In 2012 a well-known company in the field of high precision optics assigned the University of Applied Sciences Deggendorf to determine a suitable parameter field for the active fluid jet polishing (AFJP) process in order to reach a surface accuracy of at least lambda / 5. The active fluid jet polishing is a relatively new and an affordable sub-aperture polishing process. For a fast and precise identification of the parameter field a considered design of experiment is necessary. The available control variables were the rotational speed of the nozzle, the distance between the test object and the jet, the feed rate, the material of the pin inside the nozzle and the material of the test object itself. In order to reach a significant data density on the one hand and to minimize the number of test runs on the other hand a meander shaped tool path was chosen. At each blank nine paths had been driven whereby at each path another parameter combination was picked. Thus with only one test object nine parameter settings may be evaluated. For the automatized analysis of the tracks a software tool was developed. The software evaluates ten sections which orthogonally intersect the nine tracks on the test-lens. The significant measurement parameters per section are the width and the height of each path as well as the surface roughness within the polished tracks. With the aid of these parameters and further statistical evaluations a suitable parameter field for the goal to find a constant and predictable removal spot was determined. Furthermore up to now over 60 test runs have been successfully finished with nine parameter combinations in each case. As a consequence a test evaluation by hand would be very time-consuming and the software facilitates it dramatically.
KEYWORDS: 3D metrology, Photovoltaics, Time metrology, Data analysis, Interferometers, Applied sciences, Sensors, Optical tracking, Matrices, Algorithm development
Together with the group of interferometry based systems, coordinate measurement machines are an essential part of the
metrology in the modern optical industry.
Coordinate measurement machines commonly consist of a multi axes framework. They are designed to operate in a
defined three dimensional work zone, where every possible point can be reached by the measurement tool tip. This basic
design principle leads to some interdependent challenges. A detailed measurement result needs a large amount of
measurement points to detect even minor irregularities and short-wave errors. However, a rising of the amount of
measurement points increases the corresponding measurement time analogous. On the other hand, the extended operation
time increases the access of undesired thermal and dynamic influences, which cause multiple errors to the measurement
result. Furthermore, modern production processes need rapid metrology systems to aid the machining time.
This paper discusses results obtained by operating with three different measurements in order to find an agreement
between speed and certainty of the coordinate measurement machine. The topographic coordinate measurement system TII-
3D had been re-developed at the University of Applied Sciences Deggendorf in the laboratory of optical Engineering and it
is equipped with three different measurement strategies. The first mode, the Track-Mode operates in concentric circles on
top of the surface of the object to be measured. The Spiral-Mode measures along a dynamic moveable spiral line and the
Section-Mode produces multiple cross-sections.
In the field of precision optics the interferometry is the most applied measurement method to test spherical and flat
objects. In principle, a standard interferometer setup is limited to these surface geometries, but interferometric systems
may be modified with the aid of CGH’s or the stitching technology. As a consequence aspherical shapes and even
freeform optics are measurable up to a certain extent. In an interferometric measurement the measured variable is the
optical path difference (OPD) between the reference wave and the test wave. Based on the detected OPD the surface
error of the test object is calculated by phase shifting methods for instance. It is evident, that the error from the reference
surface affects the determination of the test object surface error. One option to face this problem is the calibration of the
system prior to the measurement. For this the determination of the reference surface error may be realized with the aid of
a two sphere test or a random ball test e.g. [1]. In the well-known SSI-technology from QED technologies the reference
surface error is calculated on the basis of the sub-measurements. Due to the self-calibrating nature of the QED stitching
principle [2-4] a calibration of the system prior to the measurement is not necessary. The University of Applied Sciences
Deggendorf has implemented a similar algorithm to estimate the reference wave front error, or to be exact the error of
the whole optical system, based on a multiple set of sub-measurements. This paper describes the applied algorithm in
detail and discusses the results. To verify the implemented tool the results are compared to the outcomes of the QED
stitching software.
The manufacturing of optical components more often requires grinding and polishing of non rotational symmetric aspheres
or freeform surfaces. Although there are measurement techniques available for small diameters of some 10th of
mm the measuring of larger surfaces is not or only by extreme efforts feasible. Based on the specification for a large
mirror in semi professional and scientific astronomy with up to 1.2 m diameter and a relative aperture of F# < 1.5 a final
measurement approach for the measurement of radius and shape deviation (parameters of code number 3 of DIN ISO
10110) is described. The combination and evaluation of different sensors and measurement methods for the measurement
of high-precision optical surfaces with concave radii of 3.000 mm to infinity is examined and presented. A reproducibility
and absolute accuracy of better l/12 (PV) and l/40 (rms) is to be achieved. The absolute maximum radius difference
should be smaller than 0,1 %. Thus, also the measurement of aspheric surfaces and free-form surfaces are investigated.
For the measurement of large surfaces, up to 100 individual sub apertures with up to 100 Million Points are recorded by
deflectometric or interferometric measurement techniques and composed algorithmically to a total surface area. A precision
granite portal with multifunctional device carrier will be presented as precise movements are crucial for all tests.
The realization of the required accuracy in the portal-measurement device is verified, documented and compared with a simulation. Results on specimens of 200 and 430 mm diameter are evaluated. The measurements were taken by deflectometry and interferometry on the described test equipment. The validation of the samples with various interferometric procedures was performed. The obtained results are presented, analyzed and discussed.
The usage of stitching technologies in the interferometrical precision optics measurement technique becomes more and
more popular. There exist already a few metrology stages providing the stitching principle, such as, for example, the well
known Sub-Aperture Stitching Interferometer for Aspheres (SSI-A1) [1] [2] [3] from QED technologies. For
measurements with the SSI-A the greatest measurable diameter of the test object is approximately 280 mm [1]. As a
consequence the University of Applied Sciences Deggendorf develops an own measuring system in order to test large
telescope mirrors with a diameter of more than one meter which should be ready for application in 2012. The expected
positioning accuracy of the measuring patches is significantly lower in comparison with the high-accurate SSI-A.
Therefore a cross-correlation based translation detection tool is implemented in our current software solution. Since the
metrology system is currently being established the SSI-A and the μPhase2 interferometer from TRIOPTICS are used as
input data sources for the software development. Further this paper discusses the robustness of the translation detection
tool and presents a stabilisation method of the stitching result with the aid of physical markers.
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