linear motors
Introduction
A linear motor is an electric motor that has its stator and rotor "Rotor (electrical machine)") "distributed" in such a way that instead of producing a torque (rotation) it produces a linear force in the direction of its length. The most common mode of operation is as a Lorentz-type actuator, in which the applied force is linearly proportional to the electric current and the magnetic field.
Various designs of linear motors have been developed, which fall into two main categories, low-acceleration and high-acceleration linear motors. Low acceleration linear motors are suitable for maglev train and other uses in the field of surface transportation. High acceleration linear motors are usually relatively short and are designed to accelerate an object to very high speed, for example see the railgun.
They are generally used for hypervelocity collision studies, as weapons, or as mass drivers for spacecraft propulsion systems. High acceleration motors generally have AC linear induction motor designs with an active three-phase winding on one side of the air gap and a passive conductor plate on the other side. The railgun type homopolar direct current linear motor is another design of a high acceleration linear motor. Low acceleration, high speed, high power motors are generally of the linear synchronous motors (LSM) type, with an active winding on one side of the air coil and a set of magnets with alternating poles on the other side. These magnets can be permanent magnets or electromagnets. The engine of the Shanghai Transrapid is an LSM.
Guys
induction motor
In this design, force is produced by displacing a linear magnetic field that acts on conductors in the field. In any conductor, be it a winding, loop or simply a piece of metal, that is placed in this field, Eddy currents will be induced creating an opposite magnetic field, as determined by Lenz's law. The two opposing magnetic fields will repel each other, creating motion as the magnetic field sweeps across the metal.
synchronous motor
In this design, the speed of movement of the magnetic field is usually controlled by electronic devices to regulate the movement of the rotor. Due to cost reasons linear synchronous motors rarely use commutators, so the rotor often contains permanent magnets, or soft iron. Examples of this type of motor are coilguns and motors used in maglev systems.