Permanent Magnet Encoder Stray Field Reduction
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Solution Overview
Problem
Permanent-magnetic encoders generate stray fields that interfere with nearby magnetic field-sensitive devices like compasses, requiring a minimum distance to maintain functionality, which limits their proximity and increases device size.
Innovation Solution
A permanent-magnetic transmitter design featuring a first and second permanent magnet with opposing magnetic orientations and dipole moments, arranged to minimize stray fields, allowing for closer proximity to magnetic field-sensitive devices without impairing functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a permanent magnet is used to generate the magnetic field for position sensing, then accurate position and speed sensing is achieved, but a stray field is generated that interferes with nearby magnetic field-sensitive devices like compasses
Solution Approach 1:
The permanent magnet is segmented into multiple magnetic poles (first and second permanent magnets with opposite polarities) arranged in a specific pattern. This segmentation allows the magnetic field to be shaped such that the stray field components cancel each other out at distances, while maintaining the necessary field strength for accurate sensing at the sensor location.
Solution Approach 2:
Different regions of the permanent magnet structure are assigned different magnetic pole qualities. The first and second permanent magnets create localized magnetic field patterns where the north and south poles are strategically positioned to provide strong field gradients at the sensor location for precise measurement, while the opposing poles reduce the far-field stray field interference.
2Reliability
If the distance between the encoder and compass is increased to reduce stray field interference, then compass functionality is maintained, but the device size increases and compact designs are limited
Solution Approach 1:
The invention converts the potentially harmful stray field into a beneficial pattern by strategically arranging opposite magnetic poles. The stray field that would normally interfere with the compass is transformed into a controlled magnetic field pattern where the opposing poles create field cancellation in the radial direction, allowing the compass to function reliably at shorter distances.
Solution Approach 2:
The magnetic field parameters are changed by introducing opposite polarity regions. Instead of a single monopole-like field that extends far, the dipole-like field pattern with alternating north and south poles creates a more localized field distribution, reducing the field strength at distant locations while maintaining it at the sensor position.
3Device complexity
If a single permanent magnet is used in the encoder, then the structure is simple, but the stray field cannot be compensated and affects nearby magnetic field-sensitive devices
Solution Approach 1:
The single permanent magnet is divided into multiple segmented magnets with opposite polarities. This segmentation increases structural complexity but enables magnetic field compensation by arranging the segments such that their stray fields cancel each other out, solving the interference problem.
Solution Approach 2:
Multiple permanent magnets with opposite polarities are merged into a single encoder structure. The first and second permanent magnets are positioned and magnetized to work together, creating a combined magnetic field pattern that maintains sensing accuracy while reducing net stray field interference.
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
Significantly reduces the 'Compass safe distance' (CSD) between the encoder and magnetic field-sensitive devices, enabling more compact designs while maintaining accurate position and speed sensing capabilities.
Implementation Method 1
The first permanent magnet has a first magnetic field with a first (north-south) orientation in the alignment plane. The second permanent magnet, in contrast, has a second magnetic field with a different, second (north-south) orientation in the alignment plane.
Implementation Method 2
The first permanent magnet is surrounded by the second permanent magnet on a common alignment plane... the magnetization of the two permanent magnets is therefore, for example, rotated 180° relative to each other.
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A permanent-magnetic transmitter (1) for a sensor device is proposed, having a first permanent magnet (1a) and a second permanent magnet (1b, 1c 1d) connected thereto, wherein the first permanent magnet (1a) is surrounded on an alignment plane by the second permanent magnet (1b, 1c, d), wherein the first permanent magnet (1a) has a first magnetic field with a first alignment in the alignment plane, and the second permanent magnet (1b, 1c, 1d) has a second magnetic field with a second alignment in the alignment plane, wherein the first alignment is opposite the second alignment, wherein the first and second permanent magnets (1a, 1b, 1c, 1d) have substantially the same magnetic dipole moment and/or the first and second permanent magnets (1a, 1c, 1d) are arranged on the alignment plane at a distance from one another. A sensor device having such a transmitter is also proposed and an operating device for operating a vehicle is proposed, having such a transmitter or such a sensor device.