Linear Motor Yoke Design for Electron Microscope Magnetic Field Control
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Solution Overview
Problem
Existing linear motors for electron microscopes face challenges in balancing the suppression of leakage magnetic fields with the need for high driving performance, as the weight of the stator is unnecessarily heavy due to a lack of consideration for individual variations in leakage magnetic field magnitude.
Innovation Solution
A linear motor design featuring a stator with a first yoke having open faces and two rows of alternating permanent magnets, where a second yoke is connected to cover the open end of the first yoke, reducing leakage magnetic fields while maintaining driving performance by adjusting the thickness and material of the yoke to match the specific magnetic field requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a thick yoke is used to suppress leakage magnetic field, then magnetic field suppression is improved, but stator weight increases and driving performance deteriorates
Solution Approach 1:
The patent applies local quality by making the yoke thickness non-uniform. The first yoke portion (near permanent magnets) has greater thickness to suppress leakage magnetic field at the critical location, while the second yoke portion (extending in moving direction) has reduced thickness to minimize weight. This localized thickness variation optimizes magnetic field suppression exactly where needed without unnecessarily increasing overall stator weight.
Solution Approach 2:
The patent changes the geometric parameter of the yoke by extending it in the moving direction of the movable element. This extension allows the yoke to cover the permanent magnets more effectively, suppressing leakage magnetic field while the tapered or reduced thickness in the extended portion controls weight increase. The parameter change in yoke geometry enables better balance between magnetic field suppression and weight.
2Device complexity
If the stator is made movable to reduce part count, then device complexity is reduced, but magnetic field variation on electron orbit increases
Solution Approach 1:
The patent segments the yoke into two distinct portions: a first yoke portion adjacent to the permanent magnets and a second yoke portion extending in the moving direction. This segmentation allows the first portion to focus on suppressing leakage magnetic field at the magnet interface, while the second portion can be optimized for weight reduction. The segmented structure enables the stator to be movable while maintaining magnetic field stability through the strategically designed first yoke portion.
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 effectively suppresses leakage magnetic fields, reducing electron beam bending and focus offset, while allowing for weight reduction and improved driving performance by tailoring the yoke's thickness and material to match the specific magnetic field characteristics of each device.
Implementation Method 1
the driving force is an electromagnetic force generated between a coil energized by control current and permanent magnets
Implementation Method 2
a second yoke is connected to an open end of the first yoke so as to cover the open end of the first yoke and the permanent magnets
Data Source
AI summary
It is an object to balance suppression of a leakage magnetic field and driving performance. In a linear motor including a stator including a first yoke having an open face and two rows of permanent magnets linearly arrayed inside the first yoke so that S-poles and N-poles are alternate and a movable element arranged between the two rows of permanent magnets and linearly moving, a second yoke is connected to an open end of the first yoke so as to cover the open end of the first yoke and the permanent magnets when viewed from the open face of the first yoke.