MICRO METROLOGY| CASE STUDY
<< Figure 4: Automatic definition of section lines perpendicular to the edge contour (a), 3D view of an edge area not yet sufficiently rounded (b), section profile with fitting circle (c), distribution of radius values over the edge area length (d). >>
Because of the high requirements regarding surface quality, certain surface regions of the connectors are finished in a manual process. Due to limited repeat accuracy, an accompanying, complete control of the decisive geometry features is absolutely necessary.
In comparison to the formerly applied tactile measurement methods, fringe projection offers several advantages. The measurement is optical and therefore contact-free. This avoids mechanical stress and the possibility of surface damage is greatly reduced.
The geometry is measured within very few seconds and at high spatial resolution. The device has a spatial resolution of 2.5 µm laterally and 0.2 µm vertically, a measuring field of 1.8 x 1.2 mm2 and a vertical range of 0.5 mm. The cutting edge module of the accompanying software ODSCAD allows for an automated measurement of the outer edge radius, based on a large number of virtual section lines across the edge (figure 4). According to the manufacturers, edge radii are approximated by circles, calculated by a special algorithm with integrated flank detection, originally developed for the characterisation of tool cutting edges. The calculated radius value (arithmetic average) can be directly compared to design specifications. Using pre-defined nominal values and tolerances, a direct good/bad indication for the specific connector or adaptor type can be displayed.
Berlin Heart’s experience with the system has proven the circle- fitting algorithm to be robust enough also for measurements of radii which are larger than usual in cutting tool edges. The also included analysis of section profiles and the 3D display of the edge delivers valuable information directly for the ongoing conditioning process as well. A second, touch-screen operated system has meanwhile been acquired for intermediate checks without obligatory documentation requirements.
At Berlin Heart, the MikroCAD System replaces the formerly used system for intermediate checks as well as final examination and approval of connectors by the Quality Assurance department.
The system both documents and manages measuring data in a database. For medical device industry, this database functionality assures the crucial traceability of all manufacturing steps for components, modules and systems.
GFMESSTECHNIK GmbH
www.gfm3d.com
The German version of this article was published in: QZ 4, 2012, pp.62-63; Carl Hanser Verlag, Munich.
39 | commercial micro manufacturing international Vol 6 No.6
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