1、 Introduction

With the continuous advancement of technology, the precision manufacturing field has increasingly high requirements for the accuracy and stability of motion control systems. As a device that directly converts electrical energy into linear motion mechanical energy, ultra precision linear motors have the advantages of simple structure, high acceleration, fast response speed, and high accuracy. They have been widely used in semiconductor manufacturing, optical processing, precision measurement, and other fields. However, the performance of ultra precision linear motors largely depends on their magnetic circuit design and magnetic field uniformity control. Optimizing the magnetic circuit design can improve the thrust density and efficiency of the motor, while controlling the magnetic field uniformity can reduce thrust fluctuations and electromagnetic noise, and improve the operational stability and reliability of the motor.

2、 The influence of magnetic circuit design on the performance of ultra precision linear motors

（1） Magnetic circuit structure and motor thrust

The magnetic circuit structure is the core part of ultra precision linear motors, and its design directly affects the thrust performance of the motor. A reasonable magnetic circuit structure can effectively improve the air gap magnetic flux density, thereby increasing the thrust of the motor. For example, using a Halbach array structure can significantly enhance the air gap magnetic flux density on one side of the motor, while significantly reducing the magnetic flux density on the other side. This characteristic gives Halbach arrays a unique advantage in improving motor thrust density. At the same time, the series parallel magnetic circuit structure can reduce the thickness of the motor yoke plate, increase the thrust density of the motor, and reduce the mass of the motor rotor, thereby improving the dynamic response performance of the motor.

（2） Magnetic saturation and motor performance

In magnetic circuit design, it is necessary to consider the impact of the saturation nonlinearity of magnetic materials on motor performance. When the magnetic flux density in the magnetic circuit reaches the saturation point of the magnetic material, the magnetic permeability will sharply decrease, resulting in a decrease in the thrust performance of the motor. Therefore, in magnetic circuit design, it is necessary to choose the size and shape of the magnetic conductive material reasonably to avoid the occurrence of magnetic saturation phenomenon. By using the equivalent magnetic circuit method to construct a saturation coefficient model of the motor's magnetic material, the accuracy of the magnetic field model can be effectively improved, providing a theoretical basis for the precise design and performance optimization of the motor.

（3） Magnetic circuit loss and motor efficiency

Magnetic circuit loss is an important performance indicator of ultra precision linear motors, which directly affects the efficiency of the motor. Magnetic circuit losses mainly include hysteresis losses and eddy current losses of the iron core. Hysteresis loss is the energy loss caused by the repeated magnetization of the iron core material in an alternating magnetic field, while eddy current loss is the heat loss caused by the induced eddy currents in the iron core. In order to reduce magnetic circuit losses, high-performance silicon steel sheets can be used as the core material to optimize the structure and size of the core and reduce eddy current circuits in the core.

3、 Optimization strategy of magnetic circuit for ultra precision linear motor

（1） Using Halbach array

Halbach array is a special arrangement of permanent magnets that can significantly enhance the air gap magnetic flux density on one side of the motor, while significantly reducing the magnetic flux density on the other side. This characteristic gives Halbach arrays a unique advantage in increasing motor thrust density. By reasonably designing the shape, size, and arrangement of the permanent magnets in the Halbach array, the magnetic circuit structure of the motor can be further optimized, and the thrust performance of the motor can be improved. For example, using unequal thickness rectangular magnets to magnetize according to a certain law, or using equal thickness rectangular magnets to magnetize according to a sine law, can make the air gap magnetic density close to a sine wave, thereby improving the operational stability and accuracy of the motor.

（2） Series parallel magnetic circuit structure

The series parallel magnetic circuit structure can effectively reduce the thickness of the motor yoke plate and improve the thrust density of the motor. In the series parallel magnetic circuit structure, the permanent magnet is divided into multiple parts and connected in series and parallel. This structure can make the magnetic flux in the magnetic circuit more uniform, reduce the local saturation phenomenon of the magnetic circuit, and improve the thrust performance of the motor. Meanwhile, the series parallel magnetic circuit structure can also reduce the mass of the motor's rotor and improve the motor's dynamic response performance.

（3） Application of high-performance permanent magnet materials

The application of high-performance permanent magnet materials is the key to improving the performance of ultra precision linear motors. Rare earth permanent magnet materials such as neodymium iron boron (NdFeB) have become the mainstream choice for ultra precision linear motors due to their high magnetic energy product and excellent magnetic properties. However, with the continuous development of materials science, new permanent magnet materials such as iron cobalt nickel (Fe Co Ni) alloys and nanocomposite permanent magnet materials continue to emerge, providing more possibilities for magnetic circuit optimization of ultra precision linear motors. These new permanent magnet materials have higher magnetic energy product and better temperature stability, which can further improve the thrust density and efficiency of the motor.

4、 Method for controlling magnetic field uniformity

（1） Optimization of magnetic pole shape

The shape of magnetic poles has a significant impact on the magnetic field uniformity of ultra precision linear motors. By optimizing the shape of the magnetic poles, the air gap magnetic flux density can be made more uniform, reducing thrust fluctuations and electromagnetic noise. For example, by using hexagonal magnets or arranging magnets at unequal intervals, an approximate sine waveform of no-load back electromotive force can be obtained, thereby improving the operational stability and accuracy of the motor. In addition, adhesive magnetic pole structures can be used to further improve the uniformity of the magnetic field by adjusting the manufacturing and processing methods of the magnetic poles.

（2） Improvement of magnetization method

The magnetization method also has a significant impact on the magnetic properties of permanent magnets and the magnetic field uniformity of motors. The traditional magnetization method often fails to ensure the uniformity of the magnetic field inside the magnet, which affects the performance of the motor. To solve this problem, an axial magnetization structure or a combination of multiple unconventional magnetization methods of annular permanent magnets can be used. Axial magnetization structure can generate higher magnetic flux density and has a significant magnetic focusing effect. By combining multiple unconventional magnetization methods of annular permanent magnets, the required air gap magnetic flux density can be obtained by adjusting the height and magnetization direction of the magnetic poles, further improving the magnetic field uniformity of the motor.

（3） Finite element analysis assisted design

Finite element analysis (FEA) is a powerful tool that can accurately simulate the magnetic field distribution inside ultra precision linear motors, providing reliable basis for magnetic field uniformity control. Through finite element analysis, it is possible to visually observe the magnetic field distribution inside the motor, identify the reasons for the uneven magnetic field, and take corresponding measures for optimization. For example, the magnetic field uniformity of the motor can be improved by adjusting the size, shape, and arrangement of the magnetic poles, or changing the magnetization method of the permanent magnet. Meanwhile, finite element analysis can also be used to evaluate the performance of different design schemes, providing reference for the optimization design of motors.

5、 Experimental verification and result analysis

In order to verify the effectiveness of magnetic circuit optimization and magnetic field uniformity control methods, a series of experimental studies were conducted. The experiment used an ultra precision linear motor with Halbach array and series parallel magnetic circuit structure, and employed high-performance permanent magnet materials. The magnetic field distribution of the motor was simulated using finite element analysis software, and the magnetic circuit structure of the motor was optimized based on the simulation results. At the same time, the combination of axial magnetization structure and multiple unconventional magnetization methods of annular permanent magnets is adopted to further improve the magnetic field uniformity of the motor.

The experimental results show that the optimized magnetic circuit design and magnetic field control technology significantly improve the performance of the motor. The thrust density of the motor has increased by more than 20%, the thrust fluctuation has been reduced by about 30%, and the operational stability and accuracy of the motor have been significantly improved. At the same time, the efficiency of the motor has also been improved, and the magnetic circuit loss has been reduced by about 15%. These experimental results fully demonstrate the effectiveness of magnetic circuit optimization and magnetic field uniformity control methods in ultra precision linear motors.

6、 Conclusion

The magnetic circuit optimization and magnetic field uniformity control of ultra precision linear motors are key technologies for improving motor performance. By adopting optimization strategies such as Halbach array, series parallel magnetic circuit structure, and high-performance permanent magnet materials, the thrust density and efficiency of the motor can be effectively improved. At the same time, by optimizing the shape of the magnetic poles, improving the magnetization method, and using finite element analysis to assist in design, the magnetic field uniformity of the motor can be controlled, reducing thrust fluctuations and electromagnetic noise, and improving the operational stability and reliability of the motor. The experimental results show that the optimized magnetic circuit design and magnetic field control technology can significantly improve the performance of ultra precision linear motors, providing strong support for the development of precision manufacturing.

In the future, with the continuous advancement of technology, the performance requirements of ultra precision linear motors will continue to increase. Therefore, further in-depth research is needed on magnetic circuit optimization and magnetic field uniformity control technology, constantly exploring new optimization methods and control strategies to meet the higher requirements of ultra precision linear motors in the field of precision manufacturing. At the same time, it is necessary to strengthen cross disciplinary integration with other disciplines, such as materials science, control theory, etc., to provide broader space for the development of ultra precision linear motors.