| dc.description.abstract | The aim of this study is using a newly-developed method of intensity distribution of binary image (SdBD) for measuring surface roughness under dynamic turbulence with adaptive optics (AO) system. The focus of the study is (1) roughness measurement based on spatial average analysis of binary speckle image, (2) adaptive optics system for correcting aberrations induced by under dynamic turbulence and combinative interfaces of refractive-index-mismatch, (3) Adaptive optics-assisted imaging system for roughness measurement of metal surface.
(1) The speckle image was obtained by illuminating a laser beam and the reflected laser pattern image from a surface was binarizd and examined. The intensity distribution of binary image utilizes the combined effects of speckle and scattering phenomena. A new parameter of intensity distribution of binary image, SdBD has been proposed and the surface roughness parameter Ra of machined surfaces (ground) was correlated experimentally. Measurement results demonstrate an excellent correlation between the SdBD and Ra with correlation coefficient of 0.9706. The practicality of the proposed method In-situ roughness measurement was applied to six samples from roughness Ra 0.2 to 6.25μm (0.3 λ and 10 λ, where λ is diode laser wavelength) of steel through grinding process.
(2). This study experimentally demonstrate the capability of adaptive optics (AO) correction on aberrations induced by dynamic turbulence and combinative effects of multiple layers with convex/concave interfaces as well as Refractive-Index-Mismatch (RIM). A deformable mirror (DM) was used as a wavefront corrector, the wavefront aberration was detected by a Shack-Hartmann wavefront sensor. In the absence of AO correction scheme, induced low temporal turbulences can severely degrade the residual RMS (root-mean-square) errors of 0.26 μm. After real time closed-loop AO correction, we can improve wavefront to RMS of 0.07 μm, which not only compensate aberration error from induced disturbances, but also overall optical system. In addition, AO was found to be able to steadily compensate wavefront errors in less than 3 seconds. For Refractive-Index-Mismatch, we consider the aberration introduced by interfaces of RIM between water/oil and glass. After adaptive optics correction, we can improve wavefront with root mean square (RMS) of 2.17 to 0.17 μm for an interface between water and glass. As for the interface between oil and glass, we are capable of improving RMS of 0.24 to 0.10 μm. The benefits of AO correction are facilitated by removing low order of Zernike modes such as defocus and tip/tilt, which are found to be the two main contributing factors in serial arrangement of convex/concave interfaces and RIM. Adaptive optics system shows correction capability for multiple layers of different geometrical interfaces with RIM.
(3).This study proposes an integrated roughness measurement system based on adaptive optics (AO) and binarized analysis of speckle pattern images. The main purpose of this study is to demonstrate the necessity of AO compensation where disturbances of both heat and fluid flow exist. The speckle image was first obtained by illuminating a laser beam and the reflected laser pattern image from a surface was binarized to experimentally correlate with the intensity. In the absence of AO correction scheme, induced turbulences can severely degrade the residual RMS errors from 0.14 to 1.4 μm. After real time closed-loop AO correction, we can improve wavefront with RMS of 0.12 μm, which not only compensate aberration error from induced disturbances, but also overall optical system. In addition, AO with various gains in control system was investigated and a threshold gain value was found to be able to steadily compensate wavefront errors in less than 2 seconds. Measurement results of five steel samples from roughness Ra =0.2 to 3.125μm (0.3 λ and 5 λ, where λ is diode laser wavelength) demonstrate an excellent correlation between the SdBD and Ra with correlation coefficient of 0.9982.
We have developed an in-process measurement of surface roughness by combining an optical probe of laser scattering phenomena and adaptive optics for aberration corrections. The aim of this study is to demonstrate the necessity for AO compensation in regions containing turbulence of fluid flow. In the absence of the AO correction scheme, induced turbulence can severely increase the residual root mean square (RMS) error to 1.5 μm. After a real-time closed-loop AO correction, we can reduce the wavefront RMS error to 0.14 μm. Measurement results of five steel samples having roughness ranging from 0.2 to 3.125 μm (0.3λ and 5λ, where λ is the diode laser wavelength) demonstrate an excellent correlation between the peak power and average roughness with a correlation coefficient (R2) of 0.9967. The results were verified by the stylus method using three samples of steel (AISI 304) under various mechanical grinding conditions. The proposed AO-assisted system is in good agreement with less than 8.7% error values. Therefore, the developed system can be used as a rapid in-process roughness monitor/estimator to further increase the precision and stability of manufacturing processes in-situ.
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