MICRO METROLOGY | ARTICLE
<< Figure 2:Optical roughness
measurement, in comparison to tactile standards. Left: tactile measured nominal
averages for the roughness standards used (0.09 resp. 0.23 µm). Middle: values for 10 different lines on the standards, an optical measurement taken within a few seconds. Right: average of the optical measured
values. The deviations of the single lines are mainly resulting from the local roughness differences of the standards themselves. >>
The UV-LED light source is extremely durable while the digital light projection system, or DLP, is free from long term drift or aging. These factors help to minimise running costs and eliminate the need for maintenance. This new UV technology also has little effect on the initial equipment costs, hence the economic advantages are fully retained.
The light source also has a useful spectral component in the visible range, thus the projection light can be used for easy sample positioning. Moreover, the wavelengths used are entirely uncritical in terms of ionisation or eye safety.
The UV technology has a large effect on image quality for many technical surfaces. This comprises better reflection behaviour with metal surfaces as well as a lower volume penetration with partially transparent or opaque samples, such as certain plastic or ceramic materials.
Measuring very small roughness as well as the entire geometry Together with the high resolution, this also enables the measurement of very small roughness, together with the entire geometry, even up to measurement area sizes way over 1 mm. Another big advantage is the large measuring distance of at least 30 mm, greatly facilitating the handling of measuring samples. An important application of the new instrument is the edge measurement of cutting tools. The optimisation of these cutting edges, which is dependant on the material to be worked, is important for critical parameters such as tool life, cutting speed and surface quality. The optimal edge radius range for best results is usually very narrow and thus the cutting edge needs to be constantly controlled. Using an optical measurement system means that this work is fast and comprehensive. Automatic alignment of 3D data, together with automatic calculation of hundreds of radii along the edge deliver fast, comprehensive and reliable results, also independent of operator factors.
Roughness measurement Certain applications require an assessment of roughness, in addition to edge geometry. The MikroCAD Plus enables the measurement of very low levels of roughness over large measurement areas, while still retaining high measurement speed and hence high throughput.
Established roughness measurement methods such as by mechanical contact probes have a limited lateral resolution caused by the size and shape of the test stylus, which keeps it from entering into valleys smaller than its own shape. Optical devices, however, can provide a much higher lateral resolution. For a direct comparison of measurement results, the stylus radius has to be simulated by appropriate area filtering of the optically measured data.
A comparison with tactile results from several roughness standards, using the method of ‘wide section lines’ (an adaptation of the optical result to the lower lateral resolution of the tactile probe) is shown in figure 2. The conformity proves to be excellent, even for very small roughness values.
Figure 3 shows a typical segment of an electric shaver blade edge, as a 3D reconstruction from measured data. In spite of the sharp edge angle, even large parts of the flanks are measured in just one image.
<< Figure 3: Complete 3D
In conclusion, the MikroCAD Plus represents a significant step forward in the measurement of small surface structures. It can be used for the precision measurement of micro structures of any kind, in particular for the highly important quality control of tool cutting edge radius and roughness.
GF MESSTECHNIK GMBH
www.gfm3d.com
reconstruction from measured data of an electric shaver blade (single 3d capture). Typical edge radii involved in
such samples are 1-3 µm, with steep edges. Several hundred edge radii as well as the surface roughness were
measured within 10 seconds, using the MikroCAD Plus. >>
19 | commercial micro manufacturing international Vol 7 No.2
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