Monolithic Strain Gage with Segmented Foil for Fatigue Resistance

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Solution Overview

Problem

Existing strain gages require separate formation and bonding of strain sensitive and temperature compensation elements, leading to stress concentration and potential fatigue fracture due to step portions caused by soldering or similar methods.

Innovation Solution

A strain gage with monolithically formed strain sensitive and temperature compensation elements, where the temperature compensation element is created using a different material with lower specific resistance and higher temperature coefficient of resistance, eliminating the need for bonding and reducing stress concentration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If strain sensitive element and temperature compensation element are separately formed and bonded together, then each element can be optimized independently, but step portions occur on the bonded portion causing stress concentration and fatigue fracture

Engineering Contradiction:

Improvefatigue lifeVSAvoidbonding process

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the strain sensitive element and temperature compensation element into a single monolithic structure formed from one piece of metal foil. This eliminates the bonding process entirely, removing the step portions that cause stress concentration, and thereby prevents fatigue fracture while maintaining independent optimization of each element's function.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The monolithic element is segmented into functionally distinct regions: a strain sensitive element portion with high specific resistance and low temperature coefficient, and a temperature compensation element portion with low specific resistance and high temperature coefficient. This segmentation allows each region to perform its specific function while being formed as one continuous piece without bonding joints.

Inventive Principle:

Principle #1Segmentation

2Ease of manufacture

If separate formation and bonding of elements is used, then manufacturing flexibility is maintained, but additional steps and potential failure points are introduced

Engineering Contradiction:

Improvemanufacturing processVSAvoidthickness uniformity

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

By forming the strain sensitive element and temperature compensation element as one monolithic piece through continuous metal foil formation, the patent eliminates the bonding step that introduces thickness variations and step portions. This single-step formation process achieves both ease of manufacture and high manufacturing precision regarding thickness uniformity.

Inventive Principle:

Principle #5Merging (Combining)

3Reliability

If monolithic formation is used, then bonding steps are eliminated and fatigue fracture is prevented, but material selection becomes more constrained

Engineering Contradiction:

Improvefatigue resistanceVSAvoidmaterial selection

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent employs composite material construction within the monolithic structure, using different material compositions for the strain sensitive element portion (high specific resistance, low temperature coefficient) and the temperature compensation element portion (low specific resistance, high temperature coefficient). This allows the single piece to exhibit different electrical properties in different regions while maintaining the benefits of monolithic formation.

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 solution prevents fatigue fracture by eliminating the need for bonding, allowing for process reduction, miniaturization, and achieving high fatigue life by minimizing thickness differences between elements.

Implementation Method 1

a strain sensitive element... to detect the strain of an object to be measured

Methodology Applied

Scientific EffectPiezoresistive effect: Piezoresistive Effect

Implementation Method 2

a temperature compensation element having low specific resistance and high temperature coefficient of resistance

Methodology Applied

Scientific EffectTemperature coefficient of resistance: Thermo-resistive Effect

Data Source

PatentUS8640549B2Strain gage and manufacturing method thereof

Publication Date: 2014.02.04 MINEBEAMITSUMI INC

AI summary

A strain gage includes a strain sensitive element; and a temperature compensation element, wherein the strain sensitive element and temperature compensation element are monolithically formed. A method of manufacturing the strain gage includes: exposing and developing a strain sensitive element pattern and the temperature compensation element pattern; and etching the strain sensitive element pattern and the temperature compensation element pattern.