Confocal Displacement Sensor Aberration Cancellation

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Solution Overview

Problem

Confocal displacement sensors face measurement accuracy deterioration due to spherical aberrations in optical members, which are significant across various wavelength components, leading to blurred images and reduced precision.

Innovation Solution

The design incorporates a diffraction lens and a refraction lens with opposing spherical aberration polarities, along with an aspherical lens and additional diffraction or refraction lenses, to cancel out spherical aberrations across a wide wavelength band, and includes a fiber cable with an optical fiber pinhole for improved optical design and protection of the non-diffraction surface.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a spherical lens is used to converge detection light, then the optical system can be simplified, but spherical aberration occurs causing image blur and measurement accuracy deterioration

Engineering Contradiction:

Improveoptical system complexityVSAvoidmeasurement accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent combines a diffraction lens and a refraction lens into a composite optical member. The diffraction lens introduces spherical aberration with one polarity while the refraction lens introduces spherical aberration with the opposite polarity, achieving cancellation of spherical aberration effects across a wide wavelength band.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent changes the optical parameters by using lenses with different focal lengths and aberration characteristics. The diffraction lens has a shorter focal length and introduces positive spherical aberration, while the refraction lens has a longer focal length and introduces negative spherical aberration, creating a balance that eliminates net spherical aberration.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If an optical member is designed to minimize spherical aberration for a specific wavelength, then measurement accuracy improves for that wavelength, but spherical aberration occurs for other wavelength components

Engineering Contradiction:

Improvemeasurement accuracy for specific wavelengthVSAvoidwavelength band coverage

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The composite optical member serves multiple functions simultaneously: it converges detection light, introduces axial chromatic aberration for depth resolution, and cancels spherical aberration across a wide wavelength band. This multi-functionality allows the system to maintain measurement accuracy for all wavelength components used in white light detection.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent converts the harmful spherical aberration introduced by each individual lens into a beneficial effect by combining them. The spherical aberration from the diffraction lens and the refraction lens, which would normally be harmful, are utilized to cancel each other out, creating a net zero spherical aberration effect across the wavelength band.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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

This configuration effectively prevents spherical aberrations over a wide wavelength range, enhancing measurement accuracy and facilitating optical design, while protecting the diffraction lens surface and allowing for precise displacement measurements.

Implementation Method 1

a first diffraction lens configured to diffract the detection light

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

a first refraction lens configured to refract the detection light

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 3

an optical member that causes an axial chromatic aberration in the detection light emitted via the pinhole

Methodology Applied

Scientific EffectAxial chromatic aberration: Dispersion (of waves)

Data Source

PatentUS10215631B2Confocal displacement sensor

Publication Date: 2019.02.26 KEYENCE CORP

AI summary

To provide a confocal displacement sensor that can prevent deterioration in measurement accuracy due to a spherical aberration of an optical member. The confocal displacement sensor includes a light source for light projection configured to generate light having a plurality of wavelengths, a pinhole configured to emit detection light by allowing the light emitted from the light source for light projection to pass, an optical member configured to generate an axial chromatic aberration in the detection light emitted via the pinhole and converge the detection light toward the measurement object, a measurement control section configured to calculate displacement of the measurement object on the basis of, in the detection light irradiated on the measurement object via the optical member, detection light passed through the pinhole by being reflected while focusing on the measurement object, and a head housing configured to house the pinhole and the optical member. The optical member includes a first diffraction lens configured to diffract the detection light and a first refraction lens configured to refract the detection light. The first diffraction lens is disposed with a non-diffraction surface exposed from the head housing.