Fast and accurate in-line areal surface topography measuring instruments are required to control the quality of microscale manufactured components, without significantly slowing down the production ...process. Full-field areal optical surface topography measurement instruments are promising for in-line or on-machine measurement applications due to their ability to measure quickly, to access small features and to avoid surface damage. This paper presents the development and integration of a compact optical focus variation sensor for on-machine surface topography measurement mounted on to a hybrid ultraprecision machine tool. The sensor development is described and a case study involving the on-machine dimensional measurement of the depth of hydrophobic microscale features, including microchannels and micro-dimples, is presented. Comparisons of results between the on-machine measurements obtained by the developed sensor and a desktop focus variation microscope are presented and discussed. The comparison results show that the developed focus variation sensor is able to perform on-machine dimensional measurement of microscale features within sub-micrometre accuracy.
Highly accurate measurements of small structures are challenging in many applications. An example is the optimization of the hole geometry in fuel injectors. Due to the small size of the structure, ...tactile approaches are insufficient while standard optical measurement systems cannot provide data on complex geometries. In this paper, a new purely optical 3D micro-coordinate machine – the µCMM of Alicona and its accuracy by determining the maximum permissible translatory and stationary error is presented. Moreover, we demonstrate that the focus variation principle allows 3D measurements of such small components by presenting the measurement and evaluation of micro injection holes.
In this work, the performance of a focus variation instrument for measurement of areal topography of metal additive surfaces was investigated. Samples were produced using both laser and electron beam ...powder bed fusion processes with some of the most common additive materials: Al-Si-10Mg, Inconel 718 and Ti-6Al-4V. Surfaces parallel and orthogonal to the build direction were investigated. Measurement performance was qualified by visually inspecting the topographic models obtained from measurement and quantified by computing the number of non-measured data points, by estimating local repeatability error in topography height determination and by computing the value of the areal field texture parameter Sa. Variations captured through such indicators were investigated as focus variation-specific measurement control parameters were varied. Changes in magnification, illumination type, vertical resolution and lateral resolution were investigated. The experimental campaign was created through full factorial design of experiments, and regression models were used to link the selected measurement process control parameters to the measured performance indicators. The results indicate that focus variation microscopy measurement of metal additive surfaces is robust to changes of the measurement control parameters when the Sa texture parameter is considered, with variations confined to sub-micrometre scales and within 5% of the average parameter value for the same surface and objective. The number of non-measured points and the local repeatability error were more affected by the choice of measurement control parameters. However, such changes could be predicted by the regression models, and proved consistent once material, type of additive process and orientation of the measured surface are set.
Draft ISO specification standards on the calibration of areal surface topography measuring instruments require a determination of the measurement noise and residual flatness error. However, due to ...the effect of the instrument transfer function of focus variation microscopes, it is not possible to use every material measure with the ISO-recommended procedure. A practical approach to estimating measurement noise and flatness deviation for focus variation microscopes is presented in this paper and example measurements are given.
Adaptive shape from focus with an error estimation in light microscopy Helmli, F.S.; Scherer, S.
ISPA 2001. Proceedings of the 2nd International Symposium on Image and Signal Processing and Analysis. In conjunction with 23rd International Conference on Information Technology Interfaces (IEEE Cat,
2001
Conference Proceeding
Light microscopy enlarges the viewing angle while decreasing the depth of focus. This leads to mainly blurred images if the specimen being observed consists of significant height changes. In computer ...vision, solving this problem is known as 'shape from focus'. Algorithms exist that perform both the calculation of a sharp image and the recovery of the three dimensional structure of the specimen. In this paper, three classic approaches for detecting sharp image regions are evaluated. Three new so called focus measures are introduced and are compared to the classic approaches. A new adaptive reconstruction scheme for calculating range images as well as sharp images is presented. Experimental results on synthetic and real data demonstrate the performance of the proposed algorithm.
The focus variation method uses vertical scanning with limited depth of focus. Because of its ability to measure steep flanks and its robustness in relation to different materials, focus variation ...enables the measurement of roughness and form at the same time.
PDF
