Measurement of steep edges and undercuts in confocal microscopy.

Confocal microscopy is widely used to measure the surface topography of specimen with a precision in the micrometer range. The measurement uncertainty and quality of the acquired data of confocal microscopy depends on various effects, such as optical aberrations, vibrations of the measurement setup and variations in the surface reflectivity. In this article, the influence of steep edges and undercuts on measurement results is examined. Steep edges on the specimen's surface lead to a reduced detector signal which influences the measurement accuracy and undercuts cause surface regions, which cannot be captured in a measurement. The article describes a method to overcome the negative effects of steep edges and undercuts by capturing several measurements of the surface with different angles between the surface and the optical axis of the objective. An algorithm is introduced which stitches different angle measurements together without knowledge of the exact position and orientation of the rotation axis. Thus, the measurement uncertainty due to steep edges and undercuts can be avoided without expensive high-precision rotation stages and time consuming adjustment of the measurement setup.

Flexible calibration and measurement strategy for a multi-sensor fringe projection unit.

In this paper, a strategy for the calibration and the measurement process of a multi-sensor fringe projection unit is presented. The objective is the development of an easy to use calibration and measurement procedure. Only one simple geometrical calibration target is needed and the calibration of the projection unit is not mandatory. To make the system ready for measurement tasks, a common world coordinate system is established. The geometrical camera calibration is derived with respect to the world frame. Note, that the cameras of the system are under Scheimpflug condition which is considered using a modified camera model. Furthermore an additional optimization step of the extrinsic camera parameters is presented to compensate the uncertainties of the calibration target. For completeness, a suitable calibration strategy for the projection unit is given, too. Additionally, the quality of the presented strategy is demonstrated by experimental data.