How Magnetic Bearings Work

What is an Active Magnetic Bearing?
An active magnetic bearing (or AMB) is a type of bearing used in high speed rotating machinery that uses electromagnetic forces to levitate a rotating shaft in space, and maintains its position by actively controlling the electromagnets, leaving zero contact between the bearing and the rotating mass. This magnetic levitation allows a no contact, friction-free operation, elimination of many machine components, and a clean, reliable and efficient machine.

A typical AMB is made up of the following elements:
  • Stator
  • Rotor
  • Sensors
  • Electromagnets

AMBs can be configured as either radial or thrust (axial) bearings.

These elements are shown in the diagram below. Power amplifiers supply equal current to two pairs of electromagnets on opposite sides of a rotor. This constant tug-of-war is mediated by the controller, which offsets the current by equal but opposite amounts of current as the rotor deviates by a small amount from its center position. Sensors provide information to the controller for exact rotor position allowing the controller to interpret and control the amount of current provided by the power amplifier.

How Active Magnetic Bearings Work

The sensors are usually inductive in nature and sense in a differential mode. The power amplifiers in a modern commercial application are solid state devices which operate in a pulse width modulation (PWM) configuration. The controller is usually a microprocessor or DSP.

Active magnetic bearings have several advantages, they do not suffer from wear, they have low friction, and they can often accommodate irregularities in the mass distribution automatically, allowing it to spin around its center of mass with very low vibration.

Magnetic bearing solutions are rapidly expanding as industries from HVAC to defense and aerospace discover their unique benefits. Find out more about the technology behind these benefits - and how it can meet your needs.

 
Typical Active Magnetic Bearing System Components

 

Active Magnetic Bearing System

  • Stator
  • Rotor
  • 2 Radial Magnetic Bearings
  • 1 Thrust (Axial) Magnetic Bearing
  • Controller
  • Power Supply
  • UPS (Uninterruptable Power Supply)
Getting Information From the AMB System (Health or Condition Monitoring)

Spotting Trouble Before it Starts

The ability to monitor, identify and analyze the status of important conditions such as anomalous temperature and vibration in rotating machines. This information can be used to set alarms and schedule maintenance. Much of this information can be obtained through the magnetic bearing user interface without the need of additional bearing monitoring systems.

Synchrony has dedicated many years of research and development into creating and supplying its proprietary machine health monitoring software and condition monitoring. Much of the ability to miniaturize and simplify physical attributes of magnetic bearing systems is due to Synchrony's technological breakthroughs in controls software.

Magnetic bearings in industrial applications offer greater reliability than ever because of remote bearing monitoring capabilities that let users recognize and head off potential trouble before it even starts. That helps set Synchrony® products apart from earlier generations of magnetic bearings. Superior bearing vibration monitoring allows continuous system performance feedback to help you get the most from magnetic bearings capabilities, while keeping costs down.

Health monitoring of magnetic bearings previously required large, expensive hardware. Synchrony builds sensors right into radial and thrust bearings, and each "smart" bearing comes with its own IP address, so information can be fed into an HMI that’s easy to use and configurable to each operator’s needs. Regardless of your location.

Bearing Monitoring Capabilities:

  • Monitor trends and changes in operating conditions
  • Predict and schedule pre-emptive maintenance shutdowns
  • Maximize uptime and minimize component damage
  • Ensure maximum efficiency

 

Machine Monitoring Parameters Include:

  • Radial and axial forces
  • Eccentricity value
  • Peak to peak eccentricity
  • Radial expansion
  • Individual coil temperatures
  • Integrated power electronics temperatures
  • Individual coil current
  • Pair coil voltage
  • Velocity
  • Acceleration
  • Machine operating state (activity status, direction, etc.)
Auxiliary Bearings

A bushing or rolling element bearing is used to prevent the bearing rotor from contacting the bearing stator in the event of a total loss of power or large transient load. Synchrony provides a clearance between the rotor or shaft and the auxiliary bearings, whereas the shaft does not contact the auxiliary bearings during normal machine operation.

 

Related Links

White Paper - Advances in Magnetic Bearings (1.19 MB PDF)
NovaGlide™ Magnetic Bearings Brochure (791 KB PDF)
 

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