For better machining and electrical characteristic, the complex surfaces topography of some delicate machining tools and electronic components should be acquired precisely, including shape and size of microstructure on surface of engineering material or precision component from microscopic view, and relationship between microstructures from macroscopic viewpoint, such as spaces, distribution and so on. This so called multiscale measurement has been greatly focusing by experts and scholars from home and abroad. People researched this novel measurement in several ways: (1) putting different sensors together, which had different resolution and measuring range; (2) applying software technology, include wavelet theory, fractal theory and image mosaicing technology, to solve this multi-scale measurement problem. However, it’s difficult to cooperate with many different sensors in multi-sensors measurement technology, and mathematical modeling is very complicated in software technology. This paper used Digital Micromirror Device (DMD) as a multiscale measuring tool, and a method of measurement on lateral dimension has been proposed. As an excellent optical modulation device, DMD could modulate incident light to line structure light. Owing to controlling flexibility of DMD, the parameters of the line structure light, include line width, light intensity and scanning frequency, could be modulated by programming. This project has solved the problem of measurement error due to the angle between line structure light and field of view of specimen, and the results of experiment proved that, this method by DMD acquired lateral dimension data conveniently.
An improved Canny operator based on the method of Maximum Classes Square Error is adopted to get a self-adaptive threshold for grain recognition. First, a grinding wheel surface was measured by using a vertical scanning white light interferometric (WLI) system and reconstructed with an improved centroid algorithm; then the grains were extracted using the proposed method based on the fact that the peak intensity difference (ΔI) between maximum and minimum intensities on interferometric curve from diamond is larger than that from bond due to different reflective characteristics of different materials; third the grain protrusion parameters are investigated for grinding performance analysis. The experiments proved that the proposed grain recognition method is effective and assessment parameters are useful for understanding grinding performance.
The axial resolution of parallel confocal measurement can be improved as the laser source added into the system, but extreme monochromaticity of laser beam will produce the Talbot effect, which is an effect of many images of point light array appear along the optical path direction, and it causes to distinguish the true in-focus image from lots of Talbot images difficultly, which means the confocal measurement can’t be carried on. The author researched factors of the influences for Talbot distance, and developed some methods to weaken the impact of the Talbot effect. A LED was added into the laser parallel confocal measurement system to find the in-focus image, and there were no Talbot images nearby to impede positioning, and then the laser beam was lead into the system to measure with high precision. The difference of location of the two in-focus images with laser and LED was about 11μm in the experiment, which was shorter than one Talbot distance in the system, and the result indicated that the in-focal could be distinguished with this method.