Optical Touch Screen Using Total Internal Reflection
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Solution Overview
Problem
Conventional touch screen technologies, such as resistive and capacitive screens, face limitations including non-transparency, sensitivity to pressure, inability to discern multiple touches, and limited dynamic range for pressure intensity detection, which restrict their use in various contexts.
Innovation Solution
A touch sensitive apparatus utilizing a top plate with light sources for total internal reflection and a base plate with optically separated elements, where light is coupled from the top plate to the base plate upon touch, allowing for detection of touch presence, position, and pressure intensity, enabling multi-touch and complex motion inputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resistive or capacitive overlay is placed over LCD display surface, then touch sensitivity is achieved, but transparency is reduced and readability in direct sunlight deteriorates
Solution Approach 1:
The patent replaces the conventional resistive/capacitive overlay system with an optical system using light sources, optical fibers, and photodetectors. This substitution eliminates the need for opaque overlays while maintaining touch sensitivity through optical signal transmission and detection, thereby resolving the contradiction between touch sensitivity and transparency.
Solution Approach 2:
The patent introduces optical fibers as an intermediary medium to transmit light signals from light sources to photodetectors. This intermediary enables touch detection without requiring a transparent overlay, as the optical fibers carry the signals through the touch interface while maintaining light transmission, thus resolving the transparency issue.
2Reliability
If pressure sensitive layers are used in resistive touch screens, then touch detection is achieved, but the layers are subject to deterioration and require periodic re-calibration
Solution Approach 1:
The patent replaces pressure-sensitive resistive layers with an optical detection system using photodetectors and optical fibers. This substitution eliminates the mechanical pressure-sensitive layers that deteriorate over time, providing a more durable system that does not require re-calibration while maintaining touch detection capability.
3Reliability
If sufficient pressure is required for detection in resistive touch screens, then touch signals are generated, but light touches go undetected and pressure intensity discrimination is lost
Solution Approach 1:
The patent replaces the pressure-based resistive detection system with an optical system that detects touch through light transmission changes. This allows detection of light touches without requiring sufficient pressure, as the optical system can detect even minor disruptions to light paths, thereby resolving the contradiction between reliable touch signal generation and pressure intensity discrimination.
4Reliability
If conventional resistive or capacitive touch screens are used, then basic touch detection is achieved, but multi-touch capability is lost
Solution Approach 1:
The patent divides the touch detection surface into multiple independent optical detection zones, each with its own light sources and photodetectors. This segmentation allows the system to simultaneously detect multiple touches at different locations, enabling multi-touch capability while maintaining reliable basic touch detection in each zone.
Solution Approach 2:
The patent transitions from single-point touch detection to multi-point detection by adding spatial dimensionality to the optical detection system. Multiple light sources and photodetectors are arranged across the surface, enabling the system to detect and distinguish between multiple simultaneous touches in different spatial locations, thereby achieving multi-touch capability.
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 solution provides a versatile and reliable touch screen system capable of detecting multiple touches and pressure intensity, enhancing user interaction and functionality, and can be adapted for use in non-traditional form factors.
Implementation Method 1
a top plate having one or more light sources associated therewith, such that light from the one or more light sources is transmitted within the top plate with total internal reflection
Data Source
AI summary
A touch sensitive apparatus comprises a top plate configured such that light from the one or more light sources is transmitted within the top plate with total internal reflection; and a base plate within which, light is transmissible. The base plate comprises a plurality of base plate elements optically separated from each other. The top plate and the base plate are configured such that if an external body touches a first surface of the top plate, then light is coupled from a second surface of the top plate into an underlying base plate element for transmission within that base plate element. Each base plate element has one or more detectors for detecting light transmitted within that base plate element. A processor determines information from the detectors relating to touching of the first surface of the top plate. An associated method is also described.