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Proceedings Paper

New compact rotationally symmetric triangulation sensor with low-cost plastic optics
Author(s): Johannes Eckstein; Gao Jun; Peter Ott; Wang Lei; Wang Xiaojia
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Paper Abstract

Classical triangulation sensors are wildly used but they have some typical drawbacks. The measurement result depends always on the angular orientation of the sensor what can be especially troublesome at steps or gaps. To eliminate this disadvantage of the classical triangulation we introduced in [1] a new kind of optical triangulation - the rotationally symmetric triangulation sensor. Therefore the measurement result depends not any longer on the angular orientation of the sensor. This is achieved by imaging the scattered light from an illuminated object point to a centered and sharp ring on a low cost area detector. The diameter of the ring is proportional to the distance of the object. The theoretical limit of the measurement uncertainty of the rotationally symmetric triangulation sensor is 3 to 4 times lower than the limit of the classical triangulation [2] for comparable and application oriented designs, because a complete ring is used for distance evaluation instead of only a point. In this contribution we show for the first time a design and a corresponding hardware which is completely realized by two toriodal formed aspherical plastic lenses. These lenses can be manufactured by injection molding for approximately the same costs than ordinary aspherical plastic lenses. So it is possible to realize this new sensor for the same price than a classical triangulation sensor but with higher accuracy and a much better robustness. For the rotationally symmetric triangulation sensor a standard 2D detector is used, the same detector like in standard vision systems. Additionally it is stressed that close to the axis of toriodal lenses is enough available design space to add a second optical system to image the object. The toriodal lenses allow to realize a retrofocus typ of imaging system without increasing the number of optical elements. However, in the middle of the lenses the surfaces are used for imaging and on the outer section they are used for triangulation. These two multipurpose optical elements can still be manufactured by injection moulding. To summarize, we show a low cost system with only one standard 2D detector and two aspheric lenses that realizes two tasks, i.e. imaging the object on the detector and distance measurement by rotationally symmetric triangulation.

Paper Details

Date Published: 16 May 2007
PDF: 8 pages
Proc. SPIE 6585, Optical Sensing Technology and Applications, 65850T (16 May 2007); doi: 10.1117/12.722896
Show Author Affiliations
Johannes Eckstein, Univ. of Technology, Hefei (China)
Univ. of Heilbronn (Germany)
Gao Jun, Univ. of Technology, Hefei (China)
Institute of Intelligent Machines (China)
Peter Ott, Univ. of Heilbronn (Germany)
Wang Lei, Univ. of Technology, Hefei (China)
Wang Xiaojia, Univ. of Technology, Hefei (China)

Published in SPIE Proceedings Vol. 6585:
Optical Sensing Technology and Applications
Francesco Baldini; Jiri Homola; Robert A. Lieberman; Miroslav Miler, Editor(s)

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