What Are They?
A linear motor can be thought of as a conventional electric motor that has been "unravelled" to form a flat carpet. This causes the torque generated by the motor to instead be converted to a linear force.
Traditionally linear motors are made up of a primary (stator), and secondary (rotor). The primary function of the stator is to bring about a magnetic field through the use of electromagnets, which will interact with the magnetic field generated on the secondary. This field is generated in different ways for different motors.
There are two main types of linear motor, linear induction and linear synchronous motors.
View this slideshow to find out more
Start by considering a typical electric motor
Here is a cross-sectional view
The outer part of the motor (the stator) has coils and, when electric current flows in them, a moving magnetic field is created within the motor.
The inner rotating part of the motor is called the rotor. It has permanent magnets and they create a fixed magnetic field within the motor.
The interaction of the two magnetic fields causes the rotor to spin, as it follows the rotating field created by the current flowing in the windings.
Now, imagine cutting this motor open ...
... and unwrapping it ...
… until it is flat.
The result is a linear motor. It also has a stator (containing the windings) and a ‘rotor’ (referred to as a reaction plate).
Stator sections can be mounted end-to-end to form a long track and the reaction plate is moved backwards and forwards along it.
LINEAR INDUCTION MOTOR
The Linear Induction Motor (LIM) is an asynchronous linear motor that operates on the same principles as the rotary induction motor. The primary coils act as an electromagnet with its own magnetic field. This field induces a current within the secondary (typically induced on an aluminium plate on the moving vessel) which in turn causes an opposing magnetic field to form in the secondary. The two magnetic fields will repel one another, which ultimately causes the desired linear motion.
LINEAR SYNCHRONOUS MOTOR
The Linear Synchronous Motor (LSM) is instead synchronous, and unlike the LIM which induces a current in the secondary to generate the linear force, LSMs tend to have permanent magnets attached to the secondary to cause the necessary opposing field.