The characteristics and application of linear motor


1. Generally, the linear motor is rotating when it is working. However, vehicles driven by rotating electric motors (such as electric motor cars and electric trains in the city) need to be linearly moved, and some parts of the machine driven by the rotating electric motor also need to be linear. This requires a set of devices that convert the rotary motion into a linear motion. Can it be driven directly by a linear motion motor to save this kit? People raised this issue decades ago. Now has made a linear motion motor, that is, a linear motor.

The principle of a linear motor is not complicated. Imagine that a rotating motion induction motor is cut along the radius and flattened, which becomes a linear induction motor (Fig.). In a linear motor, it is equivalent to the stator of a rotating machine, called the primary; the equivalent of the rotor of a rotating machine, called the secondary. In the primary, the communication is carried out, and the secondary is linearly moved along the primary under the action of electromagnetic force. At this time, the primary is going to be long and extends to the position that the movement needs to reach, while the secondary does not need to be that long. In fact, a linear motor can either make the primary very long or make the secondary very long; it can be either primary fixed, secondary moving, secondary fixed, or primary moving.

Linear motor is a new type of motor, which has been widely used in recent years. The maglev train is driven by a linear motor.

The maglev train is a brand new train. In general trains, due to the friction between the wheels and the rails, the speed is increased, and the maximum operating speed that can be achieved does not exceed 300km/n. The magnetic suspension train suspends the train magnetically to disengage the train from the guide rails to reduce friction and increase the speed of the train. The train is towed by a linear motor. One stage of the linear motor is fixed to the ground and extends to the far side with the guide rail; the other stage is mounted on the train. The primary pass communicates and the train advances along the guide rails. The train is equipped with magnets (some are coils that use linear motors). When the magnets move with the train, the induced currents are generated in the coils (or metal plates) on the ground, and the magnetic field of the induced current and the magnets on the train (or coils) The electromagnetic force between them hangs the train. The advantage of the suspension train is that it runs smoothly, without bumps, with low noise, and the required traction is very small. As long as the power of several thousand kw can make the speed of the suspension train reach 550km/h. When the suspension train decelerates, the change of the magnetic field decreases, the induced current also decreases, and the magnetic field weakens, causing the suspension force to drop. The suspension train is also equipped with a wheel device. Its wheels are like airplanes. They can collect trains in time when they travel, and can be put down when docked to support the train.

In order to make a huge mass of trains magnetically suspended, a strong magnetic field is required. In practice, high-temperature superconducting coils are needed to generate such a powerful magnetic field.

In addition to being used for maglev trains, linear motors are also widely used in other applications, such as conveyor systems, electric hammers, electromagnetic stirrers, etc. In China, linear motors have also been gradually promoted and applied. Although the principle of linear motor is not complicated, it has its own characteristics in design and manufacture. The product is not as mature as the rotating motor, and needs further research and improvement.

A linear motor can be considered as a structural variant of a rotating electrical machine. It can be seen as a rotating electrical machine that is cut along its radial direction and then flattened and evolved. In recent years, with the rapid development of automatic control technology and microcomputers, higher requirements have been placed on the positioning accuracy of various automatic control systems. In this case, the conventional rotary motor is combined with a set of conversion mechanisms. Linear motion drives are far from meeting the requirements of modern control systems. To this end, in recent years, many countries around the world are researching, developing and applying linear motors, making the application of linear motors more and more extensive.

Compared with rotating electric machines, linear motors have the following characteristics: First, the structure is simple, because the linear motor does not need to add rotary motion into an additional device for linear motion, so that the structure of the system itself is greatly simplified, and the weight and volume are greatly The ground is lowered; the second is the high positioning accuracy. In places where linear motion is required, the linear motor can realize direct transmission, so that various positioning errors caused by the intermediate links can be eliminated, so the positioning accuracy is high, such as using microcomputer control, Greatly improve the positioning accuracy of the whole system; third, the reaction speed is fast, the sensitivity is high, and the followability is good. The linear motor is easy to support the magnetic levitation of the mover, so that a certain air gap is always maintained between the mover and the stator without contact, which eliminates the contact frictional resistance between the stator and the mover, thereby greatly improving the system. Sensitivity, rapidity and follow-up; Fourth, safe and reliable work and long life. The linear motor can realize the contactless transmission force, and the mechanical friction loss is almost zero, so the fault is small and maintenance-free, so the work is safe and reliable, and the service life is long.

2, linear motor is mainly used in three aspects: First, it is applied to automatic control system, such applications are more; secondly, it is used as a long-term continuous operation of the drive motor; third, the application needs to provide a huge time in a short time and a short distance. In a linear motion device.

——High-speed maglev train Maglev train is the most typical example of the practical application of linear motor. At present, the United States, Britain, Japan, France, Germany, Canada and other countries are developing linear suspension trains, of which Japan has the fastest progress.

——Linear motor-driven elevator The world’s first elevator driven by linear motor was installed in Wanshi Building, Guam District, Tokyo, Japan in April 1990. The elevator has a load capacity of 600kg, a speed of 105m/min and a lifting height of 22.9m. Since the linear motor-driven elevator does not have a traction unit, the machine room at the top of the building can be omitted. If the height of the building is increased to about 1000 meters, it is necessary to use a wire ropeless elevator. The elevator is driven by a linear motor with high-temperature superconducting technology. The coil is installed in the hoistway. The car is equipped with high-performance permanent magnet material, just like magnetic levitation. Like a train, it is controlled by radio waves or light control technology.

——Ultra-high-speed motor When the rotation exceeds a certain limit, the motor with rolling bearing will be sintered and damaged. In recent years, a linear suspension motor (electromagnetic bearing) has been developed abroad. The suspension technology is used to suspend the motor’s mover in the air, eliminating the mechanical contact and frictional resistance between the mover and the stator. The rotational speed can reach 25000. 100000r/min or more, it is widely used in high-speed motors and high-speed spindle components. For example, the 5-axis controllable electromagnetic high-speed spindle for multi-process automatic CNC lathes, which was newly developed by Yaskawa, Japan, uses two meridional electromagnetic bearings and an axial thrust electromagnetic bearing to withstand the load of the machine in any direction. In the middle of the shaft, in addition to the high-speed motor, there is also a tool automatic exchange mechanism that is compatible with the multi-process automatic CNC lathe.