This type of motors is normally spoken of in a context of technological novelty, but they have actually existed for about a century. Current mechanical transmissions, ball screws and rack pinions, used to transform the rotating movement into linear, cannot adapt to these new requirements. Structural limitations of motors can be summed up in the rigidity, the production of heat and dilatations; in balls and split nut; in variable clearances, in pre-loads and in the increase of mechanical inertias tied into the diameters and lengths of transmissions.

At high accelerations power is expended for transmission. With the aim of obtaining speed increases with high precisions and solve the problems connected to the growing lengths of the work fields, the option arises of using the linear motor.

We can classify linear motors in various types: to a single motor side, to two sides tubular motor, annular motor. The one-sided linear motor can be also synchronous and asynchronous.

The first is made up of a primary part (lamellar package with ac winding) and a secondary part (bearing iron nucleus sheathed in rare earths permanent magnets).

The second one is made up of a primary part (lamellar package with ac winding) and a secondary part (three-phase cc winding with iron core).

December.2001

Siemens