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Linux to ControlLogix solution uses OPC

17 April 2008

‘If you’ve watched a plane be deiced, you’ve probably seen a Task Force Tips (TFT) product in action,’ said president Stewart McMillan. TFT makes water delivery solutions – nozzles, hoses and valves – for clients worldwide including firefighters and aerospace firms.

Plane being deiced
Plane being deiced

Product orders are fulfilled by a robotic picker that moves among hundreds of parts bins on a 100-foot-long, multilevel picking line. The picker, controlled via serial connection by a COBOL program running on a Linux box, began having frequent breakdowns and slow command response time. To increase reliability and efficiency, TFT decided to overhaul the robot, choosing Allen-Bradley ControlLogix programmable automation controllers (PACs) and servo drives from Rockwell Automation. Then they had to figure out how to maintain the control program on the Linux box and use it to pass commands to ControlLogix.

TFT found the answer to fit the project requirements and the budget: the TOP Server OPC Server and the Cogent OPC DataHub from Software Toolbox. Using the TOP Server Allen-Bradley driver suite (specifically, the ControlLogix Ethernet driver) and the OPC DataHub, the existing Cobol program could be retained and used with new, improved control hardware.

’It is magical what this can do for our application,’ said McMillan. ‘The OPC DataHub and TOP Server allow the PLC to share any data point through ODBC to any database connection. The possibilities that this opens up for real-time connections between PLCs and corporate data processing systems will bend your imagination.’

In this application, the TOP Server is connected to the ControlLogix PLC and the OPC DataHub. The latter, through its ODBC interface, is connected to an OBDC data source. The Cobol program passes commands as parameters to this data source, which the OPC DataHub reads into OPC data points; these are then written through TOP Server to the PLC for control. Responses to the commands are passed back through the chain to the ODBC data source to be read by the Cobol program to determine the next step.
TFT has seen significant improvement in efficiency of the line and has nearly eliminated downtime. According to McMillan, ‘It is really a pretty unique application. It is so much faster than what we had before. Now we are trying to find other problems to solve. This solution has been very effective for our business results.’

The connection to the Linux Cobol systems was done by actually connecting to a database. OPC DataHub has several other ways that it can connect to non-Windows Operating Systems.

A free demo version of OPC DataHub is available, as are a number of training videos. The four-minute video entitled OPC Bridging Between OPC Servers with Data, instructs the viewer on how to connect to two OPC servers and move data from one to another, while transforming the data in the process. Connecting Excel to OPC Data Sources features a live demo of how to read/write OPC data from Excel, from local and remote OPC Servers, without using DCOM.

--edited by Renee Robbins, senior editor, Control Engineering Daily News Desk


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