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.
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.