Accelerometer Excitation Ring with Groove for Flux Concentration
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Solution Overview
Problem
Conventional magnetic return paths in accelerometers suffer from non-uniform flux distribution and vibration-induced errors due to geometric constraints, leading to increased manufacturing complexity and cost, which are exacerbated by the need for spacers and precise coil alignment.
Innovation Solution
The accelerometer design features a two-piece excitation ring with a machined groove that allows for conventional machining and epoxy bonding, concentrating magnetic flux closer to the proof mass, eliminating the need for spacers and enabling a shorter, more flexible coil configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional magnetic return path is used with geometric constraints, then the accelerometer can be constructed, but the flux distribution in the air gap becomes non-uniform and vibration-induced errors increase
Solution Approach 1:
The excitation ring is divided into two separate pieces: a base portion and a top ring. This segmentation allows each piece to be manufactured using conventional turning methods on a lathe, simplifying manufacturing while enabling precise control of the air gap geometry to achieve uniform flux distribution.
Solution Approach 2:
A groove is introduced in the base portion at a specific depth (approximately 0.020 inches) to position the top ring. This dimensional feature creates a controlled air gap that ensures uniform flux distribution across the gap, resolving the contradiction between manufacturing simplicity and flux uniformity.
2Reliability
If spacers are added between the coil and proof mass to minimize vibration effects, then vibration rectification error is reduced, but device complexity and manufacturing cost increase
Solution Approach 1:
The groove feature is extracted from the base portion to provide the spacing function previously requiring separate spacers. By integrating the spacing function into the base portion geometry, the need for additional spacer components is eliminated, reducing device complexity while maintaining vibration error minimization.
3Reliability
If short coils are used to minimize vibration output change, then vibration rectification is reduced, but manufacturing cleanliness and uniformity requirements increase
Solution Approach 1:
The groove is prepared in advance in the base portion to establish the correct positioning of the top ring and coil assembly. This preliminary geometric feature ensures that the coil is pre-positioned at the optimal location before final assembly, allowing the use of shorter coils with relaxed tolerance requirements while maintaining vibration resistance.
4Ease of manufacture
If a two-piece excitation ring with groove is used, then manufacturing is simplified and cost reduced, but the magnetic return path structure becomes more complex
Solution Approach 1:
The base portion and top ring are joined together using conventional epoxy bonding to form the complete excitation ring. This merging of two separately manufactured pieces creates a unified magnetic return path structure that is simpler to manufacture than a single complex piece, while the groove feature integrates the spacing function into the structure itself.
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 design simplifies manufacturing, reduces costs, and minimizes vibration-induced errors by concentrating magnetic flux near the proof mass, allowing for a more robust and cost-effective accelerometer with improved accuracy.
Implementation Method 1
concentrating magnetic flux closer to the proof mass
Implementation Method 2
adjusting magnetic return path with minimized reluctance
Implementation Method 3
The flux interacts with the current in the coil to produce a rebalance force proportional to the acceleration to which the device is subjected
Implementation Method 4
The flux interacts with the current in the coil to produce a rebalance force
Data Source
Figure 1
Figure 2~3
Figure 4~6
AI summary
Accelerometers having higher concentration of flux closer to the proof mass. The invention includes a proof mass, an excitation ring (114), a magnet (116), a pole piece (117), and a coil (115). The excitation ring includes a ring unit and a base unit that are attached and the ring unit or base unit includes an annular groove. The magnet is mounted to the base unit and the pole piece is mounted to the magnet. The coil is attached directly to the proof mass. A gap is formed between the ring unit and the pole piece. The pole piece includes a first section that has a radius smaller than the radius of a second section.