Vacuum Pump Motor Layout for Stray Magnetic Field Containment
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Solution Overview
Problem
Turbomolecular vacuum pumps emit stray magnetic fields due to the rotation of their motor components, which interfere with sensitive equipment like scanning electron microscopes, causing operational issues with electron beams and electrical circuits.
Innovation Solution
A vacuum pump assembly with a motor rotor magnet configured to be shorter than the stator, typically two-thirds or less in axial length, to contain and shield the magnetic field within the stator, reducing stray field emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the motor rotor magnet axial length is made comparable to the stator length for efficient magnetic material use, then motor efficiency is improved, but stray magnetic field emissions increase and interfere with sensitive equipment
Solution Approach 1:
The invention changes the axial length parameter of the motor rotor magnet from being comparable to the stator length to being shorter than the stator length. This parameter modification reduces the stray magnetic field emissions while maintaining acceptable motor efficiency, resolving the technical contradiction between energy efficiency and harmful field emissions.
2Ease of operation
If the motor rotor magnet extends beyond the stator length to enable rotation detection by Hall sensors, then motor operation detection is improved, but time varying stray fields increase and interfere with surrounding instruments
Solution Approach 1:
The invention introduces an intermediary mechanism (such as a magnetless portion or shielding structure) between the rotor magnet and the external environment. This intermediary contains the time varying magnetic fields within the motor assembly, preventing them from interfering with surrounding instruments while still allowing rotation detection to function.
3Object-generated harmful factors
If the rotor magnet axial length is reduced to two thirds or less of the stator length, then stray magnetic fields are contained within the stator, but magnetic material usage efficiency decreases
Solution Approach 1:
The invention optimizes the axial length parameter of the rotor magnet to be two thirds or less of the stator length. This parameter change successfully contains stray magnetic fields within the stator while maintaining acceptable motor performance. The reduced magnetic material quantity is compensated by optimizing other parameters such as magnet strength and stator winding configuration.
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 significantly mitigates stray magnetic fields, making the vacuum pump suitable for use in sensitive scientific instruments by containing the magnetic field within the stator, thus reducing interference and maintaining motor performance.
Implementation Method 1
a motor rotor magnet and a stator; the rotor motor magnet being configured to be rotatable relative to the stator about an axis to drive a vacuum pump mechanism
Implementation Method 2
the motor rotor magnet comprising a solid cylindrical magnet mounted within a recess provided on a vacuum pump shaft and having an axial length of two thirds or less than that of the stator
Data Source
Figure 1
Figure 2a~2b
AI summary
Aspects and embodiments provide a vacuum pump assembly comprising a motor. The motor comprises: a motor rotor magnet and a stator. The rotor motor magnet is configured to be rotatable relative to the stator about an axis to drive a vacuum pump mechanism. The motor rotor magnet has an axial length of two thirds or less than that of the stator. Such a configuration may help to mitigate the electromagnetic stray field emitted by the motor and, in turn, the vacuum pump.