Rotation Sensor Magnetic Shielding and Bearing Preload
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Solution Overview
Problem
Existing rotation sensor units face decreased measurement accuracy due to external magnetic fields affecting magnetic sensor elements, and require additional components or increased size for shielding, especially when using non-magnetic materials for the housing or protective cover.
Innovation Solution
A rotation sensor unit design where the lid, shaft, and outer race are made of magnetic materials to create a magnetically shielded space, eliminating the need for a dedicated magnetic shield cover, and applying a preload to the rolling bearing to increase rigidity and prevent displacement of the magnetic sensor element and encoder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dedicated magnetic shield cover is provided to protect the magnetic sensor element from external magnetic fields, then measurement accuracy is improved, but the number of component parts increases and the device becomes more complex
Solution Approach 1:
The patent merges the magnetic shielding function with the protective cover by making the protective cover itself from a magnetic material. This integration eliminates the need for a separate magnetic shield cover, reducing the number of component parts while maintaining measurement accuracy through effective magnetic field shielding.
Solution Approach 2:
The protective cover is given dual functionality: it provides mechanical protection for the magnetic sensor element and simultaneously acts as a magnetic shield. This multi-functionality resolves the contradiction by eliminating the need for a dedicated magnetic shield cover while maintaining both protective and shielding functions.
2Ease of manufacture
If the housing is made of a non-magnetic material such as resin or aluminum for high productivity and lightweight construction, then ease of manufacture and weight are improved, but magnetic fluxes of external magnetic fields pass through the housing decreasing measurement accuracy
Solution Approach 1:
The patent applies local quality by making only the protective cover (the specific component housing the magnetic sensor) from a magnetic material, while the main housing can remain non-magnetic for high productivity. This localized magnetic shielding precisely where needed maintains measurement accuracy without requiring the entire housing to be magnetic, preserving manufacturing efficiency.
3Measurement precision
If a large-sized magnetic shield cover is provided to shield the magnetic sensor element when the housing is non-magnetic, then measurement accuracy is improved, but the installation space required increases and the size of the entire rotation sensor unit increases
Solution Approach 1:
The patent merges the magnetic shielding function with the protective cover, which is already a necessary component of the rotation sensor unit. By integrating shielding into the existing protective cover structure rather than adding a separate large-sized magnetic shield cover, the installation space requirement is minimized while maintaining effective magnetic field shielding for accurate measurements.
4Device complexity
If the protective cover is omitted to reduce component parts, then device complexity is reduced, but the magnetic sensor element loses protection from external magnetic fields and physical damage
Solution Approach 1:
The protective cover is designed to perform both mechanical protection and magnetic shielding functions simultaneously. By making the protective cover from a magnetic material, it provides dual protection: physical protection against damage and magnetic shielding against external magnetic fields, eliminating the need for separate protective and shielding components.
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 effectively shields the magnetic sensor element from external magnetic fields without additional components, maintaining measurement accuracy and allowing for a lighter, non-magnetic housing while preventing displacement and run-out of the shaft.
Implementation Method 1
the lid, the shaft and the outer race are made of a magnetic material, and a magnetically shielded space is defined by the lid, the one axial end surface of the shaft and the outer race in which the magnetic sensor element is mounted
Implementation Method 2
the lid axially pressing one end surface of the outer race of the rolling bearing, thus applying a preload to the rolling bearing
Data Source
AI summary
In a rotation sensor unit, a lid 6 is pressed against a housing 2 to push an outer race 11 of a rolling bearing 1, thereby applying a preload to the bearing 1 and increasing the rigidity of the bearing 1, so as to prevent run-out of a shaft 3. An encoder 42 is supported on this shaft 3, and a magnetic sensor element 41 is supported on the lid 6, which is pressed against the housing 2. Thus, it is possible to prevent displacement of the magnetic sensor element 41 and the encoder 42 relative to each other. The shaft 3, lid 6 and outer race 11, etc. are made of a soft magnetic material to define a magnetically shielded space between one axial end surface of the shaft 3 and the lid 6, with the magnetic sensor element 41 mounted in the magnetically shielded space.