The majority of rotor-blade manufacturers have now responded to this and are making efforts to improve quality control within the production process. In this context, the Fraunhofer WKI has already developed a system in which rotor blades can be examined for production defects by means of active heat-flow thermography. In this way, defects can also be detected which lie several centimeters below the surface and which are not visible from the outside. This method has proven successful and is already being utilized in industry.
However, solely defects close to the surface can be detected. For the detection of defects on the inside of the rotor blade, it must also be possible to carry out thermography from the inside.
Our project partners at the Harz University of Applied Sciences and at the Institut für Automatisierung und Informatik in Wernigerode are developing a mobile robot which is inserted into the inner cavity of the rotor blade and then moves lengthwise along the rotor blade via remote control. At the Fraunhofer WKI, we are developing a suitable thermography procedure for this purpose. With the aid of an infrared radiant heater, the rotor blade is heated whilst the robot travels along it. Damaged areas such as cracks, bonding defects or air pockets exhibit a deviating thermal conductivity and therefore alter the heat flow. The thermographic camera installed in the robot records these changes in the heat flow and converts them into images. Using special software, which was also developed at the Fraunhofer WKI, the images can be viewed and optimized on the computer (e.g. contrast improvement, noise suppression, background subtraction). The camera settings can also be adjusted via the software. Furthermore, the robot records high-resolution optical images for navigation purposes and for a better assessment of material defects visible on the surface.
The robot is to be used with both horizontally stored and already installed rotor blades. As a result, it could optimally complement quality assurance both in the production process and during operation.