Electrostatic Contact Sensing With Multi-Frequency Noise Rejection
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Solution Overview
Problem
Existing contact detection devices, such as those using electrostatic capacitive sensors in steering wheels, face challenges in accurately detecting conductor contact due to noise interference at specific frequencies, which affects the measurement of electrostatic capacitance.
Innovation Solution
A contact detection device incorporating an electrostatic sensor, AC power supply, and quadrature demodulator that switches between different AC frequencies to apply voltages to the detection electrode, allowing for the extraction of quadrature components and in-phase components, and uses stored alternative components to determine contact based on predetermined error ranges, thereby reducing noise influence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If impedance measurement is used to calculate capacitive component by applying voltage waveform with constant cycle, then electrostatic capacitance measurement can be performed, but noise of frequency in vicinity of applied voltage frequency distorts applied waveform and prevents accurate measurement
Solution Approach 1:
The patent changes the frequency parameter of the applied AC voltage multiple times (first frequency, second frequency, third frequency) to avoid noise interference. By measuring impedance at different frequencies and comparing results, the system can identify and exclude measurements affected by noise, thereby improving measurement accuracy.
Solution Approach 2:
The patent applies periodic AC voltage at different frequencies in sequence to the sensor electrode. Each frequency application is a periodic action that allows measurement of the impedance component. By repeating this process at multiple frequencies, the system can distinguish between actual capacitance changes and noise-induced distortions.
2Reliability
If single frequency AC voltage is applied for contact detection, then detection speed is maintained, but noise at that frequency reduces detection reliability
Solution Approach 1:
The patent applies AC voltage at multiple different frequencies (first, second, and third frequencies) to the sensor electrode during contact detection. By comparing impedance measurements taken at these different frequencies, the system can identify consistent patterns that indicate actual contact versus noise interference, thereby improving detection reliability.
Solution Approach 2:
The patent uses feedback by comparing impedance measurements from multiple frequency applications. The system analyzes whether changes in impedance are consistent across different frequencies, using this comparison feedback to determine whether contact is genuine or caused by noise, thus improving reliability without requiring overly complex additional hardware.
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 enables accurate detection of conductor contact even with noise interference, improving the reliability and accuracy of contact detection by utilizing multiple frequency bands and stored reference components.
Implementation Method 1
an electrostatic sensor (7) which includes at least one detection electrode (22, 23) and detects contact of a conductor
Implementation Method 2
an AC power supply (11) which applies at least one AC voltage to the detection electrode (22, 23)
Implementation Method 3
a quadrature demodulator (12) which extracts at least a quadrature component in a case where an impedance of the electrostatic sensor (7) is represented by an in-phase component and the quadrature component
Data Source
AI summary
A contact detection device includes: an AC power supply switching between and applying first and second AC voltages to first and second electrode layers; a storage part storing an alternative quadrature component corresponding to a state in which a conductor is in contact with an electrostatic sensor; a quadrature component comparison part comparing between a first quadrature component extracted upon applying the first AC voltage to the second electrode layer and a second quadrature component extracted upon applying the second AC voltage to the second electrode layer; and a contact determination part that detects contact of a conductor based on the first quadrature component when the first quadrature component and the second quadrature component fall within a first quadrature error, and detects contact of a conductor based on the alternative quadrature component when the first quadrature component and the second quadrature component fall outside the first quadrature error.