Subpixelic measurement of large 1D displacements: principle, processing algorithms, performances and software

Area of Science:

• Optical Metrology
• Precision Measurement
• Image Processing

Background:

• Accurate sensing of one-dimensional (1D) rigid body displacements is crucial in various scientific and industrial applications.
• Existing methods often face trade-offs between resolution, measurement range, and processing speed.
• Sub-pixel resolution and high range-to-resolution ratios are desirable for advanced metrology.

Purpose of the Study:

• To present a novel visual measurement method for high-resolution, large-range, and high-rate 1D displacement sensing.
• To detail the measurement principle and processing algorithms for the proposed technique.
• To evaluate the theoretical and experimental performance, including resolution, range, and repeatability.

Main Methods:

• A structured target pattern composed of twin periodic grids with slightly different periods is employed.
• Fourier-like phase calculations are utilized for high-resolution measurements.
• The difference in grid periods enables phase ambiguity removal for an extended measurement range.

Main Results:

• Sub-pixelic resolution is achieved through the structured pattern and phase calculation methods.
• A high range-to-resolution ratio is demonstrated by effectively removing phase ambiguity.
• Experimental results show a 3-sigma repeatability of 5 nm over a 168 µm measurement range.
• Processing time is approximately 3 µs per line, with measurement rate limited by image acquisition.

Conclusions:

• The proposed visual measurement method offers a compelling solution for high-precision 1D displacement sensing.
• The technique effectively balances high resolution, large measurement range, and rapid processing.
• The demonstrated repeatability and processing speed indicate its potential for demanding metrology applications.