Photogrammetric endoscope for measurement of inner cylindrical surfaces using fringe projection

Abstract

We present a photogrammetric endoscope to measure three dimensional (3D) shapes of inner cylindrical surfaces by fringe projection. The basic configuration includes two identical cameras aligned with the optical axis and facing each other, conical lenses, and a 360 degrees helical fringe projector. The helical fringe pattern is phase shifted and acquired by both cameras. The phase patterns are used to acquire data from the surface in a regular cylindrical mesh. A prototype was built, calibrated, and tested. We present the results and an application to inspect internal welding seams and misalignment of welded joints in 150 mm (6 in.) diameter pipelines.

Rigid and flexible endoscopes for three dimensional measurement of inside machine parts using fringe projection

“…In 2008, Albertazzi et al [7] proposed their photogrammetric endoscope based on fringe projection for the measurement of inner cylindrical surfaces for the inspection of welded tube joints. The system configuration includes two wide angle cameras facing each other and one LED light source in between which is able to radially project a helical fringe pattern onto the inside of the measured cylinder hull.…”

Fiber Optic Projection-Imaging System for Shape Measurement in Confined Space

“…Data-processing methods: phase-shifting and Fourier transform were applied to fringe patterns obtained by an endoscope or a fiber scope, just as in free-space scenarios [14–16]. Photometric approaches were also adapted to these devices [17, 18]. …”

Flexible and miniaturized microscope for three dimensionnal measurements

“…Projection of interferograms created by muti-core fibre-based instruments is also a viable strategy [3]. Fringe projection techniques are possible as in [4] where a special helical projector illuminates the inner surface of a cylinder. More flexible pattern projection techniques use a DMD (Digital Micro-mirror Device, Texas Instrument Inc) as projection device for high speed [5] or high accuracy [6] measurements.…”