Types of magnetic bearing systems

Magnetic bearings offer a non-contact rotor support system offering benefits for a wide variety of applications.

Where conventional mechanical bearings physically interface with the shaft and require some form of lubrication, magnetic bearings are an electric technology that suspends the target rotor in a magnetic field.

Two basic types of magnetic bearing technologies are present and in use today: Active and Passive.

1. PASSIVE magnetic bearings
   
   Passive bearings are similar to mechanical bearings in that no active control is necessary for operation.
   
   (A five axis passive system is inherently unstable, and thus a passive system has at least one active or mechanical axis of control.)
   
   • One passive bearing approach utilizes repulsive effects of permanent magnets, which is essentially magnets repelling each other.
     
   • Another is reluctance centering, which is essentially two magnets or magnetic pole faces attracting to align poles.
   
   These forces act to cause the rotor to remain in the desired position. This type of bearing system is suited for very lightly loaded systems, or ones with any significant load in only one axis and very limited response necessary from the remaining axes.
   
   
2. ACTIVE magnetic bearings
   
   In active systems, non-contact position sensors monitor shaft position and feed this information to the control system. This in turn, based on the desired response of the system commands, currents to the actuator via current amplifiers. These currents are converted to forces by the actuator and act on the rotor to adjust position and provide damping to the rotor.
   
   Active systems, while more complex than passive systems, provide much higher support stiffness and are tunable for optimizing system response.

Both configurations provide very low stiffness and minimal damping.