Capacitive Sensor Contact Timing Using FIR Pulse Compression
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Solution Overview
Problem
Capacitive contact sensors face challenges in accurately detecting the time of contact and distinguishing it from noise, especially due to varying finger sizes, positions, and the use of gloves, leading to unreliable recognition and potential erroneous triggering.
Innovation Solution
A method using a digital FIR filter for pulse compression and offset elimination to generate a filter signal that reflects the dynamic behavior of the sensor signal, allowing for precise determination of the contact time by setting multiple threshold values and compensating for signal drift, thereby improving signal-to-noise ratio and reducing false triggers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a preset signal threshold value is used for contact recognition, then the sensor can detect contact in basic conditions, but the recognition becomes unreliable when finger size, position, or glove thickness varies
Solution Approach 1:
The patent applies dynamics by making the threshold value adaptive rather than fixed. The threshold is dynamically adjusted based on the measured base value of the sensor signal, allowing the system to adapt to different operating conditions such as varying finger sizes, positions, and glove thicknesses. This resolves the contradiction by enabling reliable contact recognition across diverse conditions without requiring a complex force sensor system.
Solution Approach 2:
The patent changes the parameter of the threshold value from a fixed preset to a dynamic value that depends on the base value of the sensor signal. By expressing the threshold as a function of the base value (e.g., threshold = base value + offset), the system can automatically adapt to different conditions. This parameter change enables the sensor to maintain reliability across varying finger sizes, positions, and glove conditions without additional hardware complexity.
2Reliability
If the sensor signal threshold is set to allow operation with gloves, then contact can be detected with gloves, but erroneous recognition occurs without gloves even a few millimeters above the sensor surface
Solution Approach 1:
The patent applies feedback by continuously monitoring the base value of the sensor signal and using it to dynamically adjust the threshold value. The system measures the baseline capacitance under different conditions (with and without gloves, at different positions) and adapts the threshold accordingly. This feedback mechanism prevents erroneous triggering by ensuring the threshold is always appropriate for the current operating condition, eliminating the need to choose between glove compatibility and false trigger prevention.
3Measurement precision
If integration methods are used to measure small capacitance changes, then the capacitance values can be measured, but the change in capacitance requires multiple successive cycles to be transmitted to an integration capacitor
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the base value of the sensor signal under various conditions (different finger positions, sizes, and glove conditions). Instead of performing full integration cycles for every measurement, the system uses these pre-established baseline values to quickly determine contact by comparing the current signal against the appropriate baseline. This preliminary preparation significantly reduces measurement time while maintaining precision.
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
Enables accurate and reliable recognition of contact time independently of finger size and glove use, with virtually delay-free triggering and reduced noise interference, enhancing the sensitivity and reliability of capacitive sensor systems.
Implementation Method 1
capacitive contact sensor element, a change in the capacitance value of the sensor element occurs
Implementation Method 2
filtered by a digital filter, preferably a FIR filter, that carries out pulse compression with simultaneous offset elimination
Data Source
AI summary
A method for determining a time of contact of a capacitive sensor includes continuously measuring a capacitance value of the capacitive sensor and processing the measured capacitance value into a digital sensor signal. The sensor signal is filtered to output a filter signal. Initial dynamics of the filter signal are identified upon the filter signal exceeding a first set filter threshold value. A time at which the filter signal falls below a second set filter threshold value is determined as being a potential time of contact of the capacitive sensor. An actual time of contact of the capacitive sensor is determined when the sensor signal relative to an offset of the sensor signal exceeds a sensor signal threshold value. The offset of the sensor signal is a value of the sensor signal prior to the contact of the capacitive sensor.