HoloVID is a tool originally developed for the Holographic dimensional measurement of the internal isogrid webbing of the Delta Series of (launch vehicle) Space Craft skins.
It was developed at the McDonnell Douglas Astronautics Division by Dr. Jon Dark in 1981. It was later used at Martin Aerospace to inspect the long weld seams which hold the external fuel tanks of the Space Shuttle together, using specialized models. Many corporations (Kodak, Immunex, Boeing, Johnson and Johnson, Aerospace Corp., Silverline, and others) use customized versions of the Six Dimensional Non-Contact Reader w/ Integrated Holographic Optical Processing, for applications from SuperComputer Surface Mount pad assessment, to Genetic Biochemical Assay Analysis. . HoloVid belongs to a class of sensor known as a structured light device. The use of structured light to extract three-dimensional shape information is a well known technique. (1,2). The use of single planes of light to measure the distance and orientation of objects has been reported several times. (3,4,5). The use of multiple planes (6,7,8) and multiple points (9,10) of light to measure shapes and construct volumetric estimates of objects has also been widely reported. (11). The use of segmented phase holograms to selectively deflect portions of an image wavefront... is unusual. The holographic optical components used in this device, split tessellated segments of a returning wavefront in programmable bulk areas and shaped patches to achieve a unique capability, increasing both the size of an object which can be read and the z-axis depth per point which is measurable, while also increasing the simultaneous operations possible which is a significant advance in the previous state of art.
Operational Modes: A laser beam is made to impinge onto a target surface. The angle of the initially nonlinear optical field can be non-orthagonal to the surface. This light beam is then reflected by the surface in a wide conical spread function which is geometrically related to the incidence angle, light frequency, wavelength and relative surface finish. A portion of this reflected light enters the optical system coaxially, where a 'stop' shadows the edges. In a single point reader, this edge is viewed along a radius by a photodiode array. The output of this device is a boxcar output where the photodiodes are sequentially lit diode by diode as the object distance changes in relation to the sensor until either no diodes are lit, or all diodes are lit. The residue product product charge dynamic value in each light diode cell is a function of the bias current, the dark current and the incident ionizing radiation (in this case, the returning laser light). In the multipoint system, the HoloVid, the cursor point is acousto-optically scanned in the x-axis across a K theta monaxial transformer. A monaxial holographic lens collects the wavefront and reconstructs the pattern onto the single dimensional photodiode array and a two dimensional matrix sensor. Image processing of the sensor data derives the correlation between the compressed wavefront and the actual physical object. The areas sensor acts as a reference and calibration field classifier for the HoloVID system. (MORE INFO TO FOLLOW.)
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