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Advanced shearography kit and a robotic deployment platform for on-site inspection of wind turbine blades

Periodic Reporting for period 3 - WInspector (Advanced shearography kit and a robotic deployment platform for on-site inspection of wind turbine blades)

Reporting period: 2017-12-01 to 2019-05-31

To achieve a thorough investigation for defect presence on a wind turbine blade (WTB), close inspection is required. This implies either trained staff tied with ropes on the blade or dismantling and transferring the blade in a workshop environment. While blade dismantling is scarcely used because it requires very long downtime, human inspection also involve a relatively high delay.

A solution to this problem is to utilize specially designed platforms that can reach the blade and implement faster inspections on site. However, current systems are not very agile or cannot reach close enough to the blade in order to use a high quality non-destructive technique. Hence, they are mostly used to carry out mere visual inspections.

To deal with the aforementioned challenge, our team aimed to commercialize a WInspector system. It consisted of an agile robotic platform able to climb up the wind turbine tower and deploy an advanced digital shearography unit that carries out inspection of a blade on-site.

Users of WInspector was expected to benefit through early detecting emerging defects unseen in a visual inspection performed by competing solutions, with a significantly lower downtime for the WTB, and free of the dangers of human working at height.

We planned to further demonstrate the capabilities of WInspector in relevant environment so that we were able to take the next steps and complete product development allowing us to bring WInspector to the market.
The project started with the further improvement of the robotic platform and the shearography unit. Originally, our robotic platform was designed to reach both sides of a WTB by rotating the WTB from 0° to 180°. However, a market search conducted at the beginning of the project revealed that there are many wind turbine blades on the market that have a limited pitch range, usually between 0° and 90°. The 180° of pitch control is not universally adopted by all WTB manufacturers. For instance, the G90 blade supplied by Gamesa was popular worldwide. It features a pitch range of just 90°.

In order to meet the market requirement of inspecting both sides of a WTB, the project consortium decided to develop a new deployment system which can carry the shearography system at a predefined working distance from the WTB surface.

On the other hand, our previous work showed that, in order for the shearography system to work properly to beyond the root area of the WTB, a much more stable condition is required. This led to a vacuum suction based end-effector that is able to deploy the shearography directly onto the WTB surface during inspection. With the shearography system sitting on top of the WTB, the relative motion between the WTB and the shearography system will be minimal even under windy weather conditions.

The technical work in the project was focused on implementing this concept, with multiple rounds of improvements and optimisations of the end-effector, the robotic climbing platform, and the shearography. It should be noted that existing commercial shearography systems on the market are designed for use normally on the ground where the working environment is stable. For on-site WTB inspection, we have to design a new type of shearography that is fit for purpose on a wind tower.

After all these technical developments which caused considerable delays in the project, we finally were able to deploy the integrated WInspector system to perform three field trial demonstrations at the CRES (Center for Renewable Energy Resources) wind farm in Lavrio, Greece. The first field trial occurred on 17-19 January 2019.

From the trial, more problems were identified, which were related to the attachment of the climber to the tower. This resulted in some scratches to the tower and the system dethatched from it. There was also some problems to get the ladder open. So in the end the whole system could not be fully tested, but valuable lessons were learned that allowed us to improve the system for subsequent field trials.

After further improvement, a second field trial was conducted on 18-20 March, 2019. The whole system performed as expected, with no problems in the attachment and climbing. After extensive image processing, we were able to see some shearography fringes. Although the fringe contrast is poor, this was deemed as a breakthrough for shearography to move from on the ground to in the sky. It is important to note that even under this condition we were able to obtain successful measurements from the shearography system. To our knowledge, this is the first time that shearography fringe patterns were obtained in real environment condition on a wind tower.

Our third and final field trial was carried out on 13-14 May 2019 at the CRES wind farm, with the project officer witnessed first-hand. We were able to collect more speckle videos of the WTB after thermal stressing by a heat gun, and more shearography fringe patterns were obtained. This further demonstrated that shearography could be used for on-site WTB inspection.
>>Conclusions on the project

WInspector is an ambitious project. During the past 3 years, we have developed an innovative remotely controlled NDT system for on-site WTB inspection on a wind tower. The system consists of a robotic platform, an end-effector and a shearography unit. With the control software, we were able conduct two successful field trial demonstrations at the CRES wind farm in Greece, which showed that our strategy and system are working. To our knowledge, this is the first time that shearography is proved to be working remotely on a wind tower.

However, to develop the WInspector system into a fully commercially viable produce, there are still a number of aspects that need to be optimized. These include
• Means of thermal stressing that can be efficient, stable and controllable.
• Image processing algorithms that should be highly efficient to process the vast amount of image data acquired during WTB inspection
• Tracking of the inspection trajectory that allows repeated or follow-up inspections

We will endeavour to continue to improve the technique so that the technique can be fully commercialized in the coming years.

>>Socio-economic impact of the project

Within the project, we have demonstrated that shearography with a robotic deployment system can be used for on-site WTB inspection on a wind tower. This is a highly innovative technique, which has the following main socio-economic impact:
• Help address climate change by providing an advance NDT system to the wind sector
• Reduction of maintenance costs for wind farm operators
• Avoidance of risks of working at height for humans to conduct WTB inspection
• Minimizing the risk of structural failure by detecting subsurface defects at the earlier stages
A detailed view of the inspection scenario
An overview of the field test on a wind tower