A modified fiberscope used to reconstruct difficult-to-reach inner structures is presented. By substituting the fiberscope’s original illumination system, we can project a profile-revealing light line inside the object of study. The light line is obtained using a sandwiched power light-emitting diode (LED) attached to an extension arm on the tip of the fiberscope. Profile images from the interior of the object are then captured by a camera attached to the fiberscope’s eyepiece. Using a series of those images at different positions, the system is capable of generating a 3D reconstruction of the object with submillimeter accuracy. Also proposed is the use of a combination of known filters to remove the honeycomb structures produced by the fiberscope and the use of ring gages to obtain the extrinsic parameters of the camera attached to the fiberscope and the metrological traceability of the system. Several standard ring diameter measurements were compared against their certified values to improve the accuracy of the system. To exemplify an application, a 3D reconstruction of the interior of a refrigerator duct was conducted. This reconstruction includes accuracy assessment by comparing the measurements of the system to a coordinate measuring machine. The system, as described, is capable of 3D reconstruction of the interior of objects with uniform and non-uniform profiles from 10 to 60 mm in transversal dimensions and a depth of 1000 mm if the material of the walls of the object is translucent and allows the detection of the power LED light from the exterior through the wall. If this is not possible, we propose the use of a magnetic scale which reduces the working depth to 170 mm. The assessed accuracy is around ±0.15 mm in 2D cross-section reconstructions and ±1.3 mm in 1D position using a magnetic scale, and ±0.5 mm using a CCD camera.
Periodic performance evaluation is a critical issue for ensuring the reliability
of data from terrestrial laser scanners (TLSs). With the recent introduction of the ASTM
E3125-17 standard, there now exist standardized test procedures for this purpose.
Point-to-point length measurement is one test method described in that documentary
standard. This test is typically performed using a long scale bar (typically 2 m or
longer) with spherical targets mounted on both ends. Long scale bars can become unwieldy
and vary in length due to gravity loading, fixture forces, and environmental changes. In
this paper, we propose a stitching scale bar (SSB) method in which a short scale bar
(approximately 1 m or smaller) can provide a spatial length reference several times its
length. The clear advantages of a short scale bar are that it can be calibrated in a
laboratory and has potential long-term stability. An essential requirement when
stitching a short scale bar is that the systematic errors in TLSs do not change
significantly over short distances. We describe this requirement in this paper from both
theoretical and experimental perspectives. Based on this SSB method, we evaluate the
performance of a TLS according to the ASTM E3125-17 standard by stitching a 1.15 m scale
bar to form a 2.3 m reference length. For comparison, a single 2.3 m scale bar is also
employed for direct measurements without stitching. Experimental results show a maximum
deviation of 0.072 mm in length errors between the two approaches, which is an order of
magnitude smaller than typical accuracy specifications for TLSs.
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