Capacitive Occupant Detection Guard Electrode Shielding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive occupant detection systems face challenges in accurately determining the type and mounting state of occupants due to direct capacitive coupling with the vehicle body, and unwanted coupling between detection electrodes and the ground or wire connections.
Innovation Solution
The system employs a capacitive occupant detection apparatus with a sensor unit and control unit, featuring a detection electrode, a guard electrode with a periphery guard part, and a signal application circuit that applies main and guard signals to suppress direct coupling with the vehicle body and reduce unwanted capacitive coupling between the detection electrode and the ground or wire connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a detection electrode is placed in the seat to detect capacitance changes, then occupant detection function is achieved, but direct capacitive coupling with the vehicle body increases detection error
Solution Approach 1:
A guard electrode is introduced as an intermediary element between the detection electrode and the vehicle body. The guard electrode is connected to ground potential and positioned to intercept electric field lines that would otherwise directly couple the detection electrode with the vehicle body, thereby reducing parasitic capacitance and improving measurement accuracy.
Solution Approach 2:
The harmful direct coupling capacitance is extracted and redirected through the guard electrode to ground. By providing a dedicated path for the parasitic capacitance current through the guard electrode, the interference is separated from the detection signal path, allowing accurate occupancy detection.
2Device complexity
If a wire portion is used to connect the detection electrode and control unit, then device complexity is reduced, but unwanted capacitive coupling between the wire and detection target or ground increases
Solution Approach 1:
A guard wire is introduced as an intermediary shielding element that runs parallel to the detection electrode wire. The guard wire is connected to ground potential and creates a capacitive shield that prevents unwanted coupling between the detection electrode wire and nearby conductive objects or the detection target, thereby maintaining signal integrity while using a simple wire connection.
3Ease of manufacture
If the detection electrode is stretched thin to reduce cost, then manufacturing cost is reduced, but capacitive coupling with surrounding objects increases
Solution Approach 1:
The guard electrode serves as a protective intermediary that compensates for the increased sensitivity of thin detection electrodes. By providing capacitive shielding, the guard electrode prevents the thin detection electrode from excessively coupling with surrounding objects, allowing cost-effective thin electrode design without sacrificing performance.
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 configuration improves the accuracy of determining the type and mounting state of occupants by minimizing direct capacitive coupling with the vehicle body and reducing capacitive coupling with the ground or wire connections, enhancing the overall detection performance.
Implementation Method 1
a value of an electric current of the sinusoidal signal, which changes under influence of a conductive body and/or a dielectric body (e.g., a human body) located around the detection electrode 91, is detected. Then, according to this detection result, a detected capacitance or the like is computed
Implementation Method 2
the electric field generated from the electrode 91 is directly coupled not only with a detection target (adult or child) 93, 94 but also with a conductive body 97 (vehicle body), which corresponds to a region surrounded by the dashed-line 95, 96. Thereby, the detected capacitance is increased by the amount corresponding to this direct coupling.
Implementation Method 3
The above connection manner, however, creates an unwanted capacitive coupling between the wire portion and the detection target or between the wire portion and the ground.
Data Source
AI summary
A capacitive occupant detection apparatus comprising a sensor unit and a control unit is disclosed. The sensor unit includes a detection electrode and a periphery guard electrode. The control unit includes: a signal application circuit for applying an oscillation signal to the detection electrode; an operational amplifier for applying to the guard electrode a signal having the same phase and potential as the oscillation signal applied to the detection electrode; and a control circuit for receiving current and voltage values supplied to the detection and for determining a mounting state on a seat based on the inputted current and voltage values (including phase information). The periphery guard electrode is located to surround the detection electrode when viewed from an upper side of the detection electrode.