PTB and the HIT Institute UOI (Center of Ultra-precision Optoelectronic Instrument) have developed special error
separation procedures for improving the measurement uncertainty of cylinder calibrations. Three glass cylinders, which
were custom-made by HIT, were selected to compare the performance and characteristics of the measurement
procedures. Both procedures effectively eliminate guidance errors of the measurement machines and lead to sufficiently
low measurement uncertainties.
The paper describes the manufacturing and dimensional measurements of high precision
work-pieces by PTB, which shall act as test masses (TM) for the satellite-based experiment
MICROSCOPE. The manufacturing involves turning of Ti alloys and PtRh10. The
measurements were made by in-process tactile probing, coordinate metrology, and form
measurement. The high geometrical demands of the project could be fulfilled on both the
manufacturing and the measurement sub-projects.
Form measurements of cylindrical objects are commonly done by mechanical sensing of the rotated specimen by a
stylus. The needed probing force could cause a deformation or an abrasion of the specimen. A new interferometric
measurement technique for form measurements of cylindrical objects with diameters between 0.1 and 2.5 mm is
presented. In this technique the specimen is measured contactless and no rotary table is needed. The specimen is placed
in the centre of an inverse conic mirror and is illuminated by an iodine-stabilized diode laser. The reflected light is
superposed under a slight angle with a reference beam and imaged on a CCD camera. The surface topography of the
specimen can be derived from the reconstructed spatial phase distribution, which is calculated by a spatial phase shifting
algorithm. In order to enhance the measurement range a second laser can be used to generate a synthetic wavelength.
This will allow the quantification of surface variations in the micrometer range with an aimed uncertainty of less than 0.1
&mgr;m. First results on phase measurements of different samples are presented and discussed.
The metrological concept and the optical probe system of the cylinder form coordinate measuring instrument (CMM)
MFU110WP is described. Optical and tactile scanning form and position measurement data of a variety of standards and
workpieces are discussed both in comparison to each other and to calibrated profiles of other measurement instruments.
New scanning techniques like helical and spiral shaped scanning are presented.
Very recently, in the context of measuring aspheres and complex surfaces with ultra-precision, a particular measurement principle was developed which determines the form (topography) of extended test samples by scanning measurements of curvature, being the reciprocal of the radius of curvature. The curvature sensor must be traceably calibrated with a low uncertainty. This back tracing can be done, first, by measuring radius of full spheres with a highly accurate sphere interferometer, second, by measuring roundness with highly accurate methods, and third, by measuring specially designed calibration aspheres. These procedures for traceably calibrating the curvature sensor will be described.