On the development of a low-cost rigid borescopic fringe projection system

Abstract

Examining the geometry of complex industrial free form objects, like a blade integrated disk (blisk) of a jet engine compressor, is currently subject to research. High measurement precision and speed are required and the complex geometry poses a challenge for state of the art measurement systems. In order to fulfill typical inspection requirements, the fringe projection methodology was adapted in this work to accomplish the task of fast and precise geometry examination. A low cost borescopic fringe projection system for 3D shape measurement based on consumer electronics combined with state of the art optics was developed. Nevertheless, it is able to provide measurement uncertainties comparable to professional systems. We are using a portable consumer LED-beamer, which we have modified to fit the optics of the borescope and a Raspberry Pi single-board computer with a 5 megapixel camera to capture the fringe patterns. With this setup and fringe projection algorithms, which have been developed by this institute over the last years, we were able to perform high quality measurements while still being suitable for a compact inspection system. Measurements with high point densities are possible even in narrow areas of parts with complex geometries like blisks. The measuring system and first measurement results will be presented at the conference.

Pose Estimation and Damage Characterization of Turbine Blades during Inspection Cycles and Component-Protective Disassembly Processes

“…For fast and high-precision inspection in confined spaces, the measuring method of fringe projection profilometry is adopted to a borescopic sensor design. Schlobohm et al introduced this sensor design, which enables the spatial separation of measuring head and projection and evaluation devices while keeping a rigid sensor setup [ 17 ]. This, in turn, enables a precise navigation into maintenance openings and cross sections of less than 9 diameter, which then allows for automated inspections in difficult-to-access areas.…”

“…In a first step, an initial transformation is computed based on three randomly selected features of the reference feature set r ∈ R 3×N and the measurement feature set m ∈ R 3×N ( 16). The transformation is calculated using an implementation according to Hinz et al [33] (17). The algorithms are based on the work of Besl et al [34] and Kabsch et al [35].…”

“…Instead, a borescopic fringe projection sensor 79 design enables precise navigation and high-precision 3D measurements in confined spaces 80 and addresses the special requirements of engine inspection. Schlobohm et al were able 81 to implement inspections of engine blisks using this sensor design and demonstrate the 82 automation capability [17,18]. In addition to the aforementioned requirements, a metric 83 deviation analysis must be performed in order to assess the condition of engine compo-84 nents.…”

<i>In Situ</i> Wear Measurement of Hot Forging Dies Using Robot Aided Endoscopic Fringe Projection

“…An endoscopic measuring system based on the principle of the borescopic fringe projection was developed for high-precision 3D measurement in confined spaces [16], the basic function is illustrated in Figure 4. This instrument enables navigation into holes and cross-sections of less than 10 mm diameter and can thus be applied for inspections in areas that are difficult to access.…”