Sensor structures produced with ultrashort laser pulses
Surface Sensors for Harsh Environments
Laser-structured strain gauges are used for precise force determination, even at critical points, such as in highly stressed machine tools or complex 3-D parts. Laser Zentrum in Hanover (LZH e.V.), Germany, is currently developing sensor structures produced with ultrashort laser pulses; the aim is to make high-quality thin-layer sensors economically attractive even for small and medium-sized production runs. Production takes place as follows: After full coating of the part with an insulating layer and a sensor layer, an ultrashort pulse laser creates sensor structures with lateral resolutions of 10 to 100 µm without damaging the sensitive layer by heating it. The advantages of the process are that complicated mask processes are eliminated and the sensors can be directly applied to complex three-dimensional geometries.
Until now, strain gauge films have often been bonded. The adhesive creeps or swells, falsifying the measurement results. This seriously affects the long-term stability of the sensors, particularly in harsh environments. Here, thin-film type strain gauges are preferred. The photolithographic structuring of the sensors is very complicated and usually not cost effective, particularly for small and medium-sized series. In addition, the mask technique originally used in electronics production is not suitable for processing complex parts with cylindrical, spherical or free-form surfaces, and so restricts the use of strain gauges to flat parts.
Soon, the first prototypes of laser-structured strain gauges will be integrated into the Z-axis slide of a machine tool. Apart from mechanical engineering, other possible applications of surface sensors are in automotive and bearing technology, robotics or medical equipment.
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