Surface profile control on solar concentrators is fundamental since the mirror can be imperfectly
manufactured. Optical profilometric measurements are generally addressed to detect small localised
irregularities. The paper presents an optical profilometer for linear solar collectors, which are typically
employed in thermal plants and more recently in concentrating photovoltaic systems. The profilometer
includes a source of parallel rays and a target placed at the collector focal distance. It was developed
simulating profile measurements on linear parabolic mirrors; then the method was validated by tests on a
practical realisation. The device examines the reflector surface operating on a plane transversal to the linear
collector axis; then the detection is repeated displacing the optical profilometer along the collector axis. This
experimentation allowed to deeply examine and reduce the errors of the measurement procedure.
This paper describes the development of an innovative scuba mask, which can be flooded by water and is able to provide
a correct sight both underwater and in air, thus overcoming the drawbacks of traditional diving masks. The working
principle of this new flooded device corresponds to the underwater telescope. Optical design analyses have demonstrated
that it is able to provide a well corrected vision in both underwater and above-water conditions. The development of the
optical configuration for the mask is illustrated presenting various stages of the optical project. The device has been
optically and mechanically designed and then realized. Beyond the optical requirements, the optical design takes into
account compactness, low fragility, diver comfort and other practical aspects in view of a possible mass production.
The measurement of the size distribution of a particles mixture is utilised in industrial and biomedical fields. In the current method, the laser (or monochromatic) light scattered by the sample at various scattering angles is measured; then, a simplified analysis uses the diffraction theory in order to calculate the distribution of the particle size. In particular, a set of n equations is generated: n is the number of measurements that differ by the scattering angle (it acts as control parameter), and the unknown quantities are the ratios between the number of particles that fall in a specified size range and the total number of particles (obviously n must be not less than the number of the predefined size ranges). That requires the use of a dedicated setup and accurate angular measurements. Our method requires only two measurements on the sample, carried out by a spectrophotometer equipped with an integrating sphere. The diffuse spectral transmittance (or reflectance) and the total spectral transmittance (or reflectance) are measured and their ratio is calculated, then it is generated an equations set similar to the previous, but integrated on the angular range of the diffuse spectral transmittance measurement: now we utilise as control parameter the wavelength (then, each equation has a different value of wavelength), while the unknown quantities are the same of the previous method. Due to the fact that both methods use the same equations set, they have the same applicability limits, but our method has the advantage that we can use a standard commercial spectrophotometer.
The paper presents a study to detect the three-dimensional profile of an object using a technique
based on the projection of colour-coded lines. The accessibility at low-cost of projectors and digital
photographic cameras has approved the employment and the development of these techniques. They
provide information concerning the profile through the acquisition of a couple of images. The first
one concerns a reference plane and it is captured only once, while the second one refers to the
The proposed methodology simplifies the individuation of homologous lines within the two images,
when grating projection techniques are employed. Even though these methods are conceptually very
simple, they are rarely applied because of this difficulty in stating the correspondence between
observed deformation and projected line. The attribution of a different colour to every single line, or
to a set of them, introduces an element useful for their selection.
After the image acquisition, the data pertaining to the profile are extracted examining the image by
means of an algorithm developed in Matlab language for this application. The research work is in
progress beyond the results presented in this paper, which already represent a excellent starting
point for further studies and evolutions of the technique.
A system exploiting solar energy, by means of optical collectors and fibres, has been applied for indoor
illumination. The project has been called "The Sunflowers" for the property of solar collectors to track solar
position during the day. Every "sunflower" contains several solar collectors, each of which is coupled to an
optical fibre. The "Sunflower" is provided of mechanical systems and electric accessories for solar tracking. The
light focused by the solar collector can be used in two possible ways: for internal illumination with direct solar
light; otherwise it can be accumulated for lighting when the sun is not present.
The first function is obtained coupling the optical collector to an optical fibre, which transports the solar light in
selected points within the showcases. The second one consists in focusing solar light on a photovoltaic cell of the
last generation type with high efficiency. In this configuration the photovoltaic cell converts the focused light into
electric energy to be used for illumination in case of sun absence.
A demonstrative installation has been realised applying this solar illumination system to museum lighting: a
prototype has been tested in a prestigious museum in Florence.
Optical collectors for sunlight concentration on small surfaces have been experimentally studied to evaluate their
correspondence with the optical design. Measurement set-up and testing methodologies have been developed and
adapted mainly to provide the optical characteristics that are fundamental for the concentration on small surfaces.
The collectors are lenses of different type, with various shape and dimensions. They are optically designed to be realised
in plastics and to be applied to concentrate the solar light on surfaces with dimensions of the order of 1 cm. Furthermore
the optical control compares several samples of the same collector, realised with different production procedures and
materials. The tests are aimed to verify the correspondence between the performance of the realised samples and the
theoretical features of the designed collector. A specific study has been dedicated to the application to light concentration
on PhotoVoltaic cells, whose requirements are a square-shaped image with uniform light distribution and maximum
The described instrumentation and measurement procedures examine total collection efficiency and energy distribution
in the collector image plane. A particularly accurate and critical procedure performs the study of the image uniformity,
separating the light contributions due the different collector regions. All measurements and in particular the "image
contribution test" requires to adapt the testing set-up for each collector shape.
The problem of developing the lateral surfaces of a 3D object can arise in item inspection using automated imaging systems. In an industrial environment, these control systems typically work at high rate and they have to assure a reliable inspection of the single item. For compactness requirements it is not convenient to utilise three or four CCD cameras to control all the lateral surfaces of an object. Moreover it is impossible to mount optical components near the object if it is placed on a conveyor belt. The paper presents a system that integrates on a single CCD picture the images of both the frontal surface and the lateral surface of an object. It consists of a freeform lens mounted in front of a CCD camera with a commercial lens. The aim is to have a good magnification of the lateral surface, maintaining a low aberration level for exploiting the pictures in an image processing software. The freeform lens, made in plastics, redirects the light coming from the object to the camera lens. The final result is to obtain on the CCD: - the frontal and lateral surface images, with a selected magnification (even with two different values for the two images); - a gap between these two images, so an automatic method to analyse the images can be easily applied. A simple method to design the freeform lens is illustrated. The procedure also allows to obtain the imaging system modifying a current inspection system reducing the cost.
We describe an experimental procedure for the reconstruction of the geometrical parameters of a reflecting surface. The method is based on the projection of a luminous pattern constituted by colored points. The successive chromatic selection reduces the complexity of the acquired image. We show that the colors of the points comprising the pattern are modified by the combined effect of the CCD camera and the projection system. In some situations, the chromatic components of the pattern points can generate ambiguity. Consequently, the number of colors to be projected and their chromatic separation must be studied to enable the simultaneous projection of an elevated number of points and colors.
Shape detection on objects of large and huge dimensions has always represented a challenging task, mostly by the practical point of view due to the size of the related measurement equipment. When the tested object is a mirror the measurements is additionally complicated, since the classical techniques of structured light cannot be directly applied. The method proposed in this paper has been applied to measure the curvature of a deformable mirror of 1-meter diameter for a heliostat plant. The mirror shape is obtained studying the spatial variations of a grating projected on the sample and reflected by it on a screen. The measurement set-up employs a PC projector and a digital camera. The results of this curvature assessment are compared to those derived from a simulation obtained by an optical design programme.