Gear Rotation Detection via Magnetic Field Angle
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Solution Overview
Problem
Conventional rotation detection devices that use magnetic sensors to detect magnetic flux density struggle with false detection when an air gap between the gear and the sensor changes due to vibration, as they cannot prevent false detection effectively.
Innovation Solution
A rotation detection device with a magnet forming a symmetric magnetic field and a sensor having magnetic detection elements and a signal processor that sets thresholds based on the magnetic flux density variations, ensuring accurate detection of gear rotation even with varying air gaps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a magnetic sensor that detects magnetic flux density is used, then the device can detect magnetic field strength, but false detection occurs when air gap changes due to vibration
Solution Approach 1:
The patent changes the detection parameter from magnetic flux density magnitude to magnetic field angle. The magnetic sensor detects the angle of the magnetic field vector rather than its strength, which remains constant regardless of air gap variations. This parameter transformation eliminates the false detection problem caused by vibration-induced air gap changes while maintaining accurate rotation detection capability.
2Measurement precision
If magnetic flux density detection is used, then the sensor can measure field strength, but cannot prevent false detection from air gap variation
Solution Approach 1:
The invention transforms the detection parameter from magnetic flux density (which varies with air gap) to magnetic field angle (which remains stable despite air gap changes). The magnetic sensor measures the angular orientation of the magnetic field vector formed by the magnet and gear tooth interaction, providing vibration-resistant detection that eliminates false positives from air gap variation.
3Reliability
If air gap is kept constant, then false detection is prevented, but device complexity increases to maintain positioning
Solution Approach 1:
Instead of controlling the air gap to remain constant (which would require complex positioning mechanisms), the invention changes the detection parameter to magnetic field angle. This approach passively accepts air gap variations while detecting rotation through the angular orientation of the magnetic field, which inherently remains reliable regardless of distance changes between sensor and gear.
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 device effectively prevents false detection of gear rotation by setting thresholds based on magnetic flux density variations, allowing for reliable detection even when the air gap changes due to vibration, thereby ensuring accurate measurement of rotating speed and angular speed.
Implementation Method 1
a magnet that forms a magnetic field toward a tooth surface of a gear
Implementation Method 2
a sensor having a sensor center, and the magnetic field formed by the magnet being symmetric with respect to the sensor center. The sensor includes at least a pair of magnetic detection elements that outputs signals according to a magnetic flux density
Data Source
Figure 1~2(b)
Figure 3~4
Figure 5~6
AI summary
A rotation detection device (6) includes a magnet (2) that forms a magnetic field toward a tooth surface of a gear (3); and a magnetic sensor (1) disposed between the magnet (2) and the gear (3). The magnetic sensor includes at least a pair of Hall elements that outputs signals according to a magnetic flux density in a circumferential direction of the gear (3); and a DSP that sets a first threshold Bop on the basis of signals output from the Hall elements in the case in which the distance between the tooth surface of the gear (3) and the Hall elements is set as infinite, the DSP in the magnetic sensor (1) outputting a signal according to a rotation of the gear (3) on the basis of signals output from the Hall elements according to a variation in a magnetic flux density caused by the rotation of the gear (3) and the first threshold Bop. The rotation detection device that detects a rotation of a gear while preventing occurrence of false detection of a rotation state.