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Research Papers

Optical Tracking of a Tactile Probe for the Reverse Engineering of Industrial Impellers

[+] Author and Article Information
Sandro Barone

Department of Civil and Industrial Engineering,
University of Pisa,
Largo Lucio Lazzarino, n.1,
Pisa 56126, Italy
e-mail: s.barone@ing.unipi.it

Alessandro Paoli

Department of Civil and Industrial Engineering,
University of Pisa,
Largo Lucio Lazzarino, n.1,
Pisa 56126, Italy
e-mail: a.paoli@ing.unipi.it

Armando V. Razionale

Department of Civil and Industrial Engineering,
University of Pisa,
Largo Lucio Lazzarino, n.1,
Pisa 56126, Italy
e-mail: a.razionale@ing.unipi.it

1Corresponding author.

Contributed by the Design Engineering Division of ASME for publication in the JOURNAL OF COMPUTING AND INFORMATION SCIENCE IN ENGINEERING. Manuscript received August 26, 2015; final manuscript received February 9, 2017; published online May 16, 2017. Editor: Bahram Ravani.

J. Comput. Inf. Sci. Eng 17(4), 041003 (May 16, 2017) (14 pages) Paper No: JCISE-15-1273; doi: 10.1115/1.4036119 History: Received August 26, 2015; Revised February 09, 2017

Different sensor technologies are available for dimensional metrology and reverse engineering processes. Tactile systems, optical sensors, and computed tomography (CT) are being used to an increasing extent in various industrial contexts. However, each technique has its own peculiarities, which may limit its usability in demanding applications. The measurement of complex shapes, such as those including hidden and twisted geometries, could be better afforded by multisensor systems combining the advantages of two or more data acquisition technologies. In this paper, a fully automatic multisensor methodology has been developed with the aim at performing accurate and reliable measurements of both external and internal geometries of industrial components. The methodology is based on tracking a customized hand-held tactile probe by a passive stereo vision system. The imaging system automatically tracks the probe by means of photogrammetric measurements of markers distributed over a plate rigidly assembled to the tactile frame. Moreover, the passive stereo system is activated with a structured light projector in order to provide full-field scanning data, which integrate the point-by-point measurements. The use of the same stereo vision system for both tactile probe tracking and structured light scanning allows the two different sensors to express measurement data in the same reference system, thus preventing inaccuracies due to misalignment errors occurring in the registration phase. The tactile methodology has been validated by measuring primitive shapes. Moreover, the effectiveness of the integration between tactile probing and optical scanning has been experienced by reconstructing twisted and internal shapes of industrial impellers.

Copyright © 2017 by ASME
Topics: Impellers , Probes
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References

Figures

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Fig. 1

Double-tip tactile probe

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Fig. 2

Structured light scanner composed of two digital cameras and a multimedia projector

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Fig. 3

Manual positioning of the tactile probe (a) and scheme of the reference marker tracking during the calibration process (b)

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Fig. 4

Tactile probe image processing: original left (a) and right (b) camera images, corresponding range filtered images (c) and (d), binarized images (e) and (f), results of the flood-fill morphological reconstruction and labeling process (g) and (h)

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Fig. 5

Reference marker detection: results (star marks) of a corner finder algorithm (a) and (b), epipolar constraint between the rectified left and right images (c) and (d), identification of conjugate marker pairs (cross marks) with removal of false correspondences (e) and (f)

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Fig. 6

Scheme of the probing point reconstruction process

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Fig. 7

Chessboard pattern on a planar glass surface (a) and best fit planes and corresponding residuals obtained for four different measurements of the chessboard corners within the stereo system working volume (b)

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Fig. 8

Two-dimensional geometrical model of the tactile probe

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Fig. 9

Scheme of the flatness test metrics

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Fig. 10

Scheme of the cylindrical/spherical test metrics Cmeas (a) and Ed (b)

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Fig. 11

The centrifugal closed impellers, made of cast stainless steel, with diameter of 250 mm (a) and 180 mm (b)

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Fig. 12

Technical drawings of impellers (a) and 3D simulation of the tactile probe measurement process (b)

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Fig. 13

Point cloud measured on the impeller surfaces (a) along with the primitive geometries reconstructed by best fitting the probed points and the tessellation models of the blade surfaces (b)

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Fig. 14

(a) Point clouds acquired by the SLS and automatically aligned with a turntable. (b) StL representation of the impeller surfaces obtained by a tessellation process.

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Fig. 15

Deviation map obtained comparing the probed points and the surfaces reconstructed by SLS exploiting the same placement of the stereo cameras with respect to the target object

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Fig. 16

Six different slices extracted from the CT volume acquired during the impeller measurement

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Fig. 17

Three-dimensional models obtained by segmenting the CT volume using different threshold values (a), 3D full-field deviations between the CT models and the SLS model (b), graphical illustration of the deviation occurring between the CT and the ground truth model occurring in correspondence of the cross section of the blade surfaces (c)

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Fig. 18

Identification of the correct threshold value (τopt) by analyzing the mean deviation values occurring between the models in correspondence of the two cross sections for different gray-level threshold values

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Fig. 19

Three-dimensional compare between probed points and CT model (including internal surfaces)

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Fig. 20

Three-dimensional compare between probed points and SLS model (only visible surfaces)

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