Logo of the Physikalisch-Technische Bundesanstalt

R&D project

Reduced error seperating method for divided circles

Period of the project

Start: September 2016
End:   Februar 2019

Description of the project

Over the past few years the so-called three-rosette method was established as the standard procedure for highly-accurate pitch deviation measurement. This procedure makes use of the characteristic of the pitch measurements, that the sum of the pitch errors over 360° yields zero.

The measured pitch deviations on a gear measuring instrument or a coordinate measuring machine consist of the systematic pitch deviations of three independent rosettes:

  • Pitch error of the gear
  • Pitch error of the workpiece coordinate system
  • Pitch error of the rotary table or of the coordinate measuring machine

Schematic turning of the rosettes against each another and multiple measurement of the gear allows the single errors to be completely separated from one another.


Measuring set-up for the rosette method with gear, rotary table and coordinate measuring machine

The main draw-back of the rosette method is its high measurement effort: On a gear with z teeth all 2z pitch deviations (left and right flank) have to be measured in z different relative positions. Therefore the method requires 2z2 pitch deviation measurements.

At PTB, a reduced error separation method was developed which reduces the measurement effort up to 90 % und which is applicable for arbitrary (positive integer) z. Measurement uncertainties are only marginally larger than for existing methods. For the method, a patent has been applied.

Aim of the project is to guarantee the usability and reliability of this calibration method for its use in the industry. Moreover, after completion of the project, conformity assessment bodies have the possibility to get accredited for this calibration method.

Beside the practical implementation of this method for different measuring devices, comprehensive verification measurements and the determination of the measurement uncertainty in compliance with the GUM, a focal point is the implementation of the algorithms. It is aimed that each potential user (measurement engineer, calibration service provider, manufacturer of measurement devices, ...) can write evaluation software suitable for his needs, which can be verified by the online service of PTB. For this purpose, reference algorithms and test data will be developed within the project.

Project partner

The project is being conducted together with four industrial partners.


Dr. Frank Keller und Dr. Martin Stein