Goetz Kuehnle

High-resolution absolute position detection using a multiple grating

To control electro-mechanical engines, high-resolution linear and rotary encoders are needed. Interferometric methods (grating interferometers) promise a resolution of a few nanometers, but have an ambiguity range of some microns. Incremental encoders increase the absolute measurement range by counting the signal periods starting from a defined initial point. In many applications, however, it is not possible to move to this initial point, so that absolute encoders have to be used. Absolute encoders generally have a scale with two or more tracks placed next to each other. Therefore, they use a two-dimensional grating structure to measure a one-dimensional position. We present a new method, which uses a one-dimensional structure to determine the position in one dimension. It is based on a grating with a large grating period up to some millimeters, having the same diffraction efficiency in several predefined diffraction orders (multiple grating). By combining the phase signals of the different diffraction orders, it is possible to establish the position in an absolute range of the grating period with a resolution like incremental grating interferometers. The principal functionality was demonstrated by applying the multiple grating in a heterodyne grating interferometer. The heterodyne frequency was generated by a frequency modulated laser in an unbalanced interferometer. In experimental measurements an absolute range of 8 mm was obtained while achieving a resolution of 10 nm.

Identification of Wetness on Millimeter Wave Radar Surface

Automotive radar sensors, which fundamentally use millimeter wave signals, increasingly become one of the important comfort and collision mitigation products in the automotive market. Their performance may be affected by wetness due to adverse weather conditions unless proper antenna lens or radome design used, as implemented with the Bosch Long Range Radar System. The extension of automotive radar sensors from comfort to safety systems may further require intelligent features, such as detection of weather phenomena and performance controlling during adverse weather conditions. Hence, this work examines effects of wetness on the millimeter radar performance and methods to identify such phenomena. It reveals that, effects of wetness on millimeter radar has to be generally taken in to account and will provide performance information on automotive radar sensors. The information is used for controlling automotive radar sensor performance, which makes it more intelligent and robust in adverse weather conditions. Index Terms – Electromagnetic radiation effects, Millimeter wave radar, Road vehicle radar

High-resolution heterodyne interferometric rotation encoder with frequency-modulated laser diode

A high-resolution interferometric rotation encoder has been developed and characterized. It is based on the principle of a heterodyne interferometer. The frequency shifting was done by modulation of the injection current of a laser diode and a fiber-optical delay line allowing a compact system design. Light wave aberrations produced by the scale (i.e. rotary grating disk) are pre-corrected by using computer-generated holograms (CGH). Combined analogue and digital signal processing allow high resolution as well as high measurement rates. The designed prototype yields a resolution of 0.03 arcsec (i.e. 25 bit) corresponding to 3 nm resolution of displacement of the 38 mm diameter disk-scale. The measuring rate of 1 MHz allows a rotation speed resolution of 0.013 rpm at a maximum speed of 300 rpm.

Laser diode for interferometric applications

The spectral characteristic of a light source e.g. spectral linewidth, light wavelength, stability of frequency and output power are the most important performance parameters for an interferometer. The influence of the above mentioned effects on the performance of a two- beam interferometer was experimentally tested in a heterodyne interferometer which had been developed for this purpose.