Linear motor: Difference between revisions

[[File:Linear motor U-tube.svg|thumb|right|225px|[[Free-body diagram]] of a U-channel synchronous linear motor. The view is perpendicular to the channel axis. The two coils at centre are mechanically connected, and are energized in "[[quadrature phase|quadrature]]" (meaning a phase difference of 90° (π/2 [[radian]]s) between the flux of the magnets and the flux of the coils). The bottom and upper coils in this particular case have a phase difference of 90°, making this a two phase motor. (Notnot to scale).]]

[[File:Linearmotorprinzip.png|thumb|right|Synchronous linear motors are straightened versions of permanent magnet rotor motors.]]

Linear motors are by far most commonly found in high accuracy engineering<ref>{{cite web|url=https://www.engineering.com/ProductShowcase/LinearMotors.aspx |title=Linear Motors |publisher=engineering.com |access-date=2020-09-15}}</ref> applications. It is a thriving field of applied research with dedicated scientific conferences<ref>{{cite web|url=https://archiveweb.epfl.ch/ldia2019.epfl.ch |title=International Symposium on Linear Drives for Industry Applications |publisher=epfl.ch |access-date=2020-09-15}}</ref> and engineering text books.<ref>{{cite web|url=https://isbnsearch.org/isbn/9781439842218 |title=Linear Synchronous Motors: Transportation and Automation Systems, Second Edition |publisher=isbnsearch.org |access-date=2020-09-15}}</ref>

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 rather short, and are designed to accelerate an object to a very high speed,; for example, see the [[coilgun]].

High-acceleration linear motors are typically used in studies of [[hypervelocity]] collisions, as [[weapon]]s, or as [[mass driver]]s for [[spacecraft propulsion]].{{citation needed|date=January 2016}} They are usually of the AC [[linear induction motor]] (LIM) design with an active [[three-phase]] winding on one side of the [[Air gap (magnetic)|air-gap]] and a passive conductor plate on the other side. However, the direct current [[homopolar motor|homopolar]] linear motor [[railgun]] is another high acceleration linear motor design. The low-acceleration, high speed and high power motors are usually of the '''linear synchronous motor''' (LSM) design, 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 magnet]]s or [[electromagnet]]s. The motor for the [[Shanghai maglev train]], for instance, is an LSM.

Brushless linear motors are members of the Synchronous motor family. They are typically used in standard [[linear stage]]s or integrated into custom, [[high performance positioning systems]]. Invented in the late 1980s by [[Anwar Chitayat]] at Anorad Corporation, now [[Rockwell Automation]], and hefsd\fdshelped improve the throughput and quality of industrial manufacturing processes.<ref>{{cite journal |author=<!--Staff writer(s); no by-line.--> |date= May 18, 1998|title=inear motors come into their own |url= https://www.designnews.com/automation-motion-control/linear-motors-come-their-own|journal= DesignNews}}</ref>

In this design the rate of movement of the magnetic field is controlled, usually electronically, to track the motion of the rotor. For cost reasons synchronous linear motors rarely use [[Commutator (electric)|commutators]], so the rotor often contains permanent magnets, or [[Magnetic core#Soft iron|soft iron]]. Examples include [[coilgun]]s and the motors used on some [[maglev]] systems, as well as many other linear motors. In high precision industrial automation linear motors are typically configured with a magnet stator and a moving coil. A [[Hall effect sensor]] is attached to the rotor to track the [[magnetic flux]] of the stator. The electricalelectric current is typically provided from a stationary [[servo drive]] to the moving coil by a moving cable inside a [[cable carrier]].

In this design, 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, in accordance with [[Lenz's law]].<ref name=Liasi>{{cite journal|last1=Ghaseminejad Liasi|first1=Sahand|title=What are linear motors?|date=15 May 2015|pages=1–50|doi=10.13140/RG.2.2.16250.18887|url=https://www.researchgate.net/publication/322040360_What_are_linear_motors322040360|access-date=24 December 2017}}</ref> The two opposing fields will repel each other, thus creating motion as the magnetic field sweeps through the metal.

In this design a large current is passed through a metal sabot across sliding contacts that are fed fromby two rails. The magnetic field this generates causes the metal to be projected along the rails.

Efficient and compact design applicable to the replacement of [[pneumatic cylinder]]s.

=== Piezo electricPiezoelectric ===

[[Piezoelectricity|Piezoelectric]] drive is often used to drive small linear motors.

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 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.<ref>{{cite web|url=http://cem.colorado.edu/archives/fl1997/thor.html |title=ArchivedCEM copy- 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.

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 runruns in traction LIM is mostly preferred and for short runruns LSM is mostly preferred.

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

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.

Linear motors are commonly used for actuating high performance industrial automation equipment. Their advantage, unlike any other commonly used actuator, such as a [[ball screw]], [[Toothed belt|timing belt]], or [[rack and pinion]], is that they provide any combination of high precision, high velocity, high force and long travel.

LinearA motorslinear havemotor has been used for sliding doors and various similar actuators. Also, theyThey have been used for baggage handinghandling and even large-scale bulk materials transport.

Linear motors are sometimes used to create rotary motion,. forFor example, they have been used at observatories to deal with the large radius of curvature.

A linear motor has been used forto acceleratingaccelerate cars for [[crash test]]s.<ref name="google">{{cite bookjournal|title=Popular Science|journal=The Popular Science Monthly |date=March 1967|publisher=Bonnier Corporation|issn=0161-7370|url=https://archive.org/details/bub_gb_4yADAAAAMBAJ|page=[https://archive.org/details/bub_gb_4yADAAAAMBAJ/page/n65 64]}}</ref>

=== Industrial automation ===

Synchronous linear motor [[actuator]]s, used in machine tools, provide high force, high velocity, high precision and high dynamic stiffness, resulting in high smoothness of motion and low settling time. They may reach velocities of 2&nbsp;m/s and micron-level accuracies, atwith short cycle times and a smooth surface finish.<ref>{{cite magazine|author=<!--Staff writer(s)-->|title=machine tools turn linear motors | url=https://www.designnews.com/machine-tools-turn-linear-motors|magazine= DesignNews|date=September 20, 1999}}</ref>

All of the following applications are in [[rapid transit]] and have the active part of the motor in the cars.<ref>{{cite web |url=http://home.inet-osaka.or.jp/~teraoka/old/tera98/ml98edit.htm |title=Adoption of Linear Motor Propulsion System for Subway |publisher=Home.inet-osaka.or.jp |access-date=2010-03-01 |archive-date=2017-08-06 |archive-url=https://web.archive.org/web/20170806055334/http://home.inet-osaka.or.jp/~teraoka/old/tera98/ml98edit.htm |url-status=dead }}</ref><ref>[{{cite web|title=Linear motor|url=http://www.hitachi.com/csr/highlight/activities/2007/act0701/index.html] {{webarchive|urlarchiveurl=https://web.archive.org/web/20080708193853/http://www.hitachi.com/csr/highlight/activities/2007/act0701/index.html|datearchivedate=July 8, 2008}}</ref>

* [[Line 3 Scarborough]] in Toronto (opened 1985; closed 2023)<ref>{{cite web|date= November 10, 2006 |url=http://transit.toronto.on.ca/subway/5107.shtml |title=The Scarborough Rapid Transit Line – Transit Toronto – Content |publisher=Transit Toronto |access-date=2010-03-01}}</ref>

* Two [[Osaka Metro]] lines in Osaka:

** [[Nagahori Tsurumi-ryokuchi Line]] (opened 1990)

** [[Imazatosuji Line]] (opened 2006)

* [[Toei Ōedo Line]] in Tokyo (opened 2000)

* [[Kaigan Line]] of the [[Kobe Municipal Subway]] (opened 2001)

* [[Nanakuma Line]] of the [[Fukuoka City Subway]] (opened 2005)

* [[Yokohama Municipal Subway Green Line]] (opened 2008)

* [[Sendai Subway Tōzai Line]] (opened 2015)

* [[Line 4 (Guangzhou Metro)|Line 4]] (opened 2005)

* [[Line 5 (Guangzhou Metro)|Line 5]] (opened 2009).

* [[Line 6 (Guangzhou Metro)|Line 6]] (opened 2013)

There are many roller coasters throughout the world that use LIMs to accelerate the ride vehicles. The first being ''[[Flight of Fear]]'' at [[Kings Island]] and [[Kings Dominion]], both opening in 1996. [[Battlestar Galactica (roller coaster)|Battlestar Galactica: Human VS Cylon]] & [[Revenge of the Mummy]] at [[Universal Studios Singapore]] opened in 2010. They both use LIMs to accelerate from certain point in the rides.

Revenge of the Mummy also is located at [[Universal Studios Hollywood]] and [[Universal Studios Florida]]. [[The Incredible Hulk Coaster]] and [[VelociCoaster]] at [[Universal's Islands of Adventure]] also usesuse linear motors. At [[Walt Disney World]], [[Rock 'n' Roller Coaster Starring Aerosmith]] was opened in 1999 inat [[Disney's Hollywood Studios]] thatand uses[[Guardians anof LSMthe toGalaxy: launchCosmic Rewind|''Guardians of the vehiclesGalaxy'': intoCosmic theRewind]] indoor,at [[blacklightEpcot]] both use LSM to launch their ride vehicles into their indoor ride enclosureenclosures.

* [[Elevator]] {{cite web|url=http://www.thyssenkrupp-elevator.com/Show-article.104.0.html?&L=1&cHash=08b38cb686f00ec874ad82c44c737427&tx_ttnews=546 |title=ThyssenKrupp Elevator: ThyssenKrupp develops the world's first rope-free elevator system to enable the building industry face the challenges of global urbanization: |access-date=2015-06-02 |url-status=dead |archive-url=https://web.archive.org/web/20160303215934/http://www.thyssenkrupp-elevator.com/Show-article.104.0.html?&L=1&cHash=08b38cb686f00ec874ad82c44c737427&tx_ttnews=546 |archive-date=2016-03-03 }}

* [[Magway Ltd|Magway]] - a UK freight delivery system under research and development that aims to deliver goods in pods via 90&nbsp;cm diameter pipework under and over ground.