الفهرس يوجد فقط 14 صفحة متاحة للعرض العام
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المستخلص
Restoring the part shape rapidly and accurately is a basic step when applying reverse
~ineering procedures.
Non-contact techniques can restore shape rapidly using low cost equipment, yet they lack high accuracy. Tactile techniques can scan surfaces with highest accuracy, at the expense of scanning time. Besides, higher cost equipment and intensive labor are needed. The solution lies in intewat~ a contact and a non-contact technique in one system capable of digitizing free form surfaces rapidly and accurately. In this study, an integrated vision and coordinate measurement system is introduced, and some major problems encountered when using these systems are investigated and appropriate solutions are developed.
To scan a tree form surface on a coordinate measuring machine, a ~h cost analog probe can be used, otherwise the lower cost touch trigger probe (TIP) is usually used. The application ofTTP is always encountered with the tip radius error resulting trom the unknown tip/sample contact point. In this case, the scanned point cloud must be post-processed to compensate for the tip error. Compensation of these errors requires the knowledge of the surface normal vectors of the examined part. In this study a new method is introduced to compensate for the tip radius error using the vision-acquired surface normals information.
The proposed system consists of two phases, a non-contact phase and a contact phase. At the ” DOn-contact ,phase, the _part reflectance parameters are estimated based on the Pho~ , illumination model. Then surface normal vectors are recovered through the application of pbotometric stereo theory. At the contact phase, the points cloud gathered by the TTP
Ittached to a CMM is processed to compensate for tip error using the vision-acquired slope Researchers used a sphere of the same material and surface finish as the examined part to m the problem of reflectance parameters estimation. This o_ption is not always available or
.. In the proposed method, the part reflectance parameters are estimated using the
itself by observin~ the intensity reflected off a surface of known orientation while to light sources at specmc directions.
~orithms have been develo_ped to detect a surface element of known orientation (e.g. ntal), estimate the reflectance parameters of the examined surface, recover its surface vectors, and compensate for tq, radius error. A complete simulation was performed to
” the developed algorithms and recorded good results. An experimental setup was built
\Wify the validity of the developed model and the resuhs are promising.
The intewation of contact and non-contact techniq.ues proved to be beneficial The applicability of the photometric stereo theory is enhanced through using the part itself to estimate its reflectance parameters and optimizing the used light source orientation relative to the object (light source slant angle LSSA). Experimental resuhs were compared to the simulation ones, ~ood correlation is observed between the two sets of results. Solvin~ the probe tip error problem also increases the applicability of the low cost TIP.