Testing fast aspheric convex surfaces with a linear array of sources

Campos‐García, Manuel; Díaz-Uribe, Rufino; Granados-Agustín, Fermín

doi:10.1364/ao.43.006255

Cited by 28 publications

(10 citation statements)

References 4 publications

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“…Papers [2][3][4] describe cases where profile irregularities deteriorate the image in the reflector defective points, which appear as areas of different intensity. Other procedures refer to the analysis of a calibrated mask whose image is reproduced by the concentrator [5][6][7][8]. A method using a colored pattern, projected on a screen through the concentrator, is explained in reference [9].…”

Section: Introductionmentioning

confidence: 99%

Evaluation of Surface Slope Irregularity in Linear Parabolic Solar Collectors

Francini

Fontani

Sansoni

et al. 2012

International Journal of Photoenergy

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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.

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Section: Introductionmentioning

confidence: 99%

Evaluation of Surface Slope Irregularity in Linear Parabolic Solar Collectors

Francini

Fontani

Sansoni

et al. 2012

International Journal of Photoenergy

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“…7, we show spot diagrams for several positions of the images of point objects at the lamps; we obtained the plot assuming that the diaphragm has an aperture with a 10-mm diameter (the aperture of the CCD lens used for the measurement). 3 On the other hand, in the plane of the paraxial image we found that the aberration of coma is predominant, but its magnitude is so small (< 8 µm) that it cannot be resolved by the CCD. In Fig.…”

Section: Aberrations Due To a Steep Surfacementioning

confidence: 70%

“…2 However, it can be difficult to implement these methods for fast aspheres. In a previous work 3 Campos-García et. al.…”

Section: Introductionmentioning

confidence: 94%

Error analysis in the test of fast aspheric convex surfaces with a linear array of sources

Campos‐García

Díaz-Uribe

2005

Eighth International Symposium on Laser Metrology

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To analyze the error obtained in the evaluation of the shape of the surface with the method that uses a linear array of sources, we performed a numerical simulation introducing Gaussian random errors in the coordinates of the centroids of the bright spots on the image plane, and in the coordinates of the sources (apertures of the mask). Here we found that to measure the quality of the surface with accuracy lower than 8 µm we have to place the sources with accuracy better than 0.5 mm, and measure the coordinates of the centroids with accuracy better than 0.5 pixels. Additionally, we performed an analysis of the aberrations effects on the evaluation due to a steep surface and the CCD camera lens. Here, we found that in the best image plane for all the image points the main aberration is astigmatism, which is symmetric and do not change the position of the centroid. Also, the analysis of the CCD camera lens was performed experimentally by the star test for different positions of the object in the visual field and for different apertures of the CCD diaphragm; here, in the worst case we observe changes in the positions of the centroid smaller than 0.46 pixels. In both cases, the aberrations are very small and have no influence on the determination of the centroids of the images. Finally, we analyzed the influence of the scattering at the surface have onto the evaluation. For this experiment, we observe that this effect can be considered as a very random error on the final evaluation of the surface.

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“…A positive lens is used to collect and focus these thin pencils of rays onto the CCD sensor. The effects of the aberrations introduced by the positive lens of the camera have been well explained in [18] in which coma and spherical aberrations are considered; the distortion is taken into account by calibrating the camera lens, with a method described below. Departures from a regular array of points on the CCD or image are indicative of deformations of the surface under test.…”

Section: Null-screen Methodsmentioning

confidence: 99%

“…Then the reflected ray, whose direction is given by Eq. (18), intersects the reference surface [Eq. (16)] at P s x s ; y s ; z s (see Fig.…”

Section: Surface Shape Evaluation Methodsmentioning

confidence: 99%

Surface shape evaluation with a corneal topographer based on a conical null-screen with a novel radial point distribution

et al. 2015

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In order to measure the shape of fast convex aspherics, such as the corneal surface of the human eye, we propose the design of a conical null-screen with a radial point distribution (spots similar to ellipses) drawn on it in such a way that its image, which is formed by reflection on the test surface, becomes an exact array of circular spots if the surface is perfect. Any departure from this geometry is indicative of defects on the evaluated surface. We present the target array design and the surface evaluation algorithm. The precision of the test is increased by performing an iterative process to calculate the surface normals, reducing the numerical errors during the integration. We show the applicability of the null-screen based topographer by testing a spherical calibration surface of 7.8 mm radius of curvature and 11 mm in diameter. Here we obtain an rms difference in sagitta between the evaluated surface and the best-fitting sphere less than 1 μm.

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Testing fast aspheric convex surfaces with a linear array of sources

Cited by 28 publications

References 4 publications

Evaluation of Surface Slope Irregularity in Linear Parabolic Solar Collectors

Evaluation of Surface Slope Irregularity in Linear Parabolic Solar Collectors

Error analysis in the test of fast aspheric convex surfaces with a linear array of sources

Surface shape evaluation with a corneal topographer based on a conical null-screen with a novel radial point distribution

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