Touch Panel Fringe-Capacitance Sensing for Accurate Force Detection

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Solution Overview

Problem

Existing touch sensing display devices struggle to accurately detect pressing force due to small capacitance changes from resin deformation and variations in finger contact area, leading to inaccurate force detection.

Innovation Solution

A touch panel system with an active matrix substrate and color filter substrate, incorporating drive and detection electrodes, and a liquid crystal layer, where the controller supplies drive signals and detects pressing force based on signal values from detection electrodes, minimizing capacitance changes from contact area variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If an elastic dielectric layer made of resin is used to detect pressing force through capacitance change, then the touch panel can sense pressing force, but the capacitance change is very small and insufficient for accurate detection

Engineering Contradiction:

Improvepressing force detection accuracyVSAvoidcapacitance change magnitude

Core Design Contradiction:

Measurement precisionVSQuantity of substance

Solution Approach 1:

The patent changes the detection parameter from bulk capacitance change (which is small) to fringe capacitance change at electrode edges (which is significant). By positioning detection electrodes to overlap with drive electrodes and utilizing the fringe electric field effects at the edges, the system achieves large capacitance changes that correlate with pressing force magnitude.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies local quality by creating different functional regions: drive electrodes for generating electric fields, detection electrodes for sensing, and color filters for display. The detection electrodes are specifically positioned to overlap with drive electrodes to maximize fringe capacitance effects, while color filters are placed in non-overlapping regions to avoid interference.

Inventive Principle:

Principle #3Local quality

2Measurement precision

If the electrostatic capacitance is used for detecting pressing force, then the touch panel can sense touch input, but the capacitance varies with contact area changes leading to inaccurate force detection

Engineering Contradiction:

Improvepressing force detection accuracyVSAvoidcontact area variation sensitivity

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent segments the electrode functions into separate drive electrodes and detection electrodes. The drive electrodes generate the electric field while the detection electrodes sense the capacitance changes. This segmentation allows the system to measure fringe capacitance specifically at electrode edges, which is less affected by contact area variations compared to bulk capacitance measurements.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces color filters as intermediary elements positioned between the drive and detection electrodes in certain regions. These color filters act as mediators that allow the detection of pressing force through fringe capacitance changes while blocking direct capacitive coupling that would be sensitive to contact area variations.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

Enables precise detection of pressing force with high accuracy by focusing on fringe capacitance changes, reducing the influence of contact area variations and enhancing overall detection efficiency.

Implementation Method 1

a liquid crystal layer located between the active matrix substrate and the color filter substrate

Methodology Applied

Scientific EffectLiquid crystal effect: Liquid Crystals

Implementation Method 2

the controller is configured to supply a drive signal to the drive electrode and obtain a signal value from the detection electrode and to detect a pressing force applied to the touch panel by an indicator, based on the signal value obtained from the detection electrode

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS12461623B2Touch panel system and electronic device

Publication Date: 2025.11.04 SHARP DISPLAY TECHNOLOGY CORP

AI summary

A touch panel system includes a touch panel and a controller. The touch panel includes an active matrix substrate, a color filter substrate, and a liquid crystal layer located between the active matrix substrate and the color filter substrate. The active matrix substrate includes a drive electrode and a detection electrode. The drive electrode and the detection electrode are disposed on a surface of the active matrix substrate which faces the liquid crystal layer. The color filter substrate includes a conductor. The conductor is disposed on a surface of the color filter substrate which faces the liquid crystal layer. The controller is configured to supply a drive signal to the drive electrode and obtain a signal value from the detection electrode and to detect a pressing force applied to the touch panel by an indicator, based on the signal value obtained from the detection electrode.