Faster current loop enables better servo motor control

A new software product is expected to increase the bandwidth of servo drive current control loops, opening up new possibilities for industrial motion control applications.

The software is called fast current loop, improving the current loop performance to less than one microsecond (μs).Customized for use with Texas Instruments C2000 Microcontroller, this software is suitable for servo drives used in machinery such as packaging, milling, pick and place, semiconductor processing and textile production. “The current loop is at the heart of this technology,” said Brian Fortman, TI DesignDrive marketing manager. design news. “If your current loop is improved, you have a better chance of improving your application’s speed and targeting capabilities.”

Current control loops are considered important in servo applications because they enable machines to operate faster and more accurately by providing near-instantaneous feedback. Typically, this feedback is measured in microseconds (millionths of a second). Until now, such speed increases were possible only by adding external processing components, such as field-programmable gate arrays (FPGAs).

However, fast current loop software reportedly enables engineers to improve system performance to sub-microsecond levels without adding an FPGA. As a result, it is said to simplify servo drive development, reduce system costs and consolidate board space.

“By doing this, we remove complexity from our customers’ systems from a development perspective,” Futterman said. “We show people how to achieve the performance of FPGAs while reducing system footprint and system cost.”

Fortman said that using the new software, the C2000 microcontroller can complete a current loop cycle in 960 nanoseconds (ns) – the C2000 processing time is 460 nanoseconds, plus the analog-to-digital conversion time is 500 nanoseconds. Cycle times are about one-third of what they were before, he noted.

Texas Instruments (TI) believes such enhancements are critical for manufacturers of servo drives used in industrial machinery. By eliminating the FPGA, the company says it can reduce bill-of-materials costs for drive manufacturers while improving performance for designers of CNC milling machines or packaging machines. “Precise and fast control is the basis for engineers to use electronic servo systems in the first place,” he said. “Essentially, this allows servo drive manufacturers to deliver higher and better control at a lower cost.”

TI engineers said they were able to achieve higher speeds by taking existing public domain science and software enhancements and customizing them for the C2000 MCU. “These technologies can only be applied if you have a real-time computing performance type controller,” Futterman said. “This is C2000.”

Senior Technical Editor Chuck Murray has been writing about technology for 33 years. He joined Design News in 1987 and covers electronics, automation, fluid power and automotive.

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