Resistive Touch Sensor Inset Adhesive Layer for Force Uniformity
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Solution Overview
Problem
Current resistive touch sensors require a significant increase in touch force near the peripheral edges due to their design, leading to non-uniform touch force distribution, which existing solutions either reduce the usable area or complicate the sensor, increasing the risk of shorting.
Innovation Solution
Incorporating an inset adhesive layer between the sensor top sheet and the peripheral edge seal to deform the top sheet, positioning the touch active area closer to the base layer, thereby reducing the touch force required near the edges and enhancing planarity across the sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a peripheral edge seal is used to bond the sensor top sheet to the base layer, then the structural integrity of the sensor is improved, but the touch force required increases significantly near the peripheral edges
Solution Approach 1:
The patent introduces a second adhesive layer with different properties (lower viscosity, lower elasticity) positioned specifically in the peripheral region where high touch force is problematic. This local quality change allows the peripheral area to deform more easily under touch pressure while the central area maintains its structural integrity through the first adhesive layer and peripheral edge seal.
Solution Approach 2:
The adhesive bonding system is segmented into two distinct layers: a first adhesive layer extending to the peripheral edge seal for structural support, and a second adhesive layer positioned inward to provide localized compliance. This segmentation allows each layer to perform its specific function independently, resolving the contradiction between structural integrity and touch force uniformity.
2Force
If icons are located inward from the edge of the display to reduce peripheral edge touch force issues, then touch force uniformity is improved, but the usable portion of the touch sensor decreases
Solution Approach 1:
The second adhesive layer is applied in advance during manufacturing to pre-deform the sensor top sheet in the peripheral regions. This preliminary action ensures that when the device is assembled and used, the touch force is already optimized across the entire active area, eliminating the need to reduce the usable area by moving icons inward.
3Force
If the sensitivity of touch force is adjusted to make relative touch force increase difficult to perceive, then touch force uniformity is improved, but the device complexity increases and risk of sensor shorting increases
Solution Approach 1:
The second adhesive layer uses a disposable, low-cost material with specific rheological properties (lower viscosity, lower elasticity) that can be easily applied and removed during manufacturing. This simple, inexpensive solution avoids the complexity of sophisticated electronic sensitivity adjustment mechanisms while achieving touch force uniformity through physical deformation of the adhesive layer itself.
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
This configuration increases the active area of the touch sensor while ensuring uniform touch force distribution, making more of the viewing area usable and reducing the required touch force near the edges, thus improving the robustness and reliability of the sensor.
Implementation Method 1
the second adhesive layer deforms the sensor top sheet proximate the peripheral edge seal such that the touch active area of the sensor top sheet is positioned closer to the base layer
Implementation Method 2
a first adhesive layer bonded on a peripheral edge portion of the sensor top sheet, and a second adhesive layer, inset relative to the peripheral edge seal, positioned between the first adhesive layer and the sensor top sheet
Data Source
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AI summary
A resistive touch sensor (100) includes a base layer (102), a sensor top sheet (104) positioned in spaced apart relation to a base layer, and a peripheral edge seal (108) formed between the sensor top sheet and the base layer. The sensor further includes a first adhesive layer (112) bonded on a peripheral edge portion to the sensor top sheet, and a second adhesive layer (114), inset relative to the peripheral edge seal, positioned between the first adhesive layer and the sensor top sheet. The second adhesive layer is bonded on one side to the first adhesive layer and an opposing side to the sensor top sheet corresponding to a portion of a touch active area. The second adhesive layer causes a planarity change in the sensor top sheet proximate the peripheral edge seal thereby increasing the usable area and improving uniformity of touch force across the sensor.