Editing Linear motor (section)

== History ==
[[File:Running on the Xunfeng Gang To Hengsha section of Guangzhou Metro Line 6.jpg|thumb|This [[Line 6, Guangzhou Metro|Line 6]] [[Guangzhou Metro]] train manufactured by [[CRRC]] [[Sifang Locomotive and Rolling Stock|Sifang]] and [[Kawasaki Heavy Industries]] propels itself using an aluminium induction strip placed between the rails.]]

=== Low acceleration ===
The history of linear electric motors can be traced back at least as far as the 1840s, to the work of [[Charles Wheatstone]] at [[King's College London]],<ref>{{cite web|url=http://www.kcl.ac.uk/college/history/people/wheatstone.html |title=Charles Wheatstone - College History - King's College London |publisher=Kcl.ac.uk |access-date=2010-03-01 |url-status=dead |archive-url=https://web.archive.org/web/20091021162729/http://www.kcl.ac.uk/college/history/people/wheatstone.html |archive-date=2009-10-21 }}</ref> but Wheatstone's model was too inefficient to be practical. A feasible linear induction motor is described in {{US patent|782312}} (1905 - inventor Alfred Zehden of Frankfurt-am-Main), for driving trains or lifts. The German engineer [[Hermann Kemper]] built a working model in 1935.<ref>{{cite web|url=http://cem.colorado.edu/archives/fl1997/thor.html |title=CEM - Fall/Winter 1997 Issue - Germany's Transrapid |access-date=2011-08-24 |url-status=dead |archive-url=https://web.archive.org/web/20110928000224/http://cem.colorado.edu/archives/fl1997/thor.html |archive-date=2011-09-28 }}</ref> In the late 1940s, Dr. [[Eric Laithwaite]] of [[University of Manchester|Manchester University]], later Professor of Heavy Electrical Engineering at [[Imperial College]] in [[London]] developed the first full-size working model. 

In a single sided version the magnetic repulsion forces the conductor away from the stator, levitating it, and carrying it along in the direction of the moving magnetic field. He called the later versions of it [[magnetic river]]. The technologies would later be applied, in the 1984, [[Air-Rail Link#Maglev|Air-Rail Link]] shuttle, between Birmingham's airport and an adjacent train station.

[[File:Linear Motor of Toei Ōedo Line.jpg|thumb|right|200px|A linear motor for trains running [[Toei Ōedo Line]]]]
Because of these properties, linear motors are often used in [[magnetic levitation|maglev]] propulsion, as in the Japanese [[Linimo]] [[magnetic levitation train]] line near [[Nagoya]]. However, linear motors have been used independently of magnetic levitation, as in the [[Bombardier Innovia Metro]] systems worldwide and a number of modern Japanese subways, including [[Tokyo]]'s [[Toei Ōedo Line]].

Similar technology is also used in some [[roller coaster]]s with modifications but, at present, is still impractical on street running [[tram]]s, although this, in theory, could be done by burying it in a slotted conduit.

Outside of public transportation, vertical linear motors have been proposed as lifting mechanisms in deep [[mining|mine]]s, and the use of linear motors is growing in [[motion control]] applications. They are also often used on sliding doors, such as those of [[low floor]] trams such as the [[Alstom Citadis]] and the [[Socimi Eurotram]]. Dual axis linear motors also exist. These specialized devices have been used to provide direct ''X''-''Y'' motion for precision laser cutting of cloth and sheet metal, automated [[Technical drawing|drafting]], and cable forming. Most linear motors in use are LIM (linear induction motor), or LSM (linear synchronous motor). Linear DC motors are not used due to their higher cost and linear SRM suffers from poor thrust. So for long runs in traction LIM is mostly preferred and for short runs LSM is mostly preferred.

[[File:Linear motor platen surface.jpg|thumb|right|Close-up of the flat passive conductor surface of a motion control
[[Sawyer motor]]
]]

=== High acceleration ===
High-acceleration linear motors have been suggested for a number of uses.
They have been considered for use as [[weapon]]s, since current [[armour-piercing]] ammunition tends to consist of small rounds with very high [[kinetic energy]], for which just such motors are suitable. Many amusement park [[launched roller coaster]]s now use linear induction motors to propel the train at a high speed, as an alternative to using a [[lift hill]].

The United States Navy is also using linear induction motors in the [[Electromagnetic Aircraft Launch System]] that will replace traditional [[steam catapult]]s on future aircraft carriers. They have also been suggested for use in [[spacecraft propulsion]]. In this context they are usually called [[mass driver]]s. The simplest way to use mass drivers for spacecraft propulsion would be to build a large mass driver that can accelerate cargo up to [[escape velocity]], though [[reusable launch system|RLV]] launch assist like [[StarTram]] to [[low Earth orbit]] has also been investigated.

High-acceleration linear motors are difficult to design for a number of reasons. They require large amounts of [[energy]] in very short periods of time. One rocket launcher design<ref name="coilgun">{{cite web|url=http://www.coilgun.info/theory/electroguns.htm|title=Magnetic Materials - Electromagnetic Guns|publisher=coilgun.info|access-date=2014-11-22|archive-date=2008-05-16|archive-url=https://web.archive.org/web/20080516063621/http://www.coilgun.info/theory/electroguns.htm|url-status=dead}}</ref> calls for 300 GJ for each launch in the space of less than a second. Normal [[electrical generator]]s are not designed for this kind of load, but short-term electrical energy storage methods can be used. [[Capacitors]] are bulky and expensive but can supply large amounts of energy quickly. [[Homopolar generator]]s can be used to convert the kinetic energy of a [[flywheel]] into electric energy very rapidly. High-acceleration linear motors also require very strong magnetic fields; in fact, the magnetic fields are often too strong to permit the use of [[superconductivity|superconductors]]. However, with careful design, this need not be a major problem.<ref>{{Cite journal|journal = Superconductor Science and Technology|year = 2010|title = A single-sided linear synchronous motor with a high temperature superconducting coil as the excitation system|first1 = F. |last1 = Yen|first2 = J. |last2 = Li|first3 = S. J.|last3 = Zheng|first4 = L.|last4 = Liu|first5 = G. T.|last5 = Ma|first6 = J. S.|last6 = Wang|first7 = S. Y.|last7 = Wang|volume = 23| issue=10 |pages = 105015|doi = 10.1088/0953-2048/23/10/105015|arxiv = 1010.4775|bibcode = 2010SuScT..23j5015Y| s2cid=119243251 }}</ref>

Two different basic designs have been invented for high-acceleration linear motors: [[railgun]]s and [[coilgun]]s.