Capacitive proximity switch and household appliance equipped therewith
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Solution Overview
Problem
Capacitive proximity switches struggle to distinguish between user actuation and incorrect operations due to dirt or moisture on the cover plate, leading to unclear actuation detection.
Innovation Solution
The signal output of the semiconductor switch follows a clock signal, with components proportional to the capacitance of the sensor surface, allowing for continuous evaluation of capacitance changes, and active shielding minimizes parasitic capacitances, enabling reliable actuation detection independent of absolute signal magnitude and reducing component count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitive proximity switch with a blocked semiconductor switch in idle state is used, then the switch is in a stable off state, but the ability to clearly distinguish user actuation from incorrect operation (dirt/moisture) is lost
Solution Approach 1:
The semiconductor switch transitions from a static blocked state to a dynamic state where it can switch on during charging periods. The switch state changes dynamically based on the clock signal phase and capacitance conditions, enabling continuous monitoring capability while maintaining stability during idle periods.
Solution Approach 2:
The switching circuit operates periodically with each clock signal cycle. The semiconductor switch is activated only during charging periods rather than continuously, creating a periodic evaluation rhythm that distinguishes intentional actuation (sustained capacitance change) from transient interference (dirt/moisture).
2Measurement precision
If the sensor surface is continuously monitored to distinguish actuation from incorrect operation, then detection accuracy improves, but the device complexity and component count increase
Solution Approach 1:
The system performs preliminary evaluation of capacitance changes during each charging period before making a final actuation determination. By continuously sampling and comparing capacitance values against threshold criteria during charging phases, the system builds confidence in detection accuracy without requiring complex continuous monitoring circuitry.
Solution Approach 2:
The switching circuit uses its own internal clock signal and charging/discharging cycles to perform self-evaluation of capacitance changes. The semiconductor switch automatically activates during charging periods to generate output signals that reflect capacitance state, eliminating the need for separate dedicated evaluation components.
3Speed
If the clock signal frequency is increased to improve actuation detection speed, then detection responsiveness improves, but energy consumption and component stress increase
Solution Approach 1:
The system uses periodic clock signals at optimized frequencies (e.g., 10-100 Hz) rather than continuous high-frequency signals. The semiconductor switch is activated only during specific charging periods within each clock cycle, creating a duty-cycled operation mode that maintains detection responsiveness while significantly reducing average power consumption compared to continuous operation.
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 allows for clear differentiation between user actuation and incorrect operations, improving the reliability and cost-effectiveness of capacitive proximity switches by continuously monitoring capacitance changes and reducing the need for additional components.
Implementation Method 1
The sensor surface forms one plate of an open capacitor, the capacitance of which depends on the distance to a second plate (e.g. earth), which is changed, for example, by the proximity of a user's finger.
Implementation Method 2
Since the semiconductor switch or transistor switches on as long as charge carriers flow to the sensor surface
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
The invention relates to a capacitive proximity switch (4) with an electrically conductive sensor surface (7), which is covered by an electrically non-conductive covering plate (2) and which serves as a part of a capacitor (17) with a capacitance that varies with proximity, from which the sensor surface (7) is connected to a control input (19) of a semiconductor switch (18) that has a signal input (21) with a clock signal (28) and a signal output (22). The invention also relates to a household appliance (1) equipped with this capacitive proximity switch (4). The signal output (22) of the semiconductor switch (18) has an output signal, which follows the clock signal and which has signal portions that are proportional to the capacitance of the capacitor formed with the sensor surface (7).