the maintenance training.
- Replicate the fairly complex database search and product tracking performed by the DEC PDP 11/08, which in its day was a very powerful mini-computer.
The solution was to utilize one Allen-Bradley ControlLogix PLC (CLx) to replace both the PLC3 and the DEC PDP 11/08. Local Panelviews and FTview stations provide the operator interface.
To minimize downtime, Matrix re-used the existing 1771 IO to save debug time and effort. Simulations were run to test the conveyor software and the required part tracking. These simulations ensured that the startup and commissioning went well without any lost time due to lack of parts.
The maintenance technicians were very familiar with the old PLC3 that used an elaborate but easy-to-understand scheme to utilize bits within integer words. Matrix kept the same concept, but used the CLx data structure. Maintenance training was minimal as the new code had the same look and feel as the old code.
CLx structured text was used for most of the inventory tracking and required searches to satisfy batches. The database searches had to be staged to keep the CLx scan at a rate of 50 msec that would allow the normal conveyor control to operate.
The system was totally designed and programmed within the ControlLogix (CLx) PLC, which tracks all parts of the system. Fourteen Panelview stations and four FTView stations are used for operator interface (HMI).
Loading, Storage, and Unloading Loops Are Operated with a ControlLogix (CLx) PLC
The overhead conveyor system is designed with specific conveyor loops allocated for loading, unloading, and storage. Radio Frequency Identification (RFID) is used to track the 1500 parts carriers.
Load Loops (Stations): Loading loops are used to manually load parts on a carrier, which is transported via the overhead power and free conveyor system. An operator uses a Panelview to identify the part number currently being loaded and the quantity.
Each carrier has an RFID tag attached. As a loaded carrier is released, an RFID reader scans the tag and starts the process of storing the carrier in the storage loops.
Storage Loops: The PLC uses several criteria to determine the best storage loop location for the carrier based on the loaded part number. The PLC then assigns a storage loop number to the carrier.
RFID readers are located throughout the conveyor system. The RFID tag on a carrier is scanned by the PLC, and the carrier moves to the assigned storage loop. The PLC tracks all carrier movement using the RFID scanners. Based on this information, the PLC always has a current inventory of all the carriers and the parts in the system.
Unload Loops (Stations): As parts are needed for manufacturing, unloading loops deliver the needed parts to specific points on the production line. A batching system is used by operators at an FTView HMI terminal, where the operator selects the unload station, the part number, and the amount of parts.
The batching system uses this information to select the carriers to send. The system then moves the carrier to the selected unload station using the RFID tag on the carrier.
With a new control system designed by Matrix, the plant will keep reliably moving its parts.
Matrix Technologies is one of the largest independent process design, industrial automation engineering, and manufacturing operations management companies in North America. To learn more about our automated manufacturing system capabilities and manufacturing process control solutions, contact Eric Tolles, PE is a Senior Project Engineer.
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