Capacitive Seat Occupancy Sensing with Reference Capacitor and Switch Matrix
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Solution Overview
Problem
Existing capacitive seat-occupancy recognition systems face challenges in distinguishing between a person and water, leading to increased costs and complexity due to the need for precise voltage control and measurement, and are prone to false positives from water presence.
Innovation Solution
A method and arrangement that utilize a reference capacitor and sensor electrodes integrated into a vehicle seat, with a common mat for both seat heating and capacitive recognition, employing a series of switches to charge and discharge capacitors to differentiate between occupancy statuses by measuring resulting voltages, and incorporating a thermal conductor to account for parasitic capacitance, allowing for clear distinction between water and a person.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dielectric systems with specialized circuitry are used to achieve positive recognition of persons, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent divides the capacitive sensing system into multiple independent sensor electrodes positioned at different locations (seat base, seat back, headrest). Each electrode independently measures capacitance changes, allowing the system to distinguish between water and persons through spatial pattern recognition rather than requiring complex single-point circuitry.
Solution Approach 2:
The patent makes the heating mat serve dual functions: providing thermal comfort to occupants and acting as a capacitive sensor array for occupancy detection. The heating elements are electrically connected to a control unit that can operate them as sensors, eliminating the need for separate dedicated sensor circuitry.
2Measurement precision
If dielectric systems are used to detect seat occupancy, then measurement precision is improved, but susceptibility to water interference increases
Solution Approach 1:
The patent segments the sensing area into multiple electrodes at different positions. Water typically contacts only specific areas (seat base or back), while persons contact multiple areas simultaneously. By analyzing the pattern of capacitance changes across all electrodes, the system can distinguish between water-only scenarios and actual occupancy.
Solution Approach 2:
The patent introduces a control unit that acts as an intermediary between the sensor electrodes and the occupancy determination logic. This control unit processes capacitance measurements from multiple electrodes, compares them against predetermined thresholds, and applies decision algorithms to eliminate false positives from water while maintaining sensitivity to actual occupancy.
3Loss of information
If multiple sensor electrodes are integrated into the seat, then information completeness is improved, but device complexity increases
Solution Approach 1:
The patent makes the heating mat serve dual functions: providing thermal comfort to occupants and acting as a capacitive sensor array for occupancy detection. The heating elements are electrically connected to a control unit that can operate them as sensors, eliminating the need for separate dedicated sensor circuitry.
Solution Approach 2:
The patent merges the heating function and sensing function into a single integrated system. The same electrical conductors that provide heating also serve as capacitive sensors, and the control unit handles both heating control and occupancy detection, reducing overall system complexity despite the multiple measurement points.
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 reduces the need for additional passive components, provides wide-ranging information on seat occupancy with high accuracy, and minimizes the influence of water on detection, while also recognizing charge loss for defective isolation and current leakage.
Implementation Method 1
CX is the capacitance of a sensor electrode (1) integrated into a seat
Implementation Method 2
dielectric systems are preferred when positive recognition of persons and distinction between persons and objects of similar weight and/or similar surface pressure on the seat base, are required
Data Source
AI summary
The invention relates to a method and an apparatus for capacitive seat-occupancy recognition for vehicle seats. The apparatus which is based on the method comprises a reference capacitor that possesses a capacitance with respect to a first reference potential of a vehicle, an electrode integrated into a seat sensor that possess a capacitance with respect to a first reference potential, an at least parasitically-present capacitance of the sensor electrode with respect to a second reference potential or the vehicle ground, a first switch that connects the reference capacitor and a reference-voltage source of known voltage connected with the reference potential, a second switch that connects the sensor electrode with reference capacitor, and a third switch that connects the sensor electrode with the reference potential and the at least parasitically-present capacitance with the vehicle ground.