Piezoelectric Bending Sensor Correction for Stress Relief Errors

Solution Overview

Problem

Conventional touch input devices using piezoelectric sensors suffer from errors due to stress relieving effects in bendable apparatuses, particularly when the deformation is maintained for a long time, leading to inaccurate detection of pressing forces.

Innovation Solution

A bending sensor with a piezoelectric element, voltage detection circuit, and arithmetic unit that corrects integrated values by accounting for stress relieving effects, normalizing them to accurately detect the bent state.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If adhesive or pressure-sensitive adhesive is used to attach the piezoelectric sensor to the operation plate, then the sensor can be firmly fixed, but the adhesive produces a stress relieving effect that causes output errors after load changes

Engineering Contradiction:

Improveattachment strengthVSAvoidoutput voltage accuracy

Core Design Contradiction:

StrengthVSMeasurement precision

Solution Approach 1:

The patent applies preliminary action by performing stress relief processing on the adhesive or pressure-sensitive adhesive before the piezoelectric sensor is attached to the operation plate. This preprocessing step removes residual stresses from the adhesive in advance, preventing these stresses from interfering with the piezoelectric sensor's output measurements later. The stress relief processing is conducted before the critical measurement function is activated, thereby eliminating the source of measurement errors without compromising the attachment strength.

Inventive Principle:

Principle #10Preliminary action

2Adaptability or versatility

If the operation plate is greatly deformed and the deformation is maintained for a long time, then the device achieves bendable functionality, but the error caused by excluding detection values from stress relieving effect becomes non-negligible

Engineering Contradiction:

Improvebendable functionalityVSAvoiddetection accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent applies preliminary action by performing stress relief processing on the adhesive or pressure-sensitive adhesive before the piezoelectric sensor is attached to the operation plate. This preprocessing step removes residual stresses from the adhesive in advance, preventing these stresses from interfering with the piezoelectric sensor's output measurements later. The stress relief processing is conducted before the critical measurement function is activated, thereby eliminating the source of measurement errors without compromising the attachment strength.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent replaces the mechanical stress relief method (excluding detection values) with a thermal or chemical stress relief method. By applying heat or chemical treatment to the adhesive before sensor attachment, the residual stresses are relieved through material property changes rather than mechanical exclusion of data. This substitution allows the system to maintain accurate measurements even when the operation plate is greatly deformed and held in position for extended periods.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If threshold control method is used to exclude detection values from stress relieving effect, then pressing force detection is improved for small deformations, but significant errors occur when deformation is maintained for long time

Engineering Contradiction:

Improvepressing force detection accuracyVSAvoiddeformation maintenance duration

Core Design Contradiction:

Measurement precisionVSDuration of action of stationary object

Solution Approach 1:

The patent applies preliminary action by performing stress relief processing on the adhesive or pressure-sensitive adhesive before the piezoelectric sensor is attached to the operation plate. This preprocessing step removes residual stresses from the adhesive in advance, preventing these stresses from interfering with the piezoelectric sensor's output measurements later. The stress relief processing is conducted before the critical measurement function is activated, thereby eliminating the source of measurement errors without compromising the attachment strength.

Inventive Principle:

Principle #10Preliminary 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

The sensor accurately detects the bent state by correcting for stress relieving effects, thereby reducing errors in bendable devices.

Implementation Method 1

a piezoelectric element 10 configured to generate a voltage in response to deformation of the substrate 103

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS12405176B2Bending sensor and electronic apparatus

Publication Date: 2025.09.02 MURATA MFG CO LTD

AI summary

A bending sensor is provided that includes a piezoelectric element disposed on a bendable substrate; a voltage detection circuit that detects a voltage generated in the piezoelectric element; and an arithmetic unit that calculates an integrated value by integrating the voltage detected by the voltage detection circuit and associates the integrated value with a bent state of the substrate. Moreover, the arithmetic unit calculates in advance a corrected integrated value obtained by correcting a maximum value of the integrated value with a decrease value resulting from a stress relieving effect, associates the corrected integrated value with a first bent state of the substrate, and normalizes a calculated integrated value based on the corrected integrated value.