A Grating-Angle-Positioning method for dynamic clearance measurement of rotating blades

To address the common problem of repeatable pose recognition and dynamic clearance measurement in multi-body relative motion of complex rotating machinery, this study proposes a grating-angle-positioning method for dynamic clearance measurement. This method collaboratively attaches gratings on the relative motion components and innovatively uses the grating direction angle as a spatiotemporal positioning signal to lock the repeatable meshing position from a continuous image sequence and calculate the dynamic clearance variation. Its core contribution lies in achieving precise identification of repetitive measurement positions and stable extraction of relative gap changes in complex periodic motions. To validate the effectiveness and robustness of the proposed method, it was applied to the dynamic gap measurement of a challenging dual-rotor vertical kneader, where repeatable meshing positions were accurately located with an angular error of less than 0.05°, and clearance variation sequences at the blade meshing point over 11 operating cycles were obtained. An independent verification experiment further confirmed that this method still has high measurement accuracy under non-ideal oblique imaging conditions, with an error of less than 0.02  mm. The results show that the proposed method can achieve sub-angle repetitive pose recognition and sub-millimeter dynamic gap monitoring, providing a non-contact, full-field measurement method for the state monitoring of complex rotating machinery such as vertical kneaders.