Magnetic Levitation Technology
The principle of Magnetic Levitation
Active electromagnetic levitation is based on the attractive force of a controllable electromagnet on a ferromagnetic body. A control unit adjusts the current in an electromagnet and hence the magnetic force acting on the ferromagnetic body so that the body is held in suspension. A sensor continuously measures the position of the ferromagnetic body. If the ferromagnetic body is above the desired position, the controller reduces the current in the magnet and with it the magnetic force. If the body is below the desired position, the current in the magnet is increased.
A single electromagnet is incapable of stabilizing all spatial degrees of freedom of a rotor. Two electromagnets arranged in an opposed pair are needed just to orient the position of a rotor in one direction. Two such pairs of electromagnets positioned at right angles to each other form a "radial bearing." Like a ball bearing, this configuration is capable of holding a rotor in one position in a plane (x-y direction). Since the rotor must also be prevented from tilting, it must usually be held at two points with two radial bearings. Another pair of electromagnets is needed as a thrust bearing. Thus, a completely active electromagnetic rotor bearing system requires a total of ten electromagnets. An electronic control unit modulates the current in each electromagnet by using sensor feedback from five separate sensors.
Advantages of Magnetic Bearings
Magnetic bearings have specific properties that differentiate them from mechanical bearings. The principle advantages relate to the absence of physical contact and electronic control of the rotor position.
Summary of Benefits
- No lubrication
- No abrasion
- No generation of particles
- Easy to clean and sterilize
- Ideal for clean-room operation
- Can operate under difficult environmental conditions like heat, cold, steam, vacuum, aggressive chemicals
- Excellent thermal insulation of rotor and stator
- Hermetic sealing (canning) possible
- Low vibration and noise
- Electronic adjustment of damping and stiffness
- Electronic unbalance compensation
- Electronic fine positioning of the rotor within the air gap
- Permanent monitoring of bearing load, rotor deflection and unbalance without additional equipment
Applications of Magnetic Bearings
Magnetic bearings are ideally suited for clean-room applications because they do not require lubrication and are capable of operating without generating particles. In the semiconductor industry, magnetic bearings are used in turbo molecular pumps (TMP), ultra-pure fluid pumps and wafer rotating systems. Highly reliable magnetic bearings are emerging in biomedical products such as blood pumps, respiratory support equipment, bioreactors and analytical instruments. Other application fields include turbo compressors, gas recirculation blowers, high-speed milling and grinding spindles, optical scanners and scientific instruments