Robotic deployment of stabilized shearography unit for wind turbine blade inspection

A wind turbine blade inspection system called Winspector has been developed by a European consortium to automate the in-situ non-destructive testing of wind blades. A robot platform is winched up a wind turbine tower to reach a blade locked into a 90° pitch angle. The blade region to be inspected is reached by a combination of an extension ladder and a 5-axis robot arm to place an end-effector onto the blade surface. The end-effector is critical to the success of the shearography technique used to detect subsurface defects when the blade is experiencing inevitable out-of-plane, in-plane, and root-to-tip vibrations. The paper describes the development of the end-effector which carries the shearography unit and ensures (with passive compliance and design based on analysis of aerodynamic blade shapes) that the unit remains at a constant distance from blade surface in the presence of blade vibrations. The system has been tested with three separate field trials in a wind farm near Athens in Greece. Sub-surface defect detection with shearography has been successfully demonstrated.