Fast but steady could win the race

Berkeley Process Control, Inc., Richmond, CA, makes electronic
machine-control products. In that business, it's one among many. Unlike many,
it's grown by 40% a year for the last eight years. Its success hinges on two
things: a stable of patents covering high-speed servo loops, and steady
concentration on making control systems that people can actually use.

"From the start," explains BPC President Paul Sagues, "our focus was on making machines work, not on building boards." That focus is reflected in myriad ways, from controllers that haven't changed form factor while growing from 8- to 64-bit RISC architectures over the years, to consistent, simplified wiring schemes.

Most notable: source-code compatibility that's been maintained for more than ten years. Users can take a program written for a 16-bit BPC controller, load it unmodified on a 64-bit unit, and it will work. "It's a crucial element in gaining our customer's confidence," says Sagues.

Consistency, plus performance: According to Wayne Ferrari, BPC's marketing manager, the company's Bam(R) Series 64 controller offers sophisticated multiaxis servo control, compact distributed I/O for logic control, network communications, and operator interface control in one package. Simple connections to the company's touch-screen interface, I/O rack, and Universal Servo Amplifier, and single-cable servomotor connections complete the hardware configuration.

Prime example. The ELS-II Registration and Machine Control System developed by Dri-Tech, Inc., Milwaukee, WI, with cooperation from BPC, exemplifies the performance advantage of dedicated machine controls. ELS-II synchronizes multiple servomotors driving large rotating cylinders on high-speed commercial printing equipment.

Optical encoders on each axis signal the Bam(R) controller over the distributed I/O. By monitoring the signals, the controller can dynamically adjust each cylinder, regardless of speed, achieving printing accuracies of n 0.005 inch, comparable to mechanically synchronized printers. The controller also monitors web tension and multiple zone temperatures throughout the machine, reducing scrap production.

Machine commissioning went smoothly, largely due to BPC's QuickStart(TM) utility. Quickstart interrogates control network nodes, establishing device type and voltage level. It also performs auto-tuning, measuring motor and load characteristics to optimize servo-loop performance.

Compare this approach with others vying for machine-control business. PLC- and CNC-based schemes each have their limitations says Sagues. PLCs handle logic functions well, but "they're running out of steam, they can't do high-speed multi-axis servo control well." Alternatively, CNCs do yeoman work at controlling motors, but it's difficult to perform logic operations with them.

What's common to PLCs and CNCs that's kept them in the machine-control fight? Well-defined, well-maintained operating systems that plant-floor personnel can understand and use. Which brings up bus-based, "open" systems, the third major machine-control alternative.

An open question. As Berkeley people see it, open systems have some glaring disadvantages. First, assembling boards from different vendors for various machine-control functions and getting them to work together involves writing extensive application-specific software-and won't guarantee success. "Your desktop computer can crash with no harm done," Ferrari contends, "but that's unacceptable in a production machine."

The second shortcoming is the software itself. Ad hoc software is notoriously difficult to modify as machines are modified or redesigned. Data from the semiconductor-manufacturing industry, for example, shows that

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