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23 Jul 2002
An interferometric alignment system helps Chinese engineers building what will become the world's fastest train.
A laser tracking system is to help engineers in Shanghai, China, build a new ultra-fast transportation link.
The Shanghai Maglev Railway, which is based on magnetic levitation technology, will reach a top speed of 269 miles per hour (430 km/h). The link is scheduled to start running between Shanghai and the local Pudong airport in January 2004.
Engineers are currently installing 500 concrete girders, each of which is 24 m long and weighs 175 tons, to form part of the Maglev guideway. These girders need to be manufactured and installed to a precision of better than one-thousandth of an inch.
This is where the laser system comes in. The Laser Tracker II supplied by US company Automated Precision, Inc. is an interferometric system based around a low-power helium neon laser.
The laser tracker measures the shapes of objects to the required tolerance from a distance of 5 m, and it has a maximum lateral target speed of 3 meters per second. It is used for a variety of industrial measurement applications, such as machine alignment and measuring tooling fixtures.
Developed in Germany by Transrapid International, the high-speed magnetic levitation railways have yet to become a commercial reality. The Shanghai Maglev will be the first such commercial system and is crucial to the future of the technology.
Maglev trains based on superconductors have been developed in Japan, but the Transrapid version uses a different system. On-board batteries provide electromagnetic suspension, allowing the trains to 'hover' above the track. Support magnets along the vehicle pull it up level with ferromagnetic stator packs mounted on the underside of the guideway. Guidance magnets along the length of the vehicle keep it on the track laterally, while electronic systems maintain track clearance at 10 mm.
Transrapid says that the vehicle is capable of hovering for up to 30 minutes like this. During travel, the on-board batteries are recharged by linear generators integrated into the support magnets.
When the link is finally completed, the journey from Shanghai city center to its 30 km-distant airport should take just 8 minutes.
Author
Michael Hatcher is technology editor of Opto and Laser Europe magazine.
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