Stretchable Capacitive Touchpad with Strain Gauge Compensation
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Solution Overview
Problem
Existing touch sensors and strain gauges face challenges in accurately measuring capacitance changes due to stretching, leading to errors in pressure and touch detection, particularly when implemented on stretchable substrates, and require additional ESD protection.
Innovation Solution
A capacitive stretchable touchpad with bi-directionally stretchable textile fabric incorporating resistive strain gauges as electrodes, which correct for capacitance variations and provide ESD protection, allowing for 3D measurement of elongation and touch detection without the need for separate ESD resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If touch sensors are implemented on stretchable substrates, then wearability and flexibility are improved, but measurement precision deteriorates due to capacitance variations caused by stretching
Solution Approach 1:
The patent introduces strain gauges as intermediary elements that measure the stretching of the substrate. These strain gauges provide data about the deformation state, which is then used to compensate for capacitance variations in the touch sensor readings, thereby maintaining measurement precision on stretchable substrates
Solution Approach 2:
The system implements feedback by continuously monitoring substrate deformation through strain gauges and using this information to dynamically compensate for capacitance changes in touch sensor measurements, maintaining accuracy despite stretching
2Device complexity
If resistive strain gauges are used as electrodes in capacitive touch sensors, then device complexity is reduced by eliminating separate ESD resistors, but manufacturing precision becomes more challenging
Solution Approach 1:
The patent merges the function of ESD protection resistors with the strain gauge electrodes themselves. The strain gauges serve dual purposes: as sensing elements for substrate deformation and as ESD protection components, eliminating the need for separate ESD resistors and reducing overall device complexity
Solution Approach 2:
The strain gauge conductive elements are designed to perform multiple functions simultaneously: they act as electrodes for capacitance sensing, as strain measurement devices, and as ESD protection components, thereby reducing the total number of required components
3Adaptability or versatility
If the textile fabric is stretched in various directions, then flexibility and adaptability are improved, but measurement precision deteriorates due to non-constant surface area and capacitance
Solution Approach 1:
Strain gauges are introduced as intermediary measurement devices that quantify the stretching of the fabric in different directions. This deformation data serves as a basis for compensating capacitance variations, allowing accurate pressure measurements even when the fabric is stretched non-uniformly
Solution Approach 2:
The system dynamically adjusts for changes in geometric parameters (surface area, electrode spacing) caused by fabric stretching by using strain gauge measurements to compensate for these parameter changes in the capacitance calculation, maintaining measurement precision despite dimensional changes
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 solution enhances sensitivity in touch event detection by adjusting the detection algorithm based on resistance changes, corrects parasitic capacitance errors, and integrates touch and strain gauge functions, enabling accurate elongation monitoring and improved wearability.
Implementation Method 1
resistive strain gauges which form electrodes that provide a change of capacitance signal caused by a touch
Implementation Method 2
resistive strain gauges which form electrodes
Implementation Method 3
a uni- or bi-directionally stretchable textile fabric
Data Source
Figure 1a~1b
Figure 2
Figure 3
AI summary
It is disclosed a stretchable touchpad (10) of the capacitive type including a stretchable textile fabric (20) having a plurality of conductive elements incorporated therein. The conductive elements are resistive strain gauges (30, 40) which form electrodes to detect a change of capacitance caused by a touch. It is also disclosed a method for operating a stretchable touchpad (10) comprising the steps of measuring continuously a capacitance analog signal provided by a resistive strain gauge (30, 40) of the stretchable touchpad (10); and comparing the measured capacitance signal with a threshold value in order to determine whether or not a touch has taken place, wherein the threshold value is continuously adjusted as a function of the actual measurement of capacitance and as a function of the resistance of said resistive strain gauges (30, 40) which form the capacitor electrodes of said touchpad (10).