A Tunable Diode Laser Absorption Spectroscopy setup with Wavelength Modulation has been used together with a synchronous sampling imaging sensor to obtain two-dimensional transmission-mode images of oxygen content. Modulated laser light from a 760nm DFB source has been used to illuminate a scene from the back while image frames were acquired with a high dynamic range camera. Thanks to synchronous timing between the imaging device and laser light modulation, the traditional lock-in approach used in Wavelength Modulation Spectroscopy was replaced by image processing techniques, and many scanning periods were averaged together to allow resolution of small intensity variation over the already weak absorption signals from oxygen absorption band. After proper binning and filtering, the time-domain waveform obtained from each pixel in a set of frames representing the wavelength scan was used as the single detector signal in a traditional TDLAS-WMS setup, and so processed through a software defined digital lock-in demodulation and a second harmonic signal fitting routine. In this way the WMS artifacts of a gas absorption feature were obtained from each pixel together with intensity normalization parameter, allowing a reconstruction of oxygen distribution in a two-dimensional scene regardless from broadband transmitted intensity. As a first demonstration of the effectiveness of this setup, oxygen absorption images of similar containers filled with either oxygen or nitrogen were acquired and processed.
A device based on Tunable Diode Laser Absorption Spectroscopy has been developed for non-invasive evaluation of gaseous oxygen concentration inside packed food containers. This work has been done in the context of the SAFETYPACK European project in order to enable full, automated product testing on a production line. The chosen samples at the end of the manufacturing process are modified atmosphere bags of processed mozzarella, in which the target oxygen concentration is required to be below 5%. The spectrometer allows in-line measurement of moving samples which are passing on a conveyor belt, with an optical layout optimized for bags made of a flexible scattering material, and works by sensing the gas phase in the headspace at the top of the package. A field applicable method for the calibration of this device has been identified and validated against traditional, industry standard, invasive measurement techniques. This allows some degrees of freedom for the end-user regarding packaging dimensions and shape. After deployment and setup of the instrument at the end-user manufacturing site, performance has been evaluated on a different range of samples in order to validate the choice of electro optical and geometrical parameters regarding sample handling and measurement timing at the actual measurement conditions.
An optical system for the automatic recalibration of large machine tools during the machining process has been developed. The system provides an error signal during operation in order to compensate for structural deformations of axis and sliding parts. Those signals are used to reach a global positioning error below 50 microns on 3-axis translation stages, having range of several meters. One collimated diode laser beam has been mounted to the machining table reference system. Three resistive-type 2D-position-sensing devices are used to locate the beam on each axis. Before the first two sensors in the optical path, the beam is split by a wedge pentaprism in two secondary beams. The first one propagates linearly along the sensor for the displacement measurement. The second one is deflected with a fixed 90° angle and defines the sampling direction of the next axis. By duplicating the system using a second pentaprism on the latter deflected beam, three axis are monitored. In order to avoid any active electronic devises on the milling head, a passive corner cube is placed on the side of the head. Laser beam is then back reflected on a final position-sensitive sensor mounted in proximity of the second pentaprism. Additional channels consisting in laser beams back-reflected by mirrors on similar position sensing devices were used to acquire angular measurements as well. The tests performed on the prototype demonstrate the capability of mapping the actual deviations from the ideal linear translation with an error of 25 um along the full axis travel.
The very large machine tools now available for applications ranging from aerospace to composite material castings
present a new set of challenges when trying to match the traditional machining accuracies of the mechanical
An optical system for the automatic recalibration of the machine during the machining process has been developed.
While conventional linear and rotary optical encoders are used to control axes positioning, and their resolution is
already more than compliant with the needed accuracies, our optical system provides a further error signal during
operation in order to compensate for structural deformations of axis and sliding parts. Those signals are used in
order to reach a global positioning error vector under 50 microns on a 3-axis translation stage. The system has been
installed on a test machine, with a total range on the 3-axis of 3, 1.6 and 1.2 meters. The device increases ranging
measurement accuracy by decreasing the dependence of the position to the temperature variation and other
deformations. To achieve such results, collimated diode lasers and 2D position-sensing devices have been installed
to the machine. In order to provide signals which are least affected by electrical noise, transimpedance amplifiers
and analog to digital converters have been integrated close to the detectors. The tests performed on the prototype
demonstrate the capability of mapping the actual distance from the ideal linear translation with an error of 25 um
along the full axis travel for a tracing capability of ±3.5 mm in both directions on each of the three detectors. This result is within the requirements of the end users, manufactures of travelling column type boring and milling
We present the recent results obtained by a system which measures both 3D shape and multispectral texture of artistic
and architectural cultural assets. The system consists on a rangefinder device which acquires the range and a visible
scanning spectrograph for colour texture analysis. This technique is applied to the acquisition of the cycle of Stories of
Maria, a frescoed lateral chapel painted by Girolamo Tessari in 1523-1526 located in the church of S. Francesco in
In this paper, an integrated system based on a phase-shift laser scanning for measuring shape and a imaging spectrograph for measuring color is described. The system is designed for acquisition of large areas, such as chapels or frescoed walls. The phase-shift laser range-finder provides accurate distance measurement, up to 10 meters, pointing at most target surfaces through the measurement of the phase shift. The acquisition of a complete object is performed point by point by a 2D scanning. The imaging spectrograph measures the spectrum of the light coming from on a narrow rectangular region having width and height equal to the image of the entrance slit projected on the object plane. A complete 2D image is acquired by scanning the region in the direction perpendicular to the slit height. The merging of these multiple acquisitions yields the complete spectral and spatial description of the color of the object.