Hall Effect Sensor Pressure Detection in Electric Toothbrushes
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Solution Overview
Problem
Existing power toothbrush pressure sensors inaccurately measure bristle pressure against teeth due to inclusion of loads from mouth tissues, leading to incorrect trigger points for excessive force indication, potentially causing harm or reducing effectiveness.
Innovation Solution
The use of two Hall effect sensor systems to provide direct force/displacement and dynamic force/phase shift information, processed by a microprocessor to adjust trigger points based on peak-to-peak values, distinguishing between bristle pressure and mouth tissue loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single pressure sensor is used to measure bristle force, then the device complexity is low, but the measurement precision is poor due to inclusion of mouth tissue loads
Solution Approach 1:
The measurement is divided into two independent components: a first sensor measures dynamic force through phase shift analysis, while a second sensor measures static offset force. This segmentation allows each sensor to capture specific force components, improving overall measurement precision by separating bristle pressure from mouth tissue loads.
Solution Approach 2:
Phase shift analysis serves as an intermediary method to distinguish between dynamic bristle force and static mouth tissue load. By analyzing the phase relationship between drive signal and sensor output, the system can extract dynamic force information while filtering out static offsets, thereby improving measurement accuracy.
2Reliability
If pressure sensor threshold is set high to avoid false warnings from mouth tissue loads, then false alarms are reduced, but harmful excessive pressure may not be detected
Solution Approach 1:
The system provides continuous feedback by monitoring both dynamic force (first sensor) and static offset force (second sensor) separately. By comparing both measurements against respective thresholds, the system can accurately determine when excessive bristle pressure is applied, providing reliable feedback to the user without false alarms or missed detections.
Solution Approach 2:
The system applies different threshold criteria to different force components: a first threshold for dynamic force and a second threshold for static offset force. This partial application of thresholding to specific force components allows accurate detection of harmful pressure while ignoring normal mouth tissue loads.
3Measurement precision
If multiple sensor systems are used to differentiate force components, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
A single Hall effect sensor serves multiple functions: it measures both dynamic force (through phase shift analysis of the first sensor output) and static offset force (through the second sensor output). This multi-functionality reduces the need for completely separate sensor systems while maintaining measurement precision for different force components.
Solution Approach 2:
The system replaces complex mechanical force decomposition mechanisms with electrical signal processing. By using phase shift analysis and digital signal processing on Hall effect sensor outputs, the system differentiates force components without requiring complex mechanical arrangements, thereby reducing overall device complexity.
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 approach provides more accurate and informed feedback to users about excessive pressure, ensuring effective cleaning without harm by differentiating between direct bristle pressure and mouth tissue loads, thus optimizing the cleaning experience.
Implementation Method 1
A Hall effect sensor or sensors 52, 53 is/are mounted within the power toothbrush 29... The Hall-effect sensors 52 can be mounted in various positions within the power toothbrush 29... The Hall-effect sensor recognizes the lateral displacement of the drive train due to force on the bristle field against the teeth
Implementation Method 2
A magnet 48... Mounted within the power toothbrush is a Hall-effect sensor or sensors 52, 53... The Hall-effect sensor recognizes the lateral displacement of the drive train due to force on the bristle field against the teeth
Data Source
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AI summary
The toothbrush includes a sensor system for determining pressure on the teeth by a direct force measurement such as displacement, and a system for determining pressure on the teeth by a dynamic load measurement system, such as phase shift. These different pressure results are combined with peak-to-peak bristle motion values of Hall effect output values and compared to a table to obtain a more accurate value of bristle pressure against the teeth and to raise,lower or maintain the trigger threshold of excessive pressure accordingly.