MEMS Inertial Sensor Center of Gravity Impact Resistance

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Solution Overview

Problem

Inertial sensors using MEMS techniques face issues with excessive seesaw-swing leading to collisions with projections, potential short-circuits, and operation failures due to stiction, especially under strong vibrations or impacts, which can result in breakage of movable members and contact failure.

Innovation Solution

The inertial sensor design includes a substrate with a first movable member and two additional movable members, each with a distinct rotation axis, supported by beams, and projections on the substrate or movable members to prevent excessive seesaw-swing, with a center of gravity closer to the center line than the supporting beams, enhancing impact resistance and reducing unnecessary vibration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If projections are provided to prevent excessive seesaw-swing, then the movable member is protected from short-circuit with fixed electrodes, but the movable member may collide with and break the projections under strong vibration or impact

Engineering Contradiction:

Improveshort-circuit preventionVSAvoidimpact resistance

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The movable member is divided into multiple segments (first movable member, second movable member, third movable member) connected by supporting beams. This segmentation allows each segment to move independently and absorb impact energy, preventing the entire structure from colliding with the projections while maintaining short-circuit protection functionality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The supporting beams are designed with elastic properties to provide beforehand cushioning. When impact or strong vibration occurs, these beams deform elastically to absorb energy before the movable member can collide with the projections, thus protecting both the movable member and projections from breakage while maintaining the short-circuit prevention function.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

2Device complexity

If the movable member is designed as a single rigid body, then the structure is simple, but collision with projections under vibration or impact causes breakage and stiction

Engineering Contradiction:

Improvestructure simplicityVSAvoidoperation continuity

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The movable member is segmented into multiple parts (first, second, and third movable members) connected by supporting beams. This segmentation maintains operational reliability by allowing individual segments to move independently and avoid stiction, while the overall structure remains relatively simple and can be manufactured using standard MEMS processes.

Inventive Principle:

Principle #1Segmentation

3Reliability

If the center of gravity is positioned closer to the center line than the supporting beams, then impact resistance is enhanced and unnecessary vibration is reduced, but the structure becomes more complex

Engineering Contradiction:

Improveimpact resistanceVSAvoidstructural complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The center of gravity is deliberately positioned asymmetrically closer to the center line than the supporting beams. This asymmetric positioning enhances impact resistance by optimizing the moment of inertia and reducing unnecessary vibration during impact events. The supporting beams are configured with specific length and stiffness parameters to achieve this optimal center of gravity position while maintaining manufacturing feasibility.

Inventive Principle:

Principle #4Asymmetry

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 design enhances the impact resistance and accuracy of acceleration detection by suppressing unnecessary displacement and stress concentration, allowing the inertial sensor to operate reliably under higher acceleration and impact conditions.

Implementation Method 1

a center of gravity of the second movable member is closer to the center line than the second supporting beam, and a center of gravity of the third movable member is closer to the center line than the third supporting beam

Methodology Applied

Scientific EffectInertia: Inertia

Implementation Method 2

configured to detect an acceleration in vertical directions based on changes in capacitance between the first and second mass members having different rotation moment around the rotation axis of the movable member from each other and the first and second fixed electrodes respectively placed in the facing positions

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS11674975B2Inertial sensor, electronic apparatus, and vehicle

Publication Date: 2023.06.13 SEIKO EPSON CORP

AI summary

An inertial sensor includes a substrate, a first supporting beam being a first rotation axis extending along a first direction, a first movable member swingable around the first rotation axis, a second supporting beam being a second rotation axis extending along a second direction crossing the first direction, a second movable member swingable around the second rotation axis, a third rotation axis extending along a second direction, a third movable member swingable around the third rotation axis, and a projection, wherein the second and third movable members are line-symmetrically placed with a center line of the first movable member along the second direction as an axis of symmetry, a center of gravity of the second movable member is closer to the center line than the second supporting beam, and a center of gravity of the third movable member is closer to the center line than the third supporting beam.