Differential Capacitive Sensor Cable for False Proximity Detection
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Solution Overview
Problem
Conventional capacitive proximity sensors face challenges in mass productivity, particularly for long and thin designs, and are prone to erroneous detection due to airborne objects like raindrops or fog.
Innovation Solution
A proximity sensor design featuring independent first and second detection electrodes and a shield electrode, with a sensor cable comprising parallel electrode wires and a differential output circuit to detect capacitance differences, improving manufacturing simplicity and preventing erroneous detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If independent electrodes and shield are separated by spacers to maintain electrical insulation, then detection accuracy is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent combines the first detection electrode, second detection electrode, and shield electrode into a single integrated electrode assembly where all electrodes are formed on the same flat surface. This merging eliminates the need for spacers and complex three-dimensional arrangements, reducing device complexity while maintaining detection accuracy through the differential measurement approach.
Solution Approach 2:
The patent extracts the shield electrode function from the detection electrode structure by forming it as a separate conductive layer on the same substrate. This allows the shield to be electrically connected to ground through the flexible printed circuit board without requiring physical separation spacers, simplifying the overall structure while maintaining electrical insulation through the substrate material.
2Reliability
If multiple spacers are provided to maintain electrical insulation between electrodes, then electrical insulation is improved, but mass productivity deteriorates
Solution Approach 1:
The patent replaces the mechanical spacer system with an integrated planar structure where electrical insulation is achieved through the substrate material itself rather than additional mechanical components. This substitution eliminates multiple assembly steps and improves mass productivity while maintaining reliable electrical insulation between the detection electrodes and shield.
3Object-affected harmful factors
If shield electrode completely surrounds detection electrodes, then shielding effect is improved, but manufacturing difficulty increases
Solution Approach 1:
The patent employs an asymmetric shield configuration where the shield electrode is formed as a conductive layer on the same flat surface rather than completely surrounding the detection electrodes in three dimensions. This asymmetric planar arrangement provides adequate shielding for capacitive proximity sensing while being significantly easier to manufacture using standard flexible printed circuit board techniques.
4Length of moving object
If long and thin sensor cable is manufactured with independent electrodes, then sensing range is improved, but manufacturing precision deteriorates
Solution Approach 1:
The patent merges all electrodes into a single integrated flexible printed circuit board structure, eliminating the need for separate electrode components and their associated alignment tolerances. This integrated approach maintains manufacturing precision even in long and thin sensor cables by using standard FPCB manufacturing processes that ensure consistent electrode positioning throughout the length of the cable.
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
The design enhances mass productivity and prevents erroneous detection by airborne objects while maintaining effective proximity sensing.
Implementation Method 1
a first capacitance detecting portion for detecting a first capacitance to be detected by the first electrode wire, a second capacitance detecting portion for detecting a second capacitance to be detected by the second electrode wire
Data Source
AI summary
A proximity sensor includes a sensor cable that includes a first electrode wire and a second electrode wire arranged parallel to each other, an insulation covering both the first electrode wire and the second electrode wire, and a shield partially covering a surface of the insulation so as to form an opening, the first electrode wire and the second electrode wire being arranged to have different distances to the opening, and a detector circuit that includes a first capacitance detecting portion for detecting a first capacitance to be detected by the first electrode wire, a second capacitance detecting portion for detecting a second capacitance to be detected by the second electrode wire, and a differential output portion for outputting a difference between the first capacitance and the second capacitance.