Capacitive Sensor Reference Update Logic for False Detection
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Solution Overview
Problem
Capacitive sensors, particularly mutual capacitive sensors, face challenges in accurately distinguishing between the presence of objects like fingers and conductors with weak capacitive coupling, such as IC cards, leading to false detections due to changes in mutual capacitance, especially when reference values are updated during power-off states or when objects are removed.
Innovation Solution
The input device employs a sensor unit with multiple driving and sensing electrodes forming capacitive coupling parts, a capacitance detector, and a two-dimensional data matrix system to identify target data indicating object proximity and update reference values based on patterns in sensing data, distinguishing between consecutive and approximating capacitance values to avoid false detections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reference value is updated when object is not detected for predetermined time, then measurement precision is improved, but false detection occurs when conductor with weak capacitive coupling (e.g., IC card) is present
Solution Approach 1:
The system performs preliminary detection to identify conductors with weak capacitive coupling (such as IC cards) before updating the reference value. By detecting the presence of such conductors in advance and preventing reference value updates when they are detected, the system avoids false detections while maintaining measurement precision through appropriate reference value updates under normal conditions
Solution Approach 2:
The system introduces an intermediary detection mechanism that distinguishes between different types of objects (fingers vs. conductors with weak capacitive coupling) before allowing reference value updates. This intermediary step acts as a filter to prevent harmful reference value updates caused by conductors like IC cards while permitting beneficial updates when no such conductors are present
2Device complexity
If mutual capacitance detection is used for multi-point sensing, then device complexity is reduced, but false detection occurs due to temperature changes and conductor proximity
Solution Approach 1:
The system continuously monitors mutual capacitance values and uses feedback mechanisms to distinguish between genuine object detections and false detections caused by temperature changes or conductor proximity. By comparing current readings with reference values and analyzing detection patterns over time, the system can identify and filter out false detections while maintaining the simplicity of mutual capacitance sensing
Solution Approach 2:
The system applies preliminary anti-action by implementing detection rules that specifically prevent false detections from conductors with weak capacitive coupling. When such conductors are detected, the system takes counter-actions to prevent reference value updates that would lead to false detections, thereby maintaining detection stability without compromising the simplicity of the mutual capacitance sensor structure
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 reduces false detections by accurately updating reference values and identifying object proximity, even when conductors with weak capacitive coupling are present, thereby improving the reliability of capacitive sensors in detecting object approaches.
Implementation Method 1
a capacitive sensor is relatively simple and compact... because a capacitive sensor detects a change in capacitance (self-capacitance) between a sensing electrode and an object (ground)... the mutual capacitive sensor detects a change in capacitance (mutual capacitance) between a driving electrode and a sensing electrode caused by an approach of an object
Data Source
AI summary
An input device for detecting a change in capacitance in accordance with proximity of an object is provided. The input device includes: a sensor unit including multiple capacitive coupling parts formed between multiple driving electrodes and multiple sensing electrodes; a capacitance detector for detecting a capacitance value of each of the capacitive coupling parts; and a two-dimensional data generating unit for generating a two-dimensional data matrix consisting of the capacitance values of the capacitive coupling parts. When a target row or a target column in the two-dimensional data matrix matches a first pattern indicating that multiple capacitive coupling parts each having a capacitance value greater than a reference value are arranged consecutively, the input device updates the reference value.