Online visualization of small defects for a high-speed rotating object with single-pixel oblique detection

High-speed rotating objects are widely seen in industrial applications and everyday life. The rotation speed is so high that even minor defects can lead to severe consequences. However, visualizing such small defects online is challenging for conventional imaging, as high-speed rotation results in severe motion blur. In this Letter, we propose a method for visualizing small defects on high-speed rotating objects. The method is based on "time-freezing" single-pixel imaging. It converts a dynamic imaging problem into a static imaging problem by exploiting the repetition of the object's rotation. As such, the method can capture a series of images corresponding to different rotation angles of the target object, even when the object is in operation. Thus, the proposed method enables online defect visualization. To make small defects visible, we propose the use of three equally spaced single-pixel detectors around the object to conduct oblique detection. Such a configuration enhances the contrast of small features. We demonstrate the method by imaging an open hard disk drive that rotates at ~9,700 revolutions per minute. The artificial scratches and fingerprints can be clearly seen in the reconstructed images. We believe that this method holds potential for online non-destructive testing and safety monitoring of various high-speed rotating machinery.