A linear motor is an electric motor which provides electric traction in a straight line instead of rotary as the typical electric motors do. The linear motors are applied mostly in high speed transportation applications such as high speed railways. The invention of the linear motors comes from the idea to slice a conventional electric rotary motor and roll it out into a flat configuration. The key difference between a linear motor and a rotary motor is that the active section of a linear motor has its end while a rotary motor has a continuous loop design.
To get to understand how a linear motor works, it is necessary to go through the anatomy as well as the working principles of a rotary motor because the linear motors essentially derive from a rotary motor and they share the same basic components and working principles. A conventional rotary motor has a group of permanent magnets configured in a circular loop within while a linear motor has the magnets configured linearly.
In a rotary motor, the permanent magnets make the outer circular loop which serves as the stator, the stationary part, and the rotor is the moving part that is surrounded by the stator. The stator is the electrical component which consists of a series of electro magnets with one pole of each magnet facing the center of the motor. The rotor also contains a series of electro magnets with one pole facing the stator poles.
The working principle of a rotary motor is rather simple. It applies the rule that unlike magnetic poles attract each other and like poles repel each other. The direction of the current flow changes constantly as an alternating current enters the coils in a motor. Therefore, the stator and rotor repel and attract each other and hence force the rotor to rotate. By means of changing the current flow direction, the electric energy is converted into mechanical energy.
In a conventional rotary motor, the rotor rotates inside the stator; on the other hand, in a linear motor, the stator is unwrapped and laid out flat while the rotor moves along the stator in a straight line. This design is induced since a linear motion instead of rotational motion is required by some types of machine such as the overhead traveling cranes, beltless conveyors, and the high-speed railways. In such applications, the linear motion at high speed is required and thus the introduction of the linear motors becomes necessary.
A linear motor has the stator cut open and laid out in the form of a set of flat coils. Just like the rotary motors, the coils are usually made from aluminum or copper. The stator is called the primary of a linear motor. The rotor in a linear motor does not rotate; instead, it slides along the primary propelled by the magnetic field. The rotor in this case is called secondary. The primary is also called the coil unit while the secondary is called the magnet plate.
The working principle of the linear motors is the same as the rotary motor: the unlike poles attract each other and the like poles repel each other. When the alternating current enters the coil unit, the direction of the flow changes; the poles change consequently and therefore the attraction and repellency drive the magnet plate slide. The linear motors are widely implemented not only because it changes the motion of the motor, but also because of the advantages they bring about.
The primary and the key advantage the linear motors have is the minimal, or say zero, energy loss because there is no mechanical contact between the coil unit and the magnet plate. The transmission force is generated in the air gap as the platform glides above the track on a cushion of air. That way, the friction and vibration is avoided.
A linear motor has fewer parts in composition. It does not require a gearbox to translate the rotational motion into the linear motion. Without the gearbox, there are fewer parts to maintain and less chance of error the device may make. In addition, the lack of a gearbox and translation of motion save the energy as well.
The movement of the platform is smoother since the vibration and friction are significantly reduced. Without the vibration, a linear motor works more quietly than a rotary motor does. What’s more, because the acceleration and braking of the linear motors are achieved by electromagnetism, it is able to provide a wide range of speed operation smoothly.
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