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C. Dorn, F. Bleicher:
"OPTASENS Combination and evaluation of different sensors and measuring methods for the precision form-measurement on optical surfaces";
Report for Cornet; 2009; 55 pages.

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 10 mm the measuring of larger surfaces is not or only by extreme efforts feasible.
The results of earlier tests show clearly that it is necessary to use different methods for measuring in different stages of the manufacturing process. The technical target of the project is the combination of different measurement methods in order to proof the accuracy of large (up to 800mm in diameter) optical surfaces for final zonal correction polishing techniques like MRF or AFJP. This could be established by using high precision (accuracy about 50 nm) tactile methods and optical methods as they are described by different principles (confocal-chromatic sensors, interferometry, Shack-Hartmann-Sensors, deflectometry or others).
In this complementary combination the tactile system will be used to characterize the macro geometry and the non-tactile methods to measure the local geometry, both with high precision in several stages in a new hierarchical measurement setup. The stitching of local measurement patches will be based on the knowledge from previous stages about the global surface form.
Major tasks and work packages in realization are:
. Design and evaluation of different sensors and setups for the global measurement of the data points and the local measuring patches.
. Mathematical and algorithmic combination of the different measurement methods by stitching of local measurement patches in order to get a high precision global form of the surface.
. Evaluation of mechanical influences on the measurement principle and design of appropriate components and modules. Simulation and design of the components in terms of e.g. stiffness and thermal accuracy.
. Integration in a test setup.
. Test and proof on known surfaces and sample-parts.

Manufacturing, especially in Europe, is facing high pressure to perform in terms of operating efficiency and quality. Innovative production concepts, as well as high performance technologies are needed in order to keep up with rising international competition. The request of optical free form surfaces in highest possible quality for optical applications is increasing. These elements are used in small up to large quantities in special applications such as telescopes or head up displays.
For standard sized elements the optical industry has to refer to commercially available extremely expensive US or Japanese measuring machines. For the newly requested larger size of optical elements, which is the main focus in this project, the optical industry has no access to the existing technology in Japanese and US universities or in the big companies in Europe.
The results of the project offer the ability to develop further on their own measuring equipment for their production requests to the project partners - widely independent of the size of the optical elements. The machine tool and measurement device manufacturers (mostly SME´s) can use the modules that can be built into their products. Investigations performed in this project cannot be carried out by any one of the European optical SME companies due to their volume and complexity. But the results would offer the access for machine manufacturers and as well for optics manufacturers as users of the developed measurement technology to a newly emerging market of high precision freeform optical elements, which today is closed for them due to the missing measurement technology.
Thus the recommended project in hand represents particular importance especially for the SME´s as they usually do not have access to the results of measurement technology improvements gained by the big companies and they are not able to carry out the development of this process besides their business.

The developed principles can be used for other measurement tasks such as measurements on large freeform surfaces like car surfaces such as body parts or wind shields or in general lacquered surfaces.
A project consortium of three countries (Austria, Germany and Hungary) and four R&D partners is planned.
The project´s management is performed by Mechatronic Cluster Oberösterreich.
The major tasks of the R&D partners are as following:
Technical University Vienna: Simulation of system behavior and design of modules and the whole system set-up
University of Passau: Development of algorithms for stitching of measurement patches in a hierarchically structured measuring process and mathematical reconstruction of the surface.
University of Applied Science Deggendorf: Development of a tactile senor system for the global form information, build of the test set-up and case studies on known and unknown surfaces.
University of Budapest: Evaluation and test of the different sensor systems of the hierarchically structured measuring process.