White Light Interferometer Height Mapping via PCA Vibration Separation

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Solution Overview

Problem

White light interferometry for determining height maps is affected by vibrations of the sample relative to the interferometer, leading to inaccuracies due to phase shifts, which existing vibration dampers may not sufficiently address, increasing costs and reducing accuracy, reliability, and repeatability.

Innovation Solution

A method using principal component analysis of a stack of interferograms to separate random phase shifts from phase shifts related to the sample height, employing a white light interferometer with a broad band light source, optical sensor, and processor to determine a height map by decomposing the interferogram signals into orthogonal components, and correcting the global sign of the measured phase.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If vibration dampers are used to isolate the white light interferometer from vibrational effects, then the reliability of height map determination is improved, but the overall costs increase and the dampers may not sufficiently reduce the effect of vibrations

Engineering Contradiction:

Improvereliability of height map determinationVSAvoidoverall costs

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces mechanical vibration isolation systems with a signal processing approach. By applying principal component analysis to the interferogram stack, the method separates vibration-induced phase shifts from actual height information through mathematical decomposition, eliminating the need for physical dampers and isolation equipment.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces principal component analysis as an intermediary processing step between data acquisition and height map generation. This mathematical intermediary separates the harmful vibration effects from the useful height information, allowing accurate measurement without physical isolation.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If vibration dampers are used to reduce vibrational effects, then the accuracy of height map determination is improved, but the overall costs increase and sufficiency of vibration reduction is uncertain

Engineering Contradiction:

Improveaccuracy of height map determinationVSAvoidoverall costs

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent substitutes expensive mechanical vibration isolation systems with computational signal processing. The principal component analysis method achieves vibration compensation through mathematical operations on the interferogram data, providing high measurement precision without additional hardware costs.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the approach from physical parameter control (mechanical isolation) to data parameter processing. By analyzing and decomposing the interferogram signals through principal component analysis, the method extracts height information while filtering out vibration effects in the signal domain.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If traditional white light interferometry is used without vibration compensation, then the device complexity is low, but the accuracy and reliability of height map determination deteriorate due to phase shifts from vibrations

Engineering Contradiction:

Improvedevice complexityVSAvoidaccuracy of height map determination

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent performs preliminary processing of the interferogram stack by applying principal component analysis before final height map generation. This preliminary decomposition separates vibration effects from height information, ensuring accurate measurements are achieved during the data processing stage rather than requiring complex hardware modifications.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Reduces the dependency on vibrations, improving the accuracy and reliability of height map determination by isolating random phase shifts, thereby enhancing measurement precision and quality control in production processes.

Implementation Method 1

White light interferometry relies on determining phase differences of reflected light due to differences in path length of light traveling along light paths in the interferometer

Methodology Applied

Scientific EffectInterference: Interference

Data Source

PatentEP4585880A1Method for determining a height map using a white light interferometer and white light interferometer for the same

Publication Date: 2025.07.16 MITUTOYO CORP

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AI summary

The invention relates to a method for determining a height map of a surface of a sample through white light interferometry wherein use is made of a white light interferometer with a broad band light source and an optical sensor comprising pixels. The invention further relates to a white light interferometer comprising a broad band light source, an optical sensor comprising pixels and a processor configured for performing the method of the invention. The invention further relates to a digital data carrier comprising a computer program which, when run on a processor of a white light interferometer according to the invention, causes the white light interferometer to perform the method according to the invention.