Doug Bartholomew, Samuel Greengard, Glenn Hasek, John Jesitus, Scott Leibs, Kristin Ohlson, Robert Patton, Barb Schmitz, Tim Stevens, and John Teresko contributed to this article. In the late 1960s when banks of hard-wired industrial relays provided process control on production floors, the advent of the solid-state programmable logic controller (PLC) had most seers predicting the demise of the older technology and/or industry. That didn't happen, but a significant PLC industry was born as manufacturing management took advantage of the benefits of the new control scheme. Today, history in the control arena seems to be repeating itself with an equally significant watershed event. Now, the PLC is meeting new competition. Personal computers (PCs) are vying for control of the factory floor. While predictions are again being made that one will replace the other, the more significant issue is why and how the shift is taking place. Strategic business benefits are the "why," says Steeplechase President and CEO Mike Klein, whose company offers Visual Logic Controller (VLC) software that enables PCs to perform discrete control. He emphasizes three benefits:
- Lower control investment.
- Increased productivity in design and manufacturing operations.
- Reduced downtime with built-in, flow-chart-based diagnostics.
VLC, symptomatic of Microsoft Corp.'s increasing presence in the manufacturing process, leverages the strengths of Windows NT (such as the communications and graphics-display capabilities) and can facilitate an enterprise IT strategy. "The approach can lower the investment costs by 50% or more by integrating the three major hardware components of a control system on a single PC," explains Klein. The VLC performs the logic-control/operator interface, programming, and data monitoring. The same PC also can run other Windows off-the-shelf software such as cell control, SPC, spreadsheets, or database managers. At the same time VLC has been designed to assure that a PC-based solution will perform with the integrity users have come to expect of a PLC, says Klein. VLC's goal is to achieve hard real-time control -- even in the event of Windows NT lockup or failure of the hard drive. At the March introduction of Version 3.0 Klein demonstrated that capability by deliberately causing a crash. For good measure, he removed the hard drive, yet the PC's ability to control the process was not interrupted. To eliminate the worry that the system would crash in the midst of a critical production operation, Steeplechase built VLC on the iRMX-based, real-time operating system developed by RadiSys Corp., Hillsboro, Oreg. Its presence establishes control-program execution and I/O scanning as high-priority tasks while Windows programs run in the background as low priorities. Execution of Windows applications does not impact real-time control performance. Other advantages come from the programming method used for VLC. Instead of the ladder-logic approach that was devised 25 years ago for PLCs, Steeplechase uses a flow-chart technique. Klein says flow charts can cut control-system design time by as much as 70%, and because they are intuitive and make the production process easy to understand, flow charts facilitate constant improvement on the production floor.
