“Virtual Time Freezing” Lets Scientists Inspect Spinning Devices

Scientists have created a real-time imaging system capable of capturing extended images of rapidly rotating objects. Continuously monitoring components like turbine or jet engine fan blades is vital for spotting early damage—such as cracks or wear—helping to avoid major failures and minimize maintenance requirements.

“Getting clear images of rapidly spinning objects is difficult due to blurring and graininess,” explained Zibang Zhang, a researcher from Jinan University in China. “High-speed cameras can assist, but they’re costly and unsuitable for long-term use. Our approach addresses this by virtually freezing time, taking advantage of the object’s repetitive motion.”

In a publication in Optics Letters, the researchers detail their novel imaging system, which utilizes a single-pixel detector. They demonstrate that it can capture images of an object rotating at approximately 14,700 revolutions per minute (rpm).

“This system can identify wear or cracks that develop over time in high-speed metal cutting and grinding tools—without needing to halt the machines—enhancing safety and prolonging equipment life,” said Zhang. “Looking ahead, the technology could integrate into smart manufacturing setups, aircraft maintenance systems, or even home appliances like car engines, blenders, fans,  air conditioners, and hard drives, making these devices smarter and safer.”

Stopping Time

Capturing images of fast-spinning objects is challenging for traditional imaging methods due to motion blur caused by rotation. Reducing exposure time helps minimize blur, but it often creates noisy images due to capturing fewer photons. High-speed cameras can serve this purpose, but they remain highly expensive and can’t operate for long periods.

As part of a project focused on creating an optical system for online engine inspections, the researchers developed a new system that addresses many challenges of imaging fast-spinning objects by using structured illumination and single-pixel detection.

This imaging technique projects patterned light onto a scene and captures the resulting intensity variations with a single-pixel detector, allowing a computer to reconstruct a detailed image without relying on a traditional camera sensor. Single-pixel detectors, which consist of only one pixel, offer higher sensitivity, a broader dynamic range, and quicker response times compared to conventional camera sensors, making them ideal for imaging fast-spinning objects.

“The key to the method is synchronization, which effectively freezes time by keeping the target object stationary relative to the projected pattern,” explained Zhang. “With synchronized illumination, we turn a dynamic imaging challenge into a static one.”

The imaging system captures clear images of rotating objects by aligning with their repetitive motion. This is similar to painting a sunrise over multiple days: each time the sun rises, the artist paints a small part of the scene. Even though the sun continuously moves, the entire picture can be captured by syncing the process with the sun’s daily return.

Imaging a Rotating Object

For the imaging setup, the researchers utilized a high-speed projector, specifically a digital micromirror device capable of projection speeds up to 22,000 Hz, to illuminate the rotating object with a series of patterns. The single-pixel detector captures a measurement for each projected pattern, and once the object completes one full rotation, the projector switches to the next pattern.

To synchronize the projection, the researchers “set an alarm” by directing a laser at one blade of the spinning object, generating backscattered pulses. When the pulse count matches the number of blades, it signals the projector to switch patterns—similar to setting off an alarm—enabling clear imaging of the rotating object using just the single-pixel detector.

To demonstrate the system, the researchers showed it could reconstruct high-quality still images in real time of a model jet engine (11 cm in diameter) rotating at about 2,170 rpm and a CPU cooling fan spinning at roughly 14,700 rpm. The researchers noted that the method, requiring no prior knowledge of the object, could also be used to image objects with unstable rotation speeds.

The team plans to improve the system’s portability and facilitate its integration into real aircraft engines in the future.

Read the original article on: Phys.Org

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