The 1990s saw the demise of proprietary industrial networks and the emergence of open communication systems. Users embraced this new age of open networks, but now it's time to integrate those old networks into newer communication platforms, most of which are Ethernet-based.
Sometimes, integration can be done by just upgrading the PLC to a newer version. On the other hand, as one company reports, they spent more time making their new control panel communicate with a 1980s-era legacy network than they did writing the control code for the entire system.
The pressure to integrate the plant floor with IT is one of the major reasons why manufacturers are searching for ways to connect to their legacy networks and extract data. But it isn't always easy.
Here's a pretty typical situation from The Bradbury Co. in Moundridge, Kan., which builds complete roll-forming lines, cut-to-length machines, coil-processing production lines, and automated production systems (Figure 1). "Many of our sheet-metal processing lines are still in production after 20 years," says Larry Asher, controls engineering manager at Bradbury. "Over that time, IT and manufacturing departments have been working together and a highly integrated solution is sought by all, but not at the cost of a new production line. Today, our controls department is integrating new technologies and networks with our own legacy systems to meet the needs of our customers."
In 1995, Bradbury released its first computer-integrated manufacturing system. It had a DOS-based PC with a feed program developed in C. The PLC communicated over Data Highway (DH+), the servo systems had their own network, and the I/O used DeviceNet.
Soon, customers began to ask for a better way to connect the production line to the office. Dynamic Data Exchange (DDE) was used on a Windows-based PC to exchange data with the DOS-based HMI software. A slew of networks, communication technologies and protocols came from various equipment vendors over the years. Many hours were spent trying to develop methods to collect information, ensure data integrity and make this data available to upper-level systems.
Four years ago, Bradbury began to develop an entirely new control solution based on EtherNet/IP. One goal was to maintain as much of the legacy systems as possible. Replacing functional and supportable components such as drive and I/O would make the solution cost-prohibitive.
Although EtherNet/IP works well on new systems, the problem of integrating older systems remained. Based on when the older unit was built, Bradbury uses different methods for integration.
"Typical legacy systems will have a Rockwell SLC series PLC," says Larry Asher, controls systems engineer for the company. "An SLC 5/03 or 5/04 will be upgraded to an SLC 5/05. We then will install an Ethernet-based network for the HMIs and the SCADA system, and use OPC to exchange data with the production line and the SCADA system. This provides integration to the customer's ERP system. Some older systems might not have a PLC, and in this case we'll use a PLC from the Rockwell Logix family of processors and add any required I/O."
Integrating With IT
"One of our primary IT objectives at McElroy Metal is to provide an integrated information system for our employees," explains Howell Hicks, IT director at McElroy Metal, a customer of Bradbury in Bossier City, La. "We believe integrating our business processes enables us to achieve cost savings, improved efficiencies and a competitive advantage."
McElroy Metal makes metal roofing and siding products. The company's operations include 12 manufacturing facilities, 18 service center locations and 40 Metal Mart locations. Connecting it all together was a challenge, especially when dealing with legacy networks.
"Integrating IT infrastructures with shop-floor technology is a challenge, since the methods, networks, operating systems and processing components were developed through different channels for users and equipment with different needs," Hicks explains. "The resources and skill sets employed to keep an ERP system, email system and office productivity software operable and available on a network powered by Microsoft are quite different than those required to make controllers talk to PLCs."