Capacitive Touch Sensing With Adaptive Threshold Adjustment

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Solution Overview

Problem

Existing touch sensors face challenges in accurately and swiftly determining contact or non-contact of a human body due to erroneous detections from non-human objects and delayed response times, particularly when multiple switches are pressed or metal approaches the apparatus.

Innovation Solution

A sensing apparatus that measures capacitance changes across multiple electrodes, adjusts threshold values based on cumulative measurement results, and uses a series circuit to charge and discharge capacitors to accurately determine human body presence, reducing erroneous detections by dynamically adjusting sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a predetermined period of time is awaited after contact detection to prevent erroneous operation, then false positives are reduced, but response speed deteriorates

Engineering Contradiction:

Improvedetection accuracyVSAvoidresponse speed

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent applies dynamics by making the threshold value adaptive rather than fixed. The threshold dynamically adjusts based on the sum of absolute difference values from multiple electrodes, allowing the system to respond quickly to genuine human contact while maintaining reliability by raising the threshold when multiple electrodes are activated (indicating non-human contact).

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the parameter of threshold value based on the operational state. When the sum of absolute difference values exceeds a reference value (indicating multiple electrodes activated), the threshold is set to a higher value, otherwise a lower value is used. This parameter adaptation resolves the contradiction between fast response and reliable detection.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If a fixed threshold value is used for capacitance comparison, then device complexity is reduced, but detection accuracy deteriorates due to erroneous detections

Engineering Contradiction:

Improvethreshold adjustment mechanismVSAvoidcontact detection accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The system performs self-adjustment of the threshold value based on its own measurement data from multiple electrodes. By calculating the sum of absolute difference values from its own capacitance measurements and automatically adapting the threshold, the system improves detection accuracy without requiring external calibration or complex manual adjustment mechanisms.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent implements feedback by using the measurement results from multiple electrodes to adjust the threshold value for subsequent detections. The threshold is determined based on the sum of absolute difference values, creating a feedback loop that continuously optimizes detection accuracy based on real-time operational conditions.

Inventive Principle:

Principle #23Feedback

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 speedy and accurate detection of human body contact or non-contact with reduced false positives, improving response speed and accuracy by dynamically adjusting threshold values and using a series circuit to enhance capacitance measurement precision.

Implementation Method 1

measuring capacitance of each of a plurality of first electric capacitors having unknown capacitance

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

a series circuit to charge and discharge capacitors to accurately determine human body presence

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS8106893B2Sensing apparatus and method, and program therefor

Publication Date: 2012.01.31 OMRON CORP

AI summary

Human contact/non-contact is detected speedily and accurately. A measurement section measures capacitance of each of sites to which a plurality of electrodes are connected where a human body touches, a comparison section compares the capacitance with a threshold value for each contacting electrode, and a control section determines whether a human body has come in contact based on the comparison result. A reference value calculation section calculates a reference value serving as electrode-specific reference capacitance based on the measurement results corresponding to the plurality of electrodes cumulatively stored in a storage section, a difference calculation section calculates an absolute difference value between the electrode-specific reference capacitance and a plurality of measurement results, and a threshold value adjustment section adjusts the threshold value by subtracting from the electrode-specific threshold value a value of the sum of the calculated absolute difference value for each of the electrodes other than the absolute difference value of each of the electrodes. The present invention can be applied to a touch sensor.