Magnetic linear actuator realizes energy transmission through non-contact magnetic field coupling, which avoids mechanical wear, jamming, insufficient overload capacity and other problems, improves reliability and reduces vibration and noise. Permanent magnetic drive technology is introduced into the field of linear actuator, which makes the linear actuator with high thrust density and high reliability possible.

With the continuous innovation and development of motor and power electronic technology, linear actuator is widely used in various fields of national defense construction and national economy. The traditional linear actuator mainly uses mechanical actuators such as ball screw to convert rotary motion into linear motion. However, the mechanical actuator can not avoid the problems of wear, seizure and low operation accuracy, which directly affect the performance and service life of linear actuator.

After years of development, linear motor has the advantages of high reliability, high precision, easy maintenance and direct drive, which provides a new way for the development of linear actuator. However, it is difficult to break through the thrust density of linear motor. Therefore, scholars in various countries have made in-depth research and Exploration on the topology and design methods of new linear motor, such as double stator structure and vernier structure; In addition, from the material aspect, the superconducting coil and other advanced materials are applied to linear motor.

Although the above measures can improve the thrust density of linear motor to some extent, the space for lifting is limited, and the structure complexity and manufacturing cost are increased. However, for high-end applications, the thrust density of linear motor is still insufficient.

At present, mechanical screw as a moving form conversion part is widely used in the field of industrial manufacturing, but there are some disadvantages such as mechanical wear and poor reliability. The linear motor has the advantages of high reliability, and the disadvantage is that the thrust density is low.

In recent years, with the development of permanent magnet drive technology and machining technology, the transmission capacity of permanent magnet linear actuator has been greatly improved, which has been introduced into the field of linear actuator, which can take into account the advantages of high thrust density and high reliability. With the development of magnetic materials technology, permanent magnet linear actuator has a wide application prospect in aerospace, national defense, military industry, new energy generation and other fields due to its advantages of high energy conversion, high reliability, low vibration and inherent overload protection.

1 Aerospace

Magnetic drive has the advantages of no lubrication and overload protection, which solves the difficult problem of lubrication of aerospace equipment in high altitude, high temperature and low pressure environment, and greatly improves the system reliability. The linear actuator of magnetic screw has the advantage of high thrust density. Under the same thrust demand, the quality is effectively reduced and the maneuverability of aerospace equipment is improved. Figure 1 is a model of actuator with magnetic screw for steering gear. It has obvious advantages in aerospace field based on its high reliability and high thrust characteristics.

2. Energy conversion field

The magnetic screw actuator is applied to the energy conversion field of the application background such as oscillating buoy and automobile suspension. Through magnetic drive, the linear motion of the moving sub with low speed and high thrust is transformed into the high speed and low torque rotation of the rotor, and the rotating motion is converted into electric energy. The magnetic screw system is applied to the theoretical model of energy conversion device. The device can feed the ocean wave energy and the vibration energy of the vehicle suspension system. Through the linear motion of the magnetic screw, the magnetic nut is driven to rotate, and the energy conversion can be realized.

3. Rail transit

The application of magnetic screw actuator in rail transit is shown. After integrating the magnetic nut with the outer rotor motor, it is laid on the track, and the magnetic driving part is installed at the bottom of the carriage. When the train starts, the composite rotor on the track can assist to drive the train carriage to overcome the sliding of ice and snow pavement; When the train needs to climb or overcome wind resistance, it can also provide power for the train. It is not only the output of power, but also the conversion of kinetic energy to energy when the train needs to brake or slow down to enter the station.

After nearly 10 years of research and development, the advantages of high performance magnetic screw linear actuator have been fully demonstrated, its application value has been recognized and concerned by the industry scholars, and has obvious advantages in aerospace and other high, fine and sharp applications.

As a new concept and structure of magnetic drive mechanism, there are still some problems to be discussed, including:

1) Dynamic performance

As the core part of high thrust linear transmission system, magnetic screw should not only achieve high thrust density, but also have dynamic performance. Because of the low stiffness, the response to step signal and sudden load is insufficient because of the magnetic drive. However, the advantages and disadvantages of dynamic performance are one of the problems that must be solved in the promotion and application of this kind of actuator.

2) Calculation accuracy and efficiency

The magnetic screw adopts three-dimensional spiral structure, which has many factors affecting its thrust performance, and it is often optimized by the help of finite element software. However, the huge mesh and complicated modeling seriously affect the accuracy and efficiency of the calculation. Therefore, it is of practical value to design and develop more accurate and faster analytical model of spiral magnetic field, and few reports have been reported in the literature.

3) High performance spiral magnetic circuit processing technology

Some achievements have been made in the design of the special spiral magnetic circuit of magnetic screw, but the spiral equivalence is mainly realized by using the technology of sectional assembly, which increases the complexity and error. How to realize the complete high performance spiral magnetic circuit processing needs further research.

4) Integrated design with motor

The linear actuator of magnetic screw and motor are designed in an integrated way to form a compact integrated actuator system. The motor and magnetic lead screw should be designed with better performance, and the optimal topology and parameters can be obtained by multi-objective optimization and equivalent magnetic network. Combined with the application background, the advantages of the integrated design of magnetic screw actuator and motor are explored, and a new structure is developed.