Three-dimensional (3D) inspection in the factory requires precision and speed. While customers can select from a wide spectrum of high-precision sensors, the real challenge today is "speed." We discuss the speed of 3D sensors in a general context to provide an understanding of why high-resolution 3D sensors deliver significantly fewer 3D points per second than the available camera pixel rates suggest. The major cause of low speed is the large number E of required exposures due to the unavoidable depth scanning. Through the example of structured-illumination microscopy (SIM), we demonstrate how E can be minimized without reducing precision. We further demonstrate a lateral scanning strategy that operates at a significantly higher speed for macroscopic measurements by avoiding explicit depth scanning. This paper is a follow up on an earlier paper about the precision limits of SIM and exploits the earlier results.

No abstract

The fabrication of aspheres and freeform surfaces requires a high-precision shape measurement of these elements. In terms of accuracy, interferometric systems provide the best performance for specular surfaces. To test aspherical lenses, it is necessary to adapt or partially adapt the test wavefront to the surface under test. Recently, we have proposed an interferometric setup with a diffractive zoom-lens that includes two computer generated holograms for this purpose. 1 Their surface phases are a combination of a cubic function for the adaption of aberrations and correction terms necessary to compensate substrate-induced errors. With this system based on Alvarez design a variable defocus and astigmatism controlled by a lateral shift of the second element is achieved. One of the main challenges is the calibration of the system. We use a black-box model 2 recently introduced for a non-null test interferometer, the so called tilted wave interferometer 3 (TWI). With it, the calibration data are calculated by solving an inverse problem. The system is divided in the two parts of illumination and imaging optics. By the solution of an inverse problem, we get a set of data, which describes separately the wavefronts of the illumination and imaging optics. The main difference to the TWI is the flexible diffractive element, which can be used in continuous positions. To combine the calibration data of a couple of positions with the exact placement, we designed alignment structures on the hologram. We will show the general functionality of this calibration and first simulation results.

No abstract