A measurement method for the diameter of aero-engine transmission shafts based on telecentric line-scan imaging

Abstract The transmission shaft is a critical component of aero-engine and it plays a key role in connecting transmission gears and transferring power and torque. Its geometric dimensions are a crucial factor affecting performance of aero-engines. To address the problems of probe wear, low measurement efficiency, and potential damage to the workpiece surface associated with traditional contact-based measurement methods, this paper proposes a shaft diameter measurement method for aero-engine transmission shafts based on telecentric line-scan imaging. A measurement system is designed using an imaging module composed of a line-scan camera and a telecentric lens to capture the projected contour image of the shaft axial cross-section. A precise calibration method is developed to correct imaging distortions caused by intrinsic parameter errors, motion speed fluctuations, and lens manufacturing imperfections. Edge points are extracted from the axial projection image, and those on both sides of the shaft diameter are linearly fitted to obtain a pair of parallel lines, from which the diameter is obtained. The proposed method is applied to a transmission shaft with a reference diameter of 28.002 mm, yielding a measured diameter of 28.010 mm with a standard deviation of 0.002 mm, thereby verifying its effectiveness. This method can also be extended to the diameter measurement of other shaft-like components.