Diffractive optical element-based profilometer for surface inspection

Spagnolo, Giuseppe Schirripa; Ambrosini, Dario

doi:10.1117/1.1331270

Cited by 23 publications

(1 citation statement)

References 31 publications

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“…The grating acts as a beam divider, therefore interference fringes are formed in the superposition region of the two exiting beams. It can be shown 13,14 that, using a phase saw-tooth grating as a beam divider, good diffraction efficiency is obtained. Furthermore, the light intensity on a plane at a distance R from the grating (and distance Lp from the source) represents straight fringes, which are parallel to each other (Young's fringes).…”

Section: The Fringe Generatormentioning

confidence: 99%

Simple smartphone-based artworks diagnostics by Moiré method and a diffractive optical element

Daffara,

Mazzocato,

de Rubeis

et al. 2023

Optics for Arts, Architecture, and Archaeology (O3A) IX

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The moiré method is a well-known tool in NDT; it is based on the principle of superposition of two sets of lines or gratings, which creates a moiré pattern that can reveal surface deformations caused by underlying defects or damage. In this paper, we propose a simple artwork diagnostic using the moiré method and a smartphone. The technique is based on coupling the acquisition of fringe patterns by the smartphone camera to an effective fringe generator. The fringe generator consists of a diffractive optical element (DOE) illuminated by a laser diode; this optical device proved to be very effective thanks to its ability to produce in a simple way grid patterns of different spatial frequencies. The smartphone camera is used to capture the grid patterns and to store them in the cloud. We demonstrate the proposed approach by giving some preliminary experimental results.

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Section: The Fringe Generatormentioning

confidence: 99%

Simple smartphone-based artworks diagnostics by Moiré method and a diffractive optical element

Daffara,

Mazzocato,

de Rubeis

et al. 2023

Optics for Arts, Architecture, and Archaeology (O3A) IX

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Fringe projection techniques: Whither we are?

Gorthi

Rastogi

2010

Optics and Lasers in Engineering

1,148

376

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During recent years, the use of fringe projection techniques for generating three-dimensional (3D) surface information has become one of the most active research areas in optical metrology. Its applications range from measuring the 3D shape of MEMS components to the measurement of flatness of large panels (2.5 m × .45 m). The technique has found various applications in diverse fields: biomedical applications such as 3D intra-oral dental measurements [1], non-invasive 3D imaging and monitoring of vascular wall deformations [2], human body shape measurement for shape guided radiotherapy treatment [3,4], lower back deformation measurement [5], detection and monitoring of scoliosis [6], inspection of wounds [7,8] and skin topography measurement for use in cosmetology [9,10, 11]; industrial and scientific applications such as characterization of MEMS components [12,13], vibration analysis [14,15], refractometry [16], global measurement of free surface deformations [17,18], local wall thickness measurement of forced sheet metals [19], corrosion analysis [20,21], measurement of surface roughness [22,23], reverse engineering [24,25,26], quality control of printed circuit board manufacturing [27,28,29] and heat-flow visualization [30]; kinematics applications such as measuring the shape and position of a moving object/creature [31,32] and the study of kinematical parameters of dragonfly in free flight [33,34]; biometric identification applications such as 3D face reconstruction for the development of robust face recognition systems [35,36]; cultural heritage and preservation [37,38,39] etc.One of the outstanding features of some of the fringe projection techniques is their ability to provide high-resolution, whole-field 3D reconstruction of objects in a non-contact manner at video frame rates. This feature has backed the technique to pervade new areas of applications such as security systems, gaming and virtual reality. To gain insights into the series of contributions that have helped in unfolding the technique to acquire this feature, the reader is referred to the review articles in this special issue by Song Zhang, and Xianyu Su et al.A typical fringe projection profilometry system is shown in Fig 1. It consists of a projection unit, an image acquisition unit and a processing/analysis unit. Measurement of shape through fringe projection techniques involves (1) projecting a structured pattern (usually a sinusoidal fringe pattern) onto the object surface, (2) recording the image of the fringe pattern that is phase modulated by the object height distribution, (3) calculating the phase modulation by analyzing the image with one of the fringe analysis techniques (such as Fourier transform Figure 1: Fringe projection profilometry system method, phase stepping and spatial phase detection methodsmost of them generate wrapped phase distribution) (4) using a suitable phase unwrapping algorithm to get continuous phase distribution which is proportional to the object height variations, and finally (5) calibrating the system for m...

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