220.127.116.11 Magnetically coupled rotation and translation
Magnetic couplings are used for hermetically sealed rotary or linear feedthroughs. They consist of an array of permanent magnets on the outside that drive a rotor also equipped with magnets that can rotate/move in a vacuum. Both parts are completely vacuum sealed off from one another by a thin walled pipe. The distance between the magnets of the inner and outer rotor should be as low as possible, so that the coupling force between them is as large as possible. The rotor inside is connected to the application to be moved, the outer magnetic rotor is manually moved or motor-driven. The internal bearings are lubricated with a dry lubrication that are suitable for vacuums.
Often high-performance magnets made from metals are used for rare earths, such as samarium-cobalt magnets. They ensure highest possible coupling strength with simultaneously excellent resistance to high temperatures, such they occur during bake out. Such magnetically coupled systems are suitable for UHV applications. Even though the magnetic fields are shielded for the most part, the dispersion of the magnetic field lines cannot be avoided completely. The user must therefore check whether its application is sufficiently resistant to the residual magnetic field.
With magnetically coupled systems, rotational and linear motion and simultaneous rotation/linear motion can be implemented. The transferable displacement forces and torques are limited by the number of magnets and their arrangement. The achievable accuracy depends on the mass to be moved. The magnetic fields act as a spring between the two coupling partners. The higher the external force or torque, the greater the deviation of the position between the inner and outer rotors. If the external forces and moments are low compared to the maximum allowable values, the movements can be transferred very accurately.
- Magnetic internal rotor motor
- Magnetic external rotor motor
- Vacuum housing
Figure 3.26: Magnetically coupled UHV rotary feedthrough