Rigid and flexible endoscopes for three dimensional measurement of inside machine parts using fringe projection. (February 2017)

• Record Type: Journal Article
• Authors: Pösch, Andreas; Schlobohm, Jochen; Matthias, Steffen; Reithmeier, Eduard
• Is Part Of: Optics and lasers in engineering. Volume 89(2017)
• Page Start: 178
• Page End: 183
• Publication Date: 2017-02
• Subjects: Endoscopy -- Endoscopic 3D measurement -- Fringe projection -- Structured light -- Optical 3D metrology; Lasers in engineering -- Periodicals; Optical measurements -- Periodicals; Optics -- Periodicals; Lasers en ingénierie -- Périodiques; Mesures optiques -- Périodiques; Optique -- Périodiques; 621.36605
• DOI: 10.1016/j.optlaseng.2016.05.023
• Languages: English
• ISSNs: 0143-8166

Abstract

Abstract: Routine maintenance is mandatory for safe and efficient operation of complex machines, such as airplane turbines. Occasional special events, like bird strike, entail extraordinary inspection works. Hereby, inside machine parts are hard to reach, oftentimes occluded by other parts and not directly accessible for visual inspection. Disassembly of machine parts is time-consuming and expensive and, therefore undesired. This leaves distal imaging, i.e. endoscopy, to be the only practical option for defect detection. Ordinary endoscopes, which provide two dimensional intensity image data, are insufficient to fully assess the risks caused by small three dimensional defects. As a solution to this issue, we have developed and implemented two different systems for three dimensional endoscopic measurement based on structured light projection which are capable of recording high resolution and high accuracy point cloud data. A measurement standard deviation of roughly 20 μm is achieved within a field of measurement of 20 × 30 × 30 mm 3 . Abstract : Highlights: One major highlight of the paper is, that the described technology—endoscopic 3D measurement—is already implemented in two different working examples. The data acquisition task is feasible in less than 3 s with both systems. Both setups are of low-cost and mainly built from stock components but nevertheless achieve very high data accuracy up to 20 μm standard deviation. The sensor heads are both very small so that hard to reach geometries can be measured. We present details about the working principle, the mathematical modeling and the hardware system setup. The capabilities of both realized systems are evaluated on the basis of real measurement data. Furthermore, one use scenario, the measurement of turbine blisk elements, is briefly depicted.