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Experimental validation of a 3-D vision-based measurement system applied to robot calibration

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Author(s): Motta J. M. S. T. | McMaster R. S.

Journal: Journal of the Brazilian Society of Mechanical Sciences
ISSN 0100-7386

Volume: 24;
Issue: 3;
Start page: 220;
Date: 2002;
Original page

Keywords: Robot calibration | 3-D machine vision | absolute accuracy | camera calibration | robotic measurement systems

ABSTRACT
One of the problems that slows the development of off-line programming is the low static and dynamic positioning accuracy of robots. Robot calibration improves the positioning accuracy and can also be used as a diagnostic tool in robot production and maintenance. A large number of robot measurement systems are now available commercially. Yet, there is a dearth of systems that are portable, accurate and low cost. In this work a measurement system that can fill this gap in local calibration is presented. The measurement system consists of a single CCD camera mounted on the robot tool flange with a wide angle lens, and uses space resection models to measure the end-effector pose relative to a world coordinate system, considering radial distortions. Scale factors and image center are obtained with innovative techniques, making use of a multiview approach. The target plate consists of a grid of white dots impressed on a black photographic paper, and mounted on the sides of a 90-degree angle plate. Results show that the achieved average accuracy varies from 0.2mm to 0.4mm, at distances from the target from 600mm to 1000mm respectively, with different camera orientations.
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