In-plane and out-of-plane 4-DOF encoder based on grating

Multi-degree-of-freedom measurement technology plays a significant role in precision manufacturing, optical inspection, and robotic control applications. To address the demand for high-precision measurements, this study introduces a four-degree-of-freedom(4-DOF) grating system that utilizes grating interference and ray tracing principles, enabling simultaneous high-accuracy XY displacement and XY angles. The system measures in- plane displacement using grating interference, while the out-of-plane angular variations are resolved by tracking the position changes of diffracted light on a four-quadrant photodetector (QPD). Experimental findings indicate that the in-plane displacement measurement exhibits minimal error and high repeatability. The error margin is approximately ±2 microns within an 8000 microns range. The out-of-plane angular measurement error remains below 10 arcsec across a 300 arcsec range, with the capability to detect out-of-plane motion. The system offers an innovative approach to high-precision multi-degree-of-freedom measurement and demonstrates significant potential for various applications.