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**1 Introduction**
High-speed, precision, and modularity have become the core directions in modern manufacturing technology. A new cutting theory suggests that when the cutting speed reaches a certain threshold (around 500m/min), the temperature in the cutting zone stabilizes, while the cutting force decreases, leading to reduced tool wear. This not only improves surface quality and machining accuracy but also boosts productivity.
In general, high-speed machining involves feed rates and cutting speeds that are an order of magnitude higher than conventional methods. Therefore, high-speed spindles and rapid feed systems are critical for achieving such performance. The feed system must meet several key requirements: (1) it should match the high-speed spindle with a minimum feed rate of 60m/min; (2) it needs high acceleration—ideally at least 1–2g—to reach maximum speed quickly; and (3) it must offer excellent dynamic performance, enabling fast servo control and error compensation with high positioning accuracy and stiffness.
For many years, CNC machine tools have relied on traditional feed systems consisting of "rotary servo motors and ball screws." These systems typically achieve a maximum feed rate of 90–120m/min and an acceleration of only 1.5g. However, the presence of multiple mechanical components—such as couplings, screws, nuts, bearings, and brackets—introduces delays, elastic deformation, friction, backlash, and other nonlinear errors. These elements also increase the system’s inertia, reducing its responsiveness to motion commands. Additionally, the screw, being a long rod, is prone to deformation under force and heat, affecting machining accuracy.
To address these limitations and simplify machine tool design, researchers began exploring new feed systems. Among them, linear motors stand out as a promising solution. They eliminate all intermediate transmission components between the power source and the worktable, resulting in a "direct drive" or "zero drive" system, significantly improving efficiency and precision.
**2 Principles and Classification of Linear Motors**
A linear motor is a device that converts electrical energy directly into linear motion using electromagnetic principles. In practice, the primary and secondary parts are often manufactured to different lengths to ensure consistent coupling throughout the stroke.
Similar to a rotary motor, a linear motor generates a magnetic field in the air gap when a three-phase current is applied. This magnetic field is sinusoidally distributed along the direction of motion, forming a traveling wave. The interaction between this field and the secondary part produces electromagnetic thrust, which drives the linear motion.
Linear motors can be classified based on their working principle: linear DC motors, linear induction motors, linear synchronous motors, linear stepping motors, linear piezoelectric motors, and linear reluctance motors. They can also be categorized by structure: flat plate type, U-shaped, and cylindrical types.
**3 Advantages and Disadvantages of Linear Motors**
Linear motors offer several advantages over traditional systems like "rotary motor + ball screw":
- No mechanical contact, reducing friction except from the guide rail.
- Simple structure with fewer parts and only one moving component.
- Theoretical unlimited stroke without performance degradation.
- Wide speed range, from micrometers per second to meters per second, especially excelling in high-speed applications.
- High acceleration, up to 10g.
- Smooth motion due to minimal mechanical connections.
- High accuracy and repeatability, as system accuracy depends on position detection.
- Low maintenance due to fewer parts and no mechanical wear.
However, they also face challenges:
- End effects cause magnetic field distortion, reducing thrust and increasing fluctuations.
- Complex control due to varying loads, system perturbations, and external interferences.
- Difficult installation, magnetic shielding, lower efficiency, and higher costs.
AC linear motors, particularly permanent magnet synchronous types, are increasingly used in high-speed machining centers due to their efficiency and performance.
**4 Development and Application of Linear Motors**
The development of linear motors started around the same time as rotary motors. While early models were inefficient, advancements in control, electronics, and materials led to significant progress in the mid-20th century. Pioneers like E.R. Laithwaite and Professor Yamada I contributed greatly to the field.
By the 1990s, linear motors found widespread use in machining centers, driven by the demand for high-speed, high-precision systems. Companies like Anorad and Indramat developed advanced linear motors with high performance and efficiency.
In China, research on linear motors is still in early stages, with limited funding and slow progress compared to foreign counterparts. Efforts are needed to bridge this gap through combined technological tracking and independent innovation.
**5 Development Trends and Research Directions**
Current trends in linear motor technology include:
- Dominance of permanent magnet linear motors in machine tool feed systems.
- Integration of motors, encoders, and guides to reduce size and improve usability.
- Modularization of components like rails, encoders, and connectors.
- Focus on related technologies such as position feedback and control systems.
Research aims to enhance motor performance, focusing on speed, acceleration, thrust, accuracy, and thermal characteristics. Structural and control design improvements are essential for better performance.
Control technology remains a key challenge, requiring advanced algorithms like PID, adaptive control, and fuzzy logic. Efficient testing and accurate measurement of parameters are also crucial for validating designs and ensuring reliability.
Through continuous optimization and experimental validation, high-performance linear motors will play an even greater role in future manufacturing systems.
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