3D measuring systems for sophisticated measuring tasks

Depending on the measuring tasks, the Confovis measuring systems can capture data by the confocal procedure (structured illumination) and the focus variation principle, and fuse data. This is of particular advantage when a sample contains areas of poor contrast such as polished surfaces and also steep flanks. By fusing data, the results of both measurements can be combined with each other in excess of the accuracies of the drive axles in that special algorithms compare the data quality of the different points with each other.

Structured Illumination Microscopy (SIM) and Focus variation in one scan head

The patented confocal measuring technique “structured illumination microscopy“ (SIM) is robust in two respects: For one, the measuring device does not contain any moving parts and, for another, the measuring results are very robust because optical errors caused by inaccuracies of deflecting mirrors or multi-pinhole disks cannot occur. Other drawbacks, for example, due to polarized light required for an FLCoS (ferroelectric liquid crystal on silicon) display, do not exist. With the Confovis technique, a phase-shifted grid is imaged on the sample and the differential contrast evaluated. The contrast of the images is maximum the moment at which the surface of the sample is at the focal position. To determine the topography of the sample, the focus is moved relative to the surface. Thereby are generated optical sections from which the 3D point cloud is then composed.

Confocal measuring technology for roughness measurements

  • Resolution down to 3 nm
  • Measuring results that are virtually free of artefacts
  • Flat measurement for high measurement speed and recording the entire relevant structure
  • Extensive 3D data exclusively with realistic measurement points (no compensation for measuring points on the part of the software)
  • Optical scanning with a high degree of accuracy (cf. tactile devices)
  • Only slight coherency and speckle effects (depending on technology)

When using focus variation, the limited depth of focus is utilised to generate optical sections in the area of the sharp image. It is only in the area of the sharp image that the contrast is at its maximum level.

The height information required for 3D imaging is acquired using the variation in focus height. The sections are subsequently compiled to form the 3D point cloud.

Focus variation for form measurements

  • High flank angles can be measured
  • Contour and form measurements are quick and simple
  • Touchless measurement (optical method) can be used throughout the entire process chain

    Two measurement principles via one optical beam path

    Merging measuring date in one global coordinate system

    The confocal structured illumination measuring method can also be used to measure highly reflective surfaces at a high resolution. Steep edges are measured with the focus variation method because better results can be achieved with the illumination provided by the annular light emitter along the cutting edge. This is why the combination of both measurement methods are the solution for capturing important geometric dimensions (wedge angles, cutting edge radius) and high-resolution roughness measurements.

    The confocal structured illumination technique allows for high-resolution measurements for areas in which roughness must be measured.
    Analysis of cuttung edge of an indexable insert with structured illumintion microscopy
    The focus variation method can be used to measure edges with angles of inclination. Data density is here not high enough for roughness measurements.
    Measuring an indexable insert with focus variation
    Combined measuring data of a cutting edge of a chip removing tool obtained by focus variation (yellow point cloud) and a confocal (blue point cloud). The combination of the two point clouds takes advantage of the benefits of both procedures.

    Measuring the finest roughnesses – with high-precision confocal measuring technology

    When it comes to measuring roughness, confocal measuring technology has an advantage, as it offers optical scanning with a high level of accuracy. In the process, the Confovis measurement systems can achieve a height resolution of 3 nm (in line with VDI 2655) and a lateral resolution of 267nm (according to Rayleigh) in confocal mode, subject to the illumination wavelength.  The following example shows that, with confocal measuring technology (Structured Illumination Microscopy), a reliable measurement is possible and a significantly better resolution can be achieved on the surface of the roughness standard KNT4070/03 from Halle measured here.

    The following example of a usual milling cutter (item:YG-1, E5E50060) shows that no comprehensive tool analysis is possible with one measurement principle alone. For the determination of roughness values in the flute, only the high-resolution confocal measurement technology provides reliable measurement values. The focus variation principle is ideal for measuring forms and contours, but not for roughness measurements.

    Extended tool analysis at an example of a screw tip

    When measuring micro tools such as screw taps or for small milling tools, the user uses the work piece's axis of rotation in connection with the global coordinate system in order to use the best measurement method to measure each of the relevant areas with a high level of precision and without compromises.