Capacitive Object Detection Using a Heating Conductor
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Solution Overview
Problem
Existing capacitive object detection systems, such as those used in vehicles for steering wheel and seat occupancy detection, face challenges in efficiently using electrical heating circuitry due to the need for additional decoupling elements, which increase complexity and cost.
Innovation Solution
A capacitive object detection system that utilizes an elongate conductive element, potentially a heating element, with a detection circuit connected to terminals, where the detection circuit applies signals to detect impedance changes caused by objects, employing techniques like frequency-dependent measurements and resonance to isolate the object's capacitive impedance from the inductive impedance of the conductive element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional decoupling elements (switches, inductors, common mode coils) are used to electrically decouple heating function from sensing function, then electrical decoupling is achieved, but device complexity and cost increase significantly
Solution Approach 1:
The patent extracts the sensing function from the power supply circuit by using the conductive element's inherent inductance as a natural decoupling mechanism. The sensing circuit measures impedance changes while the heating circuit supplies power through the same conductive element, with the element's inductance providing automatic electrical decoupling between the two functions without requiring additional switches, inductors, or common mode coils.
Solution Approach 2:
The conductive element serves dual functions: it provides both heating capability and inductive decoupling for sensing. The element's own inductance property is utilized to automatically decouple the sensing and heating circuits, eliminating the need for external decoupling components. The system uses the conductive element's inherent electrical characteristics to achieve the decoupling function that would otherwise require additional components.
2Reliability
If additional decoupling elements are used to achieve electrical decoupling, then heating and sensing functions are separated, but space requirements increase significantly
Solution Approach 1:
The conductive element is designed to perform multiple functions simultaneously: it serves as both a heating element and an inductive decoupling component for the sensing circuit. This multi-functionality eliminates the need for separate decoupling components, thereby reducing the overall circuit space while maintaining effective electrical decoupling between heating and sensing operations.
3Ease of manufacture
If the conductive element's impedance influence is not minimized, then circuit design is simplified, but detection accuracy decreases
Solution Approach 1:
The sensing circuit applies periodic excitation signals at specific frequencies to the conductive element and measures the impedance response. By operating at frequencies where the inductive reactance dominates and by using frequency-dependent measurements, the circuit can distinguish between the conductive element's impedance and the impedance changes caused by detected objects, thereby maintaining detection accuracy while using the element's inherent inductance.
Solution Approach 2:
The system changes the operating frequency parameter to optimize the sensing measurement. By selecting frequencies where the conductive element's inductive impedance has specific characteristics, the system can minimize the influence of the element's own impedance on the detection accuracy while maintaining the ability to detect object-induced impedance changes through frequency-dependent analysis.
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 allows for reliable and efficient detection of objects, including their position, by minimizing the influence of the conductive element's impedance, thereby reducing complexity and cost while maintaining detection accuracy.
Implementation Method 1
an oscillating electric signal is applied to at least one antenna electrode which thereupon emits an electric field into a region of space proximate to the antenna
Implementation Method 2
The influence of an object or living being on the electric field is the detected in order to determine the seat occupancy status
Implementation Method 3
The inductive impedance of the heating conductor is used to decouple the sensing function from the heating function
Implementation Method 4
employing techniques like frequency-dependent measurements and resonance to isolate the object's capacitive impedance from the inductive impedance of the conductive element
Data Source
AI summary
A system for capacitive object detection. In order to provide means for efficiently using the circuitry of an electrical heating device for capacitive object detection, the system includes: an elongate conductive element extending between a first terminal and a second terminal, wherein the first terminal is coupled to ground via a capacitive element and is connectable to an electrical power source, and the second terminal is connected to ground; and a detection circuit connected to at least one detection node disposed on the conductive element between the first and second terminal. The detection circuit is adapted to capacitively detect the presence of an object in the proximity of the conductive element based on an impedance associated with the object.