Taking Optical Form Measurements Which Adhere to GPS Standards

One significant factor in the determination of measurement process capability is the measurement set-up of the optical micro-coordinate measurement device. The measurement set-up illustrates significant aspects, including use of the correct objective, illumination, as well as vertical and lateral resolution. These should relate to the measurement task and the tolerances detailed in the technical drawing.

Standards for Geometrical Product Specifications (GPS) are being adopted by the industry more and mroe. One of these GPS standards, which is of key significance, is defined in DIN EN ISO 1101, describing the authentication of form and positional tolerances. GPS standards recommend the definition of correct measurement set-up and the verification of its measurement process capability before conducting a 3D measurement.

To determine a potential measurement set-up correctly, it is helpful to make use of prior experience based on the same measurement task and the technical specification of the measurement system supplier. Alicona recommends that a potential measurement setup based on given tolerances in regard to the specified measurement task be defined. Lastly, the measurement set-up can be verified and, if needed, optimized following the procedure of MSA or Measurement System Analysis. For the measurement set-up, it is very important to determine the evaluation modes, optimal resolution, sample positioning and illumination.

The following figure demonstrates the model method by which identify a measurement set-up:


Automation of Measurement Task

Once the measurement set-up has been determined and confirmed according to MSA, Alicona measurement instruments allow automatic measurement and evaluation of surface roughness and dimensional characteristics. This takes account of of roughness parameters alongside GD&T values such as straightness, flatness, roundness, and surface profiles (described according to DIN ISO 1101 below).


Any longitudinal section line taken out of the surface should be contained amid two parallel lines. Tolerance zone: Two parallel lines with a distance t apart (tolerance) in a plane that includes the axis of the surface.


Flatness indicates how flat a surface is without reference to any other datums or features, and is explicitly known as a flat surface, which is an areal feature. Tolerance zone: Two parallel planes a distance t (tolerance) apart.


Roundness, also known as circularity, is restricted by two concentric circles with a difference in radii in the considered cross-section. Tolerance zone: the considered cross-section is limited by two circles on a conical or cylindrical surface at a distance t (tolerance) apart along the surface.

Surface Profile

Surface Profile, also known as profile of a surface, is limited by two surfaces building a 3-dimensional tolerance zone in the region of any theoretically exact geometrical form. Tolerance zone: the geometrical form is limited by, two surfaces enveloping spheres of diameter t (Tolerance), the centers interconnecting the theoretically exact geometrical form.

This information has been sourced, reviewed and adapted from materials provided by Alicona Imaging GmbH.

For more information on this source, please visit Alicona Imaging GmbH.


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