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RE274 - v sewwvsw 6 5-DSh ‘ 2 upthgmzm 209 Figure 6-5...

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Unformatted text preview: v..- sewwvsw 6. 5-DSh ' ‘ § 2 upthgmzm 209 Figure 6-5. The line range sensor works by the same ‘ ' ‘ _ . . principle as the point ran e raiser ex thflztutlliemgistortxmllarge 1min: ol'pomts in a straight line ofligit are mapped of: a dammit-Apt: _ sun y instea one at a time. (Court Cane-i Inct, subsidi ' ‘- sion Company, Rye Brook New York) “y I. "y “11me V1 range digitizer that also detects color. (See Figures 4-33 and 4-35.) Another line ranging system is available from Vision 3D (Toulouse, France). Mallinckrodt Institute of Radiology (St. Louis, Missouri) is developing medical applications for an interesting digitizing system called Cencit. The array of six line range sensors in this system can digitize a human face and head in less than a :wond. gmhnology 15 owned by Universal Vision Company, a partnership of arsons ttemore (Rye Brook, New York and hoto a hi ‘ ‘ ' CPI Corp. (St. Louis, Missouri). ) p gr p c concessronane A method that combines triangulation with the physical phenomenon of Moiré patterns 15 planar interferometry. Here, the sensor emits a 2-dimensional grid pattern of coherent light onto the surface to be measured. The shape of the surface distorts the lines in the grid just as it does for a line range sensor. However instead of performing a triangulation calculation on individual points, the sensor allows the distorted grid to “interfere" with an image of the undistorted grid, forming a Moiré pattern. An analysis of this pattern provides relief data for the surface. For a flat relief of one surface if the area of the pro' ‘ ' . ~ , Jectod grid 15 large enough, and ifthe surface curvature 15 not too great, then a single reading may be sufi'icient Otherwise, multiple readings can be taken over different patches of the surface, and from difi'erent angles, and the data correlated to characterize the total geometry. 210 AmonmdFabflcaflon—Imflving Productivity in Manufacturing A planar interferometry scanner is available from EOS (Munich, Germany), the manufacturer of the Stereos fabricator. (See page 58.) Interesting work on planar interferometry digitizing was for a time conducted by Maurice Halioua at the New York Institute of Technology (Old Westbury, New York.) All the above optical sensors use variations of the principle of triangulation. A different approach is taken in LiDAR (light detection and ranging), which is the laser analog of radar. A pulse of light is emitted at the object, and the time for its reflection to return is measured A LiDAR digitizer is available from Peroeptron of Farmington Hills, Michigan. Spatial Sensors A spatial sensor is capable of reading the interior as well as the exterior of a solid object. The most important examples are computed tomography (CT) and nuclear-magnetic resonance (NMR), which are described briefly here. Ultrasonic sensors have also proved useful in this application. Researchers at several universities have developed software for transferring CT and NMR data directly to fabricators for imaging. In computed tomography (CT, also sometimes called CAT, for computer-aided tomography), an X—ray beam is spread out and aimed at the object, and a detector on the other side records the X—rays that pass through. The object is rotated and the procedure is repeated to obtain several profiles of X—ray opacity of the object. From this data it is possible, by a complicated mathematical procedure, to map out in three dimensions just what parts of the object are X-ray opaque. In a human body, for example, these regions are the bones. (See Figure 6-6.) But CT is beginning to be used in industrial applications as well, For example, a CT scanner can detect voids in a metal casting. For automated fabrication, CT has found application in imaging human bony systems for surgical planning and implant manufacturing. (See Figures 4-34 and 4- 36 for case studies.) While activity in this area has been limited, it has a great potential for growth since there are already over 3,500 CT scanners installed in hospitals and other medical facilities in the United States alone, Another technique for spatial sensing is nuclear-magnetic resonance (NMR. also called MRI, for magnetic resonance imaging). Here, an oscillating magnet sets up an electromagnetic wave that passes into the object. The wave is tuned to a resonant frequency of the nuclei of a particular species of atom. When the wave hits an atom of this type, the nucleus absorbs the energy from the wave, becoming a site of opacity. The parts of the wave that pass through the object unabsorbed are ...
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