We can describe an asynchronous two-sided linear motor as made up of two primary parts countered, on both sides, with a single secondary part of synchronous or asynchronous type. The driving force is, in this case, doubled.

One of the essential elements of a motor thus conceived is the so-called tubular motor, made up of a primary part, with three-phase winding, and a secondary one with cage in d.c. The drive shaft with the movement of the secondary part is supported from the inside by anti-friction bearings. This kind of motor is used where very short runs are required.

Another type of engine is the annular torque motor, made up of a stator, with three-phase winding, and by a rotor with permanent magnets. Its characteristic of high coupling with low rotation speeds, direct it towards applications on rotating table and rotating axes typical of grinding.

Then there are synchronous linear motors which operate owing to a magnetic field created by permanent magnets with rare earths. To avoid problems of temporary demagnetisation, magnets are used that have a high coercing force such as, for example, neodymium -ferro-boron placed between the poles.

One of the characteristics of permanent magnet motors is the presence of the reluctance force, tied into magnetic attraction on the teeth of the laminated nucleus containing the windings and which is also present when the motor is not powered. Thus an undulation is mad eon the produced force which is otherwise absent in asynchronous type motors.

December.2001

Lineardrives