Heterodyne interferometric phase demodulation system based on hysteresis alignment for CNC machine tool positioning errors.

To address metastability, phase misalignment, and wavelength jumps in the high-frequency heterodyne interferometric measurement of computer numerical control (CNC) machine tool positioning errors, a robust all-hardware field-programmable gate array (FPGA) phase demodulation system is developed. The architecture adopts an all-hardware design covering the complete process from signal preprocessing to synchronous data alignment. The front-end integrates time-domain constraints and multi-stage convergence to filter noise and suppress metastability. The core layer utilizes a wide-threshold hysteresis algorithm with a quarter-cycle buffer to eliminate counting errors at the fundamental level. The back-end employs synchronous latching and handshake protocols for precise data alignment. Experiments conducted on a 3.2 m guide rail demonstrate that the average repeatability of the proposed system reaches 0.59µm, outperforming the Renishaw XL-80 (0.88µm), and the nonlinear residuals of both systems exhibit high consistency. Stability tests over a 1.5 m long-distance open path further confirm that the raw fluctuations of the system remain at the sub-micrometer level, with no phase-locking failures or jumps. This timing-deterministic, jump-free hardware solution offers significant potential for precision measurement in complex industrial environments.