Fringe projection profilometry using rigid and flexible endoscopes

Abstract

Quality control is an important aspect of modern production processes. Obtaining quantitative information not only helps to ensure the function of machinery and products, but also enables cost reduction by feedback control of process parameters. A multitude of modern industrial applications feature an increasing amount of highly integrated machinery, resulting in a requirement for new measuring devices. Two new measuring systems are presented for in-situ inspection tasks in confined spaces. A combination of endoscopy techniques with structured illumination enables capturing areal 3-D geometry information of functional elements in integrated machinery. Depending on the requirements for inspection, either rigid or flexible image guides may be used to transport the structured light patterns. While a flexible endoscope allows for a more flexible positioning of the sensor head, its resolution is limited by the number of individual fiber cores. Alternatively, if constraints on the versatility of sensor positioning can be accepted, rigid endoscopes feature higher image quality. Both approaches are described in detail and compared based on evaluations on features of a calibrated micro contour standard.

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

“…Finally, a stereo calibration of camera and projector is performed. In order to estimate the reconstruction quality of the borescopic sensors, the probing error with respect to size and form was determined for endoscopic sensor assemblies [ 26 ]. According to VDI/VDE 2634-2 [ 27 ], a cylindrical feature of a calibrated microcontour standard was measured at a working distance of 30 , resulting in a probing error of 20 μ .…”

“…The radius of the calibrated microcontour standard is μ according to the calibration certificate. Please refer to [ 26 ] for further accuracy and measurement uncertainty investigations. Additionally, when measuring surfaces with limited optical cooperativity, the known physical limits of triangulating optical measurement principles apply.…”

Metal Forming Tool Monitoring Based on a 3D Measuring Endoscope Using CAD Assisted Registration

“…Between the two pairs of fibers and optics, a 30° triangulation base is formed. The measuring volume is approximately 6 mm × 6 mm × 3 mm [9]. This measuring head features the lowest measurement uncertainty and the highest magnification alike.…”

“…Therefore, a more compact design is realized, allowing a parallel arrangement of the fibers. The measuring volume is approximately 10 mm × 10 mm × 4 mm [9]. To enhance the depth of field of the measuring head with 10 mm working distance, additional liquid lenses can be added, which lead to the design of Figure 7b.…”

Full simulation model for laser triangulation measurement in an inhomogeneous refractive index field

“…The optical triangulation method is a state-of-the-art technique to acquire geometry data of complex freeform geometries and used in different scales. 1 A common industrial application is the inspection of formed metal sheets in the automotive sector by fringe projection systems, 2 whereas endoscopic systems for confined spaces with small measurements heads are being investigated for in-situ inspection tasks (e.g., the restoration of turbine blades 3 ).…”