Study Of Advanced Sliding Mode Control Theory Used In Magnetic Levitation System For NC Tool

The improvement of the machining accuracy is limited by the friction existingbetween the moving crossbeam and the stationary rail in gantry-moving type numericallycontrolled machine tool. In order to reduce the processing error caused by the friction,traditional support system is instead of crossbeam magnetic levitation system, with theadvantage of no mechanical contact, which can completely eliminate friction and achieveprecision machined parts in this paper. The main goal of this study is that singleelectromagnetic levitation system of vertical direction of the crossbeam magnetic levitationsystem is selected as the controlled object and advanced sliding mode variable structurecontrol strategy is used to ensure fast track and strong robustness of suspended air gap.Firstly, on the basis of the analysis of the suspension principle of crossbeam magneticlevitation system, mathematical model of the single-ended single electromagneticlevitation system is established. In order to facilitate the design of the controller, fornonlinear characteristics of the magnetic levitation system, mathematical model isconverted to the third-order single-input and single-output model by using coordinatetransformation theory.Secondly, for the problem of the decline of the control accuracy of suspended air gapby chattering of the sliding mode variable structure control, two advanced sliding modevariable structure control schemes are designed. The first scheme is dynamic integralsliding mode controller. By changing the design method of the sliding mode surface, thesystem chattering is eliminated. The second scheme is second-order sliding modelcontroller and the control strategy is designed by super-twisting algorithm. The chatteringcan be eliminated and the robustness of system can be guaranteed.Thirdly, for the problem of the decline of tracking speed and the worse of robustnessby reaching phase of the sliding mode variable structure control, time-varying slidingmode controller is designed. Under this control method, the faster motion of sliding mode is achieved, and the problem of Robustness of internal parameter perturbation and externalinterference of reaching phase of the sliding mode variable structure control is solvedeffectively.Finally, MATLAB simulation software is used to separately verify the effectivenessof above three advanced sliding mode variable structure control strategies for singleelectromagnetic levitation system，and simulation results show that the above controlmethods ensuring fast track and strong robustness of single electromagnetic levitationsystem can enhance the control performance of the suspension system in varying degrees.