Piezoresistive Force Sensing Unit for Multi-Touch Finger Counting
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Solution Overview
Problem
Touch-sensitive devices cannot differentiate between single and multiple finger touches, limiting the ability to trigger different commands based on the number of fingers applied, as they only measure force strength through capacitance changes without determining the number of fingers.
Innovation Solution
A substrate with force-sensitive resistors made of piezoresistive material, connected in series and applied with different voltages, allows for the identification of the number of fingers by measuring resistance variations, enabling multi-touch functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitance detection is used to measure touch force, then force strength can be detected, but the number of fingers touching cannot be determined
Solution Approach 1:
The touch sensing area is divided into multiple independent force sensing units, each containing series-connected force-sensitive resistors. By segmenting the sensing area and analyzing resistance changes in each unit separately, the system can determine both force magnitude and the number of fingers touching different regions.
Solution Approach 2:
Different regions of the touch screen are equipped with force sensing units that independently measure local pressure characteristics. Each unit provides localized resistance data that, when combined, reveals the number of fingers and their respective positions and pressures.
2Ease of operation
If only force strength measurement is implemented, then simple touch detection is achieved, but multi-touch functionality and varied command triggering are limited
Solution Approach 1:
The touch screen is divided into multiple force sensing units with readout signal lines connecting adjacent units. This segmentation allows the system to process touch information from multiple independent sensing zones, enabling multi-touch detection and diverse command triggering based on which units are activated.
Solution Approach 2:
The force sensing units serve multiple functions: detecting force magnitude, determining the number of fingers, identifying touch positions, and enabling various command operations. This multi-functionality transforms a simple force detector into a versatile multi-touch interface.
3Measurement precision
If force-sensitive resistors are connected in series with voltage application, then resistance variation can indicate force and finger number, but device complexity increases
Solution Approach 1:
Multiple force-sensitive resistors are connected in series within each force sensing unit, merging their resistance characteristics to amplify the measurable signal. The readout signal lines connect adjacent units, combining their outputs to provide comprehensive touch information while using a unified voltage application scheme across all units.
Solution Approach 2:
The series-connected force-sensitive resistors with voltage application serve multiple purposes: individual resistance measurement for force detection, collective resistance variation for finger number determination, and position identification through differential measurement across adjacent units.
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 the determination of the number of fingers touching the device and the force level applied, allowing for varied commands to be triggered based on the number of fingers and pressure, enhancing human-machine interaction.
Implementation Method 1
the force sensitive resistors are made of piezoresistive material
Data Source
AI summary
A substrate includes a plurality of force sensitive resistors, among which at least two force sensitive resistors connected in series forms a force sensing unit, wherein the first end of the force sensing unit applied with a first voltage, and the second end of the force sensing unit applied with a second voltage which is different from the first voltage; a readout signal line tapped between two adjacent force sensitive resistors connected in series; and the force sensitive resistors are made of piezoresistive material.