Drones and crawling robots equipped with scanning technology could help wind blades remain in service longer, which may help lower the cost of wind energy at a time when blades are getting bigger, pricier and harder to transport, Sandia National Laboratories researchers say.

As part of the Department of Energy’s Blade Reliability Collaborative work, funded by the Wind Energy Technologies Office, Sandia researchers partnered with energy businesses to develop machines that noninvasively inspect wind blades for hidden damage while being faster and more detailed than traditional inspections with cameras.

Wind blades are among the largest single-piece composite structures built in the world.Wind blades are among the largest single-piece composite structures built in the world.Wind blades are among the largest single-piece composite structures built in the world, the researchers said. A blade typically is subject to lightning, hail, rain, humidity and other forces while running through countless load cycles during its lifetime.

Routine inspection and repair is critical to keeping the blades in service, but current inspection methods don’t always catch damage soon enough.

Sandia said it is drawing on expertise from avionics and robotics research to change that. By catching damage before it becomes visible, smaller and less expensive repairs can fix the blade and extend its service life.

The researchers envision each wind plant having a drone or a fleet of drones that take off, fly around the wind turbines to conduct inspections and then come back and upload their data. The wind plant operator then will look through the data, which already will have been read by artificial intelligence. Based on the findings, the operator may deploy a robotic crawler to get a more detailed look at the blade and plan repairs.

In one project, Sandia outfitted a crawling robot with a scanner that searches for damage inside wind blades. In a second series of projects, Sandia paired drones with sensors that use the heat from sunlight to detect damage.

The wind industry has had two main approaches to inspecting wind blades. The first is to send an inspector out into the field with a camera. The inspector then moves from blade to blade taking photos and looking for visible damage such as cracks and erosion. The second option involves having the inspector climb a wind blade tower or maneuver a platform on a crane up and down the blade.

Researchers use crawling robots and drones with infrared cameras to look for hidden  damage to keep wind blades operational for longer and drive down the costs of wind energy. Credit: Randy Montoya, SandiaResearchers use crawling robots and drones with infrared cameras to look for hidden damage to keep wind blades operational for longer and drive down the costs of wind energy. Credit: Randy Montoya, SandiaThese visual inspections reveal only surface damage, the researchers said. But by the time a crack is visible on the outside of a blade, the damage is already severe.

Sandia’s crawling robots and drones are aimed at making the noninvasive internal inspection of wind blades a viable option for the industry.

Finding hidden damage

Sandia and partners International Climbing Machines and Dophitech built a crawling robot that can move from side-to-side up and down a wind blade. Onboard cameras provide real-time, high-fidelity images to detect surface damage, as well as small demarcations that may signal larger, subsurface damage.

While moving, the robot also uses a wand to scan the blade for damage using phased array ultrasonic imaging. Changes in the ultrasonic signatures can be automatically analyzed to indicate damage.

Sandia also outfitted drones with infrared cameras that use the heat from sunlight to detect hidden wind blade damage. This method, called thermography, can detect damage up to a half inch deep inside the blade.

Researchers developed a method to heat the blade in the sun, and then pitch it into the shade. The sunlight diffused into the blade and equalized. As that heat diffused, the surface of the blade cooled. Flaws tend to disrupt the heat flow, leaving the surface above the flaw relatively hot. The infrared camera will then read those hot spots to detect damage.

Ground-based thermography systems are currently used for other industries, such as aircraft maintenance. Because the cameras are mounted on drones for this application, concessions have to be made, Ely says.

The researchers also used optical images and lidar to provide additional information. For example, lidar, which measures how long it takes light to travel back to a point to determine the distance between objects, may be used to measure erosion on blade edges.

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