Prismatic Film Retroreflectivity for Touch Screen Positioning
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Solution Overview
Problem
Conventional touch-screen position detection systems struggle to accurately determine the coordinates of multiple objects simultaneously due to ambiguous signal data and limited accuracy caused by the retroreflective properties of prior art prismatic films, which are not brightly retroreflective over a broad range of observation angles.
Innovation Solution
A position detection system with cameras and dual radiation sources positioned adjacent to a prismatic film that includes triangular cube corner retroreflective elements with dihedral angle errors and a metallized layer, enhancing retroreflectivity over a broad range of angles and allowing for unambiguous determination of object locations using parallax-based computation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional retroreflective sheeting material is used in touch screen applications, then the system can detect object positions, but dirt and moisture penetrate the structure and adversely affect retro reflectivity
Solution Approach 1:
The patent employs a composite prismatic film structure combining multiple materials: a protective overcoat layer (topmost), a prismatic layer with cube corner elements, and a reflective layer. This multi-layer composite design protects the retroreflective elements from dirt and moisture while maintaining optical performance, directly resolving the contradiction between reliability and environmental susceptibility.
2Reliability
If conventional retroreflective sheeting material is used, then the system can provide background reflection, but the background is non-uniform with very low detected signal in corner regions
Solution Approach 1:
The patent applies local quality optimization by positioning specific prismatic elements and reflective layers at different locations within the film structure. The cube corner prisms are strategically arranged to redirect light from corner regions more effectively, ensuring uniform background illumination across the entire detection area including previously problematic corner regions.
3Measurement precision
If the spacing between source and detector is increased in the plane of the screen, then the system can detect positions more accurately, but the prismatic film must maintain brightness over larger observation angles
Solution Approach 1:
The patent employs dynamically optimized prismatic geometries with cube corner elements that are tilted and oriented at specific angles. These angular configurations are designed to maintain retroreflective brightness across a wide range of observation angles, enabling accurate position detection even when source and detector are spaced far apart in the plane of the screen.
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 system achieves accurate and unambiguous detection of multiple objects by improving the sensitivity and uniformity of the prismatic film's retroreflectivity, enabling reliable detection even at larger source separations without significant signal degradation.
Implementation Method 1
a retroreflective or prismatic film used thereby
Implementation Method 2
prismatic film that is brightly retroreflective at larger observation angles
Implementation Method 3
unambiguous determination of object locations using parallax-based computation
Data Source
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AI summary
A dual light-source position detecting system for use in touch screens is provided that utilizes parallax to determine the position of an interposing object, and a prismatic film that is brightly retroreflective over a broad entrance angle to enhance to accuracy of the parallax determination of position. The position detecting system includes at least one camera positioned to receive light radiation traversing a detection area and that generates a signal representative of an image; two spaced-apart sources of light radiation, which may be LEDs, or IR emitters positioned adjacent to the camera for outputting light radiation that overlaps over at least a portion of a detection area, and a prismatic film positioned along a periphery of at least a portion of the detection area that retroreflects the light radiation from the two sources to the camera. The prismatic film includes a plurality of triangular cube corner retroreflective elements having dihedral angle errors el7 e2, and e3 such that ex ~ e2 ? 0 and e3 ~ 0 to enhance the efficiency of the retroreflection of the light radiation from the two spaced apart LEDS or IR emitters along the sides of the detection area. If two cameras are mounted in opposing corners of a same side of the touch screen and two dual radiation sources are used in combination with these cameras, an unambiguous determination can be made of the location of two simultaneously interposing objects.