HOME

TheInfoList



OR:

A linear motor is an
electric motor An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate forc ...
that has had its stator and rotor "unrolled", thus, instead of producing a
torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of t ...
( rotation), it produces a linear
force In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a ...
along its length. However, linear motors are not necessarily straight. Characteristically, a linear motor's active section has ends, whereas more conventional motors are arranged as a continuous loop. A typical mode of operation is as a Lorentz-type actuator, in which the applied force is linearly proportional to the current and the
magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and t ...
(\vec F = I \vec L \times \vec B). Linear motors are by far most commonly found in high accuracy engineering applications. It is a thriving field of applied research with dedicated scientific conferences and engineering text books. 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 trains 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 Hypervelocity is very high velocity, approximately over 3,000 meters per second (6,700 mph, 11,000 km/h, 10,000 ft/s, or Mach 8.8). In particular, hypervelocity is velocity so high that the strength of materials upon impact is v ...
collisions, as
weapon A weapon, arm or armament is any implement or device that can be used to deter, threaten, inflict physical damage, harm, or kill. Weapons are used to increase the efficacy and efficiency of activities such as hunting, crime, law enforcement, ...
s, or as mass drivers for spacecraft propulsion. They are usually of the AC
linear induction motor A linear induction motor (LIM) is an alternating current (AC), asynchronous linear motor that works by the same general principles as other induction motors but is typically designed to directly produce motion in a straight line. Characterist ...
(LIM) design with an active three-phase winding on one side of the air-gap and a passive conductor plate on the other side. However, the direct current 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 A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nic ...
s or electromagnets. The motor for the Shanghai maglev train, for instance, is an LSM.


Types


Brushless

Brushless linear motors are members of the Synchronous motor family. They are typically used in standard
linear stage A linear stage or translation stage is a component of a precise motion system used to restrict an object to a single axis of motion. The term linear slide is often used interchangeably with "linear stage", though technically "linear slide" refe ...
s or integrated into custom, high performance positioning systems. Invented in late 1980s by Anwar Chitayat at Anorad Corporation, now Rockwell Automation, and helped improving throughput and quality of industrial manufacturing processes.


Brush

Brush (electric) linear motors were used in industrial automation applications prior to the invention of Brushless linear motors. Compared with three phase Brushless motors, which are typically being used today, brush motors operates with a single phase. Brush linear motors have lower cost since they do not need moving cables and three phase servo drives. However, they require higher maintenance since their brushes wear out.


Synchronous

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
commutators In mathematics, the commutator gives an indication of the extent to which a certain binary operation fails to be commutative. There are different definitions used in group theory and ring theory. Group theory The commutator of two elements, a ...
, so the rotor often contains permanent magnets, or soft iron. Examples include coilguns 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 electrical current is typically provided from a stationary servo drive to the moving coil by a moving cable inside a cable carrier.


Induction

In this design, the force is produced by a moving linear
magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and t ...
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 Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction or by the relative motion of a conductor in a magnet ...
s
induced Induce may refer to: * Induced consumption * Induced innovation * Induced character * Induced coma * Induced menopause * Induced metric * Induced path * Induced topology * Induce (musician), American musician See also * Inducement (disambiguation ...
in it thus creating an opposing magnetic field, in accordance with Lenz's law. The two opposing fields will repel each other, thus creating motion as the magnetic field sweeps through the metal.


Homopolar

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


Tubular

Efficient and compact design applicable to replacement of pneumatic cylinders.


Piezo electric

Piezoelectric drive is often used to drive small linear motors.


History


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, but Wheatstone's model was too inefficient to be practical. A feasible linear induction motor is described in the (1905 - inventor Alfred Zehden of Frankfurt-am-Main), for driving trains or lifts. The German engineer Hermann Kemper built a working model in 1935. In the late 1940s, Dr. Eric Laithwaite of Manchester University, later Professor of Heavy Electrical Engineering at Imperial College in
London London is the capital and List of urban areas in the United Kingdom, largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary dow ...
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 shuttle, between Birmingham's airport and an adjacent train station. Because of these properties, linear motors are often used in maglev propulsion, as in the Japanese Linimo
magnetic levitation train Maglev (derived from ''magnetic levitation''), is a system of train transportation that uses two sets of electromagnets: one set to repel and push the train up off the track, and another set to move the elevated train ahead, taking advantage ...
line near
Nagoya is the largest city in the Chūbu region, the fourth-most populous city and third most populous urban area in Japan, with a population of 2.3million in 2020. Located on the Pacific coast in central Honshu, it is the capital and the most p ...
. 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 Tokyo (; ja, 東京, , ), officially the Tokyo Metropolis ( ja, 東京都, label=none, ), is the capital and List of cities in Japan, largest city of Japan. Formerly known as Edo, its metropolitan area () is the most populous in the world, ...
's Toei Ōedo Line. Similar technology is also used in some
roller coaster A roller coaster, or rollercoaster, is a type of amusement ride that employs a form of elevated railroad track designed with tight turns, steep slopes, and sometimes inversions. Passengers ride along the track in open cars, and the rides ar ...
s with modifications but, at present, is still impractical on street running
tram A tram (called a streetcar or trolley in North America) is a rail vehicle that travels on tramway tracks on public urban streets; some include segments on segregated right-of-way. The tramlines or networks operated as public transport ...
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 mines, 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
drafting Drafting or draughting may refer to: * Campdrafting, an Australian equestrian sport * Drafting (aerodynamics), slipstreaming * Drafting (writing), writing something that is likely to be amended * Technical drawing, the act and discipline of compo ...
, 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 higher 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.


High acceleration

High-acceleration linear motors have been suggested for a number of uses. They have been considered for use as
weapon A weapon, arm or armament is any implement or device that can be used to deter, threaten, inflict physical damage, harm, or kill. Weapons are used to increase the efficacy and efficiency of activities such as hunting, crime, law enforcement, ...
s, since current armour-piercing ammunition tends to consist of small rounds with very high
kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its a ...
, for which just such motors are suitable. Many amusement park launched 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 catapults on future aircraft carriers. They have also been suggested for use in spacecraft propulsion. In this context they are usually called mass drivers. 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 In celestial mechanics, escape velocity or escape speed is the minimum speed needed for a free, non- propelled object to escape from the gravitational influence of a primary body, thus reaching an infinite distance from it. It is typically ...
, though RLV launch assist like StarTram to
low Earth orbit A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never m ...
has also been investigated. High-acceleration linear motors are difficult to design for a number of reasons. They require large amounts of
energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of hea ...
in very short periods of time. One rocket launcher design calls for 300 GJ for each launch in the space of less than a second. Normal
electrical generator In electricity generation, a generator is a device that converts motive power (mechanical energy) or fuel-based power (chemical energy) into electric power for use in an external electrical circuit, circuit. Sources of mechanical energy include s ...
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 generators 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 superconductors. However, with careful design, this need not be a major problem. Two different basic designs have been invented for high-acceleration linear motors: railguns and coilguns.


Usage

Linear motors are commonly used for actuating high performance industrial automation equipment. Their advantage, unlike any other commonly used actuator, such as ball screw, timing belt, or rack and pinion, is that they provide any combination of high precision, high velocity, high force and long travel. Linear motors are widely used. One of the major uses of linear motors is for propelling the shuttle in looms. Linear motors have been used for sliding doors and various similar actuators. Also, they have been used for baggage handing and even large-scale bulk materials transport. Linear motors are sometimes used to create rotary motion, for example, they have been used at observatories to deal with the large radius of curvature. Linear motors may also be used as an alternative to conventional chain-run lift hills for roller coasters. The coaster Maverick at Cedar Point uses one such linear motor in place of a chain lift. A linear motor has been used for accelerating cars for crash tests.


Industrial automation

The combination of high precision, high velocity, high force, and long travel makes brushless linear motors attractive for driving industrial automations equipment. They serve industries and applications such as semiconductor steppers, electronics surface-mount technology, automotive cartesian coordinate robots, aerospace chemical milling, optics
electron microscope An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a ...
, healthcare laboratory automation, food and beverage pick and place.


Machine tools

Synchronous linear motor
actuator An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover". An actuator requires a control device (controlled by control signal) a ...
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 m/s and micron-level accuracies, at short cycle times and a smooth surface finish.


Train propulsion


Conventional rails

All of the following applications are in
rapid transit Rapid transit or mass rapid transit (MRT), also known as heavy rail or metro, is a type of high-capacity public transport generally found in urban areas. A rapid transit system that primarily or traditionally runs below the surface may be c ...
and have the active part of the motor in the cars.


= Bombardier Innovia Metro

= Originally developed in the late 1970s by UTDC in Canada as the Intermediate Capacity Transit System (ICTS). A test track was constructed in Millhaven, Ontario, for extensive testing of prototype cars, after which three lines were constructed: *
Line 3 Scarborough Line 3 Scarborough (originally known as the Scarborough RT or SRT) is a light rapid transit line that is part of the Toronto subway system in Toronto, Ontario, Canada. The line runs entirely within the suburban district of Scarborough, encomp ...
in Toronto (opened 1985) * Expo Line of the Vancouver SkyTrain (opened 1985 and extended in 1994) * Detroit People Mover in Detroit (opened 1987) ICTS was sold to Bombardier Transportation in 1991 and later known as Advanced Rapid Transit (ART) before adopting its current branding in 2011. Since then, several more installations have been made: * Kelana Jaya Line in Kuala Lumpur (opened 1998 and extended in 2016) * Millennium Line of the Vancouver SkyTrain (opened 2002 and extended in 2016) * AirTrain JFK in New York (opened 2003) *
Airport Express (Beijing Subway) The Capital Airport Express of the Beijing Subway (), also known by the initials ABC, Airport Beijing City, is an airport rail link from Beixingqiao station to the Beijing Capital International Airport. The line became operational on July 19, ...
(opened 2008) * Everline in Yongin, South Korea (opened 2013) All Innovia Metro systems use third rail electrification.


= Japanese Linear Metro

= One of the biggest challenges faced by Japanese railway engineers in the 1970s to the 1980s was the ever increasing construction costs of subways. In response, the Japan Subway Association began studying on the feasibility of the "mini-metro" for meeting urban traffic demand in 1979. In 1981, the Japan Railway Engineering Association studied on the use of linear induction motors for such small-profile subways and by 1984 was investigating on the practical applications of linear motors for urban rail with the Japanese Ministry of Land, Infrastructure, Transport and Tourism. In 1988, a successful demonstration was made with the Limtrain at Saitama and influenced the eventual adoption of the linear motor for the Nagahori Tsurumi-ryokuchi Line in
Osaka is a designated city in the Kansai region of Honshu in Japan. It is the capital of and most populous city in Osaka Prefecture, and the third most populous city in Japan, following Special wards of Tokyo and Yokohama. With a population of ...
and Toei Line 12 (present-day Toei Oedo Line) in
Tokyo Tokyo (; ja, 東京, , ), officially the Tokyo Metropolis ( ja, 東京都, label=none, ), is the capital and List of cities in Japan, largest city of Japan. Formerly known as Edo, its metropolitan area () is the most populous in the world, ...
. To date, the following subway lines in Japan use linear motors and use overhead lines for power collection: *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) In addition, Kawasaki Heavy Industries has also exported the Linear Metro to the
Guangzhou Metro The Guangzhou Metro () ( and ) is the rapid transit system of the city of Guangzhou in Guangdong Province of China. It is operated by the state-owned Guangzhou Metro Corporation and was the fourth metro system to be built in mainland China, af ...
in China; all of the Linear Metro lines in Guangzhou use third rail electrification: * Line 4 (opened 2005) * Line 5 (opened 2009). * Line 6 (opened 2013)


Monorail

* There is at least one known monorail system which is not magnetically levitated, but nonetheless uses linear motors. This is the
Moscow Monorail The Moscow Monorail (russian: Московский монорельс) is a monorail line located in the North-Eastern Administrative Okrug of Moscow, Russia. It runs from the Timiryazevskaya via Fonvisinskaya and VDNHa metro stations to Serge ...
. 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. * The TELMAGV is a prototype of a monorail system that is also not magnetically levitated but uses linear motors.


Magnetic levitation

* High-speed trains: ** Transrapid: first commercial use in
Shanghai Shanghai (; , , Standard Mandarin pronunciation: ) is one of the four direct-administered municipalities of the People's Republic of China (PRC). The city is located on the southern estuary of the Yangtze River, with the Huangpu River flowin ...
(opened in 2004) ** SCMaglev, under construction in Japan (fastest train in the world, planned to open by 2027) * 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) ** HSST: Linimo line in Aichi Prefecture, Japan (opened 2005) ** Incheon Airport Maglev (opened July 2014) ** Changsha Maglev Express (opened 2016) ** S1 line of Beijing Subway (opened 2017)


Amusement rides

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 Galctica: 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 uses linear motors. At
Walt Disney World The Walt Disney World Resort, also called Walt Disney World or Disney World, is an entertainment resort complex in Bay Lake and Lake Buena Vista, Florida, United States, near the cities of Orlando and Kissimmee. Opened on October 1, 1971, ...
, Rock 'n' Roller Coaster Starring Aerosmith at Disney's Hollywood Studios and ''Guardians of the Galaxy'': Cosmic Rewind at Epcot both use LSM to launch their ride vehicles into their indoor ride enclosures.


Aircraft launching

* Electromagnetic Aircraft Launch System


Proposed and research

* Launch loop – A proposed system for launching vehicles into space using a linear motor powered loop * StarTram – Concept for a linear motor on extreme scale * Tether cable catapult system * Aérotrain S44 – A suburban commuter hovertrain prototype *
Research Test Vehicle 31 Research is "creativity, creative and systematic work undertaken to increase the stock of knowledge". It involves the collection, organization and analysis of evidence to increase understanding of a topic, characterized by a particular att ...
– A hovercraft-type vehicle guided by a track *
Hyperloop A hyperloop is a proposed high-speed transportion system for both public and goods transport. The idea was picked up by Elon Musk to describe a modern project based on the vactrain concept (first appearance in 1799). Hyperloop systems compr ...
– a conceptual high-speed transportation system put forward by entrepreneur Elon Musk *
Elevator An elevator or lift is a cable-assisted, hydraulic cylinder-assisted, or roller-track assisted machine that vertically transports people or freight between floors, levels, or decks of a building, vessel, or other structure. They ar ...
* Lift * Magway - a UK freight delivery system under research and development that aims to deliver goods in pods via 90 cm diameter pipework under and over ground.


See also

* Linear actuator *
Linear induction motor A linear induction motor (LIM) is an alternating current (AC), asynchronous linear motor that works by the same general principles as other induction motors but is typically designed to directly produce motion in a straight line. Characterist ...
* Linear motion * Maglev * Online Electric Vehicle *
Reciprocating electric motor A reciprocating electric motor is a motor in which the armature moves back and forth rather than circularly. Early electric motors were sometimes of the reciprocating type, such as those made by Daniel Davis in the 1840s. Today, reciprocating ele ...
*
Sawyer motor A Sawyer motor or planar motor (also called area drive) is a multi-coordinate drive that can perform several independent movements in one plane. Goods can be transported along any path to any location. In the industrial environment, the planar moto ...
* Tubular linear motor


References


External links


Design equations, spreadsheet, and drawings

Motor torque calculation


{{DEFAULTSORT:Linear Motor Electric motors English inventions Linear motion