Inductive Sensors for Rotating Control Stem Position Detection
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Solution Overview
Problem
Existing systems for detecting the rotation of a control stem in portable objects, such as wristwatches, face challenges in accurately determining the direction and position due to external magnetic disturbances, requiring cumbersome and costly shielding to eliminate asymmetrical influence on magnetic sensor signals.
Innovation Solution
A portable object design utilizing two inductive sensors arranged symmetrically to detect magnetic induction variations in only one direction, allowing for phase-shifted signals to determine the direction of rotation and position of the control stem, eliminating the need for external shielding by ensuring equal influence from environmental magnetic disturbances on both sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two magnetic sensors measure variations in magnetic induction in two orthogonal directions, then the rotation of the control stem can be detected, but external magnetic disturbances directed along the axis of measurement of only one sensor cannot be subtracted, requiring electromagnetic shielding
Solution Approach 1:
The patent applies asymmetry by using two magnetic sensors oriented in the same direction (parallel) rather than orthogonal directions. This asymmetric arrangement relative to the external disturbance field allows both sensors to experience identical external magnetic disturbances, enabling subtraction of the disturbance component while preserving the ability to detect control stem rotation through the differential signal.
Solution Approach 2:
The patent segments the magnetic detection function into two identical sensors that independently measure magnetic induction. By having two separate sensors instead of one sensor measuring in multiple directions, the system can distinguish between external disturbances (affecting both equally) and control stem rotation (affecting the differential measurement), eliminating the need for electromagnetic shielding.
2Measurement precision
If high sensitivity magnetic sensors are used to measure the Earth's magnetic field, then low field values can be detected, but the sensors cannot measure magnetic induction in excess of 5 mT whereas small dimension magnets frequently reach 100 mT
Solution Approach 1:
The patent uses magnetic sensors with sensitivity optimized for measuring the weak Earth's magnetic field (20-60 μT), even though these sensors have limited maximum measurement capability (5 mT). The system deliberately uses this partial measurement capability because the control stem rotation produces detectable variations within this limited range, and the high sensitivity is necessary to detect the subtle changes in the Earth's magnetic field caused by the rotation.
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 solution provides reliable and reproducible detection of the control stem's rotation and position, enhancing precision and reducing manufacturing complexity and cost by eliminating the need for magnetic shielding, even in small portable devices.
Implementation Method 1
the rotation of the control stem and the position of the latter being detected by two inductive sensors arranged to be sensitive to a variation in magnetic induction produced by rotation of the magnetized ring
Data Source
AI summary
A portable object including a control stem, actuation of which in rotation can control at least one electronic or mechanical function of the portable object, a magnetized ring driven in rotation by the control stem, rotation of the magnetized ring and position of the magnetized ring being detected by two inductive sensors configured to be sensitive to a variation in magnetic induction in only two directions in space that are parallel to each other or that converge on a same point, with exception of a case in which these two directions are perpendicular to each other.