Linear Motor System Technology
A linear motor is a type of motor that uses an alternating current (AC) as an input, as opposed to a direct current (DC). A linear motor uses the same principles for operation as a rotary induction motor but oriented in a linear fashion to provide a linear displacement output instead of a rotary displacement.
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Linear Motor Basics
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Linear motors consist of a stationary stator and a moving rotor, although rather than rotating, the rotor moves along the linear stator, which guides the rotor's motion. AC power is provided to coils in the stator, which generates a magnetic field. The stator's magnetic field induces a current in the rotor's coils, which in turn create their own magnetic field. The rotor generally has two coils that are out of phase from each other, so when the two magnetic fields interact, the controlled combinations of attraction and repulsion cause the rotor to move in one direction. By controlling the magnetic fields, the speed of the rotor can be controlled.
Low-Acceleration Linear Motors
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The standard low-acceleration linear motor design is the tubular linear motor. In this design, permanent magnet assemblies are installed in a sealed canister, allowing them to be used in many industrial settings without being damaged by dirt or debris. The design generates a sinusoidal current, allowing standard servo drives to be used to control the systems.
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High-Acceleration Linear Motors
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High--acceleration linear motors operate in a similar manner to low-acceleration linear motors, but require a much higher energy input in a very short burst. These designs require unconventional energy supply mechanisms, such as capacitors or flywheels to deliver this power. High-acceleration linear motors can generate very large magnetic fields, limiting their deployment to some environments. High-acceleration linear motors are often called rail guns or coil guns.
Transportation Applications
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Linear motors of the low-acceleration variety are often an integral part of magnetic levitation (mag-lev) train systems, resulting in a completely non-contact propulsion system. Several systems in Japan, China and Russia use linear motors as propulsion systems for some transit vehicles.
Non-Transportation Applications
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Low-acceleration linear motors are used for some material handling processes, such as in mines. High-acceleration linear motors are not widely used, although their use has been proposed for a variety of applications that require high accelerations, such as weaponry, space launch systems known as mass drivers, and aircraft carrier launch systems.
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