Franco Francini

Hartmann test modification for measuring ophthalmic progressive lenses

We describe a modified verion of the Hartmann test in which the pattern of the holes is replaced with a circular scanning laser beam. A position-sensitive detector is used to acquire the coordinates of the deflected beam. Significant data are obtained when the Fourier transform of the detector output signals is considered. Application of this test method to the mapping of optical parameters of ophthalmic progressive addition lenses is presented. Prismatic deviation, spherical power, and astigmatism are measured with appropriate accuracy.

Phase-shifting speckle interferometry: a noise reduction filter for phase unwrapping

We present a noise reduction filter for the phase unwrapping of data from phase-shifting speckle pattern interferometry. This filter is effective in reducing the noise in wrapped phase maps without affecting the edges of the phase jumps, so that a simple and fast unwrapping algorithm can be used. We also discuss a data analysis strategy, includ- ing a routine for the recovery of unwrapping errors. The filter perfor- mance has been evaluated on real data from a fiber optic phase-shifting speckle interferometer, which we built for the analysis of out-of-plane deformations. The phase shifting is introduced by current modulation of the diode laser source. Some results relative to the analysis of very noisy phase measurements are presented.

Neural networks for the optical recognition of defects in cloth

A fast system to reveal the presence and type of fabric defects during the weaving process is developed. Since the fabric is similar to a 2-D grid, its defects are clearly observed in the changes in its optical Fourier transform (OFT), which appears stationary while the fabric is moving across the loom. Previous work, based on the statistical parameters of the OFT, showed that the presence of faults can be detected when only global changes in the images are considered. We show that by selecting a small subset of pixels from the image as input to a neural network, fabric defects can not only be detected but also successfully identified. A knowledge-based system could conceivably be constructed to use this information to resolve problems with the loom in real time, without the need for operator intervention.

On-line textile quality control using optical Fourier transforms

Fourier transformation and spatial filtering offer the possibility of detecting structural defects in a fabric. In this paper a method based on an optical Fourier transform technique during the weaving process is described. Significant variations in the Fourier pattern occurring in the presence of defective fabric are recognised with a CCD sensor joined to an electronic hardware system performing a simple algorithm.

Defect detection in textured materials by optical filtering with structured detectors and self‐adaptable masks

An optical method using Fourier transformation and spatial filtering is used to reveal defects in textured materials in real time. New optical structured filter types were developed including a self-adaptable mask made of photochromic polymers. The characteristics of these materials make possible very promising applications in pattern recognition such as that represented by a fabric.

Moire with one grating and a photodiode array

La structure discrete et periodique de la barrette de photodiodes a suggere son utilisation comme reseau de reference pour produire un effet de moire et pour le balayer en meme temps

Evaluation of Surface Slope Irregularity in Linear Parabolic Solar Collectors

The paper describes a methodology, very simple in its application, for measuring surface irregularities of linear parabolic collectors. This technique was principally developed to be applied in cases where it is difficult to use cumbersome instruments and to facilitate logistic management. The instruments to be employed are a digital camera and a grating. If the reflector surface is defective, the image of the grating, reflected on the solar collector, appears distorted. Analyzing the reflected image, we can obtain the local slope of the defective surface. These profilometric tests are useful to identify and monitor the mirror portions under mechanical stress and to estimate the losses caused by the light rays deflected outside the absorber.

Pointing Sensors and Sun Tracking Techniques

Every optical system for sunlight concentration requires following the sun in its movement. The sun tracking method is essentially chosen on the base of collection geometry and optical system configuration. A simple, useful, and original technique to realise sun tracking is proposed. It is based on a double guiding system using two complementary procedures. A passive tracking device performs a preliminary collector orientation. Then an active tracking system realises its fine positioning and adjustments exploiting an optical pointing sensor. The core of this active tracking device is the sun finder. Pointing sensors for fibre-coupled, CPV (Concentrating Photo voltaic), and linear collectors are presented, illustrating in detail the working principle and practical use. All sensors were optically characterised in laboratory, under controlled and reproducible conditions. Some field tests completed the experimentation evaluating the sensors performance in outdoor working conditions.

Weaving defect detection by Fourier imaging

An optical configuration for the detection of faults was developed and tested. The optical fourier transformation is the basic working principle of the system. When good fabric passes in front of the optical system the Fourier image, captured by the camera, shows well defined spots corresponding to the spatial frequencies of the tissue. If a defect occurs during production on the loom, the pattern changes significantly and a defect is easily detected in real time. A very simple electronic image processing based on thresholding and binary histograms allows to obtain very encouraging performance for its applicability to the looms. A compact device has been realized and tested in real working conditions on the loom.

Automatic inspection with optical position sensors

Abstract The aim of this paper is to present the optical position sensors (PSD) based on a lateral photoeffect with respect to its characteristics. The optical triangulation (OT) being exploited as the sensing technique will be examined. Three experiments employing PSD and OT techniques for monitoring surface profiles in mechanical, photographic, and automotive fields are presented. They are sources for understanding the potential of these detectors as simple, efficient, and readily available means of automatic inspection in a wide range of fields of application.