Optical sensors are gaining increasing importance in the field of coordinate metrology. Especially for micro range
measurements, different optical sensor principles (e.g. white-light interferometers, autofocus sensors, and confocal
microscopes) are used. Micro measurement covers the detection and evaluation of measurands for length, size and form
of geometrical structures in the range between 1 μm and 1 mm. These reduced dimensions lead to increased
requirements for the applied measuring technique and the verification of the measurement systems. The Physikalisch-
Technische Bundesanstalt (PTB) works intensively on the development of suitable measurement standards and test
procedures to make a broader industrial use of CMMs with optical sensors possible. The test procedures are analogue to
the well-established tests for classical coordinate measuring machines (CMMs). For this purpose, adequate and
miniaturized reference standards were manufactured, calibrated and tested considering the specific characteristics of
optical sensors. This paper gives a summary of this work. Advice on future developments is given.
Optical measurements are performed in coordinate metrology in a wide range of applications, ranging from large-scale
workpieces with dimensions of several meters down to microstructures with &mgr;m-dimensions, using a large number of
different measurement devices and sensors. These different devices and sensors must be tested to check their compliance
with the specifications, to trace back the measurement results and to compare different devices. Thus, appropriate
procedures and measurement standards (artefacts) are necessary. We present test procedures and artefacts for optical
measurement systems similar to the well-known test procedures for classical tactile coordinate measuring machines
(CMMs) according to the international standard ISO 10360. It is important that the surface characteristic of the
artefacts is cooperative to the sensor. Appropriate artefacts were realized and tested. The main focus of this paper is on
micro-artefacts. Furthermore, task-related standards to trace back specific measurement tasks were developed. By means
of micro-contour artefacts, the measurement characteristics on critical geometries can be evaluated and compared. By
means of a micro-gear standard, the measurement uncertainty on micro-planetary gear can be evaluated. The
measurement deviations of measurement systems in the automotive industry can be determined with the special artefacts
to test sensors for inline measurements.
Optical microsensors are used to carry out a great variety of coordinate metrology tasks on micro-parts. For the testing of
such sensors calibrated artefacts are needed. The existing micro-artefacts have smooth surfaces and can therefore only be
used for white-light interferometry and tactile probing. For sensors based on triangulation (structured light, autofocus,
confocal...), artefacts with optically rough surfaces are needed. Consequently artefact surfaces with a small mechanical
roughness but diffuse optical scattering (high optical roughness) are required. For this purpose, different production
techniques to roughen smooth surfaces and to form parts having rough surfaces are tested successfully at the
Physikalisch-Technische Bundesanstalt (PTB). The roughness Ra is about 0.3 &mgr;m. A suitable artefact set is currently
being developed in compliance with the existing standards. A first micro-artefact (micro-contour artefact) is already
commercially available. By means of the developed artefacts it also becomes possible to analyze for different optical
sensors the dependence between the uncertainty and the measured surface as well as the surface slope.
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