Capacitance Sensing Circuit for Distinguishing Water Drops From Touch
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Solution Overview
Problem
Existing capacitance detection systems, such as those used in vehicle door locking systems, face challenges in distinguishing between human-induced operations and external factors like water adherence, leading to potential incorrect locking/unlocking scenarios due to sensitivity deterioration in humid environments.
Innovation Solution
A capacitance detection apparatus with a switched capacitance arrangement that employs three switches and distinct switching control processes to differentiate between human-induced changes and external factors by varying the closing periods of the second switch, allowing accurate determination of capacitance changes and their causes through counting repetition times and change amounts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a switched capacitor technique with extended charging period is used to reduce sensitivity deterioration in humid environments, then reliability is improved, but the ability to discriminate water adherence from human touch deteriorates
Solution Approach 1:
The patent segments the capacitance measurement into multiple distinct phases: a first charging period for sensitivity stabilization, a first discharging period for baseline reset, and a second charging period for actual measurement. This temporal segmentation allows each phase to serve a specific function, resolving the contradiction between stability and discrimination accuracy.
Solution Approach 2:
The patent implements periodic switching between different charging periods (first charging period with longer duration for stabilization, second charging period with shorter duration for measurement). This periodic alternation between different operational modes enables both sensitivity stabilization and accurate discrimination to occur in sequence, resolving the fundamental contradiction.
2Reliability
If the charging period is extended to account for leak resistance, then reliability is improved, but the response time for detection increases
Solution Approach 1:
The patent performs preliminary charging during the first charging period to stabilize the capacitor voltage and account for leak resistance effects before the actual measurement begins. This preliminary action ensures that when the second charging period starts, the system is already stabilized, eliminating the need for extended measurement time while maintaining accuracy.
Solution Approach 2:
The patent dynamically adjusts the charging period duration based on the measurement phase: using a longer first charging period for stabilization and a shorter second charging period for actual measurement. This dynamic timing adjustment optimizes both reliability and response time by matching the charging duration to the specific operational requirements of each phase.
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 system effectively discriminates between human-induced operations and external factors like water adherence, enhancing detection accuracy and precision by comparing repetition times and change amounts across different switching control processes, thereby preventing incorrect locking/unlocking events.
Implementation Method 1
a first switch operation rendering said first switch to a closed state and then returning said first switch to an opened state upon lapse of an initialization period
Implementation Method 2
a second switch operation rendering said second switch to a closed state and then returning said second switch to an opened state upon lapse of a first charging period
Implementation Method 3
a third switch operation rendering said third switch to a closed state and then returning said third switch to an opened state upon lapse of a first discharging period
Implementation Method 4
a potential determining unit for determining whether the potential of the other terminal of said reference capacitance has changed to a predetermined set potential from an initial potential
Data Source
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.