Interferometric Probe Curved Wavefront Slope Measurement

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Solution Overview

Problem

Conventional non-contact optical probes for coordinate measuring machines are limited by the need for precise positioning relative to the surface, which restricts the range of surface slopes that can be measured and increases complexity and uncertainty in measurement systems.

Innovation Solution

A non-contact optical probe using a spectrally controllable light source and a Fizeau interferometer configuration with diverging or converging wavefronts to produce localized interferometric fringes at a predetermined distance from a spherical reference surface, allowing for high sensitivity and precision in measuring a wide range of surface slopes without the need for precise alignment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional non-contact optical probes are used, then measurement sensitivity is improved, but the range of measurable surface slopes is limited and positioning precision requirements increase

Engineering Contradiction:

Improvemeasurement sensitivityVSAvoidrange of surface slopes

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent employs a spherical reference surface instead of a flat one, which fundamentally changes the interference pattern geometry. This spherical curvature allows the interferometer to accommodate a wide range of surface slopes by matching the spherical wavefront to the measurement requirements, thereby expanding the measurable surface slope range while maintaining measurement sensitivity

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The invention changes the geometric parameters of the reference surface from flat to spherical, and adjusts the optical path difference to create localized fringes. This parameter transformation enables the system to measure surfaces with varying slopes without requiring precise repositioning, thus resolving the contradiction between sensitivity and adaptability

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If conventional optical probes are reoriented to measure different surface slopes, then measurement accuracy is maintained, but system complexity and calibration requirements increase

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidsystem complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The spherical reference surface configuration provides a universal measurement capability that works for various surface slopes without requiring reorientation. The single spherical reference surface serves multiple measurement functions, eliminating the need for complex repositioning mechanisms and reducing overall system complexity while maintaining measurement accuracy

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Measurement precision

If mechanical probes are used for surface measurement, then contact measurement is achieved, but the surface may be damaged or contaminated

Engineering Contradiction:

Improvemeasurement capabilityVSAvoidsurface damage or contamination

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the mechanical contact probe with a non-contact optical interferometric measurement system. This substitution eliminates physical contact between the measurement tool and the test surface, thereby preventing surface damage or contamination while maintaining high measurement precision through optical interference patterns

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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

Enables accurate and precise measurement of various surface types with a large range of acceptance angles, overcoming the limitations of prior optical probes by allowing non-contact measurement of delicate parts with high surface slope tolerances and reducing measurement complexity.

Implementation Method 1

Interference fringes localized relative to a reference surface are used to detect the test surface position

Methodology Applied

Scientific EffectInterference: Interference

Implementation Method 2

the presence of the surface is sensed by observing changes in a particular physical quantity such as reflected light

Methodology Applied

Scientific EffectLight reflection: Reflection

Data Source

PatentEP3227633B1Interferometric non-contact optical probe and measuring method

Publication Date: 2020.02.05 APRE INSTR LLC

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AI summary

A non-contact optical probe (10,32,36) utilizes an optical reference surface (18,34,38) that projects a curved test wavefront (T) toward the test surface (S) and detects it by creating curved interferometric fringes (16) localized in space in front of the reference surface. When a point to be measured on the test surface (S) intersects the location of the fringes, the condition is detected by the probe. Because the fringes (16) are localized at a known position in space with respect to a reference system, the precise coordinate of the surface point can be established. Such localized fringes are preferably produced by a spectrally controllable light source (12). The curvature of the fringes ensures a sufficiently large angle of acceptance for the probe to capture light reflected from points of high surface slope. The probe is particularly suitable for coordinate measurement machines.