Optical Touch Screen Signal Processing for Glare and Shadow Interference
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing touch screen technologies face challenges such as reduced image clarity, susceptibility to glare, scratching, and limited input options, as well as issues with false readings due to moving shadows and bright lights, particularly in optical imaging systems.
Innovation Solution
An optical touch screen system utilizing front or back illumination, line-scan cameras, and signal processing techniques like triangulation, filtering, and ambient light subtraction to accurately detect object presence and location, independent of direct or reflected light, and capable of operating in varying light conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical imaging is used to detect touch, then object detection capability is improved, but susceptibility to false readings from ambient light and shadows increases
Solution Approach 1:
The system uses periodic modulation of infrared light sources at a specific frequency (e.g., 1kHz) and synchronously detects the modulated signal. This allows the system to distinguish between intentional touch-induced light blockage and ambient light variations or shadows, as only the modulated component at the expected frequency is processed. The periodic activation of LEDs and synchronous detection create a frequency-domain filter that rejects non-modulated ambient light interference.
Solution Approach 2:
The system employs infrared illumination and detection, operating in a specific wavelength range (infrared) that is invisible to the human eye. By using infrared light sources and infrared-sensitive detectors, the system creates a dedicated optical channel that is separate from visible ambient light. This wavelength-specific approach allows the system to ignore visible light interference while selectively detecting infrared modulated signals, effectively filtering out ambient light and shadow interference.
2Reliability
If multiple light sources are used to improve detection, then object detection reliability is improved, but susceptibility to glare and light interference increases
Solution Approach 1:
Multiple infrared LEDs are activated periodically at a specific frequency (e.g., 1kHz), and the system synchronously detects the modulated light signal. This periodic modulation allows the system to distinguish between intentional touch-induced light blockage and ambient light variations or reflections. The synchronous detection at the expected frequency creates a frequency-domain filter that rejects non-modulated ambient light interference, even when multiple light sources are present.
Solution Approach 2:
The system converts the potentially harmful effect of ambient light and reflections into a benefit by using modulation and synchronous detection. The ambient light and reflections, being non-modulated or modulated at different frequencies, are naturally rejected by the synchronous detection process tuned to the LED modulation frequency. This transforms the presence of multiple light sources and ambient illumination from a source of interference into an opportunity for frequency-based signal separation.
3Measurement precision
If front illumination is used to improve object detection, then detection accuracy is improved, but image clarity and viewing quality deteriorate
Solution Approach 1:
The system uses infrared illumination for touch detection while the display emits visible light for image presentation. The infrared wavelength range used for sensing is separate from the visible spectrum used for display, allowing both functions to operate simultaneously without interference. The display can maintain full brightness and color quality in the visible range while infrared LEDs provide illumination for touch detection, eliminating the trade-off between detection accuracy and image clarity.
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 provides reliable object detection and precise location determination, unaffected by ambient light changes or shadows, and allows for a range of input methods, enhancing usability and accuracy in diverse environments.
Implementation Method 1
said light including: direct light from said light sources, and/or reflected light from said light sources
Data Source
AI summary
A coordinate detection system can comprise a display screen, a touch surface corresponding the top of the display screen or a material positioned above the screen and defining a touch area, at least one camera outside the touch area and configured to capture an image of space above the touch surface, an illumination system comprising a light source, the illumination system configured to project light from the light source through the touch surface, and a processor executing program code to identify whether an object interferes with the light from the light source projected through the touch surface based on the image captured by the at least one camera. Light can be directed upward by sources positioned behind the screen, by sources positioned behind the screen that direct light into a backlight assembly that directs the light upward, and/or by a forward optical assembly in front of the screen that directs the light upward.