Multi-Frequency Capacitive Touchscreen Fault Detection
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Solution Overview
Problem
Self-capacitive touch-sensitive surfaces face issues with detecting faults such as dead zones and ghost touches, particularly in critical fields like aeronautics where reliability and accuracy are paramount, due to the limitations of mutual capacitive detection and the difficulty in accurately assigning rows and columns to touched intersections.
Innovation Solution
Implementing a touchscreen device with projected capacitive detection that scans the matrix at two different acquisition frequencies, using a working frequency for minimal variations and a discrimination frequency for significant variations to differentiate between press and fault signals, allowing for the detection and correction of cut rows or columns and accurate determination of touch positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If self-capacitive detection is used to reduce the number of acquisitions required, then reading speed is improved, but fault detection capability deteriorates
Solution Approach 1:
The patent implements periodic scanning at two different frequencies: a first frequency for normal touch detection and a second frequency for fault detection. By alternating between these frequencies in periodic cycles, the system maintains high reading speed during normal operation while periodically verifying the integrity of conductive elements, thus resolving the contradiction between productivity and reliability.
Solution Approach 2:
The system performs preliminary fault detection by scanning at the second frequency before normal touch detection occurs. This preliminary action identifies potential faults in rows or columns ahead of time, allowing the system to maintain high reading speed during normal operation while ensuring reliability through advance fault detection.
2Measurement precision
If mutual capacitive detection is used to improve measurement sensitivity, then detection sensitivity is improved, but the number of acquisitions required increases
Solution Approach 1:
The patent segments the detection process into two distinct frequency-based modes: normal touch detection using self-capacitive method at the first frequency, and fault detection using a second frequency. This segmentation allows the system to use the simpler self-capacitive method for routine operations while dedicating specific periodic scans to fault detection, avoiding the need for continuous mutual capacitive scanning.
3Measurement precision
If rows and columns are assigned to intersections to detect touches, then touch detection accuracy is improved, but ghost touch detection becomes difficult
Solution Approach 1:
The patent introduces a second frequency scan as an intermediary verification mechanism. When a touch is detected at the first frequency, the system performs verification scanning at the second frequency to confirm whether the detected touch is genuine or a ghost touch. This intermediary step resolves the contradiction by maintaining accurate touch detection while adding a verification layer to eliminate false detections.
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 identifies and corrects faulty rows or columns, reduces ghost touches, and enhances the reliability of touch-sensitive systems by accurately determining touch positions, even in high-resolution and large panels, ensuring system availability in critical applications.
Implementation Method 1
Projected capacitive detection consists in implementing a detection matrix composed of conductive rows and columns arranged so as to detect local variations in capacitance introduced by the proximity of the user's fingers or any other conductive pointing object.
Implementation Method 2
the electronic control means generating, for each conductive row and column, a first periodic transmission voltage transmitted at a first frequency denoted as the working frequency and a second periodic transmission voltage transmitted at a second frequency denoted as the discrimination frequency
Data Source
AI summary
The general field of the invention is that of touchscreen devices with projected capacitive detection comprising a touch-sensitive matrix panel comprising a plurality of conductive rows and conductive columns, said panel being connected to electronic control means. The electronic control means generate two periodic transmission voltages transmitted at two different frequencies. Analysis of the reception voltages is used to determine the positions of presses on the touch-sensitive panel, including when a row or column is cut. Pressing on a cut row or column is basically determined by calculating the barycenters of ‘virtual’ hollows in the reception voltages corresponding to this cut row or column.