Real-Time Imaging System Freezes Motion of Fast-Spinning Objects

In the Optica Publishing Group journal Optics Letters, researchers presented their innovative imaging system based on a single-pixel detector. They demonstrate that it can capture images of an object spinning at approximately 14,700 rounds per minute (rpm).

The researchers created a real-time imaging system capable of capturing photos of fast-spinning objects over extended periods. Real-time monitoring of rotating elements, such as turbine blades in power plants or fan blades in jet engines, is crucial for detecting early indicators of deterioration, such as wear or cracks, thereby preventing catastrophic failures and lowering maintenance requirements.

Capturing clear images of fast-spinning objects is challenging because they tend to blur or look grainy. Although high-speed cameras can help, they are expensive and cannot be used for long periods. Our method overcomes this challenge by virtually freezing time by exploiting the repetitiveness of the object’s motion.

Zibang Zhang, Research Team Member, Jinan University

The researchers describe their new imaging system, based on a single-pixel detector, in the study. They demonstrate their ability to take pictures of an object spinning at 14,700 revolutions per minute (rpm).

Zhang added, “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. 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.”

Freezing Time

Rotation causes high motion blur, making it challenging to image fast-spinning objects with conventional approaches. Although shortening exposure time can help, it often results in noisy photos since fewer photons are recorded. High-speed cameras can capture fast-spinning objects, but they are prohibitively expensive and cannot be utilized indefinitely.

As part of an effort to develop an optical system for online engine inspection, the researchers created a new technology that overcomes many of the obstacles of imaging fast-spinning objects through structured illumination and single-pixel detection.

This imaging technique distributes patterned light onto a scene and captures the associated intensity variations using a single-pixel detector. It allows a computer to rebuild a detailed image without the need for a standard camera sensor.

Single-pixel detectors are photodiodes with only one pixel available. They outperform standard camera sensors in terms of sensitivity, dynamic range, and response time, making them ideal for capturing fast-spinning objects.

Zhang further added, “The key to the method is synchronization, which essentially freezes time by keeping the target object stationary compared to the pattern projection. By using synchronized illumination, we converted a dynamic imaging problem into a static imaging problem.”

The imaging technology produces clear images of rotating objects by tracking their repeating motion. This is similar to painting a sunrise over a few days, with the artist painting a small portion of the subject each time the sun rises. Even though the sun moves continuously, users can capture the entire picture by setting an alarm to coincide with the sun's daily return.

Capturing a Spinning Object

The researchers employed a high-speed projector, especially a digital micromirror device capable of projecting at up to 22,000 Hz, to illuminate the rotating item with a succession of patterns. The single-pixel detector measures each pattern projection. Once the object has spun once, the projector moves on to the next pattern.

To synchronize the projection, the researchers “set an alarm clock” by focusing a laser onto one blade of the spinning device, resulting in backscattered pulses. When the number of pulses equals the number of blades, the projector switches patterns, similar to setting off an alarm, allowing for crisp imaging of the rotating object using only a single-pixel detector.

The researchers demonstrated the system's ability to reconstruct real-time high-quality still images of a model jet engine with a diameter of 11 cm revolving at about 2170 rpm and a CPU cooling fan rotating at approximately 14,700 rounds per minute. According to the researchers, the technology, which does not require prior knowledge of an object, can also be used to scan objects with unpredictable rotation speeds.

Next, the researchers intend to improve the system's portability and ease of integration into a real aircraft engine.

Journal Reference:

Long, S., et al. (2025) Single-pixel real-time monitoring system for a high-speed rotating object. Optics Letters. doi.org/10.1364/ol.555872.