Touch Screen Rear Projection Display IR Illumination
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Solution Overview
Problem
Touch screen displays face challenges in discerning pointer images due to reduced contrast caused by infrared light reflection off the back of the display surface, which affects camera illumination and image capture.
Innovation Solution
A touch screen display design where the infrared light source directs light at the rear surface of a diffuser screen at an acute angle, preventing reflected light from entering the camera while illuminating the pointer through the front surface, thereby improving image contrast and detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If an IR light source is positioned behind the display surface to illuminate the pointer, then the contrast of captured images is improved, but light reflected off the back of the display surface significantly reduces the contrast of the captured images
Solution Approach 1:
The patent applies local quality by directing IR light at different angles to different regions. The light source is positioned to illuminate the pointer area specifically while the rear surface reflects light away from the camera. This creates localized illumination quality where the pointer is brightly lit but the background remains dark, resolving the contradiction between illumination intensity and reflected light interference.
Solution Approach 2:
The patent employs asymmetry in the optical path configuration. The IR light source is positioned at an angle such that the incident light path and reflected light path are asymmetric with respect to the camera position. This asymmetric arrangement ensures that reflected light from the rear surface does not enter the camera, while the pointer remains illuminated, thus resolving the technical contradiction.
2Illumination intensity
If the IR light source directs light at normal incidence to illuminate the pointer, then illumination is maximized, but reflected light enters the camera and reduces image contrast
Solution Approach 1:
The patent resolves the contradiction by transitioning from normal incidence (one-dimensional perpendicular approach) to oblique incidence (introducing angular dimension). The IR light source is positioned at an oblique angle, and the rear surface is tilted relative to the camera, creating a three-dimensional optical path arrangement. This dimensional change allows the reflected light to be directed away from the camera while maintaining pointer illumination, thus improving measurement precision without sacrificing illumination intensity.
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 design enhances the visibility of pointer images by maintaining a dark background for the camera, improving contrast and facilitating effective user input detection without compromising camera functionality.
Implementation Method 1
The IR light source is disposed to direct IR light toward the rear surface of the diffuser screen
Implementation Method 2
any of the incident IR light reflected off the rear surface of the diffuser screen does not enter the camera
Data Source
AI summary
A touch screen display includes a diffuser screen, a projector, a camera, an infrared (IR) light source, and a controller. The diffuser screen has a front surface and a rear surface. The projector is disposed to project images onto the rear surface of said diffuser screen, and the images are visible to a user through the diffuser screen. The camera is disposed behind the diffuser screen and aimed to capture images of a pointer near the front surface of the diffuser screen. The IR light source is disposed to direct IR light toward the rear surface of the diffuser screen, so the rays of incident IR light form an acute angle with respect to the rear surface of the diffuser screen, and so that any of the incident IR light reflected off the rear surface of the diffuser screen does not enter the camera.