Electrostatic Capacitance Sensor With Phase-Differential Hand Detection
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Solution Overview
Problem
Existing electrostatic-capacitance detection sensors for automated driving systems, such as those using Japanese Patent No. 6177026 and Japanese Unexamined Patent Application Publication No. 2015-232542, face challenges with false detection, making it difficult to accurately determine whether a steering wheel or similar object is held by a human hand.
Innovation Solution
An electrostatic-capacitance detection sensor utilizing a self-capacitance system with a sense electrode and a drive electrode, applying alternating-current signals of the same frequency but different phases to determine if a detection target is in close proximity by calculating the subtraction difference between detection values, thereby reducing false detection and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single electrode is used for electrostatic capacitance detection, then the device structure is simple, but false detection occurs and measurement precision deteriorates
Solution Approach 1:
The single electrode is segmented into two separate electrodes: a sense electrode for detecting electrostatic capacitance and a drive electrode for generating the drive signal. This segmentation allows the detection function and drive function to be separated, enabling more accurate measurement by eliminating interference between detection and drive operations.
Solution Approach 2:
A differential amplifier is introduced as an intermediary component to amplify the difference between the sense signal and a reference signal. This intermediary device enhances the detection precision by selectively amplifying only the relevant electrostatic capacitance signal while rejecting common-mode noise and interference.
2Device complexity
If electrostatic capacitance detection is performed without phase-differentiated drive signals, then the detection process is simple, but false detection occurs due to environmental interference
Solution Approach 1:
The drive electrode applies periodic drive signals with different phases to different electrodes. By using periodic signals with distinct phase relationships, the system can distinguish between genuine electrostatic capacitance changes and environmental interference through phase-sensitive detection, thereby improving reliability.
Solution Approach 2:
The system uses the differential amplification of phase-differentiated signals as a feedback mechanism to continuously adjust and compensate for environmental interference. The phase difference between signals provides a reference that allows the system to identify and reject common-mode noise, enhancing detection reliability.
3Device complexity
If only a sense electrode is used, then the device structure is simple, but the ability to accurately determine holding state deteriorates
Solution Approach 1:
The electrode system is segmented into sense and drive electrodes with distinct functions. The sense electrode detects electrostatic capacitance changes while the drive electrode generates the excitation signal, allowing accurate determination of holding state through their coordinated operation.
Solution Approach 2:
The system changes the electrical parameters (phase and amplitude) of the drive signal applied to different electrodes. By varying these parameters in a controlled manner, the system can extract specific information about the holding state from the resulting electrostatic capacitance changes, improving detection accuracy.
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 solution effectively determines whether a detection target is held by accurately measuring the electrostatic capacitance changes, minimizing false positives and negatives, and maintaining consistency regardless of environmental changes like temperature.
Implementation Method 1
a detecting unit that detects, as a detection value, an amount of charge movement corresponding to an electrostatic capacitance of the sense electrode
Implementation Method 2
a first drive signal and a second drive signal that are different in phase with each other by 180° are sequentially applied to the drive electrode
Data Source
AI summary
A self-capacitance-system electrostatic-capacitance detection sensor includes a first electrode and a second electrode, one of the first and second electrodes being set as a sense electrode, and the other of the first and second electrodes being set as a drive electrode; a sense-signal generating unit that generates a sense signal to be applied to the sense electrode; a detecting unit that detects, as a detection value, an amount of charge movement corresponding to an electrostatic capacitance of the sense electrode; and a determining unit that determines whether or not a detection target is in close proximity to both the first and second electrodes, based on a subtraction difference between detection values detected by the detecting unit when a first drive signal is applied to the drive electrode and when a second drive signal having the same frequency and a different phase is applied to the drive electrode.