Adjust Quality in Real Time
技术分类:过程与先进控制 作者:Mark T. Hoske 发表时间:2005-12-05

"Second," Walter continues, "embedded technologies (field-programmable gate array and digital signal processors) are becoming more common in industrial control equipment. Programmable automation controllers (PACs) that incorporate these high-speed components enable engineers to achieve scan times in microseconds instead of milliseconds. This allows them to perform high-speed measurements and high-speed control." One application, he says, required closing a motion control loop at 200 kHz

to achieve the quality and throughput for semiconductor production.

CNC machine tools, as mentioned, often measure and adjust for tool wear in real-time, or do so using statistically based analysis. For instance, a tool of a certain material working aluminum at known speeds for a certain number of hours would wear a predictable amount and could result in compensation without direct sensor input.

A brief check shows that Bosch Rexroth, GE Fanuc, Makino, Siemens, and Sunnen are among many vendors offering a closed-loop adjustment feature, either with direct measurements or statistical adjustments. That feature also is available in retrofits, for the vast installed base that cannot adjust for tool wear at present.

In any closed-loop process, measurement results are transmitted. Gaging products over the last decade offer finer resolution and greater stability through digital signal processing, explains Paul Sevin, vice president, Ovation Engineering Inc. Virtually all output results via RS-232 (or better). Better logic and software process the data transfer with no impact on part cycle time, Sevin says. "Benefits are elimination of scrap and reworkable parts due to manually miskeyed operator data (transposing digits such as 0.0021 instead of 0.0012, or inadvertent omission of the data sign '-' character when a correction is made). The result is more consistent process control, since only long-term process trends (such as tool wear or thermal effects) cause a corrective action to