Optical Touch Screen With Lossy Dispersive FTIR Layer
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Solution Overview
Problem
Conventional resistive touch screens face issues such as non-transparency, deterioration of pressure-sensitive layers, periodic recalibration needs, requirement of applied pressure for detection, and inability to discern multiple touch points simultaneously, limiting their reliability and functionality, especially in bright environments.
Innovation Solution
An optical touch screen arrangement featuring an optically dispersive and lossy base plate that captures and disperses light, with sensors detecting light intensity at the edges to calculate the touch point position, utilizing total internal reflection and scattering properties to enhance accuracy and reliability, and allowing for multi-touch functionality through hyperbolic intersection algorithms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resistive touch screen overlay is used, then touch detection function is provided, but transparency and readability in direct sunlight deteriorates
Solution Approach 1:
The patent replaces the mechanical resistive overlay system with an optical detection system using a light guide and photodetectors. This substitution eliminates the need for physical contact layers, maintaining touch detection capability while significantly improving optical transparency and readability in bright sunlight conditions.
Solution Approach 2:
The patent introduces a light guide as an intermediary component between the display and the detection system. This light guide mediates the transmission of ambient light to photodetectors, enabling touch detection through optical changes without requiring opaque resistive layers, thus preserving screen transparency.
2Reliability
If pressure sensitive layers are used in resistive touch screens, then touch detection is enabled, but deterioration occurs and periodic re-calibration is required
Solution Approach 1:
The patent replaces mechanical pressure-sensitive layers with an optical detection system using a light guide and photodetectors. This substitution eliminates the deterioration issues inherent in pressure-sensitive materials, providing a more durable solution with extended service life and no recalibration requirements.
Solution Approach 2:
The optical detection system is designed to be self-calibrating, automatically adapting to environmental changes and maintaining accurate touch detection without requiring periodic manual recalibration, thereby extending operational reliability.
3Measurement precision
If conventional resistive touch screen is used, then single touch detection works, but multi-touch functionality is unable to be discerned
Solution Approach 1:
The patent divides the detection function into multiple independent photodetector elements arranged in a matrix or array. Each photodetector independently detects local optical changes, enabling the system to simultaneously identify and distinguish multiple touch points across the screen surface, thus providing multi-touch functionality while maintaining single touch precision.
4Ease of manufacture
If resistive touch screen is used, then low cost and low power consumption are achieved, but pressure application is required and insufficient pressure goes undetected
Solution Approach 1:
The patent replaces the mechanical pressure-based detection with an optical detection system that senses changes in light transmission or reflection. This substitution eliminates the need for minimum pressure thresholds, enabling detection of gentle touches while maintaining cost-effectiveness through the use of standard optical components.
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 provides a reliable, cost-effective, and transparent touch screen capable of accurate single and multi-touch detection, maintaining performance in bright conditions and reducing the need for recalibration, with improved positional accuracy and noise resistance.
Implementation Method 1
utilizing total internal reflection and scattering properties to enhance accuracy and reliability
Implementation Method 2
An optically dispersive base plate that captures and disperses light, with sensors detecting light intensity at the edges
Data Source
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AI summary
A touch sensitive screen arrangement comprising a screen including an optically dispersive base plate(18), and means for transmitting light onto said base plate in response to an external body (22) touching said screen at a touch point such that the location of incident light on the surface of said base plate is representative of the relative position of said touch point on said screen, wherein said base plate (18) is configured to capture and disperse light incident thereon by spreading and energy loss, the optically dispersive characteristic of said base plate being such that the decrease in intensity of said incident light with distance from said location of incidence on said base plate surface approximates a substantially exponential function, the arrangement further comprising at least one sensor (20) for detecting intensity of light at a respective edge of said base plate, and processing means for calculating the relative position of said touch point on said screen from said detected light intensity and said exponential function and generating a control signal representative of a control input derived from said position of said touch point.