Capacitive Door Position Sensing Without a Shield Frame
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Solution Overview
Problem
Capacitive sensor systems for refrigerators face challenges in reliably detecting human body presence due to high construction costs and interference from the refrigerator cabinet's capacitance, which complicates signal processing and requires high-resolution ADCs, making it difficult to distinguish between door movement and human body presence.
Innovation Solution
Replacing the electromagnetic shield with a capacitive electrode on the top panel that functions as an antenna, allowing the system to detect door position and human body presence by measuring capacitance changes, and calibrating the system to isolate human body movement signals from door angle-dependent capacitance variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an electromagnetic shield frame is used to block cabinet capacitance interference, then the sensor can detect human body presence, but the construction cost increases and the device complexity increases
Solution Approach 1:
The patent extracts the shielding function from a separate physical frame structure and integrates it into the existing door antenna. The door antenna is designed to serve dual purposes: as the sensing element for detecting human body presence and as the electromagnetic shield to block interference from the cabinet capacitance. This eliminates the need for a separate shield frame construction.
Solution Approach 2:
The door antenna is given multiple functions: it acts as both the sensing antenna for detecting human body capacitance changes and as the electromagnetic shield to prevent interference from the cabinet body. This multi-functional design simplifies the overall structure by eliminating the need for separate shield components.
2Reliability
If a shield frame is added to block cabinet interference, then detection capability improves, but manufacturing cost increases
Solution Approach 1:
The shielding function is extracted from a separate manufactured component and integrated into the existing door antenna design. This eliminates the need to manufacture and assemble a separate shield frame, reducing manufacturing costs while maintaining the shielding effect.
Solution Approach 2:
The patent uses the existing door antenna structure, which is already part of the refrigerator door assembly, to provide shielding functionality. This avoids the need for additional expensive shield materials and reduces overall manufacturing costs.
3Area of stationary object
If the door size is much bigger than the frame area, then the electromagnetic field between door and cabinet body adds varying capacitance, but using a normal capacitor instead of shield returns to the original problem of detecting small body parts
Solution Approach 1:
The door antenna serves as an intermediary element that simultaneously provides shielding against cabinet interference and sensing capability for detecting small body parts. By positioning the antenna at the door edge and designing it with appropriate dimensions, it creates a localized sensing zone that is sensitive to small capacitance changes from body parts while the rest of the door structure provides the shielding effect.
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 solution simplifies the mechanical construction, reduces costs, and enhances the system's ability to reliably detect human body presence near the door, improving precision for door closure detection while accepting lower precision for open conditions, thereby eliminating the need for mechanical switches.
Implementation Method 1
the capacitance between the sensor electrode and an earth electrode increases. This increase in capacitance changes the frequency of an output signal of the electrode
Data Source
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Figure 3
Figure 4~5
AI summary
The present invention relates to a capacitive sensor system comprising a sensor circuit connected to a first (15) and a second (11) antenna, the first antenna (15) is arranged on a first object (10) and the second antenna (11) is arranged on a second object (11) movable relative to said first object (10). The first antenna (15) is arranged right next to the second object (11) for the sensor circuit to detect the movement and/or position of the second object (11).