Differential Capacitive Stem Position Sensing for Timepieces
Find Innovative SolutionsGenerate Solutions
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 size, and must be contactless to extend the life of the timepiece, with current solutions requiring a higher number of electrodes for finer resolution.
Innovation Solution
A capacitive sensor system using multiple stator electrodes and two rotor electrodes arranged to create differential capacitance pairs, allowing for precise angular position measurement with improved immunity to external influences, and a sensor calculation unit to determine the instantaneous angular orientation using differential capacitance values, which simplifies the sensor design and reduces the number of electrodes needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a higher number of electrodes are used to achieve finer resolution in angular position measurement, then measurement precision is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The sensor system is segmented into two functional groups: stator electrodes (fixed) and rotor electrodes (rotating). This segmentation allows the use of fewer total electrodes while achieving high measurement precision through the differential capacitance pairs formed between the groups.
Solution Approach 2:
The patent transitions from measuring position with a single capacitance value to using differential capacitance pairs (comparing capacitances in different angular relationships). This dimensional change in measurement approach enables finer resolution without increasing electrode count.
2Measurement precision
If more electrodes are used to improve measurement precision, then angular position detection accuracy is improved, but power consumption increases
Solution Approach 1:
By segmenting the electrode system into stator and rotor groups forming differential pairs, the patent reduces the total number of electrodes required, thereby reducing the power consumption associated with driving and reading out a large number of electrode signals while maintaining high measurement precision.
3Reliability
If traditional capacitive sensors are used for contactless detection, then wear is reduced and service life is extended, but measurement precision and resolution are insufficient
Solution Approach 1:
The patent enhances traditional capacitive sensing by implementing differential capacitance pairs that compare capacitance values in different angular configurations. This dimensional enhancement provides immunity to common-mode errors and environmental factors, achieving high measurement precision while maintaining the contactless nature of the sensor for extended service life.
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 a more precise measurement of the rotatable element's position and motion with finer resolution, improved accuracy, and reduced power consumption, while maintaining a compact design and extending the serviceable life of the timepiece without increasing the number of electrodes.
Implementation Method 1
a capacitive sensor for determining an instantaneous angular position, of a rotatable element of a timepiece
Implementation Method 2
provide capacitances between each of the plurality of stator electrodes, such that each of the capacitances varies over at least a portion of the said rotation cycle due to the influence of said one rotor electrode
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A capacitive sensor is described for determining the instantaneous angular position of a rotatable element (3) in a timepiece, such as the setting stem of a wristwatch. Static electrodes (11, 12, 13, 21, 22, 23) are arranged to form, in conjunction with rotor electrodes (5a, 5b) of the rotatable element (3), a first differential capacitance pair (1) and a second differential capacitance pair (2). A sensor calculation unit is configured to sense difference values from the differential capacitances pairs (1, 2) and to evaluate the angular position of the rotatable element (3) from the difference values using predetermined information relating the differential capacitance values to angular position values.