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Production sequence of Si-spheres and interferometrical determination of the sphere volume

Traceability of roughness measurements on gear flanks

22.12.2020

With increasing requirements on the performance of gears, also the roughness measurements on gear flanks get more important and therefore the need for traceability of such measurements rises. That is why a gear roughness standard is being developed at PTB in cooperation of departments 5.1, 5.3 and 5.5 and industrial partners. This measurement standard will for the first time realise a roughness standard on a non-planar functional surface.

The roughness profile is manufactured onto an involute shape of a gear flank. The calibration then takes place on a profilometer.

In gear measurement technology, usually all parameters are defined in reference to the roll length w or the roll angle ξ respectively. However, the roughness profile is defined in reference to the arc length s on the workpiece surface. Hence, it is important to establish the transformation between the reference systems of arc length and roll length.


Figure 1: Display of the same profile in reference to the arc length (blue) and the roll length (red) respectively. The black bars each mark the distance between two peaks. This example shows the nonlinear stretching of the x-axis in comparison. This effect has to be considered when choosing the evaluated segment from the profile and calculating roughness parameters.


Figure 2: Prototype of the tooth piece with the involute shape in the marked area

In the project the relevant reference systems have been characterised and the necessary transformations between those have been developed (see fig. 1). To do that, a new description of the gear coordinates is used and a fitting algorithm to attribute the cartesian coordinates measured with a profilometer to the corresponding gear parameters has been developed. This enables the direct discrimination of the ideal involute from the measurement points and furthermore separate the form deviations in reference to the gear dimension.

The algorithm yields a common roughness profile as well as the relevant roughness parameters like R_z, R_a and the Firestone-Abbot-Curve. Once the measurement standard is finished it will be investigated using a profilometer and the embodied roughness parameters are calibrated using this algorithm.

At this point the main focus lies in the development and manufacturing of the standard (fig. 2), that is intended to be finished by the end of the year.

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