Force Sensor Signal Correction for Mechanical Relaxation

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Solution Overview

Problem

Force sensors in host devices, such as mobile devices, often produce inaccurate sensor signals due to mechanical relaxation effects when a force is applied and subsequently reduced or removed, leading to inaccuracies in button press detection.

Innovation Solution

A correction unit is introduced to estimate the mechanical relaxation effect on the sensor signal, generating a corrected signal that better represents the applied force by accounting for how the material returns to its undistorted form upon force reduction, using a mechanical model and estimation signals calculated based on elapsed time, sensor signal magnitude, and other variables.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a force sensor is used to detect button press operations, then button press detection capability is provided, but measurement precision deteriorates due to mechanical relaxation effects causing inaccurate sensor signals

Engineering Contradiction:

Improvebutton press detection capabilityVSAvoidsensor signal accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent replaces the direct mechanical measurement approach with an electrical/software-based correction system. A correction unit processes the sensor signal using a mechanical model that calculates relaxation effects, then subtracts these effects from the raw signal to produce a corrected output. This substitution of mechanical measurement with electrical correction resolves the accuracy issue while preserving button press detection capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent implements a feedback mechanism where the correction unit continuously monitors the sensor signal, estimates mechanical relaxation effects based on a mechanical model, and adjusts the output signal accordingly. The corrected signal feeds back into the system to improve subsequent measurements, eliminating the precision degradation caused by relaxation effects.

Inventive Principle:

Principle #23Feedback

2Device complexity

If the sensor system directly outputs the raw sensor signal, then device complexity is minimized, but measurement precision deteriorates due to uncorrected mechanical relaxation effects

Engineering Contradiction:

Improvesensor system structureVSAvoidforce detection accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent introduces a correction unit as an intermediary component between the force sensor and the output. This unit acts as a mediator that receives the raw sensor signal, processes it through a mechanical model to estimate relaxation effects, and generates a corrected signal. This intermediary approach improves measurement precision while adding only minimal system complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If mechanical relaxation effects are not compensated, then device complexity remains low, but reliability deteriorates due to false positives in button press detection

Engineering Contradiction:

Improvesignal processing structureVSAvoidbutton press detection accuracy

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent replaces the unreliable direct mechanical detection with an electrical correction system that compensates for relaxation effects. The correction unit uses a mechanical model to calculate and subtract relaxation effects from the sensor signal, producing a reliable output that accurately reflects actual button press operations without false positives.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The correction unit implements continuous feedback processing where the sensor signal is monitored, relaxation effects are estimated based on the mechanical model, and corrections are applied in real-time. This feedback mechanism ensures reliable button press detection by continuously eliminating the source of false positives.

Inventive Principle:

Principle #23Feedback

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 corrected signal improves the accuracy of force detection by reducing mechanical relaxation effects, resulting in more precise button press detection and reduced false positives, aligning closer to ideal sensor behavior.

Implementation Method 1

piezoresistive force sensors

Methodology Applied

Scientific EffectPiezoresistive effect: Piezoresistive Effect

Implementation Method 2

capacitive displacement sensors

Methodology Applied

Scientific EffectCapacitive sensing: Capacitance

Implementation Method 3

inductive force sensors

Methodology Applied

Scientific EffectInductive sensing: Electromagnetic Induction

Implementation Method 4

estimate an effect of the applied force on how the material will return towards an undistorted form upon a substantial reduction or removal of the applied force

Methodology Applied

Scientific EffectMechanical relaxation: Stress Relaxation

Data Source

PatentUS11520436B2Sensor signal correction

Publication Date: 2022.12.06 CIRRUS LOGIC INC

AI summary

A correction unit for use in a sensor system, the sensor system comprising a force sensor configured to output a sensor signal indicative of a temporary mechanical distortion of a material under an applied force, the correction unit configured, based on the sensor signal, to: estimate an effect of the applied force on how the material will return towards an undistorted form upon a substantial reduction or removal of the applied force; and generate a corrected signal based on the estimation.