Absolute Magnetic Encoder with Level-Difference Tracks
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Solution Overview
Problem
In absolute magnetic encoders with annular magnetic tracks of different diameters, the varying circumferential sizes of magnetic poles lead to differing magnetic flux densities, affecting detection accuracy, as multiple magnetism detection elements have uniform sensitivity, necessitating equalized magnetic flux densities for improved detection.
Innovation Solution
The configuration includes a first and second annular multipolar magnet track with alternating poles, where the second track has a different number of poles, arranged concentrically with a level difference set between their detected faces to equalize the maximum magnetic flux densities detected by a movable magnetic sensor unit, ensuring consistent sensitivity and flexibility in track positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If annular magnetic tracks of different diameters are arranged concentrically, then the encoder can detect multiple positions simultaneously, but the magnetic flux density detected by each track becomes different due to varying circumferential sizes of magnetic poles
Solution Approach 1:
The patent applies local quality by adjusting the magnetic pole circumferential sizes differently for each track. Specifically, the outer track has larger magnetic pole circumferential sizes while the inner track has smaller ones, compensating for the diameter difference to equalize the magnetic flux density detected by each track's magnetism detection element.
Solution Approach 2:
The patent changes the parameter of magnetic pole circumferential size to resolve the contradiction. By setting the circumferential size of magnetic poles in the outer track larger than those in the inner track, the magnetic flux density is equalized across tracks despite their different diameters, thereby maintaining detection accuracy while enabling multi-position detection.
2Measurement precision
If magnetic pole circumferential sizes are equalized across tracks, then magnetic flux density becomes uniform, but the encoder loses the ability to compensate for diameter variations
Solution Approach 1:
The patent implements local quality by assigning different magnetic pole circumferential sizes to different tracks based on their specific diameters. The outer track uses larger pole sizes while the inner track uses smaller ones, creating a tailored solution for each track that compensates for diameter variations and maintains both detection accuracy and system reliability.
Solution Approach 2:
The patent applies asymmetry by deliberately creating unequal magnetic pole circumferential sizes across symmetrically arranged tracks. This asymmetric design compensates for the radial distance differences, ensuring that each track detects uniform magnetic flux density despite the symmetric concentric arrangement, thereby maintaining reliability against diameter variations.
3Volume of moving object
If the magnetic flux density of each magnetic track is made different, then the magnetic sensor unit can be smaller, but the detection accuracy deteriorates
Solution Approach 1:
The patent changes the magnetic pole circumferential size parameter to equalize magnetic flux density across tracks with different diameters. This allows the use of a compact magnetic sensor unit while maintaining high detection accuracy, as each track provides consistent flux density signals to the sensor elements.
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 enhances detection accuracy and flexibility by ensuring equalized magnetic flux densities across tracks, improving the encoder's ability to handle axial runout and positional variations, allowing for a smaller magnetic sensor unit and simplified manufacturing.
Implementation Method 1
The magnetic sensor unit respectively detects the magnetic flux density of the first magnetic track and the magnetic flux density of the second magnetic track
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
An absolute magnetic encoder (1) includes a first magnetic track (21) in which magnetic poles are alternately provided at equal intervals in circumferential direction, a second magnetic track (22) in which magnetic poles are alternately provided at equal intervals in circumferential direction, the number of poles of the second magnetic track (22) being different from that of the first magnetic track(21), the second magnetic track (22) being provided concentrically with the first magnetic track (21) inside the first magnetic track (21) in radial direction, a magnetic sensor unit (30), a first detected face (21a) that is a magnetic pole face of the first magnetic track (21) opposite to the magnetic sensor unit (30), a second detected face (22a) that is a magnetic pole face of the second magnetic track (22) opposite to the magnetic sensor unit (30), and level difference (23) in the axial direction between the first detected face (21a) and the second detected face (22a), the level difference (23) being set based on the difference between the maximum magnetic flux density of the first magnetic track (21) and the maximum magnetic flux density of the second magnetic track (22) which are detected by position of the magnetic sensor unit (30).