Drone-based single-shot fault detection method for wind turbines: conception and initial feasibility study

Fringe projection profilometry (FPP) is an optical, non-contact 3D measurement method widely applied across industries. In the manufacturing industry, this method can be used to inspect structural components and detect defects such as buckles or gap sizes in automotive industries. Due to its resolution in the micrometer range, also smaller components can be measured precisely. Therefore, FPP can also be used in other areas, such as monitoring wound healing processes or deformation of brake disks. However, the usually static setup and the use of multi-step phase-shifting algorithms often limits the applicability, especially as the latter requires an interference-free system. Nevertheless, due to the large possible field of view (often several square decimeters, or even more) and the good depth resolution, the use of FPP is also interesting for inspection and fault detection of wind turbines or buildings, for example. However, as surfaces to be measured are often difficult to reach, a static setup from the ground is economically not feasible. Therefore, we present the concept of an FPP system mounted on a drone for in-flight inspection. The challenge when using a drone is due to motion sensitivity resulting in additional noise, which necessitates single-shot measurements based on the analysis of a single camera image only. Compared to conventional FFP our method projects a fixed grating and requires a complex spatially-resolved phase analysis. Although it is restricted with respect to the maximum height of steps on the surface, it promises good results in the desired applications. Initial measurement results obtained with an FPP system under laboratory conditions are presented as a feasibility analysis for drone-based investigation of rotor blades. This feasibility study aims at ensuring the basic suitability of the FFP method in the presence of typical surface coatings of rotor blades.