National intercomparison of a novel large gear ring standard

Within the project EVeQT (Erhöhung der Verfügbarkeit und Qualitätsoptimierung von Triebstrangkomponenten und Verzahnungen für Windenergieanlagen (engl. Increase of the availability and quality optimization of drivetrain components and gears for wind energy systems)), funded by the Federal Ministry for Economic Affairs and Energy (BMWi), from September 2012 to January 2017, the world’s largest gear ring measurement standard (2 m in diameter) has been developed. The gear ring embodies three different internal and external gears, equally distributed on the circumference of the ring. In a national intercomparison the measurement standard has been measured by seven participants on twelve different machines. Among the participants were measurement machine manufacturers, laboratories for calibration services and research institutes.


Figure 1 – Novel large ring gear measurement standard

The large gear ring measurement standard (see Figure 1) has a supporting base specifically designed and manufactured at PTB. Its weight including the base amounts to 3 t. The calibration has been conducted by PTB. A novel calibration method was used, combining common tactile probing on a coordinate measuring machine and an optical measurement method based on multilateration using four Laser Tracers (M3D3). Resulting calibration values and expanded measurement uncertainties (smaller than 3.5 µm for all gear parameters) have been determined.

The results have been compared to the calibrated values of the PTB and exemplarily presented for the parameters of three external gears. The two diagrams (fig. 2 and 3) show the deviations of the measurement results from the calibration values of the PTB for all 36 gear parameters. The error bars represent the expanded measurement uncertainties of the PTB calibration. Except of a few outliers most of the results are within the uncertainty ranges. The measurements of the helix (fig. 2) show, compared to the measurements of the profile (fig. 3), higher deviations due to the length of the measurement lines, which are about 100 mm for the profiles and almost 400 mm for the helices.


Figure 2 – Results of helix measurements for the external gear (fHb or ƒ_Hβ: helix slope deviation; ffb or ƒ_fβ: helix form deviation; Fb or F_β: helix total deviation)


Figure 3 – Results of profile measurements for the external gear (fHa bzw. ƒ_Hα: profile slope deviation; ffa bzw. ƒ_fα: profile form deviation; Fa bzw. F_α: profile total deviation)

These results form the basis for installing the first accredited calibration laboratory for large gears (at BIMAQ in Bremen). This will close the existing gap in the traceability chain for large-scaled gear measurements.