Design And Control Of Magnetic Suspension Linear Motion System

The magnetic levitation linear motion system employs magnetic levitation mechanism and magnetic linear propulsion motor, and has the potential to achieve ultra-precision, long-range and high-speed motion of an object. It has many advantages over traditional moving mechanisms due to its contact-free and wear-free. It has been widely used in various motion systems such as high-speed maglev trains and frictionless bearings. Therefore, it has become a feasible choice for developing ultra-precision positioning mechanisms. However, maglev transportation system is a complicated nonlinear multi-input multi-output (MIMO) coupling system. The bearing characteristic of maglev platform is not only determined by its structural configuration, but also the controller design. Therefore, it has great significance to investigate a decoupling nonlinear control system for the magnetic suspension platform.In this dissertation, a novel maglev transportation platform is constructed for realizing large travel ultra precision high-speed linear motion. The present maglev transportation platform consists of a levitation subsystem and a propulsion subsystem. In the levitation subsystem, six pairs of electromagnets are used to suspend the moving platform. For every pair of electromagnets, differential electromagnet driving mode is employed to provide suspension force. Such differential electromagnet driving gives better suspension stiffness and suspension performance. Through analyzing the magnetic coupling of electromagnets with finite-element (FE) method, an optimized electromagnets spatial distribution is designed. The optimal case uses eight U-shaped and four E-shaped electromagnets to assemble the levitation subsystem, and it greatly diminishes the magnetic coupling effects among electromagnets. With FE method, the heat generation mechanism and heat flow in electromagnet is analyzed and the cooling mechanism is also designed. A special digital DSP controller and a unique PWM power amplifier are designed for the magnetic suspension plate.To remove the redundant constraints or dynamic coupling existing among six electromagnets, a decoupling levitation control strategy is developed for the novel maglev transportation system. In the decoupling control strategy, three separate controllers are employed for three electromagnets pairs of four ones, and then by real-time computing the electromagnetic force of the three electromagnets pairs, the decoupling controller creates the corresponding decoupling control signal for the fourth electromagnets pairs. Therefore, the control of the fourth electromagnets pairs follows the changes of other three electromagnets pairs'electromagnetic forces, and the fourth electromagnets pairs bring no wallop to the existed three electromagnets pairs. All four controllers work for their own electromagnets pairs and the coupling effects among them are removed. Additionally, this decoupling levitation strategy facilitates the controller design. The experimental results show that the decoupling levitation control strategy decouples the interactions among four channels perfectly. Moreover, the controllers are simple, effective and easy to be implemented in practice.To handle the uncertainties in electromagnets and magnetic suspension stage, a novel Type 2 adaptive fuzzy control method is proposed. Because the T2 fuzzy set is three-dimensional and includes a spatial uncertainty band, the T2 fuzzy set will provide a better capability of modeling uncertainties. In the Type 2 adaptive fuzzy controller, a simple type-reducer is employed to avoid the complex iterative computation. Then to determine the quanity of T2 fuzzy control better than its Tl counterpart, a genetic algorithm is used to optimize the controller parameters and compare their performance under various settings in simulation. Finally, the new Type 2 adaptive fuzzy control method is used to control the present magnetic suspension platform. The experimental control performance verifies that the new method has better control performance and robustness.In this dissertation, a novel magnetic decoupling control method is proposed. This study gives great guidance to achieve ultra-precision and high-speed linear positioning movement, and it plays a key role in improvement of the industrial equipments and reduction of R & D periods in precision manufacturing facilities.