Performing visual inspection on fully assembled industrial systems, especially those with complex geometries, can be extremely challenging. The process must often be performed without decommissioning or disassembling the system itself, often through small access ports. One commonly used means is to deploy a small endoscopic visualization system that can be used to make the internally concealed structures of large systems visible.
Endoscopic systems are already widely used in the field of minimal invasive surgery. Here, such endoscopes are employed to reach internal organs through a small incision instead of a large opening. The endoscope tube also houses surgical tools, which are deployed while the internal organs are viewed on a monitor. Because the incisions are small, recovery times are quicker than conventional surgery and the procedure is more comfortable.
According to Patrick Eckert, the Visual Inspection Product Manager at SCHÖLLY FIBEROPTIC, the advantages of employing endoscopic systems in the aviation industry are no less important. The use of such systems enables aero engines to be inspected for defects while the engine is on the wing of the aircraft. This avoids any unnecessary removal or disassembly of the engine itself and minimizes the time that aircraft remain out of service.
“In the aviation industry, airfoils inside the engines of aircraft must be inspected regularly to find defects which could come from damage due to foreign objects entering the engines. Here, it is vital to detect those defects at an early stage. However, traditional systems can only detect surface defects around 100um in size with a precision of +/- 50um. But higher precision is needed to avoid unscheduled shop visits coming from inaccurate inspection methods,” said Mr. Eckert
Now, however, as the result of a joint project funded by the German Federal Ministry for Economic Affairs and Energy,
SCHÖLLY FIBEROPTIC has developed in collaboration with Rolls-Royce a prototype of a fully steerable full flexible video scope specifically for the purpose. With an outside diameter of just 6mm, the video scope can enter the small apertures in the aero engines to detect surface defects with a size of less than 50μm and with an accuracy of +/ - 5μm (Figure 1).
SCHÖLLY FIBEROPTIC has developed a prototype of a fully steerable full flexible video scope specifically for inspecting the airfoils inside the aircraft engines.
Two sets of optics
Traditionally, such systems have sported two sets of optics in the endoscope - one used specifically for navigating the probe and the other for capturing images of the object itself. The new system, on the other hand, combines the inspection and measurement optics though a wavelength dependent numerical aperture. Hence the endoscope can be used in an inspection mode with low resolution and high depth of field, or in measurement mode with a high optical resolution and low depth of field.
The measurement precision of the prototype endoscopic measurement system been successfully confirmed on real aero engines, according to Mr. Eckert. Once a defect has been identified in inspection mode, the measurement mode can be used to highlight the area and create a line profile showing the width and the depth across sections of the defect. In use, the endoscope has been effective at locating and measuring a defect with a depth of 85 μm and a lateral size of 239μm (Figure 2).
Once a defect has been identified in inspection mode, the measurement mode can be used to highlight the area and create a line profile showing the width and the depth across sections of the defect. In use, the endoscope has been effective at locating and measuring a defect with a depth of 85 μm and a lateral size of 239μm.
“In addition to simply capturing images inside complex parts which can then be analyzed and documented, contemporary industrial endoscopic systems also enable a variety of other functions to be performed. Having determined the locations of any potential faults, for example, functional modules fitted to the end of the endoscope can be used to actually repair or clean the faulty part while the complex industrial systems are in situ,” said Mr. Eckert.
In the aero industry, for example, the cooling apertures on the nozzle guide vanes (NGVs) of a turbine engine can become partly blocked by deposits. Rather than remove the engines from the aircraft, however, the ideal solution would be to clean the NGVs with high pressure water jets while the engine remains on the wing of the aircraft.
Steerable endoscopic snake
Within an additional project, funded by the German Federal Ministry for Economic Affairs and Energy, a system to do just that has now been developed also in collaboration with Rolls-Royce. The system integrates a LED illumination source and the camera and optics together with a miniaturized water-jet system into a steerable endoscopic snake.
The system can be steered through access ports on the engine with outside diameters of 20mm after which it can be maneuvered inside the structure to accurately locate the blocked cooling apertures. Having done so, high pressure water can be pumped to the end of the endoscope to remove any of the deposits that are present whilst withstanding the high holding forces once the water pressure is applied (Figure 3).
A system to clear the apertures on the nozzle guide vanes (NGVs) of a turbine engine has been developed as the result of a jointly funded project between Rolls-Royce and the German Federal Ministry for Economic Affairs and Energy.
According to SCHÖLLY’s Mr. Eckert, the advantages of transferring technology from the medical field to the industrial environment are profound. State of the art systems in the medical field, for example, presently allow 3D images of internal organs to be visualized by surgeons while they conduct medical procedures on a patient. Because these tools provide surgeons with a natural insight into the human body, such procedures can be performed more quickly and effectively leading to efficiency gains. Such surgical robotic systems can also enable surgeons to perform operations remotely on a patient.
“Such advantages can also be delivered to users working in an industrial environment, and to that end SCHÖLLY FIBEROPTIC has recently developed the prototype of an endoscopic system that integrates a standard 3D optical module used in medicine into a steerable flexible 3D video scope. The system captures 3D images which can be displayed to a user wearing a pair of 3D glasses, providing a natural view into a complex system that could potentially enable engineers to conduct remote diagnostics and maintenance,” he said.
Software algorithms enhance images
And just as the hardware technologies employed in medical systems design can be gainfully transferred into the industrial environment, so too can many software algorithms used to enhance the images captured by such systems.
In the medical field, for example, selective color enhancement algorithms can be employed to enhance the vessels and the tissue structure within images. In a similar fashion, such an algorithm can also be employed in the industrial field to increase the contrast of specific parts of an image to make it easier to detect corrosion in metallic parts. Similarly, smoke reduction algorithms that are used to enhance images during dissection or ablation procedures can also be gainfully employed in the industrial environment to remove smoke in video images during repair (Figure 4).
In the medical field, selective color enhancement algorithms can be employed to enhance the vessels and the tissue structure within images. In a similar fashion, such an algorithm can also be employed in industry to increase the contrast of specific parts of an image to make it easier to detect corrosion in metallic parts. Similarly, smoke reduction algorithms used to enhance images during dissection or ablation procedures can also be gainfully employed in the industrial environment to remove smoke in video images during repair.
“The latest chip-in-tip (CIT) systems that make use of miniaturized image sensors and affordable cables for light, communication, and data transmission will continue to drive developments in both the medical and the industrial field, reducing the time that patients spend in hospital and the time taken to conduct preventative maintenance in industry,” said Mr. Eckert.
Combined with intelligent software tools to analyze the images, such systems will enable end users to more effectively perform inspection and repair tasks. In addition, OEMs who partner with the developers of such components will be able to develop systems to meet the specific needs of their own applications.
Written by Dave Wilson, Senior Editor, Novus Light Technologies Today