C-Scan Ultrasonic Generation using Wireless Encoder based on Passive Markers

The increasing use of composite materials in the aerospace industry leads the construction of more and more complex and large parts. Several improvements have being performed in the last 10 years for their ultrasonic inspection using multi-robot collaborative systems. These include pulse-echo or through-transmission techniques by using one or two robots, respectively. Prior to inspection, part surface is usually laser scanned in order to set up the robot path and define the inspection strategy. The C-scan record is later linked with the re-constructed three-dimensional (3D) surface or merged with the CAD model, having detailed and accurate information of the ultrasonic signal. On the other hand, small to medium size composite parts are still manually inspected since the large preparation times makes difficult the adaptation of automated systems in a cost/effective way. Furthermore, conventional mechanical encoders are very limited in shape and many times unfeasible for such complex geometries. Because of all above, regions with signal attenuation or indications are directly marked on part surface, without the possibility of having a digital C-scan record. In this work, a 3D wireless encoder based on the recognition of passive markers is presented. The wireless encoder calculates the 3D position and orientation of the ultrasonic probe using a set of fixed cameras and applying a triangulation method. Then, a real-time processing system transforms this global localization information into standard encoder signals, making it compatible with any ultrasonic system. The system performance is evaluated by the inspection of 4 demonstrators with different geometries. These inspections have been carried out at different scanning rates and part orientations in order to assess the versatility and limitations of the system.