Real-time monitoring and mechanism study of optical ultra-precision sub-aperture polishing process based on torque sensing

For hard and brittle materials such as optical glass, sub-aperture polishing is a key technique for achieving high-quality optical surfaces, which is crucial for ensuring excellent optical performance and long service life of optical components. However, the current evaluation of the polishing process relies on offline measurements of the surface after polishing, making it difficult to dynamically monitor material removal during the polishing process. This study attempts to introduce a high-precision torque sensor to observe in real-time the relationship between torque and abrasive concentration, particle size, removal efficiency, and intermediate frequency error during the polishing process. The experimental results indicate that the torque signal can effectively reflect the material removal efficiency. As the abrasive concentration varies from 0 wt.% to 37 wt.%, the efficiency exhibits a rapid increase and stabilization, which aligns with the trend of torque signal intensity changes. This phenomenon demonstrates that once the concentration approaches saturation, the efficiency becomes relatively insensitive to changes in concentration, providing a potential for deterministic improvement of free abrasives. Notably, contrary to traditional understanding, the torque, processing efficiency, and residual mid-frequency error levels of abrasives with a median particle size of 1μm are higher than those at a particle size of 2μm. This suggests that particle size is not the sole critical factor in controlling processing quality, and the underlying principles merit further investigation. This study has demonstrated the feasibility of using torque measurement as a real-time monitoring method in the field of optical processing through a series of experiments.