Multilayer Magnetic Circuit Assembly for Accelerometer Stability
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Solution Overview
Problem
Transducers, such as accelerometers, face accuracy deviations due to dynamic conditions causing displacement variations in the proof mass assembly, leading to unstable magnetic fields and reduced measurement accuracy.
Innovation Solution
The use of magnetic circuit assemblies with high magnetic permeability materials in the excitation ring and pole piece, along with a variable permeability outer ring, creates a more stable and uniform magnetic field by preventing saturation and matching the coefficient of thermal expansion (CTE) of materials to reduce thermal stress, and incorporating linearity modules to align the magnetic field with the center of mass of the proof mass assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a monolithic outer ring with uniform magnetic permeability is used, then the manufacturing process is simple, but the magnetic flux density becomes non-uniform causing saturation in inner regions and insufficient flux in outer regions
Solution Approach 1:
The excitation ring is divided into multiple segments with different magnetic permeability values. The inner portion has higher magnetic permeability to concentrate and guide magnetic flux, while the outer portion has lower magnetic permeability to distribute flux uniformly. This segmentation resolves the contradiction by achieving uniform magnetic flux density through structural differentiation rather than uniform material properties.
Solution Approach 2:
Different regions of the excitation ring are assigned different magnetic permeability characteristics tailored to their specific functional requirements. The inner region near the magnet uses high permeability material to establish strong magnetic flux, while the outer region uses lower permeability material to prevent flux saturation and ensure uniform distribution. This local optimization resolves the contradiction between manufacturing simplicity and magnetic field uniformity.
2Manufacturing precision
If high magnetic permeability material is used throughout the excitation ring, then magnetic flux is enhanced, but saturation occurs in regions near the magnet edge reducing field uniformity
Solution Approach 1:
The excitation ring employs spatially varying magnetic permeability where the inner portion adjacent to the magnet has high permeability to channel magnetic flux efficiently, while the outer portion has reduced permeability to prevent saturation. This local differentiation ensures that magnetic flux is enhanced where needed without causing saturation that would degrade field uniformity.
Solution Approach 2:
The magnetic permeability parameter is deliberately varied across the excitation ring structure. By changing the permeability value from the inner region to the outer region, the system optimizes magnetic flux distribution to avoid saturation while maintaining field uniformity. This parameter optimization resolves the contradiction between enhancing flux and preventing saturation losses.
3Reliability
If uniform CTE material is used in the excitation ring, then manufacturing is simplified, but thermal stress develops during operation causing displacement variations
Solution Approach 1:
The excitation ring incorporates materials with different coefficient of thermal expansion (CTE) values in different regions. The inner portion uses material with one CTE value to match the magnet, while the outer portion uses material with a different CTE value to match the proof mass assembly. This local material differentiation prevents thermal stress and displacement variations during operation, resolving the contradiction between reliability and manufacturing simplicity.
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 the accuracy and stability of the transducer by maintaining a consistent magnetic field interaction with the proof mass assembly, reducing thermal-induced errors, and improving the alignment of the magnetic field, thereby enhancing measurement precision.
Implementation Method 1
The platform layer and the pole piece each have a relatively high magnetic permeability, such that a greater amount of magnetic flux may pass into the excitation ring and pole piece before saturation is reached
Implementation Method 2
a magnetic return path extends through a bottom of the magnet into the excitation ring, and magnetic flux should not saturate in a region of the excitation ring near an edge of the magnet
Implementation Method 3
the coefficient of thermal expansion (CTE) of the outer ring may be varied, such that the outer portion of the outer ring has a lower CTE than the inner portion of the outer ring. This outer portion may have a CTE that more closely matches a CTE of the proof mass assembly, thereby reducing the thermal stress on the proof mass assembly
Implementation Method 4
a magnet for generating a magnetic field and an excitation ring for providing a magnetic return path of the magnetic field
Data Source
Figure 1A
Figure 1B
Figure 2A~2B
AI summary
The disclosure describes a magnetic circuit assembly (14) that includes a magnet assembly (50) and an excitation ring (52). The magnet assembly (50) defines an input axis and includes a pole piece (56) and a magnet underlying (54) the pole piece (56). The excitation ring (52) includes a base (64) and an outer ring (62) positioned around the magnet assembly (50). The base (64) includes a platform layer (66) underlying the magnet (54) and a base layer (68+70) underlying the platform layer (66). The outer ring (62) overlies the base layer (68+70). An inner portion (74) of the outer ring (62) faces the magnet assembly (50) and an outer portion (72) of the outer ring (62) is configured to couple to an outer radial portion (24) of a proof mass assembly (20). The pole piece (56) and the platform layer (66) include a high magnetic permeability material.