Some of the regions that require inspection on WTBs are difficult to reach, even for human inspectors.
|By combining two robotic units, the climber and the crawler, SheaRIOS has been able to address these difficulties.
The climber is able to ascend the wind turbine tower and use the deployment mechanism to gently position the crawler on the WTB. The crawler then uses vacuum caterpillar tracks to traverse across the blade to reach areas of concern and perform the shearography inspection. The crawler’s vacuum caterpillar tracks are made from a dense foam that will not mark or damage the WTB.
During site trials at CRES, on a Vestas V47/66 wind turbine, the climber, deployment mechanism and robotic crawler performed as required, with the crawler navigating across a WTB, whilst leaving no trails or marks.
The SheaRIOS system must be reliably controlled from the ground and the instructions communicated to the robotic climber and crawler robot to maintain control throughout the inspection process.
|The SheaRIOS system is remotely controlled from ground level, through a high bandwidth data link within the umbilical cable. The robotic climber acts as a distribution hub for the power and communications to the crawler and inspection unit.
As a precaution, the robotic climber is also fitted with a wireless transmitter, linked to the ground-based control station, it maintains control should the data cable be compromised. In this way, should a loss of communication occur, the system can still be safely controlled from the ground and retrieved without damaging the wind turbine.
Different safety scenarios were trialled during the field testing, including loss of communication, in each case the crawler was successfully retrieved with no adverse effects to the WTB, or tower.
The SheaRIOS system requires a steady power supply for continuous operation over a long time period.
The climber uses a motorised winch for ascending and descending the wind turbine tower. Should power be lost, then the winch can be manually disengaged and the robotic climber safely lowered to the ground.
If power is lost, the crawler will remain attached to the WTB for a few minutes, as the vacuum is not instantly lost. This provides the operator time to re-establish the power supply.
If the operator cannot re-establish power before the vacuum is lost, the crawler will detach from the WTB, but cannot fall to the ground, due to a safety cable that is always held in tension. The crawler can hang from the safety cable without issue until the power is restored.
Shearographic inspection unit:
In the unlikely event of power failure, the SheaRIOS inspection system automatically shuts down and is therefore intrinsically safe.
The SheaRIOS inspection unit incorporates a Class 3B laser that is the basis for the shearographic inspection.
|The laser leaves the inner inspection unit enclosure after it has passed through a diffuser. The safe working distance (Nominal Ocular Hazard Distance) is 160mm from the diffuser. Any laser light seen outside the outer light shield is sufficiently diffuse not to cause any harm.|
|Inspection technology: |
To date, the application of shearography has been severely restricted due to the issues caused by relative motion between the inspection unit and the subject.
|The biggest barrier for the adoption of shearography as a mainstream inspection method is its susceptibility to vibration. The shearography technique is based upon the change in speckle pattern on a surface with the application of a stress. In regions where a defect is present, a differential surface response occurs locally, changing the speckle pattern. This change can be observed in the fringe pattern generated. Any relative motion caused by vibration of the sample or inspection unit, changes the speckle pattern and prevents the formation of meaningful fringe patterns.
The crawler is held on the WTB using a vacuum system, allowing the crawler and blade to move in harmony, minimising the vibrational effects. A patented mirror system is used to optimise the light path and ensure a sufficiently large field of view.
During the field trials, it was demonstrated that the vibration effects were sufficiently minimised, allowing shearography inspection of an in-situ WTB to be performed.
|Benefits||The SheaRIOS system can traverse and inspect in-situ WTBs to identify sub-surface defects.
This technique is complementary to visual inspection and enables WTBs to be inspected for sub-surface defects while still on the wind tower, thereby reducing down-time and reducing costs.