Inertial Sensor Electrode Layout to Suppress Orthogonal Sensitivity

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Solution Overview

Problem

Existing physical quantity sensors, such as those described in JP-A-2021-032819, experience increased sensitivity in directions orthogonal to the detection axis due to seesaw operations when accelerations are applied in non-target directions, leading to degraded detection accuracy.

Innovation Solution

The physical quantity sensor design includes a movable body with specific gravity center positioning and electrode thickness configurations, where hm=hr, ensuring the gravity center of the movable body and the rotation axis of the support beams coincide, reducing sensitivity in non-target directions while maintaining signal-to-noise ratio improvements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the physical quantity sensor uses a conventional structure with electrodes and support beams, then it can detect physical quantities in the target direction, but sensitivity increases in orthogonal directions causing degraded detection accuracy

Engineering Contradiction:

Improvedetection accuracyVSAvoidsensitivity in orthogonal directions

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies asymmetry by making the first and second electrode groups have different thicknesses in the third direction. Specifically, the first electrode group has a greater thickness than the second electrode group, creating an asymmetric mass distribution that positions the gravity center of the movable body at the same height as the rotation center of the support beams. This asymmetric design ensures that accelerations in orthogonal directions do not generate torque around the rotation axis, thereby reducing sensitivity in non-target directions while maintaining detection accuracy in the target direction.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent changes the thickness parameter of the electrode groups to control the gravity center position. By adjusting the thickness of the first electrode group relative to the second electrode group, the design achieves hm=hr (height of gravity center equals height of rotation center). This parameter change directly addresses the technical contradiction by eliminating the harmful seesaw operation in orthogonal directions while preserving the detection function in the target direction.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the electrode thicknesses are increased to improve signal-to-noise ratio, then detection sensitivity in target direction improves, but sensitivity in orthogonal directions increases causing interference

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidinterference from in-plane rotations

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The asymmetric thickness design allows the electrode groups to have sufficient thickness for good signal-to-noise ratio while preventing harmful seesaw operations. The first electrode group is thicker than the second, creating a specific mass distribution that positions the gravity center at the rotation center height. This asymmetric configuration ensures that even with increased thickness, accelerations in orthogonal directions do not produce torque, thus improving reliability without introducing interference.

Inventive Principle:

Principle #4Asymmetry

3Ease of manufacture

If the movable body is designed with symmetric electrode groups, then manufacturing is simplified, but seesaw operation occurs in non-target directions reducing measurement precision

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoiddetection accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent deliberately introduces asymmetry in the electrode group thicknesses to prevent seesaw operation. The first electrode group has a greater thickness than the second electrode group, which creates the necessary mass distribution to position the gravity center at the rotation center height. This asymmetric design, while slightly more complex than symmetric design, is still manufacturable and dramatically improves measurement precision by eliminating the harmful seesaw operation in non-target directions.

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 achieves high-accuracy detection of physical quantities in the target direction with reduced sensitivity in orthogonal directions, preventing interference from in-plane rotations and resonance, and enhancing the signal-to-noise ratio.

Implementation Method 1

a first movable electrode group provided at the first base portion and facing the first fixed electrode group in the second direction

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS12480969B2Physical quantity sensor and inertial measurement unit

Publication Date: 2025.11.25 SEIKO EPSON CORP

AI summary

A physical quantity sensor includes a fixed portion, a support beam, a movable body, and a first fixed electrode group. The movable body is coupled to the other end of the support beam, and the first fixed electrode group is provided at a substrate and arranged in a first direction of the support beam. The movable body includes a first coupling portion, a first base portion, and a first movable electrode group. The first movable electrode group faces the first fixed electrode group in a second direction. Further, hm=hr, where hm is a height of a gravity center position of the movable body in a third direction and hr is a height of a rotation center of the support beam in the third direction.