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With potential applications including monitoring power station turbines or detecting early signs of cracks on jet engine blades, helping prevent serious failures and reducing maintenance costs, the system was developed at Jinan University in China.
“Capturing clear images of fast-spinning objects is challenging because they tend to blur or look grainy,” said research team member Zibang Zhang. “Although high-speed cameras can help, they’re expensive and can’t be used for long periods. Our method overcomes this challenge by virtually freezing time by exploiting the repetitiveness of the object’s motion.”
The system can capture images of objects spinning at 14,700 revolutions per minute (rpm), a research announcement said. It could be used to detect wear in high-speed metal cutting and grinding tools without stopping the machines, Zhang said, improving safety and extending equipment’s lifespan.
“In the future, this technology could be integrated into smart manufacturing systems, aircraft maintenance platforms or even home appliances like car engines, blenders, fans, air conditioners and hard drives, making these devices smarter and safer.”
Imaging fast-spinning objects is not easy for conventional imaging techniques because rotation leads to severe motion blur. Although reducing exposure time can reduce the problem, this tends to create noisy images, because fewer photons are captured. High-speed cameras can capture fast-spinning objects, but are prohibitively expensive and cannot be used continuously over long time periods.
As part of a project aimed at developing an optical system for online engine inspection, the researchers developed a new system that overcomes many of those challenges by using ‘structured illumination’ and a single-pixel detector, a photodiode with only one available pixel. The technique involves projecting patterned light onto a scene and capturing the resulting intensity variations with the detector, which has higher sensitivity, a wider dynamic range and faster response compared to traditional sensors. This allows a computer to reconstruct a detailed image.
“The key to the method is synchronisation, which essentially freezes time by keeping the target object stationary compared to the pattern projection,” Zhang said. “By using synchronised illumination, we converted a dynamic imaging problem into a static imaging problem.”
The researchers used a high-speed projector with framerates up to 22,000 Hertz to illuminate rotating objects with a series of patterns. The single-pixel detector acquires a measurement for each pattern projection, switching between patterns after each spin of the object.
To demonstrate the system, the researchers showed it could reconstruct high quality still images of a model jet engine rotating at about 2,170rpm and a CPU cooling fan rotating at about 14,700rpm.
The researchers plan to improve the system’s portability and make it easier to integrate into a real aircraft engine.
The work was published in Optics Letters.
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