Metrological Network Turns Machine Tools Into Precision Measurement Systems

Better dimensional accuracy of both part and machine tool

Published: Tuesday, April 26, 2016 - 16:08

(Etalon: Braunschweig, Germany) -- Absolute Multiline Technology is a worldwide unique measurement system for monitoring the geometric accuracy of machine tools by means of high-precision length measurements: An absolute distance interferometer measuring with submicrometer resolution serves as the metrological centerpiece of a factory. It connects with any number of machines via fiber-optic network that may comprise more than 100 measurement channels. These channels, equipped with miniature optical elements, are oriented along the machines’ axes, space diagonals, and face diagonals of the machine working volume.

Absolute Multiline Technology’s metrological network is ready to cover any machine location and size; it has already been set up in factories supplying multiple machine tools with up to 12 m (39 ft) in axis length. The maximum range of measurement is 40 m (131 ft), while the optical fibers may travel several kilometers. Due to the large distances possible between the robust measurement sensors and the system electronics, measurements can be conducted under extremely rough environmental conditions.

Better dimensional accuracy of both part and machine tool

With such integration into a machine tool, Absolute Multiline Technology can continuously monitor the geometry of the machine and initiate machine compensation in order to ensure the dimensional accuracy of the manufactured parts. To perform a standard-compliant machine tool check, a reflector from the tool magazine is interchanged, and a predefined program is executed at the push of a button to move the machine along the multiple measurement beams and thus identify their deviations. This test process takes approx. 20 minutes. Measurement uncertainty (95%) is specified with 0.5 µm per meter.

Although conventional interferometers can only work with a continuous measuring beam, the Absolute Multiline Technology can deal with interruptions of its eye-safe infrared beam at any time without losing accuracy. The absolute distance is recalculated in a fraction of a second. Hence, highest geometric precision is ensured in the entire working volume of the machine. Thermal influences, wear, or collision-induced changes are reliably detected and compensated, if necessary. The machine’s geometric compensation is effected in a fully automatic way. Geometric compensation values of the machine are calculated by the software, which compares the coordinates indicated by the machine and the length measured by the interferometers.

Thanks to the machine tool’s autonomous geometrical verification in the entire working volume, it may also be used as coordinate measuring machine (CMM) to inspect the manufactured components. Especially for the quality assurance of large parts, this generates significant commercial benefits: A separate coordinate measurement machine and also time-consuming clamping and reclamping processes can be omitted.

Traceability

The metrological traceability of the Absolute Multiline Technology is ensured by the reference to fundamental physical constants: In every measurement, the molecular absorption spectrum of a gas cell is scanned, which stays constant over decades.

Presentation at Control

Etalon will showcase the Absolute Multiline Technology at Control 2016, April 26–29 in Stuttgart. Visit us in hall 3, booth 3215.

Exemplified metrological network, installed by Etalon: One Absolute Multiline system (at lower left) is permanently connected to several machine tools and CMMs. Thus, the system can continuously monitor the geometric accuracy of all machines and initiate machine compensation, if necessary.

About The Author

Etalon AG

Etalon AG, founded as a spin-off from the PTB (Physikalisch-Technische Bundesanstalt) in 2004, offers system solutions for the accurate and full geometric analysis, monitoring, and accuracy improvement of machine tools, measuring machines, and robots. In the area of machine compensation, Etalon is an official Zeiss Business Partner as well as Siemens Solution Partner. Etalon customers are companies from mechanical engineering, industrial instrumentation, automotive, and aerospace industries and the research sector.