Spherical magnetic bearings developed for experimental test rig

Airex has developed a four-band, electromagnetic gimbal that provides two rotational and three translational degrees of freedom positioning for a payload of 300 lb/ft2, azimuth and elevation excursions of +/-10deg, a slew rate of 0.40deg/s and positioning error of less than 0.008deg. Leading a team of national research laboratories and world-renowned universities, the combination motor-bearing system is said to be the first in the USA to demonstrate capabilities for toothless, integrated motor-bearing operation. The proof-of-concept rig built by Airex demonstrates high-accuracy pointing for space-based inter-satellite cross-links used in laser communications. The rig provides for measurement of bearing function dynamic and static stiffness, loaded and unloaded static torque, loaded and unloaded pointing accuracy and slew rate.

This experimental rig also allows testing of fault-tolerant and vibration-isolation algorithms developed by Louisiana State University. Fault tolerance describes the ability of the device to provide continuous functionality in spite of multiple coil or amplifier failures through the use of sophisticated digital control algorithms. Vibration isolation describes the ability of the rig to alter the dynamic compliance of the payload relative to the platform. The ability to control vibration provides an inherent advantage to magnetic suspension systems over the more conventional mechanical approach. This research and development provides an excellent model for design and test of integrated linear or rotary systems.

Commercial potential

Airex says the commercial benefit of its work in magnetic bearings includes the innovative development of a fully integrated gimbal system with integral motor-bearing functions to replace mechanical gimbals. This technology is considered useful in defence or commercial satellite tracking, antenna pointing and inter-satellite cross-links. In space applications, this electromagnetic design provides inherent vibration isolation, eliminates the need for lubricants and provides exceptional pointing accuracy. It is also useful in ground-based systems such as portable communication up links, shipboard systems or satellite tracking.

With increasing potential for future applications, the development of gimbal design and manufacturing capabilities has substantially impacted several programmes. Moreover, advances in control and drive electronics have led to new levels of commercial potential for this technology. Wear- and maintenance-free bearings that include vibration isolation, very wide speed ranges and extensive load handling capabilities have potential in applications such as:

• High-end machine tools
• Diamond turning
• High-speed grinding
• Manifacturing process equipment
• Film and web handling rolls
• High-resolution scanning/imaging
• Kinetic energy storage (flywheels)
• Power generation

Airex is designing systems similar to those described above and continuing development in this critical technology to further enhance the applicability and commercial potential. These projects, combined with associated development activities, provide a baseline for the technology and an exceptional opportunity to advance the state of the art.

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