Holographic measurement technology suits manufacturing environments

June 02, 2017 //By Christoph Hammerschmidt
The fault tolerance in precision manufacturing, especially in automotive production, is becoming increasingly smaller. Suppliers presented a problem so far: There is a lack of methods to detect micro defects in the production process. Simple visual inspection is not suitable for line-integrated measurements during production. With the development of production-ready digital holography, researchers at the Fraunhofer Institute for Physical Metrology IPM in Freiburg (Germany) end this dilemma. Digital holography makes it possible to inspect all parts in full - and at the high speed required by fast series production.

Sometimes every thousandth of a millimeter counts - for example, in mechanical components for the automotive or aviation industry. To find out whether the individual component is also fault-free and dimensionally accurate, digital holography is generally suitable. However, this method has hitherto been shock-sensitive and slow. It was therefore not suitable for production environments and so far, only samples could be investigated.

 

Researchers at Fraunhofer IPM have now brought the process of digital holography from the laboratory into production. "We were able to eliminate all the disadvantages and have developed a system that allows a hundred percent control in production," says project co-director Tobias Beckmann. "Our system can measure centimeter-sized rough objects in fractions of a second, micrometer-accurate and compensated for disturbances such as vibrations." This allows measurements for the first time in series manufacturing. Instead of taking samples as before, each individual part can be checked for dimensional accuracy and at the same time for the smallest errors. "This search for errors is about as if you wanted to measure the 3D shape of a 25-meter-high football stadium from an altitude of 300 meters so that you could find the footprint of a baby in the lawn - in fractions of a second and even when the stadium is being shaken through a light earthquake," explains a researcher.

 

Instead of applying interferometric methods by measuring the object with laser at a single wavelength, the researchers illuminate it with laser beams of different wavelengths in succession and compute the resulting images with one another. Another advantage is the evaluation algorithms. The researchers have parallelized the computation steps in a way that they exploit the complete performance of a high-end graphics card. As a result, the system is so fast that it can precisely measure objects on the micrometer within very short time. »For highly accurate three-dimensional measurements, our system is the world's fastest one currently available” explains Alexander