Differential Capacitive Setting Stem Sensing for Precise Angular Position
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Solution Overview
Problem
Existing sensors for detecting the position and motion of a rotatable setting stem in electromechanical timepieces face challenges in achieving high accuracy and precision while minimizing power consumption and maintaining compactness, especially in wearable devices where space is limited and components are tiny.
Innovation Solution
A capacitive sensor system utilizing multiple stator electrodes and two rotor electrodes, which creates differential capacitance pairs that vary over a rotation cycle, allowing for precise angular position measurement with improved immunity to external influences, and a sensor calculation unit determines the instantaneous angular orientation using differential capacitance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive sensor with multiple rotor and stator electrodes is used to detect setting stem position, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The sensor is segmented into two functional parts: a stator element with multiple stator electrodes and a rotor element with two rotor electrodes. This segmentation allows the system to achieve high measurement precision through differential capacitance pairs while keeping the rotor structure relatively simple with only two electrode segments.
Solution Approach 2:
The patent transitions from single capacitance measurement to differential capacitance measurement by creating pairs of capacitances (C1-C2 and C3-C4). This dimensional change in the measurement approach enables higher precision angular position detection through comparison of differential values, effectively resolving the contradiction between precision and complexity.
2Measurement precision
If more rotor and stator electrodes are added to increase measurement resolution, then measurement precision is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The rotor element is segmented into only two electrode parts, which is sufficient when combined with multiple stator electrodes to create the necessary differential capacitance pairs. This segmented approach achieves high resolution without requiring a large number of rotor electrodes, thereby simplifying manufacturing.
Solution Approach 2:
Instead of increasing rotor electrode count, the patent uses differential capacitance pairs formed between multiple stator electrodes and two rotor electrodes. This dimensional change in the measurement methodology achieves fine resolution while maintaining manufacturing simplicity.
3Measurement precision
If differential capacitance pairs are used to improve immunity to external influences, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple capacitance measurements into differential capacitance pairs (C1-C2 and C3-C4). By combining these measurements in a differential configuration, the system achieves improved immunity to external influences such as stray capacitances and environmental variations, while the merged differential approach actually simplifies the overall measurement architecture.
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 provides finer resolution and improved measurement accuracy with reduced power consumption, enabling incremental position detection within a 180-degree range, suitable for most watch applications, while maintaining compactness and ease of manufacturing.
Implementation Method 1
a capacitive sensor comprising a plurality of stator electrodes, and at least one rotor electrode arranged to rotate with the rotatable element, wherein the at least one rotor electrode and the stator electrodes are arranged to, during a rotation cycle of the rotatable element, provide capacitances between each of the plurality of stator electrodes
Data Source
AI summary
A capacitive sensor to determine instantaneous angular position of a rotatable element in a timepiece, such as a setting stem of a wristwatch. Static electrodes are configured to form, in conjunction with rotor electrodes of the rotatable element, a first differential capacitance pair and a second differential capacitance pair. A sensor calculation unit is configured to sense difference values from the differential capacitances pairs and to evaluate the angular position of the rotatable element from the difference values using predetermined information relating the differential capacitance values to angular position values.