Capacitive Sensor Angular Position Detection in Timepiece Wheels
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Solution Overview
Problem
Capacitive sensors in timepieces are prone to precision issues due to variations in endshake between the wheel and the sensor, affecting the accuracy of angular position detection.
Innovation Solution
A capacitive sensor system using a set of planar electrodes to measure differential capacitance, with a wheel featuring an electrically conductive plate and apertures, allowing for precise identification of angular positions by generating a curve with distinct maxima and minima, independent of endshake, through a stepping motor and measurement circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive sensor is used to detect the angular position of the wheel, then the sensitivity of the sensor is improved, but the precision of detection is worsened due to endshake between the wheel and the sensor
Solution Approach 1:
The single capacitive sensor is segmented into three separate electrodes (first electrode, second electrode, and common electrode). Each electrode independently measures capacitance at different angular positions of the aperture, allowing the system to detect the angular position by comparing multiple capacitance values rather than relying on a single measurement that is sensitive to endshake variations.
Solution Approach 2:
The system changes the measurement parameter from a single capacitance value to multiple capacitance values (C1, C2, C3) measured at different angular positions. By analyzing the relationships between these multiple parameters (specifically when C1 = C2 or C2 = C3), the system can determine angular positions independently of endshake magnitude, thus resolving the contradiction between sensitivity and precision under variation.
2Measurement precision
If a single capacitance measurement is used, then the device complexity is reduced, but the measurement precision deteriorates due to sensitivity to endshake variations
Solution Approach 1:
The measurement function is segmented across three electrodes instead of using a single sensor. This segmentation allows the system to obtain multiple capacitance measurements that can be processed to eliminate endshake sensitivity, achieving higher precision despite the increased number of components.
Solution Approach 2:
The common electrode serves multiple functions: it acts as one plate for the first capacitor (with the first electrode), another plate for the second capacitor (with the second electrode), and provides a reference potential. This multi-functionality reduces the total number of electrodes needed while still achieving the goal of measuring angular position with high precision independent of endshake.
3Reliability
If the aperture passes above a single sensor at a reference position, then the detection system is simplified, but the reliability of angular position determination deteriorates when endshake varies
Solution Approach 1:
Instead of a single reference position sensor, the detection system uses three electrodes positioned at different angular locations. Each electrode detects capacitance changes when the aperture passes its specific position, and the combination of these segmented measurements provides reliable angular position determination that is robust against endshake variations.
Solution Approach 2:
The system uses feedback from multiple capacitance measurements (C1, C2, C3) to determine angular position. By continuously monitoring which capacitance values are equal (C1=C2 or C2=C3) and using this feedback to identify characteristic positions, the system achieves reliable angular position determination that compensates for endshake effects.
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 differential capacitance measurement method provides reliable and precise determination of the wheel's angular position, even with significant endshake, by identifying characteristic positions on the measurement curve, enhancing the accuracy of angular position detection.
Implementation Method 1
a capacitive sensor system using a set of planar electrodes to measure differential capacitance
Data Source
AI summary
A timepiece includes a timepiece movement provided with an analog display and at least one wheel rotating integrally with a rotary indicator of the analog display. The wheel includes an electrically conductive plate pierced with at least one aperture. The timepiece also includes a device for detection of a reference angular position of the aperture. The detection device includes a first electrode, a second electrode, and a common electrode which are planar and arranged in a plane parallel to the wheel. The common electrode is arranged along portions of the first electrode and of the second electrode. The aperture is at least partially above or below: the first electrode in a first position of disequilibrium; the first electrode and the second electrode in a position of equilibrium; and the second electrode in a second position of disequilibrium.