A linear motor is a transmission device that directly converts electrical energy into linear motion mechanical energy without requiring any central conversion mechanism. It can be viewed as a rotary motor cut radially and unfolded into a plane. The side derived from the stator is called the primary, and the side derived from the rotor is called the secondary. In practical applications, the primary and secondary are manufactured with different lengths to ensure that the coupling between the primary and secondary remains constant within the required stroke range.
Linear motors can have a short primary and a long secondary, or a long primary and a short secondary. Considering manufacturing costs and operating expenses, let's take a linear induction motor as an example: When AC power is applied to the primary winding, a traveling wave magnetic field is generated in the air gap. The secondary winding, under the cutting of the traveling wave magnetic field, will induce an electromotive force and generate a current. This current interacts with the magnetic field in the air gap to generate electromagnetic thrust.
If the primary motor is fixed, the secondary motor will move linearly under the thrust; conversely, the primary motor will move linearly. The drive and control technology of a linear motor requires not only a high-performance linear motor but also a control system capable of meeting technical and economic requirements safely and reliably. With the development of automatic control technology and microcomputer technology, there are increasingly more control methods for linear motors.
The research on linear motor control technology can be fundamentally divided into three aspects: traditional control technology, modern control technology, and intelligent control technology. Traditional control technologies, such as PID control and decoupling control, have been widely used in AC servo systems. Among them, PID control contains information from the dynamic control process, has strong robustness, and is the most fundamental control method in AC servo motor drive systems.
To improve control performance, decoupled control and vector control techniques are often employed. When the target model is fixed, unchanged, and linear, and the operating conditions and environment are constant, traditional control techniques are simple and effective. However, in high-performance applications requiring high-precision micro-feeding, changes in the target structure and parameters must be considered.
Various nonlinear influences, changes in the operating environment, and time-varying and uncertain factors such as environmental disturbances are necessary to achieve satisfactory control effects. Therefore, modern control technology has attracted significant attention in the research of linear servo motor control. Commonly used control methods include: adaptive control, sliding mode variable structure control, robust control, and intelligent control.
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