A linear motor is a type of electric motor that, rather than generating rotary motion, produces linear motion, moving the element along a straight or curved path. Unlike conventional motors, which rotate around an axis, linear motors operate in only one dimension, allowing for more precise and direct motion control.
The operation of a linear motor is based on the Lorentz principle, where the force applied on the object is determined by the interaction between the electric current and the magnetic field. In this mode, the force is proportional to both the intensity of the current and the magnetic field generated by the magnets. This allows the motor to provide efficient and controlled motion without the need for mechanical transmission components such as gears or belts.
How does a linear motor work?
Linear motors operate under the same basic principle as traditional electric motors, but instead of generating rotary motion, they produce direct linear motion.
In a linear motor, electric current passes through a series of windings that generate a magnetic field. This field combines with a permanent magnet or electromagnet located in the stationary part, creating an attractive or repulsive force that moves the active part of the motor along a straight path.
The main difference between a rotary motor and a linear motor is the way the magnetic field and current are distributed. In a conventional motor, the magnetic field rotates around an axis, while in a linear motor, this field is "spread out" along a line, allowing the moving object to travel in a straight line without the need for transmission components such as gears, chains or belts.
The design of linear motors also allows for highly precise and efficient motion, with reduced friction due to the absence of complex moving parts. This makes them ideal for applications such as magnetic levitation train systems, high-speed elevators, and precision machinery in industry.
Furthermore, they can be low or high acceleration, depending on the application, as in linear motors used in transportation or in high-speed electromagnetic weapons systems.
Types of linear motors
Linear motors can be classified into four different types:
1. Linear induction motor
In the design of linear induction motors, the force is produced by moving a linear magnetic field acting on conductors in the field. Eddy currents will be induced in any conductor placed in this field.
Conductors can be, for example, a coil, a coil or simply a piece of metal. These eddy currents create an opposing magnetic field, as determined by Lenz's law. The two opposing magnetic fields repel each other, creating motion as the magnetic field sweeps across the metal.
2. Synchronous linear motors
Electronic devices are commonly used in the design of synchronous linear motors. These devices control the speed of travel of the magnetic field to regulate the motion of the rotor.
Linear synchronous motors rarely use commutators in order to reduce costs. For this reason, the rotor often contains permanent magnets, or a soft iron core. Examples of such motors are coilguns and motors used in Maglev systems .
3. Homopolar linear motors
In homopolar linear motors, a high current is passed through a metal sabot by sliding contacts. These contacts are powered from two rails. This action produces a magnetic field that causes the metal to be projected along the rails.
4. Piezoelectric linear motors
A piezoelectric motor is a common type of motor that uses electricity to produce vibrations to produce linear or rotary motion.
A mobile phone recreates a similar effect when moving due to vibrations when receiving a call.
Piezoelectric motors are very powerful in slow motion, but can also be very fast, have very few parts, do not require lubrication and are very energy efficient. The disadvantage is that they cannot rotate freely when stopped.
Examples of linear motors
Magnetic levitation trains (Maglev)
Magnetic levitation (Maglev) trains are a prominent example of the use of linear motors.
In these systems, such as the Shanghai Transrapid, trains have no physical contact with the tracks thanks to a magnetic levitation system, which eliminates friction and allows trains to reach very high speeds, over 400 km/h.
The linear motor in these trains generates frictionless propulsion, increasing energy efficiency and reducing wear, allowing for faster and cleaner transportation.
Conventional metal wheel trains
The AirTrain at JFK Airport in New York is an example of a system that uses linear motors on conventional metal-wheeled trains. Although it does not use magnetic levitation, the linear motor provides smooth and efficient movement for transporting passengers within the airport.
The system enables smooth acceleration and deceleration, improving user experience and reducing operating costs compared to traditional combustion engines.
Light rail
Light rail lines, such as those in Vancouver, Toronto and Kuala Lumpur, deploy linear motors to improve the efficiency of urban transport. These motors allow trains to move more smoothly, without friction between the tracks and the vehicle, resulting in greater energy efficiency and lower noise emissions, which is especially important in densely populated urban environments.
In addition, train maintenance is reduced due to less wear on moving parts.
Classic subway trains
In the case of the Tokyo Metro's Toei Oedo Line, linear motors are used in some of its more modern trains. These motors provide more efficient propulsion compared to conventional direct current systems.
The advantage of these motors is that they offer smoother and more precise operation, which improves the quality of service and reduces the level of vibrations and noise in trains, contributing to a more comfortable travel experience for passengers.
Roller coasters
Some roller coasters such as Kingda Ka (Six Flags) use linear motors to provide a fast and exciting initial boost. These linear motors allow the coasters to accelerate in fractions of a second, reaching impressive speeds in a very short time.
This propulsion system is much faster and more efficient than traditional catapult and chain systems, which improves the passenger experience by providing a feeling of speed and adrenaline from the start of the ride.
Vertical elevators for mining shafts
The proposed vertical lifts for mine shafts are designed to transport materials or people from great depths. The use of linear motors has been proposed for these systems due to their ability to move loads smoothly and efficiently under extreme conditions.
Linear motors would be ideal for this type of application, as they provide more precise and safer movement, reducing wear and vibration, crucial elements in the challenging environment of mines.
Cargo transportation system
Linear motor conveyor systems are common in factories and warehouses. These systems allow materials to be moved accurately and efficiently, with less need for maintenance than traditional wheel and chain-based systems.
Linear propulsion allows products to move quickly along production lines or between warehouses, without friction and with more precise control of movement, improving productivity and reducing operating costs.
Levitation system for futuristic vehicles
The maglev autonomous vehicles being investigated use linear motors to propel themselves without contact with the ground. Such vehicles would use a combination of magnetic levitation and linear motors to move efficiently and friction-free.
Although still in development, this system has the potential to transform futuristic transportation by offering fast, safe and wear-free movement, eliminating the need for traditional roads and reducing congestion.