Magnetic Angle Sensor Layout for Harmonic and Hysteresis Cancellation
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Solution Overview
Problem
Conventional magnetic rotational-angle detectors face challenges in achieving high accuracy due to harmonic distortions and hysteresis effects caused by the non-ideal sinusoidal output from magneto-resistive devices, which are exacerbated by the imbalance in magnetic field intensities and device sensitivity differences.
Innovation Solution
The magnetic rotational-angle detector employs axisymmetric arrangement of magneto-resistive devices on a substrate with a differential amplifier, ensuring that harmonic components and hysteresis distortions are canceled by symmetrically positioning and connecting the devices, thereby eliminating amplitude imbalances and sensitivity differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If outputs from MR devices spaced apart by predetermined intervals are added or subtracted to eliminate harmonic components, then harmonic distortions can be reduced, but amplitude imbalance among device outputs remains due to different effective distances from the rotating drum
Solution Approach 1:
The patent applies asymmetry by intentionally designing the magnetic sensor with a specific asymmetric structure where the substrate is positioned at a distance from the rotating drum, and MR devices are arranged at different radial distances. This asymmetric configuration, combined with specific spacing relationships between devices, creates signal imbalances that are then compensated through differential connections to eliminate harmonic components while maintaining amplitude balance.
Solution Approach 2:
The patent uses the counterweight principle by pairing MR devices at different radial distances from the substrate center and connecting them in differential pairs. The device closer to the drum (experiencing stronger magnetic field) is paired with a device farther away (experiencing weaker field), and their outputs are subtracted. This differential connection acts as a counterbalance that cancels out the amplitude imbalance while preserving the harmonic elimination effect.
2Ease of manufacture
If MR devices are arranged symmetrically about the center of the magnetic sensor, then structural balance is achieved, but the direction of differential among signal outputs is not reversed and harmonic components cannot be canceled
Solution Approach 1:
The patent deliberately breaks symmetry by positioning the substrate at a non-zero distance from the rotating drum and arranging MR devices at different radial distances from the substrate center. This asymmetric arrangement ensures that devices in differential pairs experience different magnetic field intensities, creating signal phase differences that enable harmonic cancellation when outputs are subtracted.
Solution Approach 2:
The patent transitions from a two-dimensional planar arrangement to a three-dimensional configuration by positioning the substrate at a distance from the drum surface and arranging devices at different radial depths. This spatial dimensionality change allows devices to experience different magnetic field strengths, enabling both harmonic elimination and amplitude balance through differential connections.
3Measurement precision
If the substrate is positioned close to the rotating drum to enhance signal strength, then detection sensitivity improves, but amplitude imbalance among MR device outputs increases due to varying effective distances
Solution Approach 1:
The patent applies the counterweight principle by creating differential pairs of MR devices where one device is positioned closer to the drum (experiencing stronger magnetic field) and the other is positioned farther away (experiencing weaker field). The outputs of these paired devices are subtracted, and the closer device's stronger signal acts as a counterbalance to the farther device's weaker signal, canceling out amplitude imbalances while maintaining high overall signal strength.
Solution Approach 2:
The patent applies local quality by assigning different radial positions to different MR devices within the array. Devices are strategically positioned at specific distances from the substrate center based on their function in differential pairs, creating local variations in magnetic field exposure that enable both high sensitivity and amplitude balance through differential signal processing.
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 configuration allows for the complete or substantial elimination of harmonic and hysteresis distortions, enabling precise detection of the rotational position and angle of the rotating member with improved accuracy.
Implementation Method 1
The magnetic sensor has magneto-resistive devices (MR device). This magnetic sensor utilizes characteristic of the MR device that an electric resistance of the MR device is changed by the magnetic field.
Implementation Method 2
a magnetic medium alternately magnetized with a magnetization pitch λ on an outer periphery of a rotating drum
Data Source
AI summary
The present invention provides a magnetic rotational-angle detector capable of detecting a position and a rotational angle of a rotating member with excellent accuracy. The magnetic rotational-angle detector includes device arrays (51, 52) constituted by a plurality of magnetic sensor devices which are arranged to cancel the n-th order harmonic components by each other. In the device arrays, the magnetic sensor devices corresponding to each other are arranged such that they are spaced apart with a distance of (2m+1)λ, and the arrangement of all the magnetic sensor devices and their orientations with respect to a power-supply terminal and a ground terminal are axisymmetrical about a straight line (2b) passing through a barycenric position (59) of all the magnetic sensor devices which is positioned on a straight line along a radial direction of a rotating drum (1).