Surface Reflection Encoder Scale Oxidation Resistance

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Solution Overview

Problem

Surface reflection encoders face reliability issues due to oxidation of the phase grating surface, which decreases diffraction efficiency, especially in harsh environments like high humidity, and existing solutions have not adequately addressed this problem.

Innovation Solution

A surface reflection encoder scale with a phase grating formed from a combination of titanium silicide and chromium, where titanium silicide is used for convex parts and chromium for concave parts, and the entire surface is coated with gold to maintain high light reflection and stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If metal materials are used for the phase grating asperities to achieve high light reflection factor, then the light reflection factor is improved, but oxidation occurs on the phase grating surface in harsh environments, causing diffraction efficiency to decrease and reliability to deteriorate

Engineering Contradiction:

Improvelight reflection factorVSAvoidreliability

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

The patent applies composite materials by combining titanium silicide and chromium in a layered structure for the phase grating asperities. The titanium silicide layer provides high light reflection factor while the chromium layer prevents oxidation in harsh environments. This composite material approach resolves the contradiction by integrating the benefits of both materials: high reflectivity and oxidation resistance, thereby maintaining diffraction efficiency and reliability simultaneously.

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If chromium and metal etching stopper combination is used to control phase grating height accurately, then manufacturing precision is improved, but oxidation easily occurs on the phase grating surface in high-humidity environments, decreasing diffraction efficiency and impairing reliability

Engineering Contradiction:

Improvephase grating height controlVSAvoidreliability

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent replaces the conventional chromium-metal etching stopper combination with a chromium-titanium silicide composite material system. This composite maintains the etching stopper function for precise height control while adding oxidation resistance through the titanium silicide layer, thereby resolving the contradiction between manufacturing precision and reliability in humid environments.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent changes the material parameters by selecting titanium silicide with specific properties (high reflection factor, oxidation resistance, and suitable etching characteristics) to replace conventional metals. This parameter change enables the material to simultaneously provide precise height control and resistance to oxidation, resolving the contradiction between manufacturing precision and reliability.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If conventional metal materials are used for the phase grating, then ease of manufacture is maintained, but the unknown cause of reliability impairment is oxidation which decreases diffraction efficiency

Engineering Contradiction:

Improveease of manufactureVSAvoidreliability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

Inventive Principle:

Principle #40Composite materials

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 material combination significantly improves the reliability of the surface reflection encoder by preventing oxidation and maintaining high diffraction efficiency, even in harsh conditions, thereby enhancing the accuracy and stability of the encoder.

Implementation Method 1

a reflection phase grating provided on the substrate and having asperities for changing a phase of reflected diffracted light on its surface

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

changing a phase of reflected diffracted light

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 3

the cause is oxidation of the phase grating surface... a material combination of metal silicide (particularly, titanium silicide) and chromium from among a large number of materials is extremely effective

Methodology Applied

Scientific EffectOxidation resistance: Oxidation

Data Source

PatentUS7916305B2Surface reflection encoder scale and surface reflection encoder using the same

Publication Date: 2011.03.29 MITUTOYO CORP

AI summary

A surface reflection encoder scale is used with a surface reflection encoder for detecting a relative movement amount of a member for making a relative move. The surface reflection encoder scale includes a substrate of the member or a substrate provided on the member and a reflection phase grating provided on the substrate and having asperities for changing a phase of reflected diffracted light on its surface. The asperities of the phase grating are formed of a deposition film of metal silicide and chromium.