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A linear induction motor (LIM) is an alternating current (AC), asynchronous linear motor that works by the same general principles as other induction motors but is typically designed to directly produce motion in a straight line. Characteristically, linear induction motors have a finite length primary or secondary, which generates end-effects, whereas a conventional induction motor is arranged in an endless loop. Despite their name, not all linear induction motors produce linear motion; some linear induction motors are employed for generating rotations of large diameters where the use of a continuous primary would be very expensive. They also, unlike their rotary counterparts, can give a levitation effect. As with rotary motors, linear motors frequently run on a three-phase power supply and can support very high speeds. However, there are end-effects which reduce the force, and it's often not possible to fit a gearbox to trade off force and speed. Linear induction motors are thus frequently less energy efficient than normal rotary motors for any given required force output. LIMs are often used where contactless force is required, where low maintenance is desirable, or where the duty cycle is low. Their practical uses include magnetic levitation, linear propulsion, and linear actuators. They have also been used for pumping liquid metals.〔(Einstein Linear induction motor )〕 ==History== The history of linear electric motors can be traced back at least as far as the 1840s, to the work of Charles Wheatstone at King's College in London, but Wheatstone's model was too inefficient to be practical. A feasible linear induction motor is described in the US patent 782312 ( 1905 - inventor Alfred Zehden of Frankfurt-am-Main ), for driving trains or lifts. The German engineer Hermann Kemper built a working model in 1935.〔http://cem.colorado.edu/archives/fl1997/thor.html〕 In the late 1940s, professor Eric Laithwaite of Imperial College in London developed the first full-size working model. In a single sided version, the magnetic field can create repulsion forces that push the conductor away from the stator, levitating it, and carrying it along in the direction of the moving magnetic field. Laithwaite called the later versions of it magnetic river. These versions of the linear induction motor use a principle called ''transverse flux'' where two opposite poles are placed side by side. This permits very long poles to be used, which permits high speed and efficiency.〔Patent number 3585423, 1971 Laithwaite et al〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「linear induction motor」の詳細全文を読む スポンサード リンク
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