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Large gear ring standard, 2 m in diameter


Within the scope of a joint project promoted by the Federal Ministry for Economic Affairs and Energy (BMWi), a new gear measurement standard has been developed at PTB. It embodies three different external and three different internal gears each, which are arranged on a ring having an outer diameter of approximately 2 m.

Large gear ring standard with an outer diameter of approximately 2 m. Arranged on the outer and on the inner circle are three gears each, with different helix angles (0°, 10° and 20°). The standard has a weight of approx. 2700 kg.

In cooperation with PTB‘s Scientific Instrumentation Department, a support has been developed and manufactured especially for this large gear measurement standard. This support guarantees as low a deflection as possible – and, in particular, a reproducible deflection – of the standard. The standard was calibrated by means of a procedure developed at PTB in the case of which the local geometry deviations of a coordinate measuring machine are corrected on the basis of the multilateration principle with at least four tracking laser interferometers (so-called “LaserTracers”) distributed in the room. At present, the measurement results are being evaluated. The aimed-at calibration uncertainty for the individual gear parameters amounts to < 4 μm.

The aim of the project is to clarify metrological issues prior to the aimed-at accreditation of the first conformity assessment body for large gears at a project partner in Bremen through the German accreditation body (DAkkS). This conformity assessment body and other possible conformity assessment bodies (CABs) are to in future meet the high demands of the manufacturing industry for large gear measurement standards. Currently, an interlaboratory comparison is being performed on the new standard. In addition to PTB, four manufacturers of measuring instruments, a manufacturer of large gear components, a calibration laboratory as well as a university institute are participating in the comparison measurements.