Common Electrode Geometry for Angular Position Detection Accuracy
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Solution Overview
Problem
Existing devices for detecting the angular position of a rotating wheel in timepiece movements suffer from inaccurate determination due to insufficient capacitive coupling between electrodes, resulting in a less pronounced maximum and minimum in the measurement curve.
Innovation Solution
The common electrode is modified to extend facing both lateral and circumferential edges of the first and second electrodes, enhancing radial and lateral coupling, resulting in a more triangular curve shape with pronounced maxima and minima.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the common electrode extends only facing lateral edges of the first and second electrodes, then the device complexity is reduced, but the capacitive coupling between electrodes is insufficient resulting in less pronounced maxima and minima in the measurement curve
Solution Approach 1:
The common electrode is extended from only lateral edge facing to include circumferential edge facing, adding a new dimensional aspect to the electrode coupling. This dimensional expansion increases the capacitive coupling area between the common electrode and the first/second electrodes, resulting in more pronounced maxima and minima in the measurement curve and improved angular position detection accuracy.
2Reliability
If the common electrode is extended to face both lateral and circumferential edges, then the capacitive coupling is enhanced, but the manufacturing complexity increases
Solution Approach 1:
The common electrode is divided into distinct functional segments: a lateral edge-facing portion and a circumferential edge-facing portion. This segmentation allows each portion to be optimized for its specific coupling direction while maintaining overall manufacturability through modular design approaches.
3Measurement precision
If the electrode coupling is increased to produce a more triangular curve shape, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
Different portions of the common electrode are given different geometric qualities: the lateral edge-facing portion provides coupling in the lateral direction while the circumferential edge-facing portion provides coupling in the circumferential direction. This local differentiation of electrode qualities creates the enhanced triangular curve shape necessary for precise angular position detection.
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 modification improves the accuracy of detecting the angular position by increasing the coupling degree, leading to a more distinct and interpretable measurement curve.
Implementation Method 1
capacitive coupling takes place between these two electrodes: the capacitance between these two electrodes is referred to as the first capacitance C1
Implementation Method 2
the wheel is not interrupting any electric field line between the first electrode E1 and the common electrode Em
Data Source
AI summary
A timepiece movement includes an analogue display, including a rotary indicator and a wheel that rotates as one with the rotary indicator. The wheel includes a plate with a locating element. The timepiece movement also includes a device for detecting at least one angular position of the locating element, which includes a board that is fixed with respect to the plate, extending substantially parallel to the plate, and on which a first electrode, a second electrode, and a common electrode are arranged. The electrodes are planar and are arranged such that, in one angular position of the wheel, the locating element is located over at least a portion of each electrode.