Ultrashort Pulse Laser Marking Metrological Scales

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Solution Overview

Problem

Existing methods for forming precision marks on metrological scales using laser light face challenges in dimensional control, thermal management, and adaptability to different surface types, particularly leading to inaccuracies and heat-related issues in thin metallic scales.

Innovation Solution

The use of an ultrashort pulse laser with controlled displacement and fluence, optimized to produce ultra-short ablative pulses for precise marking, minimizing thermal effects and ensuring accurate spacing and surface finish, with a controller adjusting for pitch errors and thermal compensation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional laser marking is used on thin metallic scales, then marking can be produced, but thermal energy transfer causes dimensional changes and inaccuracy

Engineering Contradiction:

Improvescale accuracyVSAvoidthermal energy transfer

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent changes the pulse duration parameter from conventional lengths (above 4 picoseconds) to ultrashort lengths (below 4 picoseconds). This parameter change fundamentally alters the material interaction mechanism from melting and boiling with thermal transfer to direct ablation with minimal thermal energy transfer, thereby resolving the contradiction between achieving marks and avoiding thermal damage

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs pulsed laser action rather than continuous irradiation. By delivering energy in discrete ultrashort pulses, the system allows thermal diffusion to occur between pulses while concentrating energy delivery in brief intervals, achieving effective material removal with minimized cumulative thermal buildup in the workpiece

Inventive Principle:

Principle #19Periodic action

2Manufacturing precision

If laser light is used to mark surfaces, then marks can be formed, but dimensional control of the laser light relative to the surface is difficult

Engineering Contradiction:

Improvespacing accuracyVSAvoiddimensional control system

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent replaces complex mechanical positioning and control systems with a more straightforward approach using ultrashort pulse laser ablation. The precision is achieved through the inherent characteristics of ultrashort pulse interaction with material rather than through complex mechanical dimensional control, simplifying the overall system while maintaining accuracy

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Adaptability or versatility

If laser marking is applied to different applications, then versatility is improved, but adaptation to suit different surfaces requires complex parameter selection

Engineering Contradiction:

Improveapplication rangeVSAvoidparameter control system

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent employs ultrashort pulse laser ablation as a universal marking mechanism that works across different material types and surface conditions. The fundamental ablation mechanism remains consistent regardless of material, providing a single versatile approach that eliminates the need for complex parameter optimization for each specific application

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Productivity

If continuous laser irradiation is used for marking, then marking efficiency is improved, but heat build-up causes material damage

Engineering Contradiction:

Improvemarking efficiencyVSAvoidheat build-up

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent uses periodic pulsed irradiation with ultrashort duration pulses. This allows the material to be processed efficiently through repeated ablation events while the intervals between pulses and the ultrashort pulse duration prevent thermal diffusion and cumulative heat buildup, resolving the contradiction between productivity and thermal damage

Inventive Principle:

Principle #19Periodic 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

This approach significantly improves scale accuracy by reducing thermal energy transfer, maintaining precision with minimal thermal expansion uncertainties, and achieving high optical contrast on polished substrates, especially beneficial for thin metallic scales.

Implementation Method 1

the laser produces a plurality of ultra-short output pulses of a fluence at the substrate such that the metrological scale marks are formed by laser ablation

Methodology Applied

Scientific EffectLaser ablation: Laser Ablation

Implementation Method 2

for pulse lengths below approximately 4 picoseconds (i.e. ultrashort pulses), the molten stage is omitted with the material either (depending on correct understanding of the mechanism) being sublimated straight from the solid to the gaseous or ejected from the substrate as minute solid particles

Methodology Applied

Scientific EffectAblation: Ablation

Data Source

PatentUS8466943B2Laser marking

Publication Date: 2013.06.18 RENISHAW PLC

AI summary

A method and apparatus is disclosed for producing precision marks (28) for a metrological scale in the form of a stainless steel ribbon (10). A laser (21) is used to produce ultra-short pulses, which have a fluence at the ribbon such that ablation takes place. The laser light can be scanned via scanner (25) and the pitch of the marks (28) can be controlled. The ablative technique causes little thermal input and improves the accuracy of the scale.