FTIR Touch Error Prevention in Light Guide Displays
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Solution Overview
Problem
Touch malfunctions occur due to frustrated total internal reflection (FTIR) on the reflective surface of a light guide in touch input systems, leading to unintended touches and reduced light reception by photodetectors, which can misinterpret user inputs as intended touches.
Innovation Solution
The implementation of a touch input apparatus with a light emitter and receiver positioned at the lower end of a display, utilizing a light guide with a cover portion to prevent FTIR by spacing the cover apart from the reflective surface, and processors to differentiate between intended and unintended touches by analyzing light changes and emitting error messages when FTIR occurs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a light guide is used to emit light from the lower surface to the upper end of the panel, then the bezel portion can be minimized, but frustrated total internal reflection occurs on the reflective surface when touched, causing touch malfunctions
Solution Approach 1:
The light guide is divided into two functional zones: a first light guide portion with a reflective surface for light emission, and a second light guide portion without a reflective surface that extends to the edge of the touch panel. This segmentation allows the reflective surface to be confined to a specific region, preventing FTIR at the edges while maintaining light emission functionality in the display area.
Solution Approach 2:
The reflective surface is extracted from the edge portions of the light guide and confined only to the first light guide portion. By removing the reflective surface from areas prone to user contact, the patent eliminates the source of FTIR problems while preserving the light guiding function where needed.
2Illumination intensity
If the reflective surface of the light guide is touched by a finger, then light intensity received by photodetectors is reduced, but this is misinterpreted as an intended touch input
Solution Approach 1:
The patent converts the harmful FTIR effect into a beneficial detection mechanism. By placing photodetectors along the edge of the touch panel, they can detect the characteristic light intensity changes caused by FTIR when the reflective surface is touched. This allows the system to distinguish between intentional touches on the display area and accidental touches on the light guide edge, preventing false touch inputs.
3Area of stationary object
If exterior light guide is used to minimize bezel, then device size is reduced, but unintended touch due to user touch of edge portion occurs frequently
Solution Approach 1:
The light guide is segmented into a first portion with reflective surface for light emission and a second portion without reflective surface at the edges. This segmentation creates a non-reflective zone at the periphery that does not generate FTIR when touched, allowing users to contact the edge portions without causing unintended touch inputs while maintaining the compact device design.
Solution Approach 2:
The second light guide portion acts as an intermediary zone between the reflective first portion and the touch panel edge. This intermediate region without reflective surface serves as a buffer that prevents FTIR generation during edge contact, mediating between the light emission requirements and the touch prevention requirements.
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
Prevents touch malfunctions by accurately distinguishing between intended and unintended touches, reducing false input detection and enhancing the durability of touch input systems by minimizing bezel portions and allowing diverse touch elements like gloves and styluses.
Implementation Method 1
light emitted from a lower surface of the panel may be emitted to an upper end of the panel using a light guide
Implementation Method 2
if a reflective surface of the light guide is smeared with water due to a finger touch and so on, frustrated total internal reflection (FTIR) but not total internal reflection (TIR) occurs
Data Source
Figure 1~3
Figure 4
Figure 5A
AI summary
An image forming apparatus, a touch input apparatus, and a method of preventing touch error display apparatus are provided. The image forming apparatus includes an image former, a display, a light emitter configured to emit a plurality of light beams in a first direction perpendicular to a light emitting direction of the display and a second direction perpendicular to the first direction and the light emitting direction, a light receiver, a first processor configured to determine a touch input coordinate of a user based on a variation amount of each of the plurality of light beams received by the receiver, and a second processor configured to control the display and the image former using the determined touch input coordinate, wherein the first processor suspends determination of a touch input coordinate in response to optical change being detected only in one direction within a preset first time.