Hand Dryer Drain Tank Level Detection With Large-Area Capacitance Plate
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Solution Overview
Problem
Conventional hand dryer apparatuses face challenges in accurately detecting the water level in the drain tank due to the small difference in capacitance between empty and full conditions, leading to detection errors and potential overflow issues.
Innovation Solution
A hand dryer apparatus with a drain conductive plate positioned to face the surface with the largest area of the drain tank, combined with a water detection unit that utilizes capacitance changes to accurately monitor the water level, preventing overflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the drain conductive plate is placed on the contour of the drain tank along its small vertical surface, then the device complexity is reduced, but the measurement precision of water level detection deteriorates due to small capacitance difference
Solution Approach 1:
The patent transitions from placing the drain conductive plate on a small vertical surface (one-dimensional placement) to placing it on a large horizontal surface (two-dimensional placement). This dimensional change increases the effective detection area, thereby improving capacitance difference and water level detection accuracy without increasing device complexity
Solution Approach 2:
The large horizontal surface of the drain tank serves dual purposes: it functions as both the storage surface for collected water and as the detection surface for the drain conductive plate. This multi-functionality improves measurement precision while avoiding additional structural complexity
2Reliability
If the threshold value for full tank detection is lowered to account for capacitance noise, then the reliability of detection is improved, but the productivity of the hand dryer deteriorates due to premature stopping
Solution Approach 1:
By placing the drain conductive plate on the large horizontal surface, the system performs preliminary accurate detection of the actual full tank condition. This preliminary accurate measurement allows setting an appropriate threshold value that accounts for noise without being overly conservative, thereby preventing premature stopping and maintaining productivity
Solution Approach 2:
The patent replaces the conventional threshold-based detection method (which requires lowering thresholds to account for noise) with a capacitance measurement method based on large surface area. This substitution provides inherently higher signal-to-noise ratio, allowing reliable detection without premature operation termination
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 solution enables high-accuracy detection of water level changes in the drain tank, preventing overflow and maintaining a hygienic environment by accurately determining when the tank is full.
Implementation Method 1
a water detection unit that detects a water level of the drain tank on a basis of capacitance generated in the drain conductive plate
Data Source
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AI summary
A hand dryer (1) includes a housing including a hand insertion portion (3) and a front wall nozzle (5a) and a rear wall nozzle (5b) communicating with the hand insertion portion (3), a high-pressure air stream generation device (4) placed inside the housing, a first hand detection sensor (6) and a second hand detection sensor (7) detecting a user's hand inserted into the hand insertion portion (3), a control unit (31) that, when the first hand detection sensor (6) and the second hand detection sensor (7) detect the user's hand, operates the high-pressure air stream generation device (4) to cause an air stream to jet out from the front wall nozzle (5a) and the rear wall nozzle (5b), and a drain tank (18) collecting droplets blown off the user's hand and scattered in the hand insertion portion (3). The hand dryer (1) includes a drain conductive plate (21) placed to face the top surface of the drain tank (18) and a control circuit (31a) detecting the water level of the drain tank (18) based on capacitance generated in the drain conductive plate (21).