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

Area of Science:

• Metrology and Measurement Science
• Instrumentation and Control Systems
• Digital Signal Processing

Background:

• High-frequency heterodyne interferometry is crucial for measuring computer numerical control (CNC) machine tool positioning errors.
• Existing systems face challenges with metastability, phase misalignment, and wavelength jumps, limiting accuracy.

Purpose of the Study:

• To develop a robust all-hardware Field-Programmable Gate Array (FPGA) phase demodulation system.
• To overcome limitations in high-frequency heterodyne interferometric measurements for CNC machine tools.

Main Methods:

• An all-hardware architecture was designed, encompassing signal preprocessing to synchronous data alignment.
• Front-end signal processing incorporated time-domain constraints and multi-stage convergence for noise filtering and metastability suppression.
• Core processing utilized a wide-threshold hysteresis algorithm with a quarter-cycle buffer, and back-end employed synchronous latching and handshake protocols for precise data alignment.

Main Results:

• The developed system achieved an average repeatability of 0.59µm on a 3.2m guide rail, outperforming the Renishaw XL-80 (0.88µm).
• Nonlinear residuals showed high consistency between the proposed system and the benchmark.
• Stability tests confirmed sub-micrometer raw fluctuations with no phase-locking failures or jumps over a 1.5m open path.

Conclusions:

• The timing-deterministic, jump-free hardware solution effectively addresses metastability, phase misalignment, and wavelength jumps.
• The system demonstrates significant potential for high-precision measurement in demanding industrial environments.
• The FPGA-based approach offers a robust and accurate alternative for CNC machine tool error compensation.