Steering Wheel Capacitive Detection Circuit for Linear Contact Sensing
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Solution Overview
Problem
Existing detection devices struggle to accurately determine the degree of contact and contact position on a steering wheel due to non-linear relationships between electrostatic capacitance and output voltage, leading to signal saturation issues.
Innovation Solution
The detection device incorporates a sensor electrode, a shield electrode, and a detection unit with a capacitor connected in series between the sensor electrode and the detection circuit, along with a bias unit that reduces voltage amplitude and prevents signal saturation, using a differential amplifier and ADC to accurately determine contact and degree of contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If only a sensor electrode having a large electrostatic capacitance is used to improve the linearity, then the linearity between degree of contact and output voltage is improved, but the signal voltage amplitude becomes too large causing saturation in the detection circuit
Solution Approach 1:
A capacitor is introduced as an intermediary element connected in series between the sensor electrode and the detection circuit. This capacitor mediates the signal transmission by limiting the voltage amplitude that reaches the detection circuit, preventing saturation while preserving the electrostatic capacitance detection functionality. The capacitor acts as a buffer that controls signal levels without interfering with the fundamental measurement principle.
Solution Approach 2:
The invention changes the electrical parameters of the detection system by adding a capacitor with specific capacitance value in series with the sensor electrode. This parameter modification transforms the voltage signal characteristics, ensuring that the output voltage remains within the linear detection range of the detection circuit while maintaining accurate electrostatic capacitance measurement capability.
2Reliability
If multiple capacitors are connected in series in each electrostatic sensor unit, then the electrostatic detection capability is enhanced, but the detected electrostatic capacitance value becomes determined by both degree of contact and contact position, reducing detection accuracy
Solution Approach 1:
The invention extracts the series-connected capacitors from the sensor electrode structure and relocates them to the detection circuit side. This separation allows the sensor electrode to maintain simple electrostatic capacitance sensing functionality while the capacitors in the detection circuit provide signal conditioning. The extraction resolves the conflict by removing the source of measurement ambiguity while preserving the detection enhancement benefits.
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 linearity between contact degree and output voltage without signal saturation, enabling accurate detection of contact and degree of contact on a steering wheel.
Implementation Method 1
The detection is performed on the basis of a change of the electrostatic capacitance of a sensor electrode disposed in the steering wheel
Implementation Method 2
a capacitor connected in series between the sensor electrode and the detection circuit
Data Source
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AI summary
This detection device comprises: a sensor electrode; a shield electrode that has a parasitic capacitance between the sensor electrode and the shield electrode and is driven by an AC voltage; a detection circuit that is electrically connected to the sensor electrode and the shield electrode and detects the electrostatic capacitance of the sensor electrode; a capacitor that is connected in series between the sensor electrode and the detection circuit; and a bias unit that biases the potential of the sensor electrode via a resistor.