Linear Motors: A Comprehensive Overview of Development, Features, and Principles

1.Development history of linear motors

Generally, electric motors rotate when they work. However, vehicles driven by rotating motors (such as electric locomotives and trams in cities, etc.) need to move in a straight line, and some parts of machines driven by rotating motors also need to move in a straight line. This requires adding a set of devices that convert rotary motion into linear motion. Can linear motion motors be used directly to drive, thereby eliminating this set of devices? People have raised this question, and now linear motion motors, namely linear motors, have been made. The structure of linear motors can be made into various types, such as flat, cylindrical or disc types, according to needs.

2.Characteristics of linear motors

Compared with devices driven by linear motors, linear motors have the following advantages:
The transmission device driven by linear motors does not require any conversion device and directly generates thrust.
It can eliminate the intermediate conversion mechanism, simplify the entire device or system, and has reliable operation, improved efficiency, easy maintenance, and reduced costs. The circumferential speed of ordinary rotating motors is limited due to the action of centrifugal force, while the linear speed of linear motors is not limited when they are running.
Linear motors generate electromagnetic thrust directly through electric energy, and their movement can be without mechanical contact, which greatly reduces mechanical loss.
Rotary motors convert linear motion through conversion mechanisms such as steel ropes, racks, and transmission belts, and noise is inevitable. However, linear motors are driven by electromagnetic force and have little or no noise.
Linear motors have a simple structure. The primary core can be sealed as a whole with epoxy resin after embedding the wire. They can be used in humid, corrosive or harmful and high and low temperature environments.
Linear motors have a good heat dissipation effect, especially the commonly used flat short primary linear motors. The primary core and winding ends are directly exposed to the air. At the same time, the secondary is very long, and the heat is easy to dissipate. The heat load can take a higher value, and no additional cooling device is required.
Linear motors have two main shortcomings:
Compared with rotary motors of the same capacity, the efficiency and power factor of linear motors are lower, especially at low speeds. The main reasons are: First, the primary and secondary air gaps of linear motors are generally smaller than those of rotary motors, so the required magnetizing current is larger, which increases the loss; second, because the two ends of the primary core of the linear motor are disconnected, the so-called edge effect is generated, which causes problems such as waveform distortion and also leads to increased losses. However, from the perspective of the entire system, the efficiency of the linear motor system without the intermediate transmission device is sometimes higher than that of the rotary motor system.
The starting thrust of linear motors, especially linear induction motors, is greatly affected by the power supply voltage, so relevant measures need to be taken to ensure the stability of the power supply or change the relevant characteristics of the motor to reduce or eliminate this influence.

3.The basic principle of linear motors

Linear motors are generally divided into two types: linear synchronous motors and linear induction motors. Linear induction motors (LIM), referred to as linear motors, are generally used in urban rail transit. Linear motors evolved from rotary motors. Its basic structure and working principle are similar to those of ordinary rotary motors, just like cutting a rotary motor in the radial direction and flattening it. As a result, its transmission mode changes from rotary motion to linear motion. The working principle of the linear induction motor is similar to that of the traditional rotary induction motor. It can be understood that the asymptote of the rotary induction motor is linear. The stationary stator (electromagnet and coil) of the rotary induction motor is installed on the bogie of the vehicle, and the rotating rotor (induction plate) is laid flat in the middle of the track. When the current passes through the electromagnet coil of the linear motor, a forward magnetic field is generated, and traction is generated through the interaction with the track induction plate to push the train forward; changing the direction of the magnetic field will cause the train to move backward.

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Luoyang Fonyo Heavy Industries Co., Ltd,founded in 1998,is a manufacturer in cast railway parts.Our factory covers an area of 72,600㎡, with more than 300 employees, 32 technicians, including 5 senior engineers, 11 assistant engineers, and 16 technicians.Our production capacity is 30,000 tons per year. Currently, we mainly produce casting, machining, and assembly for locomotive,railcar,high-speed trains, mining equipment,wind power,etc.Our products have been exported to Russia, the United States, Germany, Argentina, Japan, France, South Africa,Italy and other countries.
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