Multi-Probe Roundness Measurement of Large Rotors

Research output: ThesisDoctoral ThesisCollection of Articles


Multi-probe roundness measurement methods can be used to separate the roundness profile and the center point movement of a cross section from at least three measured probe signals. Multi-probe methods can also be applied when the center point movement is not repeatable between revolutions. This makes them suitable for the roundness measurement of large rotors, which can exhibit non-repeatable center point motion and can be impractical to place on traditional precision roundness measurement instruments. The aim of this research was to investigate and improve the accuracy of multi-probe roundness measurement methods. Measurement under realistic conditions was simulated to reveal the effects and significance of different sources of error present during the measurement. The problem of harmonic suppression was considered, and the probe angles were optimized for the three-point method and, for the first time, the redundant diameter four-point method. Finally, multi-probe methods were applied to quantify the errors in measurement of relative shaft displacement as required by industrial standards for electrical machines. This research gives suggestions for new optimal probe angles. The results of the simulations provide information on the accuracy of three compared multi-probe methods and reveal differing effects of the investigated positional errors to the different methods. Additionally, the simulated results confirm a correlation between the condition number of the multi-probe equation matrix and the actual uncertainties in harmonic components of the roundness profile. After the theoretical investigation and simulations, an application of multi-probe methods was presented. A four-point tactile multi-probe roundness measurement instrument was used to separate runout measured with an eddy current displacement probe into the electrical runout, center point motion and the roundness error. The results effectively reveal the sources of error in the measurement of shaft displacement as required by industrial standards for rotating machinery. Requirements for runout and the measurement of relative shaft displacement in industrial standards were assessed critically. The results of this research are relevant for solving technical problems where accurate measurement of the roundness error or center point movement of a large rotating workpiece cross section is required. The results can be exploited in industrial applications using multi-probe roundness measurement, such as the measurement and manufacturing of paper machine rolls.
Translated title of the contributionYmpyrämäisyysmittauksen monianturimenetelmät suurille roottoreille
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Viitala, Raine, Supervising Professor
Print ISBNs978-952-64-0195-9
Electronic ISBNs978-952-64-0196-6
Publication statusPublished - 2020
MoE publication typeG5 Doctoral dissertation (article)


  • multi-probe roundness
  • fourier roundness
  • harmonic suppression

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