HoloVID

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 by Dr. Jon Dark in 1981.

History

Delta Space Craft was produced by McDonnell Douglas Astronautics, until the line was purchased by Boeing Aircraft. Milled out of T6 Aluminum, on huge 40 foot by 20 foot horizontal mills, the inspection of the huge sheets took longer than the original manufacturing. It was estimated that a real time in-situ inspection device could seriously cut costs so an IRAD (Independent Research and Development ) budget was generated to solve the problem. Two solutions were worked simultaneously by J. Dark, a photo-optical techniques utilizing Holographic lens, and an ultrasonic technique utilizing configurable micro-transducer multiplexed arrays.

A pair of HoloVids for simultaneous frontside and backside weld feedback, was later used at Martin Aerospace to inspect the long weld seams which hold the external fuel tanks of the Space Shuttle together. By controlling the Weld bead profile in real time as it was TIG generated, an optimum weight vs. performance ratio could be obtained, saving the launch engines from having to waste thrust energy, while guaranteeing the highest possible web strengths.

Usage

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.

pecifications

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. [Agin, G.J., "Real Time Control of a Robot with a Mobile Camera". Technical Note 179, SRI International, Feb. 1979.] [Bolles, R.C. and M.A. Fischler, "A Ransac-based Approach to Model Fitting and its Application to Finding Cylinders in range data", "Proc. Seventh IJCAI", August 1981.] The use of single planes of light to measure the distance and orientation of objects has been reported several times. [Posdamer, J.L. and M.D. Altschuler, "Surface Measurement by Space-encoded Projected Beam Systems", "Computer Graphics and Image Processing" 181, 182, 1–7.] [Popplestone, R.J. and C.M. Brown, A.P. Ambler, and G.F. Crawford, "Forming models of plane and cylindrical faceted bodies from light stripes", "Proc. Fourth IJCAI", Sept. 1975.] [Oshima, M and Y. Shirai, "Object recognition using three dimensional information", "Proc. Seventh IJCAI", August 1981, 601-606.]

The use of multiple planes [Albus, J.E., M. Nashman, P. Mansbach and L. Palombo, "Six dimensional vision system", "Proc. SPIE" Vol. 336, 1982, 142–148.] [Okada, S., "Welding machine using shape detector", "Mitsubishi-Denki-Giho", Vol. 47-2, 1973, 157.] [Taenser, D., "Progress report on visual inspection of solder joints", M.I.T. A.I. Lab., Working Paper No. 96, 1976.] and multiple points [Nakagawa, Y., "Automatic visual inspection of solder joints on printed circuit boards", "Proc. SPIE" Vol. 336, 1982, 121–127.] [Duda, R. and D. Nitzan, "Low level processing of registered range and intensity data", Artificial Intelligence Center Technical Note 129, SRI Project 4201, March 1976.] of light to measure shapes and construct volumetric estimates of objects has also been widely reported. [Nitzan, D. A. Brain, and R,Duda, "The measurement and use of registered reflectance and range data in scene analysis", "Proc. IEEE", February 1977, 206–220.]

The use of segmented phase holograms to selectively deflect portions of an image wave front... is unusual. The holographic optical components used in this device, split tessellated segments of a returning wave front 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-orthogonal 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 wave front 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 wave front and the actual physical object.

References