A Full Field-of-View Online Visual Ferrograph Debris Detector Based on Reflected Light Microscopic Imaging

For improving the detection accuracy of wear debris visual information for online wear monitoring, a full field-of-view Online Visual Ferrograph (OLVF) debris detector is presented. In current OLVF debris detector, a semi-transparent optical diffusion film is clamped into the gap between the bottom optical quartz window and two magnetic poles as the background of full field-of-view OLVF microscopic imaging, by which the emitted light of circular ring LED array is diffusely reflected. A reflected light microscopic imaging system is developed to form the full field-of-view imaging of OLVF, and a mathematical relationship between its depth of field and the oil-pumping and oil-free axial deviations of CMOS image plane is established, by which the oil chamber height can be determined. An optical focusing mechanism is applied to adjusting the optical magnification and the optical resolution of about 7.2 μm is derived under 2.0× optical magnification. Moreover, a microscopic imaging model is proposed to evaluate the characteristics of full field-of-view OLVF microscopic imaging. The simulation results show that the high-quality microscopic imaging can be obtained near the optical axis of CMOS image plane under 2.0× optical magnification and oil attenuation coefficient of less than 2.0. Two experiments were conducted to validate the microscopic imaging performance and effectiveness of the current detector. The results show that the detector can be applied for capturing the full field-of-view reflected ferrogram of wear debris from different in-use lube oils, and it can also detect debris concentration more accurately for monitoring the fast-changing wear of the machines.