High-Resistivity Balance Wheel for Magnetic Field Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional timepiece movements are prone to stopping in magnetic fields stronger than 3000 G, and existing solutions for magnetic resistance, such as using mu-metal or permalloy screens, impose size, design, and aesthetic constraints, while prior art documents do not adequately address the need for a timepiece to operate without stopping under intense magnetic fields exceeding 8000 G with minimal residual effect.
Innovation Solution
An inertial element comprising a balance wheel made of paramagnetic or diamagnetic materials with high electrical resistivity, such as lead-free brass, CuAl7Si2, or ceramic, is used in conjunction with amagnetic staffs and hairsprings to reduce eddy current dissipation and enhance resistance to magnetic fields, allowing the timepiece to function without stopping under magnetic fields up to 35,000 G with a residual effect of less than 1 second per day.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional materials (ferromagnetic metals) are used in the balance wheel and staffs, then the timepiece can be manufactured with standard materials and processes, but the timepiece stops in magnetic fields stronger than 3000 G
Solution Approach 1:
The patent changes the magnetic properties and electrical resistivity parameters of the materials used in the balance wheel and staffs. Specifically, it uses paramagnetic or diamagnetic materials with high electrical resistivity (greater than 10^-6 Ω·m) to replace conventional ferromagnetic materials, fundamentally altering how the components interact with magnetic fields and eliminating eddy current-induced stoppage
Solution Approach 2:
The patent employs composite material strategies by combining materials with specific magnetic properties (paramagnetic or diamagnetic) and high electrical resistivity. Examples include paramagnetic stainless steel, diamagnetic ceramics, or composite structures that integrate these properties to achieve both mechanical strength and magnetic field resistance
2Reliability
If mu-metal or permalloy screens are used to enclose the movement, then magnetic field resistance is improved, but size, design, and aesthetic constraints are imposed
Solution Approach 1:
The patent extracts and eliminates the need for external magnetic screens by addressing the root cause of magnetic sensitivity directly within the oscillator components. By making the balance wheel and staffs themselves resistant to magnetic fields through material selection, the separate magnetic shielding structure becomes unnecessary
Solution Approach 2:
The patent introduces materials with specific magnetic properties (paramagnetic or diamagnetic intermediaries) between the magnetic field and the oscillator components. These materials act as mediators that allow the timepiece to interact with magnetic fields without experiencing harmful effects, replacing the need for ferromagnetic shielding screens
3Reliability
If low-resistivity materials are used in the balance wheel, then eddy current dissipation occurs in strong magnetic fields, but manufacturing with common materials is easier
Solution Approach 1:
The patent fundamentally changes the electrical resistivity parameter of the balance wheel and staff materials to greater than 10^-6 Ω·m. This parameter change reduces eddy current formation by several orders of magnitude, allowing the timepiece to maintain accurate operation even in intense magnetic fields up to 8000 G or higher
Solution Approach 2:
The patent applies specific material properties locally to the components most susceptible to magnetic field effects. The balance wheel, balance staff, and hairspring are made from materials with high electrical resistivity and appropriate magnetic properties, while other parts of the movement can use conventional materials, optimizing performance where it matters most
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 use of high-resistivity materials in the balance wheel and staffs significantly increases the magnetic field threshold at which the timepiece stops, achieving a 60% improvement over previous configurations, with the balance wheel made of lead-free brass 'Ecobrass' allowing operation up to 35,000 G and ceramic materials potentially reaching even higher thresholds, while maintaining precise timekeeping.
Implementation Method 1
The inertial element comprises a balance wheel made of a paramagnetic or diamagnetic material having an electrical resistivity of greater than 10^-6 Ω×m, preferably greater than 10^-5 Ω×m, more preferably greater than 10^-4 Ω×m
Implementation Method 2
The first material has an electrical resistivity of greater than 15 μΩ×cm, preferably greater than 20 μΩ×cm
Data Source
AI summary
An inertial element (1), in particular a balance wheel (1), for a timepiece movement (200), the inertial element including a felloe (11) made of or including a first material which is paramagnetic or diamagnetic, and which has an electrical resistivity of greater than 15 μΩ×cm, preferably greater than 20 μΩ×cm.