Control Platform Options Open Up

How Sensible Simplifying Ever-More Complex Machine Control Applications Is, and How Practical it Is Now or Might Someday Be

By Rich Merritt

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February 2007 CoverYour machine's software platform controls motors, actuators and other moving parts in real time. But real-time machine control may be evolving into the smallest part of many modern control software platforms.

Other emerging aspects of a software platform include the HMI, integration with external equipment, network communications, and support for various software packages such as machine vision, remote diagnostics, web servers and maybe even an upward path to your customer's MES and ERP systems. As a result, a machine builder just can't choose a platform based on its real-time control performance. Builders must consider a host of related issues, and select a platform that can support them all.

Difficult Decisions
Deciding to change a software platform isn't easy. Take the case of Glasstech, which builds glass tempering equipment in Perrysburg, Ohio. "We previously used a proprietary control system based on a Motorola 6809 processor, which had components that became obsolete," explains Steve Connell, Glasstech's systems engineering manager. "This forced us to upgrade our controls. We had two primary goals. The first was the capability to control all of our products on the same platform, and the second was that the platform be acceptable in the U.S. and internationally." About two-thirds of Glasstech's sales are international (See Figure 1).

Glasstech's former 6809 processor was a very robust and reliable system, Connell reports, and over the years the company developed its own motion control software for the platform. "One option was to keep a similar platform based on the Motorola 68000, but the hardware and software would require too many man-hours to develop," says Connell. "Another alternative was soft control, but we felt the software costs were too high, and support of the software controls would become obsolete eventually. We've found it's extremely difficult to support a machine running on a software platform that is 25 years old, and it's just as hard to find computer equipment to run it. We decided to require that our control systems be open, and not need a specific operating system."

In addition, Glasstech needed a system that would support simulation, enterprise integration, and remote diagnostics of those faraway systems. "We decided that the ControlLogix platform provided what we needed," Connell says. "Our simpler machines did not require servo accuracy, while our more complex machines had 18 servos. This platform is scalable for both types of systems, yet is fairly cost effective on the low end. Our goal is to have this become our control system standard for the next 15-20 years."

Going with one vendor, Rockwell Automation in Glasstech's case, is one option for machine builders. Another option is to choose an open system that isn't dependent on any particular hardware or software. For example, Greer Co. builds industrial boom cranes at its plant in Santa Ana, Calif. When developing its new MicroGuard crane control system, Greer chose a Windows CE-based system from Applied Data Systems and CAN bus I/O.

Controlling a crane is a computing-intensive environment, requiring constant calculations of the "overturning moment" of the crane. These calculations are based on real-time position and pressure sensors, comparisons to a database and modeling calculations. They're all displayed to the operator as a clear percentage of how close he is to tipping over the crane. For extra safety, as the crane reaches its safe limits, the controller (See Figure 2) steps in and throttles back on hydraulic oil flow, so the machine can't enter a dangerous configuration.

Greer chose Windows CE because of its real-time performance (more about this later), its ability to deal with real-time sensor data and perform the calculations, and its support from a host of hardware and software integrators such as ADS.

Either way, it's tough to choose one vendor or an open system. Glasstech is betting that Rockwell Automation will be around for the next 25 years, and Greer is betting that Windows CE hardware and software also will be around. From what we can see, both are pretty good bets.

Vendor-Specific Platforms
We hesitate to call vendor-specific platforms proprietary, because many of them are more or less open. Nevertheless, if you choose to go with one vendor's platform, such as Rockwell, Beckhoff, Bosch Rexroth or many others, you are, for the most part, locked into their controllers, I/O and software. Because they're "open," you can buy vision systems, motion control systems and other support hardware and software that will work with the controllers, but the basic control equipment comes from one vendor.

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