Magnetic Position Sensor for Timepiece Setting Stem
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Solution Overview
Problem
Existing sensors for detecting the position and motion of a rotatable shaft in electromechanical timepieces face challenges in accuracy, power consumption, and manufacturing complexity, particularly in wearable devices where space is limited and precise detection of tiny movements is required.
Innovation Solution
A contactless sensor system using a permanent magnet attached to the rotatable element and a three-axis magnetic sensor to detect the magnetic field changes, allowing for both angular and axial position detection with reduced wear, power consumption, and simpler manufacturing, while occupying minimal space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a contactless sensor system using permanent magnets and three-axis magnetic sensors is used, then measurement precision and responsiveness are improved, but device complexity increases
Solution Approach 1:
The patent replaces mechanical contact-based position detection with a magnetic field-based contactless sensing system. A permanent magnet is attached to the rotatable element, and a three-axis magnetic sensor detects changes in the magnetic field to determine angular and axial positions without mechanical contact, thereby improving precision while reducing wear.
Solution Approach 2:
The three-axis magnetic sensor performs multiple functions simultaneously: it detects both angular position (through rotation of the magnetic field vector) and axial position (through changes in magnetic field strength), eliminating the need for separate sensors for each measurement type and reducing overall device complexity.
2Measurement precision
If capacitive electrodes with specially-shaped rotors are used, then angular position detection is achieved, but manufacturing precision requirements increase and space is consumed
Solution Approach 1:
The patent replaces the complex capacitive sensing system with mechanically precise rotors and electrodes with a magnetic field-based system. The permanent magnet and three-axis magnetic sensor require significantly less manufacturing precision while achieving comparable or superior measurement accuracy, and the magnet can be attached using simple adhesive methods rather than precision machining.
3Adaptability or versatility
If multiple dedicated sensors are used for axial and angular detection, then comprehensive position detection is achieved, but device complexity and space requirements increase
Solution Approach 1:
The three-axis magnetic sensor serves as a multi-functional device that simultaneously measures both angular position (through the orientation of the magnetic field vector in the XY plane) and axial position (through the magnitude of the magnetic field strength), replacing what would traditionally require two separate sensors and reducing overall device complexity.
Solution Approach 2:
The patent combines axial and angular position detection capabilities into a single magnetic sensing system. The permanent magnet's three-dimensional magnetic field variations are analyzed to extract both positional information types from one sensor location, effectively merging multiple detection functions into one integrated system.
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
Enables precise, high-resolution detection of angular and axial positions with faster responsiveness and reduced power consumption, eliminating the need for additional sensors and minimizing wear, thus enhancing the accuracy and longevity of timepieces.
Implementation Method 1
A rotatable element, preferably mounted on a setting stem, has a position sensor in the form of a permanent magnet
Implementation Method 2
A contactless sensor system using a permanent magnet attached to the rotatable element and a three-axis magnetic sensor to detect the magnetic field changes
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A position sensor and method are described for determining an axial and/or an angular position of a setting stem (3) of a timepiece. A magnet (2) is provided on the setting stem (3), and at least one magnetic field sensor (5) is arranged to detect changes in magnetic field (7) strength along at least a first axis and a second axis as the rotatable element (3) rotates, the second axis being not parallel to the first axis. The changing magnetic field (7) sensed by the magnetic sensor (5) is converted into a characteristic signature path which may then be mapped on to a circular signature path in two dimensions in order to derive the angular position of the setting stem (3).