A single-pixel imaging system has been developed that provides continuous monitoring of high-speed rotating parts, like turbine and jet engine blades, in real time and for long durations. The new system could help prevent serious mechanical failures and reduce equipment maintenance by alerting businesses to the early signs of wear or damage. The imaging system was developed by a research team at Jinan University as part of a project aimed at creating an optical system for online engine inspection. The team overcame many of the challenges of imaging fast-spinning objects by using single-pixel detection and structured illumination and by exploiting the periodicity of the target object’s rotation. Imaging fast-spinning objects is difficult for conventional imaging techniques because rotation leads to severe motion blur. Reducing exposure time can ease the problem but tends to create noisy images because fewer photons are captured. Researchers from Jinan University developed a method to detect the rotation speed and capture images of spinning objects. Courtesy of Jinan University/Zibang Zhan. “Capturing clear images of fast-spinning objects is challenging because they tend to blur or look grainy,” professor Zibang Zhang said. “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 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 the need for a traditional camera sensor. Compared to traditional sensors, single-pixel detectors have higher sensitivity, a wider dynamic range, and a faster response time, making them suitable for imaging fast-spinning objects. The imaging system captures clear images of rotating objects by aligning with the object’s repetitive motion. A digital micromirror device with projection speeds of up to 22,000 Hz illuminates the rotating object with a series of patterns. The single-pixel detector acquires a measurement for each pattern projection. Once the object spins around once, the projector switches to the next pattern. To synchronize the projection, the researchers aim a laser at one blade of the rotating object, creating backscattered pulses. When the number of pulses matches the number of blades, the system signals the projector to switch patterns. This allows the rotating object to be imaged clearly using just a single-pixel detector. Synchronized structural illumination keeps the target object virtually stationary relative to the imaging system. The system can obtain clear images of a rotating object in operation with a rotation speed of about 14,700 rounds per minute (rpm). “The key to the method is synchronization, which essentially freezes time by keeping the target object stationary compared to the pattern projection,” Zhang said. “By using synchronized illumination, we converted a dynamic imaging problem into a static imaging problem.” In experiments, the researchers showed that the system could reconstruct real-time, high-quality, still images of a model jet engine 11 cm in diameter, rotating at about 2170 rpm, and of a CPU cooling fan rotating at about 14,700 rpm. The single-pixel imaging system can be used to image objects with an unstable rotation speed. A rotating object can be imaged without any prior knowledge of the object. “The system could detect wear or cracks that can develop in high-speed metal cutting and grinding tools over time — without stopping the machines — improving safety and extending the equipment’s lifespan,” Zhang said. The researchers plan to improve the system’s portability and make it easier to integrate into an actual aircraft engine. “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,” Zhang said. The research was published in Optics Letters (www.doi.org/10.1364/OL.555872).