Capacitive Occupant Detection with Dual Antenna Electrodes
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Solution Overview
Problem
Capacitive seat occupancy detection systems face challenges in accurately distinguishing between an empty seat, a seat with a child restraint system (CRS), and a person sitting on the seat, due to variations in impedance measurements caused by the CRS's changing grounding conditions and paint coating, leading to misclassification.
Innovation Solution
A capacitive sensing device with two galvanically separate antenna electrodes and an impedance measurement circuit that measures complex impedances to ground and between electrodes, allowing for accurate classification by combining these measurements to eliminate ambiguities and provide high-resolution seat occupancy detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single antenna electrode is used for capacitive sensing, then the device complexity is reduced, but the measurement precision deteriorates due to inability to distinguish between different occupancy types
Solution Approach 1:
The patent divides the sensing system into two galvanically separate antenna electrodes instead of using a single electrode. Each electrode independently measures complex impedance to ground, providing separate measurement channels that enable differentiation between various occupancy types (empty seat, child restraint system, adult occupant) through comparative analysis of their distinct electrical characteristics.
Solution Approach 2:
The patent transitions from single-parameter sensing to multi-dimensional measurement by simultaneously measuring both magnitude and phase of complex impedance at each electrode. This dimensional expansion in the measurement space creates additional discrimination capability, allowing the system to resolve ambiguities that cannot be detected with simple capacitance measurements alone.
2Reliability
If impedance measurement is performed without considering grounding conditions, then the measurement process is simplified, but the reliability deteriorates due to misclassification caused by varying CRS grounding states
Solution Approach 1:
The patent monitors changes in electrical parameters (complex impedance magnitude and phase) as the grounding condition of the child restraint system varies. By detecting these parameter variations and comparing them against expected patterns, the evaluation unit can distinguish between genuine occupancy changes and artifacts caused by grounding state changes, thereby maintaining reliable classification despite varying electrical conditions.
Solution Approach 2:
The system continuously monitors impedance measurements from both electrodes and uses the evaluation unit to compare actual readings against expected patterns for different occupancy scenarios. This feedback mechanism allows the system to adapt its interpretation of measurements based on the detected grounding conditions, correcting for variations introduced by paint coating and electrical connection changes.
3Measurement precision
If complex impedance measurements are taken at multiple electrodes, then the measurement precision improves for occupancy classification, but the use of energy increases due to multiple signal sources and measurement circuits
Solution Approach 1:
The patent divides the sensing function across two independent antenna electrodes, each with its own signal source and measurement circuit. This segmentation allows for targeted energy consumption at each electrode rather than requiring a single high-power system, enabling precise local measurements that collectively provide comprehensive occupancy detection with optimized energy distribution.
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 enables reliable and accurate classification of seat occupancies, including child and adult classes, independent of the CRS's grounding condition, ensuring correct deployment of airbag systems and compliance with safety protocols.
Implementation Method 1
The capacitive coupling is generally determined by applying an alternating voltage signal to a capacitive antenna electrode and by measuring the current flowing from the antenna electrode either towards ground
Implementation Method 2
A capacitive sensor generally comprises at least one antenna electrode, to which is applied an oscillating electric signal and which thereupon emits an electric field into a region of space proximate to the antenna electrode
Implementation Method 3
This current is usually measured by means of a transimpedance amplifier, which is connected to the sensing electrode and which converts a current flowing into said sensing electrode into a voltage, which is proportional to the current flowing into the antenna electrode
Data Source
AI summary
A capacitive seat occupancy detection and classification system with a capacitive sensor having at least two distinct antenna electrodes and a method of operating is proposed to reduce an impact of the sensor-to-object impedance ZSO on an object-to-ground impedance ZOG measurement that the system performs. By measuring the impedance between the different antenna electrodes by the system, additional information is obtainable that can be used to compensate the impact of the sensor-to-object impedance ZSO on the object-to-ground impedance. As one effect of combining both impedance measurement results, the proposed system is able to determine the object-to-ground impedance ZOG completely independent from wear of ISOFIX anchorages or human objects touching the electric ground of the vehicle, thus ensuring a stable classification of the object over the entire vehicle lifetime. The method further enables high-resolution seat occupancy classification.