Capacitive Touch Sensing by Capacitance Change Rate
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive touch sensors face challenges in accurately detecting touch inputs due to dielectric variations, environmental susceptibility, manufacturing tolerances, and inability to differentiate between gloved and ungloved fingers, often requiring costly and complex software processing to compensate for these issues.
Innovation Solution
The method involves monitoring the rate of change of capacitance to determine a touch event, using a capacitive sensor with a processing unit that detects a stimulus when the rate of change falls below a minimum value and the absolute capacitance exceeds a second predetermined value, allowing for touch detection independent of substrate thickness and dielectric variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitance sensing is used to detect touch inputs, then sensitivity to touch is improved, but susceptibility to noise and false touches increases
Solution Approach 1:
The system dynamically adjusts the reference capacitance value based on environmental conditions and substrate variations. Instead of using a fixed reference value, the system continuously adapts the reference capacitance to match current conditions, allowing the touch sensor to maintain high sensitivity while dynamically filtering out noise and false touches that would trigger with static thresholds.
Solution Approach 2:
The system changes the parameter being monitored from absolute capacitance values to the rate of change of capacitance (dC/dt). By detecting touch inputs through the temporal derivative of capacitance rather than absolute values, the system becomes insensitive to slow environmental drifts and noise while maintaining sensitivity to rapid touch events.
2Measurement precision
If averaging algorithms are used to compensate for variations, then reference value accuracy is improved, but system complexity and cost increase
Solution Approach 1:
The system extracts only the essential information needed for touch detection—the rate of change of capacitance—rather than processing complete capacitance waveforms. By focusing solely on dC/dt values, the system eliminates the need for complex averaging algorithms and software processing while maintaining accurate reference values for touch detection.
Solution Approach 2:
The system replaces software-based averaging algorithms with a hardware-based differential capacitance measurement approach. By using dedicated circuitry to measure dC/dt directly, the system substitutes complex software processing with simpler hardware circuitry, reducing overall system complexity and cost.
3Adaptability or versatility
If multiple reference values are set to account for variations, then detection accuracy under different conditions is improved, but device complexity increases
Solution Approach 1:
The system uses a single universal reference value for touch detection that works across all environmental conditions. By basing detection on the rate of change of capacitance rather than absolute capacitance values, the reference value becomes independent of substrate thickness, dielectric variations, and environmental factors, eliminating the need for multiple condition-specific reference values.
4Measurement precision
If capacitive sensors are used, then touch detection capability is improved, but inability to detect gloved touches persists
Solution Approach 1:
The system performs preliminary characterization of the substrate and environmental conditions to establish a baseline reference capacitance value before actual touch detection begins. This preliminary action allows the system to pre-adapt to the specific installation conditions, including substrate properties and dielectric materials, ensuring that subsequent touch detection works correctly for both gloved and ungloved touches.
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 improves the accuracy and sensitivity of touch detection, adapting to user preferences and reducing complexity and cost by eliminating the need for extensive software processing, while effectively distinguishing between valid and invalid stimuli, such as gloved or ungloved fingers.
Implementation Method 1
Capacitive sensors normally require at least one electrical element typically referred to as an electrode, element, or plate. In some instances, there may be one, two or more networks of capacitive electrodes, elements or plates. These elements are geometrically designed to cause the formation of a net electric field in both a non-stimulus state as well as a stimulus state.
Implementation Method 2
These elements are geometrically designed to cause the formation of a net electric field in both a non-stimulus state as well as a stimulus state.
Data Source
AI summary
A capacitive sensor for detecting a stimulus. The capacitive sensor includes an electrode and a processing unit electrically coupled to the electrode and configured to determine the presence of a stimulus based on the rate of change of the electrode capacitance. A substrate is positioned adjacent the electrode, 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 electrode capacitance. In addition, the processing unit is operative to determine the presence of a stimulus in response to the time rate of change being less than a reference value.