# The Principle of Linear Magnetic Drives

Let’s look at a conventional, rotating motor first: Alternating current flows through the motor’s stator coils (primary). The current generates an alternating magnetic field, interacting with the magnetic field of the rotor’s permanent magnet (motor’s secondary) and thus turning the rotor. The principle of a linear magnetic motor is exactly the same. The only differences are that the stator has been flattened out and stretched all the way of the drive and that the secondary now performs a linear movement along the stator.

To make the secondary move, a travelling magnetic field is required. This field is generated by a specifically-shaped current, provided by our power converters.

As soon as the current begins to flow, the travelling magnetic field will interact with the magnetic field of the secondary (the gondola) and thus push or pull it along the drive way.

An arrangement like that usually is called a Linear Synchronous Motor or in short LSM.

The transmission of forces in a linear motor is non-contacting and therefore wear-free. It is now the design of the control electronics, sensors and converters that make the linear drive suitable for various forces and velocities. Furthermore, positioning the secondary (i.e. the trolley) with very high and repeatable accuracy is comparably easy.

Using a linear magnetic drive, accelerating a vehicle with 20 m/s² (2 g) or keeping it at an exactly constant speed for a longer distance, is no magic. It’s simply the application of physical laws.

Like with a conventional asynchronous motor, the magnet of the secondary can be replaced by a metal (copper) plate. The travelling magnetic field of the stator will induct a current flow in the copper plate; and this flowing current will have its own magnetic field. Again, the two magnetic fields (the stator’s and the one induced in the copper plate) interact.

Result is that the secondary (i.e. the gondola) will travel asymmetrically to the travelling magnetic field – like being pulled using a rubber band.
An arrangement like that usually is called a Linear Induction Motor or in short LIM.

No need to take a decision now. Depending on your requirements, InTraSys will suggest to use either LIM or LSM.

The only important thing to keep in mind:

Only Prolim products will provide you with the advanced magnetic technology made by InTraSys.