Shape measurement by means of imaging using partially coherent illumination - part 2 (Spice II)

• Applicant: Professor Dr. Ralf Bernhard Bergmann
• Subject Area: Measurement Systems
• Term: since 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 284158589

Optical metrology is an important prerequisite for quality assurance in many production processes. For applications in the mass production of micro-components, a measurement technology is required that has a high measurement speed, low measurement uncertainty, an extended depth of field and is insensitive to vibrations. However, a measuring system that combines these properties is not available according to the current state of the art. For this reason, the limits and possibilities of shape measurement by means of optical imaging using spatially partially coherent light were examined in the first funding phase. The developed method enables fast, eye-safe and vibration-insensitive form measurement of micro parts with an extended depth of field. However, the measurement uncertainty of the method for objects with a rough surface is currently still in the range of a few micrometers. The reduction of the measurement uncertainty is, however, a decisive factor for an industrial application.The aim of the requested continuation project is therefore to implement a measurement method with the above-mentioned properties for measuring the shape of technical components with a measurement uncertainty of equal or less than 1 µm. To achieve this goal, the measurement object shall be illuminated sequentially or simultaneously from different directions using several LEDs as light sources. The corresponding recordings are evaluated using a pixel-based approach by principal component analysis.In the first phase of this continuation project, a measuring time of less than one second is to be achieved by using a lens (tunable lens) that can be adjusted in the focal length by means of an electrical potential.In the second phase of this continuation project, the measurement speed is then to be increased significantly by using a digital micromirror array (DMD) with a switching speed that is almost 10 times higher than that of an adjustable lens. To do this, it is necessary to compensate for the angular dispersion of the DMD due to the wavelength spectrum of the LEDs used as the source of illumination, in order to enable fast data acquisition within the depth scanning process.At the end of the continuation project applied for, a demonstrator of a fast, robust measurement system for the application described above with a measurement uncertainty of 1 µm or less should be available.

• DFG Programme: Research Grants