Along with the advances in technology and expansion of industrial applications, laser measurement technology has been widely used in various fields due to its characteristics such as non-contact, high-resolution and fast measurement speed. In this paper, two kinds of laser measurement methods are mainly studied. One is the particle sizing technique based on Fraunhofer diffraction theory. Fraunhofer diffraction-based instruments can accurately measure the size distribution of particles ranging from 2 μm to 1000 μm. The other one is dimensional measurement based on self-mixing interferometry. Self-mixing interferometry has been considered even more as a valid alternative to the classical optical instrumentations for its compact, low-cost and user-friendly setup. For the first part of this thesis work, the reconstruction method and experiments of narrow particle size distribution measurement were carried out based on the Fraunhofer diffraction. The main results are listed as follows: 1. The main methods of particle size measurement and the state-of-the-art of diffraction particle sizing were outlined. Traditional system and the traditional particle sizing algorithms for the Fraunhofer diffraction-based instruments were studied. Shortcomings of the traditional methods and systems in case of narrow particle size distributions were analyzed. 2. In order to improve the reconstruction accuracy, an iterative algorithm was introduced to reduce the deviation and the result of the dual integral inversion method was used as feedback. The PID controller was implemented in the control loop to generate the reconstructed distributions of the particles. The neural network PID and fuzzy PID were utilized to reduce the sensitivity to the initial values of the PID parameters, and the performance was verified by using numerical simulations. 3. In order to pick up the weak signals at large angles in the particle size measurement system, a modulated light was generated and the intensity values on the detectors were demodulated, followed by data acquisitions at high signal to noise ratios. Experiments were implemented on the standard particle suspension to evaluate the performance of the proposed particle sizing system. Experimental results showed that the proposed algorithm performs better than the dual integral algorithm, in cases of different background noises. For the second part of this thesis work, the self-mixing interferometry theory is used to measure the displacement and the speed of the target. The main contents are as follows: 1. By using the general theoretical model of self-mixing interferometry, the influence of model parameters on self-mixing interference signals is researched by numerical simulation. 2. A displacement measurement based on fringes counting is studied, and the basic measurement system based on self-mixing interferometry is set up. Both the simulated and the experimental results show the feasibility of this method. 3. A method oriented to the measure of the speed of a target is studied. The method based on a particular frequency-domain algorithm and has strong robustness. The feasibility and effectiveness of the method are verified by simulation and experiments.
Oltre ai progressi tecnologici e all'espansione delle applicazioni industriali, la tecnologia di misurazione laser è stata ampiamente utilizzata in vari campi grazie alle sue caratteristiche come la velocità di misurazione e l’alta risoluzione, nonché la possibilità di misure senza. In questo articolo vengono principalmente studiati due tipi di metodi di misurazione laser. Il primo è la tecnica di dimensionamento delle particelle basata sulla teoria della diffrazione di Fraunhofer. Gli strumenti basati sulla diffrazione di Fraunhofer possono misurare accuratamente la distribuzione dimensionale di particelle che vanno da 2 μm a 1000 μm. Il secondo riguarda la misurazione dimensionale basata sull'interferometria a retroiniezione. L'interferometria a retroiniezione è una valida alternativa alle classiche strumentazioni ottiche per la sua configurazione compatta, a basso costo e user-friendly. Per la prima parte di questo lavoro di tesi, il metodo di ricostruzione e gli esperimenti di misurazione della distribuzione delle dimensioni delle particelle strette sono stati effettuati sulla base della diffrazione di Fraunhofer. I risultati principali sono elencati come segue: 1. Sono stati delineati i principali metodi di misurazione delle dimensioni delle particelle e lo stato dell'arte del dimensionamento delle particelle di diffrazione. Sono stati studiati il sistema tradizionale e i tradizionali algoritmi di dimensionamento delle particelle per gli strumenti basati sulla diffrazione di Fraunhofer. Sono state analizzate le carenze dei metodi e dei sistemi tradizionali in caso di distribuzioni di dimensioni strette delle particelle. 2. Al fine di migliorare l'accuratezza della ricostruzione, è stato introdotto un algoritmo iterativo per ridurre la deviazione e il risultato del duplice metodo di inversione integrale è stato utilizzato come feedback. Il controller PID è stato implementato nell’anello di controllo per generare le distribuzioni ricostruite delle particelle. Il PID di rete neurale e il PID fuzzy sono stati utilizzati per ridurre la sensibilità ai valori iniziali dei parametri PID e le prestazioni sono state verificate utilizzando simulazioni numeriche. 3. Al fine di raccogliere i segnali deboli a grandi angoli nel sistema di misurazione delle dimensioni delle particelle, è stata generata una luce modulata e i valori di intensità sui rivelatori sono stati demodulati, seguiti da acquisizioni di dati ad elevati rapporti segnale / rumore. Per valutare le prestazioni del sistema di dimensionamento delle particelle proposto sono stati condotti diversi esperimenti con sospensione di particelle standard. I risultati sperimentali hanno mostrato che l'algoritmo proposto ha prestazioni migliori rispetto all'algoritmo a doppio integrale, in caso di rumori di fondo diversi. Per la seconda parte di questo lavoro di tesi, la teoria dell'interferometria a retroiniezione viene utilizzata per misurare lo spostamento e la velocità di un bersaglio remoto. I contenuti principali sono i seguenti: 1. Utilizzando il modello teorico generale dell'interferometria a retroiniezione, l'influenza dei parametri del modello sui segnali di interferenza è stata studiata mediante simulazione numerica. 2. È stato implementato un sistema di misura di spostamento basato sul conteggio delle frange e si è impostato un sistema basato sull'interferometria a retroiniezione che può essere applicato a diverse tipologie di misura. Sia i risultati simulati che quelli sperimentali confermano la funzionalità di questo approccio. 3. È stato studiato ed implementato un metodo di misura di velocità di un bersaglio, basato su un particolare algoritmo nel dominio della frequenza, che dimostra una notevole robustezza alle variazioni di ampiezza del segnale. La fattibilità e l'efficacia del metodo sono state verificate mediante simulazione ed esperimenti.
Measurements based on Fraunhofer diffraction theory and self-mixing interferometry
ZHANG, JIAWEN
2018/2019
Abstract
Along with the advances in technology and expansion of industrial applications, laser measurement technology has been widely used in various fields due to its characteristics such as non-contact, high-resolution and fast measurement speed. In this paper, two kinds of laser measurement methods are mainly studied. One is the particle sizing technique based on Fraunhofer diffraction theory. Fraunhofer diffraction-based instruments can accurately measure the size distribution of particles ranging from 2 μm to 1000 μm. The other one is dimensional measurement based on self-mixing interferometry. Self-mixing interferometry has been considered even more as a valid alternative to the classical optical instrumentations for its compact, low-cost and user-friendly setup. For the first part of this thesis work, the reconstruction method and experiments of narrow particle size distribution measurement were carried out based on the Fraunhofer diffraction. The main results are listed as follows: 1. The main methods of particle size measurement and the state-of-the-art of diffraction particle sizing were outlined. Traditional system and the traditional particle sizing algorithms for the Fraunhofer diffraction-based instruments were studied. Shortcomings of the traditional methods and systems in case of narrow particle size distributions were analyzed. 2. In order to improve the reconstruction accuracy, an iterative algorithm was introduced to reduce the deviation and the result of the dual integral inversion method was used as feedback. The PID controller was implemented in the control loop to generate the reconstructed distributions of the particles. The neural network PID and fuzzy PID were utilized to reduce the sensitivity to the initial values of the PID parameters, and the performance was verified by using numerical simulations. 3. In order to pick up the weak signals at large angles in the particle size measurement system, a modulated light was generated and the intensity values on the detectors were demodulated, followed by data acquisitions at high signal to noise ratios. Experiments were implemented on the standard particle suspension to evaluate the performance of the proposed particle sizing system. Experimental results showed that the proposed algorithm performs better than the dual integral algorithm, in cases of different background noises. For the second part of this thesis work, the self-mixing interferometry theory is used to measure the displacement and the speed of the target. The main contents are as follows: 1. By using the general theoretical model of self-mixing interferometry, the influence of model parameters on self-mixing interference signals is researched by numerical simulation. 2. A displacement measurement based on fringes counting is studied, and the basic measurement system based on self-mixing interferometry is set up. Both the simulated and the experimental results show the feasibility of this method. 3. A method oriented to the measure of the speed of a target is studied. The method based on a particular frequency-domain algorithm and has strong robustness. The feasibility and effectiveness of the method are verified by simulation and experiments.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/148987