Development of Moire machine vision

Three dimensional perception is essential to the development of versatile robotics systems in order to handle complex manufacturing tasks in future factories and in providing high accuracy measurements needed in flexible manufacturing and quality control. A program is described which will develop the potential of Moire techniques to provide this capability in vision systems and automated measurements, and demonstrate artificial intelligence (AI) techniques to take advantage of the strengths of Moire sensing. Moire techniques provide a means of optically manipulating the complex visual data in a three dimensional scene into a form which can be easily and quickly analyzed by computers. This type of optical data manipulation provides high productivity through integrated automation, producing a high quality product while reducing computer and mechanical manipulation requirements and thereby the cost and time of production. This nondestructive evaluation is developed to be able to make full field range measurement and three dimensional scene analysis

360-deg profilometry: new techniques for display and acquisition

Two optical methods are proposed for shape measurement and defect detection of curved surfaces in the form of a complete 360- deg profile of the object. The first one is the standard structured light approach. Display of the resulting data is the emphasis of this section. The second approach uses modulated structured light with a scanning digital camera for faster and simpler data acquisition. Quantitative processing is done off-line while real-time moire produces enhanced display of the defects for qualitative analysis.published_or_final_versio

A study of model deflection measurement techniques applicable within the national transonic facility

Moire contouring, scanning interferometry, and holographic contouring were examined to determine their practicality and potential to meet performance requirements for a model deflection sensor. The system envisioned is to be nonintrusive, and is to be capable of mapping or contouring the surface of a 1-meter by 1-meter model with a resolution of 50 to 100 points. The available literature was surveyed, and computations and analyses were performed to establish specific performance requirements, as well as the capabilities and limitations of such a sensor within the geometry of the NTF section test section. Of the three systems examined, holographic contouring offers the most promise. Unlike Moire, it is not hampered by limited contour spacing and extraneous fringes. Its transverse resolution can far exceed the limited point sampling resolution of scanning heterodyne interferometry. The availability of the ruby laser as a high power, pulsed, multiple wavelength source makes such a system feasible within the NTF

Real-time analysis keratometer

A computer assisted keratometer in which a fiducial line pattern reticle illuminated by CW or pulsed laser light is projected on a corneal surface through lenses, a prismoidal beamsplitter quarterwave plate, and objective optics. The reticle surface is curved as a conjugate of an ideal corneal curvature. The fiducial image reflected from the cornea undergoes a polarization shift through the quarterwave plate and beamsplitter whereby the projected and reflected beams are separated and directed orthogonally. The reflected beam fiducial pattern forms a moire pattern with a replica of the first recticle. This moire pattern contains transverse aberration due to differences in curvature between the cornea and the ideal corneal curvature. The moire pattern is analyzed in real time by computer which displays either the CW moire pattern or a pulsed mode analysis of the transverse aberration of the cornea under observation, in real time. With the eye focused on a plurality of fixation points in succession, a survey of the entire corneal topography is made and a contour map or three dimensional plot of the cornea can be made as a computer readout in addition to corneal radius and refractive power analysis

High precision optical measurement methods

Two wavelength techniques become very interesting for absolute distance measurement. It has been shown, that a synthetic wavelength can be generated by two shorter ones, leading to techniques for measuring optically rougher surfaces. The theory is based on the assumption that the optical path difference is to be compared with the synthetic wavelength. Therefore optically rougher surfaces can be measured and furthermore the unambigiuty range can be extended. Heterodyne interferometry is a powerful tool for high precision distance measurements and vibration analysis. Double heterodyne techniques lead to improvements with respect to environmental disturbances and to absolute distance measuring procedures. To measure the topography of optically rough surfaces fringe projection, short coherence techniques as well as confoacal methods oblique incidence and 2λ interferometry are possibilities to overcome some of the limitations pointed out. The absolute distance measuring technique can further be combined with a technique for topography measurements

Quality assessment of book covers using shadow moiré technique

Shadow moiré method is often used in various areas for measurement of displacements, such as orthopedics, PCB warpage measurement and others. In this article, we propose a method for quality assessment of book covers using shadow moiré technique. Qualitative and quantitative approaches are used to estimate the quality of the book cover. In order to get a qualitative estimation, a manual count of fringes indicates a presence of the distortions of the book cover. In the second case, quantitative estimation of the displacements on the book cover can be made by applying centerline identification technique

Projection moire measurement of glass specimens retrofitted with safety film

Protection of buildings and critical public infrastructure against blast load has been recently improved by retrofitting glass windows with a safety film. As the exact physical mechanisms of the interaction between glass and safety film are not quite well understood, intensive research is conducted on the properties of this assembly. The loadings on the glass/film assembly are typically dynamic (blast, wind pressure, impact), so the lab tests are done on a drop weight set-up, where a mass is falling on a retrofitted glass plate. In this work, the drop weight setup was combined with pattern projection (moire) technique to study the time history of the out-of-plane deformations of the glass/film assembly. The fringe pattern, projected on the back side of the specimen, was generated by means of a sinusoidal phase grating under divergent high intensity infrared illumination. The whole process was recorded with a high speed camera. Local routines based on fast Fourier transform were used to process the captured images, and to extract the phase. The exact out-of-plane displacements were calculated by means of calibration based on previous shape measurements of several different objects with known dimensions

Optical methods for surface measurements : state of the art

Die Einsatzgebiete der optischen Meßtechnik haben sich durch die Einführung entsprechender Bildverarbeitung ausgeweitet. Neben der Triangulation und den Moire-Verfahren bieten sich interferometrische Verfahren für die hochgenaue Messung an; ein großes Potential, das noch nicht voll ausgenutzt wird. Ansätze zur Reduzierung der Störanfälligkeit, aber auch der Auflösung werden diskutiert.Different optical methods can be used for distance and topography measurement. The range and sensitivity need to be selected. The methods are contactless and fast. Interferometric methods are sometimes, however too sensitive with respect to environmental disturbances and roughness of technical objects. Furthermore surface roughness leads to unwanted speckles to be taken care of by the analysis and information processing. Methods will be developement measure topography of optically rough surfaces. Obligue incidence and 2λ interferometry are possibilities to overcome some of the limitations