Magnetic Arbor Centering with a Soft Ferromagnetic Pad
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Solution Overview
Problem
Current magnetic centering devices for watch movements suffer from high scrap rates due to off-centered magnetic fields, making industrialization difficult and requiring complex structures to achieve precise spatial alignment for accurate chronometric functions.
Innovation Solution
A magnetic centering device with a centering pad made of soft ferromagnetic material that recenters the magnetic field lines, increasing the magnetic return force and radial gradient to ensure proper axis alignment, using a simplified structure with magnets and ferromagnetic pads to maintain the shaft along a determined axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a magnetic bearing with a magnet is used to center a shaft, then the shaft can be held along a determined axis with reduced friction, but the magnetic field may be off-centered by too great a value leading to high scrap rates
Solution Approach 1:
A centering pad made of soft ferromagnetic material is introduced as an intermediary element between the magnet and the shaft pivot. This pad acts as a flux concentrator that redirects and centers the magnetic field lines, ensuring accurate magnetic centering while compensating for manufacturing tolerances in the magnet positioning.
Solution Approach 2:
The magnetic properties of the centering pad (high magnetic permeability of soft ferromagnetic material) are utilized to change the distribution parameters of the magnetic field. The pad concentrates and redirects the magnetic flux, transforming an off-centered field into a centered one without requiring precise magnet positioning.
2Manufacturing precision
If complex structures are used to achieve precise spatial alignment, then accurate chronometric functions can be obtained, but the device complexity increases and industrialization becomes difficult
Solution Approach 1:
The centering pad serves as a simple intermediary component that achieves precise spatial alignment through its magnetic flux concentrating property rather than through complex mechanical positioning structures. This simplifies the overall device while maintaining high precision.
Solution Approach 2:
The patent replaces complex mechanical centering structures with a magnetic field-based solution using a soft ferromagnetic pad. This substitutes mechanical alignment complexity with a simpler magnetic flux distribution approach that is easier to manufacture and assemble.
3Ease of manufacture
If magnets are positioned without precise centering, then the device is easier to manufacture, but the magnetic field is off-centered leading to a large number of rejected parts
Solution Approach 1:
The centering pad compensates for imprecise magnet positioning by acting as a flux redistributing intermediary. Even when the magnet is off-center, the pad redirects the magnetic field lines to converge at the correct center point, eliminating the need for reject parts due to positioning errors.
Solution Approach 2:
The patent converts the potentially harmful effect of off-centered magnet positioning into a beneficial feature. The soft ferromagnetic pad is specifically designed to capture and redirect the off-center flux, transforming what would be a manufacturing defect into a functional characteristic that still achieves accurate centering.
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
The solution effectively reduces the number of rejected parts by 2 to 3 times, simplifies the magnetic bearing structure, and ensures accurate centering of the shaft, enhancing the reliability and precision of horological mechanisms.
Implementation Method 1
at least one magnetic bearing equipped with a magnet arranged to exert an attraction force on a pivot made of magnetic material
Implementation Method 2
a magnet arranged to exert an attraction force on a pivot made of magnetic material of the shaft
Implementation Method 3
a centering pad made of soft ferromagnetic material that recenters the magnetic field lines
Implementation Method 4
which for centering the magnetic field flux generated by the magnet
Data Source
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AI summary
The magnetic centering device for a shaft (1) about a predetermined axis in a watch movement comprises at least one first magnetic bearing (20) equipped with a magnet (6) to exert an attractive force on a first ferromagnetic end pivot (2) of the shaft (1). The first magnetic bearing includes a central piece (4) made of soft ferromagnetic material mounted between the magnet and the first end pivot of the shaft. The central piece is positioned centrally within a washer (8) made of non-magnetic material to center the magnetic field flux generated by the permanent magnet through the central piece to magnetically attract the first end pivot of the shaft about the predetermined axis. The diameter of the central piece may be the same as, 0 to 20% smaller than, or 0 to 20% larger than, the diameter of the first end pivot.