Subproject C2 Fast Measurement of Complex Geometries

Subproject C2 researches the development of rigid endoscopic fringe projection sensors for 3D measurement. The sensor system should enable an exact geometric measurement of components that are difficult to access, as well as geometric inspection in tight spaces. In particular, the measurement of complex aircraft engine components such as turbine blades will be researched.

MOTIVATION AND OBJECTIVES

For aircraft engine maintenance, in particular the inspection of a blisk, the engines are partially disassembled and analyzed with flexible video endoscopes. This subjective visual inspection is conducted by specially trained employees. In order to enable a quantitative analysis, research is carried out a high-precision miniature 3D measuring system based on the fringe projection method. This sensor is implemented via a borescope, that is equipped with a chip-on-the-tip camera. The combination of high-precision actuators and a sensor with specially developed calibration and stitching procedures can achieve automated 3D measurements. This system will enable a precise quantitative quality control that increases the safety and efficiency of engine maintenance. 

RESULTS

Within the first two funding periods, a rigid endoscopic fringe projection system for the holistically measurement of complex shaped components was developed. While the research of algorithms for inverse fringe projection was at the center of attention of the first funding period, an approach for the compensation of artifact formation for miniaturized fringe projection systems was researched in the second funding period. Also the imaging properties of a rigid endoscope were modeled and suitable compensation strategies for the gravitational influences on the endoscope were developed. It could be shown that the developed sensor system is particular suitable for detecting critical engine damages such as dents and breakout on turbine blades. In combination with the measurement methods “eddy current analysis” and “white light interferometry” from sub-projects A1 and A2, a holistic defect detection can be realized.

This is the prototype sensor system from the second funding period. It is able to analyze the geometry of a disassembled turbine blisk. A full 3D measurement of an engine blisk can be realized autonomous.

CURRENT RESEARCH AND OUTLOOK

In the third funding period, the research will focus on the prediction of measurement uncertainty of endoscopic fringe projection sensors. With the additional uncertainty information, a detailed planning of the measurement strategy can be prepared. In particular, the artifact formation caused by multi-reflections of the measuring light on the work piece should be avoided by a smart measuring pose planning. In the further progress of the third funding period, the fringe projection sensor will be integrated into a milling machine (as a tool). The high precision actuators and measuring systems enable the automated generation of a “digital twin” of the real work piece. A digital twin can map the machining process as well as the actual and the target geometry for each individual component. In the end of the project all research will be used to develop an even more.


PUBLICATIONS

  • Matthias, S.; Schlobohm, J.; Kästner, M.; Reithmeier, E. (2017) Fringe projection profilometry using rigid and flexible endoscopestm - Technisches Messen 84 (2)
    DOI: 10.1515/teme-2016-0054
  • Pösch A.; Schlobohm, J.; Matthias, S.; Reithmeier, E. (2016) Rigid and flexible endoscopes for three dimensional measurement of inside machine parts using fringe projectionOptics and Lasers in Engineering 2016
    DOI: 10.1016/j.optlaseng.2016.05.023
  • Schlobohm J.; Bruchwald, O.; Frackowiak, W.; Li, Y.; Kästner, M.; Pösch, A.; Reimche, W.; Reithmeier, E.; Maier, H. J. (2016) Turbine blade wear and damage – An overview of advanced characterization techniquesMaterials Testing 58 (5), S. 389–394
    DOI: 10.3139/120.110872
  • Schlobohm J.; Pösch, A.; Reithmeier, E.; Rosenhahn, B. (2016) Improving contour based pose estimation for fast 3D measurement of free form objectsMeasurement 92 (92), S. 79–82
    DOI: 10.1016/j.measurement.2016.05.093
  • Schlobohm, J.; Li, Y.; Pösch, A.; Kästner, M.; Reithmeier, E. (2016) Multiscale measurement of air foils with data fusion of three optical inspection systemsIn: CIRP Journal of Manufacturing Science and Technology 2016
    DOI: 10.1016/j.cirpj.2016.07.006
  • Schlobohm, J.; Pösch, A.; Reithmeier, E. (2016) A Raspberry Pi Based Portable Endoscopic 3D Measurement SystemIn: Electronics 5 (3), S. 43
    DOI: 10.3390/electronics5030043
All publications of the Collaborative Research Centre

SUBPROJECT LEADER