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linear motor[′lin·ē·ər ′mōd·ər]
an electric motor in which one of the components of the magnetic system is open and has an unfolded winding, which generates a traveling magnetic field, and the other component is designed as a guiding member to produce linear displacement of the moving part of the motor. A DC linear motor consists of an armature, with a winding located on it that also serves as a commutator (guiding component), and an open magnetic circuit whose field windings (the moving part) are so arranged that the force vectors arising under the poles of the magnetic circuit are of identical direction. In such a motor, regulation of the speed of the moving part is very simple.
Alternating-current linear motors may be asynchronous or synchronous. The armature of an asynchronous linear motor is in the shape of a bar, usually of rectangular cross section, and has no windings; it is mounted along the path of travel of the moving part of the motor. The moving part has a magnetic circuit with unfolded polyphase windings connected to a source of alternating current. The interaction of the magnetic field in the magnetic circuit of the moving part with the armature field generates forces that cause accelerated displacement of the moving part of the motor with respect to the fixed armature. The displacement continues until the velocity of the motor and the velocity of the traveling magnetic field become equal. A very promising development is the use of asynchronous linear motors in electric traction drives for transportation vehicles in combination with magnetic cushions and air cushions, which makes possible an increase in the running speed of trains to 450–500 km/hr. Virtually no synchronous linear motors are made. The main advantage of a linear motor is its ability to generate large forces and, as a result, to develop significant acceleration. The latter is important for transportation vehicles. The absence of reduction gears in the motor is also considered an advantage.
REFERENCEKnuth, I. “Elektrische Maschinen mit geradliniger Bewegung und ihre technische Anwendung.” Elektro-Praktiker, 1969, no. 1.
IU. M. IN’KOV