Optical Touch Sensing System Using Retro-Reflective Plates and Dual Thresholds
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Solution Overview
Problem
Infrared type touch screens face issues with dead zones, accuracy, and difficulty in detecting multiple touch points due to the positioning of infrared sensors and threshold level settings, leading to inefficiencies and incorrect touch detections, especially with reflective materials and fine touches.
Innovation Solution
A method using infrared cameras positioned at least at three corners and retro-reflecting plates to set both upper and lower threshold levels for improved touch detection, allowing for accurate sensing of light quantities and determining touches based on these thresholds, thereby enhancing detection accuracy and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If infrared sensors are positioned at corners for touch detection, then the device structure is simplified, but dead zones are created where touches cannot be detected
Solution Approach 1:
The touch screen is divided into multiple detection regions, each associated with specific infrared sensor pairs. The screen is segmented into four quadrants with each quadrant's touch detection handled by specific sensor combinations, allowing comprehensive coverage without dead zones while maintaining simple corner positioning of sensors
Solution Approach 2:
The patent introduces a dual-threshold detection mechanism (upper threshold and lower threshold) adding a dimensional layer to the detection process. This allows the system to distinguish between different touch scenarios (reflective materials vs. fine touches) and eliminates dead zones by providing multiple detection pathways rather than relying on a single threshold
2Device complexity
If a single threshold level is used for touch detection, then the detection process is simple, but accuracy is reduced for reflective materials and fine touches
Solution Approach 1:
The patent applies different threshold levels (upper threshold and lower threshold) for different detection scenarios. The upper threshold is used for detecting reflective materials while the lower threshold is used for detecting fine touches. This localized application of different threshold qualities enables accurate detection across various touch types without requiring a complex adaptive threshold system
Solution Approach 2:
The system changes the detection parameter (threshold level) based on the detection scenario. By switching between upper threshold and lower threshold depending on the touch type (reflective vs. fine touch), the system maintains simple structure while achieving high measurement precision across different touch conditions
3Measurement precision
If infrared cameras are positioned at three corners with retro-reflecting plates, then detection sensitivity is improved, but the system becomes more complex
Solution Approach 1:
The retro-reflecting plates serve multiple functions: they reflect infrared light back to the sensors, create detection zones, and enable the dual-threshold detection mechanism. This multi-functionality allows the system to achieve high sensitivity without adding separate components for each function, thereby limiting the increase in device complexity
Solution Approach 2:
The retro-reflecting plates act as intermediaries between the infrared cameras and the touch surface. They mediate the light path to enable detection while maintaining a relatively simple optical system structure. The dual-threshold mechanism then processes the intermediate signals to achieve high sensitivity without requiring complex camera positioning
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 approach eliminates dead zones, improves accuracy for multiple touch points, and effectively detects touches with reflective materials and fine touches, enhancing the overall efficiency and reliability of touch screen systems.
Implementation Method 1
retro-reflecting plates for reflecting light from the infrared camera to the infrared camera again
Data Source
AI summary
An optical touch sensing method includes sensing light corresponding to a touch region, comparing a first amount of the light sensed corresponding to the touch region with a first lower threshold, determining that a touch is made if the first amount is less than or equal to the first lower threshold, comparing the first amount of the light sensed corresponding to the touch region with an upper threshold, and determining that a touch is made if the first amount is greater than or equal to the upper threshold.