Optical Touch Detection Using Frustrated Total Internal Reflection
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Solution Overview
Problem
Current touch-sensitive technologies face challenges in scaling to larger screen sizes, handling multitouch events efficiently, and meeting increasing resolution demands, often resulting in high costs and low yields due to the need for increased special processing or elements, and struggle to distinguish between finger and instrument touch events.
Innovation Solution
An optical touch-sensitive device with multiple emitters and detectors that multiplex optical beams, using frustrated total internal reflection and other mechanisms to detect and differentiate between finger and instrument touch events based on contact area, attenuation rates, temporal behavior, and wavelength, allowing for improved scalability and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If traditional touch-sensitive technologies are scaled to larger screen sizes, then screen area increases, but manufacturing cost increases and yield decreases due to requiring N2 times as many special elements or special processing
Solution Approach 1:
The touch-sensitive display is divided into multiple segments, each with its own independent light source and sensor array. This segmentation allows each segment to be manufactured separately with standard processes, then assembled into a larger display, avoiding the need to scale up special processing across the entire large area.
Solution Approach 2:
Light guides are introduced as intermediary elements that distribute light from localized sources across the touch-sensitive surface. This allows the light distribution function to be separated from the touch sensing function, enabling standard manufacturing processes while achieving large-area coverage.
2Area of stationary object
If technologies require specially processed surfaces or special elements scaled by linear factor N, then screen area increases by N2, but manufacturing complexity and cost increase prohibitively
Solution Approach 1:
The light guides serve multiple functions: they distribute light across the touch surface, act as structural elements, and facilitate the separation of light source placement from touch sensing areas. This multi-functionality reduces the need for specialized single-purpose components.
Solution Approach 2:
Standard light guide technologies from other industries are adapted and applied to touch-sensitive displays, allowing proven manufacturing processes to be reused rather than developing new specialized processes for touch displays.
3Adaptability or versatility
If technologies handle multitouch events with multiple simultaneous touch events, then touch detection capability improves, but computational complexity increases and sampling rate requirements cannot be met
Solution Approach 1:
The touch-sensitive display is divided into multiple segments, each with its own independent light source and sensor array. This segmentation allows each segment to be processed independently at high speed, and results combined to achieve full-screen multitouch capability without requiring a single complex processor to handle all touches simultaneously.
4Measurement precision
If touch resolution requirements increase with larger screens and smaller touch point accuracy, then effective resolution R increases, but the number of required special elements increases by N2
Solution Approach 1:
The patent replaces mechanical/optical systems requiring numerous physical elements with acoustic wave-based sensing. Acoustic waves can achieve high spatial resolution with fewer sensors by utilizing wave interference patterns and signal processing, thereby reducing the number of special elements needed while maintaining or improving resolution.
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 enables efficient detection and differentiation of touch events on larger screens with high resolution, reducing costs and improving multitouch handling by using optical beams to distinguish between fingers and instruments, thus enhancing the scalability and performance of touch-sensitive systems.
Implementation Method 1
Touch events disturb the optical beams, for example due to frustrated total internal reflection
Data Source
AI summary
A touch-sensitive device includes multiple emitters and detectors and at least one acoustic sensor. Each emitter produces optical beams which are received by the detectors. Touch objects (e.g., fingers, pens, styluses) disrupt some of the optical beams and generate vibrations that are detected by the acoustic sensor. The touch-sensitive device determines information about touch events based on beam data derived from the output of the detectors and acoustic data derived from the output of the acoustic sensor.