Homogenized Laser Illumination Line via Linear Diffuser

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Solution Overview

Problem

Laser light-based measurements are impaired by sparkle and speckle effects caused by spurious reflections and interference from facetted and optically-rough surfaces, leading to uneven and distorted images of illumination lines, which reduce measurement accuracy.

Innovation Solution

A system comprising a fan-shaped beam generator and a linear diffuser, which spreads the laser light to form a homogenized and de-speckled illumination line by diffusing the light along a predetermined direction, using a combination of linear diffusers, Powell lenses, or cylindrical lenses, and allowing for relative motion between these components to further reduce speckle patterns.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If laser light is projected directly to form an illumination line, then the illumination line provides sharp and bright lighting, but sparkle and speckle effects occur causing uneven and distorted images

Engineering Contradiction:

Improvebrightness of illumination lineVSAvoidsparkle and speckle effects

Core Design Contradiction:

Illumination intensityVSObject-affected harmful factors

Solution Approach 1:

A diffuser is introduced as an intermediary component between the laser light source and the object. The diffuser scatters the coherent laser light to create a homogenized illumination line, eliminating speckle patterns caused by direct coherent light reflection while maintaining sufficient brightness for measurement applications.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The coherence parameter of the laser light is modified by passing it through the diffuser. This transforms the highly coherent laser beam into partially coherent light that illuminates the object without producing speckle interference patterns, while preserving the spatial distribution needed for accurate surface profiling.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If a diffuser is used to reduce speckle effects, then speckle patterns are minimized, but the illumination line becomes less bright and more diffuse

Engineering Contradiction:

Improvespeckle patternsVSAvoidbrightness of illumination line

Core Design Contradiction:

Object-affected harmful factorsVSIllumination intensity

Solution Approach 1:

Instead of completely diffusing the laser light which would eliminate brightness, a controlled amount of diffusion is applied through the diffuser. This partial diffusion approach sufficiently reduces speckle patterns while maintaining adequate illumination intensity for practical measurement applications.

Inventive Principle:

Principle #16Partial or excessive action

3Stability of the object's composition

If the illumination line is homogenized along the predetermined direction, then uniformity is improved, but the Gaussian profile perpendicular to the direction may be altered

Engineering Contradiction:

Improveuniformity of illumination lineVSAvoidGaussian profile

Core Design Contradiction:

Stability of the object's compositionVSShape

Solution Approach 1:

The diffuser is designed to apply different diffusion characteristics in different directions. Along the predetermined direction (e.g., horizontal), the diffuser creates strong homogenization for uniform illumination. Perpendicular to this direction (e.g., vertical), the diffuser maintains the natural Gaussian profile of the laser beam, preserving the desired spatial characteristics for measurement accuracy.

Inventive Principle:

Principle #3Local quality

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

The solution results in a homogenized illumination line that is free from speckle, maintaining the original Gaussian profile perpendicular to the diffusion direction, enhancing measurement accuracy and ensuring laser safety by distributing the light intensity over a longer source length.

Implementation Method 1

a linear diffuser disposed between the light source and the object, such that each of the fan-shaped beam generator and the linear diffuser spreads, along a predetermined direction, light transmitted there through

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

The fan-shaped beam generator and the linear diffuser can be moved relative to each other along the predetermined direction. In either of these cases, laser light transmitted through the fan-shaped beam generator and the linear diffuser is projected in a sheet or fan to an object where its intersection with the sheet or fan forms an illumination line that (i) is homogenized along the predetermined direction and (ii) has a Gaussian profile

Methodology Applied

Scientific EffectSpeckle reduction through motion:

Data Source

PatentUS11598973B2Forming a homogenized illumination line which can be imaged as a low-speckle line

Publication Date: 2023.03.07 COGNEX CORP

AI summary

A system for forming a homogenized illumination line which can be imaged as a low-speckle line is disclosed. The system includes a laser configured to emit a collimated laser beam; and an illumination-fan generator that includes one or more linear diffusers. The illumination-fan generator is arranged and configured to (i) receive the collimated laser beam, (ii) output a planar fan of diffused light, such that the planar fan emanates from a light line formed on the distal-most one of the one or more linear diffusers, and (iii) cause formation of an illumination line at an intersection of the planar fan and an object.