Capacitive Sensor Rate-of-Change Touch Detection
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Solution Overview
Problem
Existing touch sensing technologies, such as projected capacitance, capacitive, and differential sensing, rely on predetermined threshold values for detecting touch inputs, which are prone to errors due to manufacturing tolerances, dielectric variations, and environmental factors, leading to false or under/over sensitive responses.
Innovation Solution
A capacitive sensor system that determines the presence of a stimulus by monitoring the rate of change of capacitive coupling between electrodes, using time domain differential sensing techniques to analyze the signature of a touch event, eliminating the need for predetermined threshold values and enhancing touch detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If predetermined threshold values are used for touch detection, then the device complexity is reduced, but the reliability and measurement precision deteriorate due to manufacturing tolerances and environmental factors
Solution Approach 1:
The patent changes the detection parameter from absolute capacitance threshold to rate of change of capacitance (dC/dt). This parameter transformation allows the system to detect touch events based on the dynamic change rather than a fixed value, making it immune to manufacturing variations and environmental drift while maintaining simple implementation through basic differentiation circuitry.
Solution Approach 2:
The patent transitions from static threshold detection to dynamic rate-of-change detection. By monitoring how capacitance changes over time rather than comparing against a fixed threshold, the system adapts to varying operating conditions and maintains reliable touch detection across different environments and manufacturing tolerances.
2Ease of operation
If predetermined threshold values are used for touch detection, then the ease of operation is improved, but the measurement precision deteriorates leading to false or under/over sensitive responses
Solution Approach 1:
The patent transforms the detection criterion from static capacitance threshold to dynamic rate of change (dC/dt). This parameter change enables precise touch detection by capturing the transient signal characteristic of finger contact, eliminating false positives from environmental factors while keeping the implementation simple through basic temporal differentiation.
3Reliability
If rate of change of capacitive coupling is monitored, then the reliability and measurement precision are improved, but the device complexity increases due to additional processing requirements
Solution Approach 1:
The patent changes the detection parameter to rate of change (dC/dt), which can be implemented through simple temporal differentiation circuitry or basic software algorithms. This parameter transformation improves reliability by capturing the dynamic signature of touch events while avoiding the need for complex adaptive thresholding or machine learning systems.
Solution Approach 2:
The patent employs periodic sampling of capacitance values at discrete time intervals. By taking measurements at regular intervals and computing the difference between consecutive samples, the system achieves rate-of-change detection using simple periodic operations rather than continuous complex processing, thereby maintaining low device complexity.
4Measurement precision
If rate of change of capacitive coupling is monitored, then the measurement precision is improved, but the loss of time increases due to additional sampling and processing steps
Solution Approach 1:
The patent uses periodic sampling at optimized intervals to compute rate of change. By selecting appropriate sampling frequencies that capture the essential touch signal dynamics, the system achieves high measurement precision without excessive sampling overhead, balancing accuracy with minimal processing time.
Solution Approach 2:
The patent implements rate of change detection using only a limited number of consecutive capacitance samples rather than extensive historical data or complex analysis. This partial action approach achieves sufficient precision for touch detection while minimizing the time and computational resources required, avoiding excessive processing.
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 provides consistent and reliable touch detection, regardless of environmental conditions or object characteristics, such as gloved fingers, and allows for more precise identification of touch events and gestures, improving the accuracy and reliability of human-machine interaction.
Implementation Method 1
a capacitive sensor includes first and second electrodes defining a capacitive coupling and a processing unit electrically coupled to the first and second electrodes to determine the presence of a stimulus based on the rate of change of the capacitive coupling
Implementation Method 2
Capacitance, projected capacitance, and differential sensing have at least two common attributes: 1) they all use electric fields as the stimulus for measuring the human machine interaction
Data Source
AI summary
A capacitive sensor for detecting a stimulus. The capacitive sensor includes first and second electrodes defining a capacitive coupling, and a processing unit electrically coupled to the first and second electrodes to determine the presence of a stimulus based on the rate of change of the capacitive coupling. A substrate is positioned adjacent the first and second electrodes, wherein the stimulus corresponds to the placement of an object against the substrate. The processing unit is operative to determine a time rate of change based on successive measurements of the capacitive coupling and in response to the capacitive coupling being greater than a predetermined reference value.