Integration eines optischen 3D-Sensors in ein Koordinatenmessgerät für die Digitalisierung komplexer Oberflächen
The aim of this dissertation was the integration of a fringe projection system in a coordinate measuring machine. As a result large and complex workpieces can be digitalized fast, flexible and accurate. By digitalization of complex or large workpieces with the fringe projection system it is not possible to get the measuring data of the complete surface in one view. So it is necessary to merge sub-measuring fields respectively the point-clouds. In this dissertation workpiece surfaces are considered large or complex, if the workpiece that has to be digitalized is larger than the measuring field of the fringe projection system. If workpieces cannot be digitalized in one view because of reflection or shadowing effects, they are also considered large or complex. The registration (merging) of the sub-measuring fields results from the defined sensor position to the measuring object in the coordinate measuring machine. For this procedure it is necessary to know the relative position of the sensor coordinate system and the coordinate system of the CMM to each other. This is warranted by a special, that was developed in this dissertation, calibration procedure of the fringe projection system referring to the coordinate measuring machine. The digitalization of complex shaped workpieces demands a high flexibility in the positioning of the sensor to the measuring object. In this way all surface areas can be touched with the sensor in an optimal way. Therefore, the calibration procedure is realized in five degrees of freedom: three translatory degrees of freedom to implement the linear movement of the fringe projection system in three orthogonal directions inside the measuring volume of the CMM as well as two rotational degrees of freedom. On the one hand the rotational degrees of freedom allow the possibility of rotation of a clamped measuring object. On the other hand the rotation of the fringe projection system around the measuring object can be realized. The calibration procedure is afflicted with an uncertainty, which has an effect on the precision of the registration process. The resulting residual error in the total point-clouds results in height offsets between the partial point-clouds. Based on the residual error of the registered point-clouds, the concept of roughly-registered point-clouds was introduced in the framework of this dissertation. The minimization of the existing residual error in the roughly-registered point clouds was reached with an additional fine registration on basis of an iterative-closest-point algorithm. In particular different minimization methods based on simulated annealing, simplex procedure or conjugate-gradient method were examined regarding attainable precision. The fine registration was realised sucessfully both for norm-geometries like spheres or planes and for free form surfaces and was successfully implemented in the registration software. The present work makes a contribution to the multi-sensor application of coordinate measuring machines. For integration of the optical 3D-sensor a multi-sensor-coordinate measuring machine of the company "Werth Messtechnik" was used. Factory-made it consists of a tactile sensing device, an image processing unit and a video autofocus sensor. By the integration of the fringe projection system it could be expanded the functionality of the multi-sensor coordinate measuring machine with the objective of the flexible and exact three-dimensional surface digitalization.
info:eu-repo/classification/ddc/530, Physik, optische 3D-Messtechnik, Streifenprojektion, Koordinatenmesstechnik, Oberflächendigitalisierung, Reverse Engineering
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