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Christoph Weichert, Jens Flügge, Paul Köchert, Rainer Köning, Rainer Tutsch
STABILITY OF A FIBER-FED HETERODYNE INTERFEROMETER

A heterodyne interferometer with spatially separated input beams is presented. The optical design realizes symmetric paths through glass and air, which results in a minimal dead path. An automatic correction of phase variations introduced by feeding the optics with fibers and by angle variations between the optics and the mirror is demonstrated. In addition to the resolution and linearity in the single digit picometer range, the long-term stability of the interferometer setup is investigated, involving the previous analysis of all different components of the setup. It is shown, that the long-term stability is still limited by the variations of the environmental conditions.

Arjan J. H. Meskers, Jo W. Spronck, Robert H. Munnig Schmidt, Jonathan D. Ellis
DISPLACEMENT INTERFEROMETRY WITH FIBER-COUPLED DELIVERY

Heterodyne interferometry is a widely applied technique for length and displacement measurements in precision systems. Free-space optical beam delivery couples the source directly to the interferometer location. Conversely, fiber delivery is desired to decouple the source and interferometer. Drawbacks to using fibers are either time consuming alignment (PM fiber) or time varying polarization output (MM fiber). Jones matrices were used to analyze Joo-type interferometers to simulate the effects of using MM fiber inputs. The results showed loss of interference at some instances from the rotating polarization states. Measurements with a MM fiber coupled interferometer showed minimal polarization rotation and no interference loss.

T. Wakayama, T. Yoshizawa
INNER PROFILE MEASUREMENT AND FLAW INSPECTION OF PIPES AND TUBES

Inner profile measurement is an important matter in such fields as mechanical engineering including car and aircraft industries, and heavy industry relating to jet engines and power plant. In addition, we can find many applications in medicine and/or surgery related field. Here we describe recent development of our measurement principle for inner diameter and profile of pipes and/or tubes. The key device in this technique is a ring beam device which consists of a conical mirror and a laser diode (LD). And the fundamental principle is based on optical sectioning without using any contact typestylus. The optically sectioned profile of an inner wall of a pipe-like object is analyzed to give the inner profile in addition to the inner diameter. This optical instrument with simple and small configuration has been under development for practical uses. In our experimentalworks up to now, the availability of this instrument has been evaluated in many cases. This ring beam device consisting of a conical mirror and a LD is assembled in a glass pipe and the beam emitted from the LD is deformed, after reflected by the top of the conical mirror, into a disk-like circular light sheet. We show measurement result of pipes, and, at the same time, report a few examples that are developed for practical purposes. Both the ring beam device and a miniaturized CCD camera are fabricated into a glass tube for easier practical applications. We have already reported the fundamental principle of this measurement system and showed some applications. Here we report our trial to extend our technique to checking defects and flaws on the inner wall of pipe-like objects.

Albert Weckenmann, Johannes Bernstein
OPTICAL BI-SENSOR-METHOD FOR IN-LINE MEASUREMENT OF OBJECTS WITH LARGE ASPECT RATIOS

At the Chair Quality Management and Manufacturing Metrology (QFM) a prototypic optical measurement method for in-line measuring of extruding with 800°C and movement speeds up to 10 m/s has been investigated and evaluated in the shop successfully. The method combines multiple light-section systems and a shadow system for measuring concave extruding more accurate than before. The measurement uncertainties operate down to 10 µm in measurement ranges of 100 mm. The already evaluated method can fundamentally be used as well for measuring other objects, e.g. with high aspect ratios. The here presented approach shows that the measuring principle can be adapted for flat objects like textiles and carbon-fiber compounds in-process. The results contain information about the set-up, the adjusting, influence quantities, calibration of the measurement system and the user-interface as well as the measurement results and possibilities for further improvements.

B. Bodermann, S. Bonifer, E. Buhr, A. Diener, M. Wurm
HIGH PRECISION DIMENSIONAL METROLOGY OF PERIODIC NANOSTRUCTURES USING LASER SCATTEROMETRY

At PTB different laser scatterometers with partly novel and outstanding metrological capabilities have been developed and are available for high-resolution dimensional metrology of periodic nanostructures. Two different systems are described and their metrological potential discussed: a laser diffractometer for pitch calibration and a versatile goniometric scatterometer for multi-parameter characterisation of nanostructures.

A.V. Latyshev
CRYSTALLINE SURFACES FOR LASER METROLOGY

The number of methodological recommendations has been pronounced to describe correctly low-dimensional structures up to atomic resolution and to fabricate crystalline surfaces for applicability in nanoscale metrology. Technology of an extremely flat mirror for optical and laser metrology has been demonstrated on the base of crystalline surface. Stepped crystalline surface with controlled steps distribution is a precise calibrator at nanoscale measurements which is suitable for high-resolution techniques. The precision of measurements performed by atomic-force microscopy (AFM) and high-resolution electron microscopy (HREM) for solving problems of metrology and diagnostics of solid nanostructures is discussed.

Wolfram Lyda, Avinash Burla, Marc Gronle, Wolfgang Osten, Jan Zimmermann, Oliver Sawodny
AUTOMATED MULTISCALE MEASUREMENT SYSTEM FOR TECHNICAL SURFACE INSPECTION

Inspection systems with multiple sensor systems offer the opportunity to select the most suitable sensor according to the measurement task. A challenging objective consists of an automatic selection of the relevant sensors and their embedding into an effective measurement chain. In this publication, we present the implementation of an automated multiscale inspection strategy into a system for the inspection of MEMS and micro lens arrays and give an extended outlook on future challenges which have to be solved to adapt such a system to inspect complex technical components.

Toshitaka Wakayama, Toru Yoshizawa
COMPACT CAMERA FOR REAL-TIME 3D MEASUREMENT: DEVELOPMENT OF MEMS SCANNER WITH HIGH SPEED PHASE SHIFT

To improve difficulties inherent to the conventional three-dimensional profiling system based on pattern projection method, we have proposed incorporating a recent digital device such as a MEMS scanner into projection optics. We have used the MEMS scanner which is not a digital mirror device (DMD) but a single MEMS mirror.Due to this revision, first of all, such a small size system like a palm-top camera was attainable, and low cost measurement system was potentially realized. In the projection system, a laser diode and the single MEMS mirror are employed. We can control the scanner to produce the projection pattern with an appropriate periodical structure and a sinusoidal intensity distribution. Due to this flexible pattern projection, phase-shifting technique becomes applicable for industrial inspections and measurements in the automobile industry and others. The camera is as small as a photographic digital camera in size. We finally aim at developing a high speed 3D measurement. In this paper, the measurement speed is 0.6 seconds for acquiring 3D profile.

Fumio Kobayashi, Yukitoshi Otani, Toru Yoshizawa
PROJECTION MOIRÉ PROFILOMETRY USING LIQUID CRYSTAL DIGITAL GRATINGS

A projection moiré profilometry using a pair of liquid crystal digital gratings (LCDG) is applied to determine a step height using two liquid crystal digital gratings (LCDGs). Moiré contours are filtered over to remove the images of the original grating from the moiré counter when a pairs of grating images are traveled to the same direction in-phase electrically. The new idea of this report is proposed to overcome the 2 π ambiguity of moiré contour by changing the fringe interval of Moiré contours which are adjusted the period of LCDGs. The measured accuracy has been achieved to ±0.7 mm in the range of 96 mm of steep height by projecting two different of grating periods as 6.7 and 13.3 time of original grating.

B. Ribbens, S. Vanlanduit, J. J. J. Dirckx, P. Cools
FRINGE PROJECTION SIMULATION SOFTWARE FOR 3D SHAPE MEASUREMENTS

Profilometry with LCD or DLP beamers has become a common three-dimensional scanning technique. Many attempts are made to enhance the accuracy of these measurement systems, by developing new algorithms or improving the existing ones. Comparing these algorithms to the existing methods requires building a validation setup. This validation setup has to be carefully calibrated to obtain realistic measurement data. Additionally the distortions of the different components need to be compensated. Building these setups often takes a lot of valuable research time while the goal of many research projects is to improve the mathematical fringe analysis tools without having to deal with practical problems of a test setup. This paper presents the ‘Fringe Projection Simulator’, a program which can simulate three commonly used fringe projection setups. All three setups contain a beamer and a camera with a diverging lens. The program is available for download free of charge at: http://www.fringesimulator.com.

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