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A Calibration Method for a Laser Triangulation Scanner Mounted on a Robot Arm for Surface Mapping

1
Faculty of Gama-FGA, Department Electronics Engineering, University of Brasilia, Brasilia-DF 72.444-240, Brazil
2
Faculty of Technology-FT, Department of Mechanical and Mechatronics Engineering, University of Brasilia, Brasilia-DF 70910-900, Brazil
3
Faculty of Gama-FGA, Department Software Engineering, University of Brasilia, Brasilia-DF 72.444-240, Brazil
*
Author to whom correspondence should be addressed.
Sensors 2019, 19(8), 1783; https://doi.org/10.3390/s19081783
Received: 13 February 2019 / Revised: 6 March 2019 / Accepted: 12 March 2019 / Published: 14 April 2019
(This article belongs to the Special Issue Laser Sensors for Displacement, Distance and Position)
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Abstract

This paper presents and discusses a method to calibrate a specially built laser triangulation sensor to scan and map the surface of hydraulic turbine blades and to assign 3D coordinates to a dedicated robot to repair, by welding in layers, the damage on blades eroded by cavitation pitting and/or cracks produced by cyclic loading. Due to the large nonlinearities present in a camera and laser diodes, large range distances become difficult to measure with high precision. Aiming to improve the precision and accuracy of the range measurement sensor based on laser triangulation, a calibration model is proposed that involves the parameters of the camera, lens, laser positions, and sensor position on the robot arm related to the robot base to find the best accuracy in the distance range of the application. The developed sensor is composed of a CMOS camera and two laser diodes that project light lines onto the blade surface and needs image processing to find the 3D coordinates. The distances vary from 250 to 650 mm and the accuracy obtained within the distance range is below 1 mm. The calibration process needs a previous camera calibration and special calibration boards to calculate the correct distance between the laser diodes and the camera. The sensor position fixed on the robot arm is found by moving the robot to selected positions. The experimental procedures show the success of the calibration scheme. View Full-Text
Keywords: 3D scanner calibration; laser scanning; vision triangulation; robot calibration; robotic vision; surface mapping; robotic welding; turbine blade repairing 3D scanner calibration; laser scanning; vision triangulation; robot calibration; robotic vision; surface mapping; robotic welding; turbine blade repairing
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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MDPI and ACS Style

Idrobo-Pizo, G.A.; Motta, J.M.S.T.; Sampaio, R.C. A Calibration Method for a Laser Triangulation Scanner Mounted on a Robot Arm for Surface Mapping. Sensors 2019, 19, 1783.

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