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'[[Image:Linear motor U-tube.svg|thumb|right|225px|[[Free-body diagram]] of a U-channel linear motor. The view is perpendicular to the channel axis. The two coils at center are mechanically connected, and are energized in "[[quadrature]]" (with a phase difference of 90° (π/2 [[radian]]s)). If the bottom coil (as shown) leads in phase, then the motor will move downward (in the drawing), and vice versa. (Not to scale)]] [[Image:Linear Motor of Toei Ōedo Line.jpg|thumb|right|225px|A linear motor for trains running Toei Oedo line.]] A '''linear motor''' or '''linear induction motor''' is an [[alternating current]] (AC) [[electric motor]] that has had its [[stator]] "unrolled" so that instead of producing a [[torque]] ([[rotation]]) it produces a linear [[force]] along its length. The most common mode of operation is as a [[Lorentz force|Lorentz]]-type actuator, in which the applied force is [[linear equation | linearly proportional]] to the [[electric current | current]] and the [[magnetic field]] ('''F''' = q'''v''' × '''B'''). Many designs have been put forward for linear motors, falling into two major categories, low-acceleration and high-acceleration linear motors. Low-acceleration linear motors are suitable for [[maglev train]]s and other ground-based transportation applications. High-acceleration linear motors are normally quite short, and are designed to accelerate an object up to a very high speed and then release it, like [[roller coaster]]s. They are usually used for studies of [[hypervelocity]] collisions, as [[weapon]]s, or as [[mass driver]]s for [[spacecraft propulsion]]. The high-acceleration motors are usually of the linear induction design (LIM) with an active [[three-phase]] winding on one side of the air-gap and a passive conductor plate on the other side. The low-acceleration, high speed and high power motors are usually of the linear synchronous design (LSM), with an active winding on one side of the air-gap and an array of alternate-pole magnets on the other side. These magnets can be permanent magnets or energized magnets. The [[Transrapid]] Shanghai motor is an LSM. ==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|King's College]] in London [http://www.kcl.ac.uk/college/history/people/wheatstone.html], but Wheatstone's model was too inefficient to be practical. A feasible linear induction motor is described in the 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 [http://cem.colorado.edu/archives/fl1997/thor.html]. In the late 1940s, professor [[Eric Laithwaite]] of [[Imperial College]] in [[London]] developed the first full-size working model. In his design, and in most low-acceleration designs, the force is produced by a moving linear [[magnetic field]] acting on conductors in the field. Any conductor, be it a loop, a coil or simply a piece of plate metal, that is placed in this field will have [[eddy current]]s [[electromagnetic induction|induced]] in it thus creating an opposing magnetic field. The two opposing fields will repel each other, thus forcing the conductor away from the stator and carrying it along in the direction of the moving magnetic field. 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 [[Bombardier Transportation|Bombardier]]'s [[Bombardier Advanced Rapid Transit|Advanced Rapid Transit]] systems worldwide and a number of modern Japanese subways, including [[Tokyo]]'s [[Toei Oedo 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. [[Image:JFK_AirTrain.agr.jpg|thumb|left|250px|[[Bombardier Advanced Rapid Transit|ART]] trains propel themselves using an aluminium induction strip placed between the rails.]] 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]] [[tram]]s such as the [[Citadis]] and the [[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. Mostly used linear motors are LIM (Linear Induction Motor), LSM (linear Synchronous Motor). Linear DC motors are not used as it includes more cost and Linear SRM suffers from poor thrust. So for long run in traction LIM is mostly preferred and for short run LSM is mostly preferred. '''From concept to industrial use''' In the 1980s British engineer [[Hugh-Peter Kelly]] designed the first tubular linear motor by enclosing the permanent magnets in a sealed stainless steel cylinder. It was brought to market by linear motor manufacturer Linear Drives (now [http://www.copleycontrols.com/motion/ Copley Motion Systems]) . The patented permanent magnet arrangement induces a sinusoidal response in the coils that are enclosed in a square profile body. This allowed machine builders to use the new linear motors with standard sinusoidal servo drives commonly used in motion control. '''Tubular Linear Motors''' Tubular linear motors are more rugged than early flat bed and u-channel linear motors allowing them to be used in dirty industrial environments such as food packaging and machine tools. The tubular construction protects the permanent magnets from the external environment and automatically balances attractive forces so that the motor is easier to integrate into machines. These motors operate at 5- 9 m/s with high acceleration for dynamic motion control. A new type of linear motor, called the ServoTube (see [http://www.eurekamagazine.co.uk/article/3006/Novel-linear-motor-offers-alternative-to-pneumatics.aspx Eureka March 2005]) has allowed linear motors to be used in industrial environments by integrating the position sensing electronics into the motor body (called a forcer). ==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 [[armor-piercing]] ammunition tends to consist of small rounds with very high [[kinetic energy]], for which just such motors are suitable. Many amusement park [[roller coasters]] 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|steam catapults]] 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]]. 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 (see [http://www.coilgun.info/theory/electroguns.htm]) 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. Two different basic designs have been invented for high-acceleration linear motors: [[railgun]]s and [[coilgun]]s. == Usages of a Linear Motor for Train Propulsion == ===Usage with conventional rails=== All applications are in [[rapid transit]]. * [[Bombardier Advanced Rapid Transit|Bombardier ART]]: ** [[Airport Line, Beijing Subway|Airport Express]] in Beijing (opened 2008) ** [[AirTrain JFK]] in New York (opened 2003) ** [[Detroit People Mover]] in Detroit (opened 1987) ** [[EverLine Rapid Transit System]] in Yongin (under construction) ** [[Kelana Jaya Line]] in Kuala Lumpur (opened 1998) ** [[Scarborough RT]] in Toronto (opened 1985) ** [[Vancouver SkyTrain|SkyTrain]] in Vancouver ([[Expo Line]] opened 1985 and [[Millennium Line]] open in 2002) * Several Subways in [[Japan]] and [[China]], built by [[Kawasaki Heavy Industries]]: **Limtrain in [[Saitama, Saitama|Saitama]] (short-lived demonstration track, 1988) **[[Nagahori Tsurumi-ryokuchi Line]] in Osaka (opened 1990) **[[Toei Ōedo Line]] in Tokyo (opened 2000) **[[Kaigan Line]] in Kobe (opened 2001) **[[Nanakuma Line]] in Fukuoka (opened 2005) **[[Green Line (Yokohama)|Green Line]] in Yokohama (opened 2008) **Tōzai Line in [[Sendai]] (under construction) ** Line 4 of [[Guangzhou Metro]], China (opened 2005). Line 5 and 6 under construction. [http://www.urbanrail.net/as/guan/guangzhou.htm] **Beijing Subway Capital Airport Track Both the Kawasaki-Trains and Bombardier's ART have the active part of the motor in the cars and use overhead wires (Japanese Subways[http://home.inet-osaka.or.jp/~teraoka/old/tera98/ml98edit.htm][http://www.hitachi.com/csr/highlight/activities/2007/act0701/index.html]) or a third rail (ART[http://transit.toronto.on.ca/subway/5107.shtml]) to transfer power to the train. === Usage with monorails === {{Unreferenced|date=July 2009}} * There is at least one known monorail system which is '''not''' magnetically levitated, but nonetheless uses linear motors. This is the [[Moscow Monorail]]. Originally, traditional motors and wheels were to be used. However, it was discovered during test runs that the proposed motors and wheels would fail to provide adequate traction under some conditions, for example, when ice appeared on the rail. Hence, wheels are still used, but the trains use linear motors to accelerate and slow down. This is possibly the only use of such a combination, due to the lack of such requirements for other train systems. ===Usage with magnetic levitation=== {{main|Maglev (transport)}} * High-speed trains: ** [[Transrapid]]: first commercial use in [[Shanghai Maglev|Shanghai]] (opened in 2004) ** [[JR-Maglev]] * Rapid transit: ** Birmingham Airport, UK (opened 1984, closed 1995) ** [[M-Bahn]] in Berlin, Germany (opened in 1989, closed in 1991) ** Daejeon EXPO, Korea (ran only 1993) [http://maglev.de/index.php?en_korea] ** [[HSST]]: [[Linimo]] line in Aichi, Japan (opened 2005) ==See also== * [[California Screamin']] Roller coaster LIM application * [[capacitor]] * [[coilgun]] * [[compulsator]] * [[doubly-fed electric machine]] * [[flywheel]] * [[homopolar generator]] * [[launch loop]] a proposed system for launching vehicles into space using a linear motor powered loop * [[linear actuator]] * [[Maverick (roller coaster)|Maverick]] - a roller coaster LSM application * [[transformer types#pulse transformers|pulse transformer]] * [[railgun]] * [[SkyTrain (Vancouver)]], Canada - Rapid transit system * [[tether propulsion#Tether cable catapult system|Tether cable catapult system]] * [[Tomorrowland Transit Authority]] Slow ride LIM application * [[Tower of Terror (roller coaster)|Dreamworld, Australia]] LSM reverse freefall roller coaster * [[Research Test Vehicle 31]], a hovercraft-type vehicle guided by a track __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________Ethan is gay ==External links== * [http://www.instructables.com/id/Electromagnetic-Actuator/?ALLSTEPS Design equations, spreadsheet, and drawings] * [http://www.coilgun.info/theory/electroguns.htm Electromagnetic Guns] - A page describing recent research at MIT. * [http://www.utexas.edu/research/cem/Maglev_Davey.html Maglev ] - Defunct * [http://www.linear-actuator.net Linear Motors for Nanopositioning Applications ] * [http://www.aerotech.com/products/PDF/LMAppGuide.pdf Linear Motors Application Guide] <!--spacing, please do not remove--> {{Electric motor}} [[Category:Electric motors]] [[Category:Automation]] [[Category:English inventions]] [[Category:Magnetic propulsion devices| ]] [[ar:محرك خطي]] [[cs:Lineární elektromotor]] [[da:Linear-motor]] [[de:Linearmotor]] [[hr:Linearni motor]] [[it:Motore lineare]] [[he:מנוע השראה ישר]] [[ms:Motor linear]] [[nl:Lineaire inductiemotor]] [[ja:リニアモーター]] [[pl:Silnik liniowy]] [[ru:Линейный двигатель]] [[sr:Linearni motor]] [[sv:Linjärmotor]] [[zh:直線電動機]]'