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Motion control with character

Motion control with character

For all the power inherent in today's microprocessor-based motion controllers, programming them too often remains an esoteric science that engineers keep at arm's length from machine design. Not so at nuLogic, Inc., Needham, MA.

"We want to make motion control a tool, like CAD," explains nuLogic President Jeffrey Seiden. "Ease of use is as important as functionality."

Ease of use could be the mantra of the six-year-old company, whose first product Seiden, a veteran of several start-up electronics companies, put together in his basement. Called nuControl(TM), it was a single-board, three-axis controller designed for the newly introduced nuBus for the Apple Macintosh(R).

The then-novel ability to run servomotors by manipulating icons rather than specialized programming commands presented a market opportunity, Seiden recalls. Although Apple's product represented a small market, nuControl was different enough to garner attention, giving the new company the revenue and experience it needed to grow.

nuLogic became profitable in 1990 and hasn't looked back. The company bootstrapped itself to sales now in the "single-digit millions," without relying on outside venture capital.

Other products followed. nuStep (TM) a nuBus-based stepper-motor controller complemented the original nuControl. Later, the company made the transition to IBM-compatible computers with pcControl (TM) and pcStep(TM) . Each product shared the original's dual-processor architecture that permits high-speed motion control without taxing the host. Software innovations included compatibility with National Instruments' LabView(TM) , which further simplified programming and allowed a highly graphical user interface.

Turning point. Through its first five years, Seiden admits, nuLogic played technological leapfrog with competing companies in bus-based control. And though nuLogic has grown 90% annually, that market grew slowly: PC or Mac, office-automation hardware for industrial control is an idea that has taken time for engineers to accept.

That situation has changed. The emergence of broad industry acceptance, powerful new processors, and advances in software design forms the opportunity for the company's latest product, the FlexMotion TM board. According to Seiden, "It represents a turning point." Capable of controlling as many as 10 axes of any combination of servo or stepper motors from a single PC ISA slot, FlexMotion has the functionality and connectability to cover 98% of the electronic motion-control market, he says.

As with earlier boards, the FlexMotion board is a dual-processor design. A Motorola 68331 32-bit CPU handles such chores as communications, trajectory planning, I/O interrupts, PID, and velocity-feed-forward control. An Analog Devices AD2111 digital signal processor handles number crunching.

The board's peripheral hardware design further enhances its utility. For example, flash memory stores the controller's firmware, making program upgrades or customization easy. Termination options let designers minimize noise in encoder signals, whatever the signal frequency. Field-programmable gate arrays allow it to be configured through software for a range of feedback devices. Similarly, its software-configurable, 16-bit, digital-to-analog-converters give users options like dual-loop motor feedback or torque limiting without interrupts--a feature that puts the controller's lag or "latency" into the nanosecond range.

Software options. As with prior nuLogic products, FlexMotion can be run through LabView Motion Virtual Instruments. But Seiden says OEM or larger embedded-control manufacturers will probably find that the company's pcRunner(R) software more closely meets their needs.

Included with each FlexMotion board, Windows-based pcRunner presents a graphical user interface that makes it easy to get machines running quickly. Pull-down menus give users access to the more than 120 functions for precise motion-scheme definition.

Source communication, function, and driver codes, as well as programming samples in C, C++, DOS, and Basic, are also available. So is a nuLogic graphical software tool called Servo Tune (TM), which lets users model and exercise their system's PID loops to get the desired response. "We think it saves users from the trade-offs of conventional auto-tuning programs," Seiden says.

Capabilities. FlexMotion is just emerging from beta-site testing. To date, users, including several large production-equipment manufacturers, report good results.

Equally important, the capabilities arising from synergy of FlexMotion's hardware and software design speak for themselves. The system's library of functions include point-to-point, linear interpolation, jogging, and circular, spherical, and cylindrical interpolation, as well as S-curve acceleration control.

Because of the dual-processor design, the FlexMotion board can combine any or all of these functions in defining multiaxis motion, changing the definition, if desired, with each 60-musec update. Called Infinite Trajectory Control Processing (TM), this capability is further enhanced by a novel "blend" command that lets users anticipate motion changes and achieve extremely high motion-profile fidelity.

The ability to put together complex, high-precision motion profiles from a graphical menu, says Seiden, "puts motion control at the level of CAD." That's important, he feels, because "to be successful, we have to be attentive to the designer's expectations."

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