A Spectral Confocal Measurement Method for High-Aspect-Ratio Deep Holes Based on Stepped Ring Gauge and Hierarchical...

Area of Science:

• Metrology
• Optical Measurement
• Precision Engineering

Background:

• Spectral confocal microscopy faces challenges in deep-hole measurement, including uneven accuracy and profile distortion due to multi-source errors.
• Existing methods struggle to address geometric deviation, structural error, and dynamic process error comprehensively.

Purpose of the Study:

• To develop and validate a novel measurement method for spectral confocal deep-hole metrology.
• To enhance accuracy and repeatability in measuring deep holes with large length-to-diameter ratios.
• To provide a robust technical foundation for high-precision non-destructive testing of deep holes.

Main Methods:

• A hierarchical compensation system is proposed: "geometric calibration-structural correction-dynamic filtering".
• Global calibration uses a stepped ring gauge and the Levenberg-Marquardt (LM) algorithm to identify geometric parameters.
• Structural errors are corrected using a statics model, while periodic harmonic errors and random noise are filtered using least-squares harmonic fitting and adaptive wavelet threshold filtering.

Main Results:

• The method limits maximum absolute deviation in inner diameter measurement to within 0.2 μm.
• Measurement repeatability for deep holes (length-to-diameter ratio > 30:1) is stabilized between 0.8-1.6 μm.
• Expanded uncertainty is U = 3.8 μm (k = 2), enabling precise reconstruction of inner wall topography.

Conclusions:

• The proposed method effectively compensates for multi-source errors in spectral confocal deep-hole measurement.
• It achieves high precision and repeatability for deep holes with large aspect ratios.
• This technique offers a versatile solution for non-destructive testing of critical deep-hole components.