Capacitive Milk Level Sensing With Tilt and Touch Compensation
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Solution Overview
Problem
Existing capacitive sensors for breast pumps face inaccuracies due to varying dielectric factors, conductive object interference, and tilting, leading to false fluid level readings in milk containers.
Innovation Solution
A capacitive sensor system with multiple elements of varying sensitivities and an electric shield, combined with an accelerometer, to differentiate between fluid level changes and conductive object interference, and correct for tilting, using signal processing to enhance accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single capacitive sensor element is used to monitor fluid level, then the device complexity is low, but the measurement precision deteriorates due to inability to differentiate between fluid level changes and conductive object interference
Solution Approach 1:
The capacitive sensor is divided into multiple sensor elements (first, second, third, and fourth elements) with different sensitivities to fluid level changes versus conductive object interference. Each element contributes differently to the measurement, allowing the system to differentiate between genuine fluid level changes and parasitic effects from conductive objects touching the container.
Solution Approach 2:
The patent utilizes parameter changes by varying the sensitivity characteristics of different sensor elements. The first sensor element has high sensitivity to fluid level changes, while the second has low sensitivity to fluid level but similar sensitivity to conductive objects. By processing signals from elements with different parameter characteristics, the system achieves accurate fluid level measurement while compensating for interference.
2Measurement precision
If multiple capacitive sensor elements with different sensitivities are used to reduce parasitic errors, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The capacitive sensor is segmented into multiple specialized elements, each optimized for specific measurement aspects. The first element detects fluid level changes, the second detects conductive object interference, and the third element projects the electric field into the reservoir. This segmentation allows parallel detection of different parameters, improving overall measurement precision while maintaining manageable complexity through functional specialization.
Solution Approach 2:
The third capacitive sensor element acts as an intermediary by projecting the electric field belonging to the first sensor element into the reservoir. This intermediary element facilitates better field penetration and interaction with the fluid, enhancing the measurement capability of the first sensor element without requiring direct modification of the primary sensing mechanism.
3Measurement precision
If the capacitive sensor is highly sensitive to fluid level changes, then the measurement precision improves, but the sensitivity to conductive object interference also increases
Solution Approach 1:
Different sensor elements are assigned different local qualities in terms of sensitivity characteristics. The first sensor element has high sensitivity to fluid level changes, while the second sensor element has low sensitivity to fluid level but similar sensitivity to conductive objects. This local differentiation of sensitivity qualities allows the system to selectively detect fluid level changes while using the second element to identify and compensate for conductive object interference, thereby maintaining high fluid level detection sensitivity without proportionally increasing vulnerability to interference.
Solution Approach 2:
The patent changes the sensitivity parameters of different sensor elements to create a differential measurement system. By having elements with different sensitivity profiles (high sensitivity to fluid for the first element, similar sensitivity to conductive objects for the second element), the system can process these varying parameters to extract accurate fluid level information while filtering out interference from conductive objects.
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 system accurately determines fluid levels in milk containers by reducing parasitic errors, improving sensitivity to fluid changes while minimizing interference from conductive objects and tilting.
Implementation Method 1
the capacitance of the capacitive sensor is typically proportional to a dielectric factor assigned to a liquid inside the container
Implementation Method 2
the capacitance of the capacitive sensor is typically proportional to a dielectric factor assigned to a liquid inside the container, wherein said dielectric factor varies due to a changing volume of liquid inside the milk container
Implementation Method 3
the third capacitive sensor element is configured to provide respective electric shield
Data Source
AI summary
This disclosure generally relates to a capacitive sensor for determining a fluid level in a milk container. In one embodiment, the capacitive sensor may be attached to a milk container of a breast pump device. The breast pump may include a breast shield adapted to at least in part receive a breast of a lactating user, an aggregate for generating suction for expressing milk from the breast, a milk container (4) providing a reservoir (26) for the expressed milk, a capacitive sensor (8) adapted to generate a signal indicative of the filling level within the reservoir (26) and a controller (12) for controlling the aggregate (14) and processing the signal of the capacitive sensor (8), wherein the capacitive sensor (8) includes at least two capacitive sensor elements (44, 46) having a different sensitivity to a change of the filling level and a similar sensitivity to a conductive object touching the milk container (4).