Capacitance Detection Discriminating Human Touch from Water
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Solution Overview
Problem
Existing capacitance detection systems struggle to accurately differentiate between human-induced operations and external factors like water droplets, leading to potential unintended locking/unlocking of vehicle doors due to sensitivity issues in high-humidity environments.
Innovation Solution
A capacitance detection apparatus employing a switched capacitance technique with distinct switching control processes and periods to differentiate between human touch and water adherence by counting repetition times and calculating change amounts, allowing precise determination of capacitance changes and their causes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitance detection apparatus uses a switched capacitor technique with extended measurement periods to improve sensitivity and reduce the effect of leak resistance, then sensitivity deterioration is alleviated, but the apparatus becomes unable to effectively discriminate between water adherence and human touch, leading to false triggering
Solution Approach 1:
The measurement process is segmented into multiple distinct phases: initialization period, first charging period, first discharging period, second charging period, and second discharging period. Each phase serves a specific function in characterizing the capacitance response. By segmenting the measurement into these temporal phases with different durations, the system can capture both the magnitude and temporal characteristics of capacitance changes, enabling differentiation between water adherence (slow response) and human touch (fast response) while maintaining high sensitivity through the extended overall measurement window.
2Measurement precision
If the capacitance detection apparatus extends the measurement period to capture slow capacitance changes from water adherence, then detection sensitivity improves, but the discrimination between water drops and human-induced operations deteriorates
Solution Approach 1:
The system employs dynamic switching between different measurement modes with varying time constants. The switched capacitor technique dynamically adjusts the effective measurement duration by alternating between fast charging/discharging cycles (for detecting rapid human touch) and slower integration periods (for detecting gradual water adherence). This dynamic adaptation allows the same hardware to optimize for different detection scenarios without requiring separate dedicated circuits for each function.
Solution Approach 2:
The measurement process utilizes periodic switching sequences with distinct charging and discharging phases. By implementing periodic alternation between different charging periods and discharging periods, the system samples the capacitance response at multiple time points throughout the measurement cycle. This periodic sampling captures both immediate responses (human touch) and gradual changes (water adherence), enabling the system to maintain high detection sensitivity while preserving discrimination capability through temporal pattern recognition.
3Reliability
If the switch closed period is extended to reduce the effect of leak resistance, then sensitivity deterioration is reduced, but the ability to distinguish human touch from water adherence is lost
Solution Approach 1:
The system changes the temporal parameters of the switching sequence by implementing multiple phases with different charging period durations and discharging period durations. The initialization period sets the baseline, followed by alternating sequences of charging and discharging phases with progressively varying time constants. By varying these temporal parameters across different phases, the system maintains stable sensitivity against leak resistance while capturing the distinct temporal signatures of different events (water vs. human touch) through the pattern of capacitance changes across the parameter-varying phases.
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
The apparatus effectively discriminates between human-induced operations and external factors, enhancing detection accuracy and preventing false triggering, even in challenging environmental conditions.
Implementation Method 1
a capacitance detection apparatus for detecting an unknown capacitance to be determined... a measured capacitance Cx1 to be measured... a reference capacitance Cs
Data Source
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AI summary
Provided is a capacitance detection apparatus capable of effectively discriminating between an external factor due to e.g. water drops and a human-induced operation and allowing detection of occurrence of the human-induced operation with a simple arrangement. The apparatus alternately executes a first switching control process and a second switching control process, the first and second switching control processes executing a second switch operation with different charging periods from each other. In each of the first and second switching control processes, the number of repetition times of the second switch operation is counted until the potential of a terminal of a reference capacitance changes to a set potential. Based on the number of repetition times in at least one of the two switching control processes, presence/absence of change in determined capacitance (i.e. capacitance to be determined) is determined and based on the numbers of repetition times in the two control processes, it is determined whether the change in the determined capacitance is due to an event of detection interest or not.