A linear motor is an electric motor that does not generate a rotary movement but a linear one. Unlike rotary motors, a linear motor moves the element along a linear or curved path.
The most common mode of operation is as a Lorentz type actuator. In this mode the applied force is linearly proportional to the electric current and the magnetic field.
Linear motors are divided into two large groups:
Low acceleration linear motors: used in transportation.
High-acceleration linear motors: used in weapons such as the magnetic cannon and space artifacts.
Types of Linear Motors
Linear motors can be classified into four different types:
1. Linear Induction Motor
In the design of linear induction motors, the force is produced by displacing a linear magnetic field that acts on conductors in the field. Eddy currents will be induced in any conductor placed in this field.
The conductors can be, for example, a winding, loop or simply a piece of metal. These eddy currents create an opposing magnetic field, as determined by Lenz's law. The two opposing magnetic fields repel each other, creating motion as the magnetic field sweeps across the metal.
2. Synchronous Linear Motors
Electronic devices are generally used in synchronous linear motor design. These devices control the speed of travel of the magnetic field to regulate the movement of the rotor.
Linear synchronous motors rarely use commutators in order to reduce costs. For this reason, the rotor often contains permanent magnets, or a soft iron core. Some examples of this type of motors are coilguns and motors used in Maglev systems .
3. Homopolar Linear Motors
In homopolar linear motors, a high current is passed through a metallic sabot by sliding contacts. These contacts are powered from two rails. This action produces a magnetic field that causes the metal to project down the tracks.
4. Piezoelectric Linear Motors
A piezoelectric motor is a common type of motor that uses electricity to produce vibrations in a way that produces linear or rotary motion.
A mobile recreates a similar effect when moving due to vibrations when receiving a call.
Piezoelectric motors have a lot of force in slow movements, but they can also be very fast, have very few parts, do not need lubrication and are very energy efficient. It has the disadvantage that they cannot rotate freely when they are stopped.
How Does a Linear Motor Work?
Linear motors differ from rotary motors in that an electric current circulates through the active part that moves. On the other hand, the part that remains immobile provides a magnetic field normally created by permanent magnets.
Linear drives do not need transmission elements such as chains, belts or the like. Therefore, a motion can be implemented directly to them and we refer to these motors as direct drives.
They are divided into 2 types:
Operation of a Low Acceleration Linear Motor
The operation of this motor involves the production of an electromagnetic field by a long series of windings that are activated in cascade, in relation to the object to be transported.
This type of engine is normally used in trains as they offer high performance by not having so many friction surfaces.
Operation of a High Acceleration Linear Motor
This type of engine is used to develop weapons.
In the case of railguns, there are two rails of conductive material, on which a bullet is fixed. Everything is inserted inside a powerful electromagnet.
When the cannon is going to fire, it first has to charge the electricity inside a large stack of supercapacitors and when these are charged, all the electricity is released through the rails and the electromagnet of the fire barrel.
This transforms the bullet into the conductor that closes the circuit, this produces a magnetic field inside it that opposes the electromagnetic field of the barrel. In this way, the bullet flows into the exit light with powerful acceleration.
Examples of Linear Motors
This system is used in magnetic levitation transport systems such as the Shanghai Transrapid, in railway lines with conventional metal wheels, in some light subways, such as those in Vancouver, Toronto and Kuala Lumpur and for the AirTrain at JFK airport in New York. There are also some classic subways such as the Toei Oedo line of the Tokyo subway.
This system is also used in some roller coasters and has been proposed in vertical execution as a lift for mining shafts.