Millimeter-wave radar distance measurements in micro machining

Abstract

In production and automation engineering the need for highest precision distance sensors is ubiquitous especially in the field of micro-machining processes where an extremely accurate positioning is indispensable. Although the work pieces become smaller and smaller many machine tools stay big and heavy. The reason for this is that a high precision is necessary and in this way the machine tools must be robust and stiff in their rails to prevent positioning errors due to tilts or twists. By using accurate sensors integrated in the rails of the machine tool the positioning error increases since the distance between the measurement of the position and the machine tool itself is relatively large. For this reason it might be advantageous to measure as close as possible at the tool center point (TCP) which could also allow for a reduction in machine sizes. A radar system might be a promising approach for this measurement due to the progressive development in radar technology along with new and fast algorithms. In this paper an frequency modulated continuous wave (FMCW) radar system is presented working around a center frequency of 80 GHz with a modulation bandwidth of 10 GHz. In combination with an innovative signal processing concept that uses frequency and phase evaluation a sub-micrometer accuracy can be achieved over distances up to several meters. The high accuracy of ±0.5 μm is demonstrated in a novel measurement setup for a kinematic using compliant mechanisms with flexure hinges.