Watch Wheel Position Sensing Layout to Reduce Parasitic Capacitance
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Solution Overview
Problem
Existing watch movement detection devices experience capacitive coupling issues between the common electrode and the wheel's conductive plate due to fluctuations in potential caused by shocks or sudden movements, leading to parasitic capacitance and inaccurate angular position detection.
Innovation Solution
The common electrode is designed with a special shape that minimizes its coupling with the wheel's conductive plate while maintaining effective coupling with the first and second electrodes, achieved by optimizing the relative lengths and distances between electrode branches and the wheel's shaft.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the common electrode is positioned close to the wheel's conductive plate for effective coupling, then the coupling between the common electrode and the first and second electrodes is improved, but parasitic capacitance increases due to shocks or sudden movements
Solution Approach 1:
The common electrode is divided into multiple separate branches (first branch, second branch, third branch) arranged in a specific pattern. This segmentation reduces the overall parasitic capacitance with the wheel's conductive plate while maintaining effective coupling with the first and second electrodes through the distributed branch structure.
Solution Approach 2:
The common electrode branches are designed with asymmetric positioning and varying lengths relative to the first and second electrodes. The first and second branches are positioned to optimize coupling with their respective electrodes, while the third branch provides additional coupling paths. This asymmetric arrangement allows optimization of coupling effectiveness while minimizing parasitic capacitance exposure.
2Measurement precision
If the common electrode has a larger surface area for better coupling, then the coupling with the first and second electrodes is improved, but the parasitic capacitance with the wheel's conductive plate increases
Solution Approach 1:
Instead of using a single large common electrode, the design employs multiple smaller branches (first, second, and third branches) distributed across the electrode structure. This segmentation achieves the necessary coupling surface area while reducing the continuous exposure to the wheel's conductive plate, thereby minimizing parasitic capacitance formation.
Solution Approach 2:
The common electrode is arranged in a multi-dimensional configuration with branches extending in different directions and at different radial positions. This spatial distribution optimizes the coupling surface area for detecting angular position while reducing the parasitic capacitance by minimizing the projected area facing the wheel's conductive plate.
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 configuration reduces parasitic capacitance, enhancing the accuracy of angular position detection by stabilizing the common electrode's interaction with the wheel, even under shock or movement conditions.
Implementation Method 1
a capacitive coupling occurs between these two electrodes: the capacitance between these two electrodes is called the first capacitance C1
Implementation Method 2
This electronic assembly allows for the measurement of (C2-C1)/(C1+C2) as a function of the opening position when the wheel MB rotates
Implementation Method 3
This results in a parasitic capacitance formed between the PT plate and the common electrode Em
Data Source
Figure 1~5
AI summary
The invention relates to a watch movement comprising: - an analog display, including a rotating indicator and a wheel (MB) fixed to the rotation of said rotating indicator, said wheel (MB) including a plate (PT) comprising a locating element (OV), - a device for detecting at least one angular position of the locating element (OV), comprising a plate (PAa, PAb, PAc) fixed relative to the plate (PT), extending substantially parallel to the plate (PT), and on which are arranged a first electrode (E1a, E1b, E1c), a second electrode (E2a, E2b, E2c) and a common electrode (Ema, Emb, Emc) positioned between the first electrode (E1a, E1b, E1c) and the second electrode (E2a, E2b, E2c), the electrodes being flat and arranged such that, in an angular position of the wheel (MB), the locating element (OV) is located above at least one portion of each electrode, the first electrode (E1a, E1b,E1c) and the second electrode (E2a, E2b, E2c) having the shape of two sectors of a ring centered on the intersection between the wheel axis (MB) and the plate (PAa, PAb, PAc),