5.applications of optical 3d measurement systems by using radially symmetric structured light projection
the main advantage of the measurement method outline above is the independence of the illumination and the camera perpendicular to the optical axis. thus measurement systems with minimal diameter can be designed.the principle is ideally suited for endoscopes and other inspection systems with limited diameters.
advantageous structured light projectors use a laser that illuminates a holographic grating. such projectors are able to project structures with a wide depth of focus. a projector of minimal dimensions may consist of a laser diode or a monomode fiber and a small holographic grating. further essential components of such a system are a beam splitter, the optics for image formation (see the sketch of a minimal configuration,fig 9), and a camera, an image conduit, or a fiber bundle.
in the system developed here (e.g.,fig.10),the light structure selected consists of seven concentric circles. when the inspection robot is guided centrically through a cylindrical sewer pipe, it measures one complete section perpendicular to the pipe axis per measurement interval . by comparison of measured and tolerable radii,defects in the pipe are automatically detected
the visual inspection of the sewer pipe should not be affected by the 3d measurements. thus the solution for the tube inspection robot was an optical system consisting of the following elements with virtually the same optical axis (see fig.11)
a structured light projector consisting of a semiconductor laser, a holographic grating, and optics for beam expansion.
a color tv camera for visual inspection.
a monochrome camera for measurements.
both cameras use the same zoom-objective lens and are combined with an erecting prism to compensate for image rotation, occurring when the optics is rotated and/or directed to the wall of the pipe , they observe the same object segment but are completely separated by wavelength (by the use of a dichroic beam splitter for a laser wavelength of 780 nm ). this system allows comfortable visual inspections of sewer pipes: detected defects (automatically) are precisely measurable by directing the optics on the defects and zooming, whereas the horizontal orientation of the image is controlled by the erecting prism. interesting points of the defects are marked by the operator in the color tv image and automatically measured by the 3d system. becase the 3d system is observing exactly the same scene, this is performed without further action of the operator. thus the operator works only on the basis of the color tv image, and the 3d measurement system automatically extracts the interesting object structures, without the need of special attention from the operator.
the authors acknowledge the support of the german ministry of education and research (formerly the ministry of research and technology).
the main advantage of the measurement method outline above is the independence of the illumination and the camera perpendicular to the optical axis. thus measurement systems with minimal diameter can be designed.the principle is ideally suited for endoscopes and other inspection systems with limited diameters.
advantageous structured light projectors use a laser that illuminates a holographic grating. such projectors are able to project structures with a wide depth of focus. a projector of minimal dimensions may consist of a laser diode or a monomode fiber and a small holographic grating. further essential components of such a system are a beam splitter, the optics for image formation (see the sketch of a minimal configuration,fig 9), and a camera, an image conduit, or a fiber bundle.
in the system developed here (e.g.,fig.10),the light structure selected consists of seven concentric circles. when the inspection robot is guided centrically through a cylindrical sewer pipe, it measures one complete section perpendicular to the pipe axis per measurement interval . by comparison of measured and tolerable radii,defects in the pipe are automatically detected
the visual inspection of the sewer pipe should not be affected by the 3d measurements. thus the solution for the tube inspection robot was an optical system consisting of the following elements with virtually the same optical axis (see fig.11)
a structured light projector consisting of a semiconductor laser, a holographic grating, and optics for beam expansion.
a color tv camera for visual inspection.
a monochrome camera for measurements.
both cameras use the same zoom-objective lens and are combined with an erecting prism to compensate for image rotation, occurring when the optics is rotated and/or directed to the wall of the pipe , they observe the same object segment but are completely separated by wavelength (by the use of a dichroic beam splitter for a laser wavelength of 780 nm ). this system allows comfortable visual inspections of sewer pipes: detected defects (automatically) are precisely measurable by directing the optics on the defects and zooming, whereas the horizontal orientation of the image is controlled by the erecting prism. interesting points of the defects are marked by the operator in the color tv image and automatically measured by the 3d system. becase the 3d system is observing exactly the same scene, this is performed without further action of the operator. thus the operator works only on the basis of the color tv image, and the 3d measurement system automatically extracts the interesting object structures, without the need of special attention from the operator.
the authors acknowledge the support of the german ministry of education and research (formerly the ministry of research and technology).
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