Capacitive Door Position Sensing With Antenna-Based Capacitance Compensation
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Solution Overview
Problem
Capacitive sensor systems for refrigerator doors face high construction costs and precision issues due to the electromagnetic shield's inefficiency and the varying capacitance caused by the door's angle, making it difficult to distinguish human body presence from door movement.
Innovation Solution
Replacing the electromagnetic shield with a metal strip electrode on the fridge's top panel, which acts as an antenna, allowing the system to detect door position and human body presence by calculating total capacitance using the electrode's capacitance and door angle-dependent capacitance, enabling calibration for precise human body detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an electromagnetic shield (frame) is installed between the door and fridge body to block the cabinet body's influence on capacitance, then the shield should remove the influence caused by the cabinet body, but the construction cost increases significantly due to the need for thin conductive foil, plastic covering elements, and complex electrical connections
Solution Approach 1:
The patent extracts the shielding function from a complex physical frame structure and relocates it to the electrical circuit level. Instead of using a physical electromagnetic shield between the door and fridge body, the invention introduces a dummy capacitor in the measurement circuit that electronically compensates for the parasitic capacitance caused by the cabinet body, thereby achieving the same shielding effect without the mechanical complexity
Solution Approach 2:
The patent introduces a dummy capacitor as an intermediary element in the measurement circuit. This dummy capacitor acts as a mediator that absorbs and compensates for the unwanted parasitic capacitance from the cabinet body, allowing the sensor to accurately detect the door's capacitance changes without being interfered by the cabinet body's electromagnetic influence
2Reliability
If a frame shield is used to block electromagnetic influence, then the shield should remove the influence caused by the cabinet body, but the frame is not a real shield because the door size is much bigger than the frame area, allowing an electromagnetic field C3 to form between the door and fridge body that adds varying capacitance to the measurement circuit
Solution Approach 1:
The dummy capacitor serves as an electrical intermediary that compensates for the ineffective physical shielding. By adding a programmable capacitor in parallel with the door antenna, the system electronically balances out the parasitic capacitance C3 that forms between the door and fridge body, thereby restoring measurement precision without requiring a more extensive physical shield
Solution Approach 2:
The patent dynamically adjusts the capacitance parameter of the dummy capacitor based on the door's position and the measured parasitic capacitance. The control board calculates the appropriate compensation value and programs the dummy capacitor accordingly, allowing the system to adapt to changing electromagnetic conditions and maintain accurate measurements despite the presence of electromagnetic field C3
3Stability of the object's composition
If the door capacitance to the fridge body is made constant by electrically connecting the door to a shield, then the movement of the door process should not change the door capacitance to the fridge body, but the capacitance C3 depends on the door angle and influences the total capacitance of the circuit, making it difficult to detect human body movement
Solution Approach 1:
The patent implements a feedback mechanism where the sensor circuit continuously monitors the total capacitance, which includes the parasitic capacitance C3 that varies with door angle. The control board processes this feedback information, separates the door position-related capacitance changes from human body-related capacitance changes, and adjusts the dummy capacitor accordingly to maintain accurate human body detection
Solution Approach 2:
The dummy capacitor acts as an intermediary that isolates the measurement circuit from the variable parasitic capacitance C3. By providing a programmable compensation capacitance in parallel with the door antenna, the dummy capacitor mediates between the unstable door-to-fridge capacitance and the sensor circuit, allowing the system to detect human body movements with high precision despite door angle variations
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 reduces construction costs, simplifies mechanical components, and enhances precision in detecting human body presence near the door, particularly for the door close condition, while accepting lower precision for the open condition, thus improving the overall functionality of the capacitive sensing system.
Implementation Method 1
a sensor circuit connected to a first and a second antenna, the first antenna is arranged on a first object and the second antenna is arranged on a second object movable relative to said first object
Data Source
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).