Control Dynamics, Inc. has developed a high-speed conveyor sortation applications using Entivity VLC software. The requirements of identifying, tracking and diverting cartons at up to 600fpm can be very demanding on a control system. TrueSort® easily handles the situation using the VLC, Interbus I/O and some custom developed OPC applications.
The most recent installation of TrueSort® is an order fulfillment application in a distribution warehouse located in Mississauga, Ontario. The sortation conveyor runs at 230 fpm, has 11 diverts and can sort cartons in excess of 85 cartons per minute.
To facilitate picking products from the pallet rack system, an IBM AS/400 computer generates a barcode label. The label tells the picking operator the location and quantity of cartons required for each order. As the operator places each carton on the conveyor, they attach a label at the top of the box.
The conveyor system moves cartons to the sortation area through two multi-line merges. Scanners from Accusort read the top label and the SCC product label on the carton sides. The system sends barcode information to the AS/400 to confirm that the correct cartons were picked for the order and to get a shipping destination for each carton. Typically, the AS/400 responds to the destination request in less than .25 seconds. After TrueSort® delivers the carton to the correct destination, it sends a message to the AS/400 confirming the delivery.
Fast Program Scan Time & Deterministic I/O
To maintain a high level of accuracy in delivering cartons to their proper destination, TrueSort® analyzes carton length and gap between cartons at each photoelectric sensor in the system. According to Mike Bridle, Principal Engineer of Control Dynamics, “The fast and deterministic logic solve time, coupled with the similar characteristics of the Phoenix Contact Interbus Inline I/O, helps us keep system costs down by allowing us to connect incremental encoders directly to discrete I/O instead of high speed encoder modules. Even though our logic solve time is fixed at 2ms, the VLC actually solves in less than .2ms and it scans the Interbus I/O every 2-3ms. This high speed allows us to realize about 1″ of tracking resolution while running at speeds in excess of 600fpm.”
Large Data Storage
Unlike PLCs, the data storage capabilities of the VLC are virtually limitless. Bridgle continued, “We are able to define multi-dimensional arrays for keeping track of carton tracking information. This allows us to retain and display historical carton information for several thousand cartons.” This feature is very helpful in troubleshooting carton routine issues. Storage of the label, tracking data, host computer destination, and carton sizing and routing decisions for each carton lets the operator see exactly what happened.
A critical function of TrueSort® is to communicate to the AS/400 and display large amounts of information to the operator in an organized way. Without being able to get information into and out of TrueSort® in a fast and efficient manner, the system would not function. Using the VLC connectivity through OPC, Control Dynamics wrote their own OPC client applications. They created a transaction management system, called TrueComm, that lets the AS/400 communicate directly with the VLC through an Ethernet network.
They also developed a Data Grid capable of displaying OPC data in a scrolling window. This lets them display large amounts of array data. The scrolling nature of the grid allows Control Dynamics to configure the software for different sized systems without having to redraw the operator interface screens for each project.