Resistive Touch-Pad Ghost Finger Error Reduction
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Solution Overview
Problem
Resistive touch-pads designed for multiple interactions face the challenge of introducing additional undesirable conduction paths, leading to 'ghost finger' errors, which reduce sensitivity and accuracy in pressure measurements, particularly in the Z dimension.
Innovation Solution
A method involving a multiplexing array with QTC sensor-elements and a microcontroller that performs sequential energization of drive lines and scanning of intersecting scan lines to validate and remove erroneous positions, using two scanning operations at different resolutions to distinguish real from ghost interactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sense lines are grounded to eliminate ghost finger errors, then reliability of touch detection is improved, but sensitivity to pressure measurement in the Z dimension deteriorates
Solution Approach 1:
The patent divides the touch detection process into two separate scanning operations: a first scanning operation that grounds non-active sense lines to eliminate ghost finger errors, and a second scanning operation that leaves non-active sense lines floating to preserve pressure measurement sensitivity. This segmentation of the detection process allows each operation to optimize for its specific purpose without compromising the other.
Solution Approach 2:
The patent implements periodic alternating scanning operations between two modes: one mode with grounded non-active sense lines for accurate position detection, and another mode with floating non-active sense lines for sensitive pressure measurement. This periodic switching between configurations resolves the contradiction by ensuring both reliability and measurement precision are maintained at different intervals.
2Adaptability or versatility
If additional conduction paths are introduced to enable multiple finger detection, then adaptability to multiple interactions is improved, but ghost finger errors increase
Solution Approach 1:
The patent applies preliminary action by grounding the non-active sense lines before performing the first scanning operation to detect touch positions. This preliminary grounding prevents the formation of ghost finger errors caused by parasitic conduction paths, ensuring that only genuine touch interactions are detected while maintaining the array's capability for multiple finger detection.
3Object-generated harmful factors
If current is reduced in grounded paths to eliminate ghost finger, then ghost finger errors are reduced, but overall current available for pressure detection deteriorates
Solution Approach 1:
The patent segments the scanning operations into two distinct phases: the first scanning operation uses grounded non-active sense lines to eliminate ghost finger errors, while the second scanning operation uses floating non-active sense lines to maximize current availability for pressure measurement. This segmentation ensures that current is optimized for pressure detection in the second operation without being depleted by grounding paths in the first operation.
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 effectively reduces ghost finger errors while maintaining sensitivity by accurately identifying and removing erroneous positions, ensuring precise pressure measurements and expanded user interaction capabilities.
Implementation Method 1
An element of variable resistance is provided at each intersection of the array, presenting a high resistance at each intersection until mechanical pressure is applied, whereupon resistance reduces significantly thereby allowing conduction to take place
Data Source
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AI summary
The detection of multiple manual interactions upon a touch-pad is shown. Drive lines intersect a scan lines and each intersection between a drive line and a scan line includes an element of variable resistance. A scanning processor energises the drive lines and monitors the scan lines. The scanning processor is configured to identify positions of manual interaction, validate identified positions to identify potentially erroneous positions and remove positions identified as erroneous. However, removed positions are re-introduced when they are not in the vicinity of other identified positions.